Finite element analysis & Die profile optimisation for a cold forging process

Abstract

Throughout the world, almost every machine that moves requires the use of bolts in one form or another. Bolts, or Fasteners, are made in bolt making machines by a process of cold forming. At a particular stage in the bolt making process a Trim Die is used to form the familiar hexagonal head on the bolt. Hi-Life Tools based in Shannon together with the parent company SPS Technologies in the USA are the largest supplier of Trim Dies in the Western World. Customers of Hi-Life Tools reported erratic tool life compared to that achieved using competitors Trim Dies. The objective of this study was to reduce the likelihood of Trim Die failure by establishing an 'Optimum' Trim Die profile. To that end the investigations performed in this project had to provide a better understanding of the trimming process than was currently available. A combination of finite element techniques, experimental testing and evaluation was undertaken to assist the design process in achieving the 'optimum' Trim Die profile. An analysis of failed Trim Dies enabled the prediction of the most likely failure mechanism. The Trim Die fracture was induced by fatigue, which originated at surface defects on the coating, and assisted by hard carbide particle segregation inherent within the trim die material.