METHOD FOR MANUFACTURING A REINFORCED CAVITY SHOVEL

Description

Technical Field

[0001] The present invention relates to the general field of blades, propellers or vanes made of composite material having an internal cavity. Previous technique

[0002] In the field of aircraft engines, turbomachine blades can be made of composite materials to achieve equivalent or greater strength than metal, but with a lower overall mass. Indeed, improving turbomachine performance, particularly in terms of fuel consumption, requires a reduction in mass.

[0003] In the case of composite blades produced by three-dimensional weaving, the composite material at the core of the blade has only a limited influence on the mechanical performance of the part, even though it accounts for a significant portion of the blade's mass. Therefore, it is advantageous to manufacture hollow blades with a composite skin produced by three-dimensional weaving. Such a manufacturing process is described, for example, in document US2015040396A1.

[0004] However, the presence of a cavity inside the blade can be detrimental, particularly in the case of a long blade and a large cavity. Indeed, in this case, the thin composite material skins of the blade exhibit low natural vibration modes that closely resemble the natural modes of the operating engine. Thus, the thin composite material skins can begin to vibrate, or even resonate.

[0005] In addition, the presence of a large cavity inside the blade reduces resistance to torsion and aerodynamic forces.

[0006] Document FR 2 559 422 A1 discloses a manufacturing process for a blade profile element comprising a laminated hollow envelope hosting a corrugated support structure. Description of the invention

[0007] The present invention aims to provide a solution that makes it possible to produce turbomachine blades from composite material having a reinforced internal cavity, while remedying the aforementioned disadvantages.

[0008] To this end, the invention proposes a method for manufacturing a turbomachine blade made of composite material having a cavity, comprising at least: the production of a core having the shape of the cavity of the blade to be manufactured, said core comprising a reinforcing structure occupying only part of the volume of the core, the remaining volume of the core being occupied by a fugitive material, the formation of a skin of composite material around the core, and the removal of the fugitive material to obtain a blade of composite material having a cavity reinforced by the reinforcing structure.

[0009] Thus, the resulting blade cavity is reinforced by a strengthening structure, giving the blade greater mechanical strength and reducing the risk of skin vibration. By occupying a limited volume of the blade cavity, the strengthening structure does not add excessive mass to the blade.

[0010] By "fugitive material" we mean here a material that can be removed mechanically, chemically or thermally.

[0011] According to a particular feature of the invention, the reinforcement structure has at least partly a lattice architecture.

[0012] According to another particular feature of the invention, the reinforcement structure includes at least one support element joining two walls of the cavity opposite each other.

[0013] This support element can, for example, take the form of a shell, a plate, or a solid body. On the final blade, these support elements can simultaneously support the two skins forming the intrados and extrados of the blade, thereby increasing the blade's mechanical strength and limiting the risk of skin vibration.

[0014] According to another particular feature of the invention, the support element is positioned on one or more antinodes of the natural modes of vibration of the walls of the cavity.

[0015] By placing one or more support elements on the antinodes of the natural modes of vibration, the blade cavity or blade can be effectively reinforced with reduced and lightweight support elements.

[0016] According to another particular feature of the invention, the support element is a solid body conforming to the shape of a part of the cavity.

[0017] According to another particular feature of the invention, the reinforcement structure includes protrusions projecting outwards from the core.

[0018] These protruding protrusions ensure a better mechanical connection between the reinforcement structure and the composite material skin of the blade.

[0019] According to another particular feature of the invention, the composite material skin is produced by injecting a matrix precursor resin into a fibrous preform covering the core, the process further comprising the treatment of said resin to obtain a skin comprising a fibrous reinforcement densified by said matrix.

[0020] According to another particular feature of the invention, the fibrous preform is made by inserting the core into a debinding of a fibrous blank made in one piece by three-dimensional weaving of yarns.

[0021] According to another particular feature of the invention, the fibrous preform is obtained by draping fibrous layers around the core.

