Showing papers in "Advanced Materials Research in 2005"
TL;DR: In this paper, two production processes of flexibly rolled blanks, one with longitudinal and the other one with latitudinal thickness transitions, have been developed at the Institute of Metal Forming (IBF) and yet found their way into series production.
Abstract: Light weight construction is a construction philosophy which aims at maximum weight reduction. Reasons for light weight construction can be very diverse. One main cause can be to improve fuel efficiency. This can be achieved by use of load optimised sheet thicknesses. Another reason can be the increasing demands on crash performances by optimisation of local properties. This paper presents two production processes of flexibly rolled blanks, one with longitudinal and the other one with latitudinal thickness transitions. Both of them have been developed at the Institute of Metal Forming (IBF) and yet found their way into series production. The potential of these processes is already proved by a large range of products, especially in automotive industries. Some special deep drawing tests with flexibly rolled blanks have been conducted and their results are presented. Also process simulation has been carried out at the IBF and will be explained. One possibility with regard to optimise these products is shortly introduced. Completing this paper an outlook is given.
78 citations
TL;DR: In this article, the forces measured in forming cones and truncated pyramids from AA 3003-0 are described and the magnitude of these forces are used to determine if the equipment available is capable of forming sheet metal by either one of the two preceding processes.
Abstract: Forces have been measured in Two Point Incremental Forming and Single Point Incremental Forming of Sheet Metal. It is necessary to know the magnitude of these forces when trying to determine if the equipment available is capable of Forming Sheet Metal by either one of the two foregoing processes. The magnitude of forces is also needed when developing appropriate models for the Incremental Sheet Forming. The forces measured in forming cones and truncated pyramids from AA 3003-0 are described.
71 citations
TL;DR: In this article, the material properties of the hot stamping steel 22MnB5 have been investigated and a survey of the as-delivered conditions with hardness tests, micrographs and flow curves is given.
Abstract: Basic research concerning the material properties of the hot stamping steel 22MnB5 has been carried out. A survey is given about the as-delivered conditions with hardness tests, micrographs and flow curves. The process window of the austenitization time, before hot stamping can take place, is defined by austenitization tests. Also a new experimental set-up to detect the cooling rate in dependency on the contact pressure is presented. In addition to that the cooling experiments were simulated with ABAQUS and the heat transfer coefficient for each contact pressure is determined by inverse modeling.
57 citations
TL;DR: A new incremental sheet forming machine has been built in Cambridge and was commissioned in October 2004 as discussed by the authors, where the tool-mounting has been designed to rotate freely but passively, and to allow for simple exchange of tool tips.
Abstract: A new incremental sheet forming machine has been built in Cambridge and was commissioned in October 2004. The basis for the machine design is described, including estimates of tool forces, the need for access to the reverse side of the workpiece, and the need to cope with high horizontal loads at the tool tip. The tool-mounting has been designed to rotate freely but passively, and to allow for simple exchange of tool tips. The workpiece is mounted on a set of load cells providing a six degree of freedom constraint without moment loading of the cells. The initial operation of the machine is briefly described.
57 citations
TL;DR: In this paper, a novel process is proposed to overcome the major problems in forming aluminium sheet components, such as springback, low formability and microstructure variation, which is combined Solution Heat Treatment (SHT) hot stamping followed by cold die quenching.
Abstract: To overcome the major problems in forming aluminium sheet components, such as springback, low formability and microstructure variation a novel process is proposed in this paper. That is combined Solution Heat Treatment (SHT) hot stamping followed by cold die quenching. To determine the feasibility of such process a series of thermal-mechanical tests have been designed and carried out on aluminium alloy AA6082. Three aspects of the forming process are investigated and represented in the paper. The first is to investigate the effects of SHT proportions on the mechanical properties of the material. The second is the effects of quenching rates on the mechanical properties after SHT. The third is the effect of predeformation after the SHT and the quenching rate on the mechanical properties of the formed parts. Summaries are given for each aspect of the study. These tests are to investigate the effects of Solution Heat Treatment time proportion. Variables are also introduced during the cold die quenching, including clearance between the testpiece and dies as well as the applied load. Finally the relationship between quench rate and predeformation is investigated.
