WO2025120290A1 - Soluble core for the manufacture of hollow parts made of organic matrix composite material - Google Patents

Abstract

The invention relates to a forming core (50) comprising a liquid-soluble body (52) and a skin (54) comprising at least one layer of a mould release agent coating the soluble body (52). The invention also relates to a method for obtaining the forming core. The invention also relates to a hollow part (62) made of organic matrix composite material comprising a cavity (80), wherein the cavity (80) is covered with a skin (54) comprising at least one layer of a mould release agent coating the soluble body. The invention also relates to a method for the manufacture of the hollow part (62).

Description

DESCRIPTION TITLE: SOLUBLE CORE FOR THE MANUFACTURE OF HOLLOW PARTS MADE OF ORGANIC MATRIX COMPOSITE MATERIAL

Technical field

[0001] The present disclosure relates to the manufacture of hollow parts made of organic matrix composite material, in particular turbomachinery, in particular hollow parts made of organic matrix composite material (OMC). More specifically, the present disclosure relates to a molding core used in the manufacture of OMC parts, a method of manufacturing such a molding core, a method of manufacturing such a hollow OMC part, for example a hollow OMC part, and the part thus obtained.

Prior art

[0002] CMO parts are commonly used in aeronautical engines such as aircraft turbomachines in order to reduce their mass, while guaranteeing the desired mechanical properties, in particular, their stiffness.

[0003] These CMO parts are notably commonly used in the production of fan module parts, for example fan blades or outlet guide vanes (OGV in accordance with the English acronym for “Outlet Guide Vane”).

[0004] These CMO parts can be obtained by using a fibrous reinforcement made from a three-dimensional weave in which the threads intertwine in a three-dimensional manner (so-called “3D interlock” weave) and which is impregnated in an organic matrix.

[0005] The organic matrix can be injected by liquid means according to the LCM process (in accordance with the acronym in English for “Liquid Composite Molding”), for example according to the VARTM process (in accordance with the acronym in English for “Vacuum Assisted Resin Transfer Molding”).

[0006] Processes such as stamping, thermocompression or additive manufacturing can also be used. [0007] CMOs withstand temperatures ranging from 100°C to 250°C. These materials replace metal parts in certain parts of turbomachines, particularly for fan blades and/or outlet guide vanes.

[0008] Furthermore, their use contributes to optimizing the performance of turbomachines or turbomachine equipment, in particular by reducing the overall mass of the turbomachine, thus reducing fuel consumption which in turn leads to a reduction in harmful emissions (CO, _CO2 , _NOx , etc.).

[0009] Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various restrictions on carbon emissions have been, are being or will be adopted by various states. In particular, an ambitious standard applies both to new types of aircraft and those in circulation requiring the implementation of technological solutions in order to make them compliant with current regulations. Civil aviation has been mobilizing for several years now to make a contribution to the fight against climate change.

[0010] Technological research efforts have already made it possible to significantly improve the environmental performance of aircraft. The factors impacting all phases of design and development to obtain less energy-intensive, more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental consequences are taken into account with the aim of improving the energy efficiency of aircraft.

[0011] Consequently, the reduction of negative climate impact is a permanent subject of improvement through the use of methods and the exploitation of virtuous development and manufacturing processes and minimizing greenhouse gas emissions to the minimum possible to reduce the environmental footprint.

[0012] This sustained research and development work covers new generations of aircraft engines, the lightening of aircraft, in particular through the materials used and lighter on-board equipment, and the development of the use of electrical technologies. to ensure propulsion, and, essential complements to technological progress, aeronautical biofuels.

[0013] In order to lighten the fan blades and/or the CMO outlet guide vanes, it is known to manufacture hollow blades.

[0014] Manufacturing processes that enable parts to be directly obtained in the desired shape are particularly advantageous from an industrial point of view. Indeed, they generally allow for a better production rate. Such parts are obtained using molds having the shape of the desired part.

[0015] However, not all parts are compatible with such processes. Although molding processes have been widely developed and can be used for a very wide variety of different materials, the desired geometry of the parts is still very often limiting.

