EP4204216A1

EP4204216A1 - System and method for joining high-performance thermoplastic components

Info

Publication number: EP4204216A1
Application number: EP21820641.5A
Authority: EP
Inventors: Laurent Dubreuil
Original assignee: Airbus Atlantic SAS
Current assignee: Airbus Atlantic SAS
Priority date: 2020-12-11
Filing date: 2021-12-09
Publication date: 2023-07-05
Also published as: FR3117400A1; CA3193859A1; WO2022122881A1; FR3117400B1; US20240025127A1

Abstract

A device (1) for joining a first component (A1) to be welded to a second component (A2) to be welded, the joining device (1) comprising at least one electrically conductive, resistive heating film (2) which comprises a central connection portion (21) and two lateral electrical connection portions (22). The joining device (1) comprises at least one first electrical insulation member (3A) which is positioned in contact with the first face (FA) of the heating film (2), and at least one second electrical insulation member (3B) which is positioned in contact with the second face (FB) of the heating film (2), the two electrical insulation members (3A, 3B) being configured to allow the transfer of heat and to prevent the flow of electric current between the heating film (2) and each component (A1, A2) to be welded.

Description

System and method for joining high-performance thermoplastic parts

The present invention relates to the field of the assembly of thermoplastic parts and more specifically the joining by resistive welding of high-performance thermoplastic parts, in particular, in the aeronautical field.

In known manner, the parts intended to be mounted on an aircraft, generally made of a metallic material, are secured by riveting or by other added fasteners. However, the addition of inserts significantly increases the weight of the aircraft. Also, such an assembly is increasingly replaced by a welding method which makes it possible both to limit the number of parts (allowing a saving of time and mass).

Moreover, in the aeronautical field, metal parts are most often replaced by lighter parts made of composite material. It is in particular known to use parts made of a high performance thermoplastic material, such as polyaryletherketone known under the designation PAEK, or polyetherketoneketone, known under the designation PEKK, having good mechanical properties. Reinforcing fibers, commonly carbon fibers, are generally impregnated in the thermoplastic matrix to reinforce the part, giving it both strength and lightness.

As is known, high performance thermoplastic parts are generally assembled by an induction welding method. As such, the document WO2020079010 is known in which an insert comprising a conductive structure is positioned between two parts to be assembled and moved along the connecting zone defined between the two parts. By heating, the conductive structure locally melts the thermoplastic matrix at the interface between the two parts on a local portion of the connection zone. When the material is melted in the local portion, the insert is moved to another local portion and the two parts to be assembled are pressed against each other to be welded after cooling and solidification of the molten thermoplastic matrix. The insert makes it possible to successively heat each of the local portions of the connection zone and is removed at the end of the assembly.

However, such induction welding locally heats too much and non-uniformly, which can impact the mechanical performance of the parts to be welded. In addition, if the parts are too far apart at a local portion, if they are too stiff, it is not possible to flatten the two parts at any point, which can locally alter the resistance. of the connection area. Such a defect is known to those skilled in the art as a "docking defect".

To remedy this drawback, document EP3488999A1 describes a method for joining two composite parts to be welded, in which a film of graphene is deposited at the interface between the two parts along the entire connection zone. Graphene, which has significant thermal diffusion properties, is connected to a resistive heating system. By heating, the graphene uniformly melts the thermoplastic matrix at the interface between the two parts to be welded along the entire bonding area, which is advantageous. The two parts are then welded together by mixing their thermoplastic matrices.

However, in such a process, the graphene, having melted the thermoplastic matrix in the bonding zone, can come into contact with the carbon fibers of the parts to be welded. The graphene connected to the resistive heating system conducts electricity and transfers it by contact to the carbon fibers. This can lead to short circuits which can cause local overheating and damage the parts to be welded. The welding is then of poor quality.

An immediate solution would be to use thermoplastic parts comprising fibers that are not conductive. However, such a solution is not feasible in terms of performance and cost.

To date, there is no system or process for joining composite parts comprising reinforcing fibers impregnated in a high-performance thermoplastic matrix in an effective manner without risking damage to the parts to be welded.

The invention thus aims to eliminate at least some of these drawbacks by proposing a system and a method for securing two simple and effective thermoplastic parts, making it possible both to ensure the connection between the two parts at any point of the interface zone, while eliminating the risk of damaging the parts.

We know from document JP5560121 a system for assembling two composite parts in which a heating element, placed between the two composite parts to be assembled, comprises an insulating surface, obtained by a surface treatment. The insulating surface makes it possible to limit the transfer of electric current between the heating film and the two parts to be joined together. Also known are documents US20170043528 and US5389184, assembly systems comprising a heating film and two electrical insulation members, which make it possible to limit the flow of electric current between the heating film and each composite part, so as to protect them. . However, the assembly systems described in the documents US20170043528 and US5389184 are configured to be integrated into the welded zone after the assembly operation of the two parts and are bulky, which can alter the mechanical properties of the composite parts and of the welded area between the composite parts.

PRESENTATION OF THE INVENTION

au moins un film chauffant résistif électriquement conducteur, le film chauffant présentant une première face plane et une deuxième face plane opposée à la première face, le film chauffant comprenant :
- une portion centrale de liaison, configurée pour être montée selon la zone de soudage commune entre les surfaces intérieures des deux pièces à souder pour les souder, et
- deux portions latérales de connexion électrique, configurées pour être montées en dehors de la zone de soudage commune, les portions latérales étant configurées pour être reliées électriquement à une source de courant de manière à permettre une élévation de la température de la portion centrale jusqu’à une température de fonctionnement.

