Numerical modelling of the material flow during extrusion of aluminium alloys and transverse weld formation

A comprehensive numerical model of the hot extrusion process for aluminium alloys has been developed and validated. Reflecting the complex thermomechanical changes effected in the alloys during extrusion, the model incorporated heat flow and plastic deformation during extrusion. This paper presents the overall numerical development of a hot extrusion process for AA3003 and validation of the numerical model, by comparison to industrial data. The plasticity module was developed using a commercial finite element package, DEFORM®, a 2-D transient Lagrangian model which couples the thermal and deformation phenomena and is able to predict the temperature, strain rate and strain distribution in the billet/extrudate at any position in the container and die. A new algorithm using MATLAB was also developed so that details of the material flow and formation of the transverse weld and how it is affected by the feeder geometry could be quantified. Validation of the DEFORM model and the MATLAB algorithm of the material flow against industrial data indicated that it gave excellent predictions of the pressure and temperature history during extrusion as well as material flow effects such as surface cladding as one billet is fed in after another through the die. The results indicated that the die feeder design has a significant effect on the transverse weld formation with tapered dies showing lower transverse weld lengths compared to regular feeder plates.