Welding process between parts made of thermoplastic matrix composite material

Abstract

A welding process between parts made of thermoplastic matrix composite material (10, 20) comprising respective joining surfaces (11, 21) includes holding the joining surfaces of the parts opposite each other so as to form a welding interface (5) between said parts. The process further includes injecting a thermoplastic welding material (40) at the welding interface. The thermoplastic welding material is injected at a temperature above the glass transition or melting temperature of each thermoplastic matrix of the parts (10, 20). Figure for the abstract: Fig. 3.

Description

Title of the invention: Welding process between parts made of thermoplastic matrix composite material Technical field

[0001] The present invention relates to the general field of parts made of thermoplastic material and, more particularly, to the assembly by welding of such parts. Prior art

[0002] Thermoplastic materials and in particular composite materials comprising reinforcing fibers, for example carbon fibers and / or glass fibers, dispersed in a thermoplastic polymer matrix have numerous possible uses, and in particular, in the field of aeronautics. For the production of certain structures, it may be necessary to assemble several parts made of thermoplastic material, such as, for example, for a thrust reverser flap, a stiffened panel, stiffeners, fairing elements, etc. These composite parts can be assembled by welding, in particular using technology such as:

[0003] - induction welding,

[0004] - resistive welding,

[0005] - welding by heating and pressure,

[0006] - ultrasonic welding, laser welding.

[0007] Documents FR 3 111 585 and FR 3 111 582 describe induction welding processes in which an assembly formed of two parts to be welded made of thermoplastic matrix composite material and one or more elements acting as susceptors at the interface between the parts is subjected to a magnetic field. In document FR 3 111 585, metallic fillers are added to the material of the parts in the vicinity of the welding interface. In document FR 3 111 582, a susceptor, for example a grid made of metallic material, is interposed in the interface between the two parts. The magnetic field causes the temperature of the metallic fillers or the susceptor to rise to a temperature allowing the softening or melting of the thermoplastic resin. In the case of the use of a susceptor, it is overmolded at the assembly interface between the two parts.

[0008] While these induction welding processes have the advantage of allowing localized heating of the thermoplastic material of the parts at the interface to be welded, they nevertheless have the disadvantage of leaving metallic elements in the the resulting assembly. The presence of these metallic elements can lead to premature thermal aging problems due to the difference in coefficient of expansion between the composite material of the parts and the metallic material, which can reduce the life of the assembly.

[0009] Another solution for avoiding the presence of metallic elements in the assembly consists of heating the two parts by conduction or radiation and exerting pressure on the area to be welded. However, in this case, the heating is no longer localized at the welding interface, which affects the characteristics of the parts of the assembly at locations far from the area to be welded (geometric deformation for example). Statement of the invention

[0010] The main aim of the present invention is therefore to propose a solution for welding parts made of thermoplastic material which does not have the aforementioned drawbacks.

[0011] According to the invention, this aim is achieved by means of a method of welding between two parts made of thermoplastic matrix composite material comprising respective assembly surfaces, the method comprising holding the assembly surfaces of the parts opposite each other so as to form a welding interface between said parts, characterized in that the method further comprises injecting a thermoplastic welding material at the welding interface and in that the thermoplastic welding material is injected at a temperature higher than the glass transition or melting temperature of each thermoplastic matrix of the parts.

[0012] By injecting a thermoplastic welding material at the welding interface at a temperature higher than the glass transition or melting temperature of each thermoplastic matrix of the parts, a localized heat input is carried out which makes it possible to remelt the thermoplastic matrix of the two parts locally at the assembly surfaces, without having to incorporate foreign elements into the assembly and without deformation of the welded parts. This local remelting makes it possible to obtain a good chemical bond with the thermoplastic welding material and thus a good bond between the two parts.

[0013] According to a particular characteristic of the method of the invention, the thermoplastic welding material is preferably injected at a temperature at least 5% higher than the glass transition melting temperature of each thermoplastic matrix of the parts.

