Technical field of the invention

​The present invention relates to the field of turbomachine parts made of composite material for aircraft. In particular, the invention relates to the design and/or production of said composite parts and to the corresponding tool.

​Technical background

​The turbomachines are additionally equipped with complex shaped parts and at least partially made of composite materials. These composite materials comprise a fibrous reinforcement embedded in a matrix so as to reduce the masses and improve the thermomechanical resistances of these parts, and on the other hand, to improve the performance of the turbomachine. Examples of composite materials are described in documents US-A1-2014/175709, US-B2-8 419 875 and US-A1-2013/099427.

​Generally, the fibrous reinforcement, which is composed of dry fibers, is deposited in a rigid mold and then a die is injected at low pressure into the previously closed mold. The most known method is the RTM technology, the acronym of which means a Resin Transfer molding which makes it possible to produce parts of a very good quality and with good repeatability.​However, this method is not suitable for the very complex shapes that may be, for example, a variable discharge valve conduit that is intended to discharge a portion of the air from the primary flow circulating in the compressor to the secondary flow in order to regulate the flow rate of the compressor.

​The variable unloading valve conduit is made in one piece from composite materials and includes outgoing pipes, elbows, fittings, etc. The difficulty for this kind of part is the placement of fibrous plies or fibrous structures that compose the fibrous reinforcement. The fibrous plies have a certain stiffness due to weaving of the strands or yarns (a strand is composed of several thousands of filaments).​Generally, the fibrous reinforcement that forms the fibrous preform of the unloading valve conduit is pre-shaped on an outer support and is stiffened to facilitate placement in the injection mold and subsequent injection of the die into the injection mold. In this example, the fibrous reinforcement is shaped in the rigid injection mold.

​For this purpose, a tackifier or deionized water is applied to the different plies to temporarily bond the different plies together and to maintain the pleats in the mold, and to permit injection of the die. The water allows breakage of the electrical attraction between the negatively charged chains, as well as breakage of the hydrogen bonds and peptide bonds when the pleats are wetted. These bonds are activated during drying.​With regard to the tackifier, it is a kind of low-bond glue.

​The use of either of these products results in a long enough drying time that impacts the manufacturing time of the final part and a sufficiently low mechanical strength to maintain the folds therebetween, which involves decoction and loss of certain pieces of wrinkles. The time of draping by a manually operator and the size of the parts do not make it possible to properly hold the fibers as a whole.​Also, if the fibers move during the injection of the matrix or its misplaced, the final part will not have the expected mechanical properties. In particular, during the injection of the matrix, the latter binds to the tackifier while the latter is expected to push the tackifier upon injection of the matrix, thereby reducing the mechanical properties of the latter.​Once the work piece has been made, the tackifying resin has not been pushed by the resin, in particular, causes defects in the workpiece such as porosities or delaminations.

​This problem of placing the fibrous reinforcement in the mould, adds the demoulding of the preform to its shaping support, in particular for the unloading valve duct having A complex shape and which does not have clearance angles. The pre-shaped and rigidified preform is impossible to demold if the support is rigid and A single piece.​The manufacturing time of the preform and the mold release difficulties result in a non-negligible loss of time as well as a number of rebuses due to the decoction of the dry fibers of certain fiber pieces.

​In particular, the objective of the present invention is to simplify and facilitate the shaping of a fibrous preform for a composite material part of complex shape so as to optimize matrix injection for densification.

​SUMMARY OF THE INVENTION

​This is achieved in accordance with the invention by means of a tool for pre-forming a fibrous preform comprising:

​a first inflatable membrane for receiving the fibrous preform with a fibrous reinforcement,

​-a second membrane intended to attach via a fastening system to the first membrane and so as to form a sealed internal cavity between the first and the second membrane, and

​A device for evacuating the internal cavity between the first membrane and the second membrane.

​Thus, this solution makes it possible to achieve the above-mentioned objective. In particular, the tooling makes it possible to facilitate the placement of the folds intended to form the fibrous preform on the first membrane (called male), in compacting the preform between the first membrane and the second membrane (called female) using the vacuum​, facilitating demolding of the preformed preform by removing the second female membrane once the void is cut and extracting the first male membrane once the latter is deflated. In particular, the tooling allows for a time gain since the tooling also enables the drying of the plies forming the fibrous preform and its release without the risk of decohesion and deformation of the preformed fibrous preform prior to injection of the matrix.

​In the present invention, we apply the preforming term to shaping and maintaining the shape of the preform before a matrix impregnates the fibers thereof. The pre-formed preform has or approaches the shape that the final part is to have.

​The tooling also includes one or more of the following features, taken alone or in combination:

​The first membrane includes a wall that is closed to form a chamber.

​At least the first membrane is made of an elastic material.

​The elastic material includes a silicone.

​The first membrane and the second membrane are removably secured together.

