Improvements in FE-analysis of real-life sheet metal forming

An overview will be presented of recent developments concerning the application and development of computer codes for numerical simulation of sheet metal forming processes. In this paper attention is paid to some strategies which are followed to improve the accuracy and to reduce the computation time of a finite element simulation. Special attention will be paid to the mathematical modeling of the material deformation and friction, and the effect of these models on the results of simulations. An equivalent drawbead model is developed which avoids a drastic increase of computation time without significant loss of accuracy. The real geometry of the drawbead is replaced by a line on the tool surface. When an element of the sheet metal passes this drawbead line an additional drawbead restraining force, lift force and a plastic strain are added to that element. A commonly used yield criterion for anisotropic plastic deformation is the Hill yield criterion. This description is not always sufficient to accurately describe the material behavior. This is due to the determination of material parameters by uni-axial tests only. A new yield criterion is proposed, which directly uses the experimental results at multi-axial stress states. The yield criterion is based on the pure shear point, the uni-axial point, the plane strain point and the equi-biaxial point.