Method of manufacturing acoustic component by stamping

Abstract

The invention relates to a method of manufacturing an acoustic component, the method comprising: arranging a preform (10) of thermoplastic material between a first portion (210) and a second portion (220) of a stamping tool (200), the two portions being heated to a first temperature higher than the glass transition or melting temperature of the preform; forming the thermoplastic material preform (10) by joining the first (210) and second (220) portions of the stamping tool (200), both portions being maintained at a first temperature during forming of the preform; compacting the shaped preform in a stamping tool (200) at a compaction pressure value (PCOMP) and a first temperature; the forming surfaces (211, 221) of the first portion (210) and the second portion (220) of the stamping tool (200) are cooled to a second temperature lower than or equal to the curing temperature of the thermoplastic material.

Description

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 for reducing the noise generated in an aeroengine, such as a gas turbine or its exhaust device. Prior art

[0002] Acoustic attenuation structures generally consist of an acoustic surface panel or skin permeable to the sound waves to be attenuated and a reflective solid panel or skin called a "closure panel", between which a cellular body such as a honeycomb or porous structure is arranged. It is well known that such panels form Helmholtz-type resonators capable of attenuating sound waves in a certain frequency range. This type of acoustic attenuation structure is described in particular in documents US 5,912,442 and GB 2,314,526.

[0003] These acoustic attenuation structures are limited to simple honeycomb shapes, such as the honeycombs of traditional type structures. Using this technique, the frequency processed is approximately the reciprocal of a quarter of the cavity height. To process low frequencies, very high cavities are required, which, in the case of a propulsion system, significantly increases its drag. In addition, the acoustic performance obtained is limited to absorbing a very narrow frequency range.

[0004] A solution for extending the acoustic attenuation frequency range is to stack two cellular bodies with different honeycomb shapes and sizes. The drawback of this solution is a significant increase in the size and drag of the acoustic attenuation structure.

[0005] Another known solution is to place open truncated cones in the honeycomb, as described in EP 0,738,865 and FR 3,082,987. Although this solution allows the size of the acoustic attenuation structure to be reduced, the mass of the structure remains large and is therefore disadvantageous for aeronautical applications which are always seeking to control the total mass.

[0006] Document WO 2021 / 198610 discloses a method for manufacturing a complex acoustic multi-component panel consisting of a plurality of acoustic elements having a conical shape or the like, made by injecting a thermoplastic material. However, traditional injection methods, namely injecting a thermoplastic material into a closed temperature-controlled mold, are not suitable for manufacturing very thin acoustic elements, especially when the wall thickness is less than 1 mm, more precisely between 0.1 mm and 0.6 mm, especially when the thermoplastic material is of the polyetherimide (PEI) or polyetheretherketone (PEEK) type. Summary of the invention

[0007] Accordingly, the object of the present invention is to propose a preparation solution for an acoustic attenuation structure made of a thermoplastic material which does not have the above-mentioned drawbacks.

[0008] According to the present invention, this object is achieved by a method for manufacturing an acoustic component comprising a plurality of hollow complex acoustic elements, each element tapering from the bottom to the top, and these hollow complex acoustic elements being interconnected by one or more adjacent edges. The method comprises:

[0009] · Placing a thermoplastic preform between a first part and a second part of a stamping tool, the forming surface of the first part comprising a plurality of cavities whose shapes correspond to the shapes of the hollow complex acoustic elements of the acoustic component to be manufactured; the forming surface of the second part comprising a plurality of protrusions complementary to the cavity shapes, and heating the first part and the second part of the stamping tool to a first temperature higher than the glass transition or melting temperature of the preform;

[0010] · Forming the thermoplastic preform by bringing the first part and the second part of the stamping tool together at a certain rate, thereby gradually compressing the preform between the forming surfaces of the first part and the second part until the stamping tool reaches a closed position, and gradually increasing the pressure applied between the first part and the second part of the stamping tool to a compaction pressure value. During the forming of the preform, the first part and the second part of the stamping tool are maintained at the first temperature;

[0011] · Compacting the formed preform in the closed position of the stamping tool, the compaction being carried out at the compaction pressure value and a determined compaction duration. During the compaction of the preform, the first part and the second part of the stamping tool are maintained at the first temperature;

[0012] · Cooling the forming surfaces of the first part and the second part of the stamping tool to a second temperature lower than or equal to the curing temperature of the thermoplastic material;

[0013] · Demolding the acoustic component comprising a plurality of hollow complex acoustic elements;

[0014] In this method, the total duration of forming and compacting the thermoplastic preform is less than a reference duration which is a fraction of the degradation duration of the thermoplastic material of the preform at the first temperature.

