Metal Forming Handbook [1 ed.] 3-540-61185-1, 9783540611851

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M etal Forming Handbook

Metal Forming Handbook /Schuler (c) Springer-Verlag Berlin Heidelberg 1998

3 Berlin Heidelberg New York Barcelona Budapest Hong Kong London Milan Paris Santa Clara Singapore Tokyo

Metal Forming Handbook /Schuler (c) Springer-Verlag Berlin Heidelberg 1998

M ETA L F O R M I N G HANDBOOK

123 Metal Forming Handbook /Schuler (c) Springer-Verlag Berlin Heidelberg 1998

SCHULER GmbH Bahnhofstr. 41 73033 Göppingen Germany

Consulting editor: Professor Taylan Altan Director, Engineering Research Center for Net Shape Manufacturing The Ohio State University, USA Cataloging-in-Publication Data applied for Die Deutsche Bibliothek – CIP-Einheitsaufnahme Metal forming handbook / Schuler. – Berlin ; Heidelberg ; New York ; Barcelona ; Budapest ; Hong Kong ; London ; Milan ; Paris ; Santa Clara ; Singapore ; Tokyo : Springer, 1998 Dt. Ausg. u. d. T.: Handbuch der Umformtechnik ISBN 3-540-61185-1 ISBN 3-540-61185-1 Springer-Verlag Berlin Heidelberg New York This work is subject to copyright.All rights are reserved, whether the whole part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag. Violations are liable for prosecution under the German Copyright Law. © Springer-Verlag Berlin Heidelberg 1998 Printed in Germany The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Cover design by MEDIO, Berlin Layout design and data conversion by MEDIO, Berlin Printing and binding by Konrad Triltsch Druck- und Verlagsanstalt, Würzburg SPIN: 10514857 3020/ 62/ 5 4 3 2 1 0 – Printed on acid-free paper.

Metal Forming Handbook /Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Preface

Followin g th e lon g trad ition of th e Sch u ler Com p an y, th e Metal Form in g Han d book p resen ts th e scien tific fu n d am en tals of m etal form in g tech n ology in a way wh ich is both com p act an d easily u n d erstood . Th u s, th is book m akes th e th eory an d p ractice of th is field accessible to teach in g an d p ractical im p lem en tation . Th e first Sch u ler “Metal Form in g Han d book” was p u blish ed in 1930. Th e last ed ition of 1966, alread y revised fou r tim es, was tran slated in to a n u m ber of lan gu ages, an d m et with resou n d in g ap p roval arou n d th e globe. Over th e last 30 years, th e field of form in g tech n ology h as been rad ically ch an ged by a n u m ber of in n ovation s. New form in g tech n iq u es an d exten d ed p rod u ct d esign p ossibilities h ave been d evelop ed an d in trod u ced . Th is Metal Form in g Han d book h as been fu n d am en tally revised to take accou n t of th ese tech n ological ch an ges. It is both a textbook an d a referen ce work wh ose in itial ch ap ters are con cern ed to p rovid e a su rvey of th e fu n d am en tal p rocesses of form in g tech n ology an d p ress d esign . Th e book th en goes on to p rovid e an in -d ep th stu d y of th e m ajor field s of sh eet m etal form in g, cu ttin g, h yd roform in g an d solid form in g. A large n u m ber of relevan t calcu lation s offers state of th e art solu tion s in th e field of m etal form in g tech n ology. In p resen tin g tech n ical exp lan ation s, p articu lar em p h asis was p laced on easily u n d erstan d able grap h ic visu alization . All illu stration s an d d iagram s were com p iled u sin g a stan d ard ized system of fu n ction ally orien ted color cod es with a view to aid in g th e read er’s u n d erstan d in g. It is sin cerely h op ed th at th is Han d book h elp s n ot on ly d issem in ate sp ecialized kn owled ge bu t also p rovid es an im p etu s for d ialogu e between th e field s of p rod u ction en gin eerin g, p rod u ction lin e con stru ction , teach in g an d research .

Metal Forming Handbook /Schuler (c) Springer-Verlag Berlin Heidelberg 1998

M etal Forming Handbook

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Th is Han dbook is th e p rodu ct of dedicated com m itm en t an d th e wide ran ge of sp ecialized kn owledge con tribu ted by m an y em p loyees of th e SCHULER Grou p in close coop eration with Prof. Dr.-In g. H. Hoffm an n an d Dip l.-In g. M. Kasp arbau er of th e utg, In stitu te for Metal Form in g an d Castin g at th e Tech n ical Un iversity of Mu n ich . In close coop eration with th e SCHULER team , th ey h ave created a solid fou n dation for th e p ractical an d scien tific com p eten ce p resen ted in th is Han dbook. We wish to offer ou r sin cere th an ks an d ap p reciation to all th ose in volved. Goep p in gen , March 1998 Sch u ler Gm bH Board of Man agem en t

Metal Forming Handbook /Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Contributors

ADAM , K., Dipl.-In g. (FH), SMG Sü ddeu tsch e Masch in en bau Gm bH & Co BAREIS, A., Dipl.-In g. (FH), Sch u ler Pressen Gm bH & Co BIRZER, F., Prof. Dipl.-In g., Fein tool AG BLASIG , N., Dipl.-In g. (FH), Sch leich er Au tom ation Gm bH & Co BRANDSTETTER, R., Dipl.-In g. (FH), Sch u ler Pressen Gm bH & Co BREUER, W., Dipl.-In g., Sch u ler Pressen Gm bH & Co FRONTZEK, H., Dr.-In g., Sch u ler Gm bH H OFFMANN , H., Prof. Dr.-In g., Leh rstu h l fü r Um form tech n ik u n d Gieß ereiwesen , Tech n isch e Un iversität Mü n ch en JAROSCH , B., Dipl.-In g. (FH), Sch u ler Pressen Gm bH & Co KÄSMACHER, H., SMG En gin eerin g fü r In du striean lagen Gm bH KASPARBAUER, M., Dipl.-In g., Leh rstu h l fü r Um form tech n ik u n d Gieß ereiwesen , Tech n isch e Un iversität Mü n ch en KELLENBENZ, R., Dipl.-In g. (FH), Sch u ler Pressen Gm bH & Co KIEFER, A., Dipl.-In g. (BA), GMG Au tom ation Gm bH & Co KLEIN , P., Gräben er Pressen system e Gm bH & Co. KG KLEMM , P., Dr.-In g., Sch u ler Pressen Gm bH & Co KNAUß , V., Dipl.-In g. (FH), Sch u ler Werkzeu ge Gm bH & Co KOHLER, H., Dipl.-In g., Sch u ler Gu ß Gm bH & Co KÖRNER, E., Dr.-In g., Sch u ler Pressen Gm bH & Co KUTSCHER, H.-W., Dipl.-In g. (FH), Gräben er Pressen system e Gm bH & Co. KG LEITLOFF, F.-U., Dr.-In g., Sch äfer Hydroform in g Gm bH & Co M ERKLE, D., Sch u ler Pressen Gm bH & Co O SEN , W., Dr.- In g., SMG Sü ddeu tsch e Masch in en bau Gm bH & Co PFEIFLE, P., Dipl.-In g. (FH), Sch u ler Pressen Gm bH & Co REITMEIER, C., Dipl.-In g., Sch äfer Hydroform in g Gm bH & Co REMPPIS, M., In g. grad., Sch u ler Pressen Gm bH & Co ROSENAUER, K., Dipl.-In g. (FH), Sch u ler Werkzeu ge Gm bH & Co

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SCHÄFER, A.W., Sch äfer Hydroform in g Gm bH & Co SCHMID , W ., Dipl.-In g. (FH), Sch u ler Werkzeu ge Gm bH & Co SCHMITT, K. P., Sch u ler Pressen Gm bH & Co SCHNEIDER, F., Dipl.-In g. (FH), Sch u ler Pressen Gm bH & Co SIMON , H., Dr.-In g., Sch u ler Werkzeu ge Gm bH & Co STEINMETZ, M., Dipl.-Wirt.-In g., SMG En gin eerin g fü r In du striean lagen Gm bH STROMMER, K., Dipl.-In g. (FH), Sch u ler Pressen Gm bH & Co VOGEL, N., Dipl.-In g., Sch leich er Au tom ation Gm bH & Co W EGENER, K., Dr.-In g., Sch u ler Pressen Gm bH & Co

Metal Forming Handbook /Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Contents

In dex o f fo rm ula sym bo ls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . XV

1 In tro ductio n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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2 Basic prin ciples o f m etal fo rm in g . . . . . . . . . . . . . . . . . . . . . .

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2.1 Meth o ds o f fo rm in g an d cuttin g tech n o lo gy . . . . 2.1.1 Su m m ary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.2 Form in g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.3 Divid in g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.4 Com bin ation s of p rocesses in m an u factu rin g

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2.2 Basic 2.2.1 2.2.2 2.2.3 2.2.4 2.2.5

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3 Fun dam en tals o f press design . . . . . . . . . . . . . . . . . . . . . . . . . .

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3.1 Press 3.1.1 3.1.2 3.1.3 3.1.4

term s . . . . . . . . . . . . . . . . . . . . . Flow con d ition an d flow cu rve. Deform ation an d m aterial flow Force an d work . . . . . . . . . . . . . Form ability . . . . . . . . . . . . . . . . Un its of m easu rem en t . . . . . . .

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types an d press co n structio n . . . . . . . . . Press fram e . . . . . . . . . . . . . . . . . . . . . . . Slid e d rive . . . . . . . . . . . . . . . . . . . . . . . . Drive system s for d eep d rawin g p resses . Draw cu sh ion s . . . . . . . . . . . . . . . . . . . .

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3.2 Mech an ical presses . . . . . . . . . . . . . . . . . . . . . 3.2.1 Determ in ation of ch aracteristic d ata . . 3.2.2 Typ es of d rive system . . . . . . . . . . . . . . 3.2.3 Drive m otor an d flywh eel . . . . . . . . . . . 3.2.4 Clu tch an d brake . . . . . . . . . . . . . . . . . 3.2.5 Lon gitu d in al an d tran sverse sh aft d rive 3.2.6 Gear d rives . . . . . . . . . . . . . . . . . . . . . . 3.2.7 Press crown assem bly . . . . . . . . . . . . . . 3.2.8 Slid e an d blan k h old er . . . . . . . . . . . . . 3.2.9 Pn eu m atic system . . . . . . . . . . . . . . . . . 3.2.10 Hyd rau lic system . . . . . . . . . . . . . . . . . . 3.2.11 Lu brication . . . . . . . . . . . . . . . . . . . . . .

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3.3 Hydraulic presses . . . . . . . . . . . . . . . . 3.3.1 Drive system . . . . . . . . . . . . . . . 3.3.2 Hyd rau lic oil . . . . . . . . . . . . . . . 3.3.3 Parallelism of th e slid e . . . . . . . 3.3.4 Stroke lim itation an d d am p in g 3.3.5 Slid e lockin g . . . . . . . . . . . . . . .

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3.4 Ch an gin g dies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.1 Die h an d lin g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.2 Die clam p in g d evices . . . . . . . . . . . . . . . . . . . . . . .

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3.5 Press co n tro l system s . . . . . . . . . . . . . . . . . . . . . 3.5.1 Fu n ction s of th e con trol system . . . . . . . . 3.5.2 Electrical com p on en ts of p resses . . . . . . . 3.5.3 Op eratin g an d visu alization system . . . . . 3.5.4 Stru ctu re of electrical con trol system s . . . 3.5.5 Fu n ction al stru ctu re of th e con trol system 3.5.6 Major electron ic con trol com p on en ts . . . 3.5.7 Arch itectu re an d h ard ware con figu ration 3.5.8 Arch itectu re of th e PLC software . . . . . . . 3.5.9 Fu tu re ou tlook . . . . . . . . . . . . . . . . . . . . .

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3.6 Press safety an d certificatio n . . . . . . 3.6.1 Accid en t p reven tion . . . . . . . . 3.6.2 Legislation . . . . . . . . . . . . . . . . 3.6.3 Eu rop ean safety req u irem en ts 3.6.4 CE m arkin g . . . . . . . . . . . . . . .

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3.6.5 3.6.6

Measu res to be u n d ertaken by th e u ser . . . . . . . . . 115 Safety req u irem en ts in th e USA . . . . . . . . . . . . . . . 117

3.7 Castin g co m po n en ts fo r presses . . . . . . . . . . . . . . . . . . . 120 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

4 Sh eet m etal fo rm in g an d blan kin g 4.1 Prin ciples o f die m an ufacture 4.1.1 Classification of d ies . . . 4.1.2 Die d evelop m en t . . . . . 4.1.3 Die m aterials . . . . . . . . . 4.1.4 Castin g of d ies . . . . . . . . 4.1.5 Try-ou t eq u ip m en t . . . . 4.1.6 Tran sfer sim u lators . . . .

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4.2 Deep 4.2.1 4.2.2 4.2.3

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draw in g an d stretch draw in g . . . . . . . Form in g p rocess . . . . . . . . . . . . . . . . . Materials for sh eet m etal form in g . . . Friction , wear an d lu brication d u rin g sh eet m etal form in g . . . . . . . . . . . . . . 4.2.4 Hyd ro-m ech an ical d eep d rawin g . . . . 4.2.5 Active h yd ro-m ech an ical d rawin g . . .

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123 123 123 128 142 142 148 154

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4.3 Co il lin es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 4.4 Sh eet m etal fo rm in g lin es . . . . . . . . . . . . . . . . . . . . . . 4.4.1 Un iversal p resses . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.2 Prod u ction lin es for th e m an u factu re of flat rad iator p lates . . . . . . . . . . . . . . . . . . . . . . . 4.4.3 Lin es for sid e m em ber m an u factu re . . . . . . . . . . 4.4.4 Destackers an d blan k tu rn over station s . . . . . . 4.4.5 Press lin es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.6 Tran sfer p resses for sm all an d m ed iu m sized p arts . . . . . . . . . . . . . . . . . . . . . . . 4.4.7 Large-p an el tri-axis tran sfer p resses . . . . . . . . . . 4.4.8 Crossbar tran sfer p resses . . . . . . . . . . . . . . . . . . . 4.4.9 Presses for p lastics . . . . . . . . . . . . . . . . . . . . . . . . 4.4.10 Stackin g u n its for fin ish ed p arts . . . . . . . . . . . . . 4.4.11 Con trol system s for large-p an el tran sfer p resses

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208 210 217 222

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4.5 Blan kin g pro cesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 4.6 Sh earin g lin es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6.1 Slittin g lin es . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6.2 Blan kin g lin es . . . . . . . . . . . . . . . . . . . . . . . . . 4.6.3 High -sp eed blan kin g lin es . . . . . . . . . . . . . . . 4.6.4 Lin es for th e p rod u ction of electric m otor lam in ation s . . . . . . . . . . . . . . . 4.6.5 Prod u ction an d p rocessin g of tailored blan ks 4.6.6 Perforatin g p resses . . . . . . . . . . . . . . . . . . . . . 4.6.7 Con trol system s for blan kin g p resses . . . . . . .

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4.7 Fin e blan kin g . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7.1 Fin e blan kin g p rocess . . . . . . . . . . . . . . 4.7.2 Fin e blan kin g m aterials, forces, q u ality ch aracteristics an d p art variety . . . . . . . 4.7.3 Fin e blan kin g tools . . . . . . . . . . . . . . . . 4.7.4 Fin e blan kin g p resses an d lin es . . . . . .

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4.8 Ben din g . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.1 Ben d in g p rocess . . . . . . . . . . . . . . . . 4.8.2 Roll form in g an d variety of section s . 4.8.3 Roller straigh ten in g . . . . . . . . . . . . .

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4.9 Organ izatio n o f stam pin g plan ts . . . . . . . . . . . . 4.9.1 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.2 Layou t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.3 Qu ality assu ran ce th rou gh q u ality con trol

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389 389 391 398

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5 Hydro fo rm in g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 5.1 Gen eral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 5.2 Pro cess tech n o lo gy an d ex am ple applicatio n s 5.2.1 Process tech n ology . . . . . . . . . . . . . . . . . . 5.2.2 Typ es of h yd roform ed com p on en ts . . . . . 5.2.3 Field s of ap p lication . . . . . . . . . . . . . . . . .

Metal Forming Handbook /Schuler (c) Springer-Verlag Berlin Heidelberg 1998

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5.3 Co m po n en t develo pm en t . . . . . . . . . . . . . 5.3.1 User-orien ted p roject m an agem en t 5.3.2 Feasibility stu d ies . . . . . . . . . . . . . . 5.3.3 Com p on en t d esign . . . . . . . . . . . . .

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413 413 414 416

5.4 Die en gin eerin g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420 5.4.1 Die layou t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420 5.4.2 Lu brican ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422 5.5 Materials an d prefo rm s fo r pro ducin g h ydro fo rm ed co m po n en ts . . . . . . . . . . . . . . 423 5.5.1 Materials an d h eat treatm en t . . . . . . . . . . . . . . . . . 423 5.5.2 Preform s an d p rep aration . . . . . . . . . . . . . . . . . . . . 424 5.6 Presses fo r h ydro fo rm in g . . . . . . . . . . . . . . . . . . . . . . . . . 426 5.7 Gen eral co n sideratio n s . . . . . . . . . . . . . . . . . . . . . . . . . . . 429 5.7.1 Prod u ction tech n ology issu es . . . . . . . . . . . . . . . . . 429 5.7.2 Tech n ical an d econ om ic con sid eration s . . . . . . . . 431 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432

6 So lid fo rm in g (Fo rgin g) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433 6.1 Gen eral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433 6.2 Ben efits o f so lid fo rm in g . . . . . . . . . . . . . . . . . . . . . . . . . 441 6.2.1 Econ om ic asp ects . . . . . . . . . . . . . . . . . . . . . . . . . . 441 6.2.2 Workp iece p rop erties . . . . . . . . . . . . . . . . . . . . . . . . 443 6.3 Materials, billet pro ductio n an d surface 6.3.1 Materials. . . . . . . . . . . . . . . . . . . . . 6.3.2 Billet or slu g p rep aration . . . . . . . . 6.3.3 Su rface treatm en t . . . . . . . . . . . . . .

treatm en t ......... ......... .........

... .... .... ....

450 450 454 459

6.4 Fo rm ed part an d pro cess plan . . . . . . . . . . . . . . . . . . . . . 464 6.4.1 Th e form ed p art . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464 6.4.2 Process p lan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467 6.5 Fo rce an d w o rk requirem en t . . . . . . . . . . . . . . . . . . . . . . 469 6.5.1 Forward rod extru sion . . . . . . . . . . . . . . . . . . . . . . . 469 6.5.2 Forward tu be extru sion . . . . . . . . . . . . . . . . . . . . . . 474

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M etal Forming Handbook

XIV

6.5.3 6.5.4 6.5.5 6.5.6 6.5.7

Backward cu p extru sion an d cen terin g Red u cin g (op en d ie forward extru sion ) . Iron in g . . . . . . . . . . . . . . . . . . . . . . . . . . Up settin g . . . . . . . . . . . . . . . . . . . . . . . . Lateral extru sion . . . . . . . . . . . . . . . . . .

. . . . .

. . . . .

. . . . .

. . . . .

. . . . .

. . . . .

. . . . .

. . . . .

. . . . .

474 475 476 476 477

6.6 Part tran sfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478 6.6.1 Load in g station . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479 6.6.2 Tran sfer stu d y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481 6.7 Die design . . . . . . . . . . . . . . . . 6.7.1 Die h old ers . . . . . . . . . . 6.7.2 Die an d p u n ch d esign . 6.7.3 Die an d p u n ch m aterials 6.7.4 Die closin g system s (m u ltip le-action d ies) . .

.... .... .... ...

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

485 488 491 496

. . . . . . . . . . . . . . . . . . . . . 502

6.8 Presses used fo r so lid fo rm in g . . . . . . . . . . . . . . . . . 6.8.1 Ch oice of p ress . . . . . . . . . . . . . . . . . . . . . . . . . 6.8.2 Mech an ical p resses . . . . . . . . . . . . . . . . . . . . . . 6.8.3 Hyd rau lic p resses . . . . . . . . . . . . . . . . . . . . . . . 6.8.4 Su p p lem en tary eq u ip m en t . . . . . . . . . . . . . . . 6.8.5 Sp ecial featu res of h ot an d warm form in g lin es 6.8.6 Sizin g an d coin in g p resses . . . . . . . . . . . . . . . . 6.8.7 Min tin g an d coin blan kin g lin es . . . . . . . . . . .

. . . . .

. . . . . . .. ..

. . . . . . . .

505 505 507 514 517 520 522 526

Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541 In d ex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543

Metal Forming Handbook /Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Index of formula symbols

a

rib an gle, ben d in g an gle, clearan ce an gle, d ie op en in g an gle, corn er an gle for blan kin g

° ° ° °

a1

req u ired ben d in g an gle

°

a2

d esired ben d in g an gle

°

b

d raw ratio, corn er an gle wh en ben d in g

°

btot

total d raw ratio

bm ax

m axim u m d raw ratio

«

elon gation , startin g m easu rem en t

«A

relative cross section ch an ge

h

efficien cy

hA

degree of u tilization of th e sh eet m etal, u tilization force

hF

form in g efficien cy factor

m

coefficien t of friction

·

%

V

volu m etric flow

s

stress

N/ m m 2

sm

m ean stress

N/ m m 2

sm ax

largest stress

N/ m m 2

sm d

m ean com p arative stress

N/ m m 2

sm in

sm allest stress

N/ m m 2

sN

n orm al con tact stress

N/ m m 2

sr

rad ial stress

N/ m m 2

Metal Forming Handbook /Schuler (c) Springer-Verlag Berlin Heidelberg 1998

1/ s

M etal Forming Handbook

XVI

st

tan gen tial stress

N/ m m 2

sv

com p arative stress, effective stress

N/ m m 2

sz

critical bu cklin g stress

N/ m m 2

s1

greatest p rin cip le stress

N/ m m 2

s2

m ean p rin cip le stress

N/ m m 2

s3

sm allest p rin cip le stress

N/ m m 2

tR

friction al sh ear stress

N/ m m 2

w

d egree of d eform ation , strain , logarith m ic/ tru e strain

w·

strain rate, d eform ation rate, d eform ation sp eed

wB

fractu re strain

wg

p rin cip le d eform ation

w1,w2,w3

d eform ation in m ain d irection s

A

su rface

mm2

a

blan kin g p late m easu rem en t, rim wid th , leg len gth d u rin g ben d in g, slot wid th

mm mm

A0

in itial su rface, su rface of blan k cross section

mm2

a1

blan kin g p u n ch d im en sion

mm

A1

su rface of blan k cross section , en d su rface

mm2

A5 , A80 AG

u ltim ate elon gation

%

ejector su rface, su rface area u n d er p ressu re by th e ejector

mm2

aR

sp ace between th e rows

mm

AS

sh eared su rface

mm2

ASt

cross section of th e p u n ch , su rface area of h ole p u n ch

mm2 mm2

AZ

blan k su rface, area of th e blan k

mm2

b

web wid th , leg len gth d u rin g ben d in g, strip wid th , section wid th

mm mm

B

d eflection

mm

bA

sh ell-sh ap ed tear wid th

mm

bE

d ie roll wid th

mm

bS

strip wid th

mm

c

m aterial coefficien t

D

blan k d iam eter, p late d iam eter, m an d rel d iam eter

Metal Forming Handbook /Schuler (c) Springer-Verlag Berlin Heidelberg 1998

mm mm

Index of formular symbols

d

XVII

in n er d iam eter, h ole d iam eter, (p erforatin g) p u n ch d iam eter

mm mm

d’

in sid e d iam eter of bottom d ie

mm

d0

blan k d iam eter, in itial billet d iam eter

mm

d1

d iam eter of th e d raw p u n ch in th e first d rawin g op eration , p u n ch d iam eter, en d d iam eter

mm mm

d2

u p p er cu p d iam eter, ou tsid e d iam eter

mm

d3

ou tsid e flan ge d iam eter

mm

e

off-cen ter p osition of force ap p lication

mm

E

elasticity m od u le

F

force

N/ m m 2 kN

f1 , f2 , f3

offset factors

FA

ejection force

kN

FB

blan k h old er force

kN

Fb

ben d in g force

kN

FG

cou n terforce

kN

FGa

ejection force

kN

FGes

total m ach in e force

kN

FN

n orm al force

kN

FN0

rated p ress force, n om in al load

kN

FR

rad ial ten sion force, friction force, vee-rin g force

kN

FRa

strip p in g force

kN

FRe

reaction force

kN

FS

blan kin g force for p u n ch with flat grou n d work su rface, sh earin g force

kN kN

FST

slid e force

kN

Ft

tan gen tial com p ression force

kN

FU

p ressin g force, form in g force, m axim u m d rawin g force

kN kN

g

gravitation al acceleration

h

m / s2

form in g p ath , d rawin g stroke, d istan ce, h eigh t,

mm

p u n ch d isp lacem en t; lu brication gap

mm mm

H

p late th ickn ess

mm

h0

in itial billet h eigh t, h eigh t of blan k

mm

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M etal Forming Handbook

XVIII

h1

fin al h eigh t of a bod y after com p ression

mm

h 1’

in term ed iate h eigh t, h eigh t of th e tru n cated con e

mm

h2

cu p h eigh t

mm

hE

d ie roll h eigh t

mm

hG

flash h eigh t

mm

h eigh t of vee-rin g

mm

h R, H R h S1

sm ooth cu t section in case of fractu re

%

h S2

m in im al sm ooth cu t section in case of sh ell-sh ap ed fractu re

%

i k k 2a

sid e cu tter scrap

mm

correction factor correction coefficien t (an gle)

kf

flow stress

N/ m m 2

k f0

flow stress at th e start of th e form in g p rocess

N/ m m 2

k f1

flow stress toward s th e en d of th e form in g p rocess

N/ m m 2

k fm

m ean stability factor

N/ m m 2

kh

correction coefficien t (h eigh t)

kR

sp rin gback factor

kS

sh earin g resistan ce, sh earin g stren gth , relative blan kin g force

N/ m m 2 N/ m m 2

kw

d eform ation resistan ce

N/ m m 2

m ean d eform ation resistan ce

N/ m m 2

k wm l

rib len gth

mm

L

strip len gth , m an d rel len gth

mm

la

rim len gth

mm

le

web len gth , strip len gth

mm

lR

len gth of vee-rin g

mm

lS

len gth of sh eared con tou r cu t

mm

m

m ass, m od u le of a gear

Mx

eccen tric m om en t of load arou n d th e x axis

kNm

My

eccen tric m om en t of load arou n d th e y axis

kNm

kg

P

p erform an ce, d rive p ower

W, kW

p

p ressu re

N/ m m 2

pB

sp ecific blan k h old er p ressu re

N/ m m 2

Metal Forming Handbook /Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Index of formular symbols

XIX

pG

average com p ressive stress on th e cou n terp u n ch

N/ m m 2

pi

in tern al p ressu re

N/ m m 2

pj

com p ressive stress at th e wall of th e bottom d ie

N/ m m 2

pm

m ean (h yd rau static) p ressu re

N/ m m 2

p St

average com p ressive stress on th e p u n ch , average form in g p ressu re

N/ m m 2 N/ m m 2

qG

sp ecific cou n terforce, cou n terp ressu re

N/ m m 2

r

rad iu s

mm

R

corn er rad iu s

mm

ra

extern al rad iu s of an in sid e con tou r

mm

Ra

extern al rad iu s of an ou tsid e con tou r

mm

ReL

lower yield stren gth

N/ m m 2

com p ression lim it

N/ m m 2

Rp 0,2 ri

in sid e ben d in g rad iu s, in tern al rad iu s of an in sid e con tou r

mm mm

Ri

in tern al rad iu s of an ou tsid e con tou r

mm

r i1

in sid e rad iu s at th e d ie

mm

r i2

in sid e rad iu s at th e workp iece

mm

Rm

ten sile stren gth of th e m aterial

N/ m m 2

Rt

su rface rou gh n ess

mm

Rw

roller rad iu s

mm

Rz

su rface rou gh n ess

mm

s

sh eet m etal th ickn ess, wall th ickn ess, blan k th ickn ess

mm mm

sR

p osition of th e cen ter of force (x s- u n d y s : coord in ates of th e force), cen ter of gravity

mm

t

p itch

mm

tw

roller p itch

mm

u

blan kin g clearan ce

mm

U

sp eed / strokin g sp eed , cu t con tou r circu m feren ces, p u n ch p erim eter

v

cou n terbalan ce valu e d u rin g ben d in g, com p en sation factor

mm mm

V

feed step , volu m e

mm mm3

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XX

V0

startin g volu m e, overall volu m e, p art volu m e

mm3

V1

in term ed iate volu m e, com p en sation valu e

mm3

V1’

in term ed iate volu m e, com p en sation valu e

mm3

V2

in term ed iate volu m e, com p en sation valu e

mm3

Vd

volu m e d isp laced d u rin g d eform ation

mm3

W

d eform ation / form in g work

w

d ie wid th

Nm , kNm J, kJ mm

Wb

ben d in g work

Wd

d rawin g work on d ou ble-action p resses, d raw en ergy of a d ou ble-action p ress

Nm , kNm Nm , kNm

We

d rawin g work on sin gle-action p resses, d raw en ergy of a sin gle-action p ress

Nm , kNm Nm , kNm

w id

referen ced deform ation work, specific form in g work

WN

n om in al work for con tin u ou s strokin g

Nm , kNm

WS

blan kin g work, blan kin g en ergy, sh earin g work

Nm , kNm

Nm

Nm m /m m 3

x

correction factor

xs

location of th e resu ltin g blan kin g force in th e x d irection

mm

location of th e resu ltin g blan kin g force in th e y d irection

mm

ys z

n o. of teeth of a gear, n o. of workpieces

zw

roller feed valu e

Metal Forming Handbook /Schuler (c) Springer-Verlag Berlin Heidelberg 1998

mm

1 Introduction

Tech n ology h as exerted a far greater in flu en ce on th e develop m en t of ou r p ast th an m ost h istory books give credit for. As late as th e 19th cen tu ry, craftm an sh ip an d tech n ology were p ractically syn on ym ou s. It is on ly with th e adven t of m ech an isation – th rou gh th e u se of m ach in es – th at th e term tech n ology took on a n ew m ean in g of its own . Tod ay, tech n ology is on e of th e bastion s of ou r m od ern lifestyle an d th e basis for ou r p rosp erity, in wh ich m etal form in g tech n ology p lays a cen tral role. Alon gsid e th e m an u factu re of sem i-fin ish ed p rod u cts th rou gh rollin g, wire d rawin g an d extru sion , th e p rod u ction of d iscrete com p on en ts u sin g sh eet m etal an d solid form in g tech n iq u es is of m ajor sign ifican ce. Its field s of ap p lication ran ge from au tom otive en gin eerin g, p rod u ction lin e an d con tain er con stru ction th rou gh to th e bu ild in g con stru ction , h ou seh old ap p lian ce an d p ackagin g in d u stries. Th e m ach in e tool, with its cap acity to p recisely gu id e an d d rive on e or m ore tools for th e m ach in in g of m etal, h as becom e a sym bol of econ om ic m etalworkin g. In th e p ast, th e work p rocesses typ ically seen in m etal form in g tech n ology u sed to be execu ted in a series of in d ivid u al op eration s on m an u ally op erated m ach in e tools. Tod ay, h owever, au tom atic p rod u ction cells an d in terlin ked in d ivid u al m ach in es th rou gh to th e com p act p rod u ction lin e with in tegrated feed , tran sp ort, m on itorin g an d fin ish ed p art stackin g system s are th e state of th e art. Develop m en ts in th is field created th e tech n ological basis to allow th e ben efits of form ed workp ieces, su ch as a m ore favorable flow lin e, op tim u m stren gth ch aracteristics an d low m aterial an d en ergy in p u t, to be com bin ed with h igh er p rod u ction ou tp u t, d im en sion al con trol an d su rface q u ality. As a rep u ted Germ an m an u factu rer of m ach in e tools, th e com p an y SCHULER h as played a determ in in g role in th is developm en t over a period

Metal Forming Handbook /Schuler (c) Springer-Verlag Berlin Heidelberg 1998

M etal Forming Handbook

2

of m ore th an 150 years: From th e m an u ally op erated sh eet m etal sh ear to th e fu lly au tom atic tran sfer p ress for com p lete car bod y sid e p an els. Over th e m illen n iu m s, th e h an d workin g of m etal by form in g reach ed wh at m ay still tod ay be con sid ered a rem arkable d egree of skill, resu ltin g in th e creation of m agn ificen t works in gold , silver, bron ze, cop p er an d brass. It was on ly in arou n d 1800 th at iron sh eet p rod u ced in rollin g p lan ts began to fin d its way in to th e craftsm en ’s worksh op s, req u irin g com p letely n ew p rocessin g tech n iq u es: In con trast to n on ferrou s m etals, th e m u ch h ard er an d m ore brittle n ew m aterial cou ld be m ore econ om ically worked with th e aid of m ach in es. In 1839, m aster locksm ith Louis Schuler fou n d ed a m od est worksh op com p risin g p rim arily a tin sm ith ’s sh op , as well as a blacksm ith ’s forge an d a sm ith y. Driven by h is Swabian bu sin ess sen se, h e con sid ered th e p ossibilities op en ed u p by th e n ewly available, ch eap er iron sh eet. He was q u ick to realize th at th e in creased in p u t req u ired in term s of p h ysical stren gth an d workin g tim e, an d th u s th e m an u factu rin g costs in volved in p rod u cin g th e fin ish ed article were far too h igh to ben efit from th e favorable p rice of th e iron sh eet itself. Step by step , Louis Schuler accord in gly began to rep lace m an u al work p rocesses by m ech an ical fixtu res an d d evices. He began to m ech an ise h is worksh op with sh eet sh ears, ben d in g m ach in es an d p ress breaks, wh ich were con sid erable in n ovation s in th ose d ays. In sp ired by th e World Exh ibition in Lon d on in 1851, Louis Schuler d ecid ed to con cen trate h is activities en tirely on p rod u cin g m ach in es for sh eet m etal workin g. His p rod u ction ran ge was con tin u ou sly exten d ed to in clu d e sh eet m etal straigh ten in g m ach in es, m etal sp in n in g an d levellin g ben ch es, eccen tric p resses, sp in d le p resses, tu rret, cran k an d d rawin g p resses, both m ech an ically an d h yd rau lically p owered , n otch in g p resses as well as cu ttin g an d form in g tools an d d ies. As early as 1859, h e exp orted h is first sh eet m etal form in g m ach in es. At th e en d of th e 1870s, Schuler registered h is first p aten t for “In n ovation s in p u n ch in g d ies, sh ears an d sim ilar”. In 1895, h e p aten ted “Hyd rau lic d rawin g p resses with two p iston s fitted in to each oth er”, an d in th e sam e year was also award ed first p rize at th e Sh eet Metal In d u stry Trad e Exh ibition in Leip zig. With exp an sion of th e p rod u ction p rogram , th e workforce as well as th e com p an y p rem ises h ad u n d ergon e con tin u ou s growth (Fig. 1.1). Th e Sch u ler m ach in e tool com p an y

Metal Forming Handbook /Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Introduction

Fig. 1.1 L. Schuler, M achine tool factory and foundry, Goeppingen, around 1900

was on e of th e foresigh ted en terp rises of th e d ay to p ion eer th e p rocess of d ifferen tiation takin g p lace in th e field of m ach in e tool en gin eerin g. As a su p p lier of m ach in es an d p rod u ction lin es for in d u strial m an u factu re – in p articu lar series p rod u ction – th e com p an y’s rep u tation in creased rap id ly. Th e in creasin g exp ort volu m e an d a con sisten t p rocess of d iversification in th e field of form in g tech n ology led to an early p rocess of globalisation an d to th e d evelop m en t of th e in tern ation al SCHULER Grou p of Com p an ies. Th e SCHULER Grou p ’s p rocess of globalisation got u n d er way at th e begin n in g of th e sixties with th e fou n d in g of foreign su bsid iaries. Tod ay, SCHULER ru n s n ot on ly eigh t m an u factu rin g p lan ts in Germ an y bu t also ad d ition al five p rod u ction facilities in Fran ce, th e US, Brazil an d Ch in a. Alon gsid e its world -wid e n etwork of sales agen cies, SCHULER h as also set u p its own sales an d service cen ters in Sp ain , In d ia, Malaysia an d Th ailan d . An in tern ation ally-based n etwork of p rod u ction facilities coord in ated from th e p aren t p lan t in Goep p in gen p erm its rap id resp on se to th e ch an ges takin g p lace in th e targeted m arkets. Prod u ction in overseas location s brin gs abou t n ot on ly a red u ction in costs bu t also creates

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M etal Forming Handbook

4

m ajor strategic ben efits by in creasin g “local con ten t” an d so en su rin g an im p roved m arket p osition . Th e North an d Sou th Am erican m arkets are su p p lied locally. Th e NAFTA area is coord in ated by Sch u ler In c. in Oh io, wh ile Sou th Am erica’s com m on m arket, th e Mercosu l, is su p ervised from Brazil. Th e h igh stan d ard of q u ality ach ieved by th e SCHULER p lan t in Brazil h as op en ed u p even th e m ost d em an d in g m arkets. In th e growin g m arket of Ch in a, th e SCHULER Grou p ru n s two join t ven tu re corp oration s in coop eration with Ch in ese p artn ers for th e m an u factu re of m ech an ical p resses an d h yd rau lic p resses. Tod ay, we stan d on th e th resh old to a n ew m illen n iu m m arked by in creasin g m arket globalisation an d rap id ly ch an gin g organ ization al an d p rod u cin g stru ctu res. Un d er th ese rap id ly ch an gin g con d ition s, it is SCHULER’s workforce wh ich rem ain s th e sin gle m ost im p ortan t d eterm in in g factor between su ccess an d failu re. Th e tech n ological orien tation of th e staff p rovid es th e in n ovative im p etu s wh ich will secu re th e com p an y’s d evelop m en t as it m oves in to th e 21st cen tu ry. Th is Metal Form in g Han d book reflects th e tech n ical com p eten ce, th e rich sou rce of id eas an d th e creativity of th e SCHULER Grou p ’s workforce. Th e book takes an in -d ep th look at th e p ion eerin g stage of d evelop m en t reach ed by tod ay’s p resses an d form in g lin es, an d at related p rod u ction p rocesses, with p articu lar em p h asis on th e d evelop m en t of con trol en gin eerin g an d au tom ation . Develop m en ts in th e classical field s of d esign , m ech an ical en gin eerin g, d yn am ics an d h yd rau lics are n ow bein g in flu en ced to an ever greater d egree by m ore recen tly d evelop ed tech n ologies su ch as CAD, CAM, CIM, m ech atron ics, p rocess sim u lation an d com p u ter-aid ed m easu rem en t an d p rocess con trol tech n ology. In tod ay’s en viron m en t, th e m ain objective of ach ievin g en h an ced p rod u ct q u ality an d p rod u ctivity is cou p led with lower in vestm en t an d op eratin g costs. In ad d ition , q u estion s of reliability, u p tim e, accid en t p reven tion , p rocess accou n tin g, econ om ical u se of resou rces an d en viron m en tal con servation p lay also a cen tral role. In view of th e fu n d am en tal im p ortan ce of m etal form in g tech n ology tod ay, th is Han d book offers th e read er a referen ce work wh ose u sefu ln ess stretch es to p ractically every bran ch of in d u stry. Th e book p rovid es an in -d ep th an alysis of m ost of th e im p ortan t m an u factu rin g tech n ologies as a system com p risin g th e th ree elem en ts: p rocess, p rod u ction lin e an d p rod u ct.

Metal Forming Handbook /Schuler (c) Springer-Verlag Berlin Heidelberg 1998

2 Basic principles of metal forming

2.1 M ethods of forming and cutting technology 2.1.1 Summary As d escribed in DIN 8580, m an u factu rin g p rocesses are classified in to six m ain grou p s: p rim ary sh ap in g, m aterial form in g, d ivid in g, join in g, m od ifyin g m aterial p rop erty an d coatin g (Fig. 2.1.1). Prim ary shaping is th e creation of an in itial sh ap e from th e m olten , gaseou s or form less solid state. Dividin g is th e local sep aration of m aterial. Join in g is th e assem bly of in dividu al workp ieces to create su bassem blies an d also th e fillin g an d satu ration of p orou s workp ieces. Coatin g m ean s th e ap p lication of th in layers on com p on en ts, for exam p le by galvan ization , p ain tin g an d foil wrap p in g. Th e p u rp ose of m odifyin g m aterial p rop erty is to alter m aterial ch aracteristics of a workp iece

dividing

primary shaping

forming coating

joining

modifying material property

Fig. 2.1.1 Overview of production processes

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to ach ieve certain u sefu l p rop erties. Su ch p rocesses in clu de h eat treatm en t p rocesses su ch as h arden in g or recrystallization an n ealin g. Form ing – as th e tech n ology form in g th e cen tral su bject m atter of th is book – is d efin ed by DIN 8580 as m an u factu rin g th rou gh th e th reed im en sion al or p lastic m od ification of a sh ap e wh ile retain in g its m ass an d m aterial coh esion . In con trast to d eform ation , form in g is th e m od ification of a sh ap e with con trolled geom etry. Form in g p rocesses are categorized as ch ip less or n on -m aterial rem oval p rocesses. In p ractice, th e field of “form in g tech n ology” in clu d es n ot on ly th e m ain category of form in g bu t also su btop ics, th e m ost im p ortan t of wh ich are dividing an d joining through form ing (Fig. 2.1.2). Com bin ation s with oth er m an u factu rin g p rocesses su ch as laser m ach in in g or castin g are also u sed .

2.1.2 Forming Form in g tech n iq u es are classified in accord an ce with DIN 8582 d ep en d in g on th e m ain d irection of ap p lied stress (Fig. 2.1.3): form in g form in g form in g form in g form in g

u n d er com p ressive con d ition s, u n d er com bin ed ten sile an d com p ressive con d ition s, u n d er ten sile con d ition s, by ben d in g, u n d er sh ear con d ition s.

parting

dividing

forming under shear conditions

forming by bending

forming under tensile conditions

forming under compressive and tensile conditions

forming under compressive conditions

forming

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

joining

joining through forming

– – – – –

Fig. 2.1.2 Production processes used in the field of forming technology

M ethods of forming and cutting technology

7

forming

tw isting

displacement

forming under shearing conditions DIN 8587

bending w ith rotary die movement

bending w ith linear die movement

forming by bending DIN 8586

stretch forming

expanding

extending by stretching

forming under tensile conditions DIN 8585

w rinkle bulging

spinning

flanging

deep draw ing

stripping

forming under compressive and tensile conditions DIN 8584

forming by forcing through an orifice

coining

closed die forming

open die forming

rolling

forming under compressive conditions DIN 8583

Fig. 2.1.3 Classification of production processes used in forming in accordance w ith DIN 8582

Th e DIN stan d ard d ifferen tiates between 17 d istin ct form in g p rocesses accord in g to th e relative m ovem en t between d ie an d workp iece, d ie geom etry an d workp iece geom etry (Fig. 2.1.3). Form ing under com pressive conditions Cast slabs, rod s an d billets are fu rth er p rocessed to sem i-fin ish ed p rod u cts by rolling. In ord er to keep th e req u ired rollin g forces to a m in im u m , form in g is p erform ed in itially at h ot form in g tem p eratu re. At th ese tem p eratu res, th e m aterial h as a m alleable, p aste-like an d easily form able con sisten cy wh ich p erm its a h igh d egree of d eform ation with ou t p erm an en t work h ard en in g of th e m aterial. Hot form in g can be u sed to p rod u ce flat m aterial of th e typ e req u ired for th e p rod u ction of sh eet or p late, bu t also for th e p rod u ction of p ip e, wire or p rofiles. If th e th ickn ess of rolled m aterial is below a certain m in im u m valu e, an d wh ere p articu larly strin gen t d em an d s are im p osed on d im en sion al accu racy an d su rface q u ality, p rocessin g is p erform ed at room tem p eratu re by cold rollin g. In ad d ition to rollin g sem i-fin ish ed p rod u cts, su ch as sh eet an d p late, gears an d th read s on d iscrete p arts are also rolled u n d er com p ressive stress con d ition s. Open die form ing is th e term u sed for com p ressive form in g u sin g tools wh ich m ove toward s each oth er an d wh ich con form eith er n ot at all or on ly p artially to th e sh ap e of th e workp iece. Th e sh ap e of th e workp iece is created by th e execu tion of a free or d efin ed relative m ovem en t

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Basic principles of metal forming

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die w orkpiece

Fig. 2.1.4 Open die forming

between th e workp iece an d tool sim ilar to th at u sed in th e h am m er forgin g p rocess (Fig. 2.1.4). Closed die form ing is a com p ressive form in g p rocess, wh ere sh ap ed tools (d ies) m ove toward s each oth er, wh ereby th e d ie con tain s th e workp iece eith er com p letely or to a con sid erable exten t to create th e fin al sh ap e (Fig. 2.1.5). Coining is com p ressive form in g u sin g a d ie wh ich locally p en etrates a workp iece. A m ajor ap p lication wh ere th e coin in g p rocess is u sed is in m an u factu rin g of coin s an d m ed allion s (Fig. 2.1.6). Form ing by forcing through an orifice is a form in g tech n iqu e wh ich in volves th e com plete or partial pressin g of a m aterial th rou gh a form in g d ie orifice to obtain a red u ced cross-section or d iam eter. Th is tech n iq u e in clu d es th e su bcategories free extrusion, extrusion of sem i-finished products and extrusion of com ponents (cf. Sect. 6.1).

upper die w orkpiece

low er die

Fig. 2.1.5 Closed die forming

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

M ethods of forming and cutting technology

9

embossing punch

w orkpiece

Fig. 2.1.6 Coining

Du rin g free extrusion, a billet is p artially red u ced with ou t u p settin g or bu lgin g of th e n on -form ed p ortion of th e workp iece (Fig. 2.1.7 an d cf. Sect. 6.5.4). Free extru sion of h ollow bod ies or tap erin g by free extru sion in volves p artial red u ction of th e d iam eter of a h ollow bod y, for exam p le a cu p , a can or p ip e, wh ereby an extru sion con tain er m ay be req u ired d ep en d in g on th e wall th ickn ess. In extrusion of sem i-finished products a h eated billet is p laced in a con tain er an d p u sh ed th rou gh a d ie op en in g to p rod u ce solid or h ollow extru sion s of d esired cross-section . Cold extrusion of discrete parts in volves form in g a workp iece located between section s of a d ie, for exam p le a billet or sh eet blan k (cf. Sects. 6.5.1 to 6.5.3 an d 6.5.7). In con trast to free extru sion , larger d eform ation s are p ossible u sin g th e extru sion m eth od .

punch

w orkpiece press bush

Fig. 2.1.7 Free extrusion of shafts

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Basic principles of metal forming

10 punch w orkpiece press bush blank

ejector

Fig. 2.1.8 Backw ard can extrusion

Extru sion is u sed for th e m an u factu re of sem i-fin ish ed item s su ch as lon g p rofiles with con stan t cross section s. Cold extru sion is u sed to p rod u ce in d ivid u al com p on en ts, e. g. gears or sh afts. In both m eth od s, form in g takes p lace u sin g eith er rigid d ies or active m ed ia. In ad d ition , a d ifferen ce is d rawn d ep en d in g on th e d irection of m aterial flow relative to th e p u n ch m ovem en t – i. e. forward s, backward s or lateral – an d th e m an u factu re of solid or h ollow sh ap es (cf. Fig. 6.1.1). Based on th e com bin ation of th ese d ifferen tiatin g featu res, in accord an ce with DIN 8583/ 6 a total of 17 p rocesses exist for extru sion . An exam p le of a m an u factu rin g m eth od for can s or cu p s m ad e from a solid billet is backward cu p extru sion (Fig. 2.1.8). Form ing under com bination of tensile and com pressive conditions Drawing is carried ou t u n d er ten sile an d com p ressive con d ition s an d in volves d rawin g a lon g workp iece th rou gh a red u ced d ie op en in g. Th e m ost sign ifican t su bcategory of d rawin g is strip drawing. Th is in volves d rawin g th e workp iece th rou gh a closed d rawin g tool (d rawin g d ie, lower d ie) wh ich is fixed in d rawin g d irection . Th is allows th e m an u factu re of both solid an d h ollow sh ap es. In ad d ition to th e m an u factu re of sem i-fin ish ed p rod u cts su ch as wires an d p ip es, th is m eth od also p erm its th e p rod u ction of d iscrete com p on en ts. Th is p rocess in volves red u cin g th e wall th ickn ess of d eep -d rawn or extru d ed h ollow cu p s by iron in g, an d h as th e effect of m in im izin g th e m aterial in p u t, p articu larly for p ressu re con tain ers, with ou t alterin g th e d im en sion s of th e can bottom (Fig. 2.1.9 an d cf. Sect. 6.5.5).

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

M ethods of forming and cutting technology

11

punch

sinking die

w orkpiece

Fig. 2.1.9 Can ironing

Deep drawing is a m eth od of form in g u n d er com p ressive an d ten sile con d ition s wh ereby a sh eet m etal blan k is tran sform ed in to a h ollow cu p , or a h ollow cu p is tran sform ed in to a sim ilar p art of sm aller d im en sion s with out an y in ten tion of alterin g th e sh eet th ickn ess (cf. Sect. 4.2.1). Usin g th e single-draw deep drawing technique it is p ossible to p rod u ce a d rawn p art from a blan k with a sin gle workin g stroke of th e p ress (Fig. 2.1.10). In case of large d eform ation s, th e form in g p rocess is p erform ed by m eans of redrawing, gen erally u sin g a n u m ber of d rawin g op eration s. Th is can be p erform ed in th e sam e d irection by m ean s of a telescop ic p u n ch (Fig. 2.1.11) or by m eans of reverse drawing, wh ich in volves th e secon d p u n ch actin g in op p osite d irection to th e p u n ch m otion of th e p reviou s d eep -d rawin g op eration (Fig. 2.1.12).

punch blank holder blank draw n part die

Fig. 2.1.10 Single-draw deep draw ing w ith blank holder

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Basic principles of metal forming

12 punch for 2nd draw punch for 1st draw as blank holder for redraw initial hollow body 2nd draw n part die

Fig. 2.1.11 M ultiple-draw deep draw ing w ith telescopic punch

Th e m ost sign ifican t variation of d eep d rawin g is d on e with a rigid tool (Fig. 2.1.10). Th is com p rises a p u n ch , a bottom d ie an d a blan k h old er, wh ich is in ten d ed to p reven t th e form ation of wrin kles as th e m etal is d rawn in to th e d ie. In sp ecial cases, th e p u n ch or d ie can also be from a soft m aterial. Th ere are d eep d rawin g m eth od s wh ich m ake u se of active m ed ia an d active en ergy. Deep d rawin g u sin g active m ed ia is th e d rawin g of a blan k or h ollow bod y in to a rigid d ie th rou gh th e action of a m ed iu m . Active m ed ia in clu d e form less solid su bstan ces su ch as san d or steel balls, flu id s (oil, water) an d gases, wh ereby th e form in g work is p erform ed by a p ress u sin g a m eth od sim ilar to th at em p loyed with th e rigid tools. Th e greatest field of ap p lication of th is tech n iq u e is hydrom echanical drawing, for exam p le for th e m an u factu re of com p on en ts from stain less steel (Fig. 2.1.13, cf. Sects. 4.2.4 an d 4.2.5).

blank holder for 1st draw die for 1st draw punch for1 st draw as die for reverse draw blank holder for reverse draw punch for reverse draw

Fig. 2.1.12 Reverse draw ing

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

M ethods of forming and cutting technology

punch blank holder w orkpiece seal pressure medium pressure medium container

Fig. 2.1.13 Hydromechanical deep draw ing

Flanging is a m eth od of form in g u n d er com bin ed com p ressive an d ten sile con d ition s u sin g a p u n ch an d d ie to raise closed rim s (flan ges or collars) on p ierced h oles (Fig. 2.1.14). Th e h oles can be on flat or on cu rved su rfaces. Flan ges are often p rovid ed with fem ale th read s for th e p u rp ose of assem bly. Spinning is a com bin ed com p ressive an d ten sile form in g m eth od u sed to tran sform a sh eet m etal blan k in to a h ollow bod y or to ch an ge th e p erip h ery of a h ollow bod y. On e tool com p on en t (sp in n in g m an d rel, sp in n in g bu sh ) con tain s th e sh ap e of th e workp iece an d tu rn s with th e workp iece, wh ile th e m atin g tool (roll h ead ) en gages on ly locally (Fig. 2.1.15). In con trast to sh ear form in g, th e in ten tion of th is p rocess is n ot to alter th e sh eet m etal th ickn ess. W rinkle bulging or u p set bu lgin g is a m eth od of com bin ed ten sile an d com p ressive form in g for th e local exp an sion or red u ction of a gen erally tu bu lar sh ap ed p art. Th e p ressu re forces exerted in th e lon gitu d in al d irection resu lt in bu lgin g of th e workp iece toward s ou tsid e, in sid e or in lateral d irection (Fig. 2.1.16).

punch blank holder

w orkpiece die

Fig. 2.1.14 Flanging w ith blank holder on a flat sheet

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

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Basic principles of metal forming

14

spinning mandrel

circular blank

w orkpiece

spinning roller

Fig. 2.1.15 Spinning a hollow body

Form ing under tensile conditions Extending by stretching is a m eth od of ten sile form in g by m ean s of a ten sile force ap p lied alon g th e lon gitu d in al axis of th e workp iece. Stretch form in g is u sed to in crease th e workp iece d im en sion in th e d irection of force ap p lication , for exam p le to ad ju st to a p rescribed len gth . Ten sile test is also a p u re stretch in g p rocess. Straigh ten in g by stretch in g is th e p rocess of exten d in g for straigh ten in g rod s an d p ip es, as well as elim in atin g d en ts in sh eet m etal p arts.

pressure ring w orkpiece

punch

container

ejector

Fig. 2.1.16 Wrinkle bulging to the outside

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M ethods of forming and cutting technology

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mandrel

w orkpiece

Fig. 2.1.17 Expanding by stretching

Exp an d in g is ten sile form in g to en large th e p erip h ery of a h ollow bod y. As in case of d eep d rawin g, rigid (Fig. 2.1.17) as well as soft tools, active m ed ia an d active en ergies are also u sed . Stretch form ing is a m eth od of ten sile form in g u sed to im p art im p ression s or cavities in a flat or con vex sh eet m etal p art, wh ereby su rface en largem en t – in con trast to d eep d rawin g – is ach ieved by red u cin g th e th ickn ess of th e m etal. Th e m ost im p ortan t ap p lication for stretch form in g m akes u se of a rigid d ie. Th is typ e of p rocess in clu d es also stretch drawing an d em bossing. Stretch d rawin g is th e creation of an im p ression in a blan k u sin g a rigid p u n ch wh ile th e workp iece is clam p ed firm ly arou n d th e rim (Fig. 2.1.18). Em bossin g is th e p rocess of creatin g an im p ression u sin g a p u n ch in a m atin g tool, wh ereby th e im p ression or cavity is sm all in com p arison to th e overall d im en sion of th e workp iece (Fig. 2.1.19).

s1

collet

s0

w orkpiece punch

s1< s 0

Fig. 2.1.18 Stretch forming

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Basic principles of metal forming

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punch w orkpiece die

Fig. 2.1.19 Embossing

Form ing by bending In bending with a linear die m ovem ent th e d ie com p on en ts m ove in a straigh t lin e (cf. Sect. 4.8.1). Th e m ost im p ortan t p rocess in th is su bcategory is die bending, in wh ich th e sh ap e of th e p art is im p acted by th e d ie geom etry an d th e elastic recovery (Fig. 2.1.20). Die ben d in g can be com bin ed with d ie coin in g in a sin gle stroke. Die coin in g is th e restrikin g of ben t workp ieces to relieve stresses, for exam p le in ord er to red u ce th e m agn itu d e of sp rin gback. Bending with rotary die m ovem ent in clu d es roll ben d in g, swivel ben d in g an d circu lar ben d in g. Du rin g roll ben d in g, th e ben d in g m om en t is ap p lied by m ean s of rollin g. Usin g th e roll ben d in g p rocess, it is p ossible to m an u factu re cylin d rical or tap ered workp ieces (Fig. 2.1.21). Th e roll ben d in g p rocess also in clu d es roll straigh ten in g to elim in ate u n d esirable d eform ation s in sh eet m etal, wire, rod s or p ip es (Fig. 2.1.22 an d cf. Sect. 4.8.3) as well as corru gatin g an d roll form in g (Fig. 2.1.23 an d cf. Sect. 4.8.2).

punch w orkpiece bending die

U die

Fig. 2.1.20 Die bending

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

V die

M ethods of forming and cutting technology

17

w orkpiece rollers

Fig. 2.1.21 Roll bending

Swivel bending is ben d in g u sin g a tool wh ich form s th e p art arou n d th e ben d in g ed ge (Fig. 2.1.24). Circular bending is a con tin u ou s p rocess of ben d in g wh ich p rogresses in th e d irection of th e sh an k u sin g strip , p rofile, rod , wire or tu bes (Fig. 2.1.25). Circu lar ben d in g at an an gle greater th an 360°, for exam p le is u sed in th e p rod u ction of sp rin gs an d is called coilin g. Form ing under shear conditions Displacem ent is a m eth od of form in g wh ereby ad jacen t cross-section s of th e workp iece are d isp laced p arallel to each oth er in th e form in g zon e by a lin ear d ie m ovem en t (Fig. 2.1.26). Disp lacem en t alon g a closed d ie ed ge can be u sed for exam p le for th e m an u factu re of weld in g bosses an d cen terin g in d en tation s in sh eet m etal com p on en ts.

straightening rollers

w orkpiece

Fig. 2.1.22 Roll straightening

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Basic principles of metal forming

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Twisting is a m eth od of form in g u n d er sh earin g con d ition s in wh ich ad jacen t cross-section al su rfaces of th e workp ieces are d isp laced relative to each oth er by a rotary m ovem en t (Fig. 2.1.27).

Fig. 2.1.23 Roll forming

clamping jaw s

w orkpiece

cheek

Fig. 2.1.24 Sw ivel bending

w orkpiece support w orkpiece bending mandrel clamping fixture

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Fig. 2.1.25 Circular bending

M ethods of forming and cutting technology

19

blank holder

punch

w orkpiece

Fig. 2.1.26 Displacement

ϕ MT w orkpiece

MT

Fig. 2.1.27 Tw isting

2.1.3 Dividing Dividing is th e first su bgrou p u n d er th e h ead in g of p artin g, bu t is gen erally categorized as a “form in g tech n iq u e” sin ce it is often u sed with oth er com p lem en tary p rod u ction p rocesses (cf. Fig. 2.1.2). Accord in g to th e d efin ition of th e term , d ivid in g is taken to m ean th e m ech an ical sep aration of workp ieces with ou t th e creation of ch ip s (n on -cu ttin g). Accord in g to DIN 8588, th e d ivid in g category in clu d es th e su bcategories sh ear cu ttin g, wed ge-action cu ttin g, tearin g an d breakin g (Fig. 2.1.28). Of th ese, th e sh ear cu ttin g is th e m ost im p ortan t in in d u strial ap p lication .

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Basic principles of metal forming

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parting

dividing

shear cutting

w edge-action cutting

tearing

breaking

Fig. 2.1.28 Parting techniques classified under forming

Shear cutting – kn own in p ractice as sh earin g for sh ort – is th e sep aration of workp ieces between two cu ttin g ed ges m ovin g p ast each oth er (Fig. 2.1.29 an d cf. Sect. 4.5). Du rin g sin gle-stroke sh earin g, th e m aterial sep aration is p erform ed alon g th e sh earin g lin e in a sin gle stroke, in m u ch th e sam e way as u sin g a com p ou n d cu ttin g tool. Nibblin g, in con trast, is a p rogressive, m u ltip le-stroke cu ttin g p rocess u sin g a cu ttin g p u n ch du rin g wh ich sm all waste p ieces are sep arated from th e workp iece alon g th e cu ttin g lin e. Fine blanking is a sin gle-stroke sh earin g m eth od th at u ses an an n u lar serrated blan k h old er an d a cou n terp ressu re p ad . Th u s th e gen erated blan ked su rface is free of an y in cip ien t bu rrs or flaws, wh ich is freq u en tly u sed as a fu n ction al su rface (Fig. 2.1.30 an d cf. Sect. 4.7).

punch die

open shearing

blanking contour

Fig. 2.1.29 Shearing

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M ethods of forming and cutting technology

21

punch annular serrated blank holder serrated ring die counterpunch

Fig. 2.1.30 Fine blanking

W edge-action cutting of workp ieces is gen erally p erform ed u sin g a wed ge-sh ap ed cu ttin g ed ge. Th e workp iece is d ivid ed between th e blad e an d a su p p ortin g su rface. Bite cu ttin g is a m eth od u sed to d ivid e a workp iece u sin g two wed ge-sh ap ed blad es m ovin g toward s each oth er. Th is cu ttin g m eth od is em p loyed by cu ttin g n ip p ers or bolt cu tters (Fig. 2.1.31). Th e p rocesses tearing an d breaking su bject th e workp iece eith er to ten sile stress or ben d in g or rotary stress beyon d its u ltim ate breakin g or ten sile stren gth .

tool w orkpiece

Fig. 2.1.31 Bite cutting

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Basic principles of metal forming

22

2.1.4 Combinations of processes in manufacturing Variou s com bin ation s of d ifferen t form in g p rocesses or com bin ation s of form in g, cu ttin g an d join in g p rocesses h ave been fou n d to be su ccessfu l over m an y years. Stretch drawing and deep drawing, for exam p le, assu m e an im p ortan t role in th e sh eet m etal p rocessin g in d u stry (cf. Sect. 4.2.1). Du rin g stretch d rawin g, th e blan k is p reven ted from slid in g in to th e d ie u n d er th e blan k h old er by m ean s of a lockin g bead an d bead in g rod s or by ap p lyin g a su fficien tly h igh blan k h old er force (Fig. 2.1.32). As a resu lt, th e blan k is su bjected to ten sile stress d u rin g p en etration of th e p u n ch . So th e sh eet m etal th ickn ess is red u ced . Deep d rawin g, in con trast, is a p rocess of form in g u n d er com bin ed ten sile an d com p ression con d ition s in wh ich th e sh eet is form ed u n d er tan gen tial com p ressive stress an d rad ial ten sile stress with ou t an y in ten tion to alter th e th ickn ess of th e sh eet m etal (cf. Fig. 4.2.1). For exam p le wh en d rawin g com p lex bod y p an els for a p assen ger car, stretch d rawin g an d d eep d rawin g m ay be con d u cted sim u ltan eou sly. Th e tool com p rises a p u n ch , d ie an d blan k h old er (Fig. 2.1.32). Th e blan k h old er is u sed d u rin g stretch d rawin g to act as a brake on th e m etal, an d d u rin g d eep d rawin g to p reven t th e form ation of wrin kles. Mod ern p ressin g tech n iq u es tod ay p erm it th e d esired m od ification of th e blan k h old er force d u rin g th e d rawin g stroke. Th e blan k h old er forces can be ch an ged in d ep en d en tly at variou s location s of th e blan k h old er d u rin g th e d rawin g stroke. Th e blan k is in serted in th e d ie an d clam p ed by th e blan k h old er. Th e form in g p rocess begin s with p en etra-

draw ing w ith blank holder

stretch forming

punch

deep draw ing

F St FBl

blank holder

FSt FBl

FBl

FBl

blank die

s0

=

s0 s1

+

s0

s0

Fig. 2.1.32 Overlapping deep draw ing and stretch forming in the sheet metal forming process

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

M ethods of forming and cutting technology

tion of th e p u n ch to p erform a stretch d rawin g p rocess in wh ich th e wall th ickn ess of th e stretch ed blan k is red u ced . Th e bottom of th e d rawn p art is su bseq u en tly form ed . Th e d eep d rawin g p rocess begin s on ce th e req u ired blan k h old in g force h as been red u ced to th e exten t th at th e blan k m aterial is able to flow with ou t gen eratin g wrin kles over th e rou n d ed section s of th e d ie. At th e en d of th e d rawin g p rocess, th e blan k h old er force is freq u en tly in creased again in ord er to obtain a rep rod u cible fin al geom etry by resp ectin g th e stretch in g p ortion of th e d rawin g stroke. In ad d ition to d eep d rawin g, bod y p an els are ad d ition ally p rocessed in th e stam p in g p lan t by form in g u n d er ben d in g, com p ressive an d sh earin g con d ition s. A ch aracteristic of th e bending p rocess is th at a cam ber is forced on th e workp iece in volvin g an gu lar ch an ges an d swivel m otion s bu t with ou t an y ch an ge in th e sh eet th ickn ess. Th e sp rin gback of th e m aterial resu ltin g from its elastic p rop erties is com p en sated for by overben din g (cf. Sect. 4.8.1). An oth er p ossibility for obtain in g dim en sion ally p recise workp ieces is to com bin e com p ressive stresses with in tegrated restrikin g of th e workp iece in th e area of th e bottom dead cen ter of th e slide m ovem en t. Form ing is alm ost always com bin ed with cutting. Th e blan k for a sh eet m etal p art is cu t ou t of coil stock p rior to form in g. Th e form in g p rocess is followed by trim m in g, p iercin g or cu t-ou t of p arts (cf. Sect. 4.1.1). If n eith er th e cu ttin g n or th e form in g p rocess d om in ates th e p rocessin g of a sh eet m etal p art, th is com bin ation of m eth od s is kn own as blanking. W h ere greater p iece n u m bers are p rod u ced , for m ost sm all an d m ed iu m -sized p u n ch ed p arts a p rogressive tool is u sed , for exam p le in th e case of fin e-ed ge blan kin g (cf. Sect. 4.7.3). However, solid form in g p rocesses often also com bin e a n u m ber of d ifferen t tech n iq u es in a sin gle set of d ies (cf. Sect. 6.1). Th e call for greater cost red u ction s d u rin g p art m an u factu re h as brou gh t abou t th e in tegration of ad d ition al p rod u ction tech n iq u es in th e form in g p rocess. Stackin g an d assem bly of p u n ch ed p arts, for exam p le, com bin es n ot on ly th e classical blan kin g an d form in g p rocesses bu t also join in g for th e m an u factu re of fin ish ed stator an d rotor assem blies for th e electric m otor in d u stry (Fig. 2.1.33, cf. Fig. 4.6.22 an d 4.6.23). Sh eet m etal p arts can also be join ed by m ean s of form in g, by th e so-called h em m in g or flan gin g (Fig. 2.1.34).

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23

Basic principles of metal forming

24

Dividing, coating and m odifying m aterial property technologies will su bstan tially exp an d th e field of ap p lication covered by form in g tech n ology in th e fu tu re. Th is will allow fin ish p rocessin g in on ly a sm all n u m ber of station s, wh ere p ossible in a sin gle lin e, an d will red u ce costs for h an d lin g an d logistics th rou gh ou t th e p rod u ction seq u en ce.

Fig. 2.1.33 Joining by parting

Fig. 2.1.34 Joining by forming: hemming

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

2 Basic principles of metal forming

2.2 Basic terms 2.2.1 Flow condition and flow curve Metallic m aterials m ay be sh ap ed by ap p lyin g extern al forces to th em with ou t red u cin g th eir stru ctu ral coh esion . Th is p rop erty is kn own as th e form ability of m etal. Deform ation or flow occu rs wh en th e rows of atom s with in th e in d ivid u al crystallin e grain s are able, wh en stressed beyon d a certain lim it, to slid e again st on e an oth er an d coh esion between th e rows of atom s takes p lace at th e followin g atom ic lattice. Th is slid in g occu rs alon g p lan es an d d irection s d eterm in ed by th e crystallin e stru ctu re an d is on ly m ad e p ossible by, for exam p le, d islocation s (fau lts in th e arran gem en t of th e atom ic lattice). Oth er flow m ech an ism s su ch as twin crystal form ation , in wh ich a p erm an en t d eform ation is cau sed by a rotation of th e lattice from on e p osition to an oth er, p lay on ly a m in or role in m etal form in g tech n ology. Flow com m en ces at th e m om en t wh en th e p rin cip le stress d ifferen ce (sm ax – sm in ) reach es th e valu e of th e flow stress k f, or wh en th e sh ear strain cau sed by a p u rely sh earin g stress is eq u al to h alf th e flow stress, given by:

k f = σ max – σ min By n eglectin g th e p rin cip le stress s2 , th is m ath em atical exp ression rep resen ts an ap p roxim ate solu tion of th e sh earin g stress h yp oth esis with th e greatest p rin cip le stress s1 an d th e sm allest p rin cip le stress s3 :

k f = σ1 – σ 3

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26

Th e valu e of th e flow stress d ep en d s on th e m aterial, th e tem p eratu re, th e d eform ation or strain , w, an d th e sp eed at wh ich d eform ation or . strain rate is carried ou t, w. Below th e recrystallisation tem p eratu re, th e flow stress gen erally rises with in creasin g d eform ation , wh ile th e tem p eratu re an d d eform ation rate exert on ly a m in im al in flu en ce. Excep tion s to th is ru le are form in g tech n iq u es su ch as rollin g an d forgin g, in wh ich extrem ely h igh d eform ation rates are u sed . Above th e recrystallisation tem p eratu re, th e flow stress is gen erally su bject to th e tem p eratu re an d d eform ation rate, wh ile a p reviou s d eform ation h istory h as on ly m in im al in flu en ce. Th e flow stress gen erally d rop s with in creasin g tem p eratu re an d d ecreasin g d eform ation rate. Accord in gly, DIN 8582 d ifferen tiates between m etal form in g p rocesses in volvin g a lastin g ch an ge in stren gth p rop erties an d th ose in volvin g n o ap p reciable ch an ge in stren gth p rop erties, p reviou sly d esign ated as cold an d h ot form in g. In th e tem p eratu re ran ge between , d eform ation in volves on ly a tem p orary ch an ge in th e stren gth p rop erties of th e m aterial. In th is case, th e d eform ation sp eed is h igh er th an th e recovery or recrystallisation rate. Recrystallisation starts on ly after com p letion of th e form in g p rocess. Th e ru les of m etal form in g with lastin g ch an ge in th e stren gth p rop erties ap p ly in th is case. Th e DIN 8582 stan d ard also breaks d own th e p rocess accord in g to form in g with ou t h eatin g (cold form in g) an d form in g after th e ap p lication of h eat (h ot form in g). Th ese term s sim p ly sp ecify wh eth er h eatin g d evices are n ecessary. Un like th eir form er m ean in g, th ese term s are n ot p h ysically related to th e m aterial con cern ed . Th e flow stress of th e in d ivid u al m aterials is d eterm in ed by exp erim en ts in fu n ction of d eform ation (or strain ) an d d eform ation rate (or strain rate) at th e variou s tem p eratu re ran ges, an d d escribed in flow cu rves. On e of th e u ses of flow cu rves is to aid th e calcu lation of p ossible d eform ation , force, en ergy an d p erform an ce.

