Improved manufacturing method for an acoustic complex by additive manufacturing and acoustic complex obtained by such a method

Abstract

Improved manufacturing method of an acoustic complex by additive manufacturing and acoustic complex obtained by such a method. Method of manufacturing an acoustic complex (16) for an acoustic panel (10) by additive manufacturing, the acoustic complex (16) comprising cells (18), each extending along a central axis (A), the method comprising: the fabrication of first wall portions (181) from a lower end (161) of the acoustic complex to an upper end (162) of the acoustic complex, the first wall portions (181) being parallel to the central axis (A), and the fabrication of support portions (185) extending between the first wall portions (181), the support portions (185) each comprising a lower face forming a second wall portion (182) delimiting an upper part of the cell (18) and having an arched shape,and an upper face delimiting the upper end (162) of the acoustic assembly (16), such that a maximum angle (α) between the second portion of the wall (182) and a construction direction (D) is less than or equal to 45°. Figure for the abbreviation: Fig. 4.

Description

Description Title of the invention: Improved manufacturing method of an acoustic complex by additive manufacturing and acoustic complex obtained by such a process Technical field

[0001] = This disclosure relates to the field of acoustic panels used in aircraft propulsion systems. More specifically, this presentation concerns a manufacturing process of an acoustic complex for acoustic panel by fa- additive manufacturing, and an acoustic complex obtained by such a process. Prior art

[0002] — In the aeronautical industry, it is common to use laminated parts, particularly in thermoplastic matrix composite. For example, in the context of the insulation of aircraft engines and the reduction of noise emitted by these engines, Current solutions use acoustic panels, called “sandwich panels”, using such materials. However, the nacelles, fuselage or interior of the cabins can also be equipped with these acoustic panels.

[0003] — The structure of these panels consists of a stack of skins and structures in honeycombs, also called acoustic complexes. These structures can include a layer of honeycombs (or acoustic complex), we then speak of a structure “SDOF” (from the English “single degree of freedom”) or two levels of honeycombs, we then speak of a “2DOF” structure (from the English “2 degrees of freedom”). In a single-story honeycomb structure, for example, one of the skins is porous to sounds (the acoustic skin), and the other is hermetic (the closing skin), the whole forming a Helmholtz cell (or resonator).

[0004] — [Fig.1] represents a partial perspective view of a 10° acoustic panel "SDOF" comprising an acoustic skin 12, a closing skin 14, and a acoustic complex 16, which is a core with a honeycomb structure sandwiched between these two skins. The acoustic complex 16 is made up of a network of alveoli 18 in honeycomb shape, in this example hexagonal base. The acoustic skin 12 is perforated by a plurality of orifices 20, each orifice 20 opening onto a alveolus 18 of the acoustic complex 16, several orifices 20 being able to open onto a same cell 18.

[0005] — As is known, the skins used in acoustic panels can be deposited by automated draping of a thermoplastic or thermo- matrix composite hardenable. Such a process allows an improvement in manufacturing quality for large parts, a gain in cost and performance, particularly in a context of increasing constraints on the acoustic functions of propulsion systems, and increasing constraints on aircraft drag reduction. In this method, a first skin, for example the acoustic skin 12, is draped over a draping tool (not shown), more precisely over the surface (or substrate) of said tool. This draping is carried out by deposition tools (not shown) known per se, such as so-called "AFP" robots, for "automated fiber placement" in English, successively depositing wicks, or thermoplastic or thermosetting pre-impregnated strips, parallel to each other and on several layers, called "plies", or even by "ATL" for "automated tape layer" in English, by depositing pre-impregnated sheets of greater width than the strips deposited in the "AFP" technique. These sheets are deposited one after the other. The skin is then polymerized in an autoclave for several hours. Then, the acoustic complex 16 in honeycombs is deposited on the first skin 12 by additive manufacturing, then a second skin, here the closing skin 14, is draped over the acoustic complex 16 by the same techniques as for the first skin 12. It will be noted that the acoustic complexes according to the prior art can also be manufactured by bonding an aluminum honeycomb on a skin. One of the recurring problems during the automatic draping of the second skin 14 using the “AFP” technique for example, concerns the so-called “telegraphing” phenomenon, in which the parts of the pre-impregnated rovings or strips extending between two walls 180 of the cells 18 of the acoustic complex 16 tend to collapse under their own weight, as illustrated in [Fig.2], image (a). Furthermore, draping tools generally use laying heads comprising a compacting roller R, allowing the application of pressure promoting adhesion, that is to say the adhesion of the pre-impregnated strips 14 to the acoustic complex. However, this pressure P is likely to cause crushing and deformation of the thermoplastic walls 180 obtained by additive manufacturing, as illustrated in [Fig.2], image (b).In addition, the pressure exerted by the roller R accentuates the phenomenon of “telegraphing”, and the walls 180 of the cell 18 constitute an obstacle interfering in the movement of the roller R, as illustrated in [Fig.2], image (c), the cross on this image symbolizing the obstacle generated by the wall 180. Furthermore, a solution consisting of increasing the density of the cells, or alveoli of the honeycomb structure of the acoustic complex, in order to better distribute the pressure exerted by the roller and to limit the phenomenon of "telegraphing", is not optimal because it significantly increases the mass of the panel, can modify its acoustic properties and increase the removal time and the costs. There is therefore a need to at least partially overcome the aforementioned drawbacks. Statement of the invention The present disclosure relates to a method of manufacturing an acoustic complex for an acoustic panel by additive manufacturing, the acoustic complex comprising a plurality of cells, each cell extending along a central axis, the method comprising: - the manufacture of first wall portions from a lower end of the acoustic complex to an upper end of the acoustic complex, the first wall portions being parallel to the central axis, - the manufacture of support portions extending between the first wall portions, the support portions each comprising a lower face forming a second wall portion delimiting an upper part of the cell and having a vaulted shape, and an upper face delimiting the upper end of the acoustic complex, such that a maximum angle between the second wall portion and a construction direction is less than or equal to 45°. In the present disclosure, the cells of the acoustic complex may have different shapes, for example a circular, rectangular or hexagonal cross-section. In the case of a circular cross-section for example, the cells are each delimited by a single wall (cylindrical in shape and circular in section). Furthermore, the terms "lower", "upper" and their derivatives are considered relative to the central axis of the cells, and relative to the stacking direction of the layers of materials in the construction direction during additive manufacturing. Thus, the acoustic complex extends between a lower end intended to rest on the first skin, and an upper end, on which the second skin is intended to be manufactured. It is understood that in the present disclosure, additive manufacturing is a technique known per se in which layers of materials, for example layers of powder or filaments, or manufacturing layers, are stacked on top of each other in the construction direction. By "construction direction" is understood the direction in which the acoustic complex is constructed, i.e. in which the layers of materials are stacked on top of each other. For example, when the acoustic complex is manufactured on the first skin, the construction direction corresponds to a direction orthogonal to the first skin. It is also understood that the first wall portions extend along the central axis of the alveoli, from the base of the alveoli, that is to say the lower end of the acoustic complex, to the upper end of the complex. acoustic. In other words, the first wall portions extend over the entire height of the acoustic complex, parallel to the central axis of the cells, and correspond substantially to the usual walls of an acoustic complex according to the prior art without support portions. It is understood in this disclosure that the support portions are not supports in the usual sense, used during additive manufacturing to stabilize a part or support geometries that could collapse during its manufacture, and which are removed when the printing of the part is finished. The support portions (or support or support element) according to this disclosure are an integral part of the acoustic complex thus manufactured, preferably in the same material as the rest of the structure, and are not intended to be removed. Furthermore, it is understood that the support portions extend between the first wall portions, in an upper part of the acoustic complex. The lower face of these support portions, forming the second wall portions, delimit the upper part, or ceiling, of the cell, the second wall portions being vaulted and giving the ceiling the shape of an ogive. It is thus understood that the second wall portions extend from the first wall portion, that is to say from an intermediate portion of the first wall portion, between the lower end and the upper end thereof. In other words, during additive manufacturing, material is added along the first wall portion such that the second wall portion gradually moves away, layer after layer, from the first wall portion.We therefore understand that the second portions of wall of the same