[0014] According to another particular characteristic of the method of the invention, the thermoplastic welding material has a glass transition temperature or melting above the melting temperature of the thermoplastic matrix of at least one of the parts made of thermoplastic matrix composite material, the welding material being injected at a temperature below the degradation temperature of the thermoplastic matrix of the parts.

[0015] According to another particular characteristic of the method of the invention, during the injection of the thermoplastic welding material at the welding interface, the parts made of composite material with a thermoplastic matrix are heated to a temperature lower than the glass transition or melting temperature of each matrix of said parts. This makes it possible to facilitate the local remelting of the thermoplastic matrix of the two parts by reducing the temperature gradient between the injected thermoplastic welding material and the parts.

[0016] According to another particular characteristic of the method of the invention, the thermoplastic welding material comprises an unfilled thermoplastic resin or a filled thermoplastic resin.

[0017] According to another particular characteristic of the method of the invention, the latter further comprises, after the injection of the thermoplastic welding material at the welding interface, the application of a compressive force on at least one of the parts so as to bring the assembly surfaces of the parts closer together. This makes it possible to facilitate the injection of the welding material by having a greater distance between the parts for the injection, which facilitates the flow of the injected material between the parts, the compression then makes it possible to return to the target dimension by migrating the welding material over the entire contact surface.

[0018] According to another particular characteristic of the method of the invention, at least one of the parts comprises one or more injection orifices opening onto the assembly surface, the thermoplastic welding material being injected at the welding interface through the injection orifice(s). This makes it easier to inject the welding material into the welding interface, in particular when the parts to be welded have large dimensions.

[0019] The invention also relates to a method of welding between at least two parts made of thermoplastic matrix composite material having respective assembly surfaces, characterized in that it comprises the deposition of a thermoplastic welding material on an assembly surface of one of the parts, the thermoplastic welding material being deposited at a temperature higher than the glass transition or melting temperature of each thermoplastic matrix of the parts and the bringing into contact of the assembly surface of the other part with the deposited thermoplastic welding material, the parts made of thermoplastic matrix composite material being heated to a temperature lower than the glass transition or melting temperature of the matrix of said parts during the deposition of the thermoplastic material. welding plastic and contacting the assembly surface of the other part with the deposited thermoplastic welding material.

[0020] By depositing a thermoplastic welding material at a temperature above the glass transition or melting temperature of each thermoplastic matrix of the parts, a localized heat input is carried out which allows the thermoplastic matrix of the two parts to be remelted locally at the assembly surfaces, without having to incorporate foreign elements into the assembly and without deformation of the welded parts. This local remelting makes it possible to obtain a good chemical bond with the thermoplastic welding material and thus a good bond between the two parts.

[0021] According to a particular characteristic of the method of the invention, the thermoplastic welding material is preferably injected at a temperature at least 5% higher than the glass transition or melting temperature of each thermoplastic matrix of the parts.

[0022] According to a particular characteristic of the invention, the thermoplastic welding material has a glass transition or melting temperature higher than the melting temperature of the thermoplastic matrix of at least one of the parts made of composite material with a thermoplastic matrix, the welding material being injected at a temperature lower than the degradation temperature of the thermoplastic matrix of the parts.

[0023] According to another particular characteristic of the method of the invention, the thermoplastic welding material comprises an unfilled thermoplastic resin or a filled thermoplastic resin. Brief description of the drawings

[0024] [Fig.l] [Fig.l] is a schematic perspective view of two pieces of thermoplastic material to be welded,

[0025] [Fig.2A] [Fig.2A] is a schematic perspective view showing a welding tool in which the two parts of [Fig.1] are held in the welding position in accordance with one embodiment of the invention,

[0026] [Fig.2B] [Fig.2B] is a schematic sectional view of the welding tooling of [Fig.2A],

[0027] [Fig.3] [Fig.3] is a schematic sectional view of the welding tool of [Fig.2A] after injection of a thermoplastic welding material,

[0028] [Fig.4] [Fig.4] is a schematic perspective view showing the assembly obtained from the two parts of [Fig.1] in accordance with one embodiment of the invention,

[0029] [Fig.5] [Fig.5] is a schematic perspective view of two pieces of material thermoplastic to weld,

