TOOL FOR PREFORMING A FIBER PREFORM AND METHOD FOR PREFORMING A FIBER PREFORM - Patent application

Abstract

The present invention relates to a tool for preforming fiber preforms, comprising: an inflatable first membrane (11) intended to receive the fiber preform; a second membrane (18) intended to be attached to the first membrane (11) via a fastening system (20) so as to form a liquid-tight internal cavity (19) between the first and second membranes; and an evacuation device (25) for forming a vacuum in the internal cavity between the first membrane (11) and the second membrane (18).

Description

[Technical field]

[0001] The present invention relates to the field of composite turbomachinery parts for aircraft, in particular the invention encompasses the design and / or manufacture of these composite parts and the corresponding tools. [Background technology]

[0002] Turbomachines increasingly comprise parts with complex geometries and at least partially made of composite materials, which comprise fiber reinforcements embedded in a matrix so as to reduce the mass and improve the thermomechanical resistance of these parts on the one hand and to improve the performance of the turbomachine on the other hand. Examples of composite materials are described in documents US 2014 / 175709, US 8,419,875 and US 2013 / 099427.

[0003] Generally, the fiber reinforcement, composed of dry fibers, is deposited in a rigid mold, and then the matrix is ​​injected at low pressure into the previously closed mold. The best known method is the RTM technique, which stands for Resin Transfer Molding, which allows to manufacture parts of very high quality and good reproducibility. However, this method is not suitable for very complex geometries, which can be presented, for example, by a variable discharge valve conduit intended to discharge part of the air from the primary flow circulating through the compressor to a secondary flow to regulate the compressor flow rate.

[0004] The variable discharge valve conduit is a single piece of composite material, with the outlet pipe, elbow, fittings, etc. The difficulty with this type of part is the arrangement of the fiber folds or fiber structure that constitute the fiber reinforcement. The fiber folds have a certain rigidity due to the weaving of the yarns or threads (yarns are composed of several thousand filaments). Generally, the fiber reinforcement that forms the fiber preform of the discharge valve conduit is preformed on an external support and reinforced to facilitate its placement in the injection mold and the subsequent injection of the matrix into the injection mold. In this example, the fiber reinforcement is molded in a rigid injection mold.

[0005] For this purpose, a tackifier or deionized water is applied to the different folds to temporarily bind them to each other, hold the folds in the mold and allow the injection of the matrix. The water allows the breaking of the electrical attraction between the negatively charged chains, as well as the breaking of hydrogen bonds and peptide bonds when the folds are wetted. These bonds are activated during the drying process. Tackifiers are a type of weakly adhesive adhesive.

[0006] The use of any of these products results in a rather long drying time, which impacts the production time of the final part, as well as a rather low mechanical strength to hold the folds together, which means delamination and loss of some of the folds. The manual draping time and the size of the part do not allow the fibers to be held correctly as a whole. Also, if the fibers move or are poorly positioned during the injection of the matrix, the final part will not have the expected mechanical properties. Especially in the case of tackifiers, during the injection of the matrix, the matrix bonds to the tackifier, but the tackifier is thought to be pushed by the matrix when injected, which reduces the mechanical properties of this matrix. Once the part is made, the tackifier, especially if it is not pushed by the resin, will cause defects in the part, such as porosity or delamination.

[0007] In addition to this problem of placing the fiber reinforcement in the mold, there is also the problem of demolding the preform from its molded support, especially for the discharge valve conduit, which has a complex shape and does not have any draft. A preform that is preformed and reinforced is impossible to demold if the support is rigid and in one piece. The production time of the preform as well as the difficulty of demolding results in a significant loss of time as well as a certain number of rejects due to the detachment of the dry fiber from certain parts of the fiber. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] US Patent Application Publication No. 2014 / 175709 [Patent Document 2] U.S. Patent No. 8,419,875 [Patent Document 3] US Patent Application Publication No. 2013 / 099427 Summary of the Invention [Problem to be solved by the invention]

[0009] The invention aims in particular to simplify and facilitate the shaping of fibre preforms for composite parts of complex shape so as to optimise the injection of the matrix for its densification. [Means for solving the problem]

[0010] This is according to the invention a tool for preforming fiber preforms, comprising: an inflatable first membrane intended to receive a fiber preform having a fiber reinforcement; a second membrane attached to the first membrane via an attachment system, the second membrane being intended to form a liquid-tight internal cavity between the first membrane and the second membrane; a device for evacuating the internal cavity between the first and second membranes; This is achieved by a tool comprising:

[0011] This solution therefore makes it possible to achieve the above-mentioned objectives. In particular, the tool makes it possible to facilitate the placement of the folds intended to form the fiber preform on a first membrane (called male membrane) and a second membrane (called female membrane) by compressing the preform between them using a vacuum, removing the second female membrane when the vacuum is cut off, and facilitating the demolding of the preformed preform by extracting the first male membrane after it has been shrunk. In particular, the tool makes it possible to save time, since it also allows the drying of the folds forming the fiber preform and their demolding, without the risk of peeling and deformation of the preformed fiber preform before the injection of the matrix.

