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Introduction of a full automated process for the production of automotive steel parts

: Behrens, B.-A.; Fischer, D.; Haller, B.; Rassili, A.; Klemm, H.; Flüß, A.; Walkin, B.; Karlsson, M.; Robelet, M.; Cucatto, A.

8th International Conference on Semi-Solid Processing of Alloys and Composites, S2P 2004. Proceedings : September 21 - 23, 2004, Limassol, Cyprus
Limassol, 2004
International Conference on Semi-Solid Processing of Alloys and Composites (S2P) <8, 2004, Limassol/Cyprus>
Conference Paper
Fraunhofer IKTS ()
Process automation; Thixoforming; Thixotools

Thixoforming or semi-solid-metal forming is a steadily growing alternative production technique to conventional processes such as casting or forging. The main advantages of this technique are the feasibility of production of complex part geometries in combination with a high dimensional accuracy (near net shape). Unlike for alloys with a low melting point - e.g. aluminum - the thixoforming of steel alloys causes still many technological problems that make an industrial application of this technique more difficult. For example, it is hard to find tool materials that withstand the thermal and thermo-shock stresses. Furthermore, the conduction of the whole process requires a high accuracy and reproducibility. In order to overcome these problems the thixoforging process chain is subject of research work at the IFUM. This paper gives an overview about the progress of setting-up a production line that shows the principle feasibility to establish the thixoforming technology for mass-production of industrial relevant parts. The thixotropic behavior of steel can only be obtained in a rather narrow temperature window at a temperature level between the solidus and liquidus temperature. In the introduced production line a computerized process control of the inductive heating process allows the precise setting of the desired temperature. This control system was developed on the basis of simulation and experimental work. In order to avoid oxidation and premature cooling of the parts the handling is done using ceramic transport containers with an inert gas atmosphere inside. Due to the low heat conductivity of the ceramic it is assured that the loss of temperature of the billet will be tolerable. The billet is placed automatically in a previously closed die and formed immediately. The path of the forming force is optimized in order to obtain a good die filling behavior and a pore-free microstructure. After the forming step the die opens and the thixoforged part is ejected and taken away also automatically. The die consists of a ceramic inlay that is armored with steel rings to enable the necessary mechanical rigidity. The die is fed with hot slugs in closed state and can be opened completely to eject the part. The tool concept allows the controlling of its heat balance by means of auxiliary heating and cooling devices. This is an important feature in order to avoid thermal cracking of the ceramic inlay of the die. All steps of the production chain are carried out and controlled automatically. This is a necessary requirement to achieve reproducible and predictable results.