Abstract:
A method for manufacturing a motor vehicle panel from a melt, including a thermoplastic material and long glass fibers, and a film utilizes a mold assembly including a stationary mold, a movable mold, and a mold cavity defined therebetween. The method of manufacturing includes the steps of: securing the film to the movable mold; moving the movable mold towards the stationary mold; introducing the melt into the mold cavity when the mold cavity is at a predetermined thickness; and closing the movable mold against the stationary mold to compress the melt and form the motor vehicle panel with the film molded thereto.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a method of manufacturing a motor vehicle panel. More particularly, the invention relates to a method of manufacturing a motor vehicle panel having a Class A surface finish via injection-compression molding. 
       DESCRIPTION OF RELATED ART 
       [0002]    There is a significant market for motor vehicle finishes, particularly finishes for exterior panels. The most commonplace material utilized for such finished exterior panels is painted steel. The painted steel panels are formed by stamping steel sheets into discrete parts followed by assembly and painting. There are, however, certain disadvantages associated with such painted steel finishes. Specifically, the production process for the painted steel panels is highly polluting and consumes a great deal of energy. In addition, the resulting panels add significant weight to the motor vehicle, which in turn further increases energy consumption. Moreover, a significant capital investment and tooling cost is required before the production process for the painted steel panels even begins. 
         [0003]    In light of the foregoing problems with using painted steel, thermoplastic composites have become an attractive alternative. In many cases, the manufacture of thermoplastic composites with finishes is more cost-effective than the production of painted steel panels. In addition, thermoplastic composites are lighter in weight and have more environment-friendly finishes than their painted steel counterparts. Further, thermoplastic composites allow for more styling options and a variety of decorative finishes. 
         [0004]    Injection molding and compression molding are both well-known processes that utilize long fibers, either glass or carbon, to reinforce the thermoplastic composite in order to provide a panel with improved physical properties, including strength, stiffness, and dimensional stability. But while strength and stiffness are gained, the surface finish is degraded during these molding processes. As a result, a Class A surface finish that is suitable for the automotive industry is not achieved. 
         [0005]    Therefore, there is a need for a method of manufacturing a panel from a thermoplastic composite reinforced by long glass fibers that has a Class A surface finish. 
       SUMMARY OF THE INVENTION 
       [0006]    According to one aspect of the invention, a method of manufacturing a panel from a melt, including thermoplastic material and long glass fibers, and a film utilizes a mold assembly including a stationary mold, a movable mold, and a mold cavity defined therebetween. The method of manufacturing the panel includes the steps of: securing the film to the movable mold; moving the movable mold towards the stationary mold; introducing the melt into the mold cavity when the mold cavity is at a predetermined thickness; and closing the movable mold against the stationary mold to compress the melt and form the motor vehicle panel with the film molded thereto. 
         [0007]    According to another aspect of the invention, a method of manufacturing a panel from a melt, including thermoplastic material and long glass fibers, and a film utilizes a mold assembly including a stationary mold, a movable mold, and a mold cavity defined therebetween. The method of manufacturing the panel includes the steps of: securing the film to the movable mold; mixing the thermoplastic material with the long glass fibers to form the melt; moving the movable mold towards the stationary mold; introducing the melt into the mold cavity when the mold cavity is at a predetermined thickness; and closing the movable mold against the stationary mold to compress the melt and form the motor vehicle panel with the film molded thereto. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
           [0009]      FIG. 1  is a side view of an inline compounder and injection unit for delivering melt to a horizontal mold assembly; 
           [0010]      FIG. 2  is a side view of the mold assembly including a stop pad and a shear edge seal-off; 
           [0011]      FIG. 3  is a cross-sectional view of a motor vehicle panel formed in the mold assembly; and 
           [0012]      FIG. 4  is a side view of an inline compounder and injection unit for delivering melt to a vertical mold assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0013]    Referring to  FIGS. 1 and 2 , a mold assembly, generally shown at  10 , includes a movable platen  12  and a fixed platen  14 . The movable platen  12  moves relative to the fixed platen  14  by any of numerous methods known to those skilled in the art. A movable mold  16  is fixedly mounted to the movable platen  12  and a stationary mold  18  is fixedly mounted to the fixed platen  14 . Therefore, the movable mold  16  is able to move relative to the stationary mold  18 . In an exemplary embodiment, the mold assembly  10  is a horizontal mold in which the movable mold  16  moves in a horizontal plane. It is, however, appreciated that the mold assembly  10  may be a vertical mold, as shown in  FIG. 4 , in which the movable mold  16  moves in a vertical plane. 
         [0014]    The movable  16  and stationary  18  molds define a mold cavity  20  therebetween. A stop pad  22  is fixedly secured to one of the movable  16  and stationary  18  molds to stop movement of the movable mold  16  towards the stationary mold  18  when the movable mold  16  is at a predetermined distance from the stationary mold  18 . The size of the stop pad  22  may vary, which in turn allows for variation in the predetermined thickness of the mold cavity  20 . The movable mold  16  includes a show surface  24  facing the inside of the mold cavity  20 . A shear edge seal-off  26  is formed along the movable mold  16  adjacent the show surface  24  thereof and operates in the die draw direction. 
         [0015]    Referring now to  FIG. 1 , an inline compounder, generally indicated at  28 , is spaced apart from the mold assembly  10 . The inline compounder  28  includes a barrel  30  for accommodating twin screws  31 ,  32 . The twin screws  31 ,  32  run in the same direction and mesh with one another. A feed hopper  34  supplies a thermoplastic material in pellet form to the barrel  30 , and a glass feeder  36  is positioned downstream of the feed hopper  34  to provide long glass fibers into the barrel  30 . The inline compounder  28  melts the thermoplastic material and then mixes the thermoplastic material with the long glass fibers. A valve  38  regulates the flow of the resulting melt, including the thermoplastic material and the long glass fibers, exiting the inline compounder  28 . 
