Numerically controlled bending performance of medium strength TA18 titanium alloy tubes under different die sets

Abstract

The rapid development of aviation and aerospace technologies has led to increased interest in the application of numerically controlled (NC) technology for bending light-weight titanium alloy tubes. In order to study and develop advanced NC bending technology, it is necessary to understand the bending performance of medium strength TA18 (Ti-3Al-2.5V, ASTM Gr. 9) titanium alloy tubes during NC bending under different die sets. This paper focuses on the bending performance of medium strength TA18 tubes under different NC bending die sets, including the variations in the stress, strain, wall thickness, cross sectional deformation, and defects. The results show that adding a wiper die to the base die set decreases the radial, hoop, and tangential compressive stress and the tangential compressive strain, and adding a mandrel to the base die set also decreases these stresses, but increases the radial and hoop tensile stress and decreases the hoop compressive strain obviously, and brings about a three-dimensional tensile stress concentration where the mandrel provides support. For the NC bending of medium strength TA18 tubes, the flattening of cross section is more sensitive index than the thinning of wall thickness. Introducing a mandrel can improve the flattening of cross section obviously but it has a little worse effect on the thinning of wall thickness, and adding a wiper die to the base die set can inhibit the occurrence of the inside bulge but worsen the flattening of the cross section remarkably. Considering the above effects of the mandrel and wiper die on bending performance, it is reasonable to apply the die set comprising a bending die, clamp die, and pressure die for tubes with a small diameter and the die set including an appropriate mandrel additionally for tubes with a larger diameter, in order to bend the medium strength TA18 tubes with high quality and at low cost.