2.2.2 Deformation and material flow Actu al d eform ation

w, also called logarith m ic or tru e strain , is given by: h1

ϕ1 =

∫

h0

dh h = ln 1 h h0

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Basic terms

27

in wh ich w1 is d eform ation in on e p rin cip le axis an d w2 an d w3 in th e oth er two p rin cip le axes. Th is eq u ation will give, for exam p le, th e am ou n t of com p ression in a bod y with h eigh t h (Fig. 2.2.1). w is calcu lated from th e com p ression relative to th e startin g m easu rem en t e or from th e relative d eform ation

ε1 =

h1 – h 0 ∆h = , h0 h0

in wh ich h 0 stan d s for th e h eigh t of th e bod y before com p ression an d h 1 th e fin al h eigh t of th e bod y after com p ression :

ϕ1 = ln

h1 = ln(1 + ε1 ) h0

In accord an ce with th e law of volu m e con stan cy, accord in g to wh ich th e volu m e is n ot altered by th e d eform ation p rocess (Fig. 2.2.1), th e su m of all d eform ation valu es is always eq u al to zero:

ϕ1 + ϕ 2 + ϕ 3 = 0

F

V0 = l 0 b 0 h 0 = V1 = l 1 b 1 h 1

h0

h1 b1

b0 l0

l1

Fig. 2.2.1 Dimensional changes in frictionless upsetting of a cube

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Basic principles of metal forming

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Th e greatest d eform ation , wh ich is eq u al to th e su m of th e two oth er d eform ation s, is d esign ated th e p rin cip le d eform ation jg:

ϕ 1 = − (ϕ 2 + ϕ 3 ) = ϕ g Th e p rin cip le d eform ation m u st be a kn own q u an tity, as it form s th e basis for every calcu lation , for exam p le of d eform ation force. It is easy to d eterm in e, as it carries a d ifferen t sign to th e oth er two. In th e com p ression of a cu bic bod y, for exam p le, th e in crease of wid th (b 1 > b 0 ) an d len gth (l1 > l 0 ) resu lts in a p ositive sign , wh ile th e d ecrease of h eigh t (h 1 < h 0 ) p rod u ces a n egative sign (Fig. 2.2.1). Accord in gly, th e absolu te greatest d eform ation is alon g th e vertical axis j1 . . Sim ilar to th e su m of d eform ation s, th e su m of d eform ation rates j m u st always be eq u al to zero: ˙ 2 + ϕ˙ 3 = 0 ϕ˙ 1 + j Th e flow law ap p lies ap p roxim ately:

ϕ 1: ϕ 2: ϕ 3 = (σ 1− σ m ) : (σ 2 − σ m ) : (σ 3 − σ m ) , with th e m ean stress

sm given by σm =

σ1 + σ 2 + σ 3 3

Th e m aterial flow alon g th e d irection of th e stress wh ich lies between th e largest stress sm ax an d th e sm allest stress sm in will th erefore be sm all an d will be zero in cases of p lan e strain m aterial flow, wh ere d eform ation is on ly in on e p lan e.

2.2.3 Force and w ork In calcu latin g th e forces req u ired for form in g op eration s, a d istin ction m u st be m ad e between op eration s in wh ich forces are ap p lied d irectly an d th ose in wh ich th ey are ap p lied in d irectly. Direct ap p lication of force m ean s th at th e m aterial is in d u ced to flow u n d er th e d irect ap p li-

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Basic terms

29

cation of an exterior force. Th is requ ires su rfaces to m ove directly again st on e an oth er u n der pressu re, for exam ple wh en u psettin g an d rollin g. In direct application of force, in con trast, in volves th e exertion of a force som e distan ce from th e actu al form in g zon e, as for exam ple wh en th e m aterial is drawn or forced th rou gh a n ozzle or a clearan ce. Addition al stresses are gen erated du rin g th is process wh ich in du ce th e m aterial to flow. Exam ples of th is m eth od in clu de wire drawin g or deep drawin g. In th e d irect ap p lication of force, th e force F is given by:

F = A ⋅ kw wh ere A is th e area u n d er com p ression an d k w is th e d eform ation resistan ce. Th e d eform ation resistan ce is calcu lated from th e flow stress k f after takin g in to accou n t th e losses arisin g, u su ally th rou gh friction . Th e losses are com bin ed in th e form in g efficien cy factor ηF:

ηF =

kf kw

Th e force ap p lied in in d irect form in g op eration s is given by:

F = A ⋅ k wm ⋅ ϕ g = A ⋅

k fm ηF

⋅ ϕg = A ⋅

w id ηF

wh ere A represen ts th e tran sverse section area th rou gh wh ich th e force is tran sm itted to th e form in g zon e, k wm is th e m ean deform ation resistan ce an d k fm th e m ean stability factor, both of wh ich are given by th e in tegral m ean of th e flow stress at th e en try an d exit of th e deform ation zon e. Th e arith m etic m ean can u su ally be u sed in place of th e in tegral valu e. Th e referen ced deform ation work w id is th e work n ecessary to deform a volu m e elem en t of 1 m m 3 by a certain volu m e of displacem en t: ϕg

wid =

∫ k f ⋅ d ϕ ≅ k fm⋅ ϕ g 0

Th e sp ecific form in g work can be obtain ed by grap h ic or n u m erical in tegration u sin g available flow cu rves, an d in exactly th e sam e way as th e flow stress, sp ecified as a fu n ction of th e d eform ation jg. Figure 2.2.2 illu strates th e flow cu rves an d related work cu rves for d ifferen t m aterials.

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Basic principles of metal forming

30

Nmm mm 3

N mm 2

800

800

700

700

600

600

500

500

400

400

300

300

200

200

100

0

flow stress k f

1000

specific deformation w ork w id

1000

St 14 St 37 C 35 (normally annealed)

100

0

0,2

0,4

0,6

1,2 0,8 1,0 log. principle deformation ϕg

Fig. 2.2.2 Flow curves and curves show ing the specific deformation w ork for different materials

If th ere is n o flow cu rve available for a p articu lar m aterial, it can be d eterm in ed by exp erim en tation . A ten sile, com p ressive or h yd rau lic in d en tation test wou ld be a con ceivable m eth od for th is. If th e sp ecific d eform ation work w id an d th e en tire volu m e V or th e d isp laced volu m e Vd are kn own q u an tities, th e total d eform ation work W is calcu lated on th e followin g basis:

W = V⋅

wid ηF

≅ V ⋅ ϕg ⋅

k fm k = Vd ⋅ fm ηF ηF

2.2.4 Formability Th e iden tification of form ability sh ou ld on ly be based on th ose cases of m aterial failu re cau sed as a resu lt of disp lacem en t or cleavage fractu res wh ere n o fu rth er deform ation is p ossible with ou t failu re. If, th erefore, a m aterial breaks before reach in g m axim u m force as a resu lt of a cleavage

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Basic terms

31

fractu re, th is ch aracteristic m ay be taken as a p oin t of referen ce in th e d eterm in ation of form ability, for exam p le d u rin g a ten sile test. However, cases of failu re in wh ich th e stability criterion between th e ou ter an d in n er forces is in d icative of th e ach ievable d eform ation , can n ot be u sed as a basis for d eterm in in g form ability. Su ch cases in clu d e for exam p le th e u n iform strain of a m aterial with m arked n eckin g. Th e form ability of d ifferen t m aterials d iffers even th ou gh oth er con d ition s are eq u al. Th u s it is th at som e m aterials are d escribed as m alleable an d oth ers as brittle. Th ese d escrip tion s are u su ally based on th e ch aracteristics revealed in ten sile testin g for fractu res d u e to sh rin kage or elon gation . Th e form ability of a m aterial is n ot a fixed q u an tity, h owever, it d ep en d s on th e m ean h yd rostatic p ressu re p m exerted d u rin g th e form in g op eration :

pm =

p1 + p 2 + p 3 3

Th u s, for exam p le, a m aterial can h ave a low form ability for on e typ e of form in g op eration wh ere th e m ean h yd rostatic p ressu re is low. However, if a differen t form in g process is em ployed in wh ich th e m ean h ydrostatic pressu re is h igh er, th e sam e m aterial can be form ed with ou t problem s. Even m arble can be plastically deform ed if th e m ean h ydrostatic pressu re exerted is su fficien tly great.

2.2.5 Units of measurement Sin ce th e im p lem en tation of th e law govern in g stan d ard ised u n its of m easu rem en t, it is on ly p erm issible to u se th e variables p rescribed by th e statu tory in tern ation al u n it system (SI u n its). Table 2.2.1 p rovid es a com p arison of th e u n its ap p lied in th e old tech n ical system of m easu rem en t an d th e SI u n its. Th e given variables can be tran sferred to th e in tern ation al m etric system u sin g th e factor 9.81. For ap p roxim ate calcu lation s, it is gen erally su fficien t to u se factor 10, for exam p le:

1 kp ≈ 10 N

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Basic principles of metal forming

32

Table 2.2.1: Conversion of technical to SI units of measurement Unit system

Technical (m kp s)

SI (M KS)

Time: t Length: l Speed: v Revolutions /no. of strokes: Acceleration: a M ass: G

1s 1m 1 m/s rpm 1 m/s 2 9,81 kg = 1 kp s 2/m

1s 1m 1 m/s rpm 1 m/s 2 1 kg 1 t = 1000 kg

Density: r Force: F

9,81 kg/m 3 = 1 kp s 2/m 4 9,81 kg m/s 2 = 1 kp 1M P = 1000 kp 9,81 N/m 2 = 1 kp/m 2 0,0981 bar = 1 at 1,333 mbar = 1 Torr 9,81 N/mm 2 = 1 kp/mm 2 9,81 N m = 1 kp m

1 kg/m 3 1 N (New ton) = 1 kg m/s 2 1 kN = 1000 N 1 N/m 2 = 1 Pa (Pascal) = 1 kg/m s 2 105 N/m 2 = 1 bar

Pressure: p

Tension: s Torque: M

Work: W

9,81 kg m 2 = 1 kp m s 2 9,81 W = 1 kp m/s 0,7355 kW = 1 PS 9,81 J = 1 kp m

Quantity of heat: Q Sound pressure level: L

4,19 kJ = 1 kcal 1 dB(A)

M ass moment of inertia: J Performance: P

1 N/mm 2 1N m 1 kN m = 1000 N m 1 kgm 2 1 N m/s = 1 W (Watt) 1kW = 1000 W 1 J (Joule) = 1 N m = 1 W s 1kJ = 1000 J 1 kJ 1 dB(A)

Bibliography DIN 8580 (Entw urf): M anufacturing M ethods, Classification, Beuth Verlag, Berlin. DIN 8582: M anufacturing methods, forming, classification, subdivision, Beuth Verlag, Berlin. DIN 8583: M anufacturing methods, forming under compressive conditions, Part 1 - 6, Beuth Verlag, Berlin. DIN 8584: M anufacturing methods, forming under combination of tensile and compressive conditions, part 1 - 6, Beuth Verlag, Berlin. DIN 8585: M anufacturing methods, forming under tensile conditions, part 1 - 4, Beuth Verlag, Berlin. DIN 8586: M anufacturing methods, forming by bending, Beuth Verlag, Berlin. DIN 8587: M anufacturing methods, forming under shearing conditions, Beuth Verlag, Berlin. DIN 8588: M anufacturing methods, terms, dividing, Beuth Verlag, Berlin. Lange, K: Umformtechnik, Band 1: Grundlagen, Springer-Verlag, Heidelberg (1984).

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

3 Fundamentals of press design

3.1 Press types and press construction Th e fu n ction of a p ress is to tran sfer on e or m ore forces an d m ovem en ts to a tool or d ie with th e p u rp ose of form in g or blan kin g a workp iece. Press d esign calls for sp ecial kn owled ge of th e p rod u ction p rocess to be u sed . Dep en d in g on th e in ten d ed ap p lication , th e p ress is d esign ed eith er to execu te a sp ecific p rocess or for m ain ly u n iversal u se. In a “sp ecialized p rod u ction lin e”, in view of econ om ic p rod u ction , th e ou tp u t is th e m ost im p ortan t issu e, wh ile m ain tain in g th e req u ired p art q u ality. Material-related in flu en ces su ch as th e m axim u m d eep d rawin g sp eed or workp iece-related in flu en ces su ch as th e su itability of p arts for tran sp ortation , as well as asp ects su ch as op eratin g ergon om ics an d workin g safety all h ave to be taken in to con sid eration . Th e p u rp ose of a universal production line, in con trast, is to offer flexibility an d u se a larger variety of d ies coverin g as wid e a p art sp ectru m as p ossible. Ach ievem en t of th e m axim u m p ossible u p tim e is a d eterm in in g factor in th e d esign of an y p ress, with th e objective of red u cin g u n p rod u ctive or d own tim e to a m in im u m – for exam p le n ecessary for ch an gin g d ies, m ain ten an ce or tryou t. Fu rth erm ore, all p resses are exp ected to en su re th e lon gest p ossible service life of tools an d d ies. Th erefore, for exam p le, th e p recision gu id an ce of th e slid e is req u ired .

On th e basis of th e p rod u ction tech n iq u es u sed , p resses are d ivid ed in to th e followin g su bcategories: – sh eet m etal form in g p resses (cf. Sect. 4.4), – blan kin g p resses (cf. Sects. 4.6 an d 4.7.4),

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– p resses for solid form in g, su ch as forgin g, extru sion an d coin in g p resses (cf. Sect. 6.8), – p resses for in tern al h igh -p ressu re form in g (cf. Sect. 5.6), – p ressu re form in g, stretch in g an d stam p in g p resses. Sh ears are also com m on ly u sed , gen erally in sep arate lin es, for th e m an u factu re of sh eet m etal blan ks (cf. Sects. 4.6.1 an d 4.6.2).

3.1.1 Press frame Th e fu n ction of th e p ress fram e is to absorb forces, to p rovid e a p recise slid e gu id an ce an d to su p p ort th e d rive system an d oth er au xiliary u n its. Th e stru ctu ral d esign of th e fram e d ep en d s on – th e p ressin g force – th is d eterm in es th e req u ired rigid ity, – th e d im en sion s of d ies in flu en cin g th e size of th e tool area, – work area accessibility th at d eterm in es on th e sh ap e of th e p ress fram e, – th e d egree of gu id an ce p recision . Th is in flu en ces both th e sh ap e an d th e rigid ity of th e fram e. Presses with relatively low p ress forces, u p to 2,500 kN, freq u en tly m ake u se of th e open-front press d esign (cf. Fig. 4.6.14). Th is con stru ction is ch aracterized p articu larly by th e easy access to th e tool area. However, its d rawback lies in th e asym m etrical d eflection of th e fram e, wh ich con tribu tes to red u ction s in p art accu racy an d d ie life, p articu larly in blan kin g ap p lication s. In clin ed or h orizon tal d esign s p erm it faster p art ejection m akin g u se of gravity followin g th e form in g process, for exam ple wh en forgin g or coin in g (cf. Fig. 6.8.20). As a ru le, open -fron t presses are u sed in con ju n ction with sin gle dies. Presses with a n om in al p ressin g force over 4,000 kN are con stru cted exclu sively in a gan try-typ e d esign . Th ese are kn own as straight-side presses (Fig. 3.1.1). In th is p ress typ e, th e p ress bed with th e bed p late, th e two u p righ ts an d th e crown form th e fram e. Th e ap p lication sp ectru m of straigh t-sid e p resses ran ges from sm all p arts p rod u ced u sin g p rogression d ies, com p ou n d p rogression d ies or tran sfer d ies th rou gh to in d ivid u al d ies for varyin g p art sizes (cf. Sect. 4.1.1). W h en u sin g p rogression tools, th e p arts are con veyed by th e sh eet strip itself. Con -

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versely, wh en u sin g in d ivid u al d ies, an ad d ition al grip p er rail is gen erally in tegrated in th e p ress. A p articu larly econ om ical p rod u ction p rocess can be ach ieved by accom m od atin g in d ivid u al resp . tran sfer d ies in on e an d th e sam e p ress. W h en au tom ated , u sin g a tran sfer system , th is typ e of lin e is kn own as a transfer press. Origin ally, p ress fram es were p rod u ced of gray cast iron . Progress m ad e in th e field of weld in g tech n ology su bseq u en tly allowed th ick

tie rod nut press crown cylinder bridge

slide gib surface

tie rod uprights bed plate press bed

bridge for the draw cushion

upright clearance

monoblock frame Fig. 3.1.1 Design of a straight-side press frame

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

multiple-part frame

Fundamentals of press design

36

Fig. 3.1.2 FEM optimization of the press frame: Distribution of stresses under off-center load

p late m etal to be reliably join ed togeth er, op en in g u p a h igh d egree of d esign flexibility. Th u s, p resses with weld ed fram es can be con stru cted p recisely for in d ivid u al req u irem en ts. Com p ou n d design s in tegratin g welded an d cast com p on en ts are also p ossible. Sm all straigh t-side p resses are bu ilt exclu sively u sin g th e welded m onoblock fram e typ e, wh ile larger design s u se a m ultiple-part fram e con stru ction wh ich effectively lim it th e size of com p on en ts to facilitate both p rocessin g an d tran sp ort. Th e in dividu al com p on en ts are assem bled togeth er u sin g tie rods wh ich gen erally reach alon g th e en tire h eigh t of th e p ress, an d p re-ten sion ed to a determ in ed force (Fig. 3.1.1). Carefu l configuration of the fram e is essen tial, as it is su bjected to stress both by th e drive elem en ts an d au xiliary u n its, an d is also req u ired to en su re p recise gu idan ce of th e p ress slide. Care m u st be taken n ot to exceed th e load an d elastic deform ation lim it of th e fram e. To satisfy th ese com p lex design req u irem en ts, p ress fram es are op tim ized with th e aid of th e Finite Elem ent Method (FEM). Th is in volves th e com p u tation an d dep iction of stresses also u n der eccen tric loads (Fig. 3.1.2). By en su r-

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in g th e correct distribu tion of m aterial an d con figu ration of tran sition al radii between th e bed an d u p righ ts, as well as between th e u p righ ts an d p ress crown , it is p ossible to avoid exceedin g th e m axim u m p erm issible stress levels, also at rated force. An oth er ben efit of FEM-calcu lated com p on en ts is th e ability to save on m aterial n ot n eeded to en su re rigidity. On top of th e press bed lies th e bed p late (bolster p late) u sed to cen ter an d h old down th e lower h alf of th e die (Fig. 3.1.1 an d cf. Sect. 3.4). Th e bolster p lates on th e p ress bed an d th e slide are screwed in to p lace to allow sim p le rem oval, for exam p le to alter th e T-n otch con figu ration , to retrofit h ydrau lic clam p in g devices or to adap t th e op en in gs to n ew p ressin g req u irem en ts.

3.1.2 Slide drive Th e p ress fram e absorbs all th e forces actin g on th e p ress, an d gu id es th e slid e togeth er with th e u p p er d ie. Th e slid e, wh ich is m oved in th e vertical d irection by a d rive system actin g in th e press crown, tran sfers th e form in g or blan kin g force to th e d ie. Alon gsid e th is typ e of top driven press, th ere are p resses wh ose d rive system is located in th e p ress bed . Th is typ e of bottom -driven press is u sed p rim arily for solid form in g, sp ecifically as coin in g p resses (cf. Fig. 3.2.5). A basic d ifferen ce exists between displacem ent-related, force-related and work-related presses. Th e

one-point configuration

two-point configuration

four-point configuration

Fig. 3.1.3 Connecting rod forces at the slide in one-, tw o- and four-point presses

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Fundamentals of press design

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slide force FSt cover plate

side w all

base plate

clamping grooves gib prism eight-track slide gib

support plate

x

front plate

side opening

y

press frame front opening

Fig. 3.1.4 Design of the slide in a hydraulic press

grou p of work-related p resses in clu d es screw p resses an d forgin g h am m ers. Disp lacem en t an d work-related p resses are gen erally referred to as m echanical/hydraulic p resses. In m ech an ical p resses, force is tran sm itted to th e slid e by m ean s of con n ectin g rod s (Fig. 3.1.9), wh ile in h yd rau lic p resses th is tran sfer takes p lace via th e p iston rod s of th e h yd rau lic cylin d er (Fig. 3.1.10).

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Dep en d in g on th e n u m ber of force tran sm ittin g elem en ts, th ere are one, two or four-point configurations in the slide (Fig. 3.1.3). W h en an offcen ter load is exerted by th e d ie on th e slid e, a m u ltip le-p oin t p ress is better able to cou n ter th e resu ltin g tiltin g m om en t. Th e slid e, wh ich gen erally h as a weld ed box sh ap e, is gu id ed in th e p ress fram e (Fig. 3.1.4). In th e case of off-cen ter load s, th e slide gibs also p rovid e p art of th e su p p ortin g forces. Figure 3.1.5 illu strates som e com m on typ es of gibs. A m u ltip le-p oin t p ress, u sed in con ju n ction with a stable slid e gib system , offers th e best con d ition s for ach ievin g good p art q u ality an d a lon g d ie life as a resu lt of m in im al tiltin g of th e slid e. For large-scale p resses with two or fou r con n ectin g rod d rive system s, th e gibs h ave lon g gu id an ce len gth s an d relatively large vertical elon gation of th e fram e. Th is calls for a read ju stm en t featu re. Th e gib clearan ce sh ou ld n ot exceed 0.1 m m . Stan d ard d eep d rawin g p resses are eq u ip p ed with easily ad ju stable an d exch an geable 45° bron ze gibs. In th e case of blan kin g an d tran sfer

press w ith 2 side uprights eight-track gib for w ide side uprights

press w ith 2 side uprights eight-track gib for narrow side uprights

V-prism gib x z

y z

press w ith 4 side uprights eight-track block gib for high eccentric loads in the x and y direction

press w ith 4 side uprights eight-track gib for high eccentric loads in the y direction

slide

ball joint gib

Fig. 3.1.5 Different gib configurations

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

column gib

Fundamentals of press design

40

p resses, eigh t-track gu id es an d exch an geable bron ze gibs on th e slid e are th e state of th e art. A reliable system of cen tral lu brication is essen tial to en su re op tim u m gu id an ce. In stead of bron ze slid e gibs, p lastic gibs are also u sed . Nowadays, u n iversal p resses are freq u en tly con figu red with eigh tfold roller gibs (Fig. 3.1.6). Th is gu idan ce system is p reten sion ed free of gib clearan ce by in dividu al ap p lication of th e rollers, wh ich are each m ou n ted in roller bearin gs. Th e rollers are lu bricated an d sealed for life an d ru n on h arden ed gu ide rails on th e p ress u p righ t free of oil or grease. Bottom -d riven toggle p resses featu re a lon g p ress fram e wh ich calls for a sp ecial gu id an ce system to com p en sate for n eckin g, tilt an d p reven t h igh ed ge p ressu res (cf. Fig. 3.2.5). Card an u n iversal ball join t bearin gs com p en sate for tilts an d en su re th at th e su p p ortive fu n ction is even ly sp read over th e gibs (Fig. 3.1.5). Th ese gu id an ce com p on en ts can be u sed in an y p osition : in sid e, ou tsid e, sixfold , eigh tfold or in com bin ation .

Fig. 3.1.6 Roller gib

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Fig. 3.1.7 Eight-track slide gib in cross formation

Th e gu id an ce ratio, i. e. th e ratio of gu id e len gth to slid e len gth , can be red u ced to 1 : 3 in large-scale p resses with a h eigh t restriction . Eccen tric p ress forces can on ly be p artially absorbed by th e gibs in th is case. For h ot form in g ap p lication s, th e exp an sion of th e slid e d u e to tem p eratu re m u st be taken in to con sid eration in th e ch oice of slid e gibs. In th is case, gu id an ce system s are u sed wh ich p erm it exp an sion of th e slid e in on e d irection with ou t gen eratin g ad d ition al stresses (Fig. 3.1.7). For ejection of p arts th at m ay stick to th e u p p er d ies, th e slid e can be fitted with p n eu m atic, h yd rau lic or m ech an ical knock-out pins (cf. Fig. 3.2.12).

3.1.3 Drive systems for deep draw ing presses Sin gle an d d ou ble-action p resses are u sed for sh eet m etal form in g. Th e double-action press featu res, n ext to th e d rawin g slid e, also a sep arate blan k h old er slid e (Fig. 3.1.8, cf. Fig. 4.2.2). Both slid es are actu ated from above. After th e form in g p rocess, th e p art m u st, as a ru le, be tu rn ed u p sid e d own for th e n ext blan kin g an d form in g op eration . Th is req u ires a

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Fundamentals of press design

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press crow n

blank holder drive (toggle drive)

blank holder connecting rod blank holder slide

eight-element slide drive system

slide connecting rod draw ing slide draw punch

draw n part blank holder female die

press bed

Fig. 3.1.8 Double-action mechanical press

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

foundation

Press types and press construction

press crow n

43

slide connecting rod

eight-element slide drive system

draw ing slide

draw n part

female die

pressure pin

blank holder

hydraulic draw cushion

draw punch

Fig. 3.1.9 Single-action mechanical press w ith draw cushion

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Fundamentals of press design

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bu lky, cost-in ten sive tu rn in g device to be in stalled down stream from th e dou ble-action press. Th ere are advan tages in form in g a part in th e reverse position , i. e. th e bottom of th e part facin g u pwards. In th is case part ejection is sim pler th rou gh a slide cu sh ion in su bsequ en t form in g station s. Th e altern ative is to work with a draw cu sh ion or n itrogen cylin ders. Fu rth erm ore, th e cen terin g in su bsequ en t station s is im proved, sin ce th e parts can be position ed over th eir en tire in n er sh ape by th e bottom die. In addition , th e sen sitive su rfaces of th e m aterial – for exam ple wh en workin g with au tom otive body pan els – are less likely to su stain dam age du rin g tran sportation in th e press an d wh en cen terin g in th e die. It is also possible to in stall th e blan kin g pu n ch es at a lower level for su bsequ en t operation s if th e part h as previou sly been tu rn ed over. In th e case of single-acting deep drawing presses, in con trast, th e blan k h old er force is tran sm itted from u n d ern eath by a d raw cu sh ion (Fig. 3.1.9 an d cf. Fig. 4.2.3). Both th e form in g an d th e blan k h old er force are ap p lied by th e slid e, as th e slid e forces th e d raw cu sh ion d own ward s. After th e d rawin g, with ou t “tu rn in g over”, th e p art is id eally p osition ed for th e su bseq u en t op eration s. W h en u sed togeth er with a h yd rau lically d riven slid e m ovem en t, th e d raw cu sh ion can also be u sed for active counter-drawing (Fig. 3.1.10 an d cf. Fig. 4.2.4). From th e p oin t of view of en ergy savin gs, it is ben eficial th at th e slid e h old s th e blan k wh ile th e d raw cu sh ion ap p lies th e form in g force. In ord er to ach ieve as great a d egree of flexibility as p ossible, d ou bleaction p resses can also be con figu red with a d raw cu sh ion .

3.1.4 Draw cushions Th e fu n ction of th e d raw cu sh ion is to h old th e blan k d u rin g d eep d rawin g op eration s in m ech an ical an d h yd rau lic p resses (cf. Sect. 2.1.4). Th e cu sh ion th u s p reven ts th e form ation of wrin kles an d , as a resu lt of th e ejection fu n ction , raises th e p arts to th e tran sp ort level d u rin g th e retu rn m otion of th e slid e. Mod ern d raw cu sh ion s can be eith er h yd rau lically or p n eu m atically actu ated . A m ajor d ifferen ce between th e two is th e larger force of th e h yd rau lic d raw cu sh ion . Th e cu sh ion force is in itiated d u rin g d own ward travel of th e slid e by, for exam p le, fou r h yd rau lic cylin d ers via th e liftin g brid ges an d com -

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

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slide cylinder slide slide ejector counter draw ing die draw punch active draw cushion draw cushion cylinder

Fig. 3.1.10 Single-action hydraulic press w ith active draw cushion for counter draw ing

pression colu m n s in to th e corn er areas of th e blan k h older on th e die (Fig. 3.1.11 an d cf. Fig. 4.4.39). W h en th e slide reach es th e bottom dead cen ter, th e draw cu sh ion is m oved back to th e u pper position eith er in an u n con trolled, i. e. togeth er with th e retu rn m otion of th e slide, or a con trolled m ovem en t, i. e. after a prescribed stan dstill period, by th e lift cylin der actin g in th e cen ter of th e liftin g bridge. Im pact dam pin g is ach ieved by m ean s of optim ized proportion al valve tech n ology, en su rin g th at th e draw cu sh ion reach es its u pper en d position with ou t vibration s. Th e ben efit h ere is th at th e draw cu sh ion force can be con trolled on a path -depen den t an d a tim e-depen den t basis du rin g th e drawin g process. It is possible, for in stan ce, n ot on ly to redu ce an d in crease th e overall blan k h older force, bu t th e pressu re levels of th e fou r cylin ders can also be m odified in depen den tly of each oth er du e to th e sh ort pressu re respon se tim e with in a ran ge of 25 to 100 % of th e rated pressu re. As a resu lt, th e blan k h older pressu re can be in dividu ally con trolled over th e en tire deep drawin g process at each of th e fou r corn er poin ts of th e die. Th e precision con trol of th e blan k h older follows a prescribed force versu s tim e profile (Fig. 3.1.12).

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Th is offers th e d iem aker an d th e m ach in e op erator th e cap abilities for op tim ization of th e d rawin g p rocess an d for th e red u ction of d ie start-u p tim es. Th e stretch form in g p rocess, for exam p le, can be in itiated by briefly raisin g th e blan k h old er force, or th e m aterial flow corresp on d in gly facilitated by red u cin g th e p ressu re in certain areas of th e blan k h old er (cf. Sect. 2.1.4). To im p rove p art q u ality, ou tp u t an d tool life as well as red u cin g n oise, th e d raw cu sh ion can be p re-accelerated . Th is m ean s th at th e d raw cu sh ion is alread y set in m otion before th e slid e im p acts th e blan k. Th is red u ces th e relative sp eed between th e slid e an d blan k h old er con sid erably as com p ared to an u n con trolled d raw cu sh ion . Du e to th e red u ced im p act of th e blan k h old er, th e n u m -

female die punch draw n part blank holder

moving bolster

foundation

pressure column lifting bridge

displacement cylinder lifting cylinder

Fig. 3.1.11 Design of a hydraulic draw cushion

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ber of p ress strokes can be in creased with ou t com p rom isin g p art q u ality, wh ile at th e sam e tim e th e n oise level is red u ced by as m u ch as 8 d B(A). An im p ortan t ch aracteristic of th e h yd rau lic d raw cu sh ion with d isp lacem en t cylin d ers is th at th e blan kh old in g force, in con trast to th e p n eu m atic d raw cu sh ion , is n ot fu lly ap p lied in stan tan ou sly on ap p lication of th e slid e, an d is on ly bu ilt u p com p letely with th e start of th e p iston m ovem en t th rou gh d isp lacem en t of th e oil colu m n in th e cylin d ers. Th is allows th e vibration s com m on ly en cou n tered on im p act of th e slid e, as in d icated in Fig. 3.1.13, to be avoid ed . Th e n egative in flu en ce of vibration s an d n oise, an d also on th e d rawin g p rocess itself, are elim in ated . Th is is of p articu lar sign ifican ce wh en p rod u cin g large sh eet m etal com p on en ts with h igh strokin g rates. It is p ossible to largely avoid su p erim p osed vibration s affectin g th e d rawin g p rocess at slid e im p act sp eed s of, for exam p le, 40 % with a relatively large lead of th e

1s

pressure/ slide travel travel

80 %

damping phase

100 %

draw cushion travel

displacement pressure back left

80 % back right front left

25%

80 %

front right

time

Fig. 3.1.12 Progression of blank holder force in a hydraulic draw cushion w ith a constant displacement pressure of 100% back right, 80% back left and front right and pressure changeover from 80% to 25% front left

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p n eu m atic d raw cu sh ion (Fig. 3.1.13, top). However, it is on ly m argin ally p ossible to ach ieve a con stan t blan k h old er force at h igh im p act sp eed s (Fig. 3.1.13, bottom ). Th e con d ition s for th e h yd rau lic d raw cu sh ion with d isp lacem en t cylin d ers (Fig. 3.1.11) are sign ifican tly m ore favorable. Sin ce th e p ressu re bu ild -u p d oes n ot take p lace u n til th e begin n in g of th e p iston m ovem en t, even at m axim u m im p act sp eed th e blan k h old er force p eaks on ly m in im ally an d is q u ickly d issip ated (Fig. 3.1.12). Accord in gly, in gen eral term s a lead of th e blan k h old er in th e d ie of som e 30 m m is su fficien t to en su re th at th e en tire d rawin g p rocess takes p lace at a con stan t blan k h old er force.

impact speed 40 %

lead travel

blank holder force

point of impact w ith draw cushion start of draw ing delayed

rated blank holder force time

blank holder force

impact speed 100 %

lead travel

point of impact w ith draw cushion

start of draw ing delayed

rated blank holder force time

Fig. 3.1.13 Progression of blank holder force of a pneumatic draw cushion depending on impact speed

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

3 Fundamentals of press design

3.2 M echanical presses 3.2.1 Determination of characteristic data Th e followin g p aragrap h s will d eal with basic p rin cip les con cern in g force, work and power of m ech an ical p resses. If a weigh t of 75 kg is su sp en d ed from a cran e rop e, a force of arou n d 750 N (force F = Mass m · gravitation al acceleration g) acts on th e rop e. As lon g as th e weigh t is n ot raised , n o work is p erform ed , as th e work W [Nm ] is th e p rod u ct of force F [N] an d d istan ce h [m ]:

W = F⋅h If th is weigh t is n ow raised by 1 m , th e work p erform ed am ou n ts to:

W = 750 N ⋅ 1 m = 750 Nm Th is work can be obtain ed from th e weigh t again wh en it d rop s by 1 m . However, th e m agn itu d e of th e resu ltin g force d ep en d s on th e d istan ce over wh ich th e work takes p lace:

F = W/h If, th erefore, a force of 750 N is u n iform ly exerted to raise th e weigh t over a d istan ce of 1 m , th e sam e force will be exp en d ed if th e en tire work is p erform ed wh en lowerin g th e weigh t over a d istan ce of 1 m . A d ifferen t situ ation resu lts if th e weigh t in itially d rop s freely for h alf

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th e d istan ce an d th en th e en tire work of 750 Nm is exp en d ed over th e last 50 cm = 0.5 m . Th e force is th en given by:

F = 750 Nm / 0. 5 m = 1,500 N Sin ce th e work h as been p erform ed over on ly h alf th e d istan ce, th e force h as d ou bled . If th e en tire work is p erform ed over on ly on e ten th of th e d istan ce (i. e. 0.1 m ), th e force rises ten fold :

F = 750 Nm / 0.1 m = 7 , 500 N In Fig. 3.2.1, th e force exerted over th e relevan t d istan ce is in d icated for all th ree cases. Th e resu lts are th ree rectan gles wh ose areas corresp on d to th e product of force F · distance h an d th u s to th e work W . If a cu rve is traced th rou gh th e corn ers of th e rectan gles, p rovid ed th e existin g work of 750 Nm is p erform ed even ly over a certain d istan ce, it is p ossible to d irectly read th e m agn itu d e of th e force ap p lied . With a form in g d istan ce of 0.2 m , for in stan ce, th e force ap p lied is 3,750 N (Fig. 3.2.1). In su m m ary, it is gen erally valid th at – force an d work are two term s wh ich can be related to each oth er on ly by m ean s of a th ird variable, i. e. d istan ce. – If a force is ap p lied over a certain d istan ce, work is p erform ed . Th is corresp on d s in th e force-d istan ce grap h to th e area of th e rectan gle below th e force cu rve. – If a certain am ou n t of work is p erform ed , th e d istan ce over wh ich it is p erform ed d eterm in es th e m agn itu d e of th e gen erated force. Th e relation s d escribed h ere u sin g th e exam p le of a weigh t, ap p ly gen erally to th e field of p ress con stru ction . Th ey are ap p lied also in th e forging ham m er. Th e h am m er h as a certain weigh t an d is raised over a certain d istan ce. Th is gives it a d efin ed q u an tity of p oten tial en ergy. W h en it gives u p th e work stored in it, i. e. tran sfers its en ergy to th e d ie, th e m agn itu d e of its force at th e m om en t of im p act d ep en d s on th e d isp lacem en t over wh ich d eform ation takes p lace. Th is force can be very large if th e d isp lacem en t of th e workp iece is very sm all, an d can even resu lt in d am age to th e tool an d th e p ress. On th e oth er h an d , in

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51

,

distance s [m] ,

,6

,

W = const. = 7

Nm

,

3

6

7

force [N]

Fig. 3.2.1 Force-stroke diagram show ing the relationship betw een force and stroke for constant w ork

case d eform ation takes p lace over large d isp lacem en ts, th e p oten tial en ergy m ay be in su fficien t, resu ltin g in a n eed for rep eated h am m erin g or several blows. Th ese p rin cip les, illu strated h ere in th e exam p le of th e forgin g h am m er, also ap p ly to m ech an ical p resses. Here, in stead of a raised weigh t, th e en ergy is stored in th e rotatin g m ass of th e flywh eel (Fig. 3.2.8). However, wh ile all th e en ergy stored in th e h am m er m u st be exp en d ed , th e en ergy in th e rotatin g m ass of th e flywh eel is on ly p artially u sed d u rin g a p ress stroke. Th u s, th e electric m otor d rivin g th e flywh eel is n ot overload ed an d d oes n ot n eed to h ave a large p ower cap acity. In con tin u ou s op eration , a flywh eel slowd own between 15 an d 20 % is estim ated to be th e greatest sp eed d rop p erm issible. However, th is gives n o in d ication of th e resu ltin g forces an d of th e stress exerted on th e com p on en ts of th e p ress. Th is is illu strated m ore clearly by th e exam p le below (Fig. 3.2.2). Th e p ress is assu m ed to h ave th e followin g p aram eters:

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– rated p ress force: FN0 = 1,000 kN = 1,000,000 N at 30° before bottom d ead cen ter (BDC) – u sable en ergy p er p ress stroke d u rin g con tin u ou s op eration : W N = 5,600 Nm – con tin u ou s strokin g rate: n = 55/ m in Assu m in g a slowdown of 20 % du rin g con tin u ou s strokin g, th e u sable en ergy is 36 % of th e total en ergy available in th e flywh eel. In th e exam p le given , th erefore, th e overall en ergy stored in th e flywh eel is:

W = WN / 0.36 = 5 , 600 Nm / 0.36 ≈ 15 , 600 Nm

90 30 above BDC

80 70

20 above BDC

permissible frame load

crank position above BDC (bottom dead center) [°]

Th e given nom inal load FN0 in a m ech an ical p ress in d icates th at th is valu e is based on th e stren gth calcu lation s of th e fram e an d th e m ovin g elem en ts located in th e force flow su ch as cran k sh aft, con n ectin g rod an d slid e. Th e n om in al load is th e greatest p erm issible force in op eratin g th e p ress. Th is lim it can be d efin ed on th e basis of th e p erm issible level of stress or by th e “d eflection ” ch aracteristics. In m ost cases, th e

60 50 40 30

permissible torque

20 10

0

500

1,000

1,500

2,000 2,500 3,000 permissible pressing force [kN]

Fig. 3.2.2 Permissible press force of an eccentric press as a function of crank angle

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stress on th e fram e is kep t low to ach ieve th e m axim u m p ossible rigid ity. Th e n om in al load is sp ecified at 30° before bottom d ead cen ter to in d icate th at from h ere to th e bottom d ead cen ter, th e d rive com p on en ts th at tran sm it th e p ower, su ch as th e d rivesh aft, th e clu tch , etc., h ave also been d esign ed for th e torq u e corresp on d in g to th e n om in al p ress force. Th erefore, between 90° an d 30° before th e bottom d ead cen ter, th e m ovable p arts m u st be su bjected to sm aller stresses to avoid overload in g. Th e force versu s cran k an gle cu rve, Fig. 3.2.2, in d icates th at th e p ress in q u estion m ay be su bjected to a n om in al load of 1,000 kN between 30° before bottom d ead cen ter an d at bottom d ead cen ter, wh ile at 90° before bottom d ead cen ter a slid e load of on ly FN0 / 2 = 500 kN is p erm issible. If a p ress with th e p aram eters sp ecified h ere is u sed to p erform an op eration in wh ich a con stan t force of F = 1,000 kN is ap p lied over a d istan ce of h = 5.6 m m , th e en ergy u sed d u rin g form in g is:

W = F ⋅ h = 1, 000 , 000 N ⋅ 0.0056 m = 5 , 600 Nm Th e p ress is th en bein g u sed to th e lim its of its rated force an d en ergy. If th e sam e force were to act over a distan ce of on ly h = 3 m m = 0.003 m , th e en ergy exp en ded am ou n ts to:

W = 1, 000 , 000 N ⋅ 0.003 m = 3 , 000 Nm Th e force of th e p ress is th en fu lly u sed , wh ile th e available en ergy is n ot com p letely u sed . Th e situ ation is m u ch m ore u n favorable if th e rated flywh eel en ergy of 5,600 Nm is ap p lied over a workin g d istan ce of h = 3 m m . In th is case, th e effective force of th e slid e will be:

F = WN / h = 5 , 600 Nm / 0.003 m ≈ 1, 867, 000 N = 1, 867 kN As th e m axim u m p erm issible p ress force is on ly 1,000 kN, th e p ress is bein g severely overloaded. In sp ite of th e fact th at th e flywh eel slowdown is still with in th e n orm al lim its an d gives n o in dication of overloadin g, all elem en ts th at are su bjected to th e p ress force m ay be dam aged, su ch as th e p ress fram e, slide, con n ection rods, etc. Seriou s overloadin g often occu rs wh en p ress form in g is con du cted u sin g h igh forces

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over sm all distan ces, for in stan ce du rin g blan kin g or coin in g. Th e great dan ger is th at su ch overloadin g m ay go u n detected. For th is reason , overloading safety devices m u st be u sed to p rotect th e p ress (cf. Sect. 3.2.8). An oth er form of overload in g resu lts from takin g too m u ch en ergy from th e flywh eel. Su ch overload in g can resu lt in extrem ely h igh p ress forces if th e d isp lacem en t d u rin g d eform ation is too sm all. However, if th e en ergy is ap p lied over a large d isp lacem en t, th is typ e of overload is m u ch less dan gerou s. For exam ple, if th e press described above is brou gh t to a stop du rin g a workin g distan ce of h = 100 m m , th e en tire flywh eel en ergy of W = 15,600 Nm is u tilized. Assu m in g th at n o peak loads h ave occu rred, th e m ean press force exerted is on ly

F = W / h = 15, 600 Nm / 0.1 m = 156 , 000 N = 156 kN Th e press is th erefore by n o m ean s overloaded alth ough th e flywh eel h as been brough t to a stan dstill. In th is case, on ly th e drive m otor suffers a very large slowdown an d it is n ecessary to use a press of a larger flywh eel en ergy capacity, alth ough th e perm issible press force of 1,000 kN is m ore th an adequate. Overloads of th is type occur m ore frequen tly if deform ation is don e over a large distan ce, e. g. durin g deep drawin g, open or closed die extrusion .

3.2.2 Types of drive system Eccentric or crank drive For a lon g tim e, eccen tric or cran k d rive system s were th e on ly typ e of d rive m ech an ism s u sed in m ech an ical p resses. Th e sin u soid al slid e d isp lacem en t of an eccen tric p ress is seen in (Fig.3.2.3).Th e relatively h igh im p act sp eed on d ie closu re an d th e red u ction of slid e sp eed d u rin g th e form in g p rocesses are d rawbacks wh ich often p reclu d e th e u se of th is typ e of p ress for d eep d rawin g at h igh strokin g rates. However, in p resses with cap acities u p to a n om in al force of 5,000 kN, su ch as u n iversal or blan kin g p resses, eccen tric or cran k drive is still th e m ost effective drive system . Th is is esp ecially tru e wh en u sin g au tom ated system s wh ere th e eccen tric drive offers a good com p rom ise between tim e n ecessary for p rocessin g an d th at req u ired for p art tran sp ort. Even in th e latest crossbar tran sfer p resses, eccen tric drive system s u sed in

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

stroke [mm]

M echanical presses

55

approx. 180

900

approx.110

approx. 170

800

eccentric drive system

500

modified knuckle-joint drive system/ six-link drive system

400

eight-link drive system

700 600

300 200 100

bottom dead center (BDC)

0 0

90

180

360

270

crank angle[

Fig. 3.2.3 Displacement-time diagram: comparison of the slide motion performed by an eccentric, a knuckle-joint and a link-driven press

su bsequ en t processin g station s, after th e drawin g station , satisfy th e requ irem en ts for system sim plification . Stroke len gth s of u p to 1,300 m m are ach ieved u sin g eccen tric gears with a d iam eter of 3,000 m m . Th e eccen tric gears are m an u factu red from d u ctile iron in accord an ce with th e h igh est q u ality stan d ard s (cf. Sect. 3.7). Linkage drive Req u irem en ts for im p roved econ om y lead d irectly to h igh er strokin g rates. W h en u sin g cran k or eccen tric d rive system s, th is in volves in creasin g th e slid e sp eed . However, wh en p erform in g d eep -d rawin g work, for tech n ical reason s th e ram sp eed sh ou ld n ot exceed 0.4 to 0.5 m / s d u rin g d eform ation . Th e lin kage d rive system can be d esign ed su ch th at in m ech an ical p resses, th e slid e sp eed d u rin g th e d rawin g p rocess can be red u ced , com p ared to eccen tric d rive by between a h alf an d a th ird (Fig. 3.2.3). Th e slid e in a d ou ble-actin g d eep d rawin g p ress, for exam p le, is actu ated u sin g a sp ecially d esign ed lin kage d rive (Fig. 3.2.4 an d cf. Fig. 3.1.8).

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Fig. 3.2.4 Slide (eight-link drive system) and blank holder slide drive (toggle joint drive system) in a double-acting deep draw ing press

Th is kin em atic ch aracteristic offers id eal con d ition s for th e d eep d rawin g p rocess. Th e slid e h its th e blan k softly, allowin g to bu ild u p h igh p ress forces righ t from th e start of th e d rawin g p rocess, an d form s th e p art at a low, alm ost con stan t sp eed . In ad d ition , th is system en su res sm ooth tran sition s between th e variou s p ortion s of th e slid e m otion . Du rin g d eform ation , th e d rive lin ks are stretch ed to an alm ost exten d ed p osition . Th u s, th e clu tch torq u e, th e gear load an d th e d eceleratin g an d acceleratin g gear m asses are between 20 an d 30 % sm aller th an in a com p arable eccen tric p ress. In th e case of sin gle-actin g m ach in es, for in stan ce, red u cin g th e im p act in creases th e service life of th e d ies, th e d raw cu sh ion an d th e p ress itself.

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

M echanical presses

Th is offers a n u m ber of im p ortan t ben efits in p rod u ction : for th e sam e n om in al p ress force an d th e sam e n om in al slid e stroke, a lin kd riven p ress can be load ed su bstan tially earlier in th e stroke, becau se th e p ress force d isp lacem en t cu rve is steep er with in th e d eform ation ran ge. Th erefore, th e lin kage p ress h as a m ore favorable force-d isp lacem en t cu rve th an on an eccen trically-d riven p ress (Fig. 3.2.2). With ou t in creasin g th e im p act sp eed , it is p ossible to ach ieve an ap p reciable in crease in th e strokin g rate an d ou tp u t. Du e to th e im p roved d rawin g con d ition s, a h igh er d egree of p rod u ct q u ality is ach ieved ; even sh eet m etal of an in ferior q u ality can be u sed with satisfactory resu lts. In ad d ition , th is system red u ces stress both on th e d ie an d th e d raw cu sh ion an d also on th e clu tch an d brake. Fu rth erm ore, n oise em ission s are red u ced as a resu lt of th e lower im p act sp eed of th e slid e an d th e q u ieter h errin gbon e gears of th e d rive wh eels. In th e case of large-p an el tran sfer p resses, th e u se of six or eigh telem en t lin kage d rive system s is largely d eterm in ed by d eform ation con d ition s, th e p art tran sp ort m ovem en t an d th e overall stru ctu re of th e p resses. As a resu lt, in th e case of tran sfer p resses with tri-axis tran sfer system , a six-elem en t lin kage d rive system is freq u en tly u sed , sin ce th is rep resen ts th e best p ossible com p rom ise between op tim u m p ress geom etry an d m an u factu rin g costs (cf. Sect. 4.4.7). In th e case of crossbar tran sfer p resses, eith er an eigh t-elem en t lin kage d rive or a com bin ation of lin kage an d eccen tric d rives are u sed in ord er to op tim ize th e d ie-sp ecific tran sfer m ovem en ts (cf. Sect. 4.4.8). Th e lin kage elem en ts are m ad e of d u ctile iron , th e lin kage p in s are from steel with h ard en ed con tact su rfaces an d th e bearin g bu sh es are from h igh ly stress-resistan t n on -ferrou s alloys. A reliable system of lu brication an d oil d istribu tion gu aran tees safe op eration of th ese h igh ly stressed bearin gs (cf. Sect. 3.2.11). Knuckle-joint drive system Th is d esign p rin cip le is ap p lied p rim arily for coin in g work. Th e kn u ckle-join t d rive system con sists of an eccen tric or cran k m ech an ism d rivin g a kn u ckle-join t. Figure 3.2.5 sh ows th is con cep t u sed in a p ress with bottom d rive. Th e fixed join t an d bed p late form a com p act u n it. Th e lower join t m oves th e p ress fram e. It acts as a slid e an d m oves th e attach ed top d ie u p an d d own . Du e to th e op tim u m force flow an d th e favorable con figu ration p ossibilities offered by th e force-tran sm ittin g

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57

Fundamentals of press design

58

press frame

flyw heel

housing connecting rod fixed press bed

crankshaft

knuckle-joint

Fig. 3.2.5 Knuckle-joint press w ith bottom drive

elem en ts, a h igh ly rigid d esign with very low d eflection ch aracteristics is ach ieved . Th e kn u ckle-join t, with a relatively sm all con n ectin g rod force, gen erates a con sid erably larger p ressin g force. Th u s, with th e sam e d rive m om en t, it is p ossible to reach arou n d th ree to fou r tim es h igh er p ressin g forces as com p ared to eccen tric p resses. Fu rth erm ore, th e slid e sp eed in th e region 30 to 40° above th e bottom d ead cen ter, is ap p reciably lower (cf. Fig. 6.8.3). Both d esign featu res rep resen t a p articu lar ad van tage for coin in g work (cf. Fig. 6.8.21) or in h orizon tal p resses for solid form in g (cf. Fig. 6.8.7). By in sertin g an ad d ition al join t, th e kin em atic ch aracteristics an d th e sp eed versu s stroke of th e slid e can be m od ified . Kn u ckle-join t an d m od ified kn u ckle-join t d rive system s can be eith er top (cf. Fig. 4.4.10)

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or bottom m ou n ted . For solid form in g, p articu larly, th e m od ified top d rive system is in p op u lar u se. Figure 3.2.6 illu strates th e p rin cip le of a p ress con figu red accord in g to th is sp ecification . Th e fixed p oin t of th e m od ified kn u ckle-join t is m ou n ted in th e p ress crown . W h ile th e u p p er join t p ivots arou n d th is fixed p oin t, th e lower join t d escribes a cu rvesh ap ed p ath . Th is resu lts in a ch an ge of th e stroke versu s tim e ch aracteristic of th e slid e, com p ared to th e largely sym m etrical stroke-tim e cu rve of th e eccen tric d rive system (Fig. 3.2.3). Th is cu rve can be altered by m od ifyin g th e arran gem en t of th e join ts (or p ossibly by in tegratin g an ad d ition al join t). As a ru le, it is d esirable to red u ce th e slid e velocity d u rin g d eform ation (e. g. red u ction of th e im p act an d p ressin g sp eed of th e slid e). Usin g th is p rin cip le, th e slid e d isp lacem en t available for d eform ation can be in creased to be th ree or fou r tim es greater th an wh en u sin g eccen tric p resses with a com p arable d rive torq u e. Th is rep resen ts a fu rth er ad van tage wh en form in g from solid (cf. Linkage drive).

flyw heel drive shaft

slide adjustment

B

motion curve, point B

eccentric drive system press slide

Fig. 3.2.6 M odified knucklejoint drive system

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Th e blan k h old er d rive, som etim es u sed in d ou ble-actin g d eep d raw p resses, is a sp ecial case (Fig. 3.2.4 an d cf. Fig. 3.1.8). Th e req u ired stan d still of th e blan k h old er d u rin g th e d eep -d rawin g p h ase is ach ieved in th is typ e of m ach in e by su p erim p osin g a d ou ble kn u ckle-join t system cou p led with th e eccen tric or lin kage d rive of th e slid e. Th e stan d still of th e blan k h old er rep resen ts a cran k an gle of between 90 an d 130° with a m axim u m resid u al m ovem en t of 0.5 m m . Th is resid u al m ovem en t d oes n ot, h owever, in flu en ce th e d eep -d rawin g p rocess becau se th e blan k h old er overload safegu ard acts as a storage system an d th e elastic d eflection of th e en tire p ress, wh ich is a few m illim eters, h as an overrid in g effect. Th e slid e d rive, th e blan k h old er d rive an d th e wh eel gear are in tegrated in th e p ress crown .

3.2.3 Drive motor and flyw heel In larger-scale p resses, th e m ain d rive system is u su ally p owered by DC m otors, p rim arily in ord er to p rovid e a large strokin g rate. Freq u en cycon trolled th reep h ase m otors offer an altern ative, p articu larly wh ere a h igh p rotection class ratin g is called for. Th e ou tp u t of a p ress, wh ich is d eterm in ed by force, slid e d isp lacem en t an d sp eed , in clu d in g lost en ergy, is p rovid ed by th e m ain m otor. Period ically occu rrin g load p eaks are com p en sated by th e flywh eel wh ich stores en ergy. Th e h igh ly elastic DC d rive system is able to com p en sate for a d rop of th e flywh eel sp eed of u p to 20 % in every p ress stroke an d to rep lace th e con su m ed en ergy by acceleration of th e flywh eel p rior to th e su bseq u en t stroke. Usefu l en ergy sh ou ld also be available d u rin g set-u p op eration with a red u ced strokin g rate, for exam p le five strokes p er m in u te. In th is case, a sp eed d rop of 50 % is ad m issible. An im p ortan t criterion in con figu rin g th e en ergy balan ce is to en su re a sh ort ru n -u p tim e. Ru n n in g u p a large-p an el p ress from its m in im u m to its m axim u m p rod u ction strokin g rate gen erally takes less th an on e m in u te u n d er load . Du e to th e req u ired u sefu l en ergy an d th e p erm issible flywh eel slowd own of 20 %, th e flywh eel is gen erally d esign ed to op erate u n d er th e m ost en ergy-con su m in g con d ition , i. e. in th e lower strokin g ran ge of th e p ress. Alth ou gh a h igh flywh eel sp eed is ben eficial h ere, th is is lim ited by th e ad m issible sp eed of th e clu tch , brake an d flywh eel itself.

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

M echanical presses

In crossbar tran sfer p resses, flywh eels of u p to 2,500 m m in d iam eter an d a weigh t of 25 t are u sed . Th e m ou n tin g an d lu brication of th is typ e of flywh eel in roller bearin gs are h igh ly d em an d in g, as a large q u an tity of lu brican t an d con tin u ou s tem p eratu re m on itorin g are req u ired (cf. Sect. 3.2.11). Th e flywh eel is d riven by th e m ain m otor via a flat belt or h igh -p erform an ce V-belt. W h en th e m ain d rive system is switch ed off, th e flywh eel is brou gh t to a stan d still with in a m axim u m of 30 s by reverse brakin g of th e m otor an d by an ad d ition al p n eu m atic brake. In isolated cases, n orm al car bod y p resses an d tri-axis tran sfer p resses are eq u ip p ed with m ech an ical creep sp eed d rive system s of on e stroke p er m in u te. In th is case, th e d rive is ach ieved by a th reep h ase m otor actin g on a worm gear wh ich actu ates th e d rive sh aft via th e brake flan ge of th e m ain brake. Th e tran sm itted torq u e gen erally falls sh ort of th e n om in al d rive torq u e. However, by m ean s of a p n eu m atic or h yd rau lic servo system in th e brake, th e n om in al force m ay be ach ieved for d istan ces of u p to 10 m m . Th is is gen erally su fficien t for set-u p op eration .

3.2.4 Clutch and brake On e of th e ch aracteristics of m ech an ical p resses is th e clutch u sed to tran sm it th e m otor an d flywh eel torq u e to th e gear sh aft an d , after clu tch release, th e brake wh ich is u sed to d ecelerate th e slid e, th e top d ie an d th e gear. Particu larly wh en workin g in sin gle-stroke m od e, th e m asses in tran slation al or rotation al m otion m u st be brou gh t to a stan dstill after every stroke with in an extrem ely sh ort tim e: 200 to 300 m s for large-p an el p resses an d 100 to 150 m s in u n iversal p resses. Con versely, after en gagin g th e clu tch , th e sam e m asses m u st be accelerated from zero to op eratin g sp eed . For safety reason s, brakin g is gen erated m ech an ically by sp rin g p ower. Th e clu tch torq u e is calcu lated from th e n om in al p ress force an d th e req u ired workin g d istan ce, gen erally 13 to 25 m m above bottom d ead cen ter. Pn eu m atic sin gle-disk clu tch an d brake com bin ation s with m in im u m rotatin g m asses h ave been in su ccessfu l u se for decades (Fig. 3.2.7).

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Pn eu m atic con trol system s with safety valves an d d am p in g d evices are reason able in cost an d gen erally com p ly with req u irem en ts. On e of th e p roblem s of p n eu m atic system s, h owever, is th e lim ited switch in g freq u en cy of sin gle-stroke p resses an d th e en viron m en tal d am age cau sed by wear to th e clu tch an d brake. In ord er to elim in ate th ese d rawbacks, h yd rau lic system s are bein g u sed in creasin gly in recen t years. With th e aid of coolin g system s, th ese p erm it far h igh er switch in g load s p er tim e u n it an d are p ractically im m u n e to wear. In sin gle-stroke p resses, sep arate u n its wh ich p erm it switch in g freq u en cies of u p to 30/ m in h ave been u sed to p erm it m ore effective con trol an d to avoid oversh ootin g an d u n d ersh ootin g by th e clu tch an d brake. Large-p an el tran sfer p resses u se clu tch -brake com bin ation s based on sin tered d isk sets with u p to 20 friction su rfaces an d tran sm ission torq u e levels of u p to 500,000 Nm . Th e com p act d rive system u sed in sm aller m ech an ical p resses, con sists of a flywh eel, clu tch , brake an d p lan etary gear in a com p lete u n it. Su ch a system ach ieves a p articu larly h igh level of efficien cy with an extrem ely low m om en t of in ertia an d sm all brakin g an gle, cou p led

clutch

brake

friction blocks

drive shaft

w ear indicator

Fig. 3.2.7 Single-disk clutch and brake in a large-panel press

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with a lon g service life an d low m ain ten an ce costs (Fig. 3.2.8). Th e electric m otor d rives th e eccen tric sh aft by m ean s of a flywh eel, a clu tch brake com bin ation th at can be eith er h yd rau lically or p n eu m atically actu ated an d a h igh -p erform an ce p lan etary gear (cf. Fig. 4.4.4). Th is elim in ates th e n eed for th e red u cin g gear gen erally req u ired for u n iversal p resses. Com p act d rive system s u sin g a h yd rau lic clu tch -brake com bin ation are p articu larly en viron m en tally frien d ly, as th ey p rod u ce n o abrad ed p articles an d ru n at an extrem ely low n oise level.

3.2.5 Longitudinal and transverse shaft drive Th e design of a m ech an ical p ress is determ in ed m ain ly by th e arran gem en t of th e drive sh afts an d axles, an d by th e n u m ber of p ressu re p oin ts of th e con n ectin g rod on th e slide (cf. Fig. 3.1.3). Th e term lon gitu din al or tran sverse sh aft drive is defin ed by th e arran gem en t of th e drive sh afts relative to th e fron t of th e p ress, wh ere th e p ress op erator stan ds.

clutch-brake disks

eccentric shaft

planetary gears

flyw heel

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Fig. 3.2.8 Compact drive system used in a universal press

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Longitudinal shaft drive is u sed m ain ly in sin gle-actin g on e- an d twop oin t p resses with eccen tric d rive system s (cf. Fig. 4.4.4 an d 4.6.29). Th ese are gen erally blan kin g p resses an d u n iversal p resses in th e lower force ran ge of u p to 8,000 kN. Th is classical d rive arran gem en t is also u sed in lon g an d n arrow tran sfer p resses wh ere between two an d six p ressu re p oin ts or con n ectin g rod s are located in th e lon gitu d in al d irection . Th e con n ectin g rod s are d riven by a con tin u ou s d rive sh aft. Th e tran sfer p resses are d esign ed with n om in al p ressin g forces between 1,000 an d 35,000 kN. Th ey h ave u p to fou r p airs of u p righ ts an d th ree slid es (cf. Sect. 4.4.6). Th e con n ectin g rod s are arran ged in th e area of th e u p righ ts an d tie rod s with th e p u rp ose of m in im izin g th e ben d in g stress on th e p ress crown . Th is leaves th e top of th e work station s in th e slid e free for ejection fu n ction s. For sim p ler p rod u ction an d assem bly, in larger-scale tran sfer p resses, th e lon gitu d in al sh aft d rive is also rep laced by a tran sverse sh aft d rive system . Kn u ckle-join t p resses with sin gle-p oin t d rive, coverin g a force ran ge from 1,500 to 16,000 kN rep resen t an oth er sp ecial con stru ction . Th e transverse shaft press is d esign ed to h ave on e-, two- or fou r-p oin t con n ection s an d p ressin g forces of between 1,600 an d 20,000 kN. Th is d esign p erm its a greater bed d ep th , a lon ger stroke an d also th e u se of a join t system . Dou ble-actin g d eep d rawin g p resses are on ly available in th is con figu ration (Fig. 3.2.4). Large-p an el p resses with tri-axis tran sfer in a ran ge from 18,000 kN to 45,000 kN p ress force are also based on a tran sverse sh aft d rive system (cf. Sect. 4.4.7). To perm it th e distribu tion of pressin g forces – gen erally over fou r con n ectin g rod s p er slid e – exten sive gear u n its are req u ired wh ich are accom m od ated in m u ltip le-walled p ress crown s. Th u s, th e gear d rive system s are sim p lified an d im p roved . Th e latest d evelop m en t in th e field of large-p an el p resses is th e crossbar tran sfer p ress. Its fu n ction s in clu d e th e p rod u ction of p assen ger car sid e p an els in d ies m easu rin g u p to 5,000 3 2,600 m m (cf. Sect. 4.4.8). In a five-stage con figu ration , five tran sverse sh aft d rive u n its are join ed to form a m ach in e assem bly sim ilar to a p ress lin e, an d all six d rive sh afts con n ected by clu tch es (Fig. 3.2.9). Th is tran sform s th e com p lete p ress in to a lon gitu d in al sh aft d rive offerin g all th e ad van tages of a tran sverse sh aft d rive.

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Fig. 3.2.9 Drive system of a transfer press w ith crossbar transfer

3.2.6 Gear drives In con trast to blan kin g p resses, wh ose con tin u ou s strokin g rate corresp on ds to th e sp eed of th e flywh eel, p resses with on e or two-stage redu cin g wh eel gears are u sed for lon ger workin g strokes. In large-p an el p resses, th e con n ectin g rod an d lin ks are gen erally d riven by a twostage red u ction gear. Dep en d in g on th e n ecessary p ower d istribu tion over two, fou r or, in th e case of tran sfer p resses, u p to twelve con n ectin g rod s, th e gear u n its with wh eels an d lin ks form th e n erve cen ter of m od ern p resses. Eccen tric wh eels with a d iam eter of u p to 3,000 m m an d red u cin g gears of u p to 1,600 m m in d iam eter are m an u factu red from h igh stren gth d u ctile iron (cf. Sect. 3.7). Th e gear teeth on th e sh afts an d p in ion s are h ard en ed . Dou ble h elical gearin g gu aran tees op tim u m p ower tran sm ission an d low ru n n in g n oise (Fig. 3.2.4). Th e gears an d q u ill p in ion sh afts are m ou n ted on floatin g axles with friction bearin g bu sh in g for easy assem bly. At th e start of th e p ower train is always th e d rive sh aft with d rive p in ion , clu tch an d brake. Un like oth er gear d rives, roller bearin gs are u sed in th e sp eed ran ge from 300 to 500 rp m .

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3.2.7 Press crow n assembly Th e con n ectin g rod , lin ks, gears an d m ain d rive system d eterm in e th e cap acity an d th e size of th e p ress crown . Th e weld ed com p on en ts weigh u p to 150 t, as d o th e m ou n ted gear d rive elem en ts con tain ed in th e crown of a large-p an el p ress. Th e d im en sion al lim its of su ch large-scale p arts are arou n d 6,000 3 3,600 3 12,000 m m , wh ereby wid th , h eigh t an d weigh t d ep en d on th e p ossibilities offered for road tran sp ort on low-bed tru cks – wh ich gen erally req u ire sp ecial au th orization . Waterways rep resen t a less d ifficu lt m eth od of tran sp ortin g th is typ e of com p on en ts. Stress-relief an n ealin g of large weld ed assem blies an d also m ach in in g on drillin g cen ters is restricted to a m axim u m len gth of 12 m . Th e en tire p roblem of tran sp ort logistics p lays a m ajor role in large-p an el p ress d esign an d m u st be taken in to con sid eration righ t from th e p lan n in g stage.

3.2.8 Slide and blank holder Th e rotary m otion gen erated by th e p ress d rive is tran sm itted to th e lin ear m otion of th e slid e an d blan k h old er u sin g a su itable sp eed an d force p rogression . Th e m ost im p ortan t fu n ction al u n its, p articu larly in large-p an el p resses, are th e pressure points con tain in g slid e ad ju stm en t an d an overload safety d evice. Slide adjustm ent In in d ivid u al p resses, p ressu re p oin ts with a slid e ad ju stm en t of u p to 600 m m are u sed in th e m ain sp in d le in ord er to ad ju st th e p ress sh u t h eigh t to variou s d ie h eigh ts (Fig. 3.2.10). In u n iversal an d tran sfer p resses, slid e ad ju stm en t d istan ces of 150 m m are su fficien t. In th is case, p ressu re p oin ts with a low overall h eigh t are u sefu l. Usin g brake m otors an d worm gears, ad ju stin g sp eed s of 60 m m / m in are obtain ed . With m u ltip le-stage p resses u sed for solid form in g, to ach ieve h igh stiffn ess, wed ge ad ju stm en ts are freq u en tly u sed in th e d ie set or at th e slid e clam p in g p late. In th is case, a slid e ad ju stm en t is n o lon ger n ecessary.

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Overload safety devices Th e n om in al force of th e p ress is lim ited an d safegu ard ed by th e h yd rau lic overload safety d evice in th e slid e. If th e n om in al p ress force is exceed ed , th e p ressu re exerted on a h yd rau lic cu sh ion in tegrated in th e p ressu re p oin t is q u ickly relieved , allowin g an overload d isp lacem en t. For blan k h olders u sed in dou ble-actin g m ech an ical p resses, th e overload safety fu n ction is cou p led to th e ad ju stm en t fu n ction of th e blan k h old er force. Th e overload safety fu n ction is activated on ly wh en th e d eflection of th e fou r blan k h old er p ressu re p oin ts h as exceed ed a p erm issible m agn itu d e of ap p rox. 3 m m . Th e safety fu n ction is actu ated by an air-h yd rau lic p ressu re scale. By ch an gin g th e com p ressed air settin g, th e blan k h old er force can be ad ju sted to th e req u irem en ts of th e d ie at th e fou r p ressu re p oin ts with in a ran ge of 40 to 100 %. Slide counterbalance Th e slide weigh t is com p en sated by th e slide cou n terbalan ce system . Th u s, th e weigh t of all m ovin g p arts su ch as join ts, con n ectin g rods, th e slide an d u p p er die, is balan ced ou t by p n eu m atic cylin ders (Fig. 3.2.11). As a resu lt, th e drive system is largely free of gravity forces. Th ere are n o stresses actin g on th e slide adju stm en t an d th ere is an addi-

connecting rod connecting rod adjustment device w rist pin

w rist pin adjustment nut

adjustment nut overload bolt oil cushion slide adjustment device

pressure pad

adjustment pad overload bolt oil cushion

adjustment spindle

Fig. 3.2.10 Spindle (left) and pressure point (right)

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tion al safegu ard again st d own ward travel of th e slid e cau sed by gravity. Pn eu m atic weigh t com p en sation gu aran tees low-n oise, vibration -free op eration , sm ooth load in g of th e m otor an d sh ort brakin g d istan ces. For cou n terbalan cin g weigh ts u p to 200 t, at 10 bar air p ressu re, cylin d er sizes u p to a 900 m m d iam eter are req u ired . Lon g slid e strokes of u p to 1,300 m m an d p erm issible p ressu re sp ikes of u p to 25 % req u ire su bstan tial su rge tan ks. Th e arran gem en t of cylin d ers an d tan ks d ep en d s on th e typ e of p ress an d safety issu es. In th e case of cou n terbalan ce cylin d ers wh ich are n ot extern ally en closed , d ou ble p iston rod s are often req u ired to safegu ard again st th e risk of breakage (Fig. 3.2.11). Con versely, if th e system is in tegrated in th e p ress crown , th is ad d ition al safety featu re is n ot n ecessary. With every d ie ch an ge, th e weigh t com p en sation system m u st be au tom atically ad ju sted to th e n ew d ie weigh ts for th is p u rp ose. In d ivid u al p resses are fitted with sp ecial weigh in g an d con trol fu n ction s. Program -con trolled au tom atic system s u sed in tran sfer p resses au tom atically set th e p rogram in h eren t p ressu re valu e wh en ch an gin g d ies in ord er to red u ce set-u p tim es to a m in im u m .

piston cylinder

compressed air tank

tubular rod safety rod slide breakage sensor

Fig. 3.2.11 Compensation of slide speed w ith double piston rod

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Slide cushion Som e u sers of p resses p refer to u se slid e cu sh ion s as an ejector for th e top d ie. In th ese cases, p n eu m atic bellow cylin d ers are u sed to su p p ly th e req u ired ejection forces (Fig. 3.2.12). Here, ejection strokes can be an ywh ere between 100 an d 200 m m , with p ressu re in creases of u p to 30 %. Th e bellow cylin d ers act on an ejector p late wh ich tran slate th e force to th e p ressu re p in s of th e cu sh ion an d of th e d ie. Du rin g th e u p stroke of th e slid e, th e ejector p late an d th e p in s are retu rn ed by force from th e bellow cylin d ers to th eir lowest p osition . Dam p in g elem en ts are u sed to red u ce th e n oise resu ltin g from th e h ard im p act. Stroke adjustm ent Tod ay, th e stroke of sm all m ech an ical p resses can be ad ju sted by m otor p ower continuously accord in g to req u irem en ts of th e form ed p arts with th e aid of two in teractive eccen trics (Fig. 3.2.13). Th e stroke can , for exam p le, be set in su ch a way th at th e req u ired p art h eigh t is reach ed d u rin g th e d eep d rawin g p rocess an d th e p art can be rem oved from th e d ie with ou t d ifficu lties on com p letion of th e d eep -d rawin g op eration . Th e elastic clam p con n ection between th e eccen tric sh aft an d th e eccen tric bu sh in g is h yd rau lically released . Th is in volves exp an d in g th e

bellow s cylinder damping rail pressure pin, slide cushion

pressure pins, die ejector plate, die

Fig. 3.2.12 Slide cushion w ith bellow cylinders

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slide

pressure plate bottom stop separate slide plate upper die

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bu sh in g again st th e clam p so th at it can be rotated u sin g a glidin g m otion in an y direction on an oil cu sh ion . Sp ecial seals are u sed to p reven t oil leakage. Th e p osition of th e eccen trics in relation to each oth er is m odified from th e con trol desk in accordan ce with th e sp ecific req u irem en ts of th e die u n til th e su m of th e eccen tricities reach es th e req u ired stroke. Th e p ositive con n ection between th e eccen tric sh ells is created as a resu lt of p ressu re relief cou p led with ru n -away of th e oil th rou gh drain age grooves. For each die, it is p ossible to store th e req u ired stroke in th e die data record. Th is in form ation can be accessed again an d u sed for au tom atic adju stm en t of th e slide stroke.

