Patent Publication Number: US-2004043683-A1

Title: Method of manufacturing a trim part under low pressure operating conditions

Description:
TECHNICAL FIELD  
       [0001] The present invention relates to interior trim parts of a vehicle, and in particular to a method of manufacturing a trim part, such as an airbag cover, under low pressure operating conditions. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0002] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
     [0003]FIG. 1 is a perspective view of an airbag cover according to one embodiment of the invention;  
     [0004]FIG. 2 is a cross-sectional view of the airbag cover of FIG. 1;  
     [0005]FIG. 3 is a side elevational view of an injection mold tool for forming the airbag cover of FIG. 1;  
     [0006]FIG. 4 is a partial rear perspective view of the airbag cover of FIG. 1 with the scrim material not shown for clarity;  
     [0007]FIG. 5 is a partial rear perspective view of the airbag cover of FIG. 1 with the scrim material;  
     [0008]FIG. 6A is a perspective view a melt compression molding (MCM) tool in an open position;  
     [0009]FIG. 6B is another perspective view the MCM tool in an open position;  
     [0010]FIG. 6C is a perspective view the MCM tool in an closed position;  
     [0011]FIG. 7 is a partial rear perspective view of an airbag cover formed by the MCM tool that is pre-weakened by laser scoring the trim part; and  
     [0012]FIG. 8 is another partial rear perspective view of an airbag cover formed by the MCM tool that is pre-weakened by a groove that is formed by a frame that is inserted into the MCM tool. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0013] Referring to FIGS. 1 and 2, a vehicular trim part comprises a skin material  12  on the front “A” surface and a scrim material  14  on the rear “B” surface. If the trim part  10  is designed to be an air bag cover, the scrim material  14  encompasses a hinge portion  13  of the trim part  10 . As described in more detail below, the skin material  12  and scrim material  14  of the trim part  10  are integrally molded and bonded together in a single operation by introducing a molten substrate material  15  (FIG. 3), which becomes cured substrate  16  after an appropriate cooling time, under low-pressure operating conditions. The trim part  10  may further comprise a foam layer  20  laminated to the skin material  12 . In one embodiment of the invention, the scrim material  14  includes a gate passage  18 . The purpose of the gate passage  18  is described in more detail below.  
     [0014] The substrate  16  may be any desirable thermoplastic resin, such as, for example, Polypropylene (PP), Acrylnitril-Butadien-Styrol-Copolymere (ABS), Polycarbonate-Acrylnitril-Butadien-Styrol-Copolymere (PC/ABS), or Thermoplastic Olefin (TPO). Referring specifically to FIG. 2, the substrate  16  has a thickness, T 1 , approximately equal to 2.5 mm to 3.0 mm. The skin material  12  may be TPO or polyvinyl chloride (PVC) having a thickness, T 2 , approximately equal to 0.5 mm. It is preferable to use TPO as a main component of the substrate  16  and skin material  12  because the entire trim part  10  would be totally recyclable. If desired, the trim part  10  may also further comprise the foam layer  20  laminated to the skin material  12 , having a thickness, T 3 , approximately equal to 2.5 mm.  
     [0015] As seen in FIG. 3, the trim part  10  is molded under low-pressure operating conditions by using an injection mold tool  30 . The mold tool  30  is defined by an upper mold half  32  and a lower mold half  34 . A heated, low-vestige, nozzle tip  31  of a gate  33 , which is located on the upper mold half  32 , injects molten substrate material  15 . The upper mold half  32  is further includes a heated runner  35  and a sprue  37 , which cooperates with an injector head  36  to introduce the molten substrate material  15  into the mold tool  30 . The lower mold half  34  defines a cavity  39  having a desired contour that forms the shape of the trim part  10 .  
