Method for attaching two thermoplastic parts

Abstract

The invention relates to a method for attaching an auxiliary part (2) to a main part (1) of an aircraft, wherein the main part (1) and the auxiliary part (2) comprise a thermoplastic composite material, and wherein the method comprises: a step (E4) of at least partially enriching at least one of the auxiliary part (2) or the main part (1) with a predetermined amount of thermoplastic polymer (3); and a step (E6) of welding the main part (1) and the auxiliary part (2), wherein the predetermined amount of thermoplastic polymer (3) is placed between the main part (1) and the auxiliary part (2), wherein the enrichment step (E4) is carried out by spraying the predetermined amount of thermoplastic polymer (3) by means of a gas (G) having a pressure of between 0.4 and 1 MPa and a temperature of between 400 and 600°C, and wherein such a spray is referred to as "Coldspray".

Description

Method of fixing two thermoplastic parts

[0001] The present invention relates to the field of fastening two parts of an aircraft. More specifically, the invention relates to the welding of composite parts, comprising a thermoplastic polymer, which are intended to be mounted in an aircraft structure.

[0002] On an aircraft structure, to fix an auxiliary part to a main part made of thermoplastic polymer material, it is known to carry out thermoplastic welding. For example, an aircraft comprises an external structure comprising a skin, stiffened by a plurality of sails (also known as "frame") or stiffeners (also known as "stringers") which extend substantially orthogonally to the skin. Each sail and each stiffener is fixed to the skin by a thermoplastic welding operation.

[0003] For this, with reference to the, the auxiliary part 2 (for example a frame) comprises an auxiliary fixing surface 21 placed in contact with a main fixing surface 11 of the main part 1 (for example the skin) according to a welding zone Q. On the, the structure of the aircraft is represented in an orthogonal reference frame (X, Y, Z), in which the X axis represents the longitudinal axis along which the stringers L extend (in the length of the aircraft). As is known, to be welded, the assembly is put under pressure and heated. The viscosity of the thermoplastic polymer decreases and the fixing surfaces 11, 21 mix locally. On cooling, the viscosity of the thermoplastic polymers increases and the welding zone Q solidifies. The thermoplastic polymer then forms, after welding, a substantially continuous network of material in the welding zone Q.

[0004] However, the thermoplastic polymer of the main part 1 and auxiliary part 2 may be altered due to the pressure and temperature levels required for shaping the composite parts. Also, to enable efficient welding and ensure optimum mechanical strength, it is known to enrich the fixing surface 11 of the main part 1 and / or the fixing surface 21 of the auxiliary part 2 with thermoplastic polymer material. For this, in a known manner, a thermoplastic film is added between the main part 1 and the auxiliary part 2 during the welding operation.

[0005] The use of a thermoplastic film has the disadvantage of adding thermoplastic polymer over the entire attachment surface of the part, whereas it would only be necessary locally at the welding zones Q. In other words, the prior art method represents a significant waste of material, which increases manufacturing costs. In addition, it increases the mass of the aircraft structure.

[0006] An immediate solution would be to cut the thermoplastic polymer film to enrich only the welding areas, but this would be complex to implement and would significantly increase manufacturing times.

[0007] Furthermore, with reference to the, the manufacturing tolerances of each part may result in dimensional deviations which may result in docking clearances J between the main part 1 and the auxiliary part 2. Such docking clearances J may prevent flush contact between the two fixing surfaces 11, 21, which may affect the mechanical strength of the assembly.

[0008] To solve this drawback, as shown in the, it is known to locally add shims C made of thermoplastic material. These shims C allow during a welding operation to fill the docking clearances J and thus ensure a quality assembly.

[0009] However, to fill J-docking gaps of varying sizes, it is necessary to manufacture and store a large number of wedges of different sizes, which presents numerous logistical disadvantages.

[0010] The invention thus aims to eliminate at least some of these drawbacks by proposing a method for fixing a thermoplastic auxiliary part to a thermoplastic main part which is quick and simple to implement while limiting the mass of the aircraft.

