Improving Fatigue Life Of Cold Forging Dies By Finite Element Analysis: A Case Study

Cold forging tools fail mainly due to loss of dimensions (as a result of abrasive wear and plastic deformation) and fatigue failure. Since tooling costs represent a considerable share of the total cost in forging processes, improving fatigue life is a crucial aspect in the design of forging tools. The present study aimed to improve the fatigue life of a specific cold forging tool currently employed in the mass production of an automotive part. The stresses in the die were evaluated by means of finite element simulations, which were able to predict both the crack nucleation spot and its propagation direction, as observed in the tools employed in the production line. There is compelling evidence in the literature that fatigue life of a die is influenced by the amount of interference fit (preloading) to which it is subjected. Therefore, a slight alteration in the preloading profile was proposed, and the finite element analysis was repeated. Numerical results predicted a change from 597 MPa to 170 MPa in the highest principal stress. The design modification was then implemented in the production line and the expected mean life increased from 17,563 to 71,323 parts produced per tool. Overall, the procedure herein described may serve as a valuable tool for the design of cold working tools less prone to fatigue failure.