Manufacturing process for a honeycomb core for acoustic attenuation panels

Abstract

The invention relates to a method for manufacturing a honeycomb core for an acoustic attenuation panel, the honeycomb core comprising a plurality of cells, and obstacles within the cells, comprising: a step of forming a stack (50) comprising a plurality of strips (51, 52), at least one interlayer film (53) being intercalated between two adjacent strips, the interlayer film (53) being attached to each of the adjacent strips (51, 52) along the junction zones, and attached to itself within the portions (533a) of folds (533) located along the junction zones, the interlayer film (53) comprising, at the level of each zone of the stack (50) intended to form an end of a cell, a sacrificial fold; a step of applying pressure, during which pressure is exerted on the stack (50) in a vertical direction (VE);a forming step, during which the stack (50) is stretched along the vertical direction (VE); a step of removing sacrificial folds. Figure 4.;

Description

Title of the invention: Method for manufacturing a honeycomb core for acoustic attenuation panels technical field

[0001] The invention relates to the field of nacelles and acoustic attenuation panels with a honeycomb core for aircraft propulsion systems, and, more particularly, to a method for manufacturing a honeycomb core for such a panel. Prior art

[0002] Acoustic attenuation panels are widely used in turbomachinery for cladding areas subject to significant gas passages, such as a fan casing or a secondary flow duct located downstream of the fan in which air flows, or an exhaust nozzle or exhaust cone of the turbomachine, better known by the Anglo-Saxon acronym "plug", subject to a passage of exhaust gas.

[0003] These acoustic attenuation panels are generally made in the form of sandwich panels comprising at least a first outer skin wall, a second inner skin wall, and a core sandwiched between these first and second skin walls. The core comprises a plurality of tubular polygonal cells, each oriented at an angle to the first and second skin walls or perpendicular to them. These cores are generally made in the form of a plate of hexagonal honeycomb material. These cells are hollow along their entire height.

[0004] The height of the cells is an essential parameter that determines the panel's ability to absorb sound waves. It has been demonstrated that sound wave absorption is optimal for a conventional panel when the cells have a height corresponding approximately to one-quarter of the wavelength X of the sound wave to be processed.

[0005] Currently, for reasons of integration and compactness, it is desirable to produce acoustic attenuation panels that are thinner than conventional panels. However, it is not possible to reduce the cell height without resulting in a loss of the panel's ability to absorb sound waves.

[0006] However, it has also been observed that the capacity of a cell to absorb an acoustic wave of wavelength X is directly dependent on the length of the path traveled by the acoustic wave in the cell, that is to say, according to the foregoing, a length corresponding to one-quarter of the wavelength, or X / 4. However, it has also been observed that the length of this path does not necessarily have to be following a straight path. In other words, the acoustic wave can be effectively absorbed as long as the path traveled is of a total length close to X / 4, but this length can be distributed along a non-straight path.

[0007] French patents FR-3 070 529-B1 and FR-3 070 530-B1 describe an acoustic panel with a limited thickness that is suitable for attenuating low frequencies. This acoustic panel includes cells housing at least one partial barrier extending transversely to the main axis of the cell in question to increase the path length of the sound waves through the cell. Each barrier has a free end edge that defines a passage with a portion of the opposite cell wall.

[0008] Such an acoustic panel makes it possible, at the same height and without loss of acoustically treated surface area, to attenuate lower noise frequencies and consequently, to limit the size of the acoustic panel as well as its mass.

[0009] French patents FR-3 070 529-B1 and FR-3 070 530-B1 also propose methods particularly suited to the manufacture of such acoustic panels. In particular, a barrier within a cell is formed from a strip fixed between two plates. The strip is shaped, notably by folding along crease lines between the two plates intended to form the peripheral walls of the cells in a core. The barrier is formed by a tensile force on the plates fixed to each other, tending to separate the plates. This tensile force, taking into account the bonding of the plates at nodal points (or junction zones) and the crease zones provided on the plates, allows the plates to be shaped to constitute the cells of the honeycomb core.

