Stamping Practice: High Performance Stamping 3658347570, 9783658347574

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Matthias Kolbe

Stamping Practice High Performance Stamping

Stamping Practice

Matthias Kolbe

Stamping Practice High Performance Stamping

Matthias Kolbe Faculty of Automotive and Mechanical Engineering West Saxony University of Applied Sciences Zwickau, Germany With collaboration by Miriam Geisser, Josef Hafner and Ekkehard Fluck Translated by Phil Jackson Translations

ISBN 978-3-658-34757-4 ISBN 978-3-658-34758-1 https://doi.org/10.1007/978-3-658-34758-1

(eBook)

# Springer Fachmedien Wiesbaden GmbH, part of Springer Nature 2022 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, 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. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Editorial Contact: Ellen Klabunde This Springer Vieweg imprint is published by the registered company Springer Fachmedien Wiesbaden GmbH, part of Springer Nature. The registered company address is: Abraham-Lincoln-Str. 46, 65189 Wiesbaden, Germany

Preface

High-Performance Stamping: Precise, Fast, Modern In the global economy, the chipless manufacturing process “stamping” has established itself over many years and has developed significantly. Today’s stamped parts are highly complex, the tools achieve the largest possible tool life, and the high-performance stamping machines enable maximum stroke frequencies with extremely stable process reliability. This English-language textbook provides an overview of the basics of stamping technology, practical tips for the design of tools, and explanations of the high-performance stamping presses. Design rules and parameters from practice provide assistance in the construction of tools. The computational determination of influencing variables, basic material technology, and functional relationships support the selection of highperformance stamping presses. There is also a special chapter about optical monitoring of stamping tools and stamping processes. This edition is based on the textbook Stanztechnik in German in its 13th edition (ISBN 978-3-658-30400-3, Springer Vieweg Verlag Wiesbaden, Germany, 2020). Understanding the interrelationships between stamping processes, the design of tools and press technology require fundamental and extensive knowledge. This textbook lives up to this requirement, now also to support trainees and students in self-study in the Englishspeaking world and to impart targeted knowledge of this production technology to practitioners. I am pleased that qualified experts from the industrial practice of high-performance stamping have supported me intensively as co-authors. Special thanks go to Ms. Miriam Geisser and Mr. Dipl.-Ing. HTL Josef Hafner from Bruderer AG, Switzerland, and Mr. Ekkehard Fluck from OTTO Vision Technology GmbH, Jena, Germany! I would also like to thank Mr. Phil Jackson for the translation. May the book be a good support for trainees, students, designers, and process engineers. Zwickau, Germany October 2021

Matthias Kolbe

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Contents

1

What Does Stamping Technology Offer the Global Economy? . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 4

2

Stamping Technology Processes and Terms . . . . . . . . . . . . . . . . . . . . . . . .

5

3

Materials for Stamped Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Materials for Stamped Parts in High Performance Stamping Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Non-metallic Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Metallic Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

11

. . .

11 11 11

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The Basic Principles of Shear Cutting . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Cutting Methods and Types of Cutting . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Surface Quality of Cut Edges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Dimensional Tolerances of Cut Parts . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Cutting Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1 Determining the Cutting Force . . . . . . . . . . . . . . . . . . . . . . . . 4.4.2 Effect of the Cutting Force on the Tool and Machine . . . . . . . . 4.4.3 Reducing the Cutting Force with Inclined Shear Cutting . . . . . . 4.4.4 Reducing the Cutting Force by Offsetting the Punch Height . . . 4.4.5 Stripping Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Cutting Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6 Cutting Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7 Basic Principles and Guidelines for Cutting Tools . . . . . . . . . . . . . . . . 4.7.1 Cutting Clearance and Punch Clearance . . . . . . . . . . . . . . . . . . 4.7.2 Pulling Back the Piercing Waste . . . . . . . . . . . . . . . . . . . . . . . 4.7.3 Web Widths and Margin Widths . . . . . . . . . . . . . . . . . . . . . . .

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

13 13 16 16 16 16 20 21 22 23 23 25 25 25 27 28

5

Composite Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Basic Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.1 Layout and Construction of Tools . . . . . . . . . . . . . . . . . . . . . . 5.1.2 Design Guidelines for the Construction of Progressive Tools . . .

