Deep drawing simulation of α- titanium alloys using LS-DYNA

Titanium alloys have excellent properties for their target applications; however their use is still limited by high price and formability issues. To avoid extensive on-site trials and to cut development costs, a numerical simulation method is developed for the deep drawing process of α-titanium (hexagonal close packed) alloy sheet using LS-Dyna. The Barlat 1989 material model is adopted for modelling the plastic response of the material and the necessary input data is examined. It is found that in order to adequately capture the plastic properties of HCP titanium, load curves are needed both for strain hardening and to capture the strain dependency of the plastic strain ratio. A procedure for determining the material input data from the tensile test results is developed and an exemplary data set is given. To identify a suitable value of the Barlat flow potential exponent m a parametric analysis is carried out using a simulation of the Erichsen cupping test. Forming limit diagrams are adopted for failure prediction, the forming limit curves are determined using the Nakajima method and a simplified procedure for obtaining limiting shear strains on a tensile testing machine is presented. To confirm the method an example of a deep drawn end-cap for a motorcycle exhaust muffler is presented and the simulation compared to the physical forming process with good results.