The invention relates to a device for joining a first part to be welded to a second part to be welded according to a common welding zone, configured to form a welded zone once the parts to be welded have been joined together, each part to be welded being manufactured in a composite material comprising reinforcing fibers impregnated in a thermoplastic matrix, each part to be welded having a flat inner surface to be welded, the inner surfaces of the parts to be welded being positioned facing each other, the device securing device being configured to be at least partially integrated into the welded zone, the securing device comprising:

at least one electrically conductive resistive heating film, the heating film having a first flat face and a second flat face opposite the first face, the heating film comprising:
- a central connecting portion, configured to be mounted along the common welding zone between the inner surfaces of the two parts to be welded in order to weld them, and
- two lateral electrical connection portions, configured to be mounted outside the common welding zone, the lateral portions being configured to be electrically connected to a current source so as to allow a rise in temperature of the central portion up to an operating temperature.

au moins un premier organe d’isolation électrique, positionné au contact de la première face du film chauffant en vis-à-vis de la portion centrale et configuré pour être positionné en vis-à-vis de la surface intérieure de la première pièce à souder, et
au moins un deuxième organe d’isolation électrique, positionné au contact de la deuxième face du film chauffant en vis-à-vis de la portion centrale et configuré pour être positionné en vis-à-vis de la surface intérieure de la deuxième pièce à souder,
les deux organes d’isolation électrique étant configurés pour autoriser le transfert de chaleur et interdire la circulation de courant électrique entre le film chauffant et chaque pièce à souder.

The securing device is remarkable in that it comprises:

at least one first electrical insulation member, positioned in contact with the first face of the heating film facing the central portion and configured to be positioned facing the inner surface of the first part to be solder, and
at least one second electrical insulation member, positioned in contact with the second face of the heating film facing the central portion and configured to be positioned facing the inner surface of the second part to be solder,
the two electrical insulation members being configured to allow heat transfer and prevent the flow of electric current between the heating film and each part to be welded.

The electrical insulation members of the securing device according to the invention advantageously make it possible to limit the bringing into contact of the resistive heating film with the reinforcing fibers of the composite parts to be welded, which makes it possible to limit the transfer of electric current in the parts. solder and thus eliminate the risk of short-circuiting.

The heating film mounted between the two parts to be welded makes it possible to melt the thermoplastic matrix of the parts to be welded to allow them to be welded. The fact of heating the interface directly and quickly makes it possible to limit the diffusion of heat in the thickness of the part. Only the interface is melted, which ensures the integrity of the welded parts.

Indeed, the resistive heating film allows uniform, rapid and homogeneous heating of the interior surfaces of the parts to be welded at the level of the central connection portion, by limiting the risk of local overheating. Such a resistive heating film also makes it possible to control the heating temperature by controlling the voltage applied, which makes it possible to precisely manage the rise in temperature, in particular making it possible to maintain a temperature plateau ensuring the melting of the dies thermoplastics and their mixture, while controlling the degree of crystallinity of each thermoplastic matrix. Optimum mechanical performance is thus guaranteed in the parts to be welded, even at their interface in the common welding zone.

The securing device makes it possible to secure two parts to be welded by a welding operation, which makes it possible to limit the mass of the assembly and of the aircraft, by dispensing with the addition of assembly parts, for example rivets. Welding with a resistive heating film also allows efficient, fast welding without the risk of short-circuiting or overheating.

Preferably, the heating film is a graphene film. Graphene is a material that has a high resistance to heat and has a high electrical conductivity, allowing it to fulfill its role effectively. Also, the behavior of graphene is known.

In one embodiment, each electrical insulation member is made of a composite material comprising a thermoplastic matrix, allowing the use of electrical insulation member having a low electrical conductivity, which makes it possible to melt the thermoplastic matrix of each part to be welded, without damaging them.

Preferably, each electrical insulation member is manufactured in a high performance thermoplastic resin, more preferably in a polyaryletherketone PAEK or polyetherketoneketone PEKK polymer resin.

Preferably, each electrical insulation member comprises glass fibers, allowing the use of robust electrical insulation members while guaranteeing limited electrical conductivity. Glass fibers, non-conductive, allowing not to transfer electrical energy to the parts to be welded, in an efficient way.

Preferably again, each electrical insulation member consists of glass fibers impregnated in a thermoplastic polyaryletherketone PAEK or polyetherketoneketone PEKK matrix.

Preferably, the heating film has a thickness of between 1 μm and 50 μm. Such a thickness allows the heating film, intended to be integrated in the welded zone, not to generate any extra thickness at the interface between the two parts to be welded, which can cause a local offset of the interior surfaces of each part and thus a defect of 'assembly.

In a preferred embodiment, each electrical insulation member is in the form of an insulating film, having a thickness of between 0.05mm and 0.2mm. Such a thickness allows an electrical insulation member that is both thin enough to limit the bulk of the securing device and thick enough to form a barrier vis-à-vis the conductive graphene fibers of the heating film. Such a thickness also allows a thin, space-saving complete securing device which can remain in the welded zone after securing the two parts to be welded, without impacting the mechanical characteristics of the parts.

Preferably, the heating film has a thickness of between 0.0002 and 0.05 mm. Such a thickness is large enough to allow the heating film to be deposited in a uniform layer without being damaged while allowing homogeneous electrical properties throughout the heating film. In addition, a thickness of less than 0.05mm makes it possible to limit the size of the heating film and therefore of the securing device, while ensuring a device at a lower cost.

Preferably, the assembly formed by the heating film and the two electrical insulation members has a thickness of between 0.1 mm and 0.5 mm. The securing device thus does not impact the mechanical properties of the parts to be welded and has little impact on the mass of the assembly and therefore of the aircraft.

Preferably, the heating film having a length extending along a longitudinal axis, the heating film has a variable thickness over the length. A variable thickness makes it possible to locally vary the heating power of the heating film.

Preferably, the heating film having a width extending along a lateral axis, the heating film having a variable thickness over the width, so as to locally vary the heating power of the heating film.

Preferably, the thickness of the heating film varies by a maximum of ten times the minimum thickness of the heating film.

In a preferred embodiment, the fastening device comprises at least two electrical connection members, respectively positioned in contact with the two lateral portions of the heating film so as to allow the electrical connection of the heating film to the current source.

Preferably, each electrical connection member is in the form of a strip of copper, allowing the use of a highly conductive element, which makes it possible to limit the risks of dissipation of electrical energy. Alternatively, each electrical connection device is in the form of a conductive ink, making it possible to dispense with the addition of additional elements and simplifying the storage of the various devices.

Preferably, the electrical connection members are mounted on the same face of the heating film, which makes it possible to facilitate the mounting of the securing device, preferably on an easily accessible upper face.

Preferably, the side portions are at least partially detachable, preferably entirely, allowing them to be removed after the joining operation to lighten the assembly and improve the visual appearance. In one embodiment, the heating film comprises a pre-cut between each side portion and the central portion, allowing simple and quick removal.

