Method for manufacturing a structure made of fibrous composite material comprising a prefixing element

Abstract

The invention relates to a method for manufacturing a structure (1) made of fibrous composite material comprising at least one prefixing element (2), the method comprising the following steps: - producing a fibrous mat (3) comprising a stack of multiple fabric layers (4) which are pre-impregnated with a polymer matrix, each fabric layer (4) being formed of interwoven fibers (5), - moving a fiber portion (12) of at least one of the fibers (5) of at least one fabric layer (4) in order to form an opening (6) through the fibrous mat (3), - positioning the prefixing element (2) at least partially in the opening (6), and - polymerizing the fibrous mat (3) in order to obtain the structure (1) made of fibrous composite material.

Description

Method for manufacturing a structure made of fibrous composite material comprising a pre-fixing element Technical Field [OOOlJThe present invention relates to a method of manufacturing a structure in fibrous composite material comprising a pre-fixing element for a turbomachine turbine, which may be a turbine or part of a turbine for example. Previous technique

[0002] To manufacture structures or parts in fibrous composite material in the field of aeronautics, it is known to use a molding process involving a thermocompression step of fibrous materials pre-impregnated with thermosetting resin. [0003JII is also known to use pre-impregnated fibrous materials based on continuous fibers in the form of unidirectional fiber sheets or fabrics.

[0004] During the manufacturing of the fiber composite part, after the polymerization step of the pre-impregnated fiber material, it is sometimes necessary to machine the part to incorporate a pre-fixing element, such as an insert, in order to later provide a fastening element within the structure. The insert prevents the fastening element from being in direct contact with the fiber composite structure.

[0005] In the case of a monolithic pre-impregnated fiber composite part, it is necessary to drill a hole in the part. The insert is then placed in the hole by crimping and then bonding to prevent any part of the fastener from coming into direct contact with the composite and facilitating inter-ply or inter-laminar decohesion of the latter.

[0006] The insert, which has a cup-like shape, is placed in the hole by mechanical deformation of the hole and / or by gluing so that the insert is held within the thickness of the part.

[0007] However, this process requires machining the part after polymerization, which leads to fiber breakage and a lack of continuity in the mechanical stresses in the area surrounding the insert. Furthermore, the insert may not be properly fixed to the composite and may rotate relative to it.

[0008] This process also requires additional operations during the manufacture of the part such as machining, gluing and insert placement, with gluing being particularly time-consuming. Description of the invention

[0009] The invention therefore aims to resolve at least in part these drawbacks by proposing a manufacturing process for a structure made of fibrous composite material that avoids discontinuity of fibers and mechanical stresses around the pre-fixing element.

[0010] The invention relates to a method for manufacturing a structure made of fibrous composite material comprising at least one pre-fixing element. The method comprises the following steps: - production of a fibrous mattress comprising a stack of several layers of fabric pre-impregnated with a polymer matrix, each layer of fabric being formed of interwoven fibers, - displacement of a portion of fiber from at least one of the fibers in at least one layer of tissue to form an opening through the fibrous mat, - positioning of the prefixing element at least partially within the opening, and polymerization of the fibrous mattress to obtain the structure in fibrous composite material.[001 IJThe invention thus provides a method for manufacturing a structure in fibrous composite material making it possible to avoid a discontinuity of the fibers and mechanical stresses around the prefixing element.

[0012] The polymerization of the polymer matrix allows the pre-impregnated fibrous composite to consolidate, which hardens and traps the prefixing element mechanically and also by bonding, as the polymer matrix contained in the composite also allows the bonding of the prefixing element.

[0013] The fibers are not broken, which allows for better transmission of forces around the prefixing element and ensures very good mechanical strength of the prefixing element.

[0014] The manufacturing process is also faster because it no longer requires additional operations such as machining, gluing, and insert crimping. This results in cost savings.

[0015] Preferably, the steps of the process are carried out successively.

[0016] Unlike known insert assembly processes by machining, the insert is placed on the fibrous mat before the polymerization step.

[0017] In some embodiments, the fibrous mattress is made in a mold, the step of moving the portion of fiber and the step of positioning the prefixing element being carried out in the mold.

[0018] In some embodiments, the process includes a step of positioning the mold in an autoclave and a step of demolding the structure after the polymerization of the fibrous mat.

[0019] In some embodiments, during the fiber portion displacement step, the fiber portion is moved from an initial position in which the fiber portion is substantially straight to an offset position in which the fiber portion is curved and positioned around the opening.

[0020] In some embodiments, the opening is made using a tool configured to spread the portion of fiber apart in the first direction and in the second direction.

[0021] In some embodiments, the prefixing element comprises an internal part positioned at least partly inside the opening and an external part bearing on an external face of the fibrous mattress when the prefixing element is positioned in the opening.

