Abstract: A method of making metallic sandwich structures is disclosed using a plurality of metal blank workpieces with at least one of the blank workpieces capable of being superplastically formed against a surface of a die. At least one of the blanks is treated at selective areas to prevent bonding in those areas. The blanks are positioned in a stack with at least one of the outer workpieces of the stack having the capacity to be superplastically formed. The stack is then diffusion bonded together in the untreated areas. At least one insert, preferably made from wax, is coupled to the bonded stack such that the external configuration of the at least one insert and bonded stack conform to the external configuration of the sandwich structure. A mold is cast around the at least one insert and bonded stack, after which the at least one insert is removed from the mold. Thereafter, the bonded stack is superplastically formed within the cast mold, resulting in the desired sandwich structure.