Analysis of forming limits in metal forming processes

Forming limit plays a very important role in metal forming processes since it can be used to predict whether a blank will fracture or not. This paper examines the influence on forming limit of blank and fractured thickness. The fractured thickness of a specimen in the simple tension test is adopted as the fracture criterion of the forming limit, and is applied as fracture criterion in the FEM code. The model was based on the updated Lagrangian formulation, Prandtl-Reuss flow rule, and Hill's yield criterion. In the course of analysis, if blank thickness is equal to fractured thickness, it is considered that the forming limit of the blank has been reached. This paper has analyzed the square cup drawing process and the elliptical hole-flanging process, and calculated the forming limit ratio for each process. In addition, tools were designed to perform experiments for each process. Simulations and experiments were performed with varying processes and consistent results were obtained.