MOLDING DEVICE FOR THE MANUFACTURE OF A COMPOSITE PART

Abstract

The invention relates to a molding device (100) configured to form a part, in particular a turbomachine part, the part being formed at least from a preform (210), the molding device comprising: - a mold (110) made of a first material, defining an internal cavity (112) delimited by an internal surface (114) and intended to receive an assembly (230) formed from the preform (210) and a rigid element (220) covering at least partially the preform, and - a flexible element (120) made of a second material, the flexible element (120) covering at least a portion (116) of the internal cavity so as to be opposite the rigid element during molding, and the second material having a coefficient of thermal expansion greater than the coefficient of thermal expansion of the first material. Figure for the abstract: Figure 1

Description

Title of the invention: MOLDING DEVICE FOR THE MANUFACTURE OF A COMPOSITE PART Technical field of the invention

[0001] The technical field of the invention is that of the manufacture of aircraft turbomachine parts in composite material, in particular by resin injection molding of a part in composite material.

[0002] The present invention relates to a molding device for the manufacture of composite parts, in particular parts for an aircraft turbomachine. Technical background

[0003] The use of organic matrix composite (OMC) materials is advantageous in the aeronautical industry in particular because these materials have interesting mechanical performance for relatively low masses.

[0004] A process for manufacturing a composite part for the aeronautical industry from resin-impregnated fibers (or matrix), which is well known to those skilled in the art, is the RTM molding process, according to the English acronym for "Resin Transfer Molding". Such a process is used, for example, to manufacture fan blades or housings and comprises several successive steps.

[0005] First, a three-dimensional preform roughing is created by weaving fibers. Then, this roughing is generally cut to obtain a preform that substantially resembles the shape of the part to be produced, for example, a blade. This preform is then placed in a mold, which is closed. Next, resin is injected in liquid form into the mold while maintaining pressure on the injected resin as the part undergoes polymerization by heating.

[0006] The resins used are very fluid resins that are able to penetrate the preform fibers well, even when injected under reduced pressure. During polymerization, under the effect of heat, the injected resin successively passes from a liquid state to a gelled state and finally to a solid state.

[0007] Certain parts may require the addition of a rigid element to the composite preform. In this case, this rigid element is assembled to the preform during a resin co-injection step. Prior to this, the rigid element is positioned on the preform in the mold before the resin injection. The rigid element may be made of a metallic, thermoplastic, or other material. For example, the rigid element is a titanium leading edge guard for a fan blade.

[0008] After the manufacture of the final part, the rigid element has an external surface visible. This surface must remain clean to avoid reworking it in a subsequent step after the co-injection step.

[0009] However, the inventors observed that during the resin co-injection step, the rigid element can be coated with a thin film of resin, also known as "resin over-injection." This resin over-injection must be removed during such a post-polymerization step of the part. This necessitates working with a number of tools that risk damaging the part, particularly the aerodynamic surface of the leading edge of a fan blade. Indeed, reworking the external surfaces of a part can lead to its degradation, such that the result obtained is detrimental to the main functions of the part and / or gives an undesirable, even worrying, cosmetic appearance for the customer.

[0010] Indeed, during the molding process, the external surface of the rigid element, which is assembled with the composite preform by co-injection, is in direct contact with the co-injection mold. The mold is also made of metallic material, generally steel. Since curing the resin requires a temperature increase, it is not possible to ensure perfect metal-to-metal contact that would prevent the resin from seeping between the co-injected rigid element and the mold.

[0011] In the case of a steel-to-steel contact of the same type, theoretically, it is possible to obtain this perfect contact, even during a temperature increase, because the rigid element and the mold have the same coefficient of thermal expansion. However, the inherent variability in the production of rigid elements makes it impossible to guarantee that the geometry of the co-injected rigid element will always be identical and allow for perfect contact within the mold cavity defined by the inner surface of the mold.

