An influence of the die hollow radius on the loads and strain field in the direct extrusion

The extrusion loads as well as the strain and hydrostatic pressure distributions within the deformation zone are investigated in the paper. The distribution modes are influenced by the die geometry and, in this way, the material structure can be controlled. The objective of the present work is an analysis of an effect of the die hollow radius on the flow pattern during the direct extrusion. The effect of geometric shape of the die on the metal flow is presented. The experimental analysis was performed using axisymmetrical lead samples and a strong sensitivity of the flow pattern on the hollow radius was observed. The more uniform distribution of strains and mechanical properties in the extruded material was obtained when a die with the radius was applied. Opposite, the measurements show small influence of the die hollow radius on the extrusion loads. The finite element method (FEM) was used in the theoretical investigation of these problems. The results of calculations depend on the method of treatment of the shear zone. The best agreement between the measured and predicted loads was observed when the shear band was substituted by a tool surface and the friction force equal to the yield stress in shear was assumed at the contact surface in this region.