Method for producing an aircraft turbine engine blade

Abstract

The invention relates to a method for producing a turbine engine blade (58) having a composite aerofoil (62) and a metal root (66), the method comprising the steps of: - a) providing an aerofoil preform (68) and a spar (82) comprising a first portion (86) inserted into a cavity (80) of the preform (88) and a second portion which is external to the preform (88) and which forms the root (66); - b) applying adhesive to the first portion (86); - c) introducing the first portion into the cavity (80); - d) depositing this assembly in a mould (90); - e) heating the mould (90) to a first temperature; - f) injecting a resin into the mould (90); - g) consolidating the resin at a second curing temperature. The method is characterised in that it comprises a step i) of cooling the spar (82) to a third temperature lower than the first temperature, which begins before step e) and ends after step f).

Description

[0001] DESCRIPTION

[0002] TITLE: METHOD FOR MANUFACTURING AN AIRCRAFT TURBOMACHINE BLADE

[0003] Technical field of the invention

[0004] The invention relates to a method for manufacturing an aircraft turbomachine blade and a spar for manufacturing such a blade.

[0005] Technical background

[0006] The state of the art includes documents WO-2010 / 061139-A2, FR- 3.109.115-A1 and FR-2.291 .391 -A1.

[0007] New engine generations require blades with compact roots because their blades are designed to pivot around their radial axes in order to adapt their incidence to different flight regimes. This is the case, for example, in the case of a ducted turbomachine with a double-flow, for the outlet guide vanes or OGVs which are located downstream of the fan blades. This is also the case for the propeller blades of unducted turbomachines of the "open rotor" type.

[0008] This feature adds to the need to attach the blade to the disc or hub that carries it as deeply as possible, i.e. as close as possible to the axis of the disc or hub. It is therefore necessary to greatly reduce the size of the blade root.

[0009] However, the blade in operation is subject to numerous constraints. Indeed, the blade root is mainly subjected to bending and tensile stresses, in particular due to the centrifugal forces to which the blade is subjected and due to possible impacts with birds. In addition, the roots of the blades of "open rotor" type turbomachines can be subjected to alternating bending stresses caused by the intense bending vibrations exerted on the blades due to the absence of a nacelle conditioning the air flow, as is usually the case on ducted engines. In order to be able to oppose these alternating bending moments, the roots are prestressed in the hub and are therefore subjected to an additional circumferential mechanical load.

[0010] The blades used in this type of application generally comprise blades made of a composite material in order to improve their thermomechanical resistance capacity and reduce their mass. The composite material can be made from a preform obtained by three-dimensional (or 3D weaving) or two-dimensional (2D weaving) weaving of fibers. This weaving is intended to form a fiber reinforcement and is embedded in a matrix formed by injecting a resin during an RTM (resin transfer molding) or VARTM (vacuum assisted resin transfer molding) injection process.

[0011] Three-dimensional weaving is generally preferred in this type of application because it offers better resistance to delamination. The term "three-dimensional weaving" or "3D weaving" refers to a weaving method in which warp yarns are bonded to weft yarns in several layers. Preferably, but not limited to, the 3D weaving has an interlock structure (or reinforcement). Interlock weaving has improved impact resistance, particularly compared to a 2D weaving. Similarly, the preform is woven in a single piece.

[0012] The composite material can be monolithic or include a core, for example foam, to form a composite sandwich material. The latter provides rigidity and lightness to the final part. Indeed, the interposition of a cellular core such as a honeycomb or foam between two monolithic skins or fiber reinforcement layers (densified by a resin or not impregnated by a resin) allows on the one hand, to considerably increase the bending stiffness of the final part and on the other hand, to control in parallel the mass via the introduction of a low-density material at the core (for the core), where the mechanical loading is low. Finally, the blade has a cavity intended to receive a first part of a metal spar, a second part of which, external to the blade, forms the root of the blade.

[0013] During its manufacture, the first part of the spar is coated with glue and then inserted into the blade preform, then the assembly is placed in a two-part mold which is closed. The mold is then heated to a so-called injection temperature which allows good diffusion of the resin, generally an organic resin, into the fibers. In the case of a VARTM process, a vacuum is created in the mold, then the resin is injected. Then follows a consolidation step during which the mold is maintained at a curing temperature, generally higher than the injection temperature, to ensure crosslinking of the resin.