[0012] Furthermore, in the case of two different materials, it becomes theoretically impossible to obtain perfect contact between the rigid element and the mold, due to the fact that the two materials have two different coefficients of thermal expansion. For example, it is impossible to ensure perfect contact between titanium and steel on a complex geometry over a temperature range compatible with the manufacturing process of composite material parts such as blades with a titanium leading edge.

[0013] Consequently, it is necessary to propose a solution that avoids resin infiltration over a reliably co-injected rigid element.

[0014] The invention aims to provide a solution to remedy at least some of these drawbacks.

[0015] In particular, the present invention provides a molding device for overcoming the problem of over-injection by the resin / matrix of a rigid part or other part whose external surface must remain free of any trace of resin in order to avoid recurrence. Summary of the invention

[0016] The invention relates to a molding device configured to form a part, in particular a turbomachine part, the part being formed at least from a preform, the molding device comprising: - a mold made of a first material, defining an internal cavity delimited by an internal surface and intended to receive an assembly consisting of the preform and a rigid element covering at least partially the preform, and - a flexible element made of a second material, the flexible element covering at least a portion of the inner cavity so as to be opposite the rigid element during molding and the second material having a coefficient of thermal expansion greater than the coefficient of thermal expansion of the first material.

[0017] The invention thus offers a solution to the problems mentioned above by proposing a molding device that allows the over-injection of resin onto the rigid element during its co-injection, in particular for an RTM molding manufacturing process.

[0018] Indeed, the flexible element of the molding device being deformable and expanding more than the mold material allows for perfect contact at the external surface of the rigid element to be protected from over-injection.

[0019] The molding device according to the invention may comprise one or more of the following features, taken individually or in combination with each other in all technically possible combinations: - the flexible element is dimensioned so that it expands to come into contact with the rigid element during molding; - the flexible element has a thickness at room temperature between 3 mm and 5 mm, the thickness being defined along a direction normal to the inner surface delimiting the inner cavity; - the coefficient of thermal expansion of the first material is less than 50x106 K 1 - the first material is steel or titanium or aluminum; - the coefficient of thermal expansion of the second material is between 100x106 K1 and 500x106 K1; - the second material is inert; - the second material is an elastomer, preferably silicone; - the molding device further comprises pins having a first end bearing on the inner surface of the inner cavity and a second end opposite the first end and intended to be in contact with the element rigid when the assembly intended to form the part is installed in the inner cavity of the mold; - the pawns are made from the first material; - each pin has a height H, defined in the direction normal to the inner surface delimiting the inner cavity, equal to the thickness of the flexible element during the molding called the expanded flexible element; - each piece has a pyramidal shape with a base in contact with the inner surface.

[0020] The invention also relates to an installation for manufacturing a composite part comprising a molding device according to the invention and as described above. Brief description of the figures

[0021] The invention will be better understood and other details, features and advantages of the present invention will become more apparent upon reading the following detailed description, which includes embodiments given by way of illustration with reference to the accompanying figures and presented as non-limiting examples, which may serve to complete the understanding of the present invention and the explanation of its implementation and, where appropriate, contribute to its definition, on which: - [Fig.1] is an enlarged schematic cross-sectional view of a molding device according to the invention at room temperature; - [Fig.2] is an enlarged schematic cross-sectional view of the molding device of [Fig.1] at the consolidation temperature; - [Fig.3] is a schematic cross-sectional view of another molding device intended for manufacturing complex parts according to the invention; - [Fig.4] is an enlarged view of the interface of the rigid element with the mold of the molding device of [Fig.3] at room temperature; - [Fig. 5] is the enlarged view of [Fig. 4] when the molding device is at consolidation temperature; and - [Fig.6] is a schematic view of an installation according to the invention for manufacturing by molding a part in composite material comprising a molding device according to the invention.

[0022] Elements having the same functions in the different implementations have the same references in the figures. Detailed description of the invention

[0023] Fig. 1 schematically illustrates a cross-sectional view of a molding device 100 for a manufacturing installation for molding parts made of composite material. Such an installation will be described later.

