EP2385894A1

EP2385894A1 - Method for making an acoustic attenuation panel, in particular for aeronautics

Info

Publication number: EP2385894A1
Application number: EP09737033A
Authority: EP
Inventors: Guy Bernard Vauchel; Guillaume Ruckert
Original assignee: Aircelle SA
Current assignee: Safran Nacelles SAS
Priority date: 2008-12-22
Filing date: 2009-08-26
Publication date: 2011-11-16
Also published as: FR2940176B1; CA2743352A1; RU2011129699A; CN102256770A; FR2940176A1; RU2519382C2; WO2010072903A1; US20110254196A1; BRPI0923268A2

Abstract

The invention relates to a method for making an acoustic attenuation panel, comprising using at least one foam block (1), coating at least the acoustic surface of said foam block (1) with a fresh composite material (9), and making perforations (27; 27a, 27b, 27c, 27d, 27e) in the resulting coating.

Description

Method of manufacturing an acoustic attenuation panel, in particular for aeronautics

The present invention relates to a method of manufacturing an acoustic attenuation panel, particularly for aeronautics.

Prior art is known acoustic panels with honeycomb core, sandwiched between an acoustic skin provided with perforations and a support skin.

The acoustic skin, usually made of composite material, must be polymerized and then pierced before being assembled on the honeycomb core: a draping with this skin on the soul is indeed not possible in because of the risk of appearance of facets caused by the alveoli of the soul during the pressurization of this soul on the acoustic skin (phenomenon of "telegraphing"); moreover, a piercing of this skin after its polymerization on the soul would inevitably lead to the damage of certain parts of the soul.

It is therefore necessary to provide specific tooling for forming the acoustic skin, as well as a particular manufacturing cycle for this preliminary step. In addition, the acoustic skin during the bonding phase with the core has holes which are blocked by the adhesive or the resin, reducing the effective sound attenuation treatment surface.

The present invention is intended to overcome such a specific tooling and manufacturing cycle. This object of the invention is achieved with a method of manufacturing an acoustic attenuation panel in which at least one foam roll is taken, at least the acoustic surface of this foam roll is coated with a fresh composite material. and perforations are made in the coating thus produced. Thanks to this process, it is therefore no longer necessary to provide a preliminary phase, or specific tooling, manufacturing (polymerization + drilling) acoustic skin: it is actually the foam bread that is, by its relative rigidity, the acoustic skin molding tool, without the risk of appearance of facets (because the foam roll is full, unlike cells of the honeycomb). Due to the use of a foam bead as an acoustic attenuation material, perforations in the composite material once it is in place on the foam bead have no effect on the acoustic performance of the panel: indeed, supposing that a part of the foam is reached by these perforations, it does not in any way affect the quality of absorption or the integrity of the foam bread, contrary to what could happen if the the cells of a honeycomb structure were damaged.

It will be noted moreover that by the coating of the acoustic face of the foam roll with a composite material, a migration of the resin in the thickness of the foam roll can take place, which allows a connection intimate acoustic skin with foam bread.

According to other optional features of the method according to the invention: - the said composite material is draped freshly on said foam roll, that is to say that one:

A) freshly drapes said composite material on a mold of shape complementary to that of the acoustic face of said foam roll, B) comes to apply the acoustic face of said foam roll on said mold,

C) presses the foam roll against the mold,

D) polymerizes said composite material,

E) perforates the acoustic face thus polymerized; prior to step B), the opposite side of the foam cake is also draped, taking care to overflow and join the folds of composite material applied on both sides;

- Counter molds may be used to ensure the cohesion of the folds of composite material on the edges of said foam roll; - The molding is carried out by molding said composite material on said foam roll, that is to say that one:

A) places said roll of composite material between the two halves of a mold, providing a space especially between the acoustic face of said bread and one of the two mold halves, B) injects a thermoplastic or thermosetting resin possibly loaded into the space defined by said half-molds,

C) makes said perforations in the composite material on the side of the acoustic face of the foam cake;

the two half-molds are rigid;

which one half-mold is rigid and the other half-mold is formed by a bladder able to be placed under vacuum;

said perforations are made by molding said composite material, thanks to pins formed on one of the half-molds or on the acoustic face of the foam roll;

perforations are made by piercing said polymerized composite material after opening said mold;

said acoustic panel is made by means of several foam bars;

- Through-holes are provided in said foam roll, so as to allow the casting of reinforcements made of composite material extending between the two faces of the foam roll.