[0022] According to another particular feature of the invention, the composite material skin is made by draping pre-impregnated fibrous layers of a matrix precursor resin around the core, the process further comprising the treatment of said resin to obtain a skin comprising a fibrous reinforcement densified by said matrix. Brief description of the drawings

[0023] [ Fig. 1 ] There figure 1 is a schematic three-dimensional view of a lattice reinforcement structure according to the invention. Fig. 2 ] There figure 2 is a schematic three-dimensional view of a core according to the invention comprising the reinforcement structure of the figure 1 . [ Fig. 3 ] There figure 3 is a schematic three-dimensional view of a reinforcement structure comprising a shell according to the invention. Fig. 4 ] There figure 4is a schematic three-dimensional view of a core according to the invention comprising the reinforcement structure of the figure 3 . [ Fig. 5 ] There figure 5 is a schematic three-dimensional view of a reinforcement structure comprising a shell and a solid body according to the invention. Fig. 6 ] There figure 6 is a schematic three-dimensional view of a core according to the invention comprising the reinforcement structure of the figure 5 . [ Fig. 7 ] There figure 7 is a schematic three-dimensional view of a reinforcement structure comprising a truss, a shell, and a solid body according to the invention. Fig. 8 ] There figure 8 is a schematic three-dimensional view of a core according to the invention comprising the reinforcement structure of the figure 7 . [ Fig. 9 ] There figure 9is a schematic plan view of a woven fibrous blank intended for the production of a blade by RTM injection according to an embodiment of the invention. Fig. 10 ] There Figure 10 is a cross-sectional view of the fibrous rudiment of the figure 9 . [ Fig. 11 ] There figure 11 is a schematic view of a fibrous preform produced by inserting a core according to the invention into the fibrous blank of the Figures 9 and 10 . [ Fig. 12 ] There figure 12 is a schematic three-dimensional view of a blade made from the fibrous preform of the figure 11 . Description of the implementation methods

[0024] The invention is generally applicable to various types of composite material parts comprising an internal cavity. The invention finds advantageous application for turbomachine blades, and in particular for fixed blades or stators for aeronautical gas turbine engines of the outlet guide vane or "OGV" type.

[0025] A core is made in the shape of the internal cavity of the blade from composite material to be produced, and including a reinforcing structure.

[0026] As illustrated on the figures 1 and 2 The reinforcement structure can take the form of a truss and consist of a three-dimensional assembly of bars. figures 1 and 2 illustrate respectively a reinforcement structure 10 and a core 1 comprising the reinforcement structure 10. The truss 10 has the dimensions of the core to be produced, so that the reinforcement structure is flush with the outer surface of the core as illustrated in the figure 2 In the example illustrated on the figures 1 and 2 The bars are straight and of constant cross-section. The bars can have a non-constant cross-section or be curved.

[0027] As illustrated on the figures 3 and 4 The reinforcement structure may include one or more shell-shaped parts. figures 3 and 4 illustrate respectively a reinforcement structure 20 and a core 2 comprising the reinforcement structure 20. The reinforcement structure 20 is flush with the surface of the core.

[0028] The shell-shaped parts can be strategically positioned to support or reinforce specific areas of the blade. According to a particular embodiment of the invention, a preliminary study of the blade skin vibration modes can be conducted to determine the location of the antinodes of these vibration modes. Preferably, the study will focus on determining the simple bending and torsion modes. Thus, the shell-shaped parts will preferably be positioned orthogonally to the locations on the skin corresponding to these antinodes.

[0029] In the example illustrated on the figures 3 and 4The shell-shaped reinforcement structure 20 may include a central part 21a and two support parts 21b positioned perpendicularly on either side of the central part 21a. The central part 21a is positioned perpendicular to the two surfaces 2a and 2b of the core 2, which are intended to come into contact with the blade skins, corresponding to the intrados and extrados of the blade. Thus, the reinforcement structure can support and strengthen the two blade skins to limit their vibrations. The dimensions of the central part 21a and the two support parts 21b may differ from those shown in the diagrams. figures 3 and 4 Preferably, thinner thicknesses will be used for the central part 21a and for the support parts 21b, in order to reduce their mass.

[0030] The shell-shaped sections can also be positioned in the thickest areas of the blade. Furthermore, the shell-shaped sections can also have an acoustically advantageous geometry, for example, to reduce noise.

[0031] The reinforcement structure may also include solid bodies, which will conform to the shape of part of the blade cavity. figures 5 and 6 respectively illustrate a reinforcement structure 30 and a core 3 comprising the reinforcement structure 20.

[0032] As illustrated on the figures 5 and 6The reinforcement structure 30 comprises a solid body 32 and a shell-shaped portion 31. In particular, the shell-shaped portion 31 includes a central portion 31a and two support portions 31b positioned perpendicularly on either side of the central portion 31a. The central portion 31a is positioned perpendicular to the two surfaces 3a and 3b of the core 3 intended to come into contact with the blade skins, which will correspond to the intrados and extrados of the blade. The dimensions of the central portion 31a and the two support portions 31b may differ from those shown in the diagrams. figures 5 and 6 Preferably, thinner thicknesses will be used for the central part 31a and for the support parts 31b, in order to reduce their mass.