[0024] The molding device 100 is configured to form a part, in particular a turbomachine part.

[0025] The part is formed from a preform 210 and a rigid element 220 that at least partially covers the preform. For example, and preferably, the part to be manufactured is a turbomachine fan blade, particularly for an aircraft, having a reinforced leading edge. For example, the preform is made of composite material while the rigid element for reinforcing the leading edge is made of steel or titanium. However, the molding device according to the invention is suitable for manufacturing any part made of composite material, particularly for an aircraft engine, such as, for example, casings.

[0026] The molding device 100 comprises a mold 110 made of a first material. Preferably, the first material is steel.

[0027] The mold 110 comprises two parts 110a and 110b forming a mold and a counter-mold, defining a closed inner cavity 112 delimited by an inner surface 114. One of the two parts 110b is movable relative to the other 110a, which is fixed to close the cavity. The movable part 110b is also called a punch, while the fixed part 110a is also called a die. The inner surface 114 of the inner cavity 112 is formed by a first surface 114a of the die 110a of the mold and a second surface 114b of the punch 110b of the mold.

[0028] In Figures 1 and 2, the first surface 114a and the second surface 114b delimiting the internal cavity 112 are flat. However, they can be more complex, curved in shape, and adapted to form more complex parts, as shown in Figures 3 to 5.

[0029] The internal cavity 112 is designed to receive an assembly 230 consisting of the preform 210 and the rigid element 220, which at least partially covers the preform. Therefore, the internal cavity 112 is shaped, and thus dimensioned, to receive the preform 210 and the rigid element 220 to form the desired part.

[0030] The molding device 100 further comprises a flexible element 120 made of a second material to conform to the shapes of the rigid element 220 and prevent its over-injection.

[0031] The flexible element 120 is arranged in the inner cavity 112 so as to cover at least a portion 116 of the inner cavity, more precisely of the inner surface 114, so as to be opposite the rigid element 220 during molding.

[0032] The second material has a coefficient of thermal expansion greater than the coefficient of thermal expansion of the first material.

[0033] Advantageously, the flexible element 120 is dimensioned so as to expand to come into contact with the rigid element 220 during molding as illustrated in [Fig. 2] (and [Fig. 5]). The flexible element 120 is preferably as thin as possible to avoid generating thermal insulation of the area containing the rigid element 220. Preferably, the flexible element 120 has a thickness El at room temperature and a thickness E2 at curing temperature greater than the thickness El. The thickness of the flexible element is defined along a direction normal to the inner surface 114 delimiting the inner cavity 112. The greater the thickness of the flexible element at room temperature, the more it will expand, which determines the quality of the contact with the rigid element. Varying the thickness of the flexible element allows control over the space at room temperature between the flexible and rigid elements, as well as the pressure applied to the rigid part, in order to obtain the correct compromise between the pressure required to prevent resin leakage and the deformation of the rigid part.

[0034] As a result, the internal cavity 112 is shaped, therefore dimensioned, to receive the preform 210, the rigid element 220 to form the desired part and the flexible element 120 in its unexpanded state at room temperature and its expanded state at cooking temperature.

[0035] Advantageously, the second material is inert so as not to be the source of gas release which could generate porosity during the injection and polymerization of the resin in the assembly 230 formed by the preform 210 and the rigid element 220 to form the part to be manufactured.

[0036] Preferably, the second material is an elastomer, for example silicone or Mosites 1453®.

[0037] The coefficient of thermal expansion of the first material is less than 50 x 10⁶ K⁻¹. For example, the coefficient of thermal expansion of the first material when it is steel is less than 15 x 10⁶ K⁻¹. In the case where the first material is titanium, the coefficient of thermal expansion is less than 10 x 10⁶ K⁻¹, and if the first material is aluminum, the coefficient of thermal expansion is less than 25 x 10⁶ K⁻¹.

