Method for producing multi-component parts

Abstract

The present invention relates to a method for producing a multi-component structural part, the method comprising a first step of applying, to a first component, a thermosetting adhesive precursor prepolymer, and a second step of applying, to the prepolymer, a thermosetting resin intended to form a second component. The steps are followed by a heat treatment to form a multi-component part comprising a second component made of composite material, which is bonded to the first component.

Description

Description Title of the invention: Method for manufacturing multi-component parts Technical Field

[0001] The invention relates to the field of manufacturing structural elements comprising an assembly of several different materials including a thermosetting organic matrix composite. Prior art

[0002] Structural parts made of several materials are generally assembled by bonding the interfaces. This is the case, for example, of parts made of an organic matrix composite and a metallic element, for which two polymers are used: a resin to generate the organic matrix and an adhesive to create the bonded interfaces.

[0003] When the composite is manufactured by injecting thermosetting liquid resin into a mold, there are mainly two methods for joining a composite material to another element.

[0004] A first method consists of bonding the interfaces with a thermosetting adhesive, after the composite has been molded. A single polymer is then transformed in the molding cavity, with the interfaces being bonded in a second step. This so-called "secondary" bonding method has the disadvantage of implementing two thermal cycles, which exposes the consolidated polymer obtained after molding to a new temperature increase which causes it to age prematurely and reduces the quality of the final part.

[0005] A second method consists of successively forming two thermosetting polymers in the mold cavity, the adhesive then the resin, which requires a specific thermal cycle, reduced process window management, and potentially more part scrap. In this type of process, the injection of the fluidized resin is done while the tool is heating up. Managing two different rheokinetic behaviors, that of the adhesive and that of the resin, therefore requires a fairly complex thermal cycle.

[0006] The adhesive that has been applied to the part and placed in the cavity begins to polymerize before starting the injection of the resin, and the crosslinking of the adhesive must not be completely finished at the time of injection, in order to ensure good resistance of the interface between the adhesive and the resin. Furthermore, the very high reactivity of the adhesive requires reducing the injection temperature of the resin. The resin, whose rheology is a determining parameter of the material health of the composite, is therefore more viscous, less reactive and penetrates the porosity of a fiber reinforcement with more difficulty.

[0007] Organic matrix composite structural parts comprising a metal base are manufactured in the prior art by a similar resin transfer molding process called "co-injection" according to a thermal cycle comprising the filling of the molding cavity and the creation of the bonded interface between the metal base and the composite. During this cycle, the injection is made during the temperature rise of the tool, and the adhesive is present in the cavity from the beginning of the cycle. This adhesive being itself a thermosetting polymer, its polymerization starts from the beginning of the thermal cycle before the injection of the resin. It is then necessary to optimize the thermal cycle of the molding cavity and to make compromises on the resin injection cycle. This more complex cycle leads to a reduction of the injection window and makes material health management more difficult.It is therefore desirable to optimize the thermal cycle of the molding cavity, which leads to a reduction in the resin injection window, and makes material health management more difficult. Optimizing the cycle is even more difficult in the case of large multi-component parts, for which the mold is wider and requires greater thermal power.

[0008] There is therefore a need to reduce the manufacturing constraints that arise from bonding several components with a conventional thermosetting adhesive.

[0009] It is particularly desirable to eliminate the secondary bonding operation carried out after molding and consolidation of the composite matrix. [0010JII It is also desirable to simplify conventional co-injection processes consisting of successively polymerizing the resin and the adhesive in the mold, and to improve the material health of the multi-component parts produced. Statement of the invention

[0011] The invention meets at least one of these needs by proposing a method for manufacturing a multi-component structural part comprising a first step of applying - to a first component - a thermosetting adhesive precursor prepolymer, and a second step of applying to the prepolymer a mixture comprising a hardener for the adhesive, a precursor resin and a hardener for the precursor resin, which mixture may be a thermosetting resin. The steps are followed by a heat treatment making it possible to form a second component made of a thermosetting matrix composite material which adheres to the first component thanks to the thermosetting adhesive formed in situ.

[0012] The present invention makes it possible to overcome at least one of the difficulties encountered in implementation in the assembly methods of the prior art.

[0013] The invention allows in particular an improvement in material health and the elimination of the secondary gluing operation.