3.2.9 Pneumatic system Th e m ajor p n eu m atic fu n ction s of m ech an ical p resses are th e clu tch , brake, flywh eel brake, slid e cou n terbalan ce, slid e cu sh ion an d bed cu sh ion . In th e case of tran sfer p resses, p n eu m atic fu n ction s also in clu d e th e ap p lication of air p ressu re to th e tran sfer cam followers an d tran sp ort by su ction cu p s. Large volu m es of air req u ire com p ressed air tan ks with a m on itorin g safety fu n ction an d d rain age system . Th e m ax-

eccentric bushing grooves for pressure medium eccentric central bore for pressure medium

inner tapered ring clamping screw connecting rod

outer tapered ring

Fig. 3.2.13 Continuous stroke adjustment in an eccentric press

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im u m p n eu m atic p ressu re is gen erally 6 bar, alth ou gh h igh -p ressu re n etworks or com p ressors p rod u cin g a m axim u m of 16 bar are in creasin gly em p loyed . Th e en gin eerin g of th ese au xiliary u n its is d eterm in ed by valid stan d ard s an d legal req u irem en ts. In gen eral, galvan ized gas lin es between 1'' an d 6 '' are u sed for in stallation p u rp oses. Sm aller lin es are con figu red u sin g steel p ip in g an d cu ttin g rin g or bead ed u n ion s. Th e in stallation req u ired for a large-p an el tran sfer p ress with a stru ctu ral volu m e of arou n d 40 3 10 3 15 m can com p rise u p 40 t, in clu d in g com p ressed air tan k, p ip es an d ap p lian ces.

3.2.10 Hydraulic system Th e u se of h yd rau lics in m ech an ical p ress con stru ction is relatively m in im al. Stan d ard u se of h yd rau lic en gin eerin g in th is typ e of p ress is restricted to th e h yd rau lic overload safegu ard , raisin g th e m ovin g bolster an d h yd rau lic d ie clam p in g system s. All th ese fu n ction s are gen erally su p p lied from a cen tral h yd rau lic u n it. In th e case of tran sfer p resses, th ese basic fu n ction s are com p lem en ted by oth er fu n ction s su ch as en gagem en t of th e clu tch between th e p ress an d tran sfer d rive system s an d th e com p reh en sive system of scrap ejection flap s. In ad d ition , variou s clam p in g an d lockin g d evices arou n d th e p ress are h yd rau lically d riven . Th e m ost im p ortan t fu n ction in m ech an ical p resses, en gagin g an d brakin g th e slid e d rive system , is bein g in creasin gly d on e by h yd rau lic m ean s. Th e u se of h yd rau lics p erm its h igh er switch in g freq u en cies in sin gle p resses an d is also m ore en viron m en tally frien d ly in term s of n oise an d air p ollu tion . Th e clu tch an d brake are su p p lied by a cen tral h yd rau lic u n it eq u ip p ed with a coolin g system . A d u al-ch an n el safety con trol with regu lated d am p in g facility an d p ressu re filtration to 10 µ m is req u ired . Th e in creased u se of d eep d rawin g with sin gle-actin g p resses p laces p articu larly strin gen t d em an d s on th e blan kh old in g fu n ction an d th u s th e d raw cu sh ion in th e p ress bed (cf. Sect. 3.1.4), p articu larly in largep an el p resses. Mu ltip le-p oin t bed cu sh ion s with p ressu re con trol cap ability are th en on ly p ossible u sin g a com p lex servo h yd rau lic system .

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Th is req u ires sep arate su p p ly u n its with oil tan k, p u m p ou tp u ts of ap p rox. 150 kW an d oil flow rates of ap p rox. 1,000 l/ m in for th e d raw cu sh ion . Con trol is p erform ed u sin g p rop ortion al valves com p lyin g to DIN an d ISO stan d ard s in th e p ressu re ran ge u p to 300 bar.

3.2.11 Lubrication Th e com p lex lu brication system s u sed to su p p ly th e lu brication p oin ts in m ech an ical p resses are su bstan tially sim p lified by u sin g valve blocks (cf. Fig. 3.3.4). Th e system m ost com m on ly u sed h ere con sists of p arallel-switch in g p rogressive d istribu tors. Allocation of th e req u ired q u an tity of lu brican t is aid ed by volu m e con trollers, d ivid ers an d sim ilar elem en ts. Th e flow of oil is m on itored at th e d istribu tor blocks. To en su re op tim u m op eratin g con d ition s, a con trol system regu lates th e tem p eratu re of th e lu brican t with in a relatively n arrow ban d wid th by u sin g au xiliary h eatin g an d coolin g fu n ction s. To gu aran tee m axim u m op eratin g safety, com p lex p rod u ction in stallation s for m etal form in g are always fitted with twin su p p ly u n it elem en ts su ch as p u m p s an d filters. If on e p u m p fails, th ere is n o n eed to in terru p t p rod u ction , as th e secon d system cu ts in au tom atically. Main ten an ce or exch an ge of th e d efective system d oes n ot resu lt in p rod u ction stan d still, in creasin g u p tim e. Th e q u ality of th e oil is safegu ard ed by su p p lem en tary filtration in th e secon d ary circu it, in creasin g its service life. In sm aller p resses, an d in p articu lar by kn u ckle-join t p resses with bottom d rive, cen tral lu brication system s with m u ltip le-circu it geared p u m p s are u sed . Up to 20 m ain lu brication p oin ts are con tin u ou sly su p p lied d irectly by th e gear stages with a con stan t su p p ly of oil. Du rin g th e sh ort swivel m ovem en ts execu ted by th e th ru st elem en ts an d join ts, a con stan t flow of lu brican t is available even u n d er varyin g resistan ce levels in th e in d ivid u al u ser an d su p p ly lin es.

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3 Fundamentals of press design

3.3 Hydraulic presses 3.3.1 Drive system Hyd rau lic p resses op erate on th e p h ysical p rin cip le th at a hydrostatic p ressu re is d istribu ted even ly th rou gh a system of p ip es, an d th at a p ressu re p [N/ m 2 ], actin g on a su rface A [m 2 ], p rod u ces a force F [N]:

F = p⋅A Th e force acting on the slide of th e p ress d ep en d s on th e form in g or blan kin g p rocess p erform ed . For th is reason , th e p ressu re p actin g on th e p iston su rface is also a fu n ction of th e d eform ation p rocess con d u cted . Its m easu rem en t m ay be u sed d irectly to calcu late th e force actin g on th e slid e. Th e m axim u m slid e force can be selected by lim itin g th e m axim u m h yd rau lic p ressu re th rou gh a relief valve at an y p osition of th e slid e. Th e drive power P [W ] of a h yd rau lic p ress d ep en d s on th e volu m etric · flow of h yd rau lic flu id V [m 3 / s] an d th erefore on th e sp eed of th e slid e as well as on th e h yd rau lic p ressu re p , th e forces at th e slid e, an d th e m ech an ical an d electrical losses hges :

P=

˙ ⋅p V ηges

In con trast to m ech an ical p resses, th ere is gen erally n o reserve of en ergy available in h yd rau lic p resses. Th u s, th e en tire p ower m u st be ap p lied wh en carryin g ou t th e form in g op eration . For th is reason , h yd rau lic p resses req u ire a sign ifican tly h igh er d rive p ower th an in m ech an ical p resses, with com p arable force cap acity (cf. Sect. 4.4.1).

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Mech an ical p resses op erate accord in g to th e th rou gh feed p rin cip le, an d th e ou tp u t cap acity is d eterm in ed by th e d rive sp eed . In th e case of h yd rau lic p resses, in con trast, th e flow d irection of th e h yd rau lic m ed iu m is reversed to close an d op en th e p ress. Th e cycle tim e is m ad e u p of a n u m ber of variable com p on en ts, wh ereby th ere is an op tim u m p ress settin g valu e for each d ie set. Th e total stroke, th e d rawin g stroke, th e form in g force an d blan k h old er force are op tim ized in accord an ce with th e d ies. Each of th ese settin g valu es h as an effect on th e p ress cycle tim e, an d th u s on th e p ress ou tp u t. Th e d rive p ower is calcu lated on th e basis of th e ram d isp lacem en t versu s tim e cu rve (Fig. 3.3.1) th at is related to tim e con stan ts of th e p ress.

stroke [mm]

part transport time

press cycle acceleration

T lowering in rapid tra erse mm s

braking before T

braking

stroke

return stroke mm s drawing

drawing embossing acceleration pressure relief and re ersal

pressure holding time

time [s]

, ,

t

,

t33

t2

t4 ,7

t5

press time T cycle time T = , s + T + T

Fig. 3.3.1 Displacement-time diagram of a hydraulic press

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

, pro rated transport time T

Hydraulic presses

75

Design of the drive system Th e p iston force of th e slide cylinder, fasten ed to th e p ress crown , acts d irectly on th e slid e (Fig. 3.3.2 an d cf. Fig. 3.1.10). Th e n om in al p ress force is th e su m of th e active su rfaces of all p iston s m u ltip lied by th e h yd rau lic p ressu re. Th e m ovem en t seq u en ce d u rin g th e p ress cycle is execu ted by th e slid e cylin d er with th e slid e con trol. Th e n u m ber of active h yd rau lic cylin d ers d oes n ot affect th e p ress fu n ction . W h eth er th e slid e is d riven at on e, two or fou r p oin ts is d eterm in ed on th e basis of static calcu lation s (cf. Fig. 3.1.3). The function of the hydraulic system Hyd rau lic system s con vert electrical en ergy in to h yd rau lic en ergy, wh ich in tu rn is tran sform ed in to m ech an ical en ergy with th e aid of th e in d ivid u al h yd rau lic cylin d ers in sid e th e p ress. Th e h yd rau lic flu id in th e cylin d ers actu ates th e p ress slid e as follows:

filling al e

slide control

pressure pipe piston

return pipe

lowering module

bar

bar

bar

slide die part press bed

high-speed closure

forming

return stroke

Fig. 3.3.2 Functional principle of a hydraulic cylinder driving the slide of a hydraulic press

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– – – –

Forces are gen erated th rou gh th e action of th e h yd rau lic flu id . Disp lacem en ts are ach ieved by th e su p p ly of h yd rau lic flu id . Press (slid e) sp eed is p rop ortion al to volu m etric flow rates. Forward an d reverse m otion s are con trolled by th e d irection of flu id flow.

Design of hydraulic system s in presses Th e h ydrau lic system is su bdivided in to several fu n ction al assem blies (Fig. 3.3.3). Th e h ydrau lic flu id is stored in th e oil tank. All su ction pipes to th e pu m ps or cylin ders are su pplied with flu id from th e reservoir. Th e flu id tan k is su spen ded at th e press crown to en su re th at th e cylin ders are filled wh en th e press closes at h igh speed. Th e hydraulic drive system , com prised of pu m ps an d m otors, form s a stru ctu ral u n it togeth er with th e clu tch an d con n ectin g flan ge. Th e pu m ps u sed are eith er im m ersion

oil tank slide cylinder

secondary systems

al e control slide control

pressure accumulator

pressure and pump control

heating

cooling pump dri e filtration

M 3

P

primary circuit

P

M 3

secondary circuit

Fig. 3.3.3 Arrangement of a press hydraulic system

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

M 3

P

oil maintenance

Hydraulic presses

pu m ps su spen ded in th e oil tan k, or th ey are m ou n ted on su pports in th e press fou n dation . Th e m otors drive th e pu m ps via an elastic clu tch . Th e pu m ps are su pplied by su ction pipes, an d th e h ydrau lic flu id is con veyed to th e valve con trol by m ean s of h igh -pressu re pipes. Th e valve control system gu ides th e h ydrau lic flu id to th e appropriate u n its. Depen din g on th e fu n ction in qu estion , th e h ydrau lic cylin ders are exten ded or retracted, m oved actively or passively in th e press. Th e retu rn flow is gu ided back to th e oil tan k. Th e consum ers, cylin ders or h ydrau lic m otors, m ove th e slide or cu sh ion s, or adju st spin dles. Th ey gen erate forces, lift loads or clam p th e dies. Th e service unit operates in a bypass circu it away from th e m ain h ydrau lic flow. In th is u n it, th e flu id is recircu lated by m ean s of filters an d coolers in a separate circu it, pu rifyin g an d coolin g it to en su re th at th e press rem ain s ready for produ ction at all tim es. Pressure accum ulator drive system If th e p u m p con veys th e flu id to a p ressu re accu m u lator, it is p ossible to sm ooth ou t th e en ergy d elivery from th e m ain electrical n et. Large q u an tities of h yd rau lic oil can be d rawn from th e p ressu re accu m u lator for a sh ort tim e, wh ich h as to be rep len ish ed by th e p u m p before th e n ext p ress cycle. If th e extraction of h yd rau lic oil is followed by a lon g id le p eriod , th e accu m u lator can be su p p lied by a sm all p u m p – for exam p le wh en load in g an d u n load in g th e d ie after retraction of th e slide. However, for processes requ irin g large qu an tities of h ydrau lic flu id to be drawn in qu ick su ccession , a h igh er delivery power m u st be available – for exam p le a d rawin g op eration followed by th e op en in g of th e p ress. For th e secon d exam p le, a p ressu re accu m u lator-typ e d rive system is n ot su itable, sin ce n ot on ly a large accu m u lator system bu t also a large p u m p is req u ired . Draw p resses in volve sh ort cycle an d tran sp ort tim es wh ich often can n ot be ach ieved u sin g an accu m u lator d rive system . Table 3.3.1 d em on strates ad d ition al d ifferen ces between p u m p an d accu m u lator d rive system s.

3.3.2 Hydraulic oil Hyd rau lic system s in p resses are op erated u sin g stan d ard h yd rau lic oil (HLP) accord in g to DIN 51524 Part 2. Hyd rau lic oils are req u ired to com p ly with strict stan d ard s:

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Fundamentals of press design

78

Table 3.3.1: Comparison of hydraulic drive systems Pump drive system

Pressure accumulator drive system

The installed pump capacity determines the achievable speeds w ith the motor output.

Speeds are determined by valve cross-sections and the pressure head.

Requirement-oriented hydraulic oil delivery results in peak loads on the electrical mains.

Continuous hydraulic oil delivery exerts an even degree of stress on the mains.

Work capacity is unlimited, as the pressing force is available over the entire stroke.

Work capacity is limited by the available useful volume of the accumulator.

The system pressure corresponds directly to the pow er requirement of the die.

Pump pressure corresponds to the accumulator boost pressure. In case of a low er energy requirement, excess energy is converted into heat.

The pressing force can be simply limited by means of pressure reducing valves.

It is not possible to regulate the pressure of an accumulator, w hich alw ays operates at full capacity.

– – – – – – – – –

lu brication an d wear p rotection , con stan t viscosity level at tem p eratu res between 20 an d 60 °C, resistan ce to tem p eratu re, low com p ressibility, low foam in g ch aracteristics, low absorp tion of air, good ru st p rotection , good filtration p rop erties, low cost.

All h yd rau lic u n its are d esign ed for u se with h yd rau lic oils con form in g to th ese stan d ard s. Ch aracteristics, life exp ectan cy an d p ressu re ran ges, as well as th e ch oice of seals an d gaskets corresp on d to th e oil typ e u sed . Du e to th e com pressibility of hydraulic oil, th e volu m e of h yd rau lic flu id ch an ges u n d er p ressu re. As p ressu re is in creased , th e flu id colu m n is com p ressed . Th is p rop erty affects th e con trol an d regu latin g fu n ction s in th e p ress: th e h igh er th e p ressu re, th e lon ger th e resp on se tim e. W h en calcu latin g cycle tim es or d eterm in in g th e u se of d ifferen t d rive system s, th e com p ressibility factor m u st be taken in to accou n t, as th is h as a p ron ou n ced effect, p articu larly wh ere sh ort form in g strokes are in volved, for exam p le wh en blan kin g or coin in g. In th e case of m in eral oils, a com p ressibility factor of 0.7 to 0.8 % p er 100 bar oil p ressu re can be exp ected. Th is p rop erty of h ydrau lic flu ids also affects th e release of

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p ressu re in th e p ress cylin d er. If th e area u n d er p ressu re is op en ed too rap id ly, th is resu lts in p oten tially d am agin g p ressu re relief sp ikes. Flam e-retard an t h yd rau lic flu id s sh ou ld on ly be u sed wh ere th is is absolu tely m an d atory an d th e ap p lian ce m an u factu rer h as issu ed th e relevan t ap p roval. Th ese call for th e u se of sp ecial gaskets, in som e cases lower op eratin g p ressu re an d also sp ecial m easu res du rin g start u p . Between th e p u m p d rive system an d th e cylin d ers, th e p ress fu n ction s are con trolled by valves. Direction al, p ressu re an d n on -retu rn valves act in con ju n ction with p rop ortion al an d servo valves. Dep en d in g on th e system an d p osition – in th e p rim ary or secon d ary circu it – valves of variou s d im en sion s are u sed . Th e execu tion of all th e n ecessary p ress fu n ction s calls for a large n u m ber of h yd rau lic con n ection s wh ich are grou p ed togeth er in a block con figu ration (Fig. 3.3.4). Block hydraulic system s h ave gain ed in p op u larity, becau se: – extern al con n ection s on ly n eed to be d irected from th e p u m p an d to th e cylin d er, – th e valves are su rface-m ou n ted an d easy to exch an ge,

Fig. 3.3.4 Block hydraulic system

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– th eir n atu re in evitably resu lts in a stan d ard ization p rocess: th e valve blocks d o n ot n eed to be red esign ed for each d ifferen t p ress, – all th e valves are brou gh t togeth er to create a fu n ction al assem bly on a sin gle block, – in tegrated valves are sen sibly com bin ed with sp ace-savin g, low-cost au xiliary valves, – trou blesh ootin g is sim p lified by th e p resen ce of d rilled -in fu n ction al an d test con n ection s.

3.3.3 Parallelism of the slide Th e cap acity of th e p ress fram e to absorb eccen tric load s p lays a m ajor role. Eccen tric forces occu r d u rin g th e form in g p rocess wh en th e load of th e resu ltin g d ie force is n ot exerted cen trally on th e slid e, cau sin g it to tilt (Fig. 3.3.5). Th e stan d ard p ress is able to absorb a m axim u m eccen tric m om en t of load of

M x = 0.075 m ⋅ FN 0 [ kNm] My =

Mx [ kNm] 2

via th e slide gibs. Th is resu lts in a m axim u m slide tilt of 0.8 m m / m . If a h igh er off cen ter loadin g cap ability is desired, th en th e p ress design m u st be m ore rigid. In th is case, th e slide gibs will h ave greater stability, th e p ress fram e will be m ore rigid, an d th e slide will be h igh er. If it is n ot econ om ically p ossible to ach ieve th e allowable am ou n t of slid e tilt with in th e req u ired lim its by in creasin g p ress rigid ity, it is n ecessary to u se h yd rau lic p arallelism con trol system s, u sin g electron ic con trol tech n ology (Fig. 3.3.5), for exam p le in th e case of h yd rau lic tran sfer p resses (cf. Fig. 4.4.14). The parallelism control system s act in th e d ie m ou n tin g area to cou n ter slid e tilt. Position m easu rem en t sen sors m on itor th e p osition of th e slid e an d activate th e p arallelism con trol system (Fig. 3.3.5). Th e p arallelism con trollin g cylin d ers act on th e corn ers of th e slid e p late an d th ey are p u sh ed d u rin g th e form in g p rocess again st a cen trally ap p lied p ressu re. If th e electron ic p arallelism m on itor sen sor d etects a p osition error, th e p ressu re on th e lead in g sid e is in creased by m ean s of servo valves, an d at th e sam e tim e red u ced on th e op p osite sid e to th e sam e d egree. Th e su m of exerted p arallelism

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81

parallelism control

pressing force F1

displacement monitoring slide stroke

slide tilt

F1 = F2 + F3 w ith F3 = F4 + F5

a (b)

F4 (Fmax)

x (y)

F5 (Fmin)

F2

center of die force I

P

I

P

250 bar

Fig. 3.3.5 Control system for maintaining slide parallelism

con trol forces rem ain s con stan t, an d th e slid e tilt balan ce is restored . Dep en d in g on th e d eform ation sp eed , a slid e p arallelism of 0.05 to 0.2 m m / m is ach ieved . A cen tral d evice ad ju sts th e system to d ifferen t d ie h eigh ts by m ean s of sp in d les at th e slid e. Full-stroke parallelism control in volves th e u se of p arallel con trol cylin ders, with th eir p iston s p erm an en tly con n ected to th e slide (Fig. 3.3.6). Th ese act over th e en tire stroke of th e slide so th at n o settin g sp in dles are req u ired to adju st th e workin g stroke. Two cylin ders with th e sam e su rface area, arran ged well ou tside th e cen ter of th e p ress, are su bjected to a m ean p ressu re. Th e ten sile an d com p ressive forces are balan ced ou t by m ean s of diagon al p ip e con n ection s. Th e system is n eu tral in term s of force exerted on th e slide. If an off-cen ter load is exerted by th e die on th e slide, a tilt m om en t is gen erated. Th e slide p osition sen sor detects a deviation from p arallel an d triggers th e servo valve. Th e valve in creases th e p ressu re on th e u n derside of th e p iston actin g on th e leadin g side of th e slide, an d th u s also on th e op p osite u p p er side of th e p iston . At th e sam e tim e, th e p ressu re in th e oth er con n ectin g p ip e is redu ced. Th e

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Fundamentals of press design

82 250 bar

off center die force

Fig. 3.3.6 Full-stroke parallel control of the press slide

op p osin g su p p ortin g torq u es exerted on th e two sid es cou n teract th e tilt m om en t. Th e m axim u m d eviation m easu red at th e p arallel con trol cylin d ers is between 0.6 an d 0.8 m m d u rin g d rawin g, ben d in g an d form in g op eration s.

3.3.4 Stroke limitation and damping Th e deform ation depth , wh ich depen ds on th e slide position , is determ in ed in h ydraulic presses by th e switch over poin t at th e bottom dead cen ter (BDC) (Fig. 3.3.1). Depen din g on speed, th e slide travels past th is switch over poin t by a few m illim eters. However, repeatability rem ain s with in close lim its, m ean in g th at th e slide is reversed at th e BDC with sufficien t accuracy for m ost form in g operation s. However, if a toleran ce of less th an 1 m m is required, a m ech an ical stroke lim itation is called for. In com bin ation with a h ydraulic dam pin g system , th is can ach ieve a m arked reduction in th e blan kin g sh ock in volved in presswork (Fig. 3.3.7). Th ere

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

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83

Fig. 3.3.7 Stroke limiting and damping device

are two variation s in u se. Stan d ard d am p in g is u sed for m aterial th ickn esses exceed in g 3 m m an d for ligh t blan kin g wh ich on ly u tilizes som e 30 % of th e p ress cap acity – for exam p le trim m in g th e ed ge of a workp iece in a tran sfer p ress. W h ere h igh -stren gth m aterials an d sh eet th ickn esses below 3 m m are in volved , a p re-ten sion ed d am p in g system is req u ired , sin ce th is is cap able of absorbin g th e en ergy released in stan tan eou sly at th e m om en t of m aterial sep aration .

3.3.5 Slide locking W h en switch in g off th e p ress an d wh en workin g in th e d ie m ou n tin g area, th e slid e m u st be reliably safegu ard ed by a slid e lockin g d evice. Germ an accid en t p reven tion legislation (UVV 11.064 §12) sp ecifies th at h yd rau lic p resses with a bed d ep th of m ore th an 800 m m an d a stroke len gth of m ore th an 500 m m m u st be eq u ip p ed with at least on e fixtu re actin g on th e u p p er en d p osition of th e slid e. Th is fixtu re m u st

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84

bolt

locking cylinder

housing

slide

Fig. 3.3.8 Positive acting slide locking device

p reven t th e slid e from d rop p in g u n d er its own weigh t wh en th e con trol system is switch ed off. Th e locking device at the top dead center (TDC) is a p ositive-actin g lockin g d evice at th e u p p er p oin t of th e n om in al stroke. A bolt gu id ed in th e p ress fram e is p u sh ed by a h yd rau lic p iston in to a recess in th e slid e (Fig. 3.3.8). Th e bolt is con figu red to carry all m ovin g weigh ts, in clu d in g th at of th e d ie su p erstru ctu re. Th e infinitely variable locking device is a n on -p ositive actin g slid e safegu ard in wh ich a retain in g rod at th e slid e is gu id ed by th e clam p in g h ead in th e p ress crown (Fig. 3.3.9). Th e p ilot jaws h old th e m ovable elem en ts in an y p osition – even in case of a p ower failu re. Th is lockin g d evice, wh ich is arran ged in th e slid e area, is recom m en d ed p articu larly in p resses featu rin g a blan k h old er an d in tern al slid e. Th e slid e can be fixed in an y p osition , elim in atin g th e n eed for a sep arate safety d evice for th e blan k h old er.

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Hydraulic presses

85 retaining rod

clamping head

press crown

upright

gib rail

slide

rod fixture

Fig. 3.3.9 Non-positive acting locking device for the blank holder and the draw ing slide

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

3 Fundamentals of press design

3.4 Changing dies 3.4.1 Die handling Devices u sed for th e fast exch an ge of d ies h elp to red u ce set-u p tim es, allowin g th e econ om ical p rod u ction of d ifferen t com p on en ts even wh ere sm all batch sizes are req u ired . Sm all an d m ed iu m -sized form in g an d blan kin g d ies are tran sp orted with in th e stam p in g p lan t u sin g cran es, forklifts or oth er in d u strial tru cks. Th e tran sp ortation of largerscale d ies in to th e p ress an d th eir align m en t call for sp ecial d ie ch an gin g fixtu res, as th e d ies can n ot be d ep osited d irectly on th e p ress bed . Trou ble-free d ie ch an ge is on ly p ossible if th e u p p er an d lower d ies are p erfectly cen tered . In ad d ition , it m u st be p ossible to d ep osit th e d ies ou tsid e th e p ress. Th e p u rp ose of d ie ch an gin g fixtu res is to sim p lify an d accelerate tran sp ort in to th e d ie m ou n tin g area, to en su re sim p le h an d lin g of th e p ressu re p in s for th e d raw cu sh ion , an d to p erm it fast, reliable clam p in g of d ies. Swivelling brackets A swivelling bracket is a low-cost d ie ch an gin g fixtu re for th e tran sp ort of th e d ie in to th e p ress. Su ch fixtu res can be u sed u p to a d ie weigh t of arou n d 6 t. In th e case of d ies weigh in g u p to arou n d 2 t, in sertable brackets su sp en d ed from retain in g h ooks located in th e p ress bed are u sed . W h en h igh er d ie weigh ts are in volved , su p p ort feet, wh ere p ossible fitted with rollers, are essen tial. Dou ble-join ted swivellin g brackets can be tu rn ed in to a p arked p osition after d ie ch an ge (Fig. 3.4.1). It is p ossible for d ies to be m an u ally p u sh ed in to p osition by on e p erson u p

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87

Fig. 3.4.1 Sw ivelling brackets

to a weigh t of 3 t p rovid ed th e p ress bed an d brackets are eq u ip p ed with h ard roller bars. Motorized die change carts Rail-bou n d carts for d ie ch an gin g are d esign ed to facilitate th e exch an ge of tools u p to arou n d 20 t in weigh t. Th e u se of two ad jacen t tool tables rep resen ts a p articu larly econ om ical solu tion , as th e set of d ies can be p rep ared for u se wh en on e table is located in th e p arked p osition wh ile p rod u ction is goin g on . If th e p ress is fitted with p rotective grilles an d au tom atic d ie clam p s, au tom atic d ie ch an ge is p ossible. In th e h om e p osition , th e d ie is u n clam p ed an d th e p rotective grilles op en . Th e push-pull drive system exten d s, cou p les au tom atically to th e d ie an d p u lls th e d ie ou t of th e p ress (Fig. 3.4.2). On ce th e cart h as been released , traversed an d locked back in to th e p u sh -in p osition , th e n ew d ie can be p u sh ed in to th e assem bly area. However, in th e case of p resses with forward -p osition ed u p righ ts, th is ch an geover tech n iq u e becom es con sid erably m ore com p lex. In th is case, a sim p le p u sh -p u ll d rive is n ot su fficien t to brid ge th e d istan ce between th e exch an ge cart an d th e p ress bed . Usin g an ad d ition al m ech an ical overrun drive an d brackets with roller bars at th e p ress, th e p u sh -p u ll d rive system tran sp orts th e d ie all th e way to th e d ie stop s. Th e au tom atic cou p lin g between th e d rive an d th e d ie-set elim in ates th e n eed for in terven tion by op eratin g staff.

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88

energy supply

cart coupling

cart

bracket

catch pin

electric dri e

cart

new die double chain speed

press body

centering prism

die stop

producing die

Fig. 3.4.2 Double motorized die charge cart w ith overrun drive

In cases wh ere d ies are p osition ed on roller con veyors, th e force n eed ed to d isp lace th e d ies is m in im ized by u sin g p rofile rails with roller elem en ts in th e T-slots of th e clam p in g p late. Eq u ip p ed with sp rin g-m ou n ted ball roller elem en ts, th ese p rofile-rails offer a freed om of m ovem en t in all d irection s wh en h an d lin g ligh tweigh t d ies. Heavier d ies, in con trast, sh ou ld be tran sp orted on h yd rau lically raisable rollers, as lin ear con tact lead s to a h igh er su rface p ressu re. Th e su rface of th e d ie bod y com in g in to con tact with th e rollers m u st be h ard en ed . Die centering on th e press bed plays a determ in in g roll wh en ch an gin g dies. Man u ally displaceable dies can be align ed with su fficien t accu racy u sin g a cen tral groove in th e clam pin g plate or by m ean s of cen terin g aids in th e T-slots or clam pin g plates. Dies or presses with au tom atic tran sfer

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gear w ith guiding groove

idle gear set

driven gear set

frequency-controlled threephase motor clamping slots

speed-reducing gear

pressure pin hole

Fig. 3.4.3 M oving bolster

devices, in con trast, m u st be m ore precisely position ed in order to en su re exact position in g of th e parts in each die station (cf. Fig. 4.4.34). Moving bolsters Qu ick d ie ch an gin g system s for large p resses com p rise traversable m ovin g bolsters, au tom ated d ie clam p in g d evices, grip p er rail cou p lin gs an d d evices for au tom atic settin g of p ath , p ressu re an d tim e axes from th e d ata m em ory. Th ey can be id eally ad ju sted to th e in d ivid u al p rod u ction con d ition s of th e p art bein g form ed an d can be au tom atically accessed from th e d ata m em ory an d ed ited wh en ch an gin g d ies. Th e u p p er an d lower d ie of th e set are m oved ou t of th e p ress on m ovin g bolsters, an d th e bolsters bearin g th e n ew d ie sets are m oved in (Fig. 3.4.3 an d cf. Fig. 4.4.38). Prep aration of th e d ie-set for th e n ext p ressed p art is p erform ed ou tsid e th e p ress wh ile p rod u ction con tin u ou s. By au tom atin g th e d ie ch an gin g p rocess, th e d ies can be ch an ged , d ep en d in g on th e d ie tran sp ort system u sed , with in a p eriod of 10 to

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30 m in – in m od ern p resses in even less th an 10 m in . Th e d ie ch an gin g seq u en ce for large-p an el tran sfer p resses is d escribed in Sect. 4.4.7. Am on g m ovin g bolster typ e tool ch an gin g system s, th ose with left/ righ t-h an d exten d in g rails an d T-tracks h ave p roven to be m ost p op u lar (Fig. 3.4.4). Th e form er req u ire m ore sp ace, bu t ach ieve th e sh ortest p ossible ch an geover tim es, as both slid in g bolsters can be exten d ed an d retracted sim u ltan eou sly. Changing individual dies If th e service life of th e d ie u sed in an y p articu lar p ress station is sh orter th an th at req u ired for th e en tire p rod u ction ru n , th e d ie m u st be ch an ged d u rin g p rod u ction . Most in d ivid u al d ies of a p rogressive tool

trans erse gears

set-up position

end stop

mo ing bolster in shunting position

mo ing bolster in the press

traversing direction front-back

T-track

closed uprights mo ing bolster in set-up position gears in longitudinal direction

set-up position left

controlled stop

set-up position right

traversing direction left-right

shunting position

T-track

open uprights Fig. 3.4.4 Traversing directions for moving bolsters in presses w ith closed and open uprights

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are ch an ged in solid form in g (cf. Fig. 6.7.1). For d ies weigh in g u n d er 10 to 15 kg, th is is gen erally p erform ed m an u ally. For h eavier d ies, wh en ch an gin g in d ivid u al d ie blocks or for h ot form in g, d ie ch an gin g arm s with a h oistin g p ower of 50 to 800 kg are u sed (Fig. 3.4.5). Th e u p an d d own m ovem en t is p owered by electric m otor in m ech an ical p resses, wh ile h yd rau lic p resses are fitted with h yd rau lic liftin g cylin d ers. Th e swivel or traversin g m ovem en t in to th e d ie sp ace can be execu ted m an u ally, or con trolled by p u sh bu tton s to th e p reselected d ie p osition . Altern atively, fu lly au tom atic system s are also available.

3.4.2 Die clamping devices Th e clam pin g of dies on to th e bed an d slide clam pin g plates m u st be perform ed as qu ickly an d reliably as possible. Clam pin g devices are eith er electrically or h ydrau lically powered, in som e cases also in com bin ation with m an u al actu ation by m ean s of sprin g power, th readed spin dles, toggle lever, wedge action or self-lockin g m ech an ism s. W h ich ever m ean s is u sed , safety is always a p rior con cern (Fig. 3.4.6). Differen t clam p in g system s are often u sed for th e u p p er an d lower d ie, sin ce th e lower d ies

Fig. 3.4.5 Die changing arm for solid forming

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are p u sh ed over th e p ress bed , wh ile th e slid e is lowered vertically on th e u p p er d ies. Th e task of classifyin g th e d ifferen t clam p in g system s is excessively com p lex, as th e selection d ep en d s h eavily on th e req u ired clam p in g force, th e typ e of d ie an d p ress in volved an d th e d egree of p ress au tom ation . Sm all d ies are gen erally h eld by p u sh -in clam p s or clam p in g rails. Th e rails are fixed on th e clam p in g p late, wh ile p u sh -in clam p s are in serted in to th e T-slots on th e clam p in g p late. Th e ad van tage of workin g with th is typ e of sm all, ligh tweigh t fixtu re is th at it restricts th e u sable table su rface on ly m in im ally an d p erm its easy h an d lin g. If th e clam p in g force of th e p u sh -in clam p s is n ot su fficien t wh en con n ected to th e h yd rau lic system of th e p ress at 250 bar, it can be in creased to 50 kN by raisin g th e lin e p ressu re to 400 bar. T- slot clam p s are freq u en tly u sed to secu re m ed iu m -sized d ies (Fig. 3.4.7). A p ressu re of 250 bar is ap p lied to th e clam p in g cylin d ers by th e p ress h yd rau lic system . As a resu lt, a clam p in g force of u p to 200 kN can be gen erated . Th e clam p s can be released by m ean s of sp rin g p ower after a d rop in th e oil p ressu re. Th e safety of th e fixtu re is gu aran teed by p ositive lockin g action in th e T-slot an d m on itored by p ressu re sen sors wh ich brin g th e p ress to an im m ed iate stan d still in case of a d rop in p ressu re. For large d ies with d ifferin g wid th s, it is n ecessary to u se

T-slot

slide clamping plate upper die

clamped

released

hydraulic push-in-clamp

hydraulically

electromechanically

sw ivel-pull clamp

Fig. 3.4.6 Different die clamp designs

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

hydraulically

electromechanically

rotary-pull clamp

Changing dies

93 T-slot bar

mechanical release

bottom die

slide

bolster plate

hydraulic clamping

top die T-slot bar

mechanical release hydraulic clamping

Fig. 3.4.7 T-slot clamp for upper and low er tool

clam p s th at can be ad ju sted au tom atically to th e d im en sion s of th e d ie u sed (Fig. 3.4.8). Th ese ad ju stable fixtu res can be com bin ed with all typ es of clam p s – h yd rau lic, electric an d h yd rom ech an ical. If th ere are n o ad ju stin g d evices available, th e clam p s are m ou n ted ou tsid e th e clam p in g p lates, an d th e d ies m u st be ad ju sted to th e clam p sp acin g by u sin g ad ap ter p lates.

slide clamping plate

largest die smallest die

adjustment spindle

Fig. 3.4.8 Automatic die clamping device w ith adjusting facility: electromechanical clamp (left), hydraulic clamp (right)

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

T-slot

upper die

3 Fundamentals of press design

3.5 Press control systems 3.5.1 Functions of the control system Th e fu n ction s p erform ed by p ress con trol system s in clu d e th e read in g of sign als an d d ata tran sm itted from th e con trol elem en ts an d sen sors located on th e m ach in e an d th eir con version in to con trol com m an d s to th e m ach in e’s actu ators. Th e gen eration of con trol com m an d s d ep en d s on th e selected op eratin g m od e su ch as “set-u p ”, “au tom atic d ie ch an ge” an d “au tom atic con tin u ou s op eration ”. Fu n ction s to be m on itored or in itiated in clu d e, for exam p le, safety d evices, clu tch / brake, m ain d rive system , lu brication , d raw cu sh ion s, d ie clam p s, m ovin g bolsters, p art tran sp ort an d au tom atic d ie ch an ge. In ad d ition , th e con trol system execu tes m ach in e fu n ction s an d fau lt d iagn ostics.

3.5.2 Electrical components of presses Th e electrical com p on en ts of p resses an d th eir p erip h erals are broken d own in to th ree m ain areas: – op eratin g an d visu alization system , – electrical con trol (located cen trally in th e switch cabin et or d ecen trally d istribu ted in th e u n it), – sen sors an d actu ators in th e p ress.

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3.5.3 Operating and visualization system Process visu alization is an in stru m en t wh ich m akes th e p rod u ction seq u en ces of m ach in es an d p lan ts ergon om ically accessible. It su p p orts th e op eration , observation an d m on itorin g of tech n ical p lan t an d eq u ip m en t. Th e con trol u n its are p osition ed in variou s location s arou n d th e m ach in e an d are basically broken d own accord in g to th ree categories: – free-stan d in g op erator con soles, – op erator station s p erm an en tly in tegrated in th e m ach in e (Fig. 3.5.1) an d – m ovable p en d an t op erator station s.

Fig. 3.5.1 Operator station

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Con trol fu n ction s can be su bd ivid ed in to cen tral an d local system s: cen tral con trol fu n ction s refer to h igh er-level p ress fu n ction s, wh ile local con trol fu n ction s are u sed for m an u al op eration of in d ivid u al fu n ction s d irectly at th e p ress. Con trol u n its are com p rised of in p u t an d d isp lay u n its for op eration an d visu alization an d can ran ge from sim p le keys with p ilot lam p s th rou gh to in d u strial PCs with h igh -resolu tion color m on itors. Th e m ain fu n ction of th e visu al d isp lay system is to su p p ort th e p ress op erator on start-u p an d rep eat start-u p of th e p ress, for exam p le followin g a d ie ch an ge or m ach in e fau lt, an d to p erm it th e in p u t of variou s op eratin g p aram eters (Fig. 3.5.2). In ad d ition , th e visu al d isp lay system can be u sed to store d ie an d m ach in e d ata an d for loggin g fu n ction s. In form ation system fu n ction s wh ich are in tegrated in to th e visu al d isp lay system offer th e u ser su p p ort both for m ain ten an ce work an d trou blesh ootin g. Th ere is an in creasin g ten d en cy for th is typ e of system to m ake u se of m u lti-m ed ia tech n ology (cf. Sect. 4.6.7).

Fig. 3.5.2 Tooling data input mask for cam values

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Press control systems

3.5.4 Structure of electrical control systems Electrical con trol system s are broken d own in to fou r m ain areas: – – – –

th e con ven tion al p art, th e p rogram m able logic con troller (PLC), in p u t an d ou tp u t system s an d th e com m u n ication system .

Th e con ven tion al p art of th e electrical system con sists of th e p ower su p p ly, d rive con trollers, th e in d ivid u al electrical an d electron ic con trol d evices an d th e low-voltage switch gear for p ower con trol m on itorin g an d attach in g th e com p on en ts in th e con trol cabin ets an d th e m ach in e. Th e safety con trol rep resen ts a p articu larly im p ortan t com p on en t of th e con ven tion al p art for all fu n ction s relevan t to safety su ch as th e em ergen cy stop , m on itorin g of safety gates or safety d oors an d th e en gagem en t of th e clu tch / brake in m ech an ical p resses. In addition , th e electrical con trol system m u st reliably p reven t th e p ress from startin g u p or ru n n in g th rou gh in dep en den tly, followin g th e occu rren ce of an y in dividu al fau lt. In case of failu re of an y com p on en t, it m u st en su re th at n o fu rth er p ress closin g m ovem en t can be in itiated. Th e safety fu n ction of th e con ven tion al p art of a h yd rau lic p ress m on itors th e valves resp on sible for reliable stan d still of a m ovem en t wh ich cou ld lead to in ju ry. Th ese in clu d e th e valves located in th e lower cylin d er area wh ich con trol d ie closu re. Hyd rau lic red u n d an cy is ach ieved by m ean s of two m on itored valves. Failu re of on e of th ese d oes n ot lead to th e execu tion of a h azard ou s m ovem en t. If on e valve fails, th e p ress’s valve m on itorin g circu it au tom atically brin gs th e p ress to a stan d still. Th e PLC con trols an d m on itors all m ach in e fu n ction s n ot covered by th e con ven tion al con trol circu its an d au tom atic d ie ch an ge, p erform s fau lt d iagn ostics an d p rovid es th e in terface to oth er m ach in e section s. Th e sen sors an d actu ators of th e m ach in e are con n ected to th e cen tral PLC by m ean s of th e in p u t/ ou tp u t system . Th ere are two d ifferen t tech n ologies bein g u sed : first th e cen tral in p u t/ ou tp u t m od u les wh ich are in tegrated in th e PLC racks or in ad d ition al u n its of th e con trol cabin et; secon d , on an in creasin g basis, local in p u t/ ou tp u t m od u les with in th e p ress con n ected via fast com m u n ication system s to th e cen tral PLC u n it (Fig. 3.5.3).

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PLC

distributed I/O

sw itch cabinet

serial bus machine distributed I/O module

distributed I/O module

distributed I/O module

distributed I/O module

...

...

...

...

sensors and actuators

PLC I/O

central I/O

sw itch cabinet

parallel individual signals

parallel individual signals

machine terminal box

...

terminal box

terminal box

...

...

sensors and actuators

Fig. 3.5.3 PLC w ith central and distributed input/output systems

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

terminal box

...

Press control systems

Th e com m u n ication system con n ects th e PLC, an d p rovid es d ata exch an ge with th e visu al d isp lays with in th e m ach in e an d also com m u n ication with extern al system s.

3.5.5 Functional structure of the control system Dep en d in g on th e typ e of m ach in e or p ress, th e con trol system is broken d own accord in g to th e followin g fu n ction al grou p in gs: – – – – – – – – –

feed , m ain d rive system , safety con trol, slid e fu n ction s (in terlockin g, overload safegu ard , weigh t com p en sation , d ie clam p in g system , ad ju stm en t), draw cu sh ion or blan k h older fu n ction s (pressu re con trol, adju stm en t), m ovin g bolster fu n ction s (traversin g, liftin g/ lowerin g, clam p in g), fu n ction s of th e workp iece tran sp ort d evices an d d ies, h yd rau lic, p n eu m atic, lu brication fu n ction s, sp ecial d ie ch an gin g fu n ction s.

Cam op erated lim it switch es p lay a sp ecial role in p ress con trol system s. Th ese p ress-sp ecific fu n ction al u n its gen erate switch in g sign als for certain fu n ction s d ep en d in g on th e p osition of th e cran k an gle. A d ifferen ce m u st be d rawn between electrom ech an ical rotatin g cam lim it switch es (Fig. 3.5.4), wh ich are u sed for safety-relevan t fu n ction s, an d electron ic cam switch es th at are p rogram m able. Th e latter com p rise a m easu rin g system for th e cran k an gle of th e p ress an d an electron ic evalu atin g m od u le. In con trast to m ech an ical p resses, valves for th e d own stroke an d u p stroke of th e slid e are sep arate in a h yd rau lic p ress, so elim in atin g th e n eed for a cam op erated safety d evice.

3.5.6 M ajor electronic control components Safety con trol system s u sed in Eu rop e are gen erally still th e d u al-ch an n el, self-m on itorin g con ven tion al typ e u sin g con tactors. In con trast, sin ce th e m id -eigh ties, th e safety con trol system s u sed in large-p an el

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Fig. 3.5.4 Electromechanical rotary cam sw itch

p resses for exam p le in th e US m arket h ave been freq u en tly d esign ed to u se two PLC system s, each m on itorin g th e oth er. Am erican PLC m an u factu rers h ave offered su itable solu tion s for th is typ e of ap p lication for som e tim e. In Germ an y too, p ress safety con trol solu tion s based on red u n d an t PLC system s are becom in g in creasin gly p op u lar. Th e system s u sed are stan d ard com m ercially available PLCs (Figs. 3.5.5 an d 3.5.6). Th ey are ad ap ted to th e fu n ction al req u irem en ts of th e p ress by m ean s of in telligen t m od u les su ch as rotatin g cam lim it switch es, fast p osition in g m od u les, fast an d con ven tion al com m u n ication m od u les an d , wh ere req u ired , by in d ep en d en tly op eratin g tasksp ecific con trol system s. Op eration s in volvin g critical real-tim e fu n ction s an d com p lex d ata p rocessin g tasks wh ich are n ot su itable for th e PLC are p rocessed by in d ep en d en t su bsystem s. Th ese in clu d e th e con trol of th e d raw cu sh ion s an d m u ltip le-axis p art tran sp ort d evices or fast feed system s, acq u isition , p rocessin g an d d isp lay of sen sor ou tp u ts associated with th e d rawin g p rocess as well as acq u isition an d evalu ation of m ach in e an d p rod u ction d ata. Hyd rau lic p resses, for exam p le, are eq u ip p ed with q u ick-actin g p ressu re system s to con trol th e p arallelism of th e slid e. Digital rectifiers an d DC or th ree-ph ase asyn ch ron ou s m otors are u sed for m ain , tran sfer an d an cillary drive system s (Fig. 3.5.7). Workpiece h an dlin g system s are bein g in creasin gly equ ipped with dyn am ic digital servo drive system s, in wh ich con trol in telligen ce is often in tegrated in to th e drive system electron ics (Fig. 3.5.8).

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Press control systems

Fig. 3.5.5 PLC European manufacturer

3.5.7 Architecture and hardw are configuration Th e con trol system is d ivid ed in to m od u les accord in g to fu n ction al grou p in gs. Th is ap p lies to th e circu it d iagram , th e arran gem en t of th e switch cabin et an d stru ctu re of th e PLC software. Th e fu n ction al m od u les d o n ot n ecessarily corresp on d to th e m ech an ical stru ctu ral u n its – in som e cases sim ilar fu n ction s su ch as all em ergen cy stop circu its, all p rotective grilles an d th e lu brication are grou p ed togeth er. Criteria u sed to determ in e th e con trol stru ctu re in clu de th e logical an d fu n ction al coh eren ce between differen t system elem en ts an d th e m in im ization of in terfaces between th e in dividu al grou ps of fu n ction s. A well design ed arch itectu re of th e con trol system en h an ces clarity an d tran sparen cy of th e electrical docu m en tation an d th u s redu ces th e tim e spen t in design an d start-u p as well as in trou blesh oootin g du rin g produ ction .

3.5.8 Architecture of the PLC softw are Th e PLC software is d esign ed to corresp on d to th e fu n ction al grou p in gs of th e circu it d iagram . Fu n ction al seq u en ces, in p articu lar th ose u sed

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Fig. 3.5.6 PLC American manufacturer

for workp iece h an d lin g an d d ie ch an gin g, are p rogram m ed u sin g seq u en tial p rogram m in g m eth od s. W h ere fast resp on se tim es are called for, th e relevan t PLC in p u t sign als are d efin ed as in terru p t in p u ts wh ich , as th e n am e su ggests, in terru p t cyclically p rocessed con trol software fu n ction s an d trigger a resp on se p rogram wh ich resp on d s to extern al even ts in an extrem ely sh ort tim e.

3.5.9 Future outlook Program m able logic con trollers are id eally su ited to th eir resp ective ap p lication as sin gle-p u rp ose system s. Th ey are p articu larly well su ited for th e p rocessin g of logic op eration s. Th e tren d is toward s eq u ip p in g system s with ever m ore exten sive, cost-in ten sive p rocessin g cap ability. Develop m en t of p rogram m in g lan gu ages, on th e oth er h an d , h as slowed d own alm ost to a h alt. Program s are still bein g written in th e form of lad d er d iagram s an d in stru ction lists, wh ich are com p arable to

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Press control systems

Fig. 3.5.7 Sw itch cabinet w ith components for main press drive

an assem bler lan gu age. Th ese origin ally ap p lication -orien ted p rogram m in g lan gu ages are n ow bein g u sed for ach ievin g visu al d isp lay, d ata p rocessin g, d ata m an agem en t an d com m u n ication fu n ction s. Th e con seq u en ces of th is tren d are h igh software d evelop m en t an d m ain ten an ce costs, n on -tran sp aren t p rogram s – wh ich n ot even p rogram d esign stan d ard ization can m ake an y easier to u n d erstan d – an d lon g lead tim es to p u t th e p ress in to op eration . To p erm it th e in tegration of th is typ e fu n ction , th e PLC h as to be eq u ip p ed with ad d ition al exp en sive h ard ware m od u les. In com p arison , in d u strial com p u ters, for exam p le PCs, offer th e ben efits of grap h ic u ser in terfaces, d ata p rocessin g cap ability an d facility for object-orien ted p rogram m in g th rou gh th e u se of p owerfu l p rogram m in g tools. Th e basic req u irem en ts im p osed on a fu tu re-orien ted p ress con trol system , i. e. th e ability to access as m an y fu n ction s an d as m u ch in form ation as p ossible d irectly at th e m ach in e, are on ly ach ievable in th e fu tu re th rou gh th e u se of greater in telligen ce an d m ore com p u tin g cap acity. In ad d ition , m od ern au tom ation en gin eerin g calls for

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Fig. 3.5.8 Components of a servo drive system

con trol system s with greater n etworkin g cap ability th rou gh stan d ard n etworks for th e exch an ge of con trol, p rod u ction an d p rocess d ata as well as th e cap ability for d iagn osis an d in terven tion in th e con trol system th rou gh p u blic telecom m u n ication n etworks. Th e PLC alon e is n ot able to cop e with th ese d em an d s, alth ou gh its con tin u ed existen ce as a su bord in ate, fast m ach in e con trol con cep t is still ju stified . Practically all th e com p on en ts req u ired for realization of th e above fu n ction s are available in th e in d u strial com p u ter. Alon gsid e its com p u tin g p erform an ce, th e in d u strial com p u ter also p rofits from th e op en -en d ed software world . Fu rth erm ore, d esp ite th e stead y rise in p erform an ce lim its, th e costs of th e tech n ology are fallin g in m an y cases. In view of th is tren d , con trol stru ctu res featu rin g d istribu ted in telligen ce an d h igh er-level in d u strial com p u ters in terlin ked with fast com m u n ication system s are certain to gain in creasin gly in p op u larity. Ad d ed to th is is th e in creased u se of d istribu ted in p u t/ ou tp u t m od u les an d sen sor/ actu ator com m u n ication system s with a view to red u cin g th e n ecessary in stallation an d wirin g in p u t. Meth od s of p rogram m in g th e con trol software will becom e m ore stan d ard ized an d sim p lified in th e fu tu re, for exam p le by th e in trod u ction of th e in tern ation al stan d ard IEC 1131.

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Oth er ap p roach es exist in th e form of p rogram m in g th rou gh th e u se of statu s grap h s, ap p lication (“object”) orien ted p rogram m in g an d u ser lan gu age. In th is case, reu sable m od u les with an y d egree of com p lexity can be gen erated an d stored in a u ser-sp ecific m acro library. Th e p rep ared objects in th e library are in p aram etric form an d can be grou p ed with a m in im u m of com p lication to cover a large n u m ber of th e p ress or m ach in e fu n ction s. All th at is n ecessary to th en join th e in terfaces for d ata exch an ge. In form ation tech n ology is bein g in tegrated to an ever greater d egree in to th e p lan ts or m ach in es th em selves. As in tern ation ally stable “in form ation h igh ways” becom e available, n ew form s of fault diagn ostics an d m ain ten an ce back-up will n aturally develop, allowin g possible faults an d operatin g errors to be ascertain ed an d m ech an ical faults to be traced usin g video tech n ology or m icroph on es, so realizin g a system of tem porary or con tin uous on -lin e m on itorin g.

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3 Fundamentals of press design

3.6 Press safety and certification 3.6.1 Accident prevention Du e to th eir m od e of op eration an d th e en ergy in p u t levels in volved , p resses rep resen t – com p ared to m an y oth er m ach in es – a h igh er p oten tial h azard to th e op erator. However, as a resu lt of con sid erable effort, n otably th e revision of th e Germ an accid en t p reven tion regu lation s for p resses VBG7n 5.1 d ated Ap ril 1, 1987, th e n u m ber of seriou s accid en ts occu rrin g on or at p resses h as been su bstan tially red u ced . In ad d ition to com p lyin g with legislation on safety req u irem en ts based on th e “state of th e art”, m an u factu rers m u st also h ave th e cap ability to recogn ize an d im plem en t sen sible safety m easu res. Th e m an u factu rer’s own sph ere of respon sibility in th is field is a m ajor portion of Eu ropean safety legislation . As p art of th e service p ackage offered by m an u factu rers, th e op eratin g in stru ction m an u al con tain s sp ecial safety p rovision s an d in stru ction s. A m ajor goal is to m ake th e press operator recogn ize th e n ecessity for safety m easu res. Th e u n predictable n atu re of h u m an reaction in su rprise or em ergen cy situ ation s m u st be taken in to accou n t h ere. High ligh tin g th e acciden t risk is th e first an d m ost im portan t step wh en train in g m ach in e person n el on safety m atters. As lon g as th e operator or m ain ten an ce person n el are n ot con vin ced of th e n ecessity for safety m easu res, th ey will be in clin ed to fin d ways of bypassin g th em . Excessive or su perflu ou s safety m easu res by th e m an u factu rer are also certain to create greater willin gn ess on th e part of operatin g staff to attem pt to override safety fu n ction s. Reason s th at ju stify n egligen ce with regard to safety m easu res becom e qu ickly in sign ifican t if an acciden t does actu ally occu r.

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3.6.2 Legislation Alon gsid e legislation an d regu lation s d efin in g req u irem en ts im p osed on tech n ical p rod u cts – su ch as th e Germ an Pressu re Vessel an d Ap p lian ce Safety Acts – legislation h as also been ad op ted wh ich regu lates cases of h u m an in ju ry cau sed by tech n ical eq u ip m en t. If th e m ach in e m an u factu rer ad h eres to th e tech n ological stan d ard s d efin ed by th e socalled ch aracteristic req u irem en ts, it m ay be assu m ed th at h e will be exem p t from liability. An accid en t takin g p lace d esp ite th ese p recau tion s is d efin ed as a “statu tory accid en t”, in wh ich case th e com p an ies p rovid in g in d u strial accid en t in su ran ce are resp on sible for settlin g an y fin an cial claim s arisin g as a resu lt of th e d am age. In Eu rop e, th ese ch aracteristic req u irem en ts are d efin ed by th e EC Mach in e Directive, th e EMC (electrom agn etic com p atibility) Directive an d th e Directive Govern in g Sim p le Pressu re Vessels. Prod u ct liability is also treated on a stan d ard ized basis in Eu rop e th rou gh th e EC Directive for Harm on ization of Prod u ct Liability Legislation . In th e case of p articu larly d an gerou s m ach in es, state agen cies or in stitu tion s actin g on beh alf of state agen cies are com m ission ed to ch eck an d certify eq u ip m en t p rovid ed th e tech n ical req u irem en ts of th e eq u ip m en t h ave been correctly im p lem en ted . Foreign trad e in tech n ical p rod u cts is obstru cted to a con sid erable d egree by d ifferen ces of op in ion on th e best ways to ach ieve safety an d on th e targeted stan d ard s of safety in th e in d ivid u al cou n tries. Mach in e m an u factu rers op eratin g on a global basis n eed to stu d y th e n u m erou s d ifferen t safety req u irem en ts an d stan d ard s in force in each d ifferen t exp ort m arket. Th u s, th ey m u st becom e fam iliar with th e d ifferen t safety p h ilosop h ies, an d m u st u se locally ap p roved com p on en ts.

3.6.3 European safety requirements Sin ce Jan u ary 1, 1995, n ew safety regu lation s h ave been in effect in th e EEC (Eu rop ean Econ om ic Com m u n ity) wh ich are briefly ou tlin ed below (Fig. 3.6.1). EC legislation is based on a system of d ecrees an d d irectives. EC d ecrees ap p ly d irectly in th e resp ective m em ber state, wh ile d irectives are taken u p by th e n ation al govern m en ts, wh ich h ave to con vert th em with in a reason able p eriod in to n ation al law with or

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Fundamentals of press design

108

EC law governing technology: Objectives:

– Harmonization of safety standards in Europe – No compromises on safety in a member state – Free trade in machinery

EC regulations

EC directives 89/392/EEC (M achine Directive) 87/404/EEC (Simple Pressure Vessels) 89/655/EEC (Operating Resources)

Immediate validity

National legislation Appliance Safety Act (9. GSGV) Product Liability Act Standards

Harmonized standards

Non-harmonized standards

Standardization order from the commission, publication in the Official Journal of the EC

Other EN standards National standards

National lists of useful and important standards for implementation of the 89/392/EEC

Type A standard General principles EN292 (General principles for design)

Type B standard (horizontal standard) Definition of safety devices, stipulations of general relevance w ith different machines EN294 (Safety distances to prevent) EN574 (Tw o-hand operated devices) EN953 (Insulating safety devices)

Type C standard (vertical standard) Stipulations relating to a particular machine category EN692 (M echanical presses) EN693 (Hydraulic presses)

Fig. 3.6.1 Chart show ing European safety legislation: EC M achine Directives 89/392/EEC (ECM D) CE M ark

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with ou t th eir own ad d ition s. A series of d irectives was issu ed relatin g to th e ch aracteristic req u irem en ts of tech n ical p rod u cts. For m ach in e tool m an u factu re, th e d irectives listed in Table 3.6.1 togeth er with th e en d of th e tran sition al p eriod are of p articu lar im p ortan ce. Th e EC Mach in e Directive (ECMD) 89/ 392/ EEC establish es th e m ajor h ealth an d safety req u irem en ts im p osed on m ach in es. Th u s it is th e m ost im p ortan t d irective for th e m ach in e m an u factu rer an d was con verted in to n ation al Germ an law by th e 9 th d ecree relatin g to th e Ap p lian ce Safety Act. Th e p rod u ct liability law, wh ich h as been in effect sin ce Novem ber 15, 1989, was d erived from th e EC Directive on Harm on ization of Prod u ct Liability Legislation . Both th e EC d irectives an d EC d ecrees are based on h arm on ized EN stan d ard s form u lated on beh alf of th e Com m ission an d p u blish ed in th e EC Official Bu lletin after h arm on ization . Th ese stan d ard s allow th e m ach in e m an u factu rers to com p ly with th e relevan t d irectives. Th e m an u factu rers can , bu t are n ot obliged to, com p ly with th e stan d ard s. Th e m an u factu rer can h ave recou rse to th e p resu m p tion th at th e req u irem en ts of th e d irective are fu lfilled by ap p lication of th e h arm on ized stan d ard s. In th e stan dards, con crete solu tion s are p u t forward for ach ievem en t of th e p rescribed safety stan dard: safety grilles on p resses, for exam p le, are req u ired to h ave a closin g force of n o m ore th an 150 N. Oth erwise, a dan ger of cru sh in g exists wh ich can , h owever, also be avoided th rou gh th e u se of a con tact strip . In case of failu re to com p ly with a h arm on ized

Table 3.6.1: European standards

Directive

Content

Valid w ithout restriction from

89/392

ECM D

1/1/95

93/68

Amendment to ECM D (Identification)

1/1/95

93/44

Amendment to ECM D (Safety components)

1/1/97

91/368

Amendment to ECM D

1/1/95

87/404

Simple pressure vessels to 30 bar

1/1/93

89/336

Electromagnetic compatibility

1/1/96

73/23

Low voltage directive

1/1/97

86/188

M achine noise

1/1/90

89/655

Operating resources directive

1/1/97

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stan dard, th e m an u factu rer can fu lfill th e h ealth an d safety stan dards u sin g altern ative m eth ods. In con trast, h owever, failu re to com p ly with th e ECMD will resu lt in p rosecu tion of th e m an u factu rer, with d rawal of th e p rod u ct from th e Eu rop ean m arket an d d ecom m ission in g of th e h azard ou s p ress. EN stan d ard s are classified u n d er th ree categories, each with its own fu n ction an d p u rp ose. Gen eral gu id elin es an d safety targets are set d own in so-called A stan d ard s. B stan d ard s im p ose req u irem en ts on certain facilities, for exam p le safety eq u ip m en t u sed for d ifferen t typ es of m ach in es. C stan d ard s d efin e m ach in e categories an d th e req u irem en ts im p osed on th ese. For a given m ach in e category, th e C stan d ard s lay d own th e way in wh ich risks are likely to occu r an d h ow th ey sh ou ld be evalu ated an d safegu ard ed again st. Du e to th e gen erality with wh ich m ach in es are grou p ed to create m ach in e categories – th e m ech an ical p ress category, for exam p le, ran ges from th e n otch in g m ach in e to th e large-p an el tran sfer p ress – it can , in certain cases, be exp ed ien t to d eviate from th e stan d ard wh ile still com p lyin g with th e req u irem en ts of th e ECMD. As docu m en tary eviden ce of com p lian ce with h ealth an d safety req u irem en ts, th e m ach in e m an u factu rer issu es th e own er with a Certificate of Con form ity (Fig. 3.6.2) accordin g to an n ex II A, an d attach es th e CE m ark to th e m ach in e. No m ach in e h as been com m ission ed in th e EEC with ou t a Declaration of Con form ity or CE m ark sin ce Jan u ary 1, 1995. Th e ECMD d ifferen tiates between in d ep en d en tly workin g m ach in es an d m ach in es in ten d ed for in stallation as p art of an overall p rod u ction lin e. A p rod u ction lin e com p rised of several com p on en ts con stitu tes a m ach in e wh ich h as on ly on e CE m ark an d on ly on e d eclaration of con form ity. For all p rod u ction lin e com p on en ts wh ich are in cap able of op eratin g in d ep en d en tly, th e su bcon tractor issu es a m an u factu rer’s d eclaration in com p lian ce with an n ex II B. Un d er certain circu m stan ces, com p on en t m ach in es of th is typ e d o n ot p erm it safegu ard in g u n less in tegrated in th e overall lin e. An in d ivid u al d estacker with ou t th e p ress, for in stan ce, p erm its free access to h azard ou s m ovem en ts an d is th u s in cap able of com p lyin g with th e ECMD. Th e p arty resp on sible for th e overall lin e, wh ose fu n ction it is to issu e th e d eclaration of con form ity, m u st th erefore en su re th at th e m an u factu rer of th e com p on en ts

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Press safety and certification

– stip u lates in th e m an u factu rer’s d eclaration th at th e com p on en t com p lies as far as p ossible with th e ECMD, – h as com p iled an d arch ived th e req u ired d ocu m en tation as laid d own by an n ex V, p oin t 3, – stip u lates th e ap p lied safety stan d ard s an d – h as m ad e referen ce in th e op eratin g in stru ction s to th e safety regu lation s for th e m an u factu rer of th e lin e in to wh ich h is com p on en ts are to be in tegrated . All th ose in volved assu m e th at th e p rescribed m in im u m statem en t, as in d icated in an n ex II B, is in su fficien t an d th e m ach in e can n ot be com m ission ed u n til th e overall lin e h as been p roven to com p ly with th e ECMD. Freq u en tly, an d in p articu lar in th e case of large-scale p resses, p art of th e eq u ip m en t origin ates from th e u ser an d p art of it from th e p u rch aser of th e p ress. As th e ECMD req u ires static stability an d safe access to all p oin ts of p ossible in terven tion , with th e d eclaration of con form ity th e p rod u ction lin e m an u factu rer assu m es resp on sibility also for th e stru ctu ral work carried ou t for th e p ress, for exam p le th e con stru ction of th e n ecessary fou n d ation s. Th e id en tity of th e m an u factu rer or con stru ction forem an as d efin ed by ECMD m u st be con tractu ally laid d own in th e case of th is typ e of p rod u ction lin e. Th e resp on sible p arty th en h as th e oth er con tractu al p artn ers con firm com p lian ce with h ealth an d safety stan d ard s to th e exten t of th eir resp ective p erform an ce.

3.6.4 CE marking Th e flow ch art in Fig. 3.6.3 in d icates wh at is req u ired of th e m an u factu rer wish in g to ap p ly th e CE m ark to h is m ach in e. An u n d erlyin g d ifferen ce is d rawn between two cases. Accord in g to an n ex IV of th e ECMD, p resses in ten d ed for m an u al feed op eration h ave been classified as h azard ou s m ach in es sin ce Jan u ary 1, 1995. In th is case, a C stan d ard – th e EN692 for m ech an ical an d EN693 for h yd rau lic p resses – m u st exist, an d th e p ress m u st be con stru cted with ou t restriction s in accord an ce with th is stan d ard . If th is is n ot th e case, or if th e relevan t C stan d ard d oes n ot yet exist, th e m an u factu rer is req u ired to com m ission a typ e test of th e m ach in e by a n otified bod y (i. e. an ap p rop riate testin g

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112

EG-Declaration of Conformity per specifications of the machine directive 89/392/EEC, annex II A Applied EC-directives : x x x

machine directive 89/392/EEC and 91/368/EEC electromagnetic compatibility directive 89/336/EEC and 93/31/EEC low -voltage directive 73/23/EEC ………………………………

We herew ith declare that the follow ing identified machine / line ……………………………………………………………………………………………………… (make, type designation, year of manufacturing, order number) as marketed by us meets the essential health and safety requirements of the EC machinery directive 89/392/EEC relating to the design and construction. This declaration w ill become invalid in case of modifications of the machine / line, not accepted by us. Applied harmonized standards: x x x x x x x x x x

DIN EN 292 DIN EN 294 DIN EN 60204 T1 DIN EN 692 DIN EN 418 E DIN EN 953 DIN EN 954 DIN EN 982 DIN EN 983 DIN EN 1037

Applied national German standards and technical specifications : ………………………………… A technical construction file has been compiled and w ill remain available. An instruction manual for the machinery has been composed and delivered in : x x

community language of the manufacturers country (original version) community language of the user country …………………………………

Place, date

…………………………………

M anager design services (title and designation of the undersigned)

………………………………… (Legally binding signature of the manufacturer)

Fig. 3.6.2 Sample Declaration of Conformity

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113

Equipment

In accordance w ith annex IV (Art. 8(2)a), c)

Not in accordance w ith annex IV (Art. 8(2)a)

Fully in compliance w ith standards (Art. 8(2)c)

Not fully in compliance w ith standards (Art. 8(2)b)

M anufacturer

Compile documents in accordance w ith annex V

Notified body

M anufacturer

M anufacturer draw s up declaration of conformity * ) and applies CE mark

Compile documents in accordance w ith annex VI, send w ith model to notified body

Compile documents in accordance w ith annex VI, send to notified body

Notified body carries out EC type test on model

Notified body retains documents

Notified body issues EC type certificate

Notified body confirms receipt

Notified body issues certificate

Notified body issues EC type certificate

M anufacturer draw s up declaration of conformity * * ) and applies CE mark

M anufacturer draw s up declaration of conformity *) and applies CE mark

M anufacturer draw s up declaration of conformity * ) and applies CE mark

M anufacturer draw s up declaration of conformity * * ) and applies CE mark

Compile documents in accordance w ith annex VI, send to notified body Notified body checks w hether standards have been correctly applied

Compile documents in accordance w ith annex VI, send w ith model to notified body Notified body performs EC type test on model

* ) Declaration of conformity certifies compliance w ith underlying requirements of the directive * * ) Declaration of conformity certifies compliance w ith tested model Remark:

Fig. 3.6.3 Sequence for the conformity declaration and the CE mark

au th ority) in accord an ce with an n ex VI. Th e m an u factu rer is on ly en titled to issu e th e d eclaration of con form ity an d ap p ly th e CE m ark on th e basis of an EC typ e test certificate. If th e p ress h as been con stru cted on th e basis of th e typ e C stan d ard , th e m an u factu rer m ay ch oose an y on e of th ree fu rth er p roced u res. Eith er h e sen d s th e tech n ical d ocu m en tation to th e testin g au th ority, wh ich on ly con firm s receip t, or h e arran ges for a review of th e tech n ical d ocu m en tation , or h e com m ission s an EC typ e test of th e m ach in e. In certain m ach in es it is n ecessary to reach d irectly with th e h an d s between th e two h alves of th e d ie after each stroke. Th ese m ach in es are categorized as m ach in es with m an u al feed or rem oval. Even m ach in es in wh ich p arts are in serted m an u ally d u rin g set-u p are n ot categorized as an n ex IV m ach in es. In th e case of m ach in es n ot d esign ed to p erm it m an u al feed or rem oval, th e m an u factu rer issu es th e d eclaration of con form ity an d ap p lies th e CE m ark at h is own risk. Con seq u en tly, a p ress in ten d ed exclu sively for au tom atic op eration

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can n ot be u sed for m an u al feed op eration . Th is p ossibility is exclu d ed in th e op eratin g in stru ction s – as far as p ossible, it sh ou ld be p ossible for th e con trol system to p reven t m an u al p rod u ction . Certificates issu ed by th e m an u factu rer h im self, h owever, m u st satisfy certain con d ition s. In ad d ition to ad h erin g to th e m ajor h ealth an d safety req u irem en ts of th e ECMD, th e m an u factu rer is req u ired to d raw u p a d ocu m en t p rior to issu in g th e d eclaration of con form ity in wh ich h e p rovid es written p roof of com p lian ce with th ese safety req u irem en ts. Th e statu tory reten tion p eriod for th is d ocu m en t is 10 years. Th e d ocu m en tation , in ten d ed for th e cu stom er, com p rises th e op eratin g in stru ction m an u al, wh ich con tain s th e n ecessary in form ation for th e m ach in e u ser. Th e focal p oin t of th e d ocu m en tation is th e h azard an alysis an d risk assessm en t (Table 3.6.2). Th is in volves a system atic evalu ation of th e m ach in e by th e m an u factu rer con cern in g p oten tial h azard s, an evalu ation of th e risk in volved , an d th e ap p rop riate m easu res for th eir m in im ization . Th ese m u st be d escribed in th e d ocu m en tation . Th e ou tcom e takes on th e form of a list of solu tion s u n d ertaken to com p ly with th e p oin ts d erived from an n ex I of th e ECMD. In ad d ition , th e d ocu m en tation in clu d es p lan s an d d iagram s – circu it d iagram , h yd rau lic an d p n eu m atic d iagram s an d fu n ction al ch aracteristics –, calcu lation s, test resu lts, certificates an d m an u factu rer’s d eclaration s from su p p liers in as far as th ese are n ecessary for verification of th e req u ired safety stan d ard . Th is d ocu m en tation d oes n ot n eed to be p h ysically

Crushing, shearing

1.1, 1.2

Reaching in from front and other hazards in active area during operation x

3

0

Protection category

Bypassable

Overall frequency category

Repairs

M aintenance

Set-up

Degree of severity 3

4

Safety gear / remark

Protective shield 1st safeguarding to category 4, n.o. and n.c. contacts, early opening tS, safety distance 320 mm to match stopping time 0.2 s to EN999. Together w ith sw ivelling gripper box prevention of access to danger zones (EN294) (see draw ing)

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Doc. No.

