Method for producing a grid made of composite material

Abstract

The invention relates to a method for manufacturing a grid made of composite material for straightening the airflow of an aircraft turbine engine. The method is based on the use of longitudinal elements (301) having grooves (303) allowing connecting elements (304) to penetrate into said grooves during the manufacture of the grid.

Description

Technical Field

[0001] The present invention relates to the field of the manufacture of mechanical components for aircraft turbojet engine nacelles. In particular, the invention relates to a method for manufacturing a grid made of composite material, for example a thrust reverser grid for such a nacelle. Background Art

[0002] The prior art includes, among others, documents EP-A2-0219889, JP-A-H0716935, WO-A2-2018 / 169453, US-A-4173307 and US-B1-9587582.

[0003] Thrust reversal systems, or thrust reversers, are now widely used on aircraft. Their purpose is to utilize a portion of the airflow ejected from the rear of the turbojet engine nacelle to assist in braking the aircraft when necessary. In particular, when landing an aircraft, the aircraft's braking capability can be significantly improved by redirecting at least a portion of the air ejected by the turbojet engine forward.

[0004] More precisely, the reversers allow redirecting part of the airflow towards the front of the nacelle, which, in addition to braking by the wheels and airbrakes, creates reverse thrust.

[0005] In the case of reversers known as deflection grids (also called thrust reverser grids), the redirection of the airflow is performed by grids associated with the reverser flaps, which at least partially block the airflow duct. A sliding cover also allows these thrust reverser grids to be exposed or covered.

[0006] Figure 1a and Figure 1b An example of an embodiment of a thrust reversing grid 101 is shown. In a known manner, this grid is composed, on the one hand, of spars 102, which perform a supporting function, and, on the other hand, of blades 103, which effectively contribute to the guidance of the airflow. The spars and blades extend longitudinally in two substantially perpendicular directions and define the outline of hollow cells 104, also known as alveoles. Furthermore, the spars and blades are connected at brackets 105, the strength of which largely determines the strength of the entire grid.

[0007] These grids are made of composite materials. Traditionally, spars are made from a material called continuous (or long) fibers. Specifically, spars are formed from overlapping folds of material, while blades are formed from folds appropriately positioned to form the cells of the grid. The material or materials used have specific mechanical properties, suitable for their function, and the whole is connected by a matrix, usually a thermosetting or thermoplastic resin, which binds the different elements together, defines the overall shape of the grid, and ensures the transmission of mechanical forces.

[0008] The applicant has hitherto followed a manufacturing method aimed at producing such a grid simply and economically. Figure 2 This approach is shown where a continuous fiber spar 201 is positioned parallel to other spars (not shown) along a first direction. Connecting elements 202 made of discontinuous fiber composite material are positioned on either side of the spar 201 along its sides 204a and 204b.

[0009] The whole is placed in a hot pressing device (not shown), for example an autoclave or a pressing tool, where it is heated to a temperature and pressure that makes the material flowable, and the connecting elements are compressed by suitable compression devices 203, suitable for forming the future blades of the grid, thus defining the cells of the manufactured grid. By flowable we mean a state in which the material is suitable for flowing. During this operation, a portion of the material constituting the connecting elements migrates towards the spars and connects to the material constituting these spars by chemical and / or mechanical bonding.

[0010] However, this connection is still shallow. This is because the discontinuous fiber composite material migrates in a random manner (especially the fibers themselves). The overlapping surface area (between the material of the connecting element and the sides of the spar) can be very small, resulting in low overall mechanical strength properties.

[0011] On the one hand, the thrust reverser grid has a certain rigidity along its length and, on the other hand, provides good mechanical strength of the blade-spar interface (i.e., of the support), which can be accurately anticipated. In fact, the good mechanical strength of these interfaces determines, on the one hand, the blade's resistance to airflow pressure (especially during the thrust reversal phase) and, on the other hand, the grid's resistance to possible impacts by foreign objects. Summary of the Invention

[0012] The present invention proposes a solution that allows obtaining both a grid that benefits from the stiffness and strength properties of the unidirectional fibers used to realize the spar and a mechanical anchoring of the blade on the spar during manufacturing, thereby strengthening the blade-spar interface.

