Tube Press Hardening for Lightweight Design

Press hardening is an innovative technology being applied to meet the growing demands for both lightweight and crash performance qualities. To further increase the lightweight potential, closed profiles are being used. As a result, a method has been developed at the Fraunhofer Institute for Machine Tools and Forming Technology IWU which allows the integration of press hardening of tubes and closed profiles into the media-based forming process. Using this press hardening technology, the original material strength of 500 MPa can be increased to between 1200 and 1900 MPa, depending on the chosen material. The engineering of tube press hardening is more complex than other forming processes, specifically the time dependence in combination with heat management makes it difficult. Therefore the use of FEA is indispensible when dealing with aspects such as heat treatment, the forming process itself, the cooling caused by the gaseous forming media and the general heat management of the tooling. To control and improve the process and therefore the part quality and process reliability, all these factors and their dependencies have to be taken into account. In addition to 22MnB5, other manganese-boron alloyed steels and different heating strategies have been tested. Based on these experiments the process capability was successfully proven and technological limits were obtained. Current investigations are focused on realizing tailored properties thus creating areas with varied strength and ductility in a single part.