Pre-bulging influence on an inverse drawn shape obtained with Hydromechanical Deep Drawing (HDD)

The HDD process performance and the quality of the formed parts can be influenced by many process variables, such as: fluid pressure, blankholder force, pre-bulging pressure, friction and punch speed [1]. Many studies report how pre-bulging characterization may be done in accordance with the fluid pressure variation [2] or with the maximum bulge height [3][4] value. In this paper, the authors use the maximum bulge height to characterize pre-bulging levels influence on the process feasibility. The effects of three different pre-bulging levels as well as the traditional geometric and process parameters on a specific component characterized by an inverse drawn shape have been analyzed. In the experimental phase, for each considered process condition the Thickness Reduction (TR) has been detected on the formed component in sixteen different points of interest, to verify numerical and experimental correlation. The good accuracy shown by the numerical model allowed to develop an appropriate numerical campaign to obtain an ANOVA analysis to evaluate the pre-bulging heights influence on TR distribution. The obtained results have shown that the pre-bulging height influences the TR distribution significantly but in a less way than punch radius and blankholder forces profile.