Numerical and experimental study on formability of TC4 alloy in a novel multi-layer sheet hot stamping process

In this study, a novel modified hot stamping process is proposed to prevent the heat loss of titanium alloy sheet during transferring and stamping. A technology which is two steel sheets clamping one titanium alloy sheet (the sandwich structure) to transfer and deform was used in the multi-layer sheet hot stamping process. The formability of TC4 alloy under the triple-layer sheet hot stamping condition was studied by means of experiment and numerical simulation. The influence of sheet temperature, stamping speed, and blank holder force on the depth and thickness uniformity of parts was analyzed. The results show that the deep-drawing depth of titanium alloy parts is improved and the thickness uniformity of parts is better by using the triple-layer sheet hot stamping process proposed in this paper. On the one hand, the flow stress of the TC4 alloy is low because of the less heat loss in the triple-layer sheet hot stamping process. On the other hand, the TC4 alloy sheet can be deformed better because of the changing of the friction situation of the titanium alloy sheet. And the contact force between titanium alloy sheet and steel sheet is less because of the protection of two steel sheet under the triple-layer sheet hot stamping condition. With the sheet temperature increasing, the deep-drawing depth of titanium alloy parts increases by 22.2% from 27 mm of 750 degrees C to 33 mm of 900 degrees C. Compared with the single-layer sheet hot stamping process, the stamping depth of titanium alloy parts obtained by the triple-layer sheet hot stamping process increases by 135.7% at 900 degrees C, and the local thinning of titanium alloy sheet is improved. Due to strain rate strengthen and the uniform distribution of sheet temperature, the thickness uniformity of parts is improved with the increase of stamping speed. Based on the microstructure observation tests, it is can be seen that more equiaxed alpha phase of TC4 alloy parts can be obtained by the triple-layer sheet hot stamping process.