[0014] This conventional design carries a risk of creep of the glue film. Indeed, the vacuum created in the mold cavity of -1 bar (= -1 .105 Pa) and the concomitant drop in viscosity of the glue film exposed to the rise in temperature of the preform before consolidation tend to cause the glue to flow deep into the fiber strands of the preform by capillarity. This dispersion of the glue or creep in the preform, reduces the thickness of the glue joint and compromises the assembly of the spar to the preform.

[0015] Such dispersion should therefore be avoided in the context of structural bonding.

[0016] Summary of the invention

[0017] The invention overcomes this drawback by proposing a method for manufacturing an aircraft turbomachine blade, this blade comprising a blade made of composite material and a metal root, said method comprising at least the steps of:

[0018] - a) providing a blade preform by weaving fibers, and providing a metal spar which comprises a first part configured to be inserted into a cavity of said preform and a second part configured to remain outside the preform and to form the root of the blade, - b) applying glue to the first part of the spar,

[0019] - c) introduction of the first part of the spar covered with glue into the cavity of the preform,

[0020] - d) depositing the spar and the preform in a two-part mold,

[0021] - e) heating the mold to a first predetermined temperature called injection temperature,

[0022] - f) injection of a resin into the mold in order to impregnate the preform,

[0023] - g) consolidation of the resin, the mold being maintained at a second cooking temperature for a determined period to ensure crosslinking of the resin, characterized in that the method comprises a step i) of cooling or maintaining the spar at a third temperature which is lower than said first temperature, this step starting before step e) and ending after step f).

[0024] The method according to the invention advantageously makes it possible to maintain the spar at a temperature lower than the injection temperature, which makes it possible to avoid the creep of the glue and its dispersion in the composite material of the preform.

[0025] According to other characteristics of the process:

[0026] - during step i) the spar is kept at room temperature,

[0027] - during step i) a spar is used which is crossed by at least one internal cooling circuit in which a cooling fluid is circulated,

[0028] - step i) is carried out by circulating a flow of cooling air inside the internal cooling circuit of the spar,

[0029] - step i) is carried out by circulating a refrigerated heat transfer fluid inside the internal cooling circuit of the spar, - step b) is preceded by a step j) of preparation before bonding of the first part of the spar, by chemical attack of an external surface of this first part,

[0030] - the method comprises, prior to step d), a step k) during which at least one insulator is interposed between the second part of the spar and each of the two parts of the mold,

[0031] - that during step k) a surface of each contact between the second part of the spar and the mold is configured according to a minimum size strictly necessary to maintain the spar in position in the mold,

[0032] - the process includes a step I) of vacuuming the mold which begins after step d) and before step f).

[0033] The invention also relates to a turbomachine blade spar for implementing the method described above, said spar comprising a first part configured to be inserted into a cavity of a preform and a second part configured to remain outside the preform and to form a root of the blade, characterized in that it is crossed by an internal cooling circuit comprising at least a first duct passing through the first part and at least a second duct passing through the second part.

[0034] According to other characteristics of the spar:

[0035] - said at least one second conduit is arranged near a median axis of the second part,

[0036] - said at least one second conduit is machined,

[0037] - said at least one first conduit is molded or produced by additive manufacturing with the spar.

[0038] The invention finally relates to a molding installation for implementing a method of the type described above, characterized in that it comprises at least: - a blade preform made of composite material and a metal spar,

[0039] - glue,

[0040] - a two-part mold capable of receiving the preform and the spar,

[0041] - a means of heating the mold,

[0042] - a means of injecting a resin,

[0043] - a means of cooling the spar.

[0044] According to another feature of the casting installation, it also includes:

[0045] - at least one insulator,

[0046] - a means of vacuuming the mold,

[0047] - a means of urging the two parts of the mold towards each other.

