FR3015340A1 - TOOL FOR CARRYING OUT A VEHICLE ELEMENT COMPRISING A PROGRESSIVE OPENING NOZZLE - Google Patents

Abstract

The production tool (8) comprises an injection cavity (14) and an injection nozzle (20) of an injection material (6), comprising a body (22) extending upstream of the outlet (24) of the nozzle (20), a shutter (26) of the outlet extending into said body (22) and being movable in translation in said body (22) between a closed position, in which the shutter (26) closes the outlet (24), and an open position, in which the shutter (26) is spaced from the outlet (24), said shutter (26) comprising an end piece (28), a main part ( 30) has a shape complementary to the shape of the outlet (24) and extends in said outlet (24) in the closed position. The tip (28) comprises, downstream of the main portion (30), an end portion (32) arranged to extend into the injection cavity (14) in the closed position.

Description

The present invention relates to a tool for producing a vehicle element made of injected material, of the type comprising an injection cavity and at least one injection nozzle. an injection material for forming the element, the outlet of said nozzle being in fluid communication with the injection cavity, the nozzle comprising a body extending upstream of the exit of the nozzle, said receiving body the injection material, a shutter of the outlet of the nozzle extending into said body and being movable in translation in said body between a closed position, in which the shutter closes the outlet of the nozzle, and a position of opening, wherein the shutter is spaced from the outlet, said shutter comprising a nozzle whose main part has a shape complementary to the shape of the outlet of the nozzle, said main part cipale extending in said outlet in the closed position of the shutter. The element is in particular a vehicle lining element, such as for example an automobile door panel, which requires an impeccable exterior appearance over large dimensions. It is known to produce elements, for example trim elements such as vehicle door panels or pieces of furniture or the like, by injecting a plastic material into an injection cavity having the shape of the element. of packing to achieve. One or more injection nozzles are provided to open into the cavity to inject the injection material into the cavity and fill it to form the element. The filling of the cavity is done through the injection pressure applied to the material and the fluidity of this material. It is important that the filling of the cavity is done quickly in order to have acceptable production rates. For this purpose, it is intended to use injection nozzles having a large volume and allowing a very fast flow of material. However, when it is desired to produce elements having a very small thickness, for example for reasons of reducing the mass of the element, while having an extended visible surface, as is the case for door panels for example, the number of injection points that can be added is not sufficient to completely fill the cavity without greatly increasing the injection pressure and / or to provide an injection material having a greater great fluidity. It is then necessary to modify the production tool or to change the injection material, which considerably increases the production costs.

In addition, the nozzles are generally arranged to inject the material into a zone of the cavity situated outside the zone intended to form a visible part of the packing element. Indeed, the nozzles are not suitable for producing an element having a satisfactory appearance if they are arranged in a zone intended to form a visible zone of the element, because the very fast flow of material from each nozzle causes the presence of traces on the visible surface of the element to the right of the injection points due to the very small desired thickness of the element. Thus, it is not possible to multiply the injection points opening into the cavity without having some of these points in an area of the cavity intended to form a visible zone of the element, which leads to defects in aspects. in the element, in particular due to the fact that there is a thickening of injection material to the right of the nozzles, resulting in a cooling profile of the non-homogeneous element over its entire surface and creates marks on the element. Document FR-2 987 576 makes it possible to overcome these drawbacks by proposing a tool for producing a member having a small thickness making it possible to obtain an element having a satisfactory appearance and by using a standard injection material, while retaining acceptable production rates. However, there is a constant need to improve this type of tool, particularly from the point of view of the reliability of operation of such a tool and to improve the quality of the appearance of the visible surface of the manufactured element. by this tool. The present invention is intended in particular to fulfill this objective.

To this end, the invention relates to an embodiment tool of the aforementioned type, wherein the tip further comprises, downstream of the main part, an end portion arranged to extend into the injection cavity in the closed position. shutter, so as to reduce the thickness of said injection cavity to the right of the outlet of the nozzle in the closed position of the shutter.

By providing an end portion of the nozzle projecting from the outlet of the nozzle, the thickness of the injection cavity is reduced to the right of the nozzle. This therefore means that there is less injection material facing the nozzle when the cavity has been filled with the injection material and the nozzle is closed by the closure member. This promotes a more homogeneous profile of the cooling of the element after injection, which avoids forming marks on the element, especially at the outlet of the nozzle. The nozzle can thus be arranged in a zone intended to form a visible part of the element to be produced, even when the part produced is of reduced thickness. It is therefore possible to position the nozzle so that the cavity is completely filled during the injection of the material. This gives an element having a satisfactory appearance while having a very small thickness and can be achieved with a standard material at acceptable production rates.

