Abstract:
A unitary plastic appliance door is produced by thermoforming an outer door panel and an inner door liner and joining them together in a unitary apparatus. The inner door liner is formed of sheet plastic on a male mold member and is then positioned over a female mold member mounted alongside the male mold member. The outer door panel is formed from a second sheet of plastic in the female mold member and then the inner door liner is registered with the formed outer door panel in the female mold member and is joined thereto to form the appliance door.

Description:
This application is a divisional of application Ser. No. 07/671,858, filed on Jun. 28, 1996, now U.S. Pat. No. 5,759,591. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to the art of household appliances and, more specifically, to a method and apparatus for thermoforming a plastic appliance door from two plastic sheets. 
     2. Discussion of the Prior Art 
     It is commonly known to produce a plastic appliance door, and in particular, a refrigerator door by independently manufacturing the various components that combine to make the door and then, in a separate manufacturing step, assembling the various components. For example, as represented in FIG. 1 of this application, it is common to form an outer refrigerator door panel  5  from a single stamped sheet of metal which is folded in order to form sides  8  and inwardly turned flanges  10 . The inner liner  13  associated with such a refrigerator door is often thermoformed on a male mold member. In general, such an inner liner  13  is made on the male mold member because of the high draw ratios that would be involved with the use of a female mold member. Once the outer refrigerator door panel  5  and the inner refrigerator door liner  13  are formed, inner liner  13  is secured to door panel  5  along flanges  10 , along with an annular gasket  16 , by means of a plurality of connecting strips  18  and screws  20 . A separate handle  22  is then secured to outer refrigerator door panel  5  by means of screws  24 . Outer refrigerator door panel  5  is also generally formed with upper and lower aligned holes  27  which are adapted to receive pivot bushings  29  for mounting the assembled refrigerator door to a refrigerator cabinet. For insulation purposes, it is also known to inject foam between refrigerator door panel  5  and inner liner  13  after complete assembly of the refrigerator door. 
     The manufacturing procedure associated with constructing such a refrigerator door formed from various, individually produced components which are later assembled together, is inefficient. Such a process is extremely time consuming and requires various manufacturing stages wherein the individual components are made and assembled. In addition, since the outer refrigerator door panel  5  is made of metal, its outer surface must be painted for aesthetic purposes. The need for these multiple manufacturing stages obviously increases the overall costs associated with manufacturing such a refrigerator door. 
     It has also been proposed to manufacture a hollow refrigerator door formed entirely from plastic. Such an arrangement is generally shown in FIGS. 2,  3   a  and  3   b  and disclosed in U.S. Pat. No. 5,306,082. According to this method of making a refrigerator door, the first step in the manufacturing process involves independently making the individual components which combine to form the inner door members. As shown in FIG. 2, these inner components generally constitute opposing side members  35 ,  37  and a plurality of shelf defining members  40 - 42 . In general, these interior components are separately blow molded by arranging two parallel sheets of plastic between first and second mold members (see FIGS. 3 a  and  3   b ), closing the mold members so as to pinch the sheets about outer perimeters thereof and injecting air between the sheets so as to cause the sheets to expand against the mold members. Side members  35 ,  37  and shelf members  40 - 42  are formed with tabs  45  which are adapted to extend within slots  48  formed in an outer door panel  50  that is constituted by a hollow plastic slab which is also blow molded. In a final stage of the blow molding of the outer door panel  50 , the tabs  45  provided on side members  35 ,  37  and shelf members  40 - 42  are positioned within slots  48  such that slots  48  form about tabs  45  in order to secure side members  35 ,  37  and shelf members  40 - 42  to outer door panel  50 . An annular gasket  52  is then secured by means of connecting strips  55  and screws  57  to an outer annular flange portion  59  of door panel  50 . In addition, a separate handle  62  is secured to door panel  50  by means of screws  64 . 
     The refrigerator door construction arrangement as represented by FIGS. 2,  3   a  and  3   b  has several advantages over the construction arrangement represented in FIG.  1  and discussed above. First, the entire refrigerator door of the FIG. 2 arrangement is formed from plastic and therefore its desired shape can be readily varied. In addition, such a manufacturing operation does not require a subsequent painting stage for outer door panel  50 . Furthermore, making the outer door panel  50  from plastic can provide some additional heat efficiency benefits since the metal door panel of the FIG. 1 arrangement will be a better conductor of heat into the refrigerator than the plastic door. Finally, the use of plastic presents the ability to integrally form the outer door panel with a handle as also proposed in the prior art and represented in FIG.  4 . 