. . . .

31 31 31 38 vii

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Criteria for High-Performance Dies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 General Requirements and Design Notes . . . . . . . . . . . . . . . . . . . . . . . 6.2 Consideration of High Stroke Frequencies . . . . . . . . . . . . . . . . . . . . . . 6.3 Punch Tool Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4 Notes on Modular Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 Measures at High Stroke Frequencies . . . . . . . . . . . . . . . . . . . . . . . . . 6.6 Tool Testing and Acceptance at the Manufacturer . . . . . . . . . . . . . . . .

. . . . . . .

51 51 55 57 59 60 60

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Monitoring the Stamping Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 Monitoring the Punching Tool and the Press . . . . . . . . . . . . . . . . . . . . 7.1.1 Measurands Suitable for Evaluation . . . . . . . . . . . . . . . . . . . . . 7.1.2 Measuring Positions for Monitoring . . . . . . . . . . . . . . . . . . . . . 7.1.3 Evaluating the Measured Variables . . . . . . . . . . . . . . . . . . . . . 7.1.4 Requirements and Selection Criteria . . . . . . . . . . . . . . . . . . . . 7.1.5 Force Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Monitoring the Stamped Part Using Image Processing . . . . . . . . . . . . . 7.2.1 Inspecting Free Falling Parts in and Close by the Tool . . . . . . . 7.2.2 Inspecting Stamped Parts on the Strip . . . . . . . . . . . . . . . . . . . 7.2.3 Inspection Options for Image Processing . . . . . . . . . . . . . . . . . 7.3 Controlling the Stamping Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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

63 63 63 64 64 67 69 70 70 71 72 73 75

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High-Performance Stamping Presses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Calculation: Basic Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.1 Punching Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.2 Available Operating Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.3 Required Drive Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3 Static Accuracy of Presses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.1 Static Accuracy Unloaded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.2 Static Accuracy Loaded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4 Dynamic Accuracy of Presses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.1 Dynamic Accuracy Unloaded . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.2 Dynamic Accuracy Loaded . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5 Design Solutions for High-Speed, High-Performance Presses . . . . . . . . . 8.5.1 High-Performance Presses with Mass Balancing System for High Stroke Frequencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.2 Ram Guidance Systems in the Same Plane as the Strip . . . . . . . . 8.5.3 Thermally Neutral Guides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.4 Four-Point Drive of the Press Ram . . . . . . . . . . . . . . . . . . . . . . 8.6 Strip Feed Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.7 Controlling Stamping Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

77 77 78 78 78 80 80 80 81 81 81 82 82 82 85 86 86 86 92 95

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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What Does Stamping Technology Offer the Global Economy?

Technical progress is largely determined by manufacturing technology. Production engineers assess whether the concept of a component can be converted into a reality as well as the optimum processes to manufacture it. However, the aim of most manufacturing tasks is to improve existing workpieces through a new or alternative manufacturing process at an economic price point for market launch. Practitioners who are looking for manufacturing options are initially shown several examples to illustrate what range of workpieces i.e. stamped parts can be produced using high performance technology. Workpieces produced using high-performance stamping technology are typically used in the following industries: electronics, computers, telecommunication, television sets, video equipment, automotive, clock-making, measuring equipment, household appliances, lighting, drinks and canning, as well as in general mechanical engineering and precision engineering. Stamped parts can be found in nearly all devices in daily use as well as in jewellery. It is not possible to provide a complete list here. Instead, the intention is to inspire engineers to consider other applications for stamping technology which can integrate multiple manufacturing processes in a single operation. Figure 1.1 shows several examples of typical stamped parts. These sorts of stamped parts are used throughout the global economy in batches of millions. Stamping is a chipless or non-cutting manufacturing process which allows large quantities of highly accurate and complex workpieces to be produced from metal or other materials quickly, with optimum material usage and very low waste: it is becoming increasingly important in the global economy. Stamped parts are produced on a stamping machine from strips or sheets in one or more chipless operations. The whole stamping process can comprise parting (shear cutting) and forming, with forming covering bend forming, drawing and coining (Table 2.1, Sect. 2). However,

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What Does Stamping Technology Offer the Global Economy?

