A process for superplastically forming a part from a blank of superplastic material such as titanium alloy, including enclosing and capturing a sheet of superplastic material having uniform thickness between a die lid and a die base. The die (38) lid has a deep recess (50) where localized prethinning of the blank would minimize excessive thinning of the formed part elsewhere on its topography. The peripheral edges of the blank is clamped between the lid and the base by exerting a squeezing force, typically be a press, and the die is heated, along with the blank, to the superplastic temperature of the blank. The die base is pressurized to preform portions of the blank opposite the lid recess into the recess to form a prethinned bulge. After preforming, the die lid above the blank is pressurized to reverse the prethinned bulge down into the cavity and to form the blank into the cavity. The localized prethinning facilitates forming in areas that would tend to form slowest or least and makes material available for other areas of the part that would normally become excessively thinned by virtue of the shape of the adjacent areas or depth of the die cavity, thereby making possible the tailoring of thickness in particular areas of the formed part.
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