Abstract:
The present invention is a twinsheet door which includes a first door portion and a second door portion connected to the first door portion. The twinsheet door of the present invention is manufactured using a thermoforming process, during which a vacuum shapes the first door portion and the second door portion such that one or more closed sections are created when the first door portion is thermally bonded to the second door portion and simultaneously a vacuum is applied to form the first door portion and said second door portion. The closed section formed between the first door portion and second door portion provides additional strength and rigidity to the twinsheet door. Additionally, the forming of the closed section between the first door portion and the second door portion and the bonding between the first door portion and second door portion is achieved during a single manufacturing process.

Description:
FIELD OF THE INVENTION 
     The present invention relates to door panels which are thermoformed and bonded together. More specifically, the present invention relates to two panels which are simultaneously thermoformed and bonded together to form the door of a vehicle. 
     BACKGROUND OF THE INVENTION 
     The process of thermoforming products is generally known. Thermoforming processes are used for producing various parts such as panels for the interior of a vehicle. 
     One of the advantages of using a thermoforming process is that it provides a relatively efficient and inexpensive way to manufacture various components for a vehicle. Using a thermoforming process to manufacture panels used for the interior of a vehicle, or exterior panels which can form the body of the vehicle help to reduce costs during the manufacturing process. Typically, these panels are made from a single sheet of material conducive to a thermoforming process. One of the drawbacks in using a thermoforming process to form a panel of a vehicle using a single sheet is that often times the finished part does not have the required structural rigidity or strength to meet the desired specifications of the manufacturer. As a result, additional secondary structure is needed to provide support for the panel, resulting in increased time and cost in manufacturing, as well as increased material cost to provide the necessary structure for the part. 
     Accordingly there exists a need for a method for manufacturing a thermoformed part which also includes the structural strength required by various manufacturers. 
     SUMMARY OF THE INVENTION 
     The present invention is a twinsheet door which includes a first door portion and a second door portion connected to the first door portion. The twinsheet door of the present invention is manufactured using a thermoforming process, during which a vacuum shapes the first door portion and the second door portion such that one or more closed sections are created when the first door portion is thermally bonded to the second door portion and simultaneously a vacuum is applied to form the first door portion and said second door portion. The closed section formed between the first door portion and second door portion provides additional strength and rigidity to the twinsheet door. Additionally, the forming of the closed section between the first door portion and the second door portion and the bonding between the first door portion and second door portion is achieved during a single manufacturing process. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1A  is a side view of a twinsheet door manufactured using a thermoforming process, according to the present invention; 
         FIG. 1B  is a perspective view of a first portion of a twinsheet door located in a mold, manufactured according to a thermoforming process, according to the present invention; 
         FIG. 2A  is a second side view of a twinsheet door, manufactured according to a thermoforming process, according to the present invention; 
         FIG. 2B  is a perspective view of a second portion of a twinsheet door located in a mold, manufactured according to a thermoforming process, according to the present invention; 
         FIG. 3  is a sectional view taken along lines  3 - 3  of  FIG. 1A ; 
         FIG. 4A  is a sectional view taken along lines  4 A- 4 A of  FIG. 2A ; 
         FIG. 4B  is an enlarged perspective view of a door latch connected to a twinsheet door, according to the present invention; 
         FIG. 4C  is an enlarged view of a circled portion of  FIG. 4A ; 
         FIG. 5A  is a sectional view taken along lines  5 A- 5 A of  FIG. 1A ; 
         FIG. 5B  is an enlarged perspective view of a hinge used for a twinsheet door, according to the present invention; 
         FIG. 6  is a perspective view of a twinsheet door attached to a vehicle, according to the present invention; 
         FIG. 7  is partial a side view of a twinsheet door attached to a vehicle, according to the present invention; and 
         FIG. 8  is a sectional side view taken along lines  8 - 8  of  FIG. 1A . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     A door made according to the thermoforming process of the present invention is shown generally in  FIG. 1A  at  10 . Referring to the Figures generally, the door  10  includes a first door portion or inner skin  12  and a second door portion or outer skin  14 . In accordance with the method aspects of the present invention, both the inner skin  12  and outer skin  14  are made from what is called “sheet stock.” Sheet stock is a plastic sheet which in this embodiment is made of Thermo-Plastic Polyolefin (TPO) that is cut into blanks, which in this embodiment would be used for the skins  12 , 14 . In this embodiment, the sheet stock will have a thickness of substantially 4.5 mm, but it is within the scope of the invention that other thicknesses may be used. In accordance with another method aspect of the present invention the blanks are heated and then inserted into a mold, in this embodiment there is an inner mold  16  and an outer mold  18 . The inner mold  16  is used for producing the shape of the inner skin  12 , and the outer mold  18  is used for producing the shape of the outer skin  14 . 
