Abstract:
A method of manufacturing a filled aerofoil component ( 100 ) for a gas turbine engine ( 10 ) comprises using a capping panel ( 200 ) to cover a pocket ( 310 ) in a pocketed aerofoil body ( 300 ). During manufacture, a pre-formed filler insert ( 400 ) is provided to support the capping panel ( 200 ) in the correct position. This ensures that the outer surface of the capping panel ( 200 ) is located as accurately as possible. This means that the capping panel ( 200 ) can be made to be as thin as possible, which in turn reduces weight and material wastage. The pre-formed filler insert ( 400 ) provides a lightweight core for the finished aerofoil component in use.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from British Patent Application Number 1316732.5 filed 20 Sep. 2013, the entire contents of which are incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Disclosure 
         [0003]    The present invention relates to the manufacture of an aerofoil having a filled cavity, in particular the manufacture of an aerofoil component having a filled cavity for use in a gas turbine engine. 
         [0004]    2. Description of the Related Art 
         [0005]    Aerofoil shaped components are used throughout gas turbine engines. For example, aerofoil shaped stator vanes and rotor blades are used to guide gas through the engine, for example both in the turbine and the compressor, including the fan and associated guide vanes. 
         [0006]    Weight reduction is an important consideration in gas turbine engines, particularly, although not exclusively, for gas turbine engines used to power aircraft. Generally, the lower the weight of the component the better the performance of the aircraft to which it is fitted, for example in terms of fuel consumption. To this end, it is known to use hollow aerofoils, e.g. rotor blades and/or stator vanes, in some stages of gas turbine engines. The hollow aerofoils have an internal cavity, which may be filled with a lightweight material. 
         [0007]    One method of producing a hollow aerofoil involves forming the structure using a skin. This involves creating an internal cavity using hot creep or super plastic forming processes. Such processes may generate aerofoils with some advantageous properties, such as thin skin thickness and tight dimensional tolerance, but they involve significant material wastage. This material wastage makes these processes expensive, due at least to high material cost for a given size of hollow aerofoil component. 
         [0008]    An alternative method for producing hollow aerofoil components involves attaching a plate to an aerofoil structure out of which a pocket has been machined. The plate is placed into the pocket and attached (for example welded or bonded) therein to produce a hollow aerofoil component. 
         [0009]    An advantage of producing the hollow aerofoil by using a plate to cover a pocket in an aerofoil structure is that there is less material wastage than using a skin to produce the hollow aerofoil. However, the dimensional, tolerances are not so accurate. This may be because distortion is introduced in the process of attaching the plate to the pocketed aerofoil, which typically involves local heating at the interface between the plate and the pocketed aerofoil. Additionally, tolerance errors may “stack-up” in the process used to produce the pocketed aerofoil, the process used to produce the plate, and the process/feature used to locate the plate into position in the pocket, which typically involve placing the plate onto a supporting ledge inside the pocket. 
         [0010]    The lack of dimensional accuracy means that the plate generally has to be manufactured to be thicker than would otherwise be required. For example, the extra thickness may be required in order to ensure that there is enough material to be machined back to produce the desired aerofoil shape after it has been fixed into the pocket. Without the extra thickness, the dimensional variation resulting from tolerance “stack-up” and/or distortion may mean that there is not sufficient material to produce the desired aerofoil shape in some of the aerofoils produced by the method. 
         [0011]    However, this extra thickness means both that the component is heavier than it would otherwise need to be, and also that there is more material wastage. 
         [0012]    Regardless of how the aerofoil is formed, the internal cavity is often filled, both to support the aerofoil structure and to prevent moisture ingress to the cavity. The filler is conventionally a lightweight, non-expandable material, such as syntactic epoxy. 
         [0013]    Conventionally, such fillers are injected into the cavity after it is formed, for example by forming the hollow aerofoil using one of the methods outlined above. This means that only fillers which are injectable can be used to fill the cavity. Furthermore, to ensure the panels do not bulge due to internal pressure, foaming/expandable materials cannot be used. Even with judicious positioning of the filling/injection holes, it is not possible to completely fill the internal cavity using such injection. 
