ICHSF 2010
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Item Welding and forming of sheet metals by using magnetic pulse welding (MPW) technique(2010-09-16) Aizawa, Tomokatsu; Kashani, Mehrdad; Okagawa, KeigoItem High Speed Forming 2010(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Zittel, G.; Schäfer, R.; Pasquale, P.; Chelluri, B.; Knoth, E.; Woodward, S.; Weddeling, G.; Daehn, G. S.; Psyk, V.; Carson, B.; Tekkaya, A. E.; Shang, J.; Wilkerson, L.; Hatkevich, S.; Babusci, K.; Daehn, G.; Marré, M.; Tekkaya, A. E.; Weddeling, C.; Zhang, Y.Item Electromagnetic pulse forming technology(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Pasquale, P.; Schäfer, R.The electromagnetic pulse forming technology (EMPT) provides substantial technological benefits with respect to tube forming and joining operations. However, in the past this technology was mainly adapted in academics, military production and small batch size productions. Establishing this technology in the world of civil-industrial mass production demands for several key prerequisites to be fulfilled. This report lists these requirements and moreover provides answers on ways for their completion.Item A Historical Review of High Speed Metal Forming(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Zittel, G.This paper will present a Historical Review of High Speed Metal Forming beginning with the first thought of forming metal by using an electromagnetic impulse to today, whereby High Speed Metal Forming is an accepted production process. Although this paper will briefly cover the basic physics of the process, it will not dwell on it. It will rather show how the industrial acceptance of High Speed Metal Forming is tightly connected to the knowledge acquired from many applications studies. These studies determined the main characteristics of the process and defined the requirements for reliable Forming Equipment. This paper will show where the process is most effectively used by presenting real industrial product applications and industrial forming equipment.Item Powder Forming Using Dynamic Magnetic Compaction(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Chelluri, B.; Knoth, E.Conventional powder forming of metals, ceramics and composites uses room temperature pressing approaches such as static uniaxial pressing, isotropic pressing - cold isostatic pressing (CIP) or elevated temperature hot isostatic pressing (HIP) methods. In this paper, description of a unique dynamic pressing approach for powder materials will be presented where very high pulse pressures (of GPa range) are applied for a short duration (of < 1 millisecond) on powders. Such a dynamic pressing offers the ability to form uniformly high density net shape parts with fine microstructures. The method can be applied to wide range of materials such as metals, ceramics, composites and soft and hard magnetic materials. A broad range of powder particle size distributions, from coarse micron size to fine nano size powders, can be used in the process. The principles of dynamic pressing method along with the summary of results on various powder material systems will be presented. The performance of parts made with dynamic method will be compared with conventional processes.Item Commercialization of Fuel Cell Bipolar Plate Manufacturing by Electromagnetic Forming(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Daehn, G. S.; Hatkevich, S.; Shang, J.; Wilkerson, L.The cost of manufacturing bipolar plates is a major component to the overall cost structure of a Proton Exchange Membrane (PEM) fuel cell stack. To achieve the commercialization of PEM fuel cells, a high volume and low cost manufacturing process for the bipolar plate must be developed. American Trim has identified high velocity electromagnetic forming as a suitable technology to manufacture metallic fuel cell bipolar plates, because of its low capital cost, flexible tooling and rapid prototyping capability. Through the support from the State of Ohio Third Frontier Fuel Cell Program, a group of collaborators consisting of American Trim, The Ohio State University and General Motors have developed a commercially viable prototype production process to manufacture metallic fuel cell bipolar plates in which electromagnetic coils and forming dies were integrated. To manufacture fuel cell bipolar plates, a metal sheet is accelerated by electromagnetic force to impact against, and take the shape of, the forming die surface. A novel approach which introduces a compliant layer eliminates the need for expendable driver plates in order to reduce the production cost. This process enables continuous manufacturing of fuel cell bipolar plates in short-time cycles at very low cost, which demonstrates strong potential for commercialization. This paper will introduce the electromagnetic forming process developed to manufacture metallic bipolar plates, and include a discussion of the preliminary results. The benefits of using this high velocity electromagnetic forming process over a traditional stamping press will also be discussed. To commercialize electromagnetic forming, coil life and die wear are being investigated. The results of some preliminary experiments involving coil durability and die wear will also be presented.Item Agile Production of Sheet Metal Aviation Components Using Disposable Electromagnetic Actuators(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Carson, B.; Daehn, G.; Psyk, V.; Tekkaya, A. E.; Weddeling, C.; Woodward, S.Electromagnetic forming is a process used to produce high strain rates that improve the formability of sheet metal. The objective of this paper is to discuss the feasibility of the use of disposable