Effect of anisotropy in commercial purity titanium on deep drawability at elevated temperatures

Abstract

Commercial purity Ti sheets (0.88 mm thick) were deep drawn by a complex working process at two temperatures using a hot die and a cool punch. The working temperature ranged from 25 to 400°C. Generally, the limiting drawing ratios (LDRs) along both the rolling direction (RD) and transverse direction (TD) increased with increasing operating temperature, while the optimal blank holding force decreased with temperature. The LDR(RD) is larger than the LDR(TD) at all temperatures in the range tested and the difference (ΔLDR) is largest at 200°C or higher. The deep drawn cups failed at the cup wall near the die throat along the TD. The thickness strain along the TD was consistently smaller than that along the RD. The anisotropy index δ _011¯1 increased significantly at 100°C and the largest δ _hkil values were found in δ ₀₀₀₂ along the RD and δ _112¯0 along the TD. The reorientation bands that appeared when drawn at 25°C are a result of work hardening, but the microshear bands that occurred in the 400°C specimen are a result of large deformation. The difference in microstructures along the TD and RD may explain the anisotropy in deep drawing properties.