         [0014]    Furthermore, injecting a filler material into a cavity necessarily results in a filler with homogeneous properties, whereas some composite or foamed structures, which are not injectable, may be stiffer, have lower density and better damping than such homogeneous fillers. As such, the type and selection of filler materials which can be used is limited, and materials which may have advantageous properties may be precluded from use in such an injection filling process 
         [0015]    Furthermore, filling the cavity by injecting the filler into injection holes after the hollow aerofoil has been formed means that the cavity must be defined such that the filler material can be pumped in from one end and vent out the other end so as to ensure that the cavity is filled as completely as possible. As such any internal pocket definition of the aerofoil, such as stiffening ribs, is compromised because of the need to ensure that such features do not obstruct the flow of the filler, which may result in an unacceptable level of fill. 
       OBJECTS AND SUMMARY 
       [0016]    It is therefore desirable to manufacture hollow aerofoil components by using a plate to cover a pocket (so as to take advantage of the generally lower material wastage), but with improved dimensional tolerance, better structural properties and improved cavity filling. 
         [0017]    According to an aspect, there is provided a method of manufacturing an aerofoil having a filled cavity comprising: 
         [0018]    providing a pocketed aerofoil body having an open pocket formed in a surrounding hollowed surface; 
         [0019]    inserting a pre-formed filler insert into the open pocket; 
         [0020]    locating a capping panel over the open pocket in a capping position, the capping panel having an inner surface (which faces into the pocket when in the capping position) and an opposing outer surface; 
         [0021]    supporting the inner surface of the capping panel on the filler insert with the capping panel in the capping position; and 
         [0022]    forming a permanent joint between the capping panel and the pocketed aerofoil body so as to fix the capping panel in position relative to the pocketed aerofoil body, thereby producing the aerofoil having a filled cavity. 
         [0023]    When the capping panel is in the capping position, its outer surface may be in a position relative to the pocketed aerofoil body that forms at least a part of gas washed surface of the finished aerofoil in use. Indeed, both the outer surface of the capping panel and the surrounding hollowed surface of the pocketed aerofoil body may form gas washed surfaces of the finished aerofoil in use. 
         [0024]    Using a pre-formed filler insert to provide support to the capping panel may result in tighter dimensional tolerance, for example by providing support to the capping panel during the step of forming a permanent joint with the pocketed aerofoil body. Use of a pre-formed filler insert may also avoid the need to compromise the design of the internal structure/cavities of the aerofoil. This may result in an improved structure, which may be stronger and/or lighter than conventional filled aerofoil structures. Any desired material may be used for the pre-formed filler insert, as it does not need to be injectable. This means that materials with improved properties, for example in terms of weight, density, and vibration damping, may be used. For example, anisotropic materials may be used and/or the properties and/or type of the material of the pre-formed filler insert may vary through the insert. The pre-formed filler insert may form the material that fills the cavity of the finished aerofoil. 
         [0025]    Any suitable process may be used to form the permanent joint between the capping panel and the pocketed aerofoil body, such as, for example welding. 
         [0026]    Any type of welding may be used as desired. For example, the welding may comprise using an energy beam, such as laser welding or electron beam welding. Laser welding may be particularly suitable due to the relatively small heat affected zone (HAZ). 
         [0027]    The pre-formed filler insert may be a foaming pre-formed filler insert. The foaming pre-formed filler insert may be activated so as to exert pressure on the inner surface of the capping panel. For example, the pre-formed filler insert may be activated after the step of locating the capping panel in the capping position but before the step of forming a permanent joint between the capping panel and the pocketed aerofoil body. After activation, the pre-formed filler insert may therefore comprise foam. Where the term foam or foaming is used herein, this should be taken to include both closed-cell and open-cell structures. Thus, the term foam as used herein includes both foam and sponge structures. 
         [0028]    Where a pre-formed filler insert is a foaming pre-formed filler insert that requires activation, the activation may be performed at any desired time and/or in any suitable manner. For example, activation may be by way of chemical activation, for example by providing a suitable activating agent to the filler insert. Where such chemical activation is used, the activating agent may be provided at any suitable time. For example, the activating agent may be provided prior to inserting the filler insert into the open pocket of the pocketed aerofoil body. In that case, the activating agent may take a predetermined time to cause the insert to foam or expand at least to its final shape. Thus, there may be a delay between activating the pre-formed filler insert and the pre-formed filler expanding, for example to its final size and/or shape. In general, regardless of how the pre-formed filler insert is activated, it may be activated before being inserted into the open pocket of the aerofoil body or after being inserted into the open pocket. 
