Effect of stress distribution on springback in hydroforming process

Stress of sheet metal forming was analyzed by using the Hill theory, and the moment formula about bending shallow part was derived in sheet hydroforming. The offset distance in the stamping direction is as the size of the springback. The formulas about springback solution were obtained under the action of hydraulic pressure during the stretch bending. According to the formula, with the liquid chamber pressure increased, the force T increased, the moment M decreased, and the springback decreased. The neutral layer of stress moved to the inside of the plate under fluid pressure, and the sections of sheet are mostly in a tensile stress state and less springback after the end of hydroforming. Combined with the results of theoretical analysis and numerical simulation, the experimental method of getting the springback about bending sheet under liquid pressure is proposed, and the 3D model was got by using reverse engineering. It got the springback by comparing the punch surfaces. The test results show that the smaller the springback, the greater the fluid pressure in the forming pressure range about stainless steel metal, which accords with the theory analysis.