Fundamental aspects for the evaluation of the fatigue behaviour of cold forging tools

The service life of cold forging tools is mainly limited by high-cycle fatigue (HCF). The prediction of the expectable tool life is an essential precondition for an optimisation of the tool resistance against fatigue and the evaluation of optimisation measures during early design stages. In this context, the numerical process simulation (primarily the finite element method) enables the calculation of the load conditions at the critical tool areas. Nevertheless, many investigations show that numerous fundamental aspects must be taken into consideration to obtain calculated lifetime values with sufficient accuracy. One goal of this publication is to discuss aspects concerning the finite element models and the evaluation of several influences concerning the lifetime calculation. Finally, a close connection between the fatigue strength of powder-metallurgical tool steels and the size of the stressed volume has been quantified based on four-point bending tests. In the framework of the investigations presented, these results have been applied to carry out an advanced volume-dependent lifetime calculation.