Method for manufacturing a blade from composite material comprising a serration element

Abstract

The invention relates to a method for manufacturing a blade (7) from composite material for a turbine engine, comprising the following steps: (a) weaving fibres to produce a fibrous preform intended to form part of the airfoil of the blade; (b) shaping and stiffening the fibrous preform in a preforming tool; (c) inserting the fibrous preform into a mould; (d) densifying the fibrous preform with a resin in order to form the blade, wherein, - before and / or after step (c), the method further comprises a step (i) of inserting plies of fibres into the mould such that at least a portion of an edge of the fibrous preform is covered, these plies of fibres having a corrugated or toothed edge; - during step (d), the plies of fibres are also densified by the resin to form the serration element.

Description

[0001] DESCRIPTION

[0002] TITLE: METHOD FOR MANUFACTURING A BLADE MADE OF COMPOSITE MATERIAL COMPRISING A SERRATION ELEMENT

[0003] Technical field

[0004] The invention relates to the field of turbomachines, in particular aircraft turbomachines, and in particular to the propulsion propellers of these turbomachines which comprise blades. More particularly, the invention relates to a method of manufacturing a blade made of composite material for such turbomachines, and more precisely to improving the noise reduction of these blades in operation.

[0005] Technical background

[0006] The state of the art includes in particular document FR-A1-3111660.

[0007] An aircraft turbomachine typically comprises a gas generator that drives at least one propeller. The gas generator comprises at least one compressor, a combustion chamber, and at least one turbine. The rotor or one of the rotors of the gas generator is connected to the rotor of the propeller to drive it in rotation.

[0008] A propeller can be shrouded. This is the case for a fan in a turbomachine such as a turbojet or turbofan, for example.

[0009] A propeller can be unducted. This is the case for a turboprop or an "open-rotor" type architecture, for example.

[0010] A propeller comprises an annular row of blades rotating around a longitudinal axis of the turbomachine. Each blade comprises a blade having a lower surface and an upper surface connected to each other by a leading edge and a trailing edge. It is known to produce turbomachine blades, such as blades of a fan or a turbomachine rectifier, from a composite material to reduce the mass while having good mechanical properties. For example, composite material blades are produced by injecting a resin, for example by injection molding of a liquid resin (RTM, acronym for the English expression "Resin Transfer Molding") into a fiber preform.The search for minimizing polluting emissions linked to air transport involves, in particular, improving all the efficiencies of propulsion systems (or, in other words, turbomachines), and more particularly the propulsive efficiency which characterizes the efficiency with which the energy communicated to the air passing through the engine is converted into useful thrust.

[0011] The elements influencing this propulsive efficiency in the first order are those linked to the low pressure parts of the turbomachine, such as a low pressure turbine, a low pressure transmission system, the propeller and a secondary flow guiding the flow of this propeller. These low pressure parts make an immediate contribution to the generation of thrust. The known guiding principle for improving the propulsive efficiency is to reduce the compression ratio of the propeller, thereby reducing the flow velocity at the turbomachine outlet and the kinetic energy losses linked to it.

[0012] One of the main consequences of this reduction in flow velocity at the outlet of the turbomachine is that it is necessary to process a higher mass flow of air in the low pressure part (in particular the secondary flow) in order to ensure a given thrust level, which is set by the characteristics of the aircraft. This therefore leads to an increase in the bypass ratio of the turbomachine. The bypass ratio or BPR (English acronym for "ByPass Ratio") is defined as the ratio between the mass flow passing in the secondary flow (or otherwise called cold flow) around the gas generator, and the mass flow passing in the primary flow (or otherwise called hot flow) in the gas generator and supplying in particular the combustion chamber.This increase in secondary flow has the direct effect of requiring an increase in the diameter of the propeller, and consequently the external dimensions of the retention casing surrounding it in the case of the ducted propeller, as well as the nacelle constituting the aerodynamic envelope of this retention casing. To target high dilution rates, the retention casing is removed to move to configurations with unducted propellers since this retention casing was becoming too large, too heavy and generated significant capture drag.

[0013] In the case of a ducted propeller, the nacelle surrounding the propeller includes an internal acoustic treatment which reduces noise emissions outside the turbomachine.

[0014] In the case of an unducted propeller, other solutions must be found to reduce propulsive noise. To address the noise emission problem, a noise reduction technology already known on fans and inspired in particular by the wings of nocturnal raptors consists of arranging serration elements (or otherwise known as serrations) on the trailing edges of the blades (such as the so-called fan rotor blades) or on the leading edges of the blades (such as the so-called stator blades of a turbomachine rectifier). Serrations are aero-acoustic elements. They are characterized by a geometry in the form of more or less numerous teeth, more or less large and evolving along the trailing edge or the leading edge. Serrations can cause variations in the blade chord depending on the radial height, with variable thicknesses and a very thin trailing or leading edge.

[0015] The principle of reducing noise emissions generated by blades is based on spatially shifting the noise sources distributed along the leading edge or the trailing edge by means of serrations (or otherwise known as undulations or teeth), which may or may not be identical. For this principle to apply, the dimensions (height, length, thickness, etc.) of the serrations must be adapted to the incident aerodynamic field (such as the airflow passing through the blades with more or less turbulence) which varies according to the engine speed of the turbomachine.

