Sheet Bulk Metal Forming: Research Results of the TCRC73 [1 ed.] 9783030619015, 9783030619022

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Lecture Notes in Production Engineering

Marion Merklein A. Erman Tekkaya Bernd-Arno Behrens   Editors

Sheet Bulk Metal Forming Research Results of the TCRC73

Lecture Notes in Production Engineering

Lecture Notes in Production Engineering (LNPE) is a new book series that reports the latest research and developments in Production Engineering, comprising: • • • • • • • • •

Biomanufacturing Control and Management of Processes Cutting and Forming Design Life Cycle Engineering Machines and Systems Optimization Precision Engineering and Metrology Surfaces

LNPE publishes authored conference proceedings, contributed volumes and authored monographs that present cutting-edge research information as well as new perspectives on classical fields, while maintaining Springer’s high standards of excellence. Also considered for publication are lecture notes and other related material of exceptionally high quality and interest. The subject matter should be original and timely, reporting the latest research and developments in all areas of production engineering. The target audience of LNPE consists of advanced level students, researchers, as well as industry professionals working at the forefront of their fields. Much like Springer’s other Lecture Notes series, LNPE will be distributed through Springer’s print and electronic publishing channels. To submit a proposal or request further information please contact Anthony Doyle, Publishing Editor ([email protected]).

More information about this series at http://www.springer.com/series/10642

Marion Merklein A. Erman Tekkaya Bernd-Arno Behrens •

•

Editors

Sheet Bulk Metal Forming Research Results of the TCRC73

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Editors Marion Merklein Lehrstuhl für Fertigungstechnologie Friedrich-Alexander-Universität Erlangen-Nürnberg Erlangen, Bayern, Germany

A. Erman Tekkaya Institut für Umformtechnik & Leichtbau Technische Universität Dortmund Dortmund, Nordrhein-Westfalen, Germany

Bernd-Arno Behrens Institut für Umformtechnik und Umformmaschinen Leibniz Universität Hannover Garbsen, Niedersachsen, Germany

ISSN 2194-0525 ISSN 2194-0533 (electronic) Lecture Notes in Production Engineering ISBN 978-3-030-61901-5 ISBN 978-3-030-61902-2 (eBook) https://doi.org/10.1007/978-3-030-61902-2 © Springer Nature Switzerland AG 2021 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. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface Marion Merklein and Hinnerk Hagenah Institute of Manufacturing Technology, Egerlandstraße 13, 91058, Erlangen, Germany

Abstract. This book is presenting the results and insights researched during the 12 years the Transregional Collaborative Research Center 73 “Manufacturing of complex functional components with variants by using a new sheet metal forming process - Sheet-Bulk Metal Forming” existed. The structure and the structural changes taking place during that period will be highlighted and explained in this preface. The most recent and most important results of the individual projects will be presented in the following chapters.

Introduction The Transregional Collaborative Research Center (TCRC) 73 is a joint research initiative of several institutes of each of the involved universities: the Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), the Technical University of Dortmund (TUD) and the Leibniz University of Hannover (LUH). It has been funded by the German Research Foundation (DFG) for 12 years. The TCRC “Manufacturing of complex functional components with variants by using a new sheet metal forming process—Sheet-Bulk Metal Forming” was founded in order to develop that new forming technology, sheet-bulk metal forming (SBMF). This new forming technology will unite the advantages of sheet and bulk metal forming processes. Cold forging has among others the advantages of strain hardening during the forming process, high surface quality and near-net shape production. Sheet metal forming enables flat, large workpieces. Both forming technologies provide high productivity in terms of quantity of workpieces. The combination is to exceed the limits of both existing technologies. As one of the major outputs of the TCRC73 the definition of this new class of manufacturing processes was agreed upon: “Sheet-Bulk Metal Forming (SBMF) processes are defined as forming of sheets with intended three-dimensional material flow as in bulk forming processes. In order to make the definition more precise, additional information on sheet-bulk metal forming processes as well as its features will be

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given: The class of sheet-bulk metal forming processes consists of several well-known processes that are newly combined as well as extended in their application. Sheet-bulk metal forming processes are forming processes in which often conventional sheet and bulk forming operations are combined. These processes are applied to sheets or plates. The processes summarized in this new class are characterized by the complex interaction between forming zones of high and low strains as well as locally varying two- and three-dimentional stress and strain states. Further characteristic aspects of the processes in question are incremental cyclic loading of the material and the influence of the materials anisotropy on the resulting forming.” [1]. The TCRC73 is creating the scientific fundamentals in order to satisfy the increasing demand for individual, easily adjustable, technical systems with ever increasing functional density by means of new forming processes. Forming processes are known to satisfy two main demands of our days; they are highly economic and resource efficient. In addition, forming processes are often applied to produce high value technical systems. However, the conventional bulk and sheet metal forming processes are pushed beyond their limits by todays requirements of functional elements, e.g. synchronizers. By applying bulk forming processes to sheet metal material, the TCRC73 is providing a significant contribution to the development of forming technologies and thus to the solution of several of today’s economic and ecological challenges. Research within the TCRC73 is aiming at the understanding and application of the possibilities to increased functional density and improved functionality of mechanical workpieces made from sheet metal by means of forming. The higher functionality is a result of an increasing geometrical

Fig. 1. Classification of sheet-bulk metal forming processes [2].