Preferably, the operating temperature is between 330 and 450°C, so as to ensure the melting of the thermoplastic matrix of each part to be welded, without risking local overheating.

In one embodiment, the securing device is packaged in a roll, allowing simple and rapid removal on the inner surface of one of the parts to be welded. The securing device can thus advantageously be cut to the desired length directly at the place of assembly and in a practical manner. Packaging on a roll, like an adhesive roll, makes it possible to precisely install a sufficient and not excessive length in the common welding zone, making it possible to limit the risk of error in underestimated dimensions (source of loss of time) and waste. Alternatively, the securing device can be packaged in the form of a plate or a pre-cut patch.

In one embodiment, the fastening device comprises at least one thickness compensation member, positioned on at least one of the electrical insulation members, so as to compensate for a difference between the electrical insulation member and the piece to be welded, the thickness compensation member being formed at least in part from a thermoplastic matrix. The addition of one or more thickness compensation device(s) makes it possible, for example, to compensate for a lack of docking between the parts to be welded or to locally fill in a relief.

Preferably, each thickness compensation member is formed from the same thermoplastic matrix as the thermoplastic matrix of the heating film, ensuring material continuity. In an alternative embodiment, each thickness compensation member comprises glass fibers impregnated in a thermoplastic matrix, preferably a PAEK thermoplastic matrix.

In one embodiment, the fastening device comprises a member for measuring the internal temperature, so as to control in real time the temperature inside the fastening device itself, in the welding zone. Preferably, the internal temperature measuring device is mounted directly on the heating film, allowing optimal reading at the heart of the interface between the two parts to be welded. Preferably, the member for measuring the internal temperature is in the form of one or more optical fibre(s) with a Bragg grating inserted between the heating film and one of the electrical insulation.

Preferably, the securing device comprises at least one filler member making it possible to fill a useful portion of one of the parts to be welded in terms of mechanical strength, for example a chamfer. The piece to be welded is thus not weakened by the joining operation and is welded efficiently. Each filler member is preferably made from a PAEK thermoplastic matrix and may comprise glass fibers impregnated in the thermoplastic matrix.

In one embodiment, the securing device comprises at least one positioning guide extending projecting from the electrical insulation member, so as to facilitate the positioning of the part to be welded vis-à-vis the securing device. solidarity. In such an embodiment, the part to be welded comprising for example a notch, the positioning guide is configured to cooperate by form complementarity with the notch of the part to be welded. Preferably, each positioning guide is made of PAEK thermoplastic material.

The invention also relates to an assembly of a first part to be welded, a second part to be welded and at least one securing device as described above, each part to be welded being made of a thermoplastic material comprising fibers of reinforcement impregnated in a thermoplastic matrix, the securing device being configured to allow the securing of the first part to be welded and of the second part to be welded according to a common welding zone, each part to be welded comprising an inner surface, the inner surface of the first part to be welded being mounted facing the inner surface of the second part to be welded, the securing device being mounted between the inner surface of the first part to be welded and the inner surface of the second part to be welded according to common welding area.

In a preferred embodiment, the securing device is premounted on one of the two parts to be welded.

Furthermore, the invention relates to a securing system comprising at least one securing device as described previously and at least one pressure member configured to apply a pressure, comprised between 0.1 and 1.5 MPa, on one of the parts to be welded so as to compress together the first part to be welded, the fastening device and the second part to be welded according to the common welding zone. The pressure device makes it possible to apply sufficient pressure to allow the welding of the two parts, by mixing the thermoplastic matrices of the two parts to be welded, without damaging them.

une étape de positionnement du dispositif de solidarisation entre les surfaces intérieures des deux pièces à souder selon la zone de soudage commune, les organes d’isolation électrique étant en contact avec les surfaces intérieures des deux pièces à souder, et
une première étape de chauffage de la portion centrale du film chauffant à une température de fonctionnement supérieure à une température de fusion de la matrice thermoplastique des pièces à souder, par alimentation en courant des portions latérales du film chauffant, de manière à assembler les pièces ensemble.

Finally, the invention relates to a method for assembling a first part to be welded and a second part to be welded by means of the fastening device as described above, each part to be welded being made of a composite material comprising reinforcing fibers impregnated in a thermoplastic matrix, the method comprising:

a step of positioning the securing device between the inner surfaces of the two parts to be welded along the common welding zone, the electrical insulation members being in contact with the inner surfaces of the two parts to be welded, and
a first step of heating the central portion of the heating film to an operating temperature higher than a melting temperature of the thermoplastic matrix of the parts to be welded, by supplying current to the side portions of the heating film, so as to assemble the parts together .

Preferably, the method comprises, after the first heating step, a second step of heating the central portion to a consolidation temperature, lower than the operating temperature, so as to reinforce the welded zone between the two parts to be welded. .

Preferably, the consolidation temperature is between 200 and 270°C.

au moins un film chauffant résistif électriquement conducteur, le film chauffant présentant une première face plane et une deuxième face plane opposée à la première face, le film chauffant comprenant :
- une portion centrale de liaison, configurée pour être montée selon la zone de soudage commune entre les surfaces intérieures des deux pièces à souder pour les souder, et
- deux portions latérales de connexion électrique, configurées pour être montées en dehors de la zone de soudage commune, les portions latérales étant configurées pour être reliées électriquement à une source de courant de manière à permettre une élévation de la température de la portion centrale jusqu’à une température de fonctionnement.
au moins un premier organe d’isolation électrique, positionné au contact de la première face du film chauffant en vis-à-vis de la portion centrale et configuré pour être positionné en vis-à-vis de la surface intérieure de la première pièce à souder, et
au moins un deuxième organe d’isolation électrique, positionné au contact de la deuxième face du film chauffant en vis-à-vis de la portion centrale et configuré pour être positionné en vis-à-vis de la surface intérieure de la deuxième pièce à souder,
les deux organes d’isolation électrique étant configurés pour autoriser le transfert de chaleur et interdire la circulation de courant électrique entre le film chauffant et chaque pièce à souder.

