Manufacturing process for an acoustic component by stamping

Abstract

A method for manufacturing an acoustic component by stamping comprises: - positioning a thermoplastic preform (10) between first and second parts (210, 220) of a stamping tool (200) heated to a first temperature above the glass transition or melting temperature of the preform, - shaping the thermoplastic preform (10) by bringing the first and second parts (210, 220) of the stamping tool (200) together, which are maintained at the first temperature during the shaping of the preform, - compacting the shaped preform in the stamping tool (200) to a compaction pressure value (PC OMP) and at the first temperature, - cooling the molding surfaces (211, 221) of the first and second parts (210,220) of the stamping tooling (200) at a second temperature lower than or equal to the solidification temperature of the thermoplastic material. Figure for the abstract: Fig. 3.,

Description

Title of the invention: Method for manufacturing an acoustic component by stamping technical field

[0001] The present invention relates to the general field of acoustic attenuation structures or panels. It relates more particularly to acoustic attenuation structures used to reduce noise produced in aircraft engines such as gas turbines or exhausts thereof. Previous technique

[0002] Acoustic attenuation structures typically consist of a plate or skin with an acoustic surface permeable to the acoustic waves to be attenuated and a solid, reflective plate or skin, known as a "closing plate," with a cellular body, such as a honeycomb or a porous structure, arranged between these two surfaces. As is well known, such panels form Helmholtz resonators that attenuate acoustic waves over a certain frequency range. Acoustic attenuation structures of this type are described, in particular, in US patent 5,912,442 and GB patent 2,314,526.

[0003] These acoustic attenuation structures are limited to simple cell shapes such as the honeycomb structure of a conventional NID A® type structure. With this technology, the frequency treated is on the order of one-quarter of the inverse of the cavity height. To treat low frequencies, very tall cavities are therefore required, which, in the case of propulsion systems, considerably increases their drag. Furthermore, the acoustic performance obtained is limited to the absorption of a very narrow frequency range.

[0004] One solution for increasing the acoustic attenuation frequency range is to superimpose two cell bodies having different cell shapes and dimensions. This solution has the disadvantage of significantly increasing the size and drag of the acoustic attenuation structure.

[0005] Another known solution consists of placing open truncated cones in cavities as described in documents EP 0 738 865 and FR 3 082 987. While this solution reduces the size of the acoustic attenuation structure, the mass of the structure remains significant and, consequently, a disadvantage for uses in aircraft where control of the overall mass is always sought.

[0006] Document WO 2021 / 198610 discloses the manufacture of a complex multi-element acoustic panel comprising a plurality of acoustic elements having a cone shape or similar by injection of a thermoplastic material. However, the classic injection process, i.e. injection of a thermoplastic material into a closed mold with temperature control, is not suitable for the manufacture of very thin acoustic elements, typically having a wall thickness of less than 1 mm and more precisely between 0.1 mm and 0.6 mm, as is the case in particular when the thermoplastic material is of the polyetherimide (PEI) or polyetheretherketone (PEEK) type. Description of the invention

[0007] The main purpose of the present invention is therefore to propose a manufacturing solution for acoustic attenuation structures made of thermoplastic material which do not have the aforementioned disadvantages.

[0008] According to the invention, this objective is achieved by means of a method for manufacturing an acoustic component comprising a plurality of hollow complex acoustic elements, each having a shape that gradually narrows between a base and a vertex, the hollow complex acoustic elements being connected to each other by one or more adjacent edges, the method comprising: - the positioning of a thermoplastic preform between the first and second parts of a stamping tool, the first part having a molding surface comprising a plurality of cavities with a shape corresponding to the shape of the complex hollow acoustic elements of the acoustic component to be manufactured, the second part having a molding surface comprising a plurality of protrusions with a shape complementary to the cavities, the first and second parts of the stamping tool being heated to a first temperature higher than the glass transition or melting temperature of the preform, - the shaping of the thermoplastic preform by bringing the first and second parts of the stamping tool together at a predetermined speed so as to progressively compress the preform between the molding surfaces of said first and second parts until a closing position of the stamping tool is reached, a pressure exerted between the first and second parts of the stamping tool being progressively increased up to a compaction pressure value, the first and second parts of the stamping tool being maintained at the first temperature during the shaping of the preform, - the compaction of the preform shaped in the stamping tool in the closed position, the compaction being carried out at the compaction pressure value and over a determined compaction time, the first and second parts of the stamping tool being maintained at the first temperature during the preform compaction, - cooling the molding surfaces of the first and second parts of the stamping tooling to a second temperature lower than or equal to the solidification temperature of the thermoplastic material, - the demolding of the acoustic component comprising a plurality of complex hollow acoustic elements, process in which the shaping and compaction of the thermoplastic preform are carried out over a total time period less than a reference time corresponding to a fraction of the degradation time of the thermoplastic material of the preform at the first temperature.