[0015] The method of the present invention thus implements specific operating conditions that allow the control of the manufacturing of the target acoustic component. In fact, by maintaining the forming surface of the stamping tool at a temperature above the glass transition or melting temperature of the preform, while gradually increasing the pressure between the first and second parts of the tool during the forming of the preform, the cavity of the forming surface of the first part of the stamping tool filled with the thermoplastic material is precisely controlled. This progressive forming carried out at a temperature above the glass transition or melting temperature of the thermoplastic material of the preform allows for a uniform distribution of the thermoplastic material on the forming surface.

[0016] The forming of the preform is further followed by a compaction step to complete the closing of the stamping tool. The compaction step is carried out while maintaining the forming surface at a temperature above the glass transition or melting temperature of the thermoplastic material of the preform, which ensures a complete and uniform filling of the cavity of the forming surface with the thermoplastic material in a molten state, especially when the space between the forming surfaces is very small.

[0017] The method of the present invention is thus capable of obtaining, in an economical, reliable and repeatable manner, an acoustic component equipped with a complex-shaped acoustic element having a very thin wall thickness (generally less than 1 mm, more particularly between 0.1 mm and 0.6 mm). The acoustic component thus obtained allows the manufacture of a thinner and thus lighter acoustic attenuation structure while meeting the required specifications in terms of dimensions, mechanical properties and quality.

[0018] In addition, the total execution duration of the forming and compaction steps is controlled so as not to exceed a threshold beyond which the thermoplastic material may degrade, which allows the thermoplastic material to be exposed to the high temperatures necessary for the control of the manufacturing of the acoustic component without deteriorating the mechanical and physico-chemical properties of the material.

[0019] According to a first specific aspect of the method of the present invention, the reference duration corresponds to 80% of the degradation duration of the thermoplastic material of the preform at a first temperature.

[0020] According to a second specific aspect of the method of the present invention, the thermoplastic preform is preheated before forming. The preform is preheated to a third temperature below the softening temperature of the thermoplastic material. The preheating of the preform is carried out by a heating plate or by radiation, and is achieved by holding the preform between the first and second parts of the stamping tool for a determined time before forming the preform. This preheating step is optional. When implemented, since the preform is preheated to a temperature below the softening temperature of the thermoplastic material, the preform retains its mechanical strength. Thus, it is easy to handle and position in the stamping tool.

[0021] According to a third specific aspect of the method of the present invention, during the cooling of the forming surfaces of the first and second parts of the stamping tool, the pressure gradually decreases from the compaction pressure value to the atmospheric pressure, and the decrease in pressure is controlled so as to reach the atmospheric pressure when the forming surfaces of the first and second parts of the stamping tool reach the curing temperature of the thermoplastic material. Thus, the final forming of the acoustic component is perfectly protected.

[0022] According to a fourth specific aspect of the method of the present invention, the thermoplastic preform has a plurality of excess thickness portions located at specific positions on the film and separated from each other by connecting portions, the thickness of the connecting portions being less than the thickness of the excess thickness portions, and the positions corresponding to the positions of the cavities of the forming surface of the first part of the stamping tool. The excess thickness portions constitute a surplus of material that, once stretched or flowed into the forming cavities during the forming of the acoustic component, will allow the formation of hollow complex acoustic elements interconnected by the connecting portions.

[0023] According to a fifth specific aspect of the method of the present invention, the surface and thickness of each excess thickness portion are defined according to the projected surface and thickness of each hollow complex acoustic element. Thus, the final thickness of the walls of the hollow complex acoustic elements can be controlled, in particular in order to obtain a constant thickness over the entire acoustic component.

[0024] According to a sixth specific aspect of the method of the present invention, each excess thickness portion extends between the connecting portion and an opening or cavity located at the center of the excess thickness portion. This helps to produce the hollow complex acoustic elements. The opening or cavity can form a hole, which allows the direct formation of a hollow complex acoustic element with an opening at the top by stamping.

[0025] The present invention also relates to a method for manufacturing an acoustic attenuation structure, comprising the following steps:

[0026] · Manufacturing an acoustic component according to the method for manufacturing an acoustic component of the present invention,

[0027] · Manufacturing a complex acoustic multi-component plate that includes the acoustic component and a plurality of partitions forming acoustic cavities, each complex acoustic element of the acoustic component being received in an acoustic cavity to form an acoustic unit,

[0028] · Assembling the face of the complex acoustic multi-component plate with the assembly face of the acoustic skin.

