Method for manufacturing a variable-pitch blade for a turbomachine

Abstract

Disclosed is a method for manufacturing a variable-pitch blade (7) for a turbomachine, comprising: a) preparing the fibrous structure (20) in particular by weaving fibres, b) compacting the attachment portion (23) of the fibrous structure (20) so as to reduce its diameter with respect to the pitch axis (Y), c) inserting the compressed attachment portion (23) into the cuff (13) and shaping the attachment portion (20), and d) injecting a first polymerizable resin into the fibrous structure (20), the method comprising, between steps a) and b), a step i) of impregnating the attachment portion (23) of the fibrous structure (20) with two different impregnation solutions (S1, S2). Figure for the abstract: Figure 3

Description

[0001] DESCRIPTION

[0002] TITLE: METHOD FOR MANUFACTURING A VARIABLE-PITCHING BLADE FOR A TURBOMACHINE

[0003] Technical field of the invention

[0004] The invention relates generally to the field of turbomachinery, and in particular to turbomachine blades.

[0005] The invention relates more particularly, but not exclusively, to a method of manufacturing a variable pitch blade intended for use in an unfaired fan rotor of an aircraft engine.

[0006] Technical background

[0007] The search for minimizing polluting emissions related to air transport involves, in particular, improving all the efficiencies of propulsion systems, and more specifically the propulsive efficiency which characterizes the efficiency with which the energy communicated to the air passing through the engine is converted into useful thrust effort.

[0008] The primary factors influencing propulsive efficiency are those related to the low-pressure components of the propulsion system, which contribute directly to thrust generation: the low-pressure turbine, the low-pressure transmission system, the fan, and the secondary flow guiding its operation. The known guiding principle for improving propulsive efficiency is to reduce the fan's compression ratio, thereby decreasing the flow velocity at the engine outlet and the associated kinetic energy losses.

[0009] One of the main consequences of this decrease in flow velocity at the engine outlet is that a higher mass flow rate of air must be treated in the low-pressure section (secondary flow) to ensure a given thrust level, determined by the aircraft's characteristics. This therefore leads to an increase in the engine's bypass ratio. The bypass ratio, or BPR (Bypass Ratio), is defined as the ratio between the mass flow rate in the secondary flow (cold flow) and the mass flow rate in the primary flow (hot flow), which notably feeds the combustion chamber.

[0010] This increase in secondary flow rate directly necessitates an increase in the fan diameter, and consequently, in the external dimensions of the surrounding retention casing, as well as the nacelle that forms the aerodynamic envelope of said casing. To achieve high dilution rates, the casing becomes too large and heavy (generating significant drag), so it is removed in favor of configurations with unfaired propellers.

[0011] Several unducted turbomachinery concepts could be considered, such as the Unducted Single Fan (USF) architecture: an unducted turbomachine with (at least) one upstream variable pitch propeller wheel (or "Open Fan") and a downstream stator wheel with fixed or variable pitch.

[0012] More generally, the technical field of application lies within the context of fan blades, including rotating (rotor), unshod (propeller), and variable-pitch blades, with a potential application in the aeronautical propulsion industry. Other examples of particularly relevant architectures include Contra-Rotating Open Rotors (CROR) and turboprop engines. However, the design of such blades requires consideration of conflicting constraints.

[0013] On the one hand, the design of these blades must allow for optimal aerodynamic performance, notably maximizing efficiency and providing thrust while minimizing losses. Improving the aerodynamic performance of the fan tends towards an increase in the bypass ratio, which translates into an increase in the external diameter, and therefore the span, of these blades. On the other hand, it is also necessary to guarantee resistance to the mechanical stresses that may be exerted on these blades while limiting their acoustic signature.

[0014] Furthermore, on unshod fan designs, engine start-up is generally performed with a very open valve timing. Indeed, a very open valve timing allows power to be consumed by torque, which ensures machine safety by guaranteeing low fan speeds. However, with a very open valve timing, the blades experience turbulent, completely separated aerodynamic flow, which generates broadband vibrational excitation. In particular, on large-chord, long-span blades, the bending stress is intense, even though the engine speed is not at its maximum.

