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 A RESISTIVE MEMBRANE INTERMEDIATE LAYER OF AN ACOUSTIC COATING. technical field

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

[0002] Acoustic panels (or coverings) with two degrees of freedom, of the DDOF type (from the English acronym "double degree of freedom"), are known. These acoustic panels perform acoustic treatments aimed at reducing an incident sound wave directed towards one face of such a panel. These acoustic panels comprise two superimposed honeycomb cores (layers) separated by an intermediate resistive layer called a "septum," which intermediate layer includes openings and a multitude of tubular guides, each of which is often associated with a pair of honeycomb cells belonging respectively to one and the other of the two honeycomb cores.The honeycomb cells of such a pair are arranged opposite each other, but are not necessarily perfectly centered, and several tubular guides can be implemented for such a pair of honeycomb cells. Such DDOF-type acoustic panels are used, among other things, in aircraft nacelle walls or turbojet engine casings. Numerous components are assembled to manufacture a DDOF-type acoustic panel or cladding, including the intermediate resistive membrane, which incorporates openings, and the tubular guides (tubes) assembled in or around these openings.Generally, and depending on 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. Description of the invention

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

[0005] To this end, a method for 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 protrusions each having a surface 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 shape complementary to a shape of an outer surface of said tubular guides.

[0006] Advantageously, the manufacture of a resistive "septum" membrane for acoustic treatment panel or coating 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 features considered individually or in combination:

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

[0009] - The thermoplastic material in which the substrate is made comprises fibers referred to as "short fibers", "long fibers", or "continuous fibers".

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

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

[0012] - The thermoplastic film affixed 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 includes the insufflation of hot air via insufflation channels opening at the top of said protuberances of the stamping press. Brief description of the drawings

[0016] The features of the invention mentioned above, as well as others, will become clearer upon reading the following description of an exemplary embodiment, said description being made in relation to the accompanying drawings:

[0017] [Fig.1] illustrates an intermediate resistive septum-type membrane of a DDOF-type acoustic panel manufactured according to an embodiment;

[0018] [Fig.2] schematically illustrates a material substrate positioned in a stamping press prior to the stamping manufacture of the membrane shown [Fig.1], according to one embodiment;

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

[0020] [Fig.4] illustrates steps in the manufacturing process of a resistive intermediate membrane as shown in [Fig.1].

[0021] DETAILED STATEMENT OF IMPROVEMENTS

[0022] Figure 1 schematically and symbolically represents an intermediate resistive membrane 10, referred to as a "septum," arranged to separate two honeycomb cores of the same acoustic panel with two degrees of freedom and manufactured by hot stamping according to an embodiment of the invention. The term "panel" here refers to both an acoustic panel and an acoustic covering. The body of the intermediate resistive membrane 10 is made primarily from a substrate 11 shaped by hot stamping. According to one embodiment, the substrate 11 is made of a consolidated thermoplastic material that may comprise short fibers, long fibers, or continuous fibers and is in the form of a sheet. The characteristics of these fibers are not detailed here, as those skilled in the art will be able to select 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, with or without 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, each of which serves 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 are made in the apexes of the tubular guides 12 during hot stamping, in order to subsequently assemble the tubular guides 12 as Helmholtz resonator necks, each opposite a first cell of a first The two sections of the acoustic panel are: one with a honeycomb core, and the other with a second honeycomb core of the same acoustic panel. The tubular guides 12 each have an outer surface 12b and an inner surface 12a formed 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 formed during a hot stamping operation, possibly preceded by a pre-perforation (or punching) operation to create cutting guides in the substrate 11, which is then coated with an additional layer in the form of a thin thermoplastic film. The resistive membrane 10 has through-holes 100 obtained by stamping, forming the base of the tubular guides 12.

