IMPROVED METHOD FOR MANUFACTURING AN INTERMEDIATE RESISTIVE MEMBRANE FOR AN ACOUSTIC COATING.

Abstract

The invention relates to a method for manufacturing an intermediate resistive membrane (10), referred to as a "septum," with tubular guides (12) for a DDOF-type acoustic treatment panel with two degrees of freedom. The method is characterized in that said membrane (10) and said tubular guides (12) are manufactured during a hot stamping operation of a substrate (11) placed between two parts (100a, 100b) of a stamping press (100), optionally accompanied by the injection of hot air into said press (100) when the substrate (11) comprises an additional layer in the form of a thin thermoplastic film (11r) and pre-perforations (11p). Advantageously, the manufacture of a septum resistive membrane for an acoustic treatment panel or covering is simplified, made more reliable, and its cost is reduced. Fig. 2

Description

Title of the invention: IMPROVED METHOD FOR MANUFACTURING AN INTERMEDIATE RESISTIVE MEMBRANE OF AN ACOUSTIC COATING. Technical field

[0001] The invention relates to a method for manufacturing an intermediate resistive membrane called a "septum" of a so-called double-degree-of-freedom acoustic panel. The invention relates more particularly to a method for manufacturing a septum-type membrane comprising a plurality of integrated tubular guides, for manufacturing an aircraft acoustic panel. STATE OF THE PRIOR ART

[0002] Acoustic panels (or coverings) with a double degree of freedom, of the DDOF type (from the English acronym "double degree of freedom", and which means "double degree of freedom") are known. These acoustic panels carry out acoustic treatments aimed at reducing an incident sound wave directed towards one face of such a panel. These acoustic panels comprise two cellular cores (layers) (most often of the honeycomb type) superimposed and separated by an intermediate resistive layer called a "septum", which intermediate layer comprises openings and comprises a multitude of tubular guides, each of which is often associated with a pair of cellular cells belonging respectively to one and the other of the two cellular cores.The honeycomb cells of such a pair are arranged opposite each other, but are not necessarily completely centered relative to each other and several tubular guides can be implemented for such a pair of honeycomb cells. Such DDOF type acoustic panels are notably, but not exclusively, used in aircraft nacelles walls or in turbojet casings. Many elements are assembled for the manufacture of a DDOF type acoustic panel or covering including the intermediate resistive membrane, comprising openings, and the tubular guides (tubes) assembled in or around these openings.Generally and according to the desired characteristics, the intermediate membrane "septum" is made of glass, which facilitates the implantation of the tubes due to the transparency of the glass, on or in which tubular guides made of polymer material are assembled by means of a robot and sealed, making the manufacture of the assembly complex, delicate and expensive.

[0003] The situation can be improved. Statement of the invention

[0004] An object of the present invention is to improve the manufacturing conditions of a intermediate resistive membrane of an acoustic panel by reducing the number of steps required in order to simplify and speed up the manufacturing process and reduce its cost.

[0005] To this end, a method of manufacturing an intermediate resistive membrane with tubular guides for an acoustic panel is proposed, the method being characterized in that said membrane and said tubular guides are formed during a hot stamping operation of a substrate placed between two parts of a stamping press, said press being such that one of the two parts of the press comprises a plurality of protuberances each having a surface of shape complementary to a shape of an inner surface of said tubular guides and the other of said two parts of said press comprises a plurality of cavities each having a surface of shape complementary to a shape of an outer surface of said tubular guides.

[0006] Advantageously, the manufacture of a resistive “septum” membrane for an acoustic treatment panel or covering is simplified, made more reliable, and its cost is reduced.

[0007] The method for manufacturing an intermediate resistive membrane with tubular guides for an acoustic panel according to the invention may further comprise the following characteristics considered in isolation or in combination:

[0008] - The substrate used according to the method is made of thermoplastic material.

[0009] - The thermoplastic material from which the substrate is made comprises fibers called “short fibers”, called “long fibers” or called “continuous fibers”.

[0010] - The substrate used is covered with an additional layer in the form of of so-called low-thickness thermoplastic film.

[0011] - The thermoplastic film has a thickness less than or equal to 0.2 mm.

[0012] - The thermoplastic film applied to the substrate is loaded with fibers called fibers short.

[0013] - The substrate and the additional layer are pre-perforated prior to the operation hot stamping.

[0014] - The substrate and the additional layer are respectively pre-perforated during two independent perforation operations.

[0015] - The hot stamping operation comprises blowing hot air via blowing channels opening at the top of said protuberances of the stamping press. Brief description of the drawings

[0016] The above-mentioned and other features of the invention will become more clearly apparent from the following description of an exemplary embodiment. lization, said description being made in relation to the attached drawings:

[0017] [Fig.l] illustrates a septum-type intermediate resistive membrane of a DDOF-type acoustic panel manufactured according to one embodiment;

[0018] [Fig.2] schematically illustrates a material substrate positioned in a stamping press prior to manufacturing by stamping the membrane shown [Fig.l], according to one embodiment;

[0019] [Fig.3] schematically illustrates a material substrate positioned in a stamping press according to an alternative embodiment; and,

[0020] [Fig.4] illustrates steps in the method of manufacturing a resistive intermediate membrane as shown in [Fig.l].

