Tooling for compressing a fibrous structure and method for manufacturing a variable-pitch blade using this tooling

Abstract

Tooling (48, 68) for compressing a fibrous structure (23), comprising: - a one-piece body (50, 70) made of a material having a volumetric expansion coefficient greater than or equal to 1 x 10⁻⁴, this body (50, 70) having an external annular compression surface (50a), - at least one heating element (54) for the body (50) to cause its expansion and increase the external diameter of its external annular surface (50a), - at least one first temperature sensor (56, 74) for measuring the temperature on the external annular surface (50a) of the body (50), and - a control circuit (58) for the heating element (54). Figure for the abbreviation: Figure 10

Description

Title of the invention: TOOLING FOR COMPRESSING A FIBROUS STRUCTURE AND METHOD FOR MANUFACTURED A VARIABLE-STOP BLADE USING THIS TOOLING Technical field of the invention

[0001] The invention relates generally to the field of turbomachinery, and in particular to turbomachine blades.

[0002] The invention relates more particularly, but not exclusively, to the manufacture of a variable pitch blade intended for use in an unfaired fan rotor of an aircraft engine. Technical background

[0003] 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.

[0004] The elements influencing this propulsive efficiency to the first order are those related to the low-pressure parts of the propulsion system, which contribute directly to thrust generation: low-pressure turbine, low-pressure transmission system, fan, and secondary flow guiding its flow. The known guiding principle for improving propulsive efficiency consists of reducing the fan's compression ratio, thereby decreasing the flow velocity at the engine outlet and the associated kinetic energy losses.

[0005] 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 passing through the secondary flow (cold flow) and the mass flow rate passing through the primary flow (hot flow), which notably supplies the combustion chamber.

[0006] This increase in secondary flow rate has the direct effect of requiring an increase in the diameter of the blower, and consequently in the external dimensions of the surrounding containment casing, as well as in the nacelle constituting the envelope. aerodynamics of the housing in question. To target high dilution rates, the housing becomes too large and too heavy (generating significant drag), so it is removed to switch to configurations with unfaired propellers.

[0007] Several concepts of unducted turbomachines could be considered, such as the Unducted Single Fan (USF) type architecture: unducted turbomachine with (at least) an upstream variable pitch propeller wheel (or "Open Fan") and a downstream stator wheel with fixed or variable pitch.

[0008] More generally, the technical field of application lies within the context of fan blades, rotating (rotor), unshod (propeller) and with variable pitch, with the aeronautical propulsion industry as a potential application. Other examples of particularly relevant architectures include: Contra-Rotating Open Rotor (CROR) and Turboprop.

[0009] However, the design of such blades requires taking into account opposing constraints.

[0010] On the one hand, the sizing of these blades must allow for optimal aerodynamic performance, in particular 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.

[0011] 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.

[0012] Furthermore, on unshrouded fan designs, engine starting is generally performed with a very open timing setting. Indeed, a very open timing setting allows power to be consumed by torque, which ensures machine safety by guaranteeing low fan speeds.

[0013] However, with a very open pitch, the blades undergo turbulent, completely separated aerodynamic flow, which generates broadband vibrational excitation. In particular, on blades with a wide chord and large span, the bending stress is intense, even though the engine speed is not at its maximum.

[0014] In normal operation, namely during ground and flight phases, the pitch is modified so that the pitch angle is more closed. The aerodynamic flow is then perfectly smooth, particularly when aligned with the airfoil. Broadband stresses disappear since 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 seen by the different fan blades, depending on their angular position, varies according to the aircraft's angle of attack, creating a cyclic bending moment (commonly called the IP moment) on the blades. This cyclic bending moment generates then there are strong bending stresses on the blades in addition to the centrifugal forces due to their rotation.

[0015] These blades can be made of metallic material. While metallic blades have good mechanical resistance, they nevertheless have the disadvantage of having a relatively large mass.

[0016] Manufacturing blades from composite material is an attractive solution for reducing blade weight. However, composite blades can be fragile due to the intense aerodynamic stresses to which they are subjected. These aerodynamic stresses can therefore damage the blades and / or the hub in the interface zone between the blades and the fan rotor hub, at the blade root.

