The Stress Concentration Produced in a Die During the Cold-Forging Process

Abstract

The lateral fracture in a cold-forging die appears to be caused by the stress concentration at the internal corner fillet of the die. An investigation on the stress concentration factor for an axisymmetrical die with a circular arc fillet and with or without an ejector hole is reported. A theoretical analysis is carried out two-dimensionally by assuming a mirror pattern of the vertical section of the die. The value of the stress concentration is calculated on the case of the die without an ejector hole loaded by a uniformly distributed internal pressure and with an ejector hole applied by a partially distributed load substituting for the effect of the ejector hole. The validity of the analysis is comfirmed by the experimental results using the three-dimensional photoelasticity. The value of the stress concentration factor depends largely on the diameter of the ejector hole as well as the fillet radius.