Fig. 1.1 Precision components for the electronics industry produced using high performance stamping technology (STOCKO CONTACT, France) on high performance presses (BRUDERER AG, Switzerland)

joining, riveting, threading, resistance and laser welding are also used which means extremely complex parts can be processed completely in a single stamping sequence. In most instances, complete processing produces a finished workpiece. The forming tools have two components. Generally, they consist of upper and lower parts of the tool. If necessary, they are supplemented by lateral tools. Mechanical, hydraulic and servomechanical presses are used as the working machines which execute a stroke movement in a straight line. The dimensional and geometrical accuracy of the tool and the guidance accuracy of the machine in the working plane is decisive for the manufacturing accuracy of the stamped parts. Longer and longer presses in the direction of the strip run are required to facilitate complete processing with many sequences. This has resulted in further development of presses and the strip feed units. Conventional stamping technology produces stamped parts with medium tolerance requirements at medium stroke frequencies and is often still used in workshops and small-scale industries. Tool steels are used in the tools for smaller batch sizes. Machines also often have a C-frame design for easier access. High performance stamping technology produces stamped parts with tight tolerances from sheet steel up to approximately 3 mm thick with stroke frequencies up to 2500 strokes/min [1]. Stamping is generally carried out on mechanical presses with an O-frame design and carbide metal tools. Up to 500 million stamped parts can be produced with a single tool. This high performance stamping technology has developed in leaps and bounds in recent years. Thanks to high productivity, products are being manufactured on specialised stamping plants across the globe. The market for precision components, for example, in the computer or automotive industry, has grown significantly. The impetus for

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What Does Stamping Technology Offer the Global Economy?

3

this came in the 1970s with the development of the high performance stamping press with mass balancing (BRUDERER system [1]) which enables high stroke frequencies. This was followed by the use of carbide metals for the stamping tools and. precision wire-cut EDM and precision grinding of these materials. The further development of peripheral equipment such as coilers and strip feed units and process monitoring which allows several functional dimensions or the complete stamping process to be controlled has also increased productivity and lowered manufacturing costs. Zero-defect production is often required. Fine blanking produces complex, ready-to-use, three-dimensional, multi-featured parts from sheet steel from approximately 0.5 to 15 mm thick in very tight tolerances (up to IT8) and with precise cut edges of parts (up to Ra 0.4) [2]. It is used where functional surfaces with extremely low dimensional and geometrical tolerances and high surface quality are required. In addition to this, the flatness is significantly better than with shear cutting. The cut surfaces are strengthened with respect to the base material and can be used as functional surfaces without any further processing (at least only deburring if necessary). External and internal shapes can also be produced in a single operation which leads to extremely good external to internal positional tolerances. This technology can often replace expensive cutting machining processes. Find blanking technology has benefited significantly in recent years from the further development of suitable materials for both the stamped parts and tools. Specifically, it has been possible to increase the variety of shapes of the stamped parts and the tool service life through the use of powder metallurgy. Coating hard materials has also contributed to an increase in service life. Modern fineblanking presses with mechanical servodrives achieve a production capacity nearly twice that of conventional fine-blanking presses. A servo-controlled torque motor acts directly on the knuckle joint and flexibly controls the movement path of the ram (Feintool system [2]). Nibbling and laser cutting technology is suitable for workpieces made from sheet steel with openings which have been produced from larger sheets. CNC-controlled machines allow highly complicated shapes to be cut out. Whether to cut out using cutting tools (nibbling) or to part using a laser beam depends on the complexity of the shape and the financial costs. Items such as housings and control cabinets can then be produced using sheet bending equipment. Large sheet metal parts such as car body parts are produced using large part stamping technology. Bending and drawing operations are also mainly used here in addition to trimming the parts. Lasers are also used for parting (blanking) in the most modern manufacturing processes. Forming blanks of different thicknesses (so-called tailored blanks) which are pre-processed to the correct shape by welding the parts offers specific benefits with respect to stresses in the finished parts. Today’s press controls include numerically control systems. Once the numerical control systems first used in machined production were included, they were soon fully integrated into stamping technology with appropriate adaptations. These control systems are extremely flexible, can be easily adapted to each task, offer an intuitive interface, and can be networked. This volume deals with conventional stamping technology, high performance stamping technology and

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What Does Stamping Technology Offer the Global Economy?

fine blanking. Nibbling and laser cutting technology as well as large part stamping technology are not covered.