[0016] For example, since the final geometry includes cavities it is not possible to obtain the part directly by molding.

[0017] Solutions nevertheless exist for the preparation of parts having cavities, such as for example the arrangement in the mold of cores, which are removed or eliminated once the part is obtained.

[0018] FR3125238 discloses a core comprising a material which decomposes on contact with water or humid air. This material is present at the grain boundaries, which allows the core to fragment and therefore to be eliminated when the core is placed in the presence of water or humid air.

[0019] However, removing the core once the part is finished complicates the molding process or requires the use of special tools. Also, for removing the core, it is necessary to provide large openings between the cavity and the exterior of the part and certain part geometries are not accessible via this technology.

[0020] In the case of a soluble core, the core can be dissolved once the desired part has been obtained. Cores have thus been proposed and the geometry of the accessible parts is then limited by the constraints in the manufacture of the core.

[0021] For the manufacture of cores, the solutions proposed in the prior art all have defects, for example, on the minimum size of the cores which can be obtained or the complexity of the core manufacturing process. Also, the processes for dissolving the core can be complex and/or involve toxic compounds.

[0022] There remains a need for improvement in the processes for manufacturing hollow parts by molding processes.

Statement of the invention

[0023] The present disclosure aims to remedy at least in part these drawbacks, in particular to very significantly improve the performance of aircraft and, in this sense, contribute to reducing the environmental impact of aircraft.

[0024] For this purpose, the present disclosure relates to a forming core comprising a body soluble in a liquid and a skin comprising at least one layer of a release agent coating the soluble body.

[0025] By way of non-limiting example, the liquid may be an aqueous solution, water or an organic solvent.

[0026] The choice of a soluble body which can be dissolved by water makes it possible to have parts whose extraction openings, which allow the elimination of the soluble body, are smaller than for solutions of the prior art, in particular less than 5 millimeters or even less than 4 millimeters.

[0027] Furthermore, from an environmental and safety point of view, water is less harmful and reduces risks to operators compared to other liquids, for example a non-aqueous solvent.

[0028] Thanks to the skin comprising at least one layer of a release agent which coats the entire soluble body, the forming core is not exposed to liquids and/or humidity during the phases of storage, handling, insertion of the molding core into a fiber preform and/or the step of shaping the preform, this step possibly in particular requiring the humidification of the preform to facilitate its forming. Similarly, the forming core can be used to form an external surface of the fiber preform, the forming core then being arranged between a surface of the mold and an external surface of the fiber preform.

[0029] Thus, the forming core does not undergo degradation before its removal from the part. [0030] Furthermore, when injecting resin into the fiber preform, a forming core that has been exposed to liquids and/or moisture may begin to dissolve in the fiber preform and contaminate the impregnation resin of the fiber preform, which could result in altering the mechanical properties of the resin and therefore of the final part.

[0031] It is understood that the soluble body may comprise a material which dissolves upon contact with a liquid, either by complete dissolution of the soluble body, or by dissolution of the grain boundaries of the soluble body and fragmentation of the soluble body. The fragments can be easily removed from the cavity formed by the dissolution of the grain boundaries and the fragmentation of the soluble body.

[0032] In some embodiments, the mold release agent comprises an organic solvent.

[0033] The release agent is thus chosen so as not to be a solvent for the soluble core which dissolves on contact with an inorganic solvent such as water. Furthermore, the release agent is chosen so as to be chemically compatible with the resin injected into the fiber preform, so as not to pollute the resulting composite.

[0034] In some embodiments, the skin comprises a first layer of a release agent and at least a second layer of a release agent distinct from the release agent of the first layer.

[0035] It is understood that each layer of release agent makes it possible to obtain the aforementioned effects, but these layers may have different compositions and have different and complementary functions. By way of non-limiting example, a first layer of release agent may be a pore-filling agent, and a second layer may be a release agent.

[0036] In some embodiments, the soluble body may comprise a soluble thermoplastic polymer.

[0037] By way of non-limiting example, the soluble thermoplastic polymer is soluble in a non-aqueous solvent, for example in acetone.

