Abstract:
A method of making a part made of a reinforced plastics material in a mold including at least two portions and from a reinforced sheet or from a lay-up of reinforced sheets including at least one reinforced sheet, in which method the reinforced sheet ( 4 ) is pre-heated. The reinforced sheet or the lay-up of reinforced sheets is presented to a first portion ( 1 ) of the open mold by a picking-up device including pressers ( 6   a;    6   b;    7 ), at least a region of the reinforced sheet or of the lay-up is applied against a corresponding region of the first mold portion by pressers on the picking-up device, the remainder of its surface is applied against the first mold portion while holding stationary the region of the reinforced sheet or of the lay-up, the mold is closed, and the resulting part is removed from the mold.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method of making a part made of a reinforced plastics material by overmolding a sheet, to a device for implementing the method, and to an assembly and to a production line including said device. 
     It is already known that single-layer sheets can be used to make parts made of plastics materials and having a certain stiffness, in particular for making structural parts of motor vehicles. 
     For example, with the material known as stampable reinforced thermoplastic (SRT), which is polypropylene reinforced with glass fibers, the method consists in heating sheets of SRT, then in depositing them in an open mold, and then in closing the mold to cause the plastics material to flow and to fill the cavity of the mold. 
     It is also known that multi-layer materials can be used that are obtained by superposing sheets of SRT and sheets of Twintex (a trademark of Verotex), Twintex being a woven sheet of commingled glass fibers and polypropylene fibers. 
     The Twintex sheets become soft during the heating prior to placing the lay-up of superposed sheets in the mold, but the SRT sheets are stiff enough to enable the heated material to be handled. 
     In contrast, when one or more sheets of Twintex only are to be overmolded, it is difficult to place them in the mold because the heated Twintex sheets are too soft and therefore difficult to handle. 
     As a result, the only known methods of overmolding sheets of Twintex consist in conveying the sheets horizontally from a heating station to the mold, which mold is mounted on a vertical press so that the portion of it that is to receive the sheet(s) of Twintex is horizontal. 
     This difficulty of handling heated sheets of Twintex therefore imposes, as a first limit to their being overmolded, the obligation of using molds that are mounted on vertical presses. 
     In addition, conveying the sheet of Twintex does not enable it to be positioned accurately enough in the mold. As a result, it is preferred to leave a safety margin by cutting the sheet of Twintex larger than necessary so as to make sure that it extends over the entire desired area of the part to be made, even if the edges of the sheet of Twintex that project beyond the periphery of the part then need to be cut off after the part has been molded. 
     A second limit to overmolding sheets of Twintex lies in the fact that the resulting parts must be trimmed after they have been molded. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a method that solves all or some of the above-mentioned problems. 
     The present invention provides, in particular, a method of making a part made of a reinforced plastics material in a mold comprising at least two portions and from a reinforced sheet or from a lay-up of reinforced sheets comprising at least one reinforced sheet, in which method the reinforced sheet is pre-heated, said method being characterized by the fact that it comprises the following steps: 
     the reinforced sheet or said lay-up of reinforced sheets is presented to a first portion of the open mold by means of a picking-up device including pressers; 
     at least a region of the reinforced sheet or of said lay-up is applied against a corresponding region of the first mold portion by means of pressers on the picking-up device; 
     the remainder of its surface is applied against said first mold portion while holding stationary said region of the reinforced sheet or of said lay-up; 
     the mold is closed; and 
     the resulting part is removed from the mold. 
     In the description below, the term “application portion” is used to designate that portion of the mold against which the reinforced sheet is applied. 
     The picking-up device may optionally be used to apply the remainder of the surface of the sheet or of said lay-up against the first portion of the mold. 
     It is possible to superpose a plurality of sheets in the mold, optionally with local reinforcements sandwiched between the sheets. 
     The above-mentioned region may correspond to at least one edge, and preferably both edges of the reinforced sheet or of said lay-up, or, in a variant, to a central zone. 
     The method of the invention offers the essential advantage of making it possible to automate positioning of the sheet or of said lay-up. 
     It can also make it possible to omit the trimming step consisting in cutting off the edges of the sheet or of said lay-up that project beyond the part obtained after overmolding. This is achieved because the edges of the sheet or of said lay-up can be positioned accurately relative to the mold. Once this positioning has been performed, the remainder of the sheet or of said lay-up is applied against the remainder of the first portion of the mold. 
