Finite element method simulation of internal defects in billet-to-billet extrusion

During billet-to-billet extrusion of aluminium alloys, internal defects occur at the location where the billets are welded together. These defects are unacceptable and must be cut out from the extruded section. Hence, the efficiency of this process significantly depends on the length of these internal defects. The defects that arise inside the extruded section are the so-called back-end defect, which occurs as a result of inflow of the lateral billet surface contaminated with oxide into the extrudate, and transverse welds, which occur as a result of inflow of the face surfaces of the billets pressed together. The length of these defects depends on different process parameters such as friction, billet temperature, geometry of the tools, geometry of the extrudate, etc. In this study, finite element method (FEM) simulation is done to quantify the main parameters influencing the back-end defect and transverse weld formation. The first part of this work deals with modelling techniques that have to be developed to obtain information about the length of internal defects in extruded products from FEM simulation. Comparison is done between the simulation results and experimental studies to verify the results obtained from finite element analysis. In the second part of this work, the model is used to determine the main parameters influencing the back-end defect and the length of transverse welds in a computational investigation.