FR2537915A1 - Process for moulding an article made from thermoplastic material and device for implementing it - Google Patents

Abstract

Process for manufacturing an article made from thermoplastic material which can be made only with difficulty in a single moulding operation, consisting, after splitting this article into mouldable parts 2, 3, in simultaneously hot moulding these component parts 2, 3 and in joining these parts under pressure in the region of their zones to be assembled which are still at a temperature substantially equal to the moulding temperature of these parts in order to weld them. Device implementing this process, comprising a machine provided with a multi-cavity mould, at least one 7 of which cavities can be moved and applied against at least one other one.

Description

PROCESS FOR MANUFACTURING A PART IN
THERMOPLASTIC MATERIAL, AND DEVICE THEREOF
IMPLEMENTING
The present invention relates to a method of manufacturing a part made of thermoplastic material, and a device implementing it.

 For the manufacture of a part made of thermoplastic material having either a complicated shape or a more or less closed volume which makes it difficult to produce directly in a single molding operation, the known methods provide for a division of this part into easily moldable parts, a molding of these parts, one after the other in usual molds, and after their removal from these molds, assembling them in special welding machines to obtain the finished part.

 These known methods require, in the manufacture of this finished part, not only molding machines but also welding machines. In addition, these known methods involve numerous operations for handling the molded elements representing the component parts of the part to be manufactured, and for their storage. Mechanical damage to these molded elements during handling and storage is difficult to avoid. As a result, these known methods are long in their implementation and costly in their application.

 The object of the present invention to avoid these drawbacks is a rapid and economical process for manufacturing parts made of thermoplastic material, in particular those having a complicated shape or a more or less closed volume which makes them difficult to produce directly in a single molding operation.

It also relates to a device for implementing this method.

 According to the invention, a method of manufacturing a part made of thermoplastic material which is difficult to carry out directly in a single molding operation, providing for a division of this part into directly moldable component parts, consists in carrying out a simultaneous hot molding of these moldable component parts. and making a pressure junction of these parts which have just been molded at their zones to be assembled which are still at a temperature substantially equal to the molding temperature of these parts in order to effect their welding by interpenetration of the material and to obtain a finished piece.

 A device implementing this method comprises at least one machine provided with a hot molding mold and with several imprints, at least one of which is movable and applicable against at least one other of these imprints.

To better understand the invention, an exemplary embodiment is illustrated below, illustrated by the appended drawings, of which:
- Figure 1 shows a schematic and partial view of a machine of the device for implementing the method of the invention showing, in the release position for opening, partially in section along a horizontal plane, the two cooperating sub-assemblies of this machine, one fixed and the other mobile, which provide hot molding of the two component parts of the part to be manufactured and their assembly by welding,
FIG. 2 represents a schematic front view of the mobile sub-assembly of FIG. 1, showing the two mold cavities, one fixed and the other mobile,
FIG. 3 represents a side, partial and schematic view of the mobile sub-assembly of FIG. 1,
FIG. 4 represents a partial and schematic view of the mobile sub-assembly of FIG. 3, in section along the plane IV-IV, showing a flange sliding from one end of the pivot axis of the mobile impression,
FIG. 5 represents a partial and schematic view of the mobile sub-assembly of FIG. 3, in section along the plane VV, showing a sliding and pivoting hook for application under pressure of a mobile impression against another impression,
FIG. 6 represents a partial and schematic view of the mobile sub-assembly of FIG. 3, in section along the plane VI-VI, showing a slide ensuring the pivoting of an application hook for engaging or releasing a mobile imprint,
FIG. 7 represents a partial and schematic view of the machine of FIG. 1, showing the two cooperating sub-assemblies in the closed position during hot molding of component parts of the part to be manufactured,
- Figure 8 shows a partial and schematic view of the movable subassembly of the machine of Figure 7, showing a movable footprint carrying its own part already molded, placed in position above another footprint also carrying its own part already molded, before the application of pressure on the movable impression to achieve the junction and the welding of these molded parts.

 For the manufacture of a part made of thermoplastic material having a complicated shape or a more or less closed volume which makes it difficult to carry out directly in a single molding operation, after a division of this part into directly moldable component parts, the method according to the invention consists in carrying out a simultaneous molding of these component parts and in making a pressure junction of these parts at their zones to be assembled again at the temperature substantially equal to the temperature of the molding to effect their welding by interpenetration of the material and get a finished piece.

