Bendability of large diameter thin-walled CP-Ti tube under rotary-draw-bending with small bending radii

The study aims to identify the bendability of large diameter thin-walled commercial pure titanium tube (CP-Ti) tube in Rotary-Draw-Bending(RDB) under small bending radii R by using the experiment and numerical methods. The properties of CP-Ti tube are obtained by the uniaxial tension tests conducted under four velocities. The twist-compression test(TCT) is performed to estimate the friction between CP-Ti tube and die materials under various tribological conditions. A series of explicit/implicit elastic-plastic 3D-FE RDB models of large diameter thin-walled CP-Ti tube are developed, in which the Hill(1948) normal anisotropic yield function with isotropic hardening law, as well as Column friction law are adopted and validated by the experiments. By considering multiple indices, the bending behaviors of Ti tube in RDB are explored to identify the bendability of the Ti-tube under small R from 1.5D to 2.5D. The specification is 50.8×0.508mm (diameter Dxwall thickness t) with large size factor D/t of 100. The study shows that the ductibility and strain hardening of CP-Ti tube are sensitive to the forming speed. The wrinkling instability is the dominant defect to restrain the bending quality for thin-walled CP-Ti tube RDB. The wrinkling can be avoided with small clearance between tube and mandrel. The cross-section ovalization can be controlled within 5% and the wall thinning degree is less than 20% for call cases.