ICHSF 2008
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The Institute of Forming Technology and Lightweight Construction of the Technische
Universität Dortmund is honored to host the International Conference on High Speed
Forming for the third time. We would like to take this opportunity to thank the authors and
co-authors, the scientific committee as well as all participants of the conference for their
valuable contributions.
The current worldwide discussion about CO2 reduction illustrates the importance of
a persistent implementation of lightweight construction concepts. These strategies
include, among other techniques, the application of typical lightweight materials as
aluminum and magnesium alloys and an optimized component design. However, the
limited forming capabilities of these materials and the increased part complexity require
adapted technologies and forming strategies. High speed forming represents one
possibility to meet these challenges.
The large number of international participants from 15 different countries
emphasizes the demand for discussions especially in this niche technology. Accordingly,
the conference serves as a platform presenting research results regarding the topics
process technologies, tools and equipment, energy, materials and measurement
techniques, modelling and simulation, and industrial applications.
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Recent Submissions
Item Analysis of Blank-Die Contact Interaction in Pulsed Forming Processes(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Bessonov, N.; Davies, R.; Golovashchenko, S.During recent decade, significant efforts were dedicated to increasing the amount of Aluminum Alloys in automotive parts in order to reduce the net weight of cars. Processes of pulsed forming are known to expand the capabilities of traditional stamping operations. Propagation of pulsed electromagnetic field can be defined by quasi-stationary Maxwell equations, solved numerically using a non-orthogonal Lagrangian mesh. Suggested formulation included modelling of contact interaction of the blank with deformable die. Mild contact model based on introduction of acting-in-vicinity forces repelling the surfaces to be in contact was employed. It was tested by analyzing the elastic impact of bars and then was applied to the corner filling operation. This operation was analysed as a single pulse and as a multi pulse forming process. It indicated that some compromise between the blank formability enhancement and level of contact stresses on the die surface can be found. In addition, some examples of tubular parts pulsed press fitting using tube expansion with pulsed pressure were analyzed. Specific attention was paid to the analysis of factors playing important role in residual contact pressure between the exterior and interior tubes in pulsed press fitting operation.Item Magnetic Pulse Welding for Dissimilar and Similar Materials(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Shribman, V.The Magnetic Pulse Welding (MPW) process, a cold solid state welding process, is an industrial process, operating at several high volume manufacturing facilities. MPW is accomplished by the magnetically driven, high velocity, oblique angle, impact of two metal surfaces. At impact, the surfaces (which will always have some level of oxidation) are stripped off and ejected by the closing angle of impact. The surfaces which are then metallurgically pure, are pressed into intimate contact by the magnetic pressure, allowing valence electron sharing and atomic-level bonding. This process has been demonstrated in the joining of tubular configurations of a variety of metals and alloys [1],[2],[3]. Product designers are frequently constrained by the restrictions of traditional joining technologies, which place certain limitations on the type of joint, the materials that can be joined and the quality of the joint. Solid state welding allows manufacturers to significantly improve their product designs and production results by enabling both dissimilar and similar materials to be welded together, thus providing the opportunity to use lighter and stronger material combinations. Magnetic pulse welding is a fast, noncontact and clean solid state welding process. A review of the main elements of the process is presented here along with typical quality testing results and some applications.Item Production of Steel-Light Metal Compounds with Explosive Metal Cladding(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Koschlig, M.; Raabe, D.; Veehmayer, M.Explosive Metal Cladding is a High Speed Welding Process using the energy of an explosive to bond different metals and alloys in a 2-dimensinal areal configuration. Parameters influencing the cladding process are discussed and the potentials of the method are presented. Microscopic properties of a Cu-Al and a Steel-Ti transition zone