[0021] DETAILED DESCRIPTION OF EMBODIMENTS

[0022] [Fig.l] schematically and symbolically represents an intermediate resistive membrane 10, called a "septum", arranged to separate two honeycomb cores of the same acoustic panel with a double degree of freedom and manufactured by hot stamping according to one embodiment of the invention. The term "panel" here designates both an acoustic panel and an acoustic covering. The body of the intermediate resistive membrane 10 is made mainly from a substrate 11 shaped by hot stamping. According to one embodiment, the substrate 11 is made of consolidated thermoplastic material which may comprise short fibers, long fibers or continuous fibers and is in the form of a plate. The characteristics of these fibers are not detailed here since the person skilled in the art will be able to choose the fibers to be used according to the desired final characteristics.

[0023] According to one embodiment, the substrate 11 is coated with an additional layer in the form of a thin thermoplastic film, filled or not with short fibers. This variant is used when hot air is blown during the hot stamping operation of the substrate 11. Advantageously, the resistive membrane 10 comprises a plurality of tubular guides 12 which are each intended to serve as a Helmholtz resonator neck after assembly of a DDOF type panel or coating. In other words, the tubular guides 12 are Helmholtz resonator necks.

[0024] According to a non-limiting embodiment of the invention, the tubular guides 12 each have a frustoconical or substantially frustoconical shape. Perforations of the tops of the tubular guides 12 are made during hot stamping, with the aim of subsequently assembling the tubular guides 12 as necks of Helmholtz resonators, each facing a first cell of a first honeycomb core of an acoustic panel, on the one hand, and facing a second cell of a second honeycomb core of the same acoustic panel, on the other hand. The guides tubular membranes 12 each have an outer surface 12b and an inner surface 12a shaped by hot stamping in a stamping tool 100 also called a stamping press 100 (shown in [Fig.2]). More generally, the entire resistive membrane 10 is shaped during a hot stamping operation possibly preceded by a pre-perforation (or punching) operation for the purpose of creating cutting inlets in the substrate 11 then coated with an additional layer in the form of a thin thermoplastic film. The resistive membrane 10 has through openings 10o obtained by stamping, and forming the base of the tubular guides 12.

[0025] [Fig. 2] schematically represents a stamping press 100 configured to carry out hot stamping operations of the substrate 11 aimed at obtaining the intermediate resistive membrane 10 in its final shape after stamping. The stamping press 100 is configured for stamping operations of the substrate 11. According to an exemplary embodiment, the stamping press 100 comprises an upper part 100b and a lower part 100a. The upper part 100b of the stamping press 100 comprises a plurality of cavities 102b and the lower part 100a of the stamping press 100 comprises a plurality of protrusions 102a. According to the described embodiment, each pair consists of a protrusion 102a and a cavity 102b and is used for shaping by stamping one of the tubular guides 12 in the stamping press 100.The arrangement of the stamping press 100 is therefore made so that, during a stamping operation of the substrate 11, and after activation of the stamping press 100 by bringing the parts 100a and 100b together, the substrate crushed in residual spaces, each defined between a protuberance 102a and a cavity 102b, creates the plurality of tubular guides 12 by deformation of the substrate 11 previously inserted into the stamping press 100. The bringing together of the parts 100a and 100b of the stamping press is such that the crushing produced between the top of each protuberance 102a and the bottom of each cavity 102b tops the tubular guides 12 which then each have a through opening conforming to its function as a Helmholtz resonator neck.According to an alternative embodiment, the substrate 11 is prepared before the hot stamping operation and before its introduction into the stamping press 100 by means of a preparation tool or a second stamping press, calibrated to produce incipient openings (punching) or small openings, at the locations which will be arranged opposite the protuberances 102a before the stamping operation. These incipient openings are also called pre-perforations here. According to this alternative, the substrate comprises an additional layer in the form of a thin thermoplastic film which will also be punched or pre-perforated, for the purpose of being deformed. then under a flow of hot air, at the same time as the substrate 11 will be hot stamped, during a stamping operation in the stamping press 100.

[0026] [Fig. 3] illustrates a variant of the manufacturing method according to which the substrate 11 is coated with a thin thermoplastic film 1 Ir and is pre-perforated when it is placed in the stamping press 100. Pre-perforations 1 Ip are then arranged in the substrate 11 before hot stamping in the stamping press 100. Furthermore, according to this variant, the lower part 100a of the stamping press 100 comprises hot air blowing channels 102o configured to blow hot air at a temperature T of between 330 and 400°C for the PEKK resin during the hot stamping operation by the stamping press 100. The temperature T is adjusted according to the material and the tools used, depending on the desired mechanical properties.