[0033] The solid bodies of the reinforcement structure can be strategically placed to support or strengthen specific areas of the blade. However, if the reinforcement structure is made of metal, the presence and size of solid bodies within the metal reinforcement structure should be limited to minimize its mass.

[0034] The reinforcement structure can include and combine different types of reinforcement. Thus, as illustrated on the figures 7 and 8 , the reinforcement structure may include lattice parts 43, shell-shaped parts 41 and solid bodies 42.

[0035] THE figures 7 and 8 These figures respectively illustrate a reinforcement structure 40 and a core 4 comprising the reinforcement structure 40. Lattice sections are preferentially used for parts of the core with large volumes. Solid sections are preferentially used for parts of the core with small volumes.

[0036] As illustrated on the figures 1 and 2 The reinforcement structure may include protrusions 11 projecting outwards from the outer surface of the core. These protrusions 11 are intended to provide mechanical attachment between the reinforcement structure and the composite material skins of the blade. These protrusions 11 can be arranged in a particularly advantageous way to provide mechanical attachment to the composite material blade skins having a cavity. For example, in the case of a blade, the protrusions 11 will primarily be positioned to ensure a mechanical connection between the reinforcement structure and the upper and lower surfaces of the blade.

[0037] In the example shown on the figures 1 and 2The protruding protrusions are oriented perpendicular to the core surface. If the core is intended to be inserted into a fibrous preform, for example by unbinding, such protrusions can hinder core insertion by catching on the preform fibers before the core is fully positioned. Thus, according to a particular embodiment of the invention, if the core is initially inserted through a first surface, the protruding protrusions will be oriented opposite to said surface. Consequently, the core can be inserted through said surface without the protrusions "catching" on the fibers. When the core is correctly positioned in the fibrous preform, the protruding protrusions provide mechanical grip, particularly in the direction opposite to the core's insertion direction.

[0038] Lattice structures easily allow the passage of functional elements such as cables, pipes, conduits, or wires inside and through the internal reinforcement structure of the blade. However, it may be necessary to create bores within shell-shaped structures or solid bodies to allow the passage of these functional elements of the blade.

[0039] According to a first embodiment of the core of the invention, the metal reinforcement structure is made.

[0040] A metal with a low coefficient of thermal expansion will be preferred for manufacturing the reinforcement structure in order to limit stresses within the composite blade. The reinforcement structure metal could, for example, be titanium, Inconel, or stainless steel.

[0041] The metal reinforcement structure can be produced using additive manufacturing. Alternatively, it can be manufactured by assembling several metal parts using conventional methods. For example, the different parts can be joined by welding or bonding.

[0042] The resulting metallic reinforcement structure is then inserted into a mold shaped like the internal cavity of the blade to be produced. A condensing material 6 is injected or poured into the mold to form a core shaped like the blade cavity and containing the metallic reinforcement structure. The condensing material can be poured or injected at high temperatures, for example, above 400°C. Because the reinforcement structure is metallic, the condensing material can be handled at relatively high temperatures without damaging the reinforcement structure. If the metallic reinforcement structure has protruding protrusions, the casting or injection mold is designed to accommodate these protrusions.

[0043] The fugacious material can be a salt or a mixture of salts, for example, a mixture of potassium chloride and potassium carbonate. The fugacious material can also be sand or a mixture of sands. The use of such a fugacious material for creating a core is described, for example, in document EP0192507B1.

[0044] In one variant, the complete core can be produced in a single step, meaning the metal reinforcement structure is created simultaneously with the rest of the core. The core is produced by additive manufacturing using at least two materials: the first material is a metal used for the reinforcement structure, and the second material is used to create the ephemeral portion of the core. The second material could be, for example, a material such as ST-130™ FDM, marketed by Stratasys, which dissolves in a basic solution without damaging the composite material of the blade being manufactured. In this variant, the second material used to create the ephemeral portion of the core can be placed only on the surface of the cavity, around the metal reinforcement structure. Thus, the core is not necessarily a solid core.Using a partially empty kernel allows the fleeting part 6 to be removed more quickly during its removal step, which will be described later in the description.