     During the thermoforming process used to make the door  10  of the present invention, each sheet is heated, and one sheet is placed into the inner mold  16 , and another sheet is placed into the outer mold  18 . Both the mold  16 , 18  are connected to a vacu-former type of device (not shown) which produces a vacuum to draw the sheet stock of the inner skin  12  and outer skin  14 , respectively, away from each other into the proper shape to produce the inner skin  12  and outer skin  14 . However, during the vacu-form process, the molds  14  and  18  are also pressed together, and a melt-bond  20  is formed between a first outwardly extending flange or first outer flange  22  formed on the inner skin  12  and a secondly outwardly extending flange, or a second outer flange  24  formed on the outer skin  14  during the forming process. There are also several inner flanges formed on both the inner skin  12  and outer skin  14  which form apertures that are used for placing windows and a door latch on the door  10 . After the thermoforming process, portions of the sheet stock are cut and the door  10  is then trimmed to form the apertures. The inner skin  12  and outer skin  14  have a final target thickness of substantially 3.8 mm, but it is within the scope of the invention that other thicknesses may be used, depending up on the application. This is part of a routing operation applied to the door  10 . In this embodiment, there is a first aperture  26  cut out of the door  10 , as well as a second aperture  28  and a third aperture  30  cut out of the door  10 . 
     Surrounding the first aperture  26 , there is a first inner flange  32  which is melt-bonded to a second inner flange  34  during the thermoforming process to form another melt-bond  20 . Similarly, surrounding the second aperture  28  there is a third inner flange  36  which becomes melt-bonded to a fourth inner flange  38  during the thermoforming process to produce yet another melt-bond  20 . Once the door  10  is formed and the skins  12 , 14  are bonded together, windows, generally shown at  54  are attached to the door  10 . The windows  54  have a frame portion  56  and a window pane  58 . The frame portion  56  is attached to the door  10  through the use of any type of suitable fastener, such as a bolt, rivet, or the like. In this embodiment, there are a series of bolts  60  which are screwed through the frame portion  56  and the flanges  32 , 34  in the first aperture  26 , and through the frame portion  56  and the flanges  36 , 38  of the second aperture  28 . The windows  54  may be of the type that can be opened and closed, as shown in the first aperture  26 , or the windows  54  may be of the type that do not open and close, as shown in the second aperture  28 . 
     The first flange  22  formed on the inner skin  12  and the second flange  24  formed on the outer skin  14  extend around the periphery of the inner skin  12  and outer skin  14 , respectively. Once they are melt-bonded together, a weatherstrip  44  is placed on the molded flanges  22 , 24  for preventing moisture and other debris from entering the vehicle in which the door  10  is used. The weatherstrip  44  includes a gap  46  which receives the flanges  22 , 24  after they are molded together. 
     There is also a portion of the inner skin  12  and outer skin  14  which forms a first wall portion  48  and a second wall portion  50 . The first wall portion  48  includes a rib  52  which is melt-bonded to the second wall portion  50 . The rib  52  provides additional support and structure for the door  10 . 
     A cross-section of part of the door  10  can be seen in  FIG. 3 . As mentioned above, the skins  12 , 14  are vacuum formed to form the portions of the door  10 . The vacuuming of the skins  12 , 14  also creates a void or closed section  62 . The void  62  is created when the skins  12 , 14  (when in the form of sheet blanks) are placed into the respective molds  16 , 18 , and the vacuum force is applied, drawing a portion of the skins  12 , 14  away from each other, while simultaneously melt-bonding the flanges  22 , 24  together, creating the void or closed section  62 . The closed section  62  has a first side  64  formed by a portion of the inner skin  12 , and a second side  66  formed by a portion of the outer skin  14 . The first side  64  and second side  66  are drawn away from each other during the vacuum process, and remain substantially parallel to each other during and after the vacuum and thermoforming processes. There is also a third side, generally shown at  68 , formed by portions of both skins  12 , 14 , and a fourth side, generally shown at  70  which is also formed by portions of both skins  12 , 14 . The third side  68  and the fourth side  70  are also shaped during the vacuum process, examples of which are shown in  FIGS. 3 and 5A . The shape of the four sides  64 , 66 , 68 , 70  forming the closed section  62  improves the structural rigidity of the door  10 . The shape of the four sides  64 , 66 , 68 , 70 , and hence the cross-section of the door  10 , also varies in different areas of the door  10 . 
