Experimental and Analytical Study of Drawbead Restraining Force for Sheet Metal Drawing Operations

Design of sheet metal drawing processes requires accurate information about the distribution of restraining forces, which is usually accomplished by a set of drawbeads positioned along the perimeter of the die cavity. This study is targeting bringing together the results of finite element analysis and experimental data in order to understand the most critical factors influencing the restraining force. The experimental study of the restraining force was performed using drawbead simulator tool installed into a tensile testing machine. Based upon the experimental results, it was observed that the restraining force of the given drawbead configuration is dependent upon the depth of bead penetration, friction between the drawbead surfaces as well as the clearance between the flanges of the drawbead simulator. This clearance is often adjusted during stamping operations to increase or decrease material inflow into the die cavity without any modification in the die. Numerical simulation was performed with Autoform software following the geometry of the experimental drawbead tools used in this study. Two different surface conditions were used in the experimental tools: surface treatment 1 and surface treatment 2. Based on performed numerical simulation, the observations were made that the sheet metal does not conform with beads geometry for larger clearances between the sheet and the beads as well as for smaller bead penetrations.