Cylindrical cup drawing of a commercially pure titanium sheet: experiment and crystal plasticity finite-element simulation

Because of the strong anisotropy in mechanical properties, press forming of commercially pure titanium (CP-Ti) sheets often creates significant defects, including earing formation during drawing. However, the predictive accuracy of CP-Ti sheet drawing processes by finite-element simulations is still not satisfactory because it is difficult to accurately represent the strong anisotropy with phenomenological constitutive models. In this study, a crystal plasticity model is employed to conduct finite-element simulations of a cold-rolled Grade 2 CP-Ti sheet cup drawing process, and its applicability to the process is examined in detail by comparing it with experimental results. Experimentally, the maximum cup height appears at an angle of approximately 50° from the rolling direction, and the heights at 0° and 90° are similar. The thickness strain distribution evolution is strongly dependent on the direction. Twinning activity during drawing is the largest at 90°, followed by 45°, and then 0°. The simulation qualitatively captures the overall tendencies well, but non-negligible discrepancies are also involved in the cup height at 90°, and the thickening at the cup edge at 0° and 90°. The mechanisms that yield the discrepancies between the experiment and the simulation are examined. Moreover, parametric studies are conducted to discuss the effects of twinning activity and friction on the drawability.