[0045] According to a second embodiment of the core of the invention, the reinforcing structure is made of polymer or composite material. The polymer for manufacturing the structure may contain discontinuous or continuous fibers. The fibers may be made of glass, carbon, or aramid. The resin may be thermosetting or thermoplastic. Preferably, the polymer or composite reinforcing structure should be able to withstand, without being altered, the processing temperatures of the composite material skins. Thus, the reinforcing structure can preferably withstand temperatures up to 180°C without being altered.

[0046] The composite reinforcement structure can be produced by additive manufacturing. The composite reinforcement structure can also be manufactured by assembling several parts of composite material, for example, by bonding.

[0047] The resulting composite reinforcement structure is then introduced into a mold shaped like the internal cavity of the blade to be produced. A smoldering material is injected, cast, or compressed into the mold to form a core shaped like the blade cavity and incorporating the composite reinforcement structure. Preferably, the smoldering material should be cast, injected, or compressed at a temperature that does not damage the composite reinforcement structure. For example, Aquacore® is a ceramic material that can be used as a smoldering material to form the core because it bonds under high pressure and requires only post-firing at a temperature below 100°C. The smoldering material can be salt- or sand-based, or a mixture thereof. If the composite reinforcement structure has protruding features, the casting or injection mold must accommodate these features.

[0048] According to one variant, the complete core can be made in a single step, i.e. the composite reinforcement structure is made simultaneously with the making of the rest of the core.

[0049] According to a first example of this variant, the core is produced by additive manufacturing of at least two materials. The first material is a composite intended to form the reinforcement structure, and the second material is intended to form the ephemeral part 6 of the core. The second material could, for example, be a material such as ST-130™ FDM, marketed by Stratasys, which dissolves in a basic solution without damaging the composite material of the blade being manufactured. In this variant, the second material intended to form the ephemeral part 6 of the core can be placed only on the surface of the cavity, around the composite reinforcement structure. Thus, the core is not necessarily a solid core. The use of a partially hollow core allows for faster removal of the ephemeral part 6 during its removal step, which will be described later.

[0050] According to a second example of this variant, the core can be manufactured by shrink-fitting at least two powders, the first powder being intended to form the composite of the reinforcing structure, and the second powder being intended to form the fugitive part 6 of the core.

[0051] When the core in the shape of the internal cavity of the blade made of composite material has been produced, it is used to manufacture said blade made of composite material.

[0052] In the embodiments of the core of the invention presented above, it is important that the core surface be sealed. Indeed, during the manufacturing process of the blade from a composite material having an internal cavity, resin creep into the core would increase the blade's mass by filling the internal cavity with unwanted material. Furthermore, resin creep into the core could lead to the formation of pores or dry patches in the outer composite material.

[0053] A finishing operation can be performed on the core manufactured as described above to improve its surface finish or sealing. This finishing operation is particularly beneficial for cores produced by 3D printing.

[0054] We will now describe different embodiments of a blade comprising a reinforced cavity according to the process of the invention.

[0055] According to a first embodiment of the process of the invention presented on the figures 9 to 12 , a fibrous rough 100 is produced to envelop the core.

[0056] The blank 100 is obtained from a strip 101 woven by three-dimensional (3D) or multi-layer weaving, the strip 101 generally extending in a direction L corresponding to the longitudinal direction of the blade to be manufactured. The weaving is carried out, for example, with warp threads extending in the direction L.

[0057] A debonding 102 is formed substantially in the middle of the strip 101, over at least part of the length of the fibrous blank 100 between the longitudinal edges 101c and 101d, between boundaries 102c and 102d. Preferably, the debonding 102 should extend at least to one of the transverse edges 101a and 101b. In the example illustrated on the Figures 9 and 10The debonding extends along the entire length of the fibrous blank 100, between the transverse edges 101a and 101b. This debonding 102 allows the formation of an internal cavity in the fibrous blank 100, intended to allow the passage of the previously produced core.

[0058] The fibrous blank can be produced by 3D weaving with an interlock weave that includes unbinding. "Interlock" weaving refers to a weave structure in which each layer of weft yarns interlocks several layers of warp yarns, with all yarns in the same weft column having the same movement within the plane of the weave. As is well known, unbinding is achieved between two layers of warp yarns by omitting a weft yarn from the unbinding zone to interlock yarns from warp layers located on either side of the unbinding.

[0059] The fibrous blank 100 comprises a plurality of layers of warp yarns which are linked by 3D weaving except at the unlinking 102. Apart from the unlinking 102, the layers of warp yarns of the blank 100 are all linked together.