The invention further relates to a method for assembling a first part to be welded and a second part to be welded according to a common welding zone, configured to form a welded zone once the parts to be welded together, each part to weld being made of a composite material comprising reinforcing fibers impregnated in a thermoplastic matrix, each part to be welded having a flat inner surface to be welded, the inner surfaces of the parts to be welded being positioned facing one of the another, the method being carried out by means of a securing device, the securing device being configured to be at least partially integrated into the welded zone, the securing device comprising:

at least one electrically conductive resistive heating film, the heating film having a first flat face and a second flat face opposite the first face, the heating film comprising:
- a central connecting portion, configured to be mounted along the common welding zone between the inner surfaces of the two parts to be welded in order to weld them, and
- two lateral electrical connection portions, configured to be mounted outside the common welding zone, the lateral portions being configured to be electrically connected to a current source so as to allow a rise in temperature of the central portion up to an operating temperature.
at least one first electrical insulation member, positioned in contact with the first face of the heating film facing the central portion and configured to be positioned facing the inner surface of the first part to be solder, and
at least one second electrical insulation member, positioned in contact with the second face of the heating film facing the central portion and configured to be positioned facing the inner surface of the second part to be solder,
the two electrical insulation members being configured to allow heat transfer and prevent the flow of electric current between the heating film and each part to be welded.

une étape de positionnement du dispositif de solidarisation entre les surfaces intérieures des deux pièces à souder selon la zone de soudage commune, les organes d’isolation électrique étant en contact avec les surfaces intérieures des deux pièces à souder,
une première étape de chauffage de la portion centrale du film chauffant à une température de fonctionnement supérieure à une température de fusion de la matrice thermoplastique des pièces à souder, par alimentation en courant des portions latérales du film chauffant, de manière à assembler les pièces ensemble, et
une deuxième étape de chauffage de la portion centrale à une température de consolidation, inférieure à la température de fonctionnement, de manière à renforcer la zone soudée entre les deux pièces à souder.

The process includes:

a step of positioning the securing device between the inner surfaces of the two parts to be welded along the common welding zone, the electrical insulation members being in contact with the inner surfaces of the two parts to be welded,
a first step of heating the central portion of the heating film to an operating temperature higher than a melting temperature of the thermoplastic matrix of the parts to be welded, by supplying current to the side portions of the heating film, so as to assemble the parts together , and
a second step of heating the central portion to a consolidation temperature, lower than the operating temperature, so as to reinforce the welded zone between the two parts to be welded.

PRESENTATION OF FIGURES

The invention will be better understood on reading the following description, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects. .

The is a schematic representation of an exploded view in longitudinal section of an assembly of two parts to be welded and of a securing device according to one embodiment of the invention.

The is a schematic representation of a perspective view of the securing device of the assembly of fig 1.

The is a view in longitudinal section of the securing device of the .

The is a schematic representation of two parts to be welded comprising reinforcing fibers and the device for securing the , before joining.

The is a schematic representation of two parts to be welded comprising reinforcing fibers assembled by means of the fastening device of the , after joining.

The is a schematic representation of a fastening device according to an alternative embodiment of the invention.

The is a schematic representation of the securing device of the comprising a plurality of thickness compensation members.

The is a schematic representation of the entire , wherein the securing device comprises a filler member.

The is a schematic representation of the entire , wherein the fastening device comprises a positioning guide.

The is a schematic representation of a fastening system comprising the fastening device of the and a pressure member according to one embodiment of the invention.

The and

the are schematic representations of a fastening system comprising the fastening device of the and a pressure member according to two alternative embodiments of the invention.

The is a schematic representation of the steps of a joining method according to one embodiment of the invention.

It should be noted that the figures expose the invention in detail to implement the invention, said figures can of course be used to better define the invention if necessary.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a device 1 for securing a first part to be welded A1 and a second part to be welded A2 ( ). The invention applies in particular to the attachment of parts intended to be mounted on an aircraft.

The parts to be welded A1, A2 are made of a thermoplastic material and comprise reinforcing fibers impregnated in a thermoplastic matrix. Preferably, the thermoplastic matrix is a high performance thermoplastic polymer resin, such as polyetherketoneketone known by the acronym PEKK or polyaryletherketones known by the acronym PAEK, for example. Preferably, the reinforcing fibers are carbon fibers, giving the parts to be welded A1, A2 both strength and lightness. However, it goes without saying that the thermoplastic matrix and the reinforcing fibers could come from different materials. Carbon fibers are current conductors.

With reference to the , each piece to be welded A1, A2 has a flat inner surface to be welded SI1, SI2 and an outer surface SE1, SE2, opposite to the inner surface SI1, SI2.

The parts to be welded A1, A2 are configured to be secured along a common welding zone W and to be positioned so as to place their respective inner surfaces SI1, SI2 facing each other, as will be described in more detail later. The common welding zone W is intended to form a welded zone, once the parts to be welded A1, A2 have been joined together. In this example, the welding zone W is rectilinear but it goes without saying that it could extend in various ways, in particular, curved.

The securing device 1 according to the invention is configured to be mounted between the two parts to be welded A1, A2, so as to secure them. Once the parts to be welded A1, A2 have been joined together, the joining device 1 is at least partially integrated into the welded zone, as will be described in more detail later in this document. In other words, the securing device 1 is consumable and is configured to remain imprisoned at the interface between the two welded parts A1, A2 at the end of the securing operation. It is thus advantageously no longer necessary to store or move large equipment when assembling two thermoplastic parts to be welded.

In this example, with reference to Figures 2 and 3, the securing device 1 extends longitudinally along an X axis, laterally along a Y axis and vertically along a Z axis, so as to form an orthogonal reference (X, Y, Z). With reference to the , a longitudinal portion of the securing device 1 is shown for the sake of clarity. The length of the securing device 1 is adapted according to the welding zone W.

In this embodiment, the securing device 1 comprises a resistive heating film 2 and two electrical insulation members 3A, 3B, positioned along the vertical axis Z on either side of the heating film 2 as well as two electrical connection 4.

The heating film 2 is electrically conductive and is configured to be powered by a current source C. Preferably, the heating film 2 is in the form of a graphene film having high electrical conductivity and high heat resistance. . Alternatively, the heating film 2 can be made of a different material, for example carbon nanotubes.

