Method for manufacturing a part made of composite material with a sandwich structure

Abstract

The present invention relates to the manufacture of a part made of composite material comprising a honeycomb core (AA1) sandwiched between two skins (P1; P2) consolidated from thermoplastic composite material, which have been welded to said core by scanning (B) with a localized heat source so as to form thermoplastic bonding zones penetrating into the interior of the core.

Description

Description Title of the invention: Method for manufacturing a part made of composite material with a sandwich structure Technical Field

[0001] The present invention relates to the manufacture of a composite part comprising a core with a honeycomb structure sandwiched between two consolidated skins of thermoplastic composite material, which have been welded to this core by localized heating to form thermoplastic bond zones penetrating into the core. The invention is of particular interest for the manufacture of large parts. Previous technique

[0002] Composite materials offer a weight saving compared to metallic materials, which is of particular interest in aerospace and aeronautical applications with a view to improving performance.

[0003] The use of composites can be considered for forming large components intended for integration into a space launch vehicle, such as a shell or a tank. More specifically, the use of a sandwich composite structure can be explored, comprising a core of a cellular material, such as a honeycomb or foam, sandwiched between two skins composed of resin and fibers, to obtain lightweight and rigid structures of substantial dimensions, for example, shells several meters in diameter. The skins allow for the transfer of stresses, and the cellular core maintains a gap between the two skins, thus increasing the rigidity of the structure.

[0004] In the case of large thermoplastic parts, a difficulty lies in the availability of a heating device, such as an oven or autoclave, capable of reaching the temperatures required for curing. Investing in such a device is extremely expensive, and energy and maintenance costs are also very high.

[0005] Furthermore, the vacuum molding tools in which consolidation must be performed require a material resistant to repeated cycles at high temperatures, for example, 350°C to 400°C, and with a coefficient of thermal expansion close to that of the thermoplastic composite part to avoid any problems with differential expansion during heating and cooling. Steel tooling can withstand the temperatures but expands too much relative to the composite and can induce high stresses or deformations that can lead to material damage, or even rejection of the structure depending on the deformations obtained. The use of Invar tooling, which has a thermal expansion close to that of the composite, overcomes this problem, but its high cost can limit its use for large parts.

[0006] Furthermore, the heat treatment of a structure using a cellular material may require special precautions to avoid degrading the material. For example, an aluminum or Nomex® honeycomb structure presents a high risk of degradation at temperatures of around 300°C to 400°C, particularly at the nodal joints (junctions between strips, usually glued), which constitute the cells of the honeycomb.

[0007] These drawbacks hinder the application of thermoplastic technology for the manufacture of sandwich structures, especially large ones.

[0008] For the reasons just described, high-performance sandwich structures are generally made with thermosetting resins rather than thermoplastics.

[0009] In this case, pre-impregnated fibers with a thermosetting resin, such as epoxy resin, can be used, possibly in conjunction with an adhesive film at the interfaces with the honeycomb core. The entire sandwich structure is either cured in a single firing, or the skins are fired sequentially (one after the other). In the latter case, the surface of the polymerized skin(s) is prepared before positioning the adhesive film at the interface with the core.

[0010] The use of a thermoset material, however, requires operators to adhere to a time limit for manufacturing the structure, unlike with thermoplastics, in order to avoid exceeding the material's ambient lifespan, as this could compromise the manufacturing process or the acceptance of the resulting part. Furthermore, the curing processes described above for thermosets are carried out in an oven or autoclave, thus limiting their application to large parts, as mentioned earlier.

[0011] Also known are US2020406600, which describes a method for bonding parts made of composite material; US2004026034, which describes a technique for depositing an adhesive on a honeycomb surface; US5589016, which describes a foam for manufacturing panels; and US5316604, which describes a process for preparing sandwich structures. thermoplastics.

[0012] It is therefore desirable to have a manufacturing process for a part made of composite material having a sandwich structure including a thermoplastic material which addresses all or part of the aforementioned disadvantages. Description of the invention

[0013] This presentation concerns, according to a first embodiment, a process for manufacturing a part made of composite material, the process comprising: - obtaining a precursor sandwich assembly of the part to be manufactured by positioning (i) a first thermoplastic composite skin, whether or not it has undergone prior consolidation, on a first face of a core with a honeycomb structure, the first skin comprising a first thermoplastic resin opposite the first face of the core, and (ii) a second thermoplastic composite skin, whether or not it has undergone prior consolidation, on a second face of the core, opposite the first face, the second skin comprising a second thermoplastic resin, identical or different from the first resin, opposite the second face of the core, and - vacuum welding of skins to core by subjecting the sandwich assembly to a heat treatment comprising (i) sweeping by local heating limited to a fraction of the assembly, in relative motion with respect to the assembly, the local heating allowing to selectively melt or soften the first resin and the second resin in the heated area, and (ii) cooling, after this local heating, in order to obtain welding of the skins to the core.

[0014] The present presentation relates, according to a second embodiment, to a process for manufacturing a part made of composite material, the process comprising: - obtaining a first assembly by positioning a first thermoplastic composite skin, which may or may not have undergone prior consolidation, on a first face of a core with an alveolar structure, the first skin comprising a first thermoplastic resin opposite the first face of the core, - vacuum welding of the first skin to the core by subjecting the first assembly to a first heat treatment comprising (i) a sweep by a first local heating of limited extent to a fraction of the first assembly, in relative motion with respect to this first assembly, the first local heating allowing to selectively melt or soften the first thermoplastic resin in the heated zone, and (ii) a cooling, after this first local heating, in order to obtain the welding of the first skin to the core, - obtaining a second assembly by positioning, on the first assembly in which the first skin has been welded to the core, a second thermoplastic composite skin, whether or not it has undergone prior consolidation, on a second face of the core opposite the first face, the second skin comprising a second thermoplastic resin, identical or different from the first resin, facing the second face of the core, and - vacuum welding of the second skin to the core by subjecting the second assembly to a second heat treatment comprising (i) sweeping by a second local heating of limited extent to a fraction of the second assembly, in relative motion with respect to this second assembly, the second local heating allowing to selectively melt or soften the second thermoplastic resin in the heated area, and (ii) cooling, after this second local heating, in order to obtain the welding of the second skin to the core.

[0015] The first and second embodiments described above each propose performing vacuum welding of the skins to the core locally, with the heated zone shifting relative to the assembly being treated. The process is thus particularly well-suited to treating large composite assemblies, offering an "out-of-oven" solution. The invention therefore eliminates the need for a sufficiently large heating vessel to accommodate the assembly being treated, or for maintaining a homogeneous temperature within that vessel. The invention also offers the advantage of reducing energy consumption because it avoids heating a large volume inside the heating unit containing the assembly. Furthermore, the localized heating system eliminates the problems of differential expansion encountered with global heating of the structure. Therefore, Invar tooling can be omitted, and conventional steel tooling can be used instead.