actuators during electromagnetic forming of two aluminum components: an industry part whose main feature is a convex flange with two joggles, and a simple part with a one-dimensional curve throughout. The main forming complications after the parts were formed using conventional methods were the presence of wrinkles and excessive springback. The goal of this work is to use large, controlled electromagnetic impulses to minimize the springback of these components from a roughformed shape, with the end result being a dimensionally correct part. The optimum test protocols for electromagnetic calibration of the components were determined by optimizing parameters such as design of the actuator, tool material, and capacitor discharge energy. The use of disposable actuators for electromagnetic calibration of the parts showed significant reductions in springback compared to the parts which were only preformed using conventional techniques (hydroforming and rubber-pad forming). Springback was decreased in the curved component by up to 87%. For the flanged component, the wrinkles were eliminated, the joggles were formed properly, and the average bending angle of the part was improved from 95.3° to 90.3°, very near the target bending angle of 90°. This study demonstrates that these forming techniques can be used to improve current sheet metal production processes.Item Investigation of the Electrohydraulic Forming Process with respect to the Design of Sharp Edged Contours(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Beerwald, C.; Homberg, W.; Pröbsting, A.The overcoming of design constraints with respect to forming of sharply contoured sheet metal workpieces made of high strength steel or other materials which are difficult to form is an important aspect in sheet metal part production. One interesting solution to extend existing forming limits can be the use of electrohydraulic forming as single forming operation or in combination with quasi-static hydroforming. Apart from promising results regarding the feasible part geometries this process allows a quite efficient production due to its potential to reduce equipment expenses. Current research work at the Chair of Forming and Machining Technology (LUF) at Paderborn University deals with a comparison of investigations on both processes, quasistatic and high speed hydroforming. Recent results show an adequate comparison of achievable edge radii using an oblong die geometry and sheet metal made of thin stainless steel. It can be seen that when using electrohydraulic forming an increase of discharge energy leads to smaller radii than achievable by quasi-static hydroforming. An additional potential can be seen in the process characteristic itself because the very short pressure pulse allows a significant reduction of locking forces using only the inertia of the tooling mass.Item Pressure heterogeneity in small displacement electrohydraulic forming processes(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Daehn, G. S.; Fenton, G.; Vohnout, V. J.Electrohydraulic (submerged arc discharge) forming of sheet metal parts has been used as a specialized high speed forming method since the 1960 s. The parts formed generally had a major dimension in the 5 to 25 cm range and required gross metal expansion in the centimeter range. In the descriptions of this process found in the literature, the pressure front emanating from the initial plasma generated by the arc is considered to be uniformly spherical in nature. At least one commercial system used this model to design hardware for pressure front focusing to optimize the forming process[1] and it has been the subject of continued research [2]. Recently, there has been commercial interest in adopting the electro-hydraulic method for the production of much smaller parts requiring very high die contact pressures but little gross sheet expansion. The forming of these small shallow parts required only a few kilojoules but proved to be problematic in other terms. The process development clearly showed indications of random patterns of large pressure heterogeneity across distances in the millimeter range. The apparent pressure heterogeneity produced unacceptable small scale variation in the part geometry. A test program was designed to verify and quantify this effect using a target (die) consisting of a flat plate having small closely spaced holes. This 50 mm diameter target proved very effective in clearly showing the extent of the heterogeneity as well as the approximate local pressures. Various discharge energies were investigated along with different chamber shapes and pressure transfer mediums. The pressure heterogeneity across the target face was a common feature to all experiments. These test results indicate that a uniform pressure front model can be seriously in error for the electrohydraulic process as implemented to date. The results of a qualitative hydro-code model of the test system including the discharge event are presented. The model results are similar enough to the experimental to imply that the coaxial electrode s inherent off center discharge is a primary suspect among potential explanations for the observed heterogeneity in terms of asymmetric shock interaction. The absence of this phenomena in the earlier electrohydraulic forming literature is also discussed.Item Joining of Copper to Brass Using Magnetic Pulse Welding(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Baaten, T.; Debroux, N.; De Waele, W.; Faes, K.In magnetic pulse welding, electromagnetic pressure is used to deform, accelerate and weld workpieces. The process is mostly used for tubular specimens. In this study, experiments were performed in order to