[0014] In the case of molding the part by resin transfer, the invention makes it possible in particular to avoid a complex co-injection cycle for which optimization of the process window and material health are difficult to control, and proposes to generate the bonded interface during the resin curing cycle, and not in a separate curing cycle. The invention therefore allows simplified thermal management compared to the co-injection processes of the prior art.

[0015] In the present description, the terms "non-crosslinked polymer" or "prepolymer" may be used to designate a precursor polymer of the thermosetting adhesive intended to react with a hardener under the effect of heat to form the thermosetting adhesive. The prepolymer comprises at least one category of chemical compounds consisting of the covalent assembly of at least two monomers. The prepolymer may also include another category of compounds, which are monomers.

[0016] The prepolymer deposit applied to the first component which is obtained at the end of the first application step cannot polymerize under the effect of taking into account the absence of a sufficient quantity of hardening compound to crosslink the prepolymer in the deposit and transform the deposit into a material with adhesive properties, so that the prepolymer can be described as "inert" in the present description. This deposit is however capable of reacting with a hardener under the effect of heat to form a crosslinked material and create an adhesive interface between the two components. Also, the first application step consists of the application of a first product, which preferably consists of a prepolymer or consists essentially of a prepolymer, the term "essentially" meaning that the first product may contain compounds in small quantities which have no hardening function. The first product is not a thermosetting compound.In order for the prepolymer to crosslink and form an adhesive material, it is necessary to place it in the presence of a hardener. In the present invention, the hardener capable of reacting with the prepolymer is very advantageously provided by means of a second product during the second application step.

[0017] In a particular embodiment, the method of the invention has the originality of being able to assemble a component made of composite material to another part, during the densification of a fibrous reinforcement by a thermosetting resin, which can comprise the precursor resin of the organic matrix of the composite material, and the hardener of the precursor resin.

[0018] In order to overcome the implementation difficulties encountered in the prior art in managing two different rheokinetic behaviors for the application of the adhesive precursor composition and the resin, the invention proposes to use a composition which remains chemically inert during the temperature rise until the application of the resin.

[0019] In the case of epoxy resins, the products are formulated with an excess of hardener of approximately 25% to ensure chemical and thermal stability of the resin during its lifetime. The present invention can therefore be based on the consumption of the excess hardener present in these resins, by the inert film also composed of an epoxy constituent and possibly toughening fillers but essentially devoid of hardener. It is the excess hardener present in the resin which allows the polymerization of the prepolymer and the creation of the bonded bond between the two components.

[0020] In a first embodiment of the invention, the method is implemented by a liquid composite molding technique (LCM), for example by resin injection molding (RTM) or by vacuum resin transfer molding (VARTM). In this embodiment, the first step of applying the adhesive prepolymer to the first component is carried out, the first component covered with prepolymer and a fiber reinforcement is placed in a mold, then a mixture comprising the precursor resin, the hardener of the precursor resin and optionally another hardener of the prepolymer (which can also be referred to as a hardener of the adhesive) is injected into the closed mold.The mold is then brought to a temperature sufficient to react the adhesive prepolymer with the adhesive hardener on the one hand, and to crosslink the precursor resin with the precursor resin hardener on the other hand. The two reactions very advantageously occur concomitantly, during the same heat treatment step, and preferably during the same temperature plateau, so that the thermal cycle of the invention comprises two stages, and not three as in the prior art.

[0021] The hardening chemical compound present in the resin is advantageously identical to the compound suitable for hardening the prepolymer (compound also referred to as "adhesive hardener" in this description). Even more advantageously, the resin hardener reacts with the prepolymer during the third heat treatment step, so that it is not necessary to add a prepolymer hardener in the second applied product. In In this embodiment, the resin contains a sufficient amount of a single curing compound to cure both the prepolymer and the precursor resin.

[0022] The inventors propose to synthesize the adhesive material and the composite simultaneously, by "removing" the hardener from the adhesive compositions used in the prior art, in particular those used in the co-injection processes of the prior art, that is to say by replacing the adhesive composition of the prior art with a product that is inert due to the absence of hardener in its composition. In the process of the invention, a precursor prepolymer of the adhesive is applied to the first component, and remains inert in the molding cavity in the absence of the hardener. After deposition of the inert film of prepolymer, a mixture comprising a hardener compound of the adhesive, the precursor resin and the hardener of the precursor resin is injected into the mold cavity.