     Use is thus made of the absence of stiffness of the sheet or of said lay-up to press it against the first portion of the mold, without it projecting from the periphery of the mold. 
     In a particular implementation, pressers are used that comprise rigid chocks mounted on actuators. 
     In a variant, a rigid chock comprises a plurality of elements separated by inflatable inserts that space them apart so that the chock hugs the shape of the first mold portion as well as possible. 
     The pressers may also be constituted by inflatable cases which, in the inflated state, exactly match the shape of the first mold portion. 
     In order to position it accurately on the first mold portion, the sheet or said lay-up is advantageously retained by needles disposed on the picking-up device. 
     When sheets and/or local reinforcements are superposed, such needles advantageously serve to hold the various superposed layers in position relative to one another, by being inserted into the lay-up. 
     Preferably, the needles are mounted on the same support as the pressers. 
     In a particular implementation, the needles are substantially parallel to the direction in which the mold closes. 
     Preferably, certain needles may be suitable for moving sideways to accommodate the deformations of the sheet or of said lay-up, when said sheet or said lay-up adapts its surface to fit the real surface of the application portion of the mold. 
     This adaptation may also be referred to as “draping”, the initial surface of the sheet or of said lay-up being plane and corresponding to the developed surface area of the application portion of the mold, while the final surface of the sheet or of said lay-up has all of the relief of the application portion of the mold. 
     The needles mounted to move sideways are particularly useful when the sheet or said lay-up is not pre-shaped to the relief of the first portion of the mold. 
     In order to preform the sheet or said lay-up, it is possible, in a particular implementation, to deposit it on a rack of suitable shape and to heat it, e.g. by inserting it in an oven. 
     Pre-forming the sheet or said lay-up may further be supplemented prior to being put in place in the mold, by acting on the sheet or said lay-up at an intermediate station lying between the place at which the sheets are picked up and the mold. 
     In a particular implementation, the mold has a join plane that is substantially vertical. 
     The picking-up device may be carried by a manipulator arm which exerts the mechanical forces necessary to apply the sheet or said lay-up against the first portion of the mold. 
     In a variant, the picking-up device may be pulled towards the first mold portion to press the sheet or said lay-up thereagainst by means of a base mounted to move relative to the first mold portion. 
     This makes it possible to relieve the manipulator arm and to use a manipulator arm that is less powerful and therefore less costly. 
     Advantageously, abutments mounted to move relative to the base are used to entrain the picking-up device, these abutments being disposed to come into engagement over the picking-up device when the base is in the “out” position, and then remaining in place when the base is displaced to pull on the picking-up device. 
     In a particular implementation, the sheet or said lay-up is overmolded as applied against the first mold portion, i.e. a complementary quantity of plastics material is inserted into the mold in order to fill the entire cavity of the mold, it being possible for the filling to take place by depositing material in the open mold or by injecting material into the closed mold. 
     The present invention also provides a picking-up device for taking hold of one or more sheets. 
     This device comprises at least one presser that has a front face shaped like a region of a first mold portion, e.g. a portion of its periphery or a central zone, and first needles passing through said presser, which needles are mounted to move relative to the presser so that, in a first relative configuration of the presser and of the needles, the needles include end portions projecting beyond the front face of the presser, and, in a second relative configuration of the presser and of the needles, the same end portions of the needles are situated set back from the front face of the presser. 
     This device is used as follows. 
     With the presser(s) lying in the first configuration relative to the needles, the sheet is speared, e.g. at its periphery, with the end portions of the needles that project from the presser(s). 
     The sheet as held by the needles is then brought facing the first portion of the mold, and the device is move towards the mold so that the ends of the needles come flush with a predetermined region of the first portion of the mold, e.g. its periphery. 
     The presser(s) is/are then moved towards the first portion of the mold, while holding the needles in position relative thereto. 
     As a result, the needles are bared, and once the pressers have reached the second configuration relative to the needles, the sheet is then held only by compression between said pressers and the first portion of the mold. 
     A retaining system which may, for example, be constituted by needles or by any other mechanism integrated in the mold, then takes over from the pressers by holding the sheet in position in the mold, thereby making it possible to withdraw the picking-up device and to close the mold. 
     It can be understood that the device of the invention is particularly well suited to handling a sheet or a lay-up of sheets that is to be positioned vertically in a mold mounted on a horizontal press. 
     In a particular embodiment of the device, other needles that slope relative to the first needles serve to retain the sheet when the pressers lie in the first configuration relative to the needles. 
