GB2583013A

GB2583013A - Mold for manufacturing a soundproofing assembly of a motor vehicle and associated manufacturing method

Info

Publication number: GB2583013A
Application number: GB2001677.0A
Authority: GB
Inventors: Langiny Michel
Original assignee: Faurecia Automotive Industrie SAS
Current assignee: Adler Pelzer France Grand Est SAS
Priority date: 2019-02-11
Filing date: 2020-02-07
Publication date: 2020-10-14
Anticipated expiration: 2040-02-07
Also published as: GB2583013B; GB202001677D0; FR3092517A1; DE102020102785A1; FR3092517B1

Abstract

A mould 30 for manufacturing a soundproofing assembly for a motor vehicle, comprises first and second mould halves 32, 34 defining a cavity 46 which receives a first layer 14 of thermoplastic material, and a free part 46 which receives a foam precursor to form an absorbent layer; wherein the second mould half comprises a protruding rib 56 extending along an outer contour of the inner space. A method for manufacturing using the mould comprises closing the mould, gripping the first layer between the rib and the first mould half, injecting a foam precursor into the free part to form the absorbent layer. When closed, the rib is pressed into the first layer to close the inner space hermetically and avoiding leaks. A resilient layer may be formed on the opposite side of the first layer by injecting a foam precursor in a second mould or by fastening a resilient felt layer. A soundproofing assembly for a vehicle comprises a first layer with a heavy mass with an absorbent layer comprising foam on one face and a resilient layer on the other, wherein the first layer comprises a circumferential groove on the face receiving the resilient layer.

Description

Mold for manufacturing a soundproofing assembly of a motor vehicle and associated manufacturing method The present invention relates to a mold for manufacturing a soundproofing assembly for a motor vehicle, comprising a first half-mold and a second half-mold defining an inner space between them, the inner space being configured to receive a first layer comprising a thermoplastic material, the inner space including a free part extending between the first layer and one of the first half-mold and the second half-mold, the free part being able to receive a precursor of a foam configured to form an absorbent layer. The invention also relates to a manufacturing method implementing said mold.

Such a mold is configured to manufacture soundproofing assemblies in order to address the acoustic problems that arise in a substantially closed space, such as the passenger compartment of an automotive vehicle (mat, roof, door panel, etc.), near noise sources such as an engine (fire wall, etc.), or the tire contact with a road (wheel passage, etc.).

In general, in the low-frequency domain, the acoustic waves created by the aforementioned noise sources undergo a "damping" by materials in the form of single or double sheets (pre-stressed sandwich) having a viscoelastic behavior or by acoustic attenuation of a porous and resilient mass-spring system.

Within the meaning of the present invention, a soundproofing assembly provides "insulation" when it prevents the entry of medium and high frequency acoustic waves into the soundproofed space, essentially by reflecting waves toward the noise sources or the outside of the soundproofed space.

A soundproofing assembly operates by "sound absorption" (in the medium and high frequency field) when the energy from the acoustic waves dissipates in an absorptive material.

A high-performance soundproofing assembly must work both by providing good insulation and absorption. To characterize the performance of such an assembly, the notion of noise reduction (NR) index is used, which takes into account the notions of insulation and absorption: this index can because related using the following equation: NR(dB)=TL -10log(S/A), where TL is the sound transmission loss index (hereinafter referred to as the loss index) reflecting the insulation. The higher this index is, the better the insulation is.

A is the equivalent absorption surface. The higher A is, the better the absorption is. S is the surface area of the part.

In order to produce good soundproofing, for example for a motor vehicle passenger compartment, it is desirable to implement a set of materials that will make it possible to use these two properties wisely. This has been described in many articles, in particular in the article "Faurecia Acoustic Light-weight Concept" from 2002 during the 2002 SIA/CTTM conference in Mans.

In order to provide good acoustic insulation, it is known to use assemblies of the mass-spring type made up of a porous and resilient base layer, on which an impermeable layer with a heavy mass is arranged. This impermeable heavy mass layer generally has a high surface density, in particular greater than 1 kg/m', and a mass density that is also high of around 1500 kg/m3 to 2000 kg/ms.