[0015] In normal operation, that is, during ground and flight phases, the fan pitch is adjusted to a more closed angle. The aerodynamic flow is then perfectly controlled, particularly in relation to the airfoil. Broadband stresses disappear because the rotational speed is higher, and the bending force is controlled. However, since the engine is not enclosed in a cowling, the angle of attack experienced by the various fan blades, depending on their angular position, varies according to the aircraft's angle of attack, creating a cyclic bending moment (commonly called the 1P moment) on the blades. This cyclic bending moment then generates significant bending stresses on the blades in addition to the centrifugal forces due to their rotation.

[0016] These blades can be made of metallic material. While metallic blades have good mechanical resistance, they have the disadvantage of being relatively heavy.

[0017] Manufacturing blades from composite materials is an attractive solution for reducing blade weight. However, composite blades can be fragile due to the intense aerodynamic stresses they are subjected to. These aerodynamic stresses can damage the blades and / or the hub in the interface area between the blades and the fan rotor hub, at the blade root. To overcome these drawbacks, various solutions exist in the prior art. Most utilize reinforcing elements, particularly at the blade root, and add various structural elements to allow, for example, the blade to be attached to the pitching mechanism. Patent documents W0-A1-2022 / 018353 and W0-A1-2022 / 208002 describe the addition of reinforcing and structural elements, especially at the blade roots.However, these solutions have the drawback of requiring the manufacture of several components from potentially different materials and the assembly of these components using fastening methods. Such blades can therefore be relatively time-consuming to produce.

[0018] Hybrid-footed turbine blades exist, where the foot is formed by combining a metal tubular sleeve with a fibrous structure inserted into the sleeve. During the manufacturing of this type of blade, the fibrous structure must be compacted or compressed to reduce its diameter and allow its insertion into the sleeve. This compaction must be reversible to allow the fibrous structure to be shaped within the sleeve after insertion, and before resin injection (generally via RTM - Resin Transfer Molding). After compaction and before insertion, handling the fibrous structure is difficult and delicate because it tends to return to its original shape, and the fibers are likely to sprawl at the outer edge of the structure.Furthermore, the fibrous structure should ideally retain its compacted shape after insertion to facilitate the positioning of the assembly in an RTM injection mold.

[0019] The present invention proposes an improved method for manufacturing a blade of the aforementioned type, which provides a simple, efficient and economical solution to at least some of the problems of the prior art.

[0020] Summary of the invention: The invention proposes a method for manufacturing a variable-pitch blade for a turbomachine, this blade comprising:

[0021] - a tubular metal sleeve, this sleeve comprising a fixing part configured to be connected to a variable shimming mechanism, and a recess passing through the sleeve along a shimming axis, the recess comprising a first internal surface having a first shape, for example cylindrical, a second internal surface having a second shape, for example polygonal in cross-section, and a third internal surface which has a third shape, for example frustoconical, and which is located between the first and second internal surfaces,

[0022] - a fibrous structure obtained by weaving fibers, the fibrous structure comprising a blade with an aerodynamic profile connected to a blade root which includes an attachment portion inserted axially into the recess of the sleeve, the attachment portion comprising a first section having a first external surface in contact with said first internal surface, a second section having a second external surface in contact with said second internal surface, and a third section situated between the first and second sections and having a third external surface which is in contact with said third external surface, and

[0023] - a polymerized resin for solidifying the fibrous structure, the process comprising the following steps:

[0024] a) preparation of the fibrous structure, in particular by weaving fibers, b) compaction of the attachment portion of the fibrous structure so as to reduce its diameter relative to the alignment axis, and allow its insertion into the sleeve,

[0025] (c) insertion of the compressed attachment portion into the sleeve and shaping of the attachment portion so that the first, second and third external surfaces of the attachment portion come into contact respectively with the first, second and third internal surfaces of the sleeve, and

[0026] d) injection of a first polymerizable resin into the fibrous structure, the process comprising, between steps a) and b), a step i) of impregnating the attachment portion of the fibrous structure with two different impregnation solutions, a first impregnation solution being used to impregnate the second and third sections of the attachment portion, and a second impregnation solution, called a tackifying solution, being used to impregnate the first section of the attachment portion, the tackifying solution having the function of strengthening the cohesion between the fibers so that the fibers of the attachment portion are more cohesive in the first section of the attachment portion than in the second and third sections of the attachment portion.

