Abstract: An improvement is disclosed to the method of forming sandwich structures wherein a plurality of workpieces having opposed principal surfaces are placed in a stack contacting facing principal surfaces and thereafter diffusion bonding portions of said facing principal surfaces of said workpieces together and superplastic forming at least a portion of at least one of said workpieces. The improvement comprises coating at least one of the facing principal surfaces with a maskant. The maskant is then removed from the portions not to be diffusion bonded of the at least one coated facing principal surface. A stopoff material is applied to the portions where the maskant has been removed and thereafter the remaining maskant is removed. The preferred method of removing the maskant from the portion of the at least one coated principal surface comprises placing a template on the surface and thereafter cutting out the maskant.

Abstract: An improvement is disclosed to the method of making metallic structures from a plurality of stacked workpieces or blanks by joining first portions, preferably by diffusion bonding, of the stack and by clamping the joined stack at its periphery between forming members and superplastically forming second portions of said plurality of stacked blanks by the selective application of fluid under pressure. The improvement is a method of coupling the fluid to the second portions of the stack which comprises providing a first port through one of the outer blanks at the periphery of the stack. At least one stopoff path is provided for coupling the first port to the second portions of the stacked blanks, which are to be superplastically formed. A second port is provided in one of the forming members, which couples the first port to a source of pressurized fluid.