Study on hydroforming of aluminum alloy thin-wall curved parts based on upper layer sheet and numerical simulation

For large curved thin-walled parts, the introduction of double-layer sheet hydroforming process can obviously inhibit the defects, such as wrinkling and cracking. In this paper, 6061-T6 thin-walled semi-ellipsoidal parts are taken as the research object. Firstly, the coefficient fitting method of Fields-Backofen constitutive equation at high temperature is optimized. Secondly, the influence of upper sheet with different strength and liquid chamber loading path on the formability of parts is analyzed. At the same time, the pre-bulging process with a pressure value of 6 MPa was selected to improve the wall thickness reduction rate of the punch contact area. Through the response surface method, the interaction among the circumferential pressure, the friction coefficient between the sheets, and the thickness of the upper sheet was studied. The optimal process parameters of the part forming were predicted by the existing data, and the prediction accuracy was verified by numerical simulation. On the basis of the optimal process parameters, it is found that the parts have good forming performance at 150 °C, and the simulation results are verified by experiments.