ICHSF 2006
Permanent URI for this collection
Forming materials of low ductility, like e.g. aluminum alloys relevant for light weight
construction, not only requires an optimisation of conventional methods, but also the
invention and further development of alternative forming processes.
The implementation of high speed forming processes, including electromagnetic forming
in particular, represents an exceptionally promising approach.
The Second International Conference on High Speed Forming (ICHSF 2006) at the
Universität Dortmund will serve as a forum for the presentation of the current research
and development status and for an intensive professional exchange.
Research results regarding subjects as workpiece and material behaviour, modelling and
simulation as well as process design will be presented and discussed in a range of
selected scientific lectures.
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Recent Submissions
Item Contributing Factors to the Increased Formability Observed in Electromagnetically Formed Aluminum Alloy Sheet(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Golovashchenko, S.; Imbert, J. M.; Worswick, M. J.This paper summarizes the results of an experimental and numerical program carried out to study the formability of aluminum alloy sheet formed using electromagnetic forming (EMF). Free-formed and conical samples of AA5754 aluminum alloy sheet were studied. The experiments showed significant increases in formability for the conical samples, but no significant increase for the free-formed parts. It was found that relatively little damage growth occurred and that the failure modes of the materials changed from those observed in quasi-static forming to those observed in high hydrostatic stress environments. Numerical simulations were performed using the explicit finite element code LS-DYNA with an analytical EM force distribution. The numerical models revealed that a complex stress state is generated when the sheet interacts with the tool, which is characterized by high hydrostatic stresses that create a stress state favourable to damage suppression increasing ductility. Shear stresses and strains are also produced at impact with the die which help the material achieve additional deformation. The predicted peak strain rates for the free formed parts were on the order of 1000 s^(-1) and for the conical parts the rates are on the order of 10,000 s^(-1). Although aluminum is typically considered to be strain-rate insensitive, the strain rates predicted could be playing a role in the increased formability. The predicted strain paths for the conical samples were highly non-linear. The results from this study indicate that there is an increase in formability for AA5754 when the alloy is formed into a die using EMF. This increase in formability is due to a combination of high hydrostatic stresses, shear stresses, high strain rates, and non-linear strain paths.Item Material Characterization at High Strain Rates with Special Emphasis on Miniaturization and Size Dependencies(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Herzig, N.; Meyer, L. W.Within the present work the size-dependent flow stress and failure behaviour of various metallic materials is described. Starting with special issues of testing miniaturized specimens, the influence of manufacturing routes and manufacturing induced geometrical deviations is investigated. The specimen size and time-dependent flow stress behavior of C45E, Ti-6-22-22S, and Al7075T6 is presented. The measured behavior is explained by size-dependent friction effects. Additionally, the influence of size and time scaling on the occurring of failure is investigated. A decrease of compressive deformability with increasing size and strain rate was found. The consideration of a size-dependent thermodynamic process character provides a possible explanation for measured size dependencies.Item On the effect of current pulses on the material behavior during electromagnetic metal forming(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Bach, F.; Blum, H.; Stiemer, M.; Svendsen, B.; Unger, J.; Walden, L.Electromagnetic sheet metal forming (EMF) is an example of a high-speed forming process driven by the dynamics of a coupled electromagnetic-mechanical system. Basic physical processes involved in EMF, such as e.g. inelastic and hardening behavior or inertia, have been considered in previous works [1, 2]. The purpose of the current work is the investigation of temperature development during EMF and a possible reduction in the yield stress due to electric currents. While thermoelastic and viscoplastic effects are well-understood in this context [3], the possible influence of electric currents on dislocation motion, generally referred to as the electro-plastic effect [4, 5], is still an unresolved issue. In agreement with previous works [e.g., 6], it is concluded here that such an effect is at most of second-order and can most likely be safely neglected in the modeling and simulation of industrial EMF.Item Magnetic Pulse Acceleration(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Gafri, O.; Izhar, A.; Livshitz, Y.; Shribman, V.The present work is dedicated to describing works in the spheres of simulation, calculation, and experimental results of acceleration by pulsed electromagnetic forces where strain rates of 10,000 - 50,000 s^(-1) are common. The goal is to design a multidisciplinary model that will overcome the shortcomings of normal simulation methods that solve the EM field and