Superplastic forming process applied to aero-industrial strakelet: wrinkling, thickness, and microstructure analysis

Superplastic forming (SPF) of an aluminum sheet trough with a large depth to width ratio is challenging because of the difficulties in obtaining a satisfactory, uniform thickness distribution. To address this problem, two different SPF techniques, namely, two-stage gas forming (TSGF) and hot-bend assisted gas forming (HBAGF), were used to fabricate airplane strakelets. Undesirable wrinkling occurred in both cases, but the sites and causes of wrinkle formation were different. Thickness measurements around the edge of the circumference were relatively uniform, with a minimum thickness of ∼1.32 mm (∼34.0 % thinning percentage) for the HBAGF sample. This thickness significantly exceeded that of a sample processed by a previously developed TSGF method (∼0.8 mm, ∼60 % thinning percentage). Three-dimensional finite element analysis was implemented to accurately predict the shape and occurrence of wrinkling. Furthermore, experimental forming trials with the HBAGF die led to significant improvement of the thickness profile of superplastically formed parts.