Papers by Author: Andrea Otto

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: 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.