then apply the solution in a mechanical analysis. Improved numeric models for virtual simulation of magnetic pulse processes are detailed, along with the pulse-power equipment and a special measurement system developed to verify these models and to determine material property data. These measure both radial velocity and axial speed (collision-point progression) for tube forming and / or welding processes, while logging the pulse current and magnetic field. The results show good a correlation between test and multiphysics model and provide valuable new insights, as well as an extraction of critical parameters by way of a comparison between calculated and measured data for materials such as aluminum alloys, copper, and steel.Item Deformation and Ductile Fracture of a Low Alloy Steel under High Strain Rate Loading(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Abdel-Malek, S.; Meyer, L. M.Ductile failure of metals always occurs after a specific amount of plastic deformation. Therefore, the investigation and characterization of the deformation behaviour is required to understand the damage process and to describe the failure by a suitable constitutive relation. The effects of temperature and strain rate on the mechanical properties are important for the description of the material behavior in many applications. The MTS model is used here to describe the material behavior of some low alloy steels in a wide range of temperature and strain rates. A new part of stress is added to the MTS model in order to consider the effect of the dynamic strain aging at low strain rate and high temperature. The determination of material data at high strain and high strain rate is needed to describe the real material behaviour, specially for the simulation of high deformation and fracture. A special technique is used here to stop the deformation of tension specimen at high strain rate in the necking zone to determine the true stress and true strain. Using FEM computations (LS-DYNA 3D), the stress triaxiality in the necking zone of a tensile specimen is calculated up to the crack initiation. It is shown that the strain hardening characteristics affect the development of stress triaxiality.Item Materials Characterization at High Speed by Dynamic Tensile Tests(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Changgang, Geng; Xiangping, Li; Xin, LuIn this paper, the dynamic deformation behaviors of 2 aluminum alloys (AA6016, AA5182) and 2 steels (v 1158, FeP04) are investigated. Firstly, the test method, an improved Hopkinson pressure bar test, is introduced. Then, the test results are presented and analyzed. The strain rate range used in this study is between 290 s^(-1) and 1750 s^(-1).The test results show that the yield stresses of all four tested materials increase along with the increase of strain rate, but the ductility does not. An interesting finding is that the tested Al alloys demonstrated larger elongation than those of steels. In conventional tensile tests, as it is well known, the tensile elongation of low carbon steels is usually much higher than the one of Al alloys. So, it can be predicted that the aluminum alloys could have better formability than the steels in high speed forming processes, though the underlying mechanism is not fully understood.Item Fully-coupled 3D Simulation of Electromagnetic Forming(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Blum, H.; Stiemer, M.; Svendsen, B.; Unger, J.Electromagnetic metal forming is a contact-free high-speed forming process in which strain rates of more than 103 s^(-1) are achieved. The deformation of the workpiece is driven by a material body force, the Lorentz force, that results from the interaction of a pulsed magnetic field with eddy currents induced in the workpiece by the magnetic field itself. The purpose of this work is to present a fully-coupled 3D simulation of the process. For the mechanical structure a thermoelastic, viscoplastic, electromagnetic material model is relevant, which is incorporated in a large-deformation dynamic formulation. The evolution of the electromagnetic fields is governed by Maxwell s equations under quasistatic conditions. Their numerical solution in 3D requires particular arrangements due to a reduced regularity at material interfaces. Hence, Nédélec elements are employed. Coupling between the thermomechanical and electromagnetic subsystems takes the form of the Lorentz force, the electromotive intensity, and the current geometry of the workpiece. A staggered scheme based on a Lagrangian mesh for the workpiece and an ALE formulation for the electromagnetic field is utilized to solve the coupled system, guaranteeing the efficiency and accuracy of the data transfer between the two meshes.Item Efficient Finite Element and Contact Procedures for the Simulation of High Speed Sheet Metal Forming Processes(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Brosius, A.; Kleiner, M.; Reese, S.; Schwarze, M.A large variety of forming processes is used in industrial manufacturing processes. The numerical simulation of such processes puts high demands on the finite element technology. Usually first order isoparametric elements are preferred because of their robustness and numerical efficiency. Unfortunately, these elements tend to undesired numerical effects like "locking", predominant in situations characterized by plastic incompressibility or pure bending. To overcome this problem, several authors [1, 2, 4] propose finite element formulations based on the concept