Optimum forming loading paths for Pb-Sn superplastic sheet materials

The bulge forming performance of Pb-Sn superplastic sheet materials is evaluated under different forming pressure-time profiles. In addition, an “optimum” pressuretime profile based on variable strain rates is proposed. Results of forming time, achieved amount of deformation, and thinning behavior are reported for the different forming pressure profiles. Not only the forming time was significantly reduced, when forming with the optimum pressure profile, but the integrity of the formed part was also maintained. Furthermore, the results show that forming profiles based on uniaxial models cannot successfully predict the actual forming behavior when the loading path is biaxial. In fact, the one-dimensional strain rate hardening relation, along with von Mises criterion, predict failure at a much higher strain (time) than the actual case.