Composite blade for an aircraft engine and method for manufacturing and repairing the same

Description

Domaine technique de l'invention

[0001] The present invention relates to a composite material blade for an aircraft turbomachine, as well as methods of manufacturing and repairing this blade. Arrière-plan technique

[0002] The state of the art includes in particular documents FR-A1-2 956 057, FR-A1-3 029 134, FR-A1-3 051 386, US-A1-2011 / 194941 and US-A1-2007 / 092379, corresponding to the preamble of claim 1.

[0003] The use of composite materials is advantageous in the aeronautics industry in particular because these materials have interesting mechanical performances for relatively low masses.

[0004] A method of manufacturing a composite part for the aeronautical industry, which is well known to those skilled in the art, is the RTM molding method, the initials of which refer to the Anglo-Saxon acronym for Resin Transfer Molding.

[0005] This is a process for producing a part from a composite material based on resin-impregnated fibers. Such a process is used, for example, to manufacture a fan blade and involves several successive stages.

[0006] The first step is to weave the fibers to obtain a three-dimensional preform blank, then cut the blank to obtain a preform that substantially resembles the shape of the blade to be obtained. This preform is then placed in an injection mold, which is closed. Then, liquid resin is injected, maintaining pressure on the injected resin while the part is polymerized by heating.

[0007] The resins used are very fluid resins that are able to penetrate the fibers of the preform well, even when injected under reduced pressure. During polymerization, under the effect of heat, the injected resin successively passes from the liquid state to the gel state and finally to the solid state.

[0008] To manufacture a blade, for example a turbomachine fan blade, a preform is made by weaving and then impregnated with resin to form a blade. This blade has a lower surface and an upper surface that extend from a leading edge to a trailing edge of the blade.

[0009] The composite material of the blade is relatively fragile, and in particular sensitive to shocks, and it is known to protect it by means of a metal shield which is added and fixed on the leading edge of the blade.

[0010] The shield can be attached to the blade in two ways. One way is to glue the shield to the blade, after the resin has cured. The glue then comes in the form of a paste.

[0011] Another way is to fix the shield by co-molding with the fiber preform. The preform is placed in the mold and the shield is positioned on the edge of the preform intended to form the leading edge of the blade. The injected resin impregnates the preform and comes into contact with the shield to ensure its attachment to the blade after polymerization and hardening.

[0012] The present invention relates to an improvement to this second technology in which the shield and the preform undergo co-molding. Document US-A1-2007 / 0092379 has already proposed spreading an adhesive in the form of a paste between the shield and the preform, before injecting resin into the preform, so as to form a layer or film of adhesive between these elements. However, this operation is delicate and has several drawbacks: it is difficult to ensure that the adhesive is well spread over the entire surface to be bonded, and it is not possible to guarantee a constant thickness of adhesive on this surface. In conclusion, this solution is not optimal and is not industrializable because manufacturing can be difficult to achieve with a good level of repeatability.

[0013] The invention provides a simple, effective and economical solution to ensure correct positioning and optimal mechanical strength of the shield on the blade. Résumé de l'invention

[0014] The invention proposes a method for manufacturing a blade made of composite material for a turbomachine, in particular an aircraft, this blade comprising a blade comprising a lower surface and an upper surface which extend from a leading edge to a trailing edge of the blade, the blade further comprising a metal shield extending along the leading edge of the blade, the method comprising the steps consisting of: a) placing a preform made by weaving fibers in three dimensions in a mold, the shield being positioned on an edge of the preform intended to form the leading edge of the blade, b) injecting polymerizable resin into the mold so that it impregnates the preform so as to form the blade after solidification, characterized in that at least one double-sided adhesive film, coated or soaked on both sides with an adhesive so as to be sticky on both sides, is inserted between the shield and the edge of the preform during step a).

[0015] The invention thus proposes to ensure the attachment of the shield to the blade by co-molding and by a double-sided adhesive film, that is to say by a strip or tape of adhesive material. The adhesive film is interposed between the shield and the edge of the preform and is intended to improve and maintain the position of the shield on the edge of the preform, and also to improve the hold and resistance to tearing of the shield with respect to the blade. It is therefore understood that, during the injection of resin into the blade manufacturing mold, this resin will impregnate the preform and will also come into contact with the film or even the shield, thus ensuring optimal attachment of the shield to the blade.