[0030] [Fig.6] [Fig.6] is a schematic sectional view of the two parts of [Fig.5] held in the welding position in accordance with one embodiment of the invention,

[0031] [Fig.7] [Fig.7] is a schematic sectional view showing the injection of a thermoplastic welding material at the welding interface between the two parts of [Fig.6],

[0032] [Fig.8] [Fig.8] is a schematic sectional view showing the application of a compressive force to the parts of [Fig.7],

[0033] [Fig.9] [Fig.9] is a schematic sectional view showing the resulting assembly of the two parts of [Fig.5] in accordance with an embodiment of the invention,

[0034] [Fig. 10] [Fig. 10] is a schematic perspective view of a welding installation using an additive manufacturing type technique in accordance with an embodiment of the invention,

[0035] [Fig.11] [Fig.11] is another view of the welding installation of [Fig.10]. Description of the embodiments

[0036] The invention applies to welding between parts made of composite material with a thermoplastic matrix, i.e. parts comprising a fibrous reinforcement densified by a matrix made of thermoplastic material. The fibrous reinforcement of these parts can be produced in particular from continuous fibers of a layer or a stack (draping) of several layers of:

[0037] - three-dimensional (3D) fabric,

[0038] - two-dimensional (2D) fabric,

[0039] - one-dimensional fabric (UD),

[0040] - braid,

[0041] - knitting,

[0042] - felt,

[0043] - a multidirectional sheet (nD) obtained by superimposing several UD fabrics in different directions and bonding the UD sheets together, for example by sewing, chemical bonding agent or needling.

[0044] The fibrous reinforcement of the parts may also comprise a non-woven texture with discontinuous long fibers (DLF) or injected short fibers.

[0045] The fibers used for the fiber reinforcement may in particular be carbon, glass or aramid fibers.

[0046] The material of the thermoplastic matrix of the parts may in particular be one of the following thermoplastic materials: PAEK (PolyArylEtherCetone), PEEK (PolyEtherEtherCetone), PEKK (PolyEtherCetoneCetone), PEI (polyetherimide), PSU (polysulfone), PESU or PPS (polyphenylene sulfide), PA (polyamide) and PC (polycarbonate).

[0047] [Fig. 1] shows first and second parts made of thermoplastic matrix composite material 10 and 20. The first part 10 comprises an assembly surface or portion 11 intended to be welded with an assembly surface or portion 21 of the second part 20.

[0048] According to the invention, the assembly surfaces 11 and 21 of the parts 10 and 20 are welded together by injecting a thermoplastic welding material at a welding interface. More precisely and as illustrated in FIGS. 2A and 2B, the parts 10 and 20 are placed in a welding tool 100. In the example described here, the first part 10 is placed in a mold 110 of the welding tool 100 while the second part 20 is held in an assembly position with the part 10 by two counter-molds or keys 120 and 130 of the tool 100.

[0049] The parts 10 and 20 are held in the tooling in a determined position so that the assembly surfaces 11 and 21 to be welded are placed opposite each other, the space present between the assembly surfaces 11 and 21 forming a welding interface 5 ([Fig.2B]). The space between the assembly surfaces 11 and 21 is for example of the order of one or a few millimeters.

[0050] As illustrated in [Fig.2B], the two counter-molds 120 and 130 respectively comprise hollowed-out portions 121 and 131 delimiting between them an injection space 140 in the welding tool 100.

[0051] Still in accordance with the invention, after positioning the parts 10 and 20 in the welding tool 100, a thermoplastic welding material 40 is injected into the injection space 140 via an injection port 150 ([Fig.2A]). The welding tool can of course comprise several injection ports. During its injection, a portion of the thermoplastic welding material 40 spreads into the welding interface 5 present between the assembly surfaces 11 and 21 opposite each other as illustrated in [Fig.3].

[0052] The thermoplastic welding material 40 is injected at a temperature higher than the glass transition or melting temperature of each thermoplastic matrix of the parts 10 and 20 in order to remelt the thermoplastic matrix of the two parts locally at the assembly surfaces 11 and 21. More precisely, in the case of an amorphous thermoplastic matrix, the thermoplastic welding material is injected at a temperature higher than the glass transition temperature of the material while, in the case of a semi-crystalline thermoplastic material, the thermoplastic welding material is injected at a temperature higher than the melting temperature of the material.

