FR2563147A1 - Moulding twin headlamp reflector - Google Patents

Abstract

An article with core and outer skin is produced by injection moulding thermoplastics, first injecting the skin before the core, allowing at least the skin to harden, and demoulding. To produce a moulding with at least two symmetrical dome shapes connected by a flat plate (in partic. twin reflectors for vehicle headlamps) to process follows tages (a) the suitably shaped mould tools are prepd., with an injection gate at each centre line axis of the domes, (b) thermoplastic is injected from a common source through both gates to form the skin and the two gates are closed (c) thermoplastic from a common source is injected through the gates to form the core; the polymer feed is then interrupted (d) the skin polymer (at least) is allowed to solidify, and the moulding is ejected.

Description

 The present invention relates to a method and a device for injecting plastic parts.

It aims to perfect the technique known as bi-matibrew injection consisting, in order to produce a part comprising a core and a skin of thermoplastic materials, to
- make a mold impression of the part,
- injecting into this imprint a thermoplastic material of skin in the fluid state, the volume thus injected corresponds substantially to the volume of this material in the part to be produced but which remains assembled in the immediate vicinity of the injection orifice, in the 'footprint, insofar as this delimits a volume corresponding to the total volume of the part to be produced,
- then inject into the imprint, that is to say into the skin thermoplastic material still in the fluid state, a volume of core thermoplastic material corresponding to the volume of this material in the part to be produced, so that this material thermoplastic core, by penetrating the thermoplastic material of the skin, causes the migration of the latter in the imprint which, generally, is entirely covered with material. skin thermoplastic at the end of this injection of the core thermoplastic material,
- allow or cause a hardening of the thermoplastic skin material, at least, in order to obtain a rigid part inside the imprint,
- and release the part thus obtained from the imprint.

 The parameters of such an injection1 in terms of choice of thermoplastic materials, injection temperatures and pressures, modulation of viscosities in order to obtain an integral lining of the imprint, without rupture, by the thermoplastic skin material during the injection of the thermoplastic core material are well known to those skilled in the art.

 However, until now, this technique has only been used for the production of parts having a simple shape and modest dimensions, for which the determination of the various parameters above in the concern to avoid any break in the skin thermoplastic material during the injection of the core thermoplastic material and to ensure a homogeneous distribution of the two thermoplastic materials in the imprint remained possible, just as remained the use of a single injection orifice for both thermoplastics.

 On the other hand, as soon as the shape of the part to be produced becomes more complex, and its dimensions become larger, there were problems of lack of homogeneity in the distribution of the two thermoplastic materials in the imprint and discontinuities in one and / or the other of these materials, because certain areas of the imprint became difficult to access, for thermoplastic materials, from the single injection orifice.

 Admittedly, for the production of parts of complex shape and / or of considerable bulk, in a single thermoplastic material, a technique was known consisting in providing several injection orifices for the same imprint but, if this technique gave all satisfaction -in the case of a single thermoplastic material which it was simply a question of filling the imprint, it seemed difficult to transpose to bi-material injection when it was desired to obtain a presence, as homogeneous as possible, of the two materials thermoplastics throughout the imprint, to obtain parts having a continuous core enveloped as homogeneously as possible with a skin.

 The present invention has set itself the aim of defining an operating mode enabling bi-material injection to be carried out, as defined above, in a single impression provided with several injection orifices, in order to achieve a part having at least two d8me-shaped walls, each of which has at least approximately a symmetry of revolution about a respective axis which it intersects and which are connected together by a flat intermediate wall; by way of nonlimiting example, it aims in particular to produce, in a single piece, a plurality of reflectors in particular intended for headlights of motor vehicles, each reflector constituting one of the walls in the form of a dome; the plaintiff has already highlighted, in its patent fran Cals NO 82 11748, how the bi-material injection technique makes it possible to reconcile, in the case of such a reflector, the contradictory requirements of a smooth surface and good behavior to mechanical and thermal stresses, thanks to an appropriate choice of thermoplastic materials respectively of core (or core) and skin. (or coating layer) and to a particular operating technique of injection, applied however in the case of this prior patent to a single reflector or to any other comparable part as regards its simplicity of form and its dimensions.

To this end, the method according to the invention is characterized in that the following stages are implemented successively
a) a molding impression is made or chosen having at least two dome-shaped zones which are respectively complementary to said dome-shaped walls and each of which has at least approximately a symmetry of revolution about a respective axis which it section in an intersection zone, and a flat intermediate zone which is complementary to said intermediate wall and which connects said dome-shaped zones, by providing an injection orifice respectively in each of said intersection zones,
b) each of the injection orifices is connected to the same source of skin thermoplastic material in the fluid state, and pressure is injected into the impression, through each of the orifices, of this thermoplastic material under conditions of volume flow, duration and synchronization of the start of injection through the various orifices such that, at the same instant, through the various orifices have been introduced into the imprint of the volumes of skin thermoplastic material which, cumulatively, correspond substantially to a predetermined volume of skin thermoplastic material in the part to be produced and which, considered individually, respond to a predetermined distribution of this predetermined volume, then, at that instant, said injection is interrupted and all of the orifices are separated. injection of the skin thermoplastic source,
c) immediately, each of the injection orifices is simultaneously connected to the same source of core thermoplastic material in the fluid state and this thermoplastic material is injected under pressure into the cavity, through each of the orifices, then interrupts said injection respectively through each of these orifices and this orifice is separated from the source of core thermoplastic material at a respective instant such that, at this instant, through this orifice has been introduced into the cavity a volume of thermoplastic material of core which corresponds to a predetermined distribution of a predetermined volume of thermoplastic core material in the part to be produced, said volumes of skin material and of core material in the part to be produced and said distributions being predetermined so that s '' establishes in the intermediate zone a continuity of the skin material injected by the different orifices on the one hand, of the heart material injected by the diff other holes,
d) at least one authorizes or causes a hardening of the skin material to obtain a rigid part,
e) the latter is released from the imprint.

