Abstract:The effects of internal pressure on forming defects, corner radius and thickness distribution of 5A02 aluminum alloy shear hydro-bending tubes were studied by experiment. Numerical simulation was conducted to analyze the effect of internal pressure on axial strain and invariable lines of thickness strain. The ultra-small bending tubes were successfully manufactured when the relative internal pressure, ratio of internal pressure and yield stress of the material, is higher than 0.2. The relative bending radius of the first outer corner decreases from 0.3 to 0.025 when the relative internal pressure increases from 0.2 to 1.2. The axial thickness distribution is different in intrados and extrados. The changing rate of thickness is larger with a higher internal pressure. The minimum thickness decreases from 1.45 mm to 0.87 mm when the relative internal pressure changes from 0.2 to 1.2. The tube is divided into feeding zone, the first corner, shearing zone, the second corner and holding zone. The strain of feeding zone and the first corner is compressive caused by the feeding. The strain of the second corner and holding zone is tensile for far away from feeding punches. The strain of shearing zone changes from compressive to tensile with rising of internal pressure. On one hand, the smaller corner radius formed by higher internal pressure blocks the feeding. On the other hand, the corner filling strengthens the extensive strain of shearing zone. In the feeding zone and holding zone, thickness strain is positive, and the tube thickens. In the corner and shear zones, thickness strain is negative, and the tube thins.

Key words: aluminum alloy; shear hydro-bending; small bending radius tube; internal pressure; 3D numerical simulation