Loading path design of thin-walled aluminum alloy T-shaped tube hydroforming process based on the control of limit pressure

Due to the influence of pressure control precision, the actual pressure in hydroforming process for the tube is usually greater than the design pressure, which causes the fracture of tube. The loading path of T-shaped tube hydroforming process was designed based on the control of limit pressure. First, the limit pressure of tube P max was obtained by improving the internal pressure until the tube cracked in the T-shaped tube hydroforming process without the feeding and a theoretical model for predicting instantaneous pressure is developed. Second, the tube bulge height H max and the maximum feeding D max were explored through manual operation of feeding and pressure in hydroforming machine, in which the overflow pressure is set to P max by using an overflow valve; finally, the loading path of internal pressure and feeding was designed using the ladder growth and linear growth in T-shaped tube hydroforming experiment in which the maximum pressure, the maximum feeding, and the overflow pressure (equal to internal pressure) were set to P max , D max , and P max , respectively. The results show that the obtained limit pressure P max can avoid the overpressure of the tube and restrain the fracture of the tube through the action of the overflow valve. Meanwhile, the accuracy of the prediction model to figure up P max was verified through experiments: the theoretical prediction value of the established model was consistent with the experimental true value. Compared with the T-shaped tube formed by linear loading path, the wall thickness of the formed T-shaped tube by ladder loading path is more evenly distributed without wrinkles and fractures and the height of the formed branch tube close to H max . At the same time, it is found that under the differential lubrication tube blank, the time of obtaining a suitable loading path is significantly reduced, and the collocation of ladder mode is simpler and more efficient.