[0038] Furthermore, the coefficient of thermal expansion of the second material when it is silicone is between 100x106 K 1 and 500xl0 6 K ', and preferably between 150xl06K ' and 450x106 K1.

[0039] For example, if the part to be manufactured is a fan blade and the rigid element is a titanium leading edge fin less than 3 mm thick, the flexible element is preferably made of silicone and has a thickness less than 5 mm and greater than 3 mm. In this example, the curing temperature is generally between 110°C and 180°C. Preferably, the curing temperature is chosen at 110°C because the pressure on the rigid element is lower than at 180°C. Furthermore, at this temperature, the resin is much more viscous than at 180°C and therefore has much less infiltration capacity.

[0040] Advantageously, the molding device 100 further comprises pins 130 arranged in the inner cavity 112. More specifically, each pin 130 has a first end 132 bearing on the inner surface 114 of the inner cavity 112 and a second end 134 opposite the first end 132 and intended to be in contact with the rigid element 220 when the assembly 230 intended to form the part is installed in the inner cavity 112 of the mold 110 as illustrated in [Fig. 1].

[0041] The pins make it possible to guarantee the geometry of the part to be manufactured by facilitating the relative positioning of the flexible element with the curved element, both of which are curved in shape.

[0042] Preferably, the pins are made of the same material as the mold, that is to say, they are formed from the first material.

[0043] Each pin 130 has a defined height H in the direction normal to the inner surface 114 delimiting the inner cavity 112. The height H of the pins is equal to the thickness E2 of the flexible element 120 during molding, i.e. of the flexible element expanded at the cooking temperature.

[0044] In the illustrated example, the shape of the pins 130 flares advantageously from the second end 134 intended to be in contact with the rigid element 220 towards the first end 132 resting on the inner surface 114 of the inner cavity 112 allowing to facilitate the demolding of the manufactured part.

[0045] According to this example, each pawn 130 preferably has a pyramidal shape having a base in contact with the inner surface.

[0046] However, other shapes of the pins may also be suitable, for example cylindrical.

[0047] The pins 130 can be machined directly onto the inner surface 114 of the inner cavity 112. Alternatively, the pins 130 can be attached to the inner surface of the inner cavity. For example, each pin can extend from its first end 132, bearing against the inner surface 114 of the inner cavity 112, in a direction opposite to its second end 134, which is intended to be in contact with the rigid element 220, by means of an elongated body. The elongated body is housed in a through hole formed in the mold 110 and held by a fastening means on an outer wall of the mold, for example, by a pin retaining screw. Advantageously, a sealing gasket is arranged between the first end 132 and the inner surface 114 of the inner cavity 112 to ensure the mold is sealed and thus prevent resin from passing between the pin and the mold.

[0048] The pins 130 are evenly distributed over the inner surface 114 of the inner cavity 112. Preferably, they are spaced apart from each other by a distance that depends on the geometry of the part to be manufactured. This distance must allow to avoid buckling if the part is thin or a loss of reference.

[0049] Figure 3 shows a cross-sectional view of another example of a molding device, and more specifically of the mold for the molding device. This mold is intended for manufacturing parts with a more complex shape, i.e., parts whose outer surface is not exclusively made up of flat portions.

[0050] In particular, the preform 210 has a substantially elongated oval cross-sectional shape between "two ends" 212, and the rigid element 220 has a curved cross-sectional shape, substantially U-shaped or C-shaped, designed to enclose one of the ends 212 of the preform. Such a preform is particularly suitable for forming a part such as a fan blade having a leading edge, formed by the end 212 of the preform, covered by a rigid protective element made of titanium, for example.

[0051] Figures 4 and 5 illustrate an enlarged view of the interface between the rigid element 220 subjected to over-injection and the flexible element 120 at room temperature ([Fig.4]) and at cooking temperature ([Fig.5]), i.e. when the flexible element 120 is expanded.

[0052] Fig. 6 schematically illustrates an installation 300 for manufacturing a part according to the invention, in particular a part for a turbomachine, especially for an aircraft.