[0017] To overcome these drawbacks, various solutions exist in the prior art. Most use reinforcing elements, particularly at the blade root, and add various structural elements to allow, for example, the blade to be attached to the leveling mechanism. Patent documents WO-A1-2022 / 018353 and WO-A1-2022 / 208002 describe the addition of reinforcing and structural elements, particularly at the blade roots.

[0018] However, these solutions have the disadvantage of requiring the manufacture of several elements in potentially different materials and the assembly of these elements using fastening means. Such blades can therefore be relatively time-consuming to manufacture.

[0019] One possible technology for manufacturing blades from composite material is RTM technology, which stands for Resin Transfer Molding. A blade of this type comprises a carbon fiber structure densified by the hot and pressure injection of a thermosetting polymer resin such as an epoxy resin.

[0020] The fibrous structure includes a portion intended to form a foot and bonded to an element such as a metal sleeve. Furthermore, the fibrous structure must undergo a compression forming operation in order to shape it.

[0021] The presence of a bonding zone necessitates handling the assembly at low temperatures (<100°C and more specifically 60°C) to prevent polymerization of the adhesive before RTM injection. However, traditional forming of a fibrous structure involves wetting this structure with water and drying it at least at 120°C. In the presence of adhesive, such drying is therefore not feasible. Since the preform becomes compacted at the bonding zone at a temperature of 60°C or lower, it quickly decompresses (re-bulks) over time (re-swelling of the fibrous preform), making it impossible to continue manufacturing the blade.

[0022] Another temperature-related problem is that drying solutions are carried out in heated chambers (autoclave, oven, etc.) where it is impossible to handle the assembly. This results in very rapid re-expansion of the preform after the chamber is opened at room temperature.

[0023] The present invention proposes an improvement to existing technologies, which provides a simple, efficient and economical solution to at least some of the problems of the prior art. Summary of the invention

[0024] The invention provides a tool for compressing a fibrous structure, this tool comprising:

[0025] - a one-piece body made of a material having a coefficient of expansion volumetric greater than or equal in absolute value to 1 x 10⁴, this body comprising an internal or external annular surface subjected to compression,

[0026] - at least one body heating element for the purpose of its expansion and the increase in the external diameter of its external annular surface, or at least a body cooling device for its retraction and the decrease in the internal diameter of its internal annular surface,

[0027] - at least one first temperature measurement sensor on the annular surface internal or external to the body, and

[0028] - a control circuit for the heating or cooling unit.

[0029] The invention makes it possible to compact a fibrous structure while limiting or even preventing the formation of hot spots at the contact points between the tooling and the fibrous structure. The invention can be applied more broadly to any form of compaction, with or without adhesive, of one or more fibrous structures with simple or complex geometries. Several tooling systems, whether dependent on or independent of heating or cooling, can also be used.

[0030] In the case where the body is to undergo expansion, its coefficient of expansion is positive. In the case where the body is to undergo contraction, its coefficient of expansion is negative. In absolute value, regardless of the type of body, it has, according to the invention, a coefficient of expansion greater than or equal to 1 x 10⁴.

[0031] The tooling according to the invention may comprise one or more of the following features, taken individually or in combination with each other: • the control circuit includes at least one second sensor, of the thermocouple type, mounted in a housing in the one-piece body; • said at least one heating or cooling element is mounted in a recess in the body; • said at least one first sensor is located on the internal or external annular surface of the body;

[0032] — the body has a general cylindrical shape and includes an axis of revolution, said heating element extending along the axis of revolution and said external annular surface extending around the axis of revolution;

[0033] — said annular surface is a cylindrical, or frustoconical, or cylindrical surface and truncated conical; • said control circuit is configured to control the heating element so that the temperature measured by said at least one first sensor does not exceed a predetermined threshold value; • The body material is chosen from silicone, elastomer, rubber and polyurethane.

[0034] The present invention also relates to an assembly comprising tooling as described above, and a variable pitch blade for a turbomachine, in particular for aircraft, the tooling being used to compress a fibrous structure of the blade during its manufacture.