[0013] To this end, according to a first aspect, the invention relates to a method for producing a grid made of composite material for straightening the airflow of an aircraft turbine, comprising the following steps:

[0014] a) positioning spars extending longitudinally in a first direction in a hot press, the spars being made of a first material comprising fibers extending parallel to the first direction, the spars comprising side surfaces comprising grooves;

[0015] b) positioning a connecting element made of a second heat-compressible material between the sides of the spar in a heat press; and

[0016] c) subjecting the spar and the connecting element to a determined temperature and a determined pressure by means of a thermocompression device, the determined temperature and the determined pressure being suitable for causing a portion of the connecting element to penetrate the groove, thereby ensuring mechanical anchoring of the connecting element in the groove of the spar.

[0017] The method according to the invention may include one or more of the following features, alone or in combination with each other:

[0018] In step b), the connecting element is preferably positioned between the tool cores in a direction substantially perpendicular to the first direction.

[0019] The spar is made of continuous fibers, such as carbon fibers, arranged in a unidirectional purl, a two-dimensional weave, a three-dimensional weave, or a combination of these arrangements.

[0020] The spar is made of discontinuous long fibers.

[0021] The grooves are obtained by manual or automated cutting means, such as a machining machine, a vibrating blade, ultrasound, scissors, electron beam lithography or a punch.

[0022] The recess is a blind hole, a slot or a through hole.

[0023] The second heat-compressible material is made by cutting continuous fiber pleats pre-impregnated with resin into pieces.

[0024] The second heat-compressible material comprises fibers and a thermosetting resin belonging to the class of epoxides, benzoxazines, polyesters or bismaleimides.

[0025] The second heat-compressible material comprises fibers and a thermoplastic resin belonging to the group of polyamide, polypropylene, PEEK, PEKK, PPS, PSA or PA.

[0026] Said hot pressing means comprise compression means and / or moulding means and / or injection means suitable for forming, at the end of step c), a hollow cell delimited by said spar and said connecting element.

[0027] The formation of the hollow cells is achieved by thermoplastic injection of short fibers between tool cores.

[0028] During steps b) and c), a second heat-compressible material of a connection element made of discontinuous fibers is contained in the tool cavity and pushed out of said cavity by a piston, thereby penetrating a portion of said connection element into the groove and ensuring mechanical anchoring of said connection element to said spar.

[0029] According to a second aspect, the invention also relates to a grid made of composite material for straightening the airflow of an aircraft turbine, said grid being produced by the method according to the first aspect and comprising parallel spars formed from a first material comprising fibers extending parallel to the longitudinal extension direction of the spars and connected together by connecting elements formed from a second material and mechanically anchored in grooves in the spars.

[0030] Finally, according to a third aspect, the invention relates to a turbomachine, in particular for an aircraft, comprising a grid according to the second aspect, for example part of a thrust reverser. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The invention will be better understood and other details, features and advantages will become more apparent from the following description given by way of non-limiting example with reference to the accompanying drawings, in which:

[0032] Figure 1a is a schematic diagram of an embodiment of a grid made of a composite material according to the prior art;

[0033] Figure 1b is an enlarged view of the intersection area of ​​the spar and blade of a grid made of composite material according to the prior art;

[0034] Figure 2 is a schematic diagram of an embodiment of a method for manufacturing a grid made of a composite material according to the prior art;

[0035] Figure 3 is a schematic diagram of an embodiment of a method for manufacturing a grid made of a composite material according to the present invention;

[0036] Figure 4 is a schematic diagram of an embodiment of a grid made of a composite material according to the present invention;

[0037] Figure 5 is a perspective view of an embodiment of a spar of a grid made of composite material according to the present invention;

[0038] Figure 6 is a front view of an embodiment of a spar of a grid made of composite material according to the present invention;

[0039] Figure 7 is a schematic diagram of another embodiment of a method for manufacturing a grid made of a composite material according to the present invention; and

[0040] Figure 8 is a diagram of steps according to an embodiment of a method for manufacturing a grid made of a composite material according to the present invention;

[0041] Elements having the same function in different exemplary embodiments are provided with the same reference numerals in the figures. DETAILED DESCRIPTION

[0042] Reference Figure 3 、 Figure 4 and Figure 8 We will now describe an embodiment of a method for manufacturing a grid made of a composite material according to the present invention. The present invention relates particularly to the manufacture of a grid for straightening airflow for aircraft turbines. However, those skilled in the art will appreciate that the method is generally applicable to the manufacture of any grid made of a composite material comprising elements aligned along a first direction and elements aligned along a second direction, which together form a hollow cell.