[0016] Furthermore, the clamping element must be both easily repairable (since it is visible to passengers) and resistant to HCF (High-Cycle Fatigue) type damage which can generate cracks in the clamping element (and consequently in the blade) during operation. In addition, several other constraints must be taken into account for the production of composite material blades comprising such a clamping element, such as:

[0017] - the clamping element has a complex geometry, in particular with teeth having variations in dimensions (such as its thickness, length, shape, spacing between the teeth, cambers forming angles 02, etc.) which can alter and form a misalignment with the composite material (in particular the woven fibers) during shaping in an RTM injection mold,

[0018] - the placement of the clamping element on the leading edge or the trailing edge can be complex, particularly for complex geometries (dimensions and shape) of the aerodynamic profile blades,

[0019] - the teeth of the clamping element have low thicknesses (around 2.5 mm minimum) which can be damaged during handling, and

[0020] - produce the clamping element with a reasonable mass so as not to weigh down the propeller and with good mechanical properties to resist impact from external objects (such as birds, hailstones or lightning). In addition to the aforementioned technical constraints, the manufacture of the blade in composite material including the clamping element can be long, complex and expensive.

[0021] In this context, it is interesting to propose a solution to overcome at least one of the aforementioned drawbacks, in particular by optimizing and making robust the integration of a clamping element in a composite material blade.

[0022] Summary of the invention

[0023] The present invention provides a simple, effective and economical solution to the aforementioned drawbacks of the prior art.

[0024] To this end, the invention relates to a method for manufacturing a blade made of composite material for a turbomachine, in particular an aircraft, said blade comprising a blade having a leading edge, a trailing edge, a lower surface and an upper surface extending between the leading edge and the trailing edge, the blade further comprising at least one serration element on the leading edge and / or the trailing edge, the method comprising the following steps:

[0025] (a) production of a fiber preform by weaving fibers, this fiber preform being intended to form part of the blade,

[0026] (b) shaping and stiffening the fiber preform in a preforming tool,

[0027] (c) placing the fiber preform in a mold, and

[0028] (d) densification of the fiber preform with a resin to form the blade.

[0029] According to the invention:

[0030] - before and / or after step (c), the method further comprises a step (i) of introducing sheets of fibers into the mold so as to cover at least part of an edge of the fiber preform, these sheets of fibers having a wavy or toothed edge,

[0031] - during step (d), the fiber sheets are also densified by the resin to form said at least one serration element.

[0032] The manufacturing method according to the invention makes it possible to facilitate and make more robust the integration of the clamping element within the blade. To this end, the invention proposes to form the clamping element and the blade in a single piece (or in other words in a single piece and in a single piece) from a composite material. The fiber sheets intended to form the clamping element are thus directly attached to at least part of an edge of the fiber preform before the densification step. This single-piece connection is simple to implement (in particular in an automated manner), solid and difficult to damage during operation. In particular, the direct integration of the clamping element on the fiber preform makes it possible to form a more robust blade, in particular with regard to the technical constraints mentioned in the technical background and with good cohesion of the fibers throughout the fiber preform.This significantly improves the mechanical strength of this blade in operation, for example in the turbomachine.

[0033] Furthermore, the method according to the invention has the following advantages:

[0034] - lighten or maintain a reasonable mass of the blade by making the clamping element and the blade from a single composite material;

[0035] - facilitate the production of the complex geometry of the clamping element, in particular by directly producing the teeth and angles 02 in the mold during the densification stage;

[0036] - maintain a geometry of a reported subset of the fiber sheets on the edge of the fiber preform, so as to limit the transmission of stresses from the fiber preform to the hollow portions of the clamping element;

[0037] - facilitate the repair and / or replacement of the fiber layers of the clamping element;

[0038] - minimize the loss of fibers and / or resin, for example when cutting the fiber preform, particularly compared to a solution involving direct machining of the clamping element on the leading edge or the trailing edge;

[0039] - automate all or at least part of the steps of the process; and

[0040] - a significant saving in cost and manufacturing time of the blade.

[0041] The invention therefore has the advantage of being based on a design that is simple to produce, offering very high reliability, and is not very penalizing in terms of cost, mass and size. In this way, the blade obtained according to the method of the invention helps to limit environmental impacts, in particular by reducing the mass.

[0042] The term "serration element" means a part comprising teeth projecting from at least part of this part. These teeth may have a U and / or V shape in axial section. These teeth may be more or less numerous, more or less large and move along this serration element. The serration element may also be designated by a tooth or undulation element. The manufacturing 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:

[0043] - in which:

[0044] - before step (c), first layers of fibers are positioned directly in the mold, and

[0045] - after step (c), second fiber sheets are positioned directly on the edge of the fiber preform or even on the first fiber sheets, so that the edge of the preform is interposed between the first and second fiber sheets;

[0046] - third layers of fibers are interposed between the first and second layers and located next to the edge, without covering it;

[0047] - before or during step (i), the method also comprises a step (ii) of adding a layer of glue between the fiber sheets and the edge of the fiber preform, the layer of glue being for example epoxy-based;

[0048] - the method further comprises, before step (b), a step (iii) of cutting the fiber preform to form a recess in the fiber preform;

[0049] - the mold comprises at least one cavity, part of which has a shape complementary to the wavy or toothed edge of the fiber sheets;

[0050] - before step (d), the method comprises at least one step of compacting the fiber preform and the fiber sheets;

[0051] - the fiber sheets are made by weaving fibers or superimposing several layers of fibers;

[0052] - the fiber preform and the fiber sheets are previously impregnated with a resin before step (d);

[0053] - the resin is thermosetting or thermoplastic, for example epoxy-based;