52 citations
TL;DR: In this article, an experimental platform capable of measuring forces in process during an incremental forming procedure is described and the results garnered from it are presented, using a table type force dynamometer with incremental forming fixture mounted on top, three components of force were measured throughout the forming process.
Abstract: In this paper an experimental platform capable of measuring forces in process during an incremental forming procedure is described and the results garnered from it are presented. Some of the earliest measurements of forces in incremental forming and the changes induced on the measured load are reported. Using a table type force dynamometer with incremental forming fixture mounted on top, three components of force were measured throughout the forming process. They were found to vary as the parts were made. The reported experimental test program was focused on the influence of three different process parameters on the forming forces: the vertical step size between consecutive contours, the diameter of the tool and the steepness of the part’s wall. For the tested material, analytical results demonstrating the relationship between the respective process parameters and the induced forces are presented in this paper.
50 citations
TL;DR: In this article, a specific approach is presented for the detection of the process limits within the simulation tool and a software chain has been set up with the target to decrease the computation times.
Abstract: The use of quenched boron steel components is an economic way to achieve significant improvements in terms of weight saving and crash performance. The material and process knowledge on the hot stamping of boron steels (e.g. Arcelor’s USIBOR 1500 P®) by the stampers needs to be extended and accurate simulation tools must be developed to support the growth of this forming technology. This paper simultaneously addresses the specific requirements of the hot stamping simulation and the current state of the art in this field. A specific approach is presented for the detection of the process limits within the simulation tool. A software chain has been set up with the target to decrease the computation times.
45 citations
TL;DR: In this article, the authors describe modifications that have been made to traditional forming methods such as conventional spinning and shear forming, where deformation is localized, and demonstrate that this localized deformation can be accurately controlled and studied.
Abstract: The use of computers in manufacturing has enabled the development of several new sheet metal forming processes. This paper describes modifications that have been made to traditional forming methods such as conventional spinning and shear forming, where deformation is localized. Recent advances have enabled this localized deformation to be accurately controlled and studied. Current developments have been focused on forming asymmetric parts using CNC technology, without the need for costly dies. Asymmetric Incremental Forming has the potential to revolutionize sheet metal forming, making it accessible to all levels of manufacturing.
41 citations
TL;DR: In this paper, a couple of numerical analysis strategies were applied to simulate simple incremental forming processes, as well as a proper experimental equipment was developed to verify the accuracy of the numerical predictions.
Abstract: Incremental forming processes are characterized by a well known and particular feature: any deformation across the sheet plane determines sheet thinning, since the blank is fully clamped by means of a proper equipment. As a consequence, the availability of effective and reliable CAE tools capable to supply an accurate prediction of sheet thinning as a function of process parameters, represents a strong requirement for a wider practical application of incremental forming. The already available theoretical models (i.e. the sine law) do not provide, on the other hand, satisfactory results. Therefore in the paper a couple of numerical analysis strategies was applied to simulate simple incremental forming processes, as well as a proper experimental equipment was developed to verify the accuracy of the numerical predictions.
38 citations
TL;DR: In this article, a laser welding-brazing (LWB) process is proposed to join zinc-coated steel and aluminium sheets in an overlap geometry, where the process is divided into welding of the aluminium sheet and brazing of filler material and molten aluminium sheet onto the zinc-covered steel sheet to avoid the liquid stage of iron.