[0016] It should also be noted that the use of thermoplastic technology significantly increases industrial flexibility by overcoming the limitations related to shelf life at ambient temperature compared to thermosets. Compared to current methods using thermoset sandwich panels, it is possible to create larger and / or more integrated structures, meaning fewer separate components prepared in advance for subsequent assembly. It is also possible to produce components that can be easily stored at room temperature before final integration, without risk of waste.

[0017] Generally, the skins are bonded to the core by melting or softening the thermoplastic resin(s) on the core side to form thermoplastic bonding zones that penetrate part of the core's thickness, within the core's cells or pores opening onto the core faces. These bonding zones result from the flow of the first and second thermoplastic resins described above under the effect of vacuum and localized heating, possibly in conjunction with the resin of the interposition film and / or the anchoring resin, which will be discussed later. The resins then cool to bond the skins to the core. These thermoplastic bonding zones will be described in more detail later.

[0018] In one example, the first and second skins have each undergone prior consolidation and are each enriched with the first or second resin, depending on the skin considered, on their surface facing the core, obtaining each of the enriched first and second skins comprising: - the deposition of a first fibrous layer or several stacked first fibrous layers of thermoplastic pre-impregnated fibrous material and at least a second layer on the first layer(s) to obtain a thermoplastic pre-impregnated fibrous stack, said at least a second layer being located on the surface of said thermoplastic pre-impregnated fibrous stack and comprising at least the first resin in the case of the first skin or the second resin in the case of the second skin, the first layer(s) being impregnated with a thermoplastic resin having a melting or softening temperature higher than that of the resin of said at least a second layer, and - vacuum consolidation of the thermoplastic pre-impregnated fibrous stack thus obtained so as to melt or soften the thermoplastic resins present and weld said at least a second layer to the first layer or the first layers.

[0019] In this case, each skin is surface-enriched by the first or second resin, depending on the skin in question, which has a melting or softening temperature lower than that of the thermoplastic resin impregnating the rest of the skin. The softening temperature of the thermoplastic resin impregnating the first layer(s) may be higher than the softening temperature of the resin in said at least one second layer, or the melting temperature of the thermoplastic resin impregnating the first layer(s) may be higher than the melting temperature of the resin in said at least one second layer. Said at least one second layer may be fibrous by being impregnated with the first resin in the case of the first skin or with the second resin in the case of the second skin.Alternatively, at least a second layer can be formed from the first resin or the second resin, depending on the skin type (absence of fibrous reinforcement). The consolidation process used to obtain the first and second skins allows, in particular, for the melting or softening of the first / second resin as well as the resin impregnating the first layer(s), so as to obtain, after cooling, a bond through the interpenetration of the polymer chains present on either side of the interface(s) between the layers. Enriching the skins with the first / second resin, depending on the skin type, further improves the mechanical strength of the skin-to-core bond.In addition, the difference between the melting or softening temperature of the resins of each of the skins allows for selective melting or softening of the first / second resin (surface resin) when welding the skins to the core, thus avoiding any risk of damaging the rest of the previously consolidated structure.

[0020] In one embodiment, a thermoplastic interposition film is added between each skin and the core, and this thermoplastic interposition film is melted or softened during the local heating implemented to participate in the welding to the core of the corresponding skin, this interposition film possibly being identical to the first resin and / or the second resin.

[0021] The melting or softening of the interposition film allows it to participate in the bonding to the core of the corresponding skin, further strengthening the mechanical integrity of this bond by adding material. Following vacuum bonding of each skin to the core, after cooling, the film bonds with the core and also with the first and second resins through interpenetration of the polymer chains present on either side of the interface between the film and the skin in question.

[0022] It should be noted that the invention remains within its scope if the skins are not enriched, or if there is no intercalated film. In cases where unenriched skins are directly welded to the core, the skins may or may not have been previously consolidated.

[0023] In one embodiment, at least one of the first and second faces of the core was anchored with a thermoplastic anchoring resin before the corresponding skin was positioned, and this anchoring resin is melted or softened during local heating to participate in the welding of the corresponding skin to the core, the anchoring being achieved by: - coating of said at least one of the first and second faces with the molten thermoplastic anchoring resin, and- cooling of the molten thermoplastic anchoring resin, the anchoring resin may possibly be identical to the first resin and / or the second resin.

[0024] This case corresponds to the addition of material to the core to further reinforce the mechanical strength of the skin-to-core weld. Following vacuum welding of each skin to the core, after cooling, the anchoring resin bonds with the first and second resins, possibly via the interposition film when present, through interpenetration of the polymer chains present on either side of the interfaces.

[0025] In one example of an embodiment, each assembly is, during its heat treatment, positioned on a metallic substrate with a vacuum bag located opposite the assembly, secured in a hermetically sealed manner to the metallic substrate and applying pressure to the assembly, the assembly being positioned between the metallic substrate and the vacuum bag.

[0026] The embodiment just described makes it possible to use a material with a high coefficient of expansion, such as steel, for the metallic substrate, thus significantly reducing tooling costs compared to the use of invar mentioned above, while preserving the material integrity of the resulting part. The localized heating employed in the invention reduces, or even eliminates, the stresses or deformations imposed by differential expansion, compared to heating the assembly globally.

[0027] Alternatively, each assembly is, during its heat treatment, positioned between two vacuum bags sealed together on retaining flanges placed on the edges of the assembly, the edges being intended to form the outer perimeter(s) of the part to be obtained and the bags applying pressure to the assembly.

[0028] This feature allows for simplified tooling by eliminating the need for a metallic substrate. The flanges maintain the assembly in the correct position in the lower zone if it is oriented vertically during processing. Using flanges in combination with localized heating also ensures the geometry of the resulting part, even when steel flanges are used.

[0029] In general, the pressure applied by the vacuum bag(s), in combination with the temperature, helps to improve the contact between the skins and the core and ensures the proper formation of the menisci at the junctions between the core and the skins. In a particular case encountered with skins that have not been previously consolidated, this pressure can also allow their conformation and consolidation.

[0030] In an example embodiment, the sandwich assembly and / or the second assembly defines a median region on which the first and second skins are opposite a respective face of the core, and peripheral regions, intended to form the outer perimeter(s) of the part to be obtained, on which the first skin joins the second skin.

[0031] This case corresponds to the manufacture of a part with a "return to the skin" in which the first and second skins meet at the periphery. Such an arrangement may be particularly desirable for certain cowling parts intended for aeronautical applications and / or to facilitate subsequent assembly in the peripheral areas of the part.

[0032] In particular, the median region includes a transition zone to each peripheral region on which a spacing between the first and second faces of the core, measured transversely to these faces, gradually decreases towards the corresponding peripheral region.

[0033] This characteristic allows for a gradual return to the skin, thus improving the quality of the skin junction in peripheral areas.