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complexity as well as improved mechanical properties. The processes that are targeted by this research were classified according to [2] as shown in Fig. 1.

Structure In order to cope with the challenges given by sheet-bulk metal forming, different aspects of processes, systems and material have to be researched in order to understand their influences and interactions to enable the use of those. The TCRC73 followed a stepwise procedure structured in three funding periods that all targeted different topics. The agenda is depicted in Fig. 2. It did include the transfer of the

Fig. 2. Aims and development of the TCRC over 12 years including the transfer to industry.

findings into industrial applications from the start. The TCRC73 succeeded in initiating this transfer as can be read in the following chapters. It is expected to see ongoing transfer after the TCRC has ended its work. Throughout its runtime, TCRC73 had three project areas, namely processes, systems and materials. All projects were clustered into these areas. The structure was enhanced by a forth area in 2019 when the transfer projects were grouped in their own project area. The areas were supplemented by cross connecting working groups. Initially, three working groups were defined. On the one hand, among these the field of modeling and simulation is of particular importance for the connection between the project areas; on the other hand, quality control and management as

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well as workpiece properties and functionality are of importance as well. As the working groups are the dynamic response of the TCRC to changing questions and challenges two further working groups were added to the structure during the runtime since tools and materials were identified as additional important interconnecting topics.

Institutions From the three aforementioned universities, initially a total of 12 institutes were involved in the TCRC. They were responsible for a total of 19 research projects. Over the years, three projects were not continued as the research goal had been reached or the project heads retired. One institute changed its name and another had to finish its participation in the TCRC. On the contrary, two additional institutes joined the research center making it a total of 13 involved institutes at the end of TCRC73. Three research projects belonging to the initial three project areas as well as seven transfer projects enlarged TCRC over the funding periods. The research center consists of 26 research projects located at 13 institutes from three universities in its final stage.

People Any initiative lives from the people involved. Throughout the 12 years, more than 300 person years were funded. This included researchers as well as more than 500 students who were involved in carrying out the experiments, the programming and the evaluation of the results. The support of many technicians both funded through the TCRC and originating from the institutions fundamental equipment was given for the construction of the used experimental equipment, the carrying out of the experiments, the measurement of the specimen as well as the maintenance of machine tools and computers. Students writing their theses, colleagues open for discussions, advising group leaders and the supervising, controlling and mentoring project heads further added to the team involved in TCRC73.

Leaderboard The leaderboard had only small modifications over the years. Prof. Marion Merklein as spokesperson of the TCRC was supported by the managing director Prof. Hinnerk Hagenah for the entire 12 years. Here, surrogate in Erlangen was Prof. Harald Meerkamm for the first funding period. After his retirement, his successor Prof. Sandro Wartzack took over that duty as well. The local spokesperson in Dortmund was Prof. Erman Tekkaya for all the years. His surrogate Prof. Dirk Biermann also provided his support for the entire runtime of the TCRC73. In Hannover, Prof. Bernd-Arno Behrens took over the position as local spokesperson after being Prof. Friedrich-Wilhelm Bach’s surrogate for the first four

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years when Prof. Bach retired. The final eight years Prof. Han Jürgen Maier who succeeded Prof. Bach served as surrogate to Prof. Behrens.

Project Heads Some project heads remained responsible for their project throughout the 12 years of runtime the TCRC73 had. Others left the research center due to retirement or acceptance of calls to other universities or because they decided to accept new challenges in industry. The following project heads were retired during these 12 years: Prof. Bach, Prof. Blum, Prof. Engel, Prof. Geiger, Prof. Meerkamm, Prof. Weckenmann. Most of the projects were continued by their successors; however in some cases, this was not possible due to a shift in the focus of the institute. All retired project heads stayed in contact with the TCRC and remained available as advisors. During the 12 years, Dr.-Ing. Clausmeyer, Prof. Denkena, Dr.-Ing. Lechner, Prof. Hausotte, Prof. Menzel, Prof. Tremmel and Prof. Wartzack joined the TCRC as project heads and are still actively participating in that responsibility.