Abstract: Joining of iron with aluminium in the liquid phase is complicated due to the formation of brittle intermetallics within Fe-Al melts. In this work we present the technology of a laser weldingbrazing (LWB) process to join zinc-coated steel and aluminium sheets in an overlap geometry. The process is divided into welding of the aluminium sheet and brazing of filler material and molten aluminium sheet onto the zinc-covered steel sheet to avoid the liquid stage of iron. It is possible to join those materials with a single laser beam. However, with a second laser beam, the melt flow can be controlled more effectively and the wetting behaviour can be improved by preheating the zinc-covered steel sheet surface. This is beneficial since the process works without any flux agent. Wetting lengths increase by using this technique and generate a joint that exceeds the tensile strength of the base material. Due to the zinc cover on the steel sheet there are two possible filler materials that have miscibility with zinc as well as aluminium. Zinc based filler materials have the advantage of a lower melting point and thus lower process temperatures. And aluminium based filler wires result in more ductile brazed seams, making it possible to deform such joints in a later application as tailored blanks.
34 citations
TL;DR: In this paper, the principle of sheet metal LOM is described as well as the process chain of LOM of metal foil, and the results of the experimental work for qualifying and optimizing the sub-process are shown.
Abstract: The technology of Laminated Object Manufacturing (LOM) is not very new. For hundreds of years wooden parts are built by stacking layers together. Nowadays also paper, plastic, ceramic composite and metal sheets are treated in layers. For the manufacture of prototypes and especially technical tools, e. g. moulds for gravity casting, die casting or injection molding, out of metallic foil however the low self stiffness of this material is a great challenge. In this case it is useful to produce the parts in a two step process. The first subprocess is the stacking of the layers, which can be realised by laser beam spot welding to determine the position of the layer in combination with generating the defined contour by a laser beam cutting process. This procedure is done in a fully automated machine where the CAD-file of the desired part and the building parameters like the laser parameters and the cutting velocity are needed as input. However the stability of the produced green part is insufficient for most kind of application. Hence, a second sub-process to enhance the mechanical properties of the part is necessary. This can for example be realised by high temperature soldering or by diffusion welding in a furnace with inert gas or vacuum. During these kinds of joining processes the green part is homogeneously pressed with the help of a powder bed and at the same time it is tempered for a defined term. In this paper the principle of sheet metal LOM is described as well as the process chain of Laminated Object Manufacturing of metal foil. For each sub-process of metal foil LOM the results of the experimental work for qualifying and optimizing the sub-process are shown. Finally some examples of possible applications especially in the field of Rapid Tooling and Rapid Manufacturing are discussed.
TL;DR: In this article, the process of single point incremental forming of an aluminum cone with a 50-degree wall angle was investigated both experimentally and numerically, and the output of the simulation was given in terms of final geometry, the thickness distribution of the product, the strain history and distribution during the deformation as well as the reaction forces.
Abstract: Incremental forming is an innovative and flexible sheet metal forming technology for small batch production and prototyping, which does not require any dedicated die or punch to form a complex shape. This paper investigates the process of single point incremental forming of an aluminum cone with a 50-degree wall angle both experimentally and numerically. Finite element models are established to simulate the process. The output of the simulation is given in terms of final geometry, the thickness distribution of the product, the strain history and distribution during the deformation as well as the reaction forces. Comparison between the simulation results and the experimental data is made.
TL;DR: The 2003 International Symposium on Macro-, Meso-, Micro- and Nano-Mechanics of Materials (MM2003) was held in Hong Kong, 8-10 December 2003 as mentioned in this paper.
Abstract: International Symposium on Macro-, Meso-, Micro- and Nano-Mechanics of Materials, MM2003, Hong Kong, 8-10 December 2003
TL;DR: In this paper, the NVEB was used to join hybrid structures between zinc-coated steels and 5.xxx and 6.xxx aluminium alloys in a welding-brazing process, where the steel remained in the solid phase whereas the aluminium was molten.