​The attachment system includes sealing members.

​The vacuuming device comprises a vacuum pump or a venturi effect system or a compressor.

​The invention also relates to a method for preforming a fibrous preform comprising the following steps:

​-providing a preforming tool comprising a first inflatable membrane and a second membrane attached to the first membrane so as to form a sealed internal cavity between the first and second membranes;

​inflation of the first membrane;

​-placing fibrous plies to form a fibrous preform on the first membrane;

​applying the second membrane to the fibrous preform and to the first membrane;

​evacuating the internal cavity between the first and second membranes; and

​Demolding a preformed and dry fibrous preform.

​The method of preforming the fibrous preform also includes one or more of the following features, taken alone or in combination:

​-the step of placing the plies comprises wetting each ply forming the wetted fibrous preform.

​The fibers of the fibrous preform are not impregnated with a resin prior to humidification.

​the step of vacuumizing comprises drying and compacting the wetted fibrous preform.

​Humidification is performed with deionized water and filtered

​the step of vacuuming is performed for a predetermined period of time the step of demoulding the preformed preform comprises removing the second membrane and deflating the first membrane.

​The invention further relates to a method for producing a turbomachine part, comprising the following steps:

​performing a fibrous preform;

​pre-forming the fibrous preform according to a method having any of the above-mentioned characteristics;

​placing the preformed preform in an injection mold;

​injecting a matrix into the preformed preform.

​BRIEF DESCRIPTION OF THE FIGURES

​The invention will be better understood, and other purposes, details, characteristics and advantages thereof will become more clearly apparent upon reading the detailed explanatory description which will follow, of embodiments of the invention given as purely illustrative and non-limiting examples, with reference to the accompanying schematic drawings in which:

​Fig. 1 is a side view of an example variable unloading valve conduit of a turbomachine according to the invention;

​[Fig. 2] Figure 2 represents a top view of an example of an unloading valve conduit according to the invention; and,

​Fig. 3 schematically illustrates an example of tooling for preforming a fibrous preform according to the invention.

​DETAILED Description OF THE INVENTION

​FIG. 1 shows an aircraft turbomachine part made in a single piece of composite material.

​FIGS. 1 and 2 accurately illustrate a variable unloading valve conduit 1 intended to equip the double-flow turbomachines. This variable unloading valve pipe 1 comprises a main pipe 2 for connecting a portion of a primary vein to a portion of a secondary vein of a double-flow turbomachine.​The conduit 1 comprises a variable unloading valve installed (not shown) in the opening 3 of the main pipe 2 opening into the secondary vein. The duct 1 also comprises a secondary pipe 4 having a first end 5 which opens into a pipe for cooling the hot parts of the low-pressure turbine of the turbomachine and a second end 6 which opens into the main pipe 2.​The conduit 1 has a substantially S-shaped and substantially S-shaped shape

​Many curvilinear portions as shown in FIGS. 1 and 2. Of course, the invention can be applied to any complex shaped parts made of composite material and intended to equip a turbomachine.

La pièce de turbomachine (ici le conduit 1 ) en matériau composite est réalisée avec un renfort fibreux (non représenté) et une matrice dans laquelle est noyé le renfort fibreux. Le renfort fibreux comprend plusieurs plis, nappes, couches ou structures de fibres lié(e)s entre eux(elles). Ces plis peuvent être tridimensionnels (tissé 3D), bidimensionnels (tissé 2D) de fils ou de torons qui sont composés chacun de plusieurs filaments ou unidirectionnels.​The fibrous reinforcement is intended to form the fibrous preform which has the general shape of the part to be obtained.

​The wires or strands may be of various natures. In the exemplary embodiment, the wire material may include a carbon, a glass, a polyamide, a kevlar, a ceramic, or a mixture of these materials.

La figure 3 illustre schématiquement un outillage de préformage 10 destiné à mettre en forme, voire de figer la forme de la préforme fibreuse de telle sorte que celle-ci se rapproche autant que possible de la forme de la pièce finale à réaliser et surtout de la maintenir lors de l’imprégnation par une matrice spécifique.

L’outillage de préformage 10 comprend une première membrane 1 1 (dite mâle) qui est destinée à recevoir la préforme fibreuse. La première membrane 1 1 est gonflable (et dégonflable) de manière d’une part, à faciliter la mise en place de la préforme fibreuse et d’autre part à faciliter le démoulage ultérieure de la préforme sans risque d’abimer celle-ci. La première membrane 1 1 est réalisée dans un matériau élastique de manière à permettre son gonflement et son dégonflement.​In this way, the volume of the membrane is increased by means of a fluid. By discharging the fluid, the membrane deflates to recover its initial volume.