[0038] In some embodiments, the soluble body may comprise a material that decomposes upon contact with a liquid. [0039] By way of non-limiting example, the soluble body may decompose upon contact with a liquid, for example an aqueous solution or water.

[0040] From an environmental and safety point of view, water is less harmful and reduces risks for operators.

[0041] By way of non-limiting example, the soluble body may comprise a composite material comprising on the one hand a first phase of formula Mn+iAICn, where n = 1 to 3, and M being a transition metal chosen from the group consisting of titanium, niobium, chromium or zirconium, the composite material comprising on the other hand a second phase of formula AI ₄ C ₃ .

[0042] By way of non-limiting example, the first phase is of one of the formulas Ti ₃ AIC2, Ti ₂ AIC, Cr ₂ AIC, Zr ₂ AIC, Zr ₃ AIC ₂ , Nb ₄ AIC ₃ , or Nb ₂ AIC.

[0043] The association of this first phase, with a second phase of formula AI ₄ C ₃ , is particularly advantageous. Indeed, aluminum carbide (AI ₄ C ₃ ) is an inorganic compound, whose melting temperature is very high (2200°C), and which can easily hydrolyze at room temperature, in the presence of a water-rich atmosphere. Thus, the composite material used for the molding core of the present disclosure integrates this second phase of aluminum carbide into the grain boundaries of the first phase. This makes the composite material particularly reactive to atmospheres containing water. The degradation of the aluminum carbide is accompanied by a variation in volume and a release of gas, capable of fragmenting the grain boundary and propagating cracks in the first initial phase. It is thus possible to propagate the hydrolysis phenomenon over relatively large distances, and thus facilitate the fragmentation and detachment of the core. In other words, the composite material forming the core can be initially dense and massive, and be reduced to powder by hydrolysis.

[0044] The present disclosure also relates to a method for obtaining a forming core as defined previously comprising the steps of:

- production of the soluble body;

- coating the soluble body with a liquid release agent;

- polymerization of the liquid release agent to obtain the skin comprising at least one layer of the release agent coating the soluble body. [0045] In some embodiments, the step of manufacturing the soluble body may comprise a step of mixing powders, a step of at least partially liquefying the powder mixture, for example by heating the powder mixture, a step of forming the soluble body by casting the at least partially liquefied powder mixture into a mold, a step of solidification in the mold and a step of demolding the soluble body.

[0046] The soluble body once solidified is soluble in a liquid, for example in water.

[0047] By way of non-limiting example, the mixture of powders may be a mixture of sodium nitrate, potassium nitrate and zirconium silicate.

[0048] By way of non-limiting example, the powder mixture may comprise 13.3% by mass of sodium nitrate (NaNO ₃ ), 33.3% by mass of zirconium silicate (SiO ₄ Zr) and 53.4% by mass of potassium nitrate (KNO ₃ ).

[0049] In some embodiments, the coating step may be performed by dipping the soluble body into a bath of liquid release agent.

[0050] In some embodiments, the coating step may be carried out by applying the liquid release agent to the soluble body, for example by brush or spray.

[0051] In some embodiments, the coating step comprises applying to the soluble body a first liquid release agent and at least one second liquid release agent distinct from the first liquid release agent.

[0052] In some embodiments, the polymerization comprises heat treating the liquid release agent to form the skin comprising at least one layer of the release agent.

[0053] By way of non-limiting examples, the release agent may be a pore filler marketed under the reference Frekote B15® or a release agent marketed under the reference Frekote 44NC®.

[0054] The present disclosure also relates to a method for manufacturing a hollow part made of organic matrix composite material comprising the steps: - obtaining the forming core as defined previously;

- assembly of the forming core as defined previously and a fibrous preform forming a precursor of the hollow part made of ceramic matrix composite material;

- draping the fiber preform and the forming core in a mold;

- mold closing;

- impregnation of the fiber preform with an impregnation resin;

- polymerization of the impregnation resin in the mold to form the organic matrix;

- demolding of the hollow part made of organic matrix composite material and the forming core; and

- elimination of the soluble body.

