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Tube Hydroforming is a well accepted production technology in automotive industry while sheet hydroforming is used in selected cases for prototyping and low volume production. Research in advanced methods (warm sheet and tube hydroforming, double blank sheet hydroforming, combination of hydroforming and mechanical sizing, use of multi-point and elastic blank holders) is expanding the capabilities of hydroforming technologies to produce parts from Al and Mg alloys, as well as Ultra High Strength Steels. In the development of advanced hydroforming methods, experience based knowledge is not readily available. Thus, robust process simulation is required, along with adequate material modeling and identification of friction coefficients as input to process simulation. This paper gives an overview of advanced hydroforming methods, including examples of novel machine and tooling designs. The use of reliable process simulation is illustrated with examples that demonstrate the significance of material and friction date for making accurate predictions. Advanced simulation methods for warm forming and for programming multiple-point blank holder are also discussed. This review illustrates that hydroforming continues to make advances and has the potential to make many contributions to production technology in the near future.

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.

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.

Zinc coated steels are nowadays used for different applications as for example for household appliances, automotive or offtakes. Due to the boiling temperature of zinc (907°C), which is lower than the steel melting point, the welding of zinc coated steel sheets presents many difficulties. As a result of the violent evaporation of zinc, pores in the weld seam are present after solidification and the zinc coating near the weld is damaged. Brazing of zinc coated steels with CuSi-alloys offers some advantages, as the joining temperature is about 950-1000°C. Nevertheless the high melting point of these filler materials requires very restricted process strategies and damaging of the zinc coating near the brazing seam can’t be avoided. Although laser-, plasma- and MIG-joining with CuSi and CuAl are performed nowadays. ZnAl-alloys are characterized through low melting temperature, which are comparable to the melting point of zinc, so that the damaging of the zinc coating can be reduced. In this paper investigations carried out with ZnAl-materials for joining zinc coated steel sheets as DC04ZE75/75 and DX56Z (thickness 0,9 mm) are reported. First investigations were performed by resistance spot soldering and show that using low temperature melting materials leads to a lower damaging of the zinc coating. Further the process reliability of laser soldering with ZnAl-alloys and a Nd:YAG as well as a diode laser is reported and confirms the suitability of these alloys for a damaging free joining zinc coated steels. The low surface tension leads to a wide bearing section, so that advantageous properties are expected. The mechanical properties of edge welds are evaluated in this paper through tensile tests as well.

Compared to welding, laser brazing offers a suitable possibility to lower the working temperature and to join unweldable material combinations, while maintaining the numerous advantages of the laser joining process. Beside an acceptable joint strength, the brazed joints are characterised by a smooth surface and seams with almost no pores. As a result of this laser brazing combines the advantages of conventional brazing and laser welding. Within the scope of this paper the laser brazing process and its characteristics are explained in detail. In particular the interrelation of temperature progress, available processing time for brazing/diffusion and the thickness of the diffusion layer is discussed. Subsequently the material specific particularities of laser brazing aluminium alloys are described and discussed with respect to recently gained results.

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 < 10 µm were attained. Another possible strategy is a pure brazing process, for which an example is also given in the paper. The paper shows metallurgical and mechanical investigations, among other things results of element distribution analysis and tensile tests.

Self-piercing riveting as an alternative joining method to spot-welding has attracted considerable interest from the automotive industry and has been widely used in aluminium intensive vehicles. Pressing and stamping are important processes in automotive production and result in additional straining on the vehicle body sheet material. It is therefore important to have knowledge of the effect of sheet pre-straining on the quality of the self-piercing riveted joints and on the mechanical behaviour of the riveted aluminium alloy sheets. This paper reports the influence of sheet pre-straining on the static and fatigue behaviour of self-piercing riveted aluminium alloy sheet. Wrought aluminium alloy sheet, NG5754 with a nominal thickness value of 2mm was used to obtain pre-strained NG5754 sheets with pre-straining levels of 3%, 5% and 10%. The pre-strained NG5754 sheets were then joined in pair to create single riveted lap joints. Lap-shear and fatigue tests were performed on the self-piercing riveted joints. Microscopic inspection showed that the joint quality was satisfactory despite the increasing sheet straining levels. The results showed that by increasing the pre-straining level up to 10%, the shear and fatigue strength also increased. The rate of increase of the static and fatigue strength differed as the pre-straining levels varied.