Other characteristics and advantages of the present invention will emerge in the light of the description which follows, and on examining the appended figures, in which:

- Figures 1 to 6 show, in sectional view, different stages of a first variant of the method according to the invention,

- Figures 7 to 16 show, in sectional view (with the exception of Figures 12a and 12b, which show a top view of the element shown in Figure 12), the various steps of a second variant of the method according to the invention, and

FIGS. 17 to 21 represent different options of the method according to the invention, applicable to both the first and second variants mentioned above.

Referring now to Figure 1, there is shown a mouse roll 1 substantially in the form of a curved foam plate.

The foam of the present invention is a relatively rigid material having an open structure, i.e. having many communicating cells, conforming to this material acoustic absorption characteristics.

This foam can be formed from metal, polymer, ceramic or composite material available on the market.

The following table gives different examples of foams that can be used, depending in particular on the thermal stresses to which the panel will be subjected:

In the case chosen to illustrate the present invention, the foam roll 1 is intended to absorb the acoustic waves in a zone of an aircraft engine nacelle, but it goes without saying that this example is in no way limiting. The acoustic face 3 of the foam roll 1, that is to say the face of this foam roll which is intended to be exposed to the sound source whose acoustic energy is to be absorbed, is in this case located at the top of the attached drawing sheet.

As can be seen in FIG. 1, the foam roll 1 has a specific shape that can notably incorporate one or more cavities 5, making this foam roll suitable for a particular installation inside an engine nacelle. plane.

According to a first variant of the method according to the invention, to manufacture an acoustic attenuation panel from the foam roll of FIG. 1, the procedure is as follows.

On a tool 7 whose curve corresponds to that of the acoustic face 3 of the foam roll 1, it comes to drape freshly an organic material impregnated with resin.

The organic material may typically comprise carbon fibers, and the resin may typically comprise an epoxy resin.

The foam roll 1 is then pressed against this draped material 9.

On the face 11 of the foam bread opposite to the acoustic face 3, it is then draped one or more other layers 13 of fresh composite material (Figure 4), preferably so that the folds of composite material overflow foam bread 1 and can join in the peripheral areas 15, 17 of this foam bread.

Then comes to apply, on the assembly thus formed, a bladder 19 within which the vacuum is created (Figure 5): this has the effect of firmly press the folds of composite material 9, 13 and the foam roll 1 against each other.

If necessary, as can be seen in FIG. 5, backing molds 21, 23 may be provided on the periphery of the foam roll 1, so that the emptying bladder 19 exerts a sufficient pressure force on the zone 15, 17 of the folds of composite material 9, 13. The assembly thus obtained is then autoclaved and polymerized at a temperature suitable for the resin used.

Of course, one can also consider the use of a resin that does not require autoclaving and that allows polymerization at room temperature.

After polymerization of the folds 9 and 13, one can proceed to piercing operations of the skin, acoustic. formed by the fold 9 (Figure 6). To do this, it is possible to use a drilling tool that makes it possible to perforate all or part of the racial skin 9; as shown in Figure 6a. Note that during the application of the folds 9, 13 on the foam roll 1, a migration of the resin of these folds takes place towards the foam forming the bread 1.

This migration is interesting because it allows an intimate association of folds of composite material, with. the foam, and therefore excellent cohesion of the whole.

The perforation carried out by means of the tool 25 (FIG. 6) must take into account the migration thickness of the resin in the foam, so as to allow perfect communication between the exterior of the acoustic panel thus produced and the foam forming the bread 1. Once the perforations in the acoustic skin have been made, the panel obtained may be placed for example inside an engine nacelle, for example in the zone of the air inlet lip. of this nacelle or on the engine hood.

In the second variant shown in Figures 7 to 16, it starts from a foam bread similar to that of Figure 1 (Figure 7).