     The crossing over of the two sets of needles holds the sheet stationary on the device, thereby making it possible, in particular, to pick up a sheet from a horizontal plane. 
     The present invention also provides an assembly for applying a sheet against a first mold portion, said assembly being characterized by the fact that it includes the above-described picking-up device and a base mounted to move relative to the first mold portion so as to pull the picking-up device towards the first mold portion and to press the sheet or said lay-up thereagainst. 
     By means of this assembly, it is possible to avoid the need to use heavy-duty mechanical means to manipulate the picking-up device. 
     The base can deliver most of the forces necessary to applying the sheet against the first mold portion. 
     The assembly may include abutments mounted to move relative to the base, and suitable for engaging over the picking-up device when the base is in an “out” position, then for entraining the picking-up device when the base is displaced to pull on the picking-up device. 
     Preferably, the abutments are disposed at the ends of arms secured to the base. 
     In a particular embodiment, when the abutments are engaged over the picking-up device, they abut against at least one beam that is secured to the picking-up device and on which pressers are disposed. 
     Pressers may be fixed to the beam(s) in question with springs being interposed. 
     Advantageously, the mold has an outer side wall, and the base includes a frame that can slide in contact with said side wall. 
     The base being disposed on the first mold portion is particularly simple to implement, and also guarantees that the base is moved accurately relative to the first mold portion. 
     Preferably, the picking-up device is secured to a manipulator arm. 
     The manipulator arm may be released when the picking-up device is pulled by the base towards the first mold portion. 
     The present invention also provides a production line for manufacturing parts made of a plastics material reinforced by overmolding sheets, said production line being characterized by the fact that it includes a first picking-up device as described above, and a second picking up device serving to handle cold sheets so as to bring them firstly from a place of storage to an oven in which they are heated, then from the heating oven to a pre-forming station where they are shaped substantially to match the relief of the mold, the first picking-up device transferring the heated and pre-formed sheets to a mold. 
     In an advantageous variant, the second picking-up device is equipped both with a suction system which is suitable for picking-up cold sheets so as to transfer them to the heating oven, and also with a needle system which is suitable for picking up the heated sheets so as to transfer them to the pre-forming station, and then from the pre-forming station to the mold. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to make the invention better understood, embodiments are described below by way of examples that do not limit the scope of the invention, and with reference to the accompanying drawings, in which: 
     FIG. 1 is a section view showing a punching die of a mold serving to make a part of complex shape, and a plane reinforcement sheet that is to be put in place on said die; 
     FIG. 2 is a section view of a picking-up device provided with needles, the device being shown as it is about to pick up the reinforcement sheet; 
     FIG. 3 is a view analogous to FIG. 2, showing the device and the sheet during pre-forming, immediately before the reinforcement sheet is deposited on the die; 
     FIG. 4 is a view analogous to the preceding figures, showing the reinforcement sheet in its ultimate draped state; 
     FIG. 5 is a perspective view of a presser provided with needles of the device of FIGS. 2 to  4 ; 
     FIG. 6 is a perspective view of a presser provided with an inflatable insert; 
     FIG. 7 is an overall perspective view of a production line for manufacturing reinforced parts; 
     FIG. 8 is an elevation view of a bumper beam; 
     FIG. 9 is a view from above of FIG. 8; and 
     FIG. 10 is a diagrammatic perspective view of an assembly including the picking-up device and a base mounted to move relative to a first portion of the mold. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In section, the punching die shown in FIG. 1 has relief  2  in its central portion, this relief itself being provided with a groove  3 . 
     The die  1  serves to make a bumper beam for a motor vehicle. 
     The beam is made of polypropylene mixed with glass fibers and reinforced with a sheet  4  of a fiber-reinforced plastics material of the Twintex type. 
     The sheet of Twintex is rectangular, its width corresponding to the developed width of the die, which width is constant. 
     As described below, firstly the reinforcement sheet  4  is heated. 
     Once it has been heated, it is put in place over the die by means of a picking-up device  5  comprising two positioning side pressers  6   a  and  6   b  and a draping central presser  7 , which pressers are mounted on a slide rail  8  via actuators  9 . 
     Each of the pressers is shown in detail in FIG. 5 from which the actuators have been omitted for reasons of clarity. 
     Each presser is made up of an elongate block  10  provided with two sets of through bores  11 , the first set of bores being perpendicular to the join plane of the mold, i.e. to the front face  12  of the presser, and the second set slants relative to the first set. 
