Abstract:
A method for producing a vane for application in a component in a gas turbine engine includes casting at least one of a vane leading edge part and a vane trailing edge part and connecting the leading edge part and the trailing edge part.

Description:
BACKGROUND AND SUMMARY 
       [0001]    The present invention relates to method for producing a vane for application in a component in a gas turbine engine, especially a jet engine. The vane is especially suited for application in a stator component and primarily in an intermediate case (IMC) in an aircraft engine of the turbofan type. The invention is further directed to such a vane per se and a stator component (IMC) comprising the vane. 
         [0002]    An aircraft gas turbine engine of the turbofan type generally comprises a forward fan and booster compressor, a middle core engine, and an aft low pressure power turbine. The core engine comprises a high pressure compressor, a combustor and a high pressure turbine in a serial relationship. The high pressure compressor and high pressure turbine of the core engine are interconnected by a high pressure shaft. The high-pressure compressor, turbine and shaft essentially form a high pressure rotor. The high-pressure compressor is rotationally driven to compress air entering the core engine to a relatively high pressure. This high pressure air is then mixed with fuel in the combustor and ignited to form a high energy gas stream. The gas stream flows aft and passes through the high-pressure turbine, rotationally driving it and the high pressure shaft which, in turn, rotationally drives the high pressure compressor. 
         [0003]    The gas stream leaving the high pressure turbine is expanded through a second or low pressure turbine. The low pressure turbine rotationally drives the fan and booster compressor via a low pressure shaft, all of which form the low pressure rotor. The low pressure shaft extends through the high pressure rotor. Most of the thrust produced is generated by the fan. 
         [0004]    Part of the incoming air flow to the aircraft engine enters an inner, primary gas duct, which guides the air to the combustor, and part of the incoming air flow enters an outer, secondary gas duct (fan duct) in which the engine bypass air flows. 
         [0005]    The intermediate case (IMC) is a non-rotating component and forms a load-carrying structure. In a commercial, 2-shaft turbofan engine, the intermediate case is located between the Low Pressure Compressor and the High Pressure Compressor in the engine axial direction. At this location, the operating temperature is considered to be relatively low compared to the components downstream of the combustion chamber and is therefore referred to as a cold structure. 
         [0006]    The intermediate case comprises a core structure, which comprises the primary gas duct, and a by-pass structure, which comprises the fan duct. The present invention is especially suited for the by-pass structure. The by-pass structure comprises an inner ring, an outer ring and a plurality of circumferentially spaced vanes arranged between the inner ring and the outer ring, wherein gas flow channels are formed between the adjacent vanes. The circumferentially spaced vanes are often called Outlet Guide Vanes (OGV). 
         [0007]    The intermediate case has a number of various functions. The engine mount, i.e the connection between the engine and the aircraft, is placed on the outside of the IMC. The IMC is thereby exposed to high loads. The IMC is also a support for the bearings on the low pressure shaft and the high pressure rotor. Transmission of power between gearboxes may also be led through the intermediate case. 
         [0008]    The vanes form structural vanes, i.e load-carrying struts. The vanes may also have aerodynamic characteristics, wherein they are designed to redirect a swirling flow from the upstream fan. Such a vane is usually denoted an integrated OGV in this application. 
         [0009]    It is desirable to achieve a cost-efficient method for producing a vane, which results in a vane with low weight. The method should further be suited for producing a vane for an intermediate case in a turbofan engine. 
         [0010]    A method according to an aspect of the present invention includes the steps of casting at least one of a vane leading edge part and a vane trailing edge part, and connecting the leading edge part and the trailing edge part. It has turned out that casting gives a sufficient dimensional accuracy and surface roughness for application as an edge part in a vane in an intermediate case. Especially, it creates conditions for reaching a final shape without any subsequent machining. 
         [0011]    According to a preferred embodiment, the method comprises the step of forming the cast edge part by means of a vacuum high pressure die casting method. In this way, a low porosity is achieved, which increases the material properties and the weld ability. Further, the ductility and ultimate tensile strength is sufficiently high. 