cell, opposite each other, have a vaulted shape and move closer to each other during additive manufacturing, giving the upper part of the cell the shape of an ogive. Furthermore, during the manufacture of the support portions, a maximum angle between the second portion of the arched wall and the construction direction remains less than or equal to 45°. The inclination angles of these surfaces make it possible to avoid the installation of supports on them. Indeed, for angles less than 45° relative to the construction direction, in other words relative to a vertical direction, the layer being manufactured benefits from sufficient grip on the solidified part of the lower manufacturing layer to be able to maintain its position during the manufacture of the part, without risking the material sagging under its own weight and without needing additional support means.It is therefore not necessary to put in place supports, usually used as indicated above, on said surface, the use of such supports being excluded in this application because it would not be possible to remove them from the cells, then closed, at the end of manufacturing, and would cause an unacceptable increase in mass. The upper face of the support portions allows the definition of the upper end of the acoustic complex. Thus, the second skin of the acoustic panel can be manufactured subsequently on a solid surface formed by the support portion, or non-solid but with close support points in the case of a lattice structure for example. This limits the risks of the appearance of "telegraphing" phenomena, or crushing of the walls, here the first wall portions, of the acoustic complex. The process thus makes it possible to increase the diameter of the cells, and therefore reduce the mass of the assembly, while allowing the flatness of the second skin deposited on the acoustic complex. In addition, the acoustic complex thus obtained makes it possible to improve the adhesion of the strips of materials deposited by "AFP" or "ATL" for example, and makes it possible to improve the acceptance of the compaction forces of these strips, thus improving the quality of the second skin deposited on the acoustic complex. It will further be noted that the steps of the method are not necessarily carried out one after the other, but may be carried out simultaneously. In particular, during the manufacture of the upper part of the cells, the first wall portions and the support portions comprising the second wall portions are manufactured simultaneously, layer after layer. In some embodiments, the upper end of the acoustic complex is planar, each cell being symmetrical with respect to its central axis and being delimited in its upper part by a first support portion and a second support portion, a first maximum angle between the construction direction and the second wall portion formed by the first support portion being identical to a second maximum angle between the construction direction and the second wall portion formed by the second support portion, the first angle and the second angle being less than or equal to 45°. It is understood that the entire acoustic complex and the acoustic panel are flat, and that the upper ends of each support portion together form a flat surface facilitating the deposition of the second skin. In this case, the vaults formed by the second wall portions are symmetrical with respect to the central axis, the latter passing through the top of the ogive. In some embodiments, the upper end of the acoustic complex is curved, at least one cell not being symmetrical with respect to its central axis and being delimited in its upper part by a first support portion and a second support portion, a first maximum angle between the construction direction and the second wall portion formed by the first support portion being different from a second maximum angle between the construction direction and the second wall portion formed by the second support portion, the first angle and the second angle being less than or equal to 45°. This curved shape can be formed by the set of upper ends of each support portion, preferably involving a continuous curved surface. It is understood that in this configuration, the tip of the ogive may not be centered on the central axis of the cell, but offset from it. The arched portions of the ogive, on either side of the central axis, are therefore not symmetrical, their maximum angles being consequently different. They are nevertheless both less than or equal to 45°. Furthermore, it is of course understood that in this case, the acoustic complex as a whole is curved (corresponding to the curved shape of the nacelle for example), and not only its upper end. In some embodiments, the support portions have a lattice structure. The support portions each form a cell ceiling, i.e. the material deposited between the first wall portion, the second vaulted wall portion, and the upper end of the acoustic complex (or the second skin when the latter is deposited on said upper end). In this embodiment, this ceiling is not solid, but porous, in particular in lattice. This configuration makes it possible to create a support for the second skin while restricting the volume of the acoustic cavity to a minimum and without reducing the performance of the acoustic complex. It is also understood that the second wall portion is also in lattice. Conversely, the first wall portion is preferably solid and sealed. In some embodiments, the support portions having the lattice structure have a void content of between 1% and 99%, preferably between 50 and 95%. These values ​​allow to increase the volume of the acoustic cavity, while allowing effective support for the second skin. In some embodiments, the support portions are fabricated such that the lattice structure has a decreasing void ratio as one approaches the upper end of the acoustic complex. In other words, during additive manufacturing and the stacking of the layers of materials in the construction direction, the void rate is increasingly lower, in other words the density of the support portions is increasing, as one approaches the upper end of the acoustic complex. Conversely, the void rate of the support portions is higher, and its density lower, near the second portion of the base of the arched wall. For example, the void rate can be 90% near the base of the second portion of the arched wall, and 10% near the top of the ogive and the upper end of the acoustic complex. It is thus possible to adapt the porosity of the support portion of so as to increase its density in the regions intended to support the second skin and requiring increased rigidity, while maintaining a large volume of the acoustic cavity, by decreasing the density in the regions of the support portion further from the upper end of the acoustic complex. In some embodiments, a top of the cells is pointed or has a flattened surface, the flattened surface having a width of less than 20 mm, preferably less than 10 mm. When the top of the cells is pointed, we understand that, during additive manufacturing, the second portions of wall of the same cell, opposite each other, gradually join, layer after layer, until they join at the same point at the top of the cell, in other words at the top of the ogive, for example on the central axis of the cell. Conversely, in the presence of a flat, said second wall portions do not meet. The top of the cell may therefore have a space formed between the upper end of the second wall portions. This space may be filled with material forming a flat bridge connecting the upper ends of these second wall portions. The presence of this flat makes it possible to reduce the height of the support portions, consequently limiting the mass of the assembly. Furthermore, the fact that the flat has a width of less than 20 mm, preferably less than 10 mm, makes it possible, during additive manufacturing, to fill the space between the ends of the second arched wall portions that do not meet so as to form this bridge, by limiting the risks of sagging under its own weight of the material deposited between said ends. It will be noted that on a filament not loaded with material deposited during additive manufacturing, an inflection of said filament can occur from a distance of 10 mm between two support points. For a filament loaded with short fibers, the inflection can be observed from 20 mm. Finally, with a filament loaded with continuous fibers, tensioning during deposition makes it possible to increase this distance.It will therefore be understood that the width of the flat, and therefore the distance between the upper ends of the second portions of wall of the same cell which do not meet, depends on the stiffness and viscosity of the material used during additive manufacturing. In some embodiments, the support portions are manufactured such that they have a non-zero thickness between a top of the cells and the upper end of the acoustic complex. In other words, it is understood that the top of the ogive, pointed or with a flat, is not confused with the upper end of the acoustic complex, but that at least one additional layer of material is provided between said top of the cell and the upper end of the acoustic complex during manufacturing. additive. This or these additional layers make it possible to consolidate the stacking of layers and improve the rigidity of the support portions when draping the second skin. In some embodiments, the method includes fabricating third wall portions extending between the lower end of the acoustic complex and the first wall portion, the third wall portions having a curved shape. It is understood that each cell comprises a third wall portion delimiting a lower part of said cell. The third wall portion thus forms a connection fillet between the first wall portion and the first skin on which the acoustic complex is manufactured. Thus, in this configuration, each cell generally has an egg shape, a lower part of the cell being delimited by the third curved wall portion, an intermediate part of the cell being delimited by the first vertical wall portion (parallel to the central axis), and the upper part of the cell being delimited by the second ogive-shaped wall portion. This configuration makes it possible to improve the overall rigidity of the acoustic complex by attaching it to the first skin. In some embodiments, the method includes fabricating an acoustic cone in each cell, the acoustic cone extending from the lower end of the acoustic complex. In other words, the acoustic cone is disposed in the cell on the side opposite the warhead, and is capable of attenuating low frequencies. The present disclosure also relates to an acoustic complex for an aeronautical engine acoustic panel, obtained by a method according to any one of the preceding embodiments. This disclosure also relates to a method of manufacturing an acoustic panel comprising: - the production of a first skin, - the manufacture of an acoustic complex on the first skin, by a method of manufacturing an acoustic complex according to the present description, and - the production of a second skin on the upper end of the acoustic complex. The second skin can be manufactured and assembled to the acoustic panel by autoclave cooking, by automatic draping "AFP" or "ATL" for example, or by in-situ consolidation, in particular by means of a laser necessary for the adhesion of the last ply deposited and the one being deposited, without the need for additional thermal cycles in an autoclave. This disclosure also relates to an acoustic panel obtained by a method of manufacturing an acoustic panel according to this disclosure. Brief description of the drawings The invention and its advantages will be better understood upon reading the detailed description given below of different embodiments of the invention given as non-limiting examples. This description refers to the appended pages of figures, in which: [Fig.1] [Fig.1] represents a partial perspective view of an acoustic panel according to the prior art, [Fig.2] [Fig.2] represents a partial side and sectional view of an acoustic panel according to the prior art in different situations during its manufacture, [Fig.3] [Fig.3] represents a sectional view of a turbojet engine comprising acoustic panels according to the present disclosure, in a longitudinal plane of the turbojet engine, [Fig.4] [Fig.4] represents a partial side view and in section of an acoustic panel according to a first embodiment of the present disclosure, [Fig.5A-5D] Figures 5A to 5D represent different stages of a manufacturing process of the acoustic panel of [Fig.4], [Fig.6] [Fig.6] represents a partial side and sectional view of an acoustic panel according to a second embodiment of the present disclosure, [Fig.7] [Fig.7] represents a partial side and sectional view of an acoustic panel according to a third embodiment of the present disclosure, [Fig.8] [Fig.8] represents a partial side and sectional view of an acoustic panel according to a fourth embodiment of the present disclosure, [Fig.9] [Fig.9] represents a partial side and sectional view of an acoustic panel according to a fifth embodiment of the present disclosure, [Fig.10] [Fig.10] represents a partial side view and in section of an acoustic panel according to a sixth embodiment of the present disclosure, [Fig.11] [Fig.11] represents a partial side and sectional view of an acoustic panel according to a seventh embodiment of the present disclosure, [Fig.12A-12B] Figures 12A and 12B respectively represent a partial side and sectional view of a curved acoustic panel according to an eighth embodiment of the present disclosure, and a side and sectional view of a comparative example of a flat acoustic panel. Description of the embodiments In [Fig. 1] is shown a sectional view of a turbojet | comprising an acoustic panel 10 according to the invention, in a longitudinal plane of the turbojet 1. The turbojet 1 comprises a nacelle 2, an intermediate casing 3 and an internal casing 4. The nacelle ? and the two casings 3 and 4 are coaxial. The nacelle 2 defines at a first end an inlet channel 6 5 for a fluid flow and at a second end, opposite the first end, an exhaust channel 6 for a