FR3052718B1 - METHOD FOR MANUFACTURING A PIECE OF AUTOMOTIVE EQUIPMENT AND ASSOCIATED PIECE - Google Patents

Abstract

The method comprises the following steps: - providing a porous foam layer in a cavity (24) of a foaming mold (20); forming a foam base layer bonded to the porous layer in the cavity (24) of the foaming mold (20). The provision of the porous layer comprises producing a foam block (18) in the cavity (24) and then compressing the foam block (18) by injecting gas into the cavity (24) prior to forming of the base layer.

Description

Method of manufacturing a piece of automotive equipment and associated part

The present invention relates to a method of manufacturing a piece of automotive equipment, comprising: - providing a porous foam layer in a cavity of a foaming mold; the formation of a foam base layer bonded to the porous layer in the cavity of the foaming mold.

Such a room is particularly suitable for forming a motor vehicle soundproofing assembly. The assembly is intended to solve the acoustic problems that arise in a substantially enclosed space, such as the passenger compartment of a motor vehicle (carpet, pavilion, door panel, etc.), in the vicinity of noise sources such as a engine (apron etc), the contact of tires with a road (wheel well, etc.), etc.

In general, in the low frequency domain, the acoustic waves generated by the aforementioned noise sources are "damped" by materials in the form of single or double sheets (pre-stressed sandwich) having a viscoelastic behavior or acoustic attenuation of a porous and elastic 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 soundproof space, essentially by reflection of the waves towards the sources of noise or the outside of the soundproofed space.

A soundproofing assembly operates by "sound absorption", in the medium and high frequency range, when the energy of the acoustic waves dissipates in an absorbing material.

An efficient soundproofing system must work both by ensuring good insulation and good absorption. To characterize the performance of such a set, we use the notion of sound reduction index NR which takes into account the two notions of isolation and absorption: this index can be calculated by the following equation: NR (dB ) = TL - 10log (S / A) where TL is the sound reduction index (hereinafter weakening index) reflecting the insulation. The higher this index, the better the insulation A is the equivalent absorption surface. The higher A is, the better the absorption.

To achieve good soundproofing, for example for a car interior, it is desirable to implement a set of materials that will play wisely on these two sizes. This has been described, in particular in the article "Faurecia Acoustic Light-Weight Concept" by A Duval of 2002 during the conference SIA / CTTM 2002 at Le Mans.

In particular, it is desirable to obtain light sets, if possible recyclable, having satisfactory absorption and remaining efficient in terms of insulation. US7971683 and US8157051 disclose acoustic complexes comprising a foam base layer, and a porous layer. The layers are interconnected by an intermediate layer. The intermediate layer is made by penetrating the base layer material into the porous layer during foaming of the base layer.

The manufacture of these acoustic complexes requires the porous layer to be made in a first mold, and then the porous layer to be placed in a foaming mold. The method then comprises introducing a precursor material of the foam base layer which is expanded in the foaming mode and which attaches to the porous layer.

Such a method requires the use of different tools to achieve on the one hand, the porous layer, and on the other hand, the base layer. It also requires the displacement of the porous layer once made in the foaming mold. This significantly increases the cycle time, and the cost of manufacture.

An object of the invention is to obtain a method of manufacturing a highly acoustically effective complex, with a foam base layer and a more rigid porous layer, the complex having a reduced cost. For this purpose, the subject of the invention is a process of the aforementioned type in which: the supply of the porous layer comprises the production of a block of foam in the cavity, and then the compression of the block of foam by gas injection in the cavity, before the formation of the base layer.