Qualified Young Researchers In all funding periods, it has been the goal of the TCRC73 to qualify young researchers after finishing the PhD for a career in science. In many cases, this was done to a degree that made industry recognize these potentials as well. The following persons have been young project leaders in TCRC73 but have changed to industry during the runtime Dr.-Ing. Andreas, Dr.-Ing. Brenner, Dr.-Ing. Plettke, Dr.-Ing. Rodman, PD Dr.-Ing. Surmann, Dr.-Ing. Voges-Schwieger, Dr.-Ing. Vogli and Dr.-Ing. Weickmann. In other cases, the work as project leader or in the vicinity of the TCRC73 has been part of the education and qualification of young researchers that have made a step forward in their scientific career but, with that step, also left TCRC73: Prof. Ben Khalifa, Prof. Bouguecha, Prof. Brosius, Prof. Kersting, Prof. Löhnert, Prof. Paetzold Prof. Rademacher, Prof. Schaper, Prof. Schröder, Dr. Soyarslan, Prof. Stiemer, Prof. Tremmel, Prof. Werner. The list highlights the success as well as the effort taken by the TCRC to initiate and foster scientific careers not only to the level of PhD but beyond.

Output It is difficult to find suitable measures for the output of an TCRC. There are the qualified persons that achieved their PhD or continued their career beyond that. But there are multitudinous student assistants; bachelor, project and master theses having been written which all also present persons that have been in contact with

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and influenced by TCRC73. Among the countable outputs are the number of publications that is beyond 400 by now and keeps increasing. The most prominent publication being [1] has received more than 200 citations by now. There have been five well-visited industrial colloquia transferring results to the interested industry before this final colloquium. There have been special issues of international journals and dedicated sessions at international conferences. FEM-software producers included special features to their product [3]. The terms “sheet-bulk metal forming” or “sheet-bulk metal forming” have not been known before 2008. Checking these keywords and the German equivalent with search engines now reveals more than 30.000 hits. In summary, this very briefly expresses the attention the results that are presented in the following chapters have earned and deserved.

References 1. Merklein, M.; Allwood, J.M.; Behrens, B.; Brosius, A.; Hagenah, H.; Kuzman, K.; Mori, K.; Tekkaya, A.E.; Weckenmann, A.: Bulk forming of sheet metal. Annals of the CIRP 61(2012)2, 725–745 2. Merklein, M., Tekkaya, A.E., Brosius, A., Opel, S., Koch, J., 2011, Overview on Sheet-Bulk Metal Forming Processes, Proceedings of the 10th International Conference on Technology of Plasticity, 1109–1114. 3. http://qform3d.com/processes/sheet-bulk, accessed July 30th 2020

Contents

Process Combination for the Manufacturing of Toothed, Thin-Walled Functional Elements by Using Process Adapted Semi-finished Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Manfred Vogel, Robert Schulte, Michael Lechner, and Marion Merklein Forming of Complex Functional Elements on Sheet Metal . . . . . . . . . . . Manuel Reck, Andreas Rohrmoser, Andreas Jobst, Florian Pilz, and Marion Merklein Fundamental Research and Process Development for the Manufacturing of Load-Optimized Parts by Incremental Sheet-Bulk Metal Forming . . . . . . . . . . . . . . . . . . . . . . Sebastian Wernicke, Marlon Hahn, and A. Erman Tekkaya Strategies for Function-Oriented Optical Inspection of Formed Precision Workpieces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sebastian Metzner, Tino Hausotte, and Andreas Loderer

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Dynamic Process Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Bernd-Arno Behrens, Sven Hübner, Hendrik Wester, Daniel Rosenbusch, and Philipp Müller Simultaneous Development of a Self-learning Engineering Assistance System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 Christopher Sauer, Benjamin Schleich, and Sandro Wartzack Machining of Molds with Filigree Structures for Sheet-Bulk Metal Forming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Alexander Meijer and Dirk Biermann Generation of Predetermined Surface Structures by Simulation Based Process and Tool Design When Milling Free-Formed Surfaces . . . . . . . 172 Jonas Baumann, Alina Timmermann, and Dirk Biermann

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Amorphous Carbon Coatings for Sheet-Bulk Metal Forming Tools . . . . 192 Tim Weikert and Stephan Tremmel Application of Nanostructured Bionic Thin Layers to Enhance the Wear and Friction Behavior of Tools for Sheet-Bulk Metal Forming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 Wolfgang Tillmann and Dominic Stangier A 3D Measuring Endoscope for Use in Sheet-Bulk Metal Forming: Design, Algorithms, Applications and Results . . . . . . . . . . . . . . . . . . . . 239 Lennart Hinz, Markus Kästner, and Eduard Reithmeier Analysis of Horizontal Loads in Sheet-Bulk Metal Forming and Their Consideration in Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 Bernd-Arno Behrens, Richard Krimm, and Oliver Commichau Grinding Strategies for Local and Stress Orientated Subsurface Modification of Sheet-Bulk Metal Forming Tools . . . . . . . . . . . . . . . . . . 286 Michael Keitel, Berend Denkena, and Alexander Krödel-Worbes Constitutive Friction Law for the Description and Optimization of Tailored Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 Johannes Henneberg, Florian Beyer, Maria Löffler, Kai Willner, and Marion Merklein Multilevel Material Modeling to Study Plastic Deformation for Sheet-Bulk Metal Forming Under Different Loading Histories . . . . . 334 Shahbaz Ahmed, Tengfei Lyu, Stefan Löhnert, and Peter Wriggers On Optimization Strategies for Inverse Problems in Metalforming . . . . 354 Benjamin Söhngen, Michael Caspari, Kai Willner, and Paul Steinmann Analysis of Path-Dependent Damage and Microstructure Evolution for Numerical Analysis of Sheet-Bulk Metal Forming Processes . . . . . . 378 Florian Gutknecht, Gregory Gerstein, Kerim Isik, A. Erman Tekkaya, Hans Jürgen Maier, Till Clausmeyer, and Florian Nürnberger Fatigue Behavior of Sheet-Bulk Metal Formed Components . . . . . . . . . 412 Hans-Bernward Besserer, Florian Nürnberger, and Hans Jürgen Maier Mechanism-Based Modelling of Wear in Sheet-Bulk Metal Forming . . . 434 Markus Schewe and Andreas Menzel Orbital Forming of Tailored Blanks for Industrial Application . . . . . . . 458 Andreas Hetzel and Michael Lechner Tool Sided Surface Modifications in the Industrial Environment . . . . . . 477 Thomas Wild and Marion Merklein