[0048] Brief description of the figures

[0049] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

[0050] [Fig. 1] Figure 1 is a schematic axial sectional view of an example of a turbomachine to which the invention applies;

[0051] [Fig. 2] Figure 2 is a side view of a turbomachine blade according to the invention;

[0052] [Fig. 3] Figure 3 is a detail view of the foot of the blade of Figure 2;

[0053] [Fig. 4] Figure 4 is a perspective view cut through a transverse plane of the blade of Figure 2;

[0054] [Fig. 5] Figure 5 is a schematic view of a molding installation for implementing a conventional process;

[0055] [Fig. 6] Figure 6 is a schematic view of a molding installation for implementing the method of the invention; [Fig. 7] Figure 7 is a sectional view of a blade spar for implementing the method of the invention;

[0056] [Fig. 8] Figure 8 is a block diagram of a conventional turbomachine blade manufacturing process;

[0057] [Fig. 9] Figure 9 is a block diagram of a method of manufacturing a turbomachine blade according to the invention.

[0058] Detailed description of the invention

[0059] The invention which will now be described here applies to the manufacture of any type of parts which can be made from composite materials and in particular, in the context of turbomachine blades, to any type of blade, an example of which is described with reference to figure 1 without limitation of the invention.

[0060] The partial axial sectional view of Figure 1 shows a turbomachine 10 with a longitudinal axis X which comprises various components which can be made of composite materials, such as blades.

[0061] The turbomachine 10 of Figure 1 is, in a non-limiting manner of the invention, a turbomachine 10 with a double body and a pair of counter-rotating propellers 12, 14 of the “open rotor” type intended to be mounted on an aircraft. The invention applies here for example to the blades of these propellers but it could just as well be applied to other types of blades, such as for example outlet guide vanes OGV (acronym for Outlet Guide Vanes) used in a secondary flow channel of a shrouded double-flow turbomachine, without fundamentally changing the nature of the invention.

[0062] The turbomachine 10 shown here mainly comprises, along a central longitudinal axis X and the air flow F circulating in the turbomachine turboshaft engine from upstream to downstream, a gas generator assembly 16, a propulsion assembly 18 comprising the pair of counter-rotating propellers 12, 14 constituting the unducted fan ("open rotor") and, between the gas generator 16 and the propulsion assembly 18, a transmission assembly 20 of the power delivered by the gas generator 16 in the direction of the propellers 12, 14, at the output of which are driven, respectively, in rotation opposite to each other, two concentric external output shafts 46 and internal 48 secured to respective rotating casings 50, 52 of the upstream 12 and downstream 14 propellers of the propulsion assembly 18.

[0063] For each propeller 12, 14, a respective device 54, 56 is provided for changing the pitch of the blades 58, 60 of each propeller to independently vary the pitch of the latter according to the different operating phases of the turboshaft engine, in order to optimize the aerodynamic performance thereof.

[0064] As illustrated in Figure 2, the propellers 12, 14 each comprise blades 58, 60 each with a blade 62, 64 oriented substantially along a radial axis Z and a root 66, 68 which is rotatably mounted in a pivot (not shown) of axis Z of the associated casing 50, 52. This root 66, 68 is moved by the respective device 54, 56 for changing the pitch of the blades 58, 60 of each propeller.

[0065] In this embodiment, the blades 58, 60 of the propellers 12, 14 are made of a composite material with a fibrous blade preform embedded in a resin.

[0066] As can be seen in Figure 4 which more specifically represents a blade 58, each blade 58 comprises an aerodynamic blade 62 which extends along an axis which is parallel here to the radial axis Z. The blade 62 comprises a lower surface 70 and an upper surface 72 which are opposite along a transverse axis Y (perpendicular to the longitudinal axis X) and which are connected upstream by a leading edge 74 and downstream by a trailing edge 76.

[0067] The blade 62 comprises a casing 78 made of composite material made from a preform of the blade 62 stiffened by injection of a matrix into said preform of the blade 62. The external walls of the casing 78 form the intrados surface 70 and the extrados surface 72. The casing 78 comprises a central cavity 80 receiving a spar 82, preferably metallic. Optionally, the cavity 80 can also receive a foam core 84, interposed between the spar 82 and the casing 78, as shown here in FIG. 4, but this configuration is not limiting of the invention, the spar 82 being able to occupy the entire cavity 80 of the casing, the blade 62 then being devoid of foam.