 These component parts are kept in their respective imprints until they are assembled. Only their zones to be assembled are maintained at a temperature which is appreciably equal to the initial temperature of hot molding to facilitate welding while the other zones are cooled. A simultaneous effect carried out in the molding of the component parts of the part to be manufactured makes it possible to make them available at the same time, with a view to their assembly by hot pressure welding. A relatively long time necessary for a successive molding of different parts to be assembled from the part to be manufactured is thus avoided. Maintaining the parts already molded in their respective mold cavities until they are welded makes it possible, on the one hand, to maintain easily and economically the temperature of their zones to be assembled, substantially equal to their initial molding temperature for the welding operation, and on the other hand to advantageously eliminate most of the operations of handling the component parts of the part to be manufactured and of their storage , before their assembly by welding.

 A device allowing an implementation of the above manufacturing process mainly comprises a hot molding machine with several cavities. The number of impressions is preferably equal to that of the moldable component parts of the part to be manufactured. If the moldable component parts of a workpiece prove to be too numerous, the number of impressions of the molding machine may correspond to that of the moldable component parts of one of the subassemblies of the clamp to be manufactured . In the latter case, the device implementing the method of the invention comprises a number of hot molding machines with several cavities equal to that of the sub-assemblies of the part to be manufactured. The final assembly of these subsets is done consecutively to that of these compo ~ sante parts. The areas to be assembled of these subassemblies are maintained until they are welded, at a temperature substantially equal to their initial molding temperature. Their welding is done by pressurized junction making an interpenetration of the material of these areas to be assembled.

 In a production of a closed hollow part having the general shape of a parallelepiped 1 given as an example in FIG. 8, this part not being directly moldable, is divided into two moldable component parts 2 and 3 each having a shape of a rectangular bowl and whose areas to be joined consist of their edges which have the same dimension. The component parts 2 and 3, once molded, are assembled by pressure junction of their edges, the temperature of which is maintained at a level substantially equal to that of their initial molding temperature, in order to obtain welding by interpenetration of material.

 In the example illustrated, a device ensuring an implementation of the method of the invention in the manufacture of the hollow part made of thermoplastic material 1 comprises a machine 4 partially shown in FIGS. 1 to 3.

 The machine 4 provides simultaneous molding of these two component parts 2, 3 of the part 1 to be manufactured and a subsequent pressure welding of these parts, the areas to be assembled are maintained substantially at the molding temperature of their constituent material to obtain a finished part 1. The machine 4 comprises (FIG. 1), on a fixed frame (not shown) which is produced according to a known technique, a fixed sub-assembly 5 secured to this frame and a sub-assembly G movable in translation relative to to this fixed subset. The mobile sub-assembly in translation 6 carries two molding impressions 7 and 8 and the fixed sub-assembly 5 maintains two cores 9 and 10 cooperating respectively with these two molding impressions to form the mold 7, 9 - 8, 10 intended for hot molding of the two component parts 2 and 3 of the part to be manufactured.

 The fixed sub-assembly which carries a main channel 11 and secondary channels 12, 13 for supplying material into the mold 7, 9 - 8, 9, also serves as a cover for this mold, during the molding operation. The other parts of the machine 4 such as the mixing, heating and propulsion assemblies of the thermoplastic material constituting the part 1, the control and supply assemblies of electricity and cooling fluid, and of sliding which are produced according to the usual known techniques, are not described in detail. During molding, the mobile sub-assembly 6 is applied against the fixed sub-assembly 5 and the thermoplastic material brought to its molding temperature is introduced through the channels 11, 12 and 13 into the mold 7, 9 - 8.10 , as shown in Figure 7.

 In the mobile sub-assembly 6 which includes a support 14, the cavity 8 is fixed in this support while the mobile cavity 7 is pivotally mounted around an axis 15 (Figures 1 and 2) whose ends 16 and 17 are kept in position, free to pivot by two sliding flanges 18 and 19 (Figures 2, 3 and 4). The sliding flanges 18 and 19 are constantly pushed by springs 20 and 21 in order to bring the axis into translation 15 of the movable imprint 7 from its retracted position shown in solid lines in FIGS. 1 and 4, in its pivoting position or projecting outward position shown in broken lines (FIG. 1) relative to the mobile sub-assembly 6 The movable imprint 7 is guided in its retracted position by pins 22 secured to the support 14, and pushed into its protruding position also by springs 23. Stops 24 limit the penetration of the movable imprint 7 and determine the position when it’s retracted. mobile impression 7 pushed by the springs 20, 21 and 22 occupies the projecting position, it is disengaged from the guide pivots 22 and is in the pivoting position, that is to say that which allows it to pivot about its axis 15.

