Causes of Die Fracture in Automatic Multistage Cold-Forging of High-Strength Ball-Studs

Abstract

A thermoelastic finite-element method was applied to a geometrically simple ball-stud forging process to quantitatively examine the causes of longitudinal fractures in die inserts during cold forging. The same forging processes and die designs developed and empirically optimized for SCM435 alloy steel were used to make a geometrically equivalent ball-stud of the much higher strength alloy ESW105. A thermoelastic finite-element method for die structural analysis, coupled with a forging simulator, theoretically based on a rigid-plastic finite element method, was used to compare the two materials. The study showed that the longitudinal fractures in the die inserts were due to a non-optimized shrink fit value, which emphasizes the importance of optimal die design in the cold forging of high-strength materials.