Abstract: Against the background of the required weight reduction in transportation through lightweight construction, the application of hybrid structures, where dissimilar materials are joined together, has a high technical and economical potential. In the field of sheet machining, combinations of steel and aluminium are especially interesting. In comparison to conventional steels, the application of aluminium alloys as supporting materials makes a distinct weight reduction possible. On the other hand, steels have advantages in the fields forming and welding. The application of modern high-strength steels with reduced sheet thicknesses allows weight reduction, too. But joining of material combinations of steel and aluminium is problematic. On the one hand brittle intermetallic compounds are formed between steel and aluminium. On the other hand the aluminium melt has a bad wetting behaviour. Different physical properties of both materials have to be considered, too. To achieve sufficient mechanical properties of such joinings it is necessary to limit growth of intermetallic compounds between steel and aluminium. This can be actualized by an exact energy supply. With the electron beam on atmosphere a precise and easily controllable energy supply is possible. The publication demonstrates successful investigations, which were performed with the 175 kVNVEBW (Non Vacuum Electron Beam Welding) installation at Institut of Materials Science, University of Hanover. With NVEB joining hybrid structures between zinc coated steels and 5.xxx and 6.xxx aluminium alloys were produced. In a welding-brazing process (the steel remained in the solid phase whereas the aluminium was molten) combinations with acceptable mechanical properties could be joined. By use of optimized joining parameters as well as a surface activating flux, both, a good wetting and a thin intermetallic compound
TL;DR: In this paper, a new process technology for stretch-forming of thin sheet metals is presented, which is based on shock waves as a source for the forming energy, which are created through laser pulses.
Abstract: A new process technology for stretch-forming of thin sheet metals is presented within this paper. This new technology is based on shock waves as a source for the forming energy, which are created through laser pulses. The results of some preliminary experiments show, that stretchforming with laser pulses is possible. The influence of parameters like defocussing, power density, pulse energy, number of pulses and material are worked out with excimer-laser pulses. The results show, that uniform shaped domes with a dome height over 250 µm with diameters of 1.4 mm could be produced. More recent studies show that even better results can be reached through the use of TEA-CO2-Lasers, since no confinement is needed and ablation at the surface is avoided. The absence of ablation at the surface makes this new technology even more interesting, since not only the surface remains accurate, but also since several pulses can be applied at one point and thus higher forming degrees can be reached without increasing the power density.
TL;DR: In this paper, the electromagnetic forming (EMF) machine uses induced electromagnetic fields to generate high strain rates during the forming process, which increase the formability of aluminum materials and might reduce elastic spring-back and wrinkling of the workpiece.
Abstract: The recent push to use more aluminium in automobiles has stimulated interest in understanding electromagnetic forming (EMF), which uses induced electromagnetic fields to generate high strain rates during the forming process The high strain rates increase the formability of aluminum materials and might reduce elastic spring-back and wrinkling of the workpiece Primary emphasis is placed on including of all relevant physical phenomena, which govern the process, as well as their numerical representation by means of simplified electrical equivalent circuits for the EMF machine and fully coupled field approach of the transient electromagnetic and mechanical phenomena Moreover, the thermal effects due to Joule heating by eddy currents and plastic work are considered The numerical model predicts the electromagnetic field, temperature, stress, and deformation properties that occur during the forming process The numerical results of the tube deformation are compared with available experimental data
TL;DR: In this paper, the application of these methods on a complex automotive part is conducted followed by a comparison of computed distortion with measured values, and aspects of integration of weld modeling into the virtual product chain are addressed.
Abstract: Welding distortion is one of the major concerns of the industrial joining practice. In order to obtain optimal welding parameters many experiments have to be carried out. Numerical simulation enables a virtual examination of the welding distortion without performing expensive experiments. In this contribution some industrially applicable methods of weld modeling are discussed. They enable the fast distortion assessment in the pre-development stage. The application of these methods on a complex automotive part is conducted followed by a comparison of computed distortion with measured values. Furthermore, aspects of integration of weld modeling into the virtual product chain are addressed.