[0027] The second and third sections are less rigid, which facilitates their shaping inside the sleeve after the insertion stage. The tackifying solution further stiffens the first section, which then more easily retains its compacted or compressed state. This makes it easier to handle the first section inside the sleeve, particularly for precise positioning before resin injection.

[0028] The method according to the invention may include one or more of the following features, taken individually or in combination with each other:

[0029] -- the first, second and third external surfaces have different shapes;

[0030] -- the first, second and third internal surfaces have different shapes;

[0031] -- the first, second and third internal surfaces have shapes complementary respectively to the first, second and third external surfaces;

[0032] - the first impregnation solution is based on a first solvent; - the tackifying solution is based on a second solvent and also includes a second polymerizable resin, in particular a thermosetting resin; - the proportion of the second polymerizable resin in the tackifying solution is between 1 and 40% by mass, preferably between 10 and 30% by mass, and more preferably around 25% by mass; - the first and second solvents are different;

[0033] - the first solvent is water;

[0034] - the second solvent is acetone;

[0035] - the second resin is identical to the first resin;

[0036] - the process includes, between steps b) and c), a step ii) of drying the attachment portion, in particular by heating;

[0037] - the heating is carried out at 120°C + / -10%;

[0038] - step ii) is carried out to induce only partial polymerization of the second resin;

[0039] - the polymerization rate of the second resin at the end of step ii) does not exceed a gel point of that resin;

[0040] - at the end of step b), the attachment portion has a fiber volume ratio between 60 and 70%;

[0041] - after step i) and before step b), the process includes a step iii) of resting for several minutes;

[0042] - the resting stage corresponds to a stage of at least partial evaporation of said second solvent;

[0043] -- the attachment portion is tubular and includes a housing centered on the alignment axis, the blade further comprising an insert centered on the alignment axis and inserted axially into the housing of the attachment portion;

[0044] -- the third section has its end with the smallest diameter connected to the first section, and its end with the largest diameter connected to the second section.

[0045] Brief description of the figures

[0046] Other features and advantages will become apparent from the following description of a non-limiting embodiment of the invention with reference to the accompanying drawings in which: [Fig.1] Figure 1 schematically represents an example of an engine including an unfaired blower;

[0047] [Fig.2] Figure 2 schematically represents a blower blade according to an embodiment of the invention assembled to a shimming mechanism;

[0048] [Fig.3] Figure 3 schematically represents a blower blade according to a first embodiment of the invention;

[0049] [Fig. 4a] Figure 4a schematically represents a sleeve according to a first embodiment of the invention in perspective view J

[0050] [Fig.4b] Figure 4b schematically represents the sleeve of figure 4a in profile view;

[0051] [Fig.4c] Figure 4c schematically represents the sleeve of figures 4a and 4b into which the attachment portion and the insert are inserted; [Fig.4d] Figure 4d schematically represents the sleeve / attachment portion / insert assembly of figure 4c inserted into the locking mechanism;

[0052] [Fig.5] Figure 5 schematically represents an insert according to one embodiment of the invention;

[0053] [Fig.6] Figure 6 schematically and partially represents a blade according to the invention;

[0054] [Fig.7] Figure 7 schematically and partially represents the dawn of Figure 6;

[0055] [Fig.8] Figure 8 schematically and partially represents the dawn of figure 6, in partially exploded perspective;

[0056] [Fig.9] Figure 9 schematically and partially represents the dawn of figure 6;

[0057] [Fig. 10] Figure 10 schematically represents in cross-section the foot of a blade according to the invention; and

[0058] [Fig. 11a-11d] Figures 11a to 11d represent steps in a process according to the invention for manufacturing a blade. Detailed description of the invention

[0059] In Figure 1, the engine 1 shown is an "Open Rotor" type engine, in a configuration commonly referred to as "pusher" (i.e., the blower is placed at the rear of the power generator with an air inlet located on the side, to the right in Figure 1).

[0060] The engine comprises a nacelle 2 intended to be fixed to an aircraft fuselage, and an unfaired fan 3. The fan 3 includes two counter-rotating fan rotors 4 and 5. In other words, when the engine 1 is running, the rotors 4 and 5 are driven in rotation relative to the nacelle 2 around the same axis of rotation X (which coincides with a principal axis of the engine), in opposite directions.

