Method for manufacturing an interblade platform with a sacrificial edge

Abstract

The present invention relates to a method for manufacturing an interblade platform (100) of a turbine engine fan (1), the platform (100) comprising a base (110) having first and second sacrificial side edges (131, 132), the thicknesses of the first and second sacrificial side edges (131, 132) being less than the thickness of a central part (120) of the base (110); the method comprising producing a preform (200) of the platform (100) by three-dimensional weaving, the preform comprising a central part portion (220) and two sacrificial edge portions (231, 232), the thicknesses of the two sacrificial edge portions being less than the thickness of the central part portion (220), and the thickness difference between the side edge portions (231, 232) and the central part portion (220) being achieved by removing a plurality of warp yarns located outside the central part portion (220) and not woven with weft yarns.

Description

Technical Field

[0001] The present invention relates to a fan of a turbomachine, such as a fan of an aircraft turbojet or turboprop engine, and more particularly to an interblade platform in a fan of a turbomachine. Background Art

[0002] In a known manner, a turbomachine fan includes a rotor disk that includes a plurality of blades separated by interblade platforms at their radially inner ends. Thus, the interblade platforms of the turbomachine fan are arranged between the fan blades in the extension of the inlet cone of the fan. They particularly make it possible to delimit, on the inside, an annular flow of air at the inlet of the fan, which annular flow of air is delimited, on the outside, by a casing. These platforms generally include a base configured to delimit the annular flow of air and lugs extending radially towards the rotor disk. These lugs can form part of a box or correspond to stiffeners.

[0003] Since the blades are not connected to the platforms, the mechanical stresses to which the blade roots are subjected during operation are greatly reduced. This makes it possible to reduce the size of the blade roots to lighten the fan and thus improve the performance of the turbomachine.

[0004] The base of the platform generally includes sacrificial side edges that are designed to break in the case of a strong pressure from a blade acting on said sacrificial edges. These sacrificial side edges are generally thinner than the rest of the base. Thus, in the case of a damaged fan blade, the sacrificial edges of the two platforms located on either side of said blade yield, making it possible to dissipate part of the energy and reduce the contact force between the blade and the platform to limit structural damage. In addition, the two platforms can protect the surrounding fan blades by preventing any debris that could damage the blades from coming into contact with the radially inner ends of these blades. Thus, the risk of additional damage to the fan blades and platforms is greatly reduced.

[0005] Thus, fan platforms are generally made of composite materials and include a fiber-reinforced material densified by a matrix. It is particularly known to produce a single-piece fiber preform by three-dimensional or multi-layer weaving. For example, the three-dimensional weaving production of a π (Pi)-shaped fiber preform for a platform is described in document WO 2013 / 088040. The preform is then densified by a matrix according to a conventional method.

[0006] The sacrificial side edges are then produced by machining the edges of the base to obtain the desired reduced thickness. However, this machining operation on composite materials is complex and delicate to implement, especially in order to meet the reference dimensions of the part and the fitting of the surfaces. Summary of the Invention

[0007] Thus, the main object of the present invention is to remedy the above drawbacks by facilitating the manufacture of the interblade platforms.

[0008] To this end, the present invention proposes a method for manufacturing an interblade platform of a turbine engine fan, the platform including a base and at least two lugs, the base including a central portion, the central portion including a first surface configured to define the fuel flow of the fan, and a second surface opposite the first surface; the at least two lugs radially extend from the second surface, and the base further includes first and second sacrificial side edges that extend from either side of the central portion of the base and have a thickness less than that of the central portion of the base;

[0009] The method includes producing a fiber preform of the platform by one-piece three-dimensional weaving between multiple layers of weft yarns and multiple layers of warp yarns;

[0010] The method further includes densifying the fiber preform with a matrix to form a component having the shape of the platform to be manufactured;

[0011] The method is characterized in that the fiber preform of the platform includes a base portion of a fiber reinforcement for forming the base of the platform, the base portion of the fiber preform including a central component portion and two sacrificial edge portions having a thickness less than that of the central component portion, a first plurality of weft yarns being continuous between the central component portion and the sacrificial edge portions, the sacrificial edge portions including a first plurality of warp yarns woven into the first plurality of weft yarns, and the thickness difference between the side edge portions and the central component portion being formed by withdrawing a second plurality of warp yarns located outside the central component portion and not woven with the weft yarns.