References 1. Stamper Magazine; Information of Company, Bruderer AG, Frasnacht, Swiss (2018) 2. Birzer, F., Maurer, C., Schaltegger, M., Schneeberger, M.: Feinschneiden und Umformen. Bibliothek der Technik, Band 134 (Feintool Technologie AG). Verlag moderne industrie, Landsberg (2014)

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Stamping Technology Processes and Terms

Stamping integrates several production processes in a single operation within the feed motion of a press. The term stamping has not been standardised, but in practice, it has not only been retained but, as explained above, extended. The specific production processes included in stamping and other subdivisions in accordance with DIN 8580. Each process is classified numerically. The main processes used in separating are shear cutting and wedge-action cutting (Fig. 2.1). Both processes are known as cutting and to this end, the tools used are captured under the umbrella term cutting tools. Tool elements are derived from the prefix ‘cutting’ (e.g. cutting edge, cutting wedge, cutting gap). The prefix ‘cut’ (e.g. cut part, cutting edge, cut edges of the part) is used to describe the workpiece produced by the shear cutting process. Table 2.1 provides information on a few types of cut and the associated tools. The forces which occur during cutting are known as cutting forces and the energy required as the cutting work. The forming production process is subdivided in accordance with DIN 8582 into five groups: each group has its own DIN number (DIN 8383 . . . 8387). Each group is named according to the type of stress which has essentially produced the plastic condition of the items to be formed. The five groups are divided into several subgroups; individual subgroups are subdivided further. For example, the “stretch forming” working process (DIN 8585 sheet 4, classification number 2.3.3.1.1.1) is integrated into the classification system. In form bending, a distinction is made between bending with straight or bent bending axes and between single and multiple bending depending on the number of bending axes (Table 2.2). Joining or dressing with semi-piercing is used as a useful supplement to conventional cutting and forming methods. Stamping is further enhanced by welding. For example, precious metal contact materials are applied to pre-stamped projections using resistance welding. Laser welding has also

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Stamping Technology Processes and Terms

Fig. 2.1 Separating processes. (a) shear cutting. I Coining or blanking tool, II Cropping tool (shearing principle). (b) wedge-action cutting. I Knife cutting tool (e.g. cutting out seals), II Scrap shear. Df pressure surface, Ff free surface, Sk cutting edge, SKeil cutting wedge, us cutting gap width, “cutting edge angle of inclination”, cutting wedge angle

found its way into high-performance stamping technology. For example, in lamination stamping, the edges of the sheets which have been stamped together are welded as part of the stamping stroke at stroke rates of up to 600 strokes/min. This process is also used in the manufacture of electrical contacts: here, small preformed tubular parts are welded together along their abutting edges. Threads up to M8 can also be cut and pressed into stamped parts and fine-blanked parts in a single stroke but this requires special equipment. DIN 9870 sheet 3 replaces the previous frequently used terms of angle bending with V-form bending, upward bending with single folding, and U-form bending with multiple folding. According to the explanations in the standard, the previous terms did not provide sufficient detail on the characteristics of the specific bending process as each bend leads to an angle and folding upwards provides an indication of direction which is not necessary. The new terms of V-form bending and folding are more descriptive. “In V-form bending, a wedge-shaped punch is used in which each of the two legs is formed into an angle; in folding, only one leg is folded from its original position.” If several bends are to be carried out simultaneously in the bending tool, DIN 9870 sheet 3 designates this shaping process. As multiple V-form bending or as multiple folding and the required tool as a multiple V-form bending tool or a multiple-folding tool. If workpiece legs are set at an angle by swivelling the bending cheeks around a straight bending axis, this is known as swing folding (swing folding machines, sizes DIN 55220). Methods such as stamp flanging, stamp creasing, stamp flattening, stamp upsetting, etc. as listed under the umbrella term “stamping” in the previous edition of the standard DIN E 9870 sheet 3 are replaced in the standard DIN 8582, ‘Classification of forming methods’ with new the definitions die flanging, die beading, coining, die upsetting etc. in the following groups: tensile forming, tensile compressive forming, compressive forming, or shear forming (DIN 8583 . . . 8587). If cutting, forming and other processes are combined in a single tool, this produces a composite tool. Tools are economical if they result in the lowest cost per workpiece for the