         [0016]    An injection unit, generally indicated at  40 , is disposed between the inline compounder  28  and the mold assembly  10 . The injection unit  40  includes a cylinder  44  having an anterior cylinder space  46 . A channel  42  extends between the inline compounder  28  and the injection unit  40 . The melt exiting the inline compounder  28  travels through the channel  42  and accumulates in the anterior cylinder space  46 , which is connected to the mold cavity  20  of the mold assembly  10  by a manifold  48 . A gate  50  selectively closes the manifold  48 . The injection unit  40  also includes an injector or plunger  52 . When the anterior cylinder space  46  is filled with a predetermined amount of the melt, the injector  52  is operated to inject the melt into the mold cavity  20  via the manifold  48  at a predetermined pressure. 
         [0017]    The above-described mold assembly  10 , inline compounder  28 , and injection unit  40  are utilized to form a motor vehicle panel  54 , generally shown in  FIG. 3 , from the thermoplastic material and long glass fibers. The panel  54  has a thickness of approximately 4-5 mm and may be any of numerous horizontal and semi-structural vertical motor vehicle panels including, but not limited to, a door panel, a hood, a roof panel, a decklid panel, and a liftgate panel. 
         [0018]    The panel  54  includes a backing substrate  56 , formed from the melt including the thermoplastic material and long glass fibers, molded to a film, generally indicated at  58 . In a preferred embodiment, the thermoplastic material is polycarbonate. The long glass fibers are supplied in rovings that are fed through the glass feeder  36  to cutting elements on the twin screws  31 ,  32  prior to being mixed with the thermoplastic material. It is, however, appreciated that the long glass fibers may, in the alternative, be pre-chopped and supplied in bundles. Preferably, the long glass fibers have a length of approximately 0.5″ and account for approximately 10 to 40% of the weight or mass of the backing substrate  56 . It is, however, appreciated that the length of the long glass fibers and the percentage weight of the long glass fibers may vary. The use of polycarbonate filled with long glass fibers allows the panel  54  to meet dimensional and high temperature requirements. 
         [0019]    Any of a variety of additives may be added to the thermoplastic material and long glass fibers. Many of the additives increase the compatibility of the long glass fibers to the thermoplastic material. Some examples of additives include, but are not limited to, heat stabilizers, release agents, coupling agents, impact modifiers, colorants, and talc filler. 
         [0020]    The film  58  includes a clear outer layer  60  and an inner layer  62  that is compatible with the backing substrate  56 . The compatibility between the film  58  and the backing substrate  56  allows for a strong adhesion therebetween. One or more additional layers, such as a color layer (not shown) may be interposed between the clear outer  60  and inner  62  layers. It is appreciated that the inner layer  62  may be a color layer. The film  58 , which has a thickness of approximately 0.8 mm, is secured to the movable mold  16  so that the clear outer layer  60  abuts the show surface  24  of the movable mold  16 . In order to fit within the mold assembly  10 , the film  58  must be trimmed prior to being secured to the movable mold  16 . It is appreciated that the film  58  may be secured to the movable mold  16  in any of numerous ways. It is also contemplated that the film  58  may be secured to a show surface  63  of the stationary mold  18  with the gate  50  repositioned so as to allow introduction of the melt into the mold cavity  20 . 
         [0021]    The film  58  that is selected must provide the panel  54  with a Class A surface finish that is suitable for the automotive industry. Therefore, the film  58  must have a high-gloss and colored finish. There are numerous commercially available films that may be utilized. Preferably, a polycarbonate based film is utilized for the present invention. 
         [0022]    In a method of manufacturing the panel  54 , the film  58  is first secured to the movable mold  16  so that the clear outer layer  60  abuts the show surface  24 . Thermoplastic material, preferably polycarbonate, is fed into the barrel  30  of the inline compounder  28  via the feed hopper  34 , where it is melted and then mixed with long glass fibers, which are fed into the barrel  30  via the glass feeder  36 . When the valve  38  is open, the resulting melt flows through the channel  42  and into the cylinder  44  of the injection unit  40 . More specifically, the melt accumulates in the anterior cylinder space  46  of the cylinder  44 . The movable mold  16  begins to move towards the stationary mold  18 . When the mold cavity  20  is a predetermined thickness, the injector  52  injects the melt into the mold cavity  20  via the manifold  48  and open gate  50 . The movable mold  16  closes against the stationary mold  18  to compress the melt and force the melt to fill all areas of the mold cavity  20 . Once the stop pad  22  of the movable mold  16  abuts the stationary mold  18 , movement of the movable mold  16  stops and the mold assembly  10  is closed. At this time, the shear edge seal-offs  26  seal the outer edges of the mold cavity  20  to prevent the melt from leaking out of the mold cavity  20 . With the mold assembly  10  now closed, the backing substrate  56  is molded to the inner layer  60  of the film  58  in order to form the panel  54 . The panel  54  is then removed from the mold assembly  10 . Finally, any post-mold trimming on the panel  54  is conducted. The clear outer layer  62  of the film  58  provides the molded panel  54  with a class A surface finish that is suitable for the automotive industry. 
         [0023]    The above-described injection-compression process avoids breaking up the long glass fibers due to low shear so that fiber length is maintained throughout. In addition, the injection-compression process provides more random glass fiber orientation than what would be achieved through injection molding. As a result, warp caused by shrink differentials are reduced. 
         [0024]    The invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described.