With reference to the , the heating film 2 has a first flat face FA (lower face) and a second flat face FB (upper face), opposite the first face FA. The heating film 2 thus has a flat and thin general shape. More specifically, the heating film 2 has a length J extending along the longitudinal axis X (shown on the ), a width L extending along the lateral axis Y and a thickness Ep2 extending along the vertical axis Z (shown on the ). The thickness Ep2 is preferably between 1 μm and 50 μm. The heating film 2 is thus thin and light, and has little impact on the mechanical characteristics of the parts to be welded A1, A2 and of the assembly formed by the parts to be welded A1, A2 and the fastening device 1 In a variant, the thickness Ep2 is variable over the length J of the heating film 2, making it possible to locally vary the heating power. It goes without saying that the thickness Ep2 can also vary along the width L of the heating film 2, along the Y axis.

Still with reference to the , the heating film 2 according to the invention comprises a central connecting portion 21 and two lateral electrical connection portions 22, extending along the lateral axis Y on either side of the central connecting portion 21.

The central connecting portion 21 is configured to be mounted along the common welding zone W between the inner surfaces SI1, SI2 of the two parts to be welded A1, A2 so as to weld them, as shown in the . Conversely, the two lateral electrical connection portions 22 are configured to be mounted outside the common welding zone W.

The central portion 21 is configured to heat up to an operating temperature Tf, preferably between 330 and 450° C., which is higher than the melting temperature (which is known) of the thermoplastic matrix of the parts to be welded A1, A2, as will be described in more detail later.

The two lateral electrical connection portions 22 are configured to be electrically connected, directly or indirectly, to the external current source C (shown in FIGS. 2 and 3) so as to allow a rise in the temperature of the central portion 21 up to the operating temperature Tf.

As represented in FIGS. 4 and 5, the heating film 2 mounted between the two parts to be welded A1, A2 is configured to melt the thermoplastic matrix of the composite parts to be welded A1, A2 to allow them to be welded by mixing the thermoplastic matrices. The fact of heating the interface directly and quickly makes it possible to limit the diffusion of heat in the thickness of each part to be welded A1, A2. Only the interior surfaces SI1, SI2 are melted, which ensures the integrity of the welded parts A1, A2.

As described above, with reference to Figures 1 to 3, the fastening device 1 also comprises a first insulation member 3A and a second electrical insulation member 3B, positioned along the thickness of the fastening device 1, that is i.e. along the vertical axis Z, on either side of the heating film 2.

The first electrical insulation member 3A is positioned in contact with the first face FA of the heating film 2 facing the central portion 21 and is configured to be positioned facing the inner surface SI1 of the first piece to be welded A1, as shown in the . Similarly, the second electrical insulation member 3B is positioned in contact with the second face FB of the heating film 2 facing the central portion 21 and is configured to be positioned facing the surface interior SI2 of the second piece to be welded A2. In other words, the heating film 2 is sandwiched between the two electrical insulation members 3A, 3B located above and below the heating film 2.

Each electrical insulation member 3A, 3B is configured to allow the transfer of heat and prohibit the circulation of electric current between the heating film 2 and each part to be welded A1, A2, so as to limit the risk of short-circuit or local overheating in the parts to be welded A1, A2, making it possible to guarantee their integrity. More specifically, as shown in the , each electrical insulation member 3A, 3B is configured to limit the risk of contact between the resistive heating film 2 and the conductive reinforcing fibers of the composite parts to be welded A1, A2, as was the case in the prior art.

Preferably, each electrical insulation member 3A, 3B has a surface greater than that of the common welding zone W. Thus, any contact between the heating film 2 and the parts to be welded A1, A2 is prohibited, which eliminates any electrical risk. Each electrical insulation member 3A, 3B thus forms an electrical insulation barrier between the heating film 2 and a part to be welded A1, A2.

For this, each electrical insulation member 3A, 3B is preferably made of a composite material comprising a thermoplastic matrix, which has low electrical conductivity. Preferably again, each electrical insulation member 3A, 3B is made of a high-performance thermoplastic material, such as PEKK or PAEK described previously. In one embodiment, each electrical insulation member 3A, 3B comprises non-conductive reinforcing fibers, for example glass fibers, impregnated in the high performance thermoplastic matrix. Glass fibers make it possible to effectively dispense with the transfer of electrical energy to the parts to be welded A1, A2. Such electrical insulation members 3A, 3B made of high performance thermoplastic material are thus capable of melting under the effect of heat and participating in the welding of parts A1, A2, by mixing with the thermoplastic matrix of the welded parts A1, A2, as shown in the . The non-conductive reinforcing fibers form an electrical insulation barrier.

Preferably, each electrical insulation member 3A, 3B is in the form of an insulating film, thus having a thickness Ep3 (shown on the ), along the vertical axis Z preferably between 0.05 and 0.2 mm. Such a thickness Ep3 makes it possible to form a thin and compact fastening device 1 . Indeed, the assembly formed by the heating film 2 and the two electrical insulation members 3A, 3B thus does not generate any significant extra thickness, which allows the fastening device 1 to remain in the welded zone after fastening of the two parts. solder A1, A2, as previously described and shown in the , without impacting the mechanical characteristics of the parts to be welded A1, A2. The electrical insulation members 3A, 3B can have identical or different thicknesses.

In summary, the assembly formed by the heating film 2 and the two electrical insulation members 3A, 3B preferably has a thickness Ep1 (shown on the ) between 0.1 and 0.5mm. Such a thickness does not impact the mechanical properties of the parts to be welded A1, A2 and has little impact on the mass of the assembly and therefore of the aircraft.

In one embodiment, each electrical insulation member 3A, 3B has a variable thickness, preferably in the lateral direction Y. This makes it possible to control the transfer of heat from the heating film 2 to the parts to be welded A1, A2. In particular, the thickness of an electrical insulation member 3A, 3B can be greater close to a lateral portion 22 compared to the central portion 21 so as to reduce the heating power at the edge of the welding zone. W. The diffusion of heat at the ends of the welding zone W is limited.

In a preferred embodiment, as shown in Figures 2 and 3, the securing device 1 further comprises two electrical connection members 4, respectively positioned in contact with the two side portions 22 of the heating film 2 so as to allow the connection of the heating film 2 to the current source C. In other words, the current source C is connected indirectly to the heating film 2 via the electrical connection members 4. This makes it possible to form a robust and practical connection. Preferably, each electrical insulation member 4 is configured not to be in contact with any of the parts to be welded A1, A2 (as represented on the ).