 A toothed wheel 25 is fixed on the end 17 of the axis 15 of the pivoting imprint 7 (FIGS. 2 and 3) the rotation of the toothed wheel 25 and consequently the pivoting of the imprint 7, is controlled by a meshing of this toothed wheel on a fixed toothed rack 26 secured to the fixed sub-assembly 5 of the frame, and by the translational movement of the mobile sub-assembly 6 relative to the fixed sub-assembly 5. It follows that when the mobile sub-assembly 6 moves away from the fixed sub-assembly 5, the movable impression 7 is instantly pushed by the springs 20, 21, 22 in its pivoting position, projecting outwards (FIG. 1) and then after an engagement of the toothed wheel 25 on the rack 26, the cavity 7 pivots about its axis 15.The position of the axis 15 is determined beforehand so that the movable cavity 7 comes just in front of the fixed cavity 8 and places the edges of the already molded component part 2 on those of the already molded part 3.

The movable impression 7 is then resiliently supported in position, on one side by springs 20, 21 of the sliding flanges 18, 19 of its axis 15 and on the opposite side by retractable elastic stops 27 resting on springs 28. The footprint 7 can therefore be brought closer to fixed footprint 8 in a translational movement. The cavity 7 is thus sliding. The movable cavity 7 is provided on its two opposite sides (FIG. 2) and at its plane of symmetry 29 parallel to its pivot axis 15, with two tongues 30, 31 which allow the two hooks 32, 33 (Figures 2, 3, 5) mounted on both sides of the support 14 of the movable subassembly 6 to pull the impression 7 towards the fixed impression 8 and thereby exert a predetermined pressure on the edges hot to assemble component parts 2 and 3 of the part to be manufactured 1 to carry out their welding by interpenetration of the material. The hooks 32 and 33 sliding along the guides 34, 35 are controlled in their movement by jacks 36, 37 to bring the impression 7 closer to or away from the fixed impression 8. The hooks 32 and 33 are also pivotable around the axes 38, 39 of the yokes of their control jacks 36, 37, and constantly resiliently returned by springs 40, 41 in their hooking position with the tongues 30, 31 of the movable impression 7.

 Thanks to their pivot axes 38, 39 and their return springs 40 and 41, the hooks 32, 33 can be easily disengaged from the tongues 30, 31 when the movable impression is released 7. The disengagement of the hooks 32, 33 is done by wedge-shaped sliders 42, 43 (FIGS. 2, 3, 5, 6) which move in transverse grooves with inclined or sloping surface 44, 45 of hooks 32, 33. The sliders in the form of wedges 42, 43 are controlled in their movement by jacks 46, 47.

 The fixed imprint 8 (Figures 1, 7, 8) is provided in its bottom with passages for the passage of the mechanical ejectors 48 constituted by rods held by a sliding support 49 whose movement is controlled by a jack not shown through a axis 50. The support 49 slides along the guide pins 51.

After the edges of the component parts 2 and 3 have been welded and the movable impression 7 has been released, the finished finished piece 1 can then be released from the fixed impression 8 by the ejectors 48.

 The cavities 7, 8 and the cores 9, 10 are respectively cooled by cooling pipes 52, 53, 54, 55 arranged in the thickness of their body according to a distribution making it possible to maintain the zones or edges until they are welded. in assembling component parts being molded in the cavities, at a temperature substantially equal to the initial molding temperature to achieve their joining by pressure junction, and to cool the other zones of these component parts.

To compensate for a possible failure to maintain these zones or edges to be assembled at a temperature facilitating their welding, in the cores 9 and 10, near the place where the zones or edges to be assembled are formed, electrical resistors heaters 56, 57 (figures - 1, 7, 8). These electric heating resistors are thermally isolated from the cores 9 and 10 and their supports by insulating plates 58, 59 for example.

 To avoid any sticking to the mold of the material not yet solidified or maintained in this state, at least the parts of the cores 9 and 10 and the imprints 7, 8 surrounding the areas where this non-solidified material is located, are coated with a coating anti-sticking such as that based on fluorine or graphite.

