Sound attenuation panel and method of manufacturing the same

Abstract

The present invention relates to a sound attenuation plate (1), comprising: - a honeycomb structure (10) including a plurality of acoustic units (100) spaced apart from each other by peripheral spacers (102); - a perforated acoustic structure (20) wherein the perforated acoustic structure (20) and the honeycomb structure (10) constitute a single part in a first material; and - a porous acoustic layer (30) made of a second material and fixed to the surface of the perforated acoustic structure (20) by inserting at least one material into the second material.

Description

Technical Field

[0001] The present invention relates to a sound attenuation plate designed to absorb sound energy, particularly sound energy generated by aircraft turbines, such as those from turbojet engines or aircraft turboprop engines. Background Technology

[0002] The aircraft is driven by one or more propulsion units, each consisting of a turbojet engine / turboprop engine housed in a tubular nacelle. Each propulsion unit is connected to the aircraft via a mast, typically located under the wings or in the fuselage.

[0003] The nacelle typically has a structure comprising an upstream section forming the upper part of the engine air intake, an intermediate section designed to surround the turbojet engine fan, and a downstream section that houses the thrust reverser, is designed to surround the turbojet engine combustion chamber, and typically terminates at the exhaust nozzle. The exhaust nozzle exits downstream of the turbojet engine.

[0004] The air intake is used to optimize the capture of the required air to provide the necessary air for the turbojet engine's fan throughout the flight envelope, and to direct the air to the fan.

[0005] The air intake mainly includes an air intake lip that forms the leading edge and is connected to an annular structure.

[0006] The annular structure includes an external cowling that ensures aerodynamic continuity outside the engine nacelle, and an internal cowling that ensures aerodynamic continuity inside the engine nacelle, particularly in the fan housing in the mid-section. An intake lip ensures upstream connection between the two cowlings.

[0007] The internal cowling of the air intake is exposed to high airflow and is located near the fan blades. Therefore, the internal cowling helps to transmit the noise generated by the turbojet engine to the outside of the aircraft.

[0008] Moreover, it is known from existing technology that the fairing inside the cabin air intake is equipped with sound panels in order to reduce the propagation of noise generated by the turbojet engine.

[0009] Typically, soundboards include perforated acoustic structures and honeycomb structures, which are assembled, in particular, by bonding to the perforated acoustic structures.

[0010] The honeycomb structure comprises multiple acoustic units that form a Helmholtz resonator or a quarter-wave resonator, with the multiple acoustic units separated from each other by external spacers.

[0011] The perforated acoustic structure is directed towards the noise emission zone, allowing sound waves to penetrate the openings in the perforated acoustic structure within the acoustic unit. Sound energy dissipates through the viscous-thermal effect within these perforations.

[0012] The honeycomb structure of a soundboard may include a single thickness of cells or two thicknesses separated by microporous diaphragms to improve the acoustic performance of the board, particularly the bandwidth of the absorption frequencies.

[0013] The disadvantage of this type of plate is that the perforated acoustic structure has strong acoustic nonlinearity, which causes its surface impedance to change significantly with sound level and tangential flow velocity, especially due to the interaction between the perforations and the airflow.

[0014] The existing solution is to add a porous layer to the perforated acoustic structure by gluing, which is acoustically equivalent to a perforation with a diameter smaller than that of the perforated acoustic structure, thereby reducing the interaction of airflow.

[0015] While this solution can reduce acoustic nonlinearity, a major drawback of this structure is the need for additional components, which is disadvantageous in terms of manufacturing time and cost. Furthermore, improper assembly carries the risk of acoustic inhomogeneity. Finally, if the porous layer is made of a metallic material, there is a risk of corrosion due to exposure to airflow, limiting material selection.

[0016] Another solution is to provide a sound attenuation plate consisting of two overlapping honeycomb structures separated by porous layers.

[0017] However, this type of board makes the manufacturing process longer and more expensive, and introduces the risk of acoustic inhomogeneity due to possible misalignment of the honeycomb cells, resulting in poor aerodynamic performance. Summary of the Invention

[0018] The present invention aims to overcome at least one of the above-mentioned disadvantages, and according to a first aspect, relates to a sound attenuation plate comprising:

[0019] - A honeycomb structure, comprising multiple acoustic units spaced apart from each other by peripheral spacers.

[0020] - Perforated acoustic structure

[0021] Perforated acoustic structures and honeycomb structures form a single component in the first material.