The method according to the invention can comprise one or more of the following characteristics, taken alone or in any technically possible combination: the foam block fills the cavity before its compression, the gas injection releasing a free volume in the cavity for the formation of the base layer; the formation of the base layer comprises injecting a foam precursor material into the free volume and expanding the foam precursor material to form the base layer and bond it to the porous layer; the expansion of the foam precursor material causes additional compression of the porous layer; the formation, on the foam block, of an air-flow resistance interface layer greater than 4000 Nms-3, before the compression of the foam block, and the application of gas on the layer of foam, interface when compressing the foam block; the formation of the interface layer is carried out by applying a first face of the foam block against a cold surface of the foaming mold delimiting the cavity; a second face of the foam block opposite to the first face is applied against an opposite surface of the foaming mold, having a temperature greater than the temperature of the cold surface; the density of the foam block before compression is less than 60% of the density of the foam block after compression; the process comprises, prior to the formation of the porous layer, a step of introducing an additional layer into the cavity of the foaming mold, the porous layer being bonded to the additional layer after its formation; - The gas injection is performed on the additional layer opposite the foam block, to push the additional layer and compress the foam block. The invention also relates to a piece of motor vehicle equipment comprising: - a porous foam layer; a foam base layer bonded to the porous layer, characterized in that the porous layer is formed of a block of compressed foam, the bond between the porous layer and the base layer being obtained during the formation of the layer basic.

The part according to the invention may comprise one or more of the following characteristics, taken in isolation or in any technically possible combination: the porous layer has an air-resistance interface layer greater than 4000 Nms "3 opposite the base layer The invention will be better understood on reading the description which will follow, given solely by way of example, and with reference to the appended drawings, in which: FIG. 1 is a partial view, taken in section of a first piece of automotive equipment according to the invention; - Figures 2 to 5 are partial views, taken in section, of a manufacturing mold of the first piece, when successive steps of the manufacturing method according to the invention; - Figure 6 is a view similar to Figure 4 of an alternative manufacturing method according to the invention; - Figure 7 is a view similar to Figure 4; Another variant of the manufacturing method according to the invention.

In all that follows, the orientations are generally the usual orientations of a motor vehicle.

A first piece of automotive equipment according to the invention, manufactured by a method according to the invention, is illustrated in FIG.

The piece 10 is intended for example to constitute a soundproofing unit adapted to be arranged facing a surface of a motor vehicle.

The surface is in particular a metal sheet metal surface of the vehicle defining in particular a floor, a ceiling, a door, an apron separating the passenger compartment of the engine compartment, a hood, or a wheel arch of a motor vehicle.

With reference to FIG. 1, the part 10 comprises at least one porous layer 12 and a base layer 14 made of foam, bonded to the porous layer 12.

In this example, the part 10 further comprises an interface layer 16 located between the porous layer 12 and the foam base layer 14.

The porous layer 12 is advantageously a stiffening layer. It has a flexural stiffness B, reduced to a unit width, for example greater than 0.01 N.m, especially between 0.1 N.m and 10.0 N.m. The flexural stiffness B is for example greater than 0.4 Nm, especially greater than 3.0 Nm.

The bending stiffness B is calculated by the equation: B = E.h3 / 12, where h is the thickness of the layer 12, and E is its Young's modulus.

Its Young's modulus, however, remains greater than 105 Pa, especially in the case of significant thicknesses beyond 15 mm (limit value in flexural modulus).

The Young's modulus or modulus of elasticity is measured for example by the method described in standard NF EN ISO 527-3 (static measurement) or advantageously, according to ISO-18437-5 (dynamic method).

The porous layer 12 comprises a compressed open porous foam. As will be seen below, with reference to FIG. 3, the porous layer 12 is obtained by forming a foam block 18 in a foaming mold 20 from a precursor material, and then compressing the foam block 18 in the foaming mold 20.

The porous layer 12 is for example formed based on polyurethane, from a precursor mixture of a polyol and an isocyanate. It advantageously comprises fillers, for example chalk and / or barium sulfate. This increases the density of the layer 12 and thus its insulation properties.

Advantageously, the porous layer 12 comprises waste in the form of agglomerated and bonded foam flakes or different types of recycled materials. The thickness of the porous layer 12 is for example between 1 mm and 25 mm, and is in particular between 5 mm and 10 mm.

The porosity of the porous layer 12 is chosen so that the resistance to the passage of air of this layer 12 is greater than 300 Nm -3 .s and is advantageously between 300 Nm -3 .s and 6000 Nm -3. , especially between 2000 Nm "3.s and 5000 Nmts.

Resistance to the passage of air or its resistivity is measured by the method described in the thesis "Measurements of parameters characterizing a porous medium.Experimental study of the acoustic behavior of foams at low frequencies.", Michel HENRY, defended on October 3, 1997 at the University of Le Mans.

