ASYMPTOTIC ANALYSIS OF EXTRUSION PROCESS THROUGH TAPERING DIE

This paper studies the axisymmetrical extrusion process of metal mater ials with or without initial porosity through tapering die. The fully dense metal is considered to be rigid-perfectly-plastic, which also ob eys von Mises yield criterion. Gurson's plasticity model is used to si mulate the constitutive behaviour of the porous metal. Friction forces at the die-workpiece interface are taken into account by using Coulom b's law of friction. An asymptotic method, i.e. the regular perturbati on method, is employed to carry out the investigation. To this end, th e die is assumed to taper slowly down the processing axis. Perturbed e xpressions of the velocity components, stress components and porosity are deduced. Finally, numerical results of these variables in the mate rial workpiece are presented.