Differential pressure method and apparatus for bonding high temperature structures

A method and apparatus for bonding high temperature structures, such as face sheets to high performance honeycomb cores, using differential gas pressure at high temperatures. A high temperature resistant, foil sheet having a thickness of from about 0.0005 to 0.003 inch is welded to a support to form a vacuum bag to surround the structure to be bonded. A vacuum line is connected to the bag to allow evacuation of the bag. Typically, the structure is bonded in a vacuum furnace. Initially, the furnace is heated to the bonding temperature of the assembly while both the furnace chamber and the vacuum bag are substantially completely evacuated. Then slight pressure is allowed to return to the chamber to force the foil sheet into intimate presure contact with the structural assembly to bring the components tightly together, using the relative pressure different between the vacuum in the chamber and the vacuum within the bag. The bag material may have superplastic deformation characteristics to allow uniform pressure to be applied to complex shaped structures. The bag and structural assembly are then cooled below the bonding temperature of the assembly. This process and apparatus are particularly suitable for bonding face sheets to honeycomb cores where those components are formed from a metal such as titanium or Inconel and the components are bonded together by a thin layer or brazing material on the surfaces of the face sheets such as by liquid interface diffusion bonding.