 The guidance of the movable impression 7 by pins 22 and that of the support 49 of the ejectors 48 by pins 51 can be replaced by another known guide means which gives the same results. The molding impressions 7 and 8 are produced with a draft or undercut to allow the molded component parts to be retained in place without blocking them respectively until they are welded and ejected.

 In the example illustrated, the fixed imprint 8 is provided with ejectors 48, while the movable imprint 7 is only provided with unused passages which can possibly receive ejectors.

 During the manufacture of a part 1, the mold is closed by application of the mobile sub-assembly 6 against the fixed sub-assembly 5. A thermoplastic material previously prepared and raised to its molding temperature is introduced simultaneously through the channels 11, 12, 13, in indentations 7 and 8 (FIG. 7) to form the two component parts 2 and 3 of the part 1. A cooling fluid such as the water circulating in the pipes 52, 53, 54, 55 cools the elements thus molded which constitute the component parts of part 1, while maintaining the zones or edges to be assembled of these molded elements until they are welded to a temperature substantially equal to their initial molding temperature. , 57 can optionally be switched on to ensure, in cooperation with these cooling circuits, constituted by the pipes 52, 53, 54, 55 for such a maintenance of the temperature of these zones or bo rds to assemble. The mobile sub-assembly 6 is then moved away from the fixed sub-assembly 5. Under the thrust of the springs 20, 21, 23, the mobile impression 7 provided with molded element 2 is automatically moved from its retracted position to its projecting position towards the exterior shown in broken lines in Figure 1.

The imprint 7 released from the guide pins 22 is then in a position which allows it to pivot around its axis 15.

 The mobile sub-assembly 6 continues to move away from the fixed sub-assembly 5. The toothed wheel 25 meshes with the teeth of the fixed rack 26 and the imprint 7 pivots around its axis 15 to come in front of the fixed impression 8 in order to apply the edges to be assembled of the molded element 2 which this impression 7 carries, on the corresponding edges to be assembled of the molded element 3 located in the fixed impression 8. The toothed wheel 25 having traversed thus the entire toothed path of the rack 26 no longer rotates and the pivoting movement of the imprint 7 is interrupted. The mobile sub-assembly 6 continues its travel to a stop position which has been predetermined. The imprint 7 then rests elastically on its sliding flanges 18, 19 and retractable elastic stops 27.

The wedge-shaped slides 42, 43 are, under the action of the jacks 46, 47, released from the transverse grooves 44, 45 of the hooks 32, 33 to allow the latter to grip onto the tongues 30, 31 of the imprint 7. Under the action of the jacks 36, 37 the hooks 32, 33 bring the imprint 7 closer to the imprint 8 to obtain a crushing of the hot edges in contact with the molded elements # 2, 3 and thus carry out a welding of these edges by interpenetration of matter. When the welding is finished, the jacks 36, 37 interrupt their traction on the hooks 32, 33. Under the thrust of the springs 28 of the stops 27 and the springs -20, 21 of the flanges 18, 19, the imprint 7 returns to its position prior to welding of the edges of the molded elements 2 and 3. The slides 42 engage in the inclined grooves of the hooks 32, 33 under the action of the jacks 46, 47 to move these hooks away from the tongues 30, 31 of the imprint 7.

 The mobile sub-assembly 6 is brought again to the fixed sub-assembly 5. The toothed wheel 25 reengages on the toothed path of the rack 26 and the imprint 7 pivots in the direction which brings it back to its initial retracted position. During this time, the ejectors 48 under the action of their control jack, drives the finished part 1 from the fixed imprint 8. When the imprint 7 is in its projecting position shown in broken lines in FIG. 1, the toothed wheel 25 also ends the toothed path of the rack 26 and no longer rotates so that the imprint 7 also stops pivoting.

  The mobile sub-assembly 7 can continue its stroke until it contacts the fixed sub-assembly 8 to close the mold. A new molding cycle for parts 2 and 3 of another part 1 can thus be started again.

 In the device for implementing the method of the invention, illustrated as an example in FIGS. 1 to 8, the different control jacks 36, 37, 46, 47, the toothed wheel 25 and the rack 26 can be replaced by other known equivalent control means. The ejectors 48 can also be replaced by other types of known mechanical, electrical, pneumatic or magnetic ejectors.

 The coordination of the movements of the various organs of this device can be carried out in a known manner either by limit stops, or by electromechanical programmers, or by electronic devices or microprocessors.

