A Simplified 2D Model for Predicting Corner Failure in a Square Part

The traditional practice of setting up a new forming operation relies on years of experience and expensive die try-outs to gather the information for die design. Today's complete modeling of a 3D sheet metal forming can provide accurate information but is usually too time consuming. Currently, the time and cost effective method used in industries is to model the straight side of a 3D part as a plane strain problem and the corner section as an axisymmetric problem. Unfortunately, the axisymmetric solution often over-predicts the severity of the deformation at the corner and leads to a very conservative design. In an effort to improve the predictability of the simplified 2D model, an axisymmetric model with a center offset is proposed in this study. The proposed center offset is found to be a function of the center strains, failure height, and process parameters, which include tooling geometry, material properties, friction coefficient, and restraining force. Finite element analysis for both the 3D square box forming and the 2D axisymmetric model are utilized to verify the proposed concept and to define the function. Great improvements for the predictions of the failure heights are obtained. The simplified 2D models with a center offset proved to be a useful numerical tool that can provide accurate quantitative information for the designer to make decisions quickly on the manufacturability of the desired parts.