     [0016] Prior to partial closing the mold tool  30  (i.e. the injecting of molten substrate material  15  and the closing of the mold tool  30 ), the gate passage  18  of the scrim material  14  is placed around the nozzle tip  31  of the gate  33 . The geometry of the gate passage  18  may be optimized so that it may be secured and held in place during the partial closing of the mold tool  30  in order to prevent the scrim material  14  from migrating during the molding process. The geometry of the gate passage  18  may be any desirable configuration, such as a circular cross sectional shape, that can properly accommodate the corresponding configuration of the nozzle tip  31 . The securement of the gate passage  18  around the nozzle tip  31  may be supplemented by applying an adhesive material (not shown) to the scrim material  14 . However, the use of adhesive material should be avoided because the adhesive may leave surface blemishes that may be visible on the “A” surface of the trim part  10 .  
     [0017] In the illustrated embodiment, the nozzle tip  31  has a diameter of approximately 25 mm. The gate passage  18  of the scrim material  14  has a slightly smaller diameter than the nozzle tip  31  so that flow direction, F, (FIG. 4) of the molten substrate material  15  securely holds the scrim material  14  against the upper mold half  32  during the molding process. Essentially, the gate passage  18  of the scrim material  14  permits the molten substrate material  15  to flow directly over the skin material  12  without any interference of the flow direction, F, of the molten substrate material  15  by the scrim material  14 . Upon partial closing of the mold tool  30 , the lower mold half  34  pushes the molten substrate material  15  through mesh-pattern openings of the scrim material  14 , thereby encapsulating the scrim material  14  within the molten substrate material  15 .  
     [0018] The skin material  12 , which generally comprises the “A” surface, may be mechanically held in place on the mold tool  30 , such as with a plurality of pins  42  on the lower mold half  34 , or non-mechanically by an adhesive (not shown), such as tape. If the pins  42  are used for securing the skin material  12  to the lower mold half  34 , the upper mold half  32  will include a corresponding number of pin-receiving locations  44  for receiving the pins  42  upon placing of the mold tool  30  in a closed position.  
     [0019] During the manufacture of the trim part  10 , excess skin material  12  in the form of sheet stock material may run off the outer periphery of the lower mold half  34  or onto the outer periphery of the cavity  39 . This excess material may be trimmed off with cutting surfaces (not shown) in the mold tool  30  at the parting lines (i.e. periphery of the trim part  10 ). Alternatively, the skin material  12  may be a preformed to a predetermined size that depends on the configuration of the trim part  10  to be molded.  
     [0020] When the scrim material  14  and the skin material  12  are properly positioned and secured to the mold tool  30 , the molding process is initiated by partially closing the upper mold half  32  on the lower mold half  34  under low-pressure tonnage conditions. As used herein, low pressure operating conditions is defined as the upper mold half  32  and the lower mold half  34  being moved to a partially closed position to exert a pressure of approximately 1.5 to 2.0 tons per square inch. Specifically, the upper mold half  32  and the lower mold half  34  are partially closed to a predetermined distance apart, for example, about 4 mm to about 8 mm, so that the molten substrate material  15  is properly spread to conform to the cavity  39 . The predetermined distance depends on the configuration of the trim part  10  and the location of the gate  33  so that the molten substrate material  15  may be properly spread before the mold tool  30  is completely positioned to its predetermined distance. It will be appreciated that the invention is not limited by the pressure exerted by upper and lower mold halves  32 ,  34 , and that the invention can be practiced with any desirable pressure in which the molten substrate material  15  can be properly spread to conform to the cavity  39  when the mold halves  32 ,  34  are partially closed. In addition, the invention is not limited by the properties of the molten substrate material  15 , and that the invention can be practiced with a molten substrate material  15  with any suitable properties that will allow the molten substrate material  15  to be properly spread within the cavity  39  and encapsulate the scrim material  14 . The molten substrate material  15  may be injected prior to, during, or after the partial closing of the mold tool  30 . Preferably, the molten substrate material  15  is injected prior to or during the partial closing of the mold tool  30 .  