Avantageusement, mais non limitativement, le matériau élastique comprend un élastomère tel qu’un silicone. Le silicone est mise en forme et vulcanisé dans les dimensions prédéterminées pour accueillir la préforme fibreuse. En particulier, dans le présent exemple, la première membrane 1 1 comprend une paroi qui présente une forme destinée à donner la forme correspondante à la préforme fibreuse qui sera

​applied thereto, when the first membrane is inflated. The wall may thus have any shape.

La paroi de la première membrane est fermée de manière à former une chambre 12 recevant ici de l’air, et de préférence, sous pression. La paroi de la première membrane 1 1 comprend un orifice d’entrée 13 pour alimenter en air la chambre 12.

L’outillage 10 comprend un système de gonflage 14 (représenté schématiquement) qui est relié d’une part à une source d’air comprimé et d’autre part à une buse 15 qui est destinée à être couplée à l’orifice d’entrée 13 de la première membrane 1 1 . La source d’air comprimé fournit l’air nécessaire pour gonfler la première membrane 1 1.

La paroi de la première membrane 1 1 comprend également un orifice de sortie 16. Ce dernier est équipé d’une portion de paroi mobile de manière à occuper une première position dans laquelle l’orifice de sortie est obturé et une deuxième position dans laquelle l’orifice de sortie est ouvert.Il va de soi que dans la première position, la chambre retient l’air lors de son gonflage (remplissage d’air) ou après gonflage, et que dans la deuxième position, la chambre se vide de son air par l’orifice de sortie 16 pour dégonfler la première membrane 1 1.

L’outillage 10 comprend également une deuxième membrane 18 (dite femelle) qui se fixe de manière étanche sur la première membrane 1 1 . La deuxième membrane 18 coopère avec la première membrane de manière à former une cavité interne 19 étanche entre la première membrane et la deuxième membrane. Pour cela, l’outillage 10 comprend un système de fixation 20 qui est installé au niveau des bordures périphériques 21 , 22 de la première et deuxième membranes 1 1 , 18.

Toutefois, les première et deuxième membranes 1 1 , 18 sont fixées entre elles via le système de fixation 20 de manière amovible et pour faciliter le retrait de la préforme préformée.

Dans le présent exemple, le système de fixation 20 est situé au moins en partie sur la première membrane 1 1 et/ou sur la deuxième membrane 18. Le système de fixation peut comprendre un zip étanche.

Avantageusement, mais non limitativement, le système de fixation 20 comprend des éléments d’étanchéité comprenant un joint d’étanchéité en matériau déformable. Le joint d’étanchéité est rapporté au cours du procédé de fabrication et de la mise en place des membranes mâles et femelles. Ce matériau déformable peut être une bande de plastiline®. Les éléments d’étanchéité permettent de maintenir un espace entre les membranes et ainsi faciliter la formation de la cavité interne.

De manière alternative, le système de fixation 20 comprend des éléments clipsables entre la première et la deuxième membranes. Dans ce cas, l’une des première et deuxième membranes comprend une rainure par exemple et l’autre des première et deuxième membranes comprend une patte en forme de oméga par exemple. La patte et la rainure s’emboîtent de manière à former un joint d’étanchéité.

La deuxième membrane 18 est réalisée dans un matériau élastique également. Comme pour la première membrane, le matériau élastique peut être un silicone.

L’outillage 10 comprend un dispositif de mise sous vide 25 de la cavité interne entre la première membrane et la deuxième membrane. Le dispositif de mise sous vide comprend une pompe à vide ou un compresseur qui est relié à un orifice d’aspiration 26 ménagé ici dans la paroi de la deuxième membrane 18 au moyen d’une canalisation 27.

​Alternatively, the vacuuming device includes a venturi effect system which provides a section difference on the pipeline connected to the suction port to create a pressure difference. The venturi effect system is easy to maintain and economical.

Nous allons maintenant décrire le procédé de préformage de la préforme fibreuse. Le procédé de préformage est réalisé au moyen de l’outillage de préformage tel que décrit ci-dessus. Le procédé comprend une étape de gonflage de la première membrane 1 1 . De l’air est soufflé dans la chambre 12 de la première membrane via le système de gonflage.

Le procédé comprend ensuite une mise en place de la préforme fibreuse avec un renfort fibreux sur la première membrane 1 1 qui est alors gonflée. Pour cela, plusieurs plis fibreux sont disposés un à un sur la paroi externe de la première de manière à

former une épaisseur du renfort fibreux. Ces plis sont également humidifiés de manière à permettre un maintien des fibres entre elles le temps que tous les plis fibreux soient disposés sur la première membrane 1 1 . Nous comprenons que les fibres du renfort fibreux sont non-imprégnées. Le renfort fibreux n’est pas imprégné préalablement par une résine.

​Advantageously, but not limited, water is used to humidify the different folds. The water is filtered and deionized preferably.

