Experimental and simulative applications of double sheet hydroforming

In the automotive field the sheet hydroforming technique is used to produce hoods, fender panels, panels and box-type elements like tanks or differential covers, but its limit is the high cycle time. As a consequence double sheet hydroforming can be a valid improvement for reducing the production time by 50%. The final part quality, in terms of dimensions, can be obtained in the subsequent process operations (i.e.: trimming) so as to calibrate the sheet which is not directly in contact with the die. This paper presents the comparison between simulative and experimental results of double sheet direct hydroforming. The FEM code used has already been validated when directly hydroforming the same single part (Ceretti et al., 2003). This was the starting point to implement a new simulation campaign coupled with new experimental tests. In this research three different sheet material combinations are considered in order to investigate their behaviour. The good agreement between simulative and experimental results is the confirmation of the well designed FEM model. The accuracy of the final part shapes means this type of hydroforming can be considered a valid alternative, with respect to the classical method, for obtaining, in one shot, components with a good finishing surface and with a consequent saving in the production time.