fluid flow. The nacelle 2 and the intermediate casing 3 delimit between them a primary fluid flow vein 7. The intermediate casing 3 and the 5 internal casing A delimit between them a secondary fluid flow vein 8. The primary vein 7 and the secondary vein 8 are arranged in an axial direction of the turbo-reactor between the inlet channel 5 and the exhaust channel 6. The turbojet engine 1 further comprises a fan 9 configured to deliver an air flow F as a fluid flow, the air flow F being divided at the outlet of the fan into a primary flow Fp circulating in the primary vein 7 and into a secondary flow Fs circulating in the secondary vein 8. The turbojet engine 1 further comprises at least one acoustic panel 10 configured to attenuate the acoustic waves emitted by the turbojet engine before these waves escape radially to the outside of the nacelle 2 of the turbojet engine 1. The acoustic panel 10 is configured to attenuate acoustic waves whose frequency belongs to a predetermined frequency range. In the embodiment illustrated in [Fig. 1], the panel 10 can be integrated with the intermediate casing 3, the internal casing 4, and the nacelle 2. In the same way as the acoustic panel 10° according to the prior art shown in [Fig. 1], the acoustic panel 10 according to the invention comprises an acoustic complex 16 arranged between a first skin 12 which may be an acoustic skin comprising orifices, and a second skin 14 which may be a closing skin. The acoustic complex 16 comprises a plurality of walls delimiting cells 18, these cells being able to have, for example, but in a non-limiting manner, a circular, square or hexagonal section. It will also be noted that the embodiments are described in the remainder of the description with reference to FIGS. 1 to 11 and 12B with planar 16 acoustic complexes, and with reference to view 12A of FIGS. 12A-12B with a curved acoustic complex. The acoustic panel 10 according to the invention differs from the acoustic panel 10” according to the prior art in that the acoustic complex 16 comprises support portions 185. [Fig. 4] represents a partial and sectional view of an acoustic panel 10 according to a first embodiment of the invention, in a sectional plane parallel to the central axis A of the cells 18. As such, the terms “lower”, “upper” and their derivatives are considered according to the “low-high” direction symbolized by an arrow on the left of [Fig. 4], corresponding to a construction direction D of the acoustic complex during an additive manufacturing process described below. It will be noted that in the embodiments described with reference to FIGS. 1 to 11 and 12B, the central axis A cells 18 and construction direction D are parallel. The acoustic complex 16 extends, along the central axis A, between a lower end 161 and an upper end 162. The lower end 161 rests on the first skin 12, and the second skin 14 rests on the upper end 162. Furthermore, the acoustic complex 16 comprises first wall portions 181. The first wall portions 181 are solid and sealed, and extend vertically, that is to say parallel to the central axis λ of the cells λ, in other words perpendicular to the skins 12, 14, between the lower end 161 and the upper end 162 of the acoustic complex 16. These first wall portions 181 are similar to the walls existing in the acoustic complexes of the prior art, an example of which is notably illustrated in [Fig. 1]. The acoustic complex 16 further comprises support portions 185 extending between the first wall portions 181, in particular between upper parts of the first wall portions 181. The support portions 185 comprise a lower face forming a second wall portion 182, delimiting an upper part, in other words a ceiling, of the cells 18. It is therefore understood that the second wall portion 182 is an integral part of the support portions 185. In other words, the second wall portion 182 is the lower face of a support portion 185, the latter delimiting the ceiling of the cell 18. Each second wall portion 182 extends between a lower end 182a and an upper end 182b. The lower end 182a extends from the first wall portion 181, at an intermediate position of said first wall portion 181 between the lower and upper ends 161, 162 of the acoustic complex. The upper end 182b is, on the other hand, further away from the first wall portion 181 than the lower end 182a. The second wall portions 182 thus have a vaulted shape, giving the upper part of the cell 18 an ogival shape. In particular, in the non-limiting example shown in [Fig. 4], it is assumed that each cell 18 has a hexagonal-shaped base. In this figure, two first wall portions 181 for the same cell 18 are visible, these two first wall portions 181 being opposite each other and parallel to each other. A support portion 185 extends from each of these first wall portions 181, each support portion 185 comprising, on its lower face, a second arched wall portion 182. These two second wall portions 182 approach each other from their lower end 182a to their upper end 182b, also converging towards the central axis A, thus giving the upper part of the cell 18 the shape of an ogive. Furthermore, the second wall portions 182 are arched in such a way that, according to the section plane shown in [Fig.4], a maximum angle α between a second wall portion 182 and the construction direction D (corresponding to the central axis Δ of the cell in this example) is less than or equal to 45°, preferably between 10° and 45°. In other words, according to the section plane shown in [Fig.4], an angle α between a straight line tangent to the second wall portion 182 at a point thereof between its ends 182a, 182b, and the central axis Δ, is less than or equal to 45° regardless of the point of said second wall portion 182 considered. The support portions 185 also comprise an upper face, the upper faces of the support portions 185 together forming the upper end 162 of the acoustic complex 16, this upper end 162 being flat and continuous, thus ensuring good adhesion of the second skin 14 applied to this upper end 162. Figures 5A to 5D represent different steps of a method of manufacturing an acoustic complex 16 and an acoustic panel 10 according to the invention. In a first step, a first skin 12 is manufactured. The first skin 12, as well as the second skin 14 described later, can be manufactured for example, but in a non-limiting manner, by the “AFP” (for “automated fiber placement” in English) or “ATL” (for “automated tape layer” in English) technique known per se, by successive deposit of wicks, or pre-impregnated strips parallel to each other and on several layers, called “plies”. The deposited strips comprise a thermoplastic material TP (more simply called “TP material” in the remainder of the description), in particular, but in a non-limiting manner, a polyetheretherketone PEEK, a polyetherketoneketone PEKK, a polyaryletherketone PAEK or a polyphenylsulfone PPSU. In a second step, the acoustic complex 16 is manufactured. The acoustic complex 16 is produced by additive manufacturing on the first skin 12. The method for manufacturing the acoustic complex 16 