[0054] -- step (d) is carried out by heating to a temperature between 150°C and 200°C, preferably around 180°C; -- the fiber preform is formed from unidirectional (1 D), two-dimensional (2D) or three-dimensional (3D) woven fibers;

[0055] -- the fiber preform comprises carbon fibers, glass fibers, aramid fibers, ceramic fibers (such as silicon carbide) or a mixture of at least two of these fibers;

[0056] -- the fiber webs comprise carbon fibers, glass fibers, aramid fibers, ceramic fibers (such as silicon carbide) or a mixture of at least two of these fibers;

[0057] - the fiber sheets have an elongated shape along said edge of the fiber preform;

[0058] - the fiber sheets extend over at least 70% of the length of said edge of the fiber preform;

[0059] -- the fiber sheets extend at most over 90% of the length of said edge of the fiber preform;

[0060] - at least some of the fiber sheets have a first surface which directly covers said edge of the fiber preform and / or which is separated from this edge of the fiber preform by other fiber sheets, and a second surface which directly covers the other fiber sheets or which is covered by these other fiber sheets, the first surface having an extent greater than that of the second surface;

[0061] -- at least some of the fiber sheets are only covered by fiber sheets or intercalated between two fiber sheets;

[0062] -- at least some of the fiber sheets do not cover the edge of the fiber preform;

[0063] -- the fiber sheets are pre-impregnated, for example, with a resin;

[0064] -- the fiber sheets are dry (or otherwise said non-pre-impregnated, that is to say that these sheets are not previously impregnated with resin);

[0065] -- the fiber preform is dry (or otherwise said not pre-impregnated);

[0066] -- the fiber sheets introduced into the mold comprise first fiber sheets and second fiber sheets, and possibly third fiber sheets

[0067] -- the wavy or toothed edge is intended to form the clamping element; -- said edge of the fiber sheets is wavy and / or toothed;

[0068] -- said edge of the fiber sheets comprises undulations or teeth (or in other words projecting portions);

[0069] -- the said undulations or teeth have shapes that are identical to each other or different from each other;

[0070] -- said undulations or teeth each have a general polygonal shape (such as triangular, rectangular, etc.);

[0071] -- said undulations have a profile obeying a periodic law, for example of the sinusoidal type;

[0072] -- the ripples are in the form of a periodic signal having one or more harmonics;

[0073] -- said undulations or teeth are distributed more or less regularly along said edge of the fiber preform.

[0074] The present invention may also relate to a blade made of composite material for a turbomachine, in particular an aircraft one, this blade being obtained by a manufacturing method according to one of the features of the invention. The present invention may also relate to an aircraft turbomachine, comprising at least one blade made of composite material according to the invention.

[0075] The turbomachine can be a turbojet, turboprop or aircraft turboshaft engine.

[0076] Brief description of the figures

[0077] The present invention will be better understood and other details, characteristics and advantages of the present invention will appear more clearly on reading the description of a non-limiting example which follows, with reference to the appended drawings in which: Figure 1 is a schematic half-view in axial section showing an aircraft turbomachine with a ducted propeller and a ducted rectifier, the propeller and the rectifier each comprising blades; Figure 2 is a schematic perspective view showing a turbomachine with an unducted propeller and an unducted rectifier, the propeller and the rectifier each comprising blades; Figure 3 is a schematic profile view showing a first example of a blade of the turbomachine of Figure 1 or Figure 2, the blade comprising a serration element on a leading edge of the blade;Figure 4 is a schematic profile view showing a second example of a blade of the turbomachine of Figure 1 or Figure 2, the blade comprising a serration element on a trailing edge of the blade; Figure 5 is a block diagram of a method for manufacturing the blade of Figure 3 or Figure 4; Figure 6 is a schematic perspective view of a fiber preform intended to form a part of the blade of Figure 4; Figure 7a is a perspective view of a mold allowing densification of the fiber preform; Figure 7b is a schematic perspective and enlarged view of the mold of Figure 7a; Figure 8 is a partial axial sectional view schematically showing fiber sheets on an edge of the fiber preform according to an embodiment of the invention; Figure 9 is a schematic perspective view of the mold of Figure 8 comprising the deposition of fiber sheets;Figure 10 is a schematic perspective view of the mold of Figure 9 further comprising the deposition of the fiber preform; Figure 11 is a schematic perspective view of the mold of Figure 10 further comprising the deposition of other fiber sheets; Figure 12 is a partial axial sectional view schematically representing a layer of glue interposed between the fiber sheets and the edge of the fiber preform according to another embodiment of the invention.;

[0078] Elements having the same functions in different implementations have the same references in the figures. Detailed description of the invention

[0079] By convention, in the description below, the terms "longitudinal" and "axial" describe the orientation of structural elements extending in the direction of a longitudinal axis (such as a turbomachine or a blade). The terms "radial" or "vertical" describe an orientation of structural elements extending in a direction perpendicular to the longitudinal axis. The terms "inner" and "outer", and "internal" and "external" are used in reference to a positioning relative to the longitudinal axis. Thus, a structural element extending along the longitudinal axis has an inner face facing the longitudinal axis and an outer surface, opposite its inner surface.

[0080] The invention can be applied in a non-limiting manner to a turbomachine 10, in particular an aircraft turbomachine. The turbomachine 10 can be a turbojet, turboshaft or turboprop.

[0081] The turbomachine 10 can extend around a longitudinal axis X.

