Patent Publication Number: US-2019176366-A1

Title: Device for protecting an attachment insert during the overmoulding of same

Description:
This invention relates to the technical field of manufacturing motor vehicle parts made of plastic material, and in particular the field of overmoulding fastening inserts for automotive parts. 
     In the automotive industry, it is known to manufacture and to use parts having a metal insert and a plastic part overmoulded on the metal insert. It is also known to use plastic inserts during overmoulding. 
     The use of structural fasteners is necessary in particular for the structural parts: the fasteners used to attach seats to a floor or the seatbelt guide to a B pillar, for example. The manufacture of such parts has emerged as a solution to meet the generally conflicting requirements regarding the properties of the structural element, for example the requirements of lightness and mechanical strength, especially resistance to shocks. 
     Consequently, to manufacture such structural parts made of plastic material, functionalisation solutions are required, especially to assemble them securely either to each other or to the vehicle. Thus, it is known to use inserts, for example made of metal, comprising fastening means such as a thread (screw and/or tapped hole). 
     To produce a plastic part, it is known to use a moulding method such as compression and/or injection moulding. 
     In the case of moulding by hot compression under pressure of a thermosetting plastic material, the method is generally carried out in a mould by displacing a moving element of the mould (moved by a press) relative to a fixed element of the mould, these elements typically being made of steel. 
     Generally, a loading plane consisting of sheets of plastic material, typically a sheet moulding compound (SMC), is placed in a compression mould. The press is then actuated to close the mould. Actuation of the press then continues to transmit a moulding pressure to the plastic material. The mould is said to be in packing phase. The plastic material can then flow and take the shape of the mould cavity. Lastly, during a “curing” phase, the plastic material polymerises to form a finished part. 
     To integrate fastening inserts in a part moulded in this way, it is known to add them after moulding the part by one or more rework operations, consisting firstly in creating a housing for them, usually a hole through the thickness of the part, and produced by machining, drilling, punching, before placing the insert in this housing and fastening it by bonding, riveting, crimping or screwing. 
     This Fastening Method is Restricting for the Following Reasons:
         cost of the rework operations performed. This method in fact requires different tools, additional equipment, additional durations for each operation and therefore a longer overall cycle time per part, and resulting in a loss of material when producing the housings.   hygiene, health and maintenance of the equipment due to the dust produced.   mechanical strength due to the residual assembly clearances between the insert and the part.       

     Furthermore, it is known that an element added during rework after moulding exhibits positioning faults relative to the shapes of the part obtained by moulding. 
     There is in fact a loss of the “geometrical reference frame” since the part is taken out of the mould without the insert, then placed on a support to successively produce the housings then add the inserts. The inaccuracy of the relative positions of the inserts with respect to each other and with respect to the part makes it more difficult to assemble the part with another component or on the vehicle: for example separation distance or perpendicularity faults can prevent this assembly on vehicle. 
     As a variant, it is also known to integrate fastening inserts in a part when overmoulding the part, and in this case the fastening member must be protected from this insert to prevent the plastic material from covering this member, even partially. Thus, this fastening member, in particular when using a thread, can no longer be used to fasten an element to the part in which the insert is overmoulded if this thread is partially covered by plastic material loaded with reinforcement elements. 
     A mould system is also known from patent application FR3024386, for the positioning and accurate holding of an insert in the cavity of this mould, using a disengageable pin. 
     This solution involves manufacturing moulds integrating additional and complex mechanisms which are therefore more difficult to manufacture and maintain. 
     The invention aims to remedy these disadvantages by providing a device for protecting a fastening insert, easy to manufacture and easy to use, to overmould the fastening insert with a plastic material using a mould, the fastening insert having a fastening member. 
     This device comprises piercing means adapted to pierce at least one sheet of plastic material (thermosetting or thermoplastic), and means for sealing the fastening member to prevent infiltration of material on the fastening member during an overmoulding operation. 
     With such a protective device, it is no longer necessary to manufacture specific moulds, which are difficult to manufacture and maintain, such as moulds with movable pins. 
     Another advantage, stemming from the previous one, is that it is possible to make attachment points that are very close together, which is not the case with sophisticated mechanisms based on pins whose size in the mould prevents the fasteners from being placed close to each other. 
     Lastly, the fact of crossing the sheet of plastic material with the piercing means before shaping the material by moulding allows the material to be distributed uniformly around the fastening member, thereby limiting the join lines, and therefore improving the mechanical performance of the part comprising the fastening insert. 
     The device may further comprise one or more of the following characteristics, taken alone or in combination:
         the device forms a shaft comprising first and second ends opposite each other, the first end being provided with the piercing means, and the second end being provided with at least one portion of the sealing means;   the piercing means has a tapered shape and/or edges;   the sealing means forms a plug;   the sealing means is adapted to be tightly assembled on an insert according to one of the preceding claims, wherein the sealing means comprises shapes creating a barrier to the passage of the plastic material MP;   the fastening member is a thread;   the sealing means comprises a thread cooperating with the thread of the insert.       