         [0012]    A method according to another aspect of the present invention includes the steps of forming at least one of a vane leading edge part and a vane trailing edge part with a means for attaching the vane to an external structure on opposite sides of the edge part in a longitudinal direction of the vane, forming the edge part so that it is adapted to be load carrying in a longitudinal direction of the vane and forming the vane by connecting said edge parts. Thus, each of the edge parts forms a load-carrying structure comprising the attachment means. Thus, the attachment means is integrated in the edge part, which simplifies transfer of forces between the vane and the adjacent components. Further, this design creates further conditions for a more cost-efficient production in that the different parts can be produced separately and then assembled. 
         [0013]    According to a preferred embodiment, the method comprises the step of casting each of the leading edge part and the trailing edge part in one piece. The method further preferably comprises the step of attaching the leading edge part and the trailing edge part on opposite sides of an intermediate vane part. Thus, the final vane is assembled from three parts. The intermediate vane part is preferably formed by two plate-shaped portions at a distance from each other, which portions define opposite external surfaces of the vane. Further, the method preferably comprises the step of connecting at least one of the leading edge part and the trailing edge part to the intermediate vane part via welding. 
         [0014]    It is also desirable to achieve a vane, which is low weight and cost-efficient in production. The vane should further be suited for application in an intermediate case in a turbofan engine. 
         [0015]    Other advantageous embodiments of the invention and its associated advantages are apparent from the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The invention will be explained below, with reference to the embodiments shown on the appended drawings, wherein 
           [0017]      FIG. 1  is a schematic longitudinal sectional view illustration of an exemplary embodiment of an aircraft turbofan gas turbine engine, 
           [0018]      FIG. 2  shows a vane in a perspective side view, 
           [0019]      FIG. 3  shows the vane in  FIG. 2  in a perspective front view, 
           [0020]      FIG. 4  shows a cross section of the vane in  FIG. 2 , and 
           [0021]      FIG. 5  shows a structure of a plurality of vanes arranged in a circumferentially spaced manner. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    The invention will below be described for a turbofan gas turbine aircraft engine  1 , which in  FIG. 1  is circumscribed about an engine longitudinal central axis  2 . The engine  1  comprises an outer casing or nacelle  3 , an inner casing  4  (rotor) and an intermediate casing  5  which is concentric to the first two casings and divides the gap between them into an inner primary gas channel  6  for the compression of air and a secondary channel  7  in which the engine bypass air flows. Thus, each of the gas channels  6 , 7  is annular in a cross section perpendicular to the engine longitudinal central axis  2 . 
         [0023]    The engine  1  comprises a fan  8  which receives ambient air  9 , a booster or low pressure compressor (LPC)  10  and a high pressure compressor (HPC)  11  arranged in the primary gas channel  6 , a combustor  12  which mixes fuel with the air pressurized by the high pressure compressor  11  for generating combustion gases which flow downstream through a high pressure turbine (HPT)  13  and a low pressure turbine (LPT)  14  from which the combustion gases are discharged from the engine. 
         [0024]    A first or high pressure shaft joins the high pressure turbine  13  to the high pressure compressor  11  to substantially form a first or high pressure rotor. A second or low pressure shaft joins the low pressure turbine  14  to the low pressure compressor  10  to substantially form a second or low pressure rotor. The high pressure compressor  11 , combustor  12  and high pressure turbine  13  are collectively referred to as a core engine. The second or low pressure shaft is at least in part rotatably disposed co-axially with and radially inwardly of the first or high pressure rotor. 
         [0025]    The engine  1  comprises an intermediate case (IMC)  15 . The intermediate case  15  is located between the Low Pressure Compressor  10  and the High Pressure Compressor  11  in the engine axial direction. The intermediate case  15  comprises a core structure, which comprises the primary gas duct  6 , and a by-pass structure, which comprises the fan duct  7 . The engine  1  is mounted to an aircraft via the IMC such as by a pylon (not illustrated), which extends downwardly from an aircraft wing. 
