Domed structures and a method of making them by superplastic forming and diffusion bonding

Claim 1

A method of manufacturing a deep domed cellular metallic structure having walls of cellular construction comprising a convex surface and a concave surface opposed to the convex surface and defining a cavity, the greatest height of the cavity being at least one third of its greatest width, the method including the steps of: providing at least two metal sheets having superplastic characteristics; joining two of said sheets by face-to-face metallic bonds or welds and forming the sheets into a stack; sealing the perimeter edges of said stack but including means for the admission of pressurised inert gas between said sheets thus forming an inflatable envelope assembly; placing said stack in a fixture including means for sealingly clamping said stack within said fixture at or about its perimeter and means for the admission of a supply of pressurised inert gas to one external face of said stack; heating said stack and said fixture to a temperature suitable for superplastic forming, applying gas pressure to one external face of said stack such that the stack is expanded superplastically to a pre-defined domed shape having a height that is at least one third its width; placing said pre-formed stack in a mould tool having opposed concave and convex surfaces defining between them a space of domed form, the height of the convex surface being at least one third its width; heating the stack to a temperature suitable for superplastic forming and diffusion bonding, supplying inert gas under pressure between said sheets, thereby expanding by superplastic forming the outermost sheets of said pre-formed stack to conform to the convex and concave mould surfaces to form the said concave and convex surfaces of the structure and further causing the said sheets joining by face-to-face metallic bonds to expand about said metallic bonds to form webs extending between the convex and the concave surfaces of the structure thereby defining the said cellular construction, and further causing any sheets of the stack that are not already joined to the other sheets of the stack by face-to-face metal bonds to be diffusion bonded to at least one other sheet of the stack.

Claim 2

A method of manufacturing a deep domed cellular metallic structure having walls of cellular construction comprising a convex surface and a concave surface opposed to the convex surface and defining a cavity, the greatest height of the cavity being at least one third of its greatest width, the method including the steps of: providing at least two metal sheets having superplastic characteristics; joining two of said sheets by face-to-face metallic bonds or welds and forming the sheets into a stack; sealing the perimeter edges of said stack but including means for the admission of pressurised inert gas between said sheets thus forming an inflatable envelope assembly; placing said stack in a fixture including means for sealingly clamping said stack within said fixture at or about its perimeter and means for the admission of a supply of pressurised inert gas to one external face of said stack; heating said stack and said fixture to a temperature suitable for superplastic forming, applying gas pressure to one external face of said stack such that the stack is expanded superplastically to a pre-defined domed shape having a height that is at least one third its width; placing said pre-formed stack in a mould tool having opposed concave and convex surfaces defining between them a space of domed form, the height of the convex surface being at least one third its width; heating the stack to a temperature suitable for superplastic forming and diffusion bonding, supplying inert gas under pressure between said sheets, thereby expanding by superplastic forming the outermost sheets of said pre-formed stack to conform to the convex and concave mould surfaces to form the said concave and convex surfaces of the structure and further causing the said sheets joining by face-to-face metallic bonds to expand about said metallic bonds to form webs extending between the convex and the concave surfaces of the structure thereby defining the said cellular construction, and further causing any sheets of the stack that are not already joined to the other sheets of the stack by face-to-face metal bonds to be diffusion bonded to at least one other sheet of the stack.