[0011] Incidentally, documents WO2014088704A2 and WO2012156525 disclose a method for assembling two composite components in which a thermoplastic resin film is pre-consolidated on each of the two composite components, the melting temperature of the thermoplastic resin films being lower than the melting temperature of the thermoplastic components. The latter are then assembled by melting the two thermoplastic resin films. PRESENTATION OF THE INVENTION

[0012] The invention relates to a method for attaching an auxiliary part to a main part of an aircraft, the main part and the auxiliary part comprising a thermoplastic composite material, the main part comprising a main attachment surface comprising at least one welding zone, the auxiliary part comprising an auxiliary attachment surface configured to be attached to the main part according to the welding zone, the method comprising:a step of enriching at least in part at least one of the auxiliary attachment surface or the welding zone of the main attachment surface with a predetermined quantity of thermoplastic polymer,a step of bringing the main attachment surface of the main part and the auxiliary attachment surface of the auxiliary part into contact according to the welding zone,the predetermined amount of thermoplastic polymer being placed between the main attachment surface and the auxiliary attachment surface, anda step of welding the main part and the auxiliary part, so as to melt and mix at least the thermoplastic composite material of the main attachment surface in the welding area, the predetermined amount of thermoplastic polymer and the thermoplastic composite material of the auxiliary attachment surface.,

[0013] The method is remarkable in that the enrichment step is carried out by spraying the predetermined quantity of thermoplastic polymer using a gas having a pressure of between 0.4 and 1 MPa and a temperature of between 400 and 600°C, such spraying being referred to as “Coldspray”.

[0014] Such a method allows the main fastening surface and / or the auxiliary fastening surface to be enriched with thermoplastic polymer in a precise manner. Also, a quantity of thermoplastic polymer can be added locally or to the entire welding area or the auxiliary fastening surface simply and quickly.

[0015] In addition, enrichment of the entire welding area of ​​the main fixing surface and / or the entire auxiliary fixing surface and local enrichment with thermoplastic polymer to fill a docking gap, for example, can be carried out during the same enrichment step and using a single tool, which limits production times and costs.

[0016] The method also makes it possible to enrich the main fixing surface and / or the auxiliary fixing surface with thermoplastic polymer which has not undergone accelerated aging unlike the methods of the prior art which used preformed films or prefabricated shims which have therefore undergone treatments which could have altered the thermoplastic material. In other words, the enrichment step according to the invention allows the deposition of a thermoplastic polymer which presents no risk of having been altered by possible pressurization and / or temperature increases, as was the case in the prior art with thermoplastic films. This allows more efficient welding, which ensures optimal mechanical strength of the welded assembly.

[0017] Furthermore, only the welding area of ​​the main attachment surface can be enriched with thermoplastic polymer without the rest of the main attachment surface being enriched as was the case in the prior art with thermoplastic films. This represents a significant mass saving.

[0018] The flow pressure values ​​allow the thermoplastic polymer to reach a sufficient projection velocity to provide it with optimal kinetic energy so that it is projected onto a part and densifies upon contact. Due to such velocity levels, the thermoplastic polymer particles deform plastically upon impact, which creates an agglomeration of thermoplastic polymer. In other words, a layer of thermoplastic polymer consolidates on the surface of the part to be enriched and forms a continuous polymer layer, bonded to the composite part.

[0019] The temperature is advantageously lower than the melting temperatures of the thermoplastic material. This allows the thermoplastic polymer to be kept in a solid state during spraying, thereby limiting any risk of alteration of the thermoplastic polymer, unlike prior art methods in which the thermoplastic material is heated to be melted in order to become malleable to adapt to the desired geometries.

[0020] In one embodiment, the enrichment step is carried out locally on one or more parts of the welding zone of the main fastening surface and / or locally on one or more parts on the auxiliary fastening surface. Thus, the method makes it possible to locally deposit a predetermined quantity of thermoplastic polymer to fill docking gaps. Thanks to the method, it is not necessary to manufacture a large number of different shims or to manage large stocks, as was the case in the prior art. Logistics are greatly simplified. In addition, it is no longer necessary to choose a shim specifically for a specific docking gap, which represents a significant time saving.