[0053] The installation 300 includes at least one resin storage and distribution piston 302, a heating device 304 and a molding device 100 according to the invention and as described above.

[0054] The resin 302 storage and distribution piston has an outlet 302b in fluidic communication with an inlet 304a of the heating device 304, and the heating device 304 has an outlet 304b in fluidic communication with an inlet 100a of the mold 110 of the molding device, preferably via a resin supply valve 306.

[0055] The mold 110 further includes a purge valve 140 or outlet valve.

[0056] Advantageously, the installation may further include a pressure sensor (not shown) for measuring the pressure of the resin in the mold 110.

[0057] The piston 302, the heating device 304 and the mold 110 are fluidly connected respectively by means of pipes 308 and 310 in which the resin can circulate.

[0058] The installation 300 may include other elements, shown or not in the drawings. The mold 110 may, for example, include a vent to create a partial vacuum in the cavity of the mold 110 and thus facilitate the injection of the resin into the mold.

[0059] The various elements of the installation can be connected to remote control and command means, such as computerized means for example.

[0060] For example, the piston 302 can be controlled to maintain a predetermined pressure and / or flow rate in the fluidic circuit of the installation.

[0061] The piston 302 has the function of storing the polymerizable resin and putting it under pressure to circulate it in the installation 300.

[0062] The mold 110 generally includes means for regulating the temperature of the cavity, for example by circulating a heated liquid through channels inside the mold parts 110a, 110b. The mold may also be equipped with a pressure sensor to measure and control the resin pressure inside the mold 110, in order to allow regulation of this pressure by the piston 302.

[0063] Such an installation is particularly suitable for implementing a process according to the invention, for manufacturing a part, particularly from composite material as described above, especially for an aircraft turbomachine. Such a manufacturing process comprises a step of producing a one-piece fibrous preform 210 by three-dimensional weaving of yarns. The yarns are separated into warp and weft yarns, and the warp yarns are interlaced with the weft yarns in a three-dimensional weave. By "three-dimensional weaving" or "3D weaving," we mean a weaving method in which certain warp threads interlace or interweave with weft threads in several layers, as is preferably the case in an interlock weave. "Interlock weaving" refers to a 3D weave structure in which each warp layer is interlaced with several weft layers, so that all the threads in the same warp column have the same movement within the plane of the weave.

[0064] According to the invention, the fibrous preform 210 is obtained by any type of three-dimensional weaving as defined above. Such a fibrous structure obtained by 3D weaving makes it possible to obtain a bond between the layers, and thus to have good mechanical strength of the fibrous structure and the resulting composite material part, in a single textile operation.

[0065] The fibrous structure can be produced in a known manner using a Jacquard-type loom on which a bundle of warp yarns or strands is arranged in a plurality of layers, the warp yarns being linked by layers of weft yarns or strands also arranged in a plurality of layers. The yarns or strands used to weave the fibrous preform can be made of carbon or glass fibers or Kevlar®.

[0066] This preform 210 and the rigid element 220 are placed in the mold 110 of the molding device 100, which is then closed to hold them in the mold in a tight seal. The preform may be pre-fitted with the rigid element, or the rigid element may be positioned in the mold before or after the preform. The flexible elastomer element 120 is not in contact with the rigid element 220. subject to over-injection (figures 1 and 4). Only the possible pins 230 are in contact with the rigid element 220 subject to over-injection.

[0067] The process continues with a co-injection step consisting of injecting a resin into the assembly formed by the fibrous preform 210 and the rigid element 220 previously arranged in the mold 110 so as to produce the desired part. In other words, after being placed in a mold, assembly 230 is impregnated with resin, for example, an organic or polymer resin. The resin can be thermosetting. It can be an epoxy or bismaleimide resin.

