Superplastic forming

A method is provided for eliminating internal voids in superplastically forming parts. A blank of material 6 which is capable of being formed superplastically is held opposite a forming surface 16 of a die. The blank is heated to the superplastic forming temperature and pressure 18,20 is applied to both sides of the blank. This pressure is sufficient to prevent the formation of voids. The pressure 18 on the side of the blank farthest from the die surface 16 is then increased to superplastically form the material against the die surface. In a second embodiment, the pressure is applied after the blank has been formed either by maintaining the forming pressure to compress the material between the forming pressure and the reaction of the die, or by applying a fluid pressure to both sides of the part, thereby removing voids by plastic deformation and diffusion.