Finite element analysis of the sheet metal forming processes considering continuous contact treatment

Abstract

In the simulation of the sheet metal forming processes, contact treatment between the tool and the sheet is one of the most important factors because the blank deforms mainly by a contact force. However, errors in the contact treatment of FE-Analysis are inevitable because of the discretization of the continuous sheet into the finite elements. Furthermore, as a contact state of each node in the elements can change immediately, convergence of analysis is dependent on a step size of numerical analysis. If meshes are generated finely, this sudden change of the contact nodes may not affect the result of the analysis severely. In this study, the continuous contact treatment for the mesh of the sheet metal is dealt with in order to improve the accuracy and convergence related to the sudden change of the contact state. The contact regions between the tool and the sheet change continuously in the real forming stage. Therefore, the smoothly changing contact region should be calculated from finite meshes. In the proposed contact treatment, the contact region and the penetration depth are calculated with an analytic surface modeled by NURBS based on the current nodes of the element. Contact pressure in relation with the penetration depth, geometry of the sheet and the material properties is evaluated at all integration points. This contact force proportional to the contact area is imposed as a nodal force on each node of the element. If all of the elements are considered by the scheme for continuous contact treatment, the calculation time becomes much slower. Because the check for contact and penetration is done by using the NURBS surface in this paper, it is clear that much more time for contact treatment is spent. From this reason, it is necessary that the elements which have higher possibility to contact with the die are chosen for the continuous contact treatment adaptively during finite element analysis. In this paper, the smoothness control factor is defined based o...