[0021] In an alternative implementation mode, the enrichment step is carried out on the entire welding zone of the main fixing surface and / or on the entire auxiliary fixing surface. Thus, a quantity of pure thermoplastic polymer (i.e. one that has not been altered by different pressurization or temperature increase operations) is added in a simple manner over the entire desired surface, which makes it possible to optimize the welding and improve the mechanical strength. The welding is thus more efficient and of better quality.

[0022] Alternatively, in the enrichment step, the amount of thermoplastic polymer is added heterogeneously over the entire welding area of ​​the main attachment surface and / or over the entire auxiliary attachment surface. This allows, simply and quickly, to apply a different amount of thermoplastic polymer to the surface depending on the needs on each part. In other words, the thickness of the thermoplastic polymer layer can be adapted, for example by varying the spraying conditions, to enrich the entire surface so as to improve the welding and locally to compensate for the docking gaps. Thus, enrichment of the entire surface and local enrichment with thermoplastic polymer can be carried out simultaneously during the same enrichment step and using a single tool, which limits production times and costs.

[0023] According to a preferred aspect of the invention, the predetermined quantity of thermoplastic polymer corresponds to a powder of a thermoplastic material or a mixture of materials. A thermoplastic polymer powder allows for simpler storage of the thermoplastic polymer, unlike thermoplastic films or thermoplastic shims used in the prior art. In addition, this allows the quantity to be applied to be dosed simply and quickly.

[0024] In a first embodiment, the thermoplastic polymer of the thermoplastic polymer quantity is different from the thermoplastic composite material of each main and auxiliary part. This makes it possible, for example, to use a thermoplastic polymer with a lower viscosity, which makes it possible to facilitate the creeping of the macromolecular chains and thus to optimize the welding cycles and / or the mechanical performance of the welded joint.

[0025] In a second embodiment, the thermoplastic polymer of the thermoplastic polymer quantity is identical to the thermoplastic composite material of each main and auxiliary part. This makes it possible to obtain a homogeneous assembly with significant mechanical strength.

[0026] Preferably, the predetermined quantity of thermoplastic polymer is doped and comprises a metallic material. This advantageously makes it possible to increase the deposition rate during projection. The addition of metallic powder to the thermoplastic polymer powder also makes it possible to give it electromagnetic properties. These properties are particularly advantageous in the case of induction welding, in which the conductive particles fulfill the role of electromagnetic susceptor, and thus make it possible to localize the heating at the interface to be welded.

[0027] In a preferred embodiment, the thermoplastic polymer is projected by means of the gas flow at a projection speed of between 500 and 1000 m / s. Such a projection speed makes it possible to provide sufficient kinetic energy to the thermoplastic polymer to: be projected onto a part, deform plastically upon impact and densify upon contact, to form the consolidated thermoplastic polymer layer on the surface.

[0028] In a preferred embodiment, the method comprises, prior to the enrichment step: a step of determining the geometry of the main fixing surface and / or the auxiliary fixing surface and comparing the determined main fixing surface, respectively the determined auxiliary fixing surface, with an expected main fixing surface, respectively an expected auxiliary fixing surface, and a step of detecting at least one docking clearance to be enriched with thermoplastic polymer between the determined main fixing surface and the determined auxiliary fixing surface.

[0029] This allows the docking clearances to be predicted to ensure flush contact between the fastening surfaces of the two parts.

[0030] Preferably, the method comprises a step of determining a quantity of thermoplastic polymer to be applied to one or more parts of the main fixing surface and / or the auxiliary fixing surface, so as to fill at least the detected docking gap. This makes it possible to determine the quantities of tailor-made thermoplastic polymer to be applied in order to adapt the thickness of thermoplastic polymer according to a part of the surface to be enriched. PRESENTATION OF FIGURES

[0031] The invention will be better understood upon 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.

[0032] This is a schematic representation of an example of a main part and an auxiliary part to be fixed to the main part.

[0033] This is a schematic representation of the docking clearances between the main part and the auxiliary part of the.

[0034] This is a schematic representation of the use of shims according to the prior art.