[0082] The turbomachine 10 may conventionally comprise a gas generator which drives at least one propeller 1. The gas generator comprises at least one compressor, a combustion chamber and at least one turbine. The rotor or one of the rotors of the gas generator is connected to the rotor of the propeller for its rotational drive.

[0083] A propeller 1 can be shrouded. This is the case for a fan in a turbomachine such as a turbojet or turbofan, for example.

[0084] By way of example and in a non-limiting manner, Figure 1 illustrates such a turbomachine 10 comprising, from upstream to downstream in the direction of flow of the gases F along the longitudinal axis X, the shrouded propeller 1 (also called fan), at least one compressor (such as a low-pressure compressor 2 and / or a high-pressure compressor 4), a combustion chamber 5, at least one turbine 6 (such as a high-pressure turbine and / or a low-pressure turbine) and a nozzle (not shown in Figure 1).

[0085] A propeller 1 may be unducted (figure 2). This is the case for a turboprop engine, for example. By way of example and in a non-limiting manner, figure 2 illustrates such a turbomachine 10 comprising the unducted propeller 1.

[0086] The turbomachine 10 can therefore comprise the propeller 1, whether it is shrouded or not shrouded upstream, and a rectifier 3 downstream.

[0087] The propeller 1 may comprise blades 7 (called rotor blades) extending around the axis X. The blades 7 of the propeller 1 allow the suction of an air flow. This air flow in the case of the turbomachine 10 of FIG. 1 is in particular capable of being divided into a primary flow and a secondary flow. The primary flow passes through a primary vein of the turbomachine 10 while the secondary flow is directed towards a secondary vein surrounding the primary vein.

[0088] The rectifier 3 comprises vanes 7 (called stator vanes) extending around the axis X. The vanes 7 of the rectifier 3 make it possible to straighten the flow at the outlet of a rotor located upstream in order to provide maximum thrust at the outlet of the turbomachine 10.

[0089] In the following description, the invention will be described in the context of its application in a non-limiting manner to the blade 7, in particular with reference to FIGS. 3 and 4. This blade 7 may be mobile on the propeller 1 or fixed on the rectifier 3.

[0090] Dawn 7 can extend as follows:

[0091] - an elongation axis A (substantially vertical in figures 3 and 4) which is substantially perpendicular or inclined to the axis X of the turbomachine 10,

[0092] - a longitudinal axis B (substantially horizontal in figures 3 and 4) which is substantially perpendicular to axis B, and

[0093] - a transverse axis C which is substantially perpendicular to axes A and B.

[0094] The blade 7 comprises a blade 70 which can be connected to a root 76 of the blade. The blade 70 comprises a leading edge 73, a trailing edge 74, a lower surface 71 and an upper surface 72 extending between the leading edge 73 and the trailing edge 74.

[0095] The blade 70 may have an aerodynamic profile to form the aerodynamic part of the blade 7. For this, the blade 70 may have a curved profile of variable thickness between the leading edge 73 and its trailing edge 74 of the blade 7. In the examples of FIGS. 3 and 4, the blade 70 may extend along the axis A between a first end and a second end opposite the first end.

[0096] The foot 76 can be connected to the second end of the blade 70. It is intended to be fixed to a disk (not shown) for example mobile in rotation around the axis X. The second end is free and configured to form a tip 75 (or a head) of blade 7.

[0097] The blade 70 also comprises at least one serration element 8 on at least a portion of the leading edge 73 and / or at least a portion of the trailing edge 74. As mentioned below, the serration element makes it possible to reduce the noise of aerodynamic origin generated by the blade in operation.

[0098] The blade 70 may thus comprise a serration element 8 located either at the leading edge 73 (FIG. 3) or at the trailing edge 74 (FIG. 4), or two different serration elements 8 located, respectively, on the leading edge 73 and the trailing edge 74 (not illustrated in the figures). For example, the serration element 8 may be located on the leading edge 73 when the blade 7 corresponds to that of the propeller 1 of the unducted turbomachine. The serration element 8 may be on the trailing edge 74 when the blade 7 corresponds to that of the rectifier 3 of the ducted turbomachine.

[0099] The serration element 8 may comprise undulations or teeth 82 (or otherwise said projecting portions). For example, the serration element 8 may comprise between five and twenty teeth 82. These teeth 82 may be aligned with respect to each other in particular along the leading edge 73 or the trailing edge 74. The teeth 82 may extend partially or over the entire leading edge 73 and / or the trailing edge 74. The teeth 82 may be identical or non-identical to each other. The teeth 82 may be defined so as to reduce the noise in the average emission spectrum without excessively worsening other frequencies at other engine speeds.

[0100] The undulations or teeth 82 may have shapes that are identical to each other or different from each other. The undulations or teeth 82 may each have a general polygonal shape (such as triangular, rectangular, etc.).

[0101] The ripples may have a profile obeying a periodic law, for example of the sinusoidal type. For example, the ripples may be in the form of a periodic signal having one or more harmonics.

[0102] The undulations or teeth 82 may be distributed more or less regularly along the leading edge and / or the trailing edge.

[0103] The clamping element 8 can cause variations in the chord of the blade depending on the radial height (relative to the axis A), with variable thicknesses and a very thin leading edge 73 or trailing edge 74.

[0104] Furthermore, the blade 7 may optionally comprise a metal reinforcement (not shown in the figures). This metal reinforcement may at least partially cover the leading edge 73 or the trailing edge 74. Advantageously, the metal reinforcement may extend over the entire height (relative to the axis A) and over a portion in length (relative to the axis B) of the intrados 71 and the extrados 72 from the leading edge 73.