[0022] - A porous acoustic layer, composed of a second material, is fixed to the surface of a perforated acoustic structure by winding at least one of the second materials.

[0023] In other words, the porous acoustic layer made of the second material is fixed to the surface of the perforated acoustic structure by the first material being wrapped around the second material and / or the second material being wrapped around the first material. That is, the porous acoustic layer is attached to the surface of the perforated acoustic structure by the first material and the second material being wrapped around each other.

[0024] Therefore, thanks to the sound attenuation plate according to the invention, in which the honeycomb structure and the perforated acoustic structure are formed as a single component, and in which the connection between the perforated acoustic structure and the porous layer is achieved through the complexity of their materials, the linearity of the plate is improved, thereby optimizing aerodynamic performance. The plate is robust enough to withstand harsh weather and is easier to manufacture.

[0025] According to other features of the invention, the sound attenuation plate of the invention includes one or more of the following optional features, either individually or in all possible combinations.

[0026] - A single component consisting of a honeycomb structure and a perforated acoustic structure, made of the same material as the acoustic porous layer.

[0027] - A single component consisting of a honeycomb structure and a perforated acoustic structure, made of different materials from the acoustic porous layer.

[0028] - The perforations in the perforated acoustic structure are spaced apart from each other at a variable distance along the axial direction A.

[0029] - The perforations in the perforated acoustic structure have an increased dimension S along the axial direction A.

[0030] - The perforations in the perforated acoustic structure have a generally rectangular shape.

[0031] - The perforation of the perforated acoustic structure is equal to at least 20% of the surface area of ​​the structure, preferably at least 40% of the surface area of ​​the structure, and even more preferably at least 60% of the surface area of ​​the structure.

[0032] - The pore size of the porous acoustic layer is smaller than the perforation size S of the perforated acoustic structure.

[0033] - The pore size of the porous acoustic layer increases along the axial direction A.

[0034] - The porous acoustic layer has a woven structure, consisting of interlacing of basic yarns or fiber rovings.

[0035] - The yarns or rovings of the porous acoustic layer are partially bonded together at cross layers and / or according to edge segments, i.e., the yarns or rovings are partially glued together through parallel adjacent portions.

[0036] The thickness of the perforated acoustic structure and the peripheral spacer is between 0.5 and 5 mm, preferably between 0.5 and 2 mm.

[0037] The sound attenuation plate includes a removable cover arranged on the side of the honeycomb structure opposite the perforated acoustic structure.

[0038] - Perforated acoustic structures can be made of plastic materials, such as thermoplastic or thermosetting materials, such as polyurethane, silicone, or epoxy resin, composite materials having a thermoplastic or thermosetting matrix reinforced with short or long fibers, such as polyester fibers, polyethylene fibers, glass fibers, carbon fibers, Kevlar fibers, synthetic fibers, or metal alloys.

[0039] - The porous acoustic layer can be made of plastic materials, such as plastic yarns, composite materials, such as composite yarns, or metallic materials, such as fibers coated with a thermoplastic or thermosetting matrix, or metallic materials, such as metallic yarns comprising light alloys or iron alloys.

[0040] According to another aspect, the present invention relates to a nacelle air intake arranged upstream of a fan, the air intake including an inner surface facing the fan, the inner surface accommodating at least one sound attenuation plate as described above.

[0041] According to another aspect, the present invention relates to a method for manufacturing the aforementioned sound attenuation plate by means of a die tool (4) comprising at least one mold (40) and a reverse mold (400), the method comprising the following steps:

[0042] -Extrude the porous layer between the at least one mold and the reverse mold.

[0043] - Inject materials intended to form a perforated acoustic structure and a honeycomb structure into a molding tool.

[0044] - Wrapping materials with porous layers are intended to form perforated acoustic structures and honeycomb structures.

[0045] Remove the sound attenuation plate from the model tool.

[0046] According to other features of the invention, the method includes one or more of the following optional features, considered individually or in all possible combinations.

[0047] - The shape of the at least one mold is designed to form acoustic units with a honeycomb structure.

[0048] - The at least one mold has at least one punch, designed to form perforations in the perforated acoustic structure.

[0049] - The surface of the punch and the reverse die are coated with a flexible material, such as silicone or fluorocarbon.

[0050] - The surfaces of the punch and the die are made of a rigid material.

[0051] According to another aspect, the present invention relates to a method for manufacturing the aforementioned sound attenuation plate using a die tool including a mold and a reverse mold, the method comprising the following steps:

[0052] - By using molds and reverse molds, perforated acoustic structures and honeycomb structures can be formed in a single part.