[0010] However, the insertion of this tape creates an extra thickness between the strips intended to form the honeycomb core. This extra thickness is not uniform along the stack formed by the strips and tapes. This non-uniformity is a drawback because it will lead to a lack of homogeneity in the application of the clamping force exerted on the stack to ensure adhesion between the different elements of the stack. This lack of homogeneity is all the more significant since the manufacture of honeycomb cores involves stacks that can contain more than 200 strips and almost as many tapes, which means that the differences in thickness accumulate.

[0011] It is therefore necessary to ensure that over the entire length and width of a stack, there is the same thickness to be glued in order to ensure a uniform gluing pressure.

[0012] The objective of the present invention is to remedy the drawbacks of the prior art and in particular those set out above. Description of the invention

[0013] To this end, the invention relates to a method for manufacturing a honeycomb core for an acoustic attenuation panel for an aircraft propulsion system, the honeycomb core comprising a plurality of joined cells, and obstacles within at least a portion of the cells, the method comprising:

[0014] - a step in forming a stack comprising a plurality of strips, at least one interlayer film being sandwiched between two adjacent strips, each strip being intended to be fastened to at least one adjacent strip at junction zones extending along a longitudinal direction of the stack, the interlayer film or films being arranged between two adjacent strips and comprising, along the longitudinal direction of the stack, a succession of fastening parts intended to be alternately fastened to one and then the other of the adjacent strips, and comprising at least one fold between two successive fastening parts, the interlayer film or films being fastened to each of the adjacent strips along the junction zones, and fastened to itself within the folded portions located along the junction zones, so that the joint between two adjacent strips between which an interlayer film is sandwiched is ensured, at the junction zones,via the corresponding interlayer film, the interlayer film(s) comprising, at each stacking zone intended to form an end of a cell, a sacrificial fold;

[0015] - a pressure application step, during which pressure is exerted on the stacking along a vertical direction of the stacking, in order to ensure the bonding between the straps and the interlayer film(s) at the junction areas, and the bonding of the interlayer film(s) to the adjacent straps at the fixing parts;

[0016] - a forming step, during which the stack is stretched along the direction vertical so that the adjacent strips are only linked together at the junction zones, and form between two common and adjacent junction zones the walls of a honeycomb core cell, and so that the folds of the interlayer film(s) unfold in such a way as to form at least one obstacle in each corresponding cell;

[0017] - a step of removing the sacrificial folds from the or each interleaving film.

[0018] Thus, by incorporating sacrificial folds, intended to be removed after the stack is stretched, it is ensured that the stack has a constant thickness over its entire surface during the pressure application step. This constant thickness ensures a uniform pressure application over the entire stack. stacking during the pressure application stage, this uniformity being necessary for the good adhesion of the different elements of the stack to each other.

[0019] In one embodiment, the process includes a step of cutting the stack along a transverse direction of the stack, the cutting step making it possible to obtain several honeycomb cores from a single stack, the cutting step being carried out:

[0020] - either before the forming stage;

[0021] - either after the forming step and before the step of removing sacrificial folds.

[0022] In one embodiment, each sacrificial fold is obtained by cutting a fold of the interlayer film located at the level of an area of ​​the stack intended to form a cell end, the cut being made along the longitudinal direction of the stack, along the two junction areas framing this fold.

[0023] In one embodiment, between at least two adjacent strips, several intercalated films are intercalated, following one another along the longitudinal direction of the stack, each successive intercalated film being arranged between two areas of the stack intended to form an end of a cellular core when the stack is intended to form several cellular cores.

[0024] In one embodiment, the stack is cut at the cutting zones, and each fixing part of an interlayer film located at the boundary of a cutting zone is secured to the corresponding strip beyond this zone, over a minimum length.

[0025] In one embodiment, the dimensions of a fold are such that the length of the fold between two successive fastening parts is, after the forming step, greater than the distance between the two corresponding adjacent strips.

[0026] The invention also relates to an acoustic attenuation panel comprising at least one honeycomb core obtained by implementing the process according to one of the preceding claims.