According to another characteristic of the embodiment tool, the end portion has a diameter smaller than the diameter of the main part of the tip. Providing an end portion of the nozzle having a diameter smaller than that of the main part, a progressive opening of the nozzle is created during the injection of material, that is to say that the flow of the material The flow from the outlet of the nozzle is initially low when the main part of the nozzle releases the output and the end part still partially closes this output and the flow increases when the output is completely cleared. Providing a gradually opening nozzle makes it possible to modulate the flow of the injected material so as to avoid any visible traces on the element even though the nozzle is disposed in an area of the cavity forming a visible zone of item. According to other features of the production tool: the outlet of the nozzle is formed by a cylinder-shaped channel of revolution, the main part of the nozzle having a cylinder-shaped revolution of diameter substantially equal to the diameter the canal; the end portion has a cylindrical shape of revolution or a frustoconical shape, the largest diameter of which is smaller than the diameter of the main part of the endpiece; - The transition zone between the main part and the end part of the tip has a frustoconical shape whose largest diameter is equal to the diameter of the main part and whose smallest diameter is equal to the largest diameter of the extreme part. ; - The transition zone between the main part and the end portion of the nozzle extends into the outlet channel of the nozzle in the closed position of the shutter; the end part of the endpiece comprises a downstream tip-shaped end; the body of the nozzle comprises a frustoconical zone having a frustoconical shape in axial section, said frustoconical zone extending directly upstream of the outlet, so that the volume of the nozzle increases progressively from the exit of the nozzle towards the upstream of the nozzle, so that the displacement of the shutter towards its open position causes an increase increase in the injection rate of the injection material at the outlet of the nozzle; the body of the nozzle comprises a plurality of wings extending radially from the body of the nozzle towards the center of the nozzle, the flanges defining between them cells having a substantially frustoconical shape in radial section so that the volume of the cells increases from the center of the nozzle towards the body of the nozzle, so that the displacement of the shutter towards its open position leads to a gradual increase in the injection flow rate of the injection material at the outlet of the nozzle; and the injection cavity is delimited by a first wall intended to form the inner surface of the element and by a second wall intended to form the external surface of the element, said external surface being intended to be visible from the outside the element, the outlet of the nozzle being in fluid communication with a zone of the first wall or the second wall intended to form a visible part of the vehicle element. Other aspects and advantages of the invention will appear on reading the description which follows, given by way of example and with reference to the appended drawings, in which: FIG. 1 is a schematic representation of an element showing injection points of the injection material provided in the embodiment tool according to the invention; FIG. 2 is a diagrammatic representation in section of a portion of the embodiment of the invention showing an injection nozzle in the closed position; FIG. 3 is a schematic representation in section of the portion of the tool of FIG. 2, the injection nozzle being in an intermediate position between the closed position and the open position; FIG. 4 is a diagrammatic representation in section along the axis IV-IV of FIG. 3, - FIG. 5 is a schematic representation in section of the portion of the tool of FIG. 2, the injection nozzle in the open position, and - FIG. 6 is a schematic representation in section along the axis VI-IV of FIG. 5.

With reference to FIG. 1, there is described an element 1, such as a packing element, for example a door panel as shown in FIG. 1, comprising an outer surface 2, intended to be visible, and an inner surface 4, intended to be invisible and to be mounted on a portion of a vehicle, for example a motor vehicle. Visible means that the outer surface 2 is not covered by a coating layer, such as a film, skin or other. Thus, the visible surface of the lining element forms an appearance surface of this lining element and is intended to be visible and directly touched by a user. At least one zone of the packing element 1 has a reduced thickness e between the outer surface 2 and the inner surface 4. The thickness of the packing element is understood to mean the distance separating the outer surface 2 from the inner surface 4 .

According to one embodiment, the assembly of the packing element has a thickness e reduced between the outer surface 2 and the inner surface 4. A constant reduced thickness element on the whole element makes it possible to obtain an element of packing 1 of particularly good quality, as will be described later.