investigate the weldability of copper tubes to brass solid workpieces. The tubes had an outer diameter and wall thickness of 25,0 mm and 1,5 mm respectively. A multi-turn coil with 5 windings in combination with a field shaper was used to focus the electromagnetic flux and thus realize the high pressures needed for welding. The process parameters for joining these materials were optimised for maximum weld length. The parameters taken into account were the position of the field shaper relative to the workpieces, the width of the air gap between the tube and the internal workpiece and the energy level. The weld quality was verified based on metallographic examinations, scanning electron microscopy and hardness measurements.Item Measurements of Pressure Fields with Multi-Point Membrane Gauges at Electrohydraulic Forming(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Knyazyev, M. K.; Zhovnovatuk, Ya. S.Success of electrohydraulic forming (EHF) process depends on coincidence of the needed pressure field with the field generated by discharge chamber at sequent stages of sheet blank deformation. Impulse loading at high-voltage discharge has a very complicated character and involves many phenomena: direct shock waves, hydraulic flows, quasi-static pressure of gas bubble, reflected shock waves, cavitation, secondary shock waves, etc. Also internal shapes of a discharge chamber, design and location of electrodes have a great influence on pressure distribution along blank surface. Because of these features, the simulation of EHF processes is very complicated task to be solved for chambers equipped with single electrode pair. And difficulties are increased greatly for simulation of multi-electrode discharge blocks (MDB). First of all, reliable data on pressure distribution at various discharge conditions are necessary to reveal and describe influence of each factor of impulse loading. Multi-point membrane pressure gauges (MPG) give an opportunity to obtain pressure maps with high resolution at relatively low cost. By design MPG typically consists of body plate with large number of small holes and sensitive element - metallic membrane. Deformation of membrane in each point (hole) can be measured and recalculated into pressure. Totality of many pressure points allows plotting a pressure map. MPGs are better suitable for measurement of shock-waves pressure. For this purpose the holes diameter and membrane thickness should be specified in such a manner that membrane is sensitive only to shock waves. Combination of MPG measurements with piezoelectric sensors can give full information about pressure map changing in time. These data could be a good basis for simulation of impulse loading with approximation formulas and also could be used as a check data for the simulation programs based on theoretical relationships. Initially the method based on MPG application was designed for investigations and improvements of discharge chambers with various forms of internal (reflecting) surfaces, electrodes position and their shapes, influence of design features on pressure distribution. Vast experimental investigations were carried out with MPG application for typical single-electrode-pair discharge chambers (conical and parabolic) and multi-electrode discharge blocks.Item Impact Welding in a Variety of Geometric Configurations(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Babu, S.; Daehn, G. S.; Zhang, Y.Magnetic pulse welding is an electromagnetically assisted high strain rate impact welding technology. The physical principle is similar to explosive welding and it also belongs to solid state impact welding. This high velocity oblique impact welding has been applied to various lap joint configurations. Three different geometric configurations on plate-to-plate welding were studied in this paper. They are direct lap joint, pre-flange lap joint, and lap joint with embedded wires. All of the three welding configurations have been used to provide metallurgical bonds between both similar and dissimilar metal pairs. The welded materials include copper alloy, aluminium alloy, and steels. The plates are centimeter or more thick and often centimeter in extent. The critical welding process parameters were instrumentally investigated by Rogowski Coil and Photon Doppler Velocimetry. Metallographic analysis of the welded interface showed refined grain structure. The mechanical properties of the welded plates were studied by lap shearing, peeling and nano-indentation tests. The test results showed that the impact welded interface has a much greater micro-hardness and fracture toughness than the base metals.Item Modelling Pulse Magnetic Welding Processes(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Uhlmann, E.; Ziefle, A.In recent years pulse magnetic welding technology gained an ever increasing attention. The process was known for over 40 years, yet the poor knowledge of process parameters as well as the difficulties concerning the calculability of the process due to lack of adequate software, performance and appropriate material models hindered the application of the technology. In the past, some simulations treating the process of explosive welding were conducted. There, the assumption was made to define a friction condition to the boundary regions which was reasonable due to similar conditions in the collision region during the process. However, at pulse magnetic welding processes, the contact forces are highly transient and have big gradients over the geometry. In this paper a new empirical approach is presented, which gives the possibility of modelling the welding process by parameter-controlled bonding at the welding interface. The