Abstract: 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.
Abstract: Ever since its invention, friction stir welding has been of great interest for the joining of light weight materials. Due to joining in the solid state, friction stir welding inheres characteristic advantages that are unmatched by conventional fusion welding techniques. At the Chair of Manufacturing Technology friction stir welding is employed to develop a process chain for the production of highly load adapted car body components out of aluminum sheet metal and aluminum foam sandwich (AFS) by tailored blanking. In contrast to friction stir welding other materials, special measures have to be taken, since AFS comprises a layered material structure out of two solid aluminum sheet metal cover layers and a powder metallurgically produced core layer. After welding, the tailored blank is subjected to forming, foaming and a final laser cutting process. High temperature capability of the weld seam must be assured, hence foaming of the powder metallurgic core layer requires temperatures of up to 95% of core layer-solidus temperature. Therefore not only mechanical properties are revealed, but also temperature capability is assessed by differential scanning calorimetry (DSC). Additionally the weld seams are tested during foaming by the use of special specimen geometry. Due to the high deformation and temperature while welding and foaming, the metallurgical structure at the weld seam undergoes some modifications, which are subject to metallographic
analysis and hardness testing. As an outlook, new material developments towards 6000 aluminum alloys as cover sheet materials will be discussed with regard to the process chain.
Abstract: 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.
Abstract: 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.
Abstract: The continuing miniaturization of production systems and products poses a challenge for metal forming technologies to produce precise small scale products with microscopic geometric details. Thin metal plates with channel structures are considered to be typical examples for microfluidic applications [1,2]. In this study the coining process of sheet metal to produce channel and rib structures is examined in terms of geometrical die parameters and tool design. For this reason extensive experimental series and numerical simulations have been realized and evaluated.
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.
Abstract: The quality of the part and the robustness of the process in stamp-forming of sheet
materials are determined by a number of variables. This study looks at the application of the stamping process to a Fibre-Metal Laminate (FML) material system and the effect of the process variables on the formability characteristics of these material systems. The effect of pre-heating temperature on the splitting and wrinkling behaviour has been investigated for two different FML systems. It has been found that different FML systems exhibit different failure modes.
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.
Abstract: In order to make magnesium sheets a competitive material alternative for highly
sophisticated light-weight constructions the complete process chain for their production has to be investigated. In laboratory scale new alloys, casting techniques and optimized rolling and heat treatment schedules have been developed. At the Institute for Metal Forming and Metal Forming Machine Tools (IFUM) the forming capacity of magnesium sheets has been investigated. Derived from the strict quality requirements of e.g. the automotive industry, testing methods concerning mechanical properties, corrosion resistance and surface quality have been developed. It has been shown that the controlled development of a suited microstructure is the key factor for ensuring the requested product properties. Together with research and manufacturing partners the results were transferred to industrial practice and a closed loop process chain for the production of high quality magnesium sheets has been established.
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.