Cavity formation and enfolding defects in plane strain extrusions using a shaped punch

Summary

Expressions are obtained for a best upper bound to the load necessary to cause extrusion through square dies, under conditions of plane strain, using a punch face which is inclined to the axis of the extrusion container. The results are interpreted to suggest how for a given reduction that angle of punch face may be chosen which delays the onset of cavity deformation. The modes of deformation considered suggest the mechanism, whereby the oxide layers on the rear of a billet may become entrained down the centre of an extruded product.