[0012] In the present invention, the term "preforming" is used to mean the shaping and holding of the shape of a preform before the matrix impregnates its fibers. The preformed preform then has or approaches the shape that the final part is to have.

[0013] The tool may also comprise one or more of the following features, either alone or in combination: The first membrane comprises a wall that is closed to form a chamber. at least the first membrane is made of an elastic material; The elastic material comprises silicone. the first membrane and the second membrane are separably attached to one another; The mounting system comprises a sealing element. The exhaust device comprises a vacuum pump or a Venturi effect system or a compressor.

[0014] The present invention also provides a method for preforming a fiber preform, comprising the steps of: - providing a preform tool comprising an inflatable first membrane and a second membrane attached to the first membrane so as to form a liquid-tight internal cavity between the first membrane and the second membrane; - expanding the first membrane; - arranging on a first membrane fiber folds intended to form a fiber preform; - applying a second film onto the fiber preform and onto the first film; - evacuating an internal cavity between the first membrane and the second membrane; - demolding the preformed and dried fiber preform; The present invention relates to a method comprising:

[0015] The method for preforming a fiber preform may also comprise one or more of the following characteristics, taken alone or in combination: The step of arranging the folds comprises wetting each fold to form a wetting fibre preform. The fibres of the fibre preform are not impregnated with resin before humidification. The evacuation step comprises drying and compacting the humidified fiber preform. - Humidification is performed using deionized and filtered water. The evacuation step is carried out for a predetermined period of time. The step of demolding the preform comprises removing the second film and shrinking the first film.

[0016] The present invention further provides a method for manufacturing a turbomachine component, comprising the steps of: - producing a fibre preform; - preforming a fibre preform according to a method having any of the characteristics described above, - placing the preform in an injection mold; - injecting a matrix into the preform; The present invention relates to a method comprising:

[0017] The invention will be better understood and other objects, details, features and advantages will become more apparent on reading the following detailed description of embodiments of the invention, given purely by way of illustrative and non-limiting example, with reference to the accompanying schematic drawings, in which: [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a side view of an example variable exhaust valve conduit for a turbomachine in accordance with the present invention. [Diagram 2] FIG. 2 is a plan view of an example exhaust valve conduit according to the present invention. [Diagram 3] FIG. 3 shows a schematic example of a tool for preforming a fiber preform according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] FIG. 1 shows an aircraft turbomachinery component made from a single piece of composite material.

[0020] Figures 1 and 2 show precisely a variable discharge valve conduit 1 intended to be fitted to a dual-flow turbomachine. This variable discharge valve conduit 1 comprises a main pipe 2 enabling a part of a primary duct of a dual-flow turbomachine to be connected to a part of a secondary duct. The conduit 1 comprises a variable discharge valve (not shown) installed at an opening 3 of the main pipe 2 opening into the secondary duct. The conduit 1 also comprises a secondary pipe 4 having a first end 5 opening into a pipe enabling cooling of hot parts of the low-pressure turbine of the turbomachine and a second end 6 opening into the main pipe 2. This conduit 1 is substantially S-shaped and has a number of curved sections as shown in Figures 1 and 2. Of course, the invention can be applied to all parts of complex shape made of composite material and intended to be fitted to turbomachines.

[0021] The composite turbomachine part (here the conduit 1) is made by a fiber reinforcement (not shown) and a matrix in which the fiber reinforcement is embedded. The fiber reinforcement comprises a number of folds, wraps, layers or structures of fibers bonded together. These folds can be three-dimensional (3D weave), two-dimensional (2D weave) of threads or strands, each composed of several filaments or unidirectional strands. The fiber reinforcement is intended to form a fiber preform having the general shape of the resulting part.

[0022] The threads or yarns can be of various types, in an exemplary embodiment, the material of the threads can include carbon, glass, polyamide, Kevlar™, ceramic, or a mixture of these materials.

[0023] FIG. 3 shows diagrammatically a preforming tool 10 intended to shape or even freeze the shape of the fiber preform so as to be as close as possible to the shape of the final part to be manufactured and in particular to retain it during impregnation with a particular matrix.

[0024] The preforming tool 10 comprises a first membrane 11 (called male) intended to receive the fiber preform. The first membrane 11 is inflatable (and contractable) so as to facilitate, on the one hand, the placement of the fiber preform and, on the other hand, the subsequent demolding of the preform without the risk of damaging it. The first membrane 11 is made of an elastic material so that it can expand and contract. "Inflatable" means that the volume of the membrane increases with a fluid. When the fluid is evacuated, the membrane contracts back to its original volume.