pulse magnetic forming process was simulated by loose coupling of electromagnetic and mechanical FEM software with the commercial code ANSYS. As geometry the joining of a duct with an internally positioned conical bolt was chosen. The material used for both duct and bolt was EN AW 6063. First of all the influences of heat generation were analyzed. Therefore, the additional thermal simulation was coupled with the electromagnetic and the mechanical simulation. The heat generation caused by the plastic deformation was considered. As the resulting temperatures were below the melting temperature of the material, further simulations were carried out without thermal simulation. In order to calibrate the welding model, a set of relevant parameters were defined. It included the cumulative plastic work, the plastic deformation in collision direction, the normal and the tangential components of the collision velocity and the collision angle between the two parts. By comparing the simulation with experiments carried out at the same specific process parameters, it was possible to reduce the set of parameters to the normal collision velocity and plastic deformation. Based on their distribution, the parameter control of the bonding condition could be adjusted. Further experiments gave a high accordance to the simulations carried out with the parameters found for this model.Item Fundamentals of EMPT-Welding(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Elsen, A.; Groche, P.; Ludwig, M.; Schaefer, R.A well-suited solid state welding process for treatment of tubular structures is the electromagnetic pulse welding technique (EMPT): A pulsed magnetic pressure loads the structure to be welded within a few microseconds and accelerates one of the both contact partners (the so called "flyer" onto a stationary one. When the flyer strikes the stationary contact partner, contact normal stresses far above 1000 MPa act on the interfacial zone between flyer and stationary part. As a result of these high interfacial loads, a layer of several micrometers thickness next to the interface is severely plastically strained. Hence, the oxide layers covering both contact partners are cracked. These chipped oxide particles are blown out of the joining area by a so called "jet". This jet is caused by the air between the two joining partners being compressed and accelerated due to the movement of the flyer. The result of both phenomena - the oxide chipping by severe plastic deformation of the interfacial zone and the particle blow out caused by the jet - is a pure metallic interfacial zone, loaded by contact normal stresses. The conjunction of the highly reactive metallic surface and the contact normal stresses establishes a metallic bonding, whose strength equals at least the strength of the weaker contact partner. This report presents the results of a collaborative research project between the Institute for Production Engineering and Forming Machines (PtU) and PSTproducts GmbH. Experimental welding analysis is accompanied by numerical work for the study of the underlying mechanisms of solid state welding with respect to interfacial plastic deformation and contact loads. Additional metallographic work gives insight into the microscopical structure of the interfacial joint zone.Item Insights into intermetallic phases on pulse welded dissimilar metal joints(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Beyer, E.; Brenner, B.; Göbel, G.; Herrmannsdörfer, T.; Kaspar, J.The Magnetic Pulse Welding (MPW) process has been developed to an industrially used joining method which is considered to be a fast, noncontact, clean and "cold" solid state welding process. Unlike fusion welding, the absence of direct heat during the welding cycle makes it possible to join dissimilar metals, for instance aluminium to copper or copper to steel, without noticeable detrimental metallurgical defects. This is very desirable, as today s industry lacks technologies to join often not fusion-weldable dissimilar materials effectively. However, current metallographic studies show that for many material combinations the formation of intermetallic seams in the joint region of magnetic pulse welds can not be completely avoided. Modern technical equipment for MPW is used to join aluminium with copper in order to study the microstructure and the intermetallic phases formed in the weld region in dependence of the processing parameters. The welds are analysed by means of metallographic and electron microscopic (SEM) methods. Relations between the parameters and the microstructures formed within the weld joints are shown. Based on the obtained results conclusions will be drawn with respect to the intermetallic phase formation process and the optimization of the weld microstructure and properties.Item Development of design principles for form-fit joints in lightweight frame structures(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Brosius, A.; Daehn, G. S.; Marré, M.; Nellesen, J.; Psyk, V.; Tekkaya, A. E.; Tillmann, W.; Weddeling, C.; Woodward, S.Based on fundamental technological investigations, alternative joining strategies using electromagnetic forming (EMF) for the flexible production of lightweight frame structures are developed in the collaborative research project SFB/TR10. The results of these investigations will also be used to create general design principles for the joining process itself as well as for the joining zone. The focus of this article will be on dominating form-fit joints of aluminum frame structures and the parameters which have a significant influence on the strength of those joints. For the development of design principles regarding the joining zone, the