MODELING DRAWBEADS IN SHEET-METAL FORMING

In this paper, we describe the numerical modelling of drawbead forces required to draw a sheet metal through a bead with a constant cross se ction. The model is formulated using an elasto-plastic large strains f inite element method combined with an improved numerical technique tak ing into account the contact and friction conditions, based on linear programming techniques and fixed point conditions. The numerical simul ations were carried out with various drawbead geometries and the resul ts are expressed in terms of drawing restraining force versus drawing movement, as a function of the drawbead geometry, gap conditions and f riction conditions. With this procedure it is also possible to determi ne the main deformation paths in the drawbead region where the bending strain predominates over the membrane strain. The results obtained ar e compared with experimental data and the agreement proves to be good. The calculated results can be used as a basis to obtain better approx imations of the drawbead constitutive equations to be used in general 3D FE simulation codes in cases where it is impossible to exactly dete rmine the drawbead geometry.