[0061] Thus, in the example illustrated in Figure 1, motor 1 is an "Open Rotor" type motor, in a "pusher" configuration, with counter-rotating fan rotors. However, the invention is not limited to this configuration. The invention also applies to "Open Rotor" type motors in a "puller" configuration (i.e., the fan is placed upstream of the power generator with an air inlet located before, between, or just behind the two fan rotors).

[0062] Furthermore, the invention also applies to motors with different architectures, such as an architecture comprising a blower rotor with moving blades and a blower stator with fixed blades, or a single blower rotor.

[0063] The invention is applicable to turboprop-type architectures (comprising a single fan rotor).

[0064] In Figure 1, each blower rotor 4, 5 comprises a hub 6 mounted rotatably relative to the nacelle 2 and a plurality of blades 7 fixed to the hub 6. The blades 7 extend substantially radially with respect to the axis of rotation X of the hub.

[0065] As illustrated in Figure 2, the fan 3 further includes an actuation mechanism 8 for collectively adjusting the pitch angle of the rotor blades to adapt engine performance to different flight phases. For this purpose, each blade 7 comprises a blade root 9 and an aerodynamically profiled blade 12. The blade root 9 is rotatably mounted relative to the hub 6 around a pitch axis Y. More precisely, the blade root 9 is rotatably mounted within a mounting device 10 formed in the hub 6, via balls 11 or other rolling elements.

[0066] The aerodynamic airfoil blade 12 has a first end connected to the blade root 9 and a second end, opposite the first end. The aerodynamic airfoil portion of the blade 12 is designed to extend into an engine air stream when the engine is running, in order to generate lift. Conversely, the blade root 9 is designed to extend out of the air stream.

[0067] With reference to figures 3, 4a and 4b, the blade 7 includes a sleeve 13 having a fixing part 14 configured to be connected to a variable pitching mechanism of a turbomachine, in particular inside the attachment device 10. The sleeve 13 has a recess 17 delimited by an internal wall 18 of the sleeve 13. The recess 17 passes through the sleeve 13 along a pitching axis Y.

[0068] With reference to Figures 3, 4c and 4d, the blade 7 also includes a fibrous structure 20 obtained by weaving, preferably three-dimensional. The fibrous structure 20 includes a blade root 22 comprising an attachment portion 23 configured to be inserted into the recess 17 formed by the attachment portion 14 of the sleeve 13.

[0069] The fibrous structure 20 preferably has a tubular shape and can thus include a housing 20a centered on the alignment axis Y.

[0070] The fibrous structure 20 also includes a blade 21 with an aerodynamic profile connected to the blade root 22.

[0071] The blade 7 may also include an insert 24 shown in Figure 5 and which is configured to be inserted into the housing 20a of the attachment portion 23 so that the attachment portion 23 is radially intercalated between the insert 24 and the inner wall 18 of the sleeve 13.

[0072] The blade 7 further includes a polymerized resin for solidifying the fibrous structure 20 to at least part of the internal wall 18 of the sleeve 13.

[0073] The resin thus makes it possible to form a main force path, called default, when transmitting a torque recovery force around the Y alignment axis between the blade root 22 and the sleeve 13.

[0074] The blade 7 is thus formed from a few elements that fit together to form a single-piece blade. Since the blade 21 and the blade root 22 are formed from the same fibrous structure 20, there is no discontinuity between the blade 21 and the blade root 22. Furthermore, the blade root 22 is wedged between the insert 24 and the sleeve 13, and the fibrous structure 20 is thus securely joined to the blade root 9.

[0075] The blade 7 can therefore withstand significant aerodynamic stresses while maintaining a limited mass, and can thus be used with a variable pitch mechanism and in an "open rotor" type environment. Furthermore, since the components of the blade 7 are limited in number, it is quick to manufacture.

[0076] The resin typically comprises an organic material (thermosetting, thermoplastic, or elastomer) or a carbon matrix. For example, the matrix may comprise a plastic material, typically a polymer, such as epoxy, bismaleimide, or polyimide. The fibers of the fibrous structure 20 comprise at least one of the following materials: carbon, glass, aramid, polypropylene, and / or ceramic.