     Each set of bores  11  receives a respective set of needles  13  moved by actuators  13   a.  The two sets of needles  13  cross in the vicinity of the front face  12  of the presser, each set of needles being mounted to slide axially relative to the presser. 
     As shown in FIG. 2, the two positioning side pressers  6   a  and  6   b  and the draping central presser  7  are secured to the sheet of Twintex by the crossing over of their respective sets of needles  13 . 
     One of the side pressers ( 6   b,  i.e. the side presser on the right of the figures) is then moved in translation towards the center of the device, while the central presser  7  is placed above the initial plane of the sheet of Twintex, thereby pre-forming the sheet to the general relief of the die, as shown in FIG.  3 . 
     The sheet, as thus roughly pre-formed, is then conveyed to the die, against which it is applied, firstly via its edges that coincide with the periphery of the die, by means of the side pressers  6   a  and  6   b,  then by means of the draping central presser  7  which presses the central zone of the sheet of Twintex against the bottom of the groove  3 . 
     It is then necessary merely to withdraw the picking-up device and to close the mold in order to overmold a reinforced beam, from which beam no edge of the sheet of Twintex projects. 
     FIG. 6 shows a variant of the draping central presser  7 ′ which is made up of two elongate blocks  7 ′ a  and  7 ′ b,  one of which ( 7 ′ a ) is secured to the actuators  9 ′ that connect it to the slide rail, and the other of which ( 7 ′ b ) is connected to the first block  7 ′ a  via a transverse slide mechanism (not shown). 
     As shown by the arrows  15  and  16  in FIG. 6, the insert  14  being inflated moves the two elongate blocks apart and applies the reinforcement sheet firmly against the walls of the groove  3  in the die. 
     As a result, the reinforcement sheet is draped optimally over the die, the edges of the reinforcement sheet also being suitably positioned and held by the side pressers of the device. 
     As shown in the overall view given in FIG. 7, a mold  17  is mounted on a vertical press, and a picking-up device  18  of the above-described type is mounted in the vicinity of said mold. 
     The device is mounted on a rail which makes it sufficiently mobile to move towards and away from the mold  17 . 
     The reinforced sheets picked up by the picking-up device for the purposes of pre-forming them and putting them in place in the mold have been heated and optionally preformed on stations further up the production line. 
     From upstream to downstream, the production line is made up of a loading station  19  on which an operator places cold reinforcement sheets, of an infrared oven  20  which heats individually each reinforcement sheet that is placed on the loading station and delivers it at the end of the oven that is further from the loading station, and of a second picking-up device  21  which picks up the heated sheets and can place them in two different places depending on the type of part to be made. 
     For a part using a plurality of reinforcement sheets, the second picking-up device  21  stacks up the reinforcement sheets exiting from the oven and then, when there are enough of them, places them on a pre-forming rack. The sheets as stacked up for pre-forming purposes are inserted into a hot-air oven  22  so as to bring them to the temperature at which they were on exiting from the infrared oven  20 . 
     For a part using a single reinforcement sheet, the second picking-up device  21  makes the reinforcement sheets available directly to the first picking-up device  18  so that they can be placed immediately in the mold  17 . 
     It should be noted that the picking-up device  18  made up by pressers each having two sets of needles is particularly well suited to handling heated reinforcement sheets of the Twintex type, and to handling them in a vertical position, as applies in the production line shown in FIG.  7 . 
     Firstly, the heated sheets are easy to spear, and secondly the heated sheets are easy for the needles to hold because said needles are perpendicular to the plane of the sheet. 
     In addition, the vertical position of the sheet makes it possible to remove firstly the slanting set of needles on putting the draped sheet in place in the mold, without said sheet being released from the picking-up device. 
     Once the slanting needles have been removed, the presser(s) can be moved towards the mold by baring the needles which then serve as guides for holding the reinforcement sheet in position in the mold. 
     Thus, the needles serve not only to pick up the sheet, but also to position it accurately in the mold. 
     In the example shown in FIGS. 8 and 9, the beam  23  is of symmetrical shape over a portion  24  of its length and of asymmetrical shape over the remainder  25  of its length. FIG. 9 shows dot-dash lines  26  joining up the middles of the widths of the beam before and after draping, and it can be observed that these lines are separate in the portion  25  of the beam. 
     This non-coincidence of the middles of the widths might pose a problem for draping the reinforcement sheet if said draping were performed in this embodiment by starting from the center of the part to be made. 