[0027] The invention also relates to a structure for producing at least one honeycomb core, in particular a honeycomb core for an acoustic attenuation panel, the structure being formed by a stack comprising a plurality of strips, at least one interlayer film being sandwiched between two adjacent strips, each strip being secured to at least one adjacent strip at junction zones extending along a longitudinal direction of the stack, the interlayer film or films being arranged between two adjacent strips and comprising, along the longitudinal direction of the stack, a succession of fastening parts alternately secured to one and then the other of the adjacent strips, and comprising at least one fold between two successive fastening parts, the interlayer film or films being secured to each of the adjacent strips along the junction zones, and secured to itself within the portions of folds located along the junction zones, so that the junction between two adjacent strips between which an intercalary film is intercalated is ensured, at the level of the junction zones, by means of the corresponding intercalary film, the or each intercalary film having, at the level of each zone of the stack intended to form an end of a cell, a sacrificial fold.

[0028] In one embodiment, each sacrificial fold is obtained by cutting a fold of the interlayer film located at the level of an area of ​​the stack intended to form a cell end, the cut being made along the longitudinal direction of the stack, along the two junction areas framing this fold. Brief description of the drawings

[0029] [Fig-1] The [Fig.1] is a schematic view of an aircraft propulsion assembly.

[0030] [Fig.2] Fig.2 is a schematic view of an acoustic attenuation panel in accordance with the invention.

[0031] [Fig.3] The [Fig.3] is a schematic cross-sectional view of the panel of the [Fig.2].

[0032] [Fig.4] Fig.4 is a partial schematic view of a stacking arrangement allowing to create several alveolar cores.

[0033] [Fig.5] The [Fig.5] is a partial schematic view of a stacking enabling the realization of a single honeycomb core.

[0034] [Fig.6] The [Fig.6] is a detail view of the [Fig.5].

[0035] [Fig.7] [Fig.7] is a view showing the stacking of [Fig.5] after the step of forming.

[0036] [Fig.8] The [Fig.8] is a view showing the stacking of the [Fig.7] after elimination of the sacrificial folds.

[0037] [Fig.9] The [Fig.9] is a partial perspective view of the stacking of the [Fig.5] after the forming step.

[0038] [Fig. 10] [Fig. 10] is a view analogous to that of [Fig. 5], showing the delimitation of the different folds of the interlayer films.

[0039] [Fig. 11] The [Fig. 11] is a schematic view of a stacking allowing several alveolar cores to be made.

[0040] [Fig. 12] The [Fig. 12] is a schematic view of a stacking allowing several alveolar cores to be made.

[0041] [Fig. 13] The [Fig. 13] is a flowchart representing the steps for implementing a process according to the invention.

[0042] Fig. 1 schematically illustrates an aircraft propulsion assembly 10, comprising a turbomachine and a nacelle. Detailed description

[0043] In a known manner, the turbomachine 10 comprises, from upstream to downstream, a blower housing 12, an intermediate housing 14, a secondary flow channel 16 delimited by an inner housing 18 and by an outer housing 20, and a nozzle 22 which is delimited by an exhaust housing 24 and by an exhaust cone 26 (generally known under the Anglo-Saxon name of "plug").

[0044] The blower casing 12 is traversed by an incoming airflow F, the secondary flow duct 16 is traversed by a secondary airflow S and the nozzle 22 allows the ejection of a primary gas flow P. These different flows F, S, P, can propagate acoustic waves from the rotating parts of the turbomachine, such as the blower, compressors and turbines.

[0045] To reduce these noises, the fan casing 12, the secondary flow duct 16 and the nozzle 22 may have their walls covered with acoustic attenuation panels.

[0046] Thus, the fan housing 12, the inner housing 18 and the outer housing 20, the exhaust housing 24 and the exhaust cone 26 can be covered by acoustic attenuation panels 30, schematically illustrated in bold lines in [Fig. 1]. The acoustic attenuation panels 30 are designed to attenuate the noise emitted by the turbomachine components 10 housed in the nacelle, such as a gas engine or a fan.

[0047] Some or all of these, or other acoustic panels, may be totally or partially equipped with honeycomb cores according to the invention.

