An upper-bound analysis of a forging-extrusion process

Abstract

In many non-steady-state metalforming processes, such as closed-die forging, the deforming material must change its flow direction at various stages during the process. The complex flow mechanism makes the calculation of tool stresses and forming forces extremely difficult. This paper presents results obtained from an experimental and analytical investigation of a combined forging-extrusion process applied to an axisymmetric component. It was established that this forging-extrusion process consisted of three distinct stages. A number of upper-bound expressions were derived to account for: the energy required for plastic deformation; to overcome friction; and to account for shearing on surfaces of internal velocity discontinuities; during each stage. Very good agreement was achieved between predicted upper-bound values for the forging pressure ratio, P σ , and those determined experimentally.