     [0021] After partially closing of the mold tool  30 , the molten substrate material  15  completely bonds with both the skin material  12  and the scrim material  14  under the low pressure operating conditions in one cycling operation. As used herein, one cycling operating is defined as the partial closing of the mold tool  30  from an open position, followed by the opening of the mold tool  30  from the partially closed position. At the end of the cycling operation, the cycling of the mold tool  30  may be paused for a predetermined period of time so that the molten substrate material  15  may cool. The predetermined period of time for cooling the molten substrate material  15  may be, for example, approximately 30 to 40 seconds. Once the molten substrate material  15  is cooled, the molten substrate material  15  hardens to form the substrate  16  and the mold tool  30  can be opened to allow the trim part  10  to be ejected.  
     [0022] Once the molding process is completed and the trim part  10  is removed from the mold tool  30 , the trim part  10  may be subsequently scored by a laser in order to provide “invisible” score lines  48 . Essentially, the score lines  48  results in an airbag door  11  that renders the trim part  10  a seamless airbag cover. Any desirable, well known laser scoring machine may be used. For example, one laser scoring machine that can be used is sold under the tradename JENOPTIK® commercially available from Jenoptik Aktiengesellschaft Corporation of the Federal Republic of Germany.  
     [0023] As seen in FIG. 5, when the trim part  10  is ejected, the scrim material  14  is encapsulated within the substrate  16  adjacent to the “B” surface of the trim part  10 . Although the scrim material  14  is encapsulated in the substrate  16 , the scrim material  14  may be still visible (i.e. the scrim material  14  leaves a ripple effect on the “B” surface). Even further, the surface of the upper mold half  32  may have a plurality of grooves (not shown) in a predetermined pattern that forms ribs  46  (FIG. 4). Essentially, the molten substrate material  15  seeps through the scrim material  14  and forms the ribs  46 . If the trim part  10  is to be used as an airbag cover  10 , the ribs  46  may assist in holding the scrim material  14  during deployment of the airbag door  11 .  
     [0024] According to another embodiment of the present invention as seen in FIGS.  6 A- 6 C, a melt compression molding (MCM) mold tool  50  may mold the trim part  10  under low pressure conditions in one operation. The trim part  10  comprises the same components described above. However, the molten substrate material  15  used in the MCM mold tool  50  may be limited to Polypropylene (PP) or Thermoplastic Olefin (TPO) because the viscosity of the molten substrate material  15  for Acrylnitril-Butadien-Styrol-Copolymere (ABS) or Polycarbonate-Acrylnitril-Butadien-Styrol-Copolymere (PC/ABS) may be too high. Essentially, the MCM process also permits the scrim material  14  and the skin material  12  to be integrally bonded by the molten substrate material  15  in a single step, thereby providing a simpler and more cost-effective method as compared to conventional molding processes.  
     [0025] The MCM method substantially incorporates most of the similar steps described above in the first embodiment. However, the gate passage  18  formed in the scrim material  14  is not needed and can be eliminated because the gate  33 , the runner  35 , injector head  36 , and the sprue  37  are not included in the design of a upper mold half  54  of the MCM mold tool  50 . Even further, the scrim material  14  may not have to be attached to the MCM mold tool  50  because the scrim material  14  may be placed on a boss portion  56  of a lower mold half  52 . However, an adhesive material (not shown) may be used to hold the scrim material  14  in place against the lower mold half  52 . The skin material  12  may be mechanically held in place in a recess (not shown) formed in the upper mold half  54  by using a plurality of pins, or non-mechanically by an adhesive (not shown), such as tape, similar to the first method of the invention.  
     [0026] The MCM process includes the steps of placing the scrim material  14  on the lower mold half  52  of the MCM mold tool  50  (FIG. 6A). Next, the skin material  12  is located and secured to the upper mold half  54  of the MCM mold tool  50 . Next, the molten substrate material  15  is extruded with an extruder head  58  by laying a ribbon of molten substrate material  15  into the MCM mold tool  50  over the scrim material  14  (FIG. 6B). Then, the MCM mold tool  50  is partially closed under low pressure operating conditions so that that the molten substrate material  15  seeps through the grid-pattern of the scrim material  14  (FIG. 6C). Once the trim part  10  is molded, the MCM mold tool  50  is opened and ejector pins (not shown) are activated and pushes the trim part  10  out of the MCM mold tool  50 .  