[0009] The process of the invention thus implements specific operating conditions that allow control over the manufacturing of the intended acoustic component. Indeed, by maintaining the molding surfaces of the stamping tool at a temperature above the glass transition or melting temperature of the preform, while progressively increasing the pressure between the first and second parts of the tooling during the shaping of the preform, the filling of the cavities in the molding surface of the first part of the stamping tool by the thermoplastic material is precisely controlled. This progressive shaping at a temperature above the glass transition or melting temperature of the thermoplastic material of the preform makes it possible to obtain a homogeneous distribution of the thermoplastic material on the molding surfaces.

[0010] The shaping of the preform is further followed by a compaction step to complete the closure of the stamping tool. The compaction step is carried out with the molding surfaces maintained at a temperature above the glass transition or melting temperature of the thermoplastic material of the preform, which ensures complete and homogeneous filling of the cavities of the molding surface by the molten thermoplastic material, particularly when the space between the molding surfaces is very small.

[0011] The process of the invention thus makes it possible to obtain, economically, reliably, and repeatably, acoustic components equipped with complex-shaped acoustic elements with a very small wall thickness, typically less than 1 mm and more particularly between 0.1 mm and 0.6 mm. The acoustic component thus obtained allows the manufacture of thinner, and therefore lighter, acoustic attenuation structures while meeting the required specifications in terms of size, mechanical performance, and mass.

[0012] Furthermore, the total execution time of the shaping and compaction steps is controlled so as not to exceed a threshold beyond which the thermoplastic material could be degraded, which allows the material to be subjected thermoplastic at high temperatures which are necessary for controlling the manufacture of the acoustic component without deteriorating the mechanical and physico-chemical properties of the material.

[0013] According to a first particular aspect of the process of the invention, the reference time corresponds to 80% of the degradation time of the thermoplastic material of the preform at the first temperature.

[0014] According to a second particular aspect of the process of the invention, the thermoplastic preform is preheated before forming, the preform being preheated to a third temperature below the softening temperature of the thermoplastic material. The preheating of the preform is carried out by heating panels or by radiation by holding the preform between the first and second parts of the stamping tool for a predetermined time before forming said preform. This preheating step is optional. When implemented, the preform retains its mechanical strength because it is preheated to a temperature below the softening temperature of the thermoplastic material. It is therefore easy to handle and position in the stamping tool.

[0015] According to a third particular aspect of the process of the invention, during the cooling of the molding surfaces of the first and second parts of the stamping tool, the pressure is gradually reduced from the compaction pressure value to atmospheric pressure. The pressure reduction is controlled to reach atmospheric pressure when the molding surfaces of the first and second parts of the stamping tool have reached the solidification temperature of the thermoplastic material. The final shape of the acoustic component is thus perfectly preserved.

[0016] According to a fourth particular aspect of the process of the invention, the thermoplastic preform has a plurality of thicker portions located at specific points on the film and separated from each other by connecting portions having a thickness less than the thickness of the thicker portions, said points corresponding to the locations of the cavities in the molding surface of the first part of the stamping tool. The thicker portions constitute a surplus of material which, once stretched or flowed into the molding cavities during the shaping of the acoustic component, will allow the formation of complex hollow acoustic elements linked together by connecting portions.

[0017] According to a fifth particular aspect of the method of the invention, the surface area and thickness of each portion of the added thickness are defined as a function of a projected surface area and a thickness of each hollow complex acoustic element. It is thus It is possible to control the final wall thickness of complex hollow acoustic elements, in particular to obtain a constant thickness over the entire acoustic component.

[0018] According to a sixth particular aspect of the method of the invention, each portion of the excess thickness extends between the connecting portions and an opening or cavity present in the center of the portion of the excess thickness. This facilitates the production of complex hollow acoustic elements. The opening or cavity can form a hole, which makes it possible to directly form, by stamping, complex hollow acoustic elements with an opening at their apex.

[0019] The invention also relates to a method for manufacturing an acoustic attenuation structure comprising the following steps:

[0020] - production of an acoustic component according to the manufacturing process of a acoustic component of the invention,

[0021] - fabrication of a complex multi-element acoustic panel comprising the an acoustic component and a plurality of partitions forming acoustic cavities, each complex acoustic element of the acoustic component being housed in an acoustic cavity so as to form an acoustic cell,

[0022] - assembly of one face of the complex multi-element acoustic panel with a assembly face of an acoustic skin.