Preferably, each electrical connection member 4 is in the form of a strip of copper, electrically connected to the current source C, for example by an electric cable. Alternatively, each electrical connection member 4 is in the form of a conductive ink deposited directly on one of the faces FA, FB of the heating film 2.

Preferably, as shown in Figures 2 and 3, the two electrical connection members 4 are mounted on the same face FA, FB of the heating film 2, so as to facilitate the mounting of the securing device 1.

Preferably, the two electrical connection members 4 being mounted on the side portions 22 of the heating film 2, that is to say outside the common welding zone W, these are configured to be removed after the joining operation of the two parts to be welded A1, A2. Also, with reference to the , the electrical connection members 4 are configured not to be integrated into the welded zone, which makes it possible to cut the electrical connection between the current source C and the resistive heating film 2, making it possible to overcome the presence of a conductive element at the interface between the two parts to be welded A1, A2 which can lead to a short circuit for example.

Preferably, the side portions 22 are detachable, so that they can be removed after the joining operation. In a preferred embodiment, the heating film 2 has a pre-cut, for example a partially detached dotted line between the central portion 21 and each side portion 22, for simple and quick removal. Advantageously, such a pre-cut makes it possible to remove the side portions 22 and the electrical connection members 4 during the same operation. Thus, after securing, the securing device is no longer visible.

It goes without saying that the fastening device 1 could comprise a different number of electrical connection members 4, as is for example shown in the . By way of example, in the case of parts to be welded A1, A2 having large dimensions, the fastening device 1 may comprise a heating film 2 and two electrical insulation members 3A, 3B extended longitudinally, in this example according to l longitudinal axis X. The fastening device 1 then comprises a plurality of electrical connection members 4, aligned along the side portions 22 of the heating film 2, over the entire length of the heating film 2, along the axis X. indeed, the rise in temperature in the heating film 2 being optimal between two electrical connection members 4, an electrical connection of each lateral portion 22 is thus ensured in an optimal manner over its entire length, ensuring heating of the entire heating film 2, even if it has large dimensions.

The presence of a plurality of electrical connection members 4 also makes it possible to control the heating power for each longitudinal portion of the heating film 2. It is thus possible to configure the heating power according to the thicknesses of the parts to be welded A1, A2. The securing device 1 is thus adaptable.

Preferably, the securing device 1 can be packaged in the form of individual elements or in the form of a roll which can be cut to the desired length.

Thanks to the securing device 1, the heating film 2 according to the invention allows uniform, rapid and homogeneous heating of the entire surface of the interior surfaces SI1, SI2 of each part to be welded A1, A2 at the level of the central connecting portion 21 , limiting the risk of local overheating. The resistive heating film 2 allows control of the heating temperature of the central portion 21 by controlling the voltage applied via the lateral electrical connection portions 22. Such control makes it possible to precisely manage the rise in temperature of the heating film 2 and allows maintenance of a stable temperature level making it possible to ensure the homogeneous mixing of the thermoplastic matrices of the parts to be welded A1, A2 and of the securing device 1 (as shown in the ), as well as the control of the crystallinity rate of the thermoplastic matrix. Optimum mechanical performance is thus guaranteed, even at the interface between the two parts to be welded A1, A2 once joined together. The presence of electrical insulation members 3A, 3B eliminates any electrical risk while guaranteeing optimal heat transfer. The joining device 1, because of its small thickness, acts like a double-sided adhesive tape to join two parts to be welded A1, A2 facing each other in a robust manner and without degradation of the mechanical performance.

In one embodiment, shown in the , the securing device 1 comprises one or more thickness compensation member(s) 6, making it possible to compensate for a difference in height, a docking defect or a relief, for example on one of the interior surfaces SI1, SI2 of the parts to be welded A1, A2.

In a preferred embodiment, each thickness compensation member 6 is made of a thermoplastic material. Preferably, each thickness compensation member 6 is manufactured in a high performance thermoplastic matrix such as PEKK or PAEK described previously. In one embodiment, each thickness compensation member 6 comprises glass fibers impregnated in a PEKK or PAEK thermoplastic matrix. Preferably again, each thickness compensation member 6 is manufactured in the high performance thermoplastic matrix of each electrical insulation member 3A, 3B, the thermoplastic matrix of each electrical insulation member 3A, 3B itself being preferably identical to the thermoplastic matrix of the parts to be welded A1, A2. Thus, the securing device 1 is entirely manufactured in the same material, making it possible to overcome a risk of discontinuity of parts which would have different mechanical characteristics.

Each thickness compensation member 6 is preferably mounted on one of the electrical insulation members 3A, 3B and is positioned between the electrical insulation member 3A, 3B concerned and the inner surface SI1, SI2 of the part solder A1, A2 placed opposite each other. The thickness compensation member 6 is applied in an added manner according to the needs by the operator.

In one embodiment shown in the , the fastening device 1 comprises a member for measuring the internal temperature T, so as to control in real time the temperature inside the fastening device 1 itself, that is to say in the common welding zone W. Preferably, the device for measuring the internal temperature T is mounted directly on the heating film 2, allowing optimum reading of the temperature of the heating film 2. It is thus possible to stop the operation in the event of overheating of the heating film 2, which eliminates any risk of damage to the parts to be welded A1, A2. Preferably, the device for measuring the internal temperature T is in the form of one or more Bragg grating optical fibers inserted between the heating film 2 and one of the electrical insulation devices 3A, 3B. Such a device for measuring the temperature T also makes it possible to control the temperature drop in order to optimize the crystallization of the material.

In one embodiment, still with reference to the , the securing device 1 comprises a filler member 7A allowing cooperation with a portion of a part to be welded A1, A2 in order to form a flat inner surface, the portion being useful in terms of mechanical strength during the welding operation. solidarity. Such a useful portion may for example take the form of a chamfer. It goes without saying that the fastening device 1 can comprise a different number of filler members 7A, depending on the needs and the fragile or useful zones in terms of mechanical strength of the two parts to be welded A1, A2. Preferably, the filler member 7A is in the form of a fillet positioned at the level of the zone of curvature of a part to be welded A1.

Each filler member 7A is preferably made of high performance thermoplastic resin, preferably PEKK or PAEK thermoplastic material. Each filler member 7A can also comprise glass fibers, impregnated in a thermoplastic matrix.