 The simultaneity of the end of the injection of the thermoplastic skin material and the start of injection of the thermoplastic core material by all the injection orifices makes it possible to standardize as best as possible the conditions under which the thermoplastic core material, as it is injected, causes the thermoplastic skin material to migrate inside the impression and its plating against it, while respecting the volumes and distributions predetermined in the indicated manner allows ensure that, in the intermediate zone, continuity is established both in the skin and in the heart of the part produced; it will be noted that this choice of the intermediate zone of the imprint as the zone in which continuity is established in the thermoplastic material of the skin and in the thermoplastic material of the core coming from the various injection orifices makes it possible to ensure this continuity in optimal conditions, linked on the one hand to the simple geometry of this zone and on the other hand to the fact that it can be reached by either of the materials, from the different injection orifices, by a path as little winding as possible; moreover, in the particular case where the part produced comprises a plurality of reflectors defined by its domed walls, it is preferable that any defects, occurring rather in the skin than in the heart, be located on the intermediate wall. devoid of optical function, which is formed by the intermediate zone of the imprint, rather than in the zones constituting the reflectors proper.

 Even in the frequent case where the dome-shaped walls have different volumes, as naturally as the corresponding zones of the imprint, the simultaneity of the end of the injection of the thermoplastic material of skin with tape b is easily obtained ) by injecting the skin material through the different orifices at a substantially identical rate and for different durations, determined by the distribution, between the different orifices, of the volume of thermoplastic skin material to be provided for all of the part, and by delaying the start of the injection through the different orifices.

 It will be noted that, at the end of step c) above, there exists, opposite each of the injection orifices, in the cavity, a zone of core thermoplastic material which is not coated with thermoplastic material of skin t if necessary, it is advantageously possible, between step c) and step b), to reconnect each of the injection orifices to the source of skin thermoplastic material and thus reinject this material under pressure into the 'imprint, by each of the orifices; in the part obtained, the heart is then completely coated by the skin.

Advantageously, for this purpose, during step a), it is possible to provide in each of the intersection zones a conduit opening into the cavity opposite the corresponding injection orifice and, inside this conduit , a piston delimiting the imprint towards the latter and movable between an injection position and a retracted position, set back relative to the injection position; then, the piston is kept in the injection position during steps b) and c), but
it is placed in the retracted position after step c) and during the reinjection of skin thermoplastic material; thus, thanks to the choice of an appropriate stroke of the piston between its injection position and its retracted position as well as thanks to an appropriate choice of these two positions, it is possible to place the thermoplastic material of skin reinjected in direct extension of the material. skin thermoplastic injected during step b), if necessary; more generally, the retraction of the piston and the reinjection of skin thermoplastic material make it possible to "rinse" the injection orifices of the core thermoplastic material finding it there at the end of step c), and lining them with skin thermoplastic material to make them ready for direct processing, again from step b) in a following cycle for producing a part.

The present invention also provides, for implementing the method, a device characterized in that it comprises
- a mold delimiting a molding imprint having at least two dome-shaped zones, each of which has at least approximately a symmetry of revolution about a respective axis which it cuts in an intersection zone and an intermediate zone connecting said zones dome-shaped, said mold further having a plurality of injection orifices in the proportion of one in each intersection zone,
- a distribution block, comprising two inlets, each of which is capable of being connected to a source of thermoplastic material in the respective fluid state, of outlets in a number identical to that of the injection orifices, to each of which is capable of '' be connected a respective one of these outputs, two independent circuits each of which connects a respective one of the inputs to each of the outputs and, in the immediate vicinity of each of the outputs, respective means for, at will, closing this output or the to put in communication with one of the circuits or to put it in communication with the other circuit, the means corresponding to the different outputs being mutually independent.

 Advantageously, each circuit has the same length and the same passage section from the respective inlet to each of the outlets, and means for heating the distributor block are provided; in addition, according to a particularly advantageous embodiment, the mold comprises in each of the intersection zones the above-mentioned movable piston-piston assembly.

 Other characteristics and advantages of the method and of the device according to the invention will emerge from the description below, relating to a non-limiting mode of implementation, as well as from the appended drawings which form an integral part of this description.

 - Figures 1 and 2 show perspective views of an example of a part capable of being produced in accordance with the present invention, namely a part grouping two reflectors for headlights of motor vehicles.

 - Figure 3 shows a device for producing this part by injection, in section through a plane including the axes of the molding imprint corresponding to the optical axes of the two reflectors.

 - Figure 4 shows a view of part of the device in section along line IV-IV of Figure 3.

- Figures 5 and 6 show a view of this part of the device respectively according to arrow V in Figure 4 and in section along line VI
VI of this figure.

 - Figure 7 shows an enlarged detail of Figure 6.

 - Figure 8 is a diagram illustrating the different phases of the injection.

 - Figure 9 shows the detail IX of Figure 3 at the end of the injection of the thermoplastic core material, on a greatly enlarged scale.

 Naturally, although the invention is described with reference to the production of a part grouping two reflectors, its field of application is in no way limited to such parts and the person skilled in the art can easily foresee, without however going out within the scope of the present invention, the variants to be made to the method and device which will be described in order to adapt them to each configuration of parts.

 In the example illustrated, the part 1 to be produced is broken down, as shown in FIGS. 1 and 2, into two dome-shaped walls 2, 3, juxtaposed, intended to constitute reflectors, and into an intermediate wall 4 connecting these walls 2 and 3 between them.

 The wall 4 is flat, and delimited by two faces 11, 12 approximately planar and rectangular, mutually parallel, connected by an edge 13 this wall 4 is for example intended to ensure the fixing of the part 1, and with it reflectors formed by the walls 2 and 3, on a bodywork part of the vehicle by integrating with the general outline of the bodywork.