According to another embodiment, the packing element has a reduced thickness in the area in which the outer surface 2 is visible and a thickness greater than the reduced thickness in a zone, in which the outer surface 2 is not intended to be visible, for example at the periphery of the packing element. The visible area of the packing element 1 is formed by a zone of reduced thickness. Reduced thickness means a thickness less than or equal to 2.2 mm, more particularly a thickness of between 1.5 mm and 2.2 mm and preferably between 1.9 mm and 2.1 mm, whereas a conventional packing element generally has a thickness of between 2.5 mm and 3 mm.

The packing element 1 may also comprise one or more functional elements such as ribs, staple doors, or the like on the surface opposite to the visible surface, that is to say extending from the inner surface. 4 of the packing element 1. This or these functional elements extend projecting from the inner surface 4, substantially perpendicular to it, opposite the outer surface 2.

The reduced thickness of the packing element is measured outside the functional element or elements, which may have thicknesses smaller than the reduced thickness and which, in known manner, respect thickness ratios to avoid defects. aspects on the visible surface. The packing element 1 is made of an injection material 6, of the plastic material type, for example thermoplastic material of the polyester type, or polyolefin, homopolymer or copolymer, or for example PC + ABS (polycarbonate and acrylonitrile). butadiene-styrene), these materials being able to be reinforced by mineral fillers or fibers, natural or glass, by injection of this material into an embodiment tool 8.

The production tool 8 comprises a first part 10 and a second part 12 defining between them an injection cavity 14 having substantially the shape of the packing element 1 to be produced. Alternatively, the injection cavity 14 has a shape arranged to form a substantially planar member. The injection material 6 is conventional for this type of application. Preferably, the material has, at its specific transformation temperature, a viscosity ranging from 5 Pa.s to 1000 Pa.s in a range of injection-specific shear rates ranging from 100 s-1 to 50,000 s. 1. With this feature, the material is injectable. It can then be used in most known injection processes, such as, for example, low pressure, high pressure injection, sandwich injection, bi-injection, compression injection and overmolding. The specific transformation temperature is the temperature at which the material is sufficiently fluid to be injected into a cavity (for example between 220 and 240 ° C for polypropylenes and between 260 and 280 ° C for polycarbonates (PC) and polymers Acrylonitrile butadiene styrene (ABS) This specific transformation temperature is specific to each material Besides the means for injecting the injection material 6 into the cavity 14, the production tool 8 is also conventional for this type of application. Thus, the first and second parts 10 and 12 are movable relative to each other between a spaced position, in which the packing element can be released from the tool 8, and a closed position in which they form the injection cavity 14 sealed hermetically.The cavity 14 is delimited by a first wall 16 formed by the first part 10 and by a second wall 18 for moved by the second part 12, these walls extending opposite one another and being separated by a distance substantially equal to the thickness e of the packing element to be produced. The first wall 16 is intended to form the inner surface 4 of the lining element 1 and the second wall 18 is intended to form the outer surface 2 of the lining element 1.