[0034] In one example of implementation, the core is a honeycomb or a foam.

[0035] In one example of implementation, each local heating is achieved by a first heating wall located on the side of the first face of the core and a second heating wall located on the side of the second face of the core.

[0036] This characteristic helps to further control the temperature at the interfaces of the core with the skins.

[0037] In particular, the first and second walls may not overlap.

[0038] This characteristic helps to minimize heat transfer within the honeycomb core (transfer via only one face instead of both faces simultaneously). However, the invention is not limited to this embodiment, as will be described in more detail below.

[0039] As will be detailed below, different movements are possible for the first and second heating walls such as a joint relative movement with respect to the heat-treated assembly, a displacement of these walls in different directions, and / or with different speeds taken relative to the treated assembly.

[0040] The invention is not limited to the implementation of two heating walls located on the opposite sides of the core but, alternatively, each local heating is achieved by a single heating wall located on the side of the first face of the core or the second face of the core.

[0041] In one embodiment, each of the first and second skins comprises carbon fibers, glass fibers, aramid fibers, or a mixture of such fibers.

[0042] In one embodiment, the first thermoplastic resin and the second thermoplastic resin are a polyetherimide or a polyaryletherketone, for example a low melting point polyaryletherketone (“Low Melt PolyArylEtherKetone”; “LM-PAEK”). The polyetherimide is an amorphous resin and the polyaryletherketone is a semi-crystalline resin.

[0043] In one example of the embodiment, the part made of composite material has a cylindrical shape.

[0044] Alternatively, the composite material part is a flat or curved panel.

[0045] The invention also relates to a composite material part comprising a core with a honeycomb structure interposed between two skins consolidated from thermoplastic composite material and positioned on opposite faces of the core, the skins being bonded to the core by thermoplastic adhesion zones penetrating into the interior of the core.

[0046] The part can be obtained by implementing the process described above.

[0047] The consolidated skins each comprise a stack of layers which includes one or more thermoplastic resins and exhibit a weld between these layers due to the interpenetration of the polymer chains on either side of the interface(s).

[0048] Advantageously, each skin is impregnated with one or more high-performance thermoplastic resins, for example as detailed below.

[0049] In one embodiment, the adhesion zones include a polyetherimide, or a polyaryletherketone, for example a low melting point polyaryletherketone.

[0050] In one example embodiment, each skin comprises a stack of layers with a portion of this stack, located on the side opposite the adhesion zones, which is fibrous and impregnated with a thermoplastic resin having a melting or softening temperature higher than that of the adhesion zones.

[0051] This case may correspond to a situation in which surface-enriched skins as described above have been implemented.

[0052] In one embodiment example, the part is a ferrule of a space launcher stage, a fairing of a space launcher, a compartment bottom of a space launcher tank, a satellite tube or a satellite panel.

[0053] The invention is not, however, limited to the production of this type of part, as will be described later.

[0054] The aforementioned features and advantages, as well as others, will become apparent from the following detailed description and non-limiting examples of embodiments of the invention. This detailed description refers to the accompanying drawings. Brief description of the drawings

[0055] The attached drawings are schematic and primarily intended to illustrate the principles of the presentation. In these drawings, identical elements (or parts of elements) are identified by the same reference symbols from one figure to another.

[0056] [Fig. 1] Figure 1 represents, schematically and partially, the prior consolidation of an example of skin enriched on the surface by a thermoplastic resin which is intended to participate in the welding to the core.

[0057] [Fig. 2] Figure 2 represents, schematically and partially, the obtaining of an example of a precursor sandwich assembly of the part to be manufactured from skins consolidated according to figure 1.

[0058] [Fig. 3] Figure 3 represents, schematically and partially, a honeycomb core with hexagonal mesh.

[0059] [Fig. 4] Figure 4 represents, schematically and partially, a variant of a honeycomb core.

[0060] [Fig. 5] Figure 5 represents, schematically and partially, a vacuum welding of the skins to the core that can be carried out for the assembly of Figure 2.

[0061] [Fig. 6] Figure 6 schematically and partially represents a detail of a heating wall that can be implemented within the framework of the invention.

[0062] [Fig. 7] Figure 7 represents, schematically and partially, the composite material part obtained after vacuum welding according to Figure 5.

[0063] [Fig. 8] Figure 8 represents, schematically and partially, a variant of relative positioning of the heating walls suitable for achieving a heating sweep on both faces of the assembly.

[0064] [Fig. 9] Figure 9 represents, schematically and partially, a variant in which the skins are successively welded to the core during separate heating stages.

[0065] [Fig. 10] Figure 10 schematically and partially represents an assembly variant featuring a "return to the skin".

[0066] [Fig. 11] Figure 11 represents, schematically and partially, a variant of tooling in which the assembly is positioned between two vacuum tarpaulins.

[0067] [Fig. 12] Figure 12 schematically and partially represents an assembly variant in which a thermoplastic interposition film is added between each skin and the core.

[0068] [Fig. 13] Figure 13 represents, schematically and partially, a detail of the part obtained after vacuum welding of the skins to the core in the case of the assembly of Figure 12.

[0069] [Fig. 14] Figure 14 schematically and partially represents an assembly variant in which thermoplastic composite skins alone (without surface enrichment or interposition film) are directly positioned on the core.

[0070] [Fig. 15] Figure 15 represents, schematically and partially, a variant in which the faces of the core are each anchored by a thermoplastic anchoring resin.

[0071] [Fig. 16] Figure 16 represents, schematically and partially, a panel-shaped assembly.

[0072] [Fig. 17] Figure 17 represents, schematically and partially, an example of heated scanning to perform vacuum welding in the case of the assembly in Figure 16.

[0073] [Fig. 18] Figure 18 represents, schematically and partially, a ferrule-shaped assembly.

[0074] [Fig. 19] Figure 19 represents, schematically and partially, an example of heated scanning to perform vacuum welding in the case of the assembly in Figure 18.

[0075] [Fig. 20] Figure 20 represents, schematically and partially, the realization of a dome-shaped composite part. Description of the implementation methods

[0076] Figure 1 illustrates an example of manufacturing the first skin PI, it being understood that a similar technique can be implemented for the manufacture of the second skin P2 which is intended to be positioned on an opposite face of the core.

[0077] Stacked first layers of Cl-1 fibers are deposited onto a substrate S using a technique known per se, such as automated fiber placement (AFP) or manual draping. The use of an automated fiber placement technique is advantageous for achieving a fiber orientation precisely tailored to the requirements. The first Cl-1 layers are impregnated with a thermoplastic resin. The illustrated case involves the deposition of several first Cl-1 layers, but this does not depart from the scope of the invention if only one first layer of pre-impregnated thermoplastic fibrous material is deposited in the skin manufacturing process. One or more second Cl-2 layers are then deposited on top of the first Cl-1 layers, also using a technique known per se as described above.A second Cl-2 layer can be deposited directly onto the first Cl-1 layers (in contact with one of the first Cl-1 layers). The second Cl-2 layer(s) contain an enrichment resin and can be positioned on any one face or on both faces. In particular, placing the second Cl-2 layer(s) on the face facing the support S will ensure good flatness of this enriched face and will help improve contact with the core during the assembly operation.

