P. N. Comley, The Boeing Company, Seattle, WA

Summary:

Most parts made by superplastic forming (SPF) have been formed at an optimum strain rate. The rate is selected to give the best SPF properties of the material. However it has been proposed that multi-rate forming, where an initial high strain rate is successively reduced as the part is strained, can be used to make high strain parts in a much shorter time than traditional SPF forming. This paper examines the performance of fine grain Ti-6Al-4V alloy at very high initial strain rates, from ten to thirty times faster than usual, with step reductions at prescribed levels of strain that still enables a total strain of over 2.1 (800%) to be achieved without degradation of the material. The paper also shows that the forming time to 100% deformation can be reduced from 55 minutes to 10. This technique can be used by industry to enable faster flow times and lower production costs of SPF parts.