Improvement of Die Corner Filling of Stepped Tubes Using Warm Hybrid Forming

Aluminum and magnesium alloys are of materials for decreasing vehicle weight and consequently reducing fuel consumption. However, forming limitations regarding their low formability at room temperature are found when being manufactured by conventional forming processes. For this reason, development of new forming techniques, such as warm tube hydroforming, is needed to overcome such limitations. In addition, production of parts with sharp corners is nearly impossible using conventional forming processes. This paper investigates the possibility of forming stepped tubes with high expansion ratio, sharp corner radii and precise geometric shape using a developed hybrid hydroforming and bending method. To assess tube formability, the bulge test was adopted with different forming temperatures and axial feeds. It is shown that using the feed of 35 mm and feed rate of 15 mm/min, a stepped tube with 47.6 % expansion ratio and corner filling ratio of about 100 % (part with sharp corners) could be achieved when adopting the developed hybrid hydroforming and bending method at 150 ᵒC.