Manufacturing process for multi-component parts

Abstract

Method for manufacturing multi-component parts. The present invention relates to a method for manufacturing a multi-component structural part. The method comprises a first step of applying a thermosetting adhesive precursor pre-polymer to a first component, and a second step of applying a thermosetting resin to the pre-polymer to form a second component. These steps are followed by a heat treatment to form a multi-component part comprising a second composite material component bonded to the first component.

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. Previous technique

[0002] Structural parts comprising several materials are generally assembled by bonding the interfaces. This is the case, for example, for parts comprising 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] There are mainly two methods for assembling a composite material to another element, when the composite is manufactured by injecting thermosetting liquid resin into a mold.

[0004] The interfaces can be bonded with a thermosetting adhesive after the composite has been molded. A single polymer is then processed in the mold cavity, with the interfaces being bonded subsequently. This secondary bonding method has the disadvantage of involving two thermal cycles, which exposes the consolidated polymer obtained after molding to a further temperature increase, causing premature aging and reducing the quality of the final part.

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

[0006] The adhesive applied to the part and placed in the cavity begins to polymerize before the resin injection is initiated, and the adhesive's cross-linking must not be fully completed at the time of injection to ensure good adhesion of the interface between the adhesive and the resin. Furthermore, the adhesive's high reactivity necessitates lowering the resin injection temperature. The resin, whose rheology is a determining factor in the material health of the composite, is therefore more viscous, less reactive, and penetrates the porosity of a fibrous reinforcement with greater difficulty.

[0007] It is therefore necessary to optimize the thermal cycle of the mold cavity, which leads to a reduction in the resin injection window and makes material health management more difficult. Cycle optimization is all the more challenging in the case of large, multi-component parts, for which the mold is wider and requires greater thermal power.

[0008] The need therefore remains to reduce the manufacturing constraints that arise from bonding several components together with a thermosetting adhesive.

[0009] In particular, it is desirable to eliminate the secondary bonding operation carried out after molding and consolidation of the composite matrix.

[0010] It is also desirable to simplify the conventional co-injection processes consisting of successively polymerizing the resin and the adhesive in the mold while improving the material health of the multi-component parts produced. Description of the invention

[0011] The invention addresses these needs by providing a method for manufacturing a multi-component structural part comprising a first step of applying a thermosetting adhesive precursor pre-polymer to a first component, and a second step of applying a mixture comprising an adhesive hardener, a resin, and a resin hardener to the pre-polymer. These steps are followed by a heat treatment to form a second component made of a thermosetting matrix composite material that adheres to the first component thanks to the thermosetting adhesive formed in situ.

[0012] In this description, the terms "non-crosslinked polymer precursor of the thermosetting adhesive" or "pre-polymer" may be used to refer to the polymer intended to react with a hardener under the effect of heat to form the thermosetting adhesive.

[0013] The process 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 with a thermosetting resin.

[0014] In a first embodiment, the process of the invention is carried out by liquid composite molding (LCM), for example by resin transfer molding (RTM) or by vacuum assisted resin transfer molding (VARTM). In this embodiment, the first component coated with pre-polymer and the fiber reinforcement are placed in a mold, and then a mixture comprising the resin, the resin hardener, and the adhesive hardener is injected into the closed mold. The mold is then heated to a temperature sufficient to cause the adhesive pre-polymer to react with the hardener. adhesive on the one hand, and to crosslink the resin with the resin hardener on the other hand.

[0015] The chemical compound used as a resin hardener is advantageously identical to that used as an adhesive hardener.

[0016] The inventors propose to synthesize the adhesive and the composite simultaneously by removing the hardener from the adhesive composition used in the prior art in co-injection processes. In the process of the invention, a pre-polymer precursor of the adhesive is applied to the first component and remains inert in the mold cavity in the absence of the hardener. After deposition of the inert pre-polymer film, a mixture containing the adhesive hardener, the resin, and the resin hardener is injected into the cavity.

[0017] The adhesive is formed by the reaction of the prepolymer and the adhesive hardener during the formation of the matrix resulting from the reaction between the resin and the resin hardener. The polymerization of the adhesive creates a bond between the two components without a formal bonding step.

[0018] The process of the invention advantageously avoids the use of several thermosetting resin products in the manufacture of multi-component parts, while maintaining the mechanical performance of the materials. The process is scalable to industrial production thanks to greater flexibility in the injection and curing cycle parameters. It also reduces part scrap.

[0019] The proposed solution makes it possible to generate a bonded interface between a metallic component and a composite during the baking cycle of the composite matrix.

[0020] The process of the invention has the advantage of improving the quality of the parts produced and eliminating the secondary bonding operation performed in prior art processes. When the process of the invention is implemented by molding liquid composite, the invention advantageously simplifies the thermal management of the mold cavity.

