Linear flow splitting is a multi-station sheet-bulk metal forming process which allows continuous production of bifurcated profiles without joining, lamination or external heating of sheet metal. This process induces high hydrostatic stresses in the forming zone which leads to an elevated formability of the workpiece material. The aim of this research is to bend linear flow split profiles in transverse direction in a continuous manner. This is achieved by combining the linear flow splitting process with a continuous bending process. An analytical and a numerical model are described in this paper which predict bending moments for different radii. Results from both models are validated with experimental results. It is found that combining the linear flow splitting with a bending process leads to a severe reduction in the bending moments due to superposition of stresses in the forming zone. The superposition maintains the cross sectional shape of the bent profiles.
Linear flow splitting enables the production of bifurcated profiles out of sheet metal. Included in the Collaborative Research Centre (SFB) 666 the new roll forming procedure uses obtuse angled splitting rolls and supporting rolls to increase the surface of the band edge. High hydrostatic stresses in the deformed zone lead to an elevated formability of the high strength steel ZStE 500. As a result of the process, the flanges consist partially of an UltraFine-Grain microstructure (UFG). Produced parts are characterized by increased stiffness and high surface hardness. The new structure influences the formability in an extensive way. The investigations presented in this paper discuss the further processing of the flanges from linear flow split profiles. Therefore three point bending tests and roll forming experiments are carried out. A finite element analysis to characterize the damage is set up as well.
For the purpose of numerically simulating metal forming processes, material data are necessary, determined by testing procedures similar to the particular process. The new technology of hot tube bulge tests has been introduced recently, fulfilling the requirements of material data determination for hot hydroforming. Based on measurement data gained by this technology, selected constitutive relations for approximating the flow stress depending on temperature, strain rate and logarithmic strain were parameterized applying linear regression analysis. Using the material law with the best approximation quality among the regarded equations, a numerical simulation of an exemplary forming process was accomplished. A comparison between the experimentally obtained geometry after a hot hydroforming process and the prediction by numerical analysis is used for evaluating the quality and applicability of the determined material data for this kind of process. Additionally, a process simulation, using extrapolated material data from compression tests is presented to visualize the influence of the testing procedure on the resulting part geometry prediction.
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