[0053] Remove a single part from the mold tool.

[0054] - Place the porous acoustic layer on the perforated acoustic structure of a single component.

[0055] - Melt or partially dissolve single parts and / or porous layers formed by perforated acoustic structures and honeycomb structures to produce material winding of said single parts and porous layers.

[0056] According to another aspect, the present invention relates to a method for adhesively manufacturing a sound attenuating plate as described above, comprising the following steps:

[0057] -Deposition is intended to form materials that create porous acoustic layers.

[0058] - Deposition aims to form an additive manufacturing material that constitutes the perforated acoustic structure and bonds the perforated acoustic structure to the porous acoustic layer.

[0059] The entanglement between the material forming a porous layer on the perforation perimeter of the perforated acoustic structure and the adhering manufacturing material of the perforated acoustic material.

[0060] Therefore, the mold and the reverse mold can be omitted.

[0061] Other features and advantages of the invention will become apparent upon reading the following non-limiting description and the accompanying drawings, which illustratively illustrate a sound attenuation plate according to the invention. Attached Figure Description

[0062] Figure 1 This is a partial cross-sectional view of the sound attenuation plate according to the present invention.

[0063] Figure 2 This is an enlarged view of the cross-section of the sound attenuation plate.

[0064] Figure 3 This is a perspective view of a sound attenuation plate according to an embodiment of the present invention.

[0065] Figure 4 This is a partial perspective view of a sound attenuation plate according to an embodiment of the present invention.

[0066] Figure 5 This is a partial perspective view of a sound attenuation plate according to an embodiment of the present invention.

[0067] Figure 6 This is a schematic diagram of a method for manufacturing a soundboard according to the present invention.

[0068] Figure 7The illustration shows a propulsion unit including a nacelle, with a sound attenuation plate according to the invention installed at the nacelle air intake. Detailed Implementation

[0069] For simplicity, the same elements are identified with the same reference numerals in all the figures.

[0070] Note that in the specification and claims, the terms upstream and downstream should be understood in relation to the airflow circulation within the propulsion unit consisting of the nacelle and the turbojet engine, i.e., refer to... Figure 7 From left to right.

[0071] Figure 1 The sound attenuation plate according to the present invention ( Figure 3 Enlarged cross-sectional view of ).

[0072] The sound board 1 includes a honeycomb structure 10, a perforated acoustic structure 20, and a porous acoustic layer 30 attached to the perforated acoustic structure 20.

[0073] Therefore, the honeycomb structure 10 of the sound board according to the present invention has a free surface and a surface provided with a perforated acoustic structure 20 and a porous acoustic layer 30.

[0074] The honeycomb structure 10 and the perforated acoustic structure 20 are formed as a single part, that is, they are manufactured in one part.

[0075] This eliminates the risk of corrosion, wear, detachment, or delamination in existing soundboards, where the two structures of the soundboard are connected to each other, for example, by gluing.

[0076] The honeycomb structure 10 includes multiple acoustic units 100, which are separated from each other by peripheral spacers 102.

[0077] In this example, each unit has a square shape with sides of 5 centimeters.

[0078] In one variant, each unit may have the following characteristics: Figure 3 The rectangle shown.

[0079] The acoustic unit is not limited to the above shapes, and can also have other polygonal shapes such as triangles, pentagons, and hexagons.

[0080] Each peripheral spacer 102 extends from the perforated acoustic structure 20 at a 90° angle. In other words, each peripheral spacer extends substantially perpendicular to the perforated acoustic structure 20.

[0081] These spacers 102 may include elements designed to allow sound attenuation panels to be fixed to the cabin. Figure 7The sound-attenuating panel has protrusions or openings (not shown). In a preferred embodiment, the sound-attenuating panel is intended to be fixed or glued to the cabin duct to ensure the function of the aerodynamic surface and the silencer of the cabin duct. In the fixed case, a gap may exist between the panel and the surface of the cabin. For this purpose, a supporting sealing element, such as a joint seal, is provided in the sound-attenuating panel 1.

[0082] Preferably, the thickness of the perforated acoustic structure 20 and the peripheral spacer 102 is between 0.5 and 5 mm. For example, the thickness of the perforated acoustic structure 20 is between 0.5 and 2 mm, while the thickness of the peripheral spacer 102 is between 1 and 5 mm, or even more preferably between 1 and 3 mm.