[0025] Advantageously, but not exclusively, the elastic material comprises an elastomer, such as silicone, which is molded to predetermined dimensions and cured to accommodate the fiber preform. In particular, in this example, the first membrane 11 comprises walls having a shape intended to give the first membrane, when it expands, a shape corresponding to the fiber preform applied thereto. The walls can be of any shape.

[0026] The walls of the first membrane are preferably closed to form a chamber 12 for receiving air under pressure. The walls of the first membrane 11 are provided with an inlet orifice 13 for supplying air to the chamber 12.

[0027] The tool 10 comprises an inflation system 14 (shown diagrammatically) connected on the one hand to a source of compressed air and on the other hand to a nozzle 15 intended to be coupled to an inlet orifice 13 of the first membrane 11. The compressed air source provides the air necessary to inflate the first membrane 11.

[0028] The wall of the first membrane 11 also comprises an outlet orifice 16. The latter comprises a movable wall portion so as to occupy a first position in which the outlet orifice is closed and a second position in which the outlet orifice is open. Needless to say, in the first position the chamber holds air during or after its expansion (filling with air) and in the second position the chamber empties its air through the outlet orifice 16 causing the first membrane 11 to contract.

[0029] The tool 10 also comprises a second (called female) membrane 18 attached in a liquid-tight manner to the first membrane 11. The second membrane 18 cooperates with the first membrane to form a liquid-tight internal cavity 19 between the first and second membranes. For this purpose, the tool 10 comprises a mounting system 20 installed at the level of the peripheral edges 21, 22 of the first and second membranes 11, 18.

[0030] However, the first and second membranes 11, 18 are removably attached to one another via a mounting system 20 to facilitate removal of the preform.

[0031] In this embodiment, the attachment system 20 is at least partially disposed on the first membrane 11 and / or the second membrane 18. The attachment system may comprise a liquid-tight zipper.

[0032] Advantageously, but not exclusively, the mounting system 20 comprises a sealing element comprising a seal of deformable material. The seal is attached during the manufacturing process and the placement of the male and female membranes. This deformable material can be a plastiline® strip. The sealing element makes it possible to maintain the space between the membranes, thus facilitating the formation of the internal cavity.

[0033] Alternatively, the mounting system 20 comprises a clip-on element between the first and second membranes, where one of the first and second membranes comprises, for example, a groove and the other of the first and second membranes comprises, for example, an omega-shaped bracket, where the bracket and the groove fit together to form a seal.

[0034] The second membrane 18 is also made of an elastic material. Like the first membrane, the elastic material may be silicone.

[0035] The tool 10 comprises a device 25 for evacuating the internal cavity between the first and second membranes. The evacuation device here comprises a vacuum pump or compressor connected by a tube 27 to a suction orifice 26 formed in the wall of the second membrane 18.

[0036] Alternatively, the exhaust device comprises a Venturi effect system which provides a cross-sectional difference across a tube connected to the suction orifice to create a pressure difference. Venturi effect systems are easy and economical to maintain.

[0037] A method for preforming a fiber preform will now be described. The preforming method is carried out using the preforming tool described above. The method comprises the step of inflating the first membrane 11. Air is blown into the chamber 12 of the first membrane via an inflation system.

[0038] The method then comprises placing the fiber preform with the fiber reinforcement on the first membrane 11, which is then inflated. For this purpose, various fiber folds are placed one by one on the first outer wall so as to form the thickness of the fiber reinforcement. These folds are also moistened so as to allow the fibers to be held together until all the fiber folds are placed on the first membrane 11. We understand that the fibers of the fiber reinforcement are non-impregnated. The fiber reinforcement is not previously impregnated by resin.

[0039] Advantageously, but not exclusively, water is used to moisten the various folds. The water is preferably filtered and deionized.

[0040] A second membrane 18 is then laid over the resulting wet or humidified fiber preform and the first membrane, so that the fiber preform is located between the first and second membranes, in particular in a liquid-tight cavity 19 inside the tool.

[0041] Evacuation is performed in the internal cavity 19. This is done by the evacuation device mentioned above. The evacuation dries the fibers in the fiber folds which compress the fibers together and form a humidified fiber preform. The water is expelled by lowering its boiling point. At the end of this step, all the folds are firmly bonded to each other. Evacuation is performed for a predefined time, for example a few seconds. The evacuation is also performed at a pressure between 0.005 and 0.100 bar.

[0042] The preform is then demolded. For this purpose, the second film 18 is detached from the first film 11 and from the preform itself, and then the first film 11 is shrunk. A preform is obtained that is preformed, dried and compressed.