[0023] The complex hollow acoustic elements of the acoustic component can advantageously be combined with partitions, thereby lowering the acoustic frequencies to be treated. It is thus possible to create acoustic attenuation structures capable of attenuating lower-frequency sound waves while maintaining a compact design.

[0024] According to a particular aspect of the manufacturing process of an acoustic attenuation structure, the acoustic attenuation structure further comprises a closing skin covering the horizontal face of the complex multi-element acoustic panel opposite the horizontal face covered by the acoustic skin, the process comprising the assembly of the part joining the complex multi-element acoustic panel and the plurality of partitions with the closing skin. Brief description of the drawings

[0025] [Fig-1] Fig. 1 is a schematic cross-sectional view of a thermo tool molding showing a manufacturing step of an acoustic component according to an embodiment of the invention,

[0026] [Fig.2] Fig.2 is a schematic cross-sectional view of a thermo tool molding showing another manufacturing step of an acoustic component according to an embodiment of the invention,

[0027] [Fig.3] Fig.3 is a schematic cross-sectional view of a thermoforming tool showing another manufacturing step of an acoustic component according to an embodiment of the invention,

[0028] [Fig.4] Fig.4 is a schematic cross-sectional view of a thermo tool molding showing another manufacturing step of an acoustic component according to an embodiment of the invention,

[0029] [Fig.5] Fig.5 is a schematic perspective view of a thermoplastic film used to manufacture an acoustic component according to an embodiment of the invention.

[0030] [Fig.6] Fig.6 is a schematic perspective view of a thermoplastic film used to manufacture an acoustic component according to another embodiment of the invention,

[0031] [Fig. 7] [Fig. 7] is an enlarged detail view of a portion of the film made of material thermoplastic of the [Fig.6],

[0032] [Fig.8] Fig.8 is a schematic exploded perspective view of an acoustic attenuation structure according to an embodiment of the invention,

[0033] [Fig.9] Fig.9 is a schematic cross-sectional view of the attenuation structure acoustics of the [Fig.1] once assembled.

[0034] [Fig. 10] The [Fig. 10] is a graph showing the evolution of the temperature, pressure and position parameters of the stamping tooling during the steps of the process of the invention. Description of the implementation methods

[0035] The invention relates to the manufacture of acoustic components comprising a plurality of hollow complex acoustic elements, each having a shape that gradually narrows between a base and an apex, with an inlet at the base and an outlet at the apex. The shape of the hollow complex acoustic elements can be arbitrary, the only requirement being that the shape be demoldable. The hollow complex acoustic elements can, for example, have a conical or pyramidal shape.

[0036] The thermoplastic material used to manufacture the acoustic component of the invention is a high-performance thermoplastic resin preferably selected from grades of polyaryletherketone (PAEK) such as polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), polyetherimides (PEI), polyethersulfone (PES or PESU), and polyphenylene sulfide (PPS). The thermoplastic material may be filled or unfilled.

[0037] Figures 1 to 4 illustrate a method for manufacturing an acoustic component according to an embodiment of the invention.

[0038] Figure 1 illustrates a stamping tool 200 comprising a first part or mold 210, a second part or counter-mold 220, and a frame 240 supporting the mold 210. In the example described here, the second part 220 of the stamping tool is movable along a double direction D, while the first part 210 is fixed on the frame 240. In one embodiment, the first part may be movable relative to the second. In another embodiment, both the first and second parts are movable.

[0039] The stamping tool 200 is equipped with an actuating means (not shown in Figures 1 to 4) for moving at least the second part 220 or the first part 210 along the two directions D between an open position ([Fig. 1]) and a closed position ([Fig. 3]). The stamping tool is further associated with a press (not shown in Figures 1 to 4) for applying compaction pressure between the first and second parts 210 and 220 of the tool, as explained in detail below.

[0040] The frame 240 is equipped with side clamps 241 and 242 to hold a thermoplastic preform 10 during the formation steps of an acoustic component. The thermoplastic preform can also be placed on the tooling by an automated system or manually. It can also be conveyed by a conveyor system.

[0041] The first part 210 of the stamping tool 200 comprises a molding surface 211 having cavities 2110 intended to cooperate with protrusions 2210 of a molding surface 221 of the second part 220 of the stamping tool 200 for forming the acoustic component from the thermoplastic preform 10. The cavities 2110 of the molding surface 211 of the first part 210 have a shape corresponding to the shape of the complex hollow acoustic elements of the acoustic component to be manufactured, the protrusions 2210 of the second part 220 having a shape complementary to the cavities 2110. In the example described here, the stamping tool 200 further comprises heating panels 230 for preheating the preform 10.

