Design and experimental validation of a two-stage superplastic forming die

The conventional superplastic forming (SPF) of complex and deep geometries can result in excessive thinning and necking. To address these issues, a two-stage SPF process has been developed and demonstrated in forming trials using a superplastic aluminum sheet alloy. Within a single die, gas pressure is used to form the blank into a preform die cavity prior to the pressure being reversed to form the sheet into the final component cavity. The preforming of the blank creates length of line, while preserving metal thickness in certain regions to improve the thickness profile of the final part. In this work, a preform has been designed to improve the forming of a complex component by providing a superior thickness profile as compared to a conventional single stage forming cycle. Finite element analysis was used to guide the design of the preform cavity since the preforming surface was not intuitive and could cause wrinkling in the final part.