In one embodiment, the securing device 1 also comprises a removable blocking member 7B, configured to be positioned on the surface of the electrical insulation member 3A, 3B against the filling member 7A, so as to sandwich between the blocking member 7B and the useful portion of the part to be welded A1, A2. The blocking member 7B is configured to be pressed against the filler member 7A, so as to ensure that the filler member 7A, intended to melt under the effect of the heat emitted by the heating film 2, does not flow and does not locally generate an involuntary extra thickness.

In one embodiment, shown in the , the securing device 1 comprises one or more positioning guide(s) 8 projecting from one of the electrical insulation members 3A, 3B, so as to facilitate the positioning of the part to be welded A1, A2 vis-à-vis the fastening device 1. In this case, the part to be welded A1, A2 comprising for example a notch E, the positioning guide 8 is configured to cooperate by form complementarity with the notch E of the part solder A1, A2. Preferably, each positioning guide 8 is made of thermoplastic resin, preferably of high performance PEKK or PAEK thermoplastic material.

There is shown in Figures 10 to 12, a securing system S comprising a first part to be welded A1, a second part to be welded A2, a securing device 1 as described above and a pressure member 9. The securing device 1 is mounted between the inner surface SI1 of the first part to be welded A1 and the inner surface SI2 of the second part to be welded A2 along the common welding zone W.

In one embodiment, the securing device 1 is pre-mounted on the inner surface SI1, SI2 of one of the two parts to be welded A1, A2, allowing both simpler transport of each element and faster assembly of the S connection system.

The pressure member 9 is configured to apply a pressure P on one of the parts to be welded A1, A2 so as to compress the assembly formed by the first part to be welded A1, the securing device 1 and the second part to be welded. weld A2 along the common welding zone W. The pressure member 9 is configured to apply a pressure P sufficient to allow the joining of the two parts to be welded A1, A2, by mixing the thermoplastic matrices of the two parts to be welded A1, A2 , when melted. Preferably, the pressure member 9 is configured to apply a pressure P of between 0.1 and 1.5 MPa.

Referring to Figures 11 and 12, in the case of joining parts to be welded A1, A2 having large dimensions (in this example along the longitudinal axis X), the joining device 1 preferably comprises several electrical connection members 4 extending along the longitudinal axis X, as described above. In this case, in a first embodiment, each electrical connection member 4 is independently connected to the current source, as represented on the . The whole of the heating film 2 is then configured to heat simultaneously, allowing rapid bonding of the entire common welding zone W. As explained previously, the heating power can be adapted locally according to the thicknesses to be welded.

In a second embodiment, shown in the , the securing system S further comprises a connection device D, configured to move along the axis X successively on each electrical connection member 4, so as to locally allow the progressive heating of the heating film 2, according to the longitudinal axis X. The connection device D is preferably in the form of a roller, capable of allowing the connection of each electrical connection member 4 by contact of the roller on the electrical connection member 4. Such a form embodiment allows for example to dispense with the installation of a plurality of connection cables.

A single securing device 1 has been presented, but it goes without saying that several securing devices 1 could be associated together in order to locally vary the heating power or the docking thickness.

A method for joining two thermoplastic parts to be welded will now be described, with reference to the . The joining process allows the joining of a first part to be welded A1 and a second part to be welded A2, as described previously and is carried out by means of the joining device 1 and the joining system S described above.

As shown on the , the method according to the invention firstly comprises a step of positioning E1 of the fastening device 1 between the inner surfaces SI1, SI2 of the two parts to be welded A1, A2 according to the common welding zone W. For this, an operator positions the securing device 1 on the inner surface SI1 of the first piece to be welded A1 at the level of the common welding zone W, the first piece to be welded A1 thus serving as a support for the securing device 1. The operator then positions the second part to be welded A2 on the fastening device 1 at the level of the common welding zone W, so that the fastening device 1 is sandwiched between the inner surface SI1 of the first part to be welded A1 and the surface interior SI2 of the second piece to be welded A2.

In a second connection step E2, the operator then connects, in this example, the electrical connection members 4 to the current source C and actuates the current source C by increasing its voltage so as to electrically supply the connection members electrical 4. The current is then transmitted to the side connection portions 22 of the heating film 2.

The method then comprises a first step of heating E3 of the central portion 21 of the heating film 2 by supplying current to the side portions 22. The temperature of the central portion 21 increases until it reaches the operating temperature Tf, for example between 330° C. and 450° C. which is higher than the melting temperature of the thermoplastic matrix of each piece to be welded A1, A2, at the level of the inner surface SI1, SI2, via each electrical insulation member 3A, 3B. The molten thermoplastic matrices of the two parts to be welded A1, A2 mix with the thermoplastic matrices of the electrical insulation members 3A, 3B so as to form a robust bond. Thanks to the securing device 1 according to the invention, the thermoplastic matrix of the inner surfaces SI1, SI2 of the parts to be welded A1, A2 can melt, without the electrical energy which circulates in the heating film 2 being transferred to the fibers of reinforcement of each part to be welded A1, A2, thus eliminating any risk of short circuit for example.

During heating, the operator applies a uniform pressure P by means of a pressure member 9 on the two parts to be welded A1, A2 in order to limit their relative movements and allow a mixture of material.

Once the thermoplastic matrices of the two parts to be welded A1, A2 have melted, the operator reduces the voltage of the current source C, so as to lower the temperature of the heating film 2. The method then comprises a second heating step E4, of the central portion 21 of the heating film 2 at a consolidation temperature Tc lower than the operating temperature Tf, for example between 200 and 270° C., so as to weld together the two parts to be welded A1, A2 under the effect of the pressure P applied by the pressure member 9 which allows uniform welding. Indeed, in this step, on cooling, the mixed thermoplastic matrices of the two parts to be welded A1, A2 solidify, so as to form the welded zone. Thanks to the electrical connection members 4, the temperature of the central portion 21 of the heating film 2 is managed sequentially. Such a second heating step E4 makes it possible to lower the temperature of the heating film 2 gradually, which makes it possible to keep the mechanical characteristics of each thermoplastic matrix intact, making it possible to avoid the formation of large crystals in the welded zone.

After the solidification of the thermoplastic matrices of the two parts to be welded A1, A2, the central portion 21 of the heating film 2 is mixed with the thermoplastic matrices of the parts to be welded A1, A2. In other words, the central portion 21 of the heating film 2 is trapped at the interface between the two parts to be welded A1, A2, in the welded zone.