[0012] Thus, by densifying a fiber preform that already has substantially the same shape as the component to be manufactured, the manufacturing of the interblade platform is simplified. Accordingly, complex machining steps are eliminated, thereby also limiting material losses while ensuring compliance with dimensional tolerances.

[0013] According to a particular feature of the present invention, the densification of the fiber preform is achieved by arranging the fiber preform in an impregnation chamber of a mold including a lower surface, abutting the surface of the fiber preform that is intended to form the first surface of the central component of the platform base against the lower surface; the impregnation chamber is enclosed by a flexible membrane that separates the impregnation chamber from a compaction chamber; an impregnation fluid is injected into the impregnation chamber, and a compression fluid is injected into the compaction chamber in order to apply pressure to the membrane.

[0014] The impregnation fluid can be, for example, a slurry containing matrix precursor particles or a resin.

[0015] The film injection technique offers greater flexibility in the geometry of injection molds. In fact, using a flexible film instead of a rigid counter-mold as in the RTM technique makes it particularly easier to adapt to the specific geometry of the lugs. In addition, the film injection technique also allows for better control of the fiber volume ratio, as the exact resin volume required is introduced to obtain an exact and predetermined fiber volume ratio.

[0016] According to another specific feature of the present invention, the injection of the impregnating fluid is carried out before the injection of the compression fluid.

[0017] According to another specific feature of the present invention, the injection of the compression fluid starts before the injection of the impregnating fluid.

[0018] In this variant, an improved control of the flow of the impregnating fluid and thus of the impregnation of the fiber preform is obtained.

[0019] According to another specific feature of the present invention, the injection of the compaction liquid starts before the injection of the impregnating fluid.

[0020] The latter variant advantageously makes it possible to apply a pressure to the fiber preform, the value of which makes it possible to obtain the desired fiber volume ratio even before the injection of the impregnating fluid. Then the injection of the impregnating fluid is started, which can be carried out while continuing to inject the compression fluid in order to compensate for the pressure drop, especially in the case where the impregnating fluid is a slurry. Description of the Drawings

[0021] Figure 1 is a partial exploded schematic view of an example of a fan including an inter-blade platform.

[0022] Figure 2 is Figure 1 a cross-sectional view of the inter-blade platform shown.

[0023] Figure 3 is a partial schematic view of a plane of a fiber preform of a platform woven in three dimensions.

[0024] Figure 4 is by making Figure 3 a partial schematic view of a plane of a fiber preform obtained by shaping the fiber preform.

[0025] Figure 5 is a schematic cross-sectional view of a fiber preform of a platform in a rigid injection tool.

[0026] Figure 6 is a schematic cross-sectional view of a fiber preform of a platform in a tool including a flexible film. Detailed Description

[0027] Figure 1The turbine engine fan 1 is shown in an exploded view and includes a rotor disk 10 carrying a plurality of fan blades 20, the roots 21 of the blades 20 being engaged in axial grooves 11 formed in the rotor disk 10. The blades 20 are separated by an interblade platform 100 which is connected to the rotor disk 10.

[0028] A first direction D1 is defined as corresponding to the general direction of the air flow of the turbine engine. A second tangential and / or circumferential direction D2 is defined as corresponding to the alternating successive direction of the interblade platforms 100 and the blades. Finally, a third radial direction D3 is defined as the direction perpendicular to the first direction.

[0029] For the sake of simplicity, the first, second and third directions of the fan reference frame are also used for the platform reference frame, the directions of the platform reference frame corresponding to the directions of the fan reference frame when the said platform is mounted on the said fan.

[0030] Figure 1 and Figure 2 The interblade platform 100 shown includes a base 110 which includes a central member 120 and a first sacrificial side edge 131 and a second sacrificial side edge 132. The central member 120 of the base 110 has opposite first and second surfaces 121 and 122. The first surface 121 is for defining the flow path of the fan. When the platform 100 is mounted on the fan, the first surface 121 and the second surface 122 extend longitudinally in the first direction D1, which is the general direction of the air flow of the turbine engine, and extend laterally in the D2 direction between two adjacent blades flanking the platform 100.

[0031] The platform 100 further includes at least two lugs 150 which radially extend from the second surface 122 of the central member 120 of the base 110 and are capable of performing a reinforcement function. When the platform 100 is mounted on the fan, the lugs 150 extend in the third direction D3 towards the rotor disk. The lugs 150 also extend longitudinally along the first surface 121 and the second surface 122. Thus, when the platform 100 is mounted on the fan, the lugs 150 extend in the first direction D1, that is to say, in the general direction of the air flow of the turbine engine.

[0032] The first sacrificial side edge 131 and the second sacrificial side edge 132 extend longitudinally along the first surface 121 and the second surface 122 on either side of the central member 120 of the base 110 of the platform 100. Thus, the first sacrificial side edge 131 and the second sacrificial side edge 132 are connected to the central member 120 of the base 110 of the platform 100.

[0033] Preferably, the first sacrificial side edge 131 and the second sacrificial side edge 132 respectively include extension surfaces 131a and 132a located at the extensions of the first surface 121 of the central member 120 along the second direction D2. Preferably, the lengths of the extension surfaces 131a and 132a along the second direction D2 are between 6 mm and 11 mm.

[0034] The thickness D3 of the first sacrificial edge 131 and the second sacrificial edge 132 in the third direction is less than the thickness of the central member 120 of the base 110 in the third direction D3. Preferably, the thicknesses of the first sacrificial edge 131 and the second sacrificial edge 132 are between 1.5 mm and 2.2 mm.

[0035] Preferably, the thicknesses of the first sacrificial edge 131 and the second sacrificial edge 132 at their free ends 131b and 132b along the third direction D3 are less than or equal to 2.2 mm.

[0036] The manufacturing of the interblade platform 100 includes producing a fiber preform 200 of the platform 100 by three-dimensional weaving between a plurality of warp yarns and a plurality of weft yarns. "Three-dimensional weaving" or "3D weaving" herein refers to a weaving pattern in which at least some of the warp yarns are connected to the weft yarns on a plurality of weft yarn layers. The roles between the warp yarns and the weft yarns can be interchanged. The fiber preform may, for example, have a multi-layer satin weave, that is, a fabric obtained by three-dimensional weaving with a plurality of weft yarn layers, wherein the basic weave of each layer is equivalent to a classical satin weave, but certain points of the fabric bond the weft yarn layers together.

[0037] The fiber preform may also, for example, have an interlock weave, that is, a fabric obtained by three-dimensional weaving, wherein each layer of warp yarns is connected to a plurality of weft yarn layers, and all the yarns of the same column of warp yarns move in the same manner in the weaving plane.

[0038] Other three-dimensional weaving methods may be implemented, such as a multi-web weave. Different multi-layer weaving methods that can be used to form the fiber preform are described in document WO2006 / 136755.

[0039] The fiber preform 200 includes a lug portion 250 of the fiber reinforcement for forming the lugs 150 of the platform 100, and a base portion 210 of the fiber reinforcement for forming the base 110 of the platform 100. In particular, the base portion 210 of the fiber preform 200 includes the fiber reinforcement for forming the central member 120 of the base 110 of the platform 100, and the fiber reinforcements for forming the first sacrificial side edge 131 and the second sacrificial side edge 132 respectively. The central member 220 includes a first surface 221 and a second surface 222 for forming the first surface 121 and the second surface 122 of the central member 120 of the base 110 of the platform 100 respectively.

[0040] To produce the fiber preform 220 of the platform 100, the fiber blank 300 of the platform 100 can first be produced by three-dimensional braiding.

[0041] The sacrificial edge portions 231 and 232 are produced according to the so-called "layer exit" method. The fiber blank 300 of the fiber preform 200 is manufactured using a jacquard-type loom. Such a loom is described, for example, in document FR 3 047 744A1. With such a loom, it is possible to directly braid the blanks of the sacrificial edge portions having a thickness different from that of the blank of the central component portion.

[0042] Thus, in the fiber blank 300, the first plurality of weft yarn layers are continuous between the blank of the central component portion and the two blanks of the sacrificial side edges, that is to say, the first plurality of weft yarns pass through both the blank of the central component portion and the two blanks of the sacrificial side edges. Thus, in the fiber preform 200, the first plurality of weft yarn layers are continuous between the central component portion 220 and the two sacrificial side edge portions 231 and 232, that is to say, the first plurality of weft yarns pass through the central component portion 220 and the two sacrificial side edge portions 231 and 232.