[0048] Figures 2 and 3 illustrate a sound-attenuating panel 30 according to the invention. Such a panel is made in the form of a sandwich comprising a first skin 31, or outer skin 31, a second skin 32, or inner skin 32, and at least one honeycomb core 34 according to the invention. Of course, the panel 30 may include other intermediate layers and in particular other cores superimposed on the honeycomb core 34. As is known, the honeycomb core 34 is fixed to the outer skin 31 and the inner skin 32. Alternatively, the honeycomb core 34 may be fixed only to one of the inner skins 32 and outer skins 31, the other skin not being bonded to the honeycomb core 34. The honeycomb core 34 is bonded to one or both skins by screwing, riveting, gluing or welding, etc.

[0049] The honeycomb core 34 extends between the first skin 31 and the second skin 32. The honeycomb core 34 comprises a plurality of hexagonal tubular cells 36, each oriented along a principal axis A of extension between the first and second end faces. In the illustrated examples and in the following description, the principal axis A is perpendicular to the first and second end faces, and consequently to the first and second skins 31, 32. However, the invention also applies to a core in which the principal axis A of the hexagonal cells is inclined with respect to the first and second end faces without be perpendicular to them, for example at an angle between 0° and 45° with the normal to one of the end faces. In other words, each cell 36 extends along a vertical principal axis A, corresponding overall to an axis of propagation of sound waves, from a front end 41 of the cell 36 in contact with the outer skin 31, to a rear end 42 in contact with the inner skin 32.

[0050] The cells 36 are joined together to form an alveolar structure of height H corresponding to the height of the cells 36.

[0051] The outer skin 31 has a plurality of holes 38 that open into the cells 36. Sound waves enter the cells 36 through these holes 38 where they are partially trapped and thus attenuated. Alternatively, the outer skin 31 has a permeability formed by a grid adapted to allow sound waves to penetrate the alveolar core 34. In other words, the outer skin 31 is acoustically permeable, that is, it has a finite positive acoustic resistance. The inner skin 32 is acoustically reflective, that is, it has a virtually infinite acoustic resistance.

[0052] The outer skin 31 and the inner skin 32 extend substantially parallel to each other. By substantially parallel, it is meant that the angle between the outer skin 31 and the inner skin 32 is less than 15°, preferably less than 5°. The vertical direction V is, in this example, substantially perpendicular to the local surface of the outer skin 31.

[0053] Each cell 36 has an internal cavity 39 delimited by lateral walls 40 extending between the first and second skins 31, 32 and perpendicularly (in the illustrated examples) to the first and second skins 31, 32. In other words, the lateral walls 40 of the cells 36 extend substantially parallel to the vertical direction V from the first skin 31 to the second skin 32. The internal cavity 39 of each cell 36 communicates with at least one of the holes 38 formed in the first skin 31. However, in the case where the principal axis A of the polygonal cells is inclined with respect to the first and second end faces, the lateral walls 40 extend substantially parallel to the principal axis A from the first skin 31. Thus, the principal axis A is not necessarily parallel to the vertical direction V.Similarly, if the skins 31, 32 are not flat, the principal axis of one cell may be oriented differently from the principal axis of another cell.

[0054] Each cell comprises obstacles 45, 46 that are not entirely acoustically impermeable, each having, in this example, a through orifice 49, thus forming a baffle for the propagation of sound waves. The relative position of the through orifices of two consecutive septa is chosen so as to obtain path lengths for the sound waves to be attenuated that are compatible with their frequency. Thus, the sound waves follow a sinuous path (arrow F) between the obstacles 45, 46 from the front end 41 to the rear end 42 of the associated cell 36. This sinuous path is therefore longer than the straight-line distance between the front ends 41 and rear ends 42 of a cell 36.

[0055] Figures 4 to 13 illustrate the implementation of a manufacturing process for a honeycomb core according to the invention, such as the honeycomb core 34 of Figures 2 and 3.

[0056] Fig. 4 partially represents a stacking 50, precursor of at least one alveolar core according to the invention, and in the example of a plurality of alveolar cores.