         [0026]    The by-pass structure comprises an inner ring, an outer ring and a plurality of circumferentially spaced vanes arranged between the inner ring and the outer ring, wherein gas flow channels are formed between the adjacent vanes. The production and design of these vanes will be described below with reference to  FIGS. 2-4 . 
         [0027]    A vane  16  is shown in a perspective view in  FIG. 2 . The vane  16  has the shape of an air foil. The vane comprises a leading edge part  17  and a trailing edge part  18 . Each of the edge parts  17 , 18  extends along the complete longitudinal edge of the vane  16 . Each of the edge parts  17 , 18  is adapted to be load carrying in said longitudinal direction of the vane  16 . 
         [0028]    Each edge part  17 , 18  comprises an attachment means  19 , 20 , 21 , 22  for attaching the vane to an external structure at each end in the longitudinal direction. The inner attachment means  19 , 21  form core attachments. The outer attachment means  20 , 22  form case attachments. Each of the attachment means  19 , 20 , 21 , 22  is adapted for a bolted connection. It therefore comprises a projecting portion with bolt holes. 
         [0029]    The vane  16  further comprises an intermediate vane part  23  arranged between the leading edge part  17  and the trailing edge part  18 . The intermediate vane part  23  comprises two plate-shaped portions  24 , 25  (see  FIG. 4 ) arranged at a distance from each other, which define external surfaces of the vane  16 . Each of the plate-shaped portions  24 , 25  is formed by a metal sheet. The intermediate part is preferably hollow. It may comprise a sandwich structure. According to an alternative, the interior of the vane may be filled with a foam, preferably a plastic foam. According to a further alternative, a more rigid structure, or frame, such as a honeycomb structure, may be positioned inside the vane. 
         [0030]    Further, the intermediate vane part  23  comprises a stiffening plate  26 , 27  at each end in the longitudinal direction of the vane  16 , extending at right angles to the vane. The stiffening plate  26 , 27  is adapted for a bolted connection and comprises bolt holes. 
         [0031]    The edge parts  17 , 18  are preferably connected to the intermediate vane part  23  via weld connections. 
         [0032]    A method for producing the vane  16  will now be described. It comprises the steps of individually casting the vane leading edge part  17  and the vane trailing edge part  18 . Thus, each of the leading edge part  17  and the trailing edge part  18  is cast in one piece. A vacuum high pressure die casting method is preferably used. In high pressure die casting, a charge is injected in the die at high speed (about 40 m/s) into a tool. The metal solidifies while being subjected to a pressure from an injection piston. 
         [0033]    The method comprises the step of casting the edge part  17 , 18  with such a shape that it extends along the complete longitudinal edge of the vane  16 . Further, it comprises the step of casting the edge part  17 , 18  so that it is adapted to be load carrying in the longitudinal direction of the vane  16 . Said attachment means  19 , 20 , 21 , 22  is cast in one piece with the respective edge part  17 , 18 . 
         [0034]    The cast part  17 , 18  is preferably formed by a lightweight metal material, such as aluminium or titanium. 
         [0035]    Further, the method comprises the step of providing the intermediate vane part  23  and attaching the leading edge part  17  and the trailing edge part  18  on opposite sides of the intermediate vane part  23 . The leading edge part  17  and the trailing edge part are preferably connected to the intermediate vane part  23  via welding. 
         [0036]      FIG. 5  shows a structure  28  of a plurality of said vanes  16  arranged in a circumferentially spaced manner. Fan gas flow channels are formed between the adjacent vanes  16 . The structure  28  is designed to form part of the intermediate case  15  (see  FIG. 1 ). The intermediate case  15  comprises an annular inner structure, or ring,  29  an annular outer structure, or ring, (not shown) and the plurality of circumferentially spaced vanes arranged between the inner structure and the outer structure. 
         [0037]    The invention is not in any way limited to the above described embodiments, instead a number of alternatives and modifications are possible without departing from the scope of the following claims.