         [0029]    Where an open-cell foaming pre-formed filler insert is used, a secondary filler may optionally be provided (for example by injection) after activation of the foam. Such a secondary filler may at least partially fill the at least some of the open-cells. 
         [0030]    The method may comprise engaging a shaped tool with the outer surface of the capping panel in the capping position. If a foaming pre-formed filler insert is used, then when it is activated the capping panel may then be pressed in the direction of the shaped tool. The capping panel may be said to be urged or pushed into the shaped tool. The surface of the shaped tool that engages with the capping panel may have the desired shape of the outer surface of the capping panel, which may be the shape of at least a part of a suction or pressure surface of an aerofoil. 
         [0031]    When the capping panel is located in the capping position, there may be a gap between the pre-formed filler insert and the capping panel. 
         [0032]    In such an arrangement, the pre-formed filler insert may not be in contact with the inner surface of the capping panel when the capping panel is placed in the capping position, and may become in contact once it is activated. Alternatively, and as described herein, the pre-formed filler may be in contact with the inner surface of the capping panel as soon as the capping panel is inserted into the capping position. 
         [0033]    Where a foaming pre-formed filler insert is used, it may comprise a foaming material that is covered at least in part by a barrier material. The barrier material (which may, for example, be a barrier tape) may contain, or surround, the foaming material during activation. The barrier material may, for example, comprise a metal (such as aluminium, which may be provided in the form of a foil) and/or a polymer (such as PTFE). The barrier material may be constructed and arranged to prevent the material of the insert (for example the foam and/or any adhesive) entering the region at which the capping panel and pocketed aerofoil body are subsequently joined (for example by welding) during foaming. Thus, the barrier material may prevent contamination of the joint/weld with the material of the filler insert (which, as described elsewhere herein, may comprise an adhesive layer). 
         [0034]    A foaming pre-formed filler insert may comprise, for example, epoxy and/or any resin based material. A foaming pre-formed filler insert may, for example, comprise a syntactic material (for example it may be referred to as a syntactic filler). Such a syntactic filler may comprise lightweight, hollow microspheres. 
         [0035]    The pre-formed filler insert may have a thickness such that the step of locating the capping panel in the capping position directly results in the capping panel being supported by the pre-formed filler insert. In such an arrangement, the pre-formed filler insert may or may not be a foaming insert. Again, any suitable material may be used for the insert, including homogeneous, non-homogeneous and composite materials. 
         [0036]    Where a non-foaming pre-formed filler insert is used, it may comprise, for example, a pre-cured resin based filler and/or a syntactic filler. The pre-formed filler insert may comprise reticulated vitreous carbon sponge, for example. The pre-formed filler insert may comprise a sandwich construction, such as a rigid/viscoelastic sandwich construction. Such a structure may act as a constrained layer damper, for example during manufacture and/or during use of the final aerofoil component. 
         [0037]    The pre-formed filler insert, regardless of whether it is foaming or non-foaming, may be manufactured in any suitable manner, for example by casting, injection moulding, or machining. 
         [0038]    The pocketed aerofoil body may comprise a step formed in the hollowed surface that extends around at least a part of the pocket. For example, the step may extend around the entire perimeter (so as to form a socket, for example), or a part of the perimeter, of the pocket. When the capping panel is located in the capping position, at least a part of its inner surface may rest on the step. The step may thus assist in locating the capping panel, which may be particularly beneficial where the insert and capping panel are not in contact prior to foaming of the insert. 
         [0039]    The pre-formed filler insert may be provided with an adhesive layer over at least a part of its surface. The adhesive layer may be, for example, an adhesive film. The adhesive layer may be arranged to bond the insert to the pocketed aerofoil body and/or to the capping panel. The adhesive layer may bond the insert to the pocketed aerofoil body and/or to the capping panel prior to the step of forming a permanent joint between the capping panel and the pocketed aerofoil body. Any suitable adhesive may be used, for example an epoxy or polyurethane based adhesive. 