[0083] Such a relatively thin thickness is particularly desirable in acoustic treatment.

[0084] The perforated acoustic structure 20 includes a plurality of perforations 200 regularly formed in the perforated acoustic structure 20.

[0085] In an embodiment not shown, the perforations 200 can be spaced at a variable distance along the axial direction A.

[0086] The term "axis direction" should be related to... Figure 1 We can understand this by referring to the airflow circulation indicated by the middle arrow A.

[0087] like Figure 3 As shown, each perforation 200 of the perforated acoustic structure has a generally rectangular shape with a rounded top. In this example, each acoustic unit 100 includes four perforations 200.

[0088] The invention is not limited to this type of shape; the shape of the perforation 200 can actually vary and correspond to, for example, Figure 4 The fractal shown.

[0089] In one variation, the perforation 200 may have the following characteristics: Figure 5 The different shapes shown include at least one circular perforation 200 and at least one trapezoidal perforation.

[0090] Similarly, the size S of the perforation 200 can vary, and for example, increase along the directional axis A. This scalable distribution also allows for a larger size S near the fan and a smaller size at the far end of the latter, thereby providing acoustic treatment proportional to the sound level.

[0091] Preferably, the size of the perforation is at least 1 mm, and more preferably at least 2 mm.

[0092] The sound panel 1 has a porous acoustic layer 30. A porous layer is a layer having at least one hole formed by a perforation of various mechanical devices or by the porosity of the material of the porous acoustic layer 30.

[0093] A porous acoustic layer 30 is disposed on the surface of the perforated acoustic structure 20, which faces the side of the structure 20 from which the peripheral spacer 102 extends. The porous acoustic layer 30 extends parallel to the perforated acoustic structure 20.

[0094] The porous acoustic layer 30 is rigidly attached to the perforated acoustic structure 20 by entanglement of at least one material with a second material. Figure 2 The fixation between the porous acoustic layer 30 and the perforated acoustic structure 20 is shown in more detail. The porous acoustic layer is fixed to the perforated acoustic structure 20 by wrapping the porous acoustic layer 30 with the corresponding material of the perforated acoustic structure.

[0095] Entanglement refers to the diffusion of one material into another, or material penetration, to create a material bridge between components.

[0096] This winding is formed during the manufacturing of the sound attenuation plate, which will... Figure 2 It is shown in detail in the text.

[0097] Therefore, the fixation techniques that rely on existing adhesive bonding methods can be omitted, which can lead to problems of fixation and detachment over time, especially when porous materials are prone to corrosion.

[0098] The size of the pores 32 in the porous acoustic layer 30 is smaller than the size S of the perforations 200 in the perforated acoustic structure 20.

[0099] In an embodiment not shown, the size of the holes 32 in the porous acoustic layer 30 can be varied, for example, increased along the axial direction A.

[0100] According to one embodiment of the present invention, the honeycomb structure 10, the perforated acoustic structure 20, and the porous acoustic layer 30 are made of the same material.

[0101] According to the first example, the honeycomb structure 10, the perforated acoustic structure 20, and the porous acoustic layer 30 are made of metallic materials, preferably aluminum, and even more preferably aluminum alloys selected from the 6000 series.

[0102] The porous acoustic layer 20 can be a micro-perforated metal plate, for example, through laser-generated micro-hole drilling technology, in order to form a mesh-like layer.

[0103] Alternatively, the porous acoustic layer 30 can be made of the same series of aluminum alloys, or a series of extremely fine meshes of compatible alloys such as those selected from the 5000 series.

[0104] According to the second example, the honeycomb structure 10, the perforated acoustic structure 20, and the porous acoustic layer 30 are made of composite materials, preferably of materials composed of thermoplastic or thermosetting matrices.

[0105] According to another embodiment of the invention, the honeycomb structure 10, the perforated acoustic structure 20, and the porous acoustic layer 30 are made of different materials. For example, the honeycomb structure 10 and the perforated acoustic structure 20 are made of composite materials, while the porous acoustic layer 30 is made of a metallic material.

[0106] In an embodiment not shown, the sound attenuation plate 1 may include a removable cover (not shown) disposed on the surface of the honeycomb structure, which is opposite to the surface constituting the perforated acoustic structure 20.

[0107] Figure 6 This is a diagram illustrating a method for manufacturing a sound attenuation plate 1 according to an embodiment of the present invention.

[0108] In this example, the sound attenuation plate is produced by a forming tool 4 comprising multiple molds 40 and a reverse mold 400.