In order to improve the absorption of the soundproofing assembly, an upper porous layer is added on the heavy mass, capable of dissipating the vibrations of the mass-spring system so as to minimize their transmission toward the passenger compartment.

The upper porous layer is for example made from a foam injected into a mold directly against the heavy mass just after the thermoforming. The still-hot heavy mass is placed in a mold defining a cavity in which a precursor of the foam is injected.

Following the thermoforming of the heavy mass, the latter can have a nonuniform thickness, which may compromise the sealing of the cavity in which the foam is injected. The formed foam then has a nonhomogeneous density, and can even have collapsed regions.

One aim of the invention is to provide a mold allowing an effective injection of absorbent foam on a thermoformed heavy mass, in order to have a good homogeneity and satisfactory acoustic properties.

To that end, the invention relates to a mold of the aforementioned type, wherein the second half-mold comprises at least one rib protruding toward the first half-mold, each rib extending along an outer contour of the inner space, each rib being configured to come into contact against the first layer.

According to specific embodiments of the invention, the mold according to the invention has one or more of the following features, considered alone or according to any technically possible combination: -the rib extends continuously along the outer contour; -the rib has a width decreasing moving away from the second half-mold, in a plane orthogonal to a local extension direction of the rib along the outer contour of the inner space; -the rib has a substantially half-circle-shaped section in the plane orthogonal to the local extension direction; -the rib is integral with the second half-mold; -the first half-mold comprises a closing rim protruding toward the second half-mold, the rib extending across from the closing rim; -the mold contains a first layer pressed against the second half-mold against the or each rib, the first half-mold being able to be pressed on the first layer across from the or each rib to close the inner space hermetically.

The invention also relates to a method for manufacturing a soundproofing assembly for a motor vehicle, comprising the following steps: - providing a mold as described above, -providing a first layer comprising a heated thermoplastic material and placing the first layer in the inner space; - closing the mold by relative movement of the first half-mold toward the second half-mold, and gripping the first layer between the rib and a surface of the first half-mold; -closing a free part of the inner [space], the free part extending between the first layer and one of the first half-mold and the second half-mold; and -injecting a precursor of a foam into the free part and forming the absorbent layer.

According to specific embodiments of the invention, the method according to the invention has one or more of the following features, considered alone or according to any technically possible combination: -the rib extends continuously along the outer contour, the closing of the free part comprises the gripping of the first layer between the rib and the second half-mold, along the outer contour of the inner space, so as to close the inner space substantially hermetically; - the closing of the mold comprises the gripping of the first layer between the rib and the closing rim of the second half-mold protruding toward the first half-mold; -the method also comprises the additional steps of -placing the first layer and the absorbent layer in a second mold; -closing the second mold and forming an inner space extending across from the first layer, on the side opposite the absorbent layer; and -injecting a precursor of a foam configured to form the resilient layer in the inner space and forming the resilient layer, the resilient layer filling a groove formed by the rib during the step for closing the mold; -the method comprises an additional step for fastening a resilient felt on the first layer, on the side opposite the absorbent layer, the felt making up a resilient layer.

The invention further relates to a piece of equipment for a motor vehicle comprising a soundproofing assembly, the soundproofing assembly comprising: -a first layer with a heavy mass; -an absorbent layer comprising a foam, the absorbent layer being received on a face of the first layer; -a resilient layer received on the other face of the first layer, the first layer comprising a circumferential groove on the face receiving the resilient layer, the groove extending along a periphery of the absorbent layer. According to one specific embodiment, the part according to the invention has the following feature: -the resilient layer comprises a foam, the resilient layer filling in the groove.

The invention will be better understood upon reading the following description, provided solely as an example and done in reference to the appended drawings, in which: Figure 1 is a partial sectional schematic view of a soundproofing assembly made using a mold according to the invention; Figures 2 to 6 are schematic sectional views of successive steps for producing the soundproofing assembly of figure 1.