[0042] The process begins by preheating the thermoplastic preform 10 using heating panels 230 to a temperature below the softening temperature of the thermoplastic material. Alternatively, the preheating of the thermoplastic preform 10 can be carried out by holding the preform between the first and second parts 210 and 220 of the stamping tool 200 for a predetermined time before shaping the preform. In this case, the first and second parts 210 and 220 are heated to a predetermined temperature, thereby radiantly heating the preform to a temperature below the softening temperature of the thermoplastic material.

[0043] This first step is optional in the process of the invention. Indeed, preheating is not mandatory because it is possible to position the preform directly at room temperature in the stamping tool. In the case where a preheating phase is implemented, as in the example described here, the preform is preheated to a temperature below the softening temperature of the thermoplastic material. This ensures that the preform retains sufficient rigidity to facilitate its positioning or retention in the stamping tool, the mold being preheated to a temperature close to that chosen for the preform.

[0044] By way of non-limiting example: • For PEI or PESU grades, the maximum preheating temperature is set at 200°C • For PAEK grades, the maximum preheating temperature is set at 300°C • For PPS grades, the maximum preheating temperature is set at 250°C

[0045] The prior art stamping process requires preheating the preform to a temperature above the softening temperature of the thermoplastic matrix. Consequently, positioning the softened preform in the stamping tool requires a specific protocol capable of rapidly heating and then transporting the softened preform from a heating furnace to the stamping tool. These operations are costly (dedicated furnace, soft preform transport frame, temperature control, and automation of operations) and often complex to implement correctly. Furthermore, this process proves unsuitable for materials without reinforcement or fillers, as the presence of reinforcement ensures that the softened preform does not deform excessively during transport from the preheating furnace to the stamping unit.

[0046] The process of the invention avoids all the difficulties and limitations of prior art stamping since the preheating operation outside the stamping tooling becomes optional and, if it is carried out, it is performed at a temperature lower than the softening temperature of the thermoplastic material, thereby eliminating any difficulty in transporting and positioning the preform. One of the advantages of the process of the invention is that it can be applied indiscriminately to both filled and unfilled thermoplastic materials.

[0047] The preform is then shaped from thermoplastic material 10. The first and second parts 210 and 220 of the stamping tool 200, or at least their respective molding surfaces 211 and 221, are first heated to a temperature above the glass transition or melting temperature of the thermoplastic material of the preform 10. More specifically, in the case of an amorphous thermoplastic material, the preform is heated to a temperature TSUp higher than the glass transition temperature of the material while, in the case of a semi-crystalline thermoplastic material, the preform is heated to a temperature higher than the melting temperature of the material.

[0048] For this purpose, the first and second parts 210 and 220 of the stamping tool 200 are equipped with rapid heating means such as a forced air heating system, induction heating or any other heating system capable of reaching heating speeds ranging from 30°C / minute to 100°C / minute.

[0049] By way of non-limiting example: • For PEI or PESU grades, the TSUp temperature is between 220°C and 400°C • For PAEK grades, the TSUp temperature is between 330°C and 410°C • For PPS grades, the TSUp temperature is between 220°C and 400°C

[0050] Once the molding surfaces 211 and 221 of the first and second parts 210 and 220 of the stamping tool 200 have reached temperature TSup, the second part 220 is moved towards the first part 210 as illustrated in [Fig. 2] until the protrusions 2210 of the second part 220 fully cooperate with the cavities 2110 of the first part as shown in [Fig. 3], which corresponds to the closed position of the stamping tool 200. The thermoplastic preform 10 is locally shaped in each of the cavities 2110. During this shaping step, the molding surfaces 211 and 221 of the first and second parts 210 and 220 of the stamping tool 200 are maintained at temperature TSup. above the glass transition or melting temperature of the thermoplastic material. The shaping of the preform 10 is carried out over a predetermined time DMEF.

[0051] The first and second parts 210 and 220 of the stamping tool 200 are brought together at a controlled speed so as to progressively compress the preform between the molding surfaces of the first and second parts. Controlling the speed at which parts 210 and 220 are brought together also ensures a shear stress on the preform that is lower than the shear limit of the thermoplastic material. The shear limit of a thermoplastic material is generally indicated in the manufacturer's data but can be determined by testing if necessary. By way of non-limiting example, provided that the performance of the selected press is suitable for the dimensions of the part (in terms of clamping force), the bringing speed allows a mold compression / closing can be chosen to allow the mold to close over a period ranging from a few seconds to a few minutes.

[0052] A pressure Pc exerted between the first and second parts 210 and 220 of the stamping tool is progressively increased up to a compaction pressure value PComp-

[0053] By maintaining the molding surfaces of the stamping tool at a temperature above the glass transition or melting temperature of the preform while progressively increasing the pressure between the first and second parts of the tooling during the shaping of the preform, the filling of the cavities of the molding surface of the first part of the stamping tool by the thermoplastic material is precisely controlled.

