Improvement of the rotary draw bending process in rectangular tubes by using internal fluid pressure

The rotary draw bending has been conducted in square sections usually through techniques such as using the mandrel and wiper, which are mainly associated with inevitable defects such as wrinkling, thinning, folding, tearing, sagging, and cross-sectional distortion in the bending area. In this research, the improvement in the bending process of Al6063 rectangular tubes has been evaluated experimentally and numerically by applying the internal fluid pressure. Since the rectangular tube sealing is difficult in practice, designing a sealing system suitable for both ends of the tube has been tried. This was done to investigate the effect of different fluid pressures and without fluid pressure at the bending ratio of 3. Also, the amount of increasing in the thickness and wrinkling of the intrados area and decreasing in the thickness and sagging of the bent tube extrados is examined. The results showed that wrinkling, sagging, and cross-sectional distortion in the bending area has been reduced significantly. As a consequence, at a certain pressure, those kinds of defects almost disappeared due to the strain distribution caused by stress arising on the internal surface of the tube.