[0078] A pre-impregnated thermoplastic fibrous stack is obtained, formed by these Cl-1 and Cl-2 layers. The second Cl-2 layer(s) are fibrous and impregnated with a thermoplastic resin intended to facilitate the bonding of the skin to the core. In one variation, the second layer(s) consist of the thermoplastic resin itself, designed to facilitate the bonding of the skin to the core (no fibrous reinforcement). The second Cl-2 layer(s) define the surface of the corresponding skin, which is positioned opposite the core. In the example considered here, the skin surface was enriched by depositing the second Cl-2 layer(s), which are impregnated with a thermoplastic resin distinct from the resin impregnating the first Cl-1 layers and which has a lower melting or softening temperature.The thermoplastic resin impregnating the second layer(s) Cl-2 corresponds to the first thermoplastic resin in the case of the first skin PI, or to the second thermoplastic resin in the case of the second skin P2. The melting or softening temperature of the thermoplastic resin impregnating the first layers Cl-1 is higher than the melting or softening temperature of the first / second thermoplastic resin, allowing for selective melting or softening of the first / second resin during skin-to-core welding (the resin impregnating the first layers Cl-1 is not melted or softened during this welding). For example, the difference between the melting or softening temperature of the thermoplastic resin impregnating the first layer(s) Cl-1 and that of the resin in the second layer(s) Cl-2 can be greater than or equal to 10°C, for example, greater than or equal to 30°C.

[0079] The second Cl-2 layer(s) are then welded to the first Cl-1 layers by vacuum consolidation of the resulting fibrous stack.

[0080] A vacuum bag 12 is securely attached to the support S by means of seals, for example, formed by a sealant 11 so as to cover the fiber stack, as illustrated in drawing IA. The bag 12 is positioned on the side of the surface defined by the second layer(s) Cl-2 that is opposite the support S, but as mentioned above, this does not depart from the scope of the invention if the second layer(s) Cl-2 are arranged on the side of the support S, for example, in contact with it. The bag 12 may, without limitation, be made of polyimide or elastomeric material, reinforced or not, and constitutes a known element per se. The stack is interposed between the support S and the bag 12.

[0081] The consolidation process then proceeds by creating a vacuum in an internal volume between the support S and the sheet 12. This vacuum creates a bond between the sheet 12 and the stack, conforming it between the support S and the sheet 12 by applying a conforming pressure PC. The stack is then heated to melt or soften the first / second resin, depending on the skin layer, and the resin impregnating the first layers Cl-1. In the example considered here, the stack is heated by a heating wall 24, the structure of which will be described in more detail later in the section on skin-to-core welding. As an example, a temperature greater than or equal to 250°C can be applied during this heating, for example, greater than or equal to 300°C, or even between 300°C and 450°C or between 350°C and 450°C.

[0082] Following the application of PC pressure and heating, the stack thickness can be reduced by at least 5%, for example, by at least 10%, specifically by 5% to 15% or by 10% to 15%. Vacuum is maintained during heat treatment, during heating by localized heating, and during the cooling of the heated area after this localized heating. Consolidation can also be carried out conventionally under a vacuum bag, in an oven, or in an autoclave with the addition of extra pressure. In this case, the entire stack will be heated during the thermal consolidation cycle.

[0083] After consolidation and cooling, the PI skin, or a segment of the PI skin (in the case where the stack considered is only a part of the PI skin), is obtained. This skin is intended to be positioned on the core, which comprises first Cl-1 layers bonded to one or more second Cl-2 layers. The bond is produced by the interpenetration of the polymer chains on either side of the interfaces between the layers. This interpenetration of the polymer chains is represented by lines II in drawing IB for the case of the bonding of the second Cl-2 layer(s) to the first Cl-1 layers. If only a segment of the PI skin is formed, the process just described can be repeated to form each of these segments, which can then be positioned with a local overlap to form the complete skin.In this case, even if a large piece is being considered, it is possible to carry out the prior consolidation of the segments in an oven or autoclave.

[0084] The choice of reinforcing material and the resin(s) used for the skins depends on the intended application. The first Cl-1 and second(s) Cl-2 layers may include carbon fibers, glass fibers, aramid fibers, or a mixture of such fibers.In the case of the surface skin enrichment just described, the first / second resin impregnating the second layer(s) Cl-2 can be a high-performance thermoplastic resin, comprising for example a polyetherimide polymer (PEI), or a polyaryletherketone, for example a low-melting-point polyaryletherketone, and the resin impregnating the first layers Cl-1 can also be a high-performance thermoplastic resin, comprising for example: a polyaryletherketone polymer (PAEK), a polyetheretherketone polymer (PEEK), a polyetherketoneketone polymer (PEKK), a polysulfone polymer (PSU), a polyethersulfone polymer (PES), a poly(phenylene sulfide) polymer (PPS), or a mixture of these polymers.

[0085] Generally, the number of layers deposited to form the skins will be determined by the skilled professional. For example, between 1 and 20 layers can be deposited for the assembly formed by the first layer(s) Cl-1, and between 1 and 3 layers for the assembly formed by the second layer(s) Cl-2. Alternatively, there may be only one second layer Cl-2 and several first layers Cl-1. Each deposited assembly may or may not include areas of decreasing thickness, that is, areas with a reduced number of layers. In other words, each assembly may or may not have a variable number of layers depending on the area. The skilled professional will naturally take care to limit the temperature applied during each heat treatment so as not to degrade the material, for example, by working at least 50°C below the material's degradation temperature during each heating pass.

[0086] Figure 2 illustrates the formation of an AS1 sandwich assembly in an example according to the invention. In this example, a first skin PI, previously consolidated and surface-enriched with the first resin obtained as described above in relation to Figure 1, is positioned on a first face FAI of a honeycomb-structured AAI core. The first skin PI comprises the first Cl-1 layers and the second Cl-2 layer(s), which are impregnated with the first resin. The second Cl-2 layer(s) are positioned opposite the first face FAI, for example, in contact with it in the illustrated example. A second skin P2, previously consolidated and surface-enriched with the second resin obtained as described above in relation to Figure 1, is positioned on a second face FA2 of the AAI core opposite the first face FAI.The second skin P2 comprises first layers C2-1 and one or more second layers C2-2 impregnated with the second resin. The second layer(s) C2-2 are positioned opposite the second face FA2, for example, in contact with it in the illustrated example. The second resin may be identical or different from the first resin. The illustrated case concerns the use of skins that have been previously consolidated and surface-enriched to form the assembly, but it should be noted that the invention is not limited to this embodiment, as will be described later.