The cavity 14 may have a shape adapted to form in one piece the functional element or elements with the rest of the packing element by adapting the shape of the first wall 16 of the cavity accordingly, that is to say say by providing recessed areas having the shape of the functional elements to achieve. To form a lining element of reduced thickness, the first wall 16 is separated from the second wall 18 by a distance equal to the reduced thickness e, for example less than or equal to 2.2 mm, at least in the zone of the cavity 14 for forming the reduced thickness area of the packing element 1, as shown in FIGS. 2, 3 and 5. Thus, when a packing element of constant reduced thickness is produced, the distance separating the first wall 16 of the second wall 18 is constant and equal to the reduced thickness of the packing element. In the case where an area of the packing element has a greater thickness, the distance separating the first wall 16 from the second wall 18 increases in the area of the cavity intended to form this zone of greater thickness. The production tool 8 comprises a plurality of nozzles 20 for injecting the injection material 6 into the cavity 14. the outlet of these nozzles 20 being in fluid communication with a zone opening into the cavity 14 on the first wall 16 and or on the second wall 18. The position of these nozzles 20 with respect to the filling element to be produced is shown schematically in FIG. 1. As can be seen in this figure, most of the nozzles 20 are arranged opposite a visible zone of the packing element 1, whereas they are usually arranged outside this zone in the prior art. and arranged around the periphery of the packing member. The position of the nozzles 20 directly in a visible zone of the packing element and not at the periphery thereof allows the nozzles 20 to be distributed over a larger surface of the packing element 1, thereby reducing the thickness of the injection cavity 14 while ensuring that the injection material 6 completely fills the cavity 14 without the need to increase the injection pressure or to provide a more fluid injection material 6 with respect to the art prior. Thus, the cost of the production tool 8 and the manufacturing costs remain substantially identical to those of the prior art, while allowing to produce a lining element 1 of smaller thickness. According to the embodiment shown in FIG. 1, in connection with the production of a door panel, the production tool comprises twelve nozzles 20, ten of which are distributed opposite the visible zone of the packing element 1 and two are arranged on the periphery of this one. this. These different nozzles 20 are arranged according to a diagram provided to ensure the complete filling of the cavity 14 and are open to inject the injection material 6 into the cavity 14 in a sequence to be described later. According to the embodiment shown in the figures, the nozzles 20 are arranged in the first part 10 of the tool 8 and their outlet is in fluid communication with a zone opening into the first wall 16. Thus, the injection material 6 is injected on the side of the inner surface 4 of the packing element not to be visible from the outside thereof, and, for most of the nozzles, directly opposite the outer surface 2 for be visible from outside the packing element. More particularly, the outlet of the nozzles 20 arranged facing the visible zone of the packing element 1 extend along an axis substantially perpendicular to the second wall 18, that is to say along an axis substantially perpendicular to the visible external surface 4 of the packing element when it is in the cavity 14. Each nozzle 20 comprises a body 22 connected to a reservoir (not shown) of injection material 6 on one side and an outlet 24 in communication fluidic with the cavity 14 of the other.

As indicated above, for the nozzles 20 arranged facing the visible zone of the packing element, the outlet 24 and possibly the body 22 of the nozzle 20 extend along an axis substantially perpendicular to the second wall 18 of the the cavity 14, that is to say along an axis substantially perpendicular to the visible outer surface 4 of the packing element when it is in the cavity 14. Each nozzle 20 comprises means, known per se, for conveying the injection material 6 of the reservoir at the outlet 24 where the material is injected into the cavity 14 at a predetermined pressure and in a flow, or flow, controlled. More particularly, each nozzle 20 is adapted so that the output stream 24 of the nozzle increases gradually when the nozzle 20 is open, as will now be described. The outlet 24 is opposite a channel 25 formed in the first part 10 and connecting the body 22 of the nozzle 20 to the zone opening into the injection cavity 14. The injection material 6 therefore passes into the channel 25 prior to entering the injection cavity, thereby improving the appearance quality of the visible surface of the packing member with respect to the arrangements of the prior art, in which such a channel is not planned. Indeed, when the nozzles open directly into the cavity without an outlet channel, the temperature of the nozzle, in particular that of the nozzle body taken at the outlet arranged in the first wall of the cavity, is greater than that the first wall of the first part of the tool taken near where the nozzles open into the cavity. This difference in temperature generates differences in material flow around the injection point, which causes appearance defects on the visible surface. For the nozzles arranged opposite the visible zone of the packing element, the channel 25 extends along an axis substantially perpendicular to the second wall 18, that is to say along an axis substantially perpendicular to the external surface. 4 visible from the packing element when it is in the cavity 14 and is therefore directly opposite the visible area of the packing element. The channel has for example a cylinder shape of revolution, whose diameter is for example between 3 mm and 6 mm. The terms "upstream" and "downstream" are defined with respect to the direction of flow of the injection material 6. Thus, the body 22 extends upstream of the outlet 24 and the reservoir extends upstream of the body. Each nozzle 20 comprises a shutter 26 of the outlet 24 movable between a closed position (FIG 2) in which the shutter 26 closes the outlet 24 so as to prevent the injection material 6 from entering the cavity 14, c that is, the flow of injection material at the outlet is zero, and an open position (Fig. 5) in which the shutter is disengaged from the outlet 24 and in which the flow of injection material 6 at the outlet of the nozzle is at its maximum. Between the closed position and the open position, the shutter 26 gradually disengages (Fig. 3) from the outlet 24 and the flow of the injection material 6 at the nozzle outlet increases progressively from a zero flow to its maximum flow when the shutter 26 is in the open position. The shutter 26 is for example formed by a rod movable in translation in the body 22 of the nozzle 20 between its closed position and its open position and comprises at its downstream end a tip 28 extending into the channel 25. shutter closing position 26. The nozzle 28 comprises, from upstream to downstream, a main portion 30 and an end portion 32 connected to each other by a transition zone 34.