are studied in detail to get a better knowledge of the principle mechanisms included in the bond creation. A perspective for future applications of explosive cladding in different industries like automotive and aerospace is given.Item Coupling Experiment and Simulation in Electromagnetic Forming Using Photon Doppler Velocimetry(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Banik, K.; Daehn, G. S.; Fenton, G. K.; Golowin, S.; Henchi, I.; Johnson, J. R.; L Eplattenier, P.; Taber, G.; Vivek, A.; Zhang, Y.Modeling electromagnetic forming processes is in many ways simpler than modeling traditional metal forming processes. In electromagnetic forming the problem is often dominated by inertial acceleration by a magnetic field. This is a much better posed problem than the more traditional ones that are often dominated by complex three dimensional constitutive behavior and frictional effects. However, important aspects of the problem are dominated by the constitutive properties of the material, and often electromagnetic forming is performed in a regime where there is little reliable material strength data. Strain rates are often high (102 to 104 s-1 is the typical range for electromagnetic forming). Also, heat is generated both by ohmic heating as well as by plastic deformation, and peak temperatures can be quite high. Also, while hightemperature, high-strain-rate data is scarce, there is little or no data in cases where temperature rises significantly over very short times (tens of micro-seconds) as happens in electromagnetic metal forming. This rapid temperature rise is very important to the material response because the short time scales largely preclude the material from recovery and recrystallization processes and precipitates cannot dissolve as they normally would in an age-hardening alloy in these time scales. This presentation will show how advanced instrumentation, particularly the Photon Doppler Velocimeter (PDV) can be coupled with electromagnetic forming and provide both avenues to characterize material as well as to provide very critical tests of numerical models of the process.Item Electromagnetic Compressive Split Hopkinson Bar(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Martins, P. A. F.; Rosa, P. A. R.; Silva, C. M. A.This paper proposes a new design for the compressive split Hopkinson bar that makes use of the intense pressure created in a transient magnetic field formed by the passage of a pulse of electric current through a series of coils. The proposed technology enables to characterize the behaviour of materials under high strain-rates with a small acceleration path length of the striker bar and, because propulsion is purely electromagnetic, the overall performance can be easily controlled and nearly infinitely adjustable. The presentation is focused on the design and fabrication of the mechanical, electrical and electromagnetic components of the new compressive split Hopkinson bar and includes results from two different testing applications to demonstrate the validity of the proposed concept.Item Influence of Forming Rate on the Microstructure and Properties of Materials Subjected to Electromagnetic Forming(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Bach, F.-W.; Bormann, D.; Walden, L.Electromagnetic high speed forming has been known since the 1960's and is successfully used for frictional connexions. In addition to joining, other applications of the process include coining, stamping and cutting. Regarding product quality and manufacturing costs, the process is superior to other methods and yet its utilisation can still be extended. The synopsis of the material's microstructure and properties owing to electromagnetic forming, which is given by this article, clarifies the processes from a materials science point of view. This will not only represent an academic view point but also provide insight into a potential expansion of the process to other areas of application.Item The Mechanical Behaviour of Ultra Fine Grained Titanium Alloys at High Strain Rates(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Halle, T.; Herzig, N.; Krüger, L.; Meyer, L. W.; Musch, D.; Razorenov, S. V.; Skripnyak, E. G.; Skripnyak, V. A.Within this study the mechanical behaviour of ultra-fine grained Ti-6-22-22S titanium alloy was investigated and compared to coarse grained material. By severe plastic deformation using the cyclic channel die compression process, grain sizes between 300 and 500 nm were obtained. The mechanical behaviour was studied over a wide range of strain rates from 10^(-3) - 107 s^(-1) under compressive loading using different experimental techniques. A significant increase of flow stress with decreasing grain size compared to the coarse grain state was found. An evaluation of the strain hardening behaviour of the UFG material shows a significant increase of the strain hardening coefficient