     [0027] Once the trim part  10  is removed from the MCM mold tool  50 , the trim part  10  may be pre-weakened by scoring the trim part  10  with any well-known laser scoring technique to provide “invisible” score lines  48  (FIG. 7) defining an airbag door  11 . Once the airbag door  11  is formed by laser scoring, the trim part  10  is rendering as a seamless airbag cover  10 .  
     [0028] In an alternative method of the invention, a removable frame  70  including a plurality of pins (not shown), may be placed in the MCM mold tool  50  (FIG. 6A). The removable frame  70  may be desirably placed about the scrim material  14  and may be used to hold the scrim material  14  in place. Upon closing the MCM mold tool  50 , the frame forms a groove  60  having a reduced thickness on the “B” surface of the trim part  10  (FIG. 8). Essentially, the groove  60  reduces the thickness by approximately 75% and leaves approximately 25% of the remaining thickness of the trim part  10 . Thus, the removable frame  70  forms a weakened periphery for an airbag door  11  and the trim part  10  is rendered as a seamless airbag cover  10 . The use of the frame  70  obviates the need for pre-weakening the trim part  10 , such as by laser scoring, in a separate, subsequent step. The score lines  48  (FIG. 7) and groove  60  (FIG. 8) may be discontinuous (as shown), continuous, or define any desireable pattern in order to enhance the functionality of the airbag door  11 .  
     [0029] Because the trim part  10  is molded under low pressure conditions in both illustrated methods described above, typical thermoforming and trim operations (i.e. multi- and secondary-operations) commonly associated with trim part manufacturing are eliminated. In other words, a completely manufactured trim part  10  is formed in one operation without the need for multiple cycles (opening and closing the mold halves of the mold tool), unlike conventional molding techniques that require more than one step. According to one method of the present invention, the scrim material  14  is placed against the upper mold half  32  of the mold tool  30  about the gate  33  by a gate passage  18  (FIG. 3). According to another method of the invention, the scrim material  14  may be placed over the lower mold half  52  of the MCM mold tool  50  (FIGS.  6 A- 6 C). When the molten substrate material  15  is properly spread by partial closing of the mold halves  32 ,  34 , the flowing action of the molten substrate material  15  for both illustrated embodiments pushes the scrim material  14  against the appropriate mold half  32 ,  52  of the respective mold tools  30 ,  50 . As a result, the molten substrate material  15  encapsulates and integrally bonds the scrim material  14  to the skin material  12  in one operation.  
     [0030] Trimming of any excess skin material  12  is performed when the respective mold tools  30 ,  50  are partially closed under low pressure conditions. Although not discussed above, a vacuum may be used on the appropriate mold halves  34 ,  54  of the respective mold tools  30 ,  50  in order to secure the skin material  12  to the respective mold tools  30 ,  50 . However, the use of a vacuum may undesirably leave an uneven “A” surface on the trim part  10  that would be visible after the vacuum is released.  
     [0031] The present invention also provides a method for complete manufacturing of an airbag cover  10  in a single operation. The removable frame  70  that may be used in the MCM process (FIGS.  6 A- 6 C) forms a peripheral groove  60  and results in the pre-weakening of the airbag cover  10  for providing the airbag door  11 . If laser pre-weakening is desired rather than using the removable frame  70  to pre-weaken the trim part  10 , the laser pre-weakening may be carried out in a subsequent step.  
     [0032] Although the invention as described above is shown for molding a trim part under low pressure conditions, the invention may also apply to any vehicular trim part, such as an airbag cover, formed in a molding process having at least a scrim material, a skin material, and a substrate. It should be understood that the aforementioned and other various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby.