Experimental and Numerical Investigation on Bending Process of Thin Wall Tube with Square Section by Hydroforming Method

Tube bending is widely used in the aerospace and automotive industries. Of the main difficulties of this process are wrinkling, rupture and incomplete filling of the die. If the ratio of the bend radius to tube diameter (R/D) in the bending process is between 1 and 1.5, the bending cannot be performed by conventional methods. Therefore, it is important to develop a new technique in this respect. In this study, at first, closed-end seamless tubes were produced by multistage deep drawing and ironing processes. Then, the proposed hydroforming process of square cross-section tubes with the ratio of R/D=1 has been examined experimentally and by FEM. It is illustrated that the square cross section tubes with low R/D can successfully be produced by the developed technique. In addition, the effect of internal fluid pressure and die bend angle on the thickness distribution of the inner, outer and lateral walls of the bending area has been investigated. It is shown that with increasing the pressure, the thickness of the inner, outer and lateral tube walls increases. The reduction in the thickness is much greater for the external wall. The tube in the R / D = 1 was formed with multi of bending angles. The results exhibit with increasing the bending angle, the pressure of forming was decreased.