BHF Control Algorithm with the Design Sensitivity Analysis for the improvement of the Deep Drawn Product

Abstract

Direct determination of the variable blank holding force (BHF) is carried out with the process optimization. The scheme incorporates an elasto-plastic finite element method for calculation of the final shape and state variables such as the stress and strain. The optimization scheme adopts a sensitivity analysis scheme using a direct differentiation method in order to seek for the optimum BHF. A new control algorithm of the variable BHF is proposed in order to improve the maximum cup height in a cylindrical cup drawing process with the large drawing ratio and to reduce the amount of spingback in a U draw-bending process. The trajectory of the major strain is controlled by minimizing the objective function related with the strain distribution and the wrinkle generation is prevented by inspecting the abrupt movement of the blank holder in the cylindrical cup drawing process. The amount of springback is minimized by controlling the stress distribution along the sheet thickne! ss direction. Results demonstrate that the proposed algorithm fixes troubles which often occur in the conventional sheet metal forming process.