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Stamping Technology Processes and Terms

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Table 2.1 Types of cutting Types of cutting

Strip from: a) Coil b) Sheet Types of blank a) cut part (finished) b) blank (for further forming)

1. Blanking Closed cutting line

Tool Characteristic

Blanking tool Progressive process Single process Falls through the cutting die Remains on or in the strip Blank Types of blanking a) Single cutting b) Cutting and turning Multiple tools Only one tool in: Only one tool multi-row in pairs for both passes single row Turned strip Single strip a) single cutting tool b) multiple cutting tool

2. Cropping

a) Single cropping b) Double cropping Without waste

Open cutting line Tool Cropping tool

c) Cropping With waste Tips away

Tips away Feed V

Burr orientation a) above and below 3. Piercing

Cutting line is: a) closed b) open Characteristic

5. Combination blanking and piercing Characteristic 6. Releasing

c) below

Piercing tool

Closed cutting line 4. Progressive cutting

b1) above b2) below

Blank

Waste

Pre-piercing by a) blanking b) cropping Burr is: above on external below throughout edge below on holes a) piercing and separating in 1 operation with 1 stroke b) dimensional deviations|accuracy of the feed Blanking and piercing tool Burr below throughout a) piercing and separating in 1 operation with 1 stroke b) dimensional deviations |accuracy of the tool Releasing tool

Open cutting line

Blanks Waste

7. Trimming Cutting line is: a) open b) closed

a) blank

b) intermediate shape Finished Trimmed drawn part press blanks

waste

Trimming tool

Waste

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Stamping Technology Processes and Terms

Table 2.2 Bend forming processes

Bend forming 1. Die bending

Tools

Preform thickness remains approximately the same Bending around a straight bending axis

V-form

Folding

a) Special processes V-form bending on a die bending press Stop

Dimension t has a tolerance

Folding Multiple folding

Multiple folding

Swing folding on a swing folding press Folding rail with folding cheek

Lower tool (die)

Lower cheek

b) Form bending

Bending around a curved bending axis, e.g. stiffening ribs, indentations Tool: form bending tool flat edge

2. Roll bending

and deburred

Process: Starting shape: Manufacturing method:

Bending around a straight axis upset crimped cutting tool folding tool

around curved bending axis deep-drawn cup deep drawing tool

3. Fold-bending

Process: Starting shape: Manufacturing method:

final shape straight bending axis preform

starting shape curved bending axis deep-drawn cup

fold-bending tool

production of the required number of workpieces with low production and maintenance costs. When comparing two production options, the maximum quantity of workpieces is to be determined that can still be produced economically with this single process; this quantity is known as the marginal3, or overall quantity. Table 2.3 shows the overall quantities for a range of typical means of production. The required quantity of workpieces must be taken into consideration when designing tools.

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Stamping Technology Processes and Terms

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Table 2.3 Tools and machines for specific quantities and batch sizes when stamping small parts

Total quantitya up to 500

500 . . . 5000

5000 . . . 50
103

50
103 . . . 106

106 . . . 107

a

Tools Hand tools and sheet metal processing equipment, nibbling tools, laser beam, wire erosion Simple forming tools with steel components, with and without standardised guides, piercing tools, synthetic resin drawing tools Universal tools with sheet guide systems, some with column guide systems, with steel components Composite tools with column guidance, steel and (or) carbide metal components Special and composite tools with carbide metal components with precision column guidance systems

Machines and systems Numerically Conventional controlled Laser cuttingb Standard mechanical hand and nibbling tools and sheet machines, wire metal processing erosion machines machines

Minimum batch quantitiesc Pilot series, test runs in batches of up to 500

Simple presses (manually loaded)

