FR3071430B1 - METHOD FOR MANUFACTURING A PLASTIC VEHICLE PART COMPRISING AT LEAST ONE HEATED INJECTED TRACK - Google Patents

Abstract

The invention relates to a method for manufacturing a plastic vehicle part (2), the vehicle part (2) comprising at least one heating track (8) capable of deicing at least part of the part (4). , characterized in that the manufacturing method comprises a step of producing the heating track (8) by injection of a metal alloy.

Description

The invention relates to vehicle plastic parts comprising any type of system requiring a defrosting function, including sensors. The invention relates more particularly to the deicing of such body parts acting as a radome.

By radome is meant a piece transparent to radio waves.

Many motor vehicles today include devices placed behind a bodywork part such as distance sensors such as reversing radars. It is possible that, depending on the climatic conditions, a frost layer is formed on these parts of the vehicle, which may cause malfunctions of the devices emitting waves to pass through said parts. It is then essential to provide a defrost areas of parts that are crossed by these waves, to ensure proper operation of different devices behind the latter, for example sensors.

One solution envisaged for this deicing is the incorporation into the vehicle part placed in front of this or these devices of a heating device capable of de-icing the part or parts of the parts traversed by the waves and on which a layer of frost has formed. .

The heating device is generally made of a copper circuit. In order to insert this copper circuit into the part, a robotic arm places a copper wire in an injection mold. Once the copper circuit placed in the mold, plastic material, for example a thermoplastic material, is injected into the mold in order to overmould the copper circuit and manufacture the workpiece.

Such a method, however, has several disadvantages.

First, the positioning of the copper wire by a robotic arm is long and complex. Indeed, the robotic arm must make many movements to properly position the copper wire to achieve a circuit with many meanders. It is also essential that the circuit formed meets certain conditions, such as, for example, the transparency of the waves emitted by the sensors, thanks inter alia to the parallelism between the various heating tracks of the copper circuit and to a very precise spacing between these heating tracks. This is difficult to reproduce because of the variation of many parameters. It is therefore necessary to check the pieces one by one, which represents a waste of time and significant costs.

A heating track is understood to mean a track capable of being heated and of releasing heat energy in order to locally defrost the room on which a layer of frost has formed.

In addition, it is necessary, after overmoulding of the copper circuit, to perform a step of recovery of the piece to place a connector of the copper circuit with a power source. This recovery step to place this connector is relatively difficult because it must be possible to access the overmolded copper circuit.

Therefore, the process implemented is long (placement of the copper wire, recovery of the piece) and complex. The production rate of parts is relatively low. The production of these parts is therefore relatively expensive (low rate in addition to the cost represented by the step of recovery of the part). The prior art also comprises motor vehicle parts comprising heating tracks made from a thermoformed film. However, this film may not deform uniformly over the entire piece, for example if it is curved or has a non-planar surface, particularly for surfaces with local variations in thickness, which can cause problems. problems in terms of transparency on the airwaves.

The present invention is intended to overcome these disadvantages by providing a manufacturing process parts of the type mentioned above faster and less complex than those of the prior art. For this purpose, the invention relates to a method of manufacturing a plastic vehicle part, the vehicle part comprising at least one heating track capable of deicing at least part of the part, the manufacturing process comprising a step of producing the heating track by injection of a metal alloy.

Thus, the production of the heating track by injection makes it possible to dispense with the complex step of positioning a copper wire by a robotic arm. The injection of the metal alloy makes it possible to obtain more quickly and in a reproducible manner one or more heating tracks that fulfill the requirements for transparency of the waves emitted by the elements emitting waves, for example sensors. It is also easier to respect a parallelism of the heating tracks on a curved part or with local thickness variations by performing them by injection. The same goes for the distance between the different heating tracks. In addition, it is possible to provide an easy connection of the heating tracks with a source of energy by injection of the metal alloy in easily accessible areas. Finally, the production of the heating track (s) by injection leaves a great freedom in the choice of the shape of said heating tracks, for example according to the geometry of the parts equipped with such tracks.

The process according to the invention may also comprise one or more of the following characteristics: the process is carried out using a mold comprising a plurality of cavities and comprises the following steps: injection of a plastic material into a first cavity of the mold to obtain a support comprising at least one cavity, and - injection of the metal alloy into the cavity of the support to obtain an insert comprising the heating track, insert used for the manufacture of the part; the metal alloy has a melting point lower than a melting point of the plastic material of the support. the method further comprises a step of obtaining the piece by injecting plastic material around the insert comprising the heating track; the plastic material injected around the insert comprising the heating track is identical to the plastic material of the insert; the plastic material injected around the insert comprising the heating track is chemically compatible with the plastic material of the insert; the process is an overmolding or bi-injection process; the plastic material of the support and the plastic material injected around the insert comprising the heating track are chosen from polycarbonates, polypropylene and / or polymethylmethacrylate; the metal alloy comprises tin and silver; the heating track with a thickness and a width less than or equal to 0.5 mm; - A connector of the heating track with a power source is placed in the mold before the plastic injection step around the insert comprising the heating track; and the mold is heated during the injection of the metal alloy. The invention also relates to a vehicle part that can be obtained by the manufacturing method according to the invention.

