Method for manufacturing a hollow part made of composite materials and comprising internal stiffeners

Abstract

The invention relates to a method for manufacturing a composite part (10, 20), comprising the steps of: producing a fibre preform (36) of the composite part; manufacturing mandrels (31-34) from a moulded soluble paste; forming a fibre reinforcement (35) around each mandrel; inserting the assembled mandrels into the preform at a location for a cavity (3) to be formed in the composite part; inserting the preform containing the mandrels into a mould; injecting a resin into the mould to obtain the composite part, the resin diffusing into the preform and the fibre reinforcements; demoulding the composite part; forming a channel (38) in the composite part in order to reach the mandrels; and injecting a solvent into the channel in order to dissolve the mandrels, thereby forming the cavity in the composite part, wherein the fibre reinforcements between the mandrels form stiffeners in the cavity.

Description

[0001] DESCRIPTION

[0002] TITLE: Method for manufacturing a hollow composite material part comprising internal stiffeners

[0003] Technical field

[0004] The present invention relates to the manufacture of hollow aeronautical parts made of composite material, and more particularly the manufacture of aeronautical turbomachine blades, by methods of injecting resin into a fiber preform, but not only. More specifically, the invention relates to a method of manufacturing such a hollow aeronautical part.

[0005] State of the art

[0006] In the field of aeronautical engines, turbomachine blades are commonly made of composite materials such as organic matrix composites (OMC) in order to reduce their mass, while ensuring mechanical properties equivalent to or superior to metal. Indeed, improving the performance of the turbomachine, particularly in relation to consumption, requires a reduction in mass. These blades can be rotor or stator blades of a shrouded or unshrouded turbomachine, for example outlet guide vanes (OGV).

[0007] In the case of composite blades obtained by three-dimensional weaving, the composite material located at the core of the blade has only a limited influence on the mechanical performance of the part, while it accounts for a significant part of the blade mass. Thus, it is interesting to manufacture hollow blades, by laminating two-dimensional fiber reinforcements which are then densified by resin, or more by three-dimensional weaving of a preform which is then densified.

[0008] A common technique for manufacturing hollow blades is to form a cavity filled with high-density foam in the part. Foam has the advantage of facilitating manufacturing because thickness variations are not absorbed by the preform using the layer exits, but by the foam. This results in considerable savings in material waste and repeatability. In addition, in the case of a dry or pre-impregnated layup process, it is simpler to carry out the shaping on foam, which then serves as a support. However, foam has several disadvantages. Its cost is significant. It is fragile, absorbs moisture, and ages relatively quickly. In addition, the interfaces with the foam are more complex to control ultrasonically. This results in the need to control the humidity environment and limit its exposure to moisture.

[0009] It is also known to use a metal mandrel to form a cavity within a part. If the core of the part around the mandrel is not fusible, the latter then greatly constrains the geometry of the cavity in order to be demouldable, which is not compatible with the complex shapes of new generation parts. If the core is fusible, the process of melting the core after firing the part adds a manufacturing step and often leaves many particles (FOD - "Foreign Object Detected") on the part. This process is also expensive, and sometimes the firing step required for melting has a significant impact on the mechanical properties of the part. It should also be noted that this firing step reduces the repair potential of the part (linked to the cumulative time of subjecting the part to a temperature above 120°C).

[0010] Another technique for producing hollow parts with a non-demouldable cavity is to shape and extract internal moulded parts. However, this technique requires special shaping and extraction tools.

[0011] It is therefore desirable to be able to produce a highly hollowed-out part but with mechanical strength suited to its use. It is also desirable that the mechanical strength obtained is compatible with that of turbomachine blades, whether shrouded or not, and fixed or mobile.

[0012] Summary

[0013] Embodiments relate to a method for manufacturing a composite material part comprising steps consisting of: producing a fiber preform of the composite part; producing mandrels from a molded soluble paste; forming a fiber reinforcement around each mandrel; assembling the mandrels covered with the fiber reinforcement; inserting the assembled mandrels into the fiber preform at a location of a cavity to be formed in the composite part, the mandrels and the fiber preform defining the geometry of the cavity; inserting the fiber preform incorporating the mandrels into an injection mold; injecting a resin into the injection mold to obtain the composite part, the resin diffusing into the fiber preform and the fiber reinforcement around each mandrel; demolding the composite part after polymerization of the resin; forming a channel in the composite part to reach the mandrels from outside the composite part;and injecting a solvent into the channel to dissolve the mandrels, and form the cavity in the composite part, the fibrous reinforcements between the mandrels being configured to form stiffeners between opposing walls of the cavity.;

[0014] According to one embodiment, the formation of the channel is carried out either during the formation of the fiber reinforcement and the preform and the injection molding, or by a drilling operation after demolding of the composite part.