[0035] This is a schematic representation of an example of a main part and an auxiliary part of an aircraft with a thermoplastic polymer to be attached to the main part.

[0036] This is a schematic representation of a system for enriching a thermoplastic polymer attachment surface according to one embodiment of the invention.

[0037] This is a diagram of the steps of a method of fixing the auxiliary part to the main part according to an embodiment of the invention.

[0038] It should be noted that the figures set out the invention in detail to implement the invention, said figures can of course be used to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0039] With reference to the, there is shown an aircraft structure comprising an auxiliary part 2 intended to be fixed to a main part 1. As is known, an aircraft extends longitudinally along an X axis, laterally along a Y axis and vertically along a Z axis to form an orthogonal reference frame (X, Y, Z), and comprises an external structure comprising a skin, stiffened by a plurality of sails (also known as "frame") or stiffeners R (also known as "stringers") which extend substantially orthogonally to the skin. In practice, in this example, there is shown on thea frame, corresponding to the auxiliary part 2, intended to be fixed to the skin, corresponding to the main part 1. It goes without saying that the invention also applies to the fixing of different parts of an aircraft.

[0040] According to one aspect of the invention, the main part 1 and the auxiliary part 2 each comprise a thermoplastic composite material. Preferably, the main part 1 and the auxiliary part 2 are made of a thermoplastic material. In practice, the main part 1 and the auxiliary part 2 may be made of the same thermoplastic composite material or of different thermoplastic composite materials. In this example, the main part 1 and the auxiliary part 2 are made of one of the following materials: a material comprising a thermoplastic matrix of the polyaryletherketone (PAEK), polyphenylene sulfide (PPS) or polyetherimide (PEI) type, reinforced with carbon fibers, or glass.

[0041] The auxiliary part 2 is configured to be fixed to the main part 1 by a thermoplastic welding operation.

[0042] Still with reference to the, the main part 1 comprises a main attachment surface 11 and the auxiliary part 2 comprises an auxiliary attachment surface 21. The auxiliary part 2 is configured to be attached to the main part 1 by bringing the auxiliary attachment surface 21 into contact with the main attachment surface 11. More specifically, the main attachment surface 11 comprises a welding zone Q, the auxiliary part 2 being configured to be attached, by thermoplastic welding, to the main part 1 according to the welding zone Q. In this example, the main attachment surface 11 corresponds to the inner surface of the skin while the auxiliary attachment surface 21 corresponds to the end of the legs of a frame. In this example, the welding zone Q includes at least the inner surface of the skin which is intended to be in contact with the auxiliary attachment surface 21, that is to say, the end of the legs of a frame.

[0043] According to one aspect of the invention, a quantity of thermoplastic polymer 3 is added to one of the main fixing surface 11 or the auxiliary fixing surface 21 or to both fixing surfaces 11, 21. This is referred to as enriching the fixing surface 11, 21. Such enrichment is known to those skilled in the art under the term "wedging". The quantity of thermoplastic polymer 3 added makes it possible to define a thickness of consolidated thermoplastic polymer 3 added to the surface.

[0044] In a first embodiment, the thermoplastic polymer 3 is added to the entire welding area Q of the main fastening surface 11 or to the entire auxiliary fastening surface 21. In other words, the thermoplastic polymer 3 is added homogeneously to one of the fastening surfaces 11, 21. Homogeneous means that a similar amount of thermoplastic polymer 3 is added at every point of the fastening surface 11, 21. In other words, the added thermoplastic polymer 3 forms a layer of thermoplastic polymer 3 whose thickness is similar over the entire fastening surface 11, 21.An addition to the entire auxiliary fixing surface 21 or to the entire welding zone Q makes it possible to add pure thermoplastic polymer 3, i.e. a thermoplastic polymer which has not been altered by a previous increase in pressure or temperature (which is the case of the thermoplastic polymer of the main part 1 and of the auxiliary part 2 which has undergone shaping). The enrichment in thermoplastic polymer 3 makes it possible to optimize the thermoplastic welding, which improves the mechanical strength of the weld and therefore of the assembly.