[0087] In the example considered here, the AAI core has a honeycomb structure defining a plurality of transverse AL cells extending along its thickness, between the first face FAI and the second face FA2. The AL cells open onto each of the FAI and FA2 faces. Figures 3 and 4 illustrate examples of possible honeycomb structures, with Figure 3 representing a hexagonal honeycomb and Figure 4 a honeycomb commercially available under the name Flex-Core® from Hexcel. As with the skins, the core material depends on the intended application. The core can be metallic, for example, aluminum or aluminum alloy, titanium or titanium alloy, or steel.Alternatively, the core can be polymeric, for example, poly(p-phenyleneisophthalamide) (Nomex®), poly(p-phenylene terephthalamide) (Kevlar®), polyimide resin, phenolic resin, polybismaleimide resin, polyetherimide resin, or polyetheretherketone resin. The resins mentioned above can optionally be reinforced with fibers such as glass fibers, and / or may have been produced by 3D printing. Alternatively, the core can be made of ceramic or carbon. Generally, it should be noted that the core can be at least partially filled with syntactic foam, either in the cells or at the junctions of several core sections.

[0088] The illustrated examples concern honeycomb cores but, in an unillustrated variant, a core formed by a foam can be implemented, for example metallic, carbon or polymeric, for example polymethacrylimide, polyimide, polyetherimide, polybismaleimide or polyetherketoneketone.

[0089] Next, the skins Pl, P2 are vacuum-welded to the core AAI by subjecting the AS1 sandwich assembly to a heat treatment, one possible implementation of which is illustrated in Figure 5.

[0090] In the example shown in Figure 5, the welding is performed in a tool 10 which includes a metallic substrate 14 to which a vacuum bag 12 is attached. The bag 12 can be as described above. The substrate 14 can be made of steel. The substrate 14 can be a single piece, or demountable, consisting of a plurality of removably connected segments.

[0091] The AS1 assembly is oriented here along a vertical direction DV, that is, along the direction along the height relative to the ground. However, it remains within the scope of the invention if the assembly is oriented differently, for example, if it is positioned flat or horizontally. The AS1 assembly extends between a lower edge 31 (at the bottom) and an upper edge 32 (at the top). A beveled edge BD is positioned on the side of each edge 31, 32 to prevent damage to the edges 31 and 32. The tooling 10 includes, in its lower part, a positioning flange 16 on which the edge 31 and the associated edge BD rest. The flange 16 defines a positioning surface that is transverse, or even perpendicular, to the direction DV. In the illustrated example, the flange 16 is one piece with the substrate 14, but we do not, of course, depart from the scope of the invention if it is a separate element.The tarpaulin 12 is secured in a watertight manner to the substrate 14 and to the flange 16 by sealing joints 11, for example formed by a sealing mastic as described above for the vacuum consolidation of skins.

[0092] The AS1 assembly, positioned in the tooling 10, is sandwiched between the substrate 14 and the tarpaulin 12. The substrate 14 and the tarpaulin 12 together define an internal volume of the tooling 10 in which the AS1 assembly is located. The tarpaulin 12 is situated opposite a surface S2 of the AS1 assembly, and the substrate 14 is situated opposite a surface S1 to surface S2. It should be noted that a caul plate 13 is sandwiched between the tarpaulin 12 and the AS1 assembly in the illustrated example, but omitting this caul plate 13 does not depart from the scope of the invention.

[0093] The weld is performed hot by drawing a vacuum from the internal volume of the tooling 10. The pressure PR applied during this vacuum drawing presses the skins Pl, P2 onto the AAI core, holding them in the correct position until they are welded. A localized heating sweep, indicated by arrow B, is performed while the vacuum is being drawn, leading to the selective melting or softening of the first / second resin layers of the skins Pl, P2 in the heated area. In the example considered here, controlled localized heating is implemented, preventing the melting or softening of the resin impregnating the first layers Cl-1 and C2-1, while only melting or softening the first and second resins. The relative pressure within the internal volume of the tooling can be between -1 bar (maximum vacuum) and -0.01 bar, and preferably between -0.95 bar and -0.2 bar.A minimal void level may be sufficient when the Pl and P2 skins are already consolidated, as in the example shown in Figure 5. Furthermore, a minimal void level may be preferable for a low-density and / or relatively temperature-sensitive core to prevent any risk of cell buckling under the combined effect of high vacuum pressure and temperature. The first / second softened or molten resin flows through the corresponding FAI and FA2 face, penetrating the AL cells of the AAI core during heat treatment and locally coating the cell walls by capillary action.

[0094] Figure 5 illustrates a non-limiting example of a local heating device 20 that can be implemented within the scope of the invention.

[0095] The AS1 assembly is subjected to a heat treatment process involving a sweep B of its surfaces SI, S2 by a local heating device 20. In the illustrated example, the device 20 comprises a first heating wall 22 facing the metallic substrate 14 (and the SI surface), and a second heating wall 24 facing the tarpaulin 12 (and the S2 surface). Each wall 22, 24, or more generally the local heating element, has an extent limited to only a fraction of the SI, S2 surface of the assembly facing it, as will be further illustrated later for different assembly geometries. In the illustrated example, the local heating element, or the walls 22, 24, extends over the entire height of the AS1 assembly (taken here along the DV direction).

[0096] Figure 6 schematically illustrates an example of a usable wall 24 comprising a plurality of infrared lamps 243 attached to a frame 241. The wall 24 has an area E24 that corresponds to only a fraction of the surface of the assembly opposite it. Those skilled in the art will recognize that other means are available to produce the desired local heating. For example, the shape of the infrared lamps 243 can be varied by using curved lamps, or alternatively, pulsed flash lamps (lasers) or induction heating can be used.

[0097] Generally, the local heating element is in relative motion with respect to the assembly; that is, only the local heating element can be mobile, only the assembly can be mobile, or both the local heating element and the assembly can be mobile with relative motion between them. The local heating element can be moved continuously relative to the assembly, or alternatively, a step-by-step movement can be performed in which the local heating element is stationary to treat one area and then moved statically to treat another.

[0098] After local heating, the assembly is cooled to solidify the first and second thermoplastic resins, and in particular the fraction that has penetrated the AAI core, thus creating the bond. Figure 7 illustrates the resulting composite part with the thermoplastic bond zones of the Pl, P2 skins to the AAI core formed by this fraction that has penetrated the AAI core. There is a continuum of thermoplastic material between the ME bond zones and the Pl, P2 skins to achieve their bond to the core. The bond zones can be in the form of ME menisci, for example, with a resin buildup at the skin / core junction. The bond zones can extend over only a fraction of the eAAl thickness of the AAI core, for example, to a PME depth, measured from the corresponding FAI, FA2 face, greater than or equal to 0.1 mm, for example, between 0.1 mm and 1 mm.