[0016] The method according to the invention may comprise one or more of the following characteristics, taken in isolation from one another or in combination with one another: said adhesive film is cut according to the shape of the edge and / or the shield during step a); the adhesive film is glued to the edge of the preform prior to positioning the shield on this edge; the shield has a dihedral shape and defines a V-shaped groove, said at least one adhesive film being glued to the shield inside the groove; a first adhesive film is glued in the groove, on a first longitudinal wall of the shield, and a second adhesive film is glued in the groove, on a second longitudinal wall of the shield; prior to positioning the shield on the edge of the preform, this edge is compressed; the edge of the preform is compressed until it reaches a thickness representing 75% to 95% of a maximum width or transverse dimension of the groove at the end of step b); the preform is moistened before compressing its edge;at least one interface fabric is interposed between the preform and the adhesive film, and extends along said edge of the preform; the fabric is particularly advantageous in particular during a blade repair, as will be discussed in the following; a single interface fabric is folded and inserted inside the groove; the adhesive film, or even the interface fabric, is / are heated to promote adhesion; the adhesive film protrudes from the shield and extends over surfaces of the preform not covered by the shield.

[0017] This document also relates to a blade made of composite material for a turbomachine, in particular for an aircraft, this blade comprising a blade comprising a lower surface and an upper surface which extend from a leading edge to a trailing edge of the blade, the blade further comprising a metal shield extending along the leading edge of the blade, this blade being manufactured by a method as described above and comprising at least one adhesive film between the shield and the leading edge of the blade, or even also at least one interface fabric inserted between the blade and the adhesive film.

[0018] Finally, this document relates to a method for repairing a blade as described above when it is equipped with said interface fabric, the shield of this blade being damaged and having to be replaced, the method comprising the steps of: remove the shield and the adhesive film, the interface fabric being intended to remain on the leading edge of the blade, and stick a new shield on this interface fabric. Brève description des figures

[0019] 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: [ Fig.1 ] there figure 1 is a schematic perspective view of a composite aircraft turbomachine blade, [ Fig.2 ] there figure 2 is a block diagram showing steps of a method according to the invention for manufacturing a blade such as that shown in figure 1 , [ Fig.3 ] there figure 3 is a schematic perspective view of two adhesive films used in a manufacturing method according to the invention, [ Fig.4 ] there figure 4 is a schematic perspective view of a shield on which the two films of the figure 3 , [ Fig.5 ] there figure 5 is a schematic perspective view of an interface fabric handled by an operator during a manufacturing process according to the invention, [ Fig.6 ] there figure 6 is a schematic perspective view of a shield on which the interface fabric of the figure 5 , [ Fig.7 ] there figure 7 is a schematic perspective view of a preform with one edge undergoing compression, [ Fig.8 ] there figure 8 is a schematic perspective view of the preform of the figure 7 on one edge of which is positioned the shield of the figure 6 , [ Fig.9 ] there figure 9 is a schematic perspective view of a mold in which the preform and the shield are intended to be arranged, and into which the resin is intended to be injected, and [ Fig.10 ] there figure 10 is a schematic perspective view of a preform on one edge of which an adhesive film is glued, and illustrates an alternative embodiment of the invention. Description détaillée de l'invention

[0020] We first refer to the figure 1 which illustrates a blade 10 made of composite material for a turbomachine, this blade 10 being for example a fan blade.

[0021] The blade 10 comprises a blade 12 connected by a stilt 14 to a foot 16 which has for example a dovetail shape and is shaped to be engaged in a cell of complementary shape of a rotor disk, in order to retain the blade on this disk.

[0022] The blade 12 comprises a leading edge 12a and a trailing edge 12b for the gases flowing into the turbomachine. The blade 12 has a curved or even twisted aerodynamic profile and comprises a lower surface 18 and an upper surface 20 extending between the leading edges 12a and trailing edges 12b.

[0023] The blade 12 is made from a fiber preform obtained by three-dimensional weaving of fibers, for example carbon.