[0022] In some embodiments, the polymer matrix is ​​based on epoxy resin or BMI resin.

[0023] In some embodiments, polymerization is carried out at a temperature above 170°C and below 200°C, under a pressure above 6 bars and below 8 bars, for a duration above 1h30 and below 4h.

[0024] The invention also relates to a structure made of fibrous composite material obtained using the manufacturing process as defined above. The prefixing element comprises an external surface bonded to the fibrous mattress by the polymer matrix.

[0025] In some embodiments, the structure includes at least one fiber having a portion of fiber which is continuous in a peripheral area surrounding the prefixing element, the portion of fiber being curved.

[0026] The aforementioned features and advantages, as well as others, will become apparent upon reading the detailed description that follows. This detailed description refers to the attached drawings. Brief description of the drawings

[0027] The attached drawings are schematic and are primarily intended to illustrate the principles of the presentation.

[0028] In these drawings, from one figure to another, identical elements (or parts of elements) are identified by the same reference symbols.

[0029] [Fig. 1] Figure 1 schematically represents a fibrous mattress comprising a stack of several layers of fabric pre-impregnated with resin;

[0030] [Fig. 2] Figure 2 schematically represents a fibrous mattress including an opening;

[0031] [Fig. 3] Figure 3 schematically represents a prefixing element positioned in the opening of the fibrous mattress;

[0032] [Fig. 4] Figure 4 schematically represents a view of the prefixing element positioned in the opening according to a section AA of the fibrous mattress of figure 3;

[0033] [Fig. 5] Figure 5 schematically represents a structure in fibrous composite material obtained after a polymerization step of the fibrous mat;

[0034] [Fig. 6] Figure 6 schematically represents a view of the structure in fibrous composite material according to a section AA of the structure of figure 5. Description of the implementation methods

[0035] To make the explanation more concrete, an example of a manufacturing process for a structure made of fibrous composite material is described in detail below, with reference to the accompanying drawings. It should be noted that the invention is not limited to this example.

[0036] The invention relates to a method for manufacturing a structure 1 in fibrous composite material comprising a step of producing a fibrous mattress 3 as shown in Figure 1.

[0037] Structure 1 can be a turbomachine flap, an air guide duct including VBV (Variable Bleed Valves) type discharge valves, for example.

[0038] The fibrous mattress 3 can be obtained after a draping operation of fabric folds, for example.

[0039] The fibrous mattress 3 comprises a stack of several plies or layers of fabric 4 pre-impregnated with a polymer matrix. Each layer of fabric 4 is formed of interwoven or crossed fibers 5.

[0040] Alternatively, the fibrous mattress 3 can be made of pieces of fabric made of pre-impregnated fibers with a polymer matrix arranged parallel to an X, Y plane of the mattress. The pieces of fabric are stacked on top of each other and are arranged parallel to the X, Y plane.

[0041] The polymer matrix can be a thermosetting resin, such as epoxy or BMI (polybismaleimide), or a thermoplastic resin like PEI, PAEK, PA, etc., or a ceramic precursor. The fibers can be carbon fibers, glass fibers, Kevlar fibers, ceramic fibers such as SiC (silicon carbide) or alumina oxides, or others.

[0042] The 5 fibers can be so-called continuous fibers, that is to say strands made up of sets of parallel or twisted continuous filaments.

[0043] Fabrics can be based on a single type of fiber or a combination of fibers interwoven in patterns such as plain weave, twill, satin or braiding, or stacked in different directions and sewn together (NCF).

[0044] The 5 fibers can be crossed and interlaced along a first direction X and a second direction Y, perpendicular to the first direction X, and preferably in substantially identical proportions along each of the two directions X and Y.

[0045] The fibers 5 inside the pieces or layers of tissue 4 are arranged substantially parallel to the X, Y plane.

[0046] According to another variant, the fibrous mattress can be a combination of pieces of pre-impregnated fiber fabric and pieces of pre-impregnated unidirectional fiber web meeting the same geometric characteristics, the fibers being of the same nature or of different nature as described previously.

[0047] For example, fabrics may include low-weave textures such as 2x2 twill, 3x1 twill, 5 or 8 satin.

[0048] Figure 1 shows an example of a fibrous mattress 3 comprising a stack with superposition of three layers of fabric 4 oriented in the same direction in the X, Y plane.

[0049] Alternatively (not shown), the fibrous mattress 3 may comprise a stack with overlapping of at least two layers of fabric in the form of fabric pieces, oriented in different directions in the X, Y plane. The fabric pieces partially overlap each other. The fabric pieces have a polygonal shape and preferably quadrilateral.