[0025] Figure 2 schematically represents a stamping press 100 configured to perform hot stamping operations on the substrate 11 to obtain the intermediate resistive membrane 10 in its final shape after stamping. The stamping press 100 is configured for stamping operations on the substrate 11. In one 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 consisting of a protrusion 102a and a cavity 102b is used for forming by stamping one of the tubular guides 12 in the stamping press 100.The arrangement of the stamping press 100 is therefore designed so that, during a stamping operation of the substrate 11, and after activation of the stamping press 100 by bringing together parts 100a and 100b, the substrate, crushed in residual spaces defined between a protrusion 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 parts 100a and 100b of the stamping press is such that the crushing produced between the top of each protrusion 102a and the bottom of each cavity 102b cuts off the tubular guides 12, which then each present a through opening conforming to its function as a Helmholtz resonator neck.According to one 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 make pilot holes (punching) or small openings, at locations that will be positioned opposite the protrusions 102a before the stamping operation. These pilot holes are also referred to here as pre-perforations. According to this embodiment, the substrate comprises a . additional layer in the form of a thin thermoplastic film which will also be punched or pre-perforated, in order to be subsequently deformed 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] Figure 3 illustrates a variant of the manufacturing process in which the substrate 11 is coated with a thin thermoplastic film 1 Ir and is pre-perforated when 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. In addition, according to this variant, the lower part 100a of the stamping press 100 includes hot air blowing channels 102o configured to blow hot air at a temperature T between 330 and 400°C into the PEKK resin during the hot stamping operation by the stamping press 100. The temperature T is adjusted according to the material and tooling 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 mold temperature is adjusted according to the type of resin used and the desired characteristics of the glassy state. Thus, the mold temperature can vary depending on the material and will differ depending on whether the material is, for example, a PEEK type resin, a PAEK resin, a PEI resin, or a PEKK resin; these examples are obviously not limiting. The characteristics of these resins are not detailed here, as those 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 target thickness of the septum, the environmental conditions, and the operating temperatures of the produced septum.

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

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

[0030] An optional pre-perforation step SI of an unperforated substrate plate is performed 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, taking into account the presence of the film; otherwise, in the absence of a film, the substrate is directly stamped. In one embodiment, the pre-perforations 1 Ip are obtained by hot stamping using a secondary stamping tool (or press). In a particular, non-limiting embodiment, this operation The hot stamping process for creating pre-perforations is carried out in a heated secondary stamping press with a temperature between 330°C and 400°C, for example, for PEKK resin and depending on the tooling used. This type of stamping, using a heated secondary stamping press, allows for preforming of the perforated substrate 11, which is covered with an additional layer in the form of a thin thermoplastic film, before insertion into the stamping press 100, and therefore before stamping by the stamping press 100.

[0031] The substrate is then placed in the stamping press 100 during a step S2 and 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 thin thermoplastic film 1 Ir and there have been no pre-perforations 1 lp by means of a secondary stamping press during the step SI, then the hot stamping takes place without the blowing of hot air. Conversely, if the SI step of preparing the substrate 11 includes making the pre-perforations 1 lp of the substrate 11 coated with an additional layer in the form of a thin thermoplastic film 1 Ir, then the stamping step S3 includes blowing a flow of hot air by means of hot air blowing channels 102o opening at the tops of the protrusions 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 allows a weld to be obtained 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

Demands

1. A method for manufacturing an intermediate resistive membrane (10) with tubular guides (12) for an acoustic panel, the method being characterized in that a substrate (11) is used and covered with an additional layer in the form of a thermoplastic film (11r), said substrate (11) and said additional layer (11r) being pre-perforated prior to a stamping operation, said membrane (10) and said tubular guides (12) being formed during said hot stamping operation (S3) of said substrate (11) and said layer (11r) 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 shape complementary to a shape of an inner surface of said tubular guides (12) and the other (102) of the said two parts (100a,100b) of said press (100) comprises a plurality of cavities (102b) each having a surface shape complementary to a shape of an outer surface of said tubular guides (12), the stamping operation comprising an insufflation of hot air via insufflation channels (102o) opening at the top of said protrusions (102a).

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

4. Method of manufacturing an intermediate resistive membrane with tubular guides for acoustic panel according to any one of claims 1 to 3, wherein the thickness of said thermoplastic film is less than or equal to 0.2 mm.

5. A method for manufacturing an intermediate resistive membrane (10) with tubular guides (12) for an acoustic panel according to claim 1 or 4, wherein said substrate (11) and said layer additional (1 Ir) are respectively pre-perforated during two perforation operations independent of each other.