[0068] The spar 82 comprises a first part 86 which occupies the cavity 80 of the casing 78 and a second part arranged outside the casing 78 which forms the root 66 of the blade 58.

[0069] The composite material of the preform is obtained from a three-dimensional (or 3D weaving) or two-dimensional (2D weaving) weaving of threads. In the present invention, we understand by the expression "three-dimensional weaving" or "3D weaving" a weaving method in which warp threads are linked to weft threads on several layers. Preferably, the weaving of the composite material of the preform is three-dimensional because it offers better resistance to delamination. Preferably, but not limited to, the 3D weaving has an interlock structure (or reinforcement). The interlock weaving has improved impact resistance, in particular compared to a 2D weaving. Similarly, the preform is woven in a single piece.

[0070] The weaving of the preform is carried out by means of a weaving installation (not shown) comprising a loom which is configured for three-dimensional and / or two-dimensional weaving. The composite material comprises a plurality of warp threads and a plurality of weft threads which are respectively oriented in directions which are perpendicular (in the plane or even in the thickness for 3D weaving). The weaving is advantageously carried out flat in a general longitudinal direction.

[0071] The yarns or strands used to make the weaving include, for example, carbon, glass, ceramic, silica, silicon carbide, Kevlar, polyamide, alumina fibers or a mixture of these fibers.

[0072] As illustrated in Figures 5 and 8, to obtain such a turbomachine blade 58, a method for manufacturing an aircraft turbomachine blade 58 comprising a blade 62 made of composite material and a metal root 66, comprises at least the following steps:

[0073] - a step a) of providing a blade preform 88 by weaving fibers, and of providing a metal spar 82 which comprises a first part 86 configured to be inserted into a cavity 80 of said preform and a second part configured to remain outside the preform and to form the root 66 of the blade 58,

[0074] - a step b) of applying glue to the first 86 part of the spar 58,

[0075] - a step c) of introducing the first part 86 of the spar 82 covered with glue into the cavity 80 of the preform 88,

[0076] - a step d) of depositing the spar 82 and the preform 88 in a mold 90 in two parts 90A, 90B and closing the mold 90,

[0077] - a step e) heating the mold 90 to a first predetermined temperature using a means 91 for heating the mold 90,

[0078] - a step f) of injecting a matrix such as a resin into the mold 90 using an injector cylinder 92 in order to impregnate the preform 88.

[0079] - a step g) of consolidation of the resin during which the mold 90 is maintained at a second cooking temperature, generally higher than the first temperature, for a determined duration to ensure crosslinking of the resin.

[0080] This configuration corresponds to the basic configuration of an RTM (Resin Transfer Molding) process. Preferably, the process is a VARTM (Vacuum Assisted Resin Transfer Molding) process which generally also comprises an additional step I) of vacuuming the mold 90 which begins after step d) and before step f) during which a vacuum pump 94 performs a vacuum in the mold 90 prior to injecting the matrix into it.

[0081] A problem arises due to the difference between the operating temperature of the glue used to glue the spar 82 and the first temperature at which the resin is injected. Indeed, the injection temperature of the resin to which the mold 90 is subjected is a determined temperature which is quite high (of the order of 160°C for an epoxy resin) and which tends to fluidify the glue with which the spar 82 has been previously coated before the consolidation of the matrix occurs. As a result, the glue tends to flow from the spar 82 and to penetrate the fibers of the composite material of the preform 88, thus weakening the assembly of the spar 82 with the preform 88.

[0082] However, as shown in Figure 3, a blade 58 is subjected in operation, at the junction of its blade 62 with the spar 82, to significant tensile stresses T and bending stresses F. Any weakening of the bonded connection between the spar 82 and the preform 88 must be prohibited.

[0083] The invention proposes to remedy this drawback by preventing such creep of the glue during heating of the mold 90.

[0084] For this purpose, as illustrated in Figures 6 and 9, the invention proposes a method comprising a step i) of cooling the spar 82.

