Study on the Frictional Boundary Conditions at the Edge of a Tool-material Interface in Massive Forming : Prediction of the Deformation Characteristics by Slip-line Field Method and the Friction Testing Apparatus for Plane Strain Forging

Abstract

The influence of geometrical contact conditions at the edge of a tool-material interface on the frictional shearing stress in massive forming was investigated. The contact conditions were classified into three types : a) the die-surface extends beyond the edge of the workpiece, Edge-E_I ; b) the workpiece-surface extends beyond the edge of the die, Edge-E_II ; and c) the die and the workpiece surface continuously contact into each other at the edge, Edge-E_III. Based on slip-line or upper-bound analysis of the deformation, characteristics of the deformation and the frictional slip near the edges were shown. A frictional testing apparatus for the plane strain forging which measures the normal and frictional forces operating on a referring frictional plane between edges was made. By using this apparatus, aluminum blanks were forged at slow speed : 1 mm/min. It was shown that the frictional shearing stress was critically affected by the contact conditions.