         [0040]    The method of manufacturing an aerofoil may further comprise curing the pre-formed filer insert. The curing step may result in the pre-formed filler insert being bonded to the capping panel and/or the pocketed aerofoil body. Such a curing step may be performed prior to the step of forming a permanent joint between the capping panel and the pocketed aerofoil body. Where an adhesive is used, such a curing step may comprise curing the adhesive to form a bond. Any suitable curing process may be used, for example a thermal and/or chemical curing process. 
         [0041]    The pre-formed filler insert may comprise a vibration damping material. This may help to ensure that the finished filled aerofoil retains its manufactured shape during use and/or may help to reduce the likelihood of damage and/or failure of the aerofoil component as a result of vibration during use. 
         [0042]    The step of forming a permanent joint between the capping panel and the pocketed aerofoil body may comprise forming a permanent joint around substantially the entire interface between the capping panel and the pocketed aerofoil body. 
         [0043]    The method may comprise forming (for example machining) the pocket into an aerofoil blank in order to produce the pocketed aerofoil body. Where a step is provided around at least a part of the pocket, the method may also comprise forming (for example machining) the step. The method may comprise forming the aerofoil blank, for example by forging. Alternatively, the pocketed aerofoil body may be formed in any other suitable way, for example comprising a casting process. 
         [0044]    According to an aspect of the invention, there is provided an aerofoil manufactured according to the method described above and elsewhere herein. Such an aerofoil may be an aerofoil for a gas turbine engine. Such an aerofoil may be (or may form a part of), for example, a rotating blade or a stationary vane. Such an aerofoil may be a part of a compressor or a turbine. 
         [0045]    Purely by way of example, such an aerofoil may be an outlet guide vane of a turbofan gas turbine engine. 
         [0046]    According to an aspect of the invention, there is provided a gas turbine engine comprising an aerofoil (or aerofoil component) manufactured at least in part using a method as described above and elsewhere herein in relation to the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0047]    Embodiments of the invention will now be described by way of example only, with reference to the accompanying diagrammatic drawings, in which: 
           [0048]      FIG. 1  is a schematic sectional side view of a gas turbine engine; 
           [0049]      FIG. 2  is a schematic perspective view showing an aerofoil having a filled cavity in accordance with the invention; 
           [0050]      FIG. 3  is a schematic cross-section through a capping panel, pocketed aerofoil body and pre-formed filler insert during manufacture of an aerofoil; 
           [0051]      FIG. 4  is a schematic cross-section showing a pocketed aerofoil body and pre-formed filler insert supporting a capping panel during manufacture of an aerofoil; and 
           [0052]      FIG. 5  is a schematic cross-section showing an aerofoil having a capping panel joined to a pocketed aerofoil body, with a pre-formed filler insert inside the aerofoil. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0053]    With reference to  FIG. 1 , a ducted fan gas turbine engine generally indicated at  10  has a principal and rotational axis X-X. The direction X-X may be referred to as the axial direction of the engine. The engine  10  comprises, in axial flow series, an air intake  11 , a propulsive fan  12 , an intermediate pressure compressor  13 , a high-pressure compressor  14 , combustion equipment  15 , a high-pressure turbine  16 , an intermediate pressure turbine  17 , a low-pressure turbine  18  and a core engine exhaust nozzle  19 . A nacelle generally surrounds the engine  10  and defines the intake  11 , a bypass duct  22  and a bypass exhaust nozzle  23 . 
         [0054]    The gas turbine engine  10  works in a conventional manner so that air entering the intake  11  is accelerated by the fan  12  to produce two air flows: a first air flow A into the intermediate pressure compressor  13  and a second air flow B (which may be referred to as a bypass flow B) which passes through the bypass duct  22  to provide propulsive thrust. The intermediate pressure compressor  13  compresses the air flow A directed into it before delivering that air to the high pressure compressor  14  where further compression takes place. 