[0043] Once the preform is demolded, it can be inspected visually and by non-destructive testing (e.g., via scanning or tomography devices). If a fold is misplaced, the preform can be re-humidified to facilitate displacement of the problem fold.

[0044] Once the preform shape is attached (preformed), the dried preform is placed in an injection mold, for example by using the RTM (Resin Transfer Molding) technique. Its displacement is facilitated thanks to its preforming. There is no risk of the fibers slipping together.

[0045] The matrix is ​​injected into the mould in order to carry out the impregnation and densification of the fibres of the fibre preform and thus obtain a composite part, in this case a conduit. The mould comprises a first recess intended to receive the preform, here in the dry state. A counter mould with a second recess is intended to form together with the first recess an injection space for the matrix. The matrix is ​​selected according to the desired application. The matrix can be an epoxy-based thermosetting resin or a phenolic resin such as polybismaleimide (BMI). Before the matrix injection, the injection mould is closed by a counter mould. Other methods such as injection, RTM light or Polyflex are of course also possible.

Claims

1. A tool (10) for preforming a fiber preform, comprising: an inflatable first membrane (11) intended to receive a fiber preform on its outer surface, the first membrane having an internal volume and being in an inflated and in a deflated state; a first membrane (11) configured such that in an expanded state, an internal volume is increased by a fluid and in a contracted state, said volume is decreased, and in the expanded state, said first membrane (11) is configured to give a predetermined shape to the fiber preform; a second membrane (18) intended to be attached to the first membrane (11) via a mounting system (20) so as to form a liquid-tight internal cavity (19) between the first and second membranes; - a device (25) for evacuating the internal cavity between the first membrane (11) and the second membrane (18), A tool (10), comprising:

2. A tool (10) according to claim 1, characterized in that the first membrane (11) comprises a wall closed to form a chamber (12).

3. Tool (10) according to claim 1 or 2, characterized in that at least the first membrane (11) is made of elastic material.

4. Tool (10) according to any one of claims 1 to 3, characterized in that the elastic material comprises silicone.

5. The tool (10) according to any one of claims 1 to 4, characterized in that the first membrane (11) and the second membrane (18) are separably attached to each other.

6. The tool (10) according to any one of the preceding claims, characterized in that the liquid-tight mounting system (20) comprises a sealing element.

7. Tool (10) according to any one of the preceding claims, characterized in that the exhaust device (25) comprises a vacuum pump or a Venturi effect system or a compressor.

8. The tool of claim 1, wherein the fiber preform has the general shape of the resulting part, the part being a single piece of composite material.

9. The tool of claim 1, wherein the fibrous preform has the general shape of the resulting part, the part being substantially S-shaped.

10. The tool of claim 1, wherein the fiber preform has the general shape of a resulting part, the part including a main tube and a secondary tube, the secondary tube having a first end and a second end opening into the main tube.

11. A tool as described in claim 10, wherein the main pipe has an opening for a variable discharge valve that opens into the secondary duct.

12. 1. A method for preforming a fiber preform, comprising the steps of: - providing a preform tool (10) comprising a first membrane (11) which is inflatable and has an internal volume, and a second membrane (18) attached to the first membrane (11) so as to form a liquid-tight internal cavity (19) between the first membrane and the second membrane; - expanding the first membrane (11); - placing on a first membrane (11) a fibre layer intended to form a fibre preform; - placing a second membrane (18) on the fibre preform and on the first membrane (11); - evacuating the internal cavity (19) between the first and second membranes; - demolding the preformed and dried fibre preform; A method comprising:

13. 13. The preforming method of claim 12, wherein the step of disposing fiber layers includes humidifying each fiber layer to form a humidified fiber preform.

14. 14. A preforming method according to claim 13, characterized in that the fibres of the fibre preform are not impregnated with resin before moistening.

15. 15. A preforming method according to claim 13 or 14, characterized in that the evacuation step comprises drying and compacting the humidified fibre preform.

16. A preforming method according to any one of claims 13 to 14, characterized in that the humidification is carried out with deionized and filtered water.

17. A preforming method according to any one of claims 12 to 14, characterized in that the step for demolding the preformed fibre preform comprises removing the second film (18) and shrinking the first film (11).

18. 1. A method of manufacturing a turbomachinery component made from a composite material, comprising the steps of: - producing a fibre preform, - preforming a fibre preform according to the method of any one of claims 12 to 17, - placing the dried preform in an injection mould; - injecting a matrix into the fiber preform; A method comprising:

19. 20. The method of claim 18, wherein the first membrane has an interior volume that is increased or decreased by the fluid.

20. 20. The method of claim 18, wherein the first membrane is configured to impart a predetermined shape to a fiber preform at least in an expanded state.

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