Patent ID: 7165435

Claim:
A method of forming a sheet of superplastically formable, metal alloy composition comprising: providing a cold worked sheet of the alloy composition; controlling the temperatures of a pair of opposing heated platens to recrystallize the cold worked microstructure of the metal sheet to a fine grained microstructure for superplastic forming; the platens being movable between an open position for receiving a sheet and a closed position for conductive heating of the sheet with one side surface of the sheet facing one platen and the opposite side surface of the sheet facing the opposing platen; placing a side surface of the sheet against one platen for first stage heating of the sheet to a thermally expanded and softened condition in which it will not be mechanically deformed by contact with the opposing platen, the first stage heating being accomplished with the platens in a position other than their closed position; moving the platens and sheet to the closed position of the platens for second stage heating of the softened sheet by conductive heat transfer to its side surfaces to recrystallize the cold worked microstructure of the meal sheet to a fine grained microstructure for superplastic forming; removing the sheet from between the platens; and forming the heated sheet.