[0035] Dawn preferably includes:

[0036] - a tubular metal sleeve, this sleeve comprising a fixing part configured to be connected to a variable shimming mechanism, and a recess through the sleeve along a shimming axis, the recess being delimited by an internal wall of the sleeve;

[0037] - a fibrous structure obtained by weaving fibers, the fibrous structure comprising a blade root comprising a tubular attachment portion inserted axially into the recess of the sleeve, this attachment portion comprising a housing centered on the alignment axis, the fibrous structure further comprising an aerodynamically profiled blade connected to the blade root;

[0038] - a layer of polymerizable adhesive between the attachment portion and at least one part of said inner wall of the sleeve, and

[0039] - at least one insert centered on the alignment axis and inserted axially into the housing of the attachment portion.

[0040] The assembly according to the invention may comprise one or more of the following features, taken individually or in combination with each other: • the layer of glue is located between two complementary frustoconical surfaces respectively of the attachment portion and the inner wall of the sleeve; • said at least one insert comprises two tubular inserts engaged axially in the housing of the attachment portion, the first of the inserts comprising an external cylindrical surface and being engaged in a first part of the housing, and a second of the inserts comprising an external surface with a polygonal section and being engaged in a second part of the housing which can overlap axially with the first part of the housing;

[0041] — the second insert extends around the first insert and includes an end free axial which is beveled and extends radially inside the two frustoconical surfaces; • the tooling includes a heating element and an external annular compression surface, and the tooling is inserted axially into the housing of the attachment portion, and possibly partly inside said at least one insert.

[0042] The present invention also relates to a method for manufacturing a variable-pitch turbine blade for a turbomachine, in particular for aircraft, from an assembly as described above, comprising the following steps:

[0043] a) produce by weaving the fibrous structure comprising the attachment portion,

[0044] b) insert the attachment portion into the recess of the sleeve and against the inner wall, the layer of glue being interposed between the attachment portion (23) and the inner wall of the sleeve,

[0045] c) position said at least one insert in the housing of the attachment portion,

[0046] d) insert the tooling axially into the housing of the attachment portion, and possibly partly inside said at least one insert, and control the heating element to expand the body of the tooling and cause compression of the attachment portion against the inner wall of the sleeve, and to ensure that the temperature measured by said at least one first sensor does not exceed a predetermined threshold value,

[0047] e) insert the fibrous structure, the sleeve, said at least one insert, or even said tooling, into a mold and inject the resin into the mold.

[0048] The method according to the invention may comprise one or more of the following features or steps, taken individually or in combination with each other: • the glue is of the polymerizable type;

[0049] — the threshold value is 60°C;

[0050] — the compression time in step d) is less than or equal to 10 minutes; In practice, the compression time can be much longer if desired; with the threshold value of 60°C for example, there is no time limitation with the glue; the higher the threshold value, the shorter the compression time should be; for example, 10 minutes is the maximum time for a threshold value of 80°C. Brief description of the figures

[0051] 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:

[0052] [Fig. 1] [Fig. 1] schematically represents an example of an engine including an unfaired fan;

[0053] [Fig.2] [Fig.2] schematically represents a blower blade according to an embodiment of the invention assembled to a shimming mechanism;

[0054] [Fig.3] [Fig.3] schematically represents a blower blade according to a first embodiment of the invention;

[0055] [Fig.4a] Fig.4a schematically represents a sleeve according to a first embodiment of the invention in perspective view;

[0056] [Fig.4b] Fig.4b schematically represents the sleeve of Fig.4a in a profile view;

[0057] [Fig.4c] Fig.4c schematically represents the sleeve of figures 4a and 4b into which the attachment portion and the insert are inserted;

[0058] [Fig.4d] Fig.4d schematically represents the sleeve / portion of attachment / insert assembly of Fig.4c inserted into the shimming mechanism;

[0059] [Fig.5] Fig.5 schematically represents an insert according to one embodiment of the invention;

[0060] [Fig.6] The [Fig.6] is a view similar to that of the [Fig.4d] and illustrating a variant of the realization of a blade;

[0061] [Fig.7] The [Fig.7] is a cross-sectional view of one of the blade inserts of the [Fig.6];