     However, these previously proposed all-plastic refrigerator door arrangements suffer from various drawbacks. For example, the various components which make up each of the refrigerator doors are still separately manufactured and subsequently assembled. As indicated above, this is considered inefficient as it adds to the manufacturing time and cost associated with making such doors. Furthermore, the known all-plastic refrigerator door arrangements are generally not aesthetically appealing since the interconnection between the various components are often noticeably visible and there will be a pinch line where the mold halves close. Finally, although forming an outer door panel of plastic with an integrally formed handle reduces manufacturing costs associated with the outer door panel and is rather aesthetically appealing, the prior proposed system as represented in FIG. 4 forms the handle, generally indicated in  68 , by creating a recess in the front surface  71  of the outer door panel  74  which inherently reduces the energy efficiency of the refrigerator door as a whole due to its reduced thickness. 
     Therefore, there exists a need in the art for a plastic refrigerator door which can be produced in a minimum number of manufacturing stages so as to reduce the manufacturing costs associated with the refrigerator door. In addition, there exists a need in the art for a all-plastic refrigerator door and method of making the same wherein the energy efficiency associated with the refrigerator door is maintained or increased. Finally, there exists a need in the art for an aesthetically appealing plastic refrigerator door. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved method and apparatus for thermoforming an all-plastic appliance door which minimizes the manufacturing stages and associated costs of producing such a door. 
     It is another object of the invention to provide an improved thermoforming apparatus wherein the male and female mold members for forming the inner and outer door panels are both located on a first movable platen. 
     It is a further object of the present invention to provide an improved method of thermoforming wherein an exterior plug assist is located within a shuttle box mounted on a second movable platen. 
     It is a still further object of the invention to provide an improved method of thermoforming wherein the shuttle box and exterior plug assist are mounted for shuttle movement between the male and female molds. 
     These and other objects of the present invention are achieved by a method and apparatus for thermoforming an appliance door including providing a male mold member shaped to the contour of an inner door liner being formed and providing a female mold member shaped to the contour of an outer door panel being formed. Also provided is a movable shuttle box including a first plug assist, the shuttle box and first plug assist being moveable into registry with either of the male and female mold members. Further to this method, a first plastic sheet is moved into position with respect to the male mold member and subsequently the shuttle box and first plug assist are placed into contact with the first plastic sheet and into registry with the male mold member while applying heat and vacuum to the first plastic sheet to form the inner door liner. The shuttle box and first plug assist are then withdrawn from the male mold member with the door liner attached and the shuttle box and first plug assist are moved into a vertically aligned position with respect to the female mold member. A second plug assist, which cooperates with the female mold member, is moved into a vertical alignment position with respect to the female mold member and the female mold member is moved into contact with one side of the second plastic sheet. The second plug assist is actuated into contact with the opposite side of the second plastic sheet, into registry with the female mold member and heat and vacuum are applied to the second plastic sheet to form the outer appliance door panel. The second plug assist is retracted from the formed door panel which is retained within the female mold member and the shuttle box and first plug assist with attached door liner are moved into registry with the female mold member and attached door panel. Finally, the door liner and outer door panel are heat sealed together along respective peripheral edges thereof to form an appliance door. 
     Other objects, features and advantages of the invention should become apparent from the following detailed description of a preferred embodiment thereof when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of a refrigerator door constructed in accordance with the prior art. 
     FIG. 2 is an exploded view of another refrigerator door constructed in accordance with the prior art. 
     FIG. 3 a  is a cross-sectional view of a molding device used to make the refrigerator door of FIG. 2 in its open state. 
     FIG. 3 b  is a cross-sectional view of a molding device of FIG. 3 a  in its closed state. 
     FIG. 4 is a perspective view of another plastic refrigerator door constructed in accordance with the prior art. 
     FIG. 5 is a perspective view of a refrigerator incorporating a unitary all-plastic refrigerator door constructed in accordance with the present invention. 
     FIG. 6 is a schematic plan view of the thermoforming process layout for thermoforming a unitary plastic refrigerator door. 
     FIG. 7 illustrates the initial stage in the method of forming the inner liner of the refrigerator door shown in FIG.  5 . 
     FIG. 8 is a view of the molding apparatus of FIG. 7 in another stage of forming the inner liner. 
     FIG. 9 is a view of the molding apparatus of FIG. 8 in a subsequent manufacturing stage of forming the inner liner. 