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Incremental Sheet-Bulk Metal Forming by Application of Thermal-Controlled Grading Mechanisms . . . . . . . . . . . . . . . . . . . . . 493 Sebastian Wernicke, Stephan Rosenthal, Marlon Hahn, and A. Erman Tekkaya Superimposed Oscillation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515 Bernd-Arno Behrens, Sven Hübner, Hendrik Vogt, Nadezda Missal, and Philipp Müller Numerical Calculation of Tool Wear in Industrial Cold Forming Processes Using the Further Development of Wear Modelling . . . . . . . . 535 Bernd-Arno Behrens, Hendrik Wester, Tim Matthias, Sven Hübner, Philipp Müller, and Jonas Wälder Functionalization of Tool Topographies for Material Flow Control and Tool Life Optimization in Hot Sheet-Bulk Metal Forming – A Concept Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553 Timo Platt and Dirk Biermann Fatigue Life Compliant Process Design for the Manufacturing of Cold Die Rolled Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568 Steffen Wackenrohr, Florian Nürnberger, and Hans Jürgen Maier Author Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 587

Process Combination for the Manufacturing of Toothed, Thin-Walled Functional Elements by Using Process Adapted Semi-finished Products Manfred Vogel(&), Robert Schulte, Michael Lechner, and Marion Merklein Institute of Manufacturing Technology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 13, 91058 Erlangen, Germany [email protected]

Abstract. The scientific objective is the analysis of a process combination for the manufacturing of toothed, thin-walled functional elements from processoptimized semi-finished products. By using an upsetting, orbital forming as well as a modified flexible rolling process, tailored blanks with flow-optimized properties are manufactured. In this context, a defined material flow control plays a decisive role for the forming of different geometries. In order to pursue a holistic approach, the process limits as well as the potential of the individual processes are identified. With the application of such blanks, geometrically complex components with functional elements such as gears or carriers are formed in a new combined deep-drawing and upsetting process. The aim is to reduce the number of steps in the process chain and thus save energy and resources. Thereby, different levels of functional integration are taken into account with regard to the geometry and arrangement of the functional elements, but also combinations of both.

1 Introduction Especially in today’s age of weight-optimized design and manufacturing of complex functional components to reduce or even avoid CO2 emissions, the basic idea of lightweight construction is becoming increasingly important. An opportunity to meet this challenge is a rising functional integration already during the design phase of the functional components to fulfill multiple tasks. From the point of view of the production technology, sheet metal forming in particular offers great potential for lightweight design applications. However, this leads to a conflict of objectives between lightweight design on the one hand and the manufacturing processes due to the process limits on the other hand. In order to achieve a local adaptation and shaping of functional elements, three-dimensional stress and strain states are necessary, which are not feasible with conventional manufacturing processes. In order to combine both approaches, new processes or even a process combination of existing process classes is mandatory. In this context, the innovative process class of sheet-bulk metal forming (SBMF) was developed, a process combination of sheet- and bulk forming operations within the © Springer Nature Switzerland AG 2021 M. Merklein et al. (Eds.): TCRC73 2020, LNPE, pp. 1–29, 2021. https://doi.org/10.1007/978-3-030-61902-2_1

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TCRC 73. Thus, the advantages of both forming operations can be linked for manufacturing parts with a local adaption of the wall thickness in short process chains. However, this results in new challenges such as a defined control of the material flow in order to ensure the shaping of the target geometry. For functional components, like adaption mechanisms or switching elements, but also for synchronizer rings and driving plates increasingly finer and more precise form and functional elements are required. Based on a consistent lightweight design concept, complex and in some cases mechanically high stressed components have to be manufactured from high-strength sheet materials. In order to meet the requirements of a locally adapted material volume for the manufacturing of functional elements with simultaneous flexibility of the applied material, tailored blanks with an adapted thickness profile can be used for a process improvement. However, generally tailored blanks are manufactured by welding or bonding processes for the joining of blanks with different gauges, strengths, thicknesses or coating types. The disadvantages of these techniques, however, consists in the influence on the material structure and the subsequent formability of the semifinished product in the following process step. Due to the characteristic of a continuous fibre flow and the associated tailor-made adjustment of the geometric and mechanical properties, semi-finished products manufactured by forming processes are predestined for the production of complex functional components from semi-finished sheet materials and are investigated in the project A1 in TCRC 73.

2 State of the Art First approaches for the combination of sheet metal and bulk forming processes were worked out in [1] and [2], whereby basic descriptions of the process go back to the 1950s [3]. Previous work deals, among other things, with the investigation of the process combination of deep drawing and upsetting, whereby practical applications have already been realised in some cases [4]. Important results for the description of such processes are also presented in work on the manufacture of cups with flanges from medium and heavy plates [5] and on the upsetting of circular cylindrical cups [6]. The current state of implementation of the deep drawing/extrusion process combination envisages the forming of shelves on deep-drawn sheet metal workpieces by means of multi-stage forming processes [7] with the aim of achieving a thickening of the side wall corresponding to the strength requirements. The flange thickness should be set greater than the initial sheet thickness. The challenge here is to optimize the step design of the on-board production by combined deep drawing and upsetting in order to achieve the desired increase in wall thickness. In contrast to the scope of the research project reported for, the final geometry in the above-mentioned work is realised via one or more intermediate stages, whereby only the last stage represents a process combination of deep drawing and upsetting with comparatively low degrees of deformation. Both the production of tailor-made semi-finished products and their processing by deep drawing and upsetting in a forming stage without a blankholder have not been considered in the solution approach so far. In addition, the existing approaches are limited to a local sheet thickness change and do not include the representation of secondary shape elements. The fact that only a few cases of the successful industrial implementation of chipless

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production of functional components made of sheet metal are public and that these components meet high demands on quality and performance, proves the potential of sheet bulk metal forming and at the same time motivates the need for basic research. The development of new materials for the purpose of lightweight construction has increased considerably in recent years. Various types of tailored blanks produced by welding or rolling have also been developed. Tailor Welded Blanks are the most widely used semi-finished product, whereby materials of different chemical composition and/or different mechanical properties and sheet thicknesses are joined by welding. Position and orientation of the weld seam can have a significant effect on the forming result [8]. In order to provide tailored blanks with different sheet thicknesses, but without joining, cold rolling processes are used in which the blank material is displaced locally, thus reducing the initial local sheet thickness. With Tailor Rolled Materials, the material can be displaced in the length or width direction of the sheet and need not exhibit any regularity. Tailor rolled blanks produced by flexible rolling do not have a weld seam and heat-affected zone, but so far only straight-line blank areas can be realized [9]. Here, the periodic change of the roll gap during cold rolling by appropriate opening and closing of the rolls enables the production of strips with a defined thickness profile in longitudinal direction, which is achieved on the outlet side over the entire width of the sheet. In addition, Tailored Rolled Blanks outperform welded structures in terms of formability and are characterized by excellent processability into lightweight structures, for example by deep drawing, bending or hydroforming [10]. Based on the technology of flexible rolling, strip profile rolling was developed as a further manufacturing process with the aim to produce strips with a defined thickness distribution in the width direction, so-called tailor rolled strips, by using narrow top rolls and cylindrical bottom rolls [11].

3 Objective and Methodology The objective of this research project is the design and basic scientific analysis of a process combination for the manufacturing of geared, thin-walled functional elements using process adapted semi-finished products. The goal is to create the process-related basis for the economic manufacturing of complex and partially mechanical high stressed components made out of different classes of sheet material. The material range begins with the mild deep drawing steel DC04 and ends with the high strength steel DP600. As shown in Fig. 1, the producibility of functional components is divided into two individual steps, the manufacturing of tailored blanks and the further processing. For the manufacturing of the tailored blanks the sheet-bulk metal forming processes of upsetting, orbital forming and flexible rolling are investigated in order to achieve a defined thickness profile. The aim is not only to control the material flow for the manufacturing of rotational symmetric semi-finished products with a homogeneous material pre-distribution, but also to form different geometries as well as discrete functional elements perpendicular to the sheet plane for realizing increased components complexity. Subsequently, these tailored blanks are applied in a new forming process

