GB1157893A - Method of Diffusion Bonding Sheets together - Google Patents

Abstract

1,157,893. Making honeycomb core and bellows; welding by pressure. HEXCEL CORP. 18 July, 1966 [23 July, 1965], No. 32256/66. Headings B3A and B3R. In diffusion bonding together sheets at predetermined positions over their faces, a stack of sheets is formed with adjacent sheets separated by one or more members of a pressure transmitting material which is different from the material of the adjacent sheets and with the members offset so that no two members are directly above each other and separated by only one sheet and the stack is subjected to pressure normal to the sheets and heat to directly bond together adjacent sheets only at places above and below the members. A number of metal foils 12, Fig. 1, are arranged in a stack 11 with strips 13 between the foils in staggered relationship. The stack is arranged in an enclosure 61, Fig. 4, which may be evacuated or contain inert gas, between a press bed 62 and a movable press platen 63 which have raised portions 62<SP>1</SP>, 63<SP>1</SP> for applying pressure to the stack in the regions of the strips. Flat surfaces may alternatively be used. The platen 63 is forced downwardly by hydraulic rams 64 and while under pressure the stack is heated to diffusion welding temperature by passing current through the stack from one end to the other by clamps 67 attached to a current source. This method of heating is employed when the foils have high resistance, e.g. of stainless steel, but when the foils are of copper resistance element strip heaters are applied to the top and bottom of the stack. The regions of the foils above and below the strips are thus diffusion welded together and the welded stack is expanded to form an open cell honeycomb structure. The strips are then removed by high-pressure water or air or by etching. In one example aluminium sheets are spaced by zirconium strips and are heated in vacuo by strip heaters at the top and bottom of the stack, a pressure of 7500 p.s.i. and a temperature of 800‹ F. for 20 minutes being used and the stack being pulled apart by pins inserted into the stack edges. In another example sheets of 50% iron-50% nickel are spaced by strips of an inorganic powder in an inorganic solution and are heated in vacuo by passing current through the sheets. A pressure of 2400 p.s.i., and a temperature of 1050-1100‹ F. for 10 minutes are employed and then reduced. The strips are removed by acid. Strips may be left in the honeycomb. A number of annular sheets are similarly bonded using rings of stop weld material to provide on expansion a bellows. Sheets of titanium alloys may be welded.