     FIG. 10 is a view of the molding apparatus of FIG. 8 upon completion of forming the inner liner. 
     FIG. 11 is a view of the initial stage in the process of forming the outer door panel of the refrigerator door shown in FIG.  5 . 
     FIG. 12 is a view of the molding apparatus utilized in accordance with the present invention in a subsequent outer door panel forming stage. 
     FIG. 13 is a view of the molding apparatus in another stage of forming the outer door panel. 
     FIG. 14 is a view showing the posture of the apparatus just prior to joining the inner liner and outer door panel. 
     FIG. 15 is a view depicting the step of joining the inner liner and outer door panel 
     FIG. 16 is a view of the forming apparatus in an open state following completion of the forming operation. 
     FIG. 17 is an enlarged sectional view of a portion of the formed refrigerator door of the present invention showing in detail the trimming rule in the female mold member and the back-up plate in the shuttle box. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 5 schematically depicts a refrigerator  80  constructed in accordance with the present invention. Refrigerator  80  generally includes a cabinet  83  having various compartments (not shown) formed therein that are selectively closed off by a freezer compartment door  86  and a refrigerator compartment door  88 . Refrigerator  80  further includes a kick plate  90 . It should be noted that the structure of cabinet  83  and kick plate  90  are not considered part of the present invention and therefore will not be further discussed herein. In addition, it should be noted that, although particular reference will be made to refrigerator compartment door  88  in describing the plastic refrigerator door and its method of manufacture in accordance with the present invention, it should be readily understood that the term “refrigerator door” refers to either a freezer compartment door or a refrigerator compartment door. The present invention is equally applicable to doors for combination refrigerator/freezers or dedicated refrigerator or freezer units. 
     Refrigerator compartment door  88  includes an outer refrigerator door panel  91  and an inner refrigerator door liner (not shown in FIG. 5) as will be more fully discussed below. Outer refrigerator door panel  91  includes an outer wall portion  92  having an associated surface  93  and an inwardly turned annular sidewall  94 . Outer wall portion  92  includes a thickened portion  95  that projects slightly outwardly from surface  93 . A plateau section  99  includes left and right recess defining handles  103 ,  104  that are defined between a central plateau section  107  and left and right upstanding, thickened end portions  110 ,  111  of thickened portion  95 . As is commonly known in the art, refrigerator door panel  91  can be pivotally mounted about a vertical axis to either the left or right hand sides of cabinet  83 . For this reason, the left and right halves of refrigerator door panel  91  are preferably symmetrically formed with the left and right recess defining handles  103 ,  104 . However, it should be readily understood that refrigerator door panel  91  could be designed for use in connection with a refrigerator  80  having a predetermined door opening side wherein only one handle may be required. In addition, although thickened portion  95  is depicted in the preferred embodiment of FIG. 5 to be located at the upmost portion of refrigerator door panel  91 , it should be readily understood that thickened portion  95  could be repositioned in order to locate handles  103  and  104  at a desired location and orientation. Since thickened portion  95  projects outwardly from surface  93 , the formation of handles  103  and  104  do not detract from the overall energy efficiency of refrigerator door panel  91 . In other words, the heat transfer characteristics associated with refrigerator door panel  91  are only increased by the presence of thickened portion  95  as opposed to the inherent decrease in the desired heat transfer characteristics that could be present if a handle was defined by a recess formed inward of surface  93 . 
     In accordance with the preferred embodiment, refrigerator compartment door  88  is made by a thermoforming process which advantageously enables the particular shape of refrigerator door panel  91  to be readily altered if desired. In addition, in accordance with the present method of thermoforming a refrigerator door, refrigerator compartment door  88  can be advantageously made from two plastic sheets utilizing a single molding apparatus with the inner door liner  130  associated with refrigerator compartment door  88  being formed on a male mold member as now will be discussed with reference to FIGS. 6-17. 
     FIG. 6 shows in schematic form a plan view of the machine set-up for thermoforming the refrigerator door  88  of FIG. 5. A carousel transportation member  100  is rotatable about an axis  98  between a loading-unloading station  101 , a preheat oven  102 , a final heat oven  105  and a forming station  106  housing the forming machine or press  114 . The transportation member  100  is circular in shape and is divided into quadrants which alternately mount and transport or shuttle first and second plastic sheets  149  and  150  for rotational movement through the forming station  106 . The machine set-up for thermoforming could be linear rather than the preferred carousel arrangement shown herein. Such an arrangement is described in U.S. Pat. No. 5,533,511, issued Jul. 9, 1996 and assigned to the assignee of the present application. This linear arrangement is hereby incorporated by reference. 