[0062] [Fig.8] The [Fig.8] is a schematic perspective view of a tool according to the invention for compressing a fibrous structure;

[0063] [Fig.9] The [Fig.9] is a schematic axial cross-sectional view of the tooling of the [Fig.8]

[0064] [Fig. 10] Fig. 10 is a cross-sectional view of the tooling of Fig. 7 engaged in the foot of a variable-pitch blade during its manufacture; and

[0065] [Fig. 1 la-11b] Figures 1 la and 11b are schematic cross-sectional views of an alternative embodiment of a compression tool according to the invention. Detailed description of the invention

[0066] In [Fig. 1], the motor 1 shown is an "Open Rotor" type motor, in a configuration commonly referred to as "pusher" (i.e., the blower is placed at the rear of the power generator with an air intake located on the side, to the right in [Fig.1]).

[0067] The engine comprises a nacelle 2 intended to be fixed to an aircraft fuselage, and an unfaired fan 3. The fan 3 comprises 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.

[0068] Thus, in the example illustrated in [Fig. 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).

[0069] In addition, the invention also applies to motors having different architectures, such as an architecture comprising a blower rotor including movable blades and a blower stator including fixed blades, or a single blower rotor.

[0070] The invention is applicable to turboprop type architectures (comprising a single fan rotor).

[0071] In [Fig.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 relative to the axis of rotation X of the hub.

[0072] As illustrated in [Fig. 2], the fan 3 further comprises 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 about a pitch axis Y. More specifically, the blade root 9 is rotatably mounted within a mounting device 10 formed in the hub 6, by means of balls 11 or other rolling elements.

[0073] The aerodynamically profiled blade 12 has a first end connected to the blade root 9 and a second end, opposite the first end. The aerodynamically profiled portion of the blade 12 is designed to extend into an air stream of the engine, when the engine is running, in order to generate lift. Conversely, the blade root 9 is designed to extend out of the air stream.

[0074] With reference to Figures 3, 4a and 4b, the blade 7 comprises a sleeve 13 having a fastening portion 14 configured to be connected to a variable pitch 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 Y alignment axis.

[0075] With reference to Figures 3, 4c and 4d, the blade 7 also comprises a fibrous structure 20 obtained by weaving, preferably three-dimensional. The fibrous structure 20 comprises a blade root 22 including an attachment portion 23 configured to be inserted into the recess 17 formed by the attachment portion 14 of the sleeve 13.

[0076] The fibrous structure 20 has a tubular shape and includes a housing 20a centered on the alignment axis Y.

[0077] The fibrous structure 20 also includes a blade 21 with an aerodynamic profile connected to the blade root 22.

[0078] The blade 7 also includes an insert 24 shown in [Fig.5] 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.

[0079] The blade 7 further includes a polymerized resin for solidifying the fibrous structure 20 to the inner wall 18 of the sleeve 13.

[0080] The resin thus makes it possible to form a main force path, called default, during the transmission of a torque recovery force around the Y alignment axis between the blade root 22 and the sleeve 13.

[0081] 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.

[0082] The blade 7 can thus withstand significant aerodynamic forces while having a limited mass and can therefore be used with a variable pitch mechanism and in an "open rotor" type environment. Furthermore, since the elements forming the blade 7 are limited in number, the blade 7 is quick to manufacture.

[0083] 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.

[0084] 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 The 23" thickened portion is configured to fit into a recessed portion 18' of the inner wall 18. Thus, the portion 18' widens the recess 17 and the rest of the part of the wall 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 part of the wall 18 which narrows the recess 17 and forms a stop.

[0085] Indeed, when the fan is rotating, the blade 7 is subjected to centrifugal forces oriented in a radial direction with respect 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.

[0086] 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 having different reliefs.

[0087] The fastening 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.

[0088] 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.

[0089] The mounting portion 14 also includes a first circular groove 32 and a second circular groove 34 for forming a raceway on at least one bearing, for example a ball bearing. The mounting portion 14 thus allows the blade foot 9 to be rotatably mounted inside the attachment device 10 provided in the hub 6.

[0090] The sleeve 13 is preferably metallic and monolithic.