[0029] The hollow complex acoustic elements of the acoustic component can be advantageously combined with the partitions, which allows the reduction of the acoustic frequencies to be processed. Thus, an acoustic attenuation structure can be produced that is capable of attenuating lower frequency sound waves while having a smaller spatial volume.

[0030] According to a specific aspect of the method for manufacturing an acoustic attenuation structure, the acoustic attenuation structure further includes an enclosing skin that covers the horizontal plane of the complex acoustic multi-component plate opposite to the horizontal plane covered by the acoustic skin. The method includes assembling a workpiece that connects the complex acoustic multi-component plate and a plurality of partitions with the enclosing skin. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic cross-sectional view of a thermoforming tool showing the steps of manufacturing an acoustic component according to an embodiment of the present invention.

[0032] Figure 2 is another schematic cross-sectional view of a thermoforming tool showing the steps of manufacturing an acoustic component according to an embodiment of the present invention.

[0033] Figure 3 is another schematic cross-sectional view of a thermoforming tool showing the steps of manufacturing an acoustic component according to an embodiment of the present invention.

[0034] Figure 4 is another schematic cross-sectional view of a thermoforming tool showing the steps of manufacturing an acoustic component according to an embodiment of the present invention.

[0035] Figure 5 is a schematic perspective view of a thermoplastic material film for manufacturing an acoustic component according to an embodiment of the present invention.

[0036] Figure 6 is a schematic perspective view of a thermoplastic material film for manufacturing an acoustic component according to another embodiment of the present invention.

[0037] Figure 7 is Figure 6 an enlarged detailed view of a part of the thermoplastic material film in

[0038] Figure 8 is an exploded schematic view of an acoustic attenuation structure according to an embodiment of the present invention.

[0039] Figure 9 is Figure 1 a schematic view of the assembled acoustic attenuation structure in

[0040] Figure 10 is a chart showing the changes in temperature, pressure, and position parameters of a stamping tool in the method steps of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0041] The present invention is applicable to the manufacture of acoustic components comprising a plurality of hollow complex acoustic elements, each element tapering from the bottom to the top and having an inlet hole at the bottom and an outlet hole at the top. The shape of the hollow complex acoustic element can be arbitrary, provided only that the shape can be demolded. The hollow complex acoustic element can have, for example, a conical or pyramidal shape.

[0042] The thermoplastic material used for manufacturing the acoustic component of the present invention is a high-performance thermoplastic resin, preferably selected from the polyaryletherketone (PAEK) grades such as polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), polyetherimide (PEI), polyethersulfone (PES or PESU), and polyphenylene sulfide (PPS). The thermoplastic material can be filled or unfilled.

[0043] Figures 1 to 4 A manufacturing method of an acoustic component according to an embodiment of the present invention is illustrated.

[0044] Figure 1 A stamping tool 200 is shown, comprising a first part or die 210, a second part or counterdie 220, and a frame 240 supporting the die 210. In this example, the second part 220 of the stamping tool can be moved in a two-way direction D, while the first part 210 is fixed to the frame 240. In an alternative embodiment, the first part can be moved relative to the second part. In another alternative embodiment, both the first part and the second part can be moved.

[0045] The stamping tool 200 is equipped with a drive means ( Figures 1 to 4 ) not shown, for moving at least the second part 220 or the first part 210 in a two-way direction D between an open position ( Figure 1 ) and a closed position ( Figure 3 ). The stamping tool is also associated with a press ( Figures 1 to 4 ) not shown, for applying a compaction pressure between the first part 210 and the second part 220 of the tool, as will be explained in detail below.

[0046] The frame 240 is equipped with side clamps 241 and 242 for fixing the thermoplastic preform 10 during the step of forming the acoustic component. The thermoplastic preform can also be placed in the tool by an automaton or manually. It can also be provided by a conveying system.

[0047] The first part 210 of the stamping tool 200 includes a forming surface 211 provided with a cavity 2110 for cooperating with a protrusion 2210 on the forming surface 221 of the second part 220 of the stamping tool 200 to form an acoustic component from the thermoplastic preform 10. The cavity 2110 on the forming surface 211 of the first part 210 is shaped corresponding to the shape of the hollow complex acoustic element of the acoustic component to be manufactured, and the protrusion 2210 on the second part 220 is shaped complementary to the cavity 2110. In this example, the stamping tool 200 further includes a heating plate 230 for preheating the preform 10.