by additive manufacturing comprises the stacking of successive layers of material in a vertical direction perpendicular to the first skin 12 called the “construction direction”, from the lower end 161 of the acoustic complex 16 to the upper end 162 thereof. Typically, the additive manufacturing method is a filament deposition method called “FFF” (for “Fused Filament Fabrication” in English) or “FDM” (for “Filament Deposit Molding” in English). The deposited filaments are preferably made of polymer, for example polyetherimide (PET), polyphenylene sulfide (PPS), or from the family of polyaryletherketones (PAERK). The polymer filaments may or may not be filled. They may, for example, be filled with carbon fibers.The width of the deposited filaments can be between 0.1 mm and 2 mm. Image 5A represents a first phase of the manufacturing process of the complex acoustic 16 by additive manufacturing, in which the first wall portions 181 are being manufactured on the first skin 12, from the lower end 161. At this stage, the polymer filaments are stacked vertically on top of each other, such that the first wall portions 181 remain parallel to the central axis A of the cells of the final part. The upward-pointing arrow represents the build direction D during additive manufacturing. Image 5B represents a second phase of the method of manufacturing the acoustic complex 16 by additive manufacturing. During this phase, while the first wall portions 181 are still being manufactured, additional material is deposited from the first wall portions 181, from a point along the height thereof, this point corresponding to the lower end 182a of the second arched wall portions 182. It is understood that from this point, a greater width of material, i.e. polymer filaments, is deposited at each layer of material stacked in the construction direction. Thus, this increasingly large width of material deposited forms the support portions 185, the lower face of which forms the second wall portions 182 during manufacture. In other words, it is understood that as the layers of materials are stacked, the second wall portions 182 move further and further away from the first wall portion 181 from which they extend, to converge towards the central axis A. It is also understood that for each layer of polymer material deposited, it is necessary to ensure that the angle between the second wall portion 182 during manufacture and the central axis A remains less than or equal to 45°, in order to benefit from sufficient adhesion of the previous layer of material, as described above. Image 5C represents a final phase of the method of manufacturing the acoustic complex 16 by additive manufacturing, in which the upper end 162 of the acoustic complex 16 is reached. At this stage, the respective upper ends 182b of the second wall portions 182 have reached the top of the cell 18, the upper part of the latter then having the shape of an ogive. Furthermore, the upper face of each support portion 185 is planar, such that the upper end 162 of the acoustic complex 16 thus formed is itself planar and continuous. Image 5D represents a third step of the manufacturing process of the acoustic panel 10, in which the second skin 14 is manufactured on the acoustic complex 16 obtained by the manufacturing process described with reference to images 5A, SB and 5C. The second skin 14 can be manufactured by one of the techniques described above for the first skin 12, by automated draping using in particular a compaction roller R. The compaction roller R moves in a right-left direction of movement represented by the arrow pointing to the left in image 5D, in exerting a pressure P, represented by the downward arrow in image 5D, on the strips of thermoplastic material intended to form the second skin 14. Unlike the configuration shown in [Fig.2] corresponding to the state of the art, the presence of the support portions 185 makes it possible to withstand the pressure exerted by the compaction roller R, to limit or even eliminate the phenomenon of “telegraphing” and crushing of the first wall portions 181. The acoustic panel 10 thus obtained is shown in [Fig.4]. In an example of an acoustic panel 10 obtained by a method according to the invention, the cells 18 of the acoustic complex 16 may have the shape of a regular hexagon inscribed in a circle 20 mm in diameter, and have a height of between 10 and 80 mm between the lower end 161 and the upper end 182b of the second wall portions 182. For a cell 30 mm high for example, the base of the ogive, in other words the lower end 182a of the second wall portions 182, may start for example at a height of 20 mm relative to the lower end 161 of the acoustic complex 16. [Fig. 6] represents a second embodiment of the invention. The acoustic panel 10 according to the second embodiment differs from the acoustic panel according to the first embodiment described with reference to [Fig. 4], in that the support portions 185 are not solid but porous, and in particular have a lattice structure. The lattice structure comprises a plurality of filaments entangled with each other, in particular parallel to each other and perpendicular to each other, in the three dimensions of space. Thus, the material located between the second wall portions 182 forming the warheads, the first solid wall portions 181, and the second skin 14, is porous, thus limiting the total mass of the acoustic panel 10. It will be noted that the second wall portions 182 may themselves be porous. The void content of the lattice structure is between 1 and 99%, preferably between 50 and 95%. It will be noted that the lattice structure is also produced by additive manufacturing, preferably in the same material as the rest of the structure of the acoustic complex 16, in particular the first wall portions 181. However, alternatively, the lattice can be manufactured in a material different from the first wall portions 181. [Fig. 7] represents a third embodiment of the invention. The acoustic panel 10 according to the third embodiment differs from the acoustic panel according to the second embodiment described with reference to [Fig. 6], in that the lattice structure of the support portions 185 is not uniform, but scalable. More precisely, the lattice structure is denser (lower void ratio) at near the upper end 162 of the acoustic complex 16 than near the lower end 182a of the second wall portions 182. For example, the void rate may be 90% near the lower end 182a of the second wall portions 182, and 10% at the top of the ogive of the cells 18 near the upper end 162 of the acoustic complex 16. By “near”, it is understood that the void rate may be for example 10% over the upper third of the height of the support portions 185, between the lower end 182a of the second wall portions 182 and the upper end 162 of the acoustic complex, and 90% over the rest of the height. Alternatively, the void rate may change progressively and linearly from the lower end to the upper end of the support portions 185, [Fig. 8] represents a fourth embodiment of the invention. The acoustic panel 10 according to the fourth