     In  FIG. 3 , the third side  68  is the part of the inner skin  12  that extends in continuous fashion from the first side  64  to the first outer flange  22 , and the part of the outer skin  14  that extends in continuous fashion from the second side  66  to the second outer flange  24 . The fourth side  70  in  FIG. 3  is the part of the inner skin  12  that extends in continuous fashion from the first side  64  to the third inner flange  36 , and the part of the outer skin  14  that extends in continuous fashion from the second side  66  to the fourth inner flange  38 . 
     Referring more specifically to FIGS.  5 A, 5 B and  8 , there are also several exterior hinges, shown generally at  72 , which are used to allow the door  10  to pivot relative to a vehicle, shown generally at  88  in  FIGS. 6 and 7 . Each hinge  72  includes a base plate  74  having a pair of slots  76 . In similar fashion to  FIG. 3 , the part of the door  10  shown in  FIG. 5A  also has a closed section  62 . However, the first and second sides  64 , 66  are closer together, and the shape of the third and fourth sides  68 , 70  are different because the shape of the door  10  in the area of the cross-section shown in  FIG. 5A  is different. 
     There is also a pair of apertures  78  cut into the outer skin  14 , and a pair of bolts  80 , which extend through the slots  76  and the apertures  78  as shown in  FIGS. 5B and 8 . There is also a tapping plate  82  which has a pair of corresponding threaded apertures  84  which also receive a portion of the bolts  80 . The skins  12 , 14  are thermoformed and melt-bonded together as described above, and the third side  68  is similar to the third side  68  shown in  FIG. 3 , with the exception that the shape is different, and there is a trimmed slot  86  is cut into the inner skin  12  so the tapping plate  82  can be inserted into a location between the skins  12 , 14  as shown in  FIGS. 5A and 8 . In  FIG. 5A , the fourth side  70  is formed by a part of the inner skin  12  extending in continuous fashion from the first side  64  into the first inner flange  32 , and a part of the outer skin  14  extending in continuous fashion from the second side  66  into the second inner flange  34 . 
     Once the tapping plate  82  has been inserted, the bolts  80  are inserted through the slots  76 , apertures  78 , and into the corresponding threaded apertures  84 . When first assembled, the bolts  80  are not tightened completely, but rather, they are left loose so that the position of the base plate  74  can be adjusted to allow the door  10  to be positioned relative to the vehicle  88  properly. 
     Each hinge  72  also includes a pin  90  which is attached to the base plate  74 . In this embodiment, the pin  90  is shaped as shown in  FIGS. 1A ,  2 A,  5 B, and  6 - 8  so as to have a portion  92  which is able to be received into a cylinder  94 , with the cylinder  94  being attached to a plate  96 . To assemble, the portion  92  of the pin  90  is simply inserted into an aperture  98  formed on the cylinder  94 . The plate  96  is attached to the vehicle  88  through the use of typical fasteners  100 . In this embodiment, there are three hinges  72 , and the assembly process described is the same for all three hinges  72 . Having the portion  92  of the pins  90  simply inserted into the respective cylinders  94  allows for simple attachment and detachment of the door  10  to the vehicle  88 . 