[0023] The formation of the adhesive by reaction of the prepolymer and the adhesive hardener occurs during the formation of the matrix which results from the reaction between the resin and the resin hardener. The polymerization of the adhesive allows a bond to be created between the two components without an actual bonding step.

[0024] The method of the invention advantageously makes it possible to avoid the use of several different thermosetting products in the manufacture of multi-component parts, while maintaining the mechanical performance of the materials formed. The method can be transposed to an industrial scale thanks to greater flexibility in the injection and curing cycle parameters. It also makes it possible to reduce part scrap.

[0025] The proposed solution allows generating a bonded interface between a metal component and a composite during the curing cycle of the composite matrix. The heat treatment step can therefore be simplified by eliminating the adhesive curing cycle that is necessary in the prior art.

[0026] The method of the invention has the advantage of improving the quality of the parts produced, and of eliminating the secondary bonding operation carried out in the methods of the prior art. When the method of the invention is implemented by molding liquid composite, the invention advantageously makes it possible to simplify the thermal management of the molding cavity,

[0027] The invention finds application in particular in the manufacture of blades or propellers for turbojet engines. It is particularly advantageous in the case of large multi-component parts, such as unducted fan propellers. Description of the embodiments

[0028] Meeting at least one of these needs, the invention has as its first subject a method for manufacturing a multi-component structural part comprising an assembly of several components including a first component and a second component assembled by a thermosetting adhesive, the second component comprising a thermosetting organic matrix composite material, said method comprising: - a first step of applying to a surface of the first component, a non-crosslinked polymer precursor of the thermosetting adhesive, - a second step of applying, on the non-crosslinked polymer, an adhesive hardener, a thermosetting organic matrix precursor resin and a resin hardener, and - a third step of heat treatment of the assembly allowing the formation of the composite material and the thermosetting adhesive which assembles the first component to the second component thus formed.

[0029] The second application step follows the first application step, and the third heat treatment step follows the second application step.

[0030] In this application, the expression "between ... and ..." means a range of values ​​not including the limits, while the expression "from ... to ..." means the limits included.

[0031] Finally, the expression "a" can mean "one" or "at least one", or "one or more".

[0032] The expression "precursor resin" may designate in the present description a chemical compound capable of reacting, under the effect of heat, with a hardener to form a thermosetting material. The precursor resin essentially comprises a monomer and optionally a polymer.

[0033] The word "resin" or "thermosetting resin" may be used to designate a product in the form of a mixture, advantageously commercially available, which is fluid and which comprises at least two chemical compounds capable of reacting together under the effect of heat to form a thermosetting material, these two compounds being a precursor resin and a hardener of the precursor resin. The resin may contain other compounds, such as fillers for example.

[0034] In the present application, the uncrosslinked polymer used as a precursor of the thermosetting adhesive may also be referred to as a "prepolymer".

[0035] In a particular embodiment of the invention, the resin is an epoxy resin, and the non-crosslinked polymer is chosen from aromatic polymers comprising epoxy functions at the chain end, while the hardener of the adhesive and the hardener of the precursor resin are chosen from aromatic amines comprising two primary amine functions.

[0036] For example, a prepolymer obtained by polymerization of a monomer derived from the reaction of Bisphenol-A with epichlorohydrin or a prepolymer obtained by polymerization of a monomer derived from the reaction of Bisphenol-F with epichlorohydrin is used. The monomer may be bisphenol-A diglycidyl ether (DGEBA with a molecular mass of 228 g / mol). The monomer may also be bisphenol-F diglycidyl ether (DGEBF with a molecular mass of 200 g / mol).

[0037] It is advantageous to use a prepolymer having a molecular mass (by mass or by number) of between 300 g / mol and 1400 g / mol, for example of between 320 g / mol and 1200 g / mol, or ranging from 340 g / mol to 1100 g / mol, to favor a good interface between the adhesive and the thermosetting organic matrix formed, and to obtain a multi-component part with mechanical properties comparable to, or even superior to, those of the multi-component parts obtained by a process of the prior art comprising the application of a first resin, then the application on the deposit of the first resin of a second resin different from the first.

[0038] The average degree of polymerization of the prepolymer is between 0 and 2, preferably between 1 and 2.

