Hideo Tsutamori

Numerical Prediction of Springback Shape of Severely Bent Sheet Metal

In the sheet metal forming simulation, the shell element widely used is assumed as a plane stress state based on the Mindlin‐Reissner theory. Numerical prediction with the conventional shell element is not accurate when the bending radius is small compared to the sheet thickness. The main reason is because the strain and stress formulation of the conventional shell element does not fit the actual phenomenon. In order to predict precisely the springback of a bent sheet with a severe bend, a measurement method for through‐thickness strain has been proposed. The strain was formulated based on measurement results and calculation results from solid element. Through‐thickness stress distribution was formulated based on the equilibrium. The proposed shell element based on the formulations was newly introduced into the FEM code. The accuracy of this method’s prediction of the springback shape of two bent processes has been confirmed. As a result, it was found that the springback shape even in severe bending can b...

Surface evaluation method and stamping simulation for surface deflection of automotive outer panels

In designing dies of automotive outer panels, the most difficult process is to modify surface deflection. To fabricate high-quality outer panels without modifying dies, it is important to develop an evaluation method and a numerical analysis method for surface deflection of outer panels. In this study, we have developed a new evaluation method that uses the maximum value of curvature calculated using reflecting curves in the surface. This new evaluation method made the examiners evaluation to conform with the digital evaluation. The evaluation results with the new method shows better agreement with the sensory value than those with the conventional methods. We have proposed the new analysis method to predict surface deflection correctly. By the proposed simulation method, plastic deformation is calculated in consideration of stress in thickness direction, and restriking conditions have been examined. We have applied our methods to the fabrication of automotive outer panels, and verified that these are useful and practical.In designing dies of automotive outer panels, the most difficult process is to modify surface deflection. To fabricate high-quality outer panels without modifying dies, it is important to develop an evaluation method and a numerical analysis method for surface deflection of outer panels. In this study, we have developed a new evaluation method that uses the maximum value of curvature calculated using reflecting curves in the surface. This new evaluation method made the examiners evaluation to conform with the digital evaluation. The evaluation results with the new method shows better agreement with the sensory value than those with the conventional methods. We have proposed the new analysis method to predict surface deflection correctly. By the proposed simulation method, plastic deformation is calculated in consideration of stress in thickness direction, and restriking conditions have been examined. We have applied our methods to the fabrication of automotive outer panels, and verified that these are us...