[0045] In a second embodiment, the thermoplastic polymer 3 is added to the entire welding area Q of the main fastening surface 11 or to the entire auxiliary fastening surface 21 in a heterogeneous manner. By heterogeneous, it is indicated that the layer of thermoplastic polymer 3 formed on the surface of the parts 1, 2 has different thicknesses at different points of the fastening surface 11, 21, as shown in the. In other words, a different quantity of thermoplastic polymer 3 is added to different portions of the welding area Q of the main fastening surface 11 or to different parts of the auxiliary fastening surface 21. The quantity of thermoplastic polymer 3 can be determined according to the needs of the part, for example different docking defects to be filled, as will be described in more detail later.

[0046] In a third embodiment, the thermoplastic polymer 3 is configured to be added locally on the welding zone Q of the main attachment surface 11 or locally on the auxiliary attachment surface 21. In other words, a quantity of thermoplastic polymer 3 is added only on certain portions of the auxiliary attachment surface 21 or of the welding zone Q to fill only certain docking clearances for example. This makes it possible to add thermoplastic polymer 3 only in the areas where it is necessary, thus making it possible to limit the mass of the aircraft.

[0047] Several examples are presented in which the thermoplastic polymer 3 is added (fully or partially) only on one of the fastening surfaces 11, 21, however, the thermoplastic polymer 3 could alternatively be added on each of the fastening surfaces 11, 21. In the case of enriching each of the main fastening surface 1 (according to the welding zone Q) and the auxiliary fastening surface 21, the thermoplastic polymer 3 can be added on the whole of each surface or locally on each, in a manner analogous to the embodiments described previously.

[0048] In the example in which the thermoplastic polymer 3 is added locally or heterogeneously depending on the docking clearances between the main fixing surface 11 and the auxiliary fixing surface 21, the quantity of thermoplastic polymer 3 is determined for example depending on a difference in geometry between the actual main part 1, respectively the auxiliary part 2, and an expected geometry. By "expected geometry" is meant a geometry in which the fixing surface 11, 21 is considered to be perfect, in other words not having any defects that could cause docking clearances.

[0049] In this example, the thermoplastic polymer 3 is similar to the thermoplastic composite material of the main part 1 and / or auxiliary part 2 which it enriches. As such, the thermoplastic polymer 3 is, in this example, chosen from the following thermoplastic materials: polyaryletherketones (PAEK), polyphenylene sulfide (PPS) or polyetherimide (PEI). It goes without saying that the thermoplastic material could be different.

[0050] Alternatively, the thermoplastic polymer 3 is different from the thermoplastic composite material of each main part 1 and auxiliary part 2. In particular, in a preferred embodiment, the thermoplastic polymer 3 is doped and comprises a metallic material. This makes it possible to confer electromagnetic properties to the quantity of thermoplastic polymer 3 added to the fixing surface 11, 21, which is advantageous for certain types of welding, such as for example induction welding. In this example, the doped thermoplastic polymer 3 corresponds to polyaryletherketones (PAEK) to which particles of a metallic material are mixed. It goes without saying that the doped thermoplastic polymer 3 could be a different mixture of thermoplastic polymer and metallic particles.

[0051] In one embodiment, the grade and crystallinity of the thermoplastic polymer 3 are configured to be advantageously adapted to facilitate the subsequent welding operation. Adapting the viscosity of the thermoplastic polymer 3 at the welding interface makes it possible to accentuate the creeping capacity of the macromolecular chains, to facilitate welding. This makes it possible to reduce welding times without affecting the mechanical properties.

[0052] According to one aspect of the invention, the enrichment of thermoplastic polymer 3 is carried out by means of an enrichment system S shown in the. The enrichment system S is known under the English designation “Coldspray” and corresponds to a projection at high speed and at low temperature, as will be described in more detail later.

[0053] In this respect, the enrichment system S comprises, in this example, an acceleration nozzle 4 comprising two inlet orifices 41, 42 and an outlet orifice 43.

