Deformation behaviors of medium-strength TA18 thick-walled tubes during NC bending under various contact conditions between tube and dies

The deformation behaviors of the wall thickness variation and cross-sectional flattening in the NC bending of medium-strength TA18 thick-walled tubes under different contact conditions between tube and dies were investigated using a 3D elastic-plastic finite element model established based on ABAQUS. The election principles of the friction and the clearance between pressure die or bending die and tube in NC bending of a medium-strength TA18 tubes were determined. The results show that: the effects of the clearance between pressure die or bending die and tube on the thickening ratio is larger than that on the thinning ratio. A larger clearance between the pressure die and tube will lead an inside bulge to occur, and a larger clearance between the bending die and tube will make a severe inward collapse of outside wall. Therefore, the clearance between pressure die or bending die and tube should decrease as soon as possible. The effects of the friction between pressure die or bending die and tube on the variations of wall thickness and cross-section in NC bending of TA18 tubes is small, thus aviation lubricating oil or draw oil can be used to lubricate the interface between pressure die or bending die and tube.