[0027] According to one embodiment, the stamping operation is carried out in a mold heated to a temperature between 330°C and 400°C in order to obtain a glassy state of the PEKK resin. The exact temperature of the mold is adjusted according to the type of resin used and according to the characteristics of the desired glassy state. Thus, the temperature of the mold can vary according to the material and be different depending on whether the material is, for example, a PEEK type resin, a PAEK resin, a PEI resin or a PEKK resin, these examples obviously not being limiting. The characteristics of these resins are not detailed here insofar as the person skilled in the art will be able to choose a resin to use according to the desired final characteristics. The type of resin used is chosen according to the targeted thickness of the septum, the environmental conditions and the operating temperatures of the septum produced.

[0028] [Fig.4] is a diagram illustrating a method of manufacturing the intermediate resistive membrane 10 according to one embodiment.

[0029] An initial step S0 is a step of preparation for the process, also called an initialization step, at the end of which all the material and / or human means are normally available and operational to execute the improved manufacturing process of the resistive membrane 10, according to one embodiment.

[0030] An optional step SI of pre-perforating a substrate plate that has not yet been perforated is carried out to obtain pre-perforations (or perforation starters) 1 Ip in the substrate 11. This step SI is necessary when the substrate is coated with a film, given the presence of the film; otherwise, in the absence of film, the substrate is directly stamped. According to one embodiment, the pre-perforations 1 Ip are obtained by hot stamping using a secondary stamping tool (or press). According to a particular and non-limiting embodiment, this hot stamping operation aimed at producing the pre-perforations is carried out in a heated secondary stamping press whose temperature is between 330°C and 400°C, for example, for PEKK resin and depending on the tools used. Such stamping, using a heated secondary stamping press, makes it possible to preform the perforated substrate 11, covered with an additional layer in the form of a thin thermoplastic film, before insertion into the stamping press 100, therefore before stamping by the stamping press 100.

[0031] The substrate is then placed in the stamping press 100 during a step S2 and then the stamping operation is carried out during a step S3. In the stamping step S3, if the substrate 11 is not covered with the additional layer in the form of a thermoplastic film of low thickness 1 Ir and there have been no pre-perforations 1 Ip by means of a secondary stamping press during the step S1, then the hot stamping takes place without blowing hot air. Conversely, if the step S1 of preparing the substrate 11 comprises the production of the pre-perforations 1 Ip of the substrate 11 coated with an additional layer in the form of a thin thermoplastic film 1 Ir, then the stamping step S3 comprises blowing a flow of hot air by means of hot air blowing channels 102o opening at the tops of the protuberances 102a of the part 100a of the stamping press 100.Advantageously, the blown hot air is heated to a temperature between 330°C and 400°C, for a PEKK resin and depending on the tools used, which makes it possible to obtain a welding by mixing between the substrate 11 and the tubular guides 12, which are then mainly obtained by deformation of the additional layer of resin 11.

Claims

Claims

1. A method of manufacturing an intermediate resistive membrane (10) with tubular guides (12) for an acoustic panel, the method being characterized in that said membrane (10) and said tubular guides (12) are formed during a hot stamping operation (S3) of a substrate (11) placed between two parts (100a, 100b) of a stamping press (100), said press being such that one of the two parts (100a) of the press comprises a plurality of protrusions (102a) each having a surface of shape complementary to a shape of an inner surface of said tubular guides (12) and the other (102) of said two parts (100a, 100b) of said press (100) comprises a plurality of cavities (102b) each having a surface of shape complementary to a shape of an outer surface of said tubular guides (12).

2. A method of manufacturing an intermediate resistive membrane (10) with tubular guides (12) for an acoustic panel according to claim 1, wherein said substrate used is made of thermoplastic material.

3. Method of manufacturing an intermediate resistive membrane (10) with tubular guides (12) for an acoustic panel according to one of claims 1 and 2, according to which the substrate used is loaded with short fibers, long fibers or continuous fibers.

4. Method of manufacturing an intermediate resistive membrane (10) with tubular guides (12) for an acoustic panel according to one of claims 1 to 3, in which said substrate (11) used is covered with an additional layer in the form of a thermoplastic film (llr).

5. A method of manufacturing an intermediate resistive membrane with tubular guides for an acoustic panel according to claim 4, wherein the thickness of said thermoplastic film is less than or equal to 0.2 mm.

6. Method of manufacturing an intermediate resistive membrane with tubular guides for an acoustic panel according to one of claims 4 and 5, in which said substrate (11) and said additional layer (llr) are pre-perforated prior to said stamping operation.

7. Method of manufacturing an intermediate resistive membrane (10) with tubular guides (12) for an acoustic panel according to one of claims 4 to 6, in which said substrate (11) and said additional layer (llr) are respectively pre-perforated during two operations perforations independent of each other.

8. Method for manufacturing an intermediate resistive membrane (10) with tubular guides (12) for an acoustic panel according to one of claims 1 to 7, in which the stamping operation (S3) comprises blowing hot air via blowing channels (102o) opening at the top of said protuberances (102a).

Images