         [0055]    The compressed air exhausted from the high-pressure compressor  14  is directed into the combustion equipment  15  where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines  16 ,  17 ,  18  before being exhausted through the nozzle  19  to provide additional propulsive thrust. The high, intermediate and low-pressure turbines  16 ,  17 ,  18  respectively drive the high and intermediate pressure compressors  14 ,  13  and the fan  12  by suitable interconnecting shafts. 
         [0056]    As the air passes through the gas turbine engine  10  it is heated to high temperatures. In particular, the first airflow A reaches high temperatures as it passes through the core of the engine. Typically, particularly high temperatures may be reached at the exit of the combustion equipment  15 , and as the air subsequently passes through the high, intermediate and low-pressure turbines  16 ,  17 ,  18 . 
         [0057]    The gas turbine engine  10  comprises outlet guide vanes (OGVs)  100  extending across the bypass duct  22 , which therefore sit in the bypass flow B. Each OGV  100  takes the form of a large stator vane, and thus may be referred to as an aerofoil or aerofoil component  100 . A plurality of OGVs  100  is typically provided as an annular array in the bypass duct  22 . Because each OGV  100  is an especially large aerofoil component, it is particularly advantageous to reduce its weight. Thus, the OGV  100  in the gas turbine engine  10  is not a solid, homogeneous structure, but instead has a hollow cavity filled with a lighter weight material. 
         [0058]      FIG. 2  is a schematic of an aerofoil having a filled cavity (which may be referred to herein as a filled aerofoil) in accordance with the invention. In the  FIG. 2  example, the filled aerofoil is a filled outlet guide vane (OGV)  100 . The filled OGV  100  is manufactured by joining a capping panel  200  to a pocketed aerofoil body  300 . The capping panel  200  and the pocketed aerofoil body  300  may be any suitable material, for example metallic and/or composite, and may be the same or different materials. 
         [0059]    In  FIG. 2 , the interface between the pocketed aerofoil body  300  and the capping panel  200  is indicated by the line  110 . However, it will be appreciated that after manufacture of the filled aerofoil  100 , the join between the original capping panel  200  and the pocketed aerofoil body  300  will be seamless, and may not be visible. As such, the line  110  in  FIG. 1  is shown merely for the purpose of indicating the original interface between the capping panel  200  and the pocketed aerofoil body  300  prior to the joining and optional finishing of the filled aerofoil  100 . Furthermore, it will be appreciated that the extent of the capping panel  200  is not limited to that illustrated by the line  110  in  FIG. 2 , which is merely illustrative. 
         [0060]    In the example shown in  FIG. 2 , the filled OGV  100  comprises an inner attachment  330  (which may be a platform) and an outer attachment  340 , which may be used to attach the finished OGV  100  to the rest of the gas turbine engine. Such inner and outer attachments  330 ,  340  may be a part of the pocketed aerofoil body  300 . However, it will be appreciated that some pocketed aerofoil bodies  300  may not include one or both of the inner attachment  330  and outer attachment  340 . For example, the inner and/or outer attachments  330 / 340  may be separate features that may be attached to the filled aerofoil  100  after the capping panel  200  and the pocketed aerofoil body  300  have been joined together. 
         [0061]      FIG. 3  shows a close-up cross sectional view of the capping panel  200 , the pocketed aerofoil body  300 , and a pre-formed filler insert  400  during manufacture of the filled OGV  100 . It will be appreciated that  FIG. 3  shows only a part of the capping panel  200 , pocketed aerofoil body  300 , and pre-formed filler insert  400  (which may be referred to herein as an insert  400 ), and that the full parts extend in the chordwise direction, to the left in FIG.  3 .′ 
         [0062]    As shown in  FIG. 3 , the pocketed aerofoil body  300  comprises a pocket  310  which, prior to being covered by the capping panel  200 , is an open pocket  310 . The pocket  310  is formed in, and surrounded by, a surrounding hollowed surface  320 . In all examples, the surrounding hollowed surface  320  may have a step (which may be a recess, or pocket)  325  formed therein (for example around at least a part of the perimeter of the pocket  310 ), as in the  FIG. 3  example. The step  325  may support the capping panel  200  during manufacture, again as shown in the  FIG. 3  example. The step may or may not support the capping panel  200  in the capping position, because the capping position may be defined by the insert  400 , optionally in combination with a tool  500 . However, other examples, which may otherwise be substantially as shown in  FIG. 3 , may not have such a step  325 . Where no step  325  is provided, the capping panel  200  may be supported in any other suitable manner, for example using a different physical support, or by providing a low pressure (such as a vacuum or pseudo-vacuum) over the outer surface of the capping panel  200 . In other arrangements, such as illustrated in  FIG. 4  below, the capping panel  200  may be supported directly by the insert  400 . 
