The superplastlc blow-farming process of thin sheets Is analyzed, and an optimal stable deformation path that reduces production time is obtained. The analysis is based on an analytical model for the superplastic forming (SPF) of a long rectangular box made of Ti-6AI-4V alloy at 900 deg C, use of a microstructure-based constitutive equation for the strain rate and grain growth, a stability criterion, and a variable strain rate control. It is shown that by imposing a variable strain rate control scheme derived from the stability analysis, an optimal forming time can be developed while maintaining a stable deformation path. Some other control schemes also show effectiveness in either reducing the localized thinning in the formed sheet or reducing the required forming time. Effects of friction and initial grain sizes on the forming pressure profile and the thickness distribution of the formed sheet are also investigated.
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