TL;DR: In this article, optical measuring technologies in sheet metal forming and tooling have been used more and more in the industry and the main applications are the digitizing of metal sheet parts and tools, forming analysis of metal sheets as well as the determination of material properties.
Abstract: During recent years, optical measuring technologies in sheet metal forming and tooling have been used more and more in the industry. Main applications are the digitizing of metal sheet parts and tools, forming analysis of metal sheets as well as the determination of material properties. Good interfaces to conventional CAD/CAM and numerical simulation systems made such optical measuring systems a part of complex process chains. These process chains mainly focus on optimizing the development of products and production processes and on improving the product quality. Using optical systems considerably decreases the development time for products and production while improving the quality.
TL;DR: In this article, the authors performed FEM simulations of the forming of a cone with a 50-degree wall angle by incremental forming and investigated the influence of some crucial computational parameters on the simulation.
Abstract: Incremental forming is an innovative and highly flexible sheet metal forming technology for small batch production and prototyping that does not require any adapted dies or punches to form a complex shape. The purpose of this article is to perform FEM simulations of the forming of a cone with a 50-degree wall angle by incremental forming and to investigate the influence of some crucial computational parameters on the simulation. The influence of several parameters will be discussed: the FEM code used (Abaqus or Lagamine, a code developed at the University of Liege), the mesh size, the potential simplification due to the symmetry of the part and the friction coefficient. The output is given in terms of final geometry (which depends on the springback), strain history and distribution during the deformation, as well as reaction forces. It will be shown that the deformation is localized around the tool and that the deformations constantly remain close to a plane strain state for this geometry. Moreover, the tool reaction clearly depends on the way the contact is taken into account.
BMW1
TL;DR: In this article, a design concept due to crash, stiffness and driving performance, basic requirements have to be considered, and a cost effective combination of the mentioned high-sophisticated alloys with conventional material should be achieved.
Abstract: Sophisticated materials like high strength steel or even multi phase steel as well as aluminum require more efforts within the manufacturing process than conventional steel sheets as they have been used in the body in white recently. The manufacturing process itself as well as engineering of the parts, material of the forming tools as well as cold and warm joining technologies must be regarded separately. For forming tools coated steel inserts or sometimes even cooling is essential in terms of high-volume car series production. In mixed material solutions using steel in combination with aluminum, the common used resistance spot welding process does not work any more. To maintain high process stability of cold joining technologies combined with adhesive bonding a new process must have been developed. Other items for weight and cost savings are tailored rolled blanks or sophisticated joining technologies. Regarding the manufacturing costs, a cost effective combination of the mentioned high-sophisticated alloys with conventional material should be achieved. Developing a design concept due to crash, stiffness and driving performance, basic requirements have to be considered. This aims to check the high potential of cost intensive materials wherever high functional benefit is necessary under commercial aspects.
TL;DR: In this paper, the authors present an incremental sheet forming with an industrial robot, where a sheet metal blank is attached to a strong arm and the tool slides on the surface of the sheet and forms it incrementally to the desired shape.
Abstract: Incremental sheet forming (ISF) has been a subject of research for many research groups before. However, all of the published results so far have been related to either commercial ISF machines or ISF forming with NC mills or similar. The research reported in this paper concentrates on incremental sheet forming with an industrial robot. The test equipment is based on a strong arm robot and a moving forming table, where a sheet metal blank is attached. The tool slides on the surface of the sheet and forms it incrementally to the desired shape. The robot is capable of 5-axis forming, which enables forming of inwards curved forms. In this paper the forming limit diagram (FLD) for ISF with the robot is presented and it is compared with conventional forming limit diagrams. It will be shown that the conventional FLD does not apply to incremental forming process. Geometrical accuracy of sample pieces is also studied. Cones of different shapes are formed with the robot equipment and their correspondence with the 3D CAD model is evaluated. The results are compared with other results of accuracy of incremental sheet forming, reported earlier by other researchers. The third issue covered in this article is a product development point of view to incremental sheet forming. In addition to fast prototyping and low volume production of sheet metal parts, ISF brings new possibilities to sheet metal component design and manufacturing. These possibilities can only be exploited if design rules, that will take the possibilities and limitations of the method into account are created for ISF.
