Energy-efficiency increase through hybridization of solid forward extrusion with electrical resistance heating - Modeling the contact between electrodes and workpiece

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Focus of examination is the hybridized warm solid forward extrusion process developed at WZL. In this process the workpiece is heated during forming through resistance heating. Determined by the nature of the process local heating takes place in the area susceptible to inner chevron cracks. This results in a higher energy-efficiency compared to the conventional warm solid forward extrusion processes. As of now the effects within the hybridized warm solid forward extrusion causing increased energy-efficiency cannot be used industrially. There are two reasons for this. Firstly, due to complex superimposed electro-thermal-mechanical phenomena in the contact area between workpiece and punch as well as workpiece and counterpunch highly fluctuating heating-up times occur. These are greater than typical cold solid forward extrusion process times. Secondly, as for the tool-side of the contact area a burn-off is observed in the form of a changing surface roughness and a marginal mass loss. The burn-off reduces the tool lifetime. The high, fluctuating heating-up times as well as the burn-off result in a reduced process stability. This research aims at extensively explaining the electro-thermal-mechanical interactions within the contact system of punch, counter punch and workpiece. This knowledge enables the comprehensive derivation of a contact system with shorter heating-up times and reduced burn-off.