Patent Document

FIELD OF INVENTION  
         [0001]    The subject invention relates to a method of manufacturing an automotive panel that has an exterior class-A finish.  
         BACKGROUND OF THE INVENTION  
         [0002]    Injection molding is well known in many industries for manufacturing a wide variety of products. The automotive industry utilizes plastic injection molding to create a number of interior and exterior trim components and other like parts, such as tonneau covers and body panels, which require an aesthetically pleasing exterior surface. The desired exterior surface is typically known as an exterior class-A finish.  
           [0003]    Current techniques for molding large planar panels, such as the method disclosed in U.S. Pat. No. 4,910,067, can produce structurally rigid panels. However, the quality of the surface finish is usually slightly less than class-A. A separate skin, paint or coating must then be applied to the panel after removing the panel from the mold to create the class-A finish.  
           [0004]    It would be desirable to develop a manufacturing process which creates a class-A finish during the injection molding of the part, thereby eliminating the separate manufacturing step outside of the mold.  
         SUMMARY OF INVENTION  
         [0005]    The disadvantages of the prior art may be overcome by providing a method of manufacturing a panel utilizing a first mold half having a peripherally extending rib and a second mold half. The first mold half is moved relative to the second mold half to define a first mold cavity with the rib extending into the first mold cavity. A first molten material is injected into the first mold cavity and allowed to solidify to thereby form a notch within the first solidified material corresponding to the shape of the rib. A second mold cavity is formed which has a flow path between the first solidified material and the first mold half comprising a series of sharp turns which present a barrier to material flow. A second material is injected into the second mold cavity and allowed to cure on the first solidified material.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    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:  
         [0007]    [0007]FIG. 1 is a cross-sectional side view of a molding assembly having an upper mold half and a lower mold half in accordance with the subject invention;  
         [0008]    [0008]FIG. 2 is an enlarged fragmentary cross-sectional side view of the molding assembly with the upper and lower mold half in a completely closed position before a first injection of a first material;  
         [0009]    [0009]FIG. 3 is an enlarged fragmentary cross-sectional side view of the molding assembly after the first injection with the upper mold half in a partially raised position;  
         [0010]    [0010]FIG. 4 is an enlarged fragmentary cross-sectional side view of the molding assembly after a second injection of a second material;  
         [0011]    [0011]FIG. 5 is an enlarged fragmentary cross-sectional side view of an alternative embodiment of the upper mold half;  
         [0012]    [0012]FIG. 6 is a perspective view of a second embodiment of a molding formed utilizing the present invention;  
         [0013]    [0013]FIG. 7 is a top plan view of the molding of FIG. 6;  
         [0014]    [0014]FIG. 8 is a sectional view of the molding of FIG. 6 along the lines A-A; and  
         [0015]    [0015]FIG. 9 is a sectional view of the molding of FIG. 6 along the lines B-B. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, a molding assembly is generally shown at  10  in FIG. 1.  
         [0017]    The molding assembly  10  includes a first mold half  12  and a second mold half  14 . Both the first  12  and second  14  mold halves include an inner surface  16 ,  17  having a desired contour which correlates to the shape of a final molded product having a generally convex outer class-A surface (not shown).  
         [0018]    Preferably the inner surfaces  16 ,  17  are configured to form an automotive panel. As appreciated, the contour of the inner surfaces  16 ,  17  may be of any suitable design to create a desired automotive or non-automotive molded product generally having a large planar surface.  
         [0019]    A center plug  19  extends from the second mold half  14  that aligns with the center recess of the first mold half  12 . Center plug  19  has walls that are slightly tapered to accommodate demolding. The center plug  19  has a flange  21  extending about the perimeter of the plug  19 . Flange  21  extends about and is spaced from the inner surface  17 .  
         [0020]    The first mold half  12  has a recess  23  sized to receive center plug  19 . Recess  23  is slightly larger than the center plug  19  such that when the mold halves  12 ,  14  are closed a desired gap will be maintained between surfaces  16 ,  17 . Rib  24  extends around the recess  23 . Rib  24  is spaced from the outer periphery of the first mold half  12 . Abutment  25  extends about the outer periphery of the first mold half  12 . Abutment  25  has a thickness which corresponds to the thickness of the desire gap between the surfaces  16 ,  17 . Rib  24  has a thickness that is less than that of abutment  25 .  
         [0021]    To mold a product, the mold halves  12 ,  14  are first moved to a closed position. Abutment  25  abuts against mold half  14  forming a seal. A first molten material  20  is then injected through a plurality of apertures or gates  22 , preferably in the upper mold half  12 , into the first mold cavity  18  until completely filled. Alternatively, gates  22  could be located in mold half  14  in accordance with standard injection molding practice. Preferably, a plurality of gates are used and the flow of material is controlled by a technique known as sequential valve gating, which is more particularly described in U.S. Pat. No. 5,762,855. The gates are preferably positioned relative to the part to be molded in inconspicuous regions so that if a mark is created by the gate, this mark can be later covered or removed.  
