FR3071430A1 - 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 plastic parts for vehicles comprising any type of system requiring a defrosting function, in particular sensors. The invention relates more particularly to the defrosting of such bodywork parts acting as a radome.

By radome is meant a part 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 layer of frost forms on these parts of the vehicle, which can cause malfunctions of the devices emitting waves that must pass through said parts. It is therefore essential to provide a defrosting of the zones of the parts which are crossed by these waves, in order to ensure proper operation of the various devices placed behind them, for example sensors.

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

The heater usually consists of a copper circuit. In order to insert this copper circuit into the room, a robotic arm places a copper wire in an injection mold. Once the copper circuit is placed in the mold, plastic material, for example a thermoplastic material, is injected into the mold in order to overmold the copper circuit and to manufacture the part.

However, such a method has several drawbacks.

First, the positioning of the copper wire by a robotic arm is long and complex. Indeed, the robotic arm must make many movements to correctly position the copper wire in order to achieve a circuit comprising many meanders. It is moreover essential that the formed circuit respects certain conditions, such as for example the transparency to 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 due to the variation of many parameters. It is therefore necessary to check the parts one by one, which represents a waste of time and significant costs.

By heating track is meant a track capable of being heated and of releasing thermal energy in order to locally defrost the part on which a layer of frost has formed.

In addition, it is necessary, after overmolding the copper circuit, to carry out a step of recovery of the part in order to place a connector of the copper circuit with an energy source. This recovery step to place this connector is relatively difficult because it is necessary to be able to access the overmolded copper circuit.

Consequently, the process implemented is long (placement of the copper wire, recovery of the part) and complex. The production rate of the parts is relatively low. The production of these parts is therefore relatively expensive (low rate in addition to the cost represented by the part recovery step).

The prior art also includes parts of a motor vehicle comprising heating tracks produced from a thermoformed film. However, this film may not be deformed uniformly over the entire part, for example if it is curved or has a non-planar surface, particularly for surfaces with local thickness variations, which can cause problems in terms of transparency on the air.

The present invention aims in particular to remedy these drawbacks by providing a method of manufacturing parts of the type mentioned above faster and less complex than those of the prior art.

To this end, the subject of the invention is a method of manufacturing a plastic vehicle part, the vehicle part comprising at least one heating track capable of defrosting at least part of the part, the manufacturing method comprising a step of producing the heating track by injecting a metal alloy.

Thus, the production of the injection heating track 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 fulfilling the requirements in terms of transparency to 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 making 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 an energy source by injecting the metal alloy in easily accessible areas. Finally, the production of the heating track or tracks by injection allows great freedom in the choice of the shape of said heating tracks, for example as a function of the geometry of the parts equipped with such tracks.

The method according to the invention may also include one or more of the following characteristics:

- the process is carried out using a mold comprising several cavities and comprises the following steps:

injection of a plastic material into a first cavity of the mold in order to obtain a support comprising at least one cavity, and

- injection of the metal alloy into the cavity of the support in order to obtain an insert comprising the heating track, insert used for the manufacture of the part;

- the metal alloy has a melting point below a melting point of the plastic of the support.

- The method further comprises a step of obtaining the part 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 a molding 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 polymethyl methacrylate;

- the metal alloy includes 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 an energy source is placed in the mold before the step of injecting plastic material 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 capable of being obtained by the manufacturing process according to the invention.

Advantageously, the vehicle part is a radome.

The invention also relates to a set of a vehicle part according to the invention and a radar for a vehicle.

We will now present embodiments of the invention given by way of nonlimiting example and with the 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 intended to form a part of the vehicle part;

- Figure 4 shows a section of an insert comprising the support of Figure 3 and heating tracks, insert intended to form the vehicle part;

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

The part 2 is located in an area of the vehicle where a layer of frost can form on the latter. However, one or more parts of the part 2 are crossed by waves, for example the waves of sensors placed near the part 2. In this case, it is possible to assimilate the part to a radome.

In order to avoid discomfort in the passage of the waves due to this layer of frost, the part 2 comprises several heating tracks 8. These heating tracks 8 are able to allow defrosting of the part or parts of the part through which the waves pass and on which a layer of frost has formed thanks to local heating of the part 2. They are made of a material having a satisfactory thermal conductivity in order to be able to be raised in temperature. It must also be a material having a non negligible thermal resistance in order to allow a good diffusion of the heat in the polymer material constituting the part 2. Consequently, it is advantageous to use a metallic alloy combining at least one conductive element and at least one resistive element. As such, an alloy which can be used is an alloy comprising tin (resistive element) and silver (conductive element). Examples of alloys that can be used are the Sn95.5 / Ag3.8 / Cu0.7 alloys or SnlOONiGe. 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 levels of thermal conductivity would not be possible with a polymer loaded with thermally conductive fillers if this polymer must also 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 provision 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 seen 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 an energy source via a connector.

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

The part 2 is produced by an overmolding or bi-injection molding process II is a process using a mold comprising several 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). An injection mold known from the prior art can be used. In the embodiment shown in Figure 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, plastic material, for example chosen from those mentioned above (polycarbonates, polymethyl methacrylate or else polypropylene) is injected by the first injection screw in a first mold cavity (for example made in the mold of the mold) after closing of the latter. This cavity defines a first molding chamber and has a shape making it possible to obtain a support 10 comprising cavities 12 into which the metal alloy will be injected subsequently. These cavities 12 have dimensions and a layout that meet the conditions allowing future heating tracks to be transparent to the waves (thickness, width, parallelism).

Then, the movable part of the mold changes position (by translation or rotation) after opening the mold, in order to free the support 10, more particularly the cavities 12, from the complementary shape of the mold in order to be able to inject into the cavities 12 l liquid metal alloy making it possible to produce the heating tracks 8. The mold is again closed to create a second injection chamber into which the metal alloy is injected into the cavities 12 by the second injection screw in order to produce 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 alloy selected therefore has a relatively low melting point, and therefore an injection temperature. In addition, this alloy can be heated (during defrosting) without the risk of degrading the support 10. It is also possible to use a heated mold during the step of injecting the metal alloy. In fact, the heating tracks 8 are relatively fine compared to their length. Heating the mold (of the order of 150-180 ° C. for the alloys mentioned above) over the entire length of the injection line makes it possible to ensure good injection of the metal alloy over the entire length of the cavities 12 by slowing down the cooling of the injected material (mold with variothermal technology or heating of 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, an insert shown in FIG. 4. The mold is opened again 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 abovementioned 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 as that used to make the support 10 for reasons of chemical affinity, but this may change depending on the specifications of the surface of the visible part for example. Otherwise, it is possible to produce the part of the part 2 surrounding the insert 16 using a material chemically compatible with the plastic material of the insert 16. The injection can be carried out using the injection screw allowing the injection of the plastic material constituting the support 10.

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

In the case of FIG. 1 in which the part 2 comprises a visible part, it is possible to carry out, in addition to the above steps, a step of injecting plastic material making it possible to produce the visible surface of the part 2. In this case, a third injection screw can be provided. Otherwise (no visible surface), it is possible to simply produce a protective surface for the heating tracks 8 (surface produced during the step of producing the part of the part 2 surrounding the insert using the same plastic material).

The invention is not limited to the embodiments presented and other embodiments will be 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 set out above.

Nomenclature: vehicle part

4: visible part: supports: heating tracks: support: support cavities

16: insert

Claims (15)

claims 1. Method for manufacturing a plastic part (2) of a vehicle, the vehicle part (2) comprising at least one heating track (8) capable of defrosting at least part of the part (4), characterized in what the manufacturing process includes a step of producing the heating track (8) by injecting a metal alloy. 2. The manufacturing method according to claim 1, the method being carried out using a mold comprising several 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 - injection of the metal alloy into the cavity (12) of the support (10) in order to obtain an insert (16) comprising the heating track (8), an insert used for the manufacture of the part (2). 3. The manufacturing method according to the preceding claim, wherein the metal alloy has a melting point below 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 part (2) by injection of plastic material around the insert (16) comprising the heating track (8). 5. Method according to 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. Method according to 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. The manufacturing method according to any one of the preceding claims, the method being an overmolding or bi-injection method. 8. Manufacturing method according to any one of the preceding claims, in which 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 polymethyl methacrylate. 9. 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 a width less than or equal to 0.5 mm. 11. The manufacturing method according to any one of claims 4 to 6, in which a connector of the heating track (8) with an energy source is placed. 5 in the mold before the step of injecting plastic 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. Vehicle part (2) capable of being obtained by the manufacturing process 10 according to any one of the preceding claims. 14. Motor vehicle part according to the preceding claim, the part being a radome. 15. The assembly of a vehicle part (2) according to any one of claims 13 and 14 and of a vehicle radar.