[0077] With reference to Figures 4a, 4b and 4c, the attachment portion 23 may have an additional thickness 23” resulting from a progressive thickening of the fibrous structure 20 forming said attachment portion 23, at its free end 23'. This additional thickness 23” is configured to fit into a recessed portion 18' of the inner wall 18. Thus, the portion 18' widens the recess 17 and the remainder of the wall portion 18 narrows the recess 17. In this way, when the insert 24 is positioned in the recess 17, any translation of the attachment portion 23 away from the free end 23' is prevented by the portion of the wall 18 that narrows the recess 17 and forms a stop.

[0078] Indeed, when the fan is rotating, the blade 7 is subjected to centrifugal forces oriented in a radial direction relative to the axis of rotation of the fan, which tend to separate the aerodynamic profile blade 12 from the sleeve 13. The extra thickness 23” helps to prevent the separation of the blade 12 and the sleeve 13.

[0079] With reference to figures 3, 4a to 4d, the fixing part 14 has a rotational symmetry about the Y axis. Furthermore, the fixing part 14 has an external surface 30 with different reliefs.

[0080] The fixing part 14 has at its end through which the attachment portion 23 is inserted a first annular flange 29. This first annular flange 29 forms a stop against which the blade foot 22 is configured to bear.

[0081] The fixing part 14 also includes a second annular flange 29' at its free end opposite to the end through which the fibrous structure 20 is inserted.

[0082] The mounting portion 14 also includes a first circular groove 32 and a second circular groove 34, forming a raceway for at least one bearing, for example, a ball bearing. The mounting portion 14 thus allows the blade foot 9 to be rotatably mounted within the attachment device 10 formed in the hub 6.

[0083] Alternatively, grooves 32, 34 could be replaced by radiating shoulders, for example.

[0084] Sleeve 13 is preferably metallic and monolithic.

[0085] As previously described, the sleeve 13 has an inner wall 18 that defines the recess 17. The recess 17 can form a cylinder of constant diameter that widens as it approaches the free end of the sleeve 13, forming a beveled inner edge. The wall 18 thus has a recessed portion 18' that widens the recess 17 in a radial direction. The extra thickness 23" of the attachment portion 23 is then inserted into the recessed portion 18' so as to prevent any translation of the attachment portion 23 away from the free end 23' when the insert 24 is positioned in the recess 17. The portion of the wall 18 with a constant diameter then acts as a stop for the extra thickness 23".

[0086] The recessed portion can have a different shape and can be placed in a different position along wall 18.

[0087] The wall 18 could alternatively be thickened at its end opposite the free end so as to reduce the diameter of the recess 17 and form a stop allowing the insert 24 to be blocked and the attachment portion 23 to be wedged against the wall 18 in an optimized manner.

[0088] Figure 4d represents the sleeve into which the attachment portion 23 and the insert 24 are inserted, the sleeve being arranged in the attachment device 10, the rolling elements 11 being arranged in the aforementioned circular grooves 32 and 34 or radiating shoulders.

[0089] Referring to Figures 5 and 6, the insert 24 comprises a cylindrical body 40 having a free end 41 and a locking end 42 opposite the free end 41. In this embodiment, the locking end 42 is a rounded end. The insert 24 is preferably metallic.

[0090] The present invention relates to the manufacture of a blade 7 as shown in figures 6 to 11d. The particularity of this blade 7 is that it includes a attachment portion 23 of a particular shape, the sleeve 13 having a shape complementary to this attachment portion 23.

[0091] As mentioned above, the sleeve 13 is tubular and includes a recess 17 passing through the sleeve 13 along the Y alignment axis.

[0092] The sleeve is preferably metallic and may include a fastening part configured to be connected to a variable shimming mechanism. The recess 17 has a first internal surface 17a having a first shape, for example cylindrical, a second internal surface 17b having a second shape, for example polygonal in cross-section, and a third internal surface 17c which has a third shape, for example frustoconical, and which is located between the first and second internal surfaces 17a, 17b. The three surfaces 17a, 17b, 17c extend around the Y-axis and are thus coaxial.