[0053] This local remelting makes it possible to obtain a good chemical bond with the thermoplastic welding material and thus a good bond between the two parts. The thermoplastic welding material is preferably injected at a temperature at least 5% higher than the glass transition or melting temperature of each thermoplastic matrix of the parts.

[0054] When each matrix of the parts and the welding material are made of the same amorphous thermoplastic material, the welding material is preferably injected at a temperature between 10% and 25% higher than the glass transition temperature of the thermoplastic material. When each matrix of the parts and the welding material are made of the same semi-crystalline thermoplastic material, the welding material is preferably injected at a temperature higher than 5% of the melting temperature of the thermoplastic material but lower than the degradation temperature of said material.

[0055] Once the thermoplastic welding material 40 has cooled and after demolding, an assembly 30 is obtained consisting of the parts 10 and 20 welded as shown in [Fig. 4]. The assembly 30 comprises beads 41 and 42 of thermoplastic welding material 40 on each side of the faces of the part 20 corresponding to overmoldings formed in the injection space 140. The beads 41 and 42 reinforce the connection between the parts of the assembly.

[0056] The assembly 30 can then be subjected to finishing treatments, for example to remove an injection sprue 43 present after demolding.

[0057] The welding tool may further comprise heating means for heating the parts to be welded to a temperature below the glass transition or melting temperature of the thermoplastic matrix of each of the parts to be welded in order to facilitate the distribution of the injected thermoplastic welding material at the welding interface while avoiding deformation of the parts. The welding tool may also be equipped with a so-called "hot-cold" system which makes it possible to locally heat the parts to be welded at only their assembly surface. Such a system may for example use induction heating which allows localized heating at one or more portions of the parts.

[0058] Furthermore, injection orifices may also be made on one of the two parts to be welded in order to facilitate the injection of the thermoplastic welding material, particularly in the case of large parts and / or a compressive force may be applied to at least one of the two parts after injection as described below.

[0059] Figures 5 to 9 illustrate another embodiment which differs from the embodiment described above, in particular in that injection orifices are made in one of the parts to be welded and in that a compressive force is applied to at least one parts after hot injection of the thermoplastic welding material.

[0060] More specifically, as shown in Figures 5 and 6, welding is carried out between a first part made of thermoplastic matrix composite material 50 in the form of an angle iron, here forming a stiffener, and a second part made of thermoplastic matrix composite material 60, here forming a skin. Injection orifices or bores 52 are made in the part 50 in order to allow the injection of a thermoplastic welding material as described below. The injection orifices 52 have, for example, a diameter of between 2 mm and 10 mm. The number of injection orifices is controlled so as to limit the reduction in the mechanical properties of the part 50. The part 50 preferably comprises only one injection orifice 52 for each surface of 100 mm2 to be welded.

[0061] The parts 50 and 60 are held in a welding tool (not shown in FIGS. 5 and 6) in a determined position so as to place the assembly surface or portion 51 of the part 50 opposite the assembly surface or portion 61 of the part 60. In this embodiment, the space E ([Fig. 6]) present between the assembly surfaces 51 and 61 and delimiting a welding interface 15 is initially larger in order to allow the assembly surfaces to come together during the compression step as described below. The initial space E may, for example, be between 2 mm and 5 mm.

[0062] In the example described here, the parts 50 and 60 are heated to a temperature below the glass transition or melting temperature of their thermoplastic matrix. As indicated previously, the assembly surfaces 51 and 61 of the parts 50 and 60 can be heated locally to such a temperature, the rest of the two parts being at room temperature.