[0043] The blank of the central component portion includes multiple layers of warp yarns braided with multiple layers of weft yarns. In particular, a plurality of warp yarns are braided with the first plurality of weft yarn layers and the second plurality of weft yarn layers, that is to say, the warp yarns belonging to the blank of the central component portion are braided with the first plurality of weft yarns and the second plurality of weft yarns. Thus, in the fiber preform 200, multiple layers of warp yarns are braided with the first plurality of weft yarn layers and the second plurality of weft yarn layers, and the warp yarns belonging to the central component portion 220 are braided with the first plurality of weft yarns and the second plurality of weft yarns.

[0044] [[ID=!3]]The blank of the sacrificial side edge portion includes a first plurality of warp yarn layers braided with the first plurality of weft yarn layers, that is to say, within the blank of the sacrificial side edge portion, the first plurality of warp yarns are braided with the first plurality of weft yarns. The same braiding structure is used for the blank of the other sacrificial side edge portion. Thus, in the fiber preform 200, the sacrificial side edge portion 232 includes a first plurality of warp yarn layers braided with the first plurality of weft yarn layers, that is to say, the first plurality of warp yarns are braided with the first plurality of weft yarn layers located within the sacrificial side edge portion 232. The same braiding structure is used for the other sacrificial side edge portion 231.

[0045] The thickness difference between the blank of the central component portion and the two blanks of the sacrificial side edge portions is achieved by removing the following second plurality of warp yarns: that is to say, those located on both sides of the blank of the central component portion and different from the first plurality of warp yarns. In particular, the warp yarns belonging to the second plurality of warp yarns do not belong to the first plurality of warp yarns, and vice versa. Thus, the second plurality of warp yarns corresponds to the set of warp yarns located outside the blank of the central portion and not braided into the first plurality of weft yarns.

[0046] In order to be able to remove the second most warp yarns, the second most warp yarns are not woven with the weft yarns. Therefore, the second most warp yarns are not woven with the first most weft yarns and are not woven with the second most weft yarns.

[0047] Therefore, the second most weft yarns are only woven with the warp yarns present in the blank of the central component part. Thus, in the fiber preform 200, the second most weft yarns are only woven with the warp yarns present in the central component part 220. Therefore, the second most weft yarns correspond to the weft yarns that are not woven with the first most warp yarns.

[0048] When the weaving of the fiber blank 300 is completed, two parts of the yarns belonging to the second most weft yarns that are not woven with the blank of the central component part are cut.

[0049] While producing the side edge parts 231 and 232, the lug part 250 of the fiber preform 200 can be produced by a peeling means. Figure 3 An example of a partial schematic plan view of the fiber blank 300 of the platform 100 is shown. The fiber blank 300 of the platform 100 includes a blank 310 of the base part and a blank 350 of the lug part within its thickness range. The blank 310 of the base part and the blank 350 of the lug part are separated from each other in the weft direction by a component of the size of the fiber blank 300 through a first peeling device 301 and a second peeling device 302. The peeling devices 301 and 302 extend from the opposite edges 301b, 302b of the fiber blank 300 to the floor 301a, 302a of the peeling devices, and there is no peeling device at the center of the fiber blank 300. The base blank 310 has a first surface 321 and a second surface 322, which are respectively used to form the first surface 221 and the second surface 222 of the central component part 220 of the fiber preform 220.

[0050] Each of the base part blank 310 or the lug 350 blank of the fiber blank 300 includes multiple layers of warp yarns, where the number of warp yarn layers in the base part 310 blank and the lug 350 blank is different.

[0051] In each plane of the fiber blank 300, the same first warp yarns t 31 、t 32 、t 33 、t 34 are connected to the warp yarns in the lug part blank 350 that extend beyond the second peeling device 302 and to the warp yarns in the part of the base part blank 310 that abuts the first peeling device 301. On the contrary, the same second warp yarns t 35 、t 36 、t 37 、 38The warp threads in the portion of the base part blank 310 that abuts the second stripping device 302 are joined to the warp threads in the lug part blank 350 located below the first stripping device 301.

[0052] Thus, the paths of the first weft threads t 31 , t 32 , t 33 , t 34 cross the paths of the second weft threads t 35 , t 36 , t 37 , t 38 in the transition zone 303, which is located between the underlying layers 301a and 302a of the stripping devices 301 and 302 at the center of the fibrous blank 300.