at high strain rates for low plastic deformation. The strain rate sensitivity of the material is found to be constant within a range of strain rates from 10^(-3) to 106 s^(-1) but increases at higher plastic strains. However, compressive deformability is nearly constant up to 102 s-1 and decreased disproportionately at higher rates of strain. With decreasing grain size a significant decrease of compressive deformability was found. The strength at failure is increased with increasing strain rate.Item Failure Elongation of Steel Sheets for an Autobody at the High Strain Rate(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Huh, H.; Kim, S. B.; Lim, J. H.; Song, J. H.; Yoon, J. H.This paper presents the dynamic failure elongation of conventional mild steels and advanced high strength steel sheets such as TRIP and DP steels. The failure elongation has been obtained from the high speed tensile testing machine with various strain rates ranged from 0.003/s to 200/s. The experimental result demonstrates that the tensile elongation does not simply decrease as the strain rate increases, but it decreases from the quasi-static state to the strain rate of 0.1 or 1/s and increases again up to the strain rate of 100/s. Furthermore, some high strength steels have the tendency that the tensile elongation increases as the strain rate increases. This tendency has varieties depending on the microstructure and forming history of sheet metal. Moreover, the localized strain rate hardening in the necking region induces the increase of elongation. This phenomenon is very important not only in sheet metal forming but also in the crashworthiness evaluation to predict the fracture of sheet metal members.Item Introduction of an Electromagnetism Module in LS-DYNA for Coupled Mechanical Thermal Electromagnetic Simulations(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Ashcraft, C.; Cook, G.; L Eplattenier, P.A new electromagnetism module is being developed in LS-DYNA for coupled mechanical/thermal/electromagnetic simulations. One of the main applications of this module is Electromagnetic Metal Forming. The electromagnetic fields are solved using a Finite Element Method for the conductors coupled with a Boundary Element Method for the surrounding air/insulators. Both methods use elements based on discrete differential forms for improved accuracy. The physics, numerical methods and capabilities of this new module are presented in detail as well as its coupling with the mechanical and thermal solvers of LS-DYNA. This module is then illustrated on an Electromagnetic Metal Forming case.Item Numerical Modelling of High Speed Blanking Considering Thermoviscoplastic Effects(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Behrens, B.-A.; Peshekhodov, I.; Sidhu, K. B.To achieve the required specifications of the cut-edge profile of a blank, a time consuming trial and error procedures based on empirical information are utilized. However, the modern industry demands high quality product specifications in the shortest possible production time. Therefore, in order to predict the cut-edge profile and speed up the production process, it is essential to develop a reliable numerical model of the high speed blanking process which can predict the cut-edge profile of the blanks. In this study, the Lagrangian based finite element (FE) approach was used to model large strain deformation that takes place in the shearzone during blanking. However, the large deformation is difficult to model using Lagrangian approach as it leads to a severe distortion of the FE mesh. Therefore, in order to overcome a premature termination of the analysis due to the mesh distortion, an adaptive remeshing and rezoning technique was developed. Furthermore, to model the ductile fracture, the discrete crack propagation method was implemented in the MSC.Marc® Due to high speed of the cutting stamp, thermoviscoplastic material behaviour has to be taken into account. The Johnson-Cook plasticity model was used to model viscoplasticity. The results obtained from the FE analysis are presented in this paper.Item Modeling and Simulation of 3D EMF Processes(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Blum, H.; Reese, S.; Schwarze, M.; Stiemer, M.; Svendsen, B.; Unger, J.A recent interest in potential industrial applications of electromagnetic forming processes has inspired a demand for adequate simulation tools. Aiming at the virtual design of industrial applications, the purpose of this work is to develop algorithmic formulations particularly suitable to reduce the enormous computational cost inherent to 3D simulations. These formulations comprise a carefully chosen discretization, highly accurate methods for data transfer between electromagnetic and mechanical subsystems, an efficient solid shell formulation, and a termination criterion for the electromagnetic field computation. As