Tool Life in Solid Forward Extrusion

Abstract

Summary Tool life in bulk metal forming is limited both by wear and fracture. Due to the variation of life of Individual tools, the reliability of operation is low. For reducing tool costs a reduction of the absolute costs of tools as well as an increase of tool life should be achieved. Tool failure should either be avoided or it should be made predictable for reducing costs by Interrupted production. In cold extrusion, tool failure is often caused by fracture, especially in cases of complicated shapes of the workpieces. Until now, crack initiation and crack propagation (depending on the kind of heat treatment of the tool steel) systematically have not been studied. In the present work tool fracture in solid forward extrusion has been investigated. For this purpose mechanical properties of specimens of the tool steel were related to the tool life in extrusion tests under simulated production conditions. To understand the fracture behaviour due to fatigue, a fracture mechanics calculation was carried out using the weight-function method. The results of the investigation enable an estimation of tool life depending on the kind of heat treatment and hence, an optimized heat treatment for the special case of application.