Central bursting prediction in axisymmeric extrusion process through dies of any shape

In this paper, an upper bound analysis has been developed to model the axisymmetric extrusion process of a perfectly plastic material. A velocity field which it is valid for all possible die shapes is developed. This field permits the possible formation of a central burst during the extrusion process. The boundary at the entrance into the deformation zone is assumed to be an arbitrarily curved surface whilst the boundary at the exit is assumed to be a spherical surface. The shape of the boundary at the entrance is determined by minimising the extrusion pressure. The optimal streamlined die profiles which minimise the extrusion pressure and criteria curves for the central burst and the safe domains are presented for a wide range of process variables. It is shown that the optimal die profiles satisfy the conditions for prevention of central burst. The predictions based on the proposed criterion are in good agreement with the FEM simulation data and are in conformity with the results published.