a result the simulation time is reduced by about one order of magnitude.Item Models for Electromagnetic Metal Forming(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Bartels, G.; Leone, M.; Schätzing, W.; Scheibe, H. P.This paper presents a comparison of different simulation options for electromagnetic metal forming in order to make preliminary investigations with adequate accuracy. Four simulation models are compared. The models mainly differ in their complexity, handling and necessary precondition program packages. The user has the choice to use a simple program with a defined program algorithm or to use a program with a higher programming complexity which accepts more information.Item Fast Algorithms for the Simulation of Electromagnetic Metal Forming(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Blum, H.; Stiemer, M.; Svendsen, B.; Unger, J.Despite the comprehensive understanding of the modeling and numerical simulation of electromagnetic metal forming that has recently been gained, the simulation of real forming situations is still a challenging task due to the large computational resources required. A bottleneck is the computation of the electromagnetic fields, since 100.000 up to several million unknowns are required to represent the geometry of a typical forming device. The purpose of this article is to present new techniques to speed up the simulation of electromagnetic metal forming with particular emphasis on the computation of the electromagnetic fields. An acceleration of the electromagnetic field computation is a significant step towards a virtual design of electromagnetic forming processes.Item Modelling of the Mechanical Behaviour of Ultra-Fine Grained Titanium Alloys at High Strain Rates(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Halle, T.; Herzig, N.; Krüger, L.; Meyer, L. W.; Musch, D.; Razorenov, S. V.; Skripnyak, E. G.; Skripnyak, V. A.Results of numerical simulations of the mechanical behaviour of coarse grained and UFG titanium alloys under quasi-static uniaxial compression and plane shock wave loading are presented in this paper. Constitutive equations predict the strain hardening behaviour, the strain rate sensitivity of the flow stress and the temperature softening of titanium alloys with a range of grain sizes from 20 µm to 100 nm. Characteristics of the mechanical behaviour of UFG a and a+ß titanium alloys in wide range of strain rates are discussed.Item Flanging and Hemming of Auto Body Panels using the Electro Magnetic Forming technology(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Anderson, R.; Brännström, P.; Daehn, G. S.; Eguia, I.; Gonzalez, B.; Gutierrez, M. A.; Jimbert, P.; Olsson, S. O.; Sundberg, H.; Zhang, Y.Electro Magnetic Forming (EMF) technology has a great number of potential applications for the automotive industry. LABEIN-Tecnalia has worked with this technology for six years and has a good understanding of the automotive industry s needs and challenges. LABEIN-Tecnalia is currently developing new applications with EMF technology. Taking into account the advantages and limitations of EMF, bending and hemming processes present good geometric conditions for the use of this technology. The study presented is based largely on hemming circular configurations which are simplifications of those commonly used on hemmed automotive parts. The parameters of this new EMF bending and hemming processes have been studied, as well as their influence on the final quality of the parts obtained. Conclusions obtained from the basic geometries were tested on a more complicated geometry in order to apply the knowledge acquired. Parallel to the experimental work, fully coupled electromechanical software by LS-DYNA has been used to simulate and extend the present hemming results.Item Towards the Contact and Impact Modeling in Finite Element Simulations of High Speed Forming(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Reese, S.; Rickelt, C.; Schwarze, M.In finite element simulations of high speed sheet metal forming processes the contact between workpiece and forming tools has to be modeled very carefully. Several important aspects have to be taken into account. Robust and locking-free finite element formulations are required to model the sheet forming process, the die has to be considered as a deformable component, and the description of the contact constraints between workpiece and forming tools is a significant source of shortcomings in modeling. The contact and impact simulation makes high demands on the robustness of finite element formulations. For this reason finite elements with low order ansatz functions are preferred. Furthermore, they prove to be advantageous when automatic meshing tools are applied. To overcome the undesired effects of locking we work with an improved version of the innovative solid-shell concept proposed by [11]. It is based on the