     The invention also relates to an assembly of an insert and a device according to the invention, wherein the insert comprises a tapped hole having a thread and forming a female element, and the sealing means comprises a male element adapted to cooperate with the female element in order to sealably plug the tapped hole. 
     The invention also relates to an assembly of an insert and a device according to the invention, wherein the insert comprises a screw having a thread and forming a male element, and the sealing means comprises a female element adapted to cooperate with the male element in order to sealably cover the screw. 
     According to the invention, the sealing means is preferably tightly assembled on the insert. 
     The invention also relates to an assembly of a mould and a device according to the invention, wherein the mould comprises a housing adapted to receive a portion of the device comprising at least the piercing means. 
     According to the invention, the dimensions of the housing are advantageously defined so that when the mould is closed, a portion of the mould presses on the device so as to press the device tightly on the insert and so as to crush the device in order to fill the housing to prevent an infiltration of plastic material in the housing. 
     According to the invention, the mould may comprise a housing adapted to receive the insert so as to control its position and prevent any movement during a flow of plastic material. 
     The invention also relates to a method for moulding a motor vehicle part made of plastic material comprising at least one partially overmoulded insert, wherein the following steps are performed using an assembly according to the invention of a mould and a device:
         engaging the device in or on the insert;   introducing the insert in the mould;   pressing at least one sheet of plastic material on the device to pierce the sheet of plastic material using the piercing means;   closing the mould and applying pressure to make the plastic material flow;   opening the mould and ejecting the part carrying the overmoulded insert.       

     According to the invention, the device can be removed from the part. 
     Lastly, according to the invention, the device can be engaged in or on the insert by tight assembly, and pressure is applied when closing the mould to continue pressing on the device to provide a seal. 
    
    
     
       The invention will be better understood on reading the accompanying figures, which are given solely by way of example and not limiting in any way, in which: 
         FIG. 1  schematically illustrates an embodiment of an assembly comprising a mould, a fastening insert, and a device for protecting the insert for its overmoulding; 
         FIGS. 2A and 2B  illustrate in detail two embodiments of the device for overmoulding a fastening insert; 
         FIGS. 3A and 3B  illustrate in detail two examples of a fastening insert, one with a tapped hole ( FIG. 3A ), the other with a screw ( FIG. 3B ); 
         FIGS. 4A and 4B  illustrate in detail two examples of an assembly comprising a device inserted in or engaged on a fastening insert comprising a tapped hole ( FIG. 4A ) or a screw ( FIG. 4B ); 
         FIGS. 5A to 5D  illustrate a method for moulding a motor vehicle part made of plastic material comprising a fastening insert, using a compression mould and a device for overmoulding the fastening insert; 
         FIGS. 6A and 6B  illustrate examples of parts obtained according to the method illustrated on  FIGS. 5A to 5D . 
     