The customers’ demand for high quality and low cost products with rising functionality forces the enterprises to cost savings. In production these cost savings can be accomplished by simplification or omission of handling operations in the process chain. In laser beam welding of stamped sheet metals a previous cleaning of the sheets is usually necessary to guarantee a sufficient seam quality at a lap joint. Due to the recent trend towards low use of lubricants in forming operations the question arises, whether this process could be avoided in order to lower the production costs. The disadvantage of this measure would be a degradation of the seam quality. This reduction shows up in a falling strength of the weld due to inclusions and pore formation. This paper deals with the impact of different types of contaminations on the quality of laser welding. Therefore several liquid (oils) and solid (metallic and non-metallic) contaminants are examined. Zinc coated sheets are investigated too, because a zinc contamination arises with these sheets in the welding operation. The zinc coating evaporates because of the high temperature and this leads to a high porosity in the welding seam. In both cases also the height of the gap between the two sheets is varied in order to investigate its influence on the weld. To reduce the effort of the investigations, but not the accuracy of the results, the laboratory trials were supported by the methods of design of experiments. After the welding operation, the quality of the welding seam is evaluated by means of its mechanical properties and tightness. The results of the investigations are discussed and the developed solution strategies are presented.

Two new joining methods for sheet metal parts, dieless clinching and dieless rivet-clinching are introduced in this paper. With these methods all formable materials can be joined. Contrary to conventional technology in joining by forming these new methods are working with a flat anvil as a counter tool instead of a contoured die, which has a number of advantages. The process has become simpler, the process reliability is increased, misalignments of the joining tools don’t effect the quality of the connection anymore and even new applications, such as the joining of materials with a limited malleability become possible. Examples of realized connections and FE-calculations of the joining processes are presented.

During the joining process of complex body components in the automobile industry, dimensional accuracy is essential. In order to predict the behavior and to improve the geometrical quality of joined sheet metal parts during the welding and cooling process, a simulation method by means of finite elements is applied. This should be done in the early stage of the product’s life cycle to reduce process adjustments, which are time and money consuming. In recent years the simulation of welding was basically feasible by models consisting of volume elements. This way the metallurgical phase transformation, which is responsible for the behavior of the treated parts during the cooling process, can be established for a specific material. The use of volumes has a negative influence on the calculation time and it is not applicable for sheet metals. Especially, if effects from previous forming processes are to be considered. Additionally, the application of shells can meet the requirements of an analysis of the effects of welding when the metallurgical material properties are taken into account. In this paper an example of a sheet metal (DC04, former St 14) will be examined with the aid of a finite element analysis. Firstly, a transient temperature field is calculated in a thermal simulation by applying a certain method. In this calculation only the thermal properties of the material are used. Secondly, the transient temperature field is used as the initial load for the thermo-mechanical analysis. The distortion and the residual stresses of the work piece can be calculated using thermo-mechanical properties and material phase transformations.

The use of aluminium alloys rose in the last decade, as its specific mechanical properties allow a reduction of mass as for example in automotive. Moreover aluminium, due to its high corrosion resistance, is a very important material class in plant construction, where it is used for pipes or container till 250 °C. Aluminium can be welded with different technologies. Nowadays TIG and MIG are mainly used for example in plant construction or in mechanical engineering. Laser beam welding is a widely established technology in automotive. The advantage is the high energy concentration, which leads to a high welding speed and a narrow heat affected zone. Plasma welding is applied when joining aluminium with alternating current, as an easy removal of the oxide layer in the surface of the weld pool is possible. Plasma-Powder-Arc-Welding (PPAW) method has been developed from Plasma Transferred Arc (PTA) weld surfacing and Plasma Arc Welding (PAW) methods by combining a small PAW torch (PAW is traditionally performed with wire as filler material) with powder filler material feeding as used in PTA-equipment. The coupling leads to a better mechanisation of the welding process as the consumable is fed directly through the welding torch. In this paper investigations on aluminium sheets (£ 2 mm) AA5xxx and AA6xxx using different powder materials are reported. The influence of the processing parameters and conditions on the process reliability, when welding with industrial robots butt and corner welds is investigated. Conventional PPAW of aluminium is performed with AlSi12 filler material. A post processing of the joint, as for example anodising in order to improve corrosion resistance, leads to a very different optical aspect, as the colouration of the weld seam after anodising differs from the base material. Thanks to a correct choice of filler material it is possible to reduce the colour differences between base materials/heat affected zone and bead, so that the weldment can be set for high quality optical applications, too.