[0105] Preferably, the metal reinforcement may have a U or V shape in cross section relative to the axis A, so as to at least partially cover the leading edge 73 or the trailing edge 74.

[0106] The metal reinforcement protects the blade (especially the blade) against external impacts (gravel from a takeoff / landing runway, hailstones, birds, etc.) and against erosion of the blade.

[0107] The metal reinforcement can be fixed by gluing or by projection of a film, for example metallic.

[0108] The metallic material of the metal reinforcement is for example titanium or an alloy such as steel (for example stainless steel) or a nickel and cobalt alloy (NiCo).

[0109] The blade 7 is made of composite material. The blade 7 may comprise a fiber preform 700 which may be embedded (or otherwise densified) in a resin (or otherwise a polymer matrix after densification of the resin).

[0110] By “fiber preform” is meant an intermediate part for producing the final blade 7. The composite material may be, for example, an organic matrix composite (OMC) or a ceramic matrix composite (CMC).

[0111] Organic matrix composites (OMCs) and ceramic matrix composites (CMCs) are used as replacements for metallic parts in certain parts of turbomachines (such as blades). Furthermore, their use contributes to optimizing aircraft performance, particularly by improving the efficiency of the turbomachine and reducing the overall mass of the turbomachine, significantly reducing harmful emissions to the environment (CO, CO2, NOx, etc.).

[0112] With reference to Figures 5 to 12, the present application will now describe a method of manufacturing the blade 7 as described above.

[0113] According to the invention, the method for manufacturing the blade 7 from composite material comprises the following steps:

[0114] (a) production of a fiber preform 700 by weaving fibers,

[0115] (b) shaping and stiffening the fiber preform 700 in a preforming tool,

[0116] (c) placing the fiber preform 700 in a mold M, and

[0117] (d) densification of the fiber preform 700 by a resin to form the blade 7. One of the particularities of the invention is that:

[0118] - before and / or after step (c), the method further comprises a step (i) of introducing fiber sheets 80 into the mold M so as to cover at least part of an edge 740 of the fiber preform 700, these fiber sheets 80 having a wavy or toothed edge 800,

[0119] - during step (d), the fiber sheets 80 are also densified by the resin to form the clamping element 8.

[0120] As mentioned previously, the introduction of fiber sheets 80 on the edge 740 of the fiber preform makes it possible, in particular during the densification step (d), to bind and form in a single piece the clamping element 8 on the leading edge 73 or the trailing edge 74 of the blade.

[0121] Figure 5 summarizes the steps of the manufacturing process of the invention, in which the optional steps of the process are represented by dotted lines.

[0122] In step (a), the fiber preform 700 may be formed from two-dimensional or three-dimensional woven fibers.

[0123] The fibrous preform 700 may comprise carbon fibers, glass fibers, aramid fibers, ceramic fibers (such as silicon carbide), or a mixture of at least two of these fibers.

[0124] The fiber preform 700 may be previously impregnated with a resin, in particular before the densification step (d). Alternatively, the fiber preform 700 may be said to be “dry”, that is to say that it is not previously impregnated with resin.

[0125] The fiber preform 700 is intended to form a part of the blade 70. In particular, the fiber preform 700 can form the leading edge 73, the trailing edge 74, the intrados 71 and the extrados 72 of the blade 70.

[0126] The fiber preform 700 may comprise at least one edge 740. This edge 740 may be intended to form the leading edge 73 or the trailing edge 74 of the blade 70. In other words, the edge 740 may extend into the leading edge 73 or the trailing edge 74. The edge 740 may have an elongated shape along a plane substantially parallel to the axis A. The edge 740 may be smooth and flat.

[0127] Step (a) may also comprise pre-cutting, for example manually, of any floating fibers (such as warp yarn fibers) on the fiber preform 700 obtained after weaving the fibers.

[0128] Advantageously, the method may further comprise, before step (b), a step (iii) of cutting the fiber preform 700 to form a recess 742 in the fiber preform 700. This recess 742 makes it possible in particular to form an edge corresponding in particular to the edge 740 and with a smooth surface adapted to receive the fiber sheets 80. Alternatively, the recess surface 742 may not be smooth. In this configuration, the recess surface 742 may have a surface for example zigzag, curved or a mixture of these types of non-smooth surface.

[0129] The recess 742 (or in other words a hollowed-out portion) may be formed at the edge 740 of the fiber preform and / or towards the inside of the fiber preform 700 (namely on an intrados face and / or an extrados face of the fiber preform). Figure 6 illustrates, in a non-limiting manner, the recess 742 at the edge 740 of the fiber preform 700 which is intended to form the trailing edge 74. Alternatively, the recess 742 may be located on an edge of the fiber preform on the side of the leading edge 73.

[0130] The recess 742 may extend over at least 70% of the length of the edge 740 of the fiber preform. The length of the edge 740 may be measured substantially along the axis A. In particular, the recess 742 may extend over at most 90% of the length of the edge 740 of the fiber preform.

[0131] The cutting of the fiber preform 700 can be carried out by at least one technique chosen from: a water jet, a circular blade, an ultrasonic knife and a pair of scissors. The ultrasonic knife can have a long and pointed blade.

[0132] Step (b) allows preforming of the woven fiber preform 700 obtained at the end of step (a) or (iii). This step (b) can be carried out in a suitable preforming tool (not shown in the figures).

