Method of manufacturing a preform intended to form a part in composite material by automatic placement of fibers, and method of manufacturing a part in composite material.

Abstract

The invention relates to a method for manufacturing a preform for forming a part made of composite material, comprising the following steps: (i) forming a blank of the part to be obtained by depositing, at a deposition temperature below 30°C, onto a surface, a plurality of fibrous structures comprising ceramic or carbon fibers impregnated with an impregnation composition comprising: (a) at least one organic binder, (b) ceramic or carbon particles, and (c) at least one polymeric compound capable of forming a thixotropic gel at the deposition temperature, and distinct from the organic binder (b), the organic binder (a) and the ceramic or carbon particles (b) together representing 50 to 70% by weight of the impregnation composition, the polymeric compound (c) representing 10 to 40% by weight of the impregnation composition, and the deposition being carried out by automatic fiber placement,(ii) formation of a preform of the part to be obtained by hot compression of the blank obtained in step (i), and (iii) removal of the organic binder present in the preform after step (ii). The invention also relates to a method for manufacturing a part made of composite material comprising the manufacture of a preform by implementing a method according to the invention, and an additional step (iv), carried out after step (iii), of forming a matrix in a porosity of the preform from ceramic or carbon particles (b). Fig. 1.,

Description

Title of the invention: Method of manufacturing a preform intended to form a part in composite material by automatic placement of fibers, and method of manufacturing a part in composite material. technical field

[0001] The present description relates to a method for manufacturing a preform intended to form a part made of composite material, implementing an automated fiber placement technique (also known as AFP). The invention also relates to a method for manufacturing a part made of composite material. Previous technique

[0002] It is known to produce composite parts by draping structures, generally in the form of layers or strands, of pre-impregnated fibrous reinforcement. In some techniques, the draping is carried out manually by an operator. These techniques can lead to relatively high production costs and risks of errors in positioning the fibrous structures. This results in some variability in the mechanical performance of the resulting parts and in parts whose mechanical properties can be improved.

[0003] Other solutions have been developed, such as the automated fiber placement technique. This mechanized technique is advantageous for reducing the production cost of composite parts. In the prior art, fibrous structures impregnated with a composition including ceramic particles are draped over a surface to obtain a preform of the desired part. The resulting preform is then dried, and the ceramic particles are sintered to form the matrix within the preform's porosity. Automated fiber placement devices incorporate a heating system (laser, infrared, pulsed light) used to provide heat during deposition, thereby ensuring the adhesion of the fibrous structures to the substrate.However, the use of light-colored fibers complicates the heating process in these types of devices because high temperatures lead to fiber degradation; the organic part can burn and blacken. The resulting black spot then absorbs more radiation, causing overheating, particularly in that area.

[0004] There is therefore a real need for a manufacturing process for a part made of composite material in which the formation of a blank by automatic placement of fibers This process could be carried out without heating, and preferably at room temperature, thus eliminating the risk of fiber burns and offering advantages in terms of health, safety, and environmental (HSE) risk prevention, energy savings, and a more compact automated fiber placement system that no longer requires a laser, infrared lamp, or thermal camera. The more accessible geometry of the automated fiber placement system, along with the economic and safety benefits resulting from the absence of heating, make the process advantageous for the deployment of all types of fibers, whether light or dark. Description of the invention

[0005] The invention therefore proposes, according to a first aspect, a method for manufacturing a preform intended to form a part in composite material comprising the following steps:

[0006] (i) formation of a rough part of the part to be obtained by deposition, at a temperature deposition below 30°C, on a surface of a plurality of fibrous structures comprising ceramic or carbon fibers impregnated with an impregnation composition comprising:

[0007] (a) at least one organic binder,

[0008] (b) ceramic or carbon particles dispersed in the organic binder, and

[0009] (c) at least one polymeric compound capable of forming a thixotropic gel at the deposition temperature, and distinct from the organic binder (a),

[0010] the organic binder (a) and the ceramic or carbon particles (b) together representing 50 to 70% by weight, and preferably 51 to 60% by weight, of the impregnation composition, and

[0011] the polymeric compound (c) representing 10 to 40% by weight, and preferably 15 to 25% by weight, of the impregnation composition, and

[0012] the deposit being carried out by automatic placement of fibers,

[0013] (ii) formation of a preform of the part to be obtained by hot compression of the blank obtained during step (i), and

[0014] (iii) removal of the organic binder present in the preform after step (ii).

