A novel estimation of tearing limit in deep drawing process based on strain energy; experimental characterization and numerical validation

Abstract

Deep drawing is a forming process widely used in aerospace, military, automotive, and various industries. One of the essential useful parameters in the quality of deep-drawn products is blank holder force (BHF). By controlling BHF during the forming process, formability can be improved and it can reduce forming energy. Tearing is one of the most common and crucial defects in this process due to high radial stress in the cup’s wall, resulting in many limitations in this field. In this process, the BHF plays an indispensable role in causing tearing. Therefore, controlling BHF during the process would be inevitable to avoid tearing or even wrinkling. This study aims to calculate the tearing limit with new criteria in analytical dominating plasticity equations based on the slab method. The St14 sheet with 1 mm thickness and 200 mm diameter is used in this study. The maximum BHF in each stage of punch stroke with new criterion based on strain energy with three different frictional coefficients is calculated, compared, and verified with FEM simulation and experimental results. Analytical results with new criterion are also compared with previous procedures. Finally, it is realized that results related to energy criteria have a lot more similarity with FEM simulation and experimental results in comparison with the previous methods.