[0133] Step (b) may comprise a sub-step (bi) of applying water to the fiber preform obtained for example at the end of step (a) or step (iii). This makes it possible to wet the fiber preform 700. The fiber preform is thus moistened with water, so that it is easier to handle.

[0134] Step (b) may comprise a sub-step (bz) of positioning the fiber preform 700 obtained in step (a) or (iii) in the preforming tool. For this, the fiber preform 700 may comprise tracer fibers on the surface which may be aligned with laser projections of positrons of theoretical tracer fibers of warp and weft threads formed for example by the preforming tool. Step (b) may comprise a sub-step (bs) of drying by heating for example by placing the closed preforming tool in an oven or an autoclave. The drying may be carried out with a temperature greater than 100°C and for a duration of a few hours. The drying makes it possible in particular to dry the water used for wetting or to extract it from the fiber preform.

[0135] In step (c), the fiber preform 700 obtained in particular at the end of step (b) or (i) can be placed in a suitable mold M. The positioning of the fiber preform in the mold M can also be carried out using fiber tracers on the surface of the fiber preform and their laser projections.

[0136] With reference to figures 7a and 7b, the mold M can comprise geometries of the clamping element 8, so that the fiber preform 700 and the fiber sheets 80 densified (or embedded) in the resin are as close as possible to the geometry of the desired blade 7. The mold M can thus comprise the various undulations (in particular the angles 02 illustrated in figure 7b) and / or camber of the blade 7 and of the clamping element 8.

[0137] The angle 02 may correspond to an angle between a plane tangential to the skeleton of the trailing edge (or in other words to an external surface of the trailing edge) and the axis X. Advantageously, the mold M may comprise at least one cavity M? of which a part Mso has a shape complementary to the wavy or toothed edge 800 of the fiber sheets 80. This makes it easier to form the clamping element 80 with its desired tooth geometry 82.

[0138] In particular, the cavity M? intended to form the blade 7, may comprise a first cavity portion M700 and a second cavity portion Mso. The first cavity portion M700 may have a shape complementary to the fiber preform 700, to facilitate the positioning and subsequently the densification of the fiber preform 700 in the mold. The second cavity portion Mso may be configured to receive the fiber sheets 80 (preferably the corrugated or toothed edge 800).

[0139] Advantageously, the edge 800 may be wavy and / or toothed. The edge 800 may therefore comprise undulations or teeth (or in other words, projecting portions). These undulations or teeth of the edge 800 may have shapes that are identical to each other or different from each other.

[0140] The undulations or teeth of the edge 800 may each have a general polygonal shape (such as triangular, rectangular, etc.).

[0141] The undulations of the edge 800 may have a profile obeying a periodic law, for example of the sinusoidal type.

[0142] The 800 edge ripples may be in the form of a periodic signal having one or more harmonics.

[0143] The undulations or teeth may be distributed more or less regularly along the edge 800 of the fiber preform.

[0144] Step (i) of introducing sheets of fibers 80 into the mold M can be carried out before step (c) and / or after step (c).

[0145] The 80 fiber sheets can be made by weaving fibers or superimposing several layers of fibers.

[0146] The fiber webs 80 may comprise carbon fibers, glass fibers, aramid fibers, ceramic fibers (such as silicon carbide), or a mixture of two or more of these fibers.

[0147] The type of weaving of the 80 fiber sheets (for example two-dimensional or three-dimensional), the orientation of the fibers (for example 0° and / or 45°) and / or the nature of the fibers (for example carbon fibers, aramid fibers, etc.) can vary depending on the desired stiffness.

[0148] The fiber sheets 80 may be pre-impregnated with a resin, in particular before the densification step (d). Alternatively, the fiber sheets 80 may be said to be “dry”, that is to say that they are not pre-impregnated with resin.

[0149] The fiber sheets 80 may have an elongated shape, in particular along the edge 740 of the fiber preform.

[0150] The fiber sheets 80 may extend over at least 70% of the length of the edge 740 of the fiber preform (relative to the axis A). In particular, the fiber sheets 80 may extend over at most 90% of the length of the edge 740 of the fiber preform.

[0151] Advantageously, at least some of the fiber sheets 80 may be solely covered by fiber sheets 80 or interposed between two fiber sheets 80.

[0152] At least some of the fiber plies 80 may not cover the edge 740 of the fiber preform 700.

[0153] At least some of the fiber webs 80 have a first surface 812 and a second surface 814, the first surface 812 having a greater extent than the second surface 814. The first surface 812 directly covers the edge 740 of the fiber preform and / or is separated from this edge 740 of the fiber preform by other fiber webs. The second surface 814 directly covers the other fiber webs or is covered by these other fiber webs. In particular, when the fiber sheets 80 comprise several fiber sheets superimposed on one another, the first surface 812 of some of the fiber sheets may be that which directly covers the edge 740, and that of the superimposed fiber sheets (for example the outermost sheets with respect to the axis B) which may be separated from this edge 740 by other fiber sheets arranged between the edge 740 and the superimposed fiber sheets.

[0154] Figures 8 to 12 illustrate a preferred embodiment, in which the fiber sheets 80 may comprise first 810 and second 820 fiber sheets, and possibly third fiber sheets 830 interposed at least partially between the first 810 and second 820 fiber sheets.