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consisting of a process combination of deep-drawing and upsetting. The main objective is the analysis of the interaction and development of process strategies for the application of a deep-drawing process without a blank holder in which secondary die elements like gears or carriers can be formed in the area of the frame in only one step. Therefore, the individual processes are investigated both, separately for the interactions regarding the material flow, as well as in correlation to the manufacturing processes of the tailored blanks. This enables a deeper process understanding of the interaction between the individual processes to be examined in detail and fundamental correlations to be derived. In order to be able to establish a holistic process understanding for the manufacturing of complex functional components in short process chains, a detailed process analysis is carried out in a combined experimental and numerical approach. To achieve the overall objective of the research project, the following individual objectives have to be achieved in summary: • Fundamental analysis of significant process parameters for the manufacturing of process-adapted semi-finished products using the upsetting, orbital forming and flexible rolling processes • Development of functional correlations of the material flow for the forming of different thickening geometries • Definition of process-adapted process strategies for the individual processes • Improvement of part properties by increased process understanding and processadapted semi-finished-products In order to achieve these aims, different machines and measuring methods are used. For the manufacturing of the tailored blanks by the upsetting and orbital forming process as well as for the subsequent manufacturing by a combined deep-drawing and upsetting process, a hydraulic press of type TZP400/3 from the company Lasco is used. The flexible rolling process for the manufacturing of the adapted semi-finished products was realized using a specially developed machine, which will be presented in the course of this report. For the geometric characterisation of the tailored blanks and the final components, tactile and optical measurement technologies are used. The tactile measurement is performed with the aid of a PMM 654 coordinate measuring machine from Leitz. In order to record a digital model of the functional components, the ATOS system from GOM is used. Regarding the analysis of the mechanical properties a microhardness tester Fischerscope HM2000 is applied. Additionally to the mechanical properties the microstructure is analysed by using various light microscopes. The surfaces of the components are analysed using a tactile perthometer from Mahr and optically using the VK-X-200 laser scanning microscope from Keyence. Trimming operations are performed with a CO2 laser Lasercell TLC 7020 from Trumpf.

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Fig. 1. Methodological approach for achieving the overall objective

4 Results In the following the results of this research are presented. The focus here is on achieving the overall objective of the targeted manufacturing of complex functional components with different functional elements by using sheet material, a fundamental process analysis for the targeted adjustment of direction-dependent material flow components is indispensable. As described in the previous chapters, this could be achieved by using tailored blanks with a process adapted thickness profile. Since the forming process for the manufacturing of functional components interacts with the properties of the process adapted semi-finished products, a holistic analysis of the individual processes as well as in combination is mandatory. For this reason, the manufacturing of tailored blanks using three different processes - upsetting, orbital forming and flexible rolling - is presented followed by a process analysis of a combined deep-drawing and upsetting process for the further application. For the basic investigations, the mild deep-drawing steel DC04 with an initial sheet thickness of t0 = 2 mm is used. For the analysis of the transferability of the results the higher strength dual phase steel DP600 is used with the same initial sheet thickness.

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Geometry of the Tailored Blanks and Manufacturing Processes

For the investigations, four different geometries of tailored blanks are used to analyse the different forming processes as well as the potential and process limits. As it is shown in Fig. 2, there are one- and two sided thickness profiles available, which are manufactured from the initial blank with an external diameter of d0 = 100 mm. In all cases the material thickening starts at a radial position of ri = 40 mm with a transition zone up to rm = 42 mm. Then the parallel thickened area with a width of 8 mm starts up to a radial position of r0 = 50 mm. The geometries themselves differ according to the type of thickening into a rotational symmetric and a cyclic- symmetric geometry as well as a toothing in the form of an involute gearing with a modulus of 1 mm. A height of h = 2.5 mm results for the maximum additional sheet thickness. In order to enable the transferability and comparison of the functional components manufactured within the research collaboration centre TCRC 73 using different processes, 84 teeth were selected for this geometry, evenly distributed over the circumference. The cyclic-symmetric thickening consists of three areas with an angle of 60°, which are located on the same radius. For the rotational as well as the cyclic-symmetric geometry, a thickness profile with a height of h = 0.9 mm was defined. In order to be able to analyse the interaction of a material thickening a new tailored blank geometry with a rotational symmetric thickness profile on both sides is manufactured. All geometries have been designed and selected with the intention, that the further processing in the subsequent deep drawing and upsetting process is feasible.

Fig. 2. Tailored blank geometries used for the investigations

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Three processes have proven to be potentially suitable for the investigation of the manufacturing of tailored blanks with a process adapted material pre-distribution due to their characteristics. As shown in Fig. 3, a conventional upsetting process, an orbital forming process and a new type of rolling process with characteristics of flow-forming were used. According to Merklein et al. [12], these processes are divided into sheet thinning and thickening processes as well as rotational and translation categorization. The applicability of the different forming processes is described in detail in the following chapters.