 The walls 2 and 3 form a projection on the same face 11 of the wall 4; the wall 2 is delimited by two faces 5, 6 in the form of a paraboloid of revolution around a same axis 7 which defines the optical axis of the corresponding reflector and can be oriented perpendicular to the wall 4, in a manner not illustrated, or, as illustrated, obliquely to it; the faces 5 and 6 are connected respectively to the face 12 and to the face 11 along approximate ellipses 14, 15 ~ the paraboloid of revolution defining each of them intersects the axis 7, around which the wall 2 has a orifice 16, of cylindrical periphery of revolution around the axis 7, intended to receive a lamp; the wall 2, likewise, is delimited by two faces 8, 9 in the form of a paraboloid of revolution around an axis 10 parallel to the axis 7, these faces 8 and 9 connecting respectively to the face 12 and to the face it along approximate ellipses 17, 18; the paraboloides respectively defining the faces 8 and 9 of the wall 3 intersect the axis 10 but the wall 3 is pierced around the latter with an orifice 19 for receiving the lamp, with cylindrical periphery de-rdvolution around 19 axis 10 on note that the part obtained by the process which will be described has continuous walls 2 and 3, that is to say deprived of the orifices 16 and 19 which must be formed after the part has been removed from the impression of molding; the injection process which will be described provides a part whose walls 2, 3 in the form of a dome -cut their respective axes 7, 10.

 To produce such a part in accordance with the present invention, a mold 20 is produced or chosen as illustrated in FIG. 3.

 This mold 20 is made up of two parts 21 and 22 which are juxtaposed and joined together during injection to define a molding imprint 23 complementary to the part 1 to be produced with the exception of the orifices 16 and 19, but which can be separated to allow release.

 The footprint 23 thus delimited by the two parts 21 and 22 of the mold 20 supposed to be juxtaposed and mutually secured has two zones 24, 25 in the shape of a dome connected by a flat intermediate zone # 26; zones 24 and 25 are respectively complementary to walls 2 and 3 supposed to be deprived of orifices 16 and 19, and have the same symmetry of revolution as the latter, around a respective axis 27, 28 of the mold, the two axes 27 and 28 occupying relative positions identical to those of axes 7 and 10 on the part 1 to be produced; zones 24 and 25 intersect the respective axis 27, 28 in a respective intersection zone 29, 30; the intermediate zone 26 is itself complementary to the wall 4.

 To this end, advantageously, the part 21 has, on an approximately flat face 31 intended on the one hand for juxtaposition with the part 22 and on the other hand to form the face 12 of the wall 4, two protuberances defining convex faces 32 and 33 intended to respectively form the face 5 and the face 3, and the part 22 comprises, recessed in a face 34 matching the face 31 around the imprint 23 when the parts 21 and 22 are joined together to define such an imprint 23, a recessed face 36 intended to form the face 11 as well as, by its connection 37 with the face 34, the edge 13 of the zcme 4, and the faoe 36 having eLrvame in hollow two concave faces 39 and 40 intended to form faces 6 and 9 respectively; it will be noted that the faces 31 and 36 define the zone 26 between the zones 24 and 25 of the imprint 23.

 In each of the zones 29 and 30, and more precisely respectively at the intersection of the face 39 with the axis 27 and at the intersection of the face 40 with the axis 28, an orifice opens into the imprint 23 respective injection 41, 42, arranged in part 22 of the mold.

 Each of the orifices 41, 42 is defined by one end of a respective channel 50, 51 of a respective nozzle 43, 44 mounted in a respective bore 45, 46 of the part 22, of which the nozzles 43 and 44 are integral at least during the injection stages.

 Thus opening inside the cavity 23 through the injection orifices 41 and 42, the channels 50 and 51 also open out of this cavity 23, that is to say outside the mold 20, respectively by an input 52 and an input 53.

 Connection means for example with screws 47, 48 provided respectively on the nozzle 43 and on the nozzle 44 secure the latter with a distributor block 49 so that with the inlet 52 communicates an outlet 54 of the block 49, and qu 'with input 53 communicates an output 55 of the block.

 Each of these outlets 54 and 55 is constituted by one end of a respective channel 56, 57 furthermore having a mouth end 58, 59 in a respective bore 60, 61 of the distributor block 49.

 More precisely, each mouth end 58, 59 opens into the respective bore 60, 61, by a face of the latter, respectively 62, 63, cylindrical of revolution around a respective axis 164, 165 around which can rotate, inside the bore considered, a respective plug 64, 65 having in tight contact tee with the aforementioned cylindrical face, respectively 62, 63 of this bore a closely complementary face, that is to say also cylindrical of revolution with a substantially identical diameter, respectively 66, 67.

 It will be noted that the bores 60 and 61 are identical, as are the bushels 64 and 65 which will be described below, and just as are identical the assemblies formed on the one hand by the channels 50 and 56, rectilinear axis 27, and on the other hand by channels 51 and 57, rectilinear axis 28; in particular, the respective lengths of the assembly 50-56 along the axis 27, between the mouth end 58 and the injection orifice 41, and of the assembly 51-57, along the axis 28 , between the mouth end 59 and the injection orifice 42 are identical, as are the useful sections or respective passage sections of these assemblies.

 In the face 62 of the bore 60 open, in addition to the end 58 of the channel 56, respective ends 68, 69 of two other channels 70, 71 which are also arranged in the distribution block 49 and also have another end respective 72, 73 in which they open into the face 63 of the bore 61 between their two respective ends, 68 and 72 with regard to the channel 70, 69 and 73 with regard to the channel 71, these two channels 70 and 71 have the same developed length, and their useful sections or passage sections are identical to each other as well as to the respective passage sections of the assemblies 50-56 and 51-57.