The density of the porous layer 12 is advantageously between 10 kg / m 3 and 150 kg / m 3, preferably between 90 kg / m 3 and 100 kg / m 3.

The foam forming the porous layer 12 may have a high tortuosity, especially greater than 1.4 and advantageously between 1.4 and 3, as described in the application WO-2007/006950 of the Applicant. This tortuosity is measured by determining the slope of the curve representing the variation of the square of the refractive index for the acoustic wavelength used, as a function of the inverse of the square root of the frequency.

The foam base layer 14 is obtained according to the process according to the invention by expansion of a precursor material in the foaming mold 20 illustrated in FIG. 2.

Advantageously, the precursor material is similar to, or identical to, that used to form the porous layer 12.

The flexural stiffness B of the foam base layer 14 is smaller than that of the porous layer 12.

The foam base layer 14 advantageously has a porosity adapted to present a resistivity to the passage of air advantageously between 10000 Nm "4.s and 90000 Nm" 4.s including equal to about 30000 Nm "4.s.

The density of the foam base layer 14 is for example between 30 kg / m3 and 90 kg / m3 and in particular about 50 kg / m3. The thickness of the foam base layer 14 is advantageously between 5 mm and 30 mm, for example between 10 mm and 15 mm.

The foam base layer 14 advantageously has spring properties. In this case, the foam base layer 14 has an elastic modulus greater than 10,000 Pa. This modulus is advantageously between 20000 Pa and 100000 Pa, in particular between 30000 Pa and 40000 Pa.

The interface layer 16 has a resistance to the passage of air greater than 4000 Nm.s.sup.-3, and advantageously between 4000 N.m.s.sup.-3 and 6000 N.m.sup.-3.

In a variant, the interface layer 16 is impervious to the passage of air. By "tight passage of air" is meant that its resistance to the passage of air is too high to be measured by the method described above.

The interface layer 16 has a thickness less than that of the porous layer 12, advantageously a thickness of between 1 mm and 4 mm.

The density of the interface layer 16 is greater than 50 g / m 2 and is in particular greater than 150 g / m 2, advantageously greater than 210 g / m 2. This mass per unit area is in particular between 250 g / m2 and 1100 g / m 2.

The surface density of this interface layer 16 is in any case lower than that of a conventional heavy-mass layer which is of the order of 1500 g / m 2.

As will be seen below, the intermediate layer 16 is formed on the porous layer 12. Unlike the products mentioned in the preamble for which the intermediate layer 16 is obtained by filling the pores or interstices formed in the porous layer 12 with the aid of foaming material injected during the production of the foam base layer 14, the intermediate layer 16 according to the invention is actually an interface layer without or with very little penetration into the layer 12.

The manufacturing method according to the invention is implemented in an installation 22 visible in FIGS. 2 to 5. In addition to the mold 20 defining a cavity 24 for foaming, the installation 22 comprises an assembly 26 for injecting the precursor material intended to forming the porous layer 12 and the foam base layer 14 in the foaming cavity 24.

According to the invention, the installation 22 further comprises an assembly 27 for applying a pressure in the foaming cavity 24 by injecting gas into the foaming cavity 24. The installation 22 further comprises a set 29 of degassing, and a set 33 for selectively controlling the temperature of the mold 20.

The mold 20 comprises a first half-mold 28 for supporting the porous layer 12, and a second half-mold 30 for closing the cavity 24.

The half-molds 28, 30 are movable relative to each other between an open access position to the cavity 24 and a closed foaming position in the cavity 24.

The first half-mold 28 defines a mold surface 31 and fluid injection orifices 32, opening into the mold surface 31 and connected to the application assembly of a pressure 27.

The density of orifices 32 is for example between 1 orifice per square meter and 8 holes per square meter.

A distance, taken along the surface 31, of between 100 mm and 300 mm, in particular between 150 mm and 250 mm, advantageously separates two adjacent orifices 32. The transverse extent of each orifice 32, in particular their diameter when their section is circular, is between 3 mm and 10 mm.

The second half-mold 30 defines a closure surface 34 of the mold 20, intended to be placed facing and away from the mold surface 31. The injection assembly 26 is able to bring the precursor material into the mold. cavity 24. The pressure application assembly 27 is capable of injecting gas, through each orifice 32, to apply a pressure in the cavity 24.