[0048] The method starts with preheating the thermoplastic preform 10 by the heating plate 230 to a temperature below the softening temperature of the thermoplastic material. According to an alternative, the thermoplastic preform 10 can be preheated by holding the preform between the first part 210 and the second part 220 of the stamping tool 200 for a determined time, which is carried out before forming the preform. In this case, the first part 210 and the second part 220 are heated to a determined temperature, allowing the preform to be heated to a temperature below the softening temperature of the thermoplastic material by radiation.

[0049] This first step is optional in the method of the present invention. In fact, preheating is not mandatory because the preform can be directly placed in the stamping tool at room temperature. In this example, the preheating step is implemented, and the preform is preheated to a temperature below the softening temperature of the thermoplastic material, which ensures that the preform remains rigid enough for its positioning or fixing in the stamping tool, and the mold is preheated to a temperature close to the temperature selected for the preform.

[0050] The following are some non-limiting examples:

[0051] · For PEI or PESU grades, the upper limit of the preheating temperature is set at 200 °C.

[0052] · For PAEK grades, the upper limit of the preheating temperature is set at 300 °C.

[0053] · For PPS grades, the upper limit of the preheating temperature is set at 250 °C.

[0054] The stamping methods of the prior art require preheating the preform to a temperature higher than the softening temperature of the thermoplastic matrix. Therefore, placing the preform in the softened state in the stamping tool requires a specific operating process that can quickly heat the preform in the softened state and transport it from the heating furnace to the stamping tool. These operations are costly (special furnaces, soft preform transport frames, temperature control, and operation automation) and are often difficult to implement correctly. This process is also not applicable to materials without reinforcements or fillers because it is the presence of the reinforcements that ensures that the softened preform does not deform excessively during the operation of transporting it from the preheating furnace to the stamping unit.

[0055] The method of the present invention avoids all the difficulties and limitations of prior art stamping because the preheating operation outside the stamping tool becomes optional and, if implemented, is carried out at a temperature below the softening temperature of the thermoplastic material, thus eliminating any difficulties in transporting and positioning the preform. One advantage of the method of the present invention is that it is applicable without distinction to filled and unfilled thermoplastic materials.

[0056] Then, the thermoplastic preform 10 is formed. First, the first part 210 and the second part 220 of the stamping tool 200 or at least their respective forming surfaces 211 and 221 are heated to a temperature higher than 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 T SUP 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.

[0057] For this purpose, the first part 210 and the second part 220 of the stamping tool 200 are equipped with rapid heating means, such as a pulsed air heating system, an induction heating system, or any other heating system capable of achieving a heating rate of 30 °C to 100 °C per minute.

[0058] The following are some non-limiting examples:

[0059] · For PEI or PESU grades, the temperature T SUP is between 220 °C and 400 °C.

[0060] · For PAEK grades, the temperature T SUP is between 330 °C and 410 °C.

[0061] · For PPS grades, the temperature T SUP is between 220 °C and 400 °C.

[0062] Once the forming surfaces 211 and 221 of the first part 210 and the second part 220 of the stamping tool 200 reach the temperature T respectivelySUP ,the second part 220 moves towards the first part 210, as Figure 2 shown, until the protrusion 2210 of the second part 220 fully mates with the cavity 2110 of the first part 210, as Figure 3 shown, which corresponds to the closed position of the stamping tool 200. The thermoplastic preform 10 is locally formed in each cavity 2110. During the forming step, the forming surfaces 211 and 221 of the first part 210 and the second part 220 of the stamping tool 200 are maintained at a temperature T above the glass transition or melting temperature of the thermoplastic material SUP . The forming of the preform 10 is completed within a determined period D MEF .

[0063] The first part 210 and the second part 220 of the stamping tool 200 are brought together at a controlled rate so as to gradually compress the preform between the forming surfaces of the first part and the second part. Controlling the rate at which the first part 210 and the second part 220 come together also ensures that the shear level on the preform is below the ultimate shear of the thermoplastic material. The ultimate shear level of the thermoplastic material is usually given in the manufacturer's data, but can also be determined by testing if necessary. As a non-limiting example, provided the performance of the selected press is suitable for the dimensions of the workpiece (in terms of the closing force), the closing rate allowing the die to compress / close can be chosen such that the die closes between a few seconds and a few minutes.

[0064] The pressure PC applied between the first part 210 and the second part 220 of the stamping tool 200 is gradually increased to a compaction pressure value P COMP .

