Springback behavior and control strategy for dimensional accuracy of hydroformed tubular parts

Hydroformed tubular parts have been widely used in a variety of applications requiring high strength and high dimensional accuracy. However, the essence and strategy for controlling dimensional accuracy of the parts have not been given an in-depth investigation. In this paper, a strategy for compensating the springback of hydroformed tubular parts is proposed to improve their dimensional accuracy. It is believed that the parts have the highest dimensional accuracy when the expansion amount of die cavity is exactly equal to the springback of tubular part by controlling the internal pressure. The theoretical calculation formula of target pressure is firstly derived under the assumption of axisymmetric plane strain without considering the influence of clamping force. The proposed control strategy was then implemented experimentally to validate its feasibility. It is shown that the diameters of SAPH440 tubular parts increase linearly with increasing internal pressure from 60 to 240 MPa. After unloading and removing the tubular parts from die cavity, a certain springback will occur on the parts. When the internal pressure reaches the target pressure of 150 MPa, the diameter of final part is exactly equal to the target value. Moreover, due to the inevitable effect of clamping force in experiments, the target pressure in the experiment is lower than that from theoretical prediction. Finally, it is further proved by repeated experiments that the diameter deviation of tubular parts can be controlled accurately within range of [-0.05 mm, + 0.05 mm]. These results provide theoretical basis and technical support for precision manufacturing of key components for automobile and aerospace.