of reduced integration with hourglass stabilization by applying the "enhanced strain method". The main advantage of the proposed new isoparametric solid-shell formulation with linear ansatz functions is the fact that the undesirable effects of locking are eliminated. The previously described element technique can be applied to analyze specific problems of high speed forming into a cavity: Working with contact surfaces discretized by first order finite elements leads to discontinuities of the normal patch vector and, subsequently, to non-smooth sliding [5]. In quasi-static forming processes these discontinuities will not influence the contact forces noticeably. However, in dynamic investigations the sudden change of contact forces due to the rough surface description leads to a very high acceleration of the contact nodes. To avoid this effect, a smoothing algorithm will be described.Item 3D Finite Element Modeling of Electromagnetic Forming Processes(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Bergheau, J. M.; Conraux, P.; Pignol, M.; Robin, V.In the electromagnetic forming process (EMF, also known as magnetic pulse forming) the metal is deformed by applying a pressure generated by an intense, transient magnetic field. A great deal of research and investigation efforts are needed for gaining better understanding on the deformation mechanism in order to develop a suitable forming strategy and equipment. One way to reach this target is to employ suitable FE software to model the process. This investigation was partly conducted in the framework of a European project called EMF (G3RD-CT-2002-00798). The first part of the paper presents the relevant physical phenomena which govern the EMF process and their interactions. The physical coupling principle as well as the required numerical models are also established. In the second section some cases for which the so developed code can be used for virtual testing is presented for validation. Finally, numerical results are compared with experiments on a 3D model, highlighting the interest of numerical modeling for process improvements.Item Mathematical Modeling of Impulsive Forming Processes Using Various Energy Sources and Transmitting Medium(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Sabelkin, V.; Taran, V.; Vovk, A.; Vovk, V.High-speed forming uses high explosives, gun powder, combustible gas mixes and compressed gases as sources of energy. Special mathematical models are used to take into account specific dynamic properties. Different technological processes of forming have been modeled in the work. They use liquid (water), elastic (polyurethane), and gaseous transmitting medium. The difference between impulse energy transference, load distribution on a blank and tool surface, and also wave propagation is shown for used transmitting medium. The developed procedures allow taking account significant thermal effects at adiabatic compression of the material and heat transference directly from products of explosion. Specially developed modules and mathematical models have allowed the application of standard software products for modeling high-speed forming and sheet metal punching processes.Item Strength of Tubular Joints Made by Electromagnetic Compression at Quasistatic and Cyclic Loading(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Barreiro, P.; Beerwald, C.; Homberg, W.; Kleiner, M.; Löhe, D.; Marré, M.; Schulze, V.Electromagnetic compression of tubular profiles with high electrical conductivity is an innovative joining process for lightweight structures. The components are joined using pulsed magnetic fields which apply radial pressures of up to 200 MPa to tubular workpieces, causing a symmetric reduction of the diameter with typical strain rates of up to 10^4 sec^(-1). This process avoids any surface damage of the workpiece because there is no contact between component and forming tool. The strength of electromagnetically formed joints made of aluminum tubes under cyclic loads is essential to establish electromagnetic forming in automotive structures. In the present paper, the quasi-static performance of tubular joints made by electromagnetic compression produced of different mandrel materials will be analyzed as to the influence of process parameters. Therefore, experimental investigations on aluminum tubes (AA6060) joined on mandrels made of different aluminum, copper, and steel alloys were carried out. Furthermore, the behavior of joints with both mandrel and tube made of AA6060 at swelling cyclic loads (R = δ_ min / δ_ max =0) has been evaluated.Item Investigation of the Process Chain Bending-Electromagnetic compression-Hydroforming on the Basis of an Industrial Demonstrator Part(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Beerwald, C.; Beerwald, M.; Henselek, A.; Homberg, W.; Kleiner, M.; Psyk, V.The increasing significance of lightweight construction concepts requires innovative and adapted production technologies and process chains for the manufacturing of complex parts made of typical lightweight materials. The feasibility and potential of such a process chain consisting of the steps Bending - Electromagnetic compression (EMC) Hydroforming is shown in the present paper on the basis of a demonstrator part similar to a structural component from the automotive industry. Here, special focus is put on the requirements on the production steps and the workpiece properties. Furthermore, the development and testing of EMC-equipment that is optimally adapted to the