embodiment differs from the acoustic panel according to the previous embodiments, in that the top of the ogive is not pointed, but comprises a flat 19. Indeed, in the termination modes described previously, the respective upper ends 182b of the second wall portions 182 meet at the same point, in particular on the central axis A, such that the cells have an ogive top ending in a point. In this embodiment, the upper ends 182b do not meet, and are at a distance D from each other, less than 20 mm, preferably less than 10 mm. The top of the cell 18 may therefore have a space of a width D formed between the upper end 182b of the second wall portions 182. This space may be filled by material forming a flat bridge connecting the upper ends of these second wall portions. The fact that the flat 19 has a width D of less than 20 mm, preferably less than 10 mm, makes it possible, during additive manufacturing, to fill the space between the upper ends 182b of the second arched wall portions 182, limiting the risks of sagging under its own weight of the material deposited between said ends 182b. Indeed, on an unfilled polymer filament deposited between the two ends 182b, an inflection of said filament can occur from a distance of 10 mm between the two support points formed by the ends 182b. For a polymer filament filled with short fibers, the inflection can be observed from 20 mm. Finally, with a filament filled with continuous fibers, tensioning during deposition makes it possible to increase this distance.It is therefore understood that the width D of the flat 19, and therefore the distance between the upper ends 182b of the second wall portions 182 of the same cell 18 not meeting, depends on the stiffness and viscosity of the polymer material used during additive manufacturing. [Fig. 9] represents a fifth embodiment of the invention. The acoustic panel 10 according to the fifth embodiment differs from the acoustic panel according to the previous embodiments, in that the top of the ogive, pointed or having a flat (in this example, pointed), is not merged with the upper end 162 of the acoustic complex 16 and directly adjacent to the second skin 14, but at a non-zero distance H from the upper end 162. It is therefore understood that during the manufacture of the acoustic complex 16 by additive manufacturing, one or more additional layers of material are provided between the top of the ogive of the cells 18 and the upper end 162 of the acoustic complex 16. [Fig. 10] represents a sixth embodiment of the invention. The acoustic panel 10 according to the sixth embodiment differs from the acoustic panel according to the previous embodiments, in that the acoustic complex 16 further comprises third wall portions 183 having a curved shape extending between the lower end 161 of the acoustic complex 16 and the first wall portions 181. In other words, during the manufacture of the acoustic complex 16 by additive manufacturing, the first layers of polymer material deposited on the first skin 12 have an increased width, this width of material gradually decreasing layer after layer in the construction direction, until reaching the normal width of the first wall portion 181 alone. The presence of these third wall portions 183, in addition to the second wall portions 182, gives the cells 18 the overall shape of an egg. [Fig. 11] shows a seventh embodiment of the invention. The acoustic panel 10 according to the seventh embodiment differs from the acoustic panel according to the previous embodiments, in that an acoustic cone 30 is arranged in each of the cells 18, on a side of the cells 18 opposite the arched ceiling. In other words, the acoustic cones 30 extend from the lower end 161 of the acoustic complex 16. View 12A of Figures 12A-12B represents a partial and sectional view, in a section plane parallel to the central axis λ of the cells 18, of an acoustic panel 10 according to an eighth embodiment of the invention in which the acoustic panel 10 is curved. View 12B of Figures 12A-12B represents a comparative example of a flat acoustic panel, corresponding to the previous embodiments. When the acoustic panel 10 is flat, the central axis λ of all the cells 18 is vertical and parallel to the construction direction D. Furthermore, the cells 18 are symmetrical with respect to the central axis λ, the latter passing through the top and the point of the ogive. Therefore, in the “plane” case of the previous embodiments, for each cell 18, the second wall portion 182' formed by a first support portion 185' arranged on one side (left side in view 12B) of the central axis A, and the second wall portion 182” formed by a second support portion 185” arranged on the opposite side (right side in view 12B) of the central axis A, are symmetrical to each other with respect to this central axis A. Consequently, the maximum angle “à between the construction direction D and the second wall portion 182', and the maximum angle B between the construction direction D and the second wall portion 182”, are identical and less than or equal to 45°. In the eighth embodiment (view 12A of figures 12A-12B), the acoustic panel 10 is curved. In this case, the cells 18 and therefore the second wall portions 182 are not all symmetrical with respect to their central axis A, the latter not always passing through the tip of the warp and not always being parallel to the construction direction D. More precisely, in the example shown in view 12A, at least one first cell 18 is indeed symmetrical with respect to its central axis A, such that the maximum angles , Bo between the construction direction D and the second wall portions 182”, 182°' respectively, located on either side of the central axis A, are identical and less than or equal to 45°, as in the “plane” case shown in view 12B. On the other hand, for an n-th cell 18,, the central axis A is not parallel to the construction direction D, and the cell 18,, in its upper part is not symmetrical with respect to the central axis A. In particular, the second wall portion 182' formed by the first support portion 185', and the second wall portion 182” formed by the second support portion 185”, are not symmetrical to each other, their curvatures being different. It is therefore understood that the support portions 185', 185' are themselves not symmetrical to each other. In this case, an angle @, maximum between the second portion of wall 182' and the construction direction D, and an angle 3, maximum between the second portion of wall 182” and the construction direction D, are different from each other, but are on the other hand both less than or equal to 45°, Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that 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 illustrated / mentioned embodiments may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense. It is also obvious that all the characteristics described with reference to a method are transposable, alone or in combination, to a device, and vice versa, all the characteristics described with reference to a device are transposable, alone or in combination, to a process.