[0109] In this example, each mold 40 has a shape intended to form the acoustic unit 100. Each mold includes a plurality of punches 42 complementary to the perforations 200, intended to perforate the acoustic structure 20 to form openings. In this example, the mold includes four punches.

[0110] In the first embodiment, the porous layer 30 is placed between a plurality of molds 40 and a reverse mold 400. Thus, the die tool 4 has a space between the molds 40 and the reverse mold 400 corresponding to the thickness of the porous layer 30.

[0111] The porous layer 30 is sandwiched between the mold 40 and the reverse mold 400, for example by moving the mold 40 or by moving the reverse mold 400.

[0112] The material used to produce the perforated acoustic structure 20 and the honeycomb structure 10 in a part is injected into the mold tool 4, so that the material penetrates into the mold portion located between two adjacent punches and fuses or coats the porous layer of material.

[0113] Therefore, the porous acoustic layer 30 is fixed to the perforated acoustic structure 20 at the portion P surrounding the perforation 200.

[0114] The material is then cured and the soundboard thus made is demolded, for example by removing mold 40 and then removing the soundboard made by reverse mold 400.

[0115] In the first variant, the perforator 42 surface of the die 400 is coated with a flexible material, such as silicone or fluorocarbon, which deforms to prevent material from transferring into the forming perforations 200. Additionally, this soft coating prevents the porous acoustic layer from deforming during the extrusion process.

[0116] In another variation, the surfaces of the punch 42 and the die 400 can be made of a rigid material, and the extrusion of the porous layer causes the latter to deform through work hardening. In a particular solution, extrusion is slightly more important in the area where the perforation 200 is formed to prevent material transfer.

[0117] In the second embodiment, during the first operation, a perforated acoustic structure 20 and a honeycomb structure 10 are manufactured from a single part, using a mold 40 and a reverse mold 400 to form the perforations of the acoustic unit 100 and the perforated acoustic structure. The single part is then hardened and demolded.

[0118] The porous acoustic layer 30 is placed against the perforated acoustic structure 20.

[0119] The connection between the porous acoustic layer 30 and the perforated acoustic structure 20 is achieved by melting or partially dissolving either or both of the materials of the single component consisting of the perforated acoustic structure 20 and the honeycomb structure 10, or the materials of the porous layer 30, so that the materials become intertwined. Fusion can be implemented via ultrasound, electromagnetic induction, the Joule effect, or by heating the mold 40 or the reverse mold 400.

[0120] In one embodiment, the perforated acoustic structure 20 has irregularities, such as a microscopically non-uniform surface, i.e., it is not smooth, in order to improve the anchoring of the porous layer 30 material in the perforated acoustic structure 20.

[0121] The newly formed sound attenuation plate is cooled, thereby forming mechanical and / or molecular bonds between the components of the plate.

[0122] Thanks to these manufacturing methods, the porous acoustic layer 30 can be reliably and effectively integrated into the perforated acoustic structure 20. The production of the perforations 200 of the sound board 1 is optimized, and the dimensions S of the perforations 200 are controlled.

[0123] The sound attenuation plate 1 can be formed as a single circular part, with 360° corresponding to the cabin size or sector configuration to accommodate multiple plates, for example, 24 plates sectored and deformed at 15°. In this case, the mold 400 can have a concave or convex shape within a 15° range, allowing the plate 1 to have the desired deformation angle. The arrangement of the assemblable sound plates facilitates the replacement of damaged plates in the cabin.

[0124] The production of sound attenuation plates is not limited to the manufacturing methods described above, and can be carried out, for example, by additive manufacturing without the use of molding tools.

[0125] This embodiment offers advantages in optimizing sound attenuation plate design, particularly in its ability to fabricate perforated acoustic structures with complex shapes. Furthermore, the structure surrounding the perforations can have variable thickness or width, thereby enabling the provision of multiple levels of stiffness for the acoustic structure.

[0126] Figure 7 This is an illustration of a propulsion unit 5 extending along the longitudinal axis X. The propulsion unit 5 includes a nacelle 50 and a turbojet engine 500. The nacelle 50 has a structure that includes an upstream section forming an air intake 52, a middle section 54 including a fan shroud, a downstream section 56 including thrust reversers and intended to surround the turbojet engine combustion chamber, and an exhaust nozzle 58. The fan shroud is intended to surround the fan 510 of the turbojet engine 500.

[0127] According to the example just described, the air inlet 52 includes an inner surface 53 facing the fan 510, which accommodates at least one sound attenuation plate 1.