[0065] By maintaining the forming surfaces of the stamping tool at a temperature T above the glass transition or melting temperature of the preform during the forming of the preform SUP , while gradually increasing the pressure between the first part and the second part of the tool, the filling of the cavity of the forming surface of the first part of the stamping tool with the thermoplastic material is precisely controlled.

[0066] This step-by-step forming at a temperature above the glass transition or melting temperature of the thermoplastic preform enables the thermoplastic material to obtain a uniform distribution on the forming surface. In the stamping methods of the prior art, the stamping tool is maintained at a temperature close to the solidification temperature of the thermoplastic material, at which time the solidification time of the material is too short and the compaction pressure is too high, so that the forming process cannot be controlled and a uniform workpiece with good quality cannot be obtained..

[0067] According to the present invention, the forming step is followed by a step of compacting the formed preform in the stamping tool. Compacting includes holding the preform in the stamping tool at the closed position ( Figure 3 ) for a determined duration DCOMP , while applying a compaction pressure P COMP , and maintaining the forming surfaces 211 and 221 of the first part 210 and the second part 220 of the stamping tool 200 at a temperature T above the glass transition or melting temperature of the thermoplastic material SUP . The compaction pressure P COMP is preferably greater than or equal to 100 bar.

[0068] The compaction step is carried out at a temperature where the forming surfaces are maintained above the glass transition temperature or melting temperature of the thermoplastic material of the preform, which ensures that the thermoplastic material in the molten state can completely and uniformly fill the cavities of the forming surfaces, especially when the spacing between the forming surfaces is very small.

[0069] At Figure 3 the closed position of the stamping tool 200 shown, the forming surfaces 211 and 221 of the first part 210 and the second part 220 are arranged opposite each other at a very small distance D 200 , which distance corresponds to the wall thickness E of the acoustic component 120 to be produced from the preform 10 120 ( Figure 4 ). The final wall thickness E 120 is determined at the end of the compaction step.

[0070] After the compaction step, the forming surfaces 211 and 221 of the first part 210 and the second part 220 are cooled to a temperature below or equal to the curing temperature of the thermoplastic material, causing the material to cure in the shape of the acoustic component 120 to be manufactured. When cooling the forming surfaces of the first part 210 and the second part 220 of the stamping tool, the pressure is gradually reduced from the compaction pressure value P COMP to atmospheric pressure, and the reduction of the pressure is controlled so that atmospheric pressure is reached when the forming surfaces of the first part and the second part of the stamping tool reach the curing temperature of the thermoplastic material.

[0071] The cooling of the forming surfaces 211 and 221 of the first part 210 and the second part 220 is preferably carried out in a controlled and accelerated manner, for example by means of a pulsed air cooling system or any other system capable of achieving a cooling rate of 30 °C to 100 °C per minute.

[0072] The die areas defining the boundaries of the forming cavities can also be temperature-controlled in a specific way to avoid burrs or material overflow at the joint surfaces of the fixed and moving parts.

[0073] Then the acoustic component 120 is demolded by moving the second part 220 in a direction opposite to the first part 210 and opening the side clamps to release the acoustic component, as Figure 4 shown.

[0074] Figure 10It is a summary chart of the steps implemented in the method of the present invention. This chart shows the variations in the temperature, pressure, and position parameters of the stamping tool during the steps of the method of the present invention.

[0075] Still according to the present invention, the forming and compaction of the thermoplastic preform last for a total duration D MEF +D COMP , and this total duration is less than a reference duration corresponding to a fraction of the degradation duration of the thermoplastic material of the preform at the first temperature. In fact, given that in the method of the present invention, the thermoplastic material of the preform is exposed to high temperatures during the forming and compaction processes, there is a risk of degradation of the thermoplastic material in these steps. The degradation duration of the thermoplastic material is usually defined in the data of the material supplier. If necessary, the degradation duration of the thermoplastic material can be measured by mechanical and / or physicochemical tests on samples exposed to the expected processing temperature for a specific duration.

[0076] Therefore, a reference duration corresponding to a fraction or percentage of the degradation duration of the thermoplastic material at the processing temperature considered in the forming and compaction steps is defined.

[0077] According to one aspect of the method of the present invention, the reference duration D REF corresponds to 80% of the material degradation duration. Thus, the cumulative duration D MEF of the forming step and the duration D COMP of the compaction step shall not exceed the duration D REF in order to maintain the mechanical and / or physicochemical properties of the thermoplastic material in the final acoustic component.

[0078] As a non-limiting example, the degradation time of a PEI grade at 400 °C is 10 minutes. If 400 °C is selected as the processing temperature for the implementation and compaction steps, the reference duration D REF will be set to 8 minutes. Then it is verified that the sum of the cumulative D MEF and D COMP does not exceed 8 minutes.