2

Active area, die mounting area

Part event

Continuous operation

1

Hazardous situation, danger Type of area danger

Number of hazard in accordance w ith EN414

Table 3.6.2: Extract from a hazard analysis w ith risk assessment

89/392, annex I

Applied standards EN692

Others

1, 2

1.1.2a,f, 1.3.7, 1.3.8, 1.4.2.2B, 1.4.1, 1.6.1

5.3.3, 5.3.5., 5.3.6, 5.3.10, 5.3.12, 5.3.15, 5.5.6, 5.5.7, 5.5.8

EN294 EN999 EN954 EN953 EN1088

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p resen t, bu t com p rises an in d ex wh ich m akes referen ce to th e variou s section s by m ean s of an id en tification n u m ber. In th e case of a h azard an alysis, safety is m on itored over each p h ase of th e m ach in e’s life, from assem bly th rou gh to com m ission in g, u tilization , rep air an d fin al scrap p in g. Protective m easu res m u st ap p ly eq u ally to m ach in e op erators, set-u p an d m ain ten an ce staff. Dep en din g on th e risk, safety m u st also be gu aran teed in case of m ach in e m alfu n ction s. As, for exam p le, th e failu re of a brake valve an d th u s th e u n ch ecked m ovem en t of th e slide cou ld lead to seriou s in ju ry, dyn am ically m on itored p ress safety valves m u st be u sed u n less it is p ossible to p rovide an eq u ivalen t degree of safety by keep in g safety devices closed. Th e m on itored valves are redu n dan t (dou ble valves) an d, dep en din g on th e req u irem en ts of th eir resp ective fu n ction s, th ey are self-m on itorin g. Th is m ean s th at desp ite a brake valve failu re, th e “brakin g” fu n ction is still p erform ed, accom p an ied by a m essage in dicatin g wh eth er th e two valves h ave op erated correctly or n ot. A p ositive “fu n ction OK” sign al is u sed for self-m on itorin g of th e sign allin g m odu le (cf. Sect. 3.5). In an alysin g p oten tial h azard s, th e m an u factu rer m u st also con sid er “foreseeable u n u su al situ ation s”, e. g. su rp rise situ ation s of th e typ e p reviou sly m en tion ed. Th e op eratin g in stru ction s m u st accordin gly in clu de a statem en t on m ach in e u tilization in accordan ce with th e in ten ded p u rp ose of th e m ach in e, an d also p roh ibit an y foreseeable cases of violation , for exam p le op eration of th e p ress wh ile observers are located beh in d th e closed p rotective gear in ord er to observe th e m ach in e op eration . In d ication s of p ossible violation of op eratin g regu lation s are often on ly p ossible after observation of op eratin g, set-u p an d m ain ten an ce staff. Th e resu lts of th e h azard an alysis are reflected in th e d esign of p rotective gear, rem arks relatin g to resid u al risk at th e m ach in e an d in th e op eratin g in stru ction m an u al. Th u s, th ey are m ad e kn own to th e m ach in e u ser.

3.6.5 M easures to be undertaken by the user W h en p u rch asin g a m ach in e, th e u ser m u st establish by m ean s of a con tractu al agreem en t th e id en tity of th e m an u factu rer as d efin ed by th e ECMD an d th e p osition with regard to item s of eq u ip m en t p rovid ed by th e u ser. W h en p u rch asin g m ach in es, wh eth er n ew or u sed , from

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foreign cou n tries ou tsid e of Eu rop e, th e u ser sh ou ld con tractu ally stip u late com p lian ce with th e cu rren t revision of 89/ EEC/ 392. Eu rop ean m an u factu rers are req u ired in an y case to com p ly with th is legal req u irem en t, m akin g a con tractu al p rovision to th is effect u n n ecessary. W h en th e u ser h im self p erform s n o con version work on th e p ress, h e is on ly req u ired to be acq u ain ted with th e p rovid ed op eratin g in stru ction s an d th e accid en t p reven tion regu lation s ap p licable for p ress op eration . In Germ an y, th e followin g accid en t p reven tion regu lation s are am on g th e m ost im p ortan t in th is con text: – – – –

VBG VBG VBG VBG

7n 5.1 for eccen tric an d related p resses, 7n 5.2 for h yd rau lic p resses, 7n 5.3 for sp in d le p resses, 5 for p ower-d riven op eratin g eq u ip m en t.

Directive 89/ 655/ EEC on th e p rovision of eq u ip m en t obliges th e u ser to retrofit all m ach in es to a d efin ed m in im u m stan d ard by Jan u ary 1, 1997. It is safe to assu m e th at u sers wh o con verted th eir m ach in es in lin e with accid en t p reven tion regu lation s valid u p u n til Decem ber 31, 1993, will be u n affected by th is ru lin g. If th e u ser in ten ds to perform h is own con version work on th e m ach in e, h e assu m es fu ll respon sibility for h is action s. He m u st accordin gly be acqu ain ted with all th e valid directives, regu lation s an d stan dards. Con version of an an n ex IV m ach in e, i. e. a press in ten ded for m an u al feedin g an d u n loadin g, requ ires n otification of th e testin g body wh ich perform ed th e EC type test. Th e con version of an au tom atic m ach in e for m an u al feedin g or u n loadin g calls for EC type testin g u n less th e com plete con stru ction h as been perform ed in com plian ce with th e C stan dard. Alth ou gh th e ECMD does n ot apply to u sed m ach in ery, i. e. m ach in es com in g in to circu lation in th e EEC prior to Decem ber 31, 1994. Th ese m ach in es do n ot bear th e CE m ark an d do con tain certain provision s wh ich are of im portan ce in th is con text. Used m ach in es from foreign cou n tries ou tside Eu rope m u st always bear th e CE m ark an d be accom pan ied by a con form ity declaration . Th e con version of u sed m ach in es m u st be perform ed with a view to th e h ealth an d safety requ irem en ts of an n ex I of th e ECMD. However, in case of m ajor m odification s, fu n ction al ch an ges or in creased perform an ce, th e en tire m ach in e or produ cton lin e m u st be su bjected to a con form an ce ch eck by th e con stru ction forem an , after wh ich it will receive th e CE m ark.

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3.6.6 Safety requirements in the USA Th e followin g brief an alysis of safety req u irem en ts in th e USA p rovid es a rep resen tative com p arison with safety regu lation s ap p licable ou tsid e Eu rop e. Alon gsid e th e ANSI (Am erican Nation al Stan d ard s In stitu te) Stan d ard B11.1-1971, th e regu lation s of th e OSHA (Occu p ation al Safety an d Health Ad m in istration ) ap p ly. ANSI n ation al stan d ard s cover a n u m ber of areas in clu d in g safety eq u ip m en t, alth ou gh ap p lication of th ese stan d ard s is volu n tary. In con trast, com p lian ce with th e OSHA regu lation s is a statu tory req u irem en t. Th is stipulates th at a Lock-Out Procedure to §1910.147 be used on all m ach in es. Th is requirem en t specifies a description of h ow each type of en ergy an d each en ergy source can be ren dered h arm less. Th is m ust be perform ed in four stages: sh ut-down of th e en ergy source, dissolution of residual en ergy, a ch eck of en ergy-free status an d safeguardin g th e en ergyfree status again st un in ten tion al restart. Th is step-by-step approach for th e isolation of en ergy sou rces h as been adop ted by th e EN1037 to ap p ly to Eu rop ean stan dards. As a m in im u m req u irem en t, m ain switch es m u st be cap able of lockin g in th e en ergy-free statu s. Th e OSHA rep resen ts th e p h ilosop h y th at every staff m em ber sh ou ld carry p adlocks u sable on ly by h im self or h erself wh ich safely elim in ate an y p ossibility of restart by th ird p arties. On ly h e or sh e can can cel th e disabled statu s. Like th e ANSI stan d ard , th e OSHA req u ires from th e m an u factu rer th e com p ilation of in stru ction s en su rin g safe m ach in e op eration an d m ain ten an ce. Accord in g to OSHA, eq u ip m en t m u st be d elivered with a lock-ou t p late in accord an ce with Fig. 3.6.4 in d icatin g th e d evices req u ired to ren d er th e eq u ip m en t h arm less u sin g th e fou r step s listed above for each of th e en ergy sou rces u sed . Th e warn in g p ictogram s are also attach ed at th e relevan t p oin ts of th e m ach in e. As m en tion ed earlier, th e OSHA p laces p articu lar em p h asis on th e train in g of op erators, set-u p p erson n el an d m ain ten an ce staff in p articu lar. Th e objective of th e train in g is to in d icate p ossible sou rces of accid en ts, p rom ote safetycon sciou s work an d p oin t ou t th e p u rp ose an d fu n ction of th e safety gear. Em p loyers sh ou ld p rovid e train in g on in itial tran sfer an d com m ission in g of th e eq u ip m en t an d th ereafter on ce a year, an d h ave th is con firm ed by m ean s of a sign atu re. Ap p lication of th e OSHA regu lation s varies from region to region , as th e OSHA orien ts its in terp reta-

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Fig. 3.6.4 Lock-out plate in accordance w ith US regulations

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tion of th e safety m easu res to th e regu lation s alread y existin g in th e resp ective com p an ies. In th e USA, th e first bu rd en of p roof lies with th e own er of th e eq u ip m en t wh o accord in gly h as an in terest in eq u ip m en t safety. For th is reason , it m akes sen se for d etails of safety en gin eerin g to be coord in ated with th e safety officer of th e com p an y ru n n in g th e m ach in e. In view of th e alm ost u n p red ictable am ou n ts reach ed by d am age claim s in th e USA, q u alified safety en gin eerin g an d good d ocu m en tation are gain in g in sign ifican ce. Ch aracteristic req u irem en ts im p osed on m ech an ical p resses are defin ed in §1910.217, an d th ose im p osed on forgin g m ach in es in §1910.218. Com p lian ce Safety an d Health Officers from th e Dep artm en t of Labor sh ou ld be given access to m on itor com p lian ce with safety req u irem en ts. Mu ch of th is resp on sibility lies with th e eq u ip m en t u ser.

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3 Fundamentals of press design

3.7 Casting components for presses Th e p rop ortion of cast com p on en ts in p resses in term s of th eir weigh t differs con siderably. In in dividu al p resses su ch as m in tin g an d coin in g p resses (cf. Sect. 6.8.7) or au tom atic n otch in g m ach in es (cf. Sect. 4.6.4), som e 80 % of th e total p ress weigh t is m ade u p of gray cast iron , in gen eral in n odu lar cast iron . Th is p rop ortion is m ade u p p redom in an tly of large com p on en ts su ch as u p righ ts, p ress fram es an d p ress bodies (cf. Fig. 3.1.1). In th e case of large p resses with in dividu al p art weigh ts exceedin g 20 t, h owever, welded con stru ction s p redom in ate. Freedom from scale, good m ach in in g p rop erties, n on -leakage of oil an d adh eren ce to m ech an ical valu es laid down in th e drawin g sp ecification s are criteria wh ich govern th e q u ality of castin gs. Th ey determ in e th e com p lian ce of castin gs with gen eral m ech an ical en gin eerin g req u irem en ts. Du e to th e size of th e castin gs an d th eir low p rodu ction volu m e, th ese p arts are typ ically m ade u sin g th e m an u al m oldin g tech n iq u e, i. e. with ou t th e u se of m ech an ical aids. Th e castin g in d u stry is ch allen ged to a far greater d egree by th e p rod u ction of com p on en ts to d rive m ech an ical p resses, in p articu lar tran sfer p resses. Eccen tric wh eels, for exam p le, cam wh eels, red u cin g gears, con n ectin g rod s an d clu tch com p on en ts rep resen t a p articu lar ch allen ge to th e castin gs p rod u cer d u e to th e sp ecial q u ality req u irem en ts in volved (cf. Sect. 3.2.6). Th e focal p oin t of th is typ e of d rive system is th e eccen tric wh eel, wh ich can h ave a p art weigh t ran gin g an ywh ere from 5 to 25 t (Fig. 3.7.1). For th is typ e of com p on en t, d u ctile castin gs in GGG-70 q u ality are in creasin gly u sed , wh ile in th e p ast it was cu stom ary to u se steel castin gs. Th is ch an ge n ecessitated exten sive exp erim en tation an d con tin u ou s fu rth er d evelop m en t from th e p oin t of view

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Fig. 3.7.1 Eccentric w heel of a large-panel transfer press

both of m etallu rgical an d castin g tech n ology. Maxim u m care in th e p rod u ction p rocess is an u n d erlyin g req u irem en t. Accord in g to th e cu rren t state of th e art in th e field of fou n d ry p ractice, th e followin g strin gen t req u irem en t criteria can be covered with GGG-70: – h igh resistan ce to wear, i. e. th e m icrostru ctu re m u st be p u rely p erlitic even with wall th ickn esses of u p to 200 m m , – gu aran teed h ard n ess of 240 to 300 HB in all wall th ickn esses – also at th e tooth root, – elon gation over 2 % in ord er to avert fractu res an d to in crease resistan ce to overload in g. In its raw cast state, i. e. with ou t tran sform ation an n ealin g, th ese m ech an ical req u irem en ts are ach ieved u sin g a selective alloyin g tech n iqu e. Th e application of coolin g elem en ts m ade of iron , steel an d silicon carbide, eith er cooled or u n cooled, also serves to en h an ce h ardn ess.

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However, th e castin g tech n ician can on ly alloy an d cool with in restricted lim its, as elon gation drops with in creasin g h ardn ess. Du e to th is type of m etallu rgical-tech n ological operation , an d becau se of th eir geom etrical sh ape, castin gs su ch as eccen tric wh eels are in evitably exposed to h igh degrees of residu al stress. As a resu lt, stress relief an n ealin g at 560 to 580 °C is an absolu te n ecessity. In th e fou n dry, qu ality stan dards m u st be assu red in order to avert th e risk of cracks an d fractu res in th e castin gs. Th e m arked ten den cy of th e m aterial to form scale su bstan tially im pedes th e produ ction of com pon en ts m ade of GGG-70. Th e porosity risk th erefore is addressed by feedin g an d selective solidification . All com pon en ts, n atu rally in clu din g also large parts for press drive system s, are su bject to h igh ly strin gen t qu ality con trols, in clu din g u ltrasou n d, X-ray, crack detection an d h ardn ess testin g, as well as testin g of m ech an ical valu es u sin g test-bar specim en , cast togeth er with produ ced com pon en t.

Bibliography Anselmann, N. (editor): Europäisches Recht der Technik, Beuth Verlag, Berlin, Vienna, Zurich (1993). ANSI B11.1-1971: Safety requirements for the construction, care, and use of mechanical pow er presses, American National Standards Institute Inc., New York (1971). Becker, U., Ostermann, H.-J.: Wegw eiser M aschinenrichtlinie, Bundesanzeiger-Verlag, Cologne (1995). Bodenschatz, W., Fichna, G., Voth, D.: Produkthaftung, M aschinenbau-Verlag, Frankfurt/M ain, 4th edition. (1990). DIN EN 692 (Draft): M echanische Pressen – Sicherheit, Beuth Verlag, Berlin (1992). DIN EN 693 (Draft): Hydraulische Pressen – Sicherheit, Beuth Verlag, Berlin (1992). DIN EN 1037 (Draft): Sicherheit von M aschinen, Trennung von der Energiezufuhr und Energieabbau, Vermeidung von unerw artetem Anlauf, Beuth-Verlag, Berlin (1993). Hoffmann, H., Schneider, F.: Schw ingen verhindert-Hydraulische Zieheinrichtung für die Fertigung mit hoher Qualität in einfachw irkenden Pressen, M aschinenmarkt 95 (1989) 51/52. Hoffmann, H.: Vergleichende Untersuchung von Zieheinrichtungen, Bänder Bleche Rohre (1991) 12 and (1992) 1. Kürzinger, F.-X.: Kraftneutrale Parallelregelung über gesamten Hub, Bänder Bleche Rohre (1995) 9. Occupational Safety and Health Administration: OSHA Regulations 29 CFR Ch XVII, Part 1910, Office of the Federal Register, Washington D.C., 7-1-92 Edition (1992). Schmidt, K.: Die neue Druckbehälterverordnung, W EKA Fachverlag, Augsburg (1995). Schw ebel, R.: Geringe Parallelitätsabw eichungen - Anw endungsspektrum hydraulischer Pressen, Industriebedarf (1994) 9. Süddeutsche M etall-Berufsgenossenschaft: Unfallverhütungsvorschriften, Carl Heymanns Verlag KG, Luxemburg (1994). TÜV Hannover-Sachsen-Anhalt: Kurzinformation EG-M aschinen-Richtlinie, Eigenverlag (1995).

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4 Sheet metal forming and blanking

4.1 Principles of die manufacture 4.1.1 Classification of dies In m etalform in g, th e geom etry of th e workpiece is establish ed en tirely or partially by th e geom etry of th e die. In con trast to m ach in in g processes, sign ifican tly greater forces are n ecessary in form in g. Du e to th e com plexity of th e parts, form in g is often n ot carried ou t in a sin gle operation . Depen din g on th e geom etry of th e part, produ ction is carried ou t in several operation al steps via on e or several produ ction processes su ch as form in g or blan kin g. On e operation can also in clu de several processes sim u ltan eou sly (cf. Sect. 2.1.4). Du rin g th e d esign p h ase, th e n ecessary m an u factu rin g m eth od s as well as th e seq u en ce an d n u m ber of p rod u ction step s are establish ed in a p rocessin g p lan (Fig. 4.1.1). In th is p lan , th e availability of m ach in es, th e p lan n ed p rod u ction volu m es of th e p art an d oth er bou n d ary con d ition s are taken in to accou n t. Th e aim is to m in im ize the num ber of dies to be used wh ile keep in g u p a h igh level of op eration al reliability. Th e p arts are greatly sim p lified righ t from th eir d esign stage by close collaboration between th e Part Design an d Prod u ction Dep artm en ts in ord er to en able several form in g an d related blan kin g p rocesses to be carried ou t in on e form in g station . Obviou sly, th e m ore op eration s wh ich are in tegrated in to a sin gle d ie, th e m ore com p lex th e stru ctu re of th e d ie becom es. Th e con seq u en ces are h igh er costs, a d ecrease in ou tp u t an d a lower reliability.

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Fig. 4.1.1 Production steps for the manufacture of an oil sump

Types of dies Th e typ e of d ie an d th e closely related transportation of the part between dies is d eterm in ed in accord an ce with th e form in g p roced u re, th e size of th e p art in q u estion an d th e p rod u ction volu m e of p arts to be p rod u ced . Th e p rod u ction of large sh eet m etal p arts is carried ou t alm ost exclu sively u sin g single sets of dies. Typ ical p arts can be fou n d in au tom otive m an u factu re, th e d om estic ap p lian ce in d u stry an d rad iator p rod u ction . Su itable tran sfer system s, for exam p le vacu u m su ction system s, allow th e in stallation of d ou ble-action d ies in a su fficien tly large m ou n tin g area. In th is way, for exam p le, th e righ t an d left d oors of a car can be form ed join tly in on e workin g stroke (cf. Fig. 4.4.34). Large size sin gle d ies are in stalled in large p resses. Th e tran sp ortation of th e p arts from on e form in g station to an oth er is carried ou t m ech an -

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ically. In a p ress lin e with sin gle p resses in stalled on e beh in d th e oth er, feed ers or robots can be u sed (cf. Fig. 4.4.20 to 4.4.22), wh ilst in largepan el tran sfer presses, system s equ ipped with gripper rails (cf. Fig. 4.4.29) or crossbar su ction system s (cf. Fig. 4.4.34) are u sed to tran sfer th e parts. Transfer dies are u sed for th e p rod u ction of h igh volu m es of sm aller an d m ed iu m size p arts (Fig. 4.1.2). Th ey con sist of several sin gle d ies, wh ich are m ou n ted on a com m on base p late. Th e sh eet m etal is fed th rou gh m ostly in blan k form an d also tran sp orted in d ivid u ally from d ie to d ie. If th is p art tran sp ortation is au tom ated , th e p ress is called a tran sfer p ress. Th e largest tran sfer d ies are u sed togeth er with sin gle d ies in large-p an el tran sfer p resses (cf. Fig. 4.4.32). In progressive dies, also kn own as progressive blanking dies, sh eet m etal p arts are blan ked in several stages; gen erally sp eakin g n o actu al form in g op eration takes p lace. Th e sh eet m etal is fed from a coil or in th e form of m etal strip s. Usin g an ap p rop riate arran gem en t of th e blan ks with in th e available width of th e sh eet m etal, an op tim al m aterial u sage is

Fig. 4.1.2 Transfer die set for the production of an automatic transmission for an automotive application

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en su red (cf. Fig. 4.5.2 to 4.5.5). Th e workp iece rem ain s fixed to th e strip skeleton u p u n til th e last op eration . Th e p arts are tran sferred wh en th e en tire strip is sh ifted fu rth er in th e work flow d irection after th e blan kin g op eration . Th e len gth of th e sh ift is eq u al to th e cen ter lin e sp acin g of th e d ies an d it is also called th e step wid th . Sid e sh ears, very p recise feed in g d evices or p ilot p in s en su re feed -related p art accu racy. In th e fin al p rod u ction op eration , th e fin ish ed p art, i. e. th e last p art in th e seq u en ce, is d iscon n ected from th e skeleton . A field of ap p lication for p rogressive blan kin g tools is, for exam p le, in th e p rod u ction of m etal rotors or stator blan ks for electric m otors (cf. Fig. 4.6.11 an d 4.6.20). In progressive com pound dies sm aller form ed p arts are p rod u ced in several seq u en tial op eration s. In con trast to p rogressive d ies, n ot on ly blan kin g bu t also form in g op eration s are p erform ed . However, th e workp iece also rem ain s in th e skeleton u p to th e last op eration (Fig. 4.1.3 an d cf. Fig. 4.7.2). Du e to th e h eigh t of th e p arts, th e m etal strip m u st be raised u p , gen erally u sin g liftin g ed ges or sim ilar liftin g d evices in ord er to allow th e strip m etal to be tran sp orted m ech an ically. Pressed m etal p arts wh ich can n ot be p rod u ced with in a m etal strip

Fig. 4.1.3 Reinforcing part of a car produced in a strip by a compound die set

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becau se of th eir geom etrical d im en sion s are altern atively p rod u ced on tran sfer sets. Next to th e d ies alread y m en tion ed , a series of special dies are available for sp ecial in d ivid u al ap p lication s. Th ese d ies are, as a ru le, u sed sep arately. Sp ecial op eration s m ake it p ossible, h owever, for sp ecial d ies to be in tegrated in to an op eration al seq u en ce. Th u s, for exam p le, in flanging dies several m etal p arts can be join ed togeth er p ositively th rou gh th e ben d in g of certain m etal section s (Fig. 4.1.4 an d cf. Fig. 2.1.34). Du rin g th is op eration rein forcin g p arts, glu e or oth er com p on en ts can be in trod u ced . Oth er sp ecial d ies locate sp ecial con n ectin g elem en ts d irectly in to th e p ress. Sorting and positioning elem ents, for exam p le, brin g stam p in g n u ts syn ch ron ised with th e p ress cycles in to th e correct p osition so th at th e punch heads can join th em with th e sh eet m etal p art (Fig. 4.1.5). If th ere is su fficien t sp ace available, form in g an d blan kin g op eration s can be carried ou t on th e sam e d ie. Fu rth er exam p les in clu d e ben d in g, collar-form in g, stam p in g, fin e blan kin g, wobble blan kin g an d weld in g op eration s (cf. Fig. 4.7.14 an d 4.7.15).

1

2

blank holder

pressure block

inner door

outer door seaming bed tilting block

Fig. 4.1.4 A hemming die

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Fig. 4.1.5 A pressed part w ith an integrated punched nut

4.1.2 Die development Trad ition ally th e bu sin ess of d ie en gin eerin g h as been in flu en ced by th e au tom otive in d u stry. Th e followin g observation s abou t th e d ie d evelop m en t are m ostly related to bod y p an el d ie con stru ction . Essen tial statem en ts are, h owever, m ad e in a fu n d am en tal con text, so th at th ey are ap p licable to all areas in volved with th e p rod u ction of sh eet-m etal form in g an d blan kin g d ies. Tim ing cycle for a m ass produced car body panel Un til th e en d of th e 1980s som e car m odels were still bein g p rodu ced for six to eigh t years m ore or less u n ch an ged or in sligh tly m odified form . Today, h owever, p rodu ction tim e cycles are set for on ly five years or less (Fig. 4.1.6). Followin g th e n ew differen t m odel p olicy, th e dem an ds on die m akers h ave also ch an ged fu n dam en tally. Com p reh en sive con tracts of m u ch greater scop e su ch as Sim u ltan eou s En gin eerin g (SE) con tracts are becom in g in creasin gly com m on . As a resu lt, th e die m aker is often in volved at th e in itial develop m en t p h ase of th e m etal p art as well as in th e p lan n in g p h ase for th e p rodu ction p rocess. Th erefore, a m u ch broader in volvem en t is establish ed well before th e actu al die develop m en t is in itiated.

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129

2-3 year period

go-ahead for a new model

trend and market research

concept phase

participation of the toolmaker in the development and production process

styling phase

prototype parts

various try-out phases w ith pilot series parts

design of the outer c ar bodyw ork

various try-out phases w ith prototype parts

design of the bodyw ork reinforcement

pilot series parts

start of series production

period up to production stop

start on development of follow -up model

Fig. 4.1.6 Time schedule for a mass produced car body panel

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The tim etable of an SE project With in th e con text of th e p rod u ction p rocess for car bod y p an els, on ly a m in im al am ou n t of tim e is allocated to allow for th e m an u factu re of th e d ies. With large scale d ies th ere is a ru n -u p p eriod of abou t 10 m on th s in wh ich d esign an d d ie try-ou t are in clu d ed . In com p lex SE p rojects, wh ich h ave to be com p leted in 1.5 to 2 years, p arallel tasks m u st be carried ou t. Fu rth erm ore, ad d ition al resou rces m u st be p rovid ed before an d after d elivery of th e d ies. Th ese sh ort p eriod s call for p recise p lan n in g, sp ecific kn ow-h ow, available cap acity an d th e u se of th e latest tech n ological an d com m u n ication s system s. Th e tim etable sh ows th e in d ivid u al activities d u rin g th e m an u factu rin g of th e d ies for th e p rod u ction of th e sh eet m etal p arts (Fig. 4.1.7). Th e tim e p h ases for large scale d ies are m ore or less sim ilar so th at th is tim etable can be con sid ered to be valid in gen eral. Data record and part drawing Th e d ata record an d th e p art d rawin g serve as th e basis for all su bseq u en t p rocessin g step s. Th ey d escribe all th e d etails of th e p arts to be

milestones: specifications production release pre-planning

pre-production pilot series series series

purchasing release design

die production

die development

project planning process planning CAD data draw development prototype parts die design casting models casting

start of SE project

machining bench w ork home try-out

Fig. 4.1.7 Timetable for an SE project

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

series try-out

Principles of die manufacture

p rod u ced . Th e in form ation given in th e p art d rawin g in clu d es: p art id en tification , p art n u m berin g, sh eet m etal th ickn ess, sh eet m etal q u ality, toleran ces of th e fin ish ed p art etc. (cf. Fig. 4.7.17). To avoid th e p rodu ction of p h ysical m odels (m aster p attern s), th e CAD data sh ou ld describe th e geom etry of th e p art com p letely by m ean s of lin e, su rface or volu m e m odels. As a gen eral ru le, h igh q u ality su rface data with a com p letely filleted an d closed su rface geom etry m u st be m ade available to all th e p articip an ts in a p roject as early as p ossible. Process plan and draw developm ent Th e p rocess p lan , wh ich m ean s th e op eration al seq u en ce to be followed in th e p rod u ction of th e sh eet m etal com p on en t, is d evelop ed from th e d ata record of th e fin ish ed p art (cf. Fig. 4.1.1). Alread y at th is p oin t in tim e, variou s bou n d ary con d ition s m u st be taken in to accou n t: th e sh eet m etal m aterial, th e p ress to be u sed , tran sfer of th e p arts in to th e p ress, th e tran sp ortation of scrap m aterials, th e u n d ercu ts as well as th e slid in g p in in stallation s an d th eir ad ju stm en t. Th e d raw d evelop m en t, i. e. th e com p u ter aid ed d esign an d layou t of th e blan k h old er area of th e p art in th e first form in g stage – if n eed be also th e secon d stage –, req u ires a p rocess p lan n er with con sid erable exp erien ce (Fig. 4.1.8). In ord er to recogn ize an d avoid p roblem s in areas wh ich are d ifficu lt to d raw, it is n ecessary to m an u factu re a p h ysical an alysis m od el of th e d raw d evelop m en t. With th is m od el, th e form in g con d ition s of th e d rawn p art can be reviewed an d fin al m od ification s in trod u ced , wh ich are even tu ally in corp orated in to th e d ata record (Fig. 4.1.9). Th is process is bein g replaced to som e exten t by in telligen t sim u lation m eth ods, th rou gh wh ich th e poten tial defects of th e form ed com pon en t can be predicted an d an alysed in teractively on th e com pu ter display. Die design After release of th e p rocess p lan an d draw develop m en t an d th e p ress, th e design of th e die can be started. As a ru le, at th is stage, th e stan dards an d m an u factu rin g sp ecification s req u ired by th e clien t m u st be con sidered. Th u s, it is p ossible to obtain a u n ified die design an d to con sider th e p articu lar req u ests of th e cu stom er related to wareh ou sin g of stan dard, rep lacem en t an d wear p arts. Man y dies n eed to be design ed so th at th ey can be in stalled in differen t typ es of p resses. Dies are freq u en tly

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131

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132

Fig. 4.1.8 CAD data record for a draw development

in stalled both in a p rod u ction p ress as well as in two d ifferen t sep arate back-u p p resses. In th is con text, th e layou t of th e d ie clam p in g elem en ts, p ressu re p in s an d scrap d isp osal ch an n els on d ifferen t p resses m u st be taken in to accou n t. Fu rth erm ore, it m u st be n oted th at d rawin g d ies workin g in a sin gle-action p ress m ay be in stalled in a d ou bleaction p ress (cf. Sect. 3.1.3 an d Fig. 4.1.16). In th e d esign an d sizin g of th e d ie, it is p articu larly im p ortan t to con sid er th e freed om of m ovem en t of th e grip p er rail an d th e crossbar tran sfer elem en ts (cf. Sect. 4.1.6). Th ese d escribe th e relative m ovem en ts between th e com p on en ts of th e p ress tran sfer system an d th e d ie com p on en ts d u rin g a com p lete p ress workin g stroke. Th e liftin g m ovem en t of th e p ress slid e, th e op en in g an d closin g m ovem en ts of th e grip p er rails an d th e len gth wise m ovem en t of th e wh ole tran sfer are all su p erim p osed . Th e d ies are d esign ed so th at collision s are avoid ed an d a m in im u m clearan ce of abou t 20 m m is set between all th e m ovin g p arts.

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Principles of die manufacture

Fig. 4.1.9 Physical analysis model of a draw development

Gu id es of th e u p p er an d lower d ies m u st carry th e sh earin g forces an d be sized accord in g to th e calcu lated an d an ticip ated forces an d fu n ction s. Large scale gibs sh ow n early n o lateral d isp lacem en t an d a con sisten t, u n ch an gin g p ressu re p attern of th e op eration al d ie (cf. Sect. 4.1.5). Fu rth erm ore, th ey red u ce th e tiltin g of th e d ie an d th e p ress slid es (Fig. 4.1.10). Th u s, a con sisten t overall h igh q u ality of p ressed p arts is ach ieved . In ord er to avoid errors an d p oten tial p roblem areas later in p rod u ction , th e so-called FMEA (Failu re Mod e an d Effects An alysis) is u sed with p roven su ccess d u rin g th e d esign stage with th e close collaboration of all th ose in volved with th e p roject. Th e d esign of th e p ressed p arts an d th eir arran gem en t an d p osition in g in th e d ies h ave a great in flu en ce on p rod u ction safety. In sh eet m etal form in g well-d esign ed p ress com p on en ts will lead to sim p le, p rod u ction -frien d ly an d low cost tools. Difficu lt to form p ress p arts, on th e oth er h an d , in volve exp en sive, com p licated an d h igh cost d ies, wh ich are less easily in tegrated

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133

Sheet metal forming and blanking

134

reduction of slide tilt

[ ] 85 82 75

7 6

64 58

3 13,5 5,9 0

6

10,5

6,5

0

offset

without gibs

columns [ mm

lugs polyamid mm

lugs brass mm

columns [ 6 mm

columns [ 6 mm

Fig. 4.1.10 Influence of the guidance system on the reduction of slide tilting and offset

in to th e p rod u ction p rocess. Tiltin g of th e p arts in th e d ies can com p en sate th e n egative asp ects of an u n favorable p art geom etry. For exam p le, for flan gin g an d blan kin g a sh eet m etal p art can be so rotated th at th e work d irection corresp on d s to th e d irection of th e flan gin g op eration e. g. th e m ovem en t of th e blan kin g p u n ch (Fig. 4.1.11). However, it is often th en n ecessary to in crease th e n u m ber of d ies, wh ich resu lts in p rod u ction cost in creases. To m eet d ead lin es, th e form in g d ies m u st be d esign ed first so th at th e castin g p attern s an d th e fin ish ed castin gs are available for u se as soon as p ossible. After m ach in in g an d try-ou t, d ies can p rod u ce stam p in gs th at are laser trim m ed an d u sed in p rototyp e p re-p rod u ction assem blies (Fig. 4.1.7). Th e u se of CAD system s for die design h as becom e in creasin gly com m on (Fig. 4.1.12) even th ou gh con ven tion al drawin g board design m ay often be m ore cost effective. Th e reason s for th is are th at th e drawin g system is n ot yet p erfected, data ban ks are in com p lete an d workstation screen s on ly allow a p ersp ective view in th e ratio of 1 : 5 u p to 1 : 10. However, con siderin g th e total p rodu ction costs, h igh q u ality CAD p rodu ced die design s an d die castin g p attern data are p rovided as a byp rodu ct. Sh rin kage an d exp an sion allowan ces can be determ in ed by com p u ter an d u sed for NC m ach in in g of castin g m odels, an econ om ic altern ative to NC m ach in in g of castin gs. A fu rth er advan tage of CAD design , in so far as it is based on a volu m e m odel, is th e p ossibility

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Principles of die manufacture

a

135

b

c

Fig. 4.1.11 Improvement to the positioning of the part by means of sw ivel movement in the folding operation: a simple die construction for press parts w ith simple geometry; b complex high cost die construction w ith a sliding element for difficult press part geometry; c simple die construction via appropriate sw ivelling of the pressed part in an improved w orking position

Fig. 4.1.12 CAD design of pivoting blanking tool

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136

of on goin g collision testin g, wh ich clearly con tribu tes to th e redu ction of errors. Jaw layou t p lan s, die con stru ction p lan s an d sin gle p art drawin gs can be m ade available by th is system . Th e gen eral u se of CAD/ CAM system s in tool m akin g h ave m an y in h eren t advan tages th at are lin ked to th e p rocess. Th erefore, in th e m ediu m term , CAD/ CAM tech n iq u es will be in creasin gly u sed to in crease th e total cost effectiven ess of p art p rodu ction . Mechanical processing Tod ay’s tech n ical p ossibilities in NC p rocessin g req u ire ever m ore easy to m an u factu re d esign s from th e d ie d esign er. In p articu lar th e u se of five-axis m illin g m ach in es allows to m ach in e com p letely com p lex castin gs with a sin gle fixtu rin g op eration . In th e p ast, becau se of restricted con d ition s, exten d ed op eratin g an d assem bly activities were carried ou t with fixtu res an d ad d ition al clearan ces. Tod ay, for exam p le, th ree-d im en sion ally located slid in g an d gu id in g com p on en ts can be cast (Fig. 4.1.17). High sp eed m illin g (HSM) is u sed in creasin gly for m ach in in g of scu lp tu red su rfaces in wh ich econ om ical cu ttin g sp eed s of 2,000 m / m in are attain able. Even stron gly p attern ed su rfaces for in n er p arts can still be m ach in ed with m ed iu m feed rates of arou n d 5 m / m in . Cerm ets an d sp ecial PVD-coated carbid es are cap able of attain in g su rface q u alities of Rt = 10 m m , wh ich red u ces th e n eed for secon d ary m an u al p olish in g to a m in im u m . Assem bly and try-out More accu rate m ach in in g an d fin ish in g op eration s togeth er with th e above-m en tion ed ad van tages of a CAD su p p orted d ie d esign , sim p lify th e assem bly task con sid erably. Th e gen eral p rocessin g of d ata gives access to fu rth er th eoretical an d error-free blan kin g an d con tou r in form ation with ou t h avin g to resort to th e u se of costly aid s. Th e exp ert kn owled ge of th e q u alified d iem aker is, h owever, still n ecessary. In p articu lar, in th e p re-ru n or try-ou t p h ases wh en th e d ie d evelop er tries to p rod u ce a good p art after th e in stallation of th e d ies in th e p ress, it becom es evid en t wh eth er or n ot th e th eoretical d esign effort h as been correct (cf. Sect. 4.1.5). Prototyp e tools or sim u lation m eth od s p rovid e, of cou rse, con sid erable h elp . Th ere are, h owever, ad d ition al factors wh ich con tribu te toward s th e q u ality of th e stam p in gs obtain ed with

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Principles of die manufacture

th e p rod u ction d ies. Th e m ach in in g of th e d ie su rfaces an d th e gibs, th e m illin g of th e free form su rface u sin g HSM op eration s an d th e tryou t on a p recisely gu id ed try-ou t p ress with ad ju stable h yd rau lic d raw cu sh ion s sh ou ld all be carried ou t efficien tly (Fig. 4.1.19 an d 4.1.20). Process control In ord er to assu re th at th e p art d ep en d en t p rocess p lan an d th e d raw d evelop m en t are correct, p rototyp e d ies or soft tools are p rod u ced (Fig. 4.1.13). In so d oin g, th e form in g beh avior of th e sh eet m etal m aterial, esp ecially wh en th e p art geom etry is com p lex an d m ore p ron e to failu re, m u st be in vestigated at th e p relim in ary stages of th e d ie d esign . However, th e p ractise of u sin g soft tools d ed icated exclu sively for th is p u rp ose is becom in g less sign ifican t as com p u ter-aid ed sim u lation p rocesses are bein g in creasin gly u sed for d ie d esign an d d evelop m en t. Prototype dies Th e p rep aration of p rototyp e or soft d ies is, h owever, worth wh ile if fu rth er objectives n eed to be attain ed . At a very early p oin t in th e p rod u ction p rocess, th e sh eet m etal p arts are m ad e available, wh ich can be u sed , for in stan ce, to con stru ct veh icles for assem bly an d crash test p u r-

Fig. 4.1.13 Prototype draw ing die in aluminium for the production of the roof of a station w agon

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138

p oses. In certain cases, th ese p arts m ay be u sed as p re-p rod u ction series (Fig. 4.1.7). A fu rth er con sid eration wh ich ju stifies th e p rod u ction of p rototyp e d ies is wh en th e tim in g of th eir m an u factu re is close to th e sch ed u le for th e begin n in g of series p rod u ction . Th u s, in form ation on th e form ability an d toleran ces of th e p arts can be obtain ed , wh ich con tribu tes to goal orien ted an d cost-effective d ie m an u factu re. Th e followin g are som e of th e p oin ts wh ich m u st be taken in to accou n t h ere: – – – – –

th e d ie m aterial th e com p lexity of th e sh eet m etal p art th e blan k m aterial th e d esign of th e d raw d evelop m en t th e geom etrical p aram eters su ch as d egree of sh rin kage, cam berin g, p restressin g – th e p rocess-related variable su ch as lu brication , blan k h old er forces, work-flow d irection , d raw bead s – th e size an d geom etry of th e blan ks – sp ecial factors an d p aram eters wh ich in flu en ce th e resu lts of th e stam p in g op eration Th e typ e an d d esign of th e p rototyp e d ies are in flu en ced by d ifferen t factors. Th e ch oice of p rototyp e m aterial will be in lin e with th e sh eet m etal sp ecification , th ickn ess an d th e n u m ber of p arts to be p rod u ced . Tod ay, p lastics, alu m in iu m alloys (Fig. 4.1.13), d ifferen t q u alities of cast m etals as well as rolled steel can be u sed as p rototyp e or soft d ie m aterial. A su m m ary of th e ch oice an d ap p lication criteria is given in Table 4.1.1. Methods of process sim ulation Com p u ter-aid ed sim u lation tech n iq u es, e. g. th e an alysis of th e form in g p rocess with ou t an y p h ysical d ies, will in creasin gly rep lace th e u se of p rototyp e an d soft d ies. Th is d evelop m en t is becom in g m ore p ractical th rou gh rap id ly growin g h ard ware d evelop m en ts wh ich allow th e p rocessin g of ever in creasin g am ou n ts of com p u terised d ata in ever sh orter tim e sp an s. In ad d ition , th e com p u ter software u sed for p rocess sim u lation h as becom e m ore reliable an d m ore u ser frien d ly.

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Die type

Plastic

Aluminium alloys

Iron alloys

w ithout additives

alloyed or fiber-reinforced

Zamak

Cerrotru

GS/GG cast iron

Plate steel

M anufacturing process

complete structure in plastic, cast in layers or w ith back as the front casting

cast steel frame as basic structure for plastic panels (punch), casting of female die shape

model production for punch and female die (possibly blank holder), casting of models, rew orking of functional surfaces

precise model manufacture, casting the punch, insertion of sheet metal thickness, casting of female die (no rew orking)

model manufacture for punch and female die (possibly blank holder), casting of models, rew orking of functional surfaces, integration of gib elements

construction of die from plates and jaw s, screw ed and pinned, rew orking of functional surfaces, integration of gib elements

Repair and possibility for modification

machinable shape punch shape or new front machinable, inserts are casting seamlessly glued in, casting of female die

w eldable, inserts machinable

melt dow n existing die and recast

w elding on, screw -mounted inserts, rew orking by means of milling

w elding on, new jaw s or inserts

Range of parts

outer bodyw ork parts in steel and aluminium

outer bodyw ork parts and reinforcements in steel and aluminium

outer bodyw ork parts and reinforcements

outer bodyw ork parts and easily formable parts

reinforcement and chassis parts w ith complex shapes

reinforcement and chassis parts w ith flat shapes

Sheet metal thickness

sheet steel up to 2 mm, aluminium up to 4 mm

up to 2.5 mm

up to 1.5 mm

up to 1.2 mm

up to 3 mm

up to 3 mm

Piece numbers

w ith max. sheet metal thickness, extremely low piece numbers, otherw ise suitable for small or pre-series

for outer bodyw ork parts, up to 1,000 pieces

easily deformable parts up to 100 pieces, complex parts up to 50 pieces

easily deformable parts up to 50 pieces, complex parts up to 20 pieces

Product. period

2 to 3 w eeks

4 to 6 w eeks

3 to 4 w eeks

2 to 3 w eeks

Principles of die manufacture

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Table 4.1.1: Allocation of prototype dies

depending on stress level and sheet metal material used, possibly w ith series capability

7 to 10 w eeks

5 to 7 w eeks

139

Sheet metal forming and blanking

140

For th e evalu ation of th e geom etry d ata, wh ich h as been establish ed by th e p rocessin g p lan an d th e d raw d evelop m en t as well as th e p rod u ction p aram eters, CAE solu tion s are available wh ich are based u p on m ath em atical an d p lasto-m ech an ical eq u ation s or on exp erim en tally p roven d ata. An alytical an d n u m erical sim u lation belon g to th ese solu tion s. Th e n u m erical m eth od s, an d h ere in p articu lar th e Fin ite Elem en t Meth od (FEM), d eliver tod ay th e m ost accu rate resu lts. Stam p in gs can be alm ost com p letely in teractively an alysed on a workstation in relation to th e m ost im p ortan t failu re criteria. Th e resu lts are th e d istribu tion of stress (tears) (Fig. 4.1.14), th e ten d en cy toward s wrin klin g (Fig. 4.1.15) an d th e variation of th e sh eet m etal th ickn ess. Th e n ecessary step s an d th e p rereq u isites for a sim u lation ru n are as follows: – p rep aration of CAD d ata for th e p u n ch , fem ale d ie an d blan k h old er as well as th e total geom etry of th e d raw d evelop m en t in th e workin g d irection (Fig. 4.1.8), – d eterm in ation an d in p u t of th e blan k size (cf. Sect. 4.2.1 an d 4.5), – in p u t of th e p rocess p aram eters su ch as sh eet m etal m aterial, rollin g d irection , blan k h old er force, friction al con d ition s, – d efin ition i. e. establish m en t of th e FE m esh (p artly au tom atic) an d – in itiation of th e calcu lation p rocess. By varyin g th e p rocess an d d ie p aram eters, th e sim u lation can be rep eated as often as req u ired u n til a failu re-free d rawin g p art is p rod u ced . Th e ad van tage of th is p rocess lies in th e fact th at an y objective an d n ecessary com p on en t ch an ges can be in trod u ced at an y tim e p rior to th e actu al m an u factu re of th e d ies. Sp ecific m easu res for th e con trollin g m etal flow, for exam p le th rou gh th e sh ap e of th e blan k or th rou gh th e u se of d raw bead s, can be sim u lated . Sim ilarly, calcu lation s can be m ad e to p red ict an d com p en sate for sp rin g back (cf. Sect. 4.8.1). Th rou gh p rocess sim u lation , p rocess p lan n ers an d d ie d esign ers receive reliable in form ation at an early stage in th e d ie d evelop m en t, wh ich really con tribu tes to th e p rod u ction of fu lly op eration al an d reliable d ies.

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Principles of die manufacture

0.00

0.0000

141

M aximum strain limit

W rinkling

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Fig. 4.1.14 Representation of stress distribution by means of FEM simulation

1.20

0.0400

Fig. 4.1.15 Representation of possible w rinkle formation by means of FEM simulation

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4.1.3 Die materials Th e p rocessin g of h igh stren gth sh eet m etal, wh ich is becom in g m ore wid ely u sed in stam p in g tech n ology, calls for h igh er p ressin g forces. Th is m ean s h igh er load s on th e d ies an d greater overall wear on th e tools. In ord er to m eet th e req u irem en ts for lon g d ie life, wh ile m ain tain in g accep table com p on en t q u ality, sp ecial m aterials – m ost of wh ich h ave been h ard en ed or coated – m u st be u sed in th e con stru ction of th e d ies. Th e basic stru ctu re of d ifferen t typ es of d ies an d th eir m ost im p ortan t com p on en ts are sh own in Figs. 4.1.16 an d 4.1.17. Table 4.1.2 lists th e variou s com p on en ts of d ies u sed for d rawin g, blan kin g, fold in g an d flan gin g as well as th e m aterials u sed to m an u factu re th em . Table 4.1.3 lists variou s su rface h ard en in g p rocesses an d coatin g m eth od s for d ies. Coatin gs, for exam p le th rou gh h ard ch rom iu m p latin g, can im p rove th e slid in g ch aracteristics in d eep d rawin g, so th at th e n eed for lu brication is greatly red u ced .

4.1.4 Casting of dies Th e castin g p rocess is on e of th e step s in th e overall p rocess of m an u factu rin g p rod u ction d ies for sh eet m etal form in g wh ere th e h igh est stan d ard s are req u ired by d ie m akers. In con trast to castin gs u sed in gen eral m ach in ery m an u factu re, in d ie m an u factu re, m u ltip le u sage of a m od el is n ot p ossible, as n o two tools are exactly th e sam e. A d isp osable p attern m ad e from p olystyren e (p olyester, h ard foam ) is th erefore u sed for th e d ie castin g p rocess (Fig. 4.1.18). Th e castin g is carried ou t as a fu ll form castin g p rocess: th e p olystyren e p attern stays in its resin -h ard en ed q u artz san d form . Th e liq u id m etal, wh ich is p ou red in , evap orates or rath er m elts th e p attern . With th e fu ll form castin g p rocess, th e fou n d ry in d u stry h as d evelop ed a p rod u ction m eth od wh ich offers a large m easu re of d esign -related , tech n ical, econ om ic an d logistical im p rovem en ts in d ie m akin g. For th e d esign er, th ere is th e p ossibility of p recise m easu rem en t an d fu n ction al con trol, as th e fu ll form p attern is id en tical in sh ap e to th e p iece bein g cast. Prod u ct d evelop m en t is m ad e easier, as th e p attern can be altered with ou t an y p roblem s by m ean s of m ach in in g or glu in g p rocesses. Fu rth erm ore, th e costs of core box, core p rod u ction , core tran sp ort an d core in stallation are red u ced .

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blank holder slide plates draw punch

female die

double-action drawing die

female die

blank holder

draw punch slide plates pressure pins die substructure

single-action drawing die

Fig. 4.1.16 Basic design of different draw dies

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bracket

upper structure

stripper

pressure plate

punch retaining plate

blanking segments

female blanking die waste chute panel retaining blocks

support

substructure pressure plate

female die retaining plate

blanking die bracket stripper (on final pressure)

upper structure

embossing block

restrike block support substructure

restrike edge bending die

upper structure

driver

driver slide filling slide blocks substructure

partial support bracket

filling slide

flanging die

Fig. 4.1.17 Basic design of different blanking, edge bending and flanging dies

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Die material No.

1.0046

1.0555

1.7140

1.2067

1.2769

1.2601

1.2363

Designation (DIN 16006)

GS-45

GS-62

GS-47 Cr M n 6

G-100 Cr 6

G-45 Cr Ni M o 42

G-X 165 Cr M o V 12

G-X 100 Cr M o V 51

Rm [N/mm2 ]

450

620

tempered, stress relieved 820-930

850

tempered to 1000-1030

800-900

800-900

Heat treatment

w eldable, not hardenable

hardening conditionally possible

w eldable surface hardenable

hardenable

surface hardenable, glow nitrided

hardenable

hardenable

Hardness after heat treatment

–

max. HRC 56 + 2 3 mm deep

HRC 56 + 2

HCR 60 + 2

w orking hardness HRC 50+/–2

HRC 60+/–2

HRC 60+/–2

thin-w alled blank holders, upper structures and substructures for small dies

blank holders, upper structures subject to high loads

forming punch, blanking segments, female blanking dies

forming punch, female die inserts, forming blocks, counterpressure pads

forming punches, female die inserts, forming blocks, blank holders and retainers w ith end pressure

blanking strips, blanking punches, coining punches, draw punches, female draw ing dies, forming punches

blanking strips, blanking punches, coining punches, draw punches, female draw ing dies, forming punches

1.2379

0.6025

0.6025 Cr M o

0.7050

0.7060

0.7070

0.7070 L

GG-25

GG-25 Cr M o

GGG-50

GGG-60

GGG-70

GGG-70 L 220-270

Application

Die material No.

Designation G-X 155 Cr V M o 12 1 (DIN 16006) Basic hardness HB max. 250

160-230

200-230

170-220

190-240

220-270

860

250-350

250

500

600

700

700

Heat treatment

hardenable, TIC-TIN coating

conditionally w eldable, glow nitriding

surface hardening, glow nitriding

surface hardening, temperable

conditionally w eldable, surface hardening, glow nitriding

conditionally w eldable, surface hardening, glow nitriding

surface hardening, glow nitriding

Hardness after heat treatment

HRC 60 + 2

approx. 1200-1400 HV2

approx. 53 HRC

approx. 54 HRC

approx. 56 HRC

approx. 56 HRC

approx. 56 HRC

blank holders, draw punches, female draw ing dies

instead of GG 25 and GS 45 w ith thin-w alled materials in particular in case of compressive stress, e.g. counterpressure pads and strippers

blank holders, draw punches female draw ing dies, brackets

blank holders, female draw ing dies

blank holders for parts w ith draw ing depths > 120 mm of outer bodyw ork parts on transfer presses

Rm [N/mm2 ]

Application

hemming blocks, standard material for edge bending blocks, cast die components, coining punches for blank holders adapters, sheet metals up to upper structures and 2,9mm, blanking cutters, substructures, bottom blanking dies, mounted parts, blanking punches drives, slides

Principles of die manufacture

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146

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Table 4.1.3: Specifications and applications for surface hardening and coating of dies S U RFA CE H A RD EN I N G P ROCES S ES electrical induction hardening

physical flame hardening glow nitriding

COATI N G P ROCES S ES CVD process

Ti C

Ti C - Ti N

hard chromium plating

Ti N

PVD process Cr N

Ti C N

hardening temperature hardening temperature through highthrough acetylene frequency induced oxygen flame eddy currents

inclusion of nitrogen through electrical discharge in a vacuum

combination of hardening and coating process: hardening of the base material to approx. 60-62 HRC, coating > 1 000 °C, austenitizing, tempering

application of chrome coat in vacuum, diffusion or electrical precipitation at around 100 °C

heating to coating temperature below 500 °C, vacuum coating, vacuum cooling, distortion-free process

Usable w orkpiece material

unalloyed and alloyed steels 0.2 - 0.6 % C e.g. Ck 45, 50 Cr M o 4

unalloyed and alloyed steels 0.2 - 0.6 % C e.g. Ck 45, 50 Cr M o 4

all ferrous materials

ledeburitic chromium steels, carbides

cast iron, steel, non-ferrous metals

e.g. 1. 2379, 1.2842, 1.2601, 1.0062, 0.6025, 1.7131

preferably 1.2379

cold and hot w ork steels, HSS, carbides, rust-proof steels e.g. 1. 2379, 1. 2601, 1. 2369, 1. 2378

Workpiece requirement

metalically bright surface

metalically bright surface

finish machined, metalically bright surface

metalically bright and polished surface, roughness Rz < 3 µm, nonfunctional surfaces (fitting surfaces) w ith allow ance, specification of tolerance field in the draw ing

metalically bright surface, no material, processing or surface faults, as a rule prior to surface hardening

electrically conductive, non-magnetic condition, no shrinkage in case of soldered parts, metalically bright surface, roughness Rz = 2 - 4 µm, no burr, no assembled parts

600 - 1 100 HV0,1, rustproof surface, increased w ear resistance, good coefficients of friction, max. layer thickness 100 µm

approx. 2 400 HV, approx. 2 000 HV, approx. 3 000 HV, max. charging max. charging max. charging temperature temperature temperature approx. 500 °C, approx 600 °C, approx. 400 °C, chemical resis- good chemical resis- layer thickness tance, layer thick- tance, layer thickup to 3 µm, ness up to 3 µm, ness up to 50-70 µm, brow n-violet gold colored silver colored

Layer characteristics

53 - 59 HRC, hardening w ear-resistant approx. 1200-1 400 HV2, approx. 4 000 HV, depth 1,5 - 3 mm, surface, w orkpiece improvement of max. charging w ear-resistant surface, core w ith high sliding properties, temperature 300 °C, w orkpiece core w ith toughness, danger of increase of strength, brittle, layer thickhigh toughness, scaling, follow ing increase of ness up to follow ing finish finish surface roughness approx. 9 µm, grey metal colored DRa = 0.1– 0.3 µm

approx. 3 000 HV, max. charging temperature approx. 450 °C, layer thickness up to approx. 9 µm, grey metal colored

active parts of forming and draw ing dies Range of parts

cast blanking cutters, gib rails, partial draw punches and female dies

lifting bolts, gib elements, cast blanking cutters, partial draw punches and female dies

all w ear active die parts and gib elements

primarily for thicker uncoated sheet steels

primarily for aluminium plated and galvanized sheet metals

active parts of blanking and separating dies and machining tools draw punches, female dies, blank holders

primarily unalloyed deep-draw n sheets

non-ferrous metals and Cr Ni steels

primarily for low and high alloyed steels, e.g. VA sheet metals

Sheet metal forming and blanking

M ethod

Principles of die manufacture

Fig. 4.1.18 Polystyrene pattern of a die

Com p ared to th e u se of oth er p attern m aterials su ch as wood , m etal, or p lastic, th e d esign er is n ot restricted by th e lim itation s of th e con ven tion al castin g tech n ology. As th e p attern rem ain s in sid e th e form , th ere is n o n eed to con sid er th e p artin g lin e, u n d ercu ts, con icity an d th e tap ers for p attern rem oval. All ferrou s m aterials are su itable as castin g m aterial for p rod u ction d ies. Th e resid u al m atter left over from th e vap orisation of th e p attern im p airs th e fin ish of th e su rface q u ality of th e d ie on ly to a m in im al d egree. However, in ord er to en su re th at th e op eratin g su rface of th e d ie can h ave th e best su rface q u ality, th is su rface is p laced face d own in th e castin g box. Th e m ain ten an ce of th e p attern d u rin g fabrication p resen ts n o p roblem s – with a sp ecific weigh t of 20 kg/ m 3 , even large p olystyren e p attern s can be tran sp orted with ou t h avin g to u se large cran es. Com p ared to con ven tion al p rep aration m eth od s su ch as weld in g, castin g tech n iq u es h ave th e followin g ad van tages:

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– ability to work with com p licated com p on en ts with sm all m an u factu rin g toleran ces, – better d istribu tion of forces in th e cast p iece via cu rvatu res an d sm ooth blen d in g of su rfaces, – better dam pin g ch aracteristics of cast iron com pared to steel plate con stru ction ; as a resu lt, qu iet an d low vibration proven com pon en ts th at can be h igh ly stressed an d provide low n oise level in produ ction , – less ten d en cy to d istortion with cast iron , wh ich en su res th at a h igh level of p recision is d elivered from th e p rod u ction system , – good wear an d slid in g ch aracteristics, – d ie m aterials th at can be h ard en ed ; th u s, th e cast com p on en t can fu llfill variou s fu n ction al req u irem en ts with ou t an y ad d ition al attach m en ts, – oil-tigh t con tain ers, etc., – n o corn ers an d cracks in th e seam s, wh ich can lead to absorp tion of m oistu re an d corrosion , – good m ach in ability, th rou gh wh ich savin gs in th e ord er of 20 to 50 % on m ach in in g costs can be ach ieved , – as a ru le, n o stress-relievin g p rocess is n ecessary.

4.1.5 Try-out equipment Try-out presses Eq u ip m en t for d ie try-ou t p lays an im p ortan t role in m od ern p resswork op eration s. Dies are tested on a try-ou t p ress before startin g p rod u ction . In th is way, th e d ie set-u p tim e on a p rod u ction lin e p ress is red u ced to a m in im u m . Press ru n n in g tim es for all p arts are con seq u en tly lim ited to set-u p an d p rod u ction tim e on ly an d th is in creases th e p rofitability of th e p rod u ction lin e. In m akin g d ies for sh eet m etal form in g, th e scu lp tu red su rface of th e d ie cavity will be m ach in ed to form th e m ale an d fem ale d ies u sin g th e CAD-gen erated d ata for th e fin ish ed p art. As a gen eral p ractice, both p arts of th e die are n orm ally p rodu ced from cast p attern s (cf. Sect. 4.1.4). Du rin g d ie d evelop m en t on a try-ou t p ress, it is p ossible to ascertain for th e first tim e, wh ere an y reworkin g n eed s to be carried ou t on th e geom etry. Th e op eration al ch aracteristics of th e d ies an d th e con tact p attern are ch ecked ou t. Th e flow of th e m aterial is evalu ated to see

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h ow it com p ares with th e th eoretical calcu lation s. Th e form ed p arts are in sp ected for p resen ce of an y wrin klin g, tears or bu lges. In p articu lar, h igh m aterial th ickn esses d o occu r in th e corn er areas of th e blan k h old er su rface becau se of tan gen tial com p ressive stresses, wh ich lead to u n d esirable h igh er su rface p ressu res an d can ad versely affect resu lts of th e d eep d rawin g p rocess. To rectify th is, it is n ecessary to rem ove m aterial an d rework sp ecific areas of th e blan k h old er. In a try-ou t p ress, th e d ie geom etry is m od ified by first form in g a p art an d th en grin d in g th e p u n ch , th e d ie an d th e blan k h old er at th e m ost critical p oin ts in ord er to obtain th e req u ired p art q u ality. Th is p roced u re, e. g. form in g an d regrin d in g, is rep eated u n til good q u ality p arts are form ed . Th e aim is to p erfect th e d ie on th e try-ou t p ress, so th at costly m od ification s for a series ru n on a p rod u ction p ress are m in im ized . Try-ou t op eration s can on ly be con sid ered com p lete wh en th e req u ired p art q u ality is ach ieved , i. e. wh en th e first good p art is p rod u ced , an d p rod u ction on th e p rod u ction p resses can th en start. If th e d raw cu sh ion of a sin gle-action p ress or for th at m atter, th e blan k h old er of a d ou ble-action p ress, is eq u ip p ed with a m u lti p oin t con troller, th e try-ou t costs can be greatly red u ced (cf. Sect. 3.1.4 an d 3.2.8) – th e p rod u ction p ress on to wh ich th e d ie will later be in stalled an d th e try-ou t p ress sh ou ld certain ly be eq u ip p ed , as far as p ossible, with a sim ilar typ e of con trol system . In stead of workin g on th e sp ecific d ie area, or u sin g d raw bead s (cf. Fig. 4.2.6 an d 4.2.7), th e req u ired d eep d rawin g resu lt can be ach ieved sim p ly by m akin g ad ju stm en ts of in d ivid u al con trol cylin d ers. An ad d ition al d evice, wh ich con trols th e p ressu re d u rin g th e d raw stroke (cf. Fig. 3.1.12) con tribu tes sign ifican tly to red u cin g try-ou t costs an d ach ievin g th e h igh est p art q u ality on th e p rod u ction p ress. Du rin g th e try-ou t p rocess, th e p aram eters of th e form in g op eration , esp ecially th ose wh ich can be ad ju sted on th e actu al p ress bein g u sed , p lay a d ecisive role. Hyd rau lic an d m ech an ical try-ou t p resses test th e d ies u n d er con d ition s wh ich are as close as p ossible to th ose fou n d in n orm al p rod u ction ru n s. In ord er to ach ieve a faster an d m ore reliable p rod u ction start-u p , a h igh d egree of com p atibility of th e m ain p ress ch aracteristics – su ch as th e rigid ity an d tran sverse ben d in g of th e bed an d slid e, etc. – between th e try-ou t p ress an d th e station s of th e p rod u ction p ress is an ad van tage. Th e closer th e ch aracteristics of th e tryou t p ress are to th ose of th e p rod u ction lin e p ress, th e sh orter will be

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th e tim e req u ired to be sp en t d u rin g p rod u ction start-u p an d th e soon er th e p rod u ction of good p arts can be ach ieved . For exam p le, th e m ost su ccessfu l way of d evelop in g d ies for m ech an ical large-p an el tran sfer p resses is to u se m ech an ical try-ou t p resses, wh ich h ave n early id en tical ch aracteristics. In p articu lar, th is m ean s th at for th e first d rawin g stage, th e try-ou t p ress, ap art from h avin g th e sam e con stru ction , also h as a sim ilar d raw cu sh ion to th at of th e sin gle-action p ress (Fig. 4.1.19, left). On e or m ore sin gle-action m ech an ical p resses with ou t a d raw cu sh ion , h owever, are u sed to d evelop th e d ies for th e su bseq u en t station s of a tran sfer p ress (Fig. 4.1.19, right). A m u ch less exp en sive solu tion is p rovid ed by h yd rau lic p resses (Fig. 4.1.20). Ad m itted ly, th eir kin em atic ch aracteristics an d , in p articu lar, th e form in g sp eed can on ly m atch th ose of a m ech an ical p ress to a lim ited d egree (cf. Fig. 3.2.3 to Fig. 3.3.1); bu t th eir en ergy cap acity d oes n ot d ep en d u p on th e strokin g rate. Th eir flexibility m akes an y d esired slid e m ovem en t p ossible irresp ective of wh eth er th e d owl ed ges sh ou ld be carefu lly tested or an y p re-p rod u ction series of stam p in gs are p ro-

Fig. 4.1.19 M echanical try-out presses for die try-out: w ith draw cushion for the first forming process (left) and w ithout draw cushion for the subsequent processes (right)

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spotting cylinder slide slide cylinder blank holder cylinder marking stop deep drawing ad ustment stepless slide locking

slide cushion with adapter hydraulic draw cushion position sensor for the draw cushion

Fig. 4.1.20 Design of a hydraulic try-out press

d u ced . In ad d ition , a sp ottin g fixtu re for th e slid e an d blan k h old er can be ap p lied to th e con tou rs of th e d ie with a p recisely con trolled sp eed . Th e d ie m ou n tin g area, th e stroke an d th e force on all try-ou t p resses are so d esign ed th at th e p ress can accom od ate th e total ran ge of large size tools. Force an d sp eed can be selected in th e ratio of at least 1 : 10, so th at th e d ies can be tried ou t by startin g with a very low ram sp eed . As a ru le, both th e p u n ch an d th e d ie m u st be reworked at th e sam e tim e d u rin g d ie try-ou t. In ord er to facilitate th e rework an d save tim e, h yd rau lic try-ou t p resses can be eq u ip p ed with a p ivotin g slid e p late (Fig. 4.1.21). At first, th e m ovin g bolster carryin g th e lower d ie m oves ou t of th e p ress. W h en p ivoted , th e top d ie is rotated th rou gh 180° an d lowered an d cen tered on to a m ovable p allet tru ck. After th is, th e slid e, th e clam p in g p late an d top d ie are lowered to a p re-d efin ed h eigh t an d locked in to th e roll-over d evice. Th e q u ick-action clam p s release th e slid e p late from th e slid e, an d th e slid e m oves to th e top d ead cen ter p osition . After th e slid e p late an d top d ie h ave been tu rn ed over, th e slid e p laces th e slid e p late with th e top d ie in th e cen terin g of th e p allet tru ck an d m oves again to th e

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Fig. 4.1.21 Rotating the slide of a hydraulic try-out press

u p p er stop p osition . After bein g taken ou t of th e back of th e p ress on th e p allet tru ck, th e top d ie is accessible from all sid es. Th is allows con ven ien t an d tim e-savin g reworkin g to be carried ou t. After reverse rotation , th e d ie d oes n ot n eed to be rep osition ed as it is alread y p osition ed by th e clam p in g p late on th e p allet tru ck. Th e electrical system of a try-ou t p ress in clu d es a sen sor system for m easu rin g th e settin g p aram eters for each d ie. Sen sors for m easu rin g variou s p rocess p aram eters an d a d ata acq u isition system allow to p erform statistical evalu ation . Th e op tim al settin g p aram eters are saved an d m ad e available as in p u t in to th e con trol system of th e p rod u ction p ress. In ord er to ach ieve p rod u ction -like con d ition s in h yd rau lic tryou t p resses, an y elastic d eform ation s or off-cen ter m ovem en ts of th e slid e, wh ich are d etected at th e d ie an d th e p rod u ction lin e m u st be con sid ered by th e con trol system . Du rin g ru n -in , th e d ies n eed to be freq u en tly m oved in an d ou t of th e p ress. A m ovin g bolster allows th is work to be carried ou t faster an d m ore safely (cf. Fig. 3.4.3). In a try-ou t cen ter for exam p le, several try-

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Fig. 4.1.22 Try-out center: try-out presses linked by T-tracks

ou t p resses m ay be lin ked togeth er with T-tracks (Fig. 4.1.22 an d cf. Fig. 3.4.4). Th is arran gem en t allows com p reh en sive testin g of th e p rogressive form in g op eration s so th at d ie sets are m ore q u ickly an d efficien tly ru n -in . Try-ou t p resses an d above all try-ou t cen ters are also su itable for p rod u cin g sh ort ru n p arts or carryin g on p rod u ction on a sm aller scale in th e even t of th e breakd own of a large p rod u ction p ress. Dep en d in g on th e task th ey h ave to p erform , su ch u n iversal p resses m ay be u sed , for exam p le, for p rod u ction as well as for try-ou t p u rp oses. Parallel lift m echanism s For an y rep airs an d reworkin g op eration s, th e top d ie h as to be lifted off th e bottom d ie. For ergon om ic (overh ead workin g) an d sch ed u lin g reason s (workin g at th e sam e tim e on th e top an d bottom d ies) both d ies are laid d own sep arately. Dies wh ich can n ot be h an d led m an u ally can be m oved with th e h elp of a h yd rau lic p arallel lift m ech an ism . Th is ap p aratu s en su res q u ick clam p in g for rep airs an d m ain ten an ce of d ies.

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Fig. 4.1.23 Parallel lift mechanism

Th e m ech an ism , seen in Fig. 4.1.23, lifts th e top d ie p arallel to th e lower d ie, an d after a 180° tu rn p laces it n ext to th e lower d ie. Th e m ech an ism en su res th at both p arts of th e d ie are lifted safely an d with con sisten t accu racy with ou t an y tiltin g.

4.1.6 Transfer simulators Tran sfer sim u lators are u sed for th e ad ju stm en t an d p re-settin g of p artd ep en d en t toolin g of th e grip p er rails an d th e vacu u m su ction crossbars of large-p an el tran sfer p resses (cf. Fig. 4.4.29 an d 4.4.34). Th e lower d ie an d th e p art-d ep en d en t toolin g are in stalled in th e sim u lator; p rior to p rod u ction th ese will be cou p led with th e p erm an en tly in stalled tran sfer com p on en ts of th e p ress (Fig. 4.1.24). Th e m ovem en ts of th e tran sfer, p art an d d ie m u st be syn ch ron ized in relation to on e an oth er so th at th ere can be n o overlap p in g at critical p oin ts an d con seq u en tly n o collision between th e tran sfer, th e p art itself an d th e d ie. Th u s, d ata on grip p er an d su ction cu p p osition s, tran sp ort p ath s, tran sp ort h eigh t, p art p osition in g an d flow d irection s is stored in a p rogram m e. Th is p rogram m e is tran sferred on to th e p rod u ction lin e. Th e p ossibility of collision s of p art an d d ie, wh ich was alread y verified as p art of th e CAD d esign p rocess, is ch ecked ou t in th e sim u lator. Th e p rim ary task for th e sim u lator is, h owever, th e m atch in g of th e p art-d ep en d en t fixtu rin g to th e sh eet m etal p art. A test is p er-

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Principles of die manufacture

Fig. 4.1.24 Transfer simulator for a large-panel transfer press w ith crossbar transfer system

form ed to ascertain wh eth er th e p art is p osition ed p recisely in its u n iversal station an d in th e d ie. In ad d ition , th e en ergy su p p ly an d con trol system of th e tran sfer rails are ch ecked for correct fu n ction in g. Mod ern system s can also sim u late th e ch an gin g of p art-sp ecific tem p lates u sed in th e u n iversal station .