[0055] As non-limiting examples, the fiber preform may comprise glass, carbon, aramid fibers, and/or a mixture of these fibers.

[0056] In some embodiments, between the assembly step and the draping step, the fiber preform may be shaped.

[0057] The shaping makes it possible to improve the positioning of the fibers of the fiber preform and to limit the forces and movements of closing the mold, in particular during the draping step and the mold closing step.

[0058] In some embodiments, the shaping may be performed on the wet fibrous preform and the shaped fibrous preform is dried prior to the draping step.

[0059] By way of non-limiting example, the drying is carried out at a temperature greater than or equal to 100°C and less than or equal to 130°C, for example 120°C.

[0060] It is understood that the shaping of the wet fibrous preform is made possible thanks to the skin comprising at least one layer of a mold release agent from the forming core which protects the soluble body from any deterioration.

[0061] In some embodiments, during the assembly step, the core may be flush with an external surface of the fiber preform.

[0062] When the hollow part made of organic matrix composite material is demolded, the forming core is accessible on the external face where the forming core is flush. It is possible to tear off the skin having the release agent layer coating the soluble body and dissolve the soluble body.

[0063] In some embodiments, the step of removing the soluble body may comprise a step of drilling a soluble body removal channel in the hollow part made of organic matrix composite material to reach the soluble body.

[0064] In some embodiments, the forming core may include a channel core configured to form a soluble body removal channel in the hollow organic matrix composite material part.

[0065] It is understood that, once the part of the soluble body forming the channel core is dissolved, a channel for eliminating the soluble body is formed in the hollow part made of organic matrix composite material.

[0066] The soluble body removal channel allows the soluble body to be dissolved or fragmented by projecting a liquid onto the soluble body.

[0067] By way of non-limiting example, the channel may have a diameter greater than or equal to 5 mm and less than or equal to a maximum thickness of the soluble body to be eliminated.

[0068] In some embodiments, the step of removing the soluble body may comprise dissolving the soluble body or fragmenting the soluble body with a jet of pressurized liquid, for example water.

[0069] In some embodiments, the water may be heated to a temperature greater than or equal to 40°C and less than or equal to 95°C.

[0070] Water heated to a temperature greater than or equal to 40°C and less than or equal to 95°C can allow more rapid dissolution of the soluble body.

[0071] The present disclosure also relates to a hollow part made of organic matrix composite material comprising a cavity, the cavity being covered with a skin comprising at least one layer of a release agent.

[0072] By way of non-limiting examples, the hollow part made of organic matrix composite material may be a fan guide vane called OGV in accordance with the English acronym for “Outlet Guide Vane”, a propeller or a FAN blade. Brief description of the drawings

[0073] Other characteristics and advantages of the subject of the present disclosure will emerge from the following description of embodiments, given as non-limiting examples, with reference to the appended figures.

[0074] [Fig. 1] Figure 1 is a schematic longitudinal sectional view of a turbomachine.

[0075] [Fig. 2] Figure 2 is a schematic representation of a step of coating a soluble body with a coating resin according to one embodiment.

[0076] [Fig. 3] Figure 3 is a schematic representation of a step of coating a soluble body with a coating resin according to a second embodiment.

[0077] [Fig. 4] Figure 4 is a schematic representation of a step of coating a soluble body with a coating resin according to a third embodiment.

[0078] [Fig. 5] Figure 5 is a flowchart representing the steps of a method for obtaining a forming core according to one embodiment.

[0079] [Fig. 6] Figure 6 is a flowchart representing the steps of a method for manufacturing a hollow part made of organic matrix composite material according to one embodiment.

[0080] [Fig. 7] Figure 7 is a schematic representation of a step of assembling the forming core and a fiber preform according to one embodiment.

[0081] [Fig. 8] Figure 8 is a schematic representation of a step of shaping the fiber preform according to one embodiment.

[0082] [Fig. 9] Figure 9 is a schematic representation of the fiber preform shaped with the soluble core in a mold according to one embodiment.

[0083] [Fig. 10] Figure 10 is a schematic representation of a step of impregnation of the fiber preform according to one embodiment.

