Fatigue Behavior of Cemented Carbide Die in Extrusion-Upsetting

Abstract

A series of experiments have been carried out using a former to investigate the fatigue behavior of cemented carbide die in the extrusion-upsetting process of a steel wire. The stress amplitude of the die in the process is controlled by changing the wall thickness of the die. The die stress generated by extrusion-upsetting is estimated by FEM simulation and verified through strain measurement using a strain gauge. It is found that a fatigue crack initiates around the inlet of extrusion approach where the tensile stress becomes maximum and the maximum shear stress is also large. It is also recognized that die life increases significantly with a decrease in tensile stress amplitude or maximum shear stress amplitude when the product shape is kept constant, as in the typical S-N curve obtained by the fatigue test. However when the stress state of the die is changed by changing the product shape, die life deviates from the curve when the product shape is kept constant. The fatigue behavior could be estimated well by using the maximum tensile strain amplitude instead of the maximum stress amplitude.