A novel hydroforming approach in manufacturing thin-walled elbow parts with small bending radius

Abstract

Bending of a thin-walled tube with small relative bending radius is a hot topic which has aroused extensive attention in recent years. The main disadvantage of tube parts with small bending radius fabricated by available bending approaches is non-uniform wall thickness, large springback, poor fatigue performance, and wrinkle that is difficult to control for thin-walled tube bending. In order to solve this problem, a Bend-Bulge Forming (BBF) process combining rotary draw bending and hydroforming that realizes the fabricating of thin-walled elbows with small bending radius has been put forward in this study, and both FEM simulations and experiments were carried out. Meanwhile, in order to reveal the deformation behavior and the failure during BBF process, theoretical and FEM analysis were conducted by free expansion with bent tubes. The results show that the axial feeds play a prominent role in the hydroforming process. It can promote the tube wall outside of the bend contact with hydroforming die and avoid the excessive thinning. At the same time, the tube wall inside of the bend which is thickened during bending operation can be deformed sufficiently. Finally, the final parts fabricated by the BBF process have approximately constant wall thickness and high precision.