Effect of internal pressure distribution on thickness uniformity of hydroforming Y-shaped tube

The hydroforming of an integral thin-walled Y-shaped tube was investigated. With axial feeding, tube material can be pushed into the die cavity to form a higher protrusion height with relatively small thinning ratio. For the Y-shaped tube, however, owing to the high-friction forces acting at internal pressure in the guiding zone between the tube and die, less metal flows into the protrusion. A multistage punch was proposed to change the internal pressure distribution in the guiding zone and to reduce the friction force between the tube and the die. Experiments of hydroforming of aluminum alloy Y-shaped tube were carried out, in which two projects with traditional punch and multistage punch were applied to comparison. The thickness distribution and thinning ratio distribution were investigated, and the results by different punches were compared.