Electro-thermo-mechanical contact model for bulk metal forming under application of electrical resistance heating

Abstract

Tools and workpieces in bulk metal forming processes such as electro-assisted upsetting or hybridized solid forward extrusion are subjected to electrical and thermo-mechanical loads. Existing electric contact models like the one of Holm do not regard the complex electro-thermo-mechanical interactions in the contact area between tool components and workpiece. Based on experimental as well as numerical analyses, this work introduces a new electro-thermo-mechanical contact model that accounts for electro-thermo-mechanical load profiles. The load profiles consist of mechanical loads that are typical for bulk metal forming processes. Therefore, it allows accounting for the influence of surface smoothing and lubrication expulsion on electric and thermal contact parameters. Upsetting experiments were performed in order to analyze the influence of lubrication on surface smoothing. All experiments were executed using cylindrical Cf53 workpieces, which were shot peened and lubricated with BERUFORGE 190. Pressure-dependent surface characterization profiles were derived and implemented in the model. The elaborated model of the electro-thermo-mechanical contact is coupled with Abaqus Software by means of user-defined thermal and electrical contact behavior. The resistance heating experiments were performed on the same workpieces to experimentally define the heating time and reached temperature. The numerical simulations of the performed resistance heating tests are used to verify the thermo-electrical part of the model. The mechanical part of the model is validated by means of electro-assisted upsetting tests data reported in the literature.