Thermo-mechanical coupled 3D-FE modeling of heat rotary draw bending for large-diameter thin-walled CP-Ti tube

The heat rotary draw bending of large-diameter thin-walled (LDTW) commercial pure titanium (CP-Ti) tube is a highly nonlinear thermo-mechanical coupled physical process. Developing a reliable finite element (FE) model for this process is an effective way to investigate the heat loading and the complex bending behaviors. In this study, considering the characteristics of multi-die constraints and local heating, a thermo-mechanical 3D-FE model was established for preheating and heat bending of LDTW CP-Ti tube in terms of both accuracy and efficiency. First, using the static implicit algorithm, a preheating model was developed to predict the temperature distribution of bending tools. In this model, the key issues such as the full-sized geometry modelling, thermal interaction definition, and automatic heating control were solved to increase the simulation accuracy and efficiency. Then, introducing the predictions of preheating model and using the dynamic explicit algorithm, a thermo-mechanical coupled 3D-FE model was established for the heat bending simulation via the geometry modelling simplification, temperature definition of bending tools, realization of non-uniform temperature distribution, etc. Considering the temperature history of bending tools and wall thickness changing of bent tube, the reliability of preheating model and heat bending model was verified by several experiments. The results showed that the maximum relative errors of both predicted temperature and wall thickness changing degree were less than 9 %. Based on the reliable models, the effects of preheating temperature on the temperature distribution of bending tools and wall thickness changing of tube were numerically evaluated. The established model provides the scientific basis for the prediction and control of bending qualities of the heat RDB process, and the modeling method is also of general significance to the other heat-aided forming process.