Study of Process Window in Square Cup Hydromechanical Deep Drawing of Aluminium/Steel Double Layer Sheet

In hydromechanical deep drawing process, the traditional matrix is replaced by pressurized fluid, and the final shape is determined based on the shape of a rigid punch. It is required to change the fluid pressure within the allowed working zone during the process to prevent the workpiece from rupturing and wrinkling,. Working zone curve represents the range of maximum available drawing ratios without rupture under the highest chamber pressure. In this paper, hydromechanical deep drawing of square cups made of aluminum-steel double layer sheets are studied by experiments and finite element simulations. In order to detect the rupture onset in simulations, experimental forming limit diagrams were obtained using for aluminum/steel double layer sheet. Experimental data were used to validate the finite element model. The effects of process parameters such as thickness of the various layers, prebulge pressure, chamber pressure and the friction coefficient were investigated on the working zone and the process window. The numerical results show that an optimum amount for the drawing ratio exists for each prebulge pressure. Also, with increasing the chamber pressure, shrinkage is reduced on the flange area. With increasing the friction between the sheet and matrix or the sheet and blank-holder, working zone becomes smaller; while with increasing the friction between the sheet and the punch it becomes larger. Experiments were performed for different drawing ratios to evaluate the numerical results, in which a good agreement was observed.