Superplastic forming

A method of manufacturing an aerofoil structure by diffusion bonding and superplastic forming to create a substantially hollow cavity within the aerofoil structure, the method comprising the steps of:

• providing first and second outer panels formed of a first material;
• providing a membrane formed of a second material;
• applying stop-off material to preselected areas on at least one side of the membrane or of the first or second panel so as to prevent diffusion bonding between the panels and the membrane at the preselected areas;
• arranging the first and second panels and the membrane in a stack so that the membrane is between the first and second panels;
• performing a diffusion bonding process to bond together the first and second panels and the membrane to form an assembly;
• performing a superplastic forming process at a forming temperature to expand the assembly to form the aerofoil structure with the hollow cavity;
• the method characterised in that the forming temperature is selected so that the second material undergoes superplastic deformation at the forming temperature and the first material does not undergo superplastic deformation at the forming temperature.