Tribological behaviors in titanium sheet and tube forming at elevated temperatures: evaluation and modeling

Warm forming has been an efficient approach to exploiting the forming potential of titanium alloy sheet and tube materials. However, the tribological condition between Ti-alloy sheet/tube and tools at elevated temperatures is a non-trivial issue and has yet not been fully explored and articulated. Taking CP-3 tube and Ti-6Al-4V sheet as case study materials, the tribological behaviors between Ti-alloy sheet/tube and tools at elevated temperature are revealed and modeled. The main results show that (1) by using the high-temperature twist-compression test combined with the design of experiments, the suitable tool materials, surface modification approaches, and lubricants are determined for warm forming of Ti-alloy sheet/tube, and the significant influential factors and their affecting rules/mechanisms on the coefficient of friction are identified; (2) a pressure- and temperature-related dynamic friction model is developed and implemented in the 3D-FE simulation of warm forming via ABAQUS/VFRIC; taking warm rotary draw bending of CP-3 tube as an application, the proposed friction model is experimentally validated, and the comparisons between the experimental results and the simulated ones indicate that the proposed model is much better than the Coulomb friction model in prediction of forming defects, such as wall thinning/thickening and wrinkling instability.