[0099] The example just described in relation to figure 5 concerns the case of heated walls 22, 24 facing each other which may have a total or partial overlap. The invention is not limited to this configuration, however, as illustrated in Figure 8 where the heating walls 22 and 24 do not overlap (they are not opposite each other). Such an arrangement minimizes heat transfer in the AAI core (transfer via only one face instead of both faces simultaneously).

[0100] The sweep B of the heating walls 22, 24 has been shown as being oriented in the same direction for each. Regardless of the embodiment considered, heating walls 22, 24 may alternatively move in opposite directions, or with different trajectories. Independently or in combination with this, the speed of movement of the heating walls 22, 24 may be identical or different. Generally, the positioning of the heating wall(s), their movement, and the vacuum level will be adjusted by a person skilled in the art, according to the materials used, in order to achieve the desired weld without damaging the assembly, particularly the core.

[0101] We have just described examples in which the two skins Pl, P2 are welded to the core AAI in a single step. However, the invention is not limited to this case and, according to another embodiment, covers a sequential process in which one skin and then the other is welded to the core, as will now be discussed in connection with Figure 9.

[0102] In the example of Figure 9, a first assembly Al is obtained by positioning the first skin PI on the first face FAI of the core AAI and by positioning this assembly Al in a tooling similar to that which has just been described, which includes a metallic substrate 14 and a tarpaulin 12 securely attached to the substrate 14.

[0103] The first skin PI is then welded to the core AAI by subjecting the first assembly Al to a scan B by local heating of a surface S3 of the first assembly Al followed by cooling, in a manner similar to what has just been described (see drawing 9A).

[0104] Once the first skin PI is welded to the core AAI in the first assembly AS1, the second skin P2 is then positioned on the second FA2 of the core AAI, and the weld to the core AAI is then performed in a manner similar to that described above (see drawing 9B). In the case considered here, the skins P1 and P2 have each been previously reinforced, but this does not depart from the scope of the invention if this is not the case. In particular, the skin PI may have been previously reinforced, but not the skin P2, and the latter is then reinforced during its weld to the core.

[0105] In the example shown in Figure 9, the heating wall 24 providing local heating is positioned on the side of surface S3, opposite the first skin PI, for the treatment of the first assembly A1, and on the side of surface S4, also opposite the first skin PI, for the treatment of the second assembly A2. Those skilled in the art will recognize that the invention is not limited to this arrangement and that, alternatively, local heating could be provided on the side of the first skin PI.

[0106] In the examples just described, the core has a substantially constant thickness. However, the invention is not limited to this type of structure, as will be described in connection with Figure 10.

[0107] Figure 10 represents an AS2 assembly (applicable to the case of sequential welding of skins P3 and P4 or during the same vacuum heating step) which defines a median region RM where the first P3 and second P4 skins are aligned with a respective face FA3 and FA4 of the core AA3 and peripheral regions RP, located on either side of the core AA3, where the second skin P4 joins the first skin P3 to form the "return to the skin". As illustrated, the median region RM may exhibit, on the side of the RP regions, a beveled transition region RT where the thickness of the core AA3 decreases as one approaches the RP regions, for example, in a substantially linear fashion as shown. The skins P3 and P4 conform to the shape of the core AA3 on each of its faces FA3 and FA4, particularly in the RT regions. The core AA3 is no longer interposed between the skins P3 and P4 in the RP regions.Skins P3, P4 can be in contact on the RP regions, or an interposition film can be interposed between these skins as will be described later.

[0108] The variant shown in Figure 11 relates to the case where the tooling includes retaining flanges arranged at each edge 31, 32 of the AS1 assembly, a first vacuum bag 12a, opposite the first skin PI, and a second vacuum bag 12b, opposite the second skin P2, being sealed tightly to these flanges 17 by the sealing gaskets 11. One or more relatively thin smoothing plates 13, which may be metallic, are positioned between the AS1 assembly and the bags 12a and 12b. In a variant not shown, these smoothing plates can be omitted.

[0109] As with figure 10, it will be recognized that the case of figure 11 applies equally to the case of a sequential welding of skins Pl, P2, or during the same vacuum heating step.

[0110] Furthermore, in the examples of figures 10 and 11, it is possible to implement heating on both sides of the assembly as illustrated in figures 5 or 8 for example, or heating on only one side like that of figure 9.

[0111] Figures 12 to 15, which will now be described, illustrate different possible variants for the adhesion interface between the skins and the core, it being understood that they can be combined with the characteristics described above for the heating sweep and the structure of the tooling in which the welding is carried out.

[0112] Figure 12 shows an AS3 sandwich assembly that differs from that of Figure 2 only in that an interposition film Fil, FI2 is sandwiched between each skin Pl, P2 and the AAI core. Each interposition film Fil, FI2 is in contact with the AAI core and with its respective skin Pl, P2. Each interposition film Fil, FI2 can be formed from a high-performance thermoplastic resin, such as a polyetherimide polymer (PEI) or a polyaryletherketone, for example, a low-melting-point polyaryletherketone. In a particular case, the interposition films Fil, FI2 and the first and second resins can be formed from the same thermoplastic resin. During the heat sweep, the interposition film Fil, FI2 is melted or softened to participate with the first / second resin in the bonding of the skins Pl, P2.

[0113] Figure 13 schematically illustrates the weld thus obtained with the formation of ME1 menisci resulting from the penetration of the first / second resin and the interposition film material Fil, FI2 into the AAI core. An interpenetration of the polymer chains is also observed on either side of the interface between each interposition film Fil, FI2 and the second Cl-2, C2-2 layers, represented by lines 12. This interpenetration makes the interposition film material bonded to each of the skins after cooling.

[0114] The variant shown in Figure 14 concerns skins P5, P6 that are not surface-enriched but comprise a stack of layers C5, C6 pre-impregnated with the first or second resin, depending on the skin in question. In this case, the first resin may be present throughout the entire thickness of the first skin P5, and the second resin may be present throughout the entire thickness of the second skin P6. The skins P5, P6 may not have been consolidated, and consolidation of the skins may be carried out during their welding to the core. Naturally, this does not depart from the scope of the invention if an interposition film, as illustrated in Figure 12, is interposed between the skins P5, P6 and the AAI core. In the case of skins that have not been previously consolidated, it should be noted that they can be draped directly onto the core, rather than onto a separate support, and then consolidated and welded using the vacuum heating process described above.Alternatively, the first skin can be draped over a support, and possibly consolidated there, then the core can be assembled with this first skin and then the second skin (consolidated or not) positioned, the welding being carried out either globally to weld the two skins in the same step or sequentially as described previously.