concept of reduced integration with hourglass stabilization. The use of this solid-shell finite element allows us to test the influence of the modeling of the die and the contact constraints in a very efficient way. An overview of so-called macro and micro deformations of forming tools in sheet metal forming simulations can be found in [8]. We show that the deformation of the die has a noticeable influence in electromagnetic sheet metal forming. However, in most commercial finite element codes taking into account elastically deformable forming tools requires a full finite element discretization of the die which leads to very high computational effort. Therefore users often assume the tools as being rigid and apply node-based spring-dashpot systems to improve the modeling of the interaction between sheet metal and die. But also in this case local interactions cannot be taken into account realistically. As a possible remedy we investigate a fully elastic description of the forming tools in combination with model reduction techniques. These significantly reduce the number of degrees-of-freedom in the finite element simulation. For this reason we present different alternatives of this technique.Item Research in Impulse Joining of Self Pierce Riveting(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Hahn, O.; Kraus, C.; Leuschen, G.; Mauermann, R.; Neugebauer, R.Results are shown in impulse joining of aluminium sheets with self-pierce-riveting. Two institutes are testing impulse-riveting with different setting velocities of the punch up to 10 m/s by using pneumatic cylinders and about 100 m/s by using a propellant charge. One aim focus consists in riveting without a C-frame against a flat anvil instead of using a C-frame with a contoured die. So accessibility is increased and disadvantages of occurring misalignments are avoidable. The strength properties of the realised joints are tested.Item Process Analysis and Physical Simulation of Electromagnetic Joining of Thin-Walled parts(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Bach, F.-W.; Brosius, A.; Demir, O. K.; Gershteyn, G.; Psyk, V.; Schaper, M.; Tekkaya, A. E.To avoid typical problems when connecting different metallic materials as aluminum and titanium as e.g. the formation of intermetallic phases, electromagnetic welding represents an alternative technology to conventional (i.e. usually thermal) joining processes. Although feasibility and potential of this technique are already proved, the fundamental correlations of part- and process-parameters have not yet been investigated systematically. As an approach to examine these, the performance of model experiments and supplementary technological tests is suggested. The resulting connection quality is evaluated using metallographic methods.Item Electromagnetic Forming of AZ31B Magnesium Alloy Sheet(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Arroyo, A.; Hurtado, I.; Imbert, J.; Salisbury, C. P.; Ulacia, I.; Worswick, M. J.In the first stage of this work, polycrystalline specimens of AZ31B magnesium alloy have been characterized by uniaxial tensile tests at quasi-static and dynamic strain rates at room temperature. The influence of the strain rate is outlined and experimental results were fitted to the parameters of Johnson-Cook constitutive material model. In the second stage of the present study, sheets of AZ31B magnesium alloy have been biaxially formed by electromagnetic forming using different coil and die configurations. Deformation values measured from electromagnetic formed parts are compared to the ones achieved with uniaxial tensile tests and also with the values obtained by conventional forming technologies. Finally, numerical simulations have been carried out using an alternative method for computing the electromagnetic fields in the EMF process simulation, a combination of Finite Element Method (FEM) for conductor parts and Boundary Element Method (BEM) for the surrounding air (or more generally insulators) that is being implemented into commercial code LS-DYNA®.Item Design and Analysis of a Deep Drawing and Inprocess Electromagnetic Sheet Metal Forming Process(Institut für Umformtechnik - Technische Universität Dortmund, 2008) Bach, F.-W.; Beerwald, C.; Brosius, A.; Dudzinski, W.; Gersteyn, G.; Risch, D.; Schaper, M.; Tekkaya, A. E.The design as well as the subsequent analysis of a deep drawing and in-process electromagnetic sheet metal forming calibration will be described in this paper. Due to the quite different forming processes concerning the occurred strain rates, an investigation on the microstructure of the formed workpieces will be pointed out. Furthermore, the design steps regarding the integrated tool coil will be presented and the resulting examples discussed. Finally, the setup of the integrated process as well as the feasibility will be shown on an exemplary semi-industrial workpiece.