     As mentioned above, there is also a third aperture  30  formed in the door  10 . However, to form the third aperture  30 , the portion cut out of the inner skin  12  is of a different size compared to the portion cut out of the outer skin  14 . The third aperture  30  therefore consists of a large cut-out portion  102  taken from the inner skin  12  and a small cut-out portion  104  taken from the outer skin  14 . The reason for this is to accommodate a door latch, generally shown at  106 . The aperture  30  in both the inner skin  12  and outer skin  14  allows the door latch  106  to be exposed to both the inside and outside of the vehicle  88  when in a closed position, enabling the door  10  to be opened and closed from the inside or outside of the vehicle  88 . The door latch  106  is a typical latch that may be used on different types of vehicles. The door latch  106  includes a paddle flap  108  which is exposed to the outside of the vehicle  88 , and also a door handle  110  which is exposed to the inside of the vehicle  88 . There are several apertures  112  which are cut into the outer skin  14  as shown in  FIG. 4C  which allows the door latch  106  to be attached to the outer skin  14  through the use of fasteners  114 . The door latch  106  includes a housing  116  which is the portion of the door latch  106  that the fasteners  114  attach to the outer skin  14 . 
     The door latch  106  functions with a catch mechanism, generally shown at  118 . The catch mechanism  118  includes a flange portion  120  which is bolted to a roll cage  122 . While a portion of the roll cage  122  is shown in  FIG. 4A , the roll cage  122  forms part of the frame of the vehicle  88 . The catch mechanism  118  also includes a lipped portion, generally shown at  124 , having an angled surface  126 . The door handle  110  also includes a rounded portion  128  and a locking mechanism  130 . The locking mechanism  130  includes an angled surface  132  and a locking surface  134 . The door  10  is shown in a closed position in  FIGS. 4A and 6 . When in the closed position, the locking surface  134  is in contact with the lipped portion  124  of the catch mechanism  118 , and prevents the door  10  from being opened. When it is desired to open the door  10  from the inside of the vehicle  88 , the handle  110  is moved to the right when looking at  FIG. 4A  such that the locking surface  134  is no longer in contact with lipped portion  124 . This will allow the door  10  to be opened, as shown in  FIG. 7 . 
     To close the door  10  from an open position, the door  10  is simply pivoted about the hinges  72  such that the door latch  106  pivots towards the vehicle  88 . As the door  10  shuts, the angled surface  132  of the locking mechanism  134  will come in contact with and slide along the angled surface  126  of the lipped portion  124 , causing the door handle  110  to move to the right when looking at  FIG. 4A , allowing the locking mechanism  130  to move around the lipped portion  124  of the catch mechanism  118  to the position shown in  FIG. 4A . The door handle  110  is attached to several mechanical components in the housing  116  which allow the handle  110  to slide along the outside of the housing  116  and work in conjunction with the paddle flap  108 . The components linking the paddle flap  108  and the handle  110  have been removed for purposes of clarity, and are not necessary for describing the invention. 
     As mentioned above, the paddle flap  108  is connected mechanically to the door handle  110 . To enter the vehicle  88  when the door  10  is closed, the paddle flap  108  is simply pulled such that the paddle flap  108  pivots, and the mechanical components inside the housing  116  will cause the door handle  110  to move to the left (when looking at  FIG. 4A ) such that the locking surface  134  is no longer in contact with lipped portion  124 , and the door  10  will then be able to be opened, as described above. 
     It can also be seen in  FIG. 4A  that there is a first rib  132  formed in the inner skin  12  near the edge of the large cut-out  102 , and a second rib  134  formed in the outer skin  14  in proximity to the first rib  132 . During the thermoforming process, the first rib  132  is formed into the inner skin  12 , and the second rib  134  is formed in the outer skin  14  while simultaneously being melt-bonded together. The melt-bond between the ribs  132 , 134  provides an additional connection between the inner skin  12  and outer skin  14 , in addition to the melt-bond between the outer flanges  22 , 24 , the inner flanges  32 , 34  surrounding the first aperture  26 , the inner flanges  36 , 38  surrounding the second aperture  28 , and the rib  52  melt-bonded to the second wall portion  50 . 
     It is also within the scope of the invention that the shape of the molds  16 , 18  may be changed to such that other melt-bonds are produced between the inner skin  12  and outer skin  14 . Once the door  10  is formed and assembled, the shape of the skins  12 , 14  provides the required structural rigidity to meet various production requirements, while at the same time accomplishing the forming of the shape of the skins  12 , 14  and producing the melt-bonds simultaneously. Producing the shape of the skins  12 , 14  and the melt-bonds  20  in a single step allows for the production of a cost-effective and efficient way to manufacture the door  10 . 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.