In the rest of this document, the orientations are generally the typical orientations of a motor vehicle. However, the terms "above", "on", "below", "under", "upper" and "lower" are to be understood as relative terms, with respect to the reference surface of the motor vehicle, in light of which the soundproofing assembly is arranged. The term "lower" is thus understood as being situated as close as possible to the surface, and the term "upper" as being situated as far as possible from this surface.

A soundproofing assembly 10 is shown in figure 1. This assembly 10 is configured to be arranged across from a surface 12 of a motor vehicle.

The surface 12 is for example a sheet metal surface of the vehicle in particular defining a floor, ceiling, door, fire wall separating the passenger compartment from the engine compartment, hood, or wheel well of the motor vehicle.

The assembly 10 is configured to be applied directly on the surface 12. It may be attached on the surface 12, advantageously using pins (for example in the case of a fire wall) or placed thereon (for example in the case of a mat). In one variant, the assembly is glued on the surface 12.

As illustrated in figure 1, the soundproofing assembly 10 includes a first central layer 14 with a heavy mass, as well as an upper absorbent layer 16 and a lower resilient layer 18.

In a variant (not shown), the soundproofing assembly 10 further includes a decorative layer, for example a decoration or a carpet, arranged above the absorbent layer 16.

The first layer 14 is formed by an airtight layer with a heavy mass.

Following its manufacture using the method according to the invention described below, the first layer 14 has a circumferential groove 20 extending along the periphery of the absorbent layer 16. The groove 20 is advantageously filled in by the resilient layer 18.

The heavy mass advantageously comprises a thermoplastic material of the polyolefin type, such as a copolymer of ethylene and vinyl acetate, a polyethylene, a polypropylene, an ethylene propylene diene monomer polymer.

The heavy mass advantageously incorporates fillers, such as bitumen, chalk and/or barium sulfate making it possible to obtain a high density for example greater than 1500 kg/m3, preferably greater than or equal to 2000 kg/m3.

The surface density of the heavy mass is advantageously between 0.2 kg/m2 and 10 kg/m2, in particular 1 kg/m2 and 4 kg/m2.

The thickness of the heavy mass is generally between 0.1 mm and 5 mm.

The absorbent layer 16 is for example made with a base of foam, in particular an injected foam or an open-cell split foam. It is for example made from polyurethane. The absorbing layer 16 is thermoformable.

The thickness of the absorbent layer 16 is greater than 5 mm and is for example comprised between 5 mm and 20 mm, and is in particular comprised between 10 mm and 15 mm.

The porosity of the absorbent layer 16 is chosen so that the air flow resistance is advantageously greater than 10000 N.m-4.s, advantageously between 10,000 N.m4.s and 90,000 N.m-4.s, in particular between 25,000 N.m-4.s and 35,000 N.m-4.s.

The resistance to air flow or the resistivity is measured using the process described in the thesis "Measurement of parameters characterizing a porous medium.

Experimental study of the acoustic behavior of low-frequency foams.", Michel HENRY, defended October 3, 1997 University of Mans.

The resilient layer 18 is advantageously light. The density of the resilient layer 18 is for example less than 30 g/I and is advantageously between 8 g/I and 25 g/I.

The resilient layer 18 is made with a base of an injected foam. It is for example made from polyurethane. It is for example made with a base of foam F25 marketed by the company HUNTSMAN.

In a variant, the foam of the resilient layer 18 also contains recycled material, as defined above, and/or 'bio-polyol'.

The density of the resilient layer 18 is between 40 g/I and 80 g/I, and in particular between 45 g/I and 60 g/I.

The thickness of the resilient layer 18, taken perpendicular to the surface 12, is advantageously between 5 mm and 30 mm, for example between 10 mm and 20 mm. In order to have spring properties, the resilient layer 18 advantageously has a Young's modulus greater than 5000 Pa. This Young's modulus is advantageously between 5,000 Pa and 60,000 Pa, in particular between 10,000 Pa and 20,000 Pa. The air flow resistance of the resilient layer 18 is advantageously greater than 10000 N.mts, advantageously between 10,000 N.m-4.s and 90,000 N.m-4.s, in particular between 25,000 N.mts and 35,000 N.m-4.s.