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4 Sheet metal forming and blanking

4.2 Deep draw ing and stretch draw ing 4.2.1 Forming process In d eep d rawin g op eration s form in g is carried ou t with tools (rigid an d flexible), active m ed ia (e. g. san d , steel p ellets, liq u id ) or active en ergy (i.e. a m agn etic field ). Th e followin g section covers p ossible ap p lication s for stretch an d d eep d rawin g p rocesses with rigid tools as a first an d su bseq u en t op eration (cf. Fig. 2.1.10 to 2.1.12). Section s 4.2.4 an d 4.2.5 will cover d eep d rawin g with active m ed ia (cf. Fig. 2.1.13). Un like in d eep d rawin g, in stretch form ing th e sh eet m etal can n ot flow becau se it is grip p ed by clam p s or h eld in a blan k h old er. Th e form in g p rocess takes p lace with a red u ction in th e th ickn ess of th e sh eet m etal. Pu re stretch d rawin g is a form in g p rocess con d u cted u n d er ten sile stresses (cf. Fig. 2.1.18). Mostly large-scale work p ieces su ch as, for exam p le, bod y p an el com p on en ts u sed in aircraft or au tom otive m an u factu rin g, are p rod u ced on sp ecial p rod u ction lin es. Th is is certain ly tru e in p rod u cin g low volu m e or large size p arts, as, for exam p le, with th e win g elem en ts of an aircraft. Th e ad van tage of th is p rocess is th at th e toolin g an d m ach in in g costs are relatively m od est in p rop ortion to th e size of th e p art bein g p rod u ced . Deep d rawin g is a com p ression -ten sion form in g p rocess accord in g to DIN 8582. Th e p roced u re with th e greatest ran ge of ap p lication s is deep drawing with rigid tooling, in volvin g d raw p u n ch es, a blan k h old er an d a fem ale d ie (cf. Fig. 2.1.10). Th e blan k is gen erally p u lled over th e d raw p u n ch in to th e d ie, th e blan k h old er p reven ts an y wrin klin g takin g p lace in th e flan ge. In p u re d eep d rawin g, th e th ickn ess of th e sh eet

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m etal rem ain s u n ch an ged sin ce an in crease in th e su rface area d oes n ot occu r, as it occu rs in a stretch d rawin g p rocess. Th e m aterial flow in th e drawin g p rocess can be con trolled, as req u ired, by adju stin g th e p ressu re of th e blan k h older in between p u re stretch drawin g, in wh ich n o sh eet m etal can flow ou t of th e flan ge area in to th e draw die, an d deep drawin g, in wh ich th ere is a wrin kle-free an d u n restricted m aterial flow (cf. Fig. 2.1.32). In deep drawin g, as a first step , a cu p is p rodu ced from th e flat blan k. Th is cu p can th en be fu rth er p rocessed, for exam p le by an addition al drawin g, reverse drawin g, iron in g or extru sion p rocess. In all deep drawin g p rocesses, th e p ressin g force is ap p lied over th e draw p u n ch on to th e bottom su rface of th e drawn p art. It is fu rth er tran sferred from th ere to th e p erim eter in th e deform ation zon e, between th e die an d th e blan k h older. Th e workp iece is su bjected to rad ial ten sion forces FR an d tan gen tial com p ression forces FT (Fig. 4.2.1). Th e m aterial is com p ressed in th e tan gen tial d irection an d stretch ed in th e rad ial d irection . As th e d raw

FT FR

FT

FR

FR

FT

FT

FR

Fig. 4.2.1 Pressing forces in deep draw ing of a round cup w ith a blank holder

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d ep th is in creased , th e am ou n t of d eform ation an d th e d eform ation resistan ce are also in creased . Th e sh eet m etal is m ost severely stretch ed in th e corn er of th e d raw p u n ch . Failu re n orm ally occu rs at th is p oin t (base fractu rin g). W h en d rawin g with a blan k h old er, th e p ress m u st also tran sfer th e blan kh old in g force on to th e d ie. Th is is ach ieved eith er from above via a blan k h old er slid e or from u n d ern eath via a d raw cu sh ion . Th ere are basically th ree p ossible ways of ap p lyin g blan k h old er force.

mounting area, slide

mounting area, die

blank holder stroke

slide stroke

part height e ector stroke

slide draw cushion

3

blank holder slide blank holder

blank die press bed

e ector

Fig. 4.2.2 A double-action top dow n draw ing die

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Deep draw ing and stretch draw ing

In double-action drawing operations th e press h as two slides actin g from above: th e drawin g slide with th e draw pun ch an d th e blan k h older slide with th e blan k h older (Fig. 4.2.2 an d cf. Fig. 3.1.8). Th e blan kh oldin g slide tran sfers th e blan kh oldin g force via th e blan k h older on to th e blan k an d th e draw die. Th e die an d th e ejector are located in th e lower die on th e press bed. Durin g form in g, th e blan k h older brin gs th e sh eet m etal in to con tact again st th e die, th e pun ch descen ds from above in to th e die an d sh apes th e part wh ile th e sh eet m etal can flow with out an y wrin klin g out of th e blan kh oldin g area. In th is case, th e drawin g process is carried out with a fixed blan k h older an d m ovin g pun ch . In double-action drawin g operation s, th e drawin g slide can on ly apply a pressin g force. A d isad van tage in d ou ble-action d rawin g is th e fact th at th e p arts for fu rth er p rocessin g in su ccessive form in g an d blan kin g d ies n eed to be rotated by 180° in an exp en sive an d bu lky rotatin g m ech an ism (cf. Sect. 3.1.3). With ou ter bod y p arts th e d an ger exists, fu rth erm ore, th at th e su rface of th e p art m ay be d am aged in th e rotatin g op eration . Single-action drawing with a draw cushion works th e oth er way rou n d: th e form in g force is exerted by th e slide above th rou gh th e die an d th e blan k h older on to th e draw cu sh ion in th e p ress bed (Fig. 4.2.3 an d cf. Fig 3.1.9). Th e draw p u n ch an d th e blan k h older of th e drawin g tool are both located in a base p late on th e p ress bed. Pressu re p in s, wh ich com e u p th rou gh th e p ress bed an d th e base p late tran sfer th e blan k h older force from th e draw cu sh ion on to th e blan k h older. Th e fem ale die an d th e ejector are m ou n ted on th e p ress slide. At th e start of th e form in g p rocess th e blan k is h eld u n der p ressu re between th e draw die an d th e blan k h older. Th e slide of th e p ress p u sh es th e blan k h older down wards over th e draw die – again st th e u p ward-actin g force of th e draw cu sh ion . Th e p art is form ed via th e down ward m ovem en t of th e die over th e station ary draw p u n ch . Th e p ress slide m u st ap p ly both th e p ressin g an d th e blan k h older forces. Th u s, u sin g a sin gle-action tool, th e p art d oes n ot h ave to be rotated after th e d rawin g p rocess. Fu rth erm ore, tod ay th e u se of h yd rau lically con trolled d raw cu sh ion s, even with d eep d rawin g p rocesses u p to d ep th s of 250 m m , p rod u ces a workp iece q u ality com p arable to th at of d ou ble-action p resses (cf. Sect. 3.1.4). An en ergy-savin g an d cost-effective altern ative in stam p in g is counter drawing or reverse drawing (Fig. 4.2.4 an d cf. Fig. 3.1.10). In th is op eration , on ce again , a sin gle-action p ress with a d raw cu sh ion is u sed – n or-

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m ally a h ydrau lic on e. Th e top die is attach ed to th e slide. Th e lower die is m ou n ted on th e p ress bed with th e blan k h older. Th e p u n ch is located in an op en in g in th e cen ter of th e p ress bed on th e draw cu sh ion . Du rin g d eform ation , th e blan kh old in g force is tran sferred via th e slid e from above an d th e d raw p u n ch force acts from below th rou gh th e

mounting area, die

slide stroke

part height

3 slide slide e ector

die

draw punch

blank holder press bed

pressure pins

draw cushion

Fig. 4.2.3 Single-action die w ith draw cushion

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active d raw cu sh ion . Th e p u n ch form s th e p art by m ean s of its u p ward m ovem en t wh ile th e blan k h old er rests on th e d ie. Th e active cou n ter drawin g com bin es th e advan tages of static blan kh oldin g an d th e low p ower u sage of dou ble-action dies with th e advan tage of a sin gle-action die, in wh ich it is n ot n ecessary to rotate th e p art. Adm ittedly, it is n ecessary to h ave a sp ecial m odification of th e dies for p erform in g th is op eration , sin ce th e forces op erate in th e op p osite direction to th ose of a n orm al sin gle-action deep drawin g p ress with draw cu sh ion . Th u s, th ese dies can n ot be in stalled in a n orm al sin gle-action p ress.

mounting area, die

slide stroke

part height

draw cushion stroke

slide blank

3

e ector die

draw cushion press bed

blank holder

active draw cushion

Fig. 4.2.4 Counter draw ing die/reverse draw ing die

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Calculation of the blank size Before startin g drawin g operation s th e size an d form of th e blan k m ust be determ in ed for th e desired fin al part geom etry an d die layout. Th is sh ould be sh own usin g th e exam ple of a sim ple rotation ally sym m etrical body. In order to calculate th e blan k diam eter, it is n ecessary to devide th e en tire axisym m etric part in to various in dividual axisym m etric com pon en ts, in accordan ce with Table 4.2.1 an d th en calculate th e surface areas of th ese com pon en ts. Th e total surface area as a sum of th e in dividual areas en ables th e calculation of th e diam eter of blan k D. Th is is sh own in Table 4.2.1 for com m on ly used drawn sh apes, startin g from th e desired in n er diam eter d. As th e m aterial will be som ewh at stretch ed in th e drawin g process, th ere is m ore surplus m aterial on th e upper edge of th e draw part, wh ich can n ot be precisely calculated. With h igh parts th is can lead to distorted edges, because of th e n on -un iform deform ation properties of th e blan k m aterial (an isotropy). Th erefore, in gen eral th e drawn parts m ust be trim m ed accordin gly on th e edge, wh en produced via deep drawin g. Th e selection of th e blan k size for n on -sym m etric an d irregular parts is often carried out on a trial an d error basis, as it is n ot possible to use sim ple form ulas. Based on practical experien ce, th e blan k geom etry is determ in ed with experim en ts. In itially a sufficien tly large blan k size is selected for th e drawin g operation . After observin g th e actual m aterial dem an d an d flow, th e blan k size is reduced to satisfy th e m aterial requirem en ts. More recen tly, com puter program s are bein g in creasin gly used for th e determ in ation of th e blan k size (cf. Sect. 4.1.2).

Table 4.2.1: Formulas for the circular blank diameter D Container shape (cross-section) rotationally symmetrical shapes 1

Blank diameter D =

h

d

2

d

d

1

d2 + 4 ⋅ d ⋅ h *

2

d 2 2 + 4 ⋅ d1 ⋅ h *

* Containers w ith small (bottom) radii r < 10 mm

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Container shape (cross-section) rotationally symmetrical shapes 3

h2

d2

d 2 2 + 4 ⋅ (d1 ⋅ h1 + d 2 ⋅ h 2 ) *

d3

4 d2

d 3 2 + 4 ⋅ (d1 ⋅ h1 + d 2 ⋅ h 2 ) *

h1

d1

h2

h1

d1

5

d2

d 12 + 4 ⋅ d 1 ⋅ h + 2 ⋅ f ⋅ ( d 1 + d 2 ) *

d1 f d3

h2

6

d2

d 2 2 + 4 ⋅ (d1 ⋅ h1 + d 2 ⋅ h 2 ) + 2 ⋅ f ⋅ (d 2 + d 3 ) *

h1

d1

7

Blank diameter D =

d

2 ⋅ d 2 = 1.414 ⋅ d

8

d2 d1

d 12 + d 2 2

9

d2 d1

1.414 ⋅

d12 + f ⋅ (d1 + d 2 )

1.414 ⋅

d2 + 2 ⋅ d ⋅ h

f

10 d

h

* Containers w ith small (bottom) radii r < 10 mm

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Container shape (cross-section) rotationally symmetrical shapes 11

Blank diameter D =

d2 d1

h

d 12 + d 2 2 + 4 ⋅ d 1 ⋅ h

d2

12 d1

1.414 ⋅ d12 + 2 ⋅ d1 ⋅ h + f ⋅ (d1 + d 2 )

h

f

13

d

2

14

h

d2 + 4 ⋅ h2

h

d22 + 4 ⋅ h2

d2 d1

d2

15 d1

h2 h1

(

d 2 2 + 4 ⋅ h 12 + d 1 ⋅ h 2

16 d

h2 h1

(

d 2 + 4 ⋅ h 12 + d ⋅ h 2

)

)

d2

17 d1

d 12 + 4 ⋅ h 2 + 2 ⋅ f ⋅ ( d 1 + d 2 )

h

f

18

d2 d1 f

h2 h1

[

d2

19 d1

s

]

d12 + 4 ⋅ h12 + d1 ⋅ h 2 + 0.5 ⋅ f ⋅ (d1 + d 2 )

d 12 + 2 ⋅ s ⋅ ( d 1 + d 2 ) *

* Containers w ith small (bottom) radii r < 10 mm

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Container shape (cross-section) rotationally symmetrical shapes 20

Blank diameter D =

d3 d2

d 12 + 2 ⋅ s ⋅ ( d 1 + d 2 ) + d 3 2 – d 2 2 *

d1 s

21

d2

h

[

d 12 + 2 ⋅ s ⋅ ( d 1 + d 2 ) + 2 ⋅ d 2 ⋅ h

d1 s

22

d2

d12 + 6.28 ⋅ r ⋅ d1 + 8 ⋅ r 2

d1

]

*

or

r

d 2 2 + 2.28 ⋅ r ⋅ d 2 – 0.56 ⋅ r 2

23

d3

d12 + 6.28 ⋅ r ⋅ d1 + 8 ⋅ r 2 + d 32 – d 2 2 or

d2

r

d1

24

d 32 + 2.28 ⋅ r ⋅ d 2 – 0.56 ⋅ r 2

d3 d2 d1

25

d12 + 6.28 ⋅ r ⋅ d1 + 8 ⋅ r 2 + 4 ⋅ d 2 ⋅ h + d 32 – d 2 2 or

h

r

d 32 + 4 ⋅ d 2 ⋅ (0.57 ⋅ r + h ) – 0.56 ⋅ r 2

d3

d12 + 6.28 ⋅ r ⋅ d1 + 8 ⋅ r 2 + 2 ⋅ f ⋅ (d 2 + d 3 ) or

d2 r

d1

f

26

d 2 2 + 2.28 ⋅ r ⋅ d 2 + 2 ⋅ f ⋅ (d 2 + d 3 ) – 0.56 ⋅ r 2

d3

d2 f

r

d1

h

d12 + 6.28 ⋅ r ⋅ d1 + 8 ⋅ r 2 + 4 ⋅ d 2 ⋅ h + 2 ⋅ f ⋅ (d 2 + d 3 ) or d 2 2 + 4 ⋅ d 2 ⋅ (0.57 ⋅ r + h + 0.5 ⋅ f ) + 2 ⋅ d 3 ⋅ f – 0.56 ⋅ r 2

27 d2 d1

h

r

(

d12 + 4 1.57 ⋅ r ⋅ d1 + 2 ⋅ r 2 + d 2 ⋅ h

)

d 2 2 + 4 ⋅ d 2 ⋅ (0.57 ⋅ r + h ) – 0.56 ⋅ r 2

* Containers w ith small (bottom) radii r < 10 mm

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Exa m ple: A cu p with a con ical ou tlin e an d flan ge is to be p rod u ced . Th e base d iam eter is 60 m m , th e u p p er d iam eter 100 m m , th e ou tsid e flan ge d iam eter 120 m m an d th e can bod y m easu rem en t 75 m m . Th e req u ired d iam eter of th e blan k p iece is calcu lated accord in g to form u la 20 from Table 4.2.1:

d 1 = 60 mm, d 2 = 100 mm, d 3 = 120 mm, s = 75 mm D = d 1 2 + 2 ⋅ s ⋅ (d 1 + d 2 ) + d 3 2 – d 2 2 = 60 2 + 2 ⋅ 75 ⋅ (60 + 100) + 120 2 – 100 2 D = 32, 000 = 178.9 mm Th erefore, for d eep d rawin g th is cu p , a circu lar blan k of 179 m m d iam eter is req u ired .

Draw ratio Th e d raw ratio b is an im p ortan t n u m erical valu e for cylin d rical d raw p arts in d eterm in in g th e req u ired n u m ber of d rawin g step s. Th e d raw ratio is th e ratio of th e d iam eter of th e in itial blan k form to th e d iam eter of th e d rawn p art. For th e first d rawin g p rocess, th at is to say for on ly on e d rawin g op eration , th e d raw ratio b [–] resu lts in th e followin g eq u ation :

β=

Blank − ∅ D , Punch − ∅ d

β=

D d

with on e d rawin g,

β1 =

D d1

for th e first d rawin g,

β2 =

d1 d2

or

β3 =

d2 , d3

an d so on . In su bseq u en t d rawin g step s, d 1 rep resen ts th e d iam eter of th e d raw p u n ch in th e first d rawin g op eration an d d 2 th e d iam eter of th e secon d , etc. Th e total d raw ratio btot is calcu lated as th e ratio of th e d iam eter of th e blan k to th e fin al d iam eter of th e d rawn p art:

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β tot =

Initial − ∅ D Final − ∅ d

Th e m axim u m d raw ratio d ep en d s on th e p rop erties of th e blan k m aterial u sed . As a rou gh estim ate, th e first d rawin g can be calcu lated as h avin g a m axim u m ratio of b = 2. To ach ieve b > 2 several d rawin gs are req u ired an d it m u st be n oted th at b, becau se of work h ard en in g, can on ly ach ieve a level of 1.3 in th e n ext d rawin g step . If th e p art is an n ealed before th e n ext d rawin g op eration , a b of 1.7 can be assu m ed . With several d rawin g step s, th e total d raw ratio becom es a p rod u ct of th e in d ivid u al d raw ratios:

β tot = β1 ⋅ β 2 ⋅ … ⋅ β n

Exa m ple: From a 1 m m th ick blan k of sh eet m etal m aterial n u m ber 1.0338 (St 14) a h ollow cylin d rical p art with a d iam eter of 45 m m an d a can bod y h eigh t of 90 m m is to be d rawn . First, th e in itial d iam eter of th e circu lar blan k D is calcu lated as p er Form u la 1 from Table 4.2.1:

D = d 2 + 4 ⋅ d ⋅ h = 45 2 + 4 ⋅ 45 ⋅ 90 = 18, 225 = 135 mm Th u s, th e total d raw ratio btot is establish ed :

β tot =

D 135 = =3 d 45

Becau se btot is greater th an th e rem ain in g lim itin g d raw ratio of 2, several d rawin g op eration s are n eed ed wh ereby b1 m ay h ave a m axim u m valu e of 2, an d all followin g b valu es are less th an 1.3.

β tot = β1 ⋅ β 2 ⋅ … ⋅ β n = 3 3 = β1 ⋅ β 2 ⋅ … ⋅ β n < 2 ⋅ 1.3 ⋅ 1.3 Th e req u ired d raw ratio can be attain ed with th ree op eration s. In ord er to h ave a robu st an d rep rod u cable p rod u ction seq u en ce, th e m axim u m p erm itted d raw ratios sh ou ld n ot be fu lly u tilised . In th e even t th at btot = 1.95 · 1.25 · 1.25 = 3 is selected . Th is calls for p u n ch d iam eters of:

➔

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d1 =

D 135 mm = = 69.2 mm ⇒ d 1 = 69 mm 1.95 β1

d2 =

d 1 69 mm = = 55.2 mm ⇒ d 2 = 55 mm 1.25 β2

d 3 = 45 mm ( before mentioned ) with β 3 =

55 mm = 1.22 45 mm

Th e m axim u m d raw ratio bm ax , d oes d ep en d h owever on oth er factors as well (cf. Sect. 4.2.3):

β max = f (D, d, µ, r − value, s …) W h en th e friction between th e d rawn p art an d th e p u n ch is low, th en failu res will occu r in th e base of th e p art. If th e friction between th e p art an d th e p u n ch is h igh , th e base of th e d rawn p art will be in creasin gly stressed with in creasin g friction in th e can bod y so th at th e failu re zon e will be m oved to th e bod y of th e d rawn can . In ord er to en su re a safe p rod u ction p rocess, it is p referable to select a d raw ratio th at is rath er m od est an d less th an th e m axim u m p ossible valu e. Drawing force For d rawin g rou n d p arts in a sin gle d rawin g, th e m axim u m d rawin g force FU can be calcu lated p er th e followin g eq u ation :

FU = π ⋅ (d1 + s) ⋅ s ⋅ R m ⋅ 1.2 ⋅

β –1 [N] β max – 1

wh ere: d1 s Rm b bm ax

= = = = =

p u n ch d iam eter [m m ] sh eet m etal th ickn ess [m m ] m aterial ten sile stren gth [N/ m m 2 ] actu al d raw ratio [–] m axim u m d raw ratio [–]

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Exa m ple: Material: 1.0338 (St 14) with ten sile stren gth Rm = 350 N/ m m 2 Sh eet m etal th ickn ess: s = 0.8 m m Pu n ch - [: d = 240 m m Draw ratio: b = 1.75 (D = 420 m m ) m ax. p erm itted d raw ratio: b1m ax = 2.0 Drawin g force calcu lated as:

FU = π ⋅ (240 + 0.8) mm ⋅ 0.8 mm ⋅ 350 N/ mm 2 ⋅ 1.2 ⋅

1 .75 – 1 = 190 ,637 N = 191 kN 2 –1

Th e calcu lated drawin g force is eq u al to th e drawin g slide force on dou ble-action drawin g p resses. With sin gle-action p resses, th e drawin g slide force in creases by th e am ou n t of force ap p lied to th e blan k h older, sin ce th e blan k h older force cou n teracts th e m ovem en t of th e drawin g slide du rin g th e com p lete drawin g cycle (Fig. 4.2.3). If several op eration s are n eeded to p rodu ce a p ressed p art, it is essen tial to calcu late th e drawin g force with th e largest diam eter p u n ch . Th e forces req u ired for th e drawin g of ellip tical, sq u are, rectan gu lar an d sim ilarly sh ap ed draw p arts, wh ere th e corn er radii are n ot too sm all, can be calcu lated in a sim ilar way to th ose for deep drawn cylin drical sh ap es:

d = 1.13 ⋅ A St [ mm] and D = 1.13 ⋅ A Z [ mm] , wh ere ASt [m m 2 ] is th e cross section of th e p u n ch an d AZ [m m 2 ] is th e area of th e blan k. Pressing force for sheet m etal with beads Bead s are stretch ed ou t of th e th ickn ess of th e sh eet m etal blan k (cf. Fig. 2.1.19), th at is to say an in crease in th e su rface area takes p lace with ou t ch an gin g th e extern al d im en sion s of th e p art. Th erefore, it is n ecessary to assu re th at p rior to th e d rawin g p rocess th ere are su fficien t “strain reserves” as th e sh eet m etal wou ld oth erwise be fractu red . Th e p ressin g force for form in g stiffen in g bead s or ribs is calcu lated as follows:

FU = l ⋅ s ⋅ p [ N ], wh ere l [m m ] is th e rib len gth , s [m m ] th e sh eet th ickn ess an d p is th e p ressu re. Th e p ressu re p in th e area of th e stiffen er in N/ m m 2 can be cal-

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cu lated grap h ically from th e d rawin g of a force p arallelogram or m ath em atically for on e sid e of th e p rofile startin g from th e ten sile stren gth Rm [N/ m m 2 ] (Fig. 4.2.5):

[

p = R m ⋅ cos α N / mm 2

]

Th u s, for a p rofile wall with a = 0°, p = Rm or p = 2 · Rm · cos a are for th e sym m etrical p rofile. Th e p ressin g force is th erefore solely dep en den t on th e tap er of th e sides an d th e stren gth of th e m aterial. Th e total force for p ressin g th e bead is th e su m of all th e sin gle forces:

FU = s ⋅ (l1 ⋅ p1 + l 2 ⋅ p 2 + … + l n ⋅ p n ) [N ]

Exa m ple: A 1 m m th ick sh eet m etal of m aterial n u m ber 1.0333 (USt 13) is to be rein forced with five sym m etrical su p p ort ribs of l = 200 m m in len gth (Fig. 4.2.5). Th e h eigh t of th e ribs h m easu res 3 m m , th e u p p er rib wid th b = 6 m m , th e an gle a = 20° an d th e ten sile stren gth Rm = 370 N/ m m 2 . Th e req u ired p ressin g force is calcu lated as:

FU = l ⋅ s ⋅ p tot = 200 mm ⋅ 1 mm ⋅ 5 ⋅ (2 ⋅ 370 N / mm 2 ⋅ cos 20˚ ) ⇒ FU = 695.4 kN Wid th b an d h eigh t h of th e su p p ort p ieces are n ot taken in to th e calcu lation , on ly th e len gth l of th e p rofile an d th e an gle a of th e ribs. As a com p arison : With an an gle of 0° th e p ressin g force in creases to th e m axim u m valu e of 740 kN, as th e an gle in creases th e req u ired force becom es sm aller, for exam p le 523.3 kN at 45°.

l b

s h

l

α

Fig. 4.2.5 Profile w ith beads: s (sheet metal thickness), l (length of ribs), a (angle of ribs)

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Deep draw ing and stretch draw ing

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Blank holder force Th e m agn itu de of blan k h older force is n ot on ly an im portan t factor in avoidin g wrin klin g of th e m aterial bu t also vital becau se of its in flu en ce on th e strain in g of th e u pper su rface. As th e blan k h older force is in creased, th e restrain in g effect on th e m aterial located between th e die an d th e blan k h older becom es stron ger so th at th e strain on th e u pper su rface layer is also in creased. Th e blan k h old er force req u ired for d eep d rawin g FB [N] is calcu lated from D [m m ], d ' [m m ] (d ie d iam eter), r [m m ] (d ie corn er rad iu s) an d p [N/ m m 2 ] (sp ecific blan k h old er p ressu re):

FB =

[

]

π 2 ⋅ D 2 – (d' +2 ⋅ r ) ⋅ p [N ] 4

Often th e d ie corn er rad iu s an d th e d ie/ p u n ch clearan ce can be n eglected , in com p arison with th e p u n ch d iam eter d [m m ], th e ap p roxim ate calcu lated valu e of th e blan k h old er force is:

FB ≈

π ⋅ D 2 – d 2 ⋅ p [N] 4

(

)

Th e req u ired level of th e sp ecific blan k h old er p ressu re d ep en d s on th e m aterial an d p u n ch d iam eters as well as on th e th ickn ess of th e sh eet m etal. It can be estim ated by u sin g th e followin g valu es: – steel: p = 2.5 N/ m m 2 – copper alloy: p = 2.0 … 2.4 N/ m m 2 – alum inium alloy: p = 1.2 … 1.5 N/ m m 2

Exa m ple: A sh eet m etal blan k from m aterial n u m ber 1.0338 (St 14) with Rm = 350 N/ m m 2 ten sile stren gth is to be form ed with a p u n ch h avin g a d iam eter of d = 240 m m an d a d raw ratio of b = 1.75 (circu lar blan k d iam eter D = 420 m m ). Th u s th e blan kh old er force is estim ated to be:

FB =

[

]

π π 2 2 ⋅ (D 2 – d 2 ) ⋅ p = ⋅ ( 420 mm ) – (240 mm ) ⋅ 2.5 N / mm 2 = 63, 303 N = 63 kN 4 4

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Draw beads With very sh allow, arch ed parts, for wh ich th e drawin g force will be relatively low, a very h igh blan k h older pressure is required so th at friction between th e blan k h older an d th e die acts to restrain th e flow of th e sh eet m etal. Th us, th e ten sion stresses are in creased an d th e m aterial is form ed aroun d th e pun ch with out form in g an y wrin kles wh ile it is stretch ed to ach ieve th e required stren gth level. In such cases, in order to lower blan k h older forces, draw beads are provided in th e toolin g. Beads are in corporated in to th e die as per Fig. 4.2.6 or in to th e blan k h older as per Fig. 4.2.7, wh ile a correspon din g recess is allowed for in th e m atch in g side of th e die. Th e sh eet m etal is pressed aroun d th e bead by th e action of th e blan kh older an d th us m ust flow over th e bead as part of th e drawin g process. Th e force required for th is deform ation is added to th e drawin g force. Draw beads assure th at th e m aterial flows in a m ore un iform way, especially in deep-drawin g n on -circular work parts. Th ey h ave th e task of distributin g th e lon gitudin al stress in th e drawn part over th e wh ole perim eter. For th is reason , th ey are position ed in location s wh ich are ligh tly stressed durin g th e drawin g process such as, for exam ple, on th e lon ger sides of rectan gular parts. If a sin gle bead is in adequate to ach ieve th e required brakin g effect, several beads can be located on e n ext to th e oth er. In sin gle-action drawin g with a draw cush ion it is possible to con trol th e blan k h older force durin g th e form in g stroke or in differen t areas of th e blan k h older in order to carry out th e form in g operation (cf. Sect. 3.1.4). With double-action m ech an ical presses, th e blan kh oldin g force can be varied by alterin g th e pressure in th e pressure poin ts of th e blan k h older slide (cf. Sect. 3.2.8).

blank holder

die

punch

draw bead

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Fig. 4.2.6 Draw bead in a die

Deep draw ing and stretch draw ing

173 punch

blank holder

brake bead

die

Fig. 4.2.7 Beads restraining material flow in the blank holder

Draw energy For d rawin g op eration s on d ou ble-action p resses, th e req u ired d raw en ergy W d [Nm ] is th e p rod u ct of th e p ressin g force FU [N], th e d rawin g stroke h [m ] an d a correction factor x [–]:

Wd = x ⋅ FU ⋅ h [ Nm] Th e correction factor, wh ich is depen den t on th e m aterial an d th e draw ratio b = D/ d, takes in to accou n t th e actu al drawin g force ch aracteristics; th is factor flu ctu ates between 0.5 an d 0.8. Th e h igh er level is for soft m aterials, wh ich can be drawn with th e m axim u m draw ratio bm ax an d for flan ged sh ells, wh ich are on ly partially bu t n ot com pletely drawn th rou gh . Th e lower level is for a sm all draw ratio, th at is to say for sh ort drawin g depth s or for h arder grades of sh eet m etal. W h en drawin g n orm al m aterials, calcu lation s can be based on x < 0.65 u p to 0.75. A su fficien tly accu rate rou gh calcu lation form u la for estim atin g th e d raw en ergy of a d ou ble-action p ress is:

Wd =

2 ⋅ FU ⋅ h [Nm] 3

With a sin gle-action p ress with a d raw cu sh ion , th e slid e force is in creased by th e blan k h old er force FB [N]:

We = (x ⋅ FU + FB ) ⋅ h [ Nm]

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Exa m ple: For a d rawn cu p from 0.8 m m th ick sh eet m etal (m aterial n u m ber 1.0338 – Rm = 350 N/ m m 2 ) with a d iam eter of 60 m m an d a h eigh t of 40 m m (circu lar blan k d iam eter 115 m m , b = 1.9) th e followin g p ressin g work for d rawin g with a d ou ble-action p ress is req u ired :

Wd =

2 2 β –1 ⋅h ⋅ FU ⋅ h = ⋅ π ⋅ (d1 + s) ⋅ s ⋅ R m ⋅ 1.2 ⋅ β max – 1 3 3

Wd =

2 1.9 – 1 ⋅ π ⋅ (60 mm + 0.8 mm ) ⋅ 0.8 mm ⋅ 350 N / mm 2 ⋅ 1.2 ⋅ ⋅ 40 mm 3 2.0 − 1

Wd =

2 ⋅ 18, 385.9 N ⋅ 0.04 m = 490.3 Nm = 490.3 J 3

Deep drawing without a blank holder is on ly carried ou t if th e p art d oes n ot ten d to wrin kle, i. e. with th ick sh eet m etal or sm all am ou n t of d eform ation (with sm all d raw ratio b). Drawing defects In ord er to elim in ate th e p ossibility of p arts bein g rejected , it is n ecessary to in vestigate th e scrap p ed p arts very th orou gh ly an d to id en tify th ereby th e cau ses of an y d efects an d to take p reven tive m easu res. Som e of th e m ost com m on d efects are illu strated in Table 4.2.2.

4.2.2 M aterials for sheet metal forming Un alloyed an d alloyed steels as well as copper alloys, copper sh eet, an d ligh t alloys are all am on g th e com m on ly u sed m aterials in sh eet m etal form in g tech n ology. Am on g alloyed steels, a differen ce is drawn between ph osph or-alloyed steels, types of steel with addition al h arden in g after h eat treatm en t (bake-h arden in g steels), ferritic ch rom iu m steels, au sten itic ch rom iu m n ickel steels an d cold-rolled sh eet with h igh er ten sile yield stren gth for cold form in g (m icro-alloyed steels). Table 4.2.3 lists popu lar m aterials with th e followin g specification s: – m aterial n u m ber, – ten sile stren gth Rm [N/ m m 2 ],

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175

Table 4.2.2: Deep draw ing defects Defect

Possible Cause

Prevention, remedy

draw ing grooves

tool w ear

replace draw punch/female die, improve lubrication

tear marks on the base of the draw n part

draw ing ratio b set too high / draw ing gap too narrow / curvature on draw punch or female die too small / blank holder force too great / draw ing speed too great

use a sheet metal w ith greater deep draw ing capability or employ multi-stage draw ing process / extend draw ing gap / check sheet metal thickness / increase die radii / reduce blank holder force / reduce forming speed

vertical tear marks on upper edge

insufficient material in the defective area / draw ing gap too w ide or draw ing edge curvature too great

replace the female die

on rectangular parts, the corners are higher than the side w alls

too much material at the corners

change the blank shape / recess material in the affected areas / trim the edge afterw ards

vertical creases in the upper area of the body (vessel w all), also in conjunction w ith vertical cracks

blank holder force too low / draw ing gap too great / curvature at the female die too great

increase blank holder force / renew female die

crease formation at the flange

blank holder pressure too low

increase blank holder pressure

other non-specific defects / faulty or irregularly formed draw n parts

incorrect blank shape / asymmetrical material location / unsuitable sheet metal / incorrect lubricant

correct blank shape / check die and stops / use suitable sheet metals and lubricants

– lower yield stren gth ReL [N/ m m 2 ] for sh eet m etals with an accen tu ated yield stren gth or 0.2 % elon gation lim it Rp 0,2 [N/ m m 2 ] for th ose with ou t accen tu ated yield stren gth , – u ltim ate elon gation A[%]: eith er relative to an in itial len gth in th e ten sile test sp ecim en L0 of 80 m m (A80 ) or to L0 = 5 · d 0 (A5 ), with an in itial ten sile test sp ecim en d iam eter of d 0 , – field of ap p lication .

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Table 4.2.3: Summary of the more commonly used sheet metal materials Unalloyed steels M aterial No.

Rm [N/mm 2]

Rp0,2 or ReL [N/mm 2]

A 80 [%]

Fields of application, examples

St 12

10330

270...410

max. 280

28

automotive engineering

USt 13

10333

270...370

max. 250

32

automotive engineering

St 14

10338

270...350

max. 225

38

automotive engineering

M aterial No.

Rm [N/mm 2]

Rp0,2 or ReL [N/mm 2]

A 80 [%]

Fields of application, examples

ZStE 220 P

10397

340...420

220...280

30

automotive engineering

ZStE 260 P

10417

380...460

260...320

28

car body w ork: doors, hoods, roofs

ZStE 300 P

10448

420...500

300...360

26

automotive engineering

M aterial No.

Rm [N/mm 2]

Rp0,2 or ReL [N/mm 2]

A 80 [%]

Fields of application, examples

ZStE 180 BH

10395

300...380

180...240

32

automotive engineering

ZStE 220 BH

10396

320...400

220...280

30

automotive engineering

ZStE 260 BH

10400

360...440

260...320

28

automotive engineering

ZStE 300 BH

10444

400...480

300...360

26

automotive engineering

M aterial No.

Rm [N/mm 2]

Rp0,2 or ReL [N/mm 2]

A 80 [%]

Fields of application, examples

Phosphor-alloyed steels

Bake-hardening steels

Ferritic chromium steels

X 6 Cr 17

14016

450...600

250...270

20

automotive engineering: bumpers, hub caps, food industry, household, appliances: deep-draw ing parts w ith high corrosion resistance properties: sink unit panelling cutlery

X 6 CrM o 17 1

14113

480...630

260...280

20

hub caps, bumpers, car w indow frames radiator grille surrounds

X 6 CrTi 12

14512

390...560

200...220

20

automotive engineering: shock absorbers, exhaust system components

X 6 CrNb 17

14511

450...600

250...260

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

20

dairy, brew ery, food industry, soap industry and dyeing plants: parts (containers) requiring w elding and w hich are exposed to w eak acid solutions

Deep draw ing and stretch draw ing

177

Austenitic CrNi steels M aterial No.

X 5 CrNi 18 10

X 5 CrNi 18 12

14301

Rm [N/mm 2]

500...700

Rp0,2 or ReL [N/mm 2]

A 80 [%]

Fields of application, examples

s 45, th ere is a d an ger of bu rstin g or bu cklin g. Th is can be p reven ted by red u cin g th e free bu cklin g len gth . If D/s < 20, th e bu cklin g len gth can be greater with in creasin g wall th ickn ess. Th in n in g of th e wall th ickn ess is p reven ted by axial d isp lacem en t of th e m aterial. However, th e sam e d isp lacem en t can also lead to com p ression of th e wall. On ly a m in im al d an ger of bu cklin g exists. Expansion/com pression and local calibration Th e m axim u m in flation cap acity is lim ited by th e u ltim ate elon gation of th e m aterial. Half th e u ltim ate elon gation rep resen ts th e lim it of ach ievable d eform ation wh ere n o axial m aterial flow is p ossible. In th is case, th e bu cklin g len gth is of n o sign ifican ce. Pure calibration Th e lim it of ach ievable d eform ation corresp on d s to h alf of th e u ltim ate elon gation of th e m aterial.

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419

5 Hydroforming

5.4 Die engineering 5.4.1 Die layout Figure 5.4.1 illu strates th e layou t of a h yd roform in g d ie. Th e d ie set wh ich com p rises an u p p er an d a lower d ie is u sed to accom m od ate th e fu n ction al elem en ts. Th e d ie h old er p lates p erm it ad ju stm en t of th e assem bly h eigh t p rescribed by th e p ress stroke or h eigh t of th e cylin d er h old er brackets. Th e seal p u n ch es wh ich are actu ated by th e d isp lacem en t or p ressu re-d ep en d en t an d con trolled h orizon tal cylin d ers, th ey seal an d p u sh th e tu be en d s d u rin g th e com p ression p rocess. Th e p iston

slide plate

centering

die holder plate top die

horizontal cylinder seal punch

cylinder holder bracket w ith sw ivel mounting

bottom die

die holder plate

bed plate

hydroformed part

Fig. 5.4.1 Schematic view of a die layout

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Die engineering

421

d iam eter an d stroke are ad ju sted to th e sp ecific req u irem en ts of th e com p on en t. Th e cylin d er h old er brackets absorb th e axial forces an d align th e h orizon tal cylin d ers con cen trically with th e en d gu id es. Th ese can be m oved an d p osition ed on th e bed or slid e p late. Th e m od u lar basic stru ctu re of th e d ies p erm its flexible im p lem en tation of th e req u ired com p on en t geom etries. Th e objective is to m in im ize p rod u ction costs, d ie ch an gin g tim es an d th e tim e req u ired to exch an ge worn p arts. In ad d ition , d u rin g th e d evelop m en t p h ase it is p ossible to try ou t d ifferen t tu be m aterials an d wall th ickn esses with ou t ch an gin g th e d ies. Th u s, it is p ossible to test variou s p reform geom etries with a m in im u m of trou ble an d exp en se. Sim p le ch an geover from p rototyp e d ies to p rod u ction d ies is p ossible if on ly cavity or slid in g in serts h ave to be exch an ged (Fig. 5.4.2). W h en d esign in g a p rototyp e d ie, its service life is on ly of m in or im p ortan ce. Excep t for th e slid in g in serts, it is n ot n ecessary to h ave tim e-con su m in g coatin gs or oth er su rface treatm en ts of th e d ie in serts. Prototyp in g – an d th u s step -by-step p rogress toward s a d ie su itable for series p rod u ction – takes p lace in several stages:

prototype die

w orkpiece

basic die

production die exchange of w earing parts modification of individual contour sections horizontal cylinder

counterpressure punch

Fig. 5.4.2 Die systems for prototyping and production

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

die cavity insert

sliding insert

Hydroforming

422

– d evelop m en t of th e basic com p on en t geom etry, – in tegration of su p p lem en tary op eration s su ch as h ole p iercin g, – p rod u ction of m od ified in serts. Here, th e followin g p aram eters in flu en ce th e selection of tool m aterials an d th e n ecessary coatin g or treatm en t: – com p on en t geom etry, – com p on en t m aterial, – m axim u m in tern al p ressu re, – sealin g system , – ap p lication (p rototyp in g, series op eration ).

5.4.2 Lubricants As is th e case in oth er cold form in g op eration s, lu brican ts are am on g th e m ost im p ortan t aid s in th e h yd roform in g p rocess, as th ey m in im ize friction at location s with relative m otion between d ie an d workp iece (cf. Sect. 4.2.3). Man y com p on en ts can on ly be m an u factu red in th e req u ired sh ap e on ly th rou gh th e u se of ap p rop riate lu brican ts. Lu brican ts p erm it to obtain m ore even wall th ickn ess variation , sim p lify th e form in g of tu bu lar bran ch es, red u ce p artial stretch in g p rocesses an d im p rove form in g in areas th at d o n ot allow an y m aterial flow by axial feed . A n u m ber of d ifferen t lu brican ts can be con sid ered for u se in h yd roform in g. Dep en d in g on th eir com p osition , th ese can be assign ed to th e followin g grou p s: – – – –

solid lu brican ts, gen erally on a grap h ite or MoS2 basis, p olym er d isp ersion -based lu brican ts, waxes, oils an d em u lsion s.

Lu brican t is gen erally ap p lied by m ean s of sp rayin g or im m ersion . Excep t in th e case of oils, th e ap p lied coatin g m u st gen erally h ave d ried an d h ard en ed p rior to th e form in g p rocess. On p rin cip le, atten tion m u st be p aid to en su re an even coatin g th ickn ess. Th e op tim u m th ickn ess of th e lu brican t layer m u st be d eterm in ed by trial an d error.

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

5 Hydroforming

5.5 M aterials and preforms for producing hydroformed components 5.5.1 M aterials and heat treatment Basically th e sam e m aterials wh ich can be u sed for oth er cold form in g tech n iqu es su ch as deep-drawin g (cf. Table 4.2.3) are su itable for h ydroform in g application s. Th e m aterial sh ou ld h ave a fin e-grain ed m icrostru ctu re an d be soft-an n ealed. Th e best form in g resu lts are ach ieved u sin g m aterials with a h igh d egree of u ltim ate elon gation , wh ereby th e u ltim ate elon gation at righ t an gles to th e lon gitu d in al d irection of th e tu be – i. e. gen erally at righ t an gles to th e rollin g d irection of th e sh eet m etal – is im p ortan t for th e con figu ration of h yd roform com p on en ts. A h igh d egree of strain h ard en in g is ben eficial. Th e tu be m an u factu rin g p rocess an d p re-form in g brin g abou t a strain h ard en in g effect wh ich m ay h ave to be elim in ated by an n ealin g for certain com p on en ts p rior to th e h yd roform in g p rocess. If th e form ability of th e m aterial is exceed ed d u rin g a p rod u ction step in th e m an u factu rin g p rocess, form in g m u st be p erform ed u sin g several stages (p rogressive form in g) with in term ed iate an n ealin g. However, d u e to th e ad d ition al costs in volved , h eat treatm en t sh ou ld on ly be carried ou t wh en all oth er p ossibilities, for exam p le d esign or m aterial m od ification s, h ave been exh au sted . Th e p referable m eth od of h eat treatm en t for austenitic steels is solu tion izin g – id eally u sin g in ert gas. For sm all p arts, a con tin u ou s fu rn ace can be u sed .

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424

In th e case of ferritic steel, th e typ e an d p racticality of h eat treatm en t d ep en d h eavily on th e resp ective m aterial an d its form in g h istory. On p rin cip le, eith er of two p ossible p rocesses can be u sed : recrystallization an d n orm al an n ealin g. Gen erally, Mn or Si alloys are u sed for alum inium . Th e m ost favorable m eth od of h eat treatm en t m u st be d eterm in ed in each in d ivid u al case, wh ereby p articu lar atten tion m u st be p aid to th e lon g-term beh avior of th e m aterial, an d in th e case of strain h ard en in g alloys, to rap id fu rth er p rocessin g.

5.5.2 Preforms and preparation For h yd roform in g, p arts m ad e of th e followin g sem i-fin ish ed p rod u cts are u sed (Fig. 5.2.8): – – – –

d rawn or weld ed tu bes, d ou ble-walled tu bes, extru d ed p rofiles, weld ed or p re-form ed tu bu lar blan ks.

In gen eral, tu bu lar p reform s with circu lar cross section s are u sed . Weld ed an d extru d ed n on -rou n d section s are u sed less freq u en tly. Th e p rod u ction step s req u ired for th e p rep aration of p reform s for tech n ically an d econ om ically op tim u m p rod u ction are d escribed in th e followin g with referen ce to tu bu lar blan ks. Th e tu be cutting p rocess m u st be extrem ely p recise in ord er to avoid u n d esirable effects su ch as leaks at th e begin n in g of th e h yd roform in g seq u en ce. Th ese wou ld lead to failu re of th e com p on en t as a resu lt of bu cklin g. Flu ctu ation s in th e wall th ickn ess alon g th e p erip h ery resu lt in a h igh scrap level, an d in extrem e cases even to failu re of th e com p on en t. Th e followin g toleran ces are gen erally ad m issible: – len gth : +/ – 0.5 m m – an gle of th e cross section relative to th e lon gitu d in al axis: +/ – 0.5° Con cen tricity at th e tu be en d s is im p ortan t in ord er to avoid u n wan ted sh earin g wh en th e d ie is closed . Th e tu bes m u st be clean ed of an y ch ip s, as th ese lead to tool d am age, form in g errors or m arks on th e su r-

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

M aterials and preforms for producing hydroformed components

face of th e com p on en t. Tu be en d s m u st be d ebu rred for th e sam e reason , alth ou gh ch am fers m u st be avoid ed u n d er an y circu m stan ces. Th e id eal p reform for th e h yd roform in g p rocess is a straigh t cylin d rical tu be. However, d eviation s from th is sh ap e are com m on , as th e tu be m u st be laid ad eq u ately in th e d ie in ord er to en su re p art q u ality. Th is n ecessitates a pre-form ing p rocess. On p rin cip le, an y p re-form in g p rocess redu ces su bseq u en t form ability an d leads to differen ces in th e wall th ickn ess an d fau lts in th e form in g beh avior of th e p arts as a resu lt of local strain h arden in g. However, su itable con figu ration of th e com p on en t an d op tim u m selection of th e p re-form in g p rocess can cou n teract th ese n egative effects. Bending is p erform ed on a m an d rel, p rofile, cam or in d u ction ben d in g m ach in e d ep en d in g on th e ben d in g rad iu s, tu be d iam eter an d wall th ickn ess (cf. Sect. 4.8). Becau se of th e n otch in g effects th at m ay occu r, su rface d am age, in p articu lar sh arp -ed ged im p ression s created by clam p in g jaws, m ay lead to p rem atu re bu rstin g of th e com p on en t. Th e toleran ce for th e straigh t en d s, as for cu ttin g, is +/ – 0.5 m m . Ben d in g errors, su ch as wrin kles on in sid e ben d s, im p ression s left by clam p in g jaws or d rawin g grooves m u st be avoid ed , p articu larly in th e case of th in -walled tu bu lar blan ks. Reduction and expansion p rocesses are u sed wh ere large p erip h eral d ifferen ces are req u ired on lon g elon gated com p on en ts or in case of p artial oversize of th e u sed tu be in th e cen tral section . Here, too, p rocesssp ecific d efects su ch as grooves, im p ression s etc. cou ld h ave a d etrim en tal effect. Pre-form ing in the hydroform die rep resen ts an id eal solu tion if it can elim in ate an y oth er p re-form in g step s req u ired on th e straigh t tu be. Pre-form in g is also carried ou t on p arts wh ich h ave been p reviou sly ben t, exp an d ed or red u ced . Pre-form ing in the die is u sed in th e case of com p lex geom etries, wh ere th e above p rocesses fail to p rod u ce satisfactory resu lts. Sp ecial p rocesses also exist for tap ered , weld ed tu bes, weld ed tu bes with n on -rou n d section s, d eep -d rawn h alf sh ells, extru d ed section s an d join ed tu bes. In th e case of com p lex com p on en ts, several p re-form in g step s can be n ecessary.

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425

5 Hydroforming

5.6 Presses for hydroforming Hyd roform in g p resses are sp ecially d esign ed p resses th at h ave: – – – –

th e th e th e th e

electron ic system , oil h yd rau lics, p ressu re m ed iu m h yd rau lics an d con trol system , bed an d slid e

adapted to th e special requ irem en ts of h ydroform in g. Th e press types u sed are eith er fou r-u prigh t presses (Fig. 5.6.1) or fram e presses (Fig. 5.6.2). Th e fou r-u prigh t con stru ction gu aran tees optim u m accessibility of dies for loadin g, process con trol an d die com pon en t ch an geover. Th e die can be m ou n ted ou tside th e press an d fed in to th e press u sin g a die ch an gin g system . In side th e press, th e die is locked in position by h ydrau lic clam ps: All th at is n ecessary to create th e h ydrau lic an d electrical con n ection s. Die ch an ge can be execu ted depen din g on requ irem en ts at th e press location on on e of th e fou r sides (cf. Sect. 3.4). Th e position of th e h orizon tal cylin der is flexible. Fram e p resses are u sed as sin gle-p u rp ose p resses for th e p rod u ction of fittin gs. Th e h orizon tal cylin d ers of th is typ e of p ress are p erm an en tly in stalled . Th e closin g force is ap p lied by m ean s of vertical p lu n ger or d ifferen tial cylin d ers (cf. Sect. 3.3). User-sp ecific factors are taken as a basis for – con figu ration of th e p lu n gers an d d ifferen tial cylin d ers, – th e stroke an d d iam eter of th e h orizon tal an d cou n terp ressu re cylin d ers, – d im en sion in g th e p ressu re in ten sifier an d – d eterm in in g th e size of th e bed .

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Presses for hydroforming

427

Fig. 5.6.1 Four-upright hydroforming press w ith a closing force of 25,000 kN

Con trollable p u m p s fill th e workp ieces u p to a d efin ed in itial p ressu re with p ressu re m ed iu m . Pressu re levels exceed in g th is are gen erated by th e p ressu re in ten sifier. Th e lin e con trol system is con figu red for at least fou r con trolled h yd rau lic axes – on e p ressu re in ten sifier, two h orizon tal cylin d ers an d on e cou n terp ressu re cylin d er. All th ese axes can be con trolled to be d isp lacem en t or p ressu re-d ep en d en t. Th e closin g p rocess for coin ed ben d s is p rovid ed as th e fifth axis. Th e n u m ber of axes can be in creased , for exam p le if d ifferen t com p on en ts or com p on en ts with su bseq u en t stroke h ave to be form ed in a sin gle p ress stroke. All th e n ecessary p rocess d ata is en tered at th e h ost com p u ter (cf. Sect. 3.5). Th e seq u en ce of th e form in g p rocess is execu ted in th e form of a series of step s con tain in g th e d ata on variou s axes an d an y ad d ition al con trol com m an d s. Th e p ressu re an d p osition of all axes can be m on itored d u rin g execu tion of th e p rocess on -lin e on th e screen . Th ey can also be record ed . Th e p rogram m ed d ata from th e step ch ain can be viewed at an y tim e in th e form of a d iagram . It is p ossible to d raw u p a

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428

filling valve

slide cylinder

slide counterpressure punch

horizontal cylinder

pressure beam w ith support roll

Fig. 5.6.2 Frame-type hydroforming press

resp on se p lan wh ich corrects certain errors au tom atically u sin g th e p rescribed m easu res wh ere th ese occu r. Takin g in to accou n t th e n ecessary safety m easu res, th e lin e can be load ed eith er fu lly au tom atically or m an u ally.

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

5 Hydroforming

5.7 General considerations 5.7.1 Production technology issues An y com p arison between h yd roform in g an d oth er p rocesses – su ch as com p ression m ou ld in g, assem bly of stam p ed p arts, castin g or assem bly of ben t tu bes – m u st take in to con sid eration all th e tech n ical as well as econ om ic asp ects. Preced in g an d su bseq u en t work step s an d th e p rop erties of th e fin ish ed com p on en t m u st also be in clu d ed in to an y evalu ation . Prod u ction by m ean s of h yd roform in g can , for in stan ce, ap p ear u n econ om ical for sm all q u an tities if on ly th e com p on en t costs are con sid ered , as th e cycle tim es req u ired are relatively lon g (Table 5.7.1). However, if we com p are th e tech n ical p rop erties of th e en d p rod u ct with th ose p rod u ced u sin g d ifferen t tech n iq u es, it is p ossible to m ake u p for th is d rawback. W h ere m ed iu m an d h igh q u an tities of a com p on en t su itable for h yd roform in g are in volved , th e tech n ical an d econ om ic ben efits of h yd roform in g can be brou gh t so effectively to bear th at n o oth er m an u factu rin g p rocesses can realistically be con sid ered .

Table 5.7.1: Cycle times for different parts Component

Automation

Components per stroke

Cycle time

exhaust manifold w ith dome

no

2

15 ... 25 s

exhaust manifold tube

yes

2 ... 4

15 ... 20 s

side member for pick-up

yes

2

40 s

instrument panel rail

yes

1

35 s

T-fittings

yes

up to 25

13 s

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430

Fig. 5.7.1 Hydroforming exhaust manifold: series production

Figure 5.7.1 an d Table 5.7.2 com p are a con ven tion al with a h yd roform in g con stru ction of an exh au st m an ifold . Further processing of parts Fu rth er processin g of h ydroform ed parts in clu des an y produ ction processes wh ich are execu ted directly on th e com pon en t followin g th e h ydroform in g sequ en ce or wh ich are u sed to join h ydroform ed parts togeth er. If th e geom etry of th e parts or specific requ irem en ts preven t th em from bein g pressed to th eir fin al dim en sion , finish processing is n ecessary. Th e requ ired fin al form is ach ieved u sin g, for exam ple, cu ttin g, stam p in g or m illin g p rocesses. Table 5.7.2: Comparison of conventional and hydroforming production for the exhaust manifold illustrated in Fig. 5.7.1

Conventional production number of individual parts service life

Hydroforming production

17

9

700 – 1,000 h

> 1,500 h

manufacturing costs

100 %

85 %

development time

100 %

33 %

flange type

varies

same

w eight

100 %

100 %

scrap

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

< 0.5 %

General considerations inw ard hole punching

431 notching and bending over

outw ard hole punching

pi

pi

Fig. 5.7.2 Hole punching, notching and bending during hydroforming

In addition , hole punching, notching, bending or threading processes can be perform ed on th e part in cases wh ere th is h as n ot already been perform ed as part of th e h ydroform in g sequen ce itself (Fig. 5.7.2). By calibratin g th e part, it is possible to produce special con tours at th e en ds of th e tubes. A separate process is required, gen erally by m ean s of weldin g, in order to assem ble add-on com ponents or to assem ble th e part with oth er com pon en ts produced usin g differen t production processes. In th e case of a production lot-related m ultiple pressing, com pon en ts th at are assem bled togeth er are form ed in a sin gle pressin g process an d m ust be separated by cuttin g.

5.7.2 Technical and economic considerations Th e m ost im p ortan t tech n ical an d econ om ic asp ects of h yd roform in g are th at: – Com p on en ts with com p lex geom etries can be m an u factu red wh ich p reviou sly cou ld n ot be p rod u ced in a sin gle p iece.

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– Th e sin gle-p art con stru ction elim in ates th e n eed for weld in g seam s. – Th e calibration p rocess en su res a h igh d egree of accu racy in th e con tou rs an d d im en sion s of h yd roform ed com p on en ts. – Strain h ard en in g gen erally len d s h yd roform ed com p on en ts a h igh d egree of torsion al rigid ity. Th eir elastic recovery p rop erties are less p ron ou n ced th an is th e case with weld ed sh eet m etal sh ells. For th is reason , it is often p ossible for th e wall th ickn ess of h yd roform ed com p on en ts to be relatively low com p ared to cast p arts or sh ell con stru ction s. Th is effect can be u sed eith er to red u ce weigh t or to en h an ce stren gth or rigid ity. – Usin g th e sam e d ie, it is p ossible to u se an d test tu bes wh ich , with in certain lim its, h ave d ifferen t wall th ickn esses an d startin g d iam eters an d are m ad e of d ifferen t m aterials (p rovid ed th e u ltim ate d eform ation is n ot exceed ed ). Th is allows th e weigh t an d stren gth p rop erties of th e p art to be op tim ized . – Exp erien ce h as sh own th at lower flow resistan ce an d larger fatigu e stren gth are ach ieved in exh au st system s. By selective com p on en t an d p rocess con figu ration , it is p ossible to save both en ergy an d m aterial an d to red u ce d evelop m en t an d p rod u ction tim es. Th u s, gen erally it is p ossible to red u ce m an u factu rin g costs.

Bibliography Leitloff, F.-U.: Innenhochdruckumformen mit dem Schäfer-ASE-Verfahren, Stahl (1995) 5. M alle, K.: Aufw eiten - Stauchen - Expandieren, VDI Journal 137 (1995) 9. N. N.: ASE-Verfahren bringt Hohlkörper in Form, Stahlmarkt (1993) 4. N. N. : Hochdruckumformen - Fertigungsverfahren mit Zukunft, Stahl (1993) 4. N. N.: M it Wasser immer in Form, Automobil-Industrie (1993) 4. N. N.: Schäfer bringt Hohlkörper in Form, Technische Informationsbroschüre zur Schäfer-ASETechnologie, W ilhelm Schäfer M aschinenbau GmbH & Co. Schäfer, A. W., Fröb, K., Bieselt, R., Hassanzadah, G.: Kaltgeformte T-Stücke für den Anlagenbau – Anforderungen und technische Realisierbarkeit, 3R International 29 (1990) 9.

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

6 Solid forming (Forging)

6.1 General Processes and parts Th e term s sh eet m etal form in g an d solid form in g are based on p ractical in d u strial ap p lication , an d su bd ivid e th e field of form in g tech n ology in to two d istin ct areas. Th is d istin ction is m ad e in ad d ition to th e d efin ition s establish ed by DIN 8582 “Form in g” (cf. Fig. 2.1.3). Solid form in g en tails th e th ree-d im en sion al form in g of “com p act” slu gs (for exam p le sh eared billets), wh ile th e sh eet m etal form in g m eth od gen erally p rocesses “flat” sh eet m etal blan ks to create th ree-d im en sion al h ollow stru ctu res with an ap p roxim ately con stan t sh eet m etal th ickn ess. Th e forces exerted d u rin g solid form in g are su bstan tially h igh er th an th ose n ecessary for sh eet m etal form in g. As a resu lt, it is n ecessary to u se relatively rigid com p act-d esign m ach in es an d d ies. Solid form in g in volves n ot on ly th e p rocesses of extru sion , in d en tation an d d rawin g wh ich are d ealt with in m ost d etail h ere, bu t also for exam p le rollin g, op en d ie forgin g (cf. Fig. 2.1.4) or closed d ie forgin g (cf. Fig. 2.1.5). Th e p rocesses cold extrusion an d drawing in volve form in g a slu g or billet p laced in a d ie, m ost com m on ly for th e production of discrete parts. Hot extru sion u ses a basically sim ilar form in g m ech an ism to create sem i-finished products such as rods, tubes and sections. Th e basic p rocesses in volved in cold extru sion (Fig. 6.1.1) are classified d ep en d in g on th eir form in g d irection as forward , backward an d lateral extru sion an d also accord in g to th e fin al form of th e workp iece as rod (solid ), tu be an d cu p extru sion . W h en p rod u cin g solid p arts, th e classical op eration s of cold extru sion tech n ology are su p p lem en ted by p rocesses like u p settin g an d iron in g (Fig. 6.1.2). Th e sh ap e variety of p arts form ed from slu gs or bil-

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434

rod e trusion

I

II

forward e trusion

I

tube e trusion

cup e trusion

II

I

II a

a

a

b

b

b

e c

c c

d f

II

I

backward e trusion

I

II

I

II a

a

a

c b

c

c

b b

f d, e

d,e

d,e

lateral e trusion

I

II

I

II

a c

b

I

II

a c

b

a

c

b

s f

e

e

d

Fig. 6.1.1 Schematic representation of the cold extrusion (cold forging) processes: I prior to forging; II after forging (BDC); a punch; b container; c w orkpiece; d ejector; e counterpunch; f mandrel

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

e

f

General

435

lets th at can be p rod u ced tod ay is in creased su bstan tially by th e u se of piercing, flow piercing, trim m ing and bending processes. Th e ran ge of p arts in clu d es n ot on ly fastening elem ents (screws, bolts, n u ts, rivets, etc.), bu t p arts for th e construction industry (L an d T-fittin gs for h eatin g system s) an d com p on en ts u sed in m echanical engineering ap p lication s (ball bearin g races, balls, rollers an d cages). Most solid form ed p arts are u sed in th e autom otive and m otor cycle industry. En gin e com p on en ts (valves, cam sh afts, cam s, con n ectin g rods), gear p arts (gear sh afts, gear wh eels, syn ch ron ou s rin gs, differen tial bevel gears), ch assis com p on en ts (stu d axles, ball h u bs, step p ed h ou sin g elem en ts, sh ock absorbers), steerin g com p on en ts (steerin g colu m n join ts, tie rod en d s), brake com p on en ts (brake p iston s) an d com p on en ts for electrical m otors (starter m otor p in ion s, drivers, p ole rotors), can be econ om ically p rodu ced by solid form in g. In addition , solid form ed p arts are u sed in h ou seh old ap p lian ces, office eq u ip m en t, clocks or m edical eq u ip m en t. Figure 6.1.3 offers an overview of differen t sh ap es wh ich can be p rodu ced. Th e form in g tech n iq u es described h ere are cu rren tly also u sed to p rodu ce gears th at can be p rodu ced very econ om ically. In m an y cases, n o m ach in in g is n ecessary or at m ost on e fin al grin din g or h arden in g p rocess m ay be req u ired at th e teeth . Com p on en ts with straigh t teeth (sp u r gears) – su ch as h u b sleeves, bevel wh eels an d gears –, h elical teeth (e. g. p lan etary gears, sm all gears) an d sp ecial teeth form s (e. g. rin g gears) can be p rodu ced. Th is typ e of gears can be form ed with an y desired tooth th at is often in volu te in sh ap e. Con tou rs are form ed on th e su rface u sin g th e in d en tation p rocesses (DIN 8583 sh eet 5) coin in g an d roll em bossin g. Here, th e com p lete

α 2

punch

punch

α ironing die

container w orkpiece upsetting die upsetting

w orkpiece extrusion

Fig. 6.1.2 Upsetting, open die extrusion, ironing

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

ironing

Solid forming (Forging)

436

Fig. 6.1.3 Range of cold, w arm and hot forged parts

workpiece or th e area to be em bossed is en closed in trapped (closed) dies. Du rin g em bossin g, th e part th ickn ess is redu ced, in som e cases by a con siderable am ou n t. Coin in g is a typical exam ple of an em bossin g process (cf. Fig. 2.1.6). Bim etal coin s are a good exam ple h ere, as th ey in volve a join in g process (DIN 8593) com bin ed with coin in g an d roll em bossin g. Em bossin g tech n iqu es are also u sed for exam ple in th e produ ction of road sign s, an d in th e cu tlery or h an d tool in du stry (Fig. 6.1.4). Cold coining of hot forged parts (sizing) (DIN 8583 sh eet 4) is u sed to im p rove d im en sion al, sh ap e an d p osition in g accu racy an d / or to im p rove su rface q u ality. Th e objective is to p ress d im en sion s an d sh ap e to th e req u ired toleran ces, an d th u s avoid th e n eed for su bseq u en t m etal cu ttin g op eration s. In con trast to in d en tation , wh en u sin g cold coin in g, th e com p on en t alread y h as alm ost its com p lete geom etry, m ean in g th at th e h eigh t red u ction d u rin g cold coin in g is relatively sm all. Sizin g of th e bosses in con n ectin g rod s (wh ich are req u ired to h ave a tigh ter th ickn ess toleran ce com p ared to castin gs), an d sizin g of p lier h alves

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

General

Fig. 6.1.4 Examples of coined parts, such as coins, medals, cutlery and various hand tools, as w ell as cold-coined hot forged parts

(wh ose fu n ction al su rfaces req u ire p articu lar p osition in g accu racy) are typ ical exam p les of th is typ e of ap p lication . Hot, warm and cold form ing and process com binations It is gen erally tru e th at alm ost all solid form in g p rocesses can th eoretically be ap p lied at d ifferen t tem p eratu res. It is on ly wh en d ifferen t factors com e togeth er to create in terrelated com p lexities th at eith er h ot, cold or warm form in g em erges as th e id eal p rod u ction m eth od in an y p articu lar case (cf. Sect. 2.2.1). Above th e recrystallization tem p eratu re, hot form ing (forging) takes p lace. Forgin g is th e old est kn own m eta form in g tech n iq u e. If th e billet or workp iece is n ot h eated p rior to p ressin g, th e m eth od u sed is referred to as cold form ing (cold forging). Th is m eth od d id n ot becom e feasible for u se with steel u n til th e th irties, wh en a su itable sep aratin g layer between th e d ie an d th e workp iece cou ld be d evelop ed . W arm form ing (or forging), th e last of th e th ree tech n iq u es, d evelop ed for th e in d u strial p ractice, was in trod u ced in th e eigh ties. For steels, for exam p le, th is m eth od works at a tem p eratu re ran ge of between 750 an d 950 °C. For m an y p arts an d sp ecial workp iece m aterials with a h igh p rop ortion of carbon , th is m eth od com bin es th e tech n ical ad van tages of h ot forgin g with th ose of cold forgin g for op tim u m econ om ical con d ition s. Th e flow stress (Fig. 6.1.5) d ecreases with in creasin g tem p eratu re. Dep en d in g on th e m aterial bein g p rocessed , wh en u sin g th e warm forgin g m eth od , th e flow stress reach es on ly arou n d on e h alf to a th ird of

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437

Solid forming (Forging)

438

th e corresp on d in g valu es for cold forgin g. W h en h ot forgin g, even lower flow stress valu es can be ach ieved , corresp on d in g to as little as on e fifth of th e flow stress level d u rin g cold forgin g. Again d ep en d in g on th e m aterial u sed , in warm forgin g an d h ot forgin g resp ectively forgeability is two or six tim es h igh er th an th at in cold forgin g. In th e h igh er tem p eratu re ran ge from arou n d 700 °C u p ward s, th e in crease in scale form ation wh ich h as a d etrim en tal effect on d im en sion al accu racy an d su rface q u ality of th e p arts m u st be taken in to accou n t. Th e tem p eratu re req u ired for warm forgin g m u st be carefu lly selected as in its “lower ran ge” it is lim ited by th e size of th e p ress force an d th e ach ievable d egree of d eform ation an d in its “u p p er ran ge” by scale form ation . Table 6.1.1 p rovid es a com p arison of th e ad van tages of all th ree m eth od s on th e basis of p rocessin g en gin eerin g criteria. Th e weigh t of th e com p on en ts p rod u ced u sin g h ot forgin g ran ges between 0.05 an d 1,500 kg, in warm an d cold forgin g between 0.001 an d 50 kg. Dim en sion al accu racy an d su rface q u ality d ecrease with in creasin g

N mm 2

5

scale layer

80 60 40 20 0

2

flow stress k f

fracture strain ϕB

µm

3

810 i Ti 1 0 C6

4

Cr N X8

1500

X1 0C r 13 ϕ.= C1 90s 5 1 ϕ.=0 ,7

1000

1

Ck 45

0

15 min

16M nCr5

500

0

15 Ck

. ϕ=70s -1

n 42 M C60

0

200

400

600

V7

5 min

1200 800 1000 forming temperature [°C]

Fig. 6.1.5 Flow stress, scale formation and achievable degree of deformation (forgeability) in function of temperature

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General

439

Table 6.1.1: Comparison betw een hot, w arm and cold forging Forming

Hot

W arm

Cold

w orkpiece w eight

0.05 – 1,500 kg

0.001 – 50 kg

0.001 – 30 kg

precision

IT 13 – 16

IT 11 – 14

surface quality Rz

. 50 – 100 mm

. 30 µm

IT 8 – 11 . 10 µm

flow stress f (T, material)

~ 20 – 30 %

~ 30 – 50 %

100 %

formability f (T, material)

w#6

w#4

w # 1.6

“ Forming costs“ VDW study 1991, Darmstadt

up to 113 %

100 %

up to 147 %

machining required

high

low

very low

tem p eratu re. Th is is d u e to th erm al exp an sion , wh ich can n ot be p red icted with accu racy, an d also to in creased d ie wear. As an exam p le, let u s con sid er warm forgin g as th e m ost econ om ical p rocess for selected p arts, su bject to tech n ical feasibility. If th is p rocess is th en assign ed a cost factor of 100, th e relative costs of h ot forgin g can be u p to 13 % an d of cold forgin g u p to 47 % h igh er. Th erefore, in warm an d esp ecially h ot forgin g th e cost of rem ovin g ad d ition al m aterial d u e to larger m ach in in g allowan ces m u st be con sid ered . In th e case of cold forgin g, in con trast, it is freq u en tly p ossible to com p en sate com p letely for th e “h igh est form in g costs” by extrem ely low or even en tirely elim in ated fin ish in g costs. In extru sion , th erefore, cold an d warm forgin g m u st be com p ared as th e m ost econ om ical p rocess altern atives. With an in creasin g d egree of geom etrical com p lexity (h igh er d egree of d eform ation , for exam p le for steerin g kn u ckles), h owever, h ot forgin g is still an econ om ical p rocess. In p ractice, th e “ideal p rocesses” of solid form in g defin ed h ere are also u sed as p rocess com bin ation s in th ree differen t resp ects. First, alm ost all com p lex workp ieces are m an u factu red today by u sin g m u ltip le-stage com bin ation s (p rocess or p rocessin g step seq u en ce) of in dividu al op eration s. To p rodu ce a bu sh in g, for exam p le, a com bin ation of th e p rocesses u p settin g, cen terin g, backward cu p extru sion , p iercin g an d iron in g are ap p lied in seq u en ce. Secon d, it is p ossible for two p rocesses to be carried ou t sim u ltan eou sly in a form in g op eration . Usin g com bin ed back-

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440

ward an d forward cu p extru sion , for exam p le, tu be-sh ap ed workp ieces with a cen tral web (Fig. 6.1.1) can be p rodu ced. Th ese an d sim ilar p rocess com bin ation s redu ce th e n ecessary n u m ber of p rocessin g step s an d gen erally in volve lower p ress forces th an th e su m of p ress forces u sed for in dividu al op eration s. Su ch p rocess com bin ation s are m ore econ om ical, bu t are on ly p ossible u sin g m u ltip le-action p resses an d dies. Th ird , in form in g p rocesses wh ere workp ieces are in itially h ot or warm forged an d th en cold forged , “p rocess com bin ation ” h as also becom e an establish ed term . Usin g th is tech n ology, it is p ossible to ben efit sim u ltan eou sly, for exam p le, from (a) th e econ om ic ben efits of warm form in g to create “n ear-n et sh ap e” com p on en ts an d (b) th e tech n ical ben efits of cold extru sion or cold forgin g, in p articu lar its d im en sion al accu racy an d su rface q u ality. In th is p rocess, th e cold form in g stage is n ot by an y m ean s restricted sim p ly to a sizin g op eration , bu t can in clu d e a m u ltip le-stage forgin g p rocess.