[0093] The fibrous structure 20 is obtained by weaving fibers and includes an aerodynamically profiled blade 12 connected to a blade root 22 which includes the attachment portion 23. The attachment portion 23 is inserted axially into the recess 17 of the sleeve 13.

[0094] The attachment portion 23 comprises a first section 23a having a first external surface 23a1 having a first shape, for example cylindrical, intended to be in contact with the first internal surface 17a, a second section 23b having a second external surface 23b1 having a second shape, for example polygonal in cross-section, intended to be in contact with the second internal surface 17b, and a third section 23c located between the first and second sections 23a, 23b and having a third external surface 23c1 having a third shape, for example frustoconical, intended to be in contact with the third external surface 17c.

[0095] Preferably, the third section 23c has its end with the smallest diameter connected to the first section 23a, and its end with the largest diameter connected to the second section 23b.

[0096] The blade 7 further includes polymerized resin for solidifying the fibrous structure 20.

[0097] The attachment portion 23 of the blade 7 is advantageously tubular and includes a housing 20a centered on the Y alignment axis. The blade 7 may further include an insert 24 centered on the Y axis and inserted axially into the housing 20a of the attachment portion 23.

[0098] Figures 8 and 9 show that the housing 20a can have a general cylindrical shape and may include an internal cylindrical surface. Due to the particular shape of the sections 23a, 23b, 23c of the attachment portion 23, the thickness (or radial dimension with respect to the Y-axis) of the attachment portion 23 can vary along the Y-axis alignment. In the example shown, the thickness of the first section 23a is less than the thickness of the second and third sections 23b, 23c.

[0099] According to the invention, the manufacturing process for blade 7 comprises the following steps:

[0100] a) preparation of the fibrous structure 20 in particular by weaving of fibers, b) compaction of the attachment portion 23 of the fibrous structure 20 so as to reduce its diameter with respect to the alignment axis Y, and allow its insertion into the sleeve 13 (figure 11b),

[0101] c) insertion of the compressed attachment portion 23 into the sleeve 13 and shaping of the attachment portion 23 so that the first, second and third external surfaces 23a1, 23b1, 23c1 of the attachment portion 23 come into contact respectively with the first, second and third internal surfaces 17a, 17b, 17c of the sleeve 13 (Figures 11c and 11d), and

[0102] d) injection of a first polymerizable resin into the fibrous structure 20.

[0103] One of the manufacturing constraints therefore lies in fitting section 23b into sleeve 13.

[0104] The insertion of the attachment portion 23 into the sleeve 13 therefore requires preliminary shaping to reduce the diameter of the attachment portion 23 before insertion. To allow its insertion into the sleeve and then into an RTM injection mold, the attachment portion 23 is compacted and maintained in a compacted state.

[0105] In one particular embodiment of the invention, section 23a initially has a thickness of approximately 30 mm. The thickness after compaction can be reduced to 17 mm for a Fiber Volume Content (FVC) close to 65%. Conversely, the second and third sections 23b and 23c must retain a certain degree of mobility so that, once inserted, the material can return to its original shape before the start of the RTM injection.

[0106] The principle of compacting a fibrous structure is facilitated by wetting the fibrous structure with an impregnation solution and drying it at high temperatures (180°C or higher). Once dried, the fibrous structure struggles to maintain its compacted state, which is not stable over time and is quite sensitive to handling. It is also very difficult with this method to ensure different levels of compaction locally on the same preform.

[0107] The geometric complexity of the attachment portion 23, the multiple manipulations planned after the compaction stage and the need to be compacted differently along the length of the fibrous structure 23 complicate the manufacture of the blade.

[0108] The distinctive feature of the invention lies in the fact that the process comprises, between steps a) and b), a step i) of impregnating the attachment portion 23 of the fibrous structure 20 with two different impregnation solutions. A first impregnation solution S1 is used to impregnate the second and third sections 23b, 23c of the attachment portion 23.

[0109] A second impregnation solution, called tackifying solution S2, is used to impregnate the first section 23a of the attachment portion 23. The tackifying solution S2 has the function of strengthening the cohesion between the fibers so that the fibers of the attachment portion 23 are more cohesive in the first section 23a of the attachment portion 23 than in the second and third sections 23b, 23c of the attachment portion 23.