During the recent years, due to the rapid development in Finite Element modeling, as well as the rapid evolution of computer techniques, numerical modeling has become an important everyday tool not only for process analysis and process optimization but for die design and rapid die manufacturing, as well. The Department of Mechanical Technology at the University of Miskolc is regarded as the leading research centre for Computer Aided Engineering of sheet metal forming processes in Hungary. The activity of the department covers the computer aided technological and tool design, the development and application of knowledge based expert systems for process planning and process optimization and die design using sophisticated FEM packages. In this latter activity, the AutoForm Engineering GmbH is a strategic partner of the department for several years. In this paper, the concept for an integrated computer aided die design system specialized for the rapid design of parametric die faces using finite element simulation technique will be presented.

This paper discusses the trends and developments in intelligent CAD of progressive die. The research efforts reviewed reveal the growing importance and relevancy of particular AI techniques for automation of progressive die design activities. Based on the knowledge base approach of AI, an intelligent CAD framework is developed and presented in this paper. The proposed intelligent CAD framework comprises different knowledge base modules for automating progressive die design process. The procedure for the development of various knowledge base modules of the proposed intelligent CAD system is described through module CCKBS which has been designed for assessing manufacturability of sheet metal parts. An illustrative example has been included for demonstrating the usefulness of the developed module CCKBS. The system framework is flexible enough to accommodate new acquired knowledge for each module. The modules of the system framework are implementable on a PC and thus can be affordable by small and medium size enterprises.

Tolerance analysis is nowadays a modern and efficient tool to simulate toleranced assemblies. As a result the designer gets the closing tolerance as well as to the priority of influencing tolerances. The closing tolerance can be calculated in worst-case or in statistical manner. These methods and tools have in common that only rigid, non-deformable geometry can be integrated. Many application cases in industry have tolerances as well as the influence of elastic deformations of components to be considered. Effects as spring-back of deformed components for assembly are reality. In this paper a method will be presented which allows a tolerance analysis of non-rigid geometry, especially for sheet metal assemblies.

Both the topics of Computer Aided Process Planning and Production Planning in the context of sheet metal air bending have been presented as standalone topics previously. This paper will focus on the interaction between both modules. Choices made by the CAPP-module seem to influence the possible gains that can be obtained in production planning and vice versa. The used procedures for both the CAPP module, including process planning and tool selection for air bending, and the Production Planning module, modelling the production planning as a Travelling Purchaser Problem, are described. The different areas of interaction between both modules are also specified. Results demonstrate that the interaction between both modules has a significant impact and should be taken into account in an integrated process and production planning system.

Ongoing miniaturisation of functional parts in electronic, optical and mechanical devices results in an increasing demand for precision. By means of laser beam forming of especially designed sheet metal parts within an assembly the needed high accuracy can be reached. The use of the so called actuators, their mounting within the assembly and their activation through laser irradiation are well known steps. The design however is a sophisticated process so far depending on the experience of the designer. It is often determined in a time consuming iterative process. In this paper concepts and methods for an assistance system for the designer of actuator geometries using kinematic chains will be presented.

Sheet metal bending is a metal forming process, in which flat sheets are bent along straight bend lines in a specific bending sequence to form three-dimensional parts. A large number of tools with different characteristics can be used in this process. The task to choose the right tooling for a requested sheet metal part is however one of the bottle necks in process planning. An inefficient tool selection may result in failure of finding a feasible bending sequence. In previous work, methodologies for tool selection and optimization have been proposed. The presented paper describes a framework to implement these methodologies into a system that allows automatic tool selection in consistent consideration of bend sequencing. As a result, automated and optimized tool selection for sheet metal bending is achieved, as illustrated by performance test results for a robust software implementation.

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.