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

6 Solid forming (Forging)

6.2 Benefits of solid forming 6.2.1 Economic aspects Th e ben efits offered by solid form in g, com pared with oth er production processes, can be sum m arized as superior quality com bin ed with lower m an u factu rin g costs. Th e stan dard of q u ality is du e to th e favorable m ech an ical properties of cold an d warm forged parts, such as h igh stren gth an d tough n ess, an un in terrupted fiber flow, close toleran ces an d a good surface quality. Th e cost ben efit ach ieved usin g forgin g tech n iques can be con siderable, but does depen d on th e specific part con sidered an d on th e previously used production m eth od. In dividual cost factors in clude: – Low m aterial input: Alm ost th e com p lete in itial volu m e of th e billet is p rocessed in to th e fin ish ed p art. Com p ared to m ach in in g, savin gs can be as great as 75 % (Fig. 6.2.1). W h ere h igh -alloyed m aterials are u sed , th e ben efit of low m aterial in p u t becom es in creasin gly sign ifican t in relation to overall m an u factu rin g costs. – Use of low-cost raw m aterials: Strain h arden in g th at occu rs du rin g warm an d cold form in g resu lts on th e on e h an d in h igh er levels of flow stress, bu t also in h igh er u ltim ate an d fatigu e stren gth . Th erefore, it is possible to u se lower-cost steel grades with lower in itial stren gth ch aracteristics in order to ach ieve th e sam e m ech an ical properties obtain able in m ach in ed parts. A workpiece with , for exam ple, a h exagon al geom etry is produ ced wh ere m ach in in g m eth ods are u sed from costly extru ded m aterial with a h exagon al cross section . By forgin g in stead of m ach in in g, th is type of part can be form ed u sin g su bstan tially less expen sive rou n d bar as startin g m aterial.

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442

Ø45

Ø52

Ø50 billet w eight 0.398kg

32

starting w orkpiece and fiber flow in a machined part

86

billet w eight 1.275kg

80

85

Ø53

starting w orkpiece and fiber flow in a forged part

Fig. 6.2.1 Comparison of the input w eight and achievable geometry for machining and forming processes

– Reduction/elim ination of subsequent m achining: Su bseq u en t m etal rem oval p rocesses are freq u en tly on ly n ecessary in th e case of geom etries wh ich p resen t a p articu lar p roblem for form in g p rocesses, for exam p le recesses, u n dercu ts or th reads. By u sin g cold forgin g tech n iq u es, su bstan tial savin gs can be ach ieved by redu cin g in vestm en t in m ach in e tools for m etal-cu ttin g an d in m etal-op eratin g staff. – Minim al process, logistic and transport costs: Th is ben efit is created as a resu lt of th e low cost of au tom ation wh ere tran sfer system s are u sed. – Generally high productivity: Sm all workp ieces p rodu ced from wire on h orizon tal forgin g m ach in es can be m an u factu red at strokin g rates of u p to 200/ m in . For larger p arts m an u factu red by forgin g from billet in vertical p resses from billet, p rodu ction sp eeds of u p to 50 p arts/ m in are p ossible. – Facility for integration of several functions/geom etries in a single com ponent: Cold extru ded p arts often p rovide an op p ortu n ity for “re-en gin eerin g” to create lower-cost design s. Th e alu m in iu m oil filter h ou sin g illu strated on th e left in Fig. 6.2.2, for exam p le, is cold extru ded in a sin gle p iece. Th is allowed th e p rodu ction of th ree in dividu al com p on en ts – flan ge, drawn cu p an d con n ectin g p iece. Th u s, th e com p lex weldin g op eration req u ired p reviou sly (Fig. 6.2.2, right) cou ld be red u ced to a sin gle extru sion op eration .

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Benefits of solid forming

443

flange cup

connecting piece

extruded

w elded

Fig. 6.2.2 Oil filter housing – extruded single component compared to three-part w elded configuration

6.2.2 Workpiece properties Du e to th e h igh d egree of geom etrical accu racy, su rface q u ality an d h igh ly favorable m ech an ical p rop erties, th e workp iece ch aracteristics of cold forged com p on en ts are gen erally very good . Th e m ech an ical ch aracteristics d ep en d on p h ysical factors an d can on ly be in flu en ced to a lim ited d egree. Th e factors in flu en cin g op eratin g accu racy in th e p rod u ction of p recise geom etries an d su rface p rop erties, wh ich are listed in Table 6.2.1, m u st be taken in to con sid eration in th e forge p lan t. In p rin cip le, th e p rim ary req u irem en t is for a h igh ly p recise an d relatively rigid forgin g p ress. If su ch a p ress is n ot available, even fu ll com p lian ce with all th e oth er factors su ch as excellen t d ie d esign can n ot com p en sate for th is d eficien cy. Next, in ord er of im p ortan ce are th e volu m e con trol of th e billet, th e p rocess con cep t, etc. Com p lian ce with an d m on itorin g of all th e p rocess p aram eters th u s en su re to ach ieve th e req u ired service ch aracteristics of a com p on en t. However, it is n ecessary to con sid er th at at th e sam e tim e p rod u ction costs also in crease. Desp ite th e h igh d egree of cost red u ction ach ieved in au tom ated forgin g lin es, it is on ly with well train ed staff, wh o are cap able of en su rin g correct op eration of th e eq u ip m en t, th at it is p ossible to ach ieve a satisfactory retu rn on su ch a large cap ital in vestm en t. To h igh ligh t th e

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

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444

im p ortan ce of th e h u m an factor h ere, th is h as been in clu ded as a sep arate item in Table 6.2.1. Th e skill of th e p ress op erator is p aram ou n t in th e su ccessfu l op eration of th e p rodu ction system . He/ sh e takes th e in flu en cin g factors in to accou n t an d evalu ates th em . Tolerances Ach ievable ISO toleran ces for d ifferen t typ es of cold forgin g an d com p lem en tary p rocesses are su m m arized in Table 6.2.2. Th e “variation

Table 6.2.1: Classification of process parameters that affect the geometrical accuracy and surface quality of a forged part Line:

M achine

Automation

Heating Cooling Billet:

Starting material M aterial form M anufacturing process Pre-treatment

Process:

Processing sequence No. of steps Temperature Intermediate treatment Lubrication and cooling

kinematics, stiffness, off-center load capacity, gib precision, heating behavior (w arm), natural frequency w eight control, careful feed and discharge, positioning accuracy, transfer, press force control type, temperature, temperature control temperature control analysis, strength, microstructure w ire, bar, thick sheet; rolled, peeled or draw n shearing, saw ing, blanking possibly soft-annealing, pickling, phosphating, coating single-step, multiple-step, process combination hot (h), cold (c), w arm (w ) recrystallization, normalization (w arm), pickling, phosphating, coating additional lubrication, spraying, flooding (w arm), lubricant and coolant (w arm)

Clearance for part transport Die:

Precision

Wear Human element:

Die designer, die manufacturer, operating staff, training and instruction

die concept, details, production process, adjustment of upper and low er die, mechanical die deflection, thermal die expansion die material, surface, coating, change interval

specialized skills

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Benefits of solid forming

445

ran ge” of a forgin g p rocess in d icated h ere sh ou ld be in terp reted so th at sm aller, ligh ter-weigh t com p on en ts fall in gen eral to th e left-h an d sid e of th e bar (lower toleran ce field s) an d larger, h eavy-d u ty com p on en ts fall m ain ly to th e righ t-h an d sid e (wid er toleran ce field s). Th e red sectors are toleran ces wh ich can be ach ieved u n d er n orm al con d ition s. Th e oran ge areas are ISO toleran ces wh ich can be ach ieved in sp ecial cases bu t with larger effort an d cost. Th is in form ation also in d icates th at th e iron in g an d red u cin g p rocesses p erm it th e im p rovem en t of accu racy levels by as m u ch as two q u ality levels. Th e h igh d egree of d im en sion al accu racy is n ot ach ieved eq u ally for all th e d im en sion s of a com p on en t, bu t sh ou ld be restricted to d im en sion s th at are critical for fu n ction al or m aterial rem oval con sid eration s. Th e ach ievable d im en sion al toleran ces (n orm al, n arrow) for cold extru sion or th e p rocess com bin ation warm extru sion an d su bseq u en t cold sizin g are in d icated for th e th ree m ost freq u en t form in g p rocesses, solid forward extru sion , cu p backward extru sion an d iron in g (Tables 6.2.3 to 6.2.5). Th is in form ation is given relative to th e m ain d im en -

Table 6.2.2: ISO tolerances for the cold extrusion and complementary processes (VDI 3138)

ITspecification as per INI uality

form ingprocess 6

7

hot e trusion warme trusion warmcold e trusion cold e trusion ironing upsetting open die forward e trusion

achie able withspecial m easures achie able without special m easures

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

3

6

Solid forming (Forging)

446

Table 6.2.3: Diameter, length and deflection tolerance of solid forw ard extruded parts, in mm tolerances D up to mm

normal

25 50 75 100

0.10 0.15 0.20 0.25

narrow

L up to mm

normal

narrow

normal

narrow

0.02 0.08 0.15 0.18

150 200 300 450

0.25 0.75 1.50 2.00

0.20 0.50 1.00 1.50

0.15 0.25 0.35 0.50

0.03 0.05 0.07 0.10

diameter D

length

deflection B

Table 6.2.4: Diameter, concentricity, w all and w eb thickness tolerance of backw ard extruded cups, in mm tolerances D up to mm 25 50 75 100

diameter

run-out

normal

narrow

D

d

D

0.20 0.30 0.35 0.40

0.15 0.20 0.30 0.50

0.10 0.125 0.15 0.175

normal

narrow

0.25 0.30 0.35 0.40

0.10 0.15 0.20 0.25

d 0.03 0.035 0.04 0.06 tolerances

s, h up to mm

w all thickness s normal narrow

2 5 10 15

0.10 0.15 0.25 0.35

bottom thickness h normal narrow

0.075 0.10 0.15 0.25

0.25 0.35 0.45 0.55

0.15 0.20 0.30 0.40

Table 6.2.5: Diameter, concentricity, w all thickness tolerance in mm of tubular components produced by ironing

D up to mm 25 50 75 100

diameter normal D

d

0.15 0.25 0.30 0.35

0.10 0.20 0.25 0.30

tolerances run-out narrow normal narrow D d

0.075 0.10 0.125 0.15

0.025 0.03 0.35 0.45

0.25 0.30 0.035 0.045

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

0.10 0.15 0.20 0.25

s up to mm 1 2 4 6

w all thickness s normal narrow 0.075 0.075 0.10 0.10

0.035 0.04 0.05 0.07

Benefits of solid forming

447

sion s from Fig. 6.2.3. As alread y in d icated , closer toleran ces can be ach ieved as a resu lt of sp ecial m easu res su ch as cen terin g of u p p er an d lower d ies. Th e len gth toleran ces refer to th e sh ou ld er len gth s with in th e u p p er or lower d ie, n ot to th e overall len gth of th e workp iece (in clu d in g excess m aterial). Surface finish On n et sh ap e an d n ear n et sh ap e com p on en ts wh ich d o n ot n eed rem ach in in g, th e su rface rou gh n ess is an im p ortan t q u ality ch aracteristic. Th e con tact su rfaces of th e core of form ed claw p oles, for exam p le, m u st n ot exceed a su rface rou gh n ess of Rz = 10 mm , as oth erwise th e req u ired m agn etic flu x ch aracteristics can n ot be ach ieved . By th e sam e token , a sim ilar req u irem en t ap p lies to forged gears. Table 6.2.6 p rovid es a su m m ary of th e ach ievable su rface rou gh n ess p rop erties Rz an d Ra for d ifferen t form in g p rocesses. Th e oran ge areas are valu es wh ich are m easu red before, th e red areas are valu es wh ich are m easu red after rem oval of th e lu brican t layer. Gu id elin e valu es on th e p h osp h ate layer are Ra = 0.3 – 0.8 mm an d after rem oval ap p rox. Ra = 0.6 – 2.5 mm . Th e su rface q u ality is p ositively in flu en ced by a h igh sp ecific p ressu re, h igh relative velocities an d su rface q u ality p rior to forgin g. Form in g p rocesses with h igh sp ecific p ressu res an d relative velocities

D

s d L d B forw ard rod extrusion

h

D

backw ard cup extrusion

s

d D

ironing

Fig. 6.2.3 M ain dimensions in solid forw ard extrusion, backw ard cup extrusion and ironing process

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Solid forming (Forging)

448

Table 6.2.6: Surface qualities Rz / Ra achieved using different forging methods

form ingprocess 5 12 15 18 20 30 40 50 60 70 80 90 100

0,5 1

2

3

4

6

8 10 12 15 20 25 30

hot e trusion warme trusion warmcold e trusion cold e trusion ironing upsetting open die e trusion

before rem o al of the lubricant carrier layer after rem o al of the lubricant carrier layer

are op en d ie extru sion , iron in g an d solid forward extru sion . Th e su rface p rop erties are in flu en ced h ere by th e followin g factors: startin g m aterial: h ot rolled , san d blasted , p eeled , cold d rawn in terface: sh eared , sawn in term ed iate an n ealin g: scale free: u n d er in ert gas with scale: san d blasted , p ickled

Mechanical properties Th e h ard n ess, ten sile stren gth an d yield stren gth are in creased by p lastic flow. However, at th e sam e tim e th e valu es for n otch im p act stren gth , elon gation an d n eckin g are d ecreased . Dep en d in g on th e d egree of tru e strain , in th e case of steels with low an d m ed iu m carbon con ten t, ten sile stren gth can in crease by u p to 120 %, yield stren gth by between 100 an d 300 %, an d h ard n ess by between 60 an d 150 %.

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Benefits of solid forming

W h ere n o h eat treatm en t is carried ou t, th is effect can be u tilized in ord er to rep lace h igh -alloy steels by lower-alloy grad es. Du rin g th e d evelop m en t of th e p rocess p lan , it is p ossible with in certain lim its to ach ieve sp ecified stren gth valu es in certain section s of a com p on en t by su itable ch oice of th e billet d iam eter an d th e p rocess seq u en ce.

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6 Solid forming (Forging)

6.3 M aterials, billet production and surface treatment Materials u sed in solid form in g are m ain ly u n alloyed, low-alloy an d h igh -alloy carbon steels, n on -ferrou s ligh t an d h eavy alloys su ch as alu m in iu m , m agn esiu m , titan iu m an d cop p er an d th eir alloys (cf. Sect. 4.2.2). Sign ifican t factors in th e selection of m aterials are form ability (flow stress), th e p ath of th e flow cu rve (cf. Fig. 6.1.5), th e p erm issible flu ctu ation s in m aterial com p osition an d issu es related to billet p rep aration in clu din g p relim in ary (h eat treatm en t, coatin g) an d in term ediate treatm en t.

6.3.1 M aterials Steels Low-carbon an d low-alloy steels are particularly suited for cold form ing. With a carbon con ten t of up to 0.2 %, th e con dition s for form in g are very favorable, up to 0.3 % favorable an d up to 0.45 % difficult, wh ich results in low form ability, true strain an d h igh er press forces. Ph osph orus an d sulph ur con ten t sh ould rem ain below 0.035 %, as th ese com pon en ts ten d to reduce form ability. Th e con ten t of n itrogen is restricted to less th an 0.01 % for reason s of susceptibility to agein g. Pre-h eat-treated steels can be used for parts wh ich are sen sitive to warpin g (valve tappet rods) an d wh ose h igh stren gth (up to 1,100 N/m m 2 ) perm it on ly m in im al deform ation . In som e cases, m icro-alloyed steels con tain in g boron , wh ich perm it pen etration h arden in g, are replacin g alloyed steels with th e prescribed full h eat treatm en t. All steels wh ich can be cold form ed, can also be warm form ed. However, it sh ou ld be em ph asized th at even steels con tain in g a h igh er carbo n

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451

co n t en t , fo r exam p le fro m 0.45 t o 1.0 %, can be easily fo rm ed , i. e. with ou t costly in term ediate h eat treatm en t. In du ctive h arden in g steels su ch as Cf 53, Cf 60 an d th e ball bearin g steels 100 Cr 6 are classical exam p les of ap p lication for warm form in g. For p ractice-orien ted calcu lation of force an d en ergy req u irem en ts, a good ap p roxim ation for th e flow stress cu rve for h ot forgin g can be obtain ed by m u ltip lyin g th e cold forgin g flow cu rve valu es with a factor of 0.3 to 0.5. Figure 6.3.1 in dicates th e tem p eratu re-dep en den t variation of th e flow stress cu rves for Ck 15 an d Cf 53. Table 6.3.1 p rovid es a su m m ary of th e m ost im p ortan t steel m aterial grou p s. It lists n ot on ly th e DIN an d Eu rostan d ard d esign ation s bu t also th e abbreviation s for sim ilar m aterials in accord an ce with th e Am erican AISI an d A.S.T.M stan d ard s as well as with th e Jap an ese JIS stan d ard . Th e last colu m n p rovid es in form ation on wh eth er th e steel is su itable for h ot form in g (H), warm form in g (W ) or cold form in g (C). For m ore in form ation on workp iece m aterials, p lease refer to DIN worksh eets 17 006, 17 100, 17 200, 17 210, 17 240, 17 440. Flow stress cu rves for cold form in g are given in th e VDI Gu id elin es 3134, 3200 sh eet 2 (ferrou s m etals) an d sh eet 3 (n on -ferrou s m etals).

material f 3

material k

flow stress kf [N mm ]

=

=

-

s

-

s

° °

°

6

6 °

° 6 °

7 ° 7 °

°

°

0,2

0,4

0,6

0,8

1,0

0,2

Fig. 6.3.1 Temperature-dependent flow curves Ck 15 and Cf 53

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

0,4

0,6

0,8

true strain

1,0

[-]

Solid forming (Forging)

452

Table 6.3.1: Selection of steels for solid forming M aterial group

No.

DIN 1654

Eurostandard

American standard AISI A.S.T.M .

general structural steel

1.0303 1.0213 1.0204 1.0160 1.0224 1.0538

QSt 32-3 QSt 34-3 UQSt 36 UPSt37-2 UQSt-38 PSt50-2

C4C C7C C11G1C

Armco

1.0301 1.1121 1.1122 1.0401 1.1141 1.1142 1.5919 1.7016 1.7131 1.7321

C10 Ck10 Cq10 C15 Ck15 Cq15 15CrNi6 17Cr3 16M nCr5 20M oCr4

1.6523 1.1151 1.1152 1.0501 1.1181 1.1172 1.0503 1.1191 1.1192 1.1193 1.1213 –

21NiCrM o2 Ck22 Cq22 C35 Ck35 Cq35 C45 Ck45 Cq45 Cf45 Cf53 Cf60

1.5508 1.5510 1.5511 1.5523 1.7076 1.7033 1.7035 1.7218 1.7220 1.7225 1.6582

22B2 28B2 35B2 19M nB4 32CrB4 34Cr4 41Cr4 25CrM o4 34CrM o4 42CrM o4 34CrNiM o6

1.4016 1.4006 1.4024 1.4303 1.4567

X6Cr17 X10Cr13 X15Cr13 X5CrNi18-12 X3CrNiCu18-9

1.3505

100Cr6

case-hardening steels

heat-treatable steels

alloyed heat-treatable steels

stainless steels

roller bearing steel

SS34

C14G1C

C10 C10E C10C C15 C15E C15C

Japanese standard JIS

SS41

C1008 C1010 C1010 C1015 C1015

S10C S 9CK S 9CK S15C S15CK S15Ck

SCr22

C22E C22C

C1020 C1020

C35E C35C

C1035

C45E C45C C45G C53G C60G

C1045

5130/ -40 5130/ -40 4120/ 32 4135 4140/ -42

S20C S30C S35K S35K S40C S45C

SCr1 SCr4 SCM 3 SCM 4

Suitable for cold (C), w arm (W) and hot (H) forming C C C H C H W, H C, W, H C, H W, H C, W, H C C C C, W, H C C C C W, H C, W C, W, H W, H C, W, H C W W W C C C C C C, W, H C, W, H C, W, H C, W, H C, W, H C, H C, ferritic C, martensitic C, H, austenitic C, austenitic C, austenitic

X10Cr13 X15Cr13 X4CrNi18-12 X3CrNiCu18-9-4 52100

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

SUJ1/ 2

C, W

M aterials, billet production and surface treatment

453

Alum inium alloys Wrou gh t alu m in iu m m aterials wh ich h ave been m an u factu red by form in g, n ot castin g, are u sed for form in g processes. Alu m in iu m with a fin egrain ed m icrostru ctu re offers a n u m ber of advan tages over coarsergrain ed alu m in iu m : Im proved form ability, su perior su rface qu ality of com pon en ts an d greater stren gth . Ultra-pu re an d pu re alu m in iu m (Table 6.3.2) perm it an extru sion ratio (cross-section al redu ction ) of u p to 95 % (tu be produ ction ). With an in creasin g m agn esiu m con ten t, it is possible to set h igh er stren gth ch aracteristics. Age-h arden able, corrosion -resistan t alu m in iu m alloys su ch as A1MgSi1 exh ibit h igh stren gth ch aracteristics as a resu lt of h eat agein g wh ich exceed th e valu es ach ieved wh en in a strain -h arden ed state. Flow cu rves for alu m in iu m m aterials are also given in th e VDI directives 3134 an d 3200.

Table 6.3.2: Selection of aluminium materials for cold and hot extrusion M aterial group

No.

DIN 1712/ 25/ 45

ISO

AA

JIS

pure/ ultra-pure aluminium

3.0285 3.0275 3.0255

Al 99,8 Al 99,7 Al 99,5

Al 99,8 Al 99,7 Al 99,5

1080A 1070A 1050A

A1080 A1070 A1050

non age-hardenable alloys

3.0515 3.3315 3.3535 3.3555

Al M n1 Al M g1 Al M g3 Al M g5

AlM n1 AlM g1 AlM g2,5 AlM g5

3103 5005A 5754 5056A

A3003

hardenable alloys

3.3206 3.2315 3.1325 3.4365

Al M g Si 0,5 AlM gSi 1 AlCuM g 1 AlZnM gCu 1,5

6060 (6063) 6082 (6061) 2017A 7075

A6063 A6082 A2017 A7075

Copper alloys Like alu m in iu m , cop p er an d its alloys offer ou tstan din g extru sion cap ability. Th e yield stress in creases with in creasin g alloyin g elem en ts, wh ereby form in g sh ou ld take p lace wh ile th e m aterial is in a softan n ealed state. In th e case of tech n ically p u re cop p er, m ain ly E-Cu an d SE-Cu are u sed, for exam p le, in th e p rodu ction of term in als. Am on g th e variety of differen t bron zes u sed, th e tin bron ze with 1 to 2 % Sn an d silicon bron ze is m ost widely form ed. If alloy elem en ts su ch as ch rom e, zircon iu m , beryliu m or silicon (Cu Ni2Si) are p resen t, m an y cop p er m ateri-

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Solid forming (Forging)

454

Table 6.3.3: Selection of copper materials for cold extrusion M aterial group

Abbreviation

No.

DIN

US designation / UNS

JIS

pure copper

E-Cu F20 SF-Cu

2.0060 2.0090

1787 1787

ETP 99,95 C0-0,04O / C11000 DHP Copper / C12200

OFCu DCu

copper alloys

CuZn10 CuZn28 CuZn40 CuNi2Si CuNi12Zn24 CuNi20Fe CuAl11Ni CuSn2

2.0230.10 2.0261.10 2.0360 2.0855 2.0730.10 2.0878.10 2.0978 2.1010

17660 17660 17660 17666 17663 17664 17665 17662

Commercial copper / C22000 Cartridge brass 70 % / C26000 M untz M etal / C28000 Silicon bronze / C64700 65Ni-12Ag / C75700 Cu-20Ni / C71000 Aluminium bronze / C63200 Phosphor bronze / C50500

BS( ), RBS ( ) RBS ( ) RBS ( ) CN ( ) 1

als are age-h arden able th rou gh h eat treatm en t. Th e m ost im portan t copper alloys are th e brass fam ily. Th e form ability of th e m aterial im proves as th e copper con ten t in creases an d th e Zn con ten t decreases. With a Zn con ten t above 36 %, th e m aterials becom e brittle an d th eir cold form ability decreases rapidly. As a resu lt, h ot form in g m eth ods sh ou ld preferably be u sed. Flow stress cu rves for copper alloys are given in th e VDI Gu idelin es 3134 an d 3200. Oth er m aterials su ch as lead , zin c, tin , titan iu m or zircon iu m an d th eir alloys can also be su ccessfu lly form ed . However, in term s of q u an tity an d econ om ic sign ifican ce, th ese p lay on ly a m in or role.

6.3.2 Billet or slug preparation Th e workp iece m aterials are sp ecified by th e u ser: An y m od ification s to th e m aterial, to exp loit th e ben efits offered by cold form in g (h ard en in g) or to sim p lify th e form in g p rocess, m u st be agreed u p on with th e d ie m aker an d th e p rod u ction en gin eer. In ad d ition to th e workp iece m aterial itself, th e n atu re of th e sem i-fin ish ed p rod u ct, its sep aration to p rep are in d ivid u al billets, an d th e h eat an d su rface treatm en t are all im p ortan t p oin ts for con sid eration . Sem i-finished products Wires, bars an d tu bes are u sed as sem i-fin ish ed p rod u cts for th e p rod u ction of billets or slu g. Wire is d elivered in coil form an d gen erally

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

M aterials, billet production and surface treatment

ran ges from 5 to 40 m m in diam eter. Wire diam eters of u p to 50 m m are processed in in dividu al cases, alth ou gh th e h an dlin g capability of th e wire bu n dle becom es in creasin gly difficu lt as th e coils in crease in weigh t. Low-cost rolled wire in accord an ce with DIN 59 110 an d 59 115 h as a wid e d iam eter toleran ce an d a rou gh su rface fin ish . It th erefore req u ires p relim in ary d rawin g on a wire breakd own m ach in e. Th e red u ction in cross section sh ou ld be between 5 an d 8 %. Th e wire m u st be an n ealed , d e-scaled an d p h osp h ated . Drawn wire after DIN 668 K (K = cold d rawn ) is u sed to p rod u ce p arts with a lower tru e strain (sm all red u ction in area), as th e m aterial h as alread y u n d ergon e a certain d egree of p relim in ary strain h ard en in g d u rin g th e d rawin g p rocess. Th is m aterial also h as to be d escaled , p h osp h ated an d p ossibly also lu bricated (stearate d rawn ). W h en a h igh er d egree of tru e strain is in volved (e. g. cu p backward extru sion ), after p relim in ary d rawin g, an n ealin g (G) or sp h eroid ized an n ealin g (GKZ) m u st be p erform ed in ord er to restore th e origin al m aterial form ability. Th e form of d elivery is sp ecified with th e d esign ation s K+G or K+GKZ. Ligh t oilin g h elp s p reven t ru st form ation on th e wire. In th e case of h igh alloy steel q u alities, a fu rth er fin ish d rawin g p rocess takes p lace after an n ealin g with cross section red u ction s of less th an 6 %. Th e form of d elivery is th en sp ecified as K+G+K or K+GKZ+K. In p ractice, bar stock can also be u sed econ om ically in th e larger d iam eter ran ges. With d iam eters of u p to 70 m m , bars of between 6 an d 12 m in len gth are p rod u ced . Hot-rolled rou n d steel to DIN 1013 an d DIN 59130 is th e m ost favorable selection in term s of cost. Th e allowable d iam eter toleran ces can n ot be red u ced by d rawin g, lead in g to volu m e variation s. Th ese m u st be fu lly com p en sated for by excess m aterial d u rin g th e form in g p rocess. For a com p on en t weigh in g arou n d 1.3 kg with a d iam eter of 46 m m , a weigh t toleran ce of 88 g (average d eviation ) or 45 g (p recision d eviation ) m u st be in tegrated in to th e d ie if th e ad m issible toleran ces are fu lly u tilized . Th e tran sform ation clearan ce in th e first stage h as to take accou n t both , th e d iam eter toleran ce an d also th e ovality of th e billet cau sed by th e sh earin g p rocess. For a m aterial with a d iam eter of 46 m m , th e first tran sform ation clearan ce will be ap p rox. 2.5 m m . W h ere rou n d steel is bein g cold forged , th e d escalin g, p h osp h atizin g an d lu bricatin g op eration s take p lace p rior to forgin g. In th e case of warm forgin g, th e billets are fed d irectly to th e h eatin g lin e.

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455

Solid forming (Forging)

456

Brigh t rou n d steel after DIN 970 an d 971 is drawn or p eeled followin g h ot rollin g, to toleran ces h 9/ h 11. Th e weigh t toleran ce for th e above given exam p le is redu ced to 5 an d 9 g resp ectively, wh ich , in clu din g an adm issible len gth toleran ce of 0.2 m m , corresp on ds to th e cu stom ary weigh t toleran ce of between 0.5 an d 1 %. By weigh in g th e billets an d adju stin g th e cu t-off len gth , it is p ossible to ach ieve weigh t toleran ces of < + 1%. Peelin g of h ot-rolled bar allows th e elim in ation of su rface in clu sion s an d seam s as well as an y su rface decarbu rization . Table 6.3.4 gives th e diam eter toleran ces for differen t rou n d m aterials. Altern atively to bar m aterial, tu bu lar or rin g-sh ap ed form ed p arts can also be p rod u ced u sin g tu be section s as billets or p reform s. Criteria to be con sid ered h ere in clu d e wall th ickn ess toleran ce, con cen tricity an d econ om y in com p arison to p rod u cin g th ese p reform s from sh eared billets th rou gh u p settin g, backward cu p extru sion , p iercin g, iron in g an d by u sin g variou s in term ed iate h eat treatm en ts. W h ere h eigh t-to-d iam eter ratios are h / d # 0.2, p rod u ction u sin g sh eared billets or blan ks cu t ou t of h ot-rolled coil stock (DIN 1016), flat steel (DIN 1017), th icker sh eet m etal (DIN 1542/ 1543) is ben eficial. Th is is th e case p articu larly wh en irregu lar startin g sh ap es (p reform s) are req u ired . W h en p rocessin g wire, it is u sefu l to h ave th e p relim in ary treatm en t p erform ed by th e sem i-fin ish ed p rod u ct su p p lier, as a large in vestm en t is req u ired for th is typ e of eq u ip m en t an d th e sp ectru m of req u ired treatm en t typ es varies greatly.

Table 6.3.4: Diameter tolerances for round materials w ith selected diameters in mm Diameter approx. in mm

15 20 25 30 35 40 45 50 80

Tolerances DIN 668 DIN 970/ 971 h9/ h11

– 0.04 / – 0.05 / – 0.05 / – 0.05 / – 0.06 / – 0.06 / – 0.06 / – 0.075 / – 0.09 /

– – – – – – – – –

DIN 59110/ 59115 DIN 59130 DIN 1013 Usual deviation

0.10 0.13 0.13 0.13 0.16 0.16 0.16 0.19 0.19

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

+/ – +/ – +/ – +/ – +/ – +/ – +/ – +/ – +/ –

0.5 0.5 0.6 0.6 0.8 0.8 0.8 1.0 1.3

DIN 1013 Precision deviation

+/ – 0.20 +/ – 0.20 +/ – 0.25 +/ – 0.25 +/ – 0.30 +/ – 0.35 +/ – 0.40 (+/ – 0.50) (+/ – 0.60)

M aterials, billet production and surface treatment

457

W h en u sin g bar an d flat m aterial, th e billets are gen erally sh eared by th e forger an d su bjected to h eat an d su rface treatm en t. Strain -h ard en in g effects wh ich occu r p artially at th e flat su rfaces of th e billet d u e to th e sh earin g p rocess are th u s elim in ated p rior to forgin g. Billet separation Th e m ost com m on ly u sed billet sep aration p rocess is sh earin g. Slicin g on th e trim m in g lath e is u sed on ly rarely, for exam p le for test p u rp oses. Blan kin g an d fin e blan kin g are exp lain ed in Sects. 4.5 an d 4.7. Sh earin g is ch aracterized by p ractically loss-free sep aration at an extrem ely h igh level of ou tp u t, in term s of q u an tity. Th e sh ear blad e p lastically d eform s th e m aterial u n til its d eform ation lim it in th e sh earin g zon e h as been exh au sted , sh earin g cracks ap p ear an d fractu re occu rs. With all fou r sh earin g p rin cip les – with ou t bar an d cu t-off h old er, with bar h old er, with bar an d cu t-off h old er an d with axial p ressu re ap p lication – p lastic flow lateral to th e sh earin g d irection is in creasin gly p reven ted , wh ile com p ressive stress in creases d u rin g th e sh earin g op eration . Both ten d en cies exercise a p ositive in flu en ce over th e geom etry (ovality, toleran ce) of th e sh eared su rface. Th e m ost accu rate billets are p rod u ced u sin g th e sh earin g p rin cip le with bar an d cu t-off h old er. For cold forgin g, th e sh eared billets sh ou ld h ave th e greatest p ossible rectan gu larity, volu m e con trol an d little p lastic d eform ation . Th e sh eared su rfaces sh ou ld be free of sh earin g d efects an d exh ibit on ly a m od erate am ou n t of strain -h ard en in g. Th e ap p earan ce of th e sh eared su rfaces is th e resu lt of in teraction s between workp iece ch aracteristics, tool, m ach in e an d friction . Th e sh earin g clearan ce exercises a m ajor in flu en ce h ere. Th e greater th e stren gth of th e steel, th e sm aller is th e sh earin g clearan ce (cf. Fig. 4.5.12). However, alu m in iu m an d lead always req u ire a sm all blan kin g clearan ce. Th e followin g valu es m ay be taken as a gu id elin e for th e sh earin g clearan ce of steel: soft steel typ es (of th e startin g m aterial d iam eter in m m ) h ard steel typ es brittle steel typ es

5 – 10 % 3–5% 1–3%

Rou gh fractu red su rfaces, tears an d seam s in d icate an excessively wid e sh earin g tool clearan ce. Cross fractu red su rfaces an d m aterial ton gu es

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Solid forming (Forging)

458

in d icate an in su fficien t tool clearan ce. With in creasin g sh earin g velocity, th e d eform ation zon e red u ces, th e h ard n ess d istribu tion becom es m ore u n iform an d th e h ard n ess in crease in th e sh eared su rface becom es less p ron ou n ced , i. e. th e m aterial ch aracteristics becom e m ore “brittle” (excep tion : au sten itic ch rom e-n ickel an d ch rom e-m an gan ese steels). Op en sh ears an d closed sh earin g gu id es are u sed as tools (Fig. 6.3.2). Sh earin g gu id es p rod u ce very h igh q u ality blan ks, bu t in volve a n u m ber of d rawbacks: Sh eared billets are m ore d ifficu lt to eject, stop s h ave to be u sed an d d em an d s on th e d iam eter toleran ce of th e startin g m aterial are m ore strin gen t. For rou n d m aterials, th e relative sh earin g clearan ce for each billet th ickn ess to be sh eared can be kep t con stan t by grin d in g an ellip tical relief cu t on th e gu id es. Th e p arts sh eared in th is way d em on strate im p roved an gu larity an d red u ced bu rr form ation at th e ed ge of th e fractu red su rface. Moreover, th e sh eared billet q u ality is less d ep en d en t on variation s in m aterial p rop erties, wh ich in tu rn red u ces variation s in volu m e. Th e sh earin g force FS an d sh earin g work W S can be calcu lated ap p roxim ately wh en sep eratin g rou n d m aterial with th e d iam eter d u sin g th e followin g form u la: FS = AS · k S

W S = x · FS · s ,

wh ereby AS is th e section al su rface to be sh eared , k S th e sh earin g resistan ce of th e billet m aterial an d s ap p rox. 20 % (h ard , brittle m aterials) to 40 % (soft, ten aciou s m aterials) of th e sh earin g stroke, i. e. th e d iam eter d . Th e correction factor x in d icates th e exten t to wh ich th e in crease in force d eviates from a rectan gu lar force-stroke cu rve. In gen eral, x is taken to be between 0.4 an d 0.7. Th e sh earin g resistan ce k S am ou n ts to ap p roxim ately 0.7 to 0.8 · Rm . Heat treatm ent of steel Soft-an n ealin g (sp h eroid ized an n ealin g) p lays a p articu larly im p ortan t role in th e h eat treatm en t of steel m aterials u sed for billet p rod u ction . Recrystallization an n ealin g, n orm alization an d u n d er certain circu m stan ces also recovery an n ealin g are typ ical h eat treatm en ts u sed for in term ed iate an n ealin g of alread y form ed workp ieces wh ose form ability h as been exh au sted .

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M aterials, billet production and surface treatment flank surface

pressure surface

elliptical relief grind

cutting edge

w edge angle

pressure surface

shearing clearance

459

cutting edge

w edge angle

shearing clearance

depth of relief grind

Fig. 6.3.2 Open and closed shearing knives and a closed shearing knife ground w ith elliptical relief

Th e soft annealing p rocess sp h eroid izes an y existin g h ard er flaky elem en ts of th e m icrostru ctu re. W h ile th e h ard n ess is retain ed , th e flow stress (cf. Sect. 2.2.3) of th e m aterial is red u ced . Recrystallization annealing is ad van tageou s for au sten itic steels with a low carbon con ten t, as with th is h eat treatm en t th e lowest flow stress levels are obtain ed . However, if coarse grain occu rs as a resu lt of locally low levels of tru e strain or d eform ation (cf. Sect. 2.2.2) d u rin g recrystallization an n ealin g, an d if th is typ e of coarse grain is n ot p erm issible, a n orm alization p rocess sh ou ld be carried ou t. As a resu lt of two-fold recrystallization (perlite + ferrite au sten ite) an even , fin e-grain ed an d fin e-lam ellar perlite m icrostru ctu re is ach ieved th rou gh norm alization. Th is can be re-an n ealed if requ ired to create grain ed perlite (soft-an n ealin g). A m arked differen ce in m icrostru ctu re (coarse an d fin e grain s) can also resu lt du rin g warm form in g as a resu lt of locally differin g coolin g con dition s an d degrees of tru e strain . Th ese differen ces can cau se cracks du rin g su bsequ en t cold sizin g operation s (redu cin g, iron in g). Th is problem can be avoided by n orm al an n ealin g. Recovery annealing offers a low-cost altern ative to recrystallization or soft an n ealin g, p rovid ed th e d eform ation in th e su bseq u en t form in g op eration is m in im al, i. e. th e level of tru e strain is n ot too large.

6.3.3 Surface treatment A d ifferen ce is d rawn between abrad in g an d d ep ositin g su rface treatm en ts. Abrad in g p rocesses in clu d e ch em ical an d m ech an ical clean in g

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Solid forming (Forging)

460

m eth od s, d egreasin g an d d escalin g. Dep ositin g p rocesses in clu d e p h osp h atin g, soap in g, m olycotin g an d th e u se of oils. Th e p h osp h ate layer serves as a carrier layer wh ich facilitates th e ad h eren ce of lu brican ts to th e su rface. Soap in g is u sed for sim p ler form in g op eration s, m olycotin g for extrem ely h igh d egrees of d eform ation (cf. Sect. 2.2.2) an d for p arts su ch as gears. In th e case of h orizon tal m u lti-station p resses op eratin g with wire, oil is u sed for lu brication an d coolin g. In vertical m u ltistation p resses, oil is u sed as a su p p lem en tary lu brican t in ad d ition to soap / m olycote (sp ray or flood ap p lication ) (cf. Sect. 6.8). Cleaning, degreasing and descaling Ch em ical clean in g an d degreasin g processes are perform ed eith er th rough im m ersion or sprayin g of solven ts, or th rough th e con den sation of solven t vapor on th e workpieces. Solven t types used in clude organ ic solven ts (h ydrocarbon s, petroleum eth er, petroleum ), ch lorin ated h ydrocarbon s (trich loroeth ylen e an d perch loroeth ylen e), an d water-soluble clean in g agen ts such as acids, acid salin e solution s an d alkalin e solution s. Th e m ech an ical m eth ods used in clude san d blastin g or tum blin g usin g lim e, san d, steel sh ot an d oth er m aterials. Th e ch oice of clean in g m eth ods an d agen ts depen ds on th e type an d exten t of th e con tam in ation , th e required degree of purity an d th e type, sh ape an d quan tity of th e item s to be clean ed. En viron m en tally frien dly water-soluble clean in g agen ts are frequen tly used. Ch em ical descalin g (picklin g) is perform ed u sin g picklin g bath s con tain in g su lph u ric acid or h ydroch loric acid solu tion s. Th e picklin g agen ts serve to release h ydrogen on th e su bstrate m etal, cau sin g th e oxide layers to split away. As th e absorption of h ydrogen in th e su bstrate m etal leads to em brittlem en t, as sh ort a picklin g tim e as possible sh ou ld be u sed. Crack form ation du rin g forgin g can , for exam ple, be th e resu lt of excessive picklin g treatm en t. San d blastin g an d tu m blin g are u sed for th e m ech an ical rem oval of th ick scale layers. Here, th e brittle scale layer is parted off from th e tou gh su bstrate m aterial th rou gh partial application of force. Phosphating Ph osp h atin g is taken to m ean th e gen eration of coh esive crystallin e p h osp h ate layers wh ich are firm ly ad h ered to th e su bstrate m aterial. For cold form in g p rocesses, m ain ly zin c p h osp h ate an d in som e cases

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M aterials, billet production and surface treatment

iron p h osp h ate layers are u sed. Ph osp h oric acid, zin c p h osp h ate an d oxidizin g agen ts are ap p lied in an aq u eou s solu tion . On im m ersion in th e solu tion , th e m etal su rface is p ickled by th e p h osp h oric acid, du rin g wh ich p rocess in solu ble zin c su lp h ate is sim u ltan eou sly p recip itated. Th e ch em ical reaction does n ot com e to a stan dstill u n til th e com p lete su rface is coated with zin c p h osp h ate crystals. Th e oxidizin g agen t tran sform s th e dissolved m etal to a p h osp h ate with low solu bility wh ich is p recip itated in th e form of slu dge an d h as to be rem oved p eriodically. In p ractice, p h osp h ate layers with a m ean th ickn ess of arou n d 8 to 15 m m are ap p lied , wh ich leave beh in d a sh in y coatin g after form in g. Th e p h osp h ate layer can resist tem p eratu res u p to 200 °C. Over 200 °C, a p artial tran sform ation takes p lace. At over 450 °C, com p lete d ecom p osition of th e p h osp h ate layer takes p lace. Dep en d in g on th e lu brican t u sed , h owever, workin g tem p eratu res of u p to 300 °C can be realized d u rin g forgin g. Soaping and m olycoting Soapin g takes place by im m ersion of th e parts in an alkalin e soap solu tion . Th e m ain com pon en t of th ese solu tion s is sodiu m stearate. A part of th e zin c ph osph ate layer reacts with th e sodiu m soap to form a waterin solu ble zin c soap layer. Th e zin c soap is addition ally coated with th e sodiu m soap. Th is com bin ation of layers h as a very low sh ear stren gth an d th u s redu ces th e effective coefficien ts of friction (cf. Sect. 4.2.3). Soapin g sh ou ld n ot take lon ger th an 5 m in , as oth erwise th e en tire ph osph ate layer will be u sed u p an d n o lon ger provide an adh esive su bstrate. To m ake su re th at th e soap coatin g offers good lu brication p rop erties it is n ecessary to d ry th e coated billets com p letely. A waitin g p eriod of on e d ay p reviou s to p rocessin g of th e treated blan ks is u su ally recom m en d ed . Th e soap s are tem p eratu re-resistan t to ap p rox. 250 °C, above wh ich ch em ical tran sform ation p rocesses take p lace. Excessive soap in g resu lts in soap d ep osits bu ild in g u p on th e d ies. Molybd en u m d isu lp h id e is u sed u n d er d ifficu lt form in g con d ition s. Com p ared to soap lu brican ts, m olybd en u m d isu lp h id e cau ses greater friction losses wh ich m ean th at larger p ress an d ejector forces h ave to be taken in to con sid eration . However, it is cap able of with stan d in g far greater levels of stress, i. e. th e lu brican t film on ly breaks away u n d er extrem ely h igh d egrees of su rface p ressu re, an d p erm its con sid erable su rface exp an sion of th e workp iece. Th erefore, m olybd en u m d isu l-

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p h id e is u sed wh en large d eform ation s, i. e. large tru e strain s, are p resen t. In ad d ition , m olybd en u m d isu lp h id e creates fewer p roblem s as regard s th e accu m u lation of su rp lu s lu brican t in th e d ies. Th e u p p er ap p lication tem p eratu re lim it is arou n d 350 °C. At h igh er tem p eratu res, m olybd en u m trisu lp h id e is created , wh ich is in effective as a lu brican t. Molybd en u m d isu lp h id e is also ap p lied in an im m ersion bath , an d in som e cases sp rayed or ap p lied by tu m blin g. Th e coated billets sh ou ld be stored for on e d ay p rior to p rocessin g. A storage p eriod of on e week sh ou ld n ot be exceed ed . As a rou gh gu id elin e, th e overall seq u en ce of su rface treatm en t with th e resp ective fu n ction s of d ifferen t bath s, bath com p osition , tim es an d tem p eratu res is su m m arized below: 1. Degreasin g:

Ch em ical d egreasin g in a 5 % sod iu m h yd roxid e solu tion at 80 to 95 °C for arou n d 5 to 10 m in .

2. Cold rin sin g:

Rem oval of sodiu m solu tion residu es, cold rin sin g in ru n n in g water for ap p rox. 2 m in (water su rface m u st always be clean ).

3. Picklin g:

Picklin g in 12 % su lp h u ric acid or 18 % h yd roch loric acid at ap p rox. 50 to 65 °C, d u ration ap p rox. 10 to 18 m in (acid con ten t is correct if th e p ickle effervesces).

4. Cold rin sin g:

Rem oval of acid resid u es, cold risin g in ru n n in g water for ap p rox. 2 m in .

5. Hot rin sin g:

Hot rin sin g to p re-h eat th e p arts – in flu en ces th e p h osp h ate layer th ickn ess, 70 – 90 °C, for arou n d 2 to 3 m in (at lower tem p eratu res, a lower layer th ickn ess resu lts).

6. Ph osp h atin g:

Main ly u sin g zin c p h osp h ate, for ru stp roof steels with iron oxolate, 70 to 80 °C for arou n d 8 to 10 m in (p h osp h atin g com p rises an in itial p icklin g reaction an d a su bseq u en t layer form in g reaction , layer th ickn ess ap p rox. 8 to 15 m m ).

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

M aterials, billet production and surface treatment

7. Cold rin sin g:

Cold rin sin g in ru n n in g water for ap p rox. 2 m in .

8. Hot rin sin g:

Hot rin sin g to p re-h eat th e p arts at arou n d 60 °C, du ration ap p rox. 3 m in .

9. Soap in g:

Soap in g at 60 to 85 °C for ap p rox. 5 m in (lower tem p eratu res resu lt in a th icker, lower tem p eratu res in a th in n er layer).

10. Dryin g:

Dryin g with h ot air at ap p rox. 120 °C for ap p rox. 10 m in .

In th e case of n on -ferrou s m etals, it is n ot n ecessary to u se lu brican t carryin g layers. Clean in g an d lu brication is all th at is req u ired . In th e case of cop p er, wh ere low d egrees of d eform ation are req u ired , lu brication can be elim in ated altogeth er. Oil as a lubricant W h ile soap in g an d m olycotin g p rocesses are m ain ly u sed with billets, in m u lti-station p resses, wh en forgin g from wire, m in eral-based oils with ad d itives (EP ad d itives) are gen erally u sed to im p rove lu brication p rop erties. Th e oil also ad h eres better to th e rou gh p h osp h ate layer. With th is typ e of p rod u ction , th e lu brication of th e flat face su rfaces p resen ts a p roblem becau se th ese are n ot coated with a p h osp h ate layer d u e to th e sh earin g p rocess. Th e oil is sp rayed or flood ed in to th e d ies or on to th e workp ieces.

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6 Solid forming (Forging)

6.4 Formed part and process plan Before p rodu cin g a p art by form in g, p rocesses (cold, warm , h ot), p rocess com bin ation s, p rocessin g step s, p relim in ary treatm en t, p rocess p lan an d in term ediate treatm en t stages m u st all be defin ed. In addition , th e force an d en ergy req u irem en ts, as well as relevan t die stress levels h ave to be com p u ted. On ly on th e basis of th ese calcu lation s it is p ossible to defin e th e p ress con figu ration con cern in g fu n ction al ch aracteristics su ch as p ress force, n u m ber of station s, distan ce between station s, strokin g rate, len gth of slide stroke an d au tom ation related q u estion s. In solid form in g ap p lication s, p rocessin g freq u en tly takes p lace at th e lim its of p h ysical feasibility for econ om ical reason s. Th is ap p lies for exam p le regard in g th e lim its of m aterial form ability (crack form ation , strain h ard en in g), th e load cap ability of d ies (in tern al p ressu res of u p to 3,000 N/ m m 2 ) an d lu brication / coolin g (cold weld in g). For th is reason , th e econ om ical ap p lication of solid form in g d ep en d s to a large d egree on th e exp erien ce of th e d esign er an d th e d ie m aker. With an efficien t com bin ation of su itable fin ite elem en t p rogram s for p rocess sim u lation an d existin g factory floor exp erien ce, in m etal form in g p lan ts a balan ced relation sh ip can be said to exist between th eory an d p ractice.

6.4.1 The formed part Lot size and m aterials Solid form in g rep resen ts a com p etitive su bstitu te for m ach in in g p rocesses an d in som e cases also for castin g p rocesses (cf. Sects. 2.1.1 an d 6.2.1). Th e h igh d evelop m en t costs an d th e d egree of in vestm en t

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req u ired for p resses an d d ies m ean th at certain m in im u m p rod u ction q u an tities are n ecessary. On th e oth er h an d , becau se of in creasin g raw m aterial an d en ergy costs, th e h igh d egree of m aterial u tilization p ossible u sin g solid form in g is exp an d in g th e lim its of econ om ic viability con tin u ou sly toward s sm aller batch sizes. Even for com p lex p arts, th is ten d en cy m ean s th at batch es as sm all as 10,000 p arts p er year can still be econ om ically p rod u ced . A precise feasibility stu dy is on ly possible by con siderin g th e in dividu al part con cern ed an d by m akin g cost com parison s with m ach in in g processes. Neverth eless, th e an n u al produ ction lot sizes listed in Table 6.4.1 can be con sidered as th e m in im u m econ om ically viable batch sizes with respect to part weigh t. Design rules W h en d esign in g a form ed p art, th ere are two areas of con sid eration : a) geom etrical asp ects of th e fin ish ed p art an d b) th e lim itation s of th e in d ivid u al p rocessin g op eration s u tilized in th e total p rocess seq u en ce. On th e basis of th e fin ish ed (assem bly read y) p art geom etry, first of all a cold or warm forged p art is d evelop ed , takin g in to accou n t th e followin g geom etrical asp ects: – m ach in in g allowan ces; – rotation ally sym m etrical geom etries are very well, axially sym m etrical geom etries well su ited for cold an d warm form in g; – wall th ickn esses can be p ressed n o lower th an 1 m m for steel, n o lower th an 0.1 m m for alu m in iu m ; – d raft an gles, u sed in h ot forgin g, are gen erally n ot req u ired for cold an d warm forged p arts (in sid e, ou tsid e); – sm all h oles with len gth to d iam eter ratios l/ d > 1.5 can n ot be econ om ically p rod u ced ; Table 6.4.1: M inimum economical batch sizes for solid forming w hen compared w ith machining Weight 0.10 – 0.25 kg 0.25 – 0.75 kg 0.75 – 2.50 kg

Production quantity per year Cold forming Warm forming 200,000 150,000 25,000

300,000 200,000 100,000

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– sm all variation s in d iam eter on th e in sid e an d ou tsid e su rface of th e form ed com p on en ts sh ou ld be avoid ed ; – m aterial overflow m u st be p rovid ed for, d u e to flu ctu ation s in billet weigh t (e. g. d u rin g forward rod extru sion in th e rod len gth , d u rin g backward cu p extru sion in th e cu p h eigh t); – tran sition rad ii m u st be con figu red as large as p ossible; sh arp ed ges can on ly be p ressed by u sin g sp lit d ies; – u n d ercu ts can be p rod u ced , bu t in crease toolin g costs; – it is gen erally n ot p ossible to p ress p lu n ge cu ts, p arallel key grooves, tran sverse bores etc.; – slip-on gearin g can be produced by pressin g, h igh -precision in volute gearin g (run n in g gears) can be produced with in creased die an d process developm en t effort. Th e p rocess en gin eerin g factors d ep en d on th e extru sion tech n iq u e, th e selected p rocessin g step s, th e workp iece m aterial, th e p erm issible d ie load in g an d th e resp ective tri-axial stress state. Process en gin eerin g con sid eration s m ay restrict th e ran ge of p art geom etries th at can be form ed from billet (cf. Sect. 6.5).

Volum e calculation Followin g tran sform ation of th e en d p rod u ct (assem bly read y p art geom etry) in to a form ed p art geom etry, volu m e calcu lation s are m ad e for th e relevan t geom etry. In p ractice, th e volu m e is calcu lated by d ivid in g th e overall p art geom etry in to sim p le volu m etric elem en ts, su ch as cylin d ers, tru n cated con es or rin gs, wh ose calcu lated in d ivid u al volu m es are ad d ed to obtain th e total p art volu m e. Th e calcu lation m u st take in to accou n t p u n ch in g an d sh earin g scrap wh ich allows for m aterial overflow d u rin g th e form in g p rocess. Exp erien ce h as sh own th at th e volu m e calcu lation of tran sition rad ii can be n eglected , as th ese volu m es p artially can cel each oth er ou t. A far m ore sign ifican t in flu en ce is d u e to volu m etric variation s th at resu lt from th e elastic d eflection an d exp an sion of forgin g d ies or m aterial overflow wh ich is d ifficu lt to calcu late. Com p lex rotation ally sym m etrical 2D geom etries are calcu lated easily u sin g CAD an d accord in g to Gu ld in ’s law. Extrem ely com p lex 3D geom etries are h an d led u sin g th e volu m etric calcu lation m od u les of 3D CAD system s.

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Formed part and process plan

6.4.2 Process plan Th e form ed p art an d th e relevan t volu m etric calcu lation rep resen t th e startin g p oin t for d evelop in g th e p rocess p lan . A creative p rocess is in itiated in wh ich a wid e ran ge of bou n d ary con d ition s – su ch as startin g d iam eter, m aterial, p rescribed stren gth levels, lot size, h eat treatm en t, n u m ber of station s, d istan ce between station s, p ress force, off-cen ter load cap acity of th e p ress an d in tern al op eratin g circu m stan ces – m u st be con sid ered sim u ltan eou sly. On th e basis of th e calcu lated volu m e, th e billet d im en sion s (p referred d iam eter an d len gth ) are d efin ed . For m an y p arts, p articu larly rod -sh ap ed p arts, th e billet d iam eter is selected from a d iam eter wh ich alread y exists in th e p art to be form ed . Th is m u st take in to accou n t th e clearan ce n ecessary to tran sp ort an d locate th e p art from on e station to th e n ext, an d th e p referred d iam eter. For all flat p arts wh ich are p rod u ced by u p settin g op eration s, th e u p set ratio an d th e len gth / d iam eter ratio of th e billet m u st be con sid ered , as th ese in flu en ce th e p ossibility of bu cklin g. Startin g with th e geom etry of th e form ed p art, d evelop m en t work p roceed s to d eterm in e th e p reviou s stages, workin g backward s toward s th e startin g billet. In itially, rou gh p rocess p lan altern atives are su fficien t h ere. Th ese p relim in ary p rocess p lan s are u sed as a basis for d efin in g th e form in g p rocesses. Volu m etric ad ju stm en t is n ot yet n ecessary at th is stage, as on ly th e d egree of tru e strain is calcu lated an d com p ared with th e corresp on d in g p rocess lim its. If th e existin g con d ition s are critical, it m ay be p ossible to alleviate th ese by ch an gin g billet d im en sion s an d th e seq u en ce of op eratin g station s. If th is is n ot p ossible, in term ed iate h eat treatm en t is u n avoid able. If on e, two or m ore in term ed iate h eat treatm en ts are n ecessary, warm form in g can offer an oth er m ore econ om ical altern ative. On ce a p rom isin g p rocess p lan altern ative h as been fou n d as a resu lt of th is in tu itive p roced u re, volu m e calcu lation s are carried ou t. Fu rth erm ore, th e feasibility is verified based on force an d en ergy calcu lation s an d on th e com p u tation of th e d ie load . If th e u se of process com bin ation s m ean s th at th ere are several processes bein g perform ed in a sin gle station , reliable prediction of th e m aterial flow is difficu lt even for experien ced form in g en gin eers. In th is case, m etal flow sim u lation with th e aid of a su itable fin ite elem en t pro-

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gram can serve to illu strate th e m etal flow in th e relevan t form in g p rocess. Th is allows to p red ict an d elim in ate p roblem s su ch as crack form ation , u n d erfillin g an d excessive d ie load s p rior to actu al d ie try-ou t (Fig. 6.4.1).

Fig. 6.4.1 FEM study of material flow for a flange upsetting process w ith relief borehole

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

6 Solid forming (Forging)

6.5 Force and w ork requirement Determ in ation of th e force an d work req u irem en t is u sed as a basis for selection of th e form in g m ach in e an d th e stru ctu ral d esign of th e form in g d ies. In p ractice, calcu lation of th ese ch aracteristics sim u ltan eou sly p rod u ces valu es of p rocess-related p aram eters su ch as th e overall d egree of tru e strain , flow stress, form in g p ressu re, com p ressive stresses on th e in sid e wall of th e extru sion con tain er, etc. (cf. Sect. 2.2). Th e p rocess lim its an d th e resp ective case of ap p lication of th e form in g m eth od m u st also be taken in to con sid eration h ere. Th e form u lae p rovid ed below are based on on ly on e m eth od of calcu lation an d m ake n o claim of com p leten ess. Th e flow stress levels are average valu es obtain ed from th e flow cu rves of VDI 3200 Sh eets 2 an d 3. To calcu late th e p rocess variables con cern in g m ach in e selection , th e u p p er lim it of a flow cu rve sh ou ld be selected . However, in m akin g calcu lation s regard in g d ie con figu ration , th e lower lim it of a flow cu rve sh ou ld be selected . Table 6.5.1 p rovid es an overall view of th e p rocess lim its for th e m ain extru sion p rocesses.

6.5.1 Forw ard rod extrusion Th e forward rod extru sion m eth od tran sform s a billet in to a solid p art with a red u ced cross section (cf. Fig. 6.1.1). Th e d ie op en in g wh ich d eterm in es th e sh ap e of th e extru d ed p arts is form ed solely by th e p ress con tain er. As a resu lt of th e wall friction wh ich occu rs – also d u rin g th e ejection p rocess – th e ratio of h eigh t to d iam eter of th e in itial billet h 0 / d 0 [–] sh ou ld be n o greater th an 5 to 10 (Fig. 6.5.1). If th e req u ired

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Table 6.5.1: Process limits of the most important extrusion methods taking into account economical die life Forw ard rod extrusion d0

Process

Forw ard tube extrusion d0 h0

h0

d1

NF-materials steels

limiting value

A max

max

d0

s1 (h 0 /d 0)max

h2

h0

s0

material

Backw ard cup extrusion d1 s1

A max

max

(h 0 /d 0)

max

A min

A max

(h 2 /d 1)

aluminium (e.g. Al99,5), lead, zinc

0.98

4

0.98

4

0.10

0.98

6

copper (E-Cu)

0.85

1.9

0.85

1.9

0.12

0.80

4

0.75

1.4

0.15

0.75

3

brass (CuZn37 - CuZn28)

0.75

1.4

easy to form (e.g. QSt32-3, Cq15)

0.75

1.4

10

0.75

1.4

15

0.15

0.75

3

difficult to form (e.g. Cq35, 15M nCr5)

0.67

1.1

6

0.67

1.1

12

0.25

0.65

2

more difficult to form (e.g. Cq45, 42CrM o4)

0.60

0.9

4

0.60

0.9

8

0.35

0.60

1.5

max

dim en sion s are greater th an th ese valu es, free or open die extru sion m u st be u sed as a su pplem en tary extru sion process. In addition , th e ratio h 0 / d 0 in th e rem ain in g (n on -extru ded) portion of th e billet m u st be n o sm aller th an 0.5. Oth erwise, th e so-called “su ck-in ” defects m ay occu r. Th e m axim u m tru e strain ach ievable with th e forward rod extru sion of steel is arou n d w = 1.6 d ep en d in g on th e m aterial. In th e case of m aterials with low form ability, th is valu e is as low as 0.5 to 0.9. Th e d ie op en in g an gles 2 a [°] m u st be with in a ran ge of ap p rox. 45 an d 130°, wh ich resu lts in tap ers on th e form ed p art with an gles between 22.5 an d 65°. Th e p art volu m e is calcu lated from th e in d ivid u al volu m etric valu es as illu strated in Fig. 6.5.1:

V0 = V1 + V2 + V1', w hereby V0 , V1 , V1' a nd V2 a re calculated by means of

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d0

d2

V2

h2

V1’

h0

h 1’ V1

α 2

h1

Fig. 6.5.1 Schematic representation of forw ard rod extrusion

d1

V0 = d 20 ⋅

π ⋅ h0 4

[mm ]

V1 = d12 ⋅

π ⋅ h1 4

[mm ]

V1' =

3

3

π ⋅ h1 ’ 2 ⋅ d 2 + d12 + d 2 ⋅ d1 12

V2 = d 22 ⋅

(

)

π ⋅ h2 4

[mm ] 3

[mm ] 3

In th is calcu lation , it is p ossible to u se d 2 < d 0 as an ap p roxim ation ; th e h eigh t of th e tru n cated con e h 1 ’ an d th e form in g stroke h are d eterm in ed by m ean s of:

h 1' =

d 2 – d1 cot α 2

h = h0 – h2

[mm]

Th e am ou n t of d eform ation (strain s) can be d eterm in ed from th e d egree of tru e strain w an d th e sp ecific cross section ch an ge «A . Th e latter can be obtain ed q u ickly from th e relevan t sq u ares of th e d iam eters in stead of u sin g th e su rfaces:

 d2  ϕ =  ln 22   d1 

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εA =

A 0 – A1 ⋅ 100 % A0

εA =

d 22 – d12 ⋅ 100 % d 22

Th e ratio between billet h eigh t h 0 an d billet d iam eter d 0 an d th e d ie op en in g an gle are taken in to accou n t with th e correction coefficien ts k h an d k 2 a [–] wh en estim atin g th e sp ecific p u n ch p ressu re an d th u s also wh en calcu latin g th e form in g force.

k h = 0.2 ⋅

h0 + 0.8 d0

k 2α =

1 ⋅ (2α ) + 0.7 200

Th e flow stress at th e start of th e form in g p rocess k f0 [N/ m m 2 ] an d toward s th e en d of th e form in g p rocess k f1 can be d erived from th e sh eets of VDI Gu id elin e 3200 for th e m aterial u sed in each case. Both valu es are u sed to estim ate th e sp ecific an d id eal form in g work w id :

w id →≈

kf o + kf l 2

 Nmm   mm 3 

⋅ϕ

As th e actu al form in g force d eviates from th e th eoretically id eal form in g force, it is corrected by u sin g th e effien cy factor hF [–].

ηF = 0.703125 ⋅

ε A (%) 100

Th e average form in g p ressu re p St [N/ m m 2 ] an d th e form in g force FU [kN] are th u s estim ated by u sin g:

p St =

 N   mm 2 

w id ⋅ k h ⋅ k 2α η

FU = p St ⋅ d 22 ⋅

π ⋅ 10 –3 4

[ kN]

Th e form in g work W is th e p rod u ct of form in g force an d form in g stroke h

W = FU ⋅ h

[J resp. Nm]

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For d ie d esign , th e p ressu re on th e con tain er wall p i [N/ m m 2 ] is d eterm in ed :

pi =

 N   mm 2 

1 (pSt + k f 0 + k f1 ) 2

Example: Th e sam p le calcu lation p rovid ed h ere is based on th e workp iece m aterial 1.0303 (QST 32-3). Th e startin g valu es are sp ecified on th e left, th e ch aracteristic valu es su bseq u en t to th e p ressin g op eration on th e righ t. d 0 = 75 m m h 0 = 110 m m

d 1 = 45 m m h 2 = 65 m m d 2 = 75.3 m m => h = 45 m m

a = 45°

Th e resu ltin g d eform ation or id eal effective strain is w = 1.03, wh ich corresp on d s to a relative cross section ch an ge of «A < 64 %, an d th e correction coefficien ts are k h < 1.09 an d k 2 a < 1.15:

(75.3

 75.32  ϕ = ln   = 1.03  452 

ε=

110  k h = 0.2 ⋅  + 0.8 ≈ 1.09  75 

k 2α =

2

– 452 )

75.32

⋅ 100 % = 64 %

1 ⋅ 2 ⋅ 45 + 0.7 ≈ 1.15 200

If th e am oun t of deform ation is 1.03, th e resultin g value for kf1 is approx. 740 N/m m 2 , (kf0 250 N/m m 2 ), m ean in g th at th e specific form in g work is approx. 471 Nm m /m m 3 . With an efficien cy of

ηF = 0.703125 ⋅ 64 / 100 = 0.67 th e sp ecific d ie load s, force an d work resu lt in :

[

p St = 510 / 0.67 ⋅ 1.09 ⋅ 1.15 ≈ 957 N / mm 2

]

FU = 957 ⋅ 75.32 ⋅ π / 4 ⋅ 10 –3 ≈ 4, 261 [ kN ] W = 4, 261 ⋅ 0.045 ≈ 192 [ kJ resp. kNm ]

[

p i = 1 / 2 (957 + 250 + 740) ≈ 974 N / mm 2

]

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6.5.2 Forw ard tube extrusion Forward tu be extru sion in volves th e p rod u ction of a tu bu lar p art with a red u ced wall th ickn ess startin g (cf. Fig. 6.1.1) from a cu p or cylin d er. Th e d ie op en in g, wh ich d eterm in es th e sh ap e of th e p rod u ced p art, is form ed by th e p ress con tain er an d th e p u n ch . If th e m an d rel is p erm an en tly m ou n ted in th e p u n ch , it is called a m ovin g m an d rel: As a resu lt of m aterial flow, ad d ition al friction al forces occu r wh ich can lead to critical levels of ten sile stress in th e m an d rel. Th is can be avoid ed by u sin g a m ovin g m an d rel, th at is m oved , with in certain lim its, by th e d eform in g m aterial. Friction -related ten sile stresses occu r d u rin g forward extru sion with th e m ovin g m an d rel an d d u rin g strip p in g of th e workp iece in both forward tu be extru sion m eth od s. Th erefore, geom etrical con d ition s m u st be set su ch th at m an d rel load d oes n ot exceed 1,800 N/ m m 2 . Th is is gen erally th e case wh en th e ratio of h eigh t to d iam eter in th e startin g m aterial h 0 / d 0 d oes n ot exceed 10 to 15. Th e ach ievable levels of d eform ation d ep en d on th e m aterial an d corresp on d to th ose ach ievable in forward rod extru sion . Th u s, com p arable (sh ou ld er) geom etries can also be form ed (Table 6.5.1).

6.5.3 Backw ard cup extrusion and centering A (th in -walled ) tu bu lar p art is p rod u ced from a solid billet. Th e d ie op en in g wh ich d eterm in es th e sh ap e of th e p art is form ed by th e p u n ch an d con tain er, or th e d ie (cf. Fig. 6.1.1). In th e backward cu p extru sion of steel, a certain lim itin g ratio of p en etration d ep th to p u n ch d iam eter h 2 / d 1 = 3 to 3.5 can n ot be exceed ed . Dep en d in g on th e m aterial, th e m axim u m ach ievable d egree of tru e strain is w = 0.9 to 1.6 («A = 60 to 80 %). However, econ om ical tool life is on ly ach ieved with som ewh at lower levels of tru e strain (Table 6.5.1). Du e to a m axim u m adm issible p u n ch stress of p St m ax # 2,300 N/ m m 2 wh en p rocessin g steel, a m in im u m level of tru e strain of at least w = 0.16 to 0.43 («A = 15 to 35 %) m u st be en su red, i. e. it is n ot p ossible to backward extru d e a cu p with an y op tion al in tern al d iam eter relative to th e ou tsid e d iam eter. It m ay be p ossible to p rod u ce sm all bores with ad d ition al secon d ary geom etries (e. g. a p rotru sion for extru sion p iercin g), p rovid ed th ese relieve th e m aterial flow in to th e cu p wall.

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Force and w ork requirement

Th e m in im u m ach ievable wall th ickn esses for steel are arou n d 1 m m , for alu m in iu m arou n d 0.1 m m . Extrem ely th in walls can be p rod u ced by a su bseq u en t iron in g p rocess followin g backward cu p extru sion . For steel, th e m in im u m cu p bottom th ickn ess is 1 to 2 m m , for NF m etals 0.1 to 0.3 m m . Th e bottom th ickn ess sh ou ld always be greater th an th e wall th ickn ess (u n d erfillin g). In th e case of th ick-walled cu p s wh ich are ad d ition ally exp ected to satisfy h igh con cen tricity req u irem en ts, it is ad visable to carry ou t a cen terin g op eration p rior to cu p extru sion . Cen terin g is a p rocess very sim ilar to backward cu p extru sion , alth ou gh with on ly a sm all d eform ation stroke. Cen terin g is gen erally p erform ed u sin g gu id ed p u n ch es.