         [0063]    During manufacture, the insert  400  is inserted (or positioned) in the cavity  310 . The insert  400  may also be referred to as a core  400 . In the  FIG. 3  example, there is a gap between the insert  400  and an inner surface  210  of the capping panel  200 . In other words, in the  FIG. 3  example, the insert  400  does not engage with, or support, the capping panel  200  when the components are initially put into position. This means that, in the  FIG. 3  example, the depth a of the pocket  310  is greater than the combined thickness (b+c) of the capping panel  200  and the insert  400  when they are initially put into position for manufacture. 
         [0064]    The insert  400  may be an expandable insert  400 , which may be referred to as a foaming insert  400 . Such a foaming insert  400  may comprise and/or be formed as described elsewhere herein. Such a foaming insert  400  may be activated under given conditions, for example under given conditions of temperature and/or pressure and/or by providing an activation agent, such as a chemical activation agent, as prescribed for the particular material. 
         [0065]    In the  FIG. 3  example, once activated the foaming insert  400  comes into contact with the capping panel  200 , in particular with the inner surface  210  of the capping panel  200 . The foaming insert  400  may then substantially fill the cavity  310  (not shown in the figures). Under activation, the foaming insert  400  may exert a force on the capping panel  200  as it tries to expand further. The capping panel  200  may be constrained from moving away from the cavity  310 , for example by appropriate tooling  500 . 
         [0066]    The tooling  500  may have an engagement surface  520  that has the shape of the desired aerofoil profile over a portion at which it engages at least with an outer surface  220  of the capping panel  200 . As such, if the capping panel is provided with a force away from the cavity  320 , for example under the action of a foaming insert  400 , it is pressed into the engaging surface  520  of the tooling  500 . This may help to form an accurate aerodynamic profile over this region. This results in an accurate gas-washed profile of the finished aerofoil. 
         [0067]    Activation (or curing) of the foaming insert  400  may result in it being bonded to the capping panel  200 , and it may therefore act to hold the capping panel  200  to the pocketed aerofoil body  300  in the desired relative position. As described in more detail elsewhere herein, the capping panel  200  and the pocketed aerofoil body  300  may then be permanently bonded or joined together, for example by welding. 
         [0068]    The foaming insert  400  may have a barrier layer  410  formed around its periphery, as in the  FIG. 3  example. The barrier layer  410  may be in the form of a tape, for example. The barrier layer  410  may be, for example, a polymer and/or a metallic barrier layer  410 . Such a barrier layer  410  may be arranged to prevent any material from the insert  400  (or any associated adhesive) entering and/or contaminating the joint or bond (for example weld) between the capping panel  200  and the pocketed aerofoil body  300 . Such a barrier layer may, of course, be provided to any insert  400  according to the invention. 
         [0069]      FIG. 4  shows a filled capping panel  400  during manufacture using an alternative process. In the arrangements shown in  FIGS. 3 and 4 , like features are provided with like reference numerals. In  FIG. 4 , the insert  400  engages with, and thus supports, the inner surface  210  of the capping panel  200  throughout manufacture. The insert  400  shown in  FIG. 4  may be a precision engineered insert  400  to ensure that the capping panel  200 , and particularly the outer surface  220  of the capping panel  200 , is located accurately in the desired position when located on the insert  400 . In contrast to the  FIG. 3  arrangement, no step  325  in the pocketed aerofoil body  300  is required in order to provide initial support to the capping panel  200 , which is instead positioned and supported on the insert  400  throughout. 
         [0070]    Any suitable material may be used for the insert  400  shown in  FIG. 4 , such as a composite or a homogeneous material. Typically, the insert  400  would not be a foaming insert such as that shown in  FIG. 3 , but would instead retain its size and shape throughout manufacture. However, the insert  400  of the  FIG. 4  arrangement may be a foaming insert, in which case a tool such as the tool  500  shown in  FIG. 3 , may be provided to constrain the capping panel  200  when the insert  400  is activated. 