[0053] Note that the first surface 321 of the base part blank 310 is woven in a surface satin weave with the surface represented by the yarn t 39 providing surface continuity, without passing through the warp thread layer and without crossing other weft threads.

[0054] Figure 3 and Figure 4 The weaves shown are schematic diagrams and thus represent fewer warp and weft threads than the actual number.

[0055] Then, as Figure 4 shown, the fibrous blank 300 of the platform 100 is shaped to obtain a fibrous preform 200 of the body 100 having a substantially π (Pi) - shaped cross - section by folding at the stripping devices 301 and 302 to form the lug portions 250.

[0056] Preferably, the length and width of the first surface 221 of the central component part 220, the length of the lug portions 250, and the spacing between the two lug portions 250 substantially correspond respectively to the length and width of the first surface of the central component 120, the length of the lugs 130, and the spacing between the two lugs 130 of the platform 100.

[0057] Document WO 2013 / |088040 specifically describes examples of the plan view of a fibrous blank that can be used to produce a fibrous platform preform with lugs.

[0058] Preferably, the fiber preform 200 corresponds to a "dry" fiber structure, that is, it is not impregnated with resin or the like. The fiber preform 200 may include various different types of yarns, especially ceramic or carbon yarns or even mixtures of such yarns. Preferably, the fiber preform 200 may be made of silicon carbide fibers. Generally speaking, the fiber preform 200 may also be made of fibers including the following materials: alumina, mullite, silica, aluminosilicate, borosilicate, carbon, or mixtures of several of these materials.

[0059] Once the fiber preform 200 of the platform 100 is obtained, the fiber preform 200 is densified through a matrix to form a component including a fiber reinforcement composed of the fiber preform 200.

[0060] Densification can be achieved by the well-known resin transfer molding (abbreviated as "RTM"), or by slurry transfer molding (abbreviated as "STM"). As Figure 5 shown, the fiber preform 200 for forming the fiber reinforcement of the platform 100 is arranged in a cavity defined by a first component 61 and a second component 62 of a mold 60. This cavity has the shape of the component to be manufactured, and this component has the overall shape of the platform 100 to be manufactured.

[0061] Generally, a slurry 6 of matrix precursor particles or resin is injected into the cavity containing the fiber preform 200 so as to pass through the fiber preform 200 due to the application of a pressure gradient P. In the case of the slurry, the mold in which the slurry 6 is injected includes a filter 63 at the outlet hole of the slurry 6 in the mold 60, so that any particles of the matrix precursor can be retained in the mold 60, and during the deposition of the matrix precursor particles into the mold 60, the fiber preform 200 is gradually impregnated.

[0062] Densification can also be achieved in a known manner by injection under a film, as Figure 6 shown. The injection method can fully control the quality of the injected resin or slurry, thereby ensuring an accurate and appropriate fiber volume ratio. Therefore, the properties of the components manufactured thereby are improved, and the differences between parts are smaller.

[0063] The fiber preform 200 for forming the fiber reinforcement of the platform 100 is arranged in a mold 70. In particular, the fiber preform 200 can be directly arranged on the lower surface of the impregnation chamber 71. This lower surface of the impregnation chamber 71 may include a filter ( Figure 6 not shown in the figure).

[0064] The mold 70 includes, on the one hand, an impregnation chamber 71 into which the fiber preform 200 is placed so as to be densified by a matrix by injecting an impregnation fluid 8; and on the other hand, a compaction chamber 72 into which a compression fluid 9 is injected so as to apply a pressure to the preform 200 during the densification of the preform 200 by the matrix. The impregnation chamber 71 and the compaction chamber 72 are separated by a flexible membrane 73. The membrane 73 makes it possible to apply a pressure to the fiber preform 200 installed in the impregnation chamber 71. The compression fluid 9 applies a pressure Q to the membrane 73, and the membrane 73 deforms and thus in turn applies a pressure to the fiber preform 200.

[0065] Preferably, as Figure 6 shown, the membrane cooperates with the lug portion 250 of the fiber preform 200 and the second surface 222 of the central member portion 220, while the first surface 221 of the central member portion 220 abuts against a wall of the impregnation chamber 71 that is opposite to the membrane 73. An insert 74 can be used to facilitate the impregnation of the fiber preform 200 of the platform 100.

[0066] The flexible membrane 73 is made of silicone resin, for example.