[0015] According to one embodiment, the method comprises, before injection molding, an operation of shaping the fiber preform in dry form, or an operation of shaping the fiber preform in wet form, followed by an operation of drying the fiber preform.

[0016] According to one embodiment, the method comprises an operation of draping the fibrous preform before injection molding.

[0017] According to one embodiment, the composite part is a turbomachine part, or a fixed or moving blade of a shrouded turbomachine, or a fixed or moving blade of an unshrouded turbomachine.

[0018] Embodiments may also relate to a composite material part comprising an outer skin, an inner cavity and stiffeners connecting opposite faces of the cavity together, the stiffeners and the skin being formed from the same resin in which fibers are embedded.

[0019] According to one embodiment, the composite material part is a turbomachine part, or a fixed or moving blade of a shrouded turbomachine, or a fixed or moving blade of an unshrouded turbomachine.

[0020] Brief description of the figures

[0021] The present invention will be better understood with the aid of the following description of exemplary embodiments with reference to the appended figures, in which identical reference signs correspond to structurally and / or functionally identical or similar elements.

[0022] Figures 1A and 1B are schematic front views of an unducted turbomachine blade and a ducted turbomachine blade, respectively,

[0023] Figure 2 is a schematic cross-sectional view of the blade of Figure 1 or 2,

[0024] Figure 3 is a schematic cross-sectional view of the blade of Figure 1 or 3, according to one embodiment,

[0025] Figures 4A to 4H are cross-sectional views of parts, illustrating steps in manufacturing a blade, according to one embodiment, Figure 5 is a schematic perspective view of a mold,

[0026] Figure 6 is a schematic perspective view of a 3D woven composite preform.

[0027] Detailed description

[0028] Figure 1A represents an unducted and fixed or mobile turbomachine blade 1. Figure 1B represents a ducted and fixed turbomachine blade 2. In the example of Figure 1A, blade 1 is a fixed outlet blade intended to be arranged downstream of the blades of an unducted fan of a flow straightener or OGV to straighten a secondary air flow. In the example of Figure 1B, blade 2 is an outlet guide vane intended to be arranged in an OGV, downstream of the blades of a ducted fan. These examples are not limiting, the invention also applying to the blades of the fan for example, or any other fan module, fixed or mobile, made of an organic composite material (OCM) with a fiber reinforcement embedded in a CMO matrix. The blade 1, 2 conventionally comprises a leading edge 11, a trailing edge 12, an extrados 13 and a intrados 14.

[0029] According to an embodiment illustrated by Figures 1A, 1B and 2, the blade 1, 2 has an internal cavity 3 extending over the majority of the volume of the blade, in order to reduce its mass. However, the presence of such a cavity 3 greatly reduces the mechanical strength of the part 1, 2. To solve this problem without significantly affecting the mass of the part, it is provided to form inside the cavity 3 of the blade stiffeners connecting together opposite walls of the cavity 3. Thus, Figure 3 represents a blade 10 which differs from the blades 1, 2 in that the cavity 3 of the blade comprises stiffeners 21, 22, 23 connecting together opposite walls of the cavity. In the particular case of blade 10, the stiffeners connect the walls forming the extrados 13 and the intrados 14 together and thus make it possible to stiffen these walls.

[0030] Figures 4A to 4H illustrate different steps of the method of manufacturing the blade 10 with the cavity 3 and the stiffeners 21, 22, 23. Figure 4A represents rigid and soluble mandrels 31, 32, 33, 34 to be used as tooling for producing the internal walls of the cavity 3 with the stiffeners 21, 22, 23. Thus, the mandrels 31-34 have the shape of parts to be left empty in the blade 10.

[0031] The mandrels 31-34 may be made by molding a fluid (paste or liquid) into a material capable of hardening and soluble in a suitable solvent, by the following steps. The fluid may be made by mixing various compositions in the form of powders, and heating the mixture to make it liquid. The fluid is then poured into molds having the required shapes, and then allowed to cool in the molds. The molding may be carried out by gravity or under pressure, for example by injection. The mandrels 31, 32, 33, 34 are then demolded.