[0063] A thermoplastic welding material 70 is then injected between the assembly surfaces 51 and 61 of the parts 50 and 60 through the injection orifices 52 using an injection nozzle 71 as illustrated in [Fig. 7]. According to the invention, the thermoplastic welding material 70 is injected at a temperature higher than the glass transition or melting temperature of each thermoplastic matrix of the parts 50 and 60 in order to remelt the thermoplastic matrix of the two parts locally at the assembly surfaces 51 and 61. This local remelting makes it possible to obtain a good chemical bond with the thermoplastic welding material and thus a good bond between the two parts. The thermoplastic welding material is preferably injected at a temperature at least 5% higher than the glass transition or melting temperature of the thermoplastic matrix of the parts.

[0064] During its injection, the thermoplastic welding material 70 spreads into the space present between the assembly surfaces 51 and 61 opposite each other.

[0065] Once the thermoplastic welding material 70 is injected, a compressive force Ep is applied to part 50 in the direction of part 60 so as to bring the assembly surfaces of the parts to be welded closer together as shown in [Fig.8].

[0066] Once the thermoplastic welding material 70 has cooled and after demolding, an assembly 80 is obtained consisting of the parts 50 and 60 welded as shown in [Fig.9]. The assembly 80 comprises beads 74, 72 and 73 of thermoplastic welding material 70 on each side of the part 50 and at the entrance to the injection orifices 52 which were formed essentially during the step of applying the compressive force. The beads 74, 72 and 73 reinforce the connection between the parts of the assembly.

[0067] The assembly 80 can then be subjected to finishing treatments, for example to remove excess welding material present at the end of manufacturing.

[0068] According to another embodiment of the invention, the welding between two parts made of thermoplastic matrix composite material can be carried out by means of an extruder using an additive manufacturing type technique.

[0069] In this case and as shown in Figures 10 and 11, the welding is preferably carried out in an enclosure 200 containing the parts made of thermoplastic matrix composite material to be welded, here a part 201 and a support or stiffener 202, an extruder 210, a first robotic arm 220 on which the extruder 210 is mounted and a second robotic arm 230 on which a gripper 231 is mounted. In the example described here the part 201 is held on a tool 205 which can be equipped with heating means (not shown in Figures 10 and 11). The enclosure 200 is heated to a temperature below the glass transition or melting temperature of their thermoplastic matrix.

[0070] A thermoplastic welding material 208 is deposited by the extruder 210 on an assembly face or portion of one of the parts to be welded, here on an assembly face 201a of the part 201 ([Fig. 10]). According to the invention, the thermoplastic welding material is deposited at a temperature higher than the melting temperature of each thermoplastic matrix of the parts to be welded. The second robotic arm 230 then positions the assembly surface or portion of the second part, here the support or stiffener 202, on the deposited thermoplastic welding material 208 ([Fig. 11]). The temperature of the thermoplastic welding material makes it possible to remelt the thermoplastic matrix of the two parts locally at the assembly surfaces. This local remelting makes it possible to obtain a good chemical bond with the thermoplastic welding material and thus a good bond between the two parts.The thermoplastic welding material is preferably injected at a temperature at least 5% higher than the glass transition or melting temperature of the thermoplastic matrix of the parts.

[0071] The thermoplastic material of the matrix of the parts to be welded and the thermo material welding plastic can be the same. For example, in the case of a common thermoplastic material of PEI (polyetherimide), the two parts to be welded are typically heated between 100 and 200°C. The injection or deposition of the thermoplastic welding material is carried out at a temperature between 360°C and 400°C, preferably at 380°C with preferably the application of a compressive force on the parts after injection or deposition.

[0072] The thermoplastic welding material may in particular be one of the following thermoplastic materials: PAEK (PolyArylEtherCetone), PEEK (PolyEtherEtherCetone), PEKK (PolyEtherCetoneCetone), PEI (polyetherimide), PSU (polysulfone), PESU or PPS (polyphenylene sulfide), PA (polyamide) and PC (polycarbonate).

[0073] The thermoplastic welding material may be a pure thermoplastic resin, i.e. unfilled, or a thermoplastic resin filled, for example, with short fibers, such as carbon, glass or aramid fibers, or other types of fillers.