Rotational

Sheet-thinning

Translational

Sheet-thinning and thickening possible

Sheet-thinning

Fig. 3. Categorisation of the forming processes according to Merklein et al. [12]

4.2

Manufacturing of Tailored Blanks - Upsetting

Especially with regard to the manufacturing of functional components with integrated functional elements, a fundamental investigation for the manufacturing of rotational symmetric tailored blanks with a circumferential material thickening is carried out. The geometry of the blanks is determined in consideration of the following process combination consisting of a deep drawing and upsetting process and in cooperation with other research projects. Contrary to the state of the art, the basic challenge in the manufacturing of semi-finished products is the upsetting of sheet metal materials perpendicular to the sheet plane with a high ratio of the contact area to the total workpiece surface. In combination with the limited formability of flat semi-finished products in the direction of the sheet thickness, this process results in high forming forces. To get a deeper process understanding, an axial symmetric FE-model was built up in order to perform a material flow analysis for the design of the tool geometry. Of particular interest was the achievable radial material flow with the maximal forming force, which is limited due to the available hydraulic press Hydrap HPDZb 630 with Fmax = 6,300 kN. This requires a multi-stage forming concept with which the radial material flow is generated step by step. The greatest effect is shown by the tribological conditions, since the low sheet thickness and high contact normal stresses make the material flow more difficult. An effective measure to improve the radial material flow is the integration of a conical contour in the upsetting punch [13]. This was also investigated by analyzing the numerical models. To confirm the plausibility of the numerical investigations, an analytical approach was used to calculate the forming force during

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cup backward extrusion according to Dipper [14], since this process is comparable to upsetting in some aspects. Although deviations in the forming force of 20–30% were observed due to the different boundary conditions, the analytical process modeling confirms the numerical results qualitatively. The subsequently developed upsetting tool is described detailed in [15]. The tool concept comprises three upsetting punches with defined die cavities in the upper punch. The transition zone of each punch starts at diameters dA,1/2/3 = 60/70/80 mm, whose dimensions were selected in consideration of the available press force. The conical punch shoulder with the angle a favors the radial material flow. The three upsetting punches were manufactured with an offset angle of a1/2/3 = 0.5°, the counter punch has a flat contour. A central recess in the counter punch can additionally improve the blank quality with regard to a homogeneous sheet thickness distribution in the centre of the blank. In the edge area, the sheet thickness could be increased from t0 = 2 mm to tmax = 2.39 mm by initial forming experiments. Even before complete levelling of the sheet thickness steps, the tip of the punch gets into contact with the blank centre, which caused the forming operation to be stopped due to a force increase. In numerical variant calculations, a decreasing offset angle of a1/2/3 = 0.8°/0.4°/0° was identified as suitable to minimise the step height at the transitions (Dt1,2 = 0.02 mm). As it was shown in [16], when using a Dionol ST V 1725-2 extrusion oil, the resulting thinning of the sheet metal is significantly lower than with the highly viscous lubricant Beruforge 150 DL, since the extrusion oil is more easily displaced from the active joint due to the high process forces and conical punch shape. 4.3

Manufacturing of Tailored Blanks – Orbital Forming

Compared to upsetting, orbital forming as a force-controlled incremental process offers several advantages for the manufacturing of tailored blanks. Due to tilting of one tool component, a smaller contact area and hence reduced forming forces as well as an improved material flow can be achieved. Based on the tooling concept of the upsetting process, the geometrical parameters width and height of the thickness profile is defined by a negative imprint of the geometry in the upper punch. As it can be seen in Fig. 4, for filling the die cavity, a material flow against the direction of the force flow is necessary. In order to increase process flexibility and to be able to control the resulting material flow, this design has been extended by the possibility of a thickening in direction of the force flow with a die cavity in the counterpunch.

Fig. 4. Tool concept with the die cavity in the a) upper punch and b) counterpunch

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Especially with regard to the further processing of the semi-finished products, the die filling, burr formation, flatness and bulging were used as important parameters for further investigations. Therefore, the forming force F and the tumbling angle H could be identified as the main influencing variables. From this context the process window, which is shown in Fig. 5, could be derived [16]. The flatness describes the bulging of the blank from the centre to the outer diameter and is caused by the tilting of the tool components combined with the rotating contact zone. According to [6], the bulge is defined as the maximum distance between the slope of the flatness and the measured sheet thickness. With a forming force of at least F = 3,140 kN at a tumbling angle of H = 0.73°, a die filling of more than 90% can be achieved for the deep drawing steel DC04 and a blank diameter of d = 100 mm. As a significant error characteristic, the burr formation in the tool gap between the upper punch and the die was determined. An effective prevention of burr formation could be realized by inserting a die cavity into the counterpunch. Furthermore, the modular tool design with the use of die cavities allows the manufacturing of different Tailored Blank geometries, which are relevant with regard to the combination of different circumferential functional elements. The basic transferability of the developed process window to the new tool concept could be proven by experimental tests and shows a comparable die filling without negative burr formation [16].