[0067] As Figure 6 shown, for example, the resin 8 can be introduced into the impregnation chamber 71 through an inlet hole, and the compression liquid 9 can be introduced into the compaction chamber 72 through an inlet hole.

[0068] Depending on the dimensions, thickness, and shape of the platform 100 to be manufactured, the injection sequence of different compression and impregnation fluids will be preferred.

[0069] For example, the impregnation fluid (such as resin) can be first injected into the impregnation chamber where the fiber preform is arranged. Once the injection of the impregnation fluid is completed, the compression fluid (such as water) is injected into the compaction chamber so as to apply a pressure to the flexible membrane. Thus, the flexible membrane applies a pressure to the fiber preform, enabling the impregnation fluid to penetrate into the preform.

[0070] Then, while maintaining the pressure applied by the membrane, the preform is heat-treated so as to form a matrix in the pores of the fiber preform.

[0071] According to another example, it can start by injecting the compression fluid into the compaction chamber. Thus, even before injecting the impregnation fluid, a pressure is applied to the fiber preform through the flexible membrane, and the value of this pressure makes it possible to obtain the desired fiber volume ratio. Then the injection of the impregnation fluid is started, which can be carried out while continuing to inject the compression fluid so as to compensate for the pressure drop, especially when the impregnation fluid is a slurry. Such an injection sequence is described, for example, in the document WO 2019 / 197757 A1.

[0072] When the densification step is completed, a composite part is obtained, whose fiber reinforcement consists of the fiber preform 200 and whose shape generally corresponds to the inter-vane platform 100 to be manufactured. A trimming or light machining step can be performed on the produced part to obtain the inter-vane platform 100 to be manufactured. Additionally, other elements can be installed or welded to the produced part to obtain the inter-vane platform 100 to be manufactured, in particular the element 140 attached to the rotor disk as Figure 1 shown.

[0073] The expression "between... and..." must be understood to include the boundaries.

Claims

1. A method for manufacturing an interblade platform (100) of a turbine engine fan (1), the platform (100) comprising a base (110) and at least two lugs (150); the base (110) comprising a central member (120) having a first surface (121) configured to define a flow path of the fan and a second surface (122) opposite the first surface (121); the at least two lugs (150) extending radially from the second surface, the base (110) further comprising first and second sacrificial side edges (131, 132) extending on either side of the central member (120) of the base (110) and having a thickness less than the thickness of the central member (120) of the base (110); the method comprising producing a fiber preform (200) of the platform (100) by three-dimensional weaving in a single piece between multiple layers of weft yarns and multiple layers of weft yarns; The method further comprises densifying the fiber preform (200) with a matrix to form a component having the shape of the platform (100) to be manufactured, The method is characterized in that the fiber preform (200) of the platform (100) comprises a base portion (210) of a fiber reinforcement for forming the base (110) of the platform (100), the base portion (210) of the fiber preform (200) comprising a central member portion (220) and two sacrificial edge portions (231, 232) having a thickness less than the thickness of the central member portion (220), a first plurality of weft yarns being continuous between the central member portion (220) and the sacrificial edge portions (231, 232), the sacrificial edge portions (231, 232) comprising a first plurality of warp yarns woven into the first plurality of weft yarns, and the thickness difference between the sacrificial edge portions (231, 232) and the central member portion (220) being achieved by removing a second plurality of warp yarns located outside the central member portion (220) and not woven with the weft yarns.

2. The manufacturing method according to claim 1, wherein Densification of the fiber preform (200) is carried out by placing the fiber preform (200) in an impregnation chamber (71) of a mold (70) comprising a lower surface, by placing the surface (221) of the fiber preform (200) which is intended to form the first surface (121) of the central member (120) of the base (110) of the platform (100) against the lower surface (221) of the fiber preform (200), the impregnation chamber (71) being closed by a flexible membrane (73) which separates the impregnation chamber (71) from a compaction chamber (72), an impregnation fluid (8) being injected into the impregnation chamber (71), and a compression fluid (9) being injected into the compaction chamber (72) in order to apply a pressure (Q) on the membrane (73).

3. The manufacturing method according to claim 2, wherein The injection of the impregnation fluid (8) starts before the injection of the compression fluid (9).

4. The manufacturing method according to claim 2, wherein, The injection of the compression fluid (9) starts before the injection of the impregnation fluid (8).

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