Numerical simulation of fine-blanking process using a mixed finite element method

In order to achieve a more intensive understanding of the forming mechanism of the fine-blanking process, a numerical simulation has been carried out by using a mixed displacement/pressure (u/p) finite element method. According to the special requirement of the fine-blanking technique, the major process attributes, such as the vee-ring, the ejector and the edge radii of tools, have been taken into account in the finite element model. The punch–die clearance was set to 0.5% of the thickness of the workpiece. To verify the effectiveness of the simulation, the equivalent strain on the sheared surface of a SS400 steel specimen has been determined experimentally. The experimental values of the equivalent strain have been estimated by measuring the relative displacements of the local grids pre-etched on the meridian plane of the specimen. The results of the finite element simulation are in proper agreement with the experimental findings. The distributions of the shear stress and the equivalent plastic strain have been computed for discussion. Moreover, a diagram of the blanking force versus the punch penetration has also been constructed. In order to investigate the fracture mechanism in the fine-blanking process, the concept of damage mechanics has been applied. By using a void growth model, the evolution of damage at different stages of the fine-blanking has been evaluated. It has been realized that the compressive hydrostatic stress built up by the fine-blanking fixture plays an important role to suppress the initiation of macrocracks.