[0068] The process then includes a densification or consolidation step of the assembly formed by the resin-impregnated fibrous preform and the rigid element to form a part. During this step, the resin is polymerized. The filled mold 110 is transported to an oven or furnace in which the fibrous preform is densified by the resin and the rigid element is bonded to the preform. The densification of the fibrous preform consists of filling the porosity of the preform, in all or part of its volume, with the constituent material of the resin.

[0069] The densification of the fibrous preform can be achieved by a resin transfer molding (RTM) process. Polymerization can also be carried out by infusion, autoclave curing, or pressing.

[0070] Thus, during this step, the temperature increases until it reaches the curing temperature. During this temperature increase, the flexible elastomer element 120 deforms and expands more than the mold material 110, allowing for perfect contact at the external surface of the rigid element 220 to be protected from over-injection (Figures 2 and 5).

[0071] Indeed, due to expansion, the thickness of the flexible elastomer element 120 increases as the temperature rises towards the curing temperature, generating pressure on the rigid element 220 and thus preventing resin infiltration at the mold / rigid element interface. It is therefore necessary to take into account the expansion of the elastomer and the pressure it generates on the assembly to correctly dimension the cavity and obtain the desired geometry once the assembly is cured. This is valid regardless of the dimensions of the rigid element 220 relative to the final manufactured part.

[0072] The part is then demolded and trimmed to remove excess resin. Thanks to the invention, the rigid element has not been over-injected; that is, it is not covered with a thin film of resin, and therefore the part does not require a step to remove this film, which would involve working with a number of tools that could damage the surface of the manufactured part, and in particular the aerodynamic surface of the leading edge of a turbomachine fan blade, for example.

[0073] The invention makes it possible to counter the over-injection of resin on a rigid element during its co-injection with a preform to form a part in composite material.

[0074] Obviously, the invention is not limited to the embodiments described above and provided by way of example only. It encompasses various modifications, alternative forms, and other variations that a person skilled in the art may consider within the scope of the invention, and in particular all combinations of the different modes of operation described above, which may be taken separately or in combination. For example, the part to be manufactured may comprise several rigid elements. In other words, the assembly intended to form the part may include several rigid elements to be integrated onto different portions of the fibrous preform. In this case, the molding device comprises as many flexible elements as rigid elements to be protected from over-injection.

Claims

Claims

1. Molding device (100) configured to form a part, in particular a turbomachine part, the part being formed at least from a preform (210), the molding device comprising: - a mold (110) made of a first material, defining an interior cavity (112) delimited by an interior surface (114) and intended to receive an assembly (230) formed of the preform (210) and a rigid element (220) at least partially covering the preform, and - a flexible element (120) made of a second material, the flexible element (120) covering at least a portion (116) of the interior cavity so as to be opposite the rigid element during molding and the second material having a coefficient of thermal expansion greater than the coefficient of thermal expansion of the first material.

2. The molding device of claim 1, wherein the flexible member (120) is sized to expand to contact the rigid member (220) during molding.

3. A molding device according to any preceding claim, wherein the coefficient of thermal expansion of the first material is less than 50x106 K1.

4. A casting device according to the preceding claim, wherein the first material is steel or titanium or aluminum.

5. A molding device according to any preceding claim, wherein the coefficient of thermal expansion of the second material is between 100x106 K1 and 500x106 K1.

6. A molding device according to any preceding claim, wherein the second material is inert.

7. A molding device according to any preceding claim, wherein the second material is elastomer, preferably silicone.

8. Molding device according to any one of the preceding claims, further comprising pins (130) comprising a first end (132) bearing on the interior surface (114) of the interior cavity (112) and a second end (134) opposite the first end and intended to be in contact with the rigid element (220) when the assembly (230) intended to form the part is installed in the interior cavity (112) of the mold (110).

9. A molding device according to claim 8, wherein the pins (130) are formed from the first material.

10. Molding device according to claim 8 or 9, in which each pin (130) has a height (H), defined in the direction normal to the interior surface (114) delimiting the interior cavity (112), equal to the thickness of the flexible element (120) during molding, said expanded flexible element.

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