[0054] The first inlet orifice 41 is configured to allow the introduction of the thermoplastic polymer 3 into the acceleration nozzle 4. As such, the thermoplastic polymer 3 is preferably in the form of thermoplastic polymer powder 3. This allows easy insertion into the enrichment system S while facilitating its storage. In the case of a doped thermoplastic polymer 3 mixture, a metal powder is mixed with the thermoplastic polymer powder 3.

[0055] The second inlet orifice 42 is configured to allow the introduction of a gas G into the acceleration nozzle 4. Preferably, the gas G is chosen from air or nitrogen. It goes without saying that the gas G could be different. In this example, the gas G is air.

[0056] In this example, the acceleration nozzle 4 is configured to increase the pressure of the gas G to a gas pressure of between 0.4 and 1 MPa and to increase the temperature of the gas G to a gas temperature value of between 400 and 600 °C. In other words, in this example, the enrichment system S is configured to form a pressurized gas flow, the displacement speed of which is thus accelerated. In this example, the gas flow is accelerated to a displacement speed of between 500 and 1000 m / s. The acceleration nozzle 4 is further configured to mix the thermoplastic polymer powder 3 and the accelerated gas G, so as to project the mixture through the outlet orifice 43. The temperature levels of the gas G, below the melting temperature of the thermoplastic polymer 3, make it possible to keep the thermoplastic polymer 3 in the solid state, which prevents the latter from any risk of alteration of its properties.

[0057] By means of the enrichment system S, a predetermined quantity of thermoplastic polymer 3 is configured to be projected onto the main attachment surface 11 (or onto the auxiliary attachment surface 21) at a speed sufficient to plastically deform the thermoplastic polymer 3 in contact with the composite part and form a continuous polymer layer, bonded to the main part 1 (or to the auxiliary part 2).

[0058] In practice, the enrichment system S is configured to spray either a similar quantity of thermoplastic polymer 3 over the entire attachment surface 11, 21 in the case of homogeneous addition, or a different quantity of thermoplastic polymer 3 at different points or on different parts of the attachment surface 11, 21, in the case of heterogeneous or local addition. The quantity of thermoplastic polymer 3 deposited preferably depends on the speed of movement of the enrichment system S opposite the attachment surface 11, 21 to be enriched, as will be described in more detail below.

[0059] In other words, the acceleration nozzle 4 of the enrichment system S is configured to transform the temperature and pressure of the gas G into kinetic energy to propel the thermoplastic polymer 3 in the solid state out of the acceleration nozzle 4 at a speed close to supersonic speeds and thus form a layer of thermoplastic polymer 3 on the surface to be enriched.

[0060] A method of fixing an auxiliary part 2 (in this example a frame of an aircraft structure) to a main part 1 (in this example the skin of the aircraft structure) will now be described, according to an embodiment of the invention, with reference to the.

[0061] In this example, the main part 1 and the auxiliary part 2 are made of a thermoplastic material, in this example of polyaryletherketones (PAEK). In this example also, the thermoplastic polymer 3 is doped and comprises a mixture of thermoplastic polymer powder and metal particles. More precisely, in this example, the doped thermoplastic polymer 3 is a mixture of polyaryletherketones (PAEK) and metal particles. Furthermore, still in this example, only the auxiliary fixing surface 21 of the auxiliary part 2 is enriched with thermoplastic polymer 3. It goes without saying that the method applies in a similar manner for the enrichment of the main fixing surface 11 of the main part 1 or for the enrichment of the fixing surfaces 11, 21 of each part 1, 2.

[0062] The method comprises a step E1 of determining the geometry of the auxiliary fixing surface 21 of the auxiliary part 2, so as to estimate the docking clearance J on the auxiliary fixing surface 21 for several points of the auxiliary fixing surface 21. In this example, the geometry of the main fixing surface 11 of the main part 1 is also determined. For this, a geometric control system SC of the three-dimensional scanner type is for example used to analyze the geometry of each part 1, 2.

