Theoretical and experimental investigations on press hardening of tubes by hot metal gas forming
In various projects the process combination of hot metal gas forming and press hardening of different component geometries (including axle, camshaft or a crash box) as well materials (LH800®, 22MnB5, 34MnB5, MW1000L, C45) was researched at the Fraunhofer IWU Chemnitz. It was possible to achieve comparatively large deformation rates together with tensile strengths up to 1,900 N/mm² and minimal geometry deviations. Using an innovative tool technology, both the feasibility of the hot metal gas forming and the manufacturability of components with tailored properties could be proven. Adapted measuring equipment allowed for the reliable recording of the tool, component and active medium temperature from the moment the component was inserted up to the time of ist removal. Using a DOE (Design of Experiments) approach, the effect of a designed set of input variables (tool temperature, pressure build-up rate, maximum internal pressure, furnace temperature) with respect to a set of relevant output variables (hardness, component radii, component failure) was determined. Starting from these experimental results, a mathematical model was developed and validated, describing the functional relationship among the above listed variables. The results showed that the method of temperature controlled internal high pressure forming with integrated press hardening, on a laboratory scale, had good process and geometric repeatability (i.e. strength, geometry, deformation). The studied part geometries combined with different materials have extensive potential for series production applications in the automotive and in other industries.