Experimental study on wall thickness variation in NC bending of 6061-T4 large diameter thin-walled tubes

To realize the precise NC bending and improve the bending quality of 6061-T4 large diameter thin-walled Al-alloy tube, physical experiments of the 6061-T4 Al-alloy tube of Φ50.8 mm×0.889 mm×101.6 mm (out diameter D×wall thickness t×bending radius R) are carried out to investigate the influence of some controllable parameters (including bending angle, mandrel extension, number of mandrel balls and bending rate) on the wall thickness variation. The results show that the strain neutral layer E moves unequally in the bending area, the amount of its movement has a linear relationship with the difference between the wall thickness change ratio of the intrados and extrados (η), and E increases with the increasing of |η|. The maximum wall thickness changing degrees at the extrados and intrados increase with the increasing of bending angle, mandrel extension and bending rate, while the influence of number of mandrel balls is nonlinear. Based on the optimized parameters, the 180° bent tube with maximum thinning ratio 22% is successfully obtained.