     As best shown in FIGS. 7-17, the forming station  106  includes a machine or press  114  that includes upper and lower movable platens  115  and  116  which in operation move toward and away from each other. The upper and lower platens  115  and  116  are each equipped with stationary stops  119  and  120  that contact each other at predetermined stages when the tool  114  is operated and assure alignment of the platens  115  and  116 . The upper platen  115  has at least four lock arms  121  which mate with at least four corresponding lower platen lock arms  122  in order to lock the upper and lower platens  115  and  116  together. In the preferred embodiment, the upper and lower lock arms  121  and  122  are engaged with a bayonet locking arrangement. 
     As further shown in FIG. 7, the lower platen has a mold mounting plate  123  mounted on a plurality of pressureizable forming air bags  124  and located by guide pins  125  at each corner of the mounting plate  123 . In the preferred embodiment, laterally spaced apart male and female molds  126  and  129  are attached to the mounting plate  123  in a substantially side-by-side arrangement. The male mold  126  is used for forming the inner door liner  130  of the refrigerator or appliance door  88  and the female mold  129  is used for forming the outer door panel  91  of a refrigerator or appliance door  88 . 
     The upper platen  115  includes a movable first plug assist member  131  which faces the male and female molds  126  and  129  that are attached to the lower platen  116 . The first plug assist member  131  can be moved laterally between the male and female molds  126  and  129  for vertical alignment therewith by means of a drive system  132  driven, in this embodiment, by an electric motor  133 . The first plug assist member  131  has a plurality of surfaces  134  that cooperate with the opposed surfaces of the male mold  126  to assist in the forming of the inner door liner  130  by pushing the plastic sheet material into conformity with the surface of male mold member  126 . 
     The first plug assist member  131  is enclosed in a box-like structure or shuttle box  136  that forms a substantially air tight pressureizable enclosure when engaged with a sheet of plastic and in registry with either the male or female molds  126  and  129 . The box-like structure or shuttle box  136  further includes a mold trimming pinch surface or back-up plate  139  extending around the full perimeter of the shuttle box  136 . The female mold  129  has an in-mold steel trimming rule  140  which likewise extends around its outer perimeter and is cooperable with the pinch surface  139  of the shuttle box  136  for trimming the joint edge of the two panels that form the refrigerator or appliance door  88  as will be further discussed with respect to FIG.  17 . 
     Located adjacent the position of the female mold  129  and horizontally movable into and out of proximity therewith, is a second plug assist member  141 . The second plug assist member  141  has a plurality of movable surfaces  142  operated by pneumatic rams  143  that aid in forming the shape of the outer door panel  91 . It is anticipated that hydraulic rams could be substituted for the pnuematic rams  143 . 
     As still further shown in FIGS. 7 and 11, the transportation member  100  includes a rail arrangement  144  between the upper and lower platens  115  and  116  for carrying sheet support members  145  and  146  that shuttle or transport plastic sheets  149  and  150  into position above the male and female molds  126  and  129  respectively. 
     Referring again to FIG. 7, the method of forming a two-panel plastic refrigerator or appliance door  88  will be described. First, the shuttle box  136  and first plug assist member  131  are aligned vertically above the male mold  126 . With the upper and lower platens  115  and  116  separated, a first plastic sheet  149  mounted on a first sheet support member  145  is shuttled or moved from a final heat oven  105  into position over the male mold  126  by way of the rail arrangement  144 . Next, as shown in FIG. 8, the lower platen  116  is moved upwardly so that dike forming portions  151  of the male mold  126  will engage and place tension on the first plastic sheet  149 . At this point, the upper platen  115  is moved downwardly toward the lower platen  116  placing the shuttle box  136  housing the first plug assist member  131  into contact with the first plastic sheet  149  and into registry with the male mold  126 . The various surfaces  134  of the first plug assist member  131  engage the upper surface of the first sheet of plastic  149  and push the plastic sheet  149  into the corners of the male mold  126  to conform the plastic sheet  149  to the surface of the male mold  126  as best shown in FIG.  9 . At approximately the same time, a vacuum is applied to the lower surface of the first plastic sheet  149  through the male mold  126 . As previously discussed, the shuttle box  136  can be pressurized and thus pressure may be applied to the inner surface of the plastic sheet  149  by pressurizing the shuttle box  136 . Thus, the first plastic sheet  149  has been formed into an inner door liner  130 . The formed inner door liner  130  is then clamped to the pressurized shuttle box  136 . 