Precision stamping machines for precision parts, laser cutting and nibbling machines

500 . . . 5000

Presses with feed units, coilers, straightening machines and stacking equipment

Precision stamping machines with bottom dead centre stabilisation, some with automatic tool and strip change as well as strip and tool magazines and waste disposal equipment (stamping machines and systems)

Order-specific, from 5
103 with computercontrolled stamping machines or systems or from 5
104 with conventional presses

Precision stamping presses for high stroke frequencies and high-speed presses with feed systems, strip feed and stacking equipment

Quantity of stamped parts that can potentially be produced with one tool with repeated sharpening For larger parts and larger quantities. For small stamped parts, the flexibility is beneficial c Number of stamped parts that can be produced economically per order b

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Stamping Technology Processes and Terms

This determines the tool design, the materials and their processing. Large-scale production tools are largely automated (loading and ejection equipment, etc.); the operating life and a rapid production sequence are critical considerations. In tools for medium quantities, workpiece holders and guide surfaces for punches and columns can be cast from synthetic resins. Small quantities from 500 to 5000 pieces are produced using unique composite tools, even if it takes longer to manufacture the workpieces. Production aids (templates etc.) or CNC laser cutting facilities are preferred for extremely small quantities up to 500 pieces. As far as possible, standardised or standard in-house parts should be used for all tool types. Non-ferrous metal sheets and steel sheets with a thickness less than 1 mm can also be cut, bent or drawn to low drawing depths in small to medium quantities using elastic plastics. A steel punch penetrates the elastic material at the same time as forming the blank, thus forming the counter or bottom die. Hydraulic presses are best suited to this type of plastic pressure pad. Note: The following abbreviations and units in accordance with DIN 1301 and DIN 1304 are used: Variable Formula symbol Unit of measurement

Surface area A mm2, cm2

Volume V mm3, cm3

Force F N, kN

Pressure p N mm2

Energy Work W Nm

Output P Nm s ¼ W, kW

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Materials for Stamped Parts

3.1

Materials for Stamped Parts in High Performance Stamping Technology

Stamped parts can be manufactured from almost any material available as strip, sheet or foil and which does not shatter. The majority of materials are metals but non-metallic materials are also processed.

3.2

Non-metallic Materials

Non-metallic materials must not be too soft or smear, i.e. they must not adhere to the tool or feed devices. Also, they must neither be too brittle and nor shatter. Taking all this into consideration, the following materials are suitable: paper, card, laminates, fibreboard, plastics such as PVC, fibre-reinforced plastics, felt, specially finished and coated textiles. The specific cutting force kS for these materials is relatively low which means the tools can be made from tool steel.

3.3

Metallic Materials

Ferrous Materials Nearly all steels processed as strip or sheet are suitable for workpieces which are produced primarily by shear cutting up to a specific cutting force of kS ¼ 1500 N/mm2 (see Table 4.1). The finer the carbide grain distribution and size, the less the wear on the tools and the less the deformation on the stamped parts produced. A proof stress for hardened steels of Rp0,2 is close to a tensile strength of Rm. For other steel materials where this is the case, a dynamic factor must also be taken into consideration # Springer Fachmedien Wiesbaden GmbH, part of Springer Nature 2022 M. Kolbe, Stamping Practice, https://doi.org/10.1007/978-3-658-34758-1_3

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3

Materials for Stamped Parts

when designing the tool (see Sect. 4.4.2). Materials which allow a high degree of deformation are suitable for workpieces produced by deep drawing. Deep-drawing sheet steel with a carbon content of up to 1% as well as tempering steel alloyed with chromium, nickel, manganese and molybdenum, stainless steels, and carbon steels alloyed with manganese and silicon are used in addition to the unalloyed soft steels. Micro-alloyed, fine-grained steel is used as a cold-rolled, light-gauge sheet metal for cars. Further information on lightgauge sheet metal is available in DIN 1623-2. Non-ferrous Metals Copper and copper alloys in sheet or strip form are predominantly used for stamping parts in the electrical and electronics industries. Both copper and brass can be processed in both a soft and hard condition (see Table 4.1). Further information on copper sheets and strips for electrical engineering is available in DIN EN 13599. Aluminium and aluminium alloys are also extremely good materials for stamping. The largest field of application for this material is the packaging industry. Further information on the characteristics of cold and hot rolled aluminium or aluminium alloy sheets and strips is available in DIN EN 485-2/1.

