WO1999061221A1

WO1999061221A1 - Method for producing a dual-shell component with integrated lambda/4 absorbers

Info

Publication number: WO1999061221A1
Application number: PCT/CH1999/000216
Authority: WO
Inventors: Robert Van Ligten
Original assignee: Rieter Automotive (International) Ag
Priority date: 1998-05-22
Filing date: 1999-05-20
Publication date: 1999-12-02

Abstract

The invention relates to a method for producing dual-shell components with integrated μ/4 resonators. A first injection-moulded part (5) provided with troughs (6) is placed on a grid (4) that is disposed in a form tool. The grid is configured in such a way that a pressure medium introduced into the enclosed mould can flow into the chambers that are formed by the grid. The first moulded part (5) also has a plurality of openings on said troughs. Preferably, a moulded part (9) that is to be joined to the injection-moulded part (5) is composed of a thermoplastic material and is permeable to air. The second moulded part (9) is joined to the first moulded part (5) when the form tool is closed and the second moulded part (9) is pressed against the second the contour of the upper half of the mould (3) by the pressure medium that is let in through the grid. This prevents the softened second moulded part (9) from sagging over the troughs that are formed in the first moulded part (5).

Description

Process for producing a two-shell component with integrated λ / 4 absorbers

The present invention relates to a method for producing a two-shell component according to the preamble of claim 1, and to a component produced by this method, in particular a vehicle part.

Today's vehicles have double-walled structures at various points, which generally consist of sandwiched, flat molded parts with an optically appealing outer skin and a dimensionally stable flat carrier part. This dimensionally stable

Carrier parts generally have bead-like deformations which lead to the formation of cavities in the assembled state. As a rule, these molded parts are glued together. The aim of this design is to create vehicle components that are as light as possible and sufficiently rigid. The separate deformation and subsequent gluing of the individual molded parts proves to be relatively expensive.

These cavities are increasingly used in modern vehicles to produce acoustically effective components. In particular, these cavities can be dimensioned such that they act as λ / 4 absorbers. Such λ / 4 absorbers and their mode of action are known, for example, from W096 / 23294. It is essential that the

Mouth openings of the individual λ / 4 resonators directly adjoin a sound-reflecting surface. If a sound wave front falls on such a surface, a sound pressure maximum builds up directly in front of this surface. The incident one runs in the mouth region of the λ / 4 resonators

However, sound wave into the resonator, is reflected at its end and runs back to the mouth opening. Sound waves, the wavelength of which is 4 times the length of the resonator, appear at the mouth opening a phase shift of half a wavelength. This leads to destructive interference with the wave of the same wavelength reflected in the mouth region of the resonator, since the standing wave generated in the resonator has its sound pressure minimum at the mouth opening, while the wave reflected in the mouth region has its sound pressure maximum there. This creates a strong sound pressure gradient in the mouth area, which contributes locally to high air flow velocities and thus to the desired dissipation of acoustic energy.

From this understanding it becomes clear that the λ / 4 resonators can be arranged in any direction and also do not necessarily have to have a straight course. Likewise, the person skilled in the art can adapt the length and cross section of the λ / 4 resonators to the desired shapes and selected resonance frequencies. In particular, the λ / 4 resonators can be tubular or pocket-shaped. If sound absorption over a wide frequency range is desired, several can

Groups of differently tuned λ / 4 absorbers are nested inside one another.

λ / 4 resonators differ significantly from ordinary Helmholtz resonators and in particular in that their absorption frequency is determined by the transit time of the incident sound wave, while in Helmholtz resonators the transit time of the incident sound waves is irrelevant. This can be explained as a model in that Helmholtz resonators can be described as a spring-mass system and their resonance frequency can be derived from the volume of the Helmholtz body and that of the resonator neck.

Methods are known to the person skilled in the art with which hollow

Moldings can be produced in a simple manner. For example, US Pat. No. 5,705,107 describes an injection molding process discloses in which a plastic melt is introduced into the mold space of a molding press and a compressed gas is introduced into the plastic melt in a controllable manner before it hardens. As a result, voids can be created in a targeted manner in the plastic part to be molded. This method is not suitable for the production of molded parts with integrated λ / 4 absorbers, in particular because of the large number of openings required for this.

For the production of vehicle parts with integrated λ / 4-

For this reason, absorbers have already been tried to construct them as two-part components. A first part, which forms the λ / 4 absorber chambers, is deep-drawn and subsequently provided with appropriate openings before it is connected to a second part. Because of these openings resp. Breakthroughs cannot be deep-drawn with the λ / 4 absorber chambers in the molding process, but have to be processed subsequently, i.e. with openings. These known deep-drawing processes are therefore not suitable for producing vehicle parts with integrated λ / 4 absorbers in a simple manner.