         [0022]    The first material  20  is preferably any thermoplastic material. Suitable non-limiting examples include polypropylene, polyethylene terephthalate (PET), NYLON, polycarbonate, and PCABS. Optionally, reinforcement materials such as a glass fibre, mineral filler or nanoparticle may be added to the thermoplastic. The molten material  20  solidifies or “freezes” to a rigid or semi-rigid base or substrate for the panel.  
         [0023]    Rib  24  forms a corresponding notch  26  within the solidified first material  20  that forms flange  27  extending about the periphery of the molded part. As shown in FIGS. 1 through 4, the rib  24  has a substantially rectangular configuration. The rib  24  preferably has a trapezoidal configuration as shown in FIG. 5 (slightly exaggerated for illustration purposes) or any other suitable shape which allows the flange  27  to demold from the rib  24 . As appreciated, the notch  26  formed in the flange  27  will directly correspond to the configuration of the rib  24 .  
         [0024]    As appreciated, it is desirable to have a well defined smooth exterior finish for the completed panel such that the exterior surface is aesthetically pleasing class-A finish.  
         [0025]    Referring also to FIGS. 3 and 4, the first mold half  12  is opened slightly to create a second desired gap between the first  12  and second  14  mold halves. This gap defines a second mold cavity  28  disposed above the first material  20  for receiving a second material  30 . The rib  24  and corresponding notch  26  have sharpened edges which creates a narrow channel or flow path having a series of sharp turns between the flange  27  and rib  24 . The series of sharp turns presents a barrier to the flow of viscous liquids, preventing the viscous liquid from being expelled from the second mold cavity  28 .  
         [0026]    After the upper mold half  12  is raised, a second injection of the second material  30  is performed. The second material  30  forms a thin skin or coating that adheres to the solidified part. The second material  30  is preferably a light stable coating such as thermosetting polyurethane or polyester, either aliphatic or aromatic. A preferred polyurethane coating is commercially available from Omnova Solutions Inc. under the trademark GENGLAZE or STYLECOAT.  
         [0027]    The second material  30  fills the second mold cavity  28  and extends through the narrow channel and partially spills into the notch  26  of the first material  20  as is illustrated in FIG. 4. The wave front of the second material  30 , however, cannot make both turns and pass through both narrow channels. Accordingly, the flow of the uncured second material is terminated and does not escape from between the mold halves  12 ,  14  during the second injection process. For illustrative purposes, the gap formed between the upper  12  and lower  14  mold halves and the narrow channels are exaggerated. The preferred thickness of the skin  30  is about 3-5 thousands of an inch or approximately 0.125 mm.  
         [0028]    During the solidification of the base, i.e., the first material  20 , heat is expelled from the first material  20 , which heat cures the coating  30  to the molded substrate. Optionally, the mold halves  12 ,  14  can be maintained at about 250° F. to enhance cross linking. Once the solidification and curing is complete, the first mold half  12  is completely opened. The molded part now has a skin defining the desired class-A finish for the panel. In addition, the panel does not require an additional painting step.  
         [0029]    An alternative method of forming the panel is also contemplated wherein the first mold half  12  is not raised above the second mold half  14 . In other words, the upper  12  and lower  14  mold halves remain in the completely closed position during the molding process. The injecting of the first material  20 , along with the forming of the notch  26 , occurs in the same manner as above. However, the second material  30  is injected while the mold halves  12 ,  14  remain closed. The first material  20  may shrink slightly during solidification and has some compressible characteristics. Hence, the injection pressure of the second material  30  will at least partially compress the first material  20  and create a small gap between the first material  20  and the first mold half  12 . The small gap is analogous to the second mold cavity  28  discussed above. The rib  24  and notch  26  of the first material  20  still operate to retain the second material  30  within the upper  12  and lower  14  mold halves during the injection thereof. This method may be preferred when using a first material  20  that is compressible after an initial solidification.  
         [0030]    Referring to FIG. 6, a molded part  100  is illustrated. Molded part  100  generally has a convex class-A outer surface having a generally planar section  40  and a flange  27  extending about a periphery of the parent part  100 . Flange  27  is preferably spaced from and extends about planar section  40 .  
         [0031]    In this embodiment, the flange  27  has a series of circumferentially extending apertures  42  separated by a series of filling webs  44 . The series of apertures  42  separate the inner region of flange  27  from an outer racetrack  46 . First and second mold halves  12 ,  14  are modified in a known manner to mold the apertures  42  by inserting walls onto either of mold half  12  or mold half  14 . The portions of rib  24  are configured to extend between the walls that form apertures  42 .  
         [0032]    The molded part is formed in the manner described above. Once the formed part is removed from the mold halves  12 ,  14 , the racetrack  46  may be removed from the parent part by cutting or shearing the webs  44 . The webs  44  should have a minimal amount of the second material  30 . This material can be easily removed or alternatively the webs  44  can be cut from the racetrack  46  whereupon the racetrack may be ground up into a regrind and fed back into the molding process as part of first material  20  as is known in the art.  
         [0033]    The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. It is now apparent to those skilled in the art that many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that the invention may be practiced otherwise than as specifically described.

Technology Category: 7