An approach to sheet metal forming using discretization techniques

The automotive industry is very interested in sheet metal forming simulation using numerical techniques such as the finite element method. A cooperative research program between the Stamping Division of FIAT Auto and the Mechanics Department of the Politecnico di Torino was established with the aim of exploring the present possibilities of these techniques. This paper deals with the simulation of the deep forming of an axisymmetrical component, the axisymmetry being characterized by a double curvature profile, and is considered to be the first feasibility study. A sheet was modelled by fournode axisymmetric elements; the punch, the die and the blankholder were modelled by gap elements. The metal sheet was free to move along the punch and the die edges, with a continuous variation of the boundary conditions. The highly non‐linear problem requires an adequate description through the carefully considered use of the appropriate options of the MARC package (release K2). Moreover, some subroutines were written ad hoc to complete the discretization. Results are presented as strain and stress histories during the stamping process and as total forming force exerted by the punch to deform the sheet. In addition the spring‐back phase was considered in order to calculate the back deformation and the residual stress. Lastly, a comparison of the behaviour obtained with two different kinds of steel are reported.