The main part 30 has a shape substantially complementary to that of the channel 25, for example a cylinder shape of revolution. Thus, the main part 30 blocks the channel 25 when the shutter 26 is in its closed position, as shown in FIG. 2, and prevents the injection material 6 from entering the injection cavity 14. The main portion 30 has a length in the axial direction such that it occupies part of the length of the channel 25 in the closed position of the The shutter 26. The outer surface of the main portion 30 is in contact along its axial length with the inner surface of the channel 25 when the shutter 26 is in its closed position. In this position, the channel is sealed by the tip 28 extending outside the nozzle 20. The sealing is ensured by the complementarity of the cylindrical forms of revolution of the main portion 30 of the nozzle 28 and the channel 25. The end portion 32 occupies the rest of the length of the channel 25 and enters the injection cavity 14 in the closed position of the shutter 26, as shown in FIG. 2. That is to say that the downstream end 36 of the end portion 32 of the nozzle 28 extends into the injection cavity 14 when the shutter 26 is in its closed position. However, it should be noted that the end portion 32 does not block the injection cavity 14, that is to say that the end 36 is not in contact with the second wall 18. According to another mode embodiment (not shown), the downstream end 36 of the end portion 32 is flush with the downstream end of the channel 25, that is to say that it does not extend into the cavity 14, in the position of Closure of the shutter 26. The end portion 32 further has a smaller diameter than the main portion 30. That is, the end portion 32 does not close the channel 25 in the closed position. The end portion 32 has, for example, a cylindrical shape of revolution or, as shown in the figures, a frustoconical shape, the largest diameter of which extends upstream of the end part 32, that is to say on the side of the main part 30, and whose smaller diameter extends downstream of the end part 3 2, that is to say on the side of the downstream end 36. The diameter of the end portion 32, constant when it is a cylinder of revolution or its smallest diameter when it is frustoconical, is by example between 1/3 and 2/3 of the main portion diameter 30.