[0084] [Fig. 11] Figure 11 is a schematic view of the hollow part made of organic matrix composite material and the soluble core after demolding according to one embodiment. [0085] [Fig. 12] Figure 12 is a schematic representation of a step of removing the soluble body according to one embodiment.

[0086] [Fig. 13] Figure 13 is a schematic view of the hollow part made of organic matrix composite material according to one embodiment.

[0087] [Fig. 14] Figure 14 is a schematic view of the hollow part made of organic matrix composite material and the soluble core after demolding according to a second embodiment.

[0088] [Fig. 15] Figure 15 is a schematic view of the hollow part made of organic matrix composite material and the soluble core after demolding according to a third embodiment.

Detailed description

[0089] Figure 1 shows in section along a vertical plane passing through its main axis A, a double-flow turbojet 10 which is an example of a turbomachine. The double-flow turbojet 10 comprises, from upstream to downstream according to the circulation of the air flow F, a fan 12, a low-pressure compressor 14, a high-pressure compressor 16, a combustion chamber 18, a high-pressure turbine 20, and a low-pressure turbine 22.

[0090] The terms “upstream” and “downstream” are defined in relation to the direction of air circulation in the turbomachine, in this case, according to the circulation of the air flow F in the turbojet 10.

[0091] The turbojet 10 comprises a fan casing 24 extended towards the rear, that is to say towards the downstream, by an intermediate casing 26, comprising an external shell 28 as well as an internal shell 30 parallel and arranged, in a radial direction R, internally with respect to the external shell 28. The radial direction R is perpendicular to the main axis A.

[0092] The terms “external” and “internal” are defined with respect to the radial direction R so that the internal part of an element is, in the radial direction, closer to the main axis A than the external part of the same element.

[0093] The intermediate casing 26 further comprises structural arms 32 distributed circumferentially and extending radially between the inner shell 30 and the outer shell 28. For example, the structural arms 32 are bolted to the outer shell 28 and to the inner shell 30. The structural arms 32 make it possible to stiffen the structure of the intermediate casing 26.

[0094] The main axis A is the axis of rotation of the turbojet 10 and of the low-pressure turbine 22. This main axis A is therefore parallel to the axial direction.

[0095] The low pressure turbine 22 comprises a plurality of bladed wheels which form the rotor of the low pressure turbine 22.

[0096] In the following, the elements common to the different embodiments are identified by the same numerical references.

[0097] Figure 2 shows a forming core 50 according to one embodiment. The forming core 50 comprises a soluble body 52 coated with a skin 54 comprising at least one layer of a release agent.

[0098] In the following, the elements common to the different embodiments are identified by the same numerical references.

[0099] The method 100 for obtaining the forming core 50 comprises a first step 102 of manufacturing the soluble body 52.

[0100] As non-limiting examples, the soluble body 52 may be soluble in a liquid; the soluble body 52 may comprise a material that decomposes upon contact with a liquid. The liquid may be an aqueous liquid, for example water, or a non-aqueous solvent.

[0101] The obtaining method 100 then comprises a step 104 of coating the soluble body 52 with a liquid release agent 56.

[0102] As shown in Figure 2, the coating step 104 can be carried out by dipping the soluble body 52 in a bath comprising the liquid release agent 56.

[0103] As shown in Figure 3, the coating step 104 can be carried out by applying the liquid release agent 56 with a brush onto the soluble body 52.

[0104] As shown in Figure 4, the coating step 104 can be carried out by applying the liquid release agent 56 by spray onto the soluble body 52.

[0105] Alternatively, the coating step 104 may comprise the application of a first liquid release agent 56, then the application of a second liquid release agent 56 distinct from the first liquid release agent. The second liquid release agent may for example serve as a pore filler, and the first liquid release agent can serve as the actual release agent. In this case, the resulting skin 54, after polymerization, comprises two layers of release agent.

[0106] Alternatively, the coating step 104 may comprise the application of a number of distinct liquid release agents 56 strictly greater than two. In this case, the resulting skin 54, after polymerization, comprises a number of layers of release agent strictly greater than two.