[0024] The leading edge 12a of the blade is reinforced and protected by a metal shield 22 which is fixed on this leading edge 12a. The shield 22 is for example made of a nickel and cobalt-based alloy.

[0025] In the present invention, this fixing is carried out on the one hand by co-molding the preform with the shield 22, and on the other hand by gluing the shield 22 by means of at least one adhesive film 24.

[0026] There figure 2 is a flowchart that illustrates steps in a method of manufacturing a composite blade 10 such as that shown in FIG. figure 1 .

[0027] The method may comprise several steps, some of which are optional. The first step a) of the method comprises several sub-steps or operations. During a first operation a1) mentioned above, a fiber preform 26 is produced by weaving fibers, this preform being notably visible at the figure 8 The preform 26 obtained is raw and can undergo operations such as cutting for example. The ends of the fibers of the preform 26 tend to protrude on the outer surface of the preform, which can cause the preform to thicken in relation to the desired final dimensions of the blade.

[0028] In another operation a2) of the process, illustrated in figure 3 , one or more adhesive films 24 are prepared. This adhesive film 24 is intended to be inserted between the shield 22 and the preform 26, before injecting the resin into the blade manufacturing mold.

[0029] This adhesive film 24 is a double-sided film, that is to say a film sticky on both sides. This film is thus coated or soaked on both sides with an adhesive, for example those marketed by the company 3M under the reference AF191K ®< or those marketed by the company Solvay under the reference FM309-1 ®<.

[0030] This adhesive film 24 has for example a thickness of between 0.1 mm and 0.2 mm. This film 24 can be in the form of a strip. It can thus have an elongated shape whose dimensions are a function of those of the shield 22. The shield 22, as shown in figure 4 , has a dihedral shape and defines a V-section groove 22a.

[0031] The adhesive film 24 is preferably glued to the shield 22, inside the groove 22a. As can be seen in the figure 3 , the simplest and most effective is to cut out two adhesive films 24 and stick them respectively on a first longitudinal wall 22b of the shield, and on a second longitudinal wall 22c of the shield, inside the groove 22a.

[0032] We then obtain the assembly of the figure 4 .

[0033] A following operation a3), which is however optional but preferred, consists of inserting an interface fabric 28 between the adhesive film(s) 24 and the preform 26, always before injecting the resin into this preform 26.

[0034] The interface fabric 28 is preferably pre-cut to the correct dimensions, as illustrated in figure 5 . Contrary to what is mentioned above concerning the film 24, a single fabric 28 can be cut. It is understood that this fabric 28 must be folded in two and inserted into the groove 22a, over the adhesive films 24, so that a lateral part of the fabric extends over the adhesive film deposited on the first longitudinal wall 22b of the shield 22, and that the other lateral part of the fabric 28 extends over the adhesive film 24 deposited on the second longitudinal wall 22c of the shield, inside the groove 22a.

[0035] We then obtain the assembly of the figure 6 .

[0036] There figure 7 illustrates an advantageous operation of the manufacturing method, which consists of compressing the edge 26a of the preform 26 on which the shield 22 is intended to be fixed (operation a4)).

[0037] This compression can be done by means of a press for example. The edge 26a of the preform 26 is preferably compressed until it reaches a thickness representing 75% to 95% of a maximum width or transverse dimension of the groove 22a of the shield 22 at the end of the process. Before compression of the preform, its thickness can be approximately 120% relative to the final thickness of the blade due to the expansion mentioned above.

[0038] There figure 8 illustrates a following operation (a5)) of the method during which the shield 22, equipped here with the adhesive films 24, and possibly with the interface fabric 28, is positioned on the edge 26a, possibly compressed, of the preform 26.

[0039] The shield of the figure 8 is then positioned in a mold 30 which is closed ( figure 9 ) for example with a counter-mold. The closing of the mold 30 must make it possible to apply sufficient pressure to the shield 22 in order to prevent resin from covering the shield during injection. This pressure can cause a deformation of the shield, in particular a reduction in the width of the groove 22a, which will thus adopt a value corresponding to the desired cumulative thickness of the blade, the film(s) and the interface fabric.