groove geometry of the connection elements was varied in terms of size and shape, and the influence of those variations was analyzed. In terms of the joining process itself the effect on the joint strength of different forming pressures for a given groove geometry was also investigated. In the first step these experiments were performed on solid mandrels. In order to reduce the weight of the structure, experiments were then performed with hollow connection elements and similar groove geometries to analyze how the reduced stiffness of those elements affected the strength of the joints.Item Impulse Hydroforming Method for Very Thin Sheets from Metallic or Hybrid Materials(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Beerwald, C.; Beerwald, M.; Dirksen, U.; Henselek, A.Forming of very thin metallic and hybrid material foils is a demanding task in several application areas as for example in food or pharmaceutical packaging industries. Narrow forming limits of very thin sheet metals as well as minor process reliability due to necessary exact tool manufacturing (small punch-die clearance), both, causes abiding interest in new and innovative forming processes. In this contribution a new method using high pressure pulses will be introduced to form small geometry elements into very thin metal foils or into hybrid polymer-metal foil. It will be shown how the acting pressure pulse will be generated by electromagnetic acceleration of a certain mass, which initiates a pressure wave within a working media. The effect of different pulse lengths has been compared and evaluated by the forming result. Finally, an outlook concerning suitable pulse power equipment and its industrial capability will be given.Item Warm Electromagnetic Forming of AZ31B Magnesium Alloy Sheet(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Arroyo, A.; Eguiy, I.; Gutiérrez, M. A.; Hurtado, I.; Ulacia, I.Historically, electromagnetic forming technology has mainly been used to form parts from aluminium and copper alloys due to their excellent electrical conductivity and limited formability by conventional methods. However, little research has been carried out in high strain rate forming of magnesium alloy sheets. Therefore, in the current contribution electromagnetic forming experiments are performed for rolled AZ31B magnesium alloy sheet at different temperatures up to 250°C. Two forming operations are studied in this paper, i.e. drawing and bending operations. The final deformations achieved for the different conditions were measured and the effect of both temperature and discharged energy on deformation is shown. Bending experiments at room temperature were recorded by means of a high speed camera and the springback behaviour at high strain rates is evaluated. In one hand, increasing the forming temperature the yield strength of the material decreases while on the other hand, the electrical conductivity and thus the induced forces are also decreased. It is observed that increasing the forming temperature, for a given discharged energy, the maximum height of the deformed part is decreased. However, increasing the discharged energy at warm temperatures, higher deformation values are achieved without failure. Additionally, bending experiments show that springback effect is also decreased at warm conditions. It is concluded that warm electromagnetic forming is a suitable procedure to manufacture magnesium parts.Item Effects of Force Distribution and Rebound on Electromagnetically Formed Sheet Metal(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Imbert, J.; L'Eplattenier, P.; Worswick, M.Electromagnetic forming (EMF) is a high speed forming process that has been shown to increase the formability of aluminum alloys under certain conditions. Many authors have reported significant increases in formability; however, there is as of yet no complete understanding of the process. Obtaining a gain in formability is not the only factor that must be considered when studying EMF. The process rapidly generates significant forces which lead to the deformation of the material at very high rates. The applied forces depend on the shape of the electromagnetic coil used, which leads to force distributions that may not be ideal for forming a particular part. Once the sheet is accelerated it will travel at high speeds until it impacts the die. This high speed impact results in the sheet rebounding from the die. Both the force distribution and the rebound affect the final shape of the part. This paper presents the results of experimental and numerical study carried out to determine the effect of the force distribution and the rebound on samples of conical and "v-channel" geometry. It was found that both sample geometries are affected by the force distribution and the rebound, with the v-channel samples being considerably more affected. The results indicate that these effects must be carefully considered when EMF processes are designed.Item Simulation of Wrinkle Formation in Free Electromagnetic Tube Compression(Institut für Umformtechnik - Technische Universität Dortmund, 2010) Demir, O. K.; Psyk, V.; Tekkaya, A. E.A 3-dimensional (3D) finite element (FE) simulation of free electromagnetic (EM) tube compression was performed with the aim of predicting wrinkle formation. Staggered coupling was applied between the EM and mechanical parts of the problem. The full 360° portion of the problem was modelled since the wrinkle formation does not represent any symmetry in circumferential direction. The initial geometric imperfections of the tube were measured and included in the model to trigger buckling. The deformed geometry with the wrinkles could be predicted accurately.