special forming task is described.Item Design and Testing of Coils for Pulsed Electromagnetic Forming(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Golovashchenko, S.; Bessonov, N.; Davies, R.Coil design influences the distribution of electromagnetic forces applied to both the blank and the coil. The required energy of the process is usually defined by deformation of the blank. However, the discharge also results in a significant amount of heat being generated and accumulating in the coil. Therefore, EMF process design involves working with three different problems: 1) propagation of an electromagnetic field through the coil-blank system and generation of pulsed electromagnetic pressure in specified areas, 2) high-rate deformation of the blank, and 3) heat accumulation and transfer through the coil with the cooling system. In the current work, propagation of an electromagnetic field in the coil, blank, die and surrounding air was defined using a consistent set of quasi stationary Maxwell equations applying a corresponding set of parameters for each media. Furthermore, a deformation of the blank driven by electromagnetic forces distributed through the volume of the blank was modeled using a solid mechanics equation of motion and the elastic plastic flow theory. During the discharge of capacitors the process was considered to be adiabatic due to the short duration of the pulse, so a heat transfer during the discharge time was neglected. The distribution of electric current density integrated during the discharge process defines the increase of temperature at every element of the coil. The distribution of temperature was calculated as a function of time using the energy conservation law.Item A Production-oriented Approach in Electromagnetic Forming of Metal Sheets(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Koch, T.; Laux, G.; Löschmann, F.; Neugebauer, R.; Putz, M.parts per unit. Especially demands of modern lightweight design seem to be hard to satisfy by stretching conventional production methods. Thus, it is necessary to find new approaches. Adapting electromagnetic forming technology for the automotive industry would gain additional benefits like - less surface damaging owing to contact-less forming, - the possibility of achieving smaller radii, - focusing on low volume production through minimizing investment costs, and - more manufacturing flexibility. An approach to start qualifying this technology under the aspect of production engineering has been attempted by establishing a high speed forming project. The Volkswagen AG, Siemens AG, H&T ProduktionsTechnologie GmbH together with Fraunhofer Institute of Machine Tools and Forming Technology started activities focusing on - clarifying the fields of research and development which are not resolved to date, - developing necessary equipment, and - a systematic research on the according technology. The analysis of available equipments brought up a number of questions with respect to production engineering requirements. It resulted in a 100 kJ pulse power generator. One of the core components to define the quality of the forming process of flat parts is the flat coil. A coil design is selected to transfer a maximum of stored energy into the sheet metal. A selection of basic and applied experiments had the aim to know the limits of the technique. The paper introduces some representative results of the project. It touches the challenges related to the process of bringing this technology to productionItem Electromagnetic Springback Reshaping(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Daehn, G.; Gonzalez, B.; Gutierrez, M.; Hayes, B.; Iriondo, E.; Vonhout, V.Electromagnetic forming is an impulse-based forming technique where high dynamic pressure is distributed to conductive materials by pure electromagnetic interaction. The aim of this paper is to present how springback can be controlled when the EMF technique is used as a second corrective step; bringing formed parts to the desired final shape by means of magnetic impulses in critical areas of the formed components. This analysis is based on the results of two experimental studies. In the first, the selected preformed specimen shape is the L-shape bent part of HSS DP600, in 0.8 and 1.95 mm thickness, and Aluminium Alloy 5754, in 1 and 2 mm thickness. The second geometries are two rocket nozzle panels made of a thick but soft copper alloy. While the geometry and the material are the similar, the first approach of this work was developed using smaller panels (about 30 cm long) and the full size (about 1 m long), in order to study the behaviour of the material and the approximate energy levels required to scale up the full size panels. Overall this study shows EM forming can have a potent effect in controlling springback.Item Efficiency Improvement and Analysis of Changes in Microstructure Associated to a Uniform Pressure Actuator(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Arroyo, A.; Daehn, G. S.; Eguia, I.; Fernandez, J. I.; Garuz, I.; Jimbert P.; Silveira, E.During the 1st international Conference on HIGH SPEED FORMING held in Dortmund in 2004 a new forming coil giving significant advantages was presented in the framework of ongoing R&D programs at OSU (The Ohio State University). It established the improvement provided by the return path for currents induced in the workpiece. To quantify the mentioned improvement, Labein has performed classical cone forming experiments with both configurations and analyzed