In this paper, a concept of a closed-loop-control system for the material flow in deep drawing processes based on a fuzzy-controller is presented. The deep drawing process is influenced by different variables as batch dependent material values, machine parameters as well as variations in the forming tools. Process stability can be improved by continuous process monitoring and process control. The control loop for controlling the material flow consists of an optical sensor, a deep drawing tool with an elastic blank holder, a fuzzy controller and a deep drawing press with a multi point drawing cushion. The controlled variable (material flow) was measured contact-free and on-line by means of an optical sensor developed at the IFUM. As control variable the different lokal blank holder forces were chosen in order to influence the material flow in different areas. In order to combine the controlled variable (material flow) and the control variable (lokal blank holder force) a fuzzy logic controller was designed. The performance of the material flow control was investigated by generating disturbances (e.g. a high blank holder force at the beginning) in the deep drawing process. This procedure shows that the fuzzy-controlled material flow can be compensated for the disturbances by means of changing the blank holder force.

Aluminum alloys, due to their low density compared to steels, are an important group of materials, in particular for light weight construction of transport vehicles. However, aside from their low specific weight, drawing of car body components made from aluminum alloys is limited by an inferior formability. To enable a modern car body design, it is necessary to enhance the formability of aluminum sheet metal. One basic approach to reach this aim is to adapt the mechanical properties of the blank for the drawing process. The general idea is to soften the deformation zone relative to the force transferring zone, which results in an improved material flow and thus to larger drawing depths. In this paper the process sequence consisting of local induction heat treatment followed by deep drawing of precipitation hardenable aluminum alloy is presented. Using an induction system, it is possible to change the mechanical properties of the 6xxx aluminum blanks in a restricted area by influencing the precipitation structure. Tensile tests characterize the conversion from the stable naturally aged condition T4 to reversible solution heat treated W conditions of AA6016 as function of temperature and time. This effect leads to a reduction of flow stress, which is used to design an material property distribution adapted for the subsequent deep drawing process. A process characterization study provides detailed information concerning induction heating parameters, to improve the deep drawing of cylindrical cups, which results in a decisive increase of the limiting drawing ratio. Accompanying the experimental investigations, a finite element analysis approach is realized as a process design and optimization tool. Following the presented strategy, it is possible to enhance the forming capability of aluminum alloys. This leads to advanced manufacturing processes, which extend the field of applications for aluminum car body parts.

Numerical simulation conducted by Finite Element Method is one of the most powerful tools for analyzing metal forming processes. Among them, Hydromechanical Deep Drawing (HDD) is, probably, the process which has gained the major interest in industries in the last few years. In this paper a numerical study of HDD of a can box is presented. The influence of geometrical features of a pressure chamber in terms of the gap with the punch is discussed, together with the main process parameters, such as counter-pressure and Blank Holder Force (BHF). The pressure path was found to be the key parameter for a successful HDD. The pressure, in fact, has to be increased very quickly in the first part of the process in order to obtain a minimum friction between the blank and the die entrance radius. The BHF is determined by the pressure path and so a simple way for understanding the correct force was developed. The results are presented in terms of thinning and wrinkles of the final product. Thickness was found to decrease in the first half of the simulation and then it remains constant; wrinkles take place in the last steps of the simulation and they depend on the BHF and on sheet metal anisotropy. The FEM commercial code Pam Stamp 2000 with Aquadraw function was utilized.

Tube hydroforming is an advanced technology for the manufacturing of lightweight components with complex shape. The forming results can be usually improved if axial feeding at the tube ends is enabled. For very long parts, however, due to the high friction forces acting at high pressure in the feeding zone between tube and die, no material movement towards the expansion area occurs. The tube is only upset in the feeding zone, no compressive stresses take place in the expansion area and the forming results are not satisfactory. This can be avoided by eliminating friction and by inducing additional tangential stresses in axial direction on the tube surface of the feeding area. This paper presents the investigations performed in this direction by using a high viscous fluid flowing along the internal and external surface of the tube. The flow helps to reduce the friction force and allows the sliding between the tube and the tool surface. Experimental tests of tube upsetting under pressure will show the effects of the medium flow on the thickening of the tube wall. Not only increased sliding and homogeneous thickening will be obtained, but even an increase of the wall thickness in the area close to the expansion zone will be shown. This effect is even stronger when the yield stress in the expansion zone is reduced by means of a previous local heat treatment.