[0060] Ceramic yarns, particularly silicon carbide (SiC) yarns, such as those supplied under the name "Nicalon" by the Japanese company Nippon Carbon, can be used for weaving. Other ceramic yarns are also suitable, including refractory oxide yarns, such as alumina (Al₂O₃) yarns, especially for oxide / oxide CMC materials (fiber reinforcement fiber and refractory oxide matrix). Preferably, carbon yarns are used for weaving, for example, for a carbon fiber-reinforced CMC material.

[0061] The fibrous tape can be treated to remove the sizing present on the fibers and the presence of oxide on the surface of the fibers as known per se.

[0062] Also known as a thin interphase coating, a debrittle layer can then be formed on the filter tape fibers by chemical vapor infiltration (CVI). Examples of interphase materials include pyrolytic carbon (PyC), boron nitride (BN), and boron-doped carbon (BC). The thickness of the formed layer is typically between 10 and 100 nanometers to maintain the deformation capacity of the fiber blanks.

[0063] The fibrous strip is then impregnated with a consolidation composition, typically a carbon precursor resin or a ceramic precursor resin, possibly diluted in a solvent. Consolidation can be carried out in an oven.

[0064] According to this first embodiment of the invention, the core is introduced into the fibrous blank 100 by the unbinding 102 so as to form a fibrous preform 200 as illustrated in the figure 11 If the nucleus has protruding protrusions on its external surface, these fit between the fibers of the fibrous precursor.

[0065] The next step involves densifying the fibrous preform 200 by filling its porosity, throughout all or part of its volume, with the material constituting the matrix. The matrix of the composite material for the part to be manufactured can be obtained using a method known per se via the liquid process.

[0066] A forming step can preferably be performed after the core has been inserted into the fibrous preform. This forming step helps to reduce the bulking of the preform. This forming step is preferably performed while the fibrous preform is warm, either wet or dry.

[0067] The liquid process involves impregnating the preform with a liquid composition containing an organic precursor of the matrix material. The organic precursor is usually in the form of a polymer, such as a resin, possibly diluted in a solvent. The preform, positioned around the core, is placed in a mold that can be sealed tightly with a cavity shaped to match the final molded part, and which may have a twisted shape corresponding to the final form of the part to be manufactured. The mold is then closed, and the liquid matrix precursor (for example, a resin) is injected into the entire cavity to impregnate all the fibrous material of the preform.

[0068] The transformation of the precursor into an organic matrix, namely its polymerization, is achieved through heat treatment, generally by heating the mold, after the removal of any solvent and crosslinking of the polymer. The preform remains in the mold, which has a shape corresponding to that of the aerodynamically profiled structure. The organic matrix can be obtained, in particular, from epoxy resins, such as the high-performance epoxy resin sold under reference PR 520 by CYTEC, or from liquid precursors of carbon or ceramic matrices.

[0069] In the case of carbon or ceramic matrix formation, heat treatment consists of pyrolyzing the organic precursor to transform the organic matrix into a carbon or ceramic matrix, depending on the precursor used and the pyrolysis conditions. For example, liquid carbon precursors can be resins with relatively high coke content, such as phenolic resins, while liquid ceramic precursors, particularly SiC, can be polycarbosilane (PCS), polytitanocarbosilane (PTCS), or polysilazane (PSZ) type resins. Several consecutive cycles, from impregnation to heat treatment, can be carried out to achieve the desired degree of densification.

[0070] The densification of the fibrous preform is preferentially achieved using the well-known resin transfer molding (RTM) process. According to the RTM process, the fibrous preform, arranged around the core, is placed in a mold with the desired external shape of the part. The core can act as a counter-mold. A thermosetting resin is injected into the internal space between the rigid part and the mold, which contains the fibrous preform. A pressure gradient is generally established in this internal space between the resin injection point and the resin discharge ports to control and optimize the resin impregnation of the preform.

[0071] The resin used can be, for example, an epoxy resin. Resins suitable for RTM processes are well-known. They preferably have a low viscosity to facilitate their injection into the fibers. The choice of temperature class and / or the chemical nature of the resin is determined according to the thermomechanical stresses to which the blade is subjected. Once the resin has been injected throughout the reinforcement, it is polymerized by heat treatment according to the RTM process.

[0072] The fugitive portion 6 of the core is then removed. If direct access to all fugitive portions of the core is not possible, bores can be made in the non-functional parts of the composite blade. For example, in the case of a flux straightener, the bores will be made in the platforms.