In a variant, the resilient layer 18 comprises a resilient felt assembled by gluing on the first layer 14 with a heavy mass.

Within the meaning of the present invention, "felt" refers to a mixture of base fibers and binder. The base fibers can be noble and/or recycled fibers, natural or synthetic, of one or several types. Examples of natural fibers that can be used are linen, cotton, hemp, bamboo, etc. Examples of synthetic fibers that can be used are inorganic fibers such as glass fibers, or organic fibers such as Kevlar, polyamide, acrylic, polyester, polypropylene.

The binder is preferably a thermosetting resin. Examples of thermosetting resins are epoxy resins, or polyester resins.

Upon leaving the felt production line, these resins have been pre-cross-linked in a furnace so as to provide a partially bonded felt able to be manipulated.

In a variant, the binder is a fusible fiber or a bi-component fiber generally having a polyester core and a co-polyester sheath with a lower melting point than the core. Upon leaving the felt production line, the fusible fibers have melted during the passage in a furnace so as to ensure the cohesion of the felt and to make it able to be manipulated.

Irrespective of the type of binder used, the felt undergoes very little pressure in the fixing furnace, so as to assume its most porous form.

In a variant, the felt comprises a higher percentage of microfibers, for example more than 50%, and advantageously 80% microfibers.

"Microfibers" refer to fibers with a size smaller than 0.9 dtex, advantageously 0.7 dtex.

In one variant, the felt contains recycled material, for example coming from waste of internal or external origin, in particular scraps from automotive equipment parts, manufacturing rejects, or end-of-life vehicle parts. This waste is for example ground and incorporated into the felt in the form of divided pieces of material made up of clumps, flakes or particles. The components of the waste can be separated before or during grinding.

The density of the resilient layer 18, when it is made from felt, is greater than 500 g/m2 and is between 500 g/m2 and 1000 g/m2, advantageously between 600 g/m2 and 750 g/m2.

Its other properties, in particular its thickness, its air flow resistance, and its stiffness in bend are advantageously similar to those described above when the resilient layer 18 is made from foam.

A mold 30 for manufacturing the soundproofing assembly 10 will now be disclosed, in reference to figures 2 to 4. The mold 30 comprises a first half-mold 32 and a second half-mold 34.

The first half-mold 32 and the second half-mold 34 extend across from one another and are translatable relative to one another along a closing direction X-X of the mold 30. The closing direction X-X is for example substantially vertical, the first half-mold 32 then being an upper half-mold and the second half-mold 34 being a lower half-mold.

The mold 30 is shown in figure 2 in the open position, in which the first half-mold 32 and the second half-mold 34 are separated from one another. The first layer 14 made up of a sheet with a heavy mass is arranged between the first half-mold 32 and the second half-mold 34.

In figure 3, the mold 30 is shown in the closed position, with the first half-mold 32 in contact with the second half-mold 34.

The first half-mold 32 and the second half-mold 34 define an inner space 35 between them, configured to receive the first layer 14.

The first half-mold 32 comprises a plate 36 having an inner face 38 extending across from the second half-mold 34 as well as a closing rim 40 and a cutting tool 42, protruding from the inner face 38 toward the second half-mold 34, along the closing direction X-X. The first half-mold 34 further comprises a channel 43 for injecting a precursor of the foam forming the absorbent layer 16, defined in the plate 36.

In figures 2 to 4, the inner face 38 is substantially planar and extends parallel to the second half-mold 34. In a variant, the inner face 38 has a more complex geometry, according to the desired shape of the soundproofing assembly 10.

The closing rim 40 and the cutting tool 42 extend substantially along a closed contour along an outer rim of the first half-mold 32, and have curved local contours or define angles, depending on the desired shape of the soundproofing assembly 10.