     Once the inner door liner  130  has been formed in this manner, the lower platen  116  is retracted. The first sheet support member  145  is then released from the formed inner door liner  130  by unclamping the clamp frames  157  as shown in FIG.  10  and the inner door liner  130  will remain clamped to the shuttle box  136 . The upper and lower platens  115  and  116  are separated from each other as shown in FIG. 10 with the inner door liner  130  held by picker devices (not shown) that engage with undercut areas of the inner door liner  130  and raise the inner door liner  130  with the upper platen  115 . 
     There is shown schematically on the sides of the shuttle box  136  in FIG. 10, heaters  147  which may be attached to the shuttle box  136  and placed adjacent the peripheral edge  158  of the formed inner door liner  130  for applying heat to the inner door liner  130  for maintaining a predetermined material temperature around the peripheral edge  158 . This heater  147  may be of any well known type such as calrod, ceramic or quartz. 
     Next, the shuttle box  136  and attached inner door liner  130  are driven or shuttled horizontally to a position vertically aligned over the top of the female mold  129 . Simultaneously, as shown in FIG. 11, a second plastic sheet  150  is shuttled or transported into position over the female mold  129  by a second sheet support member  146 . Also at this time, the second plug assist member  141  is moved into position over the top of the second plastic sheet  150  and into registration with the cavity  152  of the female mold  129 , as shown in FIG.  12 . 
     As is apparent in FIG. 12, the lower platen  116  of the press  114  is now moved upwardly to move the female mold  129  into contact with the bottom of the second plastic sheet  150  to place slight tension on the plastic sheet  150 . Next, heat is applied to second plastic sheet  150  and as shown in FIG. 13, a vacuum is applied to the lower surface of the second plastic sheet  150  through the female mold member  129  to conform the second plastic sheet  150  to the cavity  152  of the female mold  129  while at the same time, the second plug assist member  141  is actuated to deploy the movable surfaces  142  for assisting in forming at least the side wall portions of the outer door panel  91 . Thus, the second plastic sheet  150  has been formed into an outer door panel  91 . Once the outer door panel  91  has been formed onto the female mold member  129 , the second plug assist member  141  is quickly retracted as shown in FIG.  14  and is backed away as shown in FIG.  7  and into the plane of FIG.  14 . 
     With the second plug assist member  141  out of the way and the heaters  147  retracted, the shuttle box  136  including the first plug assist member  131  with the attached inner door liner  130  is lowered into a registry position on top of the formed outer door panel  91  that has been retained within the female mold  129  by lowering the upper platen  115  of the press  114  as shown in FIG.  15 . Once this is done and registry is accomplished so that the inner door liner  130  is engaged with the outer door panel  91 , the upper and lower lock arms  121  and  122  are engaged and locked and the air bags  124  are inflated to move the mold mounting plate  123  slightly upward on guide pins  125  to squeeze the inner door liner  130  and outer door panel  91  together around their periphery. At this time, pressure may be applied to the shuttle box  136  by injecting air through air ports  138  while injecting air through blow pin  137  into the space between the inner door liner  130  and the outer door panel  91  to pressure form the exterior. Differently stated, with the application of heat, the inturned edge  153  of inner door liner  130  is joined or fused to the inwardly turned annular sidewall portion  94  of outer door panel  91 , see FIGS. 15 and 17. Once these two portions of refrigerator door  88  are joined, air pressure can be immediately applied through the blow pin  137  into the interior of the newly formed refrigerator compartment door  88  and into the shuttle box  136  through air ports  138  to enhance the details of outer door panel  91  with the air pressure within the shuttle box  136  and within the refrigerator door  88  being equal. The steel rule  140  in the mold  129  will trim the outer perimeter edge of the door  88 . As best shown in the cross section of FIG. 17, the steel rule  140  has a knife edge  148  which engages with the back-up plate or pinch surface  139  for trimming the refrigerator door  88 . 
     After this joining and rough trimming operation is complete, the upper and lower platens  115  and  116  are separated as shown in FIG.  16  and the shuttle box clamps (not shown) are released leaving the door  88  on the second sheet support member  146 . The knife edge  148  is interrupted at several preselected locations around the peripheral edge  158  so that during trimming a plurality of tabs (not shown) will remain to permit the completed refrigerator door  88  to move with the second support member  146  by way of the trimmed excess material. The completed refrigerator door  88  is shuttled or transported out from between the upper and lower platens  115  and  116  and toward unloading station  101  where an operator can quickly cut away the tabs and remove the peripheral excess plastic. The shuttle box  136  is now shuttled or transported back into the initial position over the male mold member  126  and the process is repeated. 
