A unified model to predict the hot stamping and subsequent stress-relaxation process of a Ti-6Al-4V alloy

Isothermal hot stamping process, which is composed of stamping and subsequent stress-relaxation steps, is an important technology to form complex thin-walled titanium components in the aerospace industry. It is a key issue to enable the accurate simulations of these two steps simultaneously for the process design and optimization. In this study, a unified constitutive model connecting both the plastic flow behaviour in stamping and the stress-relaxation behaviour in subsequent step is developed by considering the continuous evolution of key microstructures, i.e., dislocation density, in the whole process. A series of basic mechanical tests, including tensile and stress-relaxation tests, of a typical titanium alloy Ti-6Al-4V at 750°C was performed to calibrate the developed model. The unified model was then implemented into the commercial software ABAQUS via the VUMAT subroutine, and simulations of the complete hot stamping process were done, including stamping, stress-relaxation and final springback. In addition, a typical curve-shape component was hot-stamped at 750°C and stress-relaxation for 5 minutes was performed. The predicted result from the developed constitutive model and FE model shows a good agreement of the springback with the corresponding experimental result, verifying the effectiveness of the developed model for the further applications in hot stamping process design and optimization in the industry.