Dead zone formation in indirect extrusion of aluminum

Abstract

An upper bound analysis was made. The dead zone is formed either at extrusion ratios less than 10 for indirect extrusion with frictionless flat dies or independently of reduction under the sticking friction. The experimental data using lubricated dies do not necessarily agree with the prediction. It appears necessary to examine wheather the dead metal predicted from the upper bound approach is an entirely rigid body or not. There exists a region similar to the dead zone in front of the die face without lubrication in agreement with the prediction from the upper bound analysis. The region is an uncommon arciform-type and does not entirely remain stationary. Such a feature found in indirect extrusion without lubrication will increase the possibility that the oxide skin of the billet is forced to flow into the product and gives rise to the extrusion defect.