[0021] The invention finds application in particular in the manufacture of blades or propellers for turbojet engines, in particular unfaired fan propellers whose blades have a large dimension. Description of the implementation methods

[0022] The invention relates to 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 application step on a surface of the first component, of a non-crosslinked polymer precursor of the thermosetting adhesive, and - a second application step, on the non-crosslinked polymer, of an adhesive hardener, a precursor resin of the thermosetting organic matrix and a resin hardener, - a third heat treatment stage of the assembly to form the composite material and the thermosetting adhesive which assembles the first component to the second component thus formed.

[0023] In this application, the expression "between ... and ..." refers to a range of values ​​not including the limits, while the expression "from ... to ..." means including the limits. The term "resin" may refer to a chemical compound capable of reacting with a hardener to form a thermosetting material. In the description of certain aspects of the invention, the word "resin" or "thermosetting resin" may also be used to refer to a product in the form of a mixture, which may advantageously be commercially available, comprising a chemical compound capable of reacting with a hardener under the effect of heat.

[0024] Unless otherwise specified, the temperature of the step performed is ambient temperature, and the pressure is atmospheric pressure.

[0025] In this application, the non-crosslinked polymer precursor of the thermosetting adhesive may also be referred to as the "pre-polymer". Preferably, a pre-polymer with epoxy terminations comprising aromatic rings in its main chain is used.

[0026] According to a variant of the process of the invention, the precursor resin is an epoxy resin, and the non-crosslinked polymer is an aromatic polymer comprising epoxy groups at the end of the chain.

[0027] For example, a prepolymer obtained by reacting Bisphenol-A or Bisphenol-F with epichlorohydrin is used. In one embodiment, the prepolymer is a homopolymer of bisphenol-A diglycidyl ether (DGEBA), in particular a reference polymer CAS 28064-14-4 which can be represented by the general formula in which n is a decimal number between 0 and 2.

[0028] In another embodiment, the pre-polymer is a homopolymer of bisphenol-F diglycidyl ether (DGEBF) reference CAS 9003-36-5.

[0029] It is advantageous to use a pre-polymer having a molecular mass between 300 g / mol and 1400 g / mol, for example between 320 g / mol and 1200 g / mol, or from 340 g / mol to 1100 g / mol, to favour a good interface between the adhesive and the thermosetting organic matrix, and to obtain a multi-component part with mechanical properties comparable to, or even superior to, those of multi-component parts obtained by a prior art process.

[0030] The pre-polymer is preferably sufficiently viscous to ensure good positioning on the first component, during the first step and until the beginning of the second step during which the resin and the resin hardener are applied.

[0031] In a particular embodiment, the process is carried out by resin injection molding, and the pre-polymer is applied to both the first component and a preform. The viscosity of the pre-polymer is advantageously sufficient to ensure good positioning of its deposit on the first component and the preform until the resin and resin hardener are injected into the mold.

[0032] The pre-polymer makes it possible to reduce the number of epoxy functions needed to ensure the reaction with the hardener(s), and consequently, to reduce the amount of hardener in the mixture including the resin which is used during the second step.

[0033] Therefore, a limited supply of hardener makes it possible to ensure local mechanical performance compatible with the intended application for the multi-component part.

[0034] The pre-polymer has the advantage of remaining chemically stable at the beginning of the third heat treatment step. In the case of a pre-polymer derived from bisphenol-A diglycidyl ether (DGEBA), the homopolymerization reactions between the epoxide groups of the pre-polymer advantageously occur at temperatures above 180°C.

[0035] The pre-polymer (also referred to as the non-crosslinked polymer) is advantageously applied as a film of a thickness chosen to allow good dispersion of the hardener in the pre-polymer during the heat treatment step. Thus, the non-crosslinked polymer is preferably 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.

[0036] Toughening fillers can be added to the pre-polymer before its application.

[0037] In a particular embodiment, the second component comprises a preform consolidated by the thermosetting matrix, and the first step of the process of the invention comprises the application of the pre-polymer on a surface of the first component and on a surface of the preform.

[0038] After carrying out the first step of applying the pre-polymer, the process includes a second step of applying a hardener intended to react with the pre-polymer under the effect of heat to make it crosslink and allow it to fulfill the function of adhesive between the two components.

[0039] The adhesive hardener can be an aromatic primary diamine, such as, for example, 9,9-Bis-(4-amino-3-chlorophenyl)-fluorene, also called chlorophenyl amino fluorene (CAF).

[0040] During this second step, a thermosetting resin is also applied to form the organic matrix of the second component under the effect of heat. The precursor resin may include bisphenol-F diglycidyl ether (DGEBF).

[0041] The resin hardener can be an aromatic primary diamine, such as 9,9-Bis-(4-amino-3-chlorophenyl)-fluorene.