Tumbling angle Θ

1.0

d = 100 mm DC04

Die filling ▬▬▬ > 90 %

Flatness · · · · 0.15° ······· 0.20°

Burr formation –––– 0 ––– 1

Bulging − · − 0.06 mm −··− 0.07 mm

0.8 0.7 0.6 0.5 2000 2500 3000 kN 4000 Forming force F

Fig. 5. Process window for the manufacturing of rotational symmetric tailored blanks with a one-sided material thickening [16]

Only by a defined analysis of the material flow, the process understanding and thus the process limits can be extended. Depending on the tumbling angle during the upcoming phase UU, the constant phase UC and the reset phase UR, different material flow proportions can be identified. For a rotationally symmetrical semi-finished product geometry, a dominant material flow in the radial direction in the thickened edge area was determined in the upcoming phase UU of the tumbling angle from the zero position to the maximum deflection when using circular tumbling kinematics [17]. In the following second process phase UC, this is replaced by a dominant tangential component in the circumferential direction of the blank with a constant tumbling angle [18]. In the final

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third phase UR, in which the tumbling angle is successively reset to the zero position, only a minimal material flow occurs due to the tool contact in the centre of the blank as well as the strain hardening and the filled die cavity. By means of experimental investigations, the geometric properties from the numerical material flow analysis could be validated with the sheet thickness curve in the edge area, see Fig. 6a [18]. The mechanical properties were investigated in the individual process phases. For the strain hardening of the tailored blanks, a correlating behavior with respect to material flow and sheet thickening could be demonstrated experimentally, with the greatest strengthening in the ramp-up phase. This finding permits a 50% reduction in the necessary process time, as the number of tumbling cycles in the second and third process phases can be reduced accordingly to the minimum value U = 1 without changing the geometric and mechanical properties of the tailored blanks [17]. The increase in strength in relation to the initial hardness can be adjusted between 45% and 55% for the mild deep-drawing steel DC04 by successively increasing the tumbling cycles [19]. The realization of larger sheet thickness gradients leads to a buckling of the material in the die cavity due to the deeper cavity and the associated larger empty material volume, into which the material has to be displaced outwards by the radial flow of material. Due to the incremental characteristic of tumbling with a rotating lower tool, no influence of the sheet anisotropy on the geometrical and mechanical properties of the tailored blanks could be determined for the tailored blanks manufactured by orbital forming. For a further increase of the die filling, a specific adaptation of the tribological conditions by means of tailored surfaces were investigated in cooperation with other research projects [19]. However, the high forming forces required for orbital forming lead to only minimal differences of a maximum of 2% in relation to the resulting die filling [19]. The transferability of the results to a tailored blank geometry with a cyclic-symmetric material pre-distribution showed a comparable course for the development of sheet thickening with the beginning of a saturation level in the constant process phase between 5 and 10 tumbling cycles, see Fig. 6b. Due to the cyclically symmetrical character of the geometry, differences in the material flow arise, which mainly effect on the areas between the accumulations. Here, a tangential material flow dominates over the entire process. The use of hypotrochoid kinematics for the manufacturing of tailored blanks with local material accumulations led to an improvement of die filling compared with circular kinematics due to the possibility of targeted positioning of the surface contact. Applying the process control strategies and methods developed to the high-strength steel DP600 showed that the application of the same process parameters leads to a lower thickening of 18% relative to the initial sheet thickness t0 due to the stronger hardening of DP600 [20]. By increasing the forming force to the maximum available press force of F = 4,000 kN at a maximum tumbling angle of H = 1°, the difference could be reduced to 9% [20]. The development of new process strategies by increasing the number of tumbling cycles during the upcoming phase and repeating these process strategies resulted in a further increase in sheet thickness [20].

Process Combination for the Manufacturing of Toothed

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Fig. 6. Circumferential sheet thickness in the edge area of a a) rotational symmetric and b) cyclic-symmetric tailored blank geometry [17]

However, due to a further increase of the components complexity, it is also necessary to form functional elements inside as well as outside of the drawn components. As a result, the complexity of the tailored blank geometry and thus the sheet thickness profile also has to be increased in order to shape the functional elements. In order to allow the same flexibility on both sides, an identical material thickening is required on both sides of the semi-finished product. Therefore, the tool concepts with die cavities in the punch and the counterpunch are combined, which results in a doubling of the local material volume. In order to achieve a sufficient die filling on both thickening sides, an adjustment of the significant process parameters of the tumbling angle H and forming force F is mandatory. This can also be seen in the modification of the process window in Fig. 7. To reach a die filling of over 90% on both sides of the tailored blank, an average process force of F = 3,770 kN and a tumbling angle of H = 0.85° is required. This corresponds to an increase of the forming force of about 20% and the tumbling angle of about 16%. This increase is based on the free material volume and therefore the resulting material flow. Investigations in [21] have shown in this context that a doubling of the forming force from F = 2,000 kN to F = 4,000 kN increases the radial material flow by about 18% over the entire radius range. This is also significantly influenced with an increasing tumbling angle, so that a further increase in the radial

Tumbling angle Θ

1.0

d = 100 mm

0.8 0.7 0.6 DC04 0.5 2000 2500 3000 kN 4000 Forming force F

Die filling: Punch > 90 % 100%

Bulging < 0,04

Die filling: Counterpunch > 90 % 100% Burr formation