[0155] The first 810 and second 820 fiber layers may each have:

[0156] - a surface 812a of the first surface 812 which directly covers the edge 740, - another surface 812b of the first surface 812 which is separated from this edge 740 by another sheet of fibers among the first 810 or second 820 sheets of corresponding fibers,

[0157] - a surface 814a of the second surface 814 which directly covers the third layers of fibers 830, and / or

[0158] - another surface 814b of the second surface 814 which is covered by another sheet of fibers among the first 810 or second 820 sheets of corresponding fibers.

[0159] The third fiber webs 830 may have only the second surface 814. In particular, at least some fiber webs among the third fiber webs 830 may comprise:

[0160] - the surface 814a of the second surface 814 which can directly cover the first 810 or second 820 layers of fibers, and / or

[0161] - the other surface 814b which can be covered by other fiber sheets among the third fiber sheets 830.

[0162] Figure 8 illustrates in a non-limiting manner the first fiber sheets 810 having the first surface 812, 812a, 812b and the second surface 814, 814a, 814b, and the third fiber sheets 830 having the second surface 814, 814a, 814b. The first surface 812 has an extent greater than that of the second surface 814. Thus, the second surface 814 of the fiber sheets 810, 820, 830 can extend outside the edge 740, or in other words in the extension of the edge 740.

[0163] With reference to FIG. 8, a fiber sheet among the first 810 and second 820 fiber sheets may be covered solely by another fiber sheet among the corresponding first 810 and second 820 fiber sheets. Alternatively, a fiber sheet among the first 810 and second 820 fiber sheets may be interposed between two fiber sheets among the corresponding first 810 and second 820 fiber sheets, in particular when more than two fiber sheets 810, 820 are superimposed on each other.

[0164] In Figure 8, the third fiber sheets 830 may not cover the edge 740 of the fiber preform. Advantageously, before step (c), the first fiber sheets 810 may be positioned directly in the mold M, and after step (c), the second fiber sheets 820 may be positioned directly on the edge 740 of the fiber preform 740 or even on the first fiber sheets 810, so that the edge 740 of the fiber preform 740 is interposed between the first 810 and second 820 fiber sheets.

[0165] The third fiber layers 830 may be interposed between the first 810 and second 820 layers and located next to the edge 740, without covering it.

[0166] With reference to FIG. 9, the first fiber sheets 810 can be positioned, for example manually, in the second cavity part Mso of the molded M.

[0167] With reference to FIG. 10, the fiber preform 700 obtained in step (b) can be positioned, for example manually, in the first cavity portion M700 of the mold M. More particularly, the edge 740 of the fiber preform can be positioned on the first fiber sheets 810, so that a portion of these first fiber sheets 810 covers a first face of the edge 740 (in particular at the level of the recess 742) and the other portion of these first fiber sheets 810 partially forms the wavy or toothed edge 800. With reference to FIG. 11, the second fiber sheets 820 can be positioned, for example manually, in the second cavity portion Mso of the mold M. In particular, the second fiber sheets 820 can be positioned on a second face of the edge 740 of the fiber preform (in particular of the recess 742) and on the first layers of fibers 810 (in particular at the level of the wavy or toothed edge 800).The second fiber sheets 820 may be superimposed on the first fiber sheets 810, so that the edge 740 is interposed at least partially between the first 810 and second 820 fiber sheets.

[0168] Optionally, the third fiber sheets 830 may be interposed between the first 810 and second 820 fiber sheets, outside the edge 740 of the fiber preform. The method may also comprise a step (ii) of adding a layer of glue 9 between the fiber sheets 80 and the edge 740 of the fiber preform 700. This step (ii) may be carried out before or during step (i).

[0169] Figure 12 illustrates in a non-limiting manner the layer of glue 9 interposed between the edge 740 of the fiber preform and the fiber sheets 810, 820, 830.

[0170] The adhesive layer 9 may be epoxy-based. For example, the adhesive layer 9 may be an epoxy resin of type PR520 or an epoxy of type AF191-M marketed for example by the company 3M.

[0171] The method may comprise at least one step of compacting the fiber preform 700 and the fiber sheets 80. This compaction step may be carried out before step (d). The compaction step may be carried out during or after step (c) of placing the fiber preform 700 and the fiber sheets 80 in the mold M, in which the fiber preform 700 and / or the fiber sheets 80 may be pre-impregnated or dry.

[0172] For example, the compaction step makes it possible to assemble several fiber sheets 80 on the fiber preform 700, then to place a protective film and a tarpaulin around the mold M. Next, a vacuum is created in the tarpaulin, so as to apply a predetermined pressure to compact the fiber preform 70 and the fiber sheets 80. The compaction step can be carried out over a period of, for example, approximately 15 minutes.

[0173] The compaction step may be repeated every four to five additional 80 fiber plies until the desired final number of 80 fiber plies is reached.

[0174] The compaction step makes it possible in particular to limit porosities and delaminations, and also to limit a possible height shift (in particular between the fiber sheets 80 and the fiber preform 700) which could correspond to a greater thickness than that desired.

[0175] A single compaction step may be sufficient when the number of fiber sheets 80 is, for example, less than three fiber sheets 80 to form the wavy or toothed edge. Several compaction steps may be required when the number of superimposed fiber sheets 80 is, for example, greater than four fiber sheets 80 to form the wavy or toothed edge.

[0176] The densification step (d) allows polymerization or hardening of the fiber preform 700 and the fiber sheets 80, in particular of the polymer matrix resin so as to form the blade 7 in composite material.

[0177] Step (d) may be carried out by heating to a temperature of between 150°C and 200°C, preferably about 180°C.

