Media-Based Profile Shaping and Kinematic Bending in a Continuous Process Using a Graded Temperature Field

Media-based forming processes at elevated temperatures are increasingly used to form closed profiles. In this context, the material characterization faces new challenges with regard to e.g. failure prediction. In order to record the forming limits at elevated temperatures, the “Hot-Tube-Bulge-Test” is being investigated at the IUL. In this test, tubes are sealed on both sides, heated to a forming temperature Tγ, and isothermally formed up to bursting by an increasing internal pressure p (see Figure a). A DIC system is used to record the resulting strains, which are evaluated subsequently. In order to achieve different strain paths up to the crack and, thus, to achieve different failure stages, the experimental setup is superimposed by an axial displacement v. Due to the lack of standards for an evaluation, own failure criteria are defined. The resulting strain paths are not comparable with those of standardized tests (e.g. Nakajima), but apply to free forming under high internal pressure. An exemplary FLC for a ferritic stainless steel 1.4509 at 1000 °C is shown in Figure b.