[0079] The above method allows the formation of hollow complex acoustic elements with a very thin wall thickness, which can be between 0.1 mm and 0.6 mm. In fact, by keeping the forming surface of the stamping tool at a temperature higher than the glass transition or melting temperature of the thermoplastic material during forming and compaction, it facilitates the uniform distribution of the flow of the material between the forming surfaces, thus reliably and reproducibly manufacturing the acoustic component.

[0080] Then an acoustic component 120 is obtained, as Figure 8 and Figure 9As shown, the component includes a plurality of hollow complex acoustic elements 121, each element tapering from a bottom 122 to a top 123 and having a wall thickness E 121 less than 1 millimeter ( Figure 9 ). The shape of the cavity of the mold defines the shape of the hollow complex acoustic elements of the acoustic component. In this example, the cavity 211 has a pyramid shape, allowing the formation of hollow complex acoustic elements 121 of the same shape. The cavity and thus the resulting hollow complex acoustic elements can have other shapes, such as conical, spiral, funnel-shaped or bucket-shaped.

[0081] The acoustic component manufactured according to the method of the present invention can have a planar shape, as shown in Figure 8 and Figure 9 the acoustic component 120 shown, or a curved shape with single or multiple curvatures. In the latter case, the curvature can be generated directly during the molding of the preform by using a tool with a suitable geometry, or achieved later by molding or thermoforming.

[0082] The thermoplastic preform for manufacturing the acoustic component can have a constant thickness, as shown in Figure 5 the preform 10 shown. The preform can be made of a single piece or obtained by welding several unit films together, such as the unit films 11 and 12 in Figure 5 which, once welded, form a thermoplastic preform 10 with a constant thickness E 10 . The thermoplastic preform can be manufactured from thermoplastic granules by injection or any other suitable method.

[0083] The thermoplastic preform for manufacturing the acoustic component can also have a varying thickness, as shown in Figure 6 and Figure 7 the preform 20 shown. More specifically, the thermoplastic preform 20 has a plurality of excess thickness portions 22, the thickness E 22 of which is greater than the thickness E 21 of the connecting portion 21 of the preform 20, and the connecting portion 21 is located between the excess thickness portions 22 ( Figure 7)。The excess thickness portions 22 are located at specific positions on the preform, which correspond to the positions of the cavities of the first part of the stamping tool. The excess thickness portions 22 constitute a material surplus that, once stretched or flowed into the cavities during the forming of the acoustic component, will allow the formation of a hollow complex acoustic element with a wall thickness close to the connecting portion 21. The material volume in each excess thickness portion is defined according to the wall thickness of each complex acoustic element to be manufactured. The excess thickness portions may have a circular, annular or hexagonal shape and are evenly distributed on the film. In this example, each excess thickness portion 22 extends between the connecting portion 21 and an opening or cavity 222 located at the center of the excess thickness portion. Each opening or cavity 222 is intended to be aligned with the center of the cavity of the mold. According to a specific feature, the central opening or cavity 222 forms a hole. This allows the immediate obtaining of an outlet hole for each complex acoustic element after forming. This avoids additional machining operations. The diameter of the opening or cavity 222 is preferably greater than the diameter of the tooth end of the counter mold 220. As a non-limiting example, in the case where the diameter of the tooth end of the counter mold is 5 mm, the diameter of the hole formed by the central opening is between 6 mm and 7 mm.

[0084] Each excess thickness portion is intended to form, by stretching or creep, a hollow complex acoustic element 121 whose shape tapers gradually from the bottom 122 to the top 123. Thus, it starts from the initial planar surface Spl corresponding to the excess thickness portion, which extends between the connecting portion 21 and the central opening or cavity 222, to a larger projected surface Spr corresponding to the surface of the hollow complex acoustic element 121. The ratio between the initial planar surface Spl and the projected surface Spr defines the elongation factor Fe, which can be between 2 and 5. The principle is the conservation of mass. Thus, the initial planar surface Spl and the initial thickness E of each excess thickness portion 22 22 are determined according to the final projected surface Spr and the thickness E of each hollow complex acoustic element 121 121 according to the following formula:

[0085] Spl×E 22 =Spr×E 121

[0086] In the case of seeking to produce an acoustic component with a constant thickness Ec, the thickness E of the excess thickness portion 22 22 can be determined according to the following formula:

[0087] E 22 =(Spl / Spr)×Ec=Fe×Ec

[0088] In this case, the thickness E of the connecting portion 21 that is not intended to be stretched or creeped 21 roughly corresponds to the final thickness of the acoustic component 120.

