Metal sandwich structure with integral hardpoint

A superplastically formed, diffusion bonded sandwich structure having integral metal hardpoints, made by joining two superplastic metal core sheets together into a core pack by welding or diffusion bonding along a pattern of lines which form junction lines between the core sheets when the pack is inflated by gas pressure at superplastic temperatures. Face sheets are laid under and over the core pack and metal inserts are interposed between the face sheets and the core. All of the sheets in the pack are sealed together around an outside peripheral edge to create a gas tight envelope. The pack is heated to superplastic temperatures in a cavity in a die, and the top and bottom face sheets are diffusion bonded to top and bottom surfaces of the metal insert by application of heat and pressure from top and bottom inner surfaces of the die cavity. While at superplastic temperatures, the pack is inflated by gas pressure against inside surfaces of a die to form an expanded metal sandwich structure having integral webs and integral hardpoints formed by the metal insert. After forming, the gas pressure is reduced to near atmospheric, the die is opened and the part is removed from the die.