Method of making and joining an aerofoil and root

Abstract

A ducted fan gas turbine engine aerofoil is made by electron beam welding together at least two metal sheets ( 10 ) and ( 12 ) and electron beam welding that sub assembly via an end to a root that has been manufactured in a separate operation, and then heating the whole to a temperature that will convert the electron beam welds to diffusion bonds.

1 . A method of making an at least substantially hollow aerofoil having a separately manufactured root comprising the steps of providing at least two metal sheets having edges, welding the at least two metal sheets together about their edges, manufacturing a root having a surface shaped to receive an end of said joined metal sheets, welding said end of the joined metal sheets to said surface of the root to form an assembly, and then holding the assembly in holding means via said metal sheets, and heating the assembly to convert the weld joints to diffusion bonds.  
   
   
       2 . A method of making an at least substantially hollow aerofoil as claimed in  claim 1  wherein only two metal sheets are used in the making of said aerofoil, at least one of which has a diffusion bond preventing material applied all over that surface which on assembly of the two metal sheets defines an interior surface of said assembly.  
   
   
       3 . A method of making an at least substantially hollow aerofoil as claimed in  claim 1  wherein three metal sheets are used in the making of said aerofoil, the central metal sheet being thinner than the outer metal sheets, the central sheet having strips of diffusion bond preventing material applied to both sides thereof, the positions of said strips on one side of said central metal sheet being staggered with respect to the positions of the strips on the other side of the central metal sheet.  
   
   
       4 . A method of making an at least substantially hollow aerofoil as claimed in  claim 1  including the use of holding means comprising a die, the die having inner opposing surfaces, the inner opposing surfaces having respective aerofoil suction and pressure forms, and on achievement of said diffusion bonding heating temperature, pumping an inert gas between the metal sheets via piping so as to expand them against the respective inner opposing surfaces of said die so as to cause them to adopt a corresponding aerofoil form.  
   
   
       5 . A method of making an at least substantially hollow aerofoil as claimed in  claim 3  including the use of holding means comprising a die, the die having inner opposing surfaces, the inner opposing surfaces having respective aerofoil suction and pressure forms, and on achievement of said diffusion bonding temperature, pumping an inert gas between each outer metal sheet and the respective opposing sides of said central metal sheet so as to expand said outer metal sheets against respective opposing inner surfaces of said die and cause them to adopt a corresponding aerofoil form, and to cause portions of said central metal sheet to super-plastically extend in staggered manner so as to form an aerofoil stiffening structure.  
   
   
       6 . A method of making an at least substantially hollow aerofoil as claimed in  claim 1  including the step of placing the welded metal sheets assembly in a die having inner opposed respective aerofoil suction and pressure surfaces, heating the metal sheets and subjecting the interior thereof to a pressure sufficient to expand them into the respective die inner surfaces so as to adopt the aerofoil form, and then welding the formed aerofoil to said root and converting said weld joint to a diffusion bond.  
   
   
       7 . A method of making an at least substantially hollow aerofoil as claimed in  claim 1  including the step of diffusion bonding the welded metal sheets assembly together, welding the diffusion bonded metal sheets to said root, placing the diffusion bonded metal sheets and root assembly in a die having inner opposed respective aerofoil suction and pressure surfaces, heating the metal sheets and subjecting the interior thereof to a pressure sufficient to expand them into the respective die inner surfaces so as to adopt the aerofoil form.  
   
   
       8 . A method of making an at least substantially hollow aerofoil as claimed in  claim 1  wherein the welding of said end of the joined metal sheets to said surface of the root comprises election beam welding and friction welding.