[0089] As a non - limiting example, the thickness E of the connecting portion 21 21 can be, for example, 0.5 mm, while the thickness E of the excess thickness portion 22 22 can be 1.6 mm.

[0090] This thermoplastic film with varying thickness can be manufactured by methods such as calendering, machining, stacking unit filaments, injection molding, etc.

[0091] Now, a method of manufacturing an acoustic attenuation structure according to an embodiment of the present invention will be described, with reference to Figure 8 and Figure 9 . Here, the acoustic attenuation structure 100 includes an acoustic skin or acoustic panel 110, an acoustic component 120 manufactured as described above, a plurality of partitions 131, and an enclosing skin or enclosing panel 140.

[0092] The enclosing skin 140 corresponds to a solid surface intended to reflect sound waves entering the acoustic attenuation structure. The enclosing skin can be a component of the acoustic attenuation structure, as described in this example, or correspond to the structure of an object, such as an aero - engine. In the latter case, the acoustic attenuation structure of the present invention does not include the enclosing skin but is directly mounted on the structure of the object.

[0093] The function of the acoustic skin 110 is to allow the sound waves to be attenuated to enter the acoustic attenuation structure 100. For this purpose, in this example, the acoustic skin 110 includes a plurality of perforations 111.

[0094] The acoustic component 120 is formed in one piece, extending in length and width along the horizontal direction D H and in height along the vertical direction D V . The acoustic component includes a plurality of hollow complex acoustic elements 121, and the shape of each element gradually narrows from the bottom 122 to the top 123.

[0095] In this example, the complex acoustic element 121 has a pyramid shape. The bottom 122 of each complex acoustic element 121 is in continuous contact with the bottom of adjacent complex acoustic elements to form a continuous array of edges 124.

[0096] In this example, the plurality of partitions 131 are formed in one piece, i.e., a rib array 130, which forms partitions around the complex acoustic multi - element plate 120 once assembled with it.

[0097] Still in this example, the acoustic attenuation structure 100 is assembled as a whole by combining the complex acoustic multi - element plate 120 with the plurality of partitions 131. The upper edge 131a of the partition 131 is fixed, for example, by adhesion or welding, to the lower part 122b of the bottom 122 of the complex acoustic element 121( Figure 9)。Since multiple complex acoustic elements are formed as a whole within the complex acoustic multi-element plate and multiple partitions are also formed as a whole, the assembly between these two elements is greatly simplified by the self-positioning of the complex acoustic elements and the partitions.

[0098] The closed skin 140 is fixed, for example, by adhesion or welding, to the lower edge 131b of the partition 131, while the acoustic skin 110 is fixed by adhesion or welding to the upper part 122a of the bottom 122 of the complex acoustic element 121, corresponding to the exposed surface of the edge 124. Thus, the acoustic skin and the closed skin are each fixed to a completely flat support in the horizontal direction D H above, which allows ensuring a very good seal between the skin and the assembly of the complex acoustic multi-element plate and the multiple partitions.

[0099] After assembly, the attenuation structure 100 includes multiple acoustic units 150, each acoustic unit being formed by a complex acoustic element 121 and the partition 131 surrounding it ( Figure 9 )。The height H of the complex acoustic element 121 121 is less than the height H of the acoustic unit 150 150 。More precisely, the height H of the acoustic unit 121 is between 10% and 99% of the height H of the acoustic unit 150 in the vertical direction. The height H 121 can be between 5 mm and 100 mm, for example 20 mm, and the bottom of each element 121 can be inscribed in a circle with a diameter between 5 mm and 50 mm (for example 20 mm). Additionally, due to the manufacturing method of the present invention, the hollow complex acoustic element 121 has a very thin thickness E 121 , less than 1 mm, usually between 0.1 mm and 0.6 mm.

[0100] The acoustic skin, the multiple partitions, and the closed skin can be manufactured by injecting thermoplastic or thermosetting materials (with or without filling), by injecting and compressing thermoplastic or thermosetting materials (with or without filling), or by injecting thermoplastic or thermosetting materials (with or without filling) while controlling the tool temperature.

[0101] The multiple partitions, the acoustic and closed skins, and the assembly connecting the multiple partitions and the complex acoustic multi-element plate or the multiple partitions and one of the skins into a whole can also be manufactured by injecting thermoplastic or thermosetting materials (with or without filling).