Using a molding tool 7 comprising two rigid half-molds 7a, 7b, whose shapes are adapted to match those of the foam roll 1, while providing a gap 29 at least between the acoustic face of the foam roll 1 and the associated half-mold 7a (FIG. 9). In the example shown in Figure 9, the gap 29 extends on both sides of the foam bar 1, the pins 31 being used to maintain a gap between the lower face (that is to say opposite to the acoustic face) of this foam roll 1 and the associated half-mold 7b.

From the situation of Figure 9, is injected into the mold 7 a resin such as epoxy resin optionally supplemented with one or more charges. This polymerization is then carried out resin, either under autoclave or at room temperature, depending on the nature of the chosen resin.

This leads to the table of Figure 11, wherein the polymerized resin from the previous step ^~ 'réaliseHa ^skin: acoustic 9 and skin 13 on the opposite face of the foam 1 of bread.

It should be noted that in the case where it is desired that these skins be reinforced with fibers, it is conceivable to coat the foam roll 1 with a fiber sock at the stage shown in FIG. 'Rr. vs. ^• - ^• :: ^{• •} - -

Another possibility (not shown) for this second variant is to use a rigid half-mold and a flexible half-mold, the latter being adapted to perform a vacuum of the space between the two half-molds: a An example of a suitable flexible half-mold may be a vacuum bladder.

This particular case in which a rigid half-mold is used is a particular application of the Vacuum Assisted Resin Transfer Molding (VARTM) method (see, for example, the site http://engr.ku.edu/~rhale/ae510/websites_f02/vartmwebsite/ ).

From the step shown in Figure 11, one can achieve the piercing of the acoustic skin 9 under the same conditions as those exposed in the context of the previous variant (see Figures-6 and 6a).

Another alternative for making the perforations inside the acoustic skin 9 is illustrated in FIGS. 12 to 16.

In the example shown in FIGS. 12 to 13, the foam roll 1 is machined so that its acoustic face is provided with a pattern of rectangular foam pads 33 (FIG. 12a) or hexagonal pins 35 (FIG. 12b), or any other appropriate form.

It is understood that with this type of pattern, when placing the foam roll 1 inside the mold 7 (Figure 13) the resin injected into the mold will extend between the hollow portions defined by the Plots 33 and 35. Thus, after polymerization, an acoustic skin 9 is obtained on which the foam pads 33, 35 are flush, thus achieving the desired communication between the foam forming the bread 1 and the sound emission source.

FIG. 14 further shows that it can be envisaged that the separation of the foam roll 1 with respect to the half-mold 7b is carried out not by pins 31 as represented in FIG. 9, but by heelpieces 37 between which is spread the resin defining the skin 13 opposite to the acoustic skin 9.

FIG. 15 shows yet another variant in which only the edges of the face of the foam roll opposite the acoustic face define an interstice with the mold 7b, so that the skin 13 opposite to the acoustic skin 9 does not extend only on the periphery of the moss loaf 1.

Figure 16 illustrates a. variant embodiment of the perforations in the acoustic skin of the panel according to the invention: in this variant, the pads 39 are integral with the rigid half-mold 7a, so as to define perforations in the acoustic skin 9 during the injection of resin inside the mold 7.

The length of these studs .. is..studied. way. to penetrate sufficiently deep inside the foam forming the bread 1, taking into account the migration of the resin inside this foam cake. It will be noted that the orientation of the studs 39 is substantially parallel to the demolding direction D of the molding tool 7; in the particular case where the acoustic surface of the foam roll is curved, as shown in Figure 7, the section of these pads will be studied so that the perforations made in the acoustic skin 9 all have substantially the same section.

In one or other of the variants of the method according to the invention which have just been exposed, it is possible to use a foam roll formed in fact of a plurality of foam rolls 1a, 1b, possibly possessing structural characteristics. and geometrically different, and can be superimposed or side by side, as shown in Figures 17 and 18.

A porous wall 1c may optionally be interposed between these different foam bars 1a, 1b.