[0039] In a particular embodiment, the prepolymer is a homopolymer (also called an “oligomer”) of bisphenol-A diglycidyl ether represented by the general formula: where n is a decimal number between 0 and 2.

[0040] The oligomer of DGEBA may be a reference compound CAS 25068-38-6 (with a molecular mass by weight between 340 g / mol and 700 g / mol).

[0041] In another embodiment, the prepolymer is a homopolymer (or oligomer) of bisphenol-F diglycidyl ether, for example a compound of reference CAS 9003-36-5.

[0042] The prepolymer is preferably sufficiently viscous to ensure good positioning on the first component, during the first stage and until the start of the second stage during which the resin and the resin hardener are applied.

[0043] The precursor resin may have a different chemical composition than the prepolymer, and may comprise (or consist essentially of) bisphenol-F diglycidyl ether (DGEBF). The molecular weight of the precursor resin is preferably lower than that of the prepolymer.

[0044] The thermosetting resin comprises the precursor resin, the hardener of the precursor resin and optionally another hardener, which is an adhesive hardener different from the hardener of the precursor resin. According to a very advantageous embodiment of the method of the invention, the hardener of the precursor resin and the adhesive hardener are identical compounds.

[0045] In the case of epoxy resin, the resin hardener may be an aromatic primary diamine, such as 9,9-Bis-(4-amino-3-chlorophenyl)-fluorene, also known as chlorophenyl amino fluorene (CAF). The adhesive hardener may also be an aromatic primary diamine, such as 9,9-Bis-(4-amino-3-chlorophenyl)-fluorene.

[0046] The method of manufacturing a multi-component structural part according to the invention can also be described as a method comprising an assembly of a first component and a second component with a thermosetting adhesive, the second component comprising a thermosetting organic matrix composite material, said method comprising - a first step of applying to a surface of the first component, a first product comprising a non-crosslinked polymer which is devoid of a hardener of said polymer, to form a first deposit, the first product remaining inert under the effect of heat, - a second step of applying, on the first deposit, a second product comprising a thermosetting resin, to form a second deposit on the first, and - a third step of heat treatment of the assembly formed by the first component, the first deposit and the second deposit to form the second component and the thermosetting adhesive which assembles the first component to the second component thus formed.

[0047] The method of the invention has the advantage of not requiring an intermediate heat treatment step between the first step of applying the prepolymer and the second step of applying the resin. The thermosetting adhesive is formed during a heat treatment step, which is subsequent to the step of applying the prepolymer. The heat treatment step can be carried out during or after the step of applying the resin. Advantageously, the prepolymer is transformed into an adhesive material upon contact with the resin during the resin curing cycle, by diffusion of a prepolymer hardener present in the resin, so that the adhesive and the organic matrix are formed concomitantly. Even more advantageously, it is the resin hardener that reacts with the prepolymer to form the adhesive interface.

[0048] In a particular embodiment, the method is carried out by resin injection molding, and the prepolymer is applied to both the first component and a preform. The viscosity of the prepolymer is advantageously sufficient to ensure good positioning of its deposit on the first component until the resin is injected into the mold. At the same time, it is preferred not to use a prepolymer that is too viscous (or of too high a molecular mass), so as not to hinder the diffusion of the hardener present in the resin, into the prepolymer deposit, and not to obtain a poor quality adhesive interface.

[0049] To favor a good interface with mechanical properties comparable to those of prior art adhesives, aromatic epoxy prepolymers with high molecular weights, for example DGEBA or DGEBF oligomers having a degree of polymerization greater than 1, make it possible to increase the viscosity of the applied deposit, to ensure good positioning of the film until the application of the resin, but also to reduce the number of epoxy functions. Consequently, a lower supply of hardener is sufficient to ensure local mechanical performance compatible with the intended application. The use of conventional resins containing excess hardener becomes possible, without having to add an additional quantity of hardener to form the adhesive.

[0050] The prepolymer has the advantage of remaining chemically stable at the start of the third heat treatment step. In the case of a prepolymer derived from bisphenol-A diglycidyl ether (DGEBA), homopolymerization reactions between the epoxide functions of the prepolymer generally occur at temperatures above 180°C.