Thus, when the diameter of the main portion 30 is substantially equal to 3 mm, the diameter, or smaller diameter, of the end portion 32 is for example substantially equal to 1 mm and when the diameter of the main portion 30 is substantially equal. at 6 mm, the diameter or smaller diameter of the end portion 32 is for example substantially between 3 mm and 4 mm. The tool according to the invention allows the use of shutters whose main part 30 of the nozzle 28 has a diameter greater than or equal to 3 mm, thereby improving the reliability of operation by limiting the fragility of the tip of the shutter as well as that of the channel 25. The downstream end 36 of the tip 28 has for example a pointed shape, that is to say that the downstream end 36 has a conical shape extending from the end portion 32 opposite the main portion 30. The transition zone 34 has for example a frustoconical shape, the largest diameter is equal to the diameter of the main portion 30 and the smallest diameter is equal to the diameter of the end portion 32, or the largest diameter of the end portion 32, when the latter has a frustoconical shape. Thus, the diameter of the transition zone 34 increases progressively from upstream to downstream between the main portion 30 and the end portion 32. As a variant, the transition zone 34 could be formed by a flat zone forming a shoulder between the main part 30 and the end portion 32. Because of the particular shape of the nozzle 28, it is understood that the transition from the closed position to the open position of the shutter 26 causes a gradual opening of the nozzle 20, that is to say that the flow of injection material 6 injected by the nozzle 20 increases gradually during this opening. Indeed, when the opening begins, the main part 30 of the nozzle 28 emerges from the channel 25 and releases a passage for the injection material 6. This passage is however limited firstly by the transition zone 34 when the latter has a frustoconical shape, then by the end portion 32, which extends in the channel 25 in the intermediate position of the shutter 26, as shown in FIG. 3. Due to the variation in diameter which is reduced downstream of the transition zone 34 and / or the end portion 32, the passage for the injection material 6 increases gradually as and when the shutter 26 moves to its open position. In the open position, the nozzle 28 is completely clear of the channel 25, that is to say that the end 36 of the nozzle 28 extends into the body 22 of the nozzle, and the flow of material Injection 6 is only limited by the diameter of the channel 25, as shown in FIG. 5. Directly upstream of the outlet 24 and therefore the channel 25, the body 22 of the nozzle 20 widens by flaring linearly so that the body 22 has a frustoconical shape 38 in axial section, it is that is to say along a plane extending along the axis of the nozzle 20, directly upstream of the outlet 24, so that the volume of the nozzle 20 increases progressively from the outlet 24 of the nozzle upstream of the nozzle. Other forms may of course be used, for example parabolic, these other forms to ensure that the volume of the nozzle 20 increases gradually from the outlet 24 of the nozzle upstream of the nozzle. Upstream of the frustoconical zone 30, the body 22 of the nozzle has a substantially cylindrical shape of revolution. The frustoconical zone 30 makes it possible to pass from a diameter substantially equal to that of the channel 25 directly upstream of the outlet 24 to a diameter that is substantially 3 to 6 times greater directly upstream of the frustoconical area 30. It is therefore clear that the volume injection material 6 present in the nozzle increases gradually in the frustoconical zone 30 from downstream to upstream. The body 22 of the nozzle further comprises a plurality of wings 40 extending radially from the body 22 of the nozzle towards the center of the nozzle. At their downstream end, extending in the frustoconical zone 30, the wings 40 comprise a shoulder 42 extending to the stem of the shutter 26 so as to ensure a centering of the shutter 26 in the body 22 of the nozzle and guide the tip 28 to the channel 25 when the shutter 26 moves to its closed position. As shown in FIG. 6, the body 22 of the nozzle comprises for example three flanges 40 distributed on the perimeter of the body 22 and defining between them cavities 44 extending between the body 22 of the nozzle and the shutter 26. The distance separating two flanges 40 defining a cell 44 progressively decreases from the body 22 towards the center of the nozzle so that the cells 44 have substantially a frustoconical shape in radial section, that is to say in a plane extending substantially perpendicular to the axis of the nozzle. Thus, the volume of the cells 44 progressively increases from the center of the nozzle 20 to the body 22 of the nozzle. The transition from the closed position to the open position of the shutter 26 is done by moving the tip 28 of the shutter 26 in the frustoconical zone 30 in a downstream-upstream direction, so that more and more injection material 6 can pass through the outlet 24 as the opening of the nozzle 20 due to the shape of the cells 36 and the frustoconical zone 30, as can be understood by comparing FIGS. 6 which are cross-sectional views in radial plane in which the shutter 26 is in an intermediate position between the closed position and the open position (Fig. 4) and in the open position (Fig. 6) . It can be seen between these two figures that the quantity of injection material 6 coming out of the nozzle increases progressively so that the flow of the injection material 6 increases progressively during the opening of the nozzle 20. Thus, when the nozzle 28 is outside the channel 25 in the downstream portion of the frustoconical zone 30, the injection material 6 passes only through channels 46 of small size defined by the size of the cells 44 in the downstream part of the frustoconical zone 30 as shown in FIG. 4. When the tip 28 is further upstream, as shown in FIG. 6, the channel size has increased, allowing a larger amount of injection material to pass through the outlet. Thus, the gradual increase in the flow of material begins when the transition from the closed position to the intermediate position, thanks to the shape of the nozzle 28, and continues from the intermediate position to the open position, thanks to the shape of the body 22 of the nozzle 20.

By controlling the speed of movement of the shutter 26, it is therefore possible to adjust the flow of material 6 out of the nozzle and in particular to provide for a steady increase in this flow when the nozzle 20 is opened. progressive increase and a particular opening sequence of the nozzles 20 allows for a lining element 1 having substantially no mark due to the injection of the material on its outer surface 2, although the nozzles 20 are in a zone of the injection cavity 14 arranged to form the zone of reduced thickness e, as will now be described in relation with the method of producing a lining element 1 by means of an embodiment tool 8 as described above. During a first step of the method, the injection cavity 14 is closed by moving the first and second parts 10 and 14 of the tool 8 to their closed position. Then, one or more nozzles 20, called "upstream nozzles" forming a first group of nozzles 20, are open so that the injection material 6 flows into the cavity 14 from these upstream nozzles through the channels 25 and spreads in the cavity 14 around these nozzles. The upstream nozzles are for example the nozzles disposed at the periphery of the packing element or one or more of the central nozzles. The upstream nozzles are open so as to inject the injection material at a pressure substantially equal to that which the skilled person would use to inject conventional packing elements having a thickness of between 2.5 mm and 3 mm. Due to this pressure and the fluidity of the injection material 6, the injection material from the upstream nozzles spreads in the cavity and reaches the nozzle or nozzles 20, called downstream nozzles, forming a second group of nozzles 20, arranged around the upstream nozzles, as represented by the arrow f of FIG. 2. As can be seen in this figure, as the injection material 6 from an upstream nozzle has not reached a channel 25 in fluid communication with a downstream nozzle outlet 24, this downstream nozzle remains closed and does not inject material into the cavity.

