Method of plastic flow diffusion bonding

A method for fabricating an internally stiffened, aerodynamically shaped shell structure comprising the steps of:

• a. providing first and second metallic face sheets having an excess volume of metallic material on at least one of said face sheets;
• b. Placing said first sheet in a die assembly which is configured to produce the desired basic aerodynamic shaped structure, said first face sheet having means to align said first face sheet in said die assembly;
• c. placing at least one self-stable internal stiffener fabricated from metallic material upon said first face sheet, sand internal stiffener having a sufficient thickness to provide an adequate bonding area for joining the stiffener to the face sheets, a configuration which allows said self-stable member to provide sufficient support during the subsequent joining of said self-stable member to said face sheets, first and second ends which are received in said die assembly, and a height dimension which is greater than the net height requirement by approximately 0.01 to 0.08 inches to provide sufficient excess volume of said metallic material so as to provide positive fill in said die assembly for the desired amount of plastic flow of such material, and aligning said stiffener with respect to said first face sheet;
• d. placing said second face sheet in said die assembly over said internal stiffener, said second face sheet having means to align said second face sheet in said die;
• e. applying a forming an joining force to said internally stiffened structure for a sufficient duration at sufficient elevated temperature to cause intimate contact between opposed longitudinal edges of said face sheets and between said self-stable stiffener and adjacent areas of said face sheets by plastic flowing the excess volumes of material in the height of said self-stable internal stiffener and along the longitudinal edges of said face sheets, so as to join and bond said self-stable stiffener by solid state diffusion bonding to said face sheets and to join and bond said opposed longitudinal edges by homogeneous solid state diffusion bonding, thereby producing an aerodynamically shaped structure with leading and trailing edges, said forming and joining force being substantially localized in the to-be-joined areas and determined by the amount of excess material to be flowed and the plastic flow characteristics of the metal used.