[0015] The implementation of a thixotropic impregnation composition during the step (i) combining a specific polymeric compound (c) with an organic binder (a) in which ceramic or carbon particles (b) are dispersed, allows the deposition of fibrous structures by AFP technique, without requiring a heating means, compaction with a compaction roller being sufficient to ensure adhesion between the fibrous structures and the surface on which they are deposited.

[0016] The process of the invention thus enables the formation of a blank by automatic fiber placement, without heating, at ambient temperature, thereby avoiding the risk of burning the fibrous structures and any technical fabrics used during draping. This improves the quality of the manufactured parts, reduces the manufacturing costs of composite parts, and enhances the industrial performance of the process, thanks to the use of an AFP technique that prevents health, safety, and environmental (HSE) risks, while also lightening the automatic fiber placement device. The more accessible geometry of the automatic fiber placement device, the improved quality of the manufactured parts, and the economic and safety gains resulting from the absence of heating make the process more advantageous for all types of fibers.The invention thus makes it possible to manufacture, without burning and with a reduced production cost, parts in composite material with the desired mechanical performance, while lightening the geometry of the AFP device by decluttering the robot head (absence of heating system such as laser, infrared lamp or thermal camera).

[0017] Step (i) of forming a rough part of the part to be obtained is carried out by deposition, at a deposition temperature below 30°C, and preferably at ambient temperature (20°C), without requiring a heating system.

[0018] The organic binder (a) present in the impregnation composition may be a thermosetting organic binder or a thermoplastic organic binder. In particular, the organic binder (a) is selected from polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), glycerol, dextrin, and mixtures thereof. Particularly advantageously, the organic binder (a) is selected from polyethylene glycol (PEG), glycerol, and mixtures thereof.

[0019] The ceramic or carbon particles (b) present in the impregnation composition may, for example, be particles of silicon carbide, boron carbide, mullite, silica, alumina, aluminosilicate, or carbon grains or carbon nanotubes, and preferably particles of mullite, alumina, or aluminosilicate. These particles may have a volume average size (Dv50) less than or equal to 1 pm, preferably 0.5 pm.

[0020] The particles (b) are advantageously made of a ceramic material, for example, an oxide material such as alumina, or a non-oxide material such as silicon carbide. If the particles (b) are made of an oxide ceramic material, the fibrous structures may be formed from oxide ceramic wires, such as mullite, alumina, or aluminosilicate wires, or a mixture of such wires. If the particles (b) are made of a non-oxide ceramic material, the fibrous structures may be formed from carbon wires or non-oxide ceramic wires, or a mixture of such wires.

[0021] The polymeric compound (c) capable of forming a thixotropic gel at the deposition temperature is advantageously chosen from functionalized acrylic polymers, functionalized urethane polymers, and mixtures thereof, and more particularly acrylic polymers having hydroxylated, carboxylated or epoxide groups, urethane polymers having hydroxylated, carboxylated or epoxide groups, and mixtures thereof.

[0022] In particular, the polymeric compound (c) is selected from a hydroxylated acrylic polymer, a hydroxylated styrene-acrylic copolymer, a hydroxylated urethane polymer, a hydroxylated acrylic-urethane copolymer, and mixtures thereof. The polymeric compound (c) may be selected from the commercial products Thixol™ or Coapur™ (marketed by Arkema), Acrysol™ (marketed by Univar Solutions), Rhéolate® (marketed by Elementis), or Tafigel® (marketed by Münzing Chemie).

[0023] The polymeric compound (c) forms at the deposition temperature a thixotropic gel which advantageously exhibits a viscosity ranging from 25 to 250 Pa.s at 25°C.

[0024] The impregnation composition may also include a hardening agent capable of crosslinking with the polymeric compound (c) during deposition. This hardening agent is advantageously a compound containing isocyanate functional groups, such as the MS hardener marketed by Cop Chimie, or a polyamine-based compound, such as the Ancamine® hardener marketed by Univar Solutions, capable of crosslinking with the polymeric compound (c) during deposition. This hardening agent is preferably present at a concentration of no more than 10% by weight, and more preferably between 1 and 10% by weight.

[0025] In one embodiment, the fibers are alumina fibers.

[0026] In one embodiment, the particles (b) are alumina particles.

[0027] The hot compression step (ii) can be carried out in an autoclave.

[0028] The temperature imposed on the blank during the hot compression step (ii) is greater than or equal to 100°C.

[0029] The temperature imposed on the blank during the hot compression step (ii) can be between 150°C and 250°C.

[0030] In one embodiment, the pressure applied to the blank during the hot compression of step (ii) is greater than or equal to 2 bar and less than or equal to 20 bar. The pressure applied to the blank during the hot compression step (ii) can be between 2 bar and 20 bar.