    
    
     We now refer to  FIG. 1  which describes an embodiment of a device  10  for overmoulding a fastening insert  20 , with a thermosetting plastic material MP using a compression mould  30 . The mould  30  is thus used to form a motor vehicle part  40  (see  FIGS. 6A and 6B ) made of plastic material MP comprising at least one fastening insert  20 . 
     The term “fastening insert” means a first element added to the mould cavity, during each moulding cycle, and comprising at least one fastening member. A fastening member is a functional interface area for fastening a second element to the part in which the insert is overmoulded. This fastening member can be a male or female thread carried by a screw or a tapped hole, a welding or bonding surface, a shape to be riveted, etc. 
     The device  10  can be used in particular to overmould a fastening insert  20  comprising a fastening member  22 , since it protects this fastening member  22  by preventing, in the mould cavity, the plastic material MP from covering it, even partially, in order to preserve the optimum fastening functionality of the insert  20 . 
     We now refer to  FIGS. 2A and 2B , which illustrate in detail two embodiments of the device  10 , wherein the fastening member  22  is a thread. 
     According to these two examples, the device  10  has an elongated outer shape, forming a main shaft  12  having two ends of different shape and function. According to the example illustrated, the shaft is cylindrical. The shaft cross-section may, however, have any shape: square, triangular, etc. 
     The first end is provided with piercing means  14 , adapted to cross at least one sheet of semi-finished product made of thermosetting or thermoplastic material MP. This piercing means  14 , of tapered shape and/or having edges can be attached to the shaft  12  or made in one piece with the shaft  12 . 
     The second end, opposite the first end, is provided with means  16  for sealing the fastening member  22  to prevent infiltration of plastic material MP during the overmoulding operation. This sealing means  16  can be attached to the shaft  12  or made in one piece with the shaft  12 . 
     The sealing means  16  prevents plastic material MP from flowing onto the fastening member  22  during the overmoulding operation. 
     Various solutions can be considered to perform this function. For example, the sealing means  16  can be designed according to the geometry of the fastening insert  20  and the fastening member  22 , to obtain tight pre-assembly, providing sealing by clamping. This sealing can be increased by advantageously using the compression exerted by the moving part of the mould. Thus, when closing the mould, the device  10  can be pressed more strongly against the insert  20 , to obtain a pressing area increased by a controlled additional deformation of the sealing means  16 . The moving element of the mould then presses the device  10  on the insert  20 , thereby providing a better seal during the moulding operation. 
     This solution can be replaced by or combined with other solutions. For example, the sealing means  16  may have shapes such as gadroons, ribs, beads, shoulders, pressing against the insert  20 , during the pre-assembly and/or by pressing and additional deformation obtained when closing the mould, which then create an improved barrier preventing the passage of the plastic material MP. 
     The device  10  thus forms a “piercing plug”, adapted to cover at least locally an area of the insert to protect the fastening member  22  from being covered by material MP during moulding, and adapted to pierce sheets of semi-finished product made of thermosetting or thermoplastic plastic material. 
     The piercing means  14  for piercing and crossing a sheet of semi-finished product made of plastic material, such as a sheet of SMC, may have tapered shape and/or edges. Generally, those skilled in the art will be able to find the best shape for piercing the load (set of sheets of plastic materials) introduced into the mould  30 , and required to manufacture the motor vehicle part  40 . 
     This piercing means  14  is preferably made of a polyamide-based material. 
     The device  10  forms a sealing piercing plug, i.e. a member adapted to cooperate with a member of the insert  20  carrying the fastening member  22 , to be interposed between the plastic material MP and the fastening member  22 . 
     Thus, when the insert  20  comprises a tapped hole ( FIG. 3A ) carrying the thread  22   a , and forming a female element, then the sealing means  16   a  comprises a male element ( FIG. 2A ) adapted to cooperate, by insertion for example, with this female element, in order to sealably plug the tapped hole. Thus, after engaging the device  10  in the insert  20 , or more precisely the means  16   a  in the tapped hole, the device  10  is pressed tightly against the insert  20 , forming a seal.  FIG. 4A  illustrates such an embodiment once the device  10  and the insert  20  have been assembled. 
     When the insert  20  comprises a screw ( FIG. 3B ) carrying the thread  22   b , and forming a male element, then the sealing means  16   b  comprises a female element ( FIG. 2B ) adapted to cooperate, by insertion for example, with this male element, in order to sealably cover the screw. Thus, after engaging the device  10  on the insert  20 , or more precisely the screw in the means  16   b , the device  10  is pressed tightly against the insert  20 , forming a seal.  FIG. 4B  illustrates such an embodiment once the device  10  and the insert  20  have been assembled. 
     When the insert is a weldable insert, i.e. when the insert  20  is adapted to be welded to a metal element of the vehicle, for example the body, then the sealing means  16  has a shape that is complementary to the area  22  to be welded of the insert  20 . 
     The invention also relates to an assembly of an insert  20  and a device  10  as described previously. The device  10  is adapted to the insert  20 , as illustrated by both  FIGS. 4A and 4B . 
     According to one embodiment, in order to obtain a better seal, the device  10  comprises a thread cooperating with the thread  22  of the insert. The threads of the device  10  are configured such that after engaging the insert  20  and the device  10 , the device  10  is pressed tightly against the insert  20 , forming a seal. 
     The insert  20  can be made of any material, in particular metal or plastic materials. 
     The invention also relates to an assembly of a mould  30  and a device  10  as described previously. 
     The mould  30  is a compression mould to form a motor vehicle part  40  made of plastic material MP comprising at least one fastening insert  20 . 
     The mould  30  can be used in particular to partially overmould the insert  20 . Overmoulding is said to be partial when at least one surface of the insert remains visible after overmoulding: the surface is not covered with plastic material during overmoulding. 
     As illustrated on  FIG. 1 , the mould  30  comprises two moulding portions  32  and  34 , defining the chamber for overmoulding the insert  20  and defining the mould cavity. 
     Preferably, the mould  30  comprises a housing  36  adapted to receive the insert  20  so as to control its position and prevent any movement of the insert  20  during the flow of plastic material. 
     According to one embodiment, one of the portions  32  and  34  comprises a housing  38  adapted to receive a portion of the device  10  comprising at least the piercing means  14 . The piercing means  14  thus forms a male element adapted to cooperate by insertion with the housing  38  forming a female element, so that once the mould  30  is closed, and during the compression of the plastic material MP, the device  10  is partially engaged in the housing  38 . 
     The dimensions and shapes of the housing  38  are defined so that, when the mould is closed, the portion  32  or  34  of the mould  30  carrying the housing  38  presses the device  10  to:
         press the device  10  tightly on the insert  20 , and therefore provide optimum sealing of the fastening member  22 ;   produce axial compression (i.e. in the mould closing direction) of the device  10  and thus axial crushing of the sealing means  16  or radial expansion against the housing  38 , and therefore, prevent infiltration of plastic material MP into this housing  38 .       