[0050] For example, the fabric layers 4 have a dry fabric surface mass of between 0.160 kg / m 2 and 0.6 kg / m 2 . The fabric layers 4 are impregnated with thermosetting or thermoplastic resin at a resin / fiber volume ratio of between 0.35 and 0.55, for example.

[0051] The manufacturing process of the structure 1 in fibrous composite material may optionally include a step of cutting at least one side of the fibrous mattress or blank in the fibrous mattress 3.

[0052] The manufacturing process includes, as an alternative, a step of stacking several sides of fibrous mattresses or blanks.

[0053] The manufacturing process includes, as an alternative, a preforming step of the sides of fibrous mattress 3 or of stacking the sides of fibrous mattress 3.

[0054] The manufacturing process then includes a step of positioning the pre-formed or non-pre-formed fibrous mattress 3 in a mold.

[0055] The manufacturing process then includes a step of displacing a portion of fiber 12 from at least one fiber 5 from at least one layer of fabric 4 to form an opening 6 through the fibrous mat 3, as illustrated in Figure 2.

[0056] Preferably, several portions of fiber 12 are displaced. In other words, a portion of the fibers 5 is moved aside or shifted locally.

[0057] In each layer of tissue 4, one or more portions of fiber 12 can be displaced from their initial position to form the opening 6. Portions of fiber 12 may not be displaced if they are positioned at the location of the opening 6.

[0058] According to one variant, in each layer of tissue 4, several portions of fiber 12 are displaced from their initial position to form the opening 6.

[0059] For example, a fiber 5 extending substantially straight along the first X direction initially comprises a straight fiber portion 12. This straight fiber portion 12 is locally displaced along the second Y direction from an initial position where it extends straight to an offset position where it is curved, forming a curved fiber portion 12', which is no longer straight. The fiber portions 12 are displaced in such a way as to maintain their integrity and avoid damage or severance.

[0060] The opening 6 is made using a tool configured to spread the fibers 5 along the first direction X and along the second direction Y.

[0061] The tool may be in the form of a clamp comprising two arms movable relative to each other around an axis or a rod which may have a conical end.

[0062] Because the matrix is ​​viscous, the fibers 5 remain in a staggered position after their displacement.

[0063] The opening 6 extends along a third direction Z, perpendicular to the X, Y plane.

[0064] The opening 6 has a dimension of at least 2 mm along the first direction X and a dimension of at least 2 mm along the second direction Y.

[0065] Preferably, opening 6 has a circular cross-section. Alternatively, opening 6 may have an oval cross-section.

[0066] The manufacturing process then includes a step of positioning at least a portion of the prefixing element 2 in the opening 6, as illustrated in Figures 3 and 4.

[0067] The prefixation element 2 is introduced into the opening 6 along the third direction Z.

[0068] The step of moving a portion of fiber 12 and the step of positioning the prefixing element 2 are carried out in the mold.

[0069] The prefixing element 2 is fixed to the fibrous mattress 3 in order to subsequently receive a fixing element and to prevent the fixing element from being in direct contact with the fibrous mattress 3.

[0070] As illustrated in Figure 4, the prefixing element 2 comprises an inner portion 7 positioned inside the opening 6 and an outer portion 8 bearing against an outer face 9 of the fibrous mattress 3. The outer portion 8 extends circumferentially from the inner portion 7 in the X, Y plane. The outer portion 8 is flared. The outer portion 8 allows the prefixing element 2 to be self-supporting on the fibrous mattress 3.

[0071] The inner part 7 and the outer part 8 have a circular cross-section.

[0072] Preferably, the prefixing element 2 is a cup-shaped metal insert.

[0073] The internal part 7 includes an internal opening 13 to allow the passage of the fastener later. The fastener can be a screw or a rivet.

[0074] The internal part 7 can be fully or partially inserted into the opening 6.

[0075] The prefixing element 2 comprises an external surface 10 which is surrounded by several curved fiber portions 12' which are intact and uncut after the positioning of the prefixing element 2.

[0076] In Figure 3, several fibers 5 can be observed that have been displaced and that bypass the prefixation element 2. The fibers 5 are whole in a peripheral zone 11 surrounding the prefixation element 2 and adjacent to the prefixation element 2. The fibers 5 are continuous in the peripheral zone 11.

[0077] The manufacturing process then includes a step of positioning the mold in an autoclave or oven.

[0078] The mold is closed. The manufacturing process then includes a thermocompression step of the fibrous mattress 3 to form a part comprising a structure 1 made of fibrous composite material based on woven fibers.

[0079] Compression and thermal cycling are applied to the material to compact and flow it, along the first and second X and Y directions to fill the volume of the mold cavity.

[0080] Compression can be uniaxial or multiaxial depending on the mold closing kinematics.

