Prediction of earing defect and deep drawing behavior of commercially pure titanium sheets using CPB06 anisotropy yield theory

Recently, sheet metal forming industries have shown interest in characterization of anisotropy properties, tension-compression strength differential and deep drawing behavior of commercially pure titanium (CP Ti) material for successful fabrication of lightweight components. In present work, the formability of 1.0 mm thick CP Ti sheet metal was studied using a laboratory scale deep drawing test set-up, and the limiting drawing ratio (LDR) was found to be 2.143. Four ears were observed in the LDR cup with maximum cup height along diagonal direction (DD) and troughs along both rolling direction (RD) and transverse direction (TD), and the earing height was approximately 13.7% of the total cup height. Tensile and stack compression tests were carried out along different orientations to evaluate the anisotropy properties and tension-compression strength differential, and these data were used to develop the CPB06 constitutive yield model. Also, the developed CPB06 anisotropy plasticity theory was implemented in an FE model to predict the non-uniform material flow, earing defect and thickness distribution successfully. In order to reduce earing defect, a two-stage blank modification technique was proposed incorporating directionalities of both yield strength and plastic strain ratio. A significant 83% reduction in earing height was achieved through use of modified blank with simultaneous benefit of improvement in thickness distribution and reduction in peak load.