Fatigue Analysis of Stripper Bolt Under Combined Loading for Improvement of Stamping Die Design

Abstract

A common problem of fatigue failure of stamping dies was experienced during the stamping operation with socket-head screws. In order to establish a design standard for the stripper bolt, a methodology for determination of the loads and the fatigue strength of the stripper bolt was developed. Stresses due to an impulsive load and a rectangular pulse were calculated based on a simplified spring mass system and the appropriate corrections were made to elaborate the solution. This approximate solution was validated by a finite element analysis. The stripper bolt should have an infinite fatigue life to survive a half million stamping operations. The fatigue problem involves a stress concentration with combined mean and alternating stresses. The Gerber parabola and the residual stress method were employed to treat the combined loading and the stress concentration. In order to enhance the fatigue life of the stripper bolt, a cushion is introduced at the surface where an impact load is applied. The cushion is found very effective in improving the fatigue life of the stripper bolt. An interactive computer program was developed as a tool for designing stamping dies.