Method of eliminating core distortion in diffusion bonded and

Abstract

Method for eliminating core distortion in diffusion bonded and superplastically formed structures or panels, wherein metal blanks or workpieces of metal, capable of diffusion bonding and superplastic forming such as a titanium alloy, preferably in the form of thin sheets of the order of 0.030 inch thick or less, are placed in contact with each other in a tooling apparatus or die, the sheets are joined at selected areas by diffusion bonding and are then expanded superplastically to form a desired panel or a truss core panel structure. In such method, the metal sheets are diffusion bonded at certain preselected areas under pressure and at elevated temperature, and the unbonded areas of the sheets are then expanded by superplastic forming into contact with the walls of the tool or die cavity, at elevated temperature e.g., 1600-1650.degree. F. and an internal gas pressure e.g., about 300 psi, to form the desired panel. Following superplastic forming and cooling, the thin cell walls of the core panel are often distorted or crushed. As a feature of the invention, following superplastic forming and release of the internal gas pressure, and during cooling of the panel and while the metal panel is still at a temperature where the metal remains flexible or plastic, e.g., 1200.degree.-1400.degree. F., a low internal differential gas pressure, e.g., of about 3-7 psi, is introduced into the interior of the panel, expanding the panel out to its original form against the tool or die as a restraint, and straightening the thin core cell walls of the panel which were distorted following superplastic forming.