It should be noted that both in the first and in the second variant, it is possible to envisage orifices 27a, 27b of different depths, or even orifices 27c passing through the foam roll 1, or even orifices 27d reaching another foam roll Ib (FIG. 19), or even holes 27e opening into cavities 41 formed inside the foam roll 1 (Figure 20). It will also be noted that. it is possible to envisage making machining operations passing through foam buns 1, allowing, during the injection of resin, to perform a ribbing ^• 43 to connect the acoustic skin 9 and the opposite skin 13 together, and thus to give the acoustic panel a particular rigidity, suitable for certain uses.

As will be understood from the foregoing description, the manufacturing method of an acoustic attenuation panel according to the invention is particularly simple: contrary to the state of the art, it is not necessary to first make the acoustic skin.

This is indeed obtained by direct coating of the foam board with a composite material.

Due to its relatively compact and rigid structure, the foam roll can play the role of the molding tool, in particular acoustic skin, and it is therefore not necessary to provide a specific molding tool for carrying out this process. skin,.-Δ The coating of fresh bread foam with a composite material allows for an intimate combination of these materials, and thus excellent cohesion of the whole.

Moreover, as has been illustrated previously, it is no longer necessary to take into account the piercing cycle of the acoustic skin before the manufacturing cycle of the complete acoustic attenuation panel: this piercing can indeed be performed later ( variant of the drapery or variant overmoulding), or at the same time (variant overmolding) as the polymerization of the acoustic skin.

Finally, it should be noted that the foam bread offers a compressive strength that is clearly greater than that which a honeycomb structure can offer, which makes it possible to apply to this foam roll significantly higher pressures, especially when the evacuation step illustrated in Figure 5.

Of course, the present invention is not limited to the embodiments described and shown, provided as simple examples.

Claims

CLAIMS:

1. A process for producing an acoustic attenuation panel in which at least one foam roll (1) is used, at least the acoustic face of this foam roll (1) is coated with a fresh composite material (9), and is carried out of the perforations (27 ^L R27A, ~ _27b. 7 ~ 27c, 27d7 27th ~) ~ in-the coating thus produced.

2. Method according to claim 1, characterized by the fact that said composite material (9, 13) is draped freshly on said foam cake (1), that is to say that:

A) freshly drapes said composite material on a mold (7) of shape complementary to that of the acoustic face (3) of said foam roll (1),

B) comes to apply the acoustic face (3) of said foam roll (1) on this mold (7),

C) presses the foam cake (1) against the mold

(1).

D) polymerizes said composite material (9, 13),

E) perforates the acoustic face (9) thus polymerized.

3. Process according to claim 2. characterized in that, prior to step B), the opposite face (11) of the foam cake (1) is also draped, taking care to overflow and join the folds of composite material (15, 17) applied on both sides (3, 11).

4. Method according to one of claims 2 or 3, characterized in that counter-molds (21 :, .23) are used. to ensure the cohesion of the folds of composite material (15, 17) on the edges of said foam roll (1).

5. Method according to claim 1, characterized in that one proceeds by molding said composite material on said foam roll (1), that is to say that one: A) places said roll of composite material ( 1) between the two halves of a mold (7a, 7b), by providing a space (29) in particular between the acoustic face (3) of said bread and one of the two mold halves, B) injects a thermoplastic resin or heat-curable optionally loaded in the space (29) defined by said half-molds (7a, 7b), C) produces said perforations (27; 27a, 27b, 27c, 27d, 27e) in the composite material (9) on the acoustic face side of the foam roll (1).

6. The method of claim 5, wherein the two half-molds are rigid.

7. The method of claim 5, wherein one half-mold is rigid and the other half-mold is formed by a bladder capable of being evacuated.

8. Method according to any one of claims 5 to 7, characterized in that said perforations (27; 27a, 27b, 27c, 27d,

27e) by molding said composite material, by means of pins (33; 35; 39) formed on one (7a) of the half-molds or on the acoustic face (3) of the foam roll (1).

9. Method according to any one of claims 5 to 7, characterized in that perforations are made by drilling said polymerized composite material (9) after opening said mold (7a, 7b).

10. Method according to any one of claims 5 to 9, characterized in that said acoustic panel is produced by means of several foam bars (1a, 1b, 1c).

11. Method according to any one of the preceding claims, characterized in that there are provided through holes in said foam roll (1), so as to allow the casting of reinforcements of composite material (43) extending between them. two faces (9, 13) of the foam cake (1).