[0043] A first step 801 comprises positioning a spar 301 extending longitudinally in a first direction d1 in a hot press. In the example shown, a single spar 301 is shown, aligned along a direction d1 parallel to the axis x. The hot press may be, for example, an autoclave in which the spar is placed.

[0044] The spar is made of a first material comprising fibers extending parallel to a first direction. In a non-limiting example, the spar is made of continuous fibers, for example carbon fibers, arranged in a unidirectional pleat, a two-dimensional weave, a three-dimensional weave, or a combination of these arrangements. Advantageously, these arrangements allow a defined mechanical strength to be obtained in one or more desired directions. Furthermore, for a spar made of fibers arranged in a unidirectional pleat, compaction and / or pre-curing of the spar can be performed before manufacturing the grid in order to improve the shape retention of the spar. Thus, in different variations of the method, the spar used can be referred to as raw or partially pre-cured or fully pre-cured. The optimal configuration is raw and partially pre-cured, for example, with a resin polymerization progress of 50% to 60%.

[0045] In a variant, the spar may be made of fibers called discontinuous long fibers, ie the spar is made of corrugations that are cut to a length greater than the length of fibers called short fibers, which are still cut and therefore called discontinuous fibers.

[0046] Finally, the spar includes sides 306a and 306b, which themselves include grooves 303. As will become clearer below, the presence of these grooves allows the second material used to make the grid to diffuse through the spar during the manufacturing process. This is particularly because, in the absence of these grooves, the use of continuous fibers for the spar would provide a barrier to the diffusion of another material into the spars.

[0047] The groove can be obtained by manual or automatic cutting means, for example, a processing machine, a vibrating blade, ultrasound, scissors, electron beam lithography or a punch. In addition, according to different embodiments of the manufacturing method, the groove can be a blind hole, a slot or a through hole.

[0048] Figure 5 and Figure 6 A perspective view and a front view, respectively, of an embodiment of a spar according to the invention are shown. Thus, in the example shown, the groove 303a has the form of a rectangular hole, the groove 303d has the form of a circular hole, the groove 303c opens onto the other face of the spar (not the side), and the groove 303b opens onto the cavity 501, which itself opens onto the other face of the spar.

[0049] Advantageously, the shape and distribution of the grooves can be adapted to optimize the mechanical strength obtained at the level of the supports of the grid at the end of the manufacturing method.

[0050] Step 802 involves positioning a connecting element 304 made of a second heat-compressible material between the sides of the spar in a hot press. In certain embodiments, the connecting element is positioned between the tool cores in a direction substantially perpendicular to the direction d1 of the spar. The second heat-compressible material can be a discontinuous fiber material, for example, a material made by cutting a continuous fiber pleat pre-impregnated with resin into pieces, such as HexMC from the manufacturer Hexcel. This material is particularly interesting for its ability to flow under suitable temperature and pressure conditions.

[0051] In a specific embodiment of the method, the second heat-compressible material comprises fibers and a thermosetting resin from the group consisting of epoxides, benzoxazines, polyesters, or bismaleimides. In another specific embodiment of the method, the second heat-compressible material comprises fibers and a thermoplastic resin from the group consisting of polyamides, polypropylene, PEEK, PEKK, PPS, PSA, or PA. Advantageously, the heat-compressible material used can be selected based on its flowability, its mechanical strength after curing, or any other property suitable for optimizing the performance of the overall grid.

[0052] The final step 803 of the manufacturing method involves subjecting the spar and the connecting element to a defined temperature and a defined pressure, using a hot press, suitable for causing a portion of the connecting element to penetrate the groove, thereby ensuring mechanical anchoring of the connecting element to the spar. In other words, by heating and compressing the connecting element 304, the material constituting it migrates to the sides 306a and 306b of the spar and into the grooves 303 of these sides. Advantageously, the scaffold thus formed provides high mechanical strength. This is particularly advantageous because the manufacturing method allows for fiber continuity between the spar and the connecting element, on the one hand, and between the connecting elements on either side of the spar, on the other.

[0053] Finally, if Figure 4 As shown, the grid 401 made of composite material thus manufactured comprises parallel spars 301 formed of a first material and connected together by connecting elements 402 (blades in the case of a thrust reverser grid) formed of a second material and mechanically anchored in grooves in the spars.

