Advances in rolling-spinning technique of titanium tubes

Due to the characteristics of light weight, high strength and good corrosion resistance, titanium tubes have been widely applied and needed in the fields of aviation, aerospace and weapon. Considering that the existing processes are difficult to manufacture long, thin-walled titanium tubes with large diameter in efficiency and at low cost, a new tube forming technique by combining ring-rolling and tube spinning (called rolling-spinning) is developed. In the rolling-spinning process, blanks experience continuous local loading forming under the line contact action in ring-rolling process and point contact action in tube spinning process. These forming characteristics would lead to complex deformation history, inhomogeneous microstructure and fracture, which would finally affect the performance of tubes. Therefore, based on the two-phase self-consistent model and Oyane criterion, a macro-micro finite element model coupling the damage effects is established. Using this model, the macro deformation behaviors, microstructure and damage evolutions are investigated. The results indicate that after the rolling-spinning process, the strain and α grain size are largest in the outer zone of the workpiece, while the strain and α grain size are almost same in the inner and center zones of the workpiece; the temperature and volume fraction of α phase decrease along from the outer surface to inner surface of the workpiece; the fracture would occur in the inner surface of workpiece during the spinning process due to the coupling effects of positive stress triaxiality and high strain rate.