[0063] In a second step E2, the scanned geometry of the auxiliary fixing surface 21 of the auxiliary part 2 is compared with an expected geometry of the auxiliary fixing surface 21P (in other words with a perfect geometry, without defects) to detect deviations and therefore to predict docking clearances J. In practice, in this example, only differences of more than 0.4 mm with the expected geometry are considered as a deviation that can cause a docking clearance J. In other words, such a difference corresponds to a minimum clearance to be compensated. In this example, no docking clearance J is detected for the main part 1 between the determined geometry and the expected geometry. It goes without saying that in this step, deviations from an expected geometry could be detected on the main fixing surface 11 alone or on the fixing surfaces 11, 21 of the main 1 and auxiliary 2 parts.

[0064] In a step E3, the control system SC determines different quantities of thermoplastic polymer 3 to be added to different parts of the auxiliary fixing surface 21 according to the detected docking clearances J, to ensure flush contact between the auxiliary fixing surface 21 and the main fixing surface 11 on all of the surfaces. As a result, the quantity of thermoplastic polymer 3 to be added is heterogeneous in order to fill the docking clearances J. The addition of thermoplastic polymer 3 is carried out “to measure”.

[0065] In practice, in this example, when determining the different quantities of thermoplastic polymer 3 to be applied depending on the different points of the auxiliary fixing surface 21, a trajectory of the acceleration nozzle 4 is determined as well as a displacement speed. More precisely, the displacement speed of the acceleration nozzle 4 is determined in order to be adapted at each point of the trajectory to locally add more or less significant quantities of thermoplastic polymer 3. In other words, the displacement speed makes it possible to determine the quantity of thermoplastic polymer 3 which will be added at different points of the trajectory.

[0066] In this example, the quantity of thermoplastic polymer 3 is determined so as to enrich the entire auxiliary fixing surface 21 in a heterogeneous manner. Thus the entire auxiliary fixing surface 21 is enriched with thermoplastic polymer 3 to improve welding and a greater or lesser quantity is determined locally to fill the docking gaps J.

[0067] In the case of detecting deviations between the actual geometry and the expected geometry on the main part 1 and on the auxiliary part 2, the deviations at each point of the fixing surfaces 11, 21 positioned opposite each other are added and different quantities of thermoplastic polymer 3 are determined to fill each sum of docking clearances J, in this example, greater than 0.4 mm. In this example, the quantity of thermoplastic polymer 3 is added to only one of the two fixing surfaces 11, 21, to fill all the deviations in the welded area.

[0068] The enrichment step E4 is implemented by means of the enrichment system S of the “Coldspray” type with the predetermined quantity of thermoplastic polymer 3. In this step, an operator positions the outlet orifice 43 of the enrichment system S opposite the auxiliary fixing surface 21 and controls the projection of thermoplastic polymer 3 according to the trajectory determined as a function of the detected docking clearances J. The gas G, under a pressure of between 0.4 and 1 MPa and a temperature of between 400 and 600°C, is then accelerated in the acceleration nozzle 4 and is mixed with the thermoplastic polymer 3 (comprising a mixture of thermoplastic polymer powder and metal particles) to project the latter onto the auxiliary fixing surface 21.The solid thermoplastic polymer 3 projected by the gas G deforms upon contact with the auxiliary fixing surface 21 and consolidates upon impact, forming a thickness of solidified thermoplastic polymer 3.

[0069] The acceleration nozzle 4 is moved progressively at variable speeds according to the trajectory determined along the auxiliary fixing surface 21 so that a greater or lesser quantity of thermoplastic polymer 3 is projected to enrich the entire auxiliary fixing surface 21 with locally greater or lesser thicknesses of thermoplastic polymer 3.

[0070] Once the auxiliary fixing surface 21 has been enriched, the latter is brought into contact, in a step E5, with the main fixing surface 11 of the main part 1 according to the welding zone Q. The thermoplastic polymer 3 is placed between the main fixing surface 11 and the auxiliary fixing surface 21.

[0071] The method then comprises a welding step E6 of the auxiliary part 2 to the main part 1, so as to melt and mix the thermoplastic composite material of the main fixing surface 11 in the welding zone Q, the added thermoplastic polymer 3 and the thermoplastic composite material of the auxiliary fixing surface 21. The auxiliary fixing surface 21 enriched with thermoplastic polymer 3 free from any alteration makes it possible to ensure a quality weld. The local excess thicknesses of thermoplastic polymer 3 make it possible to fill the docking gaps J and a flush contact is ensured between the entire auxiliary fixing surface 21 and the entire welding zone Q of the main fixing surface 11.