During forming of non-rotationally symmetric sheet metal parts at high pressures nonuniform deformation conditions arise in the flange area. These deformations vary in height and consequently lead to heterogeneous sheet thickness distributions. When using semi-rigid tools, high clamping forces are necessary in order to compensate for the developing sheet thickness variations in the flange area and to avoid leakages of the system or wrinkling. Moreover, the heterogeneous distribution of the clamping force is strengthened by press inaccuracies. This results in a higher surface pressure distribution on one side of the flange and finally in a non-uniform material flow out of the flange area. The development of a segmented active-elastic blank holder enables an active material flow control of the flange movement during sheet metal forming at high pressures. The local elasticity of the active-elastic blank holder is based on an optimized layout of the local tool rigidity. For this purpose, different grooves were integrated below the blank holder surface. This paper provides an overview of the developed technology, advantages with regard to the part’s quality, and recent results comparing the production of non-rotationally symmetric parts with segmented active-elastic tools vs. semi-rigid tools.

The shortening of process chains and the combination of innovative manufacturing technologies offer the possibility to enhance the complexity of technical products. The presented work describes the development of a process chain for the manufacturing of complex hollow parts out of double sheets and tubes with a big variation of the cross section, e.g. for A-pillars in the automotive sector. Two blanks and a tube are inserted in a hydroforming tool by a handling robot. The processes forming of blanks and tubes as well as joining by clinching are integrated in this tool. After these steps, the handling robot places the part in a laser station, where integrated laser welding and cutting processes take place. This paper focuses on special solutions developed both in the hydroforming and in the laser processing. In particular, the connection between blanks and tube is extremely problematic with regard to the sealing in the hydroforming process and the welding operations due to an existing gap. The requested tightness is reached by reinforcing the tube in the connection area with a ring insert, by placing sealing profiles on the outer surface of the tube and particularly by adding a sealing medium to the hydroforming fluid. In laser operations, special challenges result from complex welding and cutting paths, contaminations of the blanks with hydroforming media and lubricants, gaps between the blanks that occur due to residual stresses after forming and burr formation.

Although not standard, Forming Limit Diagrams, FLD’s, are used throughout the automotive industry as a preliminary tool to determine if a sheet metal forming process is capable of forming a good part. FLD’s show a limited range of strains on the diagram; typically the range is 0 to 1 on the major strain axis. A new rapid prototyping process called Single Pont Incremental Forming, SPIF, experiences strains over 3. As FLD’s do not typically cover that level of strain, a new method for developing FLD’s is needed. Such a method is proposed in this paper. Research has been conducted with five different shapes, formed using Single Point Incremental Forming. The part shapes utilized contain the most common combinations of angles and curves observed in formed sheet metal products. The strains encountered in forming each of these parts are measured and the strain data is then plotted on the same FLD. These new FLD’s can then be utilized as a predictive tool for engineers to determine if their design can be produced using the SPIF process.

The aim of the research presented in this paper is to investigate the feasibility of generating 3D features in sheet metal blanks using laser forming techniques. Aiming for systematic process planning and a good process control capability, only the temperature gradient mechanism is considered for this purpose. The research has been performed on a 6 kW CO2 laser CNC platform. In a first part, bending along curved lines and bending close to edges are investigated. In a second part, these findings are applied for the creation of a louver. A dimensional measurement system is used for analyzing the geometric dimensional characteristics of the formed shapes. It is found that louvers can be made as a local 3D feature in a sheet metal blank. Based on these initial results, it can be concluded that form features, which are traditionally generated by means of form tools on a punching machine, can to some extend also be obtained by means of industrial lasers, widening the application range of these machine tools.

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.

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.

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.

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.

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.

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.

Due to the high complexity and the large number of possible geometries to be formed, a systematic design of the sheet metal spinning process is, up to now, difficult and time consuming. Sustainable models of the spinning process do not exist so far. Due to this, a new approach for the systematic design and optimization of the spinning process has been developed. In a first step of the planning sequence, a prediction of initial parameter settings is given by a case-based-reasoning approach. A first adaptation of the pre-selected parameters is then realized on a fuzzy-based model. In the next step, a model based optimization using statistical design of experiments is performed. For this, a new statistical approach has been developed being optimized regarding the requirements of the spinning process. In this paper, the methods used and the implementation of the approach in a process planning software are described. The approach is verified by the example of setting up a process to manufacture a cylindrical model workpiece.

