Investigation on improvement of limit drawing ratio in two-stage hydrodynamic deep drawing of cylindrical cups

One of the most important issues in deep drawing as an industrial process is achieving parts with good quality and a higher drawing ratio in less time. In this study, using a two-stage hydrodynamic deep drawing process, the maximum drawing ratio of copper cylindrical cups was investigated numerically and experimentally. The process was investigated based on the relationship between the drawing ratio and maximum pressure. By examining the critical thicknesses of the preformed and final cups and determining the desired maximum pressures, a high maximum drawing ratio of 3.62 was achieved. Then, using the ability of two-stage hydrodynamic die design, the process was performed by creating a reverse bulging in the preformed cup. By determining the desired values of the effective parameters, namely the height of the reverse bulging and the desired maximum pressure based on the critical thickness, the final cup with a high drawing ratio of 3.94 was produced. According to the results, although the normal process in two stages led to a high drawing ratio, the positive effect of using the reverse bulging led to increasing the maximum drawing ratio. Finally, the effect of the tip and inner radii of the primary punch in the reverse bulging method on the improvement of the cup thickness was studied and the desired values were determined.