BMW1
TL;DR: In this article, the effect of different types of dry-film lubricants on the performance of the assembly process of a car body has been investigated in the Dingolfing plant of the BMW 7 series.
Abstract: The production of automotive body parts and panels is a very complex process, starting with the raw materials and ending in the paint shop. Due to the fact that aluminium sheet metal has to be lubricated before forming, all of the following processes have to be considered. Lubricants, such as oils, dry-film lubricants or recently introduced hotmelts have to protect the material’s surface, reduce friction whilst drawing the panels and should not compromise further treatments [1]. Different types of lubricants show different characteristics. This difference is especially noticeable when comparing liquid and dry-film lubricants. As dry-film lubricants do not run off the blanks’ surface and are distributed homogeneously, they show different tribological properties compared to conventional liquid lubricants. The effect on friction of aluminium sheet metal is shown through several basic experiments [2, 3]. In addition, the paper shows the effect of further operations within the production chain. The advantages and disadvantages not only for drawing, but also for assembly lines and the painting process are described in this paper. Assembly issues are carried out on stability testings of riveted and clinched assemblies. These trials show how the assembly process is affected by different proceedings. The fact that every car body has to be completely free of grease before painting, signifies the necessity to get lubrication off the car body’s surface before painting. The interactions between lubrication and paint shop are shown on typical process parameters. Most typical characteristics considering bonding and riveting were tested out on a hood assembly of the current BMW 7-series. In addition to that, experiences made in the press shop at BMW’s Dingolfing plant were figured out and carried over to a long-term strategy of pre-lubrication of aluminium sheet metal. This includes adhesive compatibility as well as the above mentioned assembly process.
TL;DR: In this article, the main influences on the process are described and a method to model and simulate this process using the finite element method using LS-DYNA is presented, where experimental investigations of the contact heat transfer have been carried out to enhance the simulation accuracy.
Abstract: In the automotive industry a general tendency to choose steels with enhanced strength for structural parts can be observed. This trend results from the increased lightweight design efforts to satisfy the fleet consumption restrictions. Hot forming and quenching of boron steel offers the possibility to improve the component strength and reduce the weight of structural parts. The main influences on the process are described and a method to model and simulate this process using the finite element method using LS-DYNA is presented. Experimental investigations of the contact heat transfer have been carried out to enhance the simulation accuracy. A prototyping tool of a structural part is used to examine the process under production conditions. Temperatures of the tool and the part are measured during the process. These temperatures are compared with the simulation results in order to reevaluate the results of the process simulation.
TL;DR: In this article, the authors present a methodology to determine the whole area of the forming limit diagram (FLD) for sheet metal in a digital environment using finite element simulation using the ABAQUS program.
Abstract: The determination of the forming limit diagrams (FLDs) for sheet metal can be influenced by testing parameters and a chosen testing procedure. Many different tests have been applied and recent work has resulted in some guidelines to decrease the influence of the testing method and the expertise of an individual laboratory. In the last years some methods have been developed which tend to be independent from the individual expertise, but comprehensive experimental work is still indispensable to obtain the material’s necking and failure limit. The experimental work could be omitted by prediction of the FLD with numerical simulations. The paper presents a methodology to determine the whole area of the FLD for sheet metal in a digital environment. The material thinning has been analysed with the finite element simulation using the ABAQUS program. The Marciniak testing procedure has been chosen to determine the FLD. The thickness strain as a function of time as well as first and second time derivation of the thickness strain have been analysed for the critical specimen areas where the onset and propagation of necking occur.