     The interconnection between inturned edge  153  of inner refrigerator door liner  130  and inwardly turned annular sidewall  94  of outer refrigerator door panel  91  is perhaps best shown in the enlarged view of FIG.  17 . Once the thermoformed refrigerator door  88  is removed from the forming area, this joined area between inner refrigerator door liner  130  and outer refrigerator door panel  91  may be rounded or beveled if desired. When refrigerator door  88  is assembled to the cabinet  83 , the trim line  154  is hidden from frontal and side view and a seam defined by the joined area is located between annular side wall portion  94  and dike portion  155  and extends substantially perpendicular to an outer wall portion of door panel  91  as clearly shown in FIG.  17 . 
     FIG. 17 also illustrates that, in accordance with the preferred embodiment of the invention, the internal chamber  156  defined between outer refrigerator door panel  91  and inner refrigerator door liner  130  can be filled with a heat insulating material. In the preferred embodiment, foam  159  is injected into internal chamber  156  and extends even into dike portion  155  in order to provide, in addition to enhanced thermal specifications for refrigerator compartment door  88 , additional structural rigidity without significantly increasing the weight of refrigerator compartment door  88 . 
     From the above discussion, it should be readily apparent that forming an all-plastic refrigerator door in accordance with the present invention minimizes the number of manufacturing steps necessary and results in reduced manufacturing costs. In addition, since the refrigerator door is completely made from plastic, it will be a more durable than conventional metal/plastic doors and can be more versatile in design. One of the key benefits to the manufacturing process is that the door can be manufactured such that the joining seam whereat the outer door panel meets the inner liner faces toward the inside of the refrigerator. Due to this positioning of the seam, a door gasket can be advantageously designed to cover the seam so as to provide an extremely aesthetically appealing overall assembly. 
     A gasket arrangement for use with the refrigerator compartment door  88  as shown herein is described, for example, in drawing FIGS. 14 and 15 and specification at column 8 of U.S. Pat. No. 5,533,311 issued Jul. 9, 1996 and assigned to the assignee of the present application. This gasket arrangement is hereby incorporated by reference. 
     Although various materials could be utilized in connection with the present invention to form the refrigerator door, in the preferred embodiment, outer refrigerator door panel  91  is formed from a sheet of a high impact polystyrene layer of approximately 92-97 mils in thickness having an acrylic cap layer of polymethylmethacrylate in the order of 3-8 mils. The refrigerator door liner  130  is preferably formed of high impact polystyrene. In addition, a foam barrier layer of a styrenic alloy may be used on the inside surfaces of both the outer refrigerator door panel  91  and the inner refrigerator door liner  130  when certain corrosive foams are injected within internal chamber  156 . It is also possible to use polyvinylchloride as the material for either of these components. If polyvinylchloride is utilized, no cap layer or foam barrier will be necessary. However, the use of the polystyrene over the polyvinylchloride is preferred based on cost factors. Instead of the polymethylmethacrylate used for the cap layer, it is also possible to utilize styrenemethylmethacrylate. 
     As indicated above, the refrigerator door constructed in accordance with the invention will be more energy efficient than conventional doors utilizing metal panels which inherently conduct more heat into the unit. This efficiency characteristic is further enhanced by locating the thickened portion of the door that contains the handles closer to the periphery of the door than to the dike. Obviously, the plastic also provides a corrosion resistant door that does not require painting. 
     It is envisioned that the sequence of various steps described for forming the refrigerator door  88  can be modified. For example, the step of moving the shuttle box  136  from being vertically aligned with the male mold member  126  and attached door liner  130  to a position vertically aligned with the female mold member  129  may be done after the second plug assist member  141  and the female mold member  129  have formed the outer door panel  91 . Also, as discussed herein, the shuttle box  136  does not have to be pressurized and it is not always necessary to inject air into the internal chamber  156  when joining the inner door liner  130  to the outer door panel  91 . Other possible changes in the sequence of steps will be apparent to persons skilled in the art. 
     Although described with respect to a preferred embodiment of the invention, it should be readily understood that various changes and/or modification can be made to the present invention without departing from the spirit thereof In general, the invention is only intended to be limited by the scope of the following claims.