[0051] A first product comprising the prepolymer is advantageously applied in the form of a film whose thickness is chosen to allow good migration of the resin hardener throughout the film during the heat treatment step, the hardener possibly being the hardener of the precursor resin or other hardener that can react with the prepolymer. For example, the first product comprising the uncrosslinked polymer is applied so as to cover the surface of the first component with a film having a thickness ranging from 15 microns to 300 microns, preferably from 15 microns to 150 microns. In a particular embodiment, the film thickness of the first product comprising the prepolymer ranges from 30 microns to 70 microns. The thickness is therefore advantageously optimized to maximize the diffusion of the prepolymer hardener present in the resin into the prepolymer film and thus to ensure the chemical transformation of the applied prepolymer.

[0052] Toughening fillers may be added to the prepolymer before its application and be contained in the first product comprising the prepolymer.

[0053] A person skilled in the art will be able to adapt the stoichiometry of the resin based on his general knowledge. Preferably, a commercially available single-component resin is used, comprising a hardener which fulfils both the function of hardener for the precursor resin and the function of hardener for the adhesive.

[0054] It will thus be possible to use an epoxy resin comprising an amine hardener in which the number of amine functions of the hardener is in excess of approximately 25% compared to the number of epoxy functions. The use of such a product makes it possible to avoid a step of adding the hardener to the adhesive, since the excess resin hardener participates in the crosslinking of the prepolymer and in the formation of the adhesive. In this embodiment, the migration of the hardener contained in excess in the resin towards the prepolymer is observed.

[0055] In a particular embodiment, the second component comprises a preform consolidated by a thermosetting matrix, and the first step of the method of the invention comprises applying the prepolymer (via the first product) to a surface of the first component and to a surface of the preform. In this embodiment, the method of the invention can be carried out by resin transfer molding, to shape the second component during injection of the resin into the preform, in particular a 3D woven preform.

[0056]

[0057] To favor a good interface between the adhesive and the organic matrix and obtain mechanical properties comparable to those of prior art adhesives, aromatic epoxy prepolymers DGEBA or DGEBF with high molecular masses will be preferred to ensure good positioning of the film until the resin is injected, but also to reduce the number of epoxy functions. A low thickness of prepolymer, preferably less than 100 microns, will also be preferred to promote good dispersion of the resin hardener in the prepolymer.

[0058] The formation of the thermosetting adhesive and the formation of the organic matrix of the second component are triggered by raising the temperature during the third heat treatment step of the method of the invention. The adhesive and the matrix are advantageously formed at the same temperature, i.e. during the same temperature plateau of the thermal cycle.

[0059] Also, according to a particular embodiment, the method of the invention is carried out by resin transfer molding, and comprises - a first stage of placing - in a mold having the external shape of the multi-component part to be produced - the first component and a fiber reinforcement, - a second step of application on the first component and on the fibrous reinforcement of a prepolymer, - a third stage of injection, into the mold, of a thermosetting resin capable of crosslinking the prepolymer, - heating the mold to a temperature sufficient to form an adhesive by reaction of the prepolymer with the resin, and to form the second component in composite material by impregnation of the fibrous reinforcement with the resin.

[0060] The prepolymer (or the first product comprising the prepolymer) may be heated to a temperature between 40°C and 80°C, before being applied to the first component and the fiber reinforcement during the second stage.

[0061] The resin can be heated to a temperature ranging from 100°C to 160°C, before being injected into the mold during the third stage.

[0062] The mold heating can be carried out sequentially in stages. A person skilled in the art will be able to choose the temperature of each stage, the duration of the stages and the heating speed of the mold, depending on the size of the mold, the thickness of the deposited prepolymer, the chemical nature of the prepolymer and the chemical nature of the resin.

[0063] The mold heating step can be carried out by heating the mold at a rate ranging from 1°C / min to 10°C / min up to a first temperature level of between 100°C and 160°C and lasting between 5 min and 30 min. The first level can be followed by a second level at a temperature of approximately 180°C, lasting between 1 hour and 3 hours.

[0064] According to an advantageous embodiment of the invention, the temperature rise of the mold is carried out after the first step of applying the prepolymer. A first ramp, during which the precursor resin and the hardener of the precursor resin can be injected, makes it possible to reach a maximum plateau temperature of approximately 160°C. The first ramp is followed by a second temperature rise ramp to reach 180°C and allow the formation of the adhesive by crosslinking of the prepolymer, and the consolidation of the fiber reinforcement by crosslinking of the precursor resin.

