Numerical and Experimental Investigations on the Service Life Estimation for Hot-Forging Dies

摘要

Hot forging dies are exposed during service to a combination of cyclic thermomechanical, tribological and chemical loads. Besides abrasive and adhesive wear on the die surface, fatigue crack initiation with subsequent fracture is one of the most frequent causes of failure. In order to extend the tool life, the finite element method (FEM) may serve as a means for process design and process optimisation. So far the FEM based estimation of the production cycles until initial cracking is limited as tool material behaviour due to repeated loading is not captured with the required accuracy. Material models which are able to account for cyclic effects are not verified for the fatigue life predictions of forging dies. Furthermore fatigue properties from strain controlled fatigue tests of relevant hot work steels are to date not available to allow for a close-to-reality fatigue life prediction. An industrial forging process, where clear fatigue crack initiation has been observed is considered for a fatigue analysis. For this purpose the relevant tool component is modelled with elasto-plastic material behaviour. The predicted sites, where crack initiation occurs, agree with the ones observed on the real die component.