energetic efficiency using well known alloys, more precisely AA 6016 and 1050. Both deformation mechanisms and contour analysis of the specimens were studied. General purpose multi-turn coils provide pressure distributions not extended to the whole forming area, resulting in zones undergoing significant delay as die the deformation sequence is referred. As a result, varied deformation patterns can be found along the contour of a cone specimen formed in such way. Firstly, a macroscopic survey of the specimens shows that uniform pressure distributes deformation over the entire formed area during the deformation process. Secondly, the effect on efficiency provided by this new coil concept is focuses not only on the ability for distributing deformation, but on the energy required to create such deformation. Finally, to validate the whole simulation, the predicted strain level, shape, and internal energy of the workpiece are compared with the experimental specimens. A key point in the validation process is checking the internal energy. It is known that the ratio of stored energy to deformation energy ranges in the order of 30 %. The procedure for the experiments follows this methodology.Item Process Investigation of Tube Expansion by Gas Detonation(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Bach, F.-W.; Beerwald, C.; Brosius, A.; Gershteyn, G.; Hermes, M.; Kleiner, M.; Olivier, H.; Weber, M.The present paper deals with the expansion of tubes by direct application of gas detonation waves, i.e. the gas is both pressure medium and energy source. After an introduction to gas detonation forming, measurements of the motion process and the internal pressures are presented. Results of free expansion and of forming into a die are thoroughly studied and compared to the results of quasi-static burst tests and hydroforming. Using pure aluminum Al99.5 and a medium strength alloy AlMgSi1, expansions by 25 % and 20 % respectively are obtained. A simulation delivers details on the deformation process and specially prepared probes of high-speed tension tests give new insight into metallographic material behavior at different strain rates.Item Aspects of Die Design for the Electromagnetic Sheet Metal Forming Process(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Baumann, I.; Beerwald, C.; Brosius, A.; Kleiner, M.; Risch, D.; Tillmann, W.; Vogli, E.Within the electromagnetic sheet metal forming process, workpiece velocities of more than 300m/s can occur, causing typical effects when forming into a die, which will be described and discussed in the present paper. These effects make numerous demands regarding the die design. In order to analyze these requirements, experimental as well as numerical investigations have been carried out. Thereby, special focus is put on the possibilities to accomplish these requirements, which are discussed in the following.Item Electromagnetic Forming and Joining for Automotive Applications(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Golovashchenko, S.In this paper some options of how electromagnetic forming (EMF) can assist to expand the capabilities of conventional forming and joining technologies are discussed. Three different areas where EMF has the potential for a significant expansion of capabilities of traditional technologies are reviewed: 1) restrike operation to fill sharp corners of automotive panels; 2) low energy method of springback calibration; 3) joining of closed frames with an openable coil. Each of these applications was demonstrated in laboratory conditions and the description of the tooling is provided in the paper. Suggested design of a flat concentrator collecting induced electric currents from a flat coil was demonstrated for a corner filling operation and a springback calibration. An efficient technique of fabricating the flat coil from a flat plate by using water jetting technology enables a cost effective coil design, which can be reinforced by a system of non-conductive bars. The insulation of the coil is produced from the flat sheet of insulation material. Suggested design allows the coil to be repaired if a shortcut or fracture of insulation strips happens. A technology of low-energy calibration of stamped parts provides an option of working with a wider variety of materials including aluminum alloys, mild steels, and advanced high-strength steels. This technology is demonstrated for calibration of U-channels.Item Purposive Design of a Magnetic Sheet Metal Forming Facility(Institut für Umformtechnik - Technische Universität Dortmund, 2006) Peier, D.; Werdelmann, P.This paper is about the identification of lumped elements within an electric circuit diagram in the context of electromagnetic sheet metal forming. Based on fundamental physical considerations the forming coil and its workpiece can be modeled as a transformer, which is loaded on its secondary side by a resistor. A systematic oriented design process relating to an aimed at purpose is introduced in order to avoid time extensive trial-anderror methods. Based upon the theory of electromagnetic field equations, the complex impedance of the sheet metal is analytically identified as a function of the radial component. Based on the introduction of a force equivalent quantity, ways of designing and optimizing the remaining free parameters are presented. Thus, a design process for a forming facility is possible as the desired electromagnetic force can be characterized by the currents running through the forming coil and the sheet metal.