TL;DR: In this article, the authors present a case study of the manufacture of a solar cooker cavity for developing country applications, and show how the possibility of manufacturing part of the solar cooker, by Single Point Incremental Forming, gives rise to the possibility to manufacturing other parts for the solar cookers less expensively.
Abstract: Single Point Incremental Forming is a new process, which has been developed to make both Rapid Prototyped products and low volume product batches from Sheet Metal. This paper presents a case study of the manufacture of a solar cooker cavity for developing country applications. In the first instance the request was for a rapid prototype, which quickly evolved into a request for low volume production of solar cookers for the developing country market. The paper describes the manufacture of the solar cooker cavity, and shows how the possibility of manufacturing part of the solar cooker, by Single Point Incremental Forming, gives rise to the possibility of manufacturing other parts for the solar cooker less expensively.
TL;DR: In this article, a new sheet metal forming process for the production of sheet metal components for limited-lot productions and prototypes is described, based on flexible shaping by means of a freely programmable path-synchronous movement of the two robots.
Abstract: This paper describes a new sheet metal forming process for the production of sheet metal components for limited-lot productions and prototypes. The kinematic based generation of the shape is implemented by means of a new forming machine comprising of two industrial robots. Compared to conventional sheet metal forming machines this newly developed sheet metal forming process offers a high geometrical form flexibility and also shows comparatively small deformation forces for high deformation degrees. The principle of the procedure is based on flexible shaping by means of a freely programmable path-synchronous movement of the two robots. The sheet metal components manufactured in first attempts are simple geometries like truncated pyramids and cones as well as spherical cups. Among other things the forming results could be improved by an adjustment of the movement strategy, a variation of individual process parameters and geometric modifications of the tools. Apart from a measurement of the form deviations of the sheet metal with a Coordinate Measurement Machine rasterised and deformed sheet metals were used for deformation analyses. In order to be able to use the potential of this process, a goal-oriented process design is as necessary as specific process knowledge. In order to achieve process stability and safety the essential process parameters and the process boundaries have to be determined.
TL;DR: In this article, the formability of laser welded patchwork blanks is investigated by means of experimental trials and finite element analysis, and the results obtained from these experimental investigations have been used to define different modelling techniques for the finite-element analysis of patchwork blank forming processes.
Abstract: Within the past decades tailored welded blanks have become a key product for the construction of lightweight automotive bodies Following the principle of applying material only where it is really needed results in an improved stiffness and crash worthiness of the body-in-white, while at the same time weight and production costs may be reduced An alternative to the concept of tailored blanks is the so-called patchwork blank technique The principle of patchwork blanks is to add a flat piece of sheet metal onto the main blank in the areas where reinforcements are required The assembly can be done by adhesive bonding, resistance spot welding or laser welding prior to forming The major benefits of this technique in comparison to tailored blanks are the abolition of cutting operations and a high flexibility regarding the shape and position of the reinforcement Even if there is a big application potential for patchwork blanks in automobile production, practical realisation of this innovative technique is hindered due to a lack of knowledge regarding the formability of patchwork blanks In this study the formability of laser welded patchwork blanks is investigated by means of experimental trials and finite element analysis In order to simulate accurately the forming processes of patchwork blanks using finite element analysis, knowledge about the characteristics of the weld metal, including the weld bead and the heat affected zone, is essential Microhardness measurements have been applied to analyse the heat affected zone and to determine its lateral dimensions The constitutive behaviour of the weld metal has been investigated by uniaxial tensile tests with a special sample geometry The results obtained from these experimental investigations have been used to define different modelling techniques for the finite element analysis of patchwork blank forming processes It can be shown that the consideration of the modified material properties along the weld seam leads to an improvement of the accuracy of the numerical calculation
TL;DR: In this paper, a new machine-concept is presented, which is based on a punch-load moving perpendicular to the sheet, where restoring forces are induced, which cause in dependence of special developed tool and work piece geometries defined stress conditions.