[0054] This progressive shaping at a temperature above the glass transition or melting temperature of the thermoplastic preform allows for a homogeneous distribution of the thermoplastic material on the molding surfaces. With the prior art stamping process, in which the stamping tooling is maintained at a temperature close to the solidification temperature of the thermoplastic material, the material's setting time is too short and the compaction pressure too high to control the shaping and obtain homogeneous, high-quality parts.

[0055] According to the invention, the shaping step is followed by a compaction step of the shaped preform in the stamping tool. The compaction consists of holding the preform in the stamping tool for a predetermined time DComp in the closed position ([Fig. 3]) while applying the compaction pressure PComp and maintaining the molding surfaces 211 and 221 of the first and second parts 210 and 220 of the stamping tool 200 at a temperature TSUp higher than the glass transition or melting temperature of the thermoplastic material. The compaction pressure PComp is preferably greater than or equal to 100 bar.

[0056] The compaction step is carried out with the molding surfaces maintained at a temperature above the glass transition or melting temperature of the thermoplastic material of the preform, which ensures complete and homogeneous filling of the cavities of the molding surface by the thermoplastic material in the molten state, in particular when the space present between the molding surfaces is very small.

[0057] In the closed position of the stamping tool 200 shown in [Fig. 3], the molding surfaces 211 and 221 of the first and second parts 210 and 220 respectively are held opposite each other at a very small distance D2oo corresponding to the wall thickness Ei20 of the acoustic component 120 to be produced. starting from preform 10 ([Fig.4]). The final wall thickness E120 is fixed at the end of the compaction stage.

[0058] After the compaction step, the molding surfaces 211 and 221 of the first and second parts 210 and 220, respectively, are cooled to a temperature lower than or equal to the solidification temperature of the thermoplastic material, thus solidifying said material in the shape of an acoustic component 120 to be manufactured. During the cooling of the molding surfaces of the first and second parts of the stamping tool, the pressure is gradually reduced from the compaction pressure value PComp to atmospheric pressure. The pressure reduction is controlled to reach atmospheric pressure when the molding surfaces of the first and second parts of the stamping tool have reached the solidification temperature of the thermoplastic material.

[0059] The cooling of the molding surfaces 211 and 221 respectively of the first and second parts 210 and 220 is preferably carried out in a controlled and accelerated manner by equipping, for example, the stamping tooling with a forced air cooling system or any other system capable of reaching cooling rates ranging from 30°C / minute to 100°C / minute.

[0060] The mold areas defining the limits of the molding cavity can also be temperature regulated in a specific way in order to avoid flashing or flashing of material at the joint plane of the fixed and moving parts.

[0061] The acoustic component 120 is then demolded by moving the second part 220 in a direction opposite to that of the first part 210 and by opening the side clamps in order to release the acoustic component as illustrated in [Fig.4].

[0062] Figure 10 is a summary graph of the steps implemented in the process of the invention. This graph shows the evolution of the temperature, pressure and position parameters of the stamping tooling during the steps of the process of the invention.

[0063] According to the invention, the shaping and compaction of the thermoplastic preform are carried out over a total time Dmef+DComp less than a reference time corresponding to a fraction of the degradation time of the thermoplastic material of the preform at the first temperature. Indeed, since in the process of the invention the thermoplastic material of the preform is exposed to high temperatures during shaping and compaction, there is a risk of degradation of the thermoplastic material during these process steps. The degradation times of a thermoplastic material are generally defined in the material supplier's data. If necessary, the degradation time of a thermoplastic material can be measured by the performance of mechanical and / or physico-chemical tests on samples exposed to the envisaged treatment temperature for determined durations.

[0064] A reference duration is thus defined corresponding to a fraction or a percentage of the degradation time of the thermoplastic material at the processing temperature considered for the shaping and compaction steps.

[0065] According to one aspect of the process of the invention, the reference duration DREF corresponds to 80% of the material's degradation time. Thus, the sum of the duration DMEF of the shaping step and the duration DComp of the compaction step must not exceed the duration Drep in order to preserve the mechanical and / or physicochemical properties of the thermoplastic material in the final acoustic component.

[0066] By way of non-limiting example, the degradation time of a PEI grade at 400°C is 10 minutes. If the processing temperature used for the application and compaction steps is 400°C, the reference duration DREF will be set at 8 minutes. It is then verified that the cumulative durations DMEF and DComp do not exceed 8 minutes.

