On the mechanism of formation of back-end defects in the extrusion process

Abstract

FEM-analysis is applied to study metal flow in aluminum extrusion with focus on how material flow defects form when the last part of the billet is extruded through an axisymmetric die. First, an overview is given of the current state of art of knowledge regarding formation of typical rear-end defects in metal extrusion. Afterwards the software DEFORM is used to model the extrusion process. It is shown how this software describes the inflow of inferior material from the outer surface and subsurface of the billet, into the core of the rear-end of the billet during the extrusion stroke. Special attention is paid on trying to understand the mechanism of formation of common defects like the funnel defect and the coring defect in the extrusion process.