[0110] Advantageously, the S2 tackifying solution must not have any polluting characteristics or be able to alter the material health of the part.

[0111] The tackifying solution S2 must therefore be able to withstand the compacted stress and prevent the natural elastic return of the fibers. In the aforementioned specific case, for compaction at 65% TVF with a thickness of 17 mm, the stress is estimated at approximately 40 bars. The first impregnation solution S1 is preferably solvent-based.

[0112] The tackifying solution S2 is preferably based on a second solvent and may further comprise a tackifier which is preferably a second polymerizable resin, in particular thermosetting.

[0113] The use of a solvent in the S2 tackifier solution reduces the resin's viscosity, thus promoting good resin impregnation within the fibrous structure. Without this solvent, the resin might not penetrate to the core of the fibrous structure, and only the outer layers of the material would remain compacted. Other types of resin, such as thermoplastics, could meet this requirement.

[0114] The mass proportion of tackifier can also be important. Too little tackifier can prevent the material from withstanding the compaction force. Too much can potentially cause material health problems during injection molding. Advantageously, the proportion of the second polymerizable resin in the tackifier solution is between 1 and 10% by mass, preferably between 3 and 7% by mass, and even more preferably 5% by mass. The second resin is preferably identical to the first resin (for example, epoxy). This choice reduces the number of components present in the part at the time of injection molding.

[0115] The first and second solvents are preferably different. The first solvent can be water. The second solvent can be acetone.

[0116] Step b) of compaction is necessary to achieve the desired level of compaction. This compaction will wring out the fibrous structure, which can lead to undesirable migration of the tackifier, particularly in dry areas. To avoid this migration, it is therefore preferable to avoid dry areas within the fibrous structure, hence the impregnation of the rest of the fibrous structure with the first impregnation solution. The presence of the first impregnation solution limits the capillary migration of the tackifier towards sections 23b and 23c. After conducting several tests, it was found that water was the most effective way to stop the migration of the tackifier.

[0117] Advantageously, the process includes, after the impregnation step (i) and before the compaction step (b), a resting step (iii) lasting several minutes. Preferably, this resting step corresponds to at least partial evaporation of the aforementioned second solvent.

[0118] The fibrous structure is, for example, left for 30 minutes in open air in a ventilated space. This step allows the solvent to evaporate and thus increase the viscosity of the tackifier before the application of the compaction force, thereby reducing the "wringing" effect.

[0119] Advantageously, the process includes, between steps b) and c), a step ii) of drying the attachment portion 23, in particular by heating. The heating can be carried out at 120°C + / -10%, in particular to allow the evaporation of water.

[0120] Step ii) is preferably carried out to induce only partial polymerization of the second resin.

[0121] Step ii) may vary depending on the resin and solvents used. For compaction to be reversible, it is necessary to control the progress of resin polymerization during this step and ensure that the resin does not reach its gel point. Otherwise, the compaction step would be irreversible.

[0122] The polymerization rate of the second resin at the end of step ii) does not exceed a gel point of that preferred resin.

[0123] In the polymerization process of a resin, the gel point marks the initiation of the material's phase change, transitioning from a viscous liquid state, where flow is possible, to a gel and then to a solid, where flow is no longer possible. In terms of polymerization rate, the gel point is typically around 60% conversion (or reaction rate), depending on the resin's chemical composition and the measurement method used.

[0124] The duration of the drying stage can therefore be calculated so as not to reach the gel point of the resin.

[0125] At the end of step b), the attachment portion 23 may have a fiber volume ratio between 60 and 70%.

[0126] The present invention offers several advantages, including:

[0127] - to maintain a compacted state of the attachment portion in a specific part thereof,

[0128] - to maintain a certain flexibility in the rest of the attachment portion, - to control the more cohesive areas from the less cohesive areas of the attachment portion,

[0129] - to eliminate buckling related to the insertion of the attachment portion into the sleeve,

[0130] - to improve the material health of the composite,

[0131] - to avoid the proliferation of the fibrous structure,

[0132] - to allow the fibrous structure to be positioned in the injection mold without having to make any special cuts in the fibrous structure,

[0133] - to have reversible compaction so that the material can return to the shape imposed by the mold before the start of RTM injection,

[0134] - to work at temperatures lower than those imposed by existing compaction techniques, etc.

