Method of making a leading edge structure of aircraft airfoil

A method of fabricating a leading edge structure of an airfoil comprising an outer skin having an upper section and a lower section continuous with the upper section, and defining a space, a front wall extended along a length of the leading edge structure in a front section of said space so as to form an anti-icing duct together with a front part of the outer skin, and provided with an air jetting hole, and a plurality of ribs disposed between the upper and lower sections of the outer skin in said space so as to form a hot air passage for a hot air supplied through the air jetting hole of the front wall;

• said method comprising the steps of:
• superposing an upper sheet of a superplastic alloy and a lower sheet of a superplastic alloy;
• inserting a pair of core sheets of a superplastic alloy between the upper and lower sheets,
• applying release agent layers between said core sheets in a region corresponding to the anti-icing duct, between the upper sheet and one of the core sheets in regions corresponding to hot air passages and between the lower sheet and the other core sheet in regions corresponding to the hot air passage, thus forming a laminar structure;
• setting the laminar structure in a forming device provided with a mold having a forming surface of a shape corresponding to an external shape of the leading edge structure;
• forming a structure having an outer skin, a front wall and ribs by joining together parts of the superposed sheets corresponding to regions not applied with the release agent layers by diffusion bonding or welding, heating the laminar structure;
• supplying a superplastic forming gas into spaces between parts of the superposed sheets corresponding to regions applied with the release agent layers to subject the same parts of the superposed sheets to superplastic deformation and to press the upper sheet and the lower sheet against the forming surface of the forming mold;
• and
• trimming the structure to complete the leading edge structure.