[0107] The obtaining method 100 comprises a step 106 of polymerization of the liquid release agent 56 to obtain the skin 54 comprising at least one layer of the release agent, as shown in FIG. 2.

[0108] By way of non-limiting example, when the polymerization of the liquid release agent 56 may comprise the exposure of the soluble body 52 to room temperature for 3 to 4 hours, or the exposure of the soluble body 52 to a temperature between 100 and 150°C for 15 to 30 minutes. The heat treatment and its duration may however vary depending on the liquid release agent(s) chosen.

[0109] By way of non-limiting example, the liquid release agent may be an agent marketed under the reference Frekote B15®, Frekote 700NC® or Frekote 44NC®. Alternatively, the liquid release agent may be dibulite ether, having the standardized CAS (for “Chemical Abstracts Service”) identifier: 142-96-1, or a hydrocarbon having the standardized CAS identifier: 64742-48-9, 90622-56-3 or 111-65-9.

[0110] The manufacturing method 200 of a hollow part 62 made of organic matrix composite material will be described on the basis of FIGS. 6 to 13.

[0111] As shown in Figures 6 and 7, the manufacturing method 200 comprises a first step 100 of obtaining the forming core 50 followed by a step 202 of assembling the forming core 50 and a fiber preform 60. The fiber preform 60 forms a precursor of the hollow part 62 made of organic matrix composite material.

[0112] As shown in Figures 6 and 8, the manufacturing method 200 may then comprise a shaping step 204 of the fiber preform 60. The shaping step 204 is an optional step. [0113] When the fiber preform 60 is wet during the shaping step 204, the shaping step 204 may include a step of drying the fiber preform 60.

[0114] The manufacturing method 200 then comprises a step 206 of draping the fiber preform 60 and the forming core 50 in a mold 70.

[0115] As shown in Figure 6, the manufacturing method 200 then comprises a step 208 of closing the mold 70. In Figure 9, the mold 70 is shown closed, that is to say once the closing step 208 is completed.

[0116] As shown in FIG. 6, the manufacturing method 200 then comprises a step 210 of impregnating the fiber preform 60 with an impregnation resin 58. In FIG. 10, the fiber preform 60 is entirely impregnated with the impregnation resin 58.

[0117] By way of non-limiting example, the impregnation resin 58 may be a thermosetting resin, for example an epoxy resin, for example an epoxy resin marketed under the reference PR520N®.

[0118] As shown in FIG. 6, the manufacturing method 200 then comprises a step 212 of polymerizing the impregnation resin 58 in the mold 70 to form the organic matrix 64 of the hollow part 62 made of organic matrix composite material.

[0119] After the polymerization step 212 of the manufacturing method 200 of the hollow body 62 made of organic matrix composite material, the impregnation resin 58 forms the organic matrix 64.

[0120] As shown in FIG. 6, the manufacturing method 200 then comprises a step 214 of demolding the hollow part 62 made of organic matrix composite material, the forming core 50 being present in the hollow part 62 made of organic matrix composite material.

[0121] Figure 11 is a schematic view of the hollow part 62 made of organic matrix composite material and the soluble core 50 after the demolding step 214.

[0122] As shown in FIG. 6, the manufacturing method 200 then comprises a step 216 of removing the soluble body 52. [0123] Figure 12 is a schematic representation of the step 216 of removing the soluble body 52 including a step of drilling an elimination channel 68 (shown in Figure 13) using a drill bit 72.

[0124] The elimination channel 68 allows access, from outside the hollow body 62 made of organic matrix composite material, to the soluble body 52.

[0125] By way of non-limiting example, the elimination step 216 comprises a step of injecting heated water, for example between 40°C and 95°C, preferably under pressure, in order to dissolve or decompose/fragment the soluble body 52 and evacuate it via the elimination channel 68.

[0126] Figure 13 is a schematic view of the hollow part 62 made of organic matrix composite material obtained after the step of removing the soluble body 52. The hollow part 62 made of organic matrix composite material comprises a cavity 80, the cavity 80 being covered with the skin 54 comprising at least one layer of the polymerized mold release agent.

