Granular medium-based tube press hardening

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Using granular materials as forming medium enables the press hardening process for tubes and profiles. However, granular material is a conglomeration of macroscopic particles unlike a fluid medium that possesses hydrostatic properties. The aim of this thesis is to investigate the physical concept of this new metal forming process, work out and extend the process limit. First, the performance of granular material as working medium and the principle of choosing appropriate granular material is identified. A calibration procedure for the material model of granular material is introduced based on the characterization strategy of using instrumented die compaction tests and high-pressure direct shear tests. The flow behavior of 22MnB5 material, which is essential for process numerical modelling, is characterized by a self-designed hot tensile test. For a better understanding of the pressure transferring mechanism, an analytical model is developed. A fully-coupled thermal-mechanical FE model of granular medium-based tube press hardening is established. Press hardening experiments for a T-shape 22MnB5 tube using granular material as forming medium are carried out. In order to specify the process limit of using granular materials as forming medium, axisymmetric tube press hardening experiments are designed and conducted as an example to define the process windows by FE simulation and experimental investigations. This thesis establishes the required fundamental knowledge for an innovative granular medium-based tube press hardening process. Also, an alternative process of passive forming is proposed. The potential of producing high strength and high stiffness components offers the applications of lightweight construction in the automotive industry.