[0057] The stack 50 is made by stacking, on a preferably flat surface, a plurality of flat strips 51, 52, some or all of the strips 51, 52 being able to frame a respective interlayer film 53 in pairs. Regardless of the number of interlayer films 53, the stack 50 begins with a lower end strip 51 and ends with an upper end strip 52 (the latter not being shown in [Fig. 4] in order to illustrate the configuration of an interlayer film 53). It should be noted that, for clarity, the accompanying figures represent stacks with a very small number of stacked elements. The stack 50 is made along a vertical direction VE and extends along a longitudinal direction LE and a transverse direction TE.The vertical directions VE and transverse directions TE correspond respectively to the longitudinal directions L and transverse directions T of the alveolar core obtained from the stacking 50. The longitudinal direction LE of the stacking corresponds to the direction of the principal axis A of the cells of the alveolar core, and therefore in the example to the vertical direction V of the alveolar core obtained from the stacking 50.

[0058] In the example shown in the figures, the stack 50 is arranged so that an interlayer film 53 is inserted between each pair of adjacent strips 51, 52, but stacks can of course be provided in which only a portion of the adjacent strips frame an interlayer film. Each interlayer film 53 has fastening portions 531, 532 intended to be attached alternately, in particular by gluing, to one and then the other of the adjacent strips. Thus, two successive fastening portions 531, 532 of the same interlayer film 53 are not attached to the same strip 51, 52. Each interlayer film 53 is shaped such that one or more folds 533 are arranged between two successive fastening portions 531, 532. In the example, simple folds 533 are provided, forming a "V" between two successive fastening parts 531, 532.

[0059] The adjacent strips 51, 52 are intended to be joined at the junction zones 510, 520 (or nodal parts), in particular by bonding. For this purpose, nodal bonding zones are provided at the junction zones 510, 520, on each strip 51, 52 and / or the corresponding interlayer film 53. The joining zones 510, 520, and therefore the corresponding nodal bonding zones, extend along the longitudinal direction LE of the stack. The nodal bonding zones are intended to be bonded in such a way as to ensure the joining of adjacent strips 51, 52 across all the corresponding joining zones 510, 520.

[0060] Bonding zones are provided at each fastening part 531, 532 of the interleaving films 53. These bonding zones extend along the transverse direction TE of the stack 50, and are intended to be bonded in such a way as to ensure the fastening of each interleaving film 53 to the adjacent strips 51, 52.

[0061] Figure 5 is a cross-sectional view, in a plane parallel to the vertical VE and longitudinal LE directions, of a stack 50 intended to form a single honeycomb core. It should be noted that, for clarity, the individual elements are shown in an expanded configuration in the VE direction, and therefore in a slightly different configuration from the actual one (in particular, the interlayer films 53 are not shown flat, in order to make the various folds visible). In the example of Figure 5, the stack comprises nine strips 51, 52 and eight interlayer films 53.Of the eight interleaving films, four interleaving films 53 are seen in cross-section at a junction zone (the first, third, fifth and seventh interleaving films 53 from the bottom), and four interleaving films 53 are seen in cross-section at a part located between two junction zones (the second, fourth, sixth and eighth interleaving films from the bottom).

[0062] As can be seen in [Fig. 6], which shows a detailed view of [Fig. 5], each interlayer film 53 is bonded to each adjacent strip 51, 52 at the junction areas 510, 520 between two adjacent strips 51, 52. In this example, the bonding is achieved by gluing (using adhesive layers C'). Furthermore, each interlayer film 53 is bonded to itself within the portions 533a of the folds 533 located along the junction areas 510, 520, in this example by gluing (using adhesive layers C). Thanks to this configuration, the junction between two adjacent strips 51, 52 between which an intercalating film 53 is intercalated is ensured, at the level of the junction zones 510, 520 common to these two strips, by means of the corresponding intercalating film 53.Thus, during the subsequent stretching of the stack 50 along the vertical direction VE, the adjacent strips 51, 52 remain linked to each other at the junction zones 510, 520 by means of the corresponding interlayer film 53, without the portions 533a of the folds 533 located at the junction zones 510, 520 being able to unfold. Between two successive junction zones 510, 520, each interlayer film 53 is bonded to each adjacent strip 51, 52 only at the points. The fastening elements 531 and 532 are shown in the example by bonding (using adhesive layers C"). Depending on the materials used for the production of the strips 51 and 52 and the interlayer films, for example, in the case of a thermoplastic material, bonding by welding may be considered. Thus, some or all of the adhesive layers C, C', and C" may be replaced by a weld. It should also be noted that the various adhesive layers C, C', and C" are visible only in [Fig. 6] and are not shown in the other figures for clarity.