[0067] The process described above makes it possible to form complex hollow acoustic elements with very thin walls, ranging from 0.1 mm to 0.6 mm. Indeed, by maintaining the molding surfaces of the stamping tooling at a temperature above the glass transition or melting temperature of the thermoplastic material during shaping and compaction, the homogeneous distribution of material flow between the molding surfaces is facilitated, thus enabling the reliable and repeatable manufacture of acoustic components.

[0068] An acoustic component 120 is then obtained, as illustrated in Figures 8 and 9, comprising a plurality of hollow complex acoustic elements 121, each having a shape that gradually narrows between a base 122 and an apex 123, and a wall thickness E^i of less than 1 mm ([Fig. 9]). The shape of the mold cavities defines the shape of the hollow complex acoustic elements of the acoustic component. In the example described here, the mold cavities 211 have a pyramidal shape, allowing the formation of hollow complex acoustic elements 121 of the same shape. The mold cavities, and consequently the resulting hollow complex acoustic elements, can have other shapes, such as conical, spiral, funnel-shaped, or hopper-shaped.

[0069] The acoustic component manufactured according to the process of the invention may have a flat shape, such as the acoustic component 120 illustrated in Figures 8 and 9, or a curved shape with a single or multiple curvature. In the latter case, the curvature(s) may be created directly during the shaping of the preform using tooling with a suitable geometry, or subsequently by shaping or hot forming.

[0070] The thermoplastic preform used to manufacture the acoustic component can have a constant thickness, such as the preform 10 illustrated in [Fig. 5]. The preform can be made in one piece or obtained by welding several unit films joined together, such as the unit films 11 and 12 of [Fig. 5], which, once welded, form a thermoplastic preform 10 of constant thickness Ei0. The thermoplastic preform can be manufactured from thermoplastic granules by injection molding or any other suitable method.

[0071] The thermoplastic preform used to manufacture the acoustic component can also have a variable thickness, such as the preform 20 illustrated in Figures 6 and 7. More specifically, the thermoplastic preform 20 has a plurality of thickened portions 22 with a thickness E22 greater than the thickness E2i of the connecting portions 21 of the preform 20 located between the thickened portions 22 ([Fig. 7]). The thickened portions 22 are located at specific points on the preform, these points corresponding to the locations of the cavities in the first part of the stamping tool. The thickened portions 22 constitute a surplus of material which, once stretched or flowed into the cavities during the shaping of the acoustic component, will allow the formation of complex hollow acoustic elements with a wall thickness close to that of the connecting portions 21.The volume of material in each portion of the reinforcement is defined according to the wall thickness of each complex acoustic element to be manufactured. The reinforcement portions can be circular, annular, or hexagonal and are distributed evenly over the film. In the example described here, each reinforcement portion 22 extends between connecting portions 21 and an opening or cavity 222 located at the center of the reinforcement portion. Each opening or cavity 222 is designed to be aligned with the center of the mold's molding cavities. According to a particular feature, the central opening or cavity 222 forms a hole. This allows the exit hole of each complex acoustic element to be obtained immediately after forming, thus avoiding an additional machining operation. The diameter of the opening or cavity 222 is preferably larger than the diameter of the tips of the teeth 221 of the counter-mold 220.As a non-limiting example, in the case where the diameter of the end of the teeth of the counter-mold is 5 mm, the hole formed by the central opening has a diameter between 6 mm and 7 mm.

[0072] Each portion of the extra thickness is intended to form, by stretching or thinning, a complex hollow acoustic element 121 having a shape that gradually narrows between its base 122 and its apex 123. Thus, we move from an initial flat surface Spl corresponding to the portion of the extra thickness that extends between portions of The connection 21 and the central opening or cavity 222 are connected to a larger projected surface Spr corresponding to the surface area of ​​the hollow complex acoustic element 121. The ratio between the initial flat surface Spl and the projected surface Spr defines a slenderness factor Fe, which can be between 2 and 5. The principle is that of mass conservation. Thus, the initial flat surface Spl and the initial thickness E22 of each portion of the added thickness 22 are defined as a function of the final projected surface Spr and the final thickness E121 of each hollow complex acoustic element 121 according to the following formula:

[0073] Spl x E22 = Spr x E121

[0074] In the case where it is desired to produce an acoustic component of constant thickness Ec, the thickness E22 of the extra thickness 22 can be determined according to the following formula:

[0075] E22 = (Spr / Spl) x Ec = Fe x Ec

[0076] In this case, the thickness E2[ of the connecting portions 21 which are not intended to be stretched or creased corresponds substantially to the final thickness of the acoustic component 120.

[0077] By way of non-limiting example, the thickness E2[ of the connecting portions 21 can for example be 0.5 mm while the thickness E22 of the overthickness portions 22 can be 1.6 mm.