[0032] The powder mixture may comprise a nitrate content greater than 60%, which facilitates subsequent dissolution of the mandrels. For example, the powder mixture may comprise sodium nitrate (NaNCh), potassium nitrate (KNO3) and zirconium silicate (SiCLZr). According to an exemplary embodiment, the powder mixture comprises mass contents of 13.3% sodium nitrate, 53.4% ​​potassium nitrate, and 33.3% zirconium silicate (SiO4Zr). The mass contents are given relative to the total weight of the composition. This mixture may be maintained at a temperature between 315°C and 325°C throughout the duration of the mixing operation. Gravity casting may be carried out in the mold heated to a temperature between 180°C and 250°C. The solidification of the mandrels is carried out by cooling to room temperature.

[0033] Figure 4B illustrates a step of draping the demolded mandrels 31, 32, 33, 34 with a fiber reinforcement 35 shaped or draped directly onto the mandrels. The fiber reinforcement 35 can be produced by forming a reinforcement layer by spraying or by winding fibers. The fiber reinforcement can be produced for example by additive manufacturing with a thermoplastic filament, soluble in water and having mechanical strength up to a temperature of 130°C, such as ST130. The fiber reinforcement can also be formed from fibers, in particular carbon (for example IM7, T1100), glass, or aramid or even plant fibers. The fiber reinforcement does not necessarily cover the entire surface of the mandrels. In this case, the parts not covered by the fibers can be filled with the resin of the composite forming the fibers, therefore with a zero local fiber volume ratio.

[0034] Figure 4C illustrates a step of assembling the mandrels 31, 32, 33, 34 with their respective fiber reinforcements 35, to form the blade 10. Thus, the free surface of the fiber reinforcement 35 covering the assembled mandrels corresponds substantially to the shape of an internal core of the blade 10.

[0035] Figure 4D illustrates a step of inserting the mandrels 31-34 assembled with the fiber reinforcement 35 into a preform or blank 36 of the blade 10. For this purpose, the preform 36 may have been previously moistened to facilitate its shaping around the assembled mandrels 31-34.

[0036] The fiber preform 36 is for example formed by three-dimensional weaving in which the threads intertwine in a three-dimensional manner (so-called "3D interlock" weaving). The preform 36 can also be obtained by braiding or draping unidirectional plies or formed from discontinuous short fibers. The manufacture of such a fiber preform is known to those skilled in the art and will not be described in detail in the present disclosure. It will be noted, however, that the fiber preform 36 comprises a decoupling zone forming an opening allowing the insertion of the mandrels 31-34 assembled with the fiber reinforcement 35. This opening can be formed for example in a part of the preform corresponding to the base of the blade to be produced.

[0037] Figure 4E illustrates a step of shaping the preform 36 covering the mandrels 31-34 assembled with the fiber reinforcement 35. This step aims to correctly position the fibers of the preform 36 according to the shape and structure of the final part 10. For this purpose, the preferred zones (the most fragile) are more densely stiffened in order to improve their structural resistance to impacts and the like, the objective being to obtain satisfactory mechanical properties. This step includes carrying out a drying operation of the preform 36 in the presence of the mandrels 31-34, in order to freeze the shape of the preform. This drying operation is conventionally carried out by heating to a temperature below 120°C depending on the nature of the fibers. In this case, the fibers of the preform 36 may in particular be made of carbon, glass or aramid.This step also includes a draping operation consisting of covering the preform with a layer 37.

[0038] Figure 4F illustrates a molding step of the preform 36 as shown in Figure 4E. This step allows the shaping, densification and consolidation of the part. This step is carried out by placing the preform 36 with the draping 37 in a mold 40 for example comprising two shells 40a, 40b delimiting between them the volume of the part to be produced 10. The molding step itself can be carried out by injecting a thermosetting or thermoplastic resin into the mold, for example according to the RTM technique ("Resin Transfer Molding"). Preferably, the resin comprises a polymer, preferably epoxy, bismaleimide or polyimide. A heat treatment allowing the polymerization or hardening of the resin is then carried out. For this purpose, the entire mold is heated in order to harden the resin and obtain the rigid final part. After polymerization of the resin injected into the mold, the part is demolded.

[0039] It should be noted that the drying operation can be carried out in the mold 40 before the molding step illustrated by FIG. 4F. A system for holding the mandrels 34-36 in their final positions in the mold can be implemented during drying. Holding the mandrels in a correct position makes it possible to obtain volumetric and compaction rates of the fibers of the preform 36, providing better mechanical strength for the final part. FIG. 4G illustrates a step of drilling the demolded part 20 to form one or more channels 38 from the outside of the part 20 to the mandrels 31-34. In the case where the part 20 is a blade, each channel 38 can be formed from the trailing edge 12.