[0072] In this example, the welding is carried out by direct induction. The metal particles added to the thermoplastic polymer 3 make it possible to give the auxiliary fixing surface 21 electromagnetic properties and make it possible to transform the electromagnetic energy into heat to localize the heating preferentially at the interface to be welded. The welding could alternatively be carried out by conduction, by indirect induction, by thermocompression, or any other known thermoplastic welding process.

[0073] By means of the method according to the invention, the auxiliary part can be welded to the main part, ensuring flush contact over the entire common surface by adding thermoplastic polymer simply and quickly. The method makes it possible to enrich the fixing surface, locally or in its entirety, with a suitable quantity of thermoplastic polymer.

Claims

A method of attaching an auxiliary part (2) to a main part (1) of an aircraft, the main part (1) and the auxiliary part (2) comprising a thermoplastic composite material, the main part (1) comprising a main attachment surface (11) comprising at least one welding zone (Q), the auxiliary part (2) comprising an auxiliary attachment surface (21) configured to be attached to the main part (1) according to the welding zone (Q), the method comprising:a step of enriching (E4) at least in part at least one of the auxiliary attachment surface (21) or the welding zone (Q) of the main attachment surface (11) with a predetermined quantity of thermoplastic polymer (3),a step of bringing into contact (E5) the main attachment surface (11) of the main part (1) and the auxiliary attachment surface (21) of the auxiliary part (2) according to the welding zone (Q),the predetermined quantity of thermoplastic polymer (3) being placed between the main fixing surface (11) and the auxiliary fixing surface (21), anda welding step (E6) of the main part (1) and the auxiliary part (2), so as to melt and mix at least the thermoplastic composite material of the main fixing surface (11) in the welding zone (Q), the predetermined quantity of thermoplastic polymer (3) and the thermoplastic composite material of the auxiliary fixing surface (21),the method is characterized in that the enrichment step (E4) is carried out by spraying the predetermined quantity of thermoplastic polymer (3) by means of a gas (G) having a pressure of between 0.4 and 1 MPa and a temperature of between 400 and 600°C, such spraying being called "Coldspray"., Fixing method according to claim 1, wherein the enrichment step (E4) is carried out locally on one or more part(s) of the welding zone (Q) of the main fixing surface (11) and / or locally on one or more part(s) on the auxiliary fixing surface (21). Fixing method according to claim 1, wherein the enrichment step (E4) is carried out on the entire welding zone (Q) of the main fixing surface (11) and / or on the entire auxiliary fixing surface (21). Fixing method according to one of claims 1 to 3, wherein in the enrichment step (E4) the quantity of thermoplastic polymer (3) is added heterogeneously over the entire welding zone (Q) of the main fixing surface (11) and / or over the entire auxiliary fixing surface (21). Method according to one of claims 1 to 4, in which the predetermined quantity of thermoplastic polymer (3) corresponds to a powder of a thermoplastic material or a mixture of materials. A method according to claim 5, wherein the predetermined amount of thermoplastic polymer (3) is doped and comprises a metallic material. Method according to one of claims 1 to 6, comprising prior to the enrichment step (E4): a step of determining (E1) the geometry of the main fixing surface (11) and / or the auxiliary fixing surface (21) and comparing the determined main fixing surface (11), respectively the determined auxiliary fixing surface (21), with an expected main fixing surface (11), respectively an expected auxiliary fixing surface (21), and a step of detecting (E2) at least one docking clearance (J) to be enriched with thermoplastic polymer (3) between the determined main fixing surface (11) and the determined auxiliary fixing surface (21). Method according to claim 7 comprising a step of determining (E3) a quantity of thermoplastic polymer (3) to be applied to one or different parts of the main fixing surface (11) and / or the auxiliary fixing surface (21), so as to fill at least the detected docking clearance (J).

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