[0065] The method of the invention advantageously makes it possible to inject the resin and the resin hardener directly into a mold at 160°C, and to eliminate the plateau generally carried out between 100°C and 130°C for 40 min to 2 hours in the methods of the prior art. This simplification of the thermal cycle is made possible by the use of a prepolymer which is not reactive during the mold heating step which precedes the injection of the resin.

[0066] The mold can be evacuated to a pressure ranging from 0.25 MPa to 2 MPa. A pressure gradient can be imposed in the closed mold cavity, between the resin injection nozzle and the discharge ports in order to control and optimize the impregnation of the fiber reinforcement by the resin.

[0067] According to a particular embodiment, the first component is made of metal, and the second component comprises a fibrous reinforcement densified by the thermosetting organic matrix. The first component is for example a structural part in the form of a metal foot.

[0068] The second component may be a thermosetting resin composite material comprising a fibrous reinforcement, the fibrous reinforcement being, for example, a preform. In the case of a resin injection molding process, the preform is placed in the mold cavity to be densified by impregnation of the fibrous network with the liquid resin precursor of the thermosetting matrix.

[0069] The preform is made from different materials such as a two-dimensional (2D) fabric, a three-dimensional (3D) fabric, a braid, a knit, a felt, a unidirectional (UD) sheet. The preform can be formed from several superimposed layers of these materials that are bonded together by sewing, by a chemical bonding agent, by implantation of threads, by implantation of rigid elements, or by needling. For example, a multi-directional (nD) sheet can be obtained by superimposing several unidirectional sheets positioned in different directions and bonded together by needling. The fibers of the fibrous reinforcement are in particular refractory fibers, such as carbon, aramid or glass fibers. In one embodiment, the fibers are carbon.

[0070] The present invention further relates to a multi-component structural part capable of being obtained by the method as described above.

[0071] In a particular embodiment of the invention, the multi-component structural part is intended for aeronautics. It may in particular be a part of a reactor or turbojet engine, such as a reactor blade. The blade comprises, for example, a structural spar made of thermosetting organic matrix composite material, and a metal foot serving as a means of attachment to a central hub.

[0072] The turbojet engine can be a fan, for example an open rotor or propfan.

Claims

Claims

1. Method for manufacturing a multi-component structural part comprising an assembly of several components including a first component and a second component assembled by a thermosetting adhesive, the second component comprising a thermosetting organic matrix composite material, said method comprising: - a first step of applying to a surface of the first component, a non-crosslinked polymer precursor of the thermosetting adhesive, - a second step of applying, to the non-crosslinked polymer, an adhesive hardener, a precursor resin of the thermosetting organic matrix and a precursor resin hardener, and - a third step of heat treatment of the assembly allowing the composite material and the thermosetting adhesive to be formed, which assembles the first component to the second component thus formed.

2. Method according to claim 1, characterized in that the first component is made of metal, and in that the second component comprises a fibrous reinforcement densified by the thermosetting organic matrix.

3. A method according to any one of the preceding claims, characterized in that the non-crosslinked polymer is applied so as to cover the surface of the first component with a film having a thickness ranging from 15 microns to 300 microns, preferably ranging from 15 microns to 150 microns.

4. Method according to any one of the preceding claims, characterized in that the precursor resin is an epoxy resin, and in that the non-crosslinked polymer is an aromatic polymer comprising epoxy functions at the chain end.

5. A method according to any one of the preceding claims, characterized in that the non-crosslinked polymer is a homopolymer of bisphenol-A diglycidyl ether.

6. A method according to any one of the preceding claims, characterized in that the precursor resin comprises bisphenol-F diglycidyl ether.

7. A method according to any one of the preceding claims, characterized in that the hardener of the adhesive is 9,9-Bis-(4-amino-3-chlorophenyl)-fluorene.

8. A method according to any one of the preceding claims, characterized in that the hardener of the resin is 9,9-Bis-(4-amino-3-chlorophenyl)-fluorene.

9. A method according to any one of the preceding claims, characterized in that the multi-component structural part is a reactor blade.

10. Multi-component structural part obtainable by the method according to any one of the preceding claims.

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