EP 0 761 412 discloses a method for molding two-shell vehicle parts, with which molded bodies with cavities can be produced starting from two thermoelastic synthetic resin plates. These plates are placed in a mold, the plates are heated and softened before hot compressed gas is introduced between these plates in order to press the softened plates against the surfaces of the two mold halves, ie apart. The hollow shaped body produced in this way is cooled while maintaining the gas pressure. This method is also unsuitable for the simple manufacture of acoustically active molded parts with λ / 4 absorbers, and in particular not for the use of plates which have been perforated beforehand, without a subsequent necessary to open the λ / 4 absorber chambers.

It is therefore an object of the present invention to provide a method with which two-shell components, respectively. Vehicle parts with integrated λ / 4 absorbers, in particular parcel shelves, in a simple manner, i.e. can be produced inexpensively.

This object is achieved according to the invention by a method having the features of claim 1 and in particular by a method in which a first molded part with a plurality of openings for the λ / 4 resonators is injection molded in a first step in a second step second plate-shaped plastic molded part is provided without openings and in a third process step the two molded parts are connected to one another with the help of a compression molding process and brought into their final shape.

Preferred developments of the method according to the invention have the features of the subclaims.

The invention will be explained in more detail below with the aid of the figures and with the aid of exemplary embodiments.

1 shows a molding tool suitable for the manufacture of openwork, two-shell vehicle parts;

2 shows an injection molded part suitable for the manufacture of openwork, two-shell vehicle parts;

Fig. 3 shows a section of the arrangement shown in Figure 1;

Fig. 4 shows a preferred injection molded part; 5 shows a two-shell molded part produced according to the invention with integrated λ / 4 absorbers.

FIG. 1 shows a mold 1 suitable for the production of two-shell vehicle parts with integrated λ / 4 absorbers, with a first mold half 2 and a second mold half 3. It goes without saying that this mold 1 is provided with means for the two mold halves to heat. The first mold half 2 is designed such that a pressure medium, for example a gas conveyed via a first pressure line 8, can be introduced into the closed mold 1. For the manufacturing method according to the invention, a grid 4 designed in a suitable manner is attached to the first mold half 2. This grid 4 supports a first injection-molded part 5 with trough-shaped or box-shaped depressions 6 such that these depressions 6 come to lie between the ribs 7 of the grid 4 and the injection-molded part 5 lies completely on the ribs 7. For this purpose, the ribs 7 of the grid 4 are adapted to the geometric arrangement and dimensioning of the preformed first molded part 5. The grid 4 has openings through which the introduced gas can flow. In the manufacturing method according to the invention, a second plate-shaped molded part 9 is placed over the first molded part 5 supported in this way, which is preferably a thermoplastic sheet product and can be provided with a decorative layer. This plate 9 must be air-impermeable for the formation of effective λ / 4 absorbers, which can be accomplished, for example, by means of a suitable film or choice of material. It goes without saying that the second mold half 3 can be provided at suitable points with vacuum lines 11 which pull the second mold part 9 against the second mold half 3 or, if the mold is closed, remove any residual air from the second mold half 3. FIG. 2 shows a top view of an injection-molded first molded part 5 with molded-in troughs 6. These troughs 6 can be trough-shaped or box-shaped, are provided with openings 12 at one of their ends and are dimensioned such that they are an effective acoustic system of λ / 4 - Form absorbers. In a preferred embodiment, these troughs 6 have a length of 50 mm to 200 mm, a depth of approximately 8 mm to 30 mm and a width of 10 mm to 20 mm. The openings 12 provided at the ends are, for example, 1.5 mm or 2 mm wide

Slits formed, which are spaced from each other by 1.75 mm or 3 mm.

