Bending behaviors of large diameter thin-walled CP-Ti tube in rotary draw bending

The rotary draw bending(RDB) of large diameter thin-walled (LDTW) tube needs the strict cooperation of multiple processing parameters to avoid possible multiple defects. Due to the specific properties, the bending behaviors of LDTW commercial pure titanium (CP-Ti) tube are much more complex to achieve precise deformation. With the CP-Ti tube of 50.8 mm (out diameter, D)×0.508 mm (wall thickness, t)×101.6 mm (bending radius, R) as a representative component, the bending behaviors of LDTW CP-Ti tube under different processing conditions were investigated. With experiments and analytical analysis, the bending characteristics of the CP-Ti tube were identified. Then, based on the orthogonal experimental design, a series of three-dimensional FE models of RDB for LDTW CP-Ti tube were established, and the effects of processing parameters on the bending behaviors were numerically investigated. The results show that: 1) Wrinkling is the primary behavior for the LDTW CP-Ti tube in RDB, and the larger the difference between the maximum wall thickening and the maximum wall thinning degrees of the bent tube, the larger the wrinkling tendency; 2) The bending behaviors of the LDTW CP-Ti tube are very sensitive to the some processing parameters, and the wrinkling is significantly affected by the mandrel shank diameter, while the wall thinning is remarkably affected by the clearance between wiper die and tube, mandrel shank diameter. The qualified bent tube with the wall thinning of 11.43%, the cross-section distortion of 2.69% and the wrinkling height less than 2% is then obtained.