[0091] 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 excess 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 that has a constant diameter then forms a stop for the excess thickness 23".

[0092] The recessed portion may have another shape and may be placed in another position along the wall 18.

[0093] Alternatively, the wall 18 could be thickened at its end opposite the free end so as to reduce the diameter of the recess 17 and form a stop allowing to block the insert 24 and wedge the attachment portion 23 against the wall 18 in an optimized manner.

[0094] Fig. 4d represents the sleeve into which the attachment portion 23 and the insert 24 are inserted, the sleeve being disposed in the attachment device 10, the rolling elements 11 being disposed in the circular grooves 32 and 34.

[0095] With reference to [Fig. 5], the insert 24 comprises a cylindrical body 40 having a free end 41 and a locking end 42 opposite the free end 41. The locking end 42 is, in this embodiment, a rounded end. The insert 24 is preferably metallic.

[0096] Figure 6 illustrates an alternative embodiment in which two inserts 24, 44 are inserted axially into the housing 20a of the attachment portion 23. The first insert 24 is similar to that described above and illustrated in [Fig.5].

[0097] The second insert 44, although optional, has a tubular shape and preferably has an external surface 44a with a polygonal cross-section as seen in [Fig.7].

[0098] The insert 44 extends around the insert 24 and includes a free axial end 44b which is beveled in the example shown.

[0099] This end 44b can extend radially inside two frustoconical surfaces 23a, 18a complementary respectively to the attachment portion 23 and the internal wall 18 of the sleeve 13.

[0100] A layer of polymerizable adhesive can be intercalated between these surfaces 23a, 18a in order to reinforce the bonding of the attachment portion 23 to the inner wall 18 of the sleeve 13.

[0101] In the case of the blade shown in [Fig.4c], which is not equipped with a second insert 44, a layer of polymerizable glue could also be intercalated between the frustoconical surfaces designated by the same references 23a and 18a.

[0102] Due to the presence of glue, it is impossible to raise above a certain temperature before RTM injection and more particularly during foot shaping because this could initiate the polymerization of the glue.

[0103] The invention thus proposes a tool 48 for compressing and shaping the fibrous structure of the foot, a first embodiment of which is illustrated in figures 8 and 9.

[0104] Tooling 48 includes:

[0105] - a one-piece body 50 made of a material having a coefficient of expansion volumetric greater than or equal in absolute value to 1.10 4, this body 50 having an external annular surface 50a for compression,

[0106] - at least one heating element 54 for the body 50 in order to facilitate its expansion and the increase in the external diameter of its external annular surface 50a,

[0107] - at least one first sensor 56 for measuring the temperature on the surface external annular 50a of the body, and

[0108] - a control circuit 58 for the heating element 54.

[0109] In the example shown, the body 50 has a general cylindrical shape and includes an axis of revolution A. The heating element 54 can extend along the axis of revolution A and the external annular surface 50a can extend around the axis of revolution A.

[0110] The heating element 54 is preferably mounted in a recess 60 of the body 50.

[0111] The control circuit 58 preferably includes at least one second sensor 62, of the thermocouple type, mounted in a housing of the monobloc body 50.

[0112] The first sensor 56 is preferably located on the internal annular surface 50a of the body so as to best monitor the temperature of this surface.

[0113] This surface 50a can be cylindrical as seen in Figures 8 and 9. Alternatively, it could be frustoconical or partly cylindrical and frustoconical as seen in [Fig. 10],

[0114] The control circuit 58 is advantageously configured to control the heating element 54 so that the temperature measured by the first sensor 56 does not exceed a predetermined threshold value, for example 60°C. This threshold value naturally depends on the adhesive used and in particular on the temperature at which the adhesive can begin to polymerize.

[0115] The material of the body 50 can be chosen from silicone, elastomer, rubber and polyurethane.

[0116] The table below shows the thermal diffusivity and volumetric expansion of these materials.