[0081] A thermal polymerization cycle is carried out when the resin is a thermosetting resin or a solidification cycle when the resin is a thermoplastic resin.

[0082] For example, when the polymer matrix is ​​based on epoxy resin, polymerization in the autoclave or oven is carried out under a pressure of 7 bar, with a 2-hour rest at a temperature of 180°C.

[0083] Alternatively, when the fibrous mattress 3 is placed in a vacuum bag, the minimum vacuum is -0.2 bar.

[0084] In another example, when the polymer matrix is ​​based on BMI resin, polymerization in the autoclave or oven is carried out under a pressure of 7 bar, with a 3-hour holding period at a temperature of 190°C. A post-curing step is carried out at 225°C for 8 hours.

[0085] Alternatively, when the fibrous mattress 3 is placed in a vacuum bag, the minimum vacuum is -0.2 bar.

[0086] The manufacturing process then includes a demolding step of structure 1 made of fibrous composite material.

[0087] We obtain a structure 1 in fibrous composite material as illustrated in figures 5 and 6.

[0088] Alternatively, the manufacturing process then includes a deburring and / or machining step of the structure 1 made of fibrous composite material.

[0089] Alternatively, the thermocompression step can be carried out by press molding, preferably by applying pressures of at least 80 to 100 bars on the material.

[0090] The prefixing element 2 is thus positioned partially inside the orifice 6 of the structure 1, and securely fixed to the structure 1. The prefixing element 2 comprises an external surface 10 bonded to the fibrous mat 3 by the polymer matrix, which is in particular a resin.

[0091] The prefixation element 2 passes through the three tissue layers 4 without damaging or severing the fibers 5. The fibers 5 are intact and unsevered in the peripheral zone 11 surrounding the prefixation element 2. Some fibers 5 include a curved fiber portion 12', which is not straight and which flows around the prefixation element 2. The curved fiber portions 12' are adjacent to the prefixation element 2. The fibers 5 conform to the shape of the prefixation element 2.

[0092] The peripheral zone 11 includes a percentage of curved fibers 12' of at least 5%, for example.

[0093] The displacement of the portion of fiber 12 is at least 5% relative to its initial position in a given direction.

[0094] Although the present invention has been described with reference to specific embodiments, it is evident that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

Claims

Demands

1. A method for manufacturing a structure (1) made of fibrous composite material comprising at least one pre-fixing element (2), the method comprising the following steps: - production of a fibrous mattress (3) comprising a stack of several layers of fabric (4) pre-impregnated with a polymer matrix, each layer of fabric (4) being formed of interwoven fibers (5), - displacement of a portion of fiber (12) from at least one of the fibers (5) of at least one layer of tissue (4) to form an opening (6) through the fibrous mat (3), - positioning of the prefixing element (2) at least partially within the opening (6), and - polymerization of the fibrous mattress (3) to obtain the structure (1) in fibrous composite material.

2. A method according to claim 1, wherein the fibrous mat (3) is made in a mold, the step of moving the portion of fiber (12) and the step of positioning the prefixing element (2) being carried out in the mold.

3. Method according to claim 2, comprising a step of positioning the mold in an autoclave and a step of demolding the structure (1) after the polymerization of the fibrous mat (3).

4. A method according to any one of claims 1 to 3, wherein during the step of moving the portion of fiber (12), the portion of fiber (12) is moved from an initial position in which the portion of fiber (12) is substantially straight to an offset position in which the portion of fiber (12) is curved and positioned around the opening (6).

5. A method according to any one of claims 1 to 4, wherein the opening (6) is made by means of a tool configured to move the portion of fiber (12) apart in the first direction (X) and in the second direction (Y).

6. A method according to any one of claims 1 to 5, wherein the prefixing element (2) comprises an internal part (7) positioned at least partly inside the opening (6) and an external part (8) bearing on an external face (9) of the fibrous mat (3) when the prefixing element (2) is positioned in the opening (6).

7. A method according to any one of claims 1 to 6, wherein the polymer matrix is ​​based on epoxy resin or BMI resin.

8. A process according to claim 7, wherein the polymerization is carried out at a temperature above 170°C and below 200°C, under a pressure above 6 bars and below 8 bars, for a duration above 1h30 and below 4h.

9. Structure (1) in fibrous composite material obtained by means of the manufacturing process as defined according to any one of claims 1 to 8, the prefixing element (2) comprising an external surface (10) bonded to the fibrous mat (3) by the polymer matrix.

10. Structure (1) according to claim 9, comprising at least one fiber (5) having a portion of fiber (12) which is continuous in a peripheral area (11) surrounding the prefixing element (2), the portion of fiber (12) being curved.

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