Claims

DEMANDS 1. Method for manufacturing a variable-pitch blade (7) for a turbomachine, this blade (7) comprising: - a tubular metal sleeve (13), this sleeve comprising a fixing part (14) configured to be connected to a variable shimming mechanism, and a recess (17) passing through the sleeve (13) along a shimming axis (Y), the recess (17) comprising a first internal surface (17a) having a first shape, a second internal surface (17b) having a second shape, and a third internal surface (17c) which has a third shape and which is located between the first and second internal surfaces (17a, 17b), - a fibrous structure (20) obtained by weaving fibers, the fibrous structure (20) comprising an aerodynamically profiled blade (12) connected to a blade root (22) which includes an attachment portion (23) inserted axially into the recess (17) of the sleeve (13), the attachment portion (23) comprising a first section (23a) having a first external surface (23a1) in contact with said first internal surface (17a), a second section (23b) having a second external surface (23b1) in contact with said second internal surface (17b), and a third section (23c) located between the first and second sections (23a, 23b) and having a third external surface (23c1) which is in contact with said third external surface (23a1, 23b1), and - a polymerized resin for solidifying the fibrous structure (20), the process comprising a step a) of preparing the fibrous structure (20), in particular by weaving fibers, characterized in that the method further comprises the following steps: b) compacting the attachment portion (23) of the fibrous structure (20) so as to reduce its diameter with respect to the alignment axis (Y), and allow its insertion into the sleeve (13), c) inserting the compressed attachment portion (23) into the sleeve (13) and shaping the attachment portion (20) so that the first, second and third external surfaces (23a1, 23b1, 23c1) of the attachment portion (23) come into contact respectively with the first, second and third internal surfaces (17a, 17b, 17c) of the sleeve (17), and d) injection of a first polymerizable resin into the fibrous structure (20), between steps a) and b), a step i) of impregnating the attachment portion (23) of the fibrous structure (20) with two different impregnation solutions (S1, S2), a first impregnation solution (S1) being used to impregnate the second and third sections (23b, 23c) of the attachment portion (23), and a second impregnation solution, called tackifying solution (S2), being used to impregnate the first section (23a) of the attachment portion (23), the tackifying solution having the function of strengthening the cohesion between the fibers so that the fibers of the attachment portion (23) are more cohesive in the first section (23a) of the attachment portion (23) than in the second and third sections (23b, 23c) of the attachment portion (23).

2. A process according to claim 1, wherein the first impregnation solution (S1) is based on a first solvent.

3. A process according to claim 2, wherein the first solvent is water.

4. A method according to any one of the preceding claims, wherein the tackifying solution (S2) is based on a second solvent and further comprises a second polymerizable resin and in particular a thermosetting resin.

5. A method according to claim 4, wherein the second resin is identical to the first resin.

6. A method according to claim 4 or 5, depending on claim 2 or 3, wherein the first and second solvents are different.

7. A method according to any one of claims 4 to 6, wherein the second solvent is acetone.

8. A process according to any one of claims 4 to 7, wherein the proportion of the second polymerizable resin in the tackifying solution (S2) is between 1 and 40% by mass, preferably between 10 and 30% by mass, and more preferably in the order of 25% by mass.

9. A method according to any one of the preceding claims, wherein it comprises, between steps b) and c), a step ii) of drying the attachment portion (23), in particular by heating.

10. Method according to claim 9, wherein the heating is carried out at 120°C + / -10%.

11. A method according to claim 9 or 10, depending on claim 3, 4, 5, 7 or 8, wherein step ii) is carried out to bring about only partial polymerization of the second resin.

12. A method according to claim 11, wherein the polymerization rate of the second resin at the end of step ii) does not exceed a gel point of that resin.

13. A method according to any one of the preceding claims, wherein, at the end of step b), the attachment portion (23) has a fiber volume ratio of between 60 and 70%.

14. A method according to any one of the preceding claims, wherein, after step i) and before step b), the method comprises a resting step iii) for several minutes.

15. A method according to claim 14, depending on any one of claims 4 to 8, wherein the resting step corresponds to an at least partial evaporation step of said second solvent.

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