The strain path and forming limit analysis of the lubricated sheet metal forming process

Few previous attempts have been made to analyze numerically the strain path and the forming limit in complex lubricated sheet metal forming. Since usual approaches of solving the lubrication model are limited to axisymmetric and plane strain cases only, this paper developed a unified procedure for combining the finite element code of sheet metal forming, the current lubrication/friction model and forming limit theory, to predict the strain path and fracture strains for either a steady or an unsteady three-dimensional process including both axisymmetric and plane strain cases. The availability of the method must be proved by a published problem, and an axisymmetric stretch forming process was therefore adopted as a benchmark. Numerical results showed that the present analysis provides good agreement with the experimental data of the strain path and the fracture strain for various tribological parameters such as lubricant viscosity and composite roughness of tooling and workpiece, and the advantage of the developed model is that it can be applied to solve the complicated 3D geometric problems.