When the injection material 6 from an upstream nozzle passes next to the channel 25 in fluid communication with the outlet 24 of a downstream nozzle, as shown in FIG. 3, the progressive opening of this downstream nozzle is initiated so that this downstream nozzle injects a progressive flow of the injection material 6 into the cavity 14, this material coming from the downstream nozzle adding to the material coming from the nozzle upstream, as represented by the arrow F of FIG. 5. Each nozzle 20 of the tool is thus progressively open when the injection material from other nozzles passes opposite the channel 25 in fluid communication with its outlet 24 until all the nozzles 20 are open. and that the injection material 6 completely fills the injection cavity. The time to move the shutter between its closed position and its open position, makes it possible to adjust the increase in the flow rate at the nozzle outlet. In any case, the travel time of the shutter 26 is adjustable so as to adjust the injection rate of the injection material 6 at the outlet 24 of the nozzle. For the nozzles arranged facing the visible zone of the packing element, the flow of injection material 6 at the outlet of the nozzle 20 is substantially perpendicular to the second wall 18, that is to say according to a axis substantially perpendicular to the visible outer surface 4 of the packing element when it is in the cavity 14, because of the orientation of the channel 25 and the outlet 24 of the nozzle 20. This flow is then reoriented according to a direction substantially parallel to the second wall 18 due to the shape of the cavity 14. It will be noted that usually the injection of the flow directly opposite the visible zone and perpendicular to it is a source of appearance defect, this is not the case with the method according to the invention and by providing a reduced thickness in the visible zone. The progressive opening of each nozzle 20 is controlled so that the flow of the injection material 6 circulating in the cavity does not undergo acceleration when the injection material 6 from this nozzle is added to the material circulating in the cavity . Indeed, for conventional nozzles opening abruptly at its maximum flow, the material from these nozzles causes an acceleration of the flow in the cavity, which forms marks on the outer surface of the element to the right places where the flow has suddenly accelerated. Due to the progressive opening of the nozzles 20, the flow undergoes substantially no acceleration and therefore does not form a mark on the outer surface 2 of the trim element produced. However, the gradual increase in the flow rate of each nozzle 20 makes it possible to maintain filling rates of the cavity and therefore production rates of the packing elements acceptable and comparable to those of the prior art. The increase in the number of injection nozzles 20 for the production of a thin packing element compared to a conventional packing element also makes it possible to respect acceptable production rates and comparable to those of the prior art. Even if the reduction of the injectable volume by the presence of frustoconical zones can be seen as a source of reduction of production rates by those skilled in the art, they are advantageously used by multiplying them and using them for the realization of trim element having a reduced thickness, ie having a reduced cavity volume. By providing that the downstream end 36 of the nozzle 28 extends into the cavity 14 when the nozzle is closed, the quantity of injection material lying opposite the outlet 24 of the nozzle after the injection is reduced. . This compensates for the presence of material in the channel 25 due to the diameter reduction of the end portion 32 of the nozzle 28. Thus, the amount of material is substantially homogeneous throughout the injection cavity 14, which allows avoid appearance defect and warping problems, because the cooling rate of the injected material 6 is then constant over the entire packing element, which avoids the appearance of a cooling temperature gradient, source of distortion of the element, that is to say that the element acquires, after cooling, a shape different from that desired and which is obtained at the outlet of the cavity 14. Such a constant amount of material is obtained by providing a packing member having a constant reduced thickness. The production tool 8 and the production method described above make it possible to obtain packing elements having a reduced thickness, for example less than or equal to 2.2 mm, or even less than or equal to 2 mm, which allows to lighten considerably the packing element thus obtained. By way of example, a packing element having a thickness substantially equal to 2 mm has a mass 15% to 20% less than that of a conventional packing element having a thickness substantially between 2.5 mm and 2.7 mm. mm. The lining element obtained has a satisfactory appearance, without mark on its external surface 2 due to the injection of the injection material 6 and the production rates are maintained without incurring additional costs on the production tool or in the choice of the injection material 6. The packing element is suitable for use directly after its completion, without finishing operation and without modifying its external surface 2, for example by adding a coating layer intended to modify its appearance and its texture.