[0115] In the variant shown in Figure 15, the first FAI and second FA2 faces of the AA4 core were each anchored with a thermoplastic anchoring resin RAI, RA2 before the corresponding skin was positioned. The anchoring resin RAI, RA2 is melted or softened during the localized heating process used to facilitate welding the corresponding skin to the core. Anchoring was achieved by depositing the RAI, RA2 resin in a molten state and subsequently cooling it. The RAI, RA2 resins may be identical or different. It remains within the scope of the invention if only one of the FAI, FA2 faces is anchored with the thermoplastic anchoring resin.

[0116] In all the examples described above, simplified representations of the scan path and assembly geometry have been used. The following section describes various possibilities for these aspects in more detail.

[0117] Figure 16 represents an ASP assembly, intended to form a composite panel, with an AAP core sandwiched between two weldable skins P1P, P2P. As illustrated in Figure 17, the skins P1P, P2P can be welded to the AAP core by scanning B of the 24P local heating device, mounted on a robotic arm, along a broken line path, for example so as to cover the entire surface of the ASP assembly (movement along the entire width and length of the assembly).

[0118] Figure 18 shows an ASV assembly, intended to form a ferrule, with a substantially cylindrical AAV core sandwiched between two weldable skins P1V, P2V. Skin P1V is located on the outer circumference of the AAV core, and skin P2V on the inner circumference of the AAV core.

[0119] Figure 19 illustrates an example of an installation for processing the cylindrical ASV assembly of Figure 18.

[0120] The ASV assembly is sandwiched between a mandrel 14, possibly metallic, and a tarpaulin 12 in a manner similar to the configuration in Figure 5. The mandrel 14 is located inside the ASV assembly, and the tarpaulin 12 is located outside the ASV assembly. The mandrel 14 extends over the entire inner circumference of the ASV assembly, and the tarpaulin 12 extends over the entire outer circumference of the ASV assembly.

[0121] In the illustrated example, the 20V local heating device comprises a first 22V heating wall internal to the ASV assembly and a second 24V heating wall external to the ASV assembly. More specifically, the first 22V wall is located inside the internal space of the annular mandrel 14, and the tarpaulin 12 is situated between the ASV assembly and the 24V wall.

[0122] Each 22V, 24V wall, or more generally the local heater, has an extent limited to a circumferential sector of the ASV assembly, or of the tooling 10. In other words, the 22V, 24V walls or the local heater extend only over a portion of the circumference of the ASV assembly. The local heater, or the 22V, 24V walls, can also extend over the entire axial dimension of the ASV assembly, that is, in this case, its entire height. Unless otherwise specified, the height is measured along the DV direction, corresponding here to the axis of the ASV assembly.

[0123] This limited extent of local heating is materialized, in figure 19, by the relative reference E24V corresponding to the arc length of the wall 24V.

[0124] The area heated by the local heating system can have an angular coverage, measured in a transverse plane (e.g., perpendicular) to the axis of the ASV assembly, of, for example, less than or equal to 120°, 90°, or 25°. This angular coverage can be between 5° and 120° (e.g., between 5° and 90° or between 5° and 25°), or it can be between 10° and 120° (e.g., between 10° and 90° or between 10° and 25°). In the illustrated example, walls 22V and 24V have full circumferential overlap, meaning that they each cover the same angular sector when viewed in a transverse plane (e.g., perpendicular) to the axis of the ASV assembly.

[0125] The first 22V and second 24V walls are connected by a 26V junction wall, which allows for the simultaneous movement of these 22V and 24V walls during the movement of the 20V device. This also provides improved thermal containment by minimizing heat loss through convection into the air. The 22V, 24V, and 26V walls thus move as a single unit. The 26V junction wall can, as illustrated, be positioned above the ASV assembly. The 22V, 24V, and 26V walls can, as illustrated, together define a housing in which the ASV assembly is located.

[0126] The 20V device includes a movement mechanism, here in the form of wheels 30, which allows it to move relative to the ASV assembly around its axis. The local heating element is thus rotated around the axis of the assembly during welding. The 20V device could also be stationary, with relative movement achieved by rotating the ASV assembly. The 20V device sweeps the circumference of the ASV assembly along the circumferential DC direction.

[0127] Figure 19 depicts a dual heating system with 22V and 24V heating elements facing each other, but those skilled in the art will recognize that this may not be the case, as described above. In particular, the 22V and 24V heating elements may have different trajectories and speeds, and may not even be directly opposite each other. In the case of the ferrule discussed here, one of the heating elements may rotate clockwise, and the other counterclockwise.

[0128] Figure 20 illustrates the welding of the skins to the core in a dome-shaped ASD assembly by implementing a variant according to the invention. Similar to what has been described previously, the 24D local heating device covers an area between two meridians of the dome, corresponding to a fraction of the dome's surface area, and rotates relative to its X-axis.

[0129] As described above, the invention applies to the manufacture of parts with various geometries. The manufactured parts can be closed or open, for example, cylinders with or without end caps, domes, ferrules, or panels. The parts can be flat or curved. They may or may not have a variable cross-section, that is, a change in their local curvature. Generally, the resulting part can be a ferrule for a space launcher stage, possibly reusable, a launcher fairing, a compartment base for a launcher tank, particularly suitable for storing cryogenic propellants, a satellite tube, or a satellite panel. Such a compartment base with a sandwich structure provides good insulation between the tank compartments.The scope of the invention is not limited to applications in the space sector; the part could alternatively find applications in the aeronautical or railway sectors (manufacturing sandwich structures for train or tram carriages). In aeronautics, the resulting part could be a passenger floor sandwich panel, a belly fairing sandwich panel under the fuselage, a sandwich hatch for closing landing gear bays, a wing leading edge, a spoiler, or an aileron.

[0130] Generally speaking, and even though it depends on the shape and dimensions of the part in question, the extent of local heating can cover a fraction of a surface of the treated assembly of between 1% and 50%, in particular between 3% and 15%, or between 5% and 10%.

[0131] Although the present invention has been described with reference to specific embodiments, modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various embodiments illustrated / mentioned may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0132] The expression "between ... and ..." should be understood as including the boundaries.

Claims

Demands

1. A method for manufacturing a part made of composite material, the method comprising: - obtaining a precursor sandwich assembly (AS1) of the part to be manufactured by positioning (i) a first thermoplastic composite skin (PI), with or without prior consolidation, on a first face (FAI) of a core (AAI) with a honeycomb structure, the first skin comprising a first thermoplastic resin opposite the first face of the core, and (ii) a second thermoplastic composite skin (P2), with or without prior consolidation, on a second face (FA2) of the core, opposite the first face, the second skin comprising a second thermoplastic resin, identical or different from the first resin, opposite the second face of the core, and - vacuum welding of skins to core by subjecting the sandwich assembly to a heat treatment comprising (i) a sweep (B) by local heating of limited extent to a fraction of the assembly, in relative motion with respect to the assembly, the local heating (24; 26) allowing to selectively melt or soften the first resin and the second resin in the heated zone, and (ii) a cooling, after this local heating, in order to obtain the welding of the skins to the core.