Claims

Claims

1. Method of manufacturing an acoustic complex (16) for panel acoustics (10) by additive manufacturing, the acoustic complex (16) comprising a plurality of cells (18), each cell (18) extending along a central axis (A), the method comprising: - the manufacture of first portions of wall (181) from a lower end (161) of the acoustic complex up to a upper end (162) of the acoustic complex, the first wall portions (181) being parallel to the central axis (A), - the manufacture of support portions (185) extending between the first wall portions (181), the support portions (185) each comprising a lower face forming a second portion wall (182) delimiting an upper part of the cell (18) and presenting a vaulted shape, and an upper face delimiting the upper end (162) of the acoustic complex (16), such that that a maximum angle (&) between the second portion of wall (182) and a construction direction (D) is less than or equal to 45°,

2. A method according to claim !, wherein the support portions (185) have a lattice structure.

3. A method according to claim 2, wherein the support portions (185) having the lattice structure have a void ratio of between 1% and 99%, preferably between 50 and 95%.

4. A method according to claim 2 or 3, wherein the portions of support (185) are manufactured such that the lattice structure has a decreasing void ratio as one approaches the upper end (162) of the acoustic complex (16).

5. A method according to any one of claims 1 to 4, wherein a the top of the alveoli (18) is pointed or has a flat surface (19), the flat (19) having a width (D) less than 20 mm, of preferably less than 10 mm.

6. A method according to any one of claims | to 5, wherein the support portions (185) are manufactured in such a way that they have a non-zero thickness (H) between a summit of the cells (18) and the upper end (162) of the acoustic complex (16).

7. A method according to any one of claims 1 to 6, comprising the manufacturing third wall portions (183) extending between the lower end (161) of the acoustic complex (16) and the first wall portion (181), the third wall portions (183) having a curved shape.

8. A method according to any one of claims 1 to 7, comprising: manufacturing an acoustic cone (30) in each cell (18), the cone acoustic (30) extending from the lower end (161) of the acoustic complex (16).

9. A method according to any one of claims 1 to 8, wherein the upper end (162) of the acoustic complex is flat, each alveolus (18) being symmetrical with respect to its central axis (A) and being delimited in its upper part by a first portion of support (185) and a second support portion (185”), a first angle (a) maximum between the construction direction (D) and the second portion of wall (182') formed by the first support portion (185') being identical to a second maximum angle (P) between the direction of construction (D) and the second portion of wall (182'') formed by the second portion of support (185''), the first angle (a) and the second angle (f3) being less than or equal to 45°,

10. A method according to any one of claims 1 to 8, wherein the upper end (162) of the acoustic complex is curved, at less than one alveolus (18,) not being symmetrical with respect to its axis central (A) and being delimited in its upper part by a first support portion (185”) and a second support portion (185), a first maximum angle (at,) between the construction direction (D) and the second portion of wall (182') formed by the first portion of support (185') being different from a second maximum angle (Pn) between the construction direction (D) and the second portion of wall (182”) formed by the second support portion (185''), the first angle (a,) and the second angle ({*,) being less than or equal to 45°.

11. | A method of manufacturing an acoustic panel (10) comprising: - the manufacture of a first skin (12), - the manufacture of an acoustic complex (16) on the first skin (12), by a method according to any one of claims 1 to 10, and - the manufacture of a second skin (14) on the upper end (162) of the acoustic complex (16).

12. Acoustic complex (16) for acoustic panel (10) of an ae- engine aeronautics, obtained by a process according to any one of the re- instructions 1 to 10.

13. Acoustic panel (10) obtained by a method according to claim ll.