​The second membrane 18 is then applied over the obtained wet or wet fibrous preform and the first membrane. The fibrous preform is thus located between the first membrane and the second membrane, and in particular in the internal cavity 19 and sealed from the tool.

Une mise sous vide est réalisée dans la cavité interne 19. Cela est réalisé au moyen du dispositif de mise sous vide précité. La mise sous vide va compacter les fibres entre elles et sécher les fibres des plis fibreux formant la préforme fibreuse humidifiée. L’eau est évacuée grâce à l’abaissement de son point d’ébullition. Tous les plis sont assemblés fermement entre eux à l’issu de cette étape.La mise sous vide est réalisée pendant une durée prédéterminée qui est par exemple de l’ordre de quelques secondes. La mise sous vide est également réalisée à une pression comprise entre 0.005 et 0.100 bar.

La préforme est ensuite démoulée. A cet effet, la deuxième membrane 18 est retirée de la première membrane 1 1 , ainsi que la préforme elle-même, puis la première membrane 1 1 est dégonflée. Nous obtenons une préforme préformée, sèche et compacte.

​From the mold release of the preformed preform, the pre-formed preform can be visually monitored and also in non-destructive testing (eg, via a scan or a tomography device). In the event that a fold would be improperly disposed, the preform may be re-moistened to facilitate movement of the ply in question.

​Once the shape of the preform is fixed (preformed), the dry preform is placed in an injection mold using, for example, RTM technology

​(Mean Resin Transfer Moulding). Its displacement is facilitated by preforming. There is no risk of sliding the fibers therebetween.

​A matrix is injected into the mould so as to carry out impregnation and densification of the fibres of the fibrous preform and thus obtain the part made of composite material, here the duct. The mold includes a first footprint for collecting the pre-formed pre-formed preform. A counter-mold having a second footprint is to form with the first footprint an injection space of the die. The matrix is selected based on the desired application.​The matrix may be an epoxy-based thermosetting resin or a phenolic resin such as polybismaleimides (BMI). Prior to die injection, the injection mold is closed with the counter mold. Other methods such as infusion, RTM light, or Polyflex are, of course, possible.

WE CLAIMS

1 ​Tooling (10) for preforming a fibrous preform, characterised in that it comprises

​A first inflatable membrane (1) for receiving the fibrous preform,

​a second membrane (18) intended to attach via a fastening system (20) to the first membrane (1 1) and so as to form an internal cavity (19) sealed between the first and second membranes, and

​A device (25) for evacuating the internal cavity between the first membrane (1 1) and the second membrane (18).

2 ​Tooling (10) according to the preceding claim, characterized in that the first membrane (1 1) comprises a wall which is closed so as to form a chamber (12).

3. ​Tooling (10) according to one of the preceding claims, characterized in that at least the first membrane (1 1) is made of an elastic material.

4. ​Tooling (10) according to the preceding claim, characterized in that the elastic material comprises a silicone.

5. ​Tooling (10) according to any one of the preceding claims, characterized in that the first membrane (1 1) and the second membrane (18) are removably secured together.

6 ​The lock (10) according to any one of the preceding claims, characterized in that the sealing system (20) comprises sealing elements.

7 ​Tooling (10) according to any one of the preceding claims, characterized in that the vacuuming device (25) comprises a vacuum pump or a venturi effect system or a compressor.

8. ​Method for preforming a fibrous preform, characterised in that it comprises the following steps:

​providing a preforming tool (10) comprising a first inflatable membrane (1 1) and a second membrane (18) fixed on the first membrane (1 1) so as to form an internal cavity (19) sealed between the first and second membranes;

​inflating the first membrane (1 1);

​placing fibrous plies to form a fibrous preform on the first membrane (1 1);

​applying the second membrane (18) to the fibrous preform and on the first membrane (1 1);

​evacuating the inner cavity (19) between the first and second membranes; and

​demolding the preformed and dry fibrous preform.

9. ​The preforming method according to the preceding claim, characterized in that the step of placing the plies comprises wetting each fibrous ply forming the wetted fibrous preform.

10. ​Preforming method according to the preceding claim, characterized in that the fibres of the fibrous preform are not impregnated with a resin prior to humidification.

1 1. ​The preforming method according to claim 9 or 10, characterized in that the step of vacuumizing comprises drying and compacting the wetted fibrous preform.

12. ​The preforming method according to any one of claims 8 to 1, characterized in that the humidification is carried out with deionized water and filtered.

13. ​The preforming method according to any one of claims 8 to 12, characterized in that the step of demoulding the preformed fibrous preform comprises a removal of the second membrane (18) and a deflation of the first membrane (1 1).

14. ​Method for manufacturing a turbomachine part made of composite material comprising the following steps:

​performing a fibrous preform;

​Pre-forming the fibrous preform according to a method according to any one of claims 8 to 13

​placing the dry preformed preform in an injection mold; injecting a matrix into the fibrous preform.