The pressure of the injected gas is for example greater than 0.5 bar relative and is in particular between 1 bar relative and 5 bar relative. The degassing assembly 29 is capable of evacuating the excess gases present in the foaming cavity 24, in particular resulting from the foaming of the precursor material. The degassing assembly 29 is for example a pilot vent, or a quick opening mechanism of the mold 20. The selective temperature control unit 33 of the mold 20 is able to regulate the temperature of the mold surface 31 to a temperature lower than that of the closure surface 34. For example, the selective control assembly 33 is able to regulate the temperature of the mold surface 31 so that this temperature is at least 10 ° C lower than the temperature closing surface 34.

A first manufacturing method according to the invention will now be described with reference to FIGS. 2 to 5.

Initially, as illustrated in FIG. 2, the mold 20 is closed to define the foaming cavity 24 between the mold surface 31 and the closure surface 34. In this example, the foaming cavity 24 is initially empty.

A foam precursor material is injected by the injection assembly 26 into the foaming cavity 24. The precursor material reacts and increases in volume to occupy the entire volume of the foaming cavity 24.

It thus forms a block of foam 18, visible in FIG. 3, having a first density, for example between 20% and 70% of the density of the porous layer 12. The selective temperature control assembly 33 is activated for regulating the temperature of the mold surface 31 to a temperature below that of the closure surface 34 by at least 10 ° C.

The temperature of the mold surface 31 is, for example, between 40 ° C. and 60 ° C., in particular between 45 ° C. and 75 ° C. The time of the closing surface 34 is for example between 45 ° C and 85 ° C, especially between 70 ° C and 80 ° C.

The mold surface 31 therefore constitutes a cold surface on which the material forming the foam block 18 forms a skin locally, constituting the interface layer 16.

The closure surface 34 constitutes a hot surface, which facilitates obtaining an open foam having satisfactory acoustic properties. The degassing assembly 29 is then activated to evacuate the excess of the gases generated by the foaming of the precursor material.

Then, as illustrated in FIG. 3, the application assembly of a pressure 27 is put into operation. Pressurized gas is injected through the orifices 32 against the interface layer 16 formed on the foam block 18.

The pressurized gas pushes the interface layer 16 toward the closure surface 34 and thereby compresses the foam block 18 to the closure surface 34.

The density of the foam block 18 thus increases to reach a value of between 90% and 100% of the density of the porous layer 12.

The volume of the foam block 18 decreases correspondingly to release a free volume 40 in the cavity 24. The free volume 40 is delimited on one side, by the mold surface 31 and on the other side, by the outer layer. interface 16.

During compression, the crushing of the foam block 18 further opens the porous cells within the foam, improving the acoustic properties, especially absorption.

Then, as illustrated in FIG. 4, the precursor material is injected again into the free volume 40 of the cavity 24. The precursor material reacts and increases in volume to occupy the entire free volume 40.

Advantageously, the precursor material which expands in the free volume 40 slightly compresses the foam block 18 by relying on the interface layer 16.

The precursor material then solidifies and adheres simultaneously on the interface layer 16.

Thus, the porous layer 12, the interface layer 16, and the base layer 14 are formed together and are joined together in the same foaming cavity 24 of the mold 20. The thickness and density of the porous layer 12 is adjusted by choosing the appropriate density of the foam block 18 before compression, and the pressure to compress it to the desired thickness of the porous layer 12.

The manufacturing process of the part 10 is particularly simple, since it is implemented in a single mold, advantageously using the same precursor material, with a minimum cycle time.

This significantly reduces the cost of the part 12 while maintaining very satisfactory acoustic properties.

In a variant, shown schematically in Figure 6, the part 12 comprises an additional layer 50, for example a carpet.

The additional layer 50 is introduced into the foaming cavity 24 prior to the formation of the foam block 18. It is applied against the closure surface 34.

The manufacturing process of this part 12 is moreover analogous to the processes described in FIGS. 3 to 5.

However, unlike this method, the foam block 18 when formed before compression, adheres to the additional layer 50. It is pressed against the additional layer 50 during the pressure applying step on the foam block 18.