In figures 2 to 4, the closing rim 40 and the cutting tool 42 are shown in cross-section, in a plane substantially perpendicular to their local extension direction. When the mold 30 is in the closed position, as shown in figure 3, the inner space 35 comprises a free part 46, defined by the inner surface 38, the closing rim 40 and the first layer 14.

Each closing rim 40 has an inner surface 44 delimiting the free part 46 of the inner space 35, and a closing face 48 of the free part 46, extending substantially parallel to the second half-mold 34.

Each cutting tool 42 comprises a sharp edge 50 oriented facing the second half-mold 34. The sharp edge 50 is for example the wire of a metal blade.

The sharp edge 50 is configured to come into contact with the second half-mold 34 in the closed position and to cut the first layer 14 along the contour of the cutting tool 42, by pinching.

The sharp edge 50 is further from the inner face 38 along the closing direction X-X than the closing face 48. Thus, as shown in figure 2, in the closed position, the closing face 48 bears against the first layer 14 and compresses it, so as to close the free part 46.

The channel 43 for injecting the precursor of the foam forming the absorbent layer 16 emerges in the free part 46 through the inner face 38. It is coupled to a precursor reservoir 51, and to an injection pump 53 able to inject the precursor into the free part 46.

The second half-mold 34 comprises a second plate 52 defining an upper face 54 extending across from the first half-mold 32, on which the first layer 14 rests. The second half-mold 34 comprises a rib 56 protruding from the upper face 54, toward the first half-mold 32, configured to come into contact with the first layer 14.

The rib 56 is in particular made from metal, and advantageously integral with the second half-mold 34. Thus, the rib 56 has improved stability and good resistance to mechanical stresses.

The rib 56 extends along the outer contour of the inner space, across from the closing rim 40. Thus, in the closing position, the rib 56 is in the vicinity of the closing face 48, so as to grip the first layer 14 against the first half-mold 32, as shown in figure 2.

The first layer 14 is then compressed between the rib 56 and the closing face 48, which closes the inner space 35 substantially hermetically, and allows an improved injection in the free part 46 of the inner space 35.

The rib 56 is able to form the groove 20 in the first layer 14 during the gripping.

Advantageously, the rib 56 has a width decreasing moving away from the second half-mold 34, in a plane orthogonal to a local extension direction of the rib 56 along the outer contour of the inner space 35. Thus, the gripping of the first layer 14 between the rib 56 and the closing rim 40 is improved.

In particular, like in the example shown in figures 2 to 6, the rib 56 has a halfcircle-shaped section. In a variant, the rib 56 has a trapezoid, triangle, half-ellipse, or other shaped section.

The rib 56 in particular has a height of between 0.5 mm and 2 mm, for example 1 mm, measured in the closing direction X-X, from the upper face 54 of the second half-mold 34.

The rib 56 in particular has a width of between 1 mm and 5 mm, for example 2 mm, measured at the upper face 54 in a direction orthogonal to the closing direction X-X and the local extension direction of the rib 56.

For example, the rib 56 has a half-circle-shaped section, with a radius equal to 1 mm.

According to a variant that is not shown, the rib 56 has at least one transverse notch, able to form a vent for discharging gases from the inner space 35. The foaming reaction of the precursor configured to form the absorbent layer 16 can generate a significant quantity of gas and form an overpressure in the inner space.2. The first layer 14 is able to deform against each notch under the effect of this overpressure, so as to form a vent on the side opposite the notch. Advantageously, each notch has a width in the extension direction of the rib of between 1 mm and 3 mm, in particular 2 mm. Such a width makes it possible to discharge the foaming gas in case of overpressure, while preventing foam leaks.

According to a variant that is not shown, the second half-mold 34 comprises a plurality of suction orifices defined in the upper face 54 and coupled to a vacuum pump. The suction orifices are arranged to keep the first layer 14 in place against the upper face 54.

A second mold 60 is further disclosed, shown in figures 5 and 6, used to form the resilient layer 18.

