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

Abstract

The invention relates to a method for manufacturing an intermediate resistive membrane (10) called a "septum" with tubular guides (12) for a DDOF type acoustic treatment panel with a double degree of freedom, the method being characterized in that said membrane (10) and said tubular guides (12) are manufactured during the same operation of injecting a resin (13) around a substrate (11) placed between two parts (100a, 100b) of a mold (100) to be injected. 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. 3

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 or carbon, which facilitates the implantation of the tubes due to the transparency of the glass, where appropriate, 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 is proposed for manufacturing an intermediate resistive membrane with tubular guides for an acoustic panel, the method being such that said membrane and said tubular guides are manufactured during the same operation of injecting a resin around a substrate placed between two parts of an injection mold, the mold being configured so that one of the two parts of the mold 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 the mold comprising a plurality of cavities each having a surface of shape complementary to a shape of an outer surface of said tubular guides,the substrate comprising perforations and said method comprising an insertion of each of said protrusions into one of said perforations of said substrate prior to or during a closing of the mold and prior to said injection operation.

[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 thermo composite material dry fiber type plastic.

[0009] - The substrate used comprises short fibers, long fibers or fibers continues.

[0010] - The perforations of the substrate used according to the method are carried out via an operation stamping.

[0011] - The stamping operation included in the process is carried out in a press heated stamping.

[0012] - The injection mold used according to the method comprises a plurality of channels injections dedicated to the manufacture of each of said tubular guides. Brief description of the drawings

[0013] The above-mentioned features of the invention, as well as others, will appear more clearly on reading the following description of an exemplary embodiment, said description being made in relation to the attached drawings:

[0014] [Fig-1] illustrates a septum-type resistive intermediate membrane of a panel DDOF type acoustics manufactured according to a first embodiment;

[0015] [Fig.2] illustrates a septum-type resistive intermediate membrane of a DDOF-type acoustic panel manufactured according to a second embodiment;

[0016] [Fig.3] schematically illustrates a material substrate positioned in an injection mold prior to resin injection manufacturing according to one embodiment; and,

[0017] [Fig.4] illustrates steps in the method of manufacturing a resistive intermediate membrane as shown in [Fig.l].

[0018] DETAILED DESCRIPTION OF EMBODIMENTS

[0019] [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, according to a first embodiment. The term "panel" here designates both an acoustic panel and an acoustic covering. The intermediate resistive membrane 10 comprises a substrate 11 (or reinforcement 11) pre-perforated (i.e. perforated before positioning in the injection mold), called a "consolidated" substrate, coated with a resin 13. The substrate 11 thus comprises a plurality of calibrated openings 11o. The body of the intermediate resistive membrane 10 is therefore made mainly of the resin 13 and the perforated substrate 11. According to this embodiment of the invention, the substrate is a sheet of rigid polymerized thermoplastic material and the resin is a PEKK-type thermoplastic resin possibly containing short fibers.These examples are not, however, limiting and variants may be chosen. For example, a PEEK, LM PAEK or PI type resin may be used depending on the target thickness of the septum, depending on the environment of use and depending on the temperatures of use. The characteristics of these resins are not detailed here since those skilled in the art will know how to choose a resin to use depending on the desired final characteristics. 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. According to a non-limiting embodiment of the invention, the tubular guides 12 each have a frustoconical or substantially frustoconical shape.Perforations 100 of the substrate are arranged opposite tubular guides 12, for the purpose of assembling the tubular guides 12 as a Helmholtz resonator neck, opposite a first cell of a first honeycomb core of an acoustic panel, on the one hand, and opposite a second cell of a second honeycomb core of the same acoustic panel, on the other hand. The tubular guides 12 each have an outer surface 12b and an inner surface 12a shaped by injecting the resin 13 into an injection mold 100 (shown in [Fig. 3]). More generally, the entire membrane . resistive 10 is shaped during a single resin injection operation into an injection mold comprising the perforated substrate 11, of consolidated type.

[0020] [Fig. 2] 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, according to a second embodiment. The term "panel" again designates both an acoustic panel and an acoustic covering. The intermediate resistive membrane 10 comprises a substrate 11' (or reinforcement 11') perforated by the protuberances 102a of the injection mold 100, when the injection mold 100 is closed, then impregnated and coated with a resin 13. The substrate 11' is made of a mesh of short, long, or continuous fibers, or a combination of two or more types of these fibers. 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.

[0021] The body of the intermediate resistive membrane 10 is therefore made mainly of the substrate 11' impregnated with the resin 13 and on which resin 13 is applied. Advantageously, the resistive membrane 10 again comprises a plurality of tubular guides 12 which are each intended to serve as necks of Helmholtz resonators after assembly of a DDOF type panel or covering. In other words, the tubular guides 12 are necks of Helmholtz resonators. According to a non-limiting embodiment of the invention, the tubular guides 12 each have a frustoconical or substantially frustoconical shape.Perforations 10a of the substrate made by inserting the protrusions 102a into the substrate 11 are also arranged opposite tubular guides 12, for the purpose of assembling the tubular guides 12 as a Helmholtz resonator neck, opposite a first cell of a first honeycomb core of an acoustic panel, on the one hand, and opposite a second cell of a second honeycomb core of the same acoustic panel, on the other hand. Just as for the first embodiment, the tubular guides 12 each have an outer surface 12b and an inner surface 12a shaped by injecting the resin 13 into the injection mold 100 (shown in [Fig. 3]). More generally, the entire resistive membrane 10 is shaped during a single resin injection operation into an injection mold comprising the substrate 11' made of a mesh of fibers.