[0117] [Tables] Body Material Thermal Diffusivity (m².s⁻¹) Thermal Expansion (mm³.K⁻¹) Elastomer (RTV) 0.1 9.9 x 10⁴ Rubber 0.07 to 0.2 6 to 8 x 10⁴ Polyurethane 0.4 >1 x 10⁴

[0118] In a particular embodiment of a tool 48 according to the invention, the body 50 has an external surface having an external diameter of 54.35 mm when cold and a heating element 54 having a heating power of 500 W. The body 50, made of RTV elastomer, is heated to 166°C by the heating element 54, which allows the external surface 50a to expand to an external diameter of 55.7 mm while maintaining a surface temperature not exceeding 56°C.

[0119] One or more tools as illustrated in Figures 8 and 9 is / are engaged in the fibrous structure as illustrated in [Fig. 10].

[0120] The tooling 48 is inserted axially into the housing 20a of the attachment portion 23, and possibly partly inside the insert(s) 24, 44.

[0121] The heating element 54 is controlled to expand the body 50 and cause compression of the attachment portion 23 against the inner wall 18 of the sleeve 13. The heating element 54 is further controlled so that the temperature measured by the first sensor 56 does not exceed a predetermined threshold value.

[0122] The compression of the fibrous structure 20 by the tooling 48 can last only a few minutes and at most 10 minutes.

[0123] The present invention also relates to a method for manufacturing a variable-pitch blade 7 for a turbomachine, in particular for an aircraft, comprising the following steps:

[0124] a) to produce by weaving the fibrous structure 20 comprising the attachment portion 23,

[0125] b) insert the attachment portion 23 into the recess 17 of the sleeve 13 and against the inner wall 18, the layer of adhesive being interposed between the attachment portion 23 and the inner wall 18 of the sleeve 13,

[0126] c) position the insert(s) 24, 44 in the housing 20a of the attachment portion 23,

[0127] d) insert the tool 48 axially into the housing 20a of the attachment portion 23, and possibly partly inside the insert(s) 24, 44, and control the heating element 54 to expand the body 50 of the tool 48 and cause compression of the attachment portion 23 against the inner wall 18 of the sleeve 13, and to ensure that the temperature measured by the sensor 56 does not exceed a predetermined threshold value,

[0128] e) insert the fibrous structure 20, the sleeve 13, the insert(s) 24, 44, and also the tooling 48, into a mold and inject the resin into the mold.

[0129] As mentioned above, the adhesive is preferably of the polymerizable type. The threshold value is, for example, 60°C. The compression time in step d) can be less than or equal to 10 minutes.

[0130] Figures 1a and 11b illustrate an alternative embodiment of tooling 68 according to the invention.

[0131] Tooling 68 comprises:

[0132] - a one-piece body 70 made of a material having a coefficient of expansion volumetric greater than or equal in absolute value to 1.10 4, this body 70 comprising an internal annular surface 70a for compression,

[0133] - at least one cooling organ 72 for the body 70 in order to facilitate its retraction and from the decrease in the internal diameter of its internal annular surface 70a,

[0134] - at least one first sensor 74 for measuring the temperature on the surface internal annular 70a of body 70, and

[0135] - a control circuit 76 for the cooling unit 72.

[0136] It is therefore understood that the fibrous structure 20 to be put into compression is intended to be surrounded by the tooling 68 and in particular by the internal cylindrical surface 70a.

[0137] In the case where the fibrous structure 20 is tubular as illustrated in the drawing, a metallic counterform 78 could be engaged inside the fibrous structure 20 in order to be able to compress it radially between the body 70 of the tooling 68 and the counterform 78.

[0138] In the case of another variant, a heating element of the body 70 of figures 1 la-11b could also be associated rather than a cooling element.

Claims

Demands

1. Tooling (48, 68) for compressing a fibrous structure (23), said tooling comprising: - a one-piece body (50, 70) made of a material having a volumetric expansion coefficient greater than or equal to 1 x 10⁴, this body (50, 70) having an internal (50a, 70a) or external annular surface for compression, - at least one heating element (54) for the body (50) for its expansion and the increase in the external diameter of its external annular surface (50a), or at least one cooling element (72) for the body (70) for its contraction and the decrease in the internal diameter of its internal annular surface (70a), - at least one first temperature sensor (56, 74) for measuring the temperature on the internal (70a) or external (50a) annular surface of the body (50, 70), and - a control circuit (58, 76) for the heating (54) or cooling (72) component.