[0128] like Figure 7 As shown, based on the example just described, other components of the cabin, such as the thrust reverser, can accommodate the sound attenuation plate 1.

[0129] Sound attenuation plates can be applied to various locations in the nacelle, such as air intakes, extended air intakes, fan housings, and even thrust reversers.

[0130] It is obvious that the present invention is not limited to the examples just described, and many modifications can be made to these examples without departing from the scope of the invention. In particular, different features, shapes, variations, and embodiments of the invention are associated with each other in various combinations, provided that they are not mutually exclusive.

Claims

1. A method for manufacturing a sound attenuation plate (1) by means of a die tool (4) comprising at least one die (40) and a reverse die (400), the sound attenuation plate (1) comprising: - A honeycomb structure (10) comprising a plurality of acoustic units (100) separated from each other by peripheral spacers (102). - A perforated acoustic structure (20), wherein the perforated acoustic structure (20) and the honeycomb structure (10) constitute a single part in a first material, and - A porous acoustic layer (30), made of a second material, is fixed to the surface of the perforated acoustic structure (20) by the first material being wound in the second material and / or the second material being wound in the first material. The method includes the following steps: - The porous acoustic layer (30) is placed in the space between the at least one mold (40) and the reverse mold (400). - Extrude the porous acoustic layer (30) between the at least one mold (40) and the reverse mold (400). - Material intended to integrally form the perforated acoustic structure (20) and the honeycomb structure (10) is injected into the molding tool (4). - The material intended to form the perforated acoustic structure (20) and the honeycomb structure (10) is wound with the material of the porous acoustic layer (30). Remove the sound attenuation plate (1) from the mold tool (4).

2. The method according to claim 1, characterized in that, The single component consisting of the honeycomb structure (10) and the perforated acoustic structure (20), as well as the porous acoustic layer (30), are made of the same material.

3. The method according to claim 1, characterized in that, The single component consisting of the honeycomb structure (10) and the perforated acoustic structure (20), as well as the porous acoustic layer (30), are made of different materials.

4. The method according to claim 1, characterized in that, The perforations (200) of the perforated acoustic structure (20) are spaced apart from each other at a variable distance along the axial direction A.

5. The method according to claim 1, characterized in that, The perforations (200) of the perforated acoustic structure (20) have an increased size S along the axial direction A.

6. The method according to claim 1, characterized in that, The perforations (200) of the perforated acoustic structure (20) have a rectangular shape.

7. The method according to claim 1, characterized in that, The perforations in the perforated acoustic structure are equal to at least 20% of the surface area of ​​the structure.

8. The method according to claim 7, characterized in that, The perforations in the perforated acoustic structure are equal to at least 40% of the surface area of ​​the structure.

9. The method according to claim 7, characterized in that, The perforations in the perforated acoustic structure are equal to at least 60% of the surface area of ​​the structure.

10. The method according to claim 1, characterized in that, The porous acoustic layer (30) has pores (32) with the size of the pores (32) being smaller than the size S of the perforations (200) of the perforated acoustic structure (20).

11. The method according to claim 1, characterized in that, The porous acoustic layer (30) has pores (32), the size of which increases along the axial direction A.

12. The method according to claim 1, characterized in that, The thickness of the perforated acoustic structure (20) and the peripheral spacer (102) is between 1 and 5 mm.

13. The method according to claim 12, characterized in that, The thickness of the perforated acoustic structure (20) and the peripheral spacer (102) is 1 to 2 millimeters.

14. The method according to claim 1, characterized in that, The sound attenuation plate (1) includes a removable cover disposed on the surface of the honeycomb structure (10) opposite to the perforated acoustic structure (20).

15. The method according to claim 1, characterized in that, The at least one mold (40) has at least one punch (42) designed to form a perforation (200) in the perforated acoustic structure (20).

16. The method according to claim 15, characterized in that, The surfaces of the at least one punch (42) and the reverse mold (400) are coated with a flexible material.

17. The method according to claim 16, characterized in that, The flexible material is silicone or a fluorocarbon compound.

18. The method according to claim 15, characterized in that, The surfaces of the punch (42) and the mold (400) are made of rigid material.

19. A nacelle (50) air inlet (52) arranged upstream of a fan (510), the air inlet (52) including an inner surface facing the fan (510), the inner surface accommodating a sound attenuation plate (1) manufactured using at least one of the methods according to any one of claims 1-18.

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