Advantageously, the vehicle part is a radome. The invention also relates to an assembly of a vehicle part according to the invention and a vehicle radar.

We will now present embodiments of the invention given by way of non-limiting example and in support of the appended figures in which: - Figure 1 shows a section of a vehicle part according to a first embodiment of the invention; - Figure 2 shows a section of a vehicle part according to a second embodiment of the invention; - Figure 3 shows a section of a support according to the invention comprising cavities for the injection of the metal alloy, support for forming a portion of the vehicle part; - Figure 4 shows a section of an insert comprising the support of Figure 3 and heating tracks, insert for forming the vehicle part;

Figures 1 and 2 partially illustrate a vehicle part 2, reference of a motor vehicle. It may for example be a bodywork part made of plastic, such as polycarbonates, polymethylmethacrylate or polypropylene. This part 2 may comprise, as shown in Figure 1, a visible surface 4. It may be, in the case where the part 2 is a bodywork part, the surface visible from outside the vehicle. The part 2 may also comprise functional parts such as for example different supports 6 or plastronic elements (plastic elements embodying electronics, not shown). In the example illustrated in Figure 2, the part 2 does not include a visible part, it is therefore a part not visible from the outside of the vehicle.

Part 2 is located in an area of the vehicle where a layer of frost may form on the latter. However, one or more parts of the room 2 are traversed by waves, for example the sensor waves placed near the room 2. In this case, the room can be likened to a radome.

In order to avoid a hindrance in the passage of the waves due to this layer of frost, the room 2 comprises several heating tracks 8. These heating tracks 8 are able to allow a defrosting of the part or parts of the room traversed by the waves and on which a layer of frost has formed through local heating of the room 2. They are made of a material having a satisfactory thermal conductivity in order to be able to be mounted in temperature. It must also be a material with a significant thermal resistance in order to allow a good diffusion of heat in the polymer material constituting part 2. Therefore, it is advantageous to use a metal alloy combining at least one conductive element and at least one resistive element. As such, an alloy that can be used is an alloy comprising tin (resistive element) and silver (conductive element). Examples of alloys that can be used are Sn95.5 / Ag3.8 / Cu0.7 or SnlOONiGe alloys. These alloys are commercially available. They have a thermal conductivity between 66 and 418 W / (m.K) (respective thermal conductivities of tin and silver), conductivity higher than steel (very resistive) but lower than copper (very conductive). These thermal conductivity levels would not be conceivable with a polymer loaded with thermally conductive fillers if this polymer also has to be injectable in a molding process (a charged polymer would not be injectable).

Beyond the nature of the alloy used, the heating tracks 8 must have a certain shape and respect a certain disposition in order to be transparent to the waves. The heating tracks 8 have a width and a thickness less than or equal to 0.5 mm. They are also parallel to each other.

It can be observed in FIG. 1 that the lowest heating track 8 is accessible from a surface of the room. This allows the heating tracks 8 to be connected to a power source via a connector.

During the manufacturing process of the part 2, the heating tracks 8 are injected in order to respect the various characteristics stated above and this by a reliable and easily reproducible method.

The part 2 is produced by an overmoulding or bi-injection molding process. This is a process involving a mold comprising a plurality of cavities and two injection screws. It is then possible to inject part of the part 2 into a mold comprising a movable part (in translation or in rotation). It is possible to use an injection mold known from the prior art. In the embodiment shown in FIG. 1, it is possible to use a mold comprising more than two injection screws, as explained later.

The first step of the process consists in producing an insert 10 shown in FIG. 1. For this purpose, plastic material, for example chosen from those mentioned above (polycarbonates, polymethylmethacrylate or polypropylene) is injected by the first injection screw in a first cavity of the mold (for example made in the matrix of the mold) after closure of the latter. This cavity defines a first molding chamber and has a shape to obtain a support 10 comprising cavities 12 in which the metal alloy will be injected later. These cavities 12 have dimensions and a layout respecting the conditions allowing the future heating tracks to be transparent to the waves (thickness, width, parallelism).