     The invention also relates to a method for moulding a motor vehicle part  40  made of plastic material comprising at least one partially overmoulded insert  20 .  FIGS. 4A and 4B  illustrate the portion of such a part comprising the insert  20 . 
       FIGS. 5A to 5D  illustrate the method. Note that these figures do not represent the whole mould  30 , but only the portion near the insert  20 . In particular, we do not see the entire overmoulding cavity, and the contacts between the portions  32  and  34  of the mould  30 . 
     According to this method, at least some of the following steps are performed using an assembly of a mould  30  and a device  10  according to the invention and using an assembly of an insert  20  and the same device  10 :
         a) engaging the device  10  in or on the insert  20 , so as to protect the fastening member  22  from infiltration of plastic material MP ( FIG. 5A );   b) introducing the insert  20  into the mould  30 , and optionally positioning it in the housing  36  ( FIG. 5A );   c) placing a loading plane, i.e. at least one sheet of semi-finished product made of plastic material, on the device  10  to pierce the sheet(s) of plastic material, using the piercing means  14  ( FIG. 5B );   d) closing the mould  30 , the device  10  partially engaging in the housing  38 , and applying pressure (during compression or injection) to make the material MP flow in the mould cavity ( FIG. 5C );   e) opening the mould  30  ( FIG. 5D ) and ejecting the part  40  carrying the overmoulded insert  20 ;   f) optionally, removing the device  10  from the part  40  ( FIG. 5D ).       

       FIGS. 6A and 6B  illustrate examples of parts  40  obtained according to this method. 
     The device  10  can be reused. In this case, the method is restarted from step b) with the same device  10  to produce another part.