 At the mid-length of each of these channels 70 and 71 opens, by an end such as 74, a respective inlet channel 75, 76, arranged in the distributor block 49 and moreover having a second end such as 77 that an internal channel such as 78 of a respective connection such as 79, secured to the block 49 by suitable means such as 80, for example h ViF connects to a respective injection head such as 81, from a respective source 82 , 83 of a thermoplastic material in the fluid state and under pressure; the injection heads such as 81 are identical, as are identical, in terms of developed length and useful section or passage section, the channels such as 78 of the fittings such as 79, as well as the inlet channels 75 and 76.

 The sources of thermoplastic material in the fluid state, under pressure, 82 and 83 can be of any type known per se, by a person skilled in the art, for injection molding and have therefore not been detailed. note that the distributor block 49 constitutes an intermediary between these sources 82 and 83 and the injection nozzles 43 and 44 and, to maintain the thermoplastic materials coming from these sources 82 and 83 in the fluid state up to these nozzles 43 and 44, the distributor block 49 is advantageously provided with own heating means shown schematically for example at 84, maintaining the distributor block 49 at a temperature higher than the plasto-elasticity temperature of the thermoplastic materials supplied, as will appear below, by the sources 82 and 83 themselves presenting such a temperature; these heating means 84 are for example constituted by electrical resistors as illustrated, but could also be of another nature.

 Therefore, as soon as the sources of thermoplastic material & fluid state and under pressure 82 and 83 are in service as well as the heating means 84, the channels 75 and 70 of the distributor block 49 are filled, up to the ends 68 and 72 of the channel 70, of thermoplastic material in the fluid state and under pressure from the source 82, while the channels 76 and 71 are filled, up to the ends 69 and 73 of the channel 71, with such a material thermoplastic in the fluid state and under pressure from the source 83.

 The entry of one or other of these thermoplastic materials into the channel 56 and / or into the channel 57 is selectively controlled by rotation of the plug 64 around its axis 164 inside the bore 60 of the body distributor 49, and / or of the plug 65 around the axis 165 inside the bore 61 of this distributor block.

 The design of plugs 64 and 65 for this purpose, as well as the relative arrangement of the ends 58, 68, 69 in the face 62 of the bore 60 and that of the ends 59, 72, 73 in the face 63 of the bore 61 , for this purpose, will now be described with reference to Figures 5 to 7, illustrating the bore 61 and the plug 65, to which the bore 60 and the plug 64 are respectively identical.

 With reference to the axis 165, the respective ends 72 and 73 of the channels 70 and 71 are diametrically opposite, while they are placed at right angles to the end 59 of the channel 57.

 To put the latter in communication with one or the other of the channels 70 and 71, selectively, or to interrupt any communication between the channel 57 and the two channels 70 and 71 without the latter ever being put in mutual communication, the plug 65 is pierced by two independent channels 85, 86 placed symmetrically to each other respectively on either side of a plane 87 linked to the plug 65 and passing through the axis 165; the channel 85 opens into the face 67 of the plug 65 by two ends 87 and 88 placed at 900 relative to one another, just as the channel 86 opens into this same face by two ends 89 and 90 also placed at 900 relative to each other, these angular differences being understood with reference to the axis 165; the two ends 87 and 89 are adjacent and angularly spaced by 450, at the rate of 22030 respectively on either side of the plane 87, with reference to the axis 165 while the adjacent ends 88 and 90 are mutually angularly spaced , with reference to axis 165, of 1350 also equally distributed on either side of plan 87.

 The channels 85 and 89 have, between their two respective ends, an identical length and a useful section or passage section equal to those, identical to each other, of the channels 57, 70, 71.

 In addition, there remains between the ends 87 of channel 85 and 89 of channel 86 a zone 91 of the face 67 of the plug 65 having an angular development, with reference to the axis 165, greater than the angular development, with reference to this axis. , from the end 59 of channel 57.

Thus, by rotation of the plug 65 around the axis 165 in the bore 61, this plug can be brought in particular into three positions, identified by the corresponding position of the plane 87:
- A first position A, identified at 87a, in which the plane 87 of the plug includes the axis 28 common to the zone 25 of the imprint 23 and to the channel 57; then, opposite the end 59 of the latter is the zone 91 of the face 67 of the plug 65, which thus closes the end 59 of the channel 57 t further, preferably, thanks to an appropriate choice of the angular spacing, with reference to the axis 165, between the ends 87 and 88 of the channel 85 on the one hand, the ends 89 and 90 of the channel 86 on the other hand, opposite the end 72 of the channel 70 is then placed an area 92 of the face 67 located between the ends 87 and 88 of the channel 85, while opposite the end 73 of the channel 71 is placed an area 93 of the face 67 located between the ends 89 and 90 of the channel 86 .; in other words, all communication is then interrupted between channel 57 on the one hand, channels 70 and 71 on the other hand, as well as between these channels 70 and 71;
- a second position B, obtained by rotation of the plug 65 on 22030 from this first position; in this position, indicated at 87b in FIG. 5 and which corresponds to the positions illustrated in FIGS. 6 and 7, the ends 87 and 88 of the known channel 85 coincide respectively with the end 59 of the channel 57 and with the end 72 of the channel 70, so that the channel 57, and with it the injection orifice 42, is in communication with the source 82; on the other hand, the end 73 of the channel 71 is preferably then still placed opposite the zone 93 of the face 67 of the plug 65, which closes it
a third position C, indicated at 87c in FIG. 5, this position being obtained by rotation of the plug 65 of 22 30 relative to the first position
A, in the opposite direction to the direction leading to the second position B; then, the ends 89 and 90 of the channel 86 are placed respectively opposite the end 59 of the channel 57 and opposite the end 73 of the channel 71, which puts the injection orifice 42 in cozmunication with the source 83; on the other hand, facing the end 72 of the channel 70, the zone 92 of the face 67 of the plug 65 is then placed, which closes the channel 70.

 The positioning of the plug 65 according to one of these orientations, with reference to the axis 165, relative to the distributor block 49 can between carried out by any known means, and for example under the action of a jack 94 having a body 95 secured to the distributor block 49 and a rod 96 connected to the plug 65 by means of a crank 97.

In a very similar way, the respective t-ends 68 and 69 of the channels 70 and 71 in the bore 60 are diametrically opposite with reference to the axis 164, and located at right angles to the end. 58 of the channel 56, and the plug 64 internally has two channels at all points similar to the channels 85 and 86, the assembly being dimensioned as described with reference to the bore 61 and the plug 65, so that the plug 64 can be brought, by rotation about the axis 164 inside the bore 60 under the action of means such as a jack 98 acting on the plug 64 via a crank 99, independently of the actuation of the plug 65 by the jack 94, in three positions, namely
- A first position A 'in which the plug 64 has opposite the end 58 of the channel 56, as well as preferably opposite the respective ends 68 and 69 of the channels 70 and 71, solid areas of its face 66, so to interrupt all communication between channels 56, 70, 71
- A second position B 'in which one of the internal channels of the plug 64 connects the end 58 of the channel 56 and the end 68 of the channel 70 while continuing on the other hand to interrupt all communication between the end 58 of the channel 56 and the end 69 of the channel 71, to put the injection orifice 41 in communication with the source 82
a third position C ′, in which the other internal channel of the plug 64 places the end 58 of the channel 56 in communication with the end 69 of the channel 71, however interrupting the communication between the end 58 of the channel 56 and the end 68 of channel 70, to put the injection orifice 41 in communication with the source 83.

 It is understandable that, it is possible to inject at will thermoplastic material coming from one or the other of the sources 82 and 83, by one or the other of the orifices 41 and 4-2, by interrupting at will this injection.

 It will be noted that, whatever that of the orifices 41 and 42 that we are considering, and whatever that of the sources 82 and 83 that we are considering, a communication between an injection orifice and a source establishes between them a circuit whose developed length is identical, with a useful section or passage section also identical, which standardizes from this point of view the conditions of injection through the orifices 41 and 42, which are injected from the material from source 82 or material from source 83.

 The arrangement of the injection orifices 41 and 42 along the axes 27, 28 of the dome-shaped zones 24, 25 of the cavity 23, preferably in the concave faces 39, 40 delimiting this cavity 23 in the mold part 22 , ensures optimum distribution of the materials thus injected.

 Incidentally, preferably, as illustrated, it is further provided opposite each of the injection orifices 41, 42 along the respective axis 27, 28, that is to say in each of the convex faces 32 , 33 of the imprint 23 in the corresponding zone 29, 30 of intersection with this axis 27, 28, a conduit, respectively 100, 101, in which a respective piston 102, 103 can move.

 Each of the conduits 100, 101 has two trunks, each of which is delimited by a cylindrical outer peripheral face of revolution around the corresponding axis 27, 28, namely a first section 104, 105 adjacent to the imprint 23 and having a larger diameter to the dimensions that the associated injection orifice 41, 42 has transversely to the axis correspca # idant 27, 28, and a second section 106, 107 of smaller diameter connecting to the first by a shoulder 108, 109 and opening outside the mold 20, and more precisely of the part 21 thereof, opposite the nozzle 43 along the axis 27 and the nozzle 44 respectively along the axis 28, respectively.

 Each of the pistons 102 and 103 is in the form of a flat disc, oriented transversely with respect to the corresponding axis 27, 28, with a diameter substantially equivalent to that of the respective peripheral faces of the sections 104 and 105 of the conduits 100, 101 so that the piston 102 can slide in the section 104 of the conduit 100, along the axis 27, while the piston 103 can slide inside the section 105 of the conduit 101 along the axis 28, thereby varying the volume of the imprint 23 respectively in the zone of intersection 29 of the zone 24 with the axis 27 or in the zone 30 of intersection of the zone 25 with the axis 28.

 To this end, each of the pistons 102 and 103 preferably has, along the corresponding axis 27, 28, a thickness less than the extent, along this axis, of the section 104, 105 of conduit 100, 101 corresponding.

Each of the pistons 102, 103 is integral with one end of a respective rod 110, 111 slidably engaged, along the corresponding axis 27, 28, in the corresponding conduit 100, 101 and more precisely in the section 106, 107 of the latter having the smallest diameter; this rod 110, 111 also has, outside of the mold part 21, a second end secured to the rod 112, 113 of a jack 114, 115 moreover having a body 116, 117 secured to the piece of mold 21; the two cylinders 114 and 115 can be controlled independently of one another to place the corresponding piston 1028 103 at will, in particular in one or the other of two positions; in a first position, called the injection position, the piston 102, by a face 118 facing inward of the cavity 23, either completes the face 32 thereof, or forms a projection relative to this following face the axis 27 while in the other of these positions, called the retraction position, it is retracted along the axis 27 inside the section 104 relative to its injection position likewise, by a face 119 turned towards the inside of the imprint 23, the piston 103 completes the face 33 of the latter or forms a projection relative to this face along the axis 28 in an injection position, while it is placed in withdrawal inside the section 105, along the axis 28, relative to this injection position in a retracted position
Such a molding device is used in the following manner, in accordance with the method according to the invention.