[0085] More particularly, as illustrated in Figure 9, the method according to the invention comprises a step i) of cooling or maintaining the spar 82 at a third temperature which is lower than the first temperature. This step i) begins before step e) and ends after step f). Then follows the consolidation step g) during which the mold 90 is maintained at the second cooking temperature for a determined duration, for example 2 hours, to ensure crosslinking of the resin.

[0086] It will be understood that this step can begin at any time before step e). However, for practical reasons, as illustrated in Figure 9, this step i) preferably occurs after step d), i.e. after the introduction of the preform 88 and the spar 82 into the mold 90.

[0087] In practice, the temperature of the spar 82 must be well below the first injection temperature. For a determined injection temperature of the order of 160°C degrees, during step i) the spar 82 is maintained at a third temperature which corresponds to ambient temperature, i.e. at a temperature of substantially 20°C.

[0088] Several methods can be used to cool the spar. Preferably, as illustrated in Figure 6 relating to a molding installation 104 according to the invention and Figure 7 relating to a spar 82 according to the invention, a spar 82 is used which is crossed by at least one internal cooling circuit 96 in which a cooling fluid is circulated. As illustrated in Figure 7, the internal cooling circuit 96 comprises at least a first conduit 98 passing through the first part 86 and at least a second conduit 100 passing through the second part 66.

[0089] Preferably, the internal cooling circuit 96 forms a loop in the spar 82. The first duct 98 is molded with the spar 86 by a lost wax casting process or manufactured with the spar 82 by additive manufacturing and it runs through the volume of the first part 86 so as to maximize the heat exchange surfaces in the first part 86. The internal cooling circuit 96 comprises two second ducts 100, respectively inlet and outlet, arranged at the ends of the first duct 98. Preferably, the second ducts 100 are machined.

[0090] As seen previously, a blade 58 is subjected in operation, at the junction of its blade 62 with the spar 82, to extremely high tensile stresses T and bending stresses F. Also, preferably the second ducts will be arranged close to a median axis Z of the second part 66, so that they are placed in zones of minimal stress.

[0091] Any suitable cooling fluid can circulate in the internal cooling circuit 96. According to a first embodiment of the invention, step i) is carried out by circulating a flow of cooling air inside the internal cooling circuit 96. Alternatively, according to a second preferred embodiment, step i) is carried out by circulating a refrigerated heat transfer fluid inside the internal cooling circuit 96 of the spar.

[0092] As illustrated in Figure 6, this heat transfer fluid is supplied by a refrigeration system 102 connected to the conduits 100 by conduits 104.

[0093] It is desirable to ensure as much as possible maximum adhesion of the glue to the spar 82. Also, preferably step b) can be preceded by a step j) of preparation before gluing of the first part 86 of the spar 82 during which a chemical attack is carried out on an external surface of this first part 86.

[0094] To limit heating of the spar 82 as much as possible, the method further comprises, prior to step d), a step k) during which at least one insulator 106 is interposed between the second part 66 of the spar 82 and each of the two parts 90A, 90B of the mold 90. This makes it possible to avoid the transmission of heat from the mold to the foot 66, since the foot 66 ensures the maintenance of the spar 82 in the mold 90. Preferably, during this step k), a surface of each contact between the second part 66 of the spar 82 and the mold 90 is configured according to a minimum size strictly necessary to maintain the spar 82 in position in the mold 90.

[0095] It will therefore be understood that at a minimum the molding installation 104 making it possible to implement the method of the invention will comprise at least:

[0096] - a preform 88 of a blade made of composite material and a metal spar 82,

[0097] - glue,

[0098] - a mold 90 in two parts 90A, 90B capable of receiving the preform 88 and the spar 82,

[0099] - a means 91 for heating the mold 90,

[0100] - a means 92 for injecting a resin,

[0101] - a means of cooling the spar 82, namely here a refrigeration system.

[0102] This is the minimum configuration of the molding installation 104 in the context of an RTM process. However, preferably, the installation 104 may also comprise, as we have seen, at least one insulator 106.

[0103] The installation 104 may also include a means for urging the two parts 90A, 90B of the mold 90 against each other, making it possible to exert pressure on the preform as represented by the arrows in Figure 6. Finally, in the context of a VARTM process, the installation 104 may include a means for drawing a vacuum from the mold, such as the vacuum pump 94.