[0063] Figures 7 to 9 partially show the stack 50 of [Fig. 5] after the forming, or drawing, operation. Figures 7 and 8 show the stack in cross-section in the same plane as [Fig. 5], while [Fig. 9] partially shows this stack in perspective. As mentioned above, the drawing operation expands the stack to form the honeycomb core, giving each cell its final shape, with a substantially hexagonal cross-section. As can be seen in Figures 7 to 9, the drawing operation also has the effect of unfolding the folds 533 within each corresponding cell 36, to form obstacles in the path of the sound waves, such as the obstacles 45, 46 of [Fig. 3]. At the junction zones 510, 520, the adjacent strips 51, 52 remain connected to each other by means of the interlayer film 53 inserted where applicable. As mentioned above, and as can be seen in particular in [Fig.[9], the bonding of each interlayer film 53 is carried out in such a way that it cannot unfold at the junction areas 510, 520, thus ensuring the connection between the two strips 51, 52 at these areas.

[0064] In accordance with the invention, and as can be seen in particular in Figures 5 to 7 and 9, the interlayer film 53 comprises, at each zone intended to form a cell end (along the longitudinal direction LE of the stack), a sacrificial fold 534. The sacrificial folds 534 are configured to have, before stretching the stack 50, a thickness close to or equal to that of the individual folds 533. Thus, the sacrificial folds 534 ensure that each interlayer film 53 has a constant thickness along the longitudinal direction LE of the stack 50. This configuration results in a stack 50 with a uniform thickness, which facilitates the application of uniform pressure during the formation and consolidation of the stack 50.

[0065] As can be seen in Figures 7 to 9, each sacrificial fold 534 is designed to be detached from the stack 50 after the latter has been stretched. To this end, during the formation of the stack 50, as shown in [Fig. 5], each sacrificial fold 534 is cut along the longitudinal direction LE of the stack 50, on either side of the sacrificial fold, along the corresponding junction zone 510, 520. These cuts D have the effect of freeing each sacrificial fold 534 once the stack 50 is stretched (and, where applicable, cut) to form a honeycomb core as seen in [Fig.8]. As also seen in [Fig.9], after the stretching operation, the sacrificial folds 534 are no longer connected to the stack 50 by the cuts D (see cell 36 left), and can therefore be easily removed, for example by suction (see cell 36 right).

[0066] Figure 10 corresponds to Figure 5, which shows the arrangement of the various folds of the interlayer films 53. Zones RI to R4 correspond to the zones over which, along the longitudinal direction LE of the stack 50, the folds 533 of the interlayer films 53 extend, forming obstacles such as the obstacles 45, 46 shown in Figure 3. However, in the example of Figures 5 to 11, the stack 50 is intended to form a honeycomb core in which each cell has four obstacles, each obstacle being formed respectively by one of the folds 533 of the interlayer film, once these are deployed. Of course, each fold 533 has at least one opening allowing sound waves to pass through (not shown in Figures 5 to 11). Zones A0 and B0 correspond to the areas over which the cuts D allowing the formation of the sacrificial folds 534 extend, according to the longitudinal direction LE of the stacking 50.

[0067] Figure 11 shows the arrangement of a stack 50 similar to that of Figure 5, allowing several honeycomb cores to be produced from a single stack. As can be seen in this figure, the stack 50 is configured such that it extends along the longitudinal direction LE over a length exceeding several times the height of a honeycomb core. In the example of Figure 11, the stack 50 is configured to allow the production of three honeycomb cores A1, A2, and A3, after cutting the stack at the cutting zones D1 and D2. Advantageously, it will be provided that, for each interlayer film 53, each fastening part 531, 532 located at the boundary of a cutting zone Dl, D2 is glued to the corresponding strip 51, 52 beyond the boundary of the corresponding cutting zone Dl, D2, over a minimum length M.This configuration ensures that the interlayer films are properly fixed to the ends of the cells, after cutting the 50 stack.