[0078] Such a film of thermoplastic material with variable thickness can be manufactured by calendering, machining, stacking of unit wires, injection molding, etc.

[0079] A method for manufacturing a sound-attenuating structure according to an embodiment of the invention is now described with reference to Figures 8 and 9. The sound-attenuating structure 100 here comprises an acoustic skin or plate 110, an acoustic component 120 manufactured as described above, a plurality of partitions 131, and a closing skin or plate 140.

[0080] The closing skin 140 corresponds to a solid surface designed to reflect sound waves entering the acoustic attenuation structure. The closing skin may be a constituent element of the acoustic attenuation structure, as in the example described here, or it may correspond to the structure of an object, for example, an aircraft engine. In the latter case, the acoustic attenuation structure of the invention does not include a closing skin and is mounted directly onto the structure of the object.

[0081] The acoustic skin 110 has the function of allowing the sound waves to be attenuated to pass through the acoustic attenuation structure 100. For this purpose and in the example described here, the acoustic skin 110 comprises a plurality of perforations 111.

[0082] The acoustic component 120 is formed in one piece and extends lengthwise and widthwise along a horizontal direction DH and heightwise along a direction vertical Dv. The acoustic component comprises a plurality of complex hollow acoustic elements 121 each having a shape that gradually narrows between a base 122 and a top 123.

[0083] In the example described here, the complex acoustic elements 121 have a pyramidal shape. The base 122 of each complex acoustic element 121 is in continuous contact with the base of the adjacent complex acoustic elements so as to form a continuous network of edges 124.

[0084] In the embodiment described here, the plurality of partitions 131 is made in one piece, namely a network of ribs 130 which, once assembled with the complex acoustic multi-element panel 120, forms the partitions around the complex acoustic elements 121.

[0085] Still in the example described here, the acoustic attenuation structure 100 is made by assembling the complex acoustic multi-element panel 120 with the plurality of partitions 131 in a single piece, the upper edge 131a of the partitions 131 being fixed, for example by gluing or welding, to the lower portion 122b of the bases 122 of the complex acoustic elements 121 ([Fig. 9]). Since the plurality of complex acoustic elements is formed in a single piece within the complex acoustic multi-element panel and the plurality of partitions is also formed in a single piece, the assembly between these two elements is greatly facilitated by the self-positioning of the complex acoustic elements with the partitions.

[0086] The closing skin 140 is fixed, for example by gluing or welding, to the lower edge 131b of the partitions 131 while the acoustic skin 110 is fixed, by gluing or welding, to the upper portion 122a of the bases 122 of the complex acoustic elements 121 corresponding to the exposed surface of the edges 124. Thus, the acoustic skin and the closing skin are each fixed to a perfectly flat support along the horizontal direction DH, which makes it possible to ensure a very good seal between the skins and the assembly of the complex multi-element acoustic panel with the plurality of partitions.

[0087] Once assembled, the attenuation structure 100 comprises a plurality of acoustic cells 150, each formed by a complex acoustic element 121 and the partitions 131 surrounding it ([Fig. 9]). The height H^i of the complex acoustic elements 121 is less than the height Hi50 of the acoustic cells 150. More precisely, the height H^i of the acoustic cells is between 10% and 99% of the height Hi50 of the acoustic cells in the vertical direction. The height Hm can be between 5 mm and 100 mm, for example 20 mm, while the base of each element 121 can be inscribed within a circle with a diameter between 5 mm and 50 mm, for example 20 mm. Furthermore, thanks to the manufacturing process of the invention, the hollow complex acoustic elements 121 have a very small thickness, less than 1 mm and typically between 0.1 mm and 0.6 mm.

[0088] The acoustic skin, the plurality of partitions and the closing skin can be made by injection of a thermoplastic or thermosetting material, filled or unfilled, by injection-compression of a thermoplastic or thermosetting material, filled or unfilled, or by injection with temperature control of the tooling of a thermoplastic or thermosetting material, filled or unfilled.

[0089] The plurality of partitions, the acoustic and closing skins as well as the assemblies bringing together in a single piece the plurality of partitions and the complex multi-element acoustic panel or the plurality of partitions and one of the skins can also be made by injection of a thermoplastic or thermosetting material, filled or unfilled.