Various embodiments for the first mold half 2 and the associated grating 4 are to be discussed with reference to FIG. 3. In one conceivable embodiment, the grid 4 is integrated with the first mold half 2. The first pressure line 8 leads the pressure medium via inlet openings 13 into each of the required lattice chambers 14. In a simplified embodiment, the walls 15 of the lattice chambers 14 are broken through in such a way that the pressure medium is passed from one of the lattice chambers 14 into all other lattice chambers 14 through only one inlet opening 13 can flow. In a preferred embodiment, the grid 4 is not an integral part of the first mold half 2, but is interchangeably placed on this mold half 2. In any case, the top of the walls 15 resp. the ribs 7 a profile, which coincides with the predetermined shape of the injection molded part 5. It is essential here that the ribs 7 of the grid 4 each abut the preformed molded part 5 and enclose the trough-shaped or box-shaped depressions 6. A plate-shaped, previously heated thermoplastic second molded part 9 is placed on the first injection-molded part 5 supported in this way before the mold 1 is closed. With the molding tool 1, the hot thermoplastic plate 9 is deformed and can with the preformed Connect injection molding 5. In order to prevent the thermoplastic molding 9 from sagging over the troughs 6, a pressure medium is introduced into the closed molding tool 1 via the pressure line 8. This pressure medium can get into each of the lattice chambers 14 and flows through the already existing openings 12 of the preformed injection molded part 5 into the troughs 6. Thereby, the thermoplastic molded part 9 in the region of the troughs 6 is pressed against the contour of the second mold half 3 while this molded part 9 in the areas supported by the grid ribs 7 with the injection molded part 5.

The injection molding 5, which is preferably designed and shown in FIG. 4, has box-shaped troughs 6. The steep arrangement of the trough walls 16 means that a grille 4 can be dispensed with if it is ensured that the pressure medium can flow through the openings 12 into each of the troughs 6.

FIG. 5 shows a two-shell molded part 19 produced according to the invention with λ / 4 absorbers 18. In the embodiment shown, an injection molded part 5 according to FIG. 4 was used and a thermoplastic molded part 9 is connected to the trough walls 16. In the embodiment shown, the thermoplastic molded part 9 has a

Decor layer 17 provided. It goes without saying that the special shape, the arrangement of the λ / 4 resonators produced in this way and their openings 12 are in the range of normal specialist trade. The person skilled in the art will adapt the special design to the respective intended use.

A preferred application of the method according to the invention can be found in the production of foldable hat racks, as are used today in small cars. These parcel shelves separate the trunk from the passenger compartment and are usually double-walled. An invention According to the rear parcel shelf produced, the openings for the λ / 4 resonators on the trunk side are provided with a decorative layer on the passenger compartment side. It goes without saying that the method according to the invention for components or Partitions of all kinds can be used in the automotive industry as well as in the machine industry or in the building sector.

The advantages of the method according to the invention are immediately apparent to the person skilled in the art and are essentially in the simple and therefore simple, i.e. to see inexpensive manufacturing.

Claims

claims

1. A method for producing a double-walled component (19), in particular a vehicle parcel shelf, in which a first and a second molded part (5, 9) are included

Are connected to one another with the aid of a compression molding process, characterized in that for producing a component (19) with integrated λ / 4 absorbers (18), the first molded part (5) is preformed in such a way that it has a plurality of trough-shaped or box-shaped depressions (6 ), each of which is perforated in the end region, preferably slot-shaped, and this preformed, first molded part (5) is inserted into a first mold half (2) of a gassable molding press (1), that a second molded part (9)

Plastic is placed over this preformed, first molded part (5) in such a way that when the molding press (1) is closed, at least the edge of each preformed depression (6) of the first molded part (5) is pressed against the second molded part (9) and thereby a plurality of λ / 4 absorber chambers (18) is formed such that when the molding press (1) is closed, a pressurized gas is let into the mold cavity of the molding press (1) such that this gas flows through openings (12) in the first molding (5) and the second molded part (9) presses against the second mold half (3) of the molding press (1) until the two molded parts (5, 9) are connected to one another at least at the edge of each preformed depression (6).

2. The method according to claim 1, characterized in that the first molded part is preformed by injection molding.

3. The method according to claim 1 or 2, characterized in that different materials are used for the first and second molded part.

4. The method according to any one of claims 1-3, characterized in that a moldable sheet product is used for the second molded part.

5. The method according to any one of claims 1-4, characterized in that a preformed in a suitable manner is used to press the first molded part to the second molded part.

6. Double-walled component, in particular vehicle parcel shelf, produced by the method according to claim 1, characterized in that it has a first molded part with a plurality of trough-shaped or box-shaped troughs, each of which is perforated in the end region, preferably slot-shaped, the first Molded part is connected to a second molded part, such that a plurality of λ / 4 absorber chambers is thereby formed.

7. The component according to claim 6, characterized in that the second molded part is multi-layered, and in particular comprises a decorative layer, preferably made of synthetic leather, felt, fabric or carpet.

8. Component according to one of claims 6 or 7, characterized in that the second molded part comprises a plastic layer filled with wood flour (Woodstock).

9. Component according to one of claims 6 to 8, characterized in that at least the first molded part consists of a thermoplastic.

10. Component according to one of claims 6 to 9, characterized in that the first molded part is an injection molded part.