In another variant, shown schematically in FIG. 7, the part 12 comprises an advantageously impermeable intermediate layer 52 interposed between the base layer 14 and the interface layer 16. The intermediate layer 52 is, for example, an impermeable layer, especially a layer of heavy mass.

The heavy-mass layer advantageously comprises a thermoplastic material of polyolefin type (Ethylene Vinyl Acetate, Polyethylene, Ethylene Propylene Diene Monomer) and incorporates fillers of the bitumen, chalk and / or barium sulfate type.

The Young's modulus of the intermediate layer 52 is less than 1000 MPa. The intermediate layer 52 has a density greater than or equal to 1500 kg / m 3, preferably greater than or equal to 2000 kg / m 3, a weight per unit area of between 0.2 kg / m 2 and 9 kg / m 2 and advantageously a thickness of between 0.1 mm and 5 mm. The injection assembly 26 comprises at least one orifice 54 for injecting precursor material on one side of the foaming cavity 24, and at least one additional orifice 56 for injecting precursor material on the other side of the foaming cavity 24.

For the implementation of the manufacturing method, the intermediate layer 52 is first applied against the mold surface 31. The foam precursor material for forming the foam block 18 is then injected through the additional orifice 56. It fills the foaming cavity 24 and is fixed on the intermediate layer 52.

Then, as previously described, the pressure application assembly 27 is activated, which pushes the intermediate layer 52 away from the mold surface 31 and compresses the foam block 18 between the intermediate layer 52 and the closure surface 34, releasing a free volume 40.

The base layer 14 is then formed as described above, by injecting precursor material through the injection orifice 54. The base layer 14 is bonded to the porous layer 12 via the intermediate layer 52.

Claims (12)

1. - A method of manufacturing a piece (10) of automotive equipment, comprising the following steps: - supply of a porous layer (12) of foam in a cavity (24) of a foaming mold (20) ; forming a foam base layer (14) bonded to the porous layer (12) in the cavity (24) of the foaming mold (20); characterized in that the provision of the porous layer (12) comprises producing a foam block (18) in the cavity (24), and then compressing the foam block (18) by injecting gas into the cavity (24), before the formation of the base layer (14). 2. - The method of claim 1, wherein the foam block (18) fills the cavity (24) before its compression, the injection of gas releasing a free volume (40) in the cavity (24) for the formation of the base layer (14). The method according to any one of claims 1 or 2, wherein the formation of the base layer (14) comprises injecting a foam precursor material into a free volume (40) and expanding the foam precursor material for forming the base layer (14) and bonding it to the porous layer (12). 4. - The method of claim 3, wherein the expansion of the foam precursor material causes additional compression of the porous layer (12). 5. - Method according to any one of the preceding claims, comprising forming, on the foam block (18), an interface layer (16) of resistance to the passage of air greater than 4000 Nms "3 prior to compressing the foam block (18), and applying gas to the interface layer (16) upon compression of the foam block (18). 6. - Method according to claim 5, wherein the formation of the interface layer (16) is performed by applying a first face of the foam block (18) against a cold surface (31) of the foaming mold ( 20) delimiting the cavity (24). 7. - The method of claim 6, wherein a second face of the foam block (18) opposite the first face is applied against an opposite surface (34) of the foaming mold (20), having a temperature above the temperature cold surface (31). 8. - Method according to any one of the preceding claims, wherein the density of the foam block (18) before compression is less than 60% of the density of the foam block (18) after compression. 9. - Process according to any one of the preceding claims, comprising, before forming the porous layer (12), the step of introducing an additional layer (50; 52) in the cavity (24) of the mold foaming agent (20), the porous layer (12) being bonded to the additional layer (50, 52) after formation thereof. The method of claim 9, wherein the gas injection is performed on the additional layer (52) opposite the foam block (18), to push the additional layer (52) and compress the block of foam (18). 11. - Piece (10) of automotive equipment comprising: - a porous layer (12) of foam; - a base layer (14) of foam bonded to the porous layer (12), characterized in that the porous layer (12) is formed of a compressed foam block (18), the connection between the porous layer (12) ) and the base layer (14) being obtained during the formation of the base layer (14). 12. - Part (10) according to claim 11, wherein the porous layer (12) has an interface layer (16) of resistance to the passage of air greater than 4000 Nms'3 opposite the layer of base (14).