[0040] It should be noted that this drilling operation can be avoided or reduced by forming all or part of the channels 38 upon forming the mandrels, the preform 36 and the lay-up 37. According to one example, the mandrels 34-36 and the channels are formed in a single piece (by molding or gluing), including connections between the mandrels. The mandrels can also be assembled to form a rigid assembly using rigid tubes connecting the mandrels together, and connecting one of the mandrels to the outside of the part 20. The tubes can be metallic, for example. However, a drilling operation can be provided to connect all of the mandrels to the outside of the part 20.

[0041] Figure 4G illustrates a step of removing the mandrels 31-34 by dissolution. This step can be carried out by injecting or spraying into the channel(s) 38 a solvent suitable for the material forming the mandrels. In the case where the mandrels are made from the powder mixture described above, the solvent can be heated and pressurized water, for example at a temperature between 80°C and 90°C and at a pressure greater than or equal to 40 bars. The use of hot water under pressure makes it possible to ensure complete removal of the mandrels, without residue in the part. The channels 38 can then be plugged, for example, with silicone such as RTV ("Room-Temperature-Vulcanizing silicone") or force-inserted plugs.

[0042] Figure 5 shows the mold 40, an orifice 44 for filling the mold, a holding tool 41 fixed to the mold 40 using fixing members 42, and pins 43 for positioning the mandrels in the mold. The steps illustrated by Figures 4C and 4D can be carried out by positioning the preform 36 in the mold 40, the preform being shaped using tracers, for example made of fiberglass or by laser projection. Such tracers are described for example in the document Bjorn's corner; Turbofan engine challenges; Part 2 - Leeham News and Analysis.

[0043] Next, the mandrels 31-34 and then the pins 43 are inserted into the preform 36 through an opening made in the preform. Finally, the holding tool 41 is fixed to the mandrels 31-34 using the pins 43. Figure 6 shows the preform 36 and an opening 39 through which the mandrels 31-34 and the pins 43 can be introduced. In the example of Figure 6, two openings 39 are made in the preform 36 at opposite ends of the latter. It will be clear to those skilled in the art that the present invention is susceptible to various variant embodiments and various applications. In particular, the invention is not limited to the manufacture of turbomachine blades, but can be applied to any part, particularly aeronautical, made of composite materials that must be lightened by the formation of one or more internal cavities.

[0044] Furthermore, the mandrels and therefore the molds for forming the mandrels do not necessarily have a shape reflecting the shape of the part to be produced.

Claims

CLAIMS 1. A method of manufacturing a part (10, 20) made of composite material comprising steps consisting of: producing a fibrous preform (36) of the composite part; producing mandrels (31-34) from a molded soluble paste; forming a fibrous reinforcement (35) around each mandrel; assembling the mandrels covered with the fibrous reinforcement; inserting the assembled mandrels into the fibrous preform at a location of a cavity (3) to be formed in the composite part, the mandrels and the fibrous preform defining the geometry of the cavity; inserting the fibrous preform incorporating the mandrels into an injection mold (40); injecting a resin into the injection mold to obtain the composite part (10, 20), the resin diffusing into the fibrous preform and the fibrous reinforcement around each mandrel; demolding the composite part after polymerization of the resin;forming a channel (38) in the composite part to reach the mandrels from outside the composite part; and injecting a solvent into the channel to dissolve the mandrels, and form the cavity in the composite part, the fibrous reinforcements between the mandrels being configured to form stiffeners between opposing walls of the cavity.; 2. Method according to claim 1, in which the formation of the channel (38) is carried out either during the formation of the fibrous reinforcement (35) and the preform and the injection molding, or by a drilling operation after demolding of the composite part.

3. Method according to claim 1 or 2, comprising, before injection molding, an operation of shaping the fiber preform (36) in dry form, or an operation of shaping the fiber preform in wet form, followed by an operation of drying the fiber preform.

4. Method according to one of claims 1 or 2, comprising an operation of draping the fibrous preform (36) before injection molding.

5. Method according to one of claims 1 to 4, in which the composite part (10, 20) is a turbomachine part, or a fixed or moving blade of a shrouded turbomachine, or a fixed or moving blade of an unshrouded turbomachine.

6. Composite material part (10, 20) comprising an external skin, an internal cavity (3) and stiffeners connecting opposite faces of the cavity together, the stiffeners and the skin being formed from the same resin in which fibers are embedded.

7. Composite material part according to claim 6, which is a turbomachine part, or a fixed or moving blade of a shrouded turbomachine, or a fixed or moving blade of an unshrouded turbomachine.

Images