[0127] Figure 14 is a schematic view of the hollow part 62 made of organic matrix composite material and of the soluble core 50 after the demolding step 214 according to a second embodiment.

[0128] In the embodiment of Figure 14, the forming core 50 includes a channel core 74 configured to form the removal channel 68. The channel core 74 is flush with the exterior surface 66 of the hollow part 62 of organic matrix composite material.

[0129] Figure 15 is a schematic view of the hollow part 62 made of organic matrix composite material and the soluble core 50 after the demolding step 214 according to a third embodiment.

[0130] In the embodiment of Figure 15, the forming core 50 is flush with the outer surface 66 of the hollow part 62 made of organic matrix composite material.

[0131] In the embodiments of figures 14 and 15, the step 216 of removing the soluble body comprises a step where the skin 54 comprising at least one layer of a release agent, flush with the outer surface 66 of the hollow part 62 made of organic matrix composite material, is torn in order to have access to the soluble body 52 from the outside of the hollow part 62 made of organic matrix composite material. [0132] The step 216 of removing the soluble body 52 is similar to the step 216 of removing described above.

[0133] Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various illustrated/mentioned embodiments may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0134] It is also obvious that all the characteristics described with reference to a method are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a method.

Claims

[Claim 1] A forming core (50) comprising a soluble body (52) in an aqueous solution or water and a skin (54) comprising at least one layer of a release agent coating the soluble body (52). [Claim 2] The forming core (50) of claim 1, wherein the mold release agent comprises an organic solvent. [Claim 3] A forming core (50) according to claim 1 or 2, wherein the skin (54) comprises a first layer of a release agent and at least a second layer of a release agent distinct from the release agent of the first layer. [Claim 4] A forming core (50) according to any one of claims 1 to 3, wherein the soluble body (52) comprises a material which decomposes upon contact with the aqueous solution or water. [Claim 5] A method of obtaining (100) a forming core (50) according to any one of claims 1 to 4 comprising the steps of: - manufacturing (102) of the soluble body (52); - coating (104) the soluble body (52) with a liquid release agent (56); - polymerization (106) of the liquid release agent (56) to obtain the skin (54) comprising at least one layer of the release agent coating the soluble body (52). [Claim 6] A method of obtaining (100) according to claim 5 wherein the coating step (104) comprises applying to the soluble body (52) a first liquid release agent and at least one second liquid release agent distinct from the first liquid release agent. [Claim 7] Method of manufacturing (200) a hollow part (62) made of organic matrix composite material comprising the steps: - obtaining (100) the forming core (50) according to claim 5 or 6; - assembly (202) of the forming core (50) according to any one of claims 1 to 6 and a fibrous preform (60) forming a precursor of the hollow part made of organic matrix composite material; - draping (206) the fiber preform (60) and the forming core (50) in a mold (70); - closing (208) of the mold (70); - impregnation (210) of the fiber preform (60) with an impregnation resin (58); - polymerization (212) of the impregnation resin (58) in the mold (70) to form the organic matrix (64); - demolding (214) the hollow part (62) made of organic matrix composite material and the forming core (50); and - elimination (216) of the soluble body (52); [Claim 8] Manufacturing method (200) according to claim 7, wherein the step of removing (216) the soluble body (52) comprises a step of drilling a channel (68) for removing the soluble body (52) in the hollow part (62) made of organic matrix composite material to reach the soluble body (52). [Claim 9] A manufacturing method (200) according to claim 7, the forming core (50) comprises a channel core (74) configured to form a soluble body removal channel (68) in the hollow part (62) of organic matrix composite material. [Claim 10] A manufacturing method (200) according to any one of claims 7 to 9, wherein the step of removing (216) the soluble body (52) comprises dissolving the soluble body (52) or fragmenting the soluble body (52) by a pressurized liquid jet. [Claim 11] Hollow part (62) made of organic matrix composite material comprising a cavity (80), the cavity (80) being covered with a skin (54) comprising at least one layer of a release agent.