[0042] According to a highly advantageous embodiment of the process of the invention, the resin hardener and the adhesive hardener have the same chemical formula. Those skilled in the art will be able to adjust the stoichiometry of the resin based on their general knowledge. Preferably, a commercially available resin is used that includes a hardener which performs both the function of resin hardener and adhesive hardener. For example, an epoxy resin comprising an amine hardener may be used in which the number of amine groups in the hardener is approximately 25% higher than the number of epoxy groups. Using such a product eliminates the need for a step involving the addition of the adhesive hardener, since the excess resin hardener contributes to the crosslinking of the prepolymer and the formation of the adhesive.In this embodiment, the migration of the excess hardener contained in the resin towards the prepolymer is observed during the injection of the resin into the 3D woven preform.

[0043] 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 process of the invention. The adhesive and the matrix are advantageously formed at the same temperature.

[0044] According to a particular embodiment, the process of the invention is carried out by resin transfer molding, and comprises - a first step of setting up - in a mold having the external shape of the multi-component part to be produced - the first component and a fibrous reinforcement (which can also be referred to as a preform), - a second application step on the first component and on the fibrous reinforcement of a pre-polymer, - a third injection stage, into the mold, of a thermosetting resin capable of consolidating the fibrous reinforcement, a resin hardener, and an adhesive hardener capable of cross-linking the pre-polymer, - heating the mold to a sufficient temperature to form an adhesive by reaction of the pre-polymer with the adhesive hardener and to form the second component in composite material by impregnation of the fibrous reinforcement with the resin.

[0045] -In a particular embodiment, the resin hardener fulfills the function of an adhesive hardener.

[0046] The pre-polymer can be heated to a temperature between 40°C and 80°C, before being applied to the first component and the fibrous reinforcement during the second step.

[0047] The resin, the resin hardener and possibly the adhesive hardener (when it is different from the resin hardener) can be heated to a temperature ranging from 100°C to 160°C, before being injected into the mold during the third step.

[0048] 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 rate of the mold, depending on the dimensions of the mold, the thickness of the deposited pre-polymer, the chemical nature of the pre-polymer and the chemical nature of the resin.

[0049] The mold heating step can be carried out by heating the mold at a rate of 1 to 10°C / min until a first temperature plateau is reached between 100°C and 160°C, lasting between 5 and 30 minutes. This first plateau can be followed by a second plateau at a temperature of 180°C, lasting between 1 and 3 hours.

[0050] According to an advantageous embodiment of the invention, the mold temperature is raised in two stages. A first ramp, during which the resin and resin hardener can be injected, allows a maximum plateau temperature of approximately 160°C to be reached. The first ramp is followed by a second temperature 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 resin with the resin hardener.

[0051] The process of the invention advantageously allows the resin and resin hardener to be injected into a mold at 160°C, and eliminates the plateau generally observed between 100°C and 130°C in prior art processes. This simplification of the thermal cycle is made possible by the use of a prepolymer that is non-reactive during the mold's temperature rise.

[0052] The mold can be placed under vacuum at a pressure ranging from 0.25 MPa to 2 MPa. A pressure gradient can be imposed in the cavity of the closed mold, between the resin injection nozzle and the discharge ports in order to control and optimize the impregnation of the fibrous reinforcement by the resin.

[0053] 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 metal foot.

[0054] The second component may be a thermosetting resin composite material comprising a fibrous reinforcement, 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 impregnating the fibrous network with a liquid precursor mixture of the thermosetting resin matrix.

[0055] The preform is made from various materials such as a two-dimensional (2D) fabric, a three-dimensional (3D) fabric, a braid, a knit, a felt, or a unidirectional (UD) web. The preform can be formed from several superimposed layers of these materials, which are bonded together by stitching, a chemical bonding agent, the implantation of threads, the implantation of rigid elements, or by needle punching. For example, a multidirectional (nD) web can be obtained by superimposing several unidirectional webs positioned in different directions and bonded together by needle punching. 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.

[0056] The present invention further relates to a multi-component structural part that can be obtained by the process as described above.

[0057] In a particular embodiment of the invention, the multi-component structural part is intended for aeronautical applications. It may, in particular, be a part of a jet engine or turbojet engine, such as a jet engine blade. The blade comprises, for example, a structural spar made of thermosetting organic matrix composite material, and a metal base serving as a means of attachment to a central hub.

[0058] The turbojet can be a fan, for example an unfaired fan (“open rotor” or “propfan” in English).

Claims

Demands

1. A method for manufacturing a multi-component structural part comprising an assembly of several components, including a first component and a second component joined 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, and - a second step of applying, to the non-crosslinked polymer, an adhesive hardener, a resin precursor of the thermosetting organic matrix and a resin hardener, - a third step of heat treating the assembly enabling the formation of the composite material and the thermosetting adhesive which joins the first component to the second component thus formed.

2. A 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. A process 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 process according to any one of the preceding claims, characterized in that the non-crosslinked polymer is a homopolymer of bisphenol-A diglycidyl ether (DGEBA).

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

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

8. A process according to any one of the preceding claims, characterized in that the resin hardener 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.