Then, the moving part of the mold changes position (by translation or rotation) after opening of the mold, and this in order to release the support 10, more particularly the cavities 12, from the complementary shape of the mold to be able to inject into the cavities 12. liquid metal alloy for performing the heating tracks 8. The mold is closed again to create a second injection chamber in which the metal alloy is injected into the cavities 12 by the second injection screw to achieve the tracks 8. The alloy used (for example the examples cited above) has a melting point lower than that of the plastic of the support 10 and this in order to avoid deforming the latter (the melting point of the alloys mentioned) above is between 220 and 230 degrees Celsius). The selected alloy therefore has a melting point, and therefore a relatively low injection temperature. In addition, this alloy can be heated (during a defrost) without the risk of degrading the support 10. It is also possible to use a heated mold during the step of injection of the metal alloy. Indeed, the heating tracks 8 are relatively thin with respect to their length. Heating the mold (of the order of 150-180 ° C. for the alloys mentioned above) along the entire length of the injection line makes it possible to ensure good injection of the metal alloy over the entire length of the moldings. cavities 12 by slowing the cooling of the injected material (mold with variotherm technology or heating the mold by external means). The injection of the metal alloy can also be carried out from several injection points.

After the step of injecting the metal alloy, an insert 16 is obtained comprising the support 10 and the heating tracks 8, the insert shown in FIG. 4. The mold is again open and this is in order to transfer the insert into a third injection chamber. Plastic material is then injected into this injection chamber around the insert 16 in order to produce the part 2. The third injection chamber makes it possible, for example, to produce the aforementioned functional elements such as, for example, the supports 6. The material plastic used to make the part of the part 2 surrounding the insert 16 may be the same material used to make the support 10 for reasons of chemical affinity, but this may change depending on the specification of the surface of the the visible piece for example. Otherwise, it is possible to make the part of the part 2 surrounding the insert 16 by using a material chemically compatible with the plastic material of the insert 16. The injection can be performed using the injection screw for the l injection of the plastic material constituting the support 10.

Before this injection step, a connector of the heating tracks 8 with a source of energy to heat them can be placed in the third injection chamber so that the part 2 already includes the mold outlet connector, this which avoids a step of recovery of the piece. It may for example be relevant that the part 2 comprises a connector accessible from a part of the part 2 not visible to the user of the vehicle. The connector may for example be connected to the heating track 8 passing through the insert 16 (track made in the lowest cavity 12 in FIG. 3), a track not covered by the plastic material of the insert at the junction with the connector.

In the case of Figure 1 in which the part 2 comprises a visible part, it is possible to perform in addition to the above steps a plastic injection step for producing the visible surface of the part 2. In this case, a third injection screw can be provided. In the opposite case (no visible surface), it is possible to simply make a protective surface of the heating tracks 8 (surface produced during the step of producing the part of the part 2 surrounding the insert 16 using the same plastic material). The invention is not limited to the embodiments presented and other embodiments will become apparent to those skilled in the art. It is for example possible to use a metal alloy other than those mentioned and fulfilling the criteria stated above.

Nomenclature 2: vehicle part 4: visible part 6: supports 8: heating tracks 10: support 12: support cavities 16: insert

Claims (15)

claims A method of manufacturing a plastic vehicle part (2), the vehicle part (2) comprising at least one heating track (8) capable of defrosting at least a part of the part (4), characterized in that the manufacturing process comprises a step of producing the heating track (8) by injection of a metal alloy. 2. The manufacturing method according to claim 1, the process being carried out using a mold comprising a plurality of cavities, the method comprising the following steps: injection of a plastic material into a first cavity of the mold in order to obtain a support (10) comprising at least one cavity (12), and - injecting the metal alloy into the cavity (12) of the support (10) in order to obtain an insert (16) comprising the heating track (8), insert used for the manufacture of the part (2). 3. Manufacturing process according to the preceding claim, wherein the metal alloy has a melting point less than a melting point of the plastic of the support (10). 4. The manufacturing method according to any one of claims 2 and 3, the method further comprising a step of obtaining the piece (2) by injection of plastic material around the insert (16) comprising the heating track (8). 5. The method of claim 4, wherein the plastic material injected around the insert (16) comprising the heating track (8) is identical to the plastic material of the insert (16). 6. The method of claim 4, wherein the plastic material injected around the insert (16) comprising the heating track (8) is chemically compatible with the plastic material of the insert (16). 7. Manufacturing process according to any one of the preceding claims, the method being a method of overmolding or bi-injection. 8. Manufacturing process according to any one of the preceding claims, wherein the plastic material of the support (10) and the plastic material injected around the insert (16) comprising the heating track (8) are chosen from polycarbonates, polypropylene and / or polymethylmethacrylate. The manufacturing method according to any one of the preceding claims, wherein the metal alloy comprises tin and silver. 10. The manufacturing method according to any one of the preceding claims, wherein the heating track (8) has a thickness and width less than or equal to 0.5 mm. 11. Manufacturing method according to any one of claims 4 to 6, wherein a connector of the heating track (8) with a power source is placed in the mold before the plastic injection step around the insert (16) comprising the heating track (8). 12. The manufacturing method according to any one of claims 2 to 11, wherein the mold is heated during the injection of the metal alloy. 13. Part (2) vehicle obtainable by the manufacturing method according to any one of the preceding claims. 14. Motor vehicle part according to the preceding claim, the part being a radome. 15. An assembly of a vehicle part (2) according to any one of claims 13 and 14 and a vehicle radar.