 A first step in implementing the method consists in making or simply choosing the two mold parts 21 and 22 suitable for being joined together to define the molding imprint 23 of the part 1 to be produced, then in bringing these two parts together from mold 21 and 22 into mold 20 .; it will be noted that an example has been illustrated in which the walls 2 and 3 of the part 1 have substantially different volumes, the wall 2 of greater volume being intended for example to form a reflector for a dipped headlight while the wall 3 lower volume is- intended to form a headlamp reflector, and that, therefore, the area 24 of the footprint 23 has a volume greater than that of the area 25 thereof.

 The assembly described is then carried out with reference to FIGS. 3 and 4, by assembling the nozzles 43 and 44 on the one hand on the distributor block 49 which is connected to the injection heads such as 81 from the sources 82 and 83, and on the other hand to the mold part 22 to define the injection orifices 41 and 42; the two plugs 64 and 65 then occupy, under the action of the jacks 94 and 98, the position A, A 'in which it # s #'. interrupts all communication respectively between the channels 56, 70, 71 and between the channels 57 , 70, 71, and the jacks 114 and 115 place and hold the pistons 102 and 103 in their injection position.

 After a purge of all the channels, thermoplastic material in the fluid state, under pressure, from the source 82 fills the inlet channel 75 and the channel 70 of the block 49 while also thermoplastic material in the fluid state and under pressure from the source 83 fills the inlet channel 76 and the channel 71, in both cases up to the bores 60 and 61 in which the plugs 64 and 65 maintain insulation from the respective mouth ends 58, 59 of the channels 56, 57 leading to the injection orifices 41, 42; the distributor block 49 is maintained by the heating means 84 at a temperature suitable for ensuring the fluidity of the two thermoplastic materials; in other words, the source 82 provides a thermoplastic material brought to a temperature higher than its plastoelasticity temperature, the source 83 provides a material. thermoplastic also brought to a temperature higher than its plastoelasticity temperature, and the block 49 is maintained by the means 84 at a temperature higher than the higher of these two plastoelasticity temperatures; these temperatures are known to those skilled in the art, according to the type of thermoplastic material used and according to the possible charges, as well as the injection pressures to be respected and these parameters will not be detailed further.

 The thermoplastic material supplied by the source 82 will be supposed intended to form the skin or coating layer of the part 1, while the plastic material coming from the source 83 will be supposed intended to form the heart or soul of this part.

 Figure 8 illustrates the different phases of the actual injection, which can then begin.

 On the abscissa were the times, and, on the ordinate, the directions of bushels 64 and 65, as defined above.

 If we define by to an initial instant when the assembly illustrated in FIG. 3 is finished, and where the thermoplastic materials coming respectively from source 82 and source 83 respectively fill channels 75 and 70 and channels 76 and 71 to the bores 60 and 61, the pistons 102 and 103 occupying their injection position, at a time tl, thanks to the jack 98, the plug 64 associated with the zone 24 of the imprint 23 is placed. -d say to the dome-shaped area of this imprint having the maximum volume, in its position B ′ in which it places the mouth end 58 of channel 56 in communication with the end 68 of channel 70, this which causes the thermoplastic skin material to enter the zone 24 of the imprint 23, with a volume flow controlled by the injection pressure, determined by a person skilled in the art, and by the useful or passage section in the channels 70, 56, 50, and in the plug channel 64 which corresponds to the plug channel 85 65; at a later time t2, the plug 65 is also placed, by means of the jack 94, in its second position B, in which its channel 85 puts the mouth end 59 of the conduit 57 in communication with the end 72 of the conduit 70 and the filling of the zone 25 of the imprint 23 then begins via the orifice 42, with a flow which, taking into account the dimensional identities described above, is equal to the flow with which began then continues the filling of the zone 24 of the imprint 23; it will be noted that, for this purpose, the inlet channel 75 as well as the channel 78 of the connector 79 have a passage section or useful section at least twice that of the duct 70.

 Then, at the same instant t31 the two plugs 64 and 65 are brought back, by the jacks 98 and 94, to their initial position A: A in which they isolate the channels 56 and-57, that is to say the orifices injection 41 and 42, vis-à-vis the two channels 70 and 71 and therefore vis-à-vis the two sources 82 and 83.

 The offset between the times t1 and t2 where D mlncent respectively the filling of the area 24 of larger volume and that of the area 25 of smaller volume can be easily determined by the skilled person so that, at this instant t31 through the injection orifices 41 and 42 have been introduced into the imprint 23 of the respective volumes of skin thermoplastic material which, cumulatively, correspond substantially to a predetermined volume of this thermoplastic material in the part 1 to be produced and which, considered individually1 respond to a predetermined distribution of this predetermined volume.

 Immediately after the end of this injection of the skin thermoplastic material, that is to say practically at instant t31, the two bushels 64 and 65 are simultaneously brought into their third position - # C in which they respectively connect the end of mouth 58 of channel 56 and end of mouth 59 of channel 57 with channel 71, that is to say with the source of core thermoplastic material 83 whose injection into the imprint 23 then begins simultaneously, by the two injection orifices 41 and 42 taking into account the dimensional characteristics indicated above, and that the channel 76 as well as the connecting channel (corresponding to channel 78) of its connection (corresponding to connection 79) with the source 83 have a useful cross section or passage at least twice that of the channel 71, the thermoplastic core material is introduced with an identical flow rate through the injection orifice 41 and through the injection orifice 42.

 As a result, the zone 25 of lower volume is filled more quickly than the zone 24 of greater volume, and, at an instant t4, the cylinder 65 is replaced by the jack 94 in its first position A to interrupt the injection. in zone 25 while it is only at a later instant t5 that the plug 24 is also replaced in its first position, by means of the jack 98, to also interrupt the injection into zone 24 of the 'imprint 23; taking into account the dimensional characteristics described above, the injection rate in the area 24 of the imprint 23 is not affected by the end of the injection in the area 25.