     However, in this embodiment of the invention, the reinforcement sheet is positioned via its edges which are applied firstly against the periphery of the mold, so draping the reinforcement sheet over a non-symmetrical die raises no difficulty. 
     That is why applying the pressers against the zones  27  shown in bold lines in FIG. 8 makes it possible to obtain the non-symmetrical beam shown in FIGS. 8 and 9. 
     Naturally, the above-described embodiments are in no way limiting, and any desirable modifications may be made to them without going beyond the ambit of the invention. 
     For example, as shown in FIG. 10, it is possible to make an assembly serving to make it possible to use a manipulator arm that is less powerful. 
     In addition to a picking-up device  30 , the assembly comprises a base  43  that is mounted to move relative to a first mold portion  40  and that is suitable for pulling the device  30  onto said mold portion to press a sheet  4  against it. 
     The picking-up device  30  is secured to a manipulator arm  31  and it includes three central pressers  32  and four peripheral pressers  35  that are shorter than the central pressers  32  and that are disposed substantially at the four corners of the picking-up device. 
     Each presser  32  or  35  has a front face  38  for applying the sheet  4  against the first mold portion  40 , and a rear face  39 . 
     The pressers  32  and  35  are supported by a set of parallel beams comprising a central beam  36 , and two side beams  33  that extend over substantially the entire width of the sheet  4 . 
     The central pressers  32  are fixed to the beams  33  and  36  with springs  34  being interposed that come into abutment at one end against the beams  33  and  36 , and at the other end against their rear faces  39 . 
     The peripheral pressers  35  may optionally be moved relative to the beams  33  while the sheet  4  is being draped over the mold portion  40  and they are provided with sets of straight needles  50  and with sets of slanting needles, as in the above-described embodiments. 
     The springs  34  make it possible for the pressers  32  to adapt to fit the shape of the first mold portion  40  on clamping the picking-up device  30  thereagainst. 
     In a variant, it is possible to replace the springs  34  by actuators. 
     However, the use of springs offers the advantage of being simpler and lower in cost than the use of actuators. 
     The first mold portion  40  is suitable for co-operating with a second mold portion (not shown) on closing the mold, the two mold portions being mounted on a horizontal press. 
     The mold portion  40  has a die  41  provided with a central groove and serving to shape the sheet  4  so as to form a beam for a motor vehicle. 
     It also has a plane peripheral surface  42  around the die  41  and serving as an abutment surface for the peripheral pressers  35 . 
     The mold portion  40  has an outer side surface  45  on which the base  43  slides, which base is mounted to move in a direction a. 
     The base  43  includes a rectangular frame on which four arms  44  are disposed, which arms extend towards the second mold portion. 
     Each of the arms  44  is provided with an abutment  47  that is mounted to move in a direction b that is perpendicular to the direction a, each abutment  47  being suitable for coming into abutment against one of the rear faces of the beams  33  when the base  43  is in an “out” position. 
     A description follows of the steps of an operation of draping the sheet  4  over the first mold portion  40  by means of said assembly, the base  43  being initially in an “out” position in which the abutments  47  have been moved to the maximum extent towards the second mold portion. 
     The picking-up device  30  starts by picking up a hot sheet  4  and presenting it to the first mold portion  40 . 
     The picking-up device  30  then applies the sheet  4  against the first mold portion  40  by exerting a small pressure on the sheet  4  so as to hold it against said mold portion. 
     The central pressers  32  engage over the die  41  and they hold the sheet  4  stationary relative to the first mold portion at the level of said die. 
     The sheet  4  is thus brought into register relative to the first mold portion. 
     The abutments  47  are then actuated so as to come into abutment against the rear faces of the beams  33 . 
     The manipulator arm  31  is declutched, and the base  43  is displaced by means of an actuator drive mechanism (not shown) over a predetermined distance away from the second mold portion so as to pull on the picking-up device  30 . 
     The central pressers  32  hold the sheet  4  applied against the die  41  and stationary relative thereto. 
     Then the abutments  47  are displaced towards the outside of the first mold portion  40 , and the picking-up device is removed, the sheet  4  being held pressed against the first mold portion  40  by retaining means (not shown) until the mold is closed. 
     The use of the base  43  makes it possible to prevent the manipulator arm  31  from having to exert large forces in order to press the sheet  4  against the first mold portion  40 , the forces necessary to clamp the picking-up device  30  against the first mold portion  40  being delivered substantially by the displacement of the base  43 .