2. Tooling (48) according to claim 1, wherein the control circuit (58) comprises at least one second sensor (62), of the thermocouple type, mounted in a housing in the one-piece body (50).

3. Tooling (48, 68) according to claim 1 or 2, wherein said at least one heating (54) or cooling (72) element is mounted in a recess in the body (50, 70).

4. Tooling (48, 68) according to any one of the preceding claims, wherein said at least one first sensor (56, 74) is located on the internal (50a) or external (70a) annular surface of the body (50, 70).

5. Tooling (48, 68) according to any one of the preceding claims, wherein said control circuit (58) is configured to control the heating element (54) so ​​that the temperature measured by said at least a first sensor (56) does not exceed a predetermined threshold value.

6. Tooling (48, 68) according to any one of the preceding claims, wherein the body material (50, 70) is selected from silicone, elastomer, rubber and polyurethane.

7. An assembly comprising tooling (48, 68) according to any one of the preceding claims, and a variable-pitch blade (7) for a turbomachine, in particular for aircraft, the tooling (48, 68) being used to compress a fibrous structure (20) of the blade during its manufacture.

8. Assembly according to claim 7, wherein the blade (7) comprises: - a tubular metal sleeve (13), this sleeve comprising a fastening portion (14) configured to be connected to a variable pitching mechanism, and a recess (17) passing through the sleeve (13) along a pitching axis (Y), the recess (17) being delimited by an internal wall of the sleeve (13); - a fibrous structure (20) obtained by weaving fibers, the fibrous structure (20) comprising a blade root (22) comprising a tubular attachment portion (23) inserted axially into the recess (17) of the sleeve (13), this attachment portion (23) comprising a housing (20a) centered on the pitching axis (Y), the fibrous structure (20) further comprising an aerodynamically profiled blade (12) connected to the blade root (22);- a layer of polymerizable adhesive between the attachment portion (23) and at least a part of said inner wall (18) of the sleeve (13), and - at least one insert (24) centered on the alignment axis (Y) and inserted axially into the housing (20a) of the attachment portion (23).;

9. Assembly according to claim 8, wherein the glue layer is located between two complementary frustoconical surfaces (23a, 18a) respectively of the attachment portion (23) and the inner wall (18) of the sleeve (13).

10. Assembly according to claim 8 or 9, wherein said at least one insert comprises two tubular inserts (24, 44) axially engaged in the housing (20a) of the attachment portion (23), a first of the inserts (24) having an external cylindrical surface and being engaged in a first part of the housing, and a second of the inserts (44) having an external surface (44a) with a polygonal cross-section and being engaged in a second part of the housing which can overlap axially with the first part of the housing.

11. Assembly according to any one of claims 8 to 10, wherein the tooling (48) comprises a heating element (54) and an external annular compression surface (50a), and the tooling (48) is inserted axially into the housing (20a) of the attachment portion (23), and optionally partially inside said at least one insert (24).

12. A method for manufacturing a variable-pitch turbine blade (7) for a turbomachine, particularly an aircraft turbomachine, from an assembly according to claim 11, comprising the following steps: a) producing by weaving the fibrous structure (20) comprising the attachment portion (23), b) inserting the attachment portion (23) into the recess (17) of the sleeve (13) and against the inner wall (18), the adhesive layer being interposed between the attachment portion (23) and the inner wall (18) of the sleeve (13), c) positioning said at least one insert (24, 44) in the housing (20a) of the attachment portion (23), d) inserting the tooling (48) axially into the housing (20a) of the attachment portion (23), and optionally partially inside said at least one insert (24, 44), and controlling the heating element (54) to expand the body (50) of the tooling (48) and cause compression of the attachment portion (23) against the inner wall (18) of the sleeve (13),and to ensure that the temperature measured by said at least one first sensor (56) does not exceed a predetermined threshold value, e) insert the fibrous structure (20), the sleeve (13), said at least one insert (24), and also said tooling (48), into a mold and inject the resin into the mold.

13. A manufacturing process according to claim 12, wherein the glue is of the polymerizable type.

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