[0073] A suitable solution is brought into contact with the fugacious parts of the core so that they can be removed. For example, to remove sand-based fugacious parts, the solution may contain at least one organic solvent such as dimethylformamide, piperidine, tetrahydrofuran, or butanone. A basic solution can also be used, for example, to remove fugacious parts made of material such as ST-130™< FDM, marketed by Stratasys. In the case of water-soluble fugacious parts, the use of pressurized water is sufficient to remove them.

[0074] This results in a blade made of composite material 300 having an internal cavity reinforced by a reinforcing structure 10, as illustrated in the figure 12If the reinforcement structure includes protruding protrusions, these are inserted between the fibers of the composite material in order to create a mechanical connection between the reinforcement structure and the part of the blade made of composite material manufactured by the RTM process.

[0075] According to a second embodiment of the process of the invention (not illustrated), the blade is made of composite material having an internal cavity in a well-known draping method. Thus, fibrous layers are applied to the previously fabricated core. The fibrous layers may be pre-impregnated with a matrix precursor resin, or may be dry layers that are densified with a resin after draping. The fibrous layers may be one-dimensional, two-dimensional, or three-dimensional fabrics, provided they have a thickness that allows for draping. The fibrous layers may also consist of discontinuous sheets of long fibers, with a controlled or random distribution.

[0076] The resin(s) impregnating the layers are cross-linked by the same heat treatment applied to all the fibrous layers. This results in a composite material envelope around the core.

[0077] The blade made of composite material can also be obtained in a well-known way by thermocompression of layered plies.

[0078] The fugitive portion 6 of the core is then removed. If direct access to all fugitive portions of the core is not possible, bores can be made in the non-functional parts of the composite blade. For example, in the case of a flux straightener, the bores will be made in the platforms.

[0079] A suitable solution is brought into contact with the fugacious parts of the core so that they can be removed. For example, to remove sand-based fugacious parts, the solution may contain at least one organic solvent such as dimethylformamide, piperidine, tetrahydrofuran, or butanone. A basic solution can also be used, for example, to remove fugacious parts made of material such as ST-130™< FDM, marketed by Stratasys. In the case of water-soluble fugacious parts, the use of water is sufficient to remove them.

[0080] This results in a composite blade with an internal cavity reinforced by a reinforcing structure. If the reinforcing structure includes protruding protrusions, these are inserted between the fibers of the composite material to create a mechanical connection between the reinforcing structure and the composite material skins of the blade.

Claims

1. A method for manufacturing a turbomachine vane (300) made of composite material and having a cavity, comprising at least: - making a core (1; 2; 3; 4) with the shape of the cavity of the vane (300) to be manufactured, said core comprising a reinforcing structure (10; 20; 30; 40) occupying only part of the volume of the core, the remaining volume of the core being occupied by a material of a fleeting nature (6), the reinforcing structure (10; 40) having at least partly lattice architecture, - forming a composite material skin around the core (1; 2; 3; 4), and - eliminating the fleeting material (6) to obtain a composite material vane (300) with a cavity reinforced by the reinforcing structure (10; 20; 30; 40).

2. The manufacturing method according to claim 1, wherein the reinforcing structure (20; 30; 40) comprises at least one support element (20; 31; 32; 41; 42) joining two walls of the cavity facing each other.

3. The manufacturing method according to claim 2, wherein the support element (20; 31; 41) is positioned on one or several antinodes of the natural modes of vibration of the walls of the cavity.

4. The manufacturing method according to claim 2 or 3, wherein the support element (32; 42) is a solid body matching the shape of a portion of the cavity.

5. The manufacturing method according to any one of claims 1 to 4, wherein the reinforcing structure (10) comprises protrusions (11) projecting towards the outside of the core (1).

6. The manufacturing method according to any one of claims 1 to 5, wherein the composite material skin is made by injection of a matrix precursor resin into a fibrous preform (200) covering the core (1), the method further comprising the treatment of said resin to obtain a skin comprising a fibrous reinforcement densified by said matrix.

7. The manufacturing method according to claim 6, wherein the fibrous preform (200) is made by insertion of the core (1) into a non-interlinking (102) of a fibrous blank (100) made in one piece by three-dimensional weaving of yarns.

8. The manufacturing method according to claim 6, wherein the fibrous preform is obtained by draping of fibrous layers around the core.

9. The manufacturing method according to any one of claims 1 to 5, wherein the composite material skin is made by draping of fibrous strata preimpregnated with a matrix precursor resin around the core, the method further comprising the treatment of said resin to obtain a skin comprising a fibrous reinforcement densified by said matrix.