Claims (10)

CLAIMS1.- Tool for producing (8) a vehicle element (1) made of injected material (6), the tool (8) comprising an injection cavity (14) and at least one injection nozzle ( 20) of an injection material (6) for forming the element, the outlet (24) of said nozzle (20) being in fluid communication with the injection cavity (14), the nozzle (20) comprising a body (22) extending upstream of the outlet (24) of the nozzle (20), said body (22) receiving the injection material (6), a shutter (26) from the outlet of the nozzle ( 20) extending into said body (22) and being movable in translation in said body (22) between a closed position, wherein the shutter (26) closes the outlet (24) of the nozzle (20), and an open position, wherein the shutter (26) is spaced from the outlet (24), said shutter (26) comprising a tip (28) having a main portion (30) having a shape complementary to the shape of the output (24) of the nozzle (20), said main portion (30) extending into said outlet (24) in the closed position of the shutter (26), characterized in that the nozzle (28) further comprises, downstream of the main part (30), an end part (32) arranged to extend into the injection cavity (14) in the closed position of the shutter (26), so as to reduce the thickness of said cavity injection (14) to the right of the outlet (24) of the nozzle (20) in the closed position of the shutter (26). 2. A production tool according to claim 1, characterized in that the end portion (32) has a diameter smaller than the diameter of the main portion (30) of the tip (28). 3.- An embodiment tool according to claim 1 or 2, characterized in that the outlet (24) of the nozzle (20) is formed by a channel (25) in the form of a cylinder of revolution, the main part (30) of the tip (28) having a cylindrical shape of revolution of diameter substantially equal to the diameter of the channel (25). 4.- an embodiment tool according to claim 3, characterized in that the end portion (32) has a shape of a cylinder of revolution or a frustoconical shape, the largest diameter is smaller than the diameter of the main part (30) of the tip (28). 5.- an embodiment tool according to claim 3 or 4, characterized in that the transition zone (34) between the main part (30) and the end portion (32) of the tip (28) has a frustoconical shape of which the largest diameter is equal to the diameter of the main portion (30) and the smallest diameter is equal to the largest diameter of the end portion (32). 6. Tool according to any one of claims 3 to 5, characterized in that the transition zone (34) between the main portion (30) and the end portion (32) of the nozzle extends into the outlet channel (25) of the nozzle (20) in the closed position of the shutter (26). 7.- An embodiment tool according to any one of claims 1 to 6, characterized in that the end portion (32) of the nozzle (28) comprises a downstream end (36) shaped tip. 8. Tool according to any one of claims 1 to 7, characterized in that the body (22) of the nozzle (20) comprises a frustoconical zone (38) having a frustoconical shape in axial section, said frustoconical zone. (38) extending directly upstream of the outlet (24), so that the volume of the nozzle (20) increases progressively from the outlet (24) of the nozzle (20) upstream of the nozzle (20). ), so that the displacement of the shutter (26) to its open position causes an increase increase in the injection rate of the injection material (6) at the outlet of the nozzle (20). 9. An embodiment tool according to any one of claims 1 to 8, characterized in that the body (22) of the nozzle comprises a plurality of wings (40) extending radially from the body (22) of the nozzle towards the center of the nozzle (20), the wings (40) defining between them cells (44) having a substantially frustoconical shape in radial section so that the volume of the cells (44) increases from the center of the nozzle (20) to the body (22) of the nozzle, so that the displacement of the shutter (26) towards its open position leads to a gradual increase in the injection flow rate of the injection material (6) at the outlet of the nozzle (20). 10. A production tool according to any one of claims 1 to 9, characterized in that the injection cavity (14) is delimited by a first wall (16) intended to form the inner surface (4) of the element (1) and by a second wall (18) intended to form the external surface (2) of the element (1), said external surface (4) being intended to be visible from the outside of the element (1). ), the outlet (24) of the nozzle (20) being in fluid communication with a region of the first wall (16) or the second wall (18) for forming a visible portion of the vehicle element.