Claims

Demands

1. A method for manufacturing an acoustic component (120) comprising a plurality of hollow complex acoustic elements (121), each having a shape that gradually narrows between a base (122) and a vertex (123), the hollow complex acoustic elements being connected to each other by one or more adjacent edges, the method comprising: - the positioning of a thermoplastic preform (10) between first and second parts (210, 220) of a stamping tool (200), the first part (210) having a molding surface (211) comprising a plurality of cavities (2110) having a shape corresponding to the shape of the hollow complex acoustic elements (121) of the acoustic component (120) to be manufactured, the second part (220) having a molding surface (221) comprising a plurality of protrusions (2210) having a shape complementary to the cavities (2110), the first and second parts of the stamping tool being heated to a first temperature higher than the glass transition or melting temperature of the preform, - the shaping of the thermoplastic preform (10) by bringing together the first and second parts (210, 220) of the stamping tool (200) at a determined speed so as to progressively compress the preform between the molding surfaces (211, 221) of said first and second parts until reaching a closing position of the stamping tool, a compaction pressure exerted between the first and second parts of the stamping tool being progressively increased up to a compaction pressure value (Pcomp), the first and second parts of the stamping tool being maintained at the first temperature during the shaping of the preform, - the compaction of the preform shaped in the stamping tool (200) in the closed position, the compaction being carried out at the compaction pressure value (Pcomp) and over a determined compaction time, the first and second parts (210, 220) of the stamping tool (200) being maintained at the first temperature during the compaction of the preform, - the cooling of the molding surfaces (211, 221) of the first and second parts (210, 220) of the stamping tooling (200) at a second temperature less than or equal to the solidification temperature of the thermoplastic material, - the demolding of the acoustic component (120) comprising a plurality of complex hollow acoustic elements (121), process in which the shaping and compacting of the preform in thermoplastic material (10) are carried out over a total time less than a reference time corresponding to a fraction of the degradation time of the thermoplastic material of the preform at the first temperature.

2. A method according to claim 1, wherein the reference time corresponds to 80% of the degradation time of the thermoplastic material of the preform (10) at the first temperature.

3. A method according to claim 1 or 2, wherein the thermoplastic material preform (10) is preheated before shaping, the preform being preheated to a third temperature lower than the softening temperature of the thermoplastic material, the preheating of the preform being carried out by heating panels or by radiation by holding the preform between the first and second parts of the stamping tooling for a determined time before shaping said preform.

4. A method according to any one of claims 1 to 3, wherein, during the cooling of the molding surfaces (211, 221) of the first and second parts (210, 220) of the stamping tool (200), the pressure is gradually decreased from the compaction pressure value (PComp) to atmospheric pressure, the decrease in pressure being controlled to reach atmospheric pressure when the molding surfaces of the first and second parts of the stamping tool have reached the solidification temperature of the thermoplastic material.

5. A method according to any one of claims 1 to 4, wherein the thermoplastic material preform (10) has a plurality of overthickness portions (22) present at determined locations and spaced from each other by connecting portions (21) having a thickness (E2i) less than the thickness (E22) of the overthickness portions, said locations corresponding to the locations of the cavities (2110) of the molding surface (211) of the first part (210) of the stamping tool (200).

6. Method according to claim 5, wherein the volume of material present in each portion of overthickness (22) is defined as a function of the wall thickness (E120) of each complex acoustic element to be manufactured.

7. Method according to claim 6, wherein the surface area (Spl) and thickness (E22) of each portion of overthickness (22) is defined as a function of a projected surface area (Spr) and a thickness (Ei2i) of each hollow complex acoustic element (121).

8. A method according to any one of claims 5 to 7, wherein each portion of excess thickness (22) extends between the connecting portions (21) and an opening or cavity (222) present in the center of the portion of excess thickness.

9. Method according to claim 8, wherein the opening or cavity (222) forms a hole.

10. A method according to any one of claims 1 to 9, wherein the cavities (2110) of the molding surface (211) of the first part (210) of the stamping tool (200) have a pyramidal, conical, spiral, funnel, or hopper shape

11. A method according to any one of claims 1 to 10, wherein the complex acoustic elements (121) of the acoustic component (120) have a wall thickness (Ei20) between 0.1 mm and 0.6 mm.

12. Method of manufacturing an acoustic attenuation structure (100) comprising the following steps: - making an acoustic component (120) according to the method as defined in any one of claims 1 to 11, - making a complex acoustic multi-element panel comprising the acoustic component and a plurality of partitions (131) forming acoustic cavities (132), each complex acoustic element of the acoustic component being housed in an acoustic cavity so as to form an acoustic cell (150), - assembling a face (122a) of the complex acoustic multi-element panel (120) with an assembly face (112) of an acoustic skin (110).

13. A method according to claim 12, wherein the acoustic attenuation structure (100) further comprises a closing skin (140) covering the horizontal face of the complex acoustic multi-element panel (120) opposite the horizontal face covered by the skin acoustic (110), the process comprising the assembly of the part uniting the complex multi-element acoustic panel (120) and the plurality of partitions (131) with the closing skin (140).

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