[0022] [Fig. 3] schematically represents an injection mold 100 configured to carry out resin injection operations from an opening 1000 and a plurality of injection channels 103a and 105a. The injection mold 100 is configured for resin injection operations 13. According to an exemplary embodiment, the injection mold 100 comprises an upper portion 100b and a lower portion 100a. The upper portion 100b of the injection mold 100 comprises a plurality of cavities 102b and the lower part 100a of the mold 100 to be injected comprises a plurality of protrusions 102a. According to the embodiment described, each pair of injection channels 103a and 105a is used for shaping by resin injection of a tubular guide 12 into the injection mold 100. The arrangement of the injection mold 100 is therefore made so that, during an operation of injecting the resin 13, and after closing the injection mold 100, the resin injected into residual spaces each defined between a protuberance 102a and a cavity 102b creates the plurality of tubular guides 12 around the perforated substrate 11 or 11' previously inserted into the injection mold 100. The structure of the injection mold 100 is such that to position the substrate 11 or before closing the injection mold 100, the substrate is introduced therein so that each of the protuberances 102 is inserted into one of the perforations 11o of the substrate 11.The closing of the injection mold 100 is carried out by bringing the lower part 100a and the upper part 100b together. When the substrate is the substrate 11', of the fiber mesh type, its perforation is carried out by the protrusions 102a when closing the injection mold 100.

[0023] [Fig.4] is a diagram illustrating a method of manufacturing the intermediate resistive membrane 10 according to one embodiment.

[0024] An initial step S0 is a preparation step for the process, also called an initialization step, at the end of which all the material and / or human resources are available to carry out the manufacturing process of the resistive membrane 10.

[0025] An optional step S1 of perforating the substrate plate is first carried out to obtain the perforations 1 lo in the substrate 11 when the latter is a substrate of the so-called consolidated type, that is to say, for example a sheet of rigid polymerized thermoplastic material as used according to the first embodiment described in relation to [Fig.l]. According to one embodiment, the perforations 11o are then obtained by stamping using a stamping tool (a press). According to a particular and non-limiting embodiment, the stamping operation is carried out in a heated stamping press whose temperature is between 330°C and 400°C for a PEKK resin and according to the tools used. Such stamping, using a heated stamping press, makes it possible to preform the perforated substrate 11, before insertion into the injection mold 100, then closing the mold 100 and injecting the resin 13.Following the perforation of the substrate 11 allowing the perforations 1 lo to be obtained, a step S2 of inserting the substrate into the injection mold 100 is carried out. When the substrate is in the form of a mesh of dry fibers, such as for example according to the second embodiment described in relation to [Fig.2] according to which the substrate is the substrate 11', the optional step S1 is omitted and the substrate 11' is inserted into the injection mold 100 during step S2 immediately after the initial step S0 of preparation for the process. During step S2, the . substrate is placed on the lower part 100a of the injection mold 100 by positioning the protrusions 102a in the perforations 100 when the substrate is pre-perforated. The parts 100a and 100b of the mold are then brought together during a step S3 until the residual space between the lower 100a and upper 100b parts determines the thickness and shape of the resistive membrane 10 which will be obtained after injection. When the substrate is not pre-perforated, that is to say when it is in the form of a mesh of dry fibers, the protrusions 102a are inserted through the mesh of the substrate and pass through it when the lower 100a and upper 100b parts of the injection mold 100 are brought together.

[0026] Finally, the injection of the resin 13 is carried out during a step S4 during which the resin 13 is inserted under pressure through the opening 1000 of the injection mold 100 and spreads throughout the residual space via the plurality of injection channels 103a and the plurality of injection channels 105a. The injection operation is carried out in the injection mold 100 heated to a temperature between 330°C and 400°C in order to obtain the desired level of viscosity of the resin, for example a PEKK resin, for injection. The temperature of the mold is adjusted according to the type of resin used and the desired viscosity and may therefore vary according to the type of resin and the expected level of viscosity. After demolding, a final step of topping the tubular guides 12 is carried out, to create openings at their tops, at the location where the injection channels 103a open. This final step is carried out, for example, by shearing or by mechanical abrasion.

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 single injection operation (S4) of a resin (13) around a substrate (11, 11') placed between two parts (100a, 100b) of an injection mold (100), said mold (100) being configured so that one (100a) of the two parts (100a, 100b) of the mold (100) comprises a plurality of protuberances (102a) each having a surface of a shape complementary to a shape of an inner surface (12a) of said tubular guides (12), and the other (100b) of said two parts (100a, 100b) of the mold (100) comprises a plurality of cavities (102b) each having a surface of shape complementary to a shape of an outer surface (12b) of said tubular guides (12),said substrate (11) comprising perforations (1 lo) and said method comprising an insertion (S2) of each of said protuberances (102a) into one of said perforations (llo) of said substrate (11) prior to or during a closing (S3) of said mold (100) and prior to said injection operation (S4).,

2. Method of manufacturing an intermediate resistive membrane (10) with tubular guides (12) for an acoustic panel according to claim 1, in which the substrate (11, 11') used is made of a thermoplastic composite material of the dry fiber type.

3. A method of manufacturing an intermediate resistive membrane (10) with tubular guides (12) for an acoustic panel according to claim 2, wherein said substrate (11, 11') used comprises 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, wherein said perforations (llo) of said substrate (11) are produced via a stamping operation (SI).

5. A method of manufacturing an intermediate resistive membrane (10) with tubular guides (12) for an acoustic panel according to claim 4, wherein said stamping operation is carried out in a heated stamping press.

6. Method of manufacturing an intermediate resistive membrane (10) with tubular guides for an acoustic panel according to one of the claims- indications 1 to 5, according to which the injection mold (100) used comprises a plurality of injection channels (103a, 103b) dedicated to the manufacture of each of said tubular guides (12).

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