[0068] In the example of [Fig. 11], each interlayer film 53 extends along the entire length of the stack 50 (along the longitudinal direction LE). Thus, each sacrificial fold 534 is, before cutting the stack 50, common to two honeycomb cores A1, A2, A3.

[0069] Alternatively, as can be seen in [Fig. 12], the interlayer films 53 may be provided that they do not extend over the entire length of the stack 50, but only over the length required to constitute a honeycomb core A1, A2, A3. In In other words, each intercalated film 53 is specific to one of the final alveolar cores A1, A2, A3. As can be seen in [Fig. 12], and contrary to the embodiment of [Fig. 11], the sacrificial folds 534 are not shared between two alveolar cores.

[0070] The interlayer films 53 shown in the accompanying figures have folds 533 which, in the example, are single folds, that is, they form "V"-shaped portions between two successive fixing parts 531, 532. Alternatively, for all or part of the interlayer films, the folds 533 may be double folds, that is, they form "W"-shaped portions between two successive fixing parts 531, 532. Similarly, the sacrificial folds 534 shown in the accompanying figures are single folds, but if one or more of the interlayer films 53 have double folds, then the sacrificial folds 534 of the corresponding interlayer films 53 must also be double, in order to ensure a uniform thickness along the same interlayer film.

[0071] The strips 51, 52 used in the context of the invention may be made of a metallic material (such as an aluminum, steel, or titanium alloy), an organic material (such as aramid paper, for example, of the type marketed under the nomex© brand, coated with phenolic resin), a composite material (such as a resin-coated fiberglass fabric), or a thermoplastic material. The interlayer films 53 may also be made of one of the materials listed above and may be of the same or different nature as the strips. The connections may be made by gluing (for example, using organic adhesive), brazing, or welding, depending on the materials used.

[0072] Figure 13 is a flowchart illustrating the steps of a process 100 according to the invention, these steps being described in detail above. Thus, process 100 comprises: - a 102 formation step of a stack as described above; - a pressure application step 104 on the stack formed in the step previous; - a forming step 108, during which the stack is stretched; - a withdrawal step 110 of sacrificial folds.

[0073] When the stack is constructed in such a way as to allow the simultaneous manufacture of several honeycomb cores, the process 100 includes a cutting step 106 of the stack 50. The cutting step 106 can be carried out before or after the forming step 108.

Claims

1. Demands Method (100) for manufacturing a honeycomb core (34) for an acoustic attenuation panel (30) for an aircraft propulsion system, the honeycomb core (34) comprising a plurality of adjoining cells (36), and barriers (45, 46) within at least a portion of the cells (36), the method comprising: - a formation step (102) of a stack (50) comprising a plurality of strips (51, 52), at least one interlayer film (53) being intercalated between two adjacent strips (51, 52), each strip (51, 52) being intended to be fastened to at least one adjacent strip (51, 52) at the level of junction zones (510, 520) extending along a longitudinal direction (LE) of the stack, the interlayer film or each interlayer film (53) being disposed between two adjacent strips and comprising, along the longitudinal direction (LE) of the stack, a succession of fastening parts (531, 532) intended to be fastened alternately to one and the other of the adjacent strips (51, 52), and comprising at least one fold (533) between two fastening parts (531, 532) successive, the interlayer film or films (53) being attached to each of the adjacent strips (51, 52) along the junction zones (510, 520),and secured to itself within the portions (533a) of folds (533) located along the junction zones (510, 520), so that the junction between two adjacent strips (51, 52) between which an intercalated film (53) is intercalated is ensured, at the level of the junction zones (510, 520), by means of the corresponding intercalated film (53), the intercalated film or each intercalated film (53) comprising, at the level of each zone of the stack (50) intended to form an end of a cell (36), a sacrificial fold (534); - a pressure application step (104), during which pressure is exerted on the stack (50) along a vertical direction (VE) of the stack (50), in order to ensure the bonding between the straps (51, 52) and the interlayer film(s) (53) at the junction areas (510, 520), and the bonding of the interlayer film(s) (53) to the straps (51, 52) adjacent at the fastening parts (531, 532); - a forming step (108), during which the stack (50) is stretched in the vertical direction (VE) so that the strips (51, 52) adjacent are linked together only at the junction zones (510, 520), and form between two common and adjacent junction zones (510, 520) the walls of a cell (36) of alveolar core (34), and so that the folds (533) of the intercalated film(s) (53) unfold in such a way as to form at least one obstacle (45, 46) in each corresponding cell (36); - a withdrawal step (110) of the sacrificial folds (534) of the intercalated film(s) (53).