Claims (16)

 1. Method for manufacturing a part made of thermoplastic material which is difficult to produce directly in a single molding operation, providing for a division of this part (1) into directly moldable component parts, characterized in that it consists of:  - carry out a simultaneous hot molding of these moldable component parts (2, 3) and  - Make a pressure junction of these parts which have just been molded at the level of their zones to be assembled which are still at a temperature substantially equal to the molding temperature of these parts to effect their welding by interpenetration of the material and obtain a finished part (1).  2. Method according to claim 1, characterized in that it comprises:  - a conservation in their respective imprints (7, 8), of the component parts which have just been molded (2, 3),  - maintaining their exclusive areas to be assembled for welding, at a temperature facilitating their welding and cooling their other areas.  3. Device for implementing the method of one of claims 1 and 2, characterized in that it comprises at least one machine provided with hot molding mold and with several cavities (7, 8), one of which (7) at least is mobile and applicable against at least one other (8) of these fingerprints.  4. Device according to claim 3, ~ characterized in that it comprises a mold formed of two sub-assemblies (5, 6), one of which (6) carrying imprints (7, 8), is movable in translation, and the other (5) carrying cores (9, 10) of these cavities, and supply channels (11, 12, 13) of molding material, and serving as a mold cover, is fixed.  5. Device according to one of claims 3 and 4, characterized in that it comprises as movable imprint, an imprint (7) pivoting in its projecting position outside the movable sub-assembly (6) and sliding this pivoting position in its retracted position in this mobile sub-assembly (6) during molding.  6. Device according to one of claims 3, 4 and 5, characterized in that it comprises as movable imprint an imprint (7) pivoting in its projecting position outside the movable sub-assembly (6) and sliding of this pivoting position in its position of application under pressure against another imprint.  7. Device according to one of claims 5 and 6, characterized in that the movable impression (7) comprises a pivot axis (15) whose ends (16, 17) are carried by sliding flanges (18, 19 ) pushed by springs (20, 21) which constantly tend to put this imprint (7) in its pivoting position projecting outwards from the mobile sub-assembly (6).  8. Device according to one of claims 5 and 7, characterized in that it comprises pins (22) guiding the sliding of the movable impression (7) between its pivoting position and its retracted position, and springs ( 23) constantly pushing the movable impression (7) from the retracted position to its pivoting position.  9. Device according to one of claims 6 and 7, characterized in that it comprises elastic stops (27) supporting the movable impression (7) and springs (28) constantly pushing these stops (27) to recall the moving impression (7) from its pressure application position against another impression (8) in its pivoting position.  10. Device according to one of claims 3 and 4, characterized in that it comprises cavities (7, 8) and cores (9, 10) provided with pipes intended for a circulation of a coolant for the parts components (2, 3) molded in order to maintain the zones to be joined of these parts, at a temperature substantially equal to the initial temperature of molding of the material constituting them, and to cool the other zones of these molded parts (2, 3).  11. Device according to one of claims 3, 4 and 10, characterized in that it comprises electric heating resistors (56) embedded in the mold near the areas to be assembled component parts (2, 3) molded, for maintain these zones at a temperature facilitating their welding by pressure junction realizing an interpenetration of material.  12. Device according to one of claims 3, 4, 6, 7, 9, 10 and 11, characterized in that it comprises in the mobile sub-assembly (6) pivoting and sliding hooks (32, 33) cooperating with protruding tabs (30, 31) of the movable impression (7) to slide the latter between its pivoting position in its position of application under pressure against another impression (8).  13. Device according to claim 12, characterized in that it comprises wedge-shaped slides (42) cooperating with transverse grooves with inclined surface (44, 45) hooks (32, 33) to pivot these between their hooking position on the protruding tabs (30, 31) of the movable impression (7) and their release position of these tabs.  14. Device according to claim 3, characterized in that it comprises ejectors (48) passing through the thickness of the cavity (8) for demolding thereof.  15. Device according to one of claims 3 and 4, characterized in that it comprises in the cavities (7, 8) and the cores (9, 10) of its mold, at least at the level where there are areas to assemble molded component parts (2, 3), an anti-stick coating.  16. Device according to one of claims 3 and 4, characterized in that it comprises in the imprints (7, 8) of its mold, a draft or an undercut intended to retain without blocking the molded parts.