[0054] Furthermore, in different embodiments of the manufacturing method, the hot pressing means may comprise compression means and / or moulding means and / or injection means suitable for forming, at the end of the manufacturing method, the hollow cells of the grid delimited by the spars and the connecting elements.

[0055] For example, in reference Figure 3 In a first embodiment, tool cores 305 are located on either side of the connecting element, and the connecting element is compressed under the action of jacks which push some of these cores in the direction of the spar.

[0056] In another embodiment, the tool core may have the ability to expand (ie, swell) under the influence of temperature or have another tool inserted therein in order to compress the connecting elements together.

[0057] exist Figure 7 In another embodiment shown, the spar is arranged between the cores 701 of the tool, and the second material of the connecting element is directly injected in a state that allows it to flow between these cores in a direction transverse to the spar. Alternatively, the injection step can be a thermoplastic injection of short fibers between the tool cores arranged to form a unit. Advantageously, the fibers contained in the second material are thus aligned during manufacture. Finally, in a complementary manner, the second material made of discontinuous fibers can be contained in a cavity of the tool and pushed out of the cavity by the action of a piston, thereby circulating between the cores of the tool.

Claims

1. A method for producing a grid (401) made of composite material for straightening the airflow of an aircraft turbine, the method comprising the following steps: a) positioning spars (301) extending longitudinally in a first direction in a hot press, the spars being made of a first material comprising fibers extending parallel to the first direction, the spars comprising side surfaces comprising grooves; b) positioning a connecting element made of a second heat-compressible material between the sides of the spar in a heat-compressing apparatus; as well as c) subjecting the spar and the connecting element to a determined temperature and a determined pressure by means of a thermocompression device, said determined temperature and determined pressure being suitable for causing a portion of the connecting element to penetrate the groove, thereby ensuring mechanical anchoring of the connecting element in the groove of the spar.

2. The method according to claim 1, wherein In step b), the connecting element is positioned between the tool cores in a direction substantially perpendicular to the first direction.

3. The method according to claim 1 or 2, wherein The spar is made of continuous fibers arranged in a unidirectional corrugation, a two-dimensional weave, a three-dimensional weave, or a combination of these arrangements.

4. The method according to claim 1 or 2, wherein: The spar is made of discontinuous long fibers.

5. The method according to claim 1 or 2, wherein: The grooves are obtained by manual or automatic cutting means.

6. The method according to claim 1 or 2, wherein: The recess is a blind hole, a slot or a through hole.

7. The method according to claim 1 or 2, wherein: The second heat-compressible material is made by cutting continuous fiber pleats pre-impregnated with resin into pieces.

8. The method according to claim 1 or 2, wherein: The second heat-compressible material comprises fibers and a thermosetting resin belonging to the class of epoxides, benzoxazines, polyesters or bismaleimides.

9. The method according to claim 1 or 2, wherein: The second heat-compressible material comprises fibers and a thermoplastic resin belonging to the group of polyamide, polypropylene, PEEK, PEKK, PPS, PSA or PA.

10. The method according to claim 1 or 2, wherein: Said hot pressing means comprise compression means and / or moulding means and / or injection means suitable for forming, at the end of step c), a hollow cell delimited by said spar and said connecting element.

11. The method according to claim 10, wherein: The formation of the hollow cells is achieved by thermoplastic injection of short fibers between tool cores.

12. The method according to claim 10, wherein: During steps b) and c), a second heat-compressible material of a connection element made of discontinuous fibers is contained in the tool cavity and pushed out of said cavity by a piston, thereby penetrating a portion of said connection element into the groove and ensuring mechanical anchoring of said connection element to said spar.

13. The method according to claim 3, wherein: The continuous fibers are carbon fibers.

14. The method according to claim 1 or 2, wherein: The grooves are obtained by a machining machine, a vibrating blade, ultrasound, scissors, electron beam lithography or a punch.

15. A grid (401) made of composite material for straightening the airflow of an aircraft turbine, said grid being made by a method according to any one of claims 1 to 14 and comprising parallel spars (301) formed from a first material comprising fibers extending parallel to the longitudinal extension direction of the spars and connected together by connecting elements formed from a second material and mechanically anchored in grooves of the spars.

16. A turbine comprising a grid according to claim 15.

17. The turbine according to claim 16, wherein: The grid is part of the thrust reverser.

18. The turbine according to claim 16, wherein: The turbine is a turbine for an aircraft.

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