The second mold 60 comprises an upper plate 62 and a lower plate 64. The second mold 60 is configured to receive, between the upper plate 62 and the lower plate 64, an assembly formed by the first layer 14 and the absorbent layer 16 bonded to one another.

The upper plate 62 has an inner surface 66 configured to accommodate the absorbent layer 16 received in the second mold 60. This makes it possible to minimize the stresses in the absorbent layer during the formation of the resilient layer 18.

The lower plate 64 has a rim 68 able to support the first layer 14, and defines an inner space 70 for forming the resilient layer, closed by the rim 68.

The lower plate 64 also comprises a pipe 72 for injecting a precursor of the foam configured to form the resilient layer, coupled to an injection pump 74 and to a reservoir 76 containing the precursor.

A method for manufacturing the soundproofing assembly 10 will now be disclosed, in reference to figures 2 to 6.

The method comprises a preliminary step for providing the mold 30 disclosed above, as well as a first layer 14, in particular made up of a heated heavy mass, placed in the inner space 35 of the mold 30 as shown in figure 1.

According to a variant that is not shown, the first layer 14 is draped over the second half-mold by suction through orifices defined in the upper face 54 of the second half-mold 34 and coupled to a vacuum pump. This improves the holding in place of the first layer 14 during the method.

The method next comprises a step for closing the mold 30 by relative movement of the first half-mold 32 and the second half-mold 34, to arrive at the closed position shown in figure 3.

During the closing step, the first layer 14 is gripped between the closing rim 40 and the rib 56, closing the inner space 35 substantially hermetically. The gripping of the first layer 14 deforms the first layer 14 in contact with the rib 56 and forms the groove 20.

The first layer 14 is also cut out by the or each cutting guide 42 during the closing step.

The method next comprises an injection step, shown in figure 4, during which a precursor of the absorbent layer 16 is injected by the pump 53 from the reservoir 51, into the free part 46 of the inner space 35, through the channel 43.

The precursor of the absorbent layer 16 polymerizes and forms the absorbent layer 16 in the inner space 35, in contact with the first layer 14.

The assembly formed by the first layer 14 and the absorbent layer 16 bonded to one another is then removed from the mold, to next form the resilient layer 18.

The assembly is placed in the second mold 60, with the absorbent layer received in contact with the upper half-mold 62, which marries the inner surface 66, as shown in figure 5.

The second mold 60 is then closed, gripping the first layer 14 between the upper half-mold 62 and the lower half-mold 64, and closing the inner space 70.

An injection step shown in figure 6 follows, during which the foam precursor forming the resilient layer 18 is injected into the inner space 70 through the channel 72, by the pump 74, from the reservoir 76.

The foam forming the resilient layer 18 advantageously fills in the groove 20. The precursor then polymerizes and forms the resilient layer 18 in contact with the first layer 14, on the side opposite the absorbent layer 16.

The soundproofing assembly 30 is next removed from the second mold 60.

According to a variant of the method for manufacturing the soundproofing assembly 30, the preceding steps implementing the second mold 60 are replaced by a preliminary step for producing a resilient felt as disclosed above, and a step for attaching the resilient felt to the first layer 14, on the side opposite the absorbent layer 16. The resilient felt is in particular attached by gluing, and forms the resilient layer 18.

The rib 56 makes it possible to compensate for the involuntary differences in thickness of the first layer 14 by becoming embedded in the heavy mass during the closing of the mold 30. This makes it possible to greatly improve the hermetic nature of the closing of the inner space 35.

The substantially hermetic nature of the inner space 35 by gripping of the first layer 14 between the rib 56 and the closing rim 40 makes it possible to avoid leaks of the precursor outside the inner space 35 and the collapses of the foam forming the absorbent layer 16.

One thus obtains a soundproofing assembly having a more homogeneous absorbent layer, and therefore improved acoustic insulation and soundproofing properties. 1. 2. 3. 4. 5. 6. 7.