Abstract: In times of highest significance of process modelling and numerical simulation characterisation of material properties is of special importance for tools’ and components’ dimensioning. But in general material properties depend on many different influencing variables, e.g. temperature, humidity and many others. Especially in fields of sheet metal forming the mechanical behaviour of components highly differs according to real stress condition. In particular yield loci combine the information of beginning of yielding with a biaxial stress condition, but nevertheless for many materials they have not been determined yet. For all others the existing values are available only at room temperature. In this paper a novel concept of the experimental setup is shown, with which plastic yielding of sheet metal can be examined also at elevated temperatures. In usual biaxial tension tests cruciform specimen are drawn in plane. The new machine-concept, which is presented in this paper, is based on a punch-load moving perpendicular to the sheet. By clamping the specimen restoring forces are induced, which cause in dependence of special developed tool and work piece geometries defined stress conditions. Using an optical measurement system for determination of strains with CCDcameras of very high frame rate allows exact identification of starting plastification by offline analysis. Experiments at elevated temperatures are realised by local heating with a diode laser and a special optical system to reach a homogenous distribution of temperatures in the forming zone. On the one hand these investigations are necessary for many materials to achieve further information on characteristic properties in warm forming, because their data are only known at room temperature. On the other hand some materials, e.g. magnesium wrought alloys, are mostly formed at elevated temperatures (here in the range of 200°C to 250°C), because of its significant higher formability. Thus, material behaviour must be characterised at these temperatures.
TL;DR: In this paper, a new methodology to quantitatively evaluate finite element calculations on incremental sheet forming (ISF) is presented, which is a new manufacturing process for prototypes and small lot sizes.
Abstract: The present paper focuses on a new methodology to quantitatively evaluate finite element calculations on incremental sheet forming (ISF). ISF is a new manufacturing process for prototypes and small lot sizes. In ISF, a part is manufactured by the CNC-driven movement of a simple tool, giving rise to very challenging problems concerning the efficient modeling of the alternating contact conditions and the material's response to the cyclic deformation. The quantitative validation of the finite element analysis is achieved by an optical deformation measurement system which has been enhanced by a new calibration procedure, yielding a precisely defined local coordinate system for deformation measurements during forming. In combination with mapping algorithms for large point sets, this allows for a quantitative validation of process simulations and material input data.
TL;DR: In this paper, an alternating magnetic field coaxial with the arc axis was demonstrated to influence melt flow and weld pool dilution, thus "stirring" the weld metal.
Abstract: In order to minimize the occurrence of hot-cracking phenomena in laser welding of hotcracking sensitive aluminum alloy sheets, it is a common technique to introduce silicon-containing filler wire into the weld metal. However, to achieve an optimum result, a homogenous distribution of not less than 2 % of silicon throughout the weld metal is strongly recommendable. Under certain circumstances, this may be a difficult task. One potential solution to achieve sufficient dilution and, consequently, a very homogenous silicon distribution might be the application of alternating magnetic fields. In foundry technology, the use of magnetic fields to influence melt flow is a wellestablished method. For TIG welding, a process called magnetic stirring was first investigated in the 1970s. It was sufficiently demonstrated by the help of an alternating magnetic field coaxial with the arc axis, that, among other effects, the degree of dilution can be increased and a refined grain structure is achieved. Since the late 1990s, some efforts have been taken to apply constant magnetic fields to laser welding processes. However, neither alternating fields nor potential effects on dilution have been in the focus of these investigations. To help this situation, basic studies on magnetically influencing melt flow during laser welding of aluminum have been conducted. To that end, alternating fields have been coaxially applied with magnetic flux densities up to 60 mT and frequencies in the range of 0 to 20 Hz. It was demonstrated by the help of a specially developed method that, depending on the parameters chosen, such fields are indeed capable of influencing melt flow and weld pool dilution, thus “stirring” the weld metal.