An upper bound solution for twist extrusion process

Abstract

Twist extrusion, a promising severe plastic deformation technique for grain refinement down to ultrafine/nanocrystalline microstructures, was introduced as an attempt to provide large plastic deformation conditions similar to those in high pressure torsion while allowing large workpiece dimensions for industrial applications. As a relatively new severe plastic deformation technique, twist extrusion requires in-depth investigation of its plastic deformation characteristics. In this study, the twist extrusion process with a square shape die cavity has been analyzed using an upper bound solution to estimate the required power, deformation pattern, and optimum process condition. The analysis has been performed based on two kinematically admissible velocity fields while the effects of friction condition, die geometry, and mean equivalent strain have been considered. The results indicate that the die geometry and process parameters can dramatically change the deformation pattern and extrusion power.