[0104] The invention therefore makes it possible to considerably improve the reliability of the bonding of a spar 82 in a preform 88.

Claims

CLAIMS 1. Method for manufacturing a blade (58) for an aircraft turbomachine, this blade comprising a blade (62) made of composite material and a metal root (66), said method comprising at least the steps of: - a) providing a blade preform (88) by weaving fibers, and providing a metal spar (82) which comprises a first part (86) configured to be inserted into a cavity (80) of said preform (88) and a second part configured to remain outside the preform (88) and to form the root (66) of the blade, - b) application of glue to the first part (86) of the spar (82); - c) introduction of the first part (86) of the spar (82) covered with glue into the cavity (80) of the preform (88), - d) depositing the spar (82) and the preform (88) in a mold (90) in two parts (90A, 90B) and closing the mold (90), - e) heating the mold (90) to a first predetermined temperature, - f) injecting a resin into the mold (90) in order to impregnate the preform (88), - g) consolidation of the resin, the mold (90) being maintained at a second cooking temperature for a determined duration to ensure crosslinking of the resin, characterized in that the method comprises a step i) of cooling or maintaining the spar (82) at a third temperature which is lower than said first temperature, this step i) starting before step e) and ending after step f).

2. Method according to the preceding claim, characterized in that during step i) the spar (82) is kept at room temperature.

3. Method according to one of the preceding claims, characterized in that during step i) a spar (82) is used which is crossed by at least one internal cooling circuit (96) in which a cooling fluid is circulated.

4. Method according to the preceding claim, characterized in that step i) is carried out by circulating a flow of cooling air inside the internal cooling circuit (96) of the spar (82).

5. Method according to claim 3, characterized in that step i) is carried out by circulating a refrigerated heat transfer fluid inside the internal cooling circuit (96) of the spar (82).

6. Method according to one of the preceding claims, characterized in that step b) is preceded by a step j) of preparation before bonding of the first part (86) of the spar (82), by chemical attack of an external surface of this first part (82).

7. Method according to one of the preceding claims, characterized in that it comprises, prior to step d), a step k) during which at least one insulator (106) is interposed between the second part (66) of the spar (82) and each of the two parts (90A, 90B) of the mold (90).

8. Method according to the preceding claim, characterized in that during step k) a surface of each contact between the second part (66) of the spar (82) and the mold is configured according to a minimum size strictly necessary to maintain the spar (82) in position in the mold (90).

9. Method according to one of the preceding claims, characterized in that it comprises a step I) of vacuuming the mold (90), which begins after step d) and before step f).

10. Turbomachine blade spar (82) for implementing a method according to one of claims 1 to 9, said spar (82) comprising a first part (86) configured to be inserted into a cavity (80) of a preform (88) and a second part configured to remain outside the preform (88) and to form a root (66) of the blade (58), characterized in that it is crossed by an internal cooling circuit (96) comprising at least a first duct (98) passing through the first part (86) and at least a second duct (100) passing through the second part (66).

11. Blade spar (82) according to the preceding claim, characterized in that said at least one second duct (100) is arranged close to a median axis (Z) of the second part (66).

12. Blade spar (82) according to the preceding claim, characterized in that said at least one second duct (100) is machined.

13. Blade spar according to one of claims 10 to 12, characterized in that said at least one first duct (98) is molded or produced by additive manufacturing with the spar.

14. Molding installation (104) for implementing a method according to one of claims 1 to 9, characterized in that it comprises at least: - a blade preform (88) made of composite material and a spar (82) according to one of claims 10 to 13 which is metallic, - glue, - a mold (90) in two parts (90A, 90B) capable of receiving the preform (88) and the spar (82), - a means (91) for heating the mold (100), - a means (92) for injecting a resin, and - a means (102) for cooling the spar.

15. Molding installation (104) according to the preceding claim, characterized in that it further comprises: - at least one insulator (106), and / or - a means (94) for vacuuming the mold (90), and / or - a means of urging the two parts (90A, 90B) of the mold against each other.

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