[0031] Step (iii) of removing the organic binder present in the preform, to obtain a debinded preform, can be carried out by heat treatment. Debinding of the preform can be achieved by applying several debinding steps to the preform. demolded. The debinding heat treatment can be carried out at a temperature between 250 and 700°C, and preferably between 300 and 550°C.

[0032] In a second aspect, the invention proposes a method for manufacturing a part in composite material comprising the manufacture of a preform by implementing a process according to the invention, and an additional step (iv), carried out after step (iii), of forming a matrix in a porosity of the preform from ceramic or carbon particles (b).

[0033] In an example of an embodiment of the manufacturing process for a part made of composite material of the invention, the particles are made of oxide ceramic material, and the step (iv) of matrix formation is carried out by sintering these particles.

[0034] The sintering step (iv) can be carried out by heat treatment, preferably at a temperature between 1000°C and 1200°C, and more preferably between 1050°C and 1150°C. The duration of the sintering step (iv) can vary from 2 to 15 hours, and preferably from 4 to 10 hours. The heat treatment carried out during step (iii) makes it possible to take advantage of the temperature ramp necessary for the sintering step (iv). Brief description of the drawings

[0035] The attached drawing is schematic and is intended primarily to illustrate the principles of the exposition. On this drawing, elements (or parts of elements) are identified by reference symbols.

[0036] [Fig-1] Fig. 1 represents, schematically, a device for putting into work of an AFP technique usable within the framework of the invention. Description of the implementation methods

[0037] To make the explanation more concrete, examples of embodiments are described in detail below, with reference to the attached drawing. It should be noted that the invention is not limited to these examples.

[0038] Fig. 1 schematically and partially illustrates the production of a blank by the AFP technique and schematically illustrates the structure of a dispensing head 1 of an AFP implementation device. The structure of the illustrated dispensing head 1 is known per se. The dispensing head 1 is fed with fibrous structure material 3 to obtain the blank. The blank is formed on the surface S of a support 13. The material 3 is conveyed by a conveying element 5 to a pressure application element 7 located on the side of the surface S. The conveying element 5 is in the form of a pair of counter-rotating rollers 5a and 5b between which the material 3 is located. The conveying element 5 advances the material 3 to the pressure application element 7 in the direction indicated by the arrow FL

[0039] The pressure application element 7 applies pressure to the material 3 in order to deposit it on the surface S. The pressure application element 7 is here in the form of a roller.

[0040] During deposition, the dispensing head 1 is movable in order to apply the material 3 to a defined area of ​​the surface S (arrow F2). Once the application has been completed on the area, the cutting element 11 of the dispensing head 1 cuts the material 3. After this cutting, fibrous structures, formed by a section of the material 3, are deposited on the surface S.

[0041] The surface S on which the blank 13 is deposited may be planar. Alternatively, the surface S may be non-planar and convex or concave. The surface S may, for example, have a developable shape, such as a conical, frustoconical, or cylindrical shape, or a non-developable shape. The fibrous structures may have substantially the same shape as the surface S on which they are deposited.

[0042] Possible structures for the blank 13 and details relating to its manufacture have just been described. The description below focuses on describing the continuation of the part formation process.

[0043] Once the formation of the blank 13 by the AFP technique is complete, a hot compression step is performed on the blank 13 to obtain a preform of the part to be produced. Hot compression can be carried out in an autoclave. The temperature applied during hot compression is chosen according to the organic binder used and is sufficient to fluidize it. The temperature applied to the blank 13 during hot compression can, for example, be greater than or equal to 70°C, for example, between 70°C and 200°C. The pressure applied to the blank 13 during hot compression can be greater than or equal to 2 bar, for example, between 2 bar and 10 bar. Hot compression can result in a reduction of at least 10% in at least one dimension of the blank 13, for example, in the thickness of the blank.

[0044] By way of example, strands of alumina fiber supplied under the name "Nextel 610" (20,000 denier) by 3M can be used for fibrous structures, along with an impregnation solution comprising a mixture of (a) an organic binder based on polyvinyl alcohol marketed under the reference OPTAPIX PAF 35 by Zschimmer & Schwarz, (b) SM8 alumina particles available from Baikovsky, and (c) either Thixol™ (an acrylic polymer marketed by Arkema) or Rheolate® (a methane polymer marketed by Elementis). The mass proportion of organic binder (a) can be approximately 15%. The mass proportion of alumina particles (b) can be approximately 46%. The mass proportion of polymeric compound (c) can be approximately 5%. One can then apply a temperature of 160°C and a pressure between 2 and 10 bars to form the preform from the blank 13.