[0040] Successive operations a1) to a5), some of which are optional, represent a first step a) of the manufacturing process.

[0041] During a second step b) of the method, resin is injected into the mold 30 and is intended to impregnate the preform 26 and to come into contact with the interface fabric 28 when it is present, or otherwise with the adhesive film and the shield. After polymerization and hardening of the resin, the shield 22 is secured to the blade by means of the adhesive films 24 and the resin.

[0042] The blade 10 thus obtained, after polymerization of the resin, is advantageous insofar as its shield 22 is perfectly positioned and held on the blade 12.

[0043] There figure 10illustrates an alternative embodiment of the manufacturing method according to the invention, in which the adhesive film 24 is glued to the preform 26 and not to the shield 22. It is then understood that the shield 22 is then positioned and mounted on the edge 26a of the preform 26, on which the adhesive film 24 is glued. The injection and polymerization of the resin in the preform located in the mold 30 can then take place.

[0044] Prior to this step, an interface fabric 28 can be positioned on the preform 26. The adhesive film 24 is then glued to the interface fabric 28, before positioning the shield 22 on the edge 26a of the preform 26 and on the adhesive film 24.

[0045] This document also relates to a composite blade 10 obtained by the aforementioned method, as well as a method for repairing this type of blade. When the shield 22 is damaged and must be replaced, the method comprises the steps of: removing the shield 22 and the adhesive film 24, the interface fabric 28 being intended to remain on the leading edge of the blade when this fabric is present, and sticking a new shield, in particular on the interface fabric when it is present.

Claims

1. A method for manufacturing a blade (10) of composite material for a turbomachine, in particular for an aircraft, this blade comprising a vane (12) comprising a pressure side (14) and a suction side (16) which extend from a leading edge (12a) to a trailing edge (12b) of the vane, the blade further comprising a metal sheath (22) extending along the leading edge of the vane, the method comprising the steps consisting in: a) placing a preform (26) made by weaving fibres in three dimensions in a mould, the sheath being positioned on an edge of the preform intended to form the leading edge of the vane, b) injecting polymerizable resin into the mould to impregnate the preform so as to form the vane after solidification, characterised in that at least one double-sided adhesive film (24), coated or soaked on its both faces with a glue so as to be adhesive on its both faces, is interposed between the sheath and the edge of the preform during the step a).

2. The method according to claim 1, wherein said adhesive film (24) is cut according to the shape of the edge (26a) and / or the sheath (22) during the step a).

3. The method according to claim 1 or 2, wherein the adhesive film (24) is glued on the edge (26a) of the preform (26) prior to the positioning of the sheath (22) on that edge.

4. The method of claim 1 or 2, wherein the sheath (22) is dihedral in shape and defines a groove (22a) with a V-shaped cross-section, said at least one adhesive film (24) being glued on the sheath within the groove.

5. The method according to the preceding claim, wherein a first adhesive film (24) is glued in the groove (22a) on a first longitudinal wall (22b) of the sheath and a second adhesive film is glued in the groove on a second longitudinal wall (22c) of the sheath.

6. The method according to one of the preceding claims, wherein, prior to the positioning of the sheath (22) on the edge (26a) of the preform (26), this edge is compressed.

7. The method according to the preceding claim, in dependence on claim 4 or 5, wherein the edge (26a) of the preform (26) is compressed until it reaches a thickness representing 75% to 95% of a maximum transverse width or dimension of the groove (22a).

8. The method of claim 6 or 7, wherein the preform (26) is moistened prior to compressing its edge (26a).

9. The method according to any of the preceding claims, wherein at least one interface fabric (28) is interposed between the preform (26) and the adhesive film (24), and extends along said edge (26a) of the preform.

10. The method according to the preceding claim, in dependence on claim 4 or 5, wherein a single interface fabric (28) is folded and inserted within the groove (22a).

11. The method of claim 9 or 10, wherein the adhesive film (24) or even the interface fabric (28) is / are heated to promote the adhesion.

12. The method of any of the preceding claims, wherein the adhesive film (24) protrudes from the sheath (22) and extends onto surfaces of the preform (26) not covered by the sheath.