[0178] The resin (for example which is injected in step (d) and / or which previously impregnates the fiber sheets 80) may be thermosetting or thermoplastic. For example, the resin may be based on epoxy, polyepoxide, polyimide, polybismaleimide, polyurethane, polyester or vinylester. Alternatively, the resin may be a polymer of the LMPAEK® type marketed by Victrex.

[0179] Advantageously, the fiber preform 700 may be formed from carbon fibers that are woven in three dimensions and this fiber preform may be embedded in the epoxy-based resin. The fiber plies 80 may be formed from carbon fibers that are woven and pre-impregnated with a resin of the HexPIy® 8552 type or of the MTM49-L type.

[0180] In the case of fiber sheets 80 previously impregnated with resin and during step (d), the injected resin (for example PR520 epoxy) makes it possible to bond these fiber sheets 80 to the edge 740 of the fiber preform. This injected resin will not be able to impregnate the fiber sheets 80 which are previously impregnated with resin (for example HexPIy® 8552 or MTM49-L resin). The heating in step (d), for example at 180°C, allows simultaneous polymerization and hardening of the injected resin (for example PR520 epoxy resin) and the resin impregnating the fiber sheets 80 (for example HexPIy® 8552 or MTM49-L resin) and the fiber preform 700.

[0181] In the case of dry fiber sheets 80, the injected resin (for example the epoxy resin PR520) in step (d) can impregnate the fibers of both the fiber sheets 80 and the fiber preform 700. The heating in step (d), for example to 180°C, thus allows simultaneous polymerization and hardening of the injected resin (for example the epoxy resin PR520) which therefore impregnates both the fiber sheets 80 and the fiber preform 700.

[0182] The method may comprise a step (e) of final finishing and completion of the blade 7. For example, step (e) may comprise machining on the contour of the blade 7 obtained in step (d) to remove an excess length. The excess length removed may be between 10 and 30 mm.

Claims

CLAIMS 1. Method for manufacturing a blade (7) made of composite material for a turbomachine (10), in particular an aircraft, said blade (7) comprising a blade (70) having a leading edge (73), a trailing edge (74), a lower surface (71) and an upper surface (72) extending between the leading edge (73) and the trailing edge (74), the blade (70) further comprising at least one serration element (8) on the leading edge (73) and / or the trailing edge (74), the method comprising the following steps: (a) producing a fiber preform (700) by weaving fibers, this fiber preform being intended to form a part of the blade (70), (b) shaping and stiffening the fiber preform (700) in a preforming tool, (c) placing the fiber preform (700) in a mold (M), (d) densification of the fibrous preform (700) by a resin to form the blade (7), characterized in that: - before and / or after step (c), the method further comprises a step (i) of introducing sheets of fibers (80) into the mold (M) so as to cover at least part of an edge (740) of the fiber preform (700), these sheets of fibers (80) having a wavy or toothed edge (800), - during step (d), the fiber sheets (80) are also densified by the resin to form said at least one serration element (8).

2. Manufacturing method according to claim 1, in which: - before step (c), first fiber sheets (810) are positioned directly in the mold (M), and - after step (c), second fiber sheets (820) are positioned directly on the edge (740) of the fiber preform or even on the first fiber sheets (810), so that the edge (740) of the preform is interposed between the first (810) and second (820) fiber sheets.

3. Manufacturing method according to claim 2, in which third layers of fibers (830) are interposed between the first (810) and second (820) layers and located next to the edge (740), without covering it.

4. Manufacturing method according to claim 1 or 2, in which, before or during step (i), the method also comprises a step (ii) of adding a layer of glue (9) between the fiber sheets (80) and the edge (740) of the fiber preform (700), the layer of glue being for example epoxy-based.

5. A manufacturing method according to any one of the preceding claims, wherein the method further comprises, before step (b), a step (iii) of cutting the fiber preform (700) to form a recess (742) in the fiber preform.

6. Manufacturing method according to any one of the preceding claims, in which the mold (M) comprises at least one cavity, a part of which has a shape complementary to the wavy or toothed edge (800) of the fiber sheets (80).

7. Manufacturing method according to any one of the preceding claims, in which before step (d), the method comprises at least one step of compacting the fibrous preform (700) and the fiber sheets (80).

8. Manufacturing method according to any one of the preceding claims, in which the fiber sheets (80) are produced by weaving fibers or superimposing several layers of fibers.

9. Manufacturing method according to any one of claims 1 to 8, in which the fiber preform (700) and the fiber sheets (80) are previously impregnated with a resin before step (d).

10. Manufacturing method according to any one of the preceding claims, in which the resin is thermosetting or thermoplastic, for example epoxy-based.

11. Manufacturing method according to any one of the preceding claims, characterized in that the fiber sheets (80) are pre-impregnated for example with a resin.

12. Manufacturing method according to any one of the preceding claims, characterized in that the fiber sheets (80) have an elongated shape along said edge (740) of the fiber preform (700).

13. Manufacturing method according to any one of the preceding claims, characterized in that the fiber sheets (80) extend over at least 70% of the length of said edge (740) of the fiber preform (700).

14. Manufacturing method according to any one of the preceding claims, characterized in that at least some of the fiber sheets (80) have a first surface (812) which directly covers said edge (740) of the fiber preform (700) and / or which is separated from this edge (740) of the fiber preform (700) by other fiber sheets (80), and a second surface (814) which directly covers the other fiber sheets (80) or which is covered by these other fiber sheets (80), the first surface (812) having an extent greater than that of the second surface (814).

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