When the material comprising the mixture of the two thermoplastic matrices of the two parts to be welded A1, A2 at the level of the welded zone is solidified, the method comprises a step E5 of removing the side portions 22 of the heating film 2 and the electrical connection members 4 , so as to remove any means of electrical connection. Since the heating film 2 is no longer electrically powered, any risk of short circuit is eliminated. All that then remains in the welded zone is the central portion 21 of the heating film 2 and the electrical insulation members 3A, 3B. Such a removal step E5 can be performed for example by detaching the side portions 22 along dotted lines, formed on a pre-cut line.

Claims

Device for securing (1) a first part to be welded (A1) to a second part to be welded (A2) along a common welding zone (W), configured to form a welded zone once the parts to be welded (A1, A2) joined together, each part to be welded (A1, A2) being made of a composite material comprising reinforcing fibers impregnated in a thermoplastic matrix, each part to be welded (A1, A2) having a flat inner surface to be welded (SI1, SI2 ), the inner surfaces (SI1, SI2) of the parts to be welded (A1, A2) being positioned facing each other, the fastening device (1) being configured to be at least partially integrated in the welded zone, the fastening device (1) comprising:

at least one electrically conductive resistive heating film (2), the heating film (2) having a flat first face (FA) and a flat second face (FB) opposite the first face (FA), the heating film (2) comprising :

a central connecting portion (21), configured to be mounted along the common welding zone (W) between the inner surfaces (SI1, SI2) of the two parts to be welded (A1, A2) to weld them, and

two lateral electrical connection portions (22), configured to be mounted outside the common welding zone (W), the lateral portions (22) being configured to be electrically connected to a current source (C) so as to allow a rise in the temperature of the central portion (21) up to an operating temperature (Tf),

the securing device (1) being characterized in that it comprises:

at least one first electrical insulation member (3A), positioned in contact with the first face (FA) of the heating film (2) facing the central portion (21) and configured to be positioned facing with respect to the inner surface (SI1) of the first piece to be welded (A1), and

at least one second electrical insulation member (3B), positioned in contact with the second face (FB) of the heating film (2) facing the central portion (21) and configured to be positioned facing opposite the inner surface (SI2) of the second part to be welded (A2),

the two electrical insulation members (3A, 3B) being configured to allow the transfer of heat and prevent the circulation of electrical current between the heating film (2) and each part to be welded (A1, A2), and

the assembly formed by the heating film (2) and the two electrical insulation members (3A, 3B) having a thickness (Ep1) of between 0.1 and 0.5 mm, the heating film (2) being a film of graphene.
Securing device (1) according to claim 1, in which each electrical insulation member (3A, 3B) is made of a composite material comprising a thermoplastic matrix.
Securing device (1) according to one of Claims 1 and 2, in which each electrical insulation member (3A, 3B) comprises glass fibres.
Securing device (1) according to one of Claims 1 to 3, in which each electrical insulation member (3A, 3B) is in the form of an insulating film, having a thickness (Ep3) of between 0, 05 and 0.2mm.
Securing device (1) according to one of Claims 1 to 4, in which the heating film (2) has a length (J) extending along a longitudinal axis (X), the heating film (2) has a thickness (Ep2) variable along the length (J).
Securing device (1) according to one of Claims 1 to 5, comprising at least two electrical connection members (4), positioned respectively in contact with the two lateral portions (22) of the heating film (2) so as to allow the electrical connection of the heating film (2) to the current source (C).
Securing device (1) according to one of Claims 1 to 6, in which the operating temperature (Tf) is between 330 and 450°C.
Securing device (1) according to one of Claims 1 to 7, comprising at least one thickness compensation member (6), positioned on at least one of the electrical insulation members (3A, 3B), of so as to compensate for a difference between the electrical insulation member (3) and the part to be welded (A1, A2), the thickness compensation member (6) being formed at least in part from a thermoplastic matrix.
Securing device (1) according to one of Claims 1 to 8, in which the heating film (2) has a thickness of between 0.0002 and 0.05 mm.
Set of a first part to be welded (A1), a second part to be welded (A2) and at least one fastening device (1) according to one of Claims 1 to 9, each part to be welded (A1 , A2) being made of a composite material comprising reinforcing fibers impregnated in a thermoplastic matrix, the fastening device (1) being configured to allow the fastening of the first part to be welded (A1) and the second part to be welded ( A2) along a common welding zone (W), each part to be welded (A1, A2) comprising an inner surface (SI1, SI2), the inner surface (SI1) of the first part to be welded (A1) being screw-mounted -towards the inner surface (SI2) of the second part to be welded (A2), the securing device (1) being mounted between the inner surface (SI1) of the first part to be welded (A1) and the inner surface (SI2) of the second part to be welded (A2) according to the common welding zone (W).
Securing system (S) comprising at least one securing device (1) according to one of Claims 1 to 9 and at least one pressure member (9) configured to apply a pressure (P) of between 0.1 and 1.5 MPa, on one of the parts to be welded (A1, A2) so as to compress together the first part to be welded (A1), the fastening device (1) and the second part to be welded (A2) according to the zone welding common (W).
Method of assembling a first part to be welded (A1) and a second part to be welded (A2) by means of the securing device (1) according to one of Claims 1 to 9, each part to be welded (A1 , A2) being made of a composite material comprising reinforcing fibers impregnated in a thermoplastic matrix, the method comprising:

a positioning step (E1) of the fastening device (1) between the internal surfaces (SI1, SI2) of the two parts to be welded (A1, A2) according to the common welding zone (W), the electrical insulation members ( 3A, 3B) being in contact with the interior surfaces (SI1, SI2) of the two parts to be welded (A1, A2), and

a first stage of heating (E3) of the central portion (21) of the heating film (2) to an operating temperature (Tf) higher than a melting temperature of the thermoplastic matrix of the parts to be welded (A1, A2), by supplying current to the side portions (22) of the heating film (2), so as to assemble the parts together.
Assembly method according to claim 12, comprising, after the first heating step (E3), a second heating step (E4) of the central portion (21) to a consolidation temperature (Tc), lower than the temperature of operation (Tf), so as to reinforce the welded zone between the two parts to be welded (A1, A2).