4

The Basic Principles of Shear Cutting

4.1

Cutting Methods and Types of Cutting

Shear cutting is a chipless method of separating material along a cutting line (see Table 2.1). In blanking, this forms a closed external or internal shape (shear cutting) (closed cutting line), whereas cropping or releasing forms an open shape (open cutting line). The main components of the tool used here are the cutting punch and cutting die or bottom die. The two cutting faces, the pressure face AD and the flank AF form the cutting edges on these components Sk, known as cutters (Fig. 4.1). The pressure faces AD on the punch and the bottom die produce the cutting force on the material to be separated and face the workpiece surface. After separating, the cut edges of the material slide along the flanks Af. In blanking (closed cutting line), pressure forces FS act on the material via the penetrating cutting punch (Fig. 4.1). During the cutting process, the material to be separated is initially elastically deformed. When pressed together, it also moves sideways. This produces lateral forces FF. Plastic deformation then occurs without separation which produces a rounded edge. The rapid formation of cracks then leads to a separating process and the components of the material slide against each other. This results in a sliding surface, also called a smooth surface, in which the material flows. Once the flow capacity is reached, cracks occur, followed by fracture and the fracture plane. The cutting process can be divided into three stages as far as the material behaviour is concerned: 1. Elastic deformation with lateral movement (Fig. 4.1a). 2. Plastic deformation by pressure (plastically deformed indentation). 3. Flow along the sliding planes (Fig. 4.1b). At this point, the parts are still not separated. This is followed by fracture due to the breaking force (Fig. 4.1c). # Springer Fachmedien Wiesbaden GmbH, part of Springer Nature 2022 M. Kolbe, Stamping Practice, https://doi.org/10.1007/978-3-658-34758-1_4

13

14

4

Sk

AD pressure zones

AD

b

c

material flows

~0,6·s

AF

cutting clearance us

~0,3·s

a

The Basic Principles of Shear Cutting

Sk AF

e frictional force

d

sheet thickness S

pressure zones

f FS F

indentation from AD

cutting burr fractured surface cut surface

eT II

rounding

S

I

Fig. 4.1 Explanation of the cutting process in piercing (closed cutting line): Cutter Sk (cutting edge) is the line of penetration of the cutting surfaces AD and AF, which form the cutting wedge. Sequence: (a) cutting starts after elastic deformation; start of flow (plastic deformation), (b) end of flow, start of fracture, (c) end of fracture, separation complete, frictional force is still acting, (d) end of working stroke, punch penetrates into the opening of the cutting die (eT insertion depth), (e) force/displacement curve, punch clearance sp I normal; II narrow, (f) cut surface elements. Sk ¼ cutter, uS ¼ cutting clearance, FS ¼ maximum forming and (or) cutting force, FF ¼ flank (lateral) force perpendicular to this, sp ¼ punch clearance ¼ 2 us

These three individual processes can be identified on the cut edges of the stamped part as three distinct areas. Area 1: rounding—narrow edge and web width, slightly tilted. Area 2: shear zone, cut edges of part, shiny and smooth. As the material flows, it is pressed onto the flanks AF. Area 3: fracture zone, fracture face with cracks and subsequent tearing, matt and granular. The distribution between the individual areas depends on several conditions:

4.1

Cutting Methods and Types of Cutting

15

1. Cutting clearance uS. The smaller the cutting clearance, the greater the proportion of cut edges on the part. 2. Deformation behaviour of the material. The more ductile the material, i.e. the more capable it is of flowing, the greater the proportion of cut edges on the part. 3. Tribological behaviour of the cutting material and strip material as well as the lubricant. In cropping (open cutting line), a pair of forces occurs due to the parallel and opposed pressure forces of equal magnitude from the cutting punch and cutting die, i.e. a torque M (Fig. 4.2a); a fixed or spring-loaded guide plate P supports this torque. Due to the lateral

a

FF P

FS

M

b 2 3 5

1 hz