2. A method (100) according to the preceding claim, comprising a cutting step (106) of the stack (50) along a transverse direction (TE) of the stack, the cutting step (106) making it possible to obtain several honeycomb cores (34, Al, A2, A3) from a single stack (50), the cutting step (106) being carried out: - either before the forming step (108); - or after the forming step (108) and before the step of removing (110) the sacrificial folds (534).

3. A method (100) according to any one of the preceding claims, wherein each sacrificial fold (534) is obtained by cutting a fold of the interlayer film (53) located at the level of an area of ​​the stack (50) intended to form a cell end (36), the cut being made along the longitudinal direction (LE) of the stack (50), along the two junction areas (510, 520) framing this fold.

4. A method (100) according to any one of the preceding claims, wherein, between at least two adjacent strips (51, 52), several interlayer films (53) are intercalated, following one another along the longitudinal direction (LE) of the stack (50), each successive interlayer film (53) being disposed between two areas of the stack (50) intended to form an end of a cellular core (34, Al, A2, A3) when the stack (50) is intended to form several cellular cores (34, Al, A2, A3).

5. Method (100) according to any one of claims 2 to 4, wherein the stack (50) is cut at the cutting zones (D1, D2), and each fastening part (531, 532) of an interlayer film (53) located at the boundary of a cutting zone (D1, D2) is attached to the corresponding strip (51, 52) beyond this zone, over a minimum length (M).

6. A method (100) according to any one of the preceding claims, wherein the dimensions of a fold (533) are such that the length of the fold (533) between two successive fastening parts (531, 532) is, after the forming step, greater than the distance between the two corresponding adjacent strips (51, 52).

7. Acoustic attenuation panel (30) comprising at least one honeycomb core (34) obtained by implementing the process (100) according to one of the preceding claims.

8. Structure for the realization of at least one honeycomb core (34), in particular a honeycomb core for an acoustic attenuation panel (30), the structure being formed by a stack (50) comprising a plurality of strips (51, 52), at least one interlayer film (53) being interposed between two adjacent strips (51, 52), each strip (51, 52) being attached to at least one adjacent strip (51, 52) at the level of junction zones (510, 520) extending along a longitudinal direction (LE) of the stack, the interlayer film or each interlayer film (53) being disposed between two adjacent strips and comprising, along the longitudinal direction (LE) of the stack, a succession of fastening parts (531, 532) attached alternately to one and the other of the strips (51, 52) adjacent, and comprising at least one fold (533) between two successive fastening parts (531, 532),the interlayer film or films (53) being attached to each of the adjacent strips (51, 52) along the junction zones (510, 520), and attached to itself within the portions (533a) of folds (533) located along the junction zones (510, 520), so that the junction between two adjacent strips (51, 52) between which an interlayer film (53) is intercalated is ensured, at the level of the junction zones (510, 520), by means of the corresponding interlayer film (53), the interlayer film or films (53) comprising, at the level of each zone of the stack (50) intended to form an end of a cell, a sacrificial fold (534).

9. Structure according to the preceding claim, wherein each sacrificial fold (534) is obtained by cutting a fold of the interlayer film (53) located at the level of an area of ​​the stack (50) intended to form a cell end (36), the cut being made along the longitudinal direction (LE) of the stack (50), along the two junction areas (510, 520) framing this fold.

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