         [0071]    The insert  400  may be substantially incompressible throughout the joining process. For example, the insert  400  may be substantially incompressible even when subjected to elevated pressure and/or temperature which may be used to activate an adhesive that may be used to bond the capping panel  200  to the insert  400 . As an alternative to being substantially incompressible, the insert  400  may experience a degree of compression, expansion, or deformation during the manufacture of the filled aerofoil  100 , but in that case the compression/expansion/deformation would be specifically designed to ensure that the capping panel  200  is retained in the desired position during subsequent joining (for example welding, as described elsewhere herein). 
         [0072]    Once the capping panel  200  has been positioned on the insert  400 , it may be held in position, for example using an adhesive, such as a film adhesive  420 . As with the  FIG. 3  example, a barrier material  410  may be provided to surround the insert  400 . 
         [0073]      FIG. 5  shows a section through a part of a completed filled aerofoil  100 . The filled aerofoil  100  shown in  FIG. 5  may be manufactured according to the invention, such as by the methods and apparatus shown and described in relation to either  FIG. 3  or  FIG. 4 . 
         [0074]      FIG. 5  shows a permanent bond or joint in the form of a weld  600  between the capping panel  200  and the pocketed aerofoil body  300 . The weld  600  may be formed by any suitable welding process. For example, the weld  600  may be a laser weld  600 . The weld  600  may, for example, extend around the interface between the capping panel  200  and the pocketed aerofoil body  300 , such as that illustrated by way of example in  FIG. 2  by the line  110 . 
         [0075]    Because the capping panel is supported by the insert  400  in the interim state prior to welding, it may not be necessary to clamp the capping panel  200  during welding. This may be particularly advantageous where no step  325  is provided in the pocketed aerofoil body  300 , such as in the example shown in  FIG. 4 . 
         [0076]    Typically, immediately after a weld is formed, the area around the weld tends to shrink as it cools. This can cause problems with distortion of the geometry. However, because the capping panel  200  is supported over a significant portion of the area of its inner surface  210  (for example substantially all of its area) according to the invention, the conventional problems associated with post-weld distortion can be avoided, or at least reduced. Instead of distorting, the capping panel  200  used in the present invention would tend to adopt a (desired) shape corresponding to the underlying insert  400 . In turn, this may allow a thinner capping panel  200  than would conventionally be required to be used, because a reduced tolerance for post-weld machining may be used. 
         [0077]    As such, the shape of the capping panel  200  may be defined at least in part by the insert  400  on which it is supported during welding. As such, the insert  400  may at least in part define the shape of the capping panel  200 , for example the shape of the inner surface  210  and/or the outer surface  220  of the capping panel  200 . 
         [0078]    In the examples described herein, the capping panel  200  forms a part of the suction surface  120  of the finished filled aerofoil  100 . However, it will be appreciated that the capping panel could form a part of the pressure surface  130 . The capping panel  200 , the weld  600 , and the surrounding hollowed surface  320  of the pocketed aerofoil body  300  may all form part of the suction surface  120  (as shown in the  FIG. 5  example) or the pressure surface. A finishing process, such as machining or linishing, may be used after forming the permanent joint  600  between the capping panel  200  and the pocketed aerofoil black  600 , for example to avoid any unwanted material remaining after the joining step. 
         [0079]    It will be appreciated that it could be applied to any aerofoil or aerofoil component, such as any rotor blade or stator vane, for example for use in a turbine, compressor, or other aerofoil-shaped component of a gas turbine engine. Purely by way of example, the aerofoil  100  may be a filled OGV  100  such as that shown by way of example in  FIGS. 1 and 2 . 
         [0080]    It will be appreciated that many designs and/or arrangements of features, such as capping panel  200 , pocketed aerofoil body  300  or insert  400 , other than those shown in and described in relation to  FIGS. 1 to 5  and not explicitly described herein fall within the scope of the invention. Furthermore, any feature described and/or claimed herein may be combined with any other compatible feature described in relation to the same or another embodiment.