 The instant t4 is determined so that between t3 and t4 has been introduced through the injection orifice 42, in the zone 25 of the imprint 23, a volume of thermoplastic core material corresponding to a predetermined distribution d '' a total predetermined volume of this thermoplastic material in the part 1 to be produced, while the instant t5 is determined so that between t3 and t5 - has also been introduced into the zone 24 of the imprint 23 a volume of thermoplastic material corresponding to such a predetermined distribution of the volume of core thermoplastic material in the part to be produced.

 The overall volumes of skin material on the one hand, of heart material on the other hand thus injected, and the distribution of these respective volumes between the two injection orifices 41 and 42 are predetermined so that at the instant t4, the core material and the skin material introduced by the orifice 42 in the zone 25 of the imprint 23, the skin material introduced first being pushed by the core material introduced second, arrive in the zone 26 of the imprint 23, and that at time t5, the core thermoplastic material and the skin thermoplastic material introduced through the orifice 41 in the zone 24 of the imprint, the core material introduced as the second push the skin material introduced first, also reach this zone 26 to ensure continuity at this level on the one hand in the thermoplastic core material, and on the other hand in the thermoplastic skin material as illustrated in Figure 9 where we designated the material re thermoplastic of heart by 120 and the thermoplastic material of skin by 121.

 Given the identity of the injection flow rates via the orifices 41 and 42, whatever the source 82 or 83 in service, the person skilled in the art can easily determine the offsets to be observed for this purpose between the instant tl and t2 on the one hand, the instants t4 and t5 on the other hand, by determining the injection times t3 - t1 t3-t2, t4-t3, t5-t3 of the different thermoplastic materials through the different injection orifices 41, 42 .

 It will be noted that at time t5, the channels 51 and 57 on the one hand, the channels 50 and 56 on the other hand are filled with core material, which means on the one hand that opposite the orifices d injection 41 and 42, there is no total coating of the thermoplastic core material with the thermoplastic skin material, and on the other hand that before repeating the injection cycle which has just been described, starting by injecting the skin thermoplastic material, it is necessary to rinse the channels 50, # 51, 56, 57 from all traces of thermoplastic core material.

 Consequently, according to a preferred embodiment of the method according to the invention, at an instant t6 immediately following the instant t51, for example, by means of the jacks 98 and 94, the plugs 64 and 65 are replaced in their second position B ', B, to put b again the mouth end 58 of the channel 56 and the mouth end 59 of the channel 57 in communication with the channel 70 and, via the latter, with the source 82 of thermoplastic skin material and a new injection of this material is carried out, via the orifices 41 and 42, until an instant t7 determined so that, at least, the thermoplastic skin material is substituted for the thermoplastic core material in the channels 50, 51, 56, 57, and this injection is interrupted at time t7 by replacing the plugs 64 and 65, by means of the jacks 98 and 94, in their initial position X, A in which they interrupt all communication between the injection orifices 41 and 42 on the one hand, and sources 82 and 83 on the other; this rinsing is facilitated by a movement of the pistons 102 and 103, under the action of the jacks 114 and 115, from their initial injection position, which they occupy at time t6, to their retraction position which they currently occupy t7.

 Then, in a manner known per se, it authorizes or causes a hardening of the thermoplastic material of the skin, at least, and possibly of the thermoplastic material of the core, by authorizing or causing a cooling of the mold 20, so as to obtain the inside the imprint 23 of the latter a rigid part, then the two mold parts 21 and 22 are separated to release the part thus obtained from the imprint 23.

 To obtain the part illustrated in FIGS. 1 and 2, it is recalled that it is then necessary to practice the orifices 16 and 19.

 Then, the pistons 102 and 103 are replaced, by means of the jacks 114 and 115, in their injection position and the parts 21 and 22 are assembled again to define an imprint 23, which again defines to to from which we can chain the injection steps described above; the heating of the block 49, by the means 84, ensures the maintenance in the fluid state of the thermoplastic materials, of # injection heads such as 81 to the injection orifices such as 41 and 42, outside the injection phases.

 Naturally, although the present invention has been described with reference to the production of a clamp having only two domed walls, joined by an approximately planar wall, the method and the device which have just been described are not limited to such a case, and a person skilled in the art will easily understand that one could achieve thus, by means of an appropriate impression 23 and by providing as many injection orifices as there are domed walls of the more complex parts; the transposition of the offsets between the injections by the two orifices 41 and 42 in the event that a greater number of orifices is provided is within the domain of normal abilities of a person skilled in the art, and therefore does not depart from the scope of the present invention which, in general, can experience many variants of implementation which are not outside its scope.

Claims (14)