Sheet Incremental Forming (SIF) is a modern technique that deforms the sheet on a positive or negative die using a simple punch mounted on a general purpose CNC machine. Several working parameters (tool path, spiral width and tool depth) have been studied in previous papers [1, 2] analyzing their influence on a simple part when working AISI 304 or Cu DHP sheets. The main problem was to study the process feasibility, that is, the possibility of correctly deforming the pieces without breaking them. The research reported here has been focused mainly on other two important variables, studying their influence on the final part quality: the punch diameter and its velocity when deforming the sheet. Surface roughness and minimum thickness of the deformed sheet have been chosen as parameters for analyzing and evaluating the process efficiency. In FEM analysis, a simulation model was developed and implemented considering Cu DHP sheet. The comparison with experimental results was used to validate the simulation model and to identify the most suitable simulation parameter values (friction coefficient between various elements and blank holder force). The developed and validated model can be used for studying the process optimization. The results obtained in this paper can also be used as guidelines for the correct design of Sheet Incremental Forming process.

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.

The manufacturing technique of driving is one of the oldest procedures for sheet metal forming and has been used in the ancient world for the production of copper pots and vases. This technique is still utilized for niche applications but today has lost its importance. The process of driving is almost completely carried out manually and thus is only appropriate for very small quantities or in case of failure of other production processes. Since individualization of products is strongly gaining in significance, forming processes have to be found, which are independent from expensive tools and equipment. Using driving as the process of choice to form sheet metal, the grade of automation of the forming process has to be increased. Numerically controlled driving, i.e. automated positioning and handling of the work piece during the production process, will need a conclusive simulation base. This paper provides results of the analysis of sheet steel angles formed by the driving sub groups of shrinking and stretching.

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.

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.

In this paper a measuring system that allows an automatic detection of waviness and form errors in sheet metal parts is introduced. The system is based on a stripe projection method using a high resolution line scan camera. Particular focus is put on achieving a short measuring time and a high resolution in depth, aiming at a reliable automatic recognition of dents and waviness of 10 µm on large curved surfaces of approximately 1 m width. On smoothly curved surfaces a spatial frequency analysis is used to detect dents. By combining this spatial frequency analysis with a CAD model, more complex parts can be inspected, too. Using an objective 100% inspection of all parts, a quality improvement can be achieved by controlling the forming process.

Tribological aspects strongly influence the deep drawing behaviour of sheet metal, being responsible for both the punch force and the material draw-in from the flange. Recent developments in lubrication technology have shown that dry film lubricants can be a good alternative to conventional fluid lubricants in case of aluminium sheets. Their main advantages are the homogeneous distribution on the blank surface, the good adhesion to the surface and the possibility of applying it already in the rolling mill. In order to introduce this technology in series production also for steel sheets more knowledge concerning the influence of the lubricant amount on the drawing forces is needed. A further important aspect to be considered is the surface quality of the steel grades and its interactions with the dry lubricant. In this paper four steel grades with different mechanical and/or surface properties are considered. After a microscopical and topographical investigation of the surface the materials were tested in a cup drawing test after applying two different amounts of the dry film lubricant Drylube E1. Further process parameters which were varied are the blank holder force FN and the drawing ration b. In this way, information about the influence of the lubricant amount on both the drawing force and on the maximum blank holder force FZ could be obtained for three different values of b. The experimental results have shown how a strong decrease of the lubricant amount (from 1.0 down to 0.5 g/m2) causes, at a given drawing ratio, only a small increase in the maximum drawing force as well as a small increase in the maximum blank holder force.

In the paper the thermal characterization of friction stir welding processes (FSW) of aluminium alloys is presented. In particular both embedded thermocouples and a thermography analysis were utilized in order to acquire the temperature vs. time curves in point of interests of the joints and the temperature distributions, respectively. Such kind of results are very important in order to investigate the material conditions during the FSW process.

In the paper the results of a wide experimental activity on friction stir welding (FSW) of aluminum alloys are reported. In particular the butt joints of two different materials, namely AA1050-O and AA6082-T6 were considered. Grains dimensions and precipitates density were investigated both in the parent materials and after the welding processes. Furthermore post-welding heat treatments effects on the joint strength were studied.