[0045] Different matrix formation techniques are conceivable.

[0046] The matrix can thus be formed by sintering the powdered matrix material. A person skilled in the art, through their general knowledge, knows how to choose the appropriate temperature based on the powdered matrix material to be sintered.

[0047] Alternatively, the matrix can be formed by infiltrating a molten composition into the porosity of the fibrous preform (melt-infiltration process). The molten composition can surround the powdered matrix material, which thus forms a particulate matrix phase dispersed within the infiltrated composition. The molten composition can be molten silicon or a molten silicon alloy. In this case, the powdered matrix material can be silicon carbide, in order to obtain a Si-SiC ceramic matrix. Carbon particles can be present prior to infiltration, as is known per se, if reactive infiltration in the melted state is desired in order to increase the proportion of SiC in the resulting ceramic matrix.

[0048] A machining step can then be carried out on the part obtained in order to adjust its dimensions and possibly cover it with one or more protective coatings.

[0049] The part obtained by the process described above can be a turbomachine part, for example an aeronautical turbomachine. It can be used for structural or non-structural applications. By way of non-limiting examples, the part can be an aft cowl, an aft pylon fairing, a mixer.

[0050] Although the present invention has been described with reference to specific embodiments, it is evident that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. Therefore, the description and drawing should be considered in an illustrative rather than a restrictive sense.

[0051] It is also evident that all the characteristics described with reference to a process are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a process.

Claims

Demands

1. A method for manufacturing a preform for forming a part of composite material comprising the following steps: (i) forming a blank of the part to be obtained by depositing, at a deposition temperature below 30°C, onto a surface, a plurality of fibrous structures comprising ceramic or carbon fibers impregnated with an impregnation composition comprising: (a) at least one organic binder, (b) ceramic or carbon particles, and (c) at least one polymeric compound capable of forming a thixotropic gel at the deposition temperature, and distinct from the organic binder (a), the organic binder (a) and the ceramic or carbon particles (b) together representing 50 to 70% by weight, and preferably 51 to 60% by weight, of the impregnation composition, the polymeric compound (c) representing 10 to 40% by weight, and preferably 15 to 25% by weight, of the composition impregnation,and the deposition being carried out by automatic fiber placement, (ii) formation of a preform of the part to be obtained by hot compression of the blank obtained during step (i), and (iii) removal of the organic binder present in the preform after step (ii).

2. A method according to claim 1, wherein the polymeric compound (c) is selected from functionalized acrylic polymers, functionalized urethane polymers, and mixtures thereof, and preferably acrylic polymers having hydroxylated, carboxylated or epoxidized groups, urethane polymers having hydroxylated, carboxylated or epoxidized groups, and mixtures thereof.

3. A method according to claim 2, wherein the polymeric compound (c) is selected from a hydroxylated acrylic polymer, a hydroxylated styrene-acrylic copolymer, a hydroxylated urethane polymer, a hydroxylated acrylic-urethane copolymer, and mixtures thereof.

4. A method according to any one of claims 1 to 3, wherein the organic binder is selected from polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), glycerol, dextrin, and mixtures thereof, and preferably from polyethylene glycol (PEG), glycerol, and mixtures thereof.

5. A method according to any one of claims 1 to 4, wherein the impregnation composition also comprises a hardening agent capable of crosslinking with the polymeric compound (c) during deposition, at a rate of at most 10% by weight, and preferably between 1 and 10% by weight.

6. A method according to claim 5, wherein the hardening agent is a compound comprising isocyanate, polyamine and / or polyamide functions, capable of crosslinking with the polymeric compound (c) during deposition.

7. A method according to any one of claims 1 to 6, wherein the fibers are mullite, alumina, or aluminosilicate fibers.

8. A method according to any one of claims 1 to 7, wherein the particles (b) are particles of silicon carbide, boron carbide, mullite, silica, alumina, aluminosilicate, or carbon grains or carbon nanotubes, and preferably particles of mullite, alumina, or aluminosilicate.

9. A method for manufacturing a part made of composite material comprising manufacturing a preform by implementing a process according to any one of claims 1 to 8, and an additional step (iv), carried out after step (iii), of forming a matrix in a porosity of the preform from ceramic or carbon particles (b).

10. A method according to claim 9, wherein the particles are made of oxide ceramic material, and wherein step (iv) of matrix formation is carried out by sintering these particles.

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