 1. Method for producing a part comprising a core and a skin by injection of thermoplastic materials, consisting in producing a molding impression of the part to be produced, in successively injecting into said imprint a thermoplastic material of skin in the fluid state and a core thermoplastic material in the fluid state, to allow or cause hardening of the skin thermoplastic material, at least, to obtain a rigid part, and to release the latter from the imprint, characterized in that, for make a part (1) having at least two walls (2, 3) in the form of a dome, each of which has at least approximately a symmetry of revolution about a respective axis (7, 10) which it cuts and which are connected between them by a flat intermediate wall, the following steps are successively implemented:  a) a molding impression (23) is produced or chosen having at least two dome-shaped zones (24, 25) which are respectively complementary to said dome-shaped walls (2, 3) and each of which has at least approximately, a symmetry of revolution about a respective axis (27, 28) which it intersects in an intersection zone (29, 30), and a flat intermediate zone (26) which is complementary to said intermediate wall (4 ) and which connects said dome-shaped zones (24, 25), by providing an injection orifice (41, 42) respectively in each of said intersection zones (29, 30),  b) each of the injection ports t41, 42) is connected to the same source (82) of skin thermoplastic material in the fluid state, and is injected under pressure into the cavity (23), by each of the orifices (41, 42), of this thermoplastic material under conditions of volume flow, duration and synchronization of the start of injection by the various orifices (41, 42) such that, at the same instant (t3), by the different orifices (41, 42) have been introduced into the impression (23) of the volumes of thermoplastic skin material which, cumulatively, correspond substantially to a predetermined volume of thermoplastic skin material in the part (1) to be produced and which, considered individually, respond to a predetermined distribution of this predetermined volume, then1 at said instant (t3), said injection is interrupted and all the injection orifices (41, 42) are separated from the source (82) of material skin thermoplastic,  c) immediately, each of the injection orifices (41, 42) is simultaneously connected to the same source (83) of thermoplastic core material in the fluid state and this thermoplastic material is injected under pressure into the cavity (23), by each of the orifices (41, 42), then said injection is interrupted respectively by each of these orifices (41, 42) and this orifice (41, 42) is separated from the source (83) of material thermoplastic core at a respective instant (t5, t) such that, at this instant (t5, t4), through this orifice (41, 42) has been introduced into the cavity (23) a volume of thermoplastic core material which corresponds to a predetermined distribution of a predetermined volume of thermoplastic material of the core in the part (1) to be produced, said volumes of skin material and of core material in the part to be produced (1) and said distributions being predetermined in such a way so that there is established in the intermediate zone (26) a continuity of the skin material (121) injected through the various orifices (41. 42) on the one hand, of the core material (120> injected through the various orifices (41, 42) on the other hand,  d) at least one authorizes or causes hardening of the skin material (121) to obtain a rigid part (1>,  e) the latter is released from the imprint (23>.  2. Method according to claim 1, characterized in that, when the ddme-shaped walls (2, 3) have different volumes, step b) is implemented by injecting the skin material by the different orifices (41, 42) at a substantially identical flow rate and for different durations (t3-t1, t2-t1> by delaying the start of injection over time by these different orifices (41, 42).  3. Method according to any one of claims 1 and 2, characterized in that, during step a), the injection orifices (41, 42) are provided in concave zones (39, 40) of the 'imprint (23).  4. Method according to any one of claims 1 to 3, characterized in that, between step c) and step d), each of the injection orifices (41, 42) is again connected to the source. (82) of thermoplastic skin material and this material is reinjected under pressure into the impression (23), through each of the orifices (41, 42), then this reinjection is interrupted and the orifices are separated from injection (41, 42) of the source (82) of skin thermoplastic material.  5. Method according to claim 4, characterized in that, during step a), there is provided in each of the intersection zones (29, 30) a conduit (100, 101) opening into the imprint ( 23) opposite the corresponding injection orifice (41, 42) and, from inside this conduit (100, 101), a piston (102, 1033 delimiting the imprint (23) towards this conduit (100 , 101) and movable between an injection position and a retracted position, set back from the position of inject # Lion,  and in that the piston (192, 103) is kept in the injection position during steps b) and c), and it is placed in the retracted position after step 4> and during said reinjection.  6. Part obtained by implementing the method according to any one of claims 1 to 5  7. Part according to claim 6, characterized in that it comprises a plurality of reflectors in particular intended for headlights of motor vehicles, each reflector constituting one of said walls (2, 3j in the shape of a dome.  8. Device for implementing the method according to any one of claims 1 to 5, characterized in that it comprises  - a mold (20) delimiting a molding imprint (23) having at least two zones (24, 25) in the form of a dome each of which has at least approximately a symmetry of revolution around a respective axis (27, 28) that 'it cuts in an intersection zone (29, 30), and an intermediate zone (26) connecting said dome-shaped zones (24, 25), said mold (20) further having a plurality of orifices injection (41, 423 at the rate of one in each intersection zone (29, 30),  - a distribution block (49), comprising two inputs (75, 76) each of which can be connected to a respective source (82, 83) of thermoplastic material in the fluid state, outputs (54, 55) in a number identical to that of the injection orifices (41, 42), to each of which can be connected a respective one of these outputs (54, 55), two independent circuits (70, 71) each of which connects a respective one of the inputs (75, 76) at each of the outputs (54, 55l and, in the immediate vicinity of each of the outputs (54, 55), respective means (64, 65) for, at will, closing this output (54, 55) or put it in communication with one or the other circuit, the means (64, 65) corresponding to the different outputs being mutually independent.  9. Device according to claim 8, characterized in that each circuit (70, 71) has the same length and the same passage section from the respective inlet (75, 76) to each of the outlets (54, 55).  10. Device according to claim 8 or 9, characterized in that it comprises means (84] for heating the distributor block (49>.  11. Device according to any one of claims 8 to 10, characterized in that the injection orifices (41, 42) are located in a concave zone (39, 40) of the impression (23).  12. Device according to any one of claims 8 to 11, characterized in that the mold (20) comprises, in each of the intersection zones (29, 30), a conduit (100, 101) opening into the cavity (23) opposite the corresponding injection orifice (41, 42> and, inside this duct (100, 101), a piston (102, 103) delimiting the cavity (23) towards this conduit (100, 101) and movable between an injection position and a retraction position, set back from the injection position, and in that means (114, 115) are provided for, at will, place the piston (102, 103) in one or the other of said positions.  13. Device according to any one of claims 8 to 12, characterized in that the means (64, 65) for, at will, close an outlet (54, 55) or put it in communication with one or the other circuits (70, 71) comprise a respective plug (64, 65) rotatably mounted in the block (49) and associated with this outlet (54, 55), and means <98, 94) to orient at will this plug (64, 65) in the block (49) in three positions in which, respectively, it closes said outlet (54, 55), puts it in communication with one of the circuits (70), puts it in communication with l 'other circuit (71).  14. Device according to any one of claims 8 to 13, in combination with two sources (82, 83) of plastic material in the fluid state each of which is connected to a respective one of the inputs (75, 76) of the block distribution (49).