The multifarious applications of aluminum alloys in different industrial domains are based on the mechanical properties as well as the light weight characteristics, which allow energy saving for the products in use. Nevertheless aluminum alloys are considered to be difficult to weld by conventional welding processes. This paper deals with cost-effective friction stir welding of thin sheet aluminum alloys in thicknesses of about 1 mm to widen the possible range of applications. Based on former studies results will be shown how an optimized tool geometry increases the mechanical properties of friction stir welded parts. The characteristics of these friction stir welded thin sheets will be analysed in a statistical evaluation in order to detect the interactions and dependencies of the process parameters. By highlighting the main process parameters and their significances a process window for friction stir welded blanks of AA5182 and AA6016 is presented.

For reasons of cost and weight, light gauge sheet is used wherever possible for metal fabrications. In sheet metal forming the process is to gather the metal into defined areas. The pulley forming process is no exception and is achieved by superimposing axial loads on top of radial loads using a pressure-controlled tailstock. Whilst the headstock-mounted tooling is fixed, that part held on the tailstock can be powered axially under controlled pressure. This pressure is governed by the width of the workpiece which changes during the forming process. Experiments have been designed to provide an understanding of the pulley forming process and to verify numerical models. The latter has been taken the form of finite element simulations to enable prediction of metal flow, tool forces and potential sources of defects and failures. There are three objectives for conducting the experiments which have been investigated in this paper: 1. providing data to define the movements of the forming tools for the finite element model, including displacements and velocities, 2. understanding the effects of the pulley forming operation on the flow of material, and 3. validating the finite element model.

Embossing is a well known method to improve the transverse rigidity of thin sheet metal plates. This paper deals with a special embossing method where bulges get embossed into the surface of a cranked workpiece by hydrostatic pressure. The base for describing the production process is the elementary bulge structuring process at which a bionic bulge pattern gets embossed into the surface of a cylindrical shell. This structure enables highest amount of stiffness. By FEMsimulations the main process parameters and the optimal dimensions of the bulges are ascertained. The identified bulge geometry is the base for the design of the structuring tool. In industrial applications the structuring process will be a rolling process with an elastomere coated pressure roll, followed by a rebending operation. The simulation of this complex process demands an analogous model based on a half shell, which is virtually straightened. Then the bending resistance of a so achieved bulge structured plate is calculated under a three-point-bending load. Using the same computing procedure a realistic automotive body part is investigated. The whole process combines CAD & FEM techniques in a new and efficient way.

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.

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.

Recent developments in infrared camera technology, testing methods and data processing algorithms have brought significant progress for high resolution spatial and temporal analysis of thermal radiation. Together with industry standard automation technology and specific infrared image data processing it became possible to non destructively inspect laser welded seams and other types of joints using heat flux analysis subsequent to thermal stimulation. High thermal diffusion coefficients of the usually metallic samples under test make the availability of high-speed infrared cameras as a key hardware component indispensable. Since high-speed infrared cameras with frame rates of at least 500 Hz have become available for commercial applications, non-destructive testing systems with a new class of performance were designed, manufactured, and implemented at industrial sites. Heat flux analysis as a new and robust method of non-destructive testing has been implemented for various types of equipment, ranging from off-line tools for laboratory use to automated robot based systems enabling fast and operator-free in-line inspection. Depending on environment, implementation surroundings, and geometry of objects to be inspected, different types of pulsed or continuous operating heat sources (e.g. flash light, laser, … ) are selected. Due to its outstanding industrial relevance non-destructive testing of laser welded seams in automobile manufacturing is shown in detail in this paper.

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.

Micro-metal forming technologies are mass production methods, net shape forming, low-cost procedures and quality controlled processes. Its scale region is in the range of the margin area between conventional precision manufacturing and silicon-based technology. The first paper to study the field of micro metal forming was written in 1989. Up to now, there have been many papers in this field but the results of the experiments do not reach the same conclusions. It should be noted that it is not possible to apply the know-how of conventional forming processes to the field of micro-metal forming due to the so-called size effects. In this study, two kinds of sheet materials such as C12000 and C26000 copper alloys are used to do a micro-upsetting experiment and micro-tensile experiment. It can be found that the size effects of micro-metal forming in C12000 agree with the description in previously published papers. However, the C26000 alloy has high matrix strength and significant fine grain strengthening that produce different size-effects of micro-metal forming. In this paper, we compare these two materials and suggest explanations for this problem. Therefore, the result can provide a general solution and discussion of micro-metal forming processes in unalloyed copper and brass.