Numerical constraint disposal for boundary friction in sheet metal forming

Based on the elastic–plastic large deformation incremental method and using the linear spring element, a constraint disposal method for the equivalent boundary friction in the global three-dimensional sheet metal forming is provided, which represents passivity of the boundary friction and ensures symmetry of the constrained stiffness matrix. Forming process of an automobile oil panel is simulated. The thickness distribution is found to be in good agreement with experimental result, at the same time the method in this paper is proved to be effective.