Claims

CLAIMSA mold (30) for manufacturing a soundproofing assembly (10) for a motor vehicle, comprising a first half-mold (32) and a second half-mold (34) defining an inner space (35) between them, the inner space (35) being configured to receive a first layer (14) comprising a thermoplastic material, the inner space (35) including a free part (46) extending between the first layer (14) and one of the first half-mold (32) and the second half-mold (34), the free part (46) being able to receive a precursor of a foam configured to form an absorbent layer (16), characterized in that the second half-mold (34) comprises at least one rib (56) protruding toward the first half-mold (32), each rib (56) extending along an outer contour of the inner space (35), each rib (56) being configured to come into contact against the first layer (14).
The mold (30) according to claim 1, wherein the rib (56) extends continuously along the outer contour.
The mold (30) according to claim 1 or 2, wherein the rib (56) has a width decreasing moving away from the second half-mold (34), in a plane orthogonal to a local extension direction of the rib (56) along the outer contour of the inner space (35).
The mold (30) according to claim 3, wherein the rib (56) has a substantially half-circle-shaped section in the plane orthogonal to the local extension direction.
The mold (30) according to any one of claims 1 to 4, wherein the rib (56) is integral with the second half-mold (34).
The mold (30) according to any one of claims 1 to 5, wherein the first half-mold (32) comprises a closing rim (40) protruding toward the second half-mold (34), the rib (56) extending across from the closing rim (40).
The mold (30) according to any one of claims 1 to 6, containing a first layer (14) pressed against the second half-mold (34) against the or each rib (56), the first half-mold (32) being able to be pressed on the first layer (14) across from the or each rib (56) to close the inner space (35) hermetically.
8. A method for manufacturing a soundproofing assembly (10) for a motor vehicle, comprising the following steps: -providing a mold (30) according to any one of claims 1 to 7; -providing a first layer (14) comprising a heated thermoplastic material and placing the first layer (14) in the inner space (35); -closing the mold (30) by relative movement of the first half-mold (32) toward the second half-mold (34), and gripping the first layer (14) between the rib (56) and a surface of the first half-mold (32); -closing a free part (46) of the inner [space] (35), the free part (46) extending between the first layer (14) and one of the first half-mold (32) and the second half-mold (34); and -injecting a precursor of a foam into the free part (46) and forming the absorbent layer (16).
9. The method according to claim 8, wherein the rib (56) extends continuously along the outer contour, the closing of the free part (46) comprises the gripping of the first layer (14) between the rib (56) and the second half-mold (34), along the outer contour of the inner space (35), so as to close the inner space (35) substantially hermetically.
10. The method according to claim 8 or 9, wherein the closing of the mold (30) comprises the gripping of the first layer between the rib (56) and the closing rim (40) of the second half-mold (34) protruding toward the first half-mold (32).
11. The method according to any one of claims 8 to 10, also comprising the following additional steps: -placing the first layer (14) and the absorbent layer (18) in a second mold (60); -closing the second mold (60) and forming an inner space (70) extending across from the first layer (14), on the side opposite the absorbent layer (16); and -injecting a precursor of a foam configured to form the resilient layer (18) in the inner space (70) and forming the resilient layer (18), the resilient layer filling a groove (20) formed by the rib (56) during the step for closing the mold (30).
12. The method according to any one of claims 8 to 10, comprising an additional step for fastening a resilient felt on the first layer (14), on the side opposite the absorbent layer (16), the felt making up a resilient layer (18).
13. A piece of equipment for a motor vehicle comprising a soundproofing assembly (10), the soundproofing assembly comprising: -a first layer (14) with a heavy mass; -an absorbent layer (16) comprising a foam, the absorbent layer (16) being received on a face of the first layer (14); -a resilient layer (18) received on the other face of the first layer (14), the first layer comprising a circumferential groove (20) on the face receiving the resilient layer (18), the groove (20) extending along a periphery of the absorbent layer (16).
14. The piece of equipment according to claim 13, wherein the resilient layer (18) comprises a foam, the resilient layer (18) filling in the groove (20).