2. A method for manufacturing a part made of composite material, the method comprising: - obtaining a first assembly (Al) by positioning a first thermoplastic composite skin (PI), whether or not it has undergone prior consolidation, on a first face (FAI) of a core (AAI) with an alveolar structure, the first skin comprising a first thermoplastic resin opposite the first face of the core, - vacuum welding of the first skin to the core by subjecting the first assembly to a first heat treatment comprising (i) a sweep (B) by a first local heating of limited extent to a fraction of the first assembly, in relative motion with respect to this first assembly, the first local heating allowing to selectively melt or soften the first thermoplastic resin in the heated zone, and (ii) a cooling, after this first local heating, in order to obtain the welding of the first skin to the core, - obtaining a second assembly (A2) by positioning, on the first assembly in which the first skin has been welded to the core, a second thermoplastic composite skin (P2), which may or may not have undergone prior consolidation, on a second face (FA2) of the core opposite the first face, the second skin comprising a second thermoplastic resin, identical or different from the first resin, facing the second face of the core, and - vacuum welding of the second skin to the core by subjecting the second assembly to a second heat treatment comprising (i) sweeping by a second local heating of limited extent to a fraction of the second assembly, in relative motion with respect to this second assembly, the second local heating allowing to selectively melt or soften the second thermoplastic resin in the heated area, and (ii) cooling, after this second local heating, in order to obtain the welding of the second skin to the core.

3. A method according to claim 1 or 2, wherein the first skin (PI) and the second skin (P2) have each undergone prior consolidation and are each enriched with the first resin or the second resin, depending on the skin considered, on their surface facing the core, obtaining each of the first and second enriched skins comprising: - the deposition of a first fibrous layer or several first layers (Cl-1; C2-1) of stacked pre-impregnated thermoplastic fibrous material and at least one second layer (Cl-2; C2-2) on the first layer(s) to obtain a pre-impregnated thermoplastic fibrous stack, said at least one second layer being located on the surface of said pre-impregnated thermoplastic fibrous stack and comprising at least the first resin in the case of the first skin or the second resin in the case of the second skin, the first layer(s) being impregnated with a thermoplastic resin having a melting or softening temperature higher than that of the resin of said at least one second layer, and - vacuum consolidation of the thermoplastic pre-impregnated fibrous stack thus obtained so as to melt or soften the thermoplastic resins present and weld said at least a second layer to the first layer or the first layers.

4. A method according to any one of claims 1 to 3, wherein a thermoplastic interposition film (Fil; FI2) is added between each skin (Pl; P2) and the core (AAI), and wherein this thermoplastic interposition film is melted or softened during localized heating implemented to participate in the welding to the skin core corresponding.

5. A method according to any one of claims 1 to 4, wherein at least one of the first (FAI) and second (FA2) faces of the core has been anchored by a thermoplastic anchoring resin (RAI; RA2) before positioning the corresponding skin (P1; P2), and wherein this anchoring resin is melted or softened during local heating to participate in welding the corresponding skin to the core, the anchoring being achieved by: - coating of said at least one of the first and second faces with the molten thermoplastic anchoring resin, and - cooling of the thermoplastic anchoring resin in its molten state.

6. A method according to any one of claims 1 to 5, wherein each assembly (AS1; Al; A2) is, during its heat treatment, positioned on a metallic substrate (14) with a vacuum bag (12) located opposite the assembly, securely attached to the metallic substrate and applying a pressure (PR) on the assembly, the assembly being positioned between the metallic substrate and the vacuum bag.

7. A method according to any one of claims 1 to 5, wherein each assembly (AS1; A1; A2) is, during its heat treatment, positioned between two vacuum bags (12a; 12b) sealed together on retaining flanges (17) arranged on edges (31; 32) of the assembly, the edges being intended to form the outer perimeter(s) of the part to be obtained and the bags applying pressure to the assembly.

8. A method according to any one of claims 1 to 7, wherein the sandwich assembly (AS2) and / or the second assembly defines a median region (RM) on which the first (P3) and second (P4) skins are opposite a respective face (FA3; FA4) of the core, and peripheral regions (RP), intended to form the outer perimeter(s) of the part to be obtained, on which the first skin joins the second skin.

9. A method according to claim 8, wherein the middle region (RM) comprises a transition zone to each peripheral region (RP) on which a spacing between the first (FA3) and the second (FA4) faces of the core, measured transversely to these faces, gradually decreases towards the corresponding peripheral region.

10. A method according to any one of claims 1 to 9, wherein the core (AAI) is a honeycomb or a foam.

11. A method according to any one of claims 1 to 10, wherein each local heating is achieved by a first heating wall (22) located on the side of the first face (FAI) of the core (AAI) and a second heating wall (24) located on the side of the second face (FA2) of the core.

12. Method according to claim 11, wherein the first (22) and second (24) walls do not overlap.

13. A method according to any one of claims 1 to 10, wherein each local heating is achieved by a single heating wall (24) located on the side of the first face (FAI) of the core (AAI) or the second face (FA2) of the core.

14. A method according to any one of claims 1 to 13, wherein each of the first (PI) and second (P2) skins comprises carbon fibers, glass fibers, aramid fibers, or a mixture of such fibers.

15. A method according to any one of claims 1 to 14, wherein the first thermoplastic resin and the second thermoplastic resin are a polyetherimide, or a polyaryletherketone, for example a low-melting-point polyaryletherketone.

16. A method according to any one of claims 1 to 15, wherein the composite material part has a cylindrical shape.

17. A method according to any one of claims 1 to 16, wherein the composite material part is a flat or curved panel.

18. A composite material part comprising a core (AAI) with a honeycomb structure interposed between two skins (P1; P2) consolidated from thermoplastic composite material and positioned on opposite faces (FAI; FA2) of the core, the skins being bonded to the core by thermoplastic adhesion zones (ME) penetrating into the interior of the core, the part being a cylinder, a dome or a ferrule.

19. A part according to claim 18, wherein the adhesion zones (ME) comprise a polyetherimide, or a polyaryletherketone, for example a low-melting-point polyaryletherketone.

20. Part according to claim 18 or 19, wherein each skin (PI; P2) comprises a stack of layers (Cl-1; Cl-2; C2-1; C2-2) with a portion of this stack, located on the side opposite the adhesion zones (ME), being fibrous and impregnated with a thermoplastic resin having a melting or softening temperature higher than that of the adhesion zones.

21. Part according to any one of claims 18 to 20, wherein the part is a ferrule of a space launcher stage, a fairing of a space launcher, a compartment bottom of a space launcher tank or a satellite tube.

Images