6.5.4 Reducing (open die forw ard extrusion) Th e p rin cip le of red u cin g is sim ilar to th at u sed for forward rod extru sion as far as th e d ie d esign is con cern ed (cf. Fig. 6.1.2). However, in con trast to forward rod extru sion , th e billet m aterial is n ot p ressed again st th e con tain er wall. Th u s, on ly a lim ited d egree of d eform ation is p ossible with ou t bu cklin g. Du rin g th e form in g p rocess, th e m aterial m u st n eith er be d eform ed (u p set) in th e con tain er n or bu ckle. In th e case of startin g billets with h 0 / d 0 > 10, red u ction s in cross section can on ly be ach ieved u sin g th is p rocess. Larger am ou n ts of d eform ation req u ire several su ccessive red u cin g op eration s. Th e ach ievable level of d eform ation d ep en d s on th e m aterial, th e p relim in ary state of strain h ard en in g an d th e d ie op en in g an gle. An overall level of d eform ation (calcu lated from th e first to th e n th red u cin g op eration ) of 50 % sh ou ld n ot be exceed ed d u e to th e form ation of cen tral bu rsts (ch evron s). Red u cin g or op en d ie forward rod extru sion is a p rocess wh ich is n ot u sed in p ractical warm form in g op eration s, as th e ach ievable d egree of d eform ation is too low d u e to sign ifican tly red u ced flow stress in warm form in g. With a d ie op en in g an gle of ap p rox. 20°, it is p ossible to ach ieve a m axim u m level of d eform ation of w = 0.3. If th e m aterial u sed h as alread y been strain h ard en ed , for exam p le as a resu lt of a p reviou s red u cin g op eration , a som ewh at h igh er d egree of d eform ation is p ossible. However, with an in creasin g d ie op en in g an gle, th e ach ievable level of d eform ation d rop s su bstan tially.

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476

Die an gles ran ge between 10 an d 45° an d gen erate tapers with sh ou lders between a = 5 an d 22.5° on th e pressed part (cf. Fig. 6.1.2). Th e pu n ch load is of m in or im portan ce, an d depen ds on th e billet m aterial. It sh ou ld n ot u pset th e billet plastically, an d cau se bu cklin g stresses in slen der billets. Neith er of th ese stress valu es sh ou ld be exceeded. Th e process is h igh ly sen sitive to flu ctu ation s in th e stren gth of th e startin g m aterials an d to th e qu ality of lu brication , i. e. ph osph atin g an d soapin g.

6.5.5 Ironing Iron in g is a process wh ereby a tubular part with a bottom (e. g. backward extruded or drawn cup) is drawn to reduce th e wall th ickn ess (cf. Fig. 6.1.2). Th is is a process in wh ich th e force is in troduced m ain ly th rough th e bottom of th e workpiece an d partially by th e m an drel friction force. As a result, in addition to com pressive stress at th e die sh oulder in let, ten sile stress also occurs after exit from th e die in th e wall of th e workpiece (drawin g process). Th is is in direct con trast to reducin g, in wh ich th e force an d th us also th e com pressive stress occurs in th e workpiece cross section before th e die sh oulder in let (press th rough process). Th e part sh ape is gen erated by th e drawin g m an drel an d th e iron in g (die) rin g. It is also possible to arran ge several iron in g rin gs on e after th e oth er. Th e m axim u m d egree of tru e strain ach ievable wh en iron in g steel is arou n d w = 0.5 («A = 40 %) d ep en d in g on th e m aterial ch aracteristics. For d ifficu lt to form m aterials th is valu e d rop s to w = 0.35 («A = 30 %). Die op en in g an gles m ay ran ge u p to arou n d 45°, wh ich resu lts in tap ers u p to 22.5° in th e fin ish ed p art (cf. Fig. 6.1.2) Cu stom ary d ie op en in g an gles for iron in g ran ge between 5 an d 36°. A m in im u m p u n ch force is ach ieved at an iron in g an gle of arou n d 12°, wh en th e p robability of wall fractu re is m in im u m . Iron in g is a p rocess in wh ich an extrem ely good su rface q u ality an d excellen t toleran ces are ach ieved , an d it is, th erefore, u sed freq u en tly as a sizin g op eration .

6.5.6 Upsetting Up settin g is d efin ed as “free form in g”, a p rocess in wh ich th e p art h eigh t is red u ced , gen erally between flat p arallel d ie su rfaces (u p settin g

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Force and w ork requirement

d ies) (cf. Fig. 6.1.2). If u p settin g is carried ou t in a closed d ie with ou t flash form ation , for exam p le in ord er to p ress cylin d rical or len s-sh ap ed p re-form s, th is is referred to as sizin g. (Free) u p settin g (cf. Fig. 2.2.1) is ch aracterized by th ree p rocess lim its: Dep en d in g on th e m aterial, th e m axim u m tru e strain of w = 1.6 can be ach ieved . Th e u p settin g ratio h 0 / d 0 (h eigh t to d iam eter of th e startin g workp iece) m ay n ot exceed 2.3 for sin gle p ressin g, 4.5 for d u al p ressin g an d 8.0 for trip le p ressin g, as oth erwise bu cklin g m ay occu r an d th e fiber flow is in terru p ted (cf. Fig. 6.2.1). Th e m axim u m d ie p ressu re is 2,300 N/ m m 2 . In con trast to u p settin g in wh ich th e exterior con tou r an d d im en sion are free form ed , in sizin g th e workp iece is fu lly en closed (trap p ed d ie). Th e sam e p rocess lim itin g valu es exist as for free u p settin g. However, th e sam e m agn itu d e of th e u p settin g p u n ch load is reach ed at lower levels of d eform ation , as th e m aterial lean s again st th e d ie wall.

6.5.7 Lateral extrusion Lateral extru sion gen erates sh ap es with flan ges, collars or oth er geom etric featu res (teeth , p rotru sion s), wh ereby th e d ie op en in g wh ich gives th e workp iece its sh ap e rem ain s u n ch an ged d u rin g th e en tire form in g p rocess (cf. Fig. 6.1.1). Th is is ach ieved by closin g th e d ies with a h igh force before th e slid e reach es th e bottom d ead cen ter. After th e d ies are closed , th e m aterial is p ressed in to th e im p ression by th e p en etratin g p u n ch . It is p ossible to p rod u ce for exam p le flan ges with a d iam eter ratio D 1 / d 0 # 2.5 in a sin gle form in g op eration . Th e ratio between flan ge th ickn ess an d startin g s/ d 0 sh ou ld n ot exceed 1.4 becau se th e m aterial m ay sep arate at th e n eu tral su rface. Th e req u ired forces are su bstan tially lower th an for u p settin g, in p articu lar wh en p ressin g secon d ary geom etric featu res. To d ate, th e actu al force req u irem en t h as been estim ated on ly th rou gh exp erim en tal tests. Becau se of th e state of com p ressive stress, actin g on all sid es, local levels of tru e strain of u p to w = 5 h ave been ach ieved u sin g th is n on station ary p rocess.

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6 Solid forming (Forging)

6.6 Part transfer Cold an d warm form in g are m ass produ ction processes wh ose h igh ou tpu t levels an d econ om y are ach ieved in particu lar by au tom ation . Au tom ation in th is con text in clu des all devices wh ich , in addition to loadin g th e wire coil or fillin g th e con tain ers with sh eared billets, perm it th e tran sfer of th e billet, th e preform ed part between form in g, an d wh ere applicable an y scrap (piercin g, trim m in g operation s) with in th e press. In stallation s th at u se wire coil h ave th e ad van tage th at on ce th e wire en d h as been fed in , th e billet m aterial always assu m es a d efin ed p osition d u rin g th e straigh ten in g (cf. Sect. 4.8.3), d rawin g an d sh earin g (cf. Sect. 6.3). Th e m aterial is tran sp orted with in th e p ress by m ean s of a m ech an ical tran sfer d evice, an d th e p arts leave th e p ress followin g th e last form in g station by slid in g d own th rou gh a ch u te. In in stallation s th at u se sh eared billets, th e billets m u st be fed in , orien ted , p ossibly weigh ed an d con veyed to th e p ick-u p p oin t of th e tran sfer d evice. Th e m ain focu s of in vestigation p art h an d lin g is th e tran sp ortation of workp ieces from on e station to th e n ext with in th e p ress. Th e objective is to u tilize kin em atic factors an d d ie layou t so to: – gu aran tee absolu tely reliable p art tran sfer – th is en tails p reven tin g th e p art from assu m in g an u n d efin ed , i. e. free p osition at an y tim e –, – en su re th at n o collision is p ossible eith er between th e d ie elem en ts or between d ie elem en ts an d grip p ers d u rin g id le strokin g of th e p ress (e. g. on start-u p or wh en ru n n in g th e p ress em p ty), an d – m in im ize con tact tim es, in p articu lar in th e case of warm form in g.

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Part transfer

Th ere is a broad ran ge of p ossible solu tion s for p art tran sfer, in clu d in g tran sp ort d evices in th e broad er sen se, su ch as tiltin g m ech an ism s for billet con tain ers, steep con veyors (p u sh er or ch ain con veyors), vibratin g con veyors, sep aratin g d evices an d scales. Th erefore, th ese will n ot be d ealt with h ere. Th is ch ap ter will con cen trate in stead on th e load in g station an d th e tran sfer stu d y for a m ech an ical cold form in g p ress with 2D tran sfer (cf. Sect. 4.4.6).

6.6.1 Loading station Th e wid e d iversity of p arts th at m u st be fed in to a form in g p ress calls for a n u m ber of d ifferen t load in g station con cep ts. W h ere cylin d rical billets with a len gth / d iam eter (L/ D) ratio greater th an 0.8 are bein g p rocessed , th ey are load ed from above in to th e feed in g station by m ean s of a feed ch an n el (Fig. 6.6.1, top). Th e bottom -m ost p arts are h eld in a h old er, gen erally cylin d rical in sh ap e, th at is p rovid ed with recesses on th e sid e to allow for th e closin g m ovem en t of th e grip p er. Followin g th e rem oval of th e first p art, th e weigh t of th e colu m n cau ses it to d rop on to th e base p late at th e level of th e tran sp ort p lan e. W h ere billets with d ifferen t d im en sion s are fed , if n ecessary th e feed ch an n el an d th e exch an geable p arts or th e com p lete feed u n it can be exch an ged with th e aid of q u ick-actin g clam p s. Th e grip p ers are eq u ip p ed for cylin d rical p arts with p rism atic active grip p er elem en ts wh ose h eigh t sh ou ld be ap p rox. 50 % of th e billet len gth to en su re a reliable grip p in g action . If th e L/ D ratio is below arou n d 0.8 to 1, or if form ed parts with relatively flat geom etry are bein g processed (Fig. 6.6.1, bottom ), th en th e parts are con veyed in to th e loadin g station side by side in specially design ed feed ch an n els. Th e parts are position ed in itially below th e tran sport plan e, an d are raised by a pu sh er to tran sport level in syn ch ron ization with th e press cycle. After th e pu sh er retu rn s to its startin g position , th e n ext part slips in to th e loadin g station to be raised to th e tran sport plan e. Th e startin g h eigh t an d feed an gle of th e feed ch an n els are con figu red in su ch a way th at th e billets con tin u e to slide u n der th eir own weigh t. In th e case of form ed parts, th e grippers are design ed for sh aped fit if a prism atic gripper exh ibits an u n favorable L/ D ratio an d th ere is a dan ger th at billets cou ld rotate wh ile bein g h eld by th e gripper.

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Solid forming (Forging)

480

Fig. 6.6.1 Loading station concepts for cylindrical (top), disc-shaped or flat shaped parts (bottom)

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Part transfer

For cold form in g p rocesses, th e grip p er u n its are m ou n ted on clam p in g rails wh ich are fixed in tu rn on a base rail (Fig. 6.6.1). W h en resettin g for p rod u cin g a d ifferen t p art, all th at h as to be exch an ged are th e clam p in g rails in clu d in g th e p re-set grip p ers. Th e fron t grip p ers are eq u ip p ed with p roxim ity switch es to m on itor p art tran sfer. Parts with a h igh er L/ D ratio (ap p rox. 3 to 8) m u st be tran sferred between station s by a 3D tran sfer. Th is in volves th e u se of an ad d ition al h orizon tal p u sh er wh ich m oves th e p art togeth er with its retain er in to a p osition from wh ere it can be raised vertically. Here, too, th e level of th e base p late on wh ich th e p arts are p osition ed is located below th e tran sp ort p lan e. Sh aft-sh ap ed p arts with a billet L/ D ratio of > 6 can also be m oved in to th e u p lift p osition u sin g sp ecial d evices su ch as rotatin g sleeve retain ers. In warm form in g, th e load in g station h as th e ad d ition al fu n ction of segregatin g p arts wh ich eith er h ave n ot been fed in correct syn ch ron ization with th e p ress, or wh ich h ave an in correct tem p eratu re. To allow th ese p arts to be ejected , an op en in g is released in th e base p late of th e load in g station th rou gh wh ich th e p arts d rop d own in to a ch u te for rem oval.

6.6.2 Transfer study Before con du ctin g a tran sfer stu dy, data on th e kin em atics of th e slide m ovem en t m u st be available in th e form of a tim e-disp lacem en t diagram . Th e stroke is defin ed based on th e ran ge of p arts, th e req u ired form in g p rocess an d th e die layou t. Th e slide cu rve is given by th e stroke h eigh t an d p ress kin em atics (eccen tric drive, kn u ckle-join t drive, m odified kn u ckle-join t drive) (cf. Fig. 3.2.3). Th e slide cu rve, wh ose bottom dead cen ter is at 180°, can on ly be disp laced vertically for tran sfer stu dy. Th e ejector stroke is d eterm in ed by th e ran ge of p arts bein g p rocessed an d th e resp ective p osition of th e form in g station s in th e d ie. Th e largest n ecessary ejector stroke is eq u al to th e su m of th e in lay d ep th of th e p art in th e d ie an d th e p art len gth . Th e ejector stroke can be ach ieved by m ean s of a m ech an ical an d an ad d ition al p n eu m atic d isp lacem en t. Th e stroke covered m ech an ically m u st eject th e p art, wh ich is stu ck in th e tool as a resu lt of elastic d eflection of th e con tain er. In ad d ition , th e p n eu m atically gen erated d isp lacem en t is able to raise th e

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482

p art. Ou r p resen t exam p le h as a m ech an ical ejector cu rve with a stroke of 200 m m wh ich is travelled th rou gh at 80° cran k an gle: In th is case, n o p n eu m atic ejector is req u ired . Th e startin g p oin t for th e ejector cu rve can be op tion ally selected , allowin g th e cu rve in th e d iagram (Fig. 6.6.2) to be d isp laced h orizon tally. Th e slop e of th e ejector cu rve can be con figu red in su ch a way th at it corresp on d s ap p roxim ately to th e lin ear p ortion of th e slid e cu rve. Startin g with th e tran sverse m ovem en t of th e con n ectin g rod , th e slid e ejector cu rve is gen erated by th e corresp on d in g kin em atic (Fig. 6.6.2, dashed line). For th e tran sfer stu d y, th is cu rve can be d isp laced on ly vertically. Th e cu rve of th e p n eu m atic ejector, wh ose actu al d istan ce from th e slid e cu rve m u st be d eterm in ed with th e tran sfer stu d y, ru n s p arallel to th e slid e cu rve (Fig. 6.6.2, broken line). Th e slid e ejector acts m ech an ically briefly after th e bottom d ead cen ter an d can be op erated p n eu m atically after th at. In addition to th ese m ain p ress m otion s, in u n iversal tran sfer devices th e cu rves for op en in g an d sh u ttin g th e grip p ers are also sign ifican t. Th e op en in g an d closin g tim es can n orm ally be adju sted with in certain lim its, e. g. with in a 30° ran ge, m akin g th e cu rves h orizon tally disp laceable in th e tran sfer stu dy. Th e op en in g stroke is determ in ed by th e req u ired diam eter of th e u p p er die (Fig. 6.6.2, op en in g stroke 100 m m ). W h ere m ostly slen der p u n ch es are u sed, th is stroke is sm aller th an for fem ale dies u sed on th e side of th e slide, for exam p le wh en p rodu cin g lon g rodsh ap ed p arts or p arts in closin g devices. Dep en din g on th e op en in g stroke, th ese m ovem en ts req u ire a sm aller (ap p rox. 30° for arou n d 40 m m ) or a larger (ap p rox. 60° for arou n d 100 m m ) cran k an gle ran ge. Th rou gh th e forward an d reverse m ovem en t, lateral tran sp ortation takes p lace. Forward m otion can be in itiated as soon as th e grip p ers en gage th e p art, an d m u st h ave been com p leted before th e grip p ers op en , i. e. th e u p p er d ie elem en ts m ake con tact with th e tran sp orted p art. Th e forward an d retu rn m otion s req u ire a cran k an gle of ap p rox. 80 to 100°. Th e retu rn m otion takes p lace d u rin g th e in feed an d p ressin g cycles. Tran sp ort stu d ies of 3D tran sfer d evices in volve a lift-u p m otion in ad d ition to th e m ovem en ts p reviou sly d escribed . Th is m otion starts briefly after th e ejector m ovem en t an d after th e closin g of th e grip p ers. It en d s with th e lowerin g m otion wh ich sh ou ld h ave been com p leted

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Part transfer

Fig. 6.6.2 Tw o-dimensional transfer study: 1 define opening starting point; 2 determine pneumatic spring travel for fed part; 3 define shortening of ejector bolt in the machine and starting point of ejector in bed; 4 define closing end point; 5 determine pneumatic spring travel for ejected part

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ju st before th e op en in g of th e grip p ers. Here, too, d ep en d in g on th e liftu p m otion , a greater or sm aller cran k an gle ran ge m ay be req u ired . A lift-u p m otion of arou n d 100 m m can req u ire a cran k an gle of arou n d 60°. All th e tran sp ort m otion s of th e p ress an d tran sfer d evice are lim ited by m axim u m allowable acceleration levels, an d m u st be sep arately d esign ed for each in d ivid u al case u n d er con sid eration .

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

6 Solid forming (Forging)

6.7 Die design In in du strial p ractice, extru sion or cold forgin g dies are freq u en tly su bject to p aram etric design s an d adap tation s, m akin g th e con figu ration of th e p u n ch es an d dies of cen tral im p ortan ce. Less freq u en tly, for exam p le wh ere a n ew p ress is u sed, q u estion s related to die h older design an d sp are an d active die sets m u st be addressed. Modern cold an d warm forgin g dies h ave a m u ltip le-station con figu ration . Most of th e m ain forgin g op eration s are com p leted with in on e to th ree station s. However, u sin g fou r or even five-station die sets it is p ossible to execu te oth er sizin g, p iercin g an d trim m in g op eration s in on e an d th e sam e p rocessin g step . Th u s, it is p ossible to ap p roach th e objective of n et sh ap e or n ear n et sh ap e p rod u ction , an d to red u ce th e tran sp ort an d p rocessin g costs in volved in an ad d ition al p ass th rou gh th e p ress. Figure 6.7.1 illu strates th e basic sch em atic layou t of a m odern m u ltip le-station die for a u n iversal p ress. An in term ediate p late is m ou n ted on th e p ress bed an d distribu tes th e p ress force in th e form of a p ressu re con e wh ich in creases in size as it acts on th e p ress bed. Th e in term ediate p late is eq u ip p ed with recesses for con n ectin g th e sh afts of th e tran sfer device clam p in g boxes, an d is able to accom m odate sen sors for p ress force m easu rem en t or roller brackets for die set ch an geover. Hydrau lic die clam p s for com p lete die ch an ge op eration s can also be located on th e in term ediate p late. Th e d ie base p late h ou ses th e d ie h old in g sleeves. As d em on strated in th e exam p le, th is p late can also h old h yd rau lic closin g d evices an d scrap ch u tes. However, wh ere th ese are u sed , th e overall h eigh t of th e p late m u st be con figu red to be h igh er. Th e d ies th em selves can be m ou n ted in a retain er block wh ich reach es over th e en tire wid th of th e

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Solid forming (Forging)

486

Fig. 6.7.1 Four-station die holder w ith hydraulic die clamping and closing system in the second station

d ie. However, for warm form in g an d in som e cases also for cold form in g, th e u se of sin gle d ie h old in g sleeves is p referred . Th u s, th e th erm al exp an sion is absorbed in each in d ivid u al d ie h old er, in d ep en d en t of oth er d ie station s. Usin g a su itable coolin g d evice, it is p ossible to p reven t th e m otion of d ie block, as a resu lt of th erm al exp an sion , relative to th e d ie h alves m ou n ted on th e slid e. In p rin cip le, th e layou t of th e u p p er die is sim ilar. However, addition al wedge adju stm en t devices (Fig. 6.7.2) are located in th e h ead p late. Th ese are u sed for in dividu al h eigh t adju stm en t of th e dies. Th e wedge adju stm en t devices h ave an adju stm en t h eigh t of abou t 3 to 5 m m .

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Die design

487 pneumatic pad

w edge adjustment

transport strap punch

die holding sleeves

clamping ring auxiliary column

die holder

dies

pressed part active components

counterpunch

exchange components part-dependent exchange components acitve component clamping

w edge adjustment

Fig. 6.7.2 Section through a die holder w ith w edge adjustment (auxiliary columns and transport straps are built in for die holder change)

If n o slide h eigh t adju stm en t is available in th e p ress, th e wedges m u st th en h ave a lon ger adju stm en t h eigh t of ap p rox. 8 to 12 m m in th e in dividu al station s. Before actu atin g a wedge adju stm en t device, th e clam p in g rin g is released, th u s allowin g th e down ward m otion of th e dies. Th e u p p er dies are relatively h igh , as th ey are design ed to accom m odate p n eu m atically su p p orted p ads for workp iece tran sfer (Fig. 6.7.3). As a resu lt, reliable p art tran sfer is en su red. Th u s, h igh er effective strokin g rates an d in creased ou tp u t can be obtain ed. Th e stroke of th e p n eu m atic ejectors is determ in ed by m ean s of a tran sfer stu dy (cf. Sect. 6.6.2). Active an d exch an ge d ie com p on en ts are located in th e d ie h old ers. Th e active d ie com p on en ts con tact th e workp iece con tou r an d are su bject to wear. Th ese m u st be reworked or rep laced p eriod ically. Th e active d ie com p on en ts in clu d e th e con tain ers, th e d ie in serts, p u n ch es an d cou n terp u n ch es, as well as for exam p le strip p er sleeves. Th e p artd ep en d en t toolin g m u st be exch an ged togeth er with th e active d ie

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Solid forming (Forging)

488

die holder

pressed part hydraulic sleeve clamping by means of w edge clamp

active and exchange dies

auxiliary column

die holding sleeves pneumatic pad active components

intermediate die sleeve

exchange components

die holding sleeve

part-dependent exchange components w edge adjustment clamping individual station

conical retainers

Fig. 6.7.3 Section through a die holder w ith w edge adjustment and hydraulic sleeve clamping

com p on en ts wh en settin g u p th e p ress for a n ew p rod u ct. Oth er u n iversally u sed exch an ge toolin g com p on en ts rem ain in th e h old in g sleeves. Th e exch an ge toolin g in clu d e m ain ly p ressu re p lates, p ressu re p in s, sp rin g elem en ts an d gu id e sleeves. For th e stru ctu ral d esign of active an d exch an ge com p on en ts of d ie sets, p lease refer to th e VDI Gu id elin es 3176, 3186 Sh eets 1 to 3.

6.7.1 Die holders Th e d ie h old ers h old both th e active an d exch an ge toolin g com p on en ts. Th eir fu n ction is to en su re th at th e lower an d u p p er d ie op erate as on -cen ter as p ossible in relation to each oth er. Th e n u m ber of station s, th e d istan ce between station s an d th e h old er sizes are gen erally grou p ed togeth er in stan d ard ized series. Table 6.7.1 illu strates a m od u -

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Die design

489

Table 6.7.1: M odular system for possible die holder sizes (w idths) (bold = frequently used sizes) for number of and distance betw een stations Number of stations

Die holder w idths w ith distances betw een stations in mm

200

250

300

350

400

2

400

500

600/750

700

800

3

600

750

900/ 1,000

1,050

1,200

4

800

1,000

1,200/ 1,250

1,400/1,500

1,600

5

1,000

1,250

1,500

1,850

2,000

6

1,200/ 1,250

1,500

–

–

–

lar system of th is typ e for a u n iversal p ress d esign freq u en tly u sed for form in g p arts of ap p rox. 0.1 to 15 kg. Of cou rse, oth er com p on en t an d d ie sizes can also be im p lem en ted . Th e d ie ch an ge system is closely lin ked with th e d ie h old er d esign . Th e ran ge of p arts to be p rod u ced an d th e in d ivid u al batch sizes are th e m ain criteria th at in flu en ce th e d ie h old er d esign an d th e layou t of th e d ie ch an gin g system . Th e com p lete d ie h old er ch an ge, req u ired wh en startin g work on a com p letely n ew p art, in volves m ovin g th e en tire d ie h old er ou t of th e m ach in e to be rep laced by a read y-p rep ared h old er located in a p rescribed waitin g p osition . Th e d ie h ead an d base p late of th e d ie h old ers are h yd rau lically clam p ed (Fig. 6.7.1). For m ovin g in an d ou t of th e p ress, th e u p p er an d lower p art are m oved togeth er by m ean s of au xiliary colu m n s an d locked togeth er with safety strap s for tran sp ort (Fig. 6.7.2). A th ird d ie h old er can be assem bled an d set-u p in th e d ie sh op d u rin g th e p ressin g or exch an gin g th e d ie h old ers. For th is m eth od of d ie h old er exch an ge, p arts of th e grip p er rails h ave to be u n cou p led , fixed on th e d ie h old er an d rem oved togeth er from th e p ress. Dep en d in g on th e size of th e h old er, th e exch an ge can take an ywh ere between 20 an d 40 m in . Th ese tim es in clu d e resettin g of th e feed in g station an d , in th e case of warm p ressin g, of th e in d u ction fu rn ace as well. In exch an gin g th e sleeves, th e base an d th e h ead p late are left in th e p ress an d th e sleeves in th e table an d slid e are rep laced in d ivid u ally. For th is p u rp ose, th e base an d h ead p late are fasten ed at th e bed an d slid e. Th ey are eq u ip p ed with con ical cen terin g rin gs (Fig. 6.7.3 an d 6.7.4).

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Solid forming (Forging)

490

Fig. 6.7.4 Four-station die holder w ith hydraulic sleeve clamping and shearing station in the fourth station

Each d ie h old in g sleeve is fasten ed by m ean s of two to fou r h yd rau lic wed ge-typ e clam p s (Fig. 6.7.3). Th is d esign is u sed for large batch sizes wh en th e tools wear at very d ifferen t rates in th e in d ivid u al station s an d h ave to be in d ivid u ally rep laced . In th is case, read y p rep ared d ie h old in g sleeves are located in a p rescribed load in g p osition an d can be m ou n ted in to th e d ie station by a d ie ch an gin g arm (cf. Fig. 3.4.5). It takes between 4 an d 8 m in to rep lace on e sleeve. Figures 6.7.3 an d 6.7.4 illu strate th e u se of in term ed iate sleeves wh ich can be assem bled with axial p re-stressin g. Mu ltip le-station forgin g p erm its su bseq u en t op eration s to be execu ted in on e p rocessin g step . As illu strated in Fig. 6.7.4 an d 6.7.5, in th e case of th is sp ecific d ie h old er, th e en d of th e extru d ed sh aft is sh eared to th e req u ired len gth by a wed ge-action p u sh er d ie in th e fou rth d ie station .

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Die design

Fig. 6.7.5 Shearing die w ith w edge-action pusher, holding sleeve hydraulically clamped

6.7.2 Die and punch design Dies are su bjected to h igh d egrees of in tern al p ressu re wh ich can q u ickly lead to d ie failu re u sin g sin gle rin g extru sion con tain ers m an u factu red with d ie steels available tod ay. Th e extrem ely h igh stresses, p resen t on th e in tern al d ie wall of th e extru sion con tain er (cf. Sect. 6.5.1) can be red u ced by p re-stressin g (sh rin k-fit) th e con tain er with on e or m ore sh rin k rin gs. Pu n ch es are su bjected in itially to p ressu re an d th en ad d ition ally, d ep en d in g on th e p rocess, to ben d in g stress as a resu lt of off-cen ter load s. Less freq u en tly, th e p ossibility of p u n ch bu cklin g m u st be taken in to con sid eration . Th e calcu lation m eth od s ou tlin ed h ere for d ies an d p u n ch es are d escribed in d etail in VDI Gu id elin es 3176, VDI 3186 an d ICFG Doc. No. 5/ 82.

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

491

Solid forming (Forging)

492

cylindrical shrink fit surface

tapered shrink fit surface

cylindrical shrink fit surface

single shrink ring

tapered shrink fit surface

double shrink ring

Fig. 6.7.6 Shrink fits w ith single and double rings – each w ith cylindrical and tapered fits

Die design In Fig. 6.7.6, variou s sh rin k rin g d esign s are illu strated . Cylin d rical sh rin k fits are sim p ler to p rod u ce, bu t can on ly be u sed u p to in terferen ces wh ich can be ach ieved by warm sh rin k fittin g, in ord er to avoid cold weld s d u rin g assem bly. Tap ered sh rin k fits p erm it sim p ler, scratch -free d isassem bly. A d rawback of th is m eth od are th e h igh p rod u ction costs. Th e tap ered sh rin k fit exh ibits d ifferen t levels of rad ial p re-stress, wh ich can lead in case of very lon g con tain ers to d im en sion al d ifferen ces on th e forged p art. Usu al tap er an gles are 0.5 an d 1°; if th e h eigh t to d iam eter ratio of th e con tain er is below 0.8, tap er an gles of 2 to 3° are u sed in ord er to avoid d isassem bly of th e sh rin k rin gs d u rin g p art ejection . An alytic ap p roxim ate op eration s are based on th e m eth od by LAMÉ an d were p u blish ed by Ad ler/ Walter. Th ese assu m e an id eal load in g situ ation wh ere an in fin itely lon g th ick-walled cylin d er is su bjected to a con stan t h yd rostatic p ressu re over its en tire len gth . Usin g Tresca’s yield con dition , wh ich can be ap p lied in th is case, th e stress distribu tion can be calcu lated. It is fou n d th at th e m axim u m valu es are at th e in tern al wall of th e con tain er an d corresp on d ap p roxim ately to th e valu e of th e in tern al p ressu re p i,

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Die design

493

for rad ial stress sr an d tan gen tial stress st (Fig. 6.7.7, left). Th e in tern al p ressu re can th erefore, d u e to

σ v = σ r + σ t = 2 pi R p0.2

, for th e effective stress sv = Rp 0.2 . Th u s, 2 for m aterial valu es of Rp 0.2 = 2,000 N/ m m 2 , m axim u m p ressu re levels of 1,000 N/ m m 2 are p erm issible. If, in th e case of th ick-walled p ip es su bjected to in tern al p ressu re, th e effective stress exceed s th e yield stren gth of a m aterial with su fficien t tou gh n ess, th en p lastic flow occu rs at th e in sid e wall of th e con tain er. If th e u ltim ate stren gth is reach ed in con tain ers or in serts from brittle m aterials, cracks occu r. As a resu lt of ad d in g com p ressive stress, th e tan gen tial stress an d th u s also th e effective stress statu s at th e in sid e wall of th e extru sion con tain er (or in sert) are red u ced (Fig. 6.7.7 center, right). Th e rad ial p re-stress is gen erated by m ean s of sh rin k rin gs. A sh rin k rin g h as an in tern al d iam eter th at is sm aller th an th e ou ter d iam eter of th e corresp on d in g in n er rin g by a selected d im en sion (in terferen ce). By m ain tain in g th e ou ter d iam eter u n ch an ged , th e p erm issible in tern al p ressu re can be in creased by u p to 100 % as a resu lt of th e sh rin k rin g com p ared to a con tain er with ou t a sh rin k rin g. For a given p erm issible in tern al p ressu re, th e ou tsid e d iam eter of th e con tain er, u sin g sh rin k am ou n t to n o m ore th an

. . . . .

a /pi

v

/pi

b

+ pi pi

t

d

/pi

r

pi

- . - .

t

t r r

-

Fig. 6.7.7 Theoretical stress distribution in a thick-w alled single-piece hollow cylinder (left), a tw o-part (center) and three-part (right) shrink fit design (red: w ithout internal pressure, blue: w ith internal pressure)

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Solid forming (Forging)

494

Table 6.7.2: Increase of the allow able internal pressure p i zul. or reduction of the outside diameter d a through single and double shrink rings Characteristic value

Press container w ithout shrink ring

w ith single shrink ring

pi zul. [N/ mm2]

690

1,160

da [mm] w ith di = 20 mm

100

40

w ith double shrink ring 1,395 36.4

rin gs, can be red u ced by abou t 60 % (Table 6.7.2). In m u ltip le-station form in g m ach in es th is resu lts in a su bstan tial red u ction of d ie d iam eters, th e d istan ces between station s, th e d im en sion s of th e d ie h old er an d th u s also th e m ach in e bed size. Carbid e can n ot be su bject to ten sile stresses. Th erefore, wh en u sin g d ies or in serts from carbid e, th e extru sion con tain er m u st be p restressed in su ch a way th at n o tan gen tial ten sile stress occu rs u n d er in tern al p ressu re. Accord in gly, th e in terferen ce d im en sion s are con sid erably h igh er th an th ose u sed for tool steels. Gu id elin es also h ave been establish ed for th e calcu lation of axial p re-stress levels; in th e th in , rin gsh ap ed lateral sp lit, su rface p ressu res of 700 to 1,000 N/ m m 2 are assu m ed as gu id elin e valu es. In extru sion d ies, th e actu al stress con d ition s d iffer from th e id eal assu m p tion s m ad e h ere, h owever. Th e extru sion con tain ers h ave a fin ite len gth , a lim ited an d p ossibly eccen tric p ressu re area, n o u n iform in tern al p ressu re exists, an d th e con tain ers h ave often off-cen ter d ie op en in gs. Realistic con d ition s in th e con figu ration of sh rin k fit assem blies can be d eterm in ed by u sin g d iscrete ap p roxim ation tech n iq u es, for exam p le th e fin ite elem en t m eth od (FEM). For p ractice-orien ted ap p lication , variou s calcu lation s h ave been con d u cted by m akin g a p aram etric stu d y u sin g FEM. Th ese resu lts h ave been m ad e accessible for p ractical ap p lication in th e form of Nom ogram s (VDI 3176, ICFG Doc. 5/ 82) an d corresp on d in g com p u ter p rogram s. Punch design Extru sion p u n ch es are su bjected to an axial force with an average com p ressive stress. Th ey are calcu lated as follows:

p St =

FSt A St

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Die design

495

Th e off-cen ter ap p lied force cau ses ad d ition al ben d in g stresses. Th e overall stress in th e p u n ch th en am ou n ts to:

σ St ges = p St (1 + 8 ⋅ e / d ) wh ereby d [m m ] is th e p u n ch d iam eter an d e [m m ] th e off-cen ter p osition of force ap p lication . Valu es for critical bu cklin g stress are p rovid ed in Fig. 6.7.8. With backward cu p extru sion , th e eccen tricity gen erally am ou n ts to e/ d = 0.01 to 0.02. Th e calcu lated p u n ch stress is com p ared to th e com p ressive yield stren gth of th e p u n ch m aterial in its h ard en ed state. Th e cou n terpu n ch is su bjected to an average com pressive stress of

pG =

FSt A0

d u rin g backward cu p extru sion .

3,000

forw ard rod extrusion

e/d = 0 0.01

2,000 0.05 0.1

backw ard cup e trusion

1,000 e md = 3,000 N/mm E = 225,000 N/mm

d

0

2

4

6

8

10

12

Fig. 6.7.8 Critical buckling stress in function of the slenderness ratio (l/d) of a punch made of high-speed steel: 1 forw ard rod extrusion; 2 backw ard cup extrusion; d punch diameter; e off-center position of force application; l (free) punch length

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Solid forming (Forging)

496

6.7.3 Die and punch materials Materials u sed for cold an d warm form in g are req u ired to h ave h igh stren gth , h igh tou gh n ess an d h igh h ard n ess. For an econ om ical d ie life, extrem ely good wear an d tem p erin g resistan ce are n ecessary. Die m aterials sh ou ld be ch osen , wh ere p ossible, to en su re good m ach in ability, an d as a resu lt, low m an u factu rin g costs (cf. Sect. 4.1.3). All th ese req u irem en ts can n ot be fu lfilled sim u ltan eou sly by each typ e of tool steel. Th e ch aracteristics wear resistan ce an d tou gh n ess, for exam p le, sh ow op p osin g ten d en cies. Th e m aterials 55NiCrMoV6 (1.2713), 57NiCrMoV7 (1.2714) an d X3NiCoMoTi1895 (1.2709) are extrem ely tou gh an d are u sed for sh rin k rin gs an d in serts wh ich are su bjected to h igh levels of elon gation . Th eir wear ch aracteristics, in

Table 6.7.3: Survey of the most frequently used cold, w arm and hot forging tool steels Die materials I / Cold forging tool steels / Active components M aterial No.

DIN

ANSI

JIS

Composition in %

to DIN

Germany

USA

Japan

C

Si

Mn

P

S

Co

Cr

Mo

Ni

V

1.2363

X100CrM oV51

A2

SKD11

1.00

0.30

0.55

0.03

0.03

–

5.00

1.10

–

1.2369 1.2379

81M 0CrV4216 X155CrVM o12 1

D2

SKD11

0.81 1.55

0.25 0.30

0.35 0.35

– 0.03

– 0.03

– –

4.00 12

4.20 0.70

– –

1.2709

X3NiCoM oTi1895

0.03

0.10

0.15

0.01

0.01

9.25

0.25

5.00

6F2

SKT4

0.55

0.30

0.60

0.03

0.03

–

0.70

0.30

SKT4

0.58

0.30

0.70

0.03

0.03

–

1.00

0.50

0.45

0.25

0.30

0.03

0.03

–

1.35

0.90

0.45

0.40

0.03

0.03

–

1.20

0.45

0.40

0.03

0.03

–

1.2713 1. NiCrM o 55NiCrM oV6 1.2714

57NiCrM oV7

1.2767 1.3207 HSS

X45NiCrM o4 S10-4-3-10

6F7 T42

SKH57

1.3343

S-6-5-2

M2

SKH51

1.3344

S-6-10-2

M 3/2

W

Ti

0.20

–

–

1.00 1.00

– –

– –

18

–

–

–

1.70

0,10

–

–

1.70

0.10

–

-

0.25

4.00

–

–

–

4.15

5.00

–

1.85

6.35

–

4.15

5.00

–

3.00

6.35

–

Die materials I / Hot-w arm forging tool steels / Active components M aterial No.

DIN

ANSI

JIS

Composition in %

to DIN

Germany

USA

Japan

C

Si

Mn

P

S

Co

Cr

Mo

Ni

V

W

Ti

6F2

SKT4

0.55

0.30

0.60

0.03

0.03

–

0.70

0.30

1.70

0.10

–

–

SKT4

0.58

0.30

0.70

0.03

0.03

–

1.00

0.50

1.70

0.10

–

–

1.2713 1. NiCrM o 55NiCrM oV6 1.2714

57NiCrM oV7

1.2343 2. CrNiM oV X32CrM oV51

H11

SKD6

0.38

1.00

0.40

0.03

0.03

–

5.30

1.10

–

0.40

–

–

1.2344

X40CrM oV51

H13

SKD61

0.40

1.00

0.40

0.03

0.03

–

5.30

1.40

–

1.00

–

–

1.2365

X32CrM oV33

H10

0.32

0.30

0.30

0.03

0.03

–

0.30

2.80

–

–

–

–

1.2367

X40CrM oV53

0.30

0.20

0.30

0.03

0.03

–

2.40

–

–

–

4.30

–

1.2606 3. W CrV

X40CrM oW 51

SKD62

1.2622

X60W CrCoV93

SKH51

SKD7

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Die design

497

Table 6.7.4: Heat treatment of cold, w arm and hot forging tool steels Die material II / Cold forging tool steels / Active components No.

Heat treatment (°C)

Hardness

Cooling

Application/hardness (HRC/N/mm2)

Quenching Annealing Hardening medium

Tempering 180-400

60 +/–1

blanking/punching dies

550

61 +/–1

punches, blanking/punching dies punches, dies

Ö,W B 400

(customary) W ater

1.2363

800-840

930-970

1.2369

800-840

1,070-1,100 Ö,W B 450-550

1.2379

840-860

1,040-1,080 Ö,L,W B 400

180-250

60 +/–1

1.2709

840

480

L

–

55

1.2713

650-700

830-870

Ö

300-650

45 +/–1

P,Ö,(W ) P,Ö,(W )

shrink ring shrink/intermediate ring and pressure pin (53+/-1 HRC, 1,150 N/mm 2)

1.2714

650-700

860-900

L

300-650

45 +/–1

1.2767

610-630

840-870

W ,Ö,L

160-250

54 +/–1

punch, mandrel, one piece press container

1.3343

1,100-900

790-820

Ö,L,W B 550

540-560

62 +/–1

punch, die (insert), press container and

1.3344

1,100-900

770-820

Ö,L,W B 550

550-570

62 +/–1

counterpunch, mandrel

Die material II / Hot, w arm forging tool steels / Active components No.

Heat treatment (°C)

Hardness

Cooling

Application/hardness

42 +2

P,Ö,(W )

shrink/intermediate ring and

300-650

42 +2

P,Ö,(W )

pressure pin (52+2 HRC, 1,150 N/mm 2)

1,000-1,040 L,Ö,W B 500-550

550-650

50 +2

W ,P,Ö

die (insert), shrink ring (45+/–1 HRC)

1,020-1,060 L,Ö,W B 500-550

550-650

50 +2

P,Ö

750-800

1,020-1,060 Ö,W B 500-550

500-670

50 +2

(W ),L,P,Ö

die (insert), punch and

750-800

1,060-1,100 L,Ö,W B 500-550

600-700

54 +2

(W ),L,P,Ö

counterpunch

1.2606

750-790

1,020-1,050 Ö,L,W B 500-550

550-650

1.2622

760-800

1,150-1,200 Ö,W B 500-550

500-650

Quenching Annealing Hardening medium

Tempering

(customary)

1.2713

650-700

830-870

Ö

300-650

1.2714

650-700

860-900

L

1.2343

750-800

1.2344

750-800

1.2365 1.2367

HRC

W = w ater

W B = w ater bath

L = air

mandrel and counterpunch

W ,L,P,Ö 56 +2

P = compressed air

L,Ö

blanking die

Ö = oil

con trast, are n ot q u ite as favorable. Th e h igh -sp eed steel S10-4-3-10 (1.3207) offers ou tstan d in g wear ch aracteristics, bu t ten d s to be m ore brittle. Th e m aterials X155CrVMo121 (1.2379) an d S-6-5-2 / S-6-10-2 (1.3343/ 44) rep resen t a com p rom ise con cern in g wear an d tou gh n ess ch aracteristics: Th eir tem p erin g resistan ce can also be con sid ered to be very good at 550 °C. Th e m ost im p ortan t criterion to be con sid ered wh en selectin g a tool m aterial is th e typ e an d exten t of load , followed by th e layou t an d geom etry of th e d ie. Table 6.7.3 p rovid es a su m m ary of th e m ost com m on ly u sed tool m aterials for cold an d warm form in g. Th e table also sp ecifies th e d esign ation s of com p arable steels from th e USA or Jap an an d th eir com p osition s. Table 6.7.4 d escribes th e h eat treatm en t, i. e. th e an n ealin g tem -

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498

p eratu re, th e h ard en in g tem p eratu re, th e q u en ch in g m ed iu m an d th e tem p erin g tem p eratu res. Th e levels of h ard n ess gen erally req u ired for d ies u sed in cold form in g ap p lication s are also given . Table 6.7.5 d escribes th e ch aracteristics of wear, tou gh n ess, m ach in ability an d grin d in g u sin g a 10-p oin t scale, wh ereby a h igh n u m ber in d icates esp ecially good cap ability. Th e tables m ake n o claim to com p leten ess, bu t p resen t a su bstan tially red u ced n u m ber of actu ally req u ired tool steels in followin g th e p rin cip les of op tim ised an d red u ced in ven tory. Th e m ost freq u en t tool m aterial u sed for cold forgin g is h igh -sp eed steel, wh ile for warm forgin g tem p eratu re-resistan t tool steel is u sed .

Table 6.7.5: Properties of cold, w arm and hot forging tool steels Die materials III / Cold forging tool steel / Active components No.

Characteristics

Remark

V

Z

B

S

1.2363

7

6

8

7

1.2369 1.2379

7/8 8

5 4

4

4

12 % Cr-steel

1.2709

5

9

5

7

special steel

1.2713

2

10

6

8

1.2767

4

10

6

8

1.3343

9 9

2 4

4 4

5 5

1.3344

10

3

3

4

1.2714

Die materials III / Hot, w arm forging tool steel / Active components No.

1.2713

Characteristics

Remark

V

Z

B

S

2

10

6

8

44 HRC 1,400 -1,480 N/mm 2 52 HRC 1,800 - 1,900 N/mm 2

1.2714 50 HRC 1,700 - 1,800 N/mm 2

1.2343

5

8

1.2344

5

8

8

8

surface w elding Capilla 521 for erosive machining

1.2365

4 5

8

8

8

surface w elding Capilla 5200 for machining 50 HRC 1,700 - 1,800 N/mm 2

7

8

8

54 HRC 1,925 - 2,050 N/mm 2

1.2367 1.2606

56 HRC 2,050 - 2,200 N/mm 2

1.2622 V = w ear resistance

Z = toughness

B = machinability

S = grindability

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Die design

Powder m etal-m an u factu red h igh -sp eed steels dem on strate very u n iform carbide distribu tion an d are segregation -free. Th is resu lts in im p roved tou gh n ess p rop erties an d extrem ely h igh com p ressive stren gth . If a larger wear resistan ce is req u ired, for exam p le for forward rod extru sion or iron in g dies, for large-p rodu ction series carbides are also u sed. Th e carbide typ es u sed com p rise tu n gsten carbide as a p h ase in a cobalt m atrix. Th e cobalt con ten t wh ich determ in es th e ch aracteristics of th e carbide, lies between 15 an d 30 %. With a risin g tu n gsten carbide con ten t, h ardn ess, com p ressive stren gth an d wear resistan ce all in crease. However, at th e sam e tim e tou gh n ess, n otch im p act stren gth , ben din g an d bu cklin g resistan ce are redu ced. Th e grain size exerts an in flu en ce h ere: fin e-grain ed carbides are u n su itable as a resu lt of p oor tou gh n ess ch aracteristics. Table 6.7.6 p rovides a su m m ary of th e m ech an ical ch aracteristics of carbides. Th e stren gth valu es ap p ly to static loads an d m u st be redu ced by 50 % for stress cycles greater th an 10 6 . Tool steels for warm form ing Th e m aterials X40CrMoV53 (1.2367), X38CrMoV51 (1.2343), X40CrMoV51 (1.2344) an d X60W CrCoV93 (1.2622) are cu rren tly u sed for warm form in g an d in con ju n ction with th e water coolin g m eth od gen erally ap p lied tod ay; In th e case of sh rin k rin gs, 55NiCrMoV6 (1.2713)/ 57NiCrMoV7 (1.2714) or X38CrMoV51 (1.2343)/ X40CrMoV51 (1.2344) can be u sed . Du e to th eir low th erm al sh ock resistan ce, carbid es, h igh -sp eed steels an d cold form in g tool steel 81MoCrV4216 (1.2369) are on ly su itable wh en u sin g water-free coolin g m eth od s wh ich were com m on in th e p ast. On closer exam in ation , it becom es clear th at m aterials for warm forgin g are gen erally th ose u sed in th e classical field of h ot forgin g. Sp ecial m aterials for warm forgin g, wh ich are cap able of with stan d in g relatively h igh p ressu re levels an d relatively h igh tem p eratu res sim u ltan eou sly, h ave n ot yet been d evelop ed for im p lem en tation in series p rod u ction . Develop m en ts of d ie m aterials for warm form in g are m ovin g in th e followin g d irection s: Com p ared to h ot forgin g tool steels, h igh -sp eed steels alread y exh ibit good wear an d h eat resistan ce p rop erties as well as im p roved tem p erin g resistan ce. By a grad u al red u ction of th e carbon con ten t, attem p ts h ave been m ad e to ach ieve a fu rth er im p rovem en t in th erm al sh ock resistan ce of h igh -sp eed steels. With sim u ltan eou s d eterioration of th e wear an d h eat resistan ce, h owever, th e th erm al sh ock resistan ce level

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Solid forming (Forging)

500

Table 6.7.6: M echanical properties of carbides

Co content

Carbide types Density Hardness

E-modulus

Ultimate strength Compressive strength Bending strength

g/cm 3

HV

N/mm 2

N/mm 2

N/mm 2

15

14.0

1,150

530,000

4,000

2,400

20

13.5

1,050

480,000

3,800

2,600

25

13.1

900

450,000

3,300

2,600

30

12.7

800

420,000

3,100

2,700

% by w eight

was far below th at of h ot form in g tool steels. In view of th e su ccessfu l im p lem en tation of en viron m en tally frien d ly water-solu ble lu brican ts, th e factor th erm al sh ock resistan ce is exp ected to con tin u e to be a su bject of p articu lar in terest. Th u s, in vestigation s are con cen trated on tool steels wh ich are d erived from h ot form in g tool steels, i. e. th ose wh ich h ave a relatively low carbon con ten t. Th ese tool steels d em on strate su p erior wear an d h eat resistan ce p rop erties as well as very good th erm al sh ock resistan ce. A n u m ber of differen t die m aterials are bein g develop ed con cu rren tly, for exam p le u sin g n ickel-based alloys (In con ell 718), wh ich h ave already p rodu ced good resu lts in bar extru sion (tem p eratu res 1,150 °C, p ressu res of 900 to 1,100 N/ m m 2 ) an d isoth erm forgin g ap p lication s. Die coatings (V DI 3198) Th e cost-effectiven ess of cold forgin g p rocesses d ep en d s largely on th e tool costs an d accord in gly on th e ach ievable service life of d ies. Die wear in flu en ces th e d im en sion al stability an d su rface q u ality of th e p rod u ced workp ieces. Th ere are two m ain typ es of wear resistan t coatin gs con sid ered for u se in forgin g tech n ology. Coatin gs, for exam p le u sin g ad d in g-on p rocesses su ch as CVD or PVD p rocesses, an d coatin gs obtain ed th rou gh reaction layers su ch as n itrid in g an d ion im p lan tation . Processes wh ich h ave p roven su ccessfu l for cold form in g d ies in clu d e th e CVD an d PVD tech n iq u es, wh ich p erm it service life to be m ore th an d ou bled (cf. Sect. 4.1.3). An essen tial p rereq u isite for a su ccessfu l coatin g is good adh esion between th e coatin g m aterial an d th e su bstrate, wh ose h ardn ess an d com p ressive stren gth m u st p rovide adeq u ate su p p ort. High -sp eed steels,

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Die design

501

ledebu ritic 12 % ch rom iu m steels (1.2379) an d carbides fu lly com p ly with th ese req u irem en ts. Coatin gs are ap p lied m ain ly by sp ecialized com p an ies. Th is m ean s th at p articu lar atten tion m u st be p aid to th e p rep aration of d ies by th e d ie m an u factu rer. Prior to coatin g, th e work su rfaces m u st be free of grooves an d p olish ed to a su rface rou gh n ess of Rz < 1 m m . Th e lim it for op tim u m coatin g of in tern al h oles is arou n d l (len gth ) = d (d iam eter) wh en u sin g th e PVD tech n iq u e. With th e CVD tech n iq u e, th ere are n o kn own lim itation s. Th e lim its for th e ratio between th e d iam eter D an d th ickn ess H of coated p an els in cases wh ere a “d eflection ” of < 0,02 m m is req u ired after treatm en t, are as follows wh en u sin g th e CVD tech n iq u e: D 20 m m ) very econ om ical (cf. Sect. 3.2.1). Th e eigh t-track slid e gib op erates accord in g to th e “fixed -loose bearin g” p rin cip le, th u s com p en satin g for th erm al exp an sion in th e slid e. Th is m akes th is p ress id eally su ited for warm an d h ot form in g (cf. Fig. 3.1.7). Th e slide stroke ran ges between 250 an d 400 m m (sp ecial design s u p to 520 m m ) (Fig. 6.8.4).

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Fig. 6.8.4 M ultiple-station press w ith modified knuckle-joint top drive (nominal press force 10,000 kN, four stations, loading system and transfer feed)

Multiple-station presses with eccentric drive Th e m ain field of ap p lication for th ese p resses with n om in al p ress forces from 6,300 kN lies in warm form in g (680 to 820 °C) an d au tom ated flash less forgin g (Fig. 6.8.5). Du e to th eir large slid e stroke of 630 to 800 m m , th ese p resses are also id eally su ited for cold form in g of lon g, sh aft-typ e p ressed p arts. Th e slid e is gu id ed in th e sam e gib system as illu strated in Fig. 3.1.7. Th is gu id an ce con cep t also p erm its n arrow gib clearan ces in warm an d h ot form in g ap p lication s, m ean in g th at it is n o lon ger n ecessary to p rovid e for an ad d ition al clearan ce to com p en sate for th e u n avoid able th erm al exp an sion of th e slid e.

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Presses used for solid forming

Fig. 6.8.5 Warm forming line comprising a multiple-station press w ith eccentric drive (nominal press force 20,000 kN, induction furnace, transfer feed and die change support)

Con seq u en tly, extrem ely p recise p ressed p arts can be p rod u ced . Cen tral offset, in p articu lar, is con sid erably lower th an wh en u sin g con ven tion al gib system s. As a resu lt, addition al m easu res su ch as lateral p u n ch adju stm en ts or colu m n gibs can be elim in ated. In warm an d h ot form in g ap p lication s, th is con cep t is su p p lem en ted by h igh ly efficien t coolin g system s wh ich su bstan tially red u ce th e overall h eat gen eration in th e d ies. Horizontal m ultiple-station presses for m anufacture of pressed parts m ade of wire Th e m ajor ben efit of h orizon tal m u ltip le-station p resses is th at wire, su itably p re-treated for cold form in g, can be u sed . Th u s, th e m an u factu re of (largely cold p ressed ) con tou red p arts is p ossible with ou t ad d i-

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

511

Solid forming (Forging)

512

tion al ch em ical or th erm al treatm en t. Th e wire is d rawn an d straigh ten ed by a wire feed d evice. An in tegrated sh earin g system with closed sh earin g d ies is u sed to p rod u ce volu m etrically p recise slu gs. Th e sp ecial grip p er tran sfer system tran sfers th e p arts from on e station to th e n ext (cf. Sect. 6.6). Th e m ain d esign featu re of th e p ress lin e illu strated in Fig. 6.8.6 is th e laterally p osition ed d ie m ou n tin g area wh ich is accessible from th e op erator’s sid e. Th is con cep t p erm its an ergon om ically favorable tool settin g an d con ven ien t tool ch an ge. Oth er im p ortan t d esign featu res in clu d e th e h igh ly robu st slid e gib again st off-cen ter load in g, th e cast m on obloc fram e stru ctu re (cf. Fig. 3.1.1) an d in d ivid u ally ad ju stable grip p er an d ejection system s for each p ress station . Th e p rod u ction strokin g rates for th is typ e of p ress are su bstan tially h igh er th an th at fou n d in com p arable vertical m u ltip le-station p resses. Th u s, th e u se of th ese p resses is h igh ly econ om ical for large-scale p ro-

Fig. 6.8.6 Horizontal multi-station press suitable for fasteners and form parts manufactured from w ire (nominal press force 1,300 kN, five stations, quick tool change system, w ire diameter max 18 mm)

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513

du ction desp ite th e h igh in itial in vestm en t costs in volved. By u sin g sem i-au tom atic an d au tom atic die resettin g an d die ch an ge system s, setu p tim es can be su bstan tially redu ced, m ean in g th at even m ediu m batch sizes of 20,000 to 40,000 p arts can be econ om ically m an u factu red (cf. Fig. 3.4.5). Th e p resses are u sed at n om in al p ress forces of between 1,000 an d 6,300 kN for wire diam eters ran gin g from 10 to 36 m m . Horizontal presses – single-station with knuckle-joint drive Th ese p ress system s are u sed m ain ly for th e p rod u ction of extru d ed p arts m ad e of alu m in iu m an d alu m in iu m alloys (Fig. 6.8.7): Th ese m ach in es are also id eally su ited for p re-form in g steel slu gs. Th e p resses are fu lly au tom ated an d m ake u se of sim p le, cam -con trolled p u sh ers for p art feed . Th e h orizon tal d esign , sim p le p art feed an d d isch arge an d th e su p erior form in g ch aracteristics of alu m in iu m p erm it h igh strokin g rages of u p to 300/ m in . Com p ared with vertical p resses, su bstan tially h igh er strokin g rates also resu lt wh en form in g steel. Nom in al p ress forces ran ge between 1,500 an d 12,000 kN.

slide

fi ed link point

punch

connecting rod

eccentric dri e dri e shaft

Fig. 6.8.7 Single-station horizontal press w ith knuckle-joint drive (nominal press forces 1,500 to 12,000 kN)

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Horizontal presses with m odified knuckle-joint If lon ger form in g strokes are n ecessary, a m od ified kn u ckle-join t d rive system can be u sed as a sp ecial variation of th e stan d ard kn u ckle-join t p ower u n it. Th e force-stroke cu rve an d th e slid e velocity corresp on d to th e vertical p ress sh own in Fig. 6.8.3.

6.8.3 Hydraulic presses Hyd rau lic p resses are also d esign ed in vertical an d h orizon tal layou ts. Th ey en joy extrem ely u n iversal ap p lication in solid form in g both on a sin gle-station an d m u ltip le-station basis, eith er with m an u al op eration for sm all batch sizes or fu lly au tom atically for p rod u ction rates of u p to 1.8 m illion p ressed p arts p er year. Th ey are freq u en tly u sed as p resses for lon g sh afts an d sh aft-typ e p arts, or for large p arts with weigh ts of u p to ap p rox. 15 kg. As in m ech an ical p resses, th e selection of th e n ecessary p ress size is m ad e on th e basis of p art geom etry, workp iece m aterial an d of th e req u ired m an u factu rin g p rocess. Th e basic p rin cip les are d escribed in Sects. 3.3 an d 6.5. Vertical design Th e h yd rau lic com p on en ts an d oil tan ks are gen erally accom m od ated in th e p ress crown (Fig. 6.8.8). A service p latform offers con ven ien t m ain ten an ce of th e easily accessible u n its. Th e u p righ ts are gen erally con figu red in th e form of a weld ed m on obloc or p an el stru ctu re (cf. Fig. 3.1.1). In sp ecial cases (for exam p le in th e even t of sp ace p roblem s or to red u ce n oise), th e p u m p s an d m otors can also be m ou n ted in th e fou n d ation or in a sep arate room . Vertical h yd rau lic p resses are gen erally u sed for cold form in g. However, it is n ot u n u su al for th em to also be u sed for h ot form in g u n d er certain circu m stan ces (cf. Sect. 6.8.5). Particu larly wh ere large p arts are in volved (weigh ts above 5 kg), h yd rau lic p resses are freq u en tly u sed for h ot forgin g. Th e u su al p ress forces lie between 1,600 an d 36,000 kN, an d p resses with slid e strokes of u p to 1.5 m h ave alread y been m an u factu red .

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Presses used for solid forming

Fig. 6.8.8 Hydraulic multiple-station press (nominal press force 20,000 kN, four stations, loading system, transfer feed and die change support)

Horizontal design Lo n g t u bu lar p art s su ch as sh o ck abso rber sleeves are d rawn fro m flat blan ks o r backward cu p ext ru sio n s m ad e fro m circu lar blan ks (cf. Fig. 6.1.1). A su bseq u en t iro n in g p ro cess o ver several st ages t h en red u ces t h e wall t h ickn ess (cf. Fig. 6.1.2). Th e wo rkp iece is h eld by a p u n ch , wh ich d raws it t h ro u gh o n e o r m o re iro n in g rin gs. Th e bo t tom th ickn ess rem ain s u n ch an ged . For th is p rocess, extrem ely lon g form in g strokes are req u ired . Th erefore, in su ch ap p lication s h yd rau lic p resses are m ost freq u en tly u sed . A h orizon tal p ress layou t h as a n u m ber of ben efits to offer h ere: – – – –

set-u p on floor level, sim p le gravity feed , sim p le d isch arge by m ean s of syn ch ron ized con veyor belts, sim ple in terlin kin g, for exam ple with autom atic edge trim m in g devices.

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516

Figure 6.8.9 illu strates th e layou t of a p articu larly econ om ical p ress system for iron in g. Th e slid e is d riven on two sid es by p lu n ger p iston s. Th e d ie sets are located on both sid es with load in g ch am bers p osition ed in fron t. Th e righ t an d left-h an d p u n ch es are gu id ed im m ed iately in fron t of th e workp iece load in g ch am ber u sin g an ad d ition al p u n ch su p p ort. With each stroke, altern atively form in g an d strip p in g of th e form ed p art take p lace on eith er sid e. Each n ew workp iece p u sh es th e p reviou sly strip p ed p art th rou gh th e workp iece h old er ou t of th e p ress. With th e sam e form in g p rocess takin g p lace in th e left an d righ t-h an d d ie sets, it is p ossible to alm ost d ou ble th e ou tp u t com p ared to a con ven tion al vertical p ress d esign . Altern atively, th e p art p rod u ced in on e of th e d ie sets can be fu rth er p rocessed in th e oth er d ie set followin g in term ed iate treatm en t. In th e case of th ick-walled blan ks, an u p stream d eep -d rawin g p rocess can be in tegrated as an in itial op eration . Precise slid e gu id an ce on th e p ress bed an d p recisely ad ju stable p u n ch gu id an ce p erm it to obtain extrem ely n arrow toleran ces con cern in g th e con cen tricity of d im en sion s.

stripper ironing ring

punch guide

die holder

slide

punch support

loading chamber

die holder

slide stroke

die chamber

Fig. 6.8.9 Horizontal hydraulic press w ith one slide and tw o press beds

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Presses used for solid forming

6.8.4 Supplementary equipment A large n u m ber of special m easu res an d equ ipm en t are available to address ever m ore strin gen t dem an ds for m axim u m possible produ ction ou tpu ts, low set-u p tim es an d th e m in im u m ach ievable m an u factu rin g costs. Th e m ost im portan t elem en ts h ere are system s for th e au tom atic loadin g an d tran sfer of parts th rou gh variou s die station s. Loading system s for blanks and pre-form ed workpieces W h ere p arts weigh in g less th an 150 g are p rod u ced , p resses are gen erally load ed u sin g vibration feed in g d evices wh ich are filled u sin g in clin ed con veyors. Heavier p arts are gen erally fed u sin g in clin ed con veyors with rotatin g steel belts or – in p articu lar wh ere p re-form ed p arts are bein g fed – by m ean s of p u sh in g con veyors. Th e ou tfeed area of th ese system s is eq u ip p ed with d evices for p art orien tation to en su re th at th e p arts are correctly align ed wh en th ey en ter th e in -feed ch an n el an d th e load in g station (Fig. 6.8.10).

Fig. 6.8.10 Loading device for cold extrusion press lines

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Feed system s A n u m ber of d ifferen t feed system s can be u sed to tran sfer th e p arts th rou gh th e p ress an d in to th e d ies. Th e so-called tran sfer feed system is th e d om in atin g m eth od for vertical m u ltip le-step p resses. Feed system s com e in a d u al-axis version , or with an ad d ition al liftin g stroke for lon g p arts, in th e form of a tri-axis tran sfer. Th e con trol cam s are d riven in m ech an ical p resses by d irect cou p lin g with th e p ress d rive system . In th e case of h yd rau lic p resses, th e variou s u n its are actu ated by servo d rive system s (Fig. 6.8.11). Hyd rau lically d riven swivel-m ou n ted grip p ers are u sed to tran sp ort h eavy p ressed p arts with weigh ts over 5 kg (Fig. 6.8.12). Th e con trolled grip p ers are con figu red for a su bstan tially h igh er clam p in g force th an is p ossible u sin g tran sfer feed system s. Th e swivel-m ou n ted grip p ers gen erally execu te a liftin g m ovem en t. A loadin g arm (swivel or lin ear m ovem en t) is u sed to tran sfer th e p arts from th e loadin g station in to th e first p ressin g station , an d on e grip p er arm is allocated to each die station .

Fig. 6.8.11 Tw o-axis transfer feed

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Fig. 6.8.12 Sw ivel arm feed for pressed parts w ith piece w eights up to 15 kg

In ad d ition to th ese system s, a n u m ber of oth er feed d evices is u sed in clu d in g th e freely p rogram m able h an d lin g robot. In h orizon tal m u ltip le-station p resses, grip p er arm s p owered in d ivid u ally by cam s or servo d rive system s are u sed . W eight control W h en billets are p rep ared , weigh t d ifferen ces are u n avoid able. Th ese are th e resu lt n ot on ly of len gth toleran ces occu rrin g d u rin g th e billet sep aration , bu t also (som etim es to a far greater exten t) of d iam eter toleran ces in th e startin g m aterial. Particu larly wh en u sin g closed (trap p ed ) d ie system s, exceed in g th e ad m issible blan k weigh t m ay cau se d ie failu re. W h en tran sp ortin g th e con tain er filled with billets to th e in term ed iate treatm en t p rocesses an d to th e p ress, it is also p ossible for p arts to be accid en tally p laced in th e wron g con tain ers. Th is can n atu rally lead to d ie d am age wh en p ressin g. In ord er to elim in ate th e risk of feed in g in correct p arts, au tom ated p ress lin es are freq u en tly eq u ip p ed with a

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d evice wh ich ch ecks p art weigh t. Th e d evices u sed h ere are electron ically con trolled au tom atic scales, wh ich are m ou n ted between th e load in g system an d th e feed in g station . Parts wh ich are too h eavy or too ligh t are au tom atically ejected . Th e weigh in g accu racy is below 0.2 % of workp iece weigh t. Th ese d evices are able to weigh au tom atically u p to 80 p arts p er m in u te. Die change Fast die ch an ge can be a decisive factor wh en it com es to th e econ om ic viability of a p ress, in p articu lar wh en workin g with sm all batch sizes. Both die set an d in dividu al die ch an gin g system s are u sed (cf. Fig. 3.4.5). Th e basic die ch an ge p rin cip le u sed in p resses for sh eet m etal form in g an d solid form in g are very sim ilar. A m ore detailed descrip tion is p rovided in Sect. 3.4. However, die ch an ge is on ly on e asp ect wh ich determ in es sh ort set-u p tim es in au tom atic p ress lin es. Fast resettin g of th e loadin g an d feed system s is eq u ally im p ortan t h ere.

6.8.5 Special features of hot and w arm forming lines Th e sp ecial su p p lem en tary eq u ip m en t d escribed in Sect. 6.8.4 is also u sed for h ot form in g. An ad d ition al an d essen tial req u irem en t of h ot form in g system s is an effective coolin g an d lu brication system . Dep en d in g on th e d egree of form in g d ifficu lty, basically two d ifferen t system s are u sed : Flooding Dies are cooled an d lu bricated by con tin u ou s floodin g u sin g sp ecial lu brican ts, som e of wh ich are m ixed with water at a ratio of between 1 : 2 an d 1 : 4. Th e lu brican t an d water m ixtu re is fed towards th e die th rou gh boreh oles an d sp ray rin gs, an d drain s away via gen erou sly dim en sion ed ch an n els. Th e lu brican t is su p p lied from a cen tral reservoir with a cap acity of between 400 an d 1,000 l by m ean s of m ediu m p ressu re p u m p s (workin g at a p ressu re level of 10 to 20 bar) (cf. Sect. 3.2.11). Used lu bricatin g em u lsion is collected, p u rified an d retu rn ed to th e reservoir, wh ich is eq u ip p ed with a re-coolin g system . Filters in th e retu rn an d p ressu re circu its take care of th e n ecessary p u rification . Th e lu brican t is m ixed with bactericid es in ord er to p reven t bacterial in fes-

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tation . As th is wou ld ren d er th e lu brican t u n u sable, bactericid es are gen erally ad d ed to th e lu brican ts by m ost su p p liers. Th e lu brican t q u an tities are set u sin g sim p le m an u al con trol d evices. Au tom atic d evices for con trollin g th e lu brican t q u an tity are available. W h ere lu brican ts con tain grap h ite, an agitatin g d evice in th e reservoir is essen tial in ord er to p reven t solid grap h ite p articles from settlin g d own in th e reservoir. Spray system s with com pressed air as carrier Mist coolan t ap p lication system s p rovide an extrem ely fin e su rface film of coolan t an d lu brican t for op tim u m coolin g an d lu brication . Coolan ts an d lu brican ts are fed u sin g a join t p ip e. Water is u sed for coolin g, wh ile dep en din g on th e p rocess in volved, differen t lu bricatin g agen ts can be u sed. Grap h ite-free em u lsion s con tain in g water-m ixable oils are gen erally u sed for sim p le form in g op eration s. W h ere m ore com p lex form in g p rocesses h ave to be p erform ed (su ch as con stan t velocity join t com p on en ts u sed in veh icle drive system s), em u lsion s m ade of oil an d grap h ite are u sed. Th ese em u lsion s com p rise a 1 : 1.3 to 1 : 4 m ixtu re with water. Th e water an d lu brican t q u an tities are con trolled altern atively by electro-valves. Com p ressed air is u sed as a carrier m ed iu m for th e lu brican t. Com p ressed air an d water or lu brican t are m ixed to create a m ist in a m ixin g valve an d fed to th e d ie th rou gh a join t p ip e. Th e electro-valves are con trolled in d ivid u ally for each station . Cooling system s for forging Du rin g au tom atic forgin g, h igh -p ressu re sp ray system s (80 –120 bar) are u sed for coolin g p u rp oses. Th ere is gen erally n o n eed for ad d ition al lu brication . In order to ach ieve th e n ecessary degree of h eat dissip ation , con siderable q u an tities of water are req u ired (between 40 an d 60 m 3 / h ). Th e coolin g water is clean ed, recooled an d th en re-u sed. Th e scale collected in th e water m u st be rem oved u sin g screen s an d filters. Billet heating Billets are h eated by in d u ction . For th e tem p eratu re ran ge of 760 to 800 °C, in du ctor ou tp u ts of ap p rox. 0.24 kW are req u ired p er kg of steel. Dep en din g on th e billet diam eter, th e freq u en cy ran ge lies between 2 an d 4 kHz. For forgin g tem p eratu res from 950 to 1,100 °C, arou n d 0.40 to 0.45 kW / kg of steel are req u ired at freq u en cies of 1 to 2 kHz. In gen -

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eral, alu m in iu m an d alu m in iu m alloys are also h eated by in d u ction to tem p eratu res between 420 an d 480 °C, d ep en d in g on th e alloy. Th e req u ired in d u ctor ou tp u t is ap p rox. 0.35 to 0.4 kW / kg with a freq u en cy of 0.5 to 1 kHz. Th yristor-con trolled system s are u sed as con verters. Con sid erable q u an tities of coolin g water are req u ired to cool th e in d u ctors. Recoolin g is p erform ed in th e p lan t’s own recoolin g system s or in sep arate in stallation s. Billet preparation Warm form in g (680 to 800 °C) of sh aft-sh ap ed p arts m ad e of steel freq u en tly calls for coatin g (p re-grap h itizin g) of blan ks. Th is m easu re serves to in crease d ie service life an d is p articu larly ben eficial for first pressin g operation s (gen erally forward extru sion or redu cin g operation s). Th e graph ite can eith er be tu m bled on prior to h eatin g, or sprayed on du rin g th e h eatin g process. Th is en tails in du ctive pre-h eatin g of th e blan ks (approx. 180 °C), followed by spray application of th e graph itewater m ixtu re. Th e water evaporates over a relatively sh ort travel, du rin g tran sport to th e m ain in du ction h eater. Th u s, th e billets are h eated with a dried-on coatin g of graph ite. Alth ou gh a proportion of th e applied grap h ite bu rn s, a relatively h igh p ercen tage (ap p rox. 60 %) still p erm its lu brication an d , togeth er with a (very th in ) scale layer, creates th e d esired lu bricatin g an d sep aratin g effect in th e d ie.

