Durability-based design for endurance strength of hydroforming tools

Hydroforming tools must be designed fatigue resistant because in case of tool rupture high costs for repair and production downtime occur. Available guidelines for lifetime estimation of cyclically loaded parts usually are of general nature. In order to examine their applicability to the special concerns of hydroforming tools, stress states occuring during operation were investigated by means of numerical simulation. Basing on the results, specimen geometries were developed, representing a typical stress state. The estimated durability was calculated using the "FKM-guideline". The real durability was determined experimentally in form of Wohler-graphs. Eventually calculation and experiments were compared. Hence, the qualtity of the lifetime prediction was evaluated and correction factors were proposed.