Numerical modeling of the multi-stage sheet pair hydroforming process

The need for reduction of the weight is an important issue in the sheet metal forming industry. The hydroforming process has become an effective manufacturing process, because it can be adapted to the manufacturing of complex structural components into a single body with high structural stiffness. Tube hydroforming has been successfully developed in industry such as in the manufacturing of the components of automotive vehicles. There still, however, remains the constraint of the geometrical shape that can be fabricated by tube hydroforming. In order to improve such a constraint in product shape of the tube hydroforming process and in the formability of conventional sheet metal forming, the hydroforming process of sheet metal has been studied. The sheet pair hydroforming process has been reported to have several important advantages compared with the conventional deep drawing process. Uniform deformation over the whole region is a main advantage in the sheet hydroforming process. However, the deformation of the sheet metal can be concentrated on a small region in the case of rectangular cup with a steep slope in the wall. In this paper, the multi-stage hydroforming process of a sheet pair is proposed in order to increase the formability of a structural parts having a shape like that of an oil pan. For the strict comparison of the proposed process, the blank holding force is controlled by a hydraulic valve to a constant value during deformation. The deformed shape and strain distribution of the manufactured parts with the proposed process are compared with the results of simulation. (C) 2004 Elsevier B.V. All rights reserved.