[0074] The thermoplastic welding material may also be different from the thermoplastic material of the matrix of the parts to be welded and have a melting temperature higher than the glass transition or melting temperature of the thermoplastic matrix of at least one of the parts made of thermoplastic matrix composite material. In this case, the welding material is injected at a temperature lower than the degradation temperature of the thermoplastic matrix(es) of the parts. Still in this case, a thermoplastic welding material is chosen which is chemically compatible with the thermoplastic material of the matrices of the parts and whose glass transition or melting temperature is lower than the degradation temperature of the thermoplastic material of the matrix of each of the parts.

[0075] The parts to be welded may also each comprise a matrix made of a different thermoplastic material. In this case, the thermoplastic material of the matrix having the highest glass transition or melting temperature is used for the welding material. The thermoplastic welding material is injected at a temperature higher than the glass transition or melting temperature of the matrix having the highest glass transition or melting temperature and lower than the degradation temperature of the matrix having the lowest glass transition or melting temperature.

[0076] The welding method of the invention makes it possible to manufacture any type of part by assembling bodies or parts made of thermoplastic matrix composite material. The parts thus obtained may correspond in particular to nacelle or fuselage parts such as skins fitted with stiffeners, skins with fixing yoke, clips, etc.

Claims

Claims

1. A method of welding between two parts made of thermoplastic matrix composite material (10, 20) having respective assembly surfaces (11, 21), the method comprising holding the assembly surfaces of the parts opposite each other so as to form a welding interface (5) between said parts, characterized in that the method further comprises injecting a thermoplastic welding material (40) at the welding interface and in that the thermoplastic welding material is injected at a temperature higher than the glass transition or melting temperature of each thermoplastic matrix of the parts (10, 20).

2. The method of claim 1, wherein the thermoplastic welding material (40) is injected at a temperature at least 5% higher than the glass transition or melting temperature of each thermoplastic matrix of the parts.

3. A method according to claim 1 or 2, wherein the thermoplastic welding material (40) has a glass transition or melting temperature higher than the glass transition or melting temperature of the thermoplastic matrix of at least one of the thermoplastic matrix composite material parts (10, 20), the welding material being injected at a temperature lower than the degradation temperature of each thermoplastic matrix of the parts.

4. Method according to any one of claims 1 to 3, in which, during the injection of the thermoplastic welding material (40) at the welding interface (5), the thermoplastic matrix composite material parts (10, 20) are heated to a temperature lower than the glass transition or melting temperature of each matrix of said parts.

5. A method according to any one of claims 1 to 4, wherein the thermoplastic welding material (40) comprises an unfilled thermoplastic resin or a filled thermoplastic resin.

6. A method according to any one of claims 1 to 4, further comprising, after injecting the thermoplastic welding material (70) at the welding interface (15), applying a compressive force (Cp) to at least one (50) of the parts (50, 60) so as to bring the assembly surfaces (51, 61) of the parts closer together.

7. A method according to any one of claims 1 to 6, wherein at at least one (50) of the parts (50, 60) comprises one or more injection orifices (52) opening onto the assembly surface (51), the thermoplastic welding material (70) being injected at the welding interface (15) through the injection orifice(s) (52).

8. Method of welding between at least two parts made of thermoplastic matrix composite material having respective assembly surfaces, characterized in that it comprises the deposition of a thermoplastic welding material on an assembly surface of one of the parts, the thermoplastic welding material being deposited at a temperature higher than the glass transition or melting temperature of each thermoplastic matrix of the parts and the contacting of the assembly surface of the other part with the deposited thermoplastic welding material, the parts made of thermoplastic matrix composite material being heated to a temperature lower than the glass transition or melting temperature of the matrix of said parts during the deposition of the thermoplastic welding material and the contacting of the assembly surface of the other part with the deposited thermoplastic welding material.

9. A method according to claim 8, wherein the thermoplastic welding material is injected at a temperature at least 5% higher than the glass transition or melting temperature of each thermoplastic matrix of the parts.

10. Method according to claim 8 or 9, in which the thermoplastic welding material has a glass transition or melting temperature higher than the glass transition or melting temperature of the thermoplastic matrix of at least one of the parts made of thermoplastic matrix composite material, the welding material being injected at a temperature lower than the degradation temperature of the thermoplastic matrix of the parts.

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