Claims

1. A method of manufacturing an acoustic component (120) comprising a plurality of hollow complex acoustic elements (121), each acoustic element tapering from a bottom (122) to a top (123), the hollow complex acoustic elements being interconnected by one or more adjacent edges, the method comprising: Placing a thermoplastic preform (10) between a first part (210) and a second part (220) of a stamping tool (200), the first part (210) having a forming surface (211) including a plurality of cavities (2110), the shape of the plurality of cavities (2110) 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 forming surface (221) including a plurality of protrusions (2210), the shape of the plurality of protrusions (2210) being complementary to the cavities (2110), the first part and the second part of the stamping tool being heated to a first temperature above the glass transition or melting temperature of the preform, The thermoplastic preform (10) is formed by closing the first part (210) and the second part (220) of the stamping tool (200) at a certain rate, thereby gradually compressing the preform between the forming surfaces (211, 221) of the first part and the second part until the stamping tool reaches the closed position, and the compaction pressure applied between the first part and the second part of the stamping tool gradually increases to the compaction pressure value (P COMP ), during the forming of the preform, the first part and the second part of the stamping tool are maintained at the first temperature, Compacting the formed preform in the closed position of the stamping tool (200), the compacting being carried out at a compacting pressure value (P COMP ) and for a defined compacting duration, during the compacting of the preform, the first part (210) and the second part (220) of the stamping tool being held at a first temperature, Cooling the forming surfaces (211, 221) of the first part (210) and the second part (220) of the stamping tool (200) to a second temperature below or equal to the curing temperature of the thermoplastic material, Demolding the acoustic component (120) comprising a plurality of hollow complex acoustic elements (121), In this method, the total duration of forming and compressing the thermoplastic preform (10) is less than a reference duration, the reference duration corresponding to a fraction of the degradation duration of the thermoplastic material of the preform at the first temperature.

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

3. The method according to claim 1 or 2, wherein the thermoplastic preform (10) 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 being effected by a heating plate or radiation and being achieved by holding the preform between the first part and the second part of the stamping tool for a determined time before forming the preform.

4. The method according to any one of claims 1 to 3, wherein when cooling the forming surfaces (211, 221) of the first part (210) and the second part (220) of the stamping tool (200), the pressure is gradually reduced from the compaction pressure value (P COMP ) to atmospheric pressure, and the reduction of the pressure is controlled so as to reach atmospheric pressure when the forming surfaces of the first part and the second part of the stamping tool reach the curing temperature of the thermoplastic material.

5. The method according to any one of claims 1 to 4, wherein the thermoplastic material preform (10) has a plurality of excess thickness portions (22) located at specific positions and separated from each other by connecting portions (21), the thickness (E 21 ) of the connecting portions being less than the thickness (E 22 ) of the excess thickness portions, and the positions corresponding to the positions of the cavities (2110) of the forming surface (211) of the first part (210) of the stamping tool.

6. The method according to claim 5, wherein the volume of material in each excess thickness portion (22) is defined according to the wall thickness (E 120 ) of each complex acoustic element to be manufactured.

7. The method according to claim 6, wherein the surface (Spl) and thickness (E 22 ) of each excess thickness portion (22) are defined according to the projected surface (Spr) and thickness (E 121 ) of each hollow complex acoustic element (121).

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

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

10. The method according to any one of claims 1 to 9, wherein the cavities (2110) of the forming surface (211) of the first part (210) of the stamping tool (200) have a pyramidal, conical, helical, funnel-shaped or bucket-shaped form.

11. The method according to any one of claims 1 to 10, wherein the acoustic component (120) of the complex acoustic element (121) has a wall thickness (E 120 ) between 0.1 mm and 0.6 mm.

12. A method of manufacturing an acoustic attenuation structure (100), Comprising the following steps: Manufacturing an acoustic component (120) according to the method according to any one of claims 1 to 11, Manufacturing a complex acoustic multi-component panel that includes acoustic components and a plurality of partitions (131) forming acoustic cavities (132), with each complex acoustic element of the acoustic components being arranged in an acoustic cavity to form an acoustic unit (150). Assembling the face (122a) of the complex acoustic multi-component panel with the assembly face (112) of the acoustic skin.

13. The method according to claim 12, wherein the acoustic attenuation structure (100) further includes an enclosing skin (140) that covers the horizontal plane of the complex acoustic multi-component panel (120) opposite to the horizontal plane covered by the acoustic skin (110), the method including assembling a workpiece connecting the complex acoustic multi-component panel (120) and the plurality of partitions (131) with the enclosing skin (140).

Images