6.8.6 Sizing and coining presses Sizing of forged and sintered parts Th e d im en sion s, toleran ces an d su rface q u ality of forged or h ot form ed p arts freq u en tly fail to m eet th e stan d ard s exp ected from fin ish ed p rod u cts. Con seq u en tly, often costly fin ish p rocessin g op eration s are n ecessary. By in trod u cin g a sizin g op eration , su bstan tially n arrower toleran ces can be ach ieved an d su bseq u en t m ach in in g p rocesses can be red u ced . Man y forged p arts are fin ish m ach in ed on m ach in in g cen ters. Th ese call for p recise clam p in g an d con tact su rfaces in ord er to assu re a rep rod u cible an d well d efin ed workp iece clam p in g. It is freq u en tly n ot p ossible to ach ieve, in forged p arts, a su rface q u ality th at is req u ired for

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adeq u ate clam p in g. In th is case, cold sizin g of th e ap p rop riate su rfaces is an essen tial p re-req u isite for su ccessfu l fu rth er p rocessin g (Fig. 6.8.13). Sin tered p arts are also freq u en tly su bjected to a su bseq u en t com p actin g or sizin g p rocess in order to com p en sate for warp in g cau sed by h eat treatm en t (Fig. 6.8.14). All th ese op eration s req u ire a large form in g force, cou p led with m in im al m ach in e an d d ie d eflection . Du e to its favorable force d istribu tion , th e kn u ckle-join t bottom d rive p ress h as been sh own to offer th e m ost su itable form in g system for coin in g ap p lication s. Th e basic p rin cip le of th is d rive typ e is d escribed in Sect. 3.2.2 an d 6.8.2 (cf. Fig. 3.2.5). Com p ared to p resses for solid form in g, th e slid e stroke an d work len gth can be su bstan tially sh orter. Sizin g is gen erally p erform ed in a sin gle station , so allowin g th e d ie m ou n tin g area or th e p ress bed to be sm aller. Ejector system s in th e slid e an d p ress bed are on ly n ecessary for coin in g work. Cutlery em bossing presses In ad d ition to p ossible ap p lication s alread y ou tlin ed h ere, th is typ e of sizin g p ress is also u sed with a good d egree of su ccess for th e form in g an d em bossin g of cu tlery. Th is op eration allows even th e fin est ch isellin g effects to be p recisely em bossed .

Fig. 6.8.13 Coined forgings

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Fig. 6.8.14 Coined sintered parts

Fig. 6.8.15 Operating sequence for the manufacture of open w renches

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Presses used for solid forming

Em bossing of hand tools An oth er field of ap p lication for calibratin g p resses is th e em bossin g of h an d tools. Figure 6.8.15 illu strates th e seq u en ce of op eration s in volved in th e m an u factu re of an op en wren ch . Usin g slu gs blan ked from p late, th e p arts are m an u factu red in eigh t op eration s on a kn u ckle-join t p ress with bottom d rive, n om in al p ress force 16,000 kN (cf. Fig. 3.2.5). Th e p rod u ction strokin g rate is 35 p arts p er m in u te. Th e p lan t op erates on a fu lly au tom atic basis. Th e slu gs are stored , an d a two-axis tran sfer is u sed as a feed system (Fig. 6.8.11). In ord er to assu re fast d ie ch an ge, d ie ch an ge sets are u sed . Th ese can be m oved in an d ou t, con trolled by p u sh bu tton , by a d ie ch an ge cart (Fig. 6.8.16). Th e d ie sets are fasten ed by m ean s of h yd rau lic clam p s (cf. Fig. 6.7.1).

Fig. 6.8.16 Line for the manufacture of open w renches (nominal press force 16,000 kN, transfer feed and die change cart)

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6.8.7 M inting and coin blanking lines Rim m ing and edge lettering m achines Coin blan ks are m an u factu red on h igh -sp eed blan kin g p resses from an in d exed sh eet m etal strip (cf. Fig. 4.6.6 and 4.6.8). Dep en d in g on th e m aterial ch aracteristics an d th e con d ition of th e d ie, a rou gh cu t su rface an d / or blan kin g bu rr are form ed at th e ou tsid e su rface of th e coin blan k (cf. Fig. 4.7.8). To ach ieve a h igh level of coin q u ality, th e ou tsid e ed ge of th e coin blan k m u st be sm ooth ed . Th is is ach ieved by a rad ial u p settin g p rocess in rim m in g an d ed ge letterin g m ach in es. W h en sm ooth in g th e ed ge, th e coin blan k is sized with in extrem ely n arrow toleran ce lim its (+/ – 0.02 m m ). Red u cin g th e d iam eter by 0.2 to 0.5 m m cau ses m aterial to accu m u late at th e p erip h ery of th e coin blan k. Dep en d in g on th e in ten d ed p u rp ose, d ifferen t u p settin g sh ap es can be selected (Fig. 6.8.17). Th e rim m in g or u p settin g p rocess h elp s to accu m u late th e m aterial n ecessary for form in g th e rim area of a coin . Th u s, th is m aterial d oes n ot h ave to be forced ou tward s from th e cen ter of th e coin blan k. As a resu lt, th e coin in g p rocess, con du cted after u p settin g, req u ires less force. Redu ction of th e coin in g force leads in tu rn to an in crease in th e service life of th e coin in g dies. Rim m in g m ach in es are u sed for a d iam eter ran ge from 14 to 50 m m both with vertically an d h orizon tally arran ged u p settin g sh afts. In rim m in g m ach in es with a vertical u p settin g sh aft, th e blan ks are fed toward s th e u p set d ie, wh ich com p rises th e u p set rin g an d u p set seg-

unprocessed blank s = blanked thickness

shape R : highly rounded

shape P : slightly rounded

t = upset thickness

D

D

D >D shape M : flat knurling

Fig. 6.8.17 Upsetting shapes on coin blanks

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m en t, by m ean s of two diam etrically arran ged m ech an ical h op p ers an d ch an n els (Fig. 6.8.18). Du rin g th e rollin g p rocess between th e u p set rin g an d u p set segm en t, diam eter redu ction takes p lace. Rim m in g m ach in es with h orizon tally arran ged u p settin g sh aft can be u sed both for rim m in g or u p settin g, an d also for em bossin g deep -set edge letterin g an d decoration of coin blan ks. Edge letterin g is carried ou t arou n d th e p erip h ery of th e coin blan k in a sep arate work cycle in wh ich th e p reviou sly u p set blan k is rolled an d deep -set between th e u p set rin g an d th e letterin g jaws. Dep en din g on th e m ach in e typ e an d th e diam eter of th e coin blan k, rim m in g m ach in es ach ieve an ou tp u t of 130,000 an d 600,000 p cs/ h ou r. Minting presses For m in tin g ap p lication s (ch an ge coin s with a d iam eter of between 14 an d 40 m m ) p referably p resses with kn u ckle-join t d rive or with m od ified kn u ckle-join t d rive system are u sed (cf. Sect. 3.2) with n om in al p ress forces from 1,000 to 2,000 kN an d strokin g rates between 650 an d 850/ m in (Fig. 6.8.19).

Fig. 6.8.18 High-performance rimming (upsetting) machine

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Min tin g p resses are d esign ed in a vertical an d also h orizon tal version . Horizon tally workin g p resses are u sed to p rod u ce rou n d coin s. Th is m ach in e d esign is ch aracterized by sim p le op eration an d a low n u m ber of coin -sp ecific exch an ge p arts (Fig. 6.8.20). Vertically op eratin g p resses can be u n iversally ap p lied for th e p rod u ction of rou n d , m u ltip le-ed ged an d bim etal coin s (Fig. 6.8.21); h owever, a greater n u m ber of coin -sp ecific exch an ge p arts is req u ired h ere. Th e m on obloc p ress fram e m ad e of n od u lar cast iron offers good d am p in g p rop erties (cf. Fig. 3.1.1). Th e p ress is d riven by m ean s of a con trollable electric m otor, flywh eel, eccen tric sh aft an d kn u ckle-join t. Th e bearin g p oin ts in th e kn u ckle-join t (friction bearin g) are con figu red for a m axim u m sp ecific com p ression stress of 110 N/ m m 2 . Th e slid e is m ou n ted with ou t backlash in p re-ten sion ed roller gibs. Th e in d exed d ial feed p late for in feed an d ou tfeed tran sp ort of th e coin blan ks an d coin s is d riven by m ean s of a syn ch ron ou s tim in g belt from th e eccen tric sh aft. Th e coin blan ks are fed by m ean s of m ech an ical h op p ers an d ch an n els toward s th e in d exed d ial feed p late. Th e ejector system is d irectly lin ked to th e slid e an d safegu ard ed again st overload in g. Th e coin in g d ies can be exch an ged (coin in g p u n ch an d m in tin g

Fig. 6.8.19 Press shop of a modern mint

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monobloc press frame punch holder

feed hopper

slide

electronic press control

main drive ejector punch holder

link drive system dial feed plate

Fig. 6.8.20 Horizontal minting press

collar) with in 2 to 3 m in . Th e m ach in e rests on vibration absorbin g elem en ts. As a resu lt, n o m ore th an 10 % of th e static load is tran sm itted in to th e fou n dation as dyn am ic loadin g. Th is m ean s th at th e p resses can be set u p on u p p er floors. Th ese p resses are gen erally eq u ip p ed with sou n d en closu res in order to m in im ize n oise gen eration . Th e coin blan ks are fed toward s a m ech an ical h op p er via an in clin ed con veyer with storage sp ace or oth er m eterin g system s (Fig. 6.8.22). Th e h op p er op erates accord in g to th e cen trifu gal p rin cip le, wh ich en su res p articu larly gen tle h an d lin g of th e blan ks. Th e p ossibility of scou rin g is m in im al, an d n oise d evelop m en t is also accord in gly low. Th e h op p ers h ave a sligh t in clin e. Th e feed p late is d irectly d riven by an ad ju stable gear m otor. Th e ou tfeed ch an n el is tan gen tially located . Dep en d in g on th e d iam eter of th e blan ks, th is arran gem en t p erm its feed rates of u p to 3,000 blan ks/ m in . W h en resettin g for th e p rod u ction of d ifferen t coin sizes, on ly th e blan k ou tfeed ch an n el an d th ickn ess n eed to be ad ju sted . No exch an ge p arts are req u ired . Dep en d in g on th e p ress d esign , th e h op p er an d feed

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punch holder

blank control and discharge device

feed hopper ejector electronic press control system

slide main drive

dial feed plate

monobloc press frame punch holder link drive system

Fig. 6.8.21 Vertical minting press

ch an n el can be swivelled ou t or m oved com p letely ou t of th e p ress for d ie ch an ge. In th e followin g ch an n el, th e blan ks are ch ecked for diam eter an d th ickn ess related defects, an d ejected if fou n d to be ou tside th e perm issible toleran ce (Fig. 6.8.23). Th e stan dstill periods cau sed by off-size blan ks wou ld seriou sly im pair th e efficien cy of h igh -speed m ach in es. Th erefore, coin blan ks with defects are au tom atically segregated in a con trol station wh ile th e m ach in e is ru n n in g. If a defective blan k reach es th e con trol station , th e flow of blan ks is in terru pted. Th e in terru ption triggers a sen sor, wh ich disables fu rth er blan k feed from th e h opper by m ean s of a stop cylin der. Th e gau ge jaws are open ed by m ean s of a lift cylin der an d th e off-size blan k is ejected in to a collectin g tray. Th e gau ge jaws retu rn to th eir h om e position , th e stop cylin der open s an d blan k feed con tin u es. Th e described cycle takes on ly fraction s of a secon d, en su rin g a con tin u ou s su pply of blan ks an d preven tin g produ ction disru ption s.

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automatic blank discharge hopper

feed channel

Fig. 6.8.22 Schematic of the rotary feed system

In horizontal operating m ach in es, th e blan ks d rop u n d er th e force of gravity in to th e in d exed d ial feed p late, wh ere th ey are fed toward s th e coin in g station . To carry ou t th e coin in g op eration , th e in d exed p late stop s. After coin in g, th e coin is ejected from th e m in tin g collar by th e ejector, wh ich is con n ected to th e p ress slid e, an d d isch arged . Th e sh ort stroke of th e lin k d rive system p erm its th e ejector m ovem en t to be d erived d irectly from th e slid e. Th e ejector travel is red u ced again in p rop ortion to th e slid e stroke by m ean s of a system of levers. Con seq u en tly, tem p oral offset between th e two m ovem en ts, as a resu lt of toleran ces an d clearan ces in th e d rive elem en ts, is elim in ated . Th e system is n ot su bject to wear, as n eith er cam s n or rollers are u sed . Th e elastic d eflection of th e p ress fram e wh ich takes p lace d u rin g coin in g is m easu red by a q u artz crystal tran sd u cer an d fed via a ch arge

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532 clamping lever

stop cylinder

sensor lift cylinder

off-size blanks

correct blanks

Fig. 6.8.23 Automatic circular blank control and discharge device

am p lifier with p eak valu e m em ory to th e p rogram m able logic con troller for evalu ation . Th e p u lses are cou n ted after th e coin in g force exceed s a certain m in im u m valu e. Th is en su res th at on ly coin in g p rocesses wh ich h ave really been carried ou t can be p icked u p an d cou n ted . At th e sam e tim e, th e coin in g force is d isp layed an d m on itored relative to a p reset lim itin g valu e. In case of a force valu e th at is above or below th e p rescribed toleran ce lim its, th e coin in g p ress is au tom atically switch ed off. In th e case of vertically operating p resses, th e blan ks are fed via a ch an n el in to a fillin g p ip e. From h ere, th ey are p u sh ed in to th e in d exed p late by m ean s of a cam -con trolled feed in g d evice (Fig. 6.8.24). Th e d rive is eq u ip p ed with a backlash -free m ech an ical in d exin g gear with extrem ely h igh in d exin g accu racy an d op tim u m acceleration an d d eceleration ch aracteristics. Th e in d exin g gear is en closed an d ru n s in an oil bath . To p rotect th e in d exin g d rive again st overload s wh ich are n ot p rocess-related , all coin in g p resses are eq u ip p ed with a syn ch ron ou s

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dial feed plate feed pocket

filling station

indexing gear

coining station

control station

Fig. 6.8.24 Feed dial plate w ith overload safeguard

overload clu tch . Th is overload clu tch is attach ed with ou t backlash to th e ou tp u t d rive sh aft of th e in d exin g d rive. Th e con n ection between th e d rive sh aft an d in d exed p late is form ed by m ean s of several sp rin gload ed rollers located in ap p rop riate recesses. In case of an overload , th e rollers d isen gage an d th e p art of th e clu tch wh ich is attach ed to th e d rive sh aft can still rotate in ball bearin gs with resp ect to th e blocked in d exed p late. It is on ly p ossible to re-en gage th e clu tch in a p osition en su rin g syn ch ron ou s m ovem en t with th e p ress. Th e cran k an gle of ap p rox. 120°, req u ired for th e in dexed p late to switch arou n d, is ach ieved in coin in g p resses with a n orm al kn u cklejoin t drive system (cf. Fig. 3.2.5) by m ean s of a su fficien tly dim en sion ed idle stroke, i. e. wh en th ere is n o con n ection between th e slide die an d slide. In p resses with m odified kn u ckle-join t drive (cf. Fig. 3.2.6), th e

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stan d still of th e slid e is reach ed at th e bottom or rear d ead cen ter. Th e id le p h ase con tin u es over on e th ird of th e total cycle tim e (Fig. 6.8.3). Du rin g th is com p aratively lon g stan d still p h ase, th e p rod u ced coin can be reliably d isch arged an d sim u ltan eou sly th e n ext coin blan k m oved p recisely in to th e coin in g p osition . In ad d ition , a firm con n ection is p rovid ed between th e slid e an d d ie. Th e ben efit of th is firm con n ection is th at it p reven ts th e im p act of th e slid e on th e back of th e p u n ch (h am m er effect) an d resu ltin g u n wan ted vibration s.

Coining dies To en h an ce th e service life of coin in g d ies, th e coin in g p u n ch es are h ard ch rom iu m p lated . Th e ach ievable service life ran ges between ap p rox. 400,000 to 800,000 coin in g strokes. Th is figu re in creases th ree or fou r-fold wh en u sin g titan iu m n itrid e-coated p u n ch es (Fig. 6.8.25). Gen erally rin gs with a carbid e in sert are u sed as m in tin g collars. Th ey h ave a service life of between 70 an d 100 m illion coin in g p rocesses. Th e ad m issible sp ecific com p ressive strain for th e coin in g p u n ch ran ges between 1,500 an d 1,800 N/ m m 2 .

Universal m inting press for coins and m edals In cases wh ere both ch an ge an d collectors’ coin s with im p roved su rface q u ality h ave to be p rod u ced , a vertical u n iversal m in tin g p ress with a n om in al p ress force of 3,000 kN is u sed . Th e d esign of th is p ress is th e sam e as th at u sed for coin in g p resses for th e p rod u ction of ch an ge coin s. However, th is p ress also offers th e facility to p reselect several coin in g blows in ord er to im p rove su rface q u ality. Up to fou r coin in g blows can be p re-selected at th e con trol d esk. In con trast to stan d ard m in tin g p resses, th e d ial feed p late is d riven in th is p ress typ e by a servo m otor in con ju n ction with an in d exin g gear. Th e d ial feed p late com es to a stan d still for execu tion of th e coin in g im p acts. Th e sam e ap p lies to th e ejector. To m an u factu re coin s with a p articu larly h igh stan d ard of su rface q u ality, th e p ress is eq u ip p ed with a m an u al feed in g d evice. Th e p ress also p rovid es a su itable facility for p u n ch clean in g. Th e m ach in e p rod u ces with in a d iam eter ran ge of 14 to 50 m m , an d reach es strokin g rates of 400/ m in wh en a sin gle coin in g blow is u sed , an d between 75 an d 150/ m in in m u ltip le blow op eration .

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Fig. 6.8.25 Titanium nitride-coated coining punches

Universal press for joining, m inting and punching Based on th e u n d erlyin g con cep t of th e vertical 1,500 kN m in tin g p ress, in ad d ition to th e m in tin g of stan d ard , m u lti-sid ed an d bim etal coin s, two fu rth er ap p lication p ossibilities are offered : – Th e p ress can be u sed to sep arate th e rin gs an d cen ters of u sed bim etal coin s wh ich are bein g with d rawn from circu lation . Sep aration of th e d ifferen t m aterials offers clear ad van tages for recyclin g. – Design ed for p iercin g, th e p ress p erm its th e m an u factu re of ou ter rin gs from u p set coin blan ks. Norm ally, rings for bim etal coins are p rod u ced at h igh strokin g rates in m u ltip le d ies on a h igh -sp eed blan kin g p ress (cf. Fig. 4.6.6 an d 4.6.8). Du e to th e m in im al stability of th e rin gs, h owever, su bseq u en t u p settin g is on ly p ossible to a lim ited d egree. Exp erien ce h as sh own th at th e red u ction in d iam eter wh ich takes p lace h ere lies arou n d 0.1 to a m axim u m of 0.2 m m . Du e to th e low web wid th , it m ay be n ecessary to u p set th e ed ge in several p asses in ord er to ach ieve th e sp ecified d iam eter. In p ractice, a cylin d rical u p settin g sh ap e with a 45° ch am fer on each sid e was fou n d to be su ccessfu l (Fig. 6.8.17). In th e case of rin gs p rod u ced on u n iversal p resses in m in ts, h owever, an y op tion al u p settin g sh ap es an d ed ge d ecoration can be u sed if th e coin blan ks are rim m ed or ed ge letterin g is carried ou t p rior to p iercin g.

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Figure 6.8.26 in d icates th e in d ivid u al p h ases req u ired for th e p iercin g p rocess: – Th e u p set coin blan k is cen tered in th e p iercin g station by th e feed in sert. Th e slid e is p osition ed in th e bottom d ead cen ter. – Th e slid e m oves u p ward s, th e coin blan k is h eld between th e fem ale p iercin g d ie an d th e sp rin g-m ou n ted strip p er. – Th e coin blan k is in serted in th e h old in g collar an d p ressed again st th e fixed p iercin g p u n ch . – At th e top d ead cen ter, th e p iercin g p rocess is com p leted , th e scrap web is p u sh ed th rou gh th e p iercin g p u n ch in to th e scrap h ole of th e fem ale p iercin g d ie. – On th e retu rn stroke of th e slid e, th e sp rin g-m ou n ted strip p er p u sh es th e p ierced coin blan k ou t of th e h old in g collar back in to th e feed in sert. Th e p ierced coin blan k is d isch arged by th e in d exed d ial feed p late, wh ile a n ew u p set u n p ierced coin blan k is fed for th e n ext cycle.

ejector piercing punch holding collar spring-loaded feeder insert stripper

piercing die dow n stroke, blank feed

contact w ith ejector

contact w ith piercing punch

Fig. 6.8.26 Piercing sequence

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

up stroke, blank pierced

dow n stroke, discharge of pierced blank

Presses used for solid forming

Medal m inting presses Presses with a n om in al force of 2,000, 3,600 an d 10,000 kN are u sed to p rod u ce m ed als an d com m em orative coin s. Dep en d in g on th e p ress typ e, th e m axim u m m ed al d iam eter is between 38 an d 80 m m . Th e strokin g rates ran ge from 45 to 120/ m in . Th e resu ltin g ou tp u t d ep en d s on th e n u m ber of coin in g strokes: Sin gle stroke: Dou ble stroke: Trip le stroke:

25 – 40 m ed als/ m in 16 – 30 m ed als/ m in 12 – 24 m ed als/ m in

Com p lex d esign s an d even d ifficu lt m ed al con tou rs can th u s be m an u factu red in a sin gle stroke. For h igh -grad e m ed als, kn u ckle-join t p resses are con figu red for m u ltip le stroke op eration , as it is on ly with rep eated coin in g th at th e req u ired stan d ard of su rface q u ality can be ach ieved . Th e p ress fram e serves as a slid e wh ich is m oved by th e kn u ckle-join t, wh ereby a rigid con n ection exists between th e p ress bed an d th e p ress h ou sin g (cf. Fig. 3.2.5). Th is resu lts in p ractically sh ock-free closu re of th e d ies. Au tom atic m ed al m in tin g m ach in es are eq u ip p ed with m ech an ical, cam -d riven ejectors. Th e d rive cam d isk sits d irectly on th e cran ksh aft an d en su res syn ch ron ou s op eration with th e p ress work cycle. For th e m ed al m in tin g p rocess, th e ejector is con trolled to wait u n til th e n u m ber of blows, p reselected in th e m u ltip le stroke d evice, h as been com p leted . For th e m an u factu re of top q u ality m edals, u ltra-clean , du st-free op eration m u st be gu aran teed. Th e m ach in es are eq u ip p ed with ven tilatin g an d filtration devices wh ich p erm it on ly filtered air to en ter th e die area. Th e die m ou n tin g area is also en closed an d is sligh tly p ressu rized. Th e h igh est degree of q u ality is ach ieved in m edal m in tin g p resses u sin g m an u al feed m eth ods (Fig. 6.8.27). In ord er to en su re th e q u ality of th e m ed als, th e p u n ch es m u st be clean ed at sh ort in tervals. By p ressin g a bu tton , th e ejector m oves to th e clean in g p osition , th e bottom d ie is raised arou n d 2 m m ou t of th e m in tin g collar an d d irt p articles or sp illed clean in g m aterials can be wip ed away. Med als with en h an ced su rface q u ality for collectors are often p rod u ced in h igh p iece n u m bers. A cassette feed system is id eally su ited for

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Solid forming (Forging)

538

th is typ e of ap p lication (Fig. 6.8.28). In view of th e strin gen t q u ality req u irem en ts, an au tom atic cassette feed system m u st en su re p articu larly gen tle tran sp ort of th e m edal blan ks. On ly on e blan k is rem oved from th e cassette m agazin e at a tim e an d lowered on to th e tran sfer level. Plastic grip p ers lift th e blan k in to an in term ediate dep osit station an d tran sp ort it to th e m in tin g station . Th e su bseq u en t blan k rem ain s clam p ed in th e m ed al m agazin e u n til th e tran sp ort area is clear. After th e m in tin g p rocess, th e grip p ers lift th e m in ted m ed al from th e bottom d ie, wh ich is located in th e ejection p osition , an d p lace it on a con veyor belt wh ich tran sp orts it ou t of th e m in tin g area. A tu rn in g station , con n ected to th e con veyor belt, p erm its th e op erator to in sp ect both sid es of th e m ed al d u rin g ru n n in g p rod u ction .

Fig. 6.8.27 M edal minting press w ith manual feed

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Presses used for solid forming

CNC-controlled hydraulic m edal m inting presses Th ese p resses p erm it p ath or p ressu re-d ep en d en t con trol of each stroke of th e slid e, as well as syn ch ron ou s op eration of th e slid e an d ejector by two CNC axes. In case of m u ltip le stroke op eration , th e d ie rem ain s closed with ou t op en in g, i. e. in con tact with th e m ed al. On ly th e coin in g stress between th e u p p er an d lower d ie is released . As a resu lt, p en etration of abrad ed m atter between th e d ies an d th e coin ed p iece is p reven ted . Th e n om in al p ress force of th e m ach in e series ran ges between 4,000 an d 12,000 kN. In ad d ition to m in tin g of m ed als, coin s an d jewellery, th e m ach in e can also be u sed for th e cold h obbin g of tools, for exam p le in th e m an u factu re of coin in g p u n ch es, d ie sin ks, jewellery m ou ld s, d ies for fasten ers, d ies for cu tlery, etc. Th e d ie sin kin g velocity req u ired for th is tech n iq u e ran ges between 0.01 an d 4 m m / s (Fig. 6.8.29).

Fig. 6.8.28 Cassette feed for medal production

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To com p ly with th e very h igh est q u ality req u irem en ts an d wh en p rod u cin g d ifficu lt an d com p lex reliefs, it is p ossible to u se an oscillatin g tech n iq u e with varyin g p ress forces (Fig. 6.8.30). Th e h yd rau lic d ou ble-action p ress com p rises a p ress fram e with a closed fram e stru ctu re, an in tegrated d rive cylin d er an d sep arate p ower d rive. Th e p ress slid e (coin in g cylin d er) is CNC-con trolled an d h as a m u ltip le-su rface d esign . Based on th e p rin cip le of d ifferen tial p ressu re su rfaces, op tim u m levels of ou tp u t are ach ieved with low en ergy con su m p tion . Th e ejector cylin d er, also con trollable by CNC, is in tegrated u n d ern eath in th e p ress fram e. Th e ch eeks of th e p ress yoke are p osition ed d irectly again st th e d ie system an d are sligh tly larger th an th e p iston rod , so gu aran teein g op tim u m rigid ity. Th e traversin g m otion s are con trolled by m ean s of servo con trol valves with in crem en tal setp oin t in p u ts an d m ech an ical actu al valu e feed back.

Fig. 6.8.29 Hydraulic medal minting press

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force

load relief stage 3 load relief stage 2 load relief stage 1 0

time 1. coining cycle

2. coining cycle

3. coining cycle

4. coining cycle

Fig. 6.8.30 Coining cycles w hen using multiple stroke w ith programmable forces and times

Bibliography Beisel, W.: Aufw and reduzieren, feine Gravuren durch Prägen, Industrieanzeiger (1995) 10. Beisel, W. , Stahl, K.: Kaltfließpressen als Alternative, Werkstatt u. Betrieb 128 (1995) 3. DIN 1543 : Steel flat products; hot rolled plate 3 to 150 mm thick; permissible deviations of dimenison, w eight and form, Beuth Verlag, Berlin (10.81). DIN 1544: Flat steel products; cold rolled steel strip, dimensions, permissible variations on dimensions and form, Beuth Verlag, Berlin (8.75). DIN 17 006 : Stahlguß, Grauguß, Hartguß, Temperguß, Beuth Verlag, Berlin (10.49). DIN 17 100 : Steels for general structural purposes; Quality standard, Beuth Verlag, Berlin (9.66). DIN 17 200 : Steels for quenching and temperating, technical delivery conditions, Beuth Verlag, Berlin (12.69). DIN 17 210 : Case hardening steels, technical delivery conditions, Beuth Verlag, Berlin (12.69). DIN 17 240 : Heat resisting and highly heat resisting materials for bolts and nuts; Quality specifications, Beuth Verlag, Berlin (1.59). DIN 17 440 : Stainless steels; technical delivery conditions for plate and sheet, hot rolled strip, w ire rod, draw n w ire, steel bars, forgings and semi-finished products, Beuth Verlag, Berlin (12.72). Geiger, R.: Stand der Kaltmassivumformung - Europa im internationalen Vergleich, Neuere Entw icklungen in der M assivumformung, DGM Verlag, Oberursel (1993). Hoffmann, H., Rahn, O., Waller, E., Blaschko, A.: Prozeßüberw achung an M aschinen der Kaltmassivumformung, Industrie Anzeiger (1988) 33. Körner, E., Knödler, R.: M öglichkeiten des Halbw armfließpressens in Kombination mit dem Kaltfließpressen, Umformtechnik 26 (1992) 6.

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Solid forming (Forging)

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Körner, E., Schöck, J. A.: Rationalisierungspotentiale im Rahmen der Werkzeug- und Presseninbetriebnahme, Umformtechnik 26 (1992) 6. Körner, E., u.a.: M echanische Fließpreßanlagen für die Kalt- und Halbw armumformung, Neuere Entw icklungen in der M assivumformung, DGM Verlag, Oberursel (1995). Kudo, H., Takahashi, A.: Extrusion technology in the Japanese automotive industry, VDI Berichte Nr. 810, VDI-Verlag, Düsseldorf (1990). Lange, K.: Umformtechnik, Volume 2: M assivumformung, Springer-Verlag, Heidelberg (1988). Schw ebel, R.: Prägen mit minimalen Toleranzen, Bleche Rohre Profile (1995) 4. Sheljaskow, Sh., Dübler, A.: Entw icklungsstand und Einsatzbereich der Halbw armumformung, Verein deutscher Werkzeugmaschinenfabriken e. V. (VDW ) Study (1991). Stahlschlüssel-Taschenbuch, Verlag Stahlschlüssel, Wegst GmbH, M arbach/N. VDI 3138 Bl. 1 : Kaltfließpressen von Stählen und NE-M etallen, Arbeitsbeispiele, W irtschaftlichkeit, Beuth Verlag, Berlin (10.70). VDI 3138 Bl. 2 : Kaltfließpressen von Stählen und NE-M etallen, Anw endung, Beuth Verlag, Berlin (10.70). VDI 3138 Bl. 1 : Kaltfließpressen von Stählen und NE-M etallen, Grundlagen, Beuth Verlag, Berlin (10.70). VDI 3176 : Vorgespannte Preßw erkzeuge für das Kaltumformen, Beuth Verlag, Berlin (10.86). VDI 3186 Bl. 1 : Werkzeuge für das Kaltfließpressen von Stahl, Aufbau, Werkstoffe (ICFG Data Sheet 4/70), Beuth Verlag, Berlin (12.71). VDI 3186 Bl. 2 : Werkzeuge für das Kaltfließpressen von Stahl, Gestaltung, Herstellung, Instandhaltung von Stempeln und Dornen (ICFG Data Sheet 5/70), Beuth Verlag, Berlin (12.71). VDI 3186 Bl. 3 (6.74): Werkzeuge für das Kaltfließpressen von Stahl, Gestaltung, Herstellung, Instandhaltung, Berechnung von Preßbüchsen und Schrumpfverbänden (ICFG Data Sheet 6/72), Beuth Verlag, Berlin und Cologne. VDI 3187 Bl. 3 : Scherschneiden von Stäben, Schneidfehler (ICFG Data Sheet 5/71), Beuth Verlag, Berlin (8.73). VDI 3198 : CVD-PVD-Verfahren, Beuth Verlag, Berlin (9.91). VDI 3200 Bl. 1 : Fließkurven metallischer Werkstoffe, Grundlagen, Beuth Verlag, Berlin (10.78). VDI 3200 Bl. 1 : Fließkurven metallischer Werkstoffe, NE-M etalle, Beuth Verlag, Berlin (10.78). VDI 3200 Bl. 2 : Fließkurven metallischer Werkstoffe, Stähle, Beuth Verlag, Berlin (4.82). Verson, M . D.: Impact machining, Verson Allsteel Press Company, Chicago (1969). Zebel, H.: Die Trennflächen von abgescherten Stababschnitten, Werkstattstechnik (1964) 54.

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Index

A.S.T.M .-standard 451 abrasion 183 accelerometer 403 accident prevention 106 accident prevention regulation 106, 116 acoustic emission 402 f. active hydro-mechanical draw ing 189-193 actuator 94, 97, 326, 329 adding-on process 500, 502 additive 184 –, EP additive 463 adhesion 182 AISI-standard 451 all-across perforating press 314 alloyed steel 174 alloying technique 121 alternating bending 384 aluminium 178, 453 aluminium alloy 178 angular section 377 annealing 423, 455, 458 ANSI-standard 117 austenitic chromium nickel steel 174, 177 automatic 257 automation 478 availability 320, 389, 395, 399 average forming pressure 472 axis control system 257 f. backw ard cup extrusion 440, 445, 447, 474 f. backw ard extrusion 433 f. baked enamel-coated lamination 301 bake-hardening-steel 174, 176 ball joint gib 39 bar holder 457 bar stock 455

basic section geometry 374 batch size 396 f., 399 beading 169, 375 –, draw bead 149 beading rod 22 bed plate 34, 37 bending 23, 425 - w ith linear die movement 16 - w ith rotary die movement 16 –, springback 23 –, overbending 23 bending 431 bending angle 366, 370 bending die 372 bending force 372 bending process 366-373, 435 bending punch 372 bending radius 366 –, minimal 368 bending w ork 372 bent leg 370 bevel angle 275 bevelled punch 275 billet heating 521 billet preparation 454-459, 522 bimetal coin 528, 535 f. bite cutting 21 blade holder 285 blank control and discharge device 529, 532 blank diameter 162-165 blank discharge 531 blank feeder 226 f. blank holder 45-48, 66-70, 156160, 171, 185, 187, 190, 250 –, force versus time profile 45 –, overload safety device 67 –, precision control 45 –, segmented 313 blank holder force 44, 47 f., 171f. blank holder pressure 171 blank holder slide 41, 158

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

blank length 370 blank size 162 blank turnover station 217-222 blank w elding line 311 blanking 23, 268 –, blanking line 20 –, single-stroke 20 blanking burr 337, 347, 349 blanking clearance 281, 295, 334, 457 f. blanking die 143 f. –, compound cutting tool 20, 297, 299, 304, 351 blanking force 274, 276 f., 332, 342, 356 f. blanking force-stroke diagram 334 blanking line 284-329, 389, 398 blanking plate 352-355 blanking press 286-289 blanking process 268-283 blanking punch 354 f. blanking segment 144 blanking shock 83 blanking w ork 274, 276 f. block hydraulic system 79 bolster plate 37, 88, 91-93 bottom dead center (BDC) 52 f. bottom drive 57, 59, 507 f., 525 bottom thickness 446 bottom-driven press 37 boundary friction 180 boundary layer 180, 182 bracket 144 brake 61-63, 226 –, hydraulic 293 –, rotating brake system 285 f. brake frame 284 f. brass 454 breaking 19, 21 buckling 415, 418, 424 –, free buckling length 418 f. buckling strength 189 f.

Index buckling stress 495 bursting 415, 418, 425

CAD data 131 calibrating 431, 436 f. calibration 405, 407 calibration pressure 406 calibration process 410, 432 cam operated limit sw itch 98, 100 cam w heel 120 camera monitoring system 318 camping rail 480 f. camshaft 316 car body panel 129 carbid 499 f. carbon content 450 f. carriage 245 cassette feed 539 casting 120 casting model/pattern 130, 136 casting of dies 143-148 CE mark 108, 110 f., 113 CE marking 111-115 center of force 278 f. centering 440, 474 f. centering device 204 central burst 475 central control desk 258 central support 360-362 certification 106-119 characteristic data 49-54 chevron 475 circuit diagram 101 circular bending 16 f. circular blade 268, 286 circular shears 284 clamp stripper 316 clamping plate 318, 320 clamping rail 92 cleaning 460 closed blanking 268 closed contour 289 closed die forming 8, 433 closed section 377 closed shearing guide 458 f. closing system 503 f. clutch-brake-combination 314 CNC feeder 227 f. coating 5, 143, 501 f. coating method 143, 146 coefficient of friction 179-181 coil 194, 288, 389, 391, 398 coil end w elding machine 380 coil guide 356 f. coil line 194-198, 229, 287, 291 f., 305, 391 coil loop 194 f., 286-288

545 coil thickness unit 292 coiling 17 coin 526-541 –, bimetal 528, 535 f. –, collector’s 534 coin blank 526 coin blanking line 526-541 coining 8, 433-436 coining die 534 cold coining 436 cold extrusion 8 f., 433 f., 439, 445, 506 –, backw ard cup/can extrusion 10, 440, 445, 447, 474 f. –, backw ards 10, 433 f. –, forw ard cup/can extrusion 440 –, forw ard rod extrusion 445, 447 f., 469-473 –, forw ard tube extrusion 474 –, forw ards 10, 433 f. –, hot extrusion 445 –, lateral 10, 433 f. –, w arm extrusion 445 cold forging flow curve 451 cold forging tool steel 498 f. cold forming 26, 437-439, 450 cold rinsing 462 f. cold sizing 523 cold w elding 182 cold-rolled sheet 174 collector’s coin 534 collision testing 136 column gib 39 communication module 100 communication system 97 f., 257 compact drive 63, 201 compensation factor 370 f. component of a die 143 compound cutting tool 20, 297, 299, 304, 351 compression/upsetting 27 f., 405, 407, 410, 435, 445, 476 f. –, free 477 concentricity tolerance 446 connecting rod 38, 65 f., 120 –, double fork 293, 295 contact condition 415 contact pattern 148 container 434 f., 491, 494 continuous stroking 52 contour blanking line 289 f. contoured blank 289 control component 99 f. control concept 255 control function 96 control softw are 104 control system 254-267 –, architecture 101 f.

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–, configuration 101 f. –, electrical 94, 97 –, functional grouping 101 –, functional structure 99 f. –, local 255 –, programmable logic controller (PLC) 97, 102, 257, 321 f. –, structure 97 f. control system 321 –, conventional 257 –, electronic 257 control unit 95 f., 258, 327 conventional control system 257 conversion 116 cooling element 121 cooling system 520 copper 177, 453 f. copper alloy 174, 177 copper sheet 174 correction factor 173 corrugating 17 counterbalance of masses 202, 293 counter-draw ing 44, 159, 161, 190, 200, 232 counterforce 332, 342, 353, 355357, 360 counterforce cylinder 426 counterforce piston 361 f. counterpressure pad/punch 20, 406 f., 421, 427 f. counterpunch 434 coupling 61-63, 120, 226 –, hydraulic 293 crack detection 122 crank drive 54 cropping shear 288, 316 f. cross section change 471 cross section deformation 369 crossbar 245 f., 249 f. crossbar transfer 245 f. –, displacement/time diagramm 246 –, motion curve 245 cup extrusion 433 f. cushion monitoring system (CM S) 264 cut contour perimeter 278 cut out 23 cut surface 274, 349 cutlery embossing press 523 cut-off holder 457 cutting 424 cut-to-length line 287, 290 cut-to-length shear 286, 288, 380 CVD technique 500-502 cycle time 198

Index cylinder –, counterpressure 426 –, differential 426 –, displacement 250 –, horizontal 406 f., 416 f., 420 f., 426-428 –, hydraulic 39, 75 –, parallelism controlling 252 –, plunger 426 cylinder deactivation 215 d/s ratio 274 damping 82 f. data acquisition 264 data record 130 DC asynchronous motor 100 declaration of conformity 110-114 decoiler 194, 284, 288 deep draw ing 11 f., 22, 156-193 - using active energy 12 - using active media 12 - w ithout blank holder 174 –, blank holder 11, 22 –, forming force 157 –, hydro-mechanical draw ing 12, 189-193 –, punch motion 11 –, redraw ing 11 –, reverse draw ing 11 –, single-draw 11 –, telescopic punch 11 – w ith rigid tool 11 deep draw ing defect 175 deep draw ing press 41-44 deep draw ing process 23 defect cause 175 defect prevention 175 deflection tolerance 446 deformation 25-28, 181, 410 –, dislocation 25 – faults in the arrangement of the atomic lettice 25 –, logarithmic 27 –, relative 27 –, sliding 25 –, true strain 27 –, tw in crystal formation 25 deformation along the vertical axis 28 deformation depth 82 deformation rate 26, 28 deformation resistance 29 deformation w ork 30 –, referenced 29 f. degreasing 460, 462 degree of difficulty 342 degree of vibration 403 descaling 455, 460

547 destacker 217-222, 226, 229, 305, 389 dial feed plate 530 diameter related defect 530 diameter tolerance 446 die 158-160, 171, 185, 190, 425 –, assembly 136 –, blanking 143 f. –, center line spacing 126 –, classification 123-127 –, coining 534 –, compound cutting tool 20, 297, 299, 304, 351 –, design 130 f. –, development 128-141, 148 –, double-action 124, 245, 274, 398 –, draw 143 –, extrusion 485 –, flanging 127, 143 –, maintenance 153 –, number 123 –, production 421 –, profile parting 380 –, progressive 125, 282, 297 –, progressive blanking 125, 307, 356 –, progressive compound 126, 345, 351-353, 356 f. –, prototype 137 f., 421 –, rolling 380 –, single 124 –, special 127 –, step w idth 126 –, structure 123 –, sw ivelling 290 –, timing cycle 128 –, transfer 125, 345, 356 –, type 124, 351 –, w edge-action pusher 490 die bending 16, 372 die cavity insert 421 die change 86-93, 97, 228, 242, 249, 257, 261, 290, 308, 520 die change cart 87 f. die change synoptic 261 die changing arm 490 f. die changing system 426, 489 die changing time 397-399 die clamp 92 f. die clamping device 91-93 die coating 500 die coining 16, 327 die corner radius 171 die data 259 die design 491-495 die handling 86-91 die holder 488-490 die holding sleeve 485-491 die lubrication 358

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

die material 142 f., 422, 496-502 die opening angle 470, 472, 475 f. – for ironing 476 die set, set-up 397 die stroke-dependent sensor 363 die system 352 die w idth 372 die-independent pressure sensing 363 die-roll 337, 348 f. differential cylinder 426 digital image generation 401 digital rectifier 100 directive –, EC 107-109 –, EM C 107 – governing Simple Pressure Vessels 107 discharge plate 306 displacement 17 displacement cylinder 249 displacement/time diagram 55 distance sleeve 284 distribution of stress 140 f. dividing 5, 19 f., 457 double fork connecting rod 293, 295 double helical gearing 65 double knuckle-joint 361 double knuckle-joint system 208, 360 double loop line 380 double part 392 double stroke 537 double-action die 124, 245, 274, 398 double-action draw ing operation 158 f. double-action draw ing press 169 double-action press 41 f., 56, 173, 185 –, blank holder drive 60 –, draw ing press 169 doubling 375 f. draft angle 465 draw bead 140, 149, 171 draw cushion 43, 44-48, 159 f., 241 f., 250, 264 –, hydraulic 44, 47 f. –, pneumatic 44, 47 f. –, segmented bed cushion 215 draw depth limit 186 draw development 130 f., 137 draw die 143, 159 draw energy 173 draw punch 156-160, 185, 187 draw ratio 166, 173, 187

Index draw ing 10, 433 –, active hydro-mechanical 189-193 –, double-action 158 f. –, single-action 159 draw ing defect 174 draw ing mandrel 476 draw ing process 476 draw ing stroke 173 draw n w ire 455 drive controller 97 drive motor 60 f. drive shaft 63 f. drive system 54-60 –, compact drive 63, 201 –, crank drive 54 –, eccentric drive 54, 510 –, hydraulic drive 76 –, knuckle-joint drive 55, 205, 513, 527, 534 –, link drive 55 f., 223, 529 –, longitudinal shaft drive 63-65 –, main drive 60, 66 –, overrun drive 87 f. –, pump drive 77 f. –, push-pull drive 87 –, servo drive 100 –, slide drive 37-41 –, top drive 59 –, transverse shaft drive 63 f. driver 144 drum turning device 220 drying 463 dual production 244, 394 dual stacking feeder 217 dual sw ivel-mounted decoiler 380 ductile castings 120 EC decree 107, 109 EC machine directive 107-109 eccentric drive 54, 510 eccentric shaft 201, 293 eccentric w heel 121 edge lettering 527 edge lettering machine 526 effective stress 416 efficiency factor 472 eight-track block gib 39 eight-track gib 39 f. – for high eccentric loads in the y direction 39 – for narrow side uprights 39 – for w ide side uprights 39 – in cross formation 41 – roller gib 40 eight-track slide gib 509 ejector 158 f., 231, 233, 353, 355, 537 f.

549 –, knock-out pins 41 –, pneumatic ejector 482, 487 ejector curve 482 ejector force 333, 353, 356, 358 ejector pin 333 –, inner form ejector 353 f. ejector stroke 481 electric motor lamination 296309 electrical control system 94, 97 electrical equipment 326 electromagnetic compatibility (EM C) 327, 329 electronic control system 257 elongation 449 –, effective stress 416 –, elongation limit 175 –, principal strain 416 –, strain rate 416 –, ultimate elongation 175, 423 embossing 15, 436 embossing block 144 embossing press 522-525 EM C directive 107 EN692 111 EN693 111 energy consumption 199 EP additive 463 equipment, electrical 326 error 262 error data 262 error message 259, 323 excess material 455, 466 exchangeable shear 284 exchanging the sleeves 489 expanding 15 expansion 405, 407, 425 –, free expansion 418 experience data base 267 extrusion die 485 extrusion of semi-finished products 8-10, 433 –, backw ards 10 –, forw ards 10 –, lateral 10 extrusion punch 494 failure diagnostics module 324 f. Failure M ode and Effects Analysis (FM EA) 133 family of parts 392 fanning magnet 217 fast communication module 100 fast communication system 104, 258 fatigue w ear 183 fault diagnostics 97

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

feasibility study 413-419 feed channel 479 feed height adjustment 362 feed hopper 529 f. feed output 194, 196 feed step 272 f. feed step pilot 356 f. –, embossing punch 357 feed system 518 feed unit 318 –, infeed roller 316 feed value 386 f. feed/straightening machine 195 feeder 217 f. –, blank 226 f. –, CNC 227 f. –, sw ing arm 226-228 feeder arm 245 feeding device 126 female blanking die 144 female die 158-160, 171, 185, 190 female die retaining plate 144 ferritic chromium steel 174, 176 fiber flow 441 field bus system 266, 329 filling slide 144 fine blanking 330-356 –, annular serrated blank holder 20 –, counterpressure pad 20 fine blanking capability 339 fine blanking oil 358 fine blanking press 360-365 finish processing 430 finite element method (FEM ) 37, 140, 494 finite element program 467 fixed punch 352, 354, 360 fixed shear 287 flanged blade 284 flanging 13 flanging die 127, 143 flanging/hemming 23 flashless forging 502 flat radiator plate 208-210 flat steel 456 flexible notching system 301, 303 flexible production cell 303 flooding 520 flow 25 flow condition 25 f. flow curve 25 f., 30, 450 f. flow law 28 flow piercing process 435 flow stress 25 f., 29, 157, 438, 450, 453 fluid lubrication, hydro-dynamic 180

Index flying shear 288 flyw heel 51-54, 60 f., 200, 293 foaming 380 folding 375 folding die 142 –, restrike edge bending die 144 force 29 f., 49-51, 53 –, bending force 372 –, blank holder force 44, 47 f., 171 f. –, blanking force 274, 276 f., 332, 342, 356 f. –, counterforce 332, 342, 353, 355-357, 360 –, direct/indirect application 29 –, forming 168, 173, 188 f., 472 –, friction force 179 f. –, mandrel friction force 476 –, pressing force 506 –, reaction force 188 f. –, restraining force 285 –, return stroke force 274 –, shearing force 458 –, slide force 188 f., 342 –, straightening force 388 –, vee-ring force 356 f., 360 force measurement 402 f. force requirement 282, 469-477 force-stroke diagram 50 force-time curve 292, 402 forged part 522 forging 91, 433, 437-439, 451f. –, flashless 502 –, hammer forging 7 forging hammer 38, 50 fork turning device 221 formability 25, 31, 450 formed element 343 forming 5 f. – after heating 26 – w ith a lasting change in strength property 26 – w ith temporary change in strength property 26 – w ithout heating 26 amount of deformation 27, 157, 438, 449, 467, 471 –, maximum 470 forming by bending 6, 16 forming by forcing through an orifice 8 f., 433 forming distance 50 f., 54 forming efficiency factor 29 forming force 168, 173, 188 f., 472 forming pressure 472 –, average 472 – on the container w all 473

551 forming process 6 f. –, classification 6 forming under combined tensile and compressive conditions 6, 10-13 –, process 156 forming under compressive conditions 6-8 forming under shear conditions 6, 17 f. forming under tensile conditions 6, 14 f. –, process 156 forming w ork 53, 472 –, specific forming w ork 472 forw ard cup extrusion 440 forw ard extrusion 433 f. forw ard rod extrusion 469-473 forw ard tube extrusion 474 four-point configuration 39 four-upright press 426 f. fracture 346 frame press 426, 428 free buckling length 418 f. free expansion 418 free extrusion 8 f., 433, 435, 445, 448, 470, 475 f. free hydroforming 406 free upsetting 477 friction 179-185 –, solid body 180 friction force 179 f. friction modifier 184 frictional shear stress 180 full form casting 143 full-stroke parallelism control 81 f. gear 65 f., 519 gear drive 65 f. gearing 435 geometrical accuracy 443 f. geometry of the die 123 geometry of w orkpiece 123 glass fiber-reinforced thermoplastics 251 gluing 380 greasing 220, 455 gripper 479 gripper rail 35 guidance ratio 41 guidance system 134 guide plate 353 f. Guldin’s law 466 f. hammer forging 7 hardness 448 hardness testing 122

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

hat section 377 hazard analysis w ith risk assessment 114 heat ageing 453 heat treatment 369, 423 f., 449 f., 453, 457 f., 497 hemming/flanging 23 high speed cutting (HSC) 136 high-performance transfer press 200 high-pressure spray system 521 high-speed blanking line 291-297, 307, 391, 536 high-speed steel 497, 499 f. hole diameter 273 hole pattern 318 f. hollow face 275 home try-out 130 hopper 529, 531 horizontal cylinder 406 f., 416 f., 420 f., 426-428 horizontal press 513 f. host computer 427 hot extrusion 445 hot forging flow curve 451 hot forging tool steel 498-500 hot forming 26, 437-439, 506 hot forming line 520-522 hot rinsing 462 f. hot rolling 456 –, hot-rolled coil stock 456 hybrid press 203-205 hydraulic brake 293 hydraulic coupling 293 hydraulic cylinder 39, 75 hydraulic drive 76 hydraulic medal minting press 540 hydraulic oil 77 –, compressibility 78 hydraulic press 38, 73-85 –, cycle time 74 –, displacement/time diagram 74 –, drive 73-77 –, drive pow er 73 –, slide cylinder 75 hydraulic redundancy 97 hydraulic system 76 –, service unit 77 –, valve control system 77 hydro-dynamic fluid lubrication 180 hydroforming 405-432 –, component development 413 –, cycle time 429 –, fields of application 412

Index –, free hydroforming 406 –, tool-dependent hydroforming 406 Hydro-M ec forming process 187 hydro-mechanical deep draw ing 185-189 hydro-mechanical reverse draw ing 185 hydrostatic pressure 73 image generation, digital 401 image processing 401 impact speed 57, 199, 204, 289, 509 inclined conveyor 517 indexing unit 298 individual electrical control device 97 induction w elding 311-313 industrial PC 103, 322 f., 329 infeed roller 316 infeed table 316 inflation limit 418 initial blanking stop 356 f. inner form ejector pin 353 f. inner form punch 353, 355 input w eight 442 input/output module 104, 266, 326 input/output system 97, 257, 329 intermediate annealing 423, 458 intermediate heat treatment 467 intermediate storage 397 f. intermediate treatment 450 f. internal pressure 417 international unit system 31 interrupt input 102 investigation part handling 478, 481-484, 506 involute gearing 466 ion implantation 500 iron phosphate layer 461 ironing 10, 435, 440, 445, 447 f., 475 f. ironing die 435 ironing die ring 476 JIS standard 451 job data acquisition 264 job management 321 joining 5, 23 - through forming 6 just-in-time production 398

553 knock-out pin 41 knuckle-joint drive 57, 205, 513, 527, 534 –, curve 59 –, double knuckle-joint system 208, 360 f. –, knuckle-joint bottom drive 208, 523 –, modified 58 f., 528 –, modified knuckle-joint top drive 509 f. –, pressing force 58 knuckle-joint press 55, 507 f., 525 L section 377 lamination stack 301 large-panel transfer press 125, 391, 393, 396 – crossbar transfer 243-250, 391, 398 – tri-axis transfer 234-243, 391 f., 398 laser w elding 311, 313 lateral extrusion 433 f., 477 layout 400 lead 454 lead press 225 –, double-action 225 leg length 371 length 14 lift beam 245 f., 249 lifting bridge 45 lifting edge 126 light alloy 174 limiting draw ratio 167, 187 line operating and information system 321 line operation 259 link 66 link drive 55 f., 223 link drive system 529 link-driven press 55 load, off-center 37, 80 f., 214 loading 393 loading station 479-481 loading system 517 local control unit 255 locking bead 22 locking device 84 f. lock-out-plate 118 lock-out-procedure 117 long section 380 longitudinal knife 268 longitudinal seam w elding 380 longitudinal shaft 64 longitudinal shaft drive 63-65 low er elongation limit 175 low -voltage sw itchgear 97

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

lubricant 179, 181, 422, 460, 463 lubricant film 180 lubrication 72, 179-185 –, hydro-dynamic fluid lubrication 180 lubrication pocket 358 f. lubrication system 361 f., 520 machine and production data 260 - 262 –, acquisition 262 machine tool 1 machining allow ance 439, 465 magnetic belt conveyor 217 main drive 60, 66 maintenance 267, 321 maintenance back-up 105 maintenance capability 320 maintenance instruction 259 maintenance interval 321 maintenance module 324 malfunction diagnostics system 261 mandrel 434 mandrel friction force 476 manufacturer’s declaration 111 manufacturing process 5 material 174-179, 423 f., 450-454 material cohesion 6, 25 material feed 305 material flow 26-28, 339 material number 174 material pair 181 material saving 269 material selection 338 material stress 339 material usage 125 material utilization 271, 273, 356 maximum friction condition 180 maximum true strain 470 mean pressure 31 mechanical hydraulic press 203 mechanical press 38, 49-72 –, design 63 medal minting press 537 metal flow 140, 148, 157, 398, 400, 468 metal forming technology 1, 6, 19, 123 micro-alloyed steel 174, 177, 450 minimal bending radius 368 minting line 526-541 modified knuckle-joint 514 modified knuckle-joint drive 58 f., 528 modified knuckle-joint top drive 509 f.

Index modified top drive 205-207 modifying material property 5 molybdenum disulphide 462 molycoting 460 f. monobloc press frame 360, 528 f. monobloc structure 514 moving bolster 89 f., 152, 228, 248-250, 290 moving punch 352 f., 360 moving stripper 316, 318 multiple pressing 431 multiple stroke 537 multiple-point press 39 multiple-station press 508-512 multi-point controller 149 NC machining 134 near net shape component 447 necking 449 net shape component 447 net shape production 485 netw orking capability 104 nibbling 20 nitriding 500, 502 noise protection 228 noise reduction 289 nominal load 52 f. normal annealing 424 normal contact stress 180 f. normal force 179 normalization 458 f. notch impact strength 449 notching 431 notching device 317 notching machine 297 –, single notch blanking 297 –, automatic notching machine 299 notching system 299 number of presses 224 off-center load 37, 80 f., 214 offset punch 275 oil flow 72 oiling 220 omega section 377 one-point configuration 39 on-line control 401 on-line monitoring 105 open contour 268 open contour blanking 268 open die forming 7, 433, 476 open front press design 34 open shears 458 f. opening angle 370

555 operating and information system 324 operating and visualization system 94-96, 258 operating capability 320 operating instruction manual 114 f. operating mode 256 operator console 95 operator prompt synoptic 260 operator station 95, 258 optoelectronic system 401 OSHA 117 outfeed roller 316 f. output 394 f. overbending 23 overload safety device 54, 66 f. overrun drive 87 f. pallet changeover 383 panel retaining block 144 panel structure 514 parallel lift mechanism 153 parallelism control system 80, 215 parallelism controlling cylinder 80, 252 parallelism of the slide 80-82 parameter 51 f. part discharge 306, 308 part draw ing 130 part family 394, 398 part transfer 131, 478-484 part-dependent tooling 154, 238, 245 peeling 456 pendent control unit 258, 326 penetration depth 294 f. penetration depth control 293296 perforating press 314-320 perforating punch 316 phosphating 455, 460 f., 463 phosphor-alloyed steel 174, 176 pickling 460, 462 piercing 23, 431, 440 piercing module 214 piercing process 435 pilot pin 126, 356 pilot series 129 f. pint holding plate 250 piston rod 39 pitch 273 pivoting slide plate 151 plasma nitriding 502 plastic press 251 f. plate-type brake 285 plunger 426 pneumatic 70

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

pneumatic ejector 482, 487 pneumatic pad 487 pointed face/finish 275 positioning module 100 positive press-off pin 356 f. pow er 49 pow er supply 97 precision blanking 330 preform 423-425, 454 pre-forming 425 pre-graphitizing 522 pre-heat-treated steel 450 preliminary draw ing 455 pre-production series 130, 138 pre-run 136 press –, blanking 286 f. –, bottom-driven 37 –, characteristics 149 –, deep draw ing 41-44 –, displacement-related 37 –, double-action 41 f., 56, 173, 185 –, embossing 522-525 –, fine blanking 360-365 –, force-related 37 –, high-speed blanking line 291-297, 307, 391, 536 –, horizontal 513 f. –, hybrid 203-205 –, hydraulic 38, 73-85 –, knuckle-joint 55, 507 f., 525 –, link-driven 55 –, mechanical 38, 49-72 –, mechanical hydraulic 203 –, perforating 314-320 –, single-action 43 f., 169, 173 –, sizing 522-525 –, straight-sided 297 –, top-driven 37 –, try-out 391 –, universal 198-208, 391 –, w ork-related 38 press bed 37 press bus system 257 f. press construction 33 f. press control system 94-105, 320-329 –, electrical equipment 94 –, function 94 –, functional structure 98 f. –, structure 97 press crow n 34, 37, 66 press frame 34-37 –, configuration 36 –, monobloc 36 –, multiple part 36 press line 124, 222-228, 391 f. press load schedule 396 f.

Index Press M anagement System (PM S) 262 press synoptic 260 press through process 476 press type 33 f. pressing force 506 pressure –, hydrostatic 73 –, mean 31 pressure accumulator drive system 77 f. pressure block 127 pressure column 45 f., 250 pressure control system 101 pressure identifier 427 pressure medium 406 f. pressure medium reservoir 185 pressure pad 250 pressure pattern 133 pressure pin 250 pressure plate 144 pressure point 66 f., 172, 293, 316 pressure sensing, dieindependent 363 pre-stretching process 190 primary shaping 5 principle deformation 28 principle strain 416 principle stress 25 f. process combination 22-24, 437, 440 process control 137 process data acquisition 403 process monitoring 402 process plan 123, 130 f. process simulation 138 process visualization 95, 322 processing plan 123, 467 f. processing time 394 production capacity 395 production cell 320 production cycle 398 f. production data 262, 399 production data acquisition 264, 321 production die 421 production log 321 production log information 324 production requirement 393 production scope 393 production stroking rate 394 f. profile 376 f. profile parting die 380 profile roll changeover 381 programmable logic controller (PLC) 97, 102, 257, 321 f. programming 105 –, sequentional 102

557 progressive blanking die 125, 307, 356 progressive compound die 126, 345, 351-353, 356 f. progressive die 125, 282, 297 properties of the cut surface 346 prototype die 137 f., 421 prototype part 130 pump drive 77 f. punch 159, 353 –, bending 372 –, bevelled 275 –, blanking 354 f. –, counterpunch 434 –, draw 156-160, 185, 187 –, extrusion 494 –, fixed 352, 354, 360 –, inner form 353, 355 –, moving 352 f., 360 –, offset 275 –, perforating 316 –, seal 406 f., 420 –, specific punch pressure 472 –, telescopic 11 punch bundling 23, 309 f. punch control beam 316 punch control unit 316 punch design 491-495 punch head 127 punch retaining plate 144 punch tightening rod 361 pusher 513 push-in clamp 92 push-pull drive 87 PVD process 500-502 quality assurance 321, 389, 400404 quality control 122, 400-404 quick die change system 192 rail section 376 rated press force 52 f., 57 reaction force 188 f. ready-to-run synoptic 260 f. recoiler 284 recovery annealing 458 f. recrystallization 26 recrystallization annealing 423, 458 f. recrystallization rate 26 recrystallization temperature 26 rectifier, digital 101 redraw 156 f., 167 reducing gear 120 reduction 9, 425

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

redundancy, hydraulic 97 reengineering 442 relative blanking force 274 relief 458 f. remote diagnostics 104 f.,321 repair 267, 321 residual risk 115 residual stress 122, 369 resistance to shear 274 resistance to w ear 121 resistance w elding 311, 313 restraining force 285 restrike block 144 restriking 16, 23 resuming operation 320 return stroke force 274 reverse draw ing 159 –, hydro-mechanical 185 rib 170 rim length 273 rim w idth 273 rimming machine 526 robot 227 f. rocker element 290 rod extrusion 433 f. roll bending 16 roll bending radius 376 roll embossing 436 roll feed 194 f., 288, 292, 305 roll forming 17, 373-383 roll forming line 379 roll stand set 380 roller gib 40, 304, 314, 528 roller pitch 385-387 roller straightening 16, 383-389 roller straightening machine 385, 387 rolling 374, 433 –, cold rolling 7 –, hot forming 7 rolling die 380 rolling direction 366 rolling ring 284 rotary feed system 531 rotating brake system 285 f. rotating shears 288 round steel 455 running gear 466 run-up time 60 safety 106-119 safety control system 97, 99, 257 safety inventor level 397 f. safety measure 106 safety officer 119 safety requirement –, European 107-111 –, USA 117-119

Index sand blasting 460 sandw ich coating 502 scale formation 438 scale forming 122 scale layer 460 scrap chute 144 screw press 38 SE project 130 seal punch 406, 420 seaming bed 127 secondary contour 407 section 376 f. –, basic section geometry 374 –, long 380 segment blank 301 segmented bed cushion 215 segmented blank holder 313 sensor 94, 97, 326, 329 separating device 479 sequential programming 102 series –, pilot series 129 f. –, pre-production series 130, 138 series run 149 series try-out 130 servo drive 101 set-up 257, 260 f. set-up time 86 shaft hole punch 300 shear 287 –, circular 284 –, cropping 288 –, cut-to-length 286, 288, 380 –, exchangeable 284 –, fixed 287 –, rotating 288 –, separating 316 f. –, stationary 287 f. –, sw ivel-mounted 287 shear cutting 19 f. sheared contour 274 shearing 457 shearing force 458 shearing guide 458 –, closed 458 f. shearing resistance 458 shearing strength 274 shearing stress hypothesis 25 f. shearing velocity 458 shearing w ork 458 shearing zone 269 shears, open 458 f. sheet metal forming 433 sheet metal thickness 140 Sheet M olding Compound (SM C) 251 sheet, cold-rolled 174 shrink fit 492 f. shrink ring 491, 493

559 SI unit 31 f. side cutter w aste 273 side member 210-216 side shear 126 silicon bronze 453 simulation 415, 468 simulator 391 Simultaneous Engineering (SE) 128, 413 single cycle 257 single die 124 single notch blanking 297 single stroke 537 single stroke operation 394 single-acting deep draw ing press 44 single-action dow nstream press 225 single-action draw ing 159 single-action press 43, 169, 173 sintered part 522, 524 sizing operation 476 sizing press 522-525 sleeve clamping 488 slew ing ring 299 slide 37, 66-70, 144, 159 –, blank holder 41, 158 slide adjustment 66 slide counterbalance 67 slide cushion 44, 69 slide drive 37-41 slide force 188 f., 342 slide gib 39, 360, 362 –, eight-track slide gib 509 –, gib type 39 f. slide impact speed 48 slide locking 83-85 –, non-positive acting 85 –, positive acting 84 slide position sensor 81 slide tilt 80, 134 slide velocity 180 f., 199 sliding component 136 sliding friction condition 179 sliding insert 421 slip-on gearing 466 slitting device 317 slitting line 284 f. slug preparation 454-459 small control system 266 smooth surface 334 f., 337, 347 soaping 460 f., 463 sodium soap 461 soft annealing 458 f. softw are system 321 solid body friction 180 solid forming 91, 433-542 –, choice of press 505 f. –, design rule 465

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

–, economic aspect 441-443 –, lot size 464 solid forw ard extrusion 445, 447 f. solutionizing 423 sorting and positioning element 127 sound enclosure 529 special die 127 specific blank holder pressure 171 specific forming w ork 472 specific punch pressure 472 speed drop 51- 54, 60 spindle pressure points 66 spinning –, roll head 13 –, spinning bush 13 –, spinning mandrel 13 splash ring 186 spotting fixture 150 spray system 521 springback 23, 140, 367, 372, 415 springback factor 367 f. stacking cart 290 stacking channel 308 stacking device 391 stacking line 290 stacking unit 253 f., 287 stamping nut 127 f. stamping plant 389-400 –, layout 389, 391 stand changeover 382 standstill 263 standstill data 262 start-stop-line 379 start-up 101, 320 stationary shear 287 f. steel 120, 450-452 –, alloyed 174 –, austenitic chromium nickel 174, 177 –, bake-hardening 174, 176 –, ferritic chromium 174, 176 –, flat 456 –, high-speed 497, 499 f. –, micro-alloyed 174, 177, 450 –, phosphor-alloyed 174, 176 –, pre-heat-treated 450 –, round 455 –, unalloyed 174, 176 –, w arm/hot forging tool steel 498-500 steel castings 120 steep conveyor 479, 529 straightener 194, 288, 384 straightening 383 straightening by stretching 14 straightening force 388

Index straightening roller 385, 388 straight-sided press 34, 297 strain hardening 415, 423, 425, 432 stress –, effective 416 –, largest 28 –, mean 28 –, principle 25 f. –, smallest 28 stress relief annealing 122 stretch draw ing 15, 22, 156-193 –, blank holder 22 stretch forming 14 f. strip draw ing 10 strip layout 356 strip length 271, 273 strip perforating press 314, 318 strip w idth 270 f., 273 stripper 144, 269, 304, 315-319 stripper slide 316 stripping 274 stripping force 333, 355 f., 358 stroke adjustment 69 stroke limitation 82 f., 191, 250 suction cup 217 surface fatigue 183 surface hardening process 142, 146 surface quality 443 f., 447 f. surface treatment 457, 459-463 sw ing arm feeder 226-228 sw itch cabinet 258, 326 sw ivel bending 16 f. sw ivel mounted shear 287 sw ivelling bracket 86 sw ivelling die 290 synchronous overload clutch 533 synchronous tapered cup 365 synoptic 260 f. system of measurement, technical 32 T section 377 tailored blank 309-313 tapering 9 team w ork 320 tearing 19, 21, 346 technical system of measurement 32 telescopic roll set 380 tensile strength 174, 449 tensile test specimen 175 T-fitting 406 f., 409 thermoplastics, glass-fiber reinforced 251 f. thickness distribution 416 thickness related defect 530

561 three-phase asynchronous motor 100 tie rod 36 tilt moment 81 f. tilting block 127 tilting mechanism 479 tin 454 tin bronze 453 titanium 179, 454 titanium alloy 179 tolerance 444 tool see „ die“ tool breakage safety system 363 tool data management 321, 323 tool-dependent hydroforming 406 tooling 391 –, part-dependent 154, 238, 245 tooling data input mask 96 top drive 59 top to tail arrangement 270 top-driven press 37 transfer 244 –, electrically driven transfer 239 –, motion curve 239 transfer die 125, 345, 355 transfer feed system 518 transfer press 35, 125, 229-234, 391 –, high-performance transfer press 201 –, large-panel transfer press 125, 391, 393, 396 transfer simulator 154 f. transformation annealing 121 transition radius 466 transport length 505 transportation time 198, 394 transverse shaft drive 63 f. tri-axis transfer 201, 231 f., 238 tribology 179 trimming 23, 435 trimming module 214 triple stroke 537 troubleshooting 101, 321 try-out 136 –, home try-out 130 –, series try-out 130 try-out center 152 f. try-out equipment 148-154 try-out press 148, 391 T-slot 88, 92 T-slot clamp 92 T-track 90, 152 f., 228, 290 tube extrusion 433 f. tube section 456 tubular blank 414, 416, 424 f. tumbling 460

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

turning device 44 turnover device for blank stacks 220 turnover station 227 –, blank turnover station 217-222 –, drum turning device 220 –, fork turning device 221 tw isting 18 tw o-point configuration 39 tw o-point slide drive 506 type test 111 U/C section 376 ultimate elongation 175, 423 ultrasound detection 122 unalloyed steel 174, 176 undercut 466 unit of measurement 31 f. unit system, international 31 universal minting press 534 universal press 198-208, 391 universal station 155, 228, 238, 247 upright 34 upset ratio 467 upsetting 440, 477 upsetting die 435, 476 upsetting/compression 27 f., 405, 407, 410, 435, 445, 476 f. uptime 395 used machine 116 utilization rate 398 f. valve 79 valve block 72 variation in diameter 466 vee-ring 332, 335 vee-ring force 356 f., 360 vee-ring piston 361 f. vee-ring plate 353 f. vibrating conveyor 479 vibration characteristic 295 viscosity 183 visualization 96 volume calculation 466 volume constancy 28, 443 volumetric adjustment 467 V-prism gib 39 w all friction 469 w all thickness 465 w all thickness tolerance 446 w arm extrusion 445 w arm forging 438 f., 451 w arm forming 437, 506 w arm forming line 520-522

Index w ashing/cleaning machine 219 w aste chute 144 w ater container 185, 187 f., 190 w ear 179-185 w ear at surface layer 182 w ear mechanism 179, 181 f. w ear resistance 183 w ear resistant coating 500 w edge adjustment 66, 486-488 w edge-action cutting 19, 21 w edge-action pusher die 490 w edge-type clamps 490 w ide strip section 377 w ire 454 f.

563 w ire feed device 512 w ork 29 f., 49-54, 506 f –, bending 372 –, blanking 274, 276 f. –, deformation 30 –, draw energy 173 –, forming 53, 472 – velocity 506 w ork hardening 339 w ork requirement 282, 469-477 w orking period 395, 398 w rinkle bulging 13 w rinkling 140 f.

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

X-ray detection 122 yield strength 449 –, low er yield strength 175 Z section 377 zinc 454 zinc phosphate layer 461 zinc soap layer 461 zirconium 454