Abstract:
In one embodiment, a system and method for the production for a vehicle tray table employing foam in place sandwich structure, whereas the encapsulated foam is employed as a labor, cost and weight saving material to bond and affix the tray table assembly components.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present disclosure generally relates to tray tables attached to vehicle seats as a support surface for writing, dining or other activities More particularly, the present disclosure relates to the methods for fabricating a seatback tray table assembly for use in vehicles. 
         [0003]    2. Description of the Related Art 
         [0004]    Most seat configurations for multiple passenger vehicles such as trains, airplanes and buses, have a tray table for the passenger that is located on the back of the seat assembly located in front of the seat occupant. The seat back will most likely possess a deployable tray table with a surface for eating, working, writing or other such uses to the passenger. These tray tables have been made in the past from progressively lighter or stronger materials and designs to save weight and thus improve efficiency of the overall vehicle fuel consumption. The cost and ease of fabrication of the tables has improved dramatically over the years. The current state of the art tray table is a foam core that provides the shear and structural medium of a sandwich structure, structurally bonded to an upper and lower plastic skin using film or liquid adhesive. Guide tubes, metal structures, hinges and other components are inserted inside the tray table as a means for attaching the tray table to the seat and allowing it to extend in a cantilevered position for use. These guide tubes (also know as sliders) are normally rectangular tube sections (though square, round and oval cross sections are not novel) that slide onto a connecting rod, hinge side, or other extending arm, which is the tray table holding device affixed to the seat back in front of the passenger. The guide tubes may also be replaced by solid rods, a single tube, hinge attachments or other means for external attachment, with features, in some configurations, where attachment methods differ from the means employed in most current designs. 
       SUMMARY 
       [0005]    Typically, a tray table is manufactured by initially producing a generic or shaped pre-cast foam part roughly simulating the interior area of the tray table. An adhesive is then applied to inside of the top and bottom plastic covers. The foam, guide tubes, and other additional components if needed, are placed inside the lower cover, the top cover is placed on and then the assembly presses together to bond the structure. The periphery then may be sealed with a solvent bond process. 
         [0006]    The novelty of the disclosed method of fabrication provides for the elimination of the adhesive liquid or film, foam shaping, custom fitting process and the associated labor employed during the assembly process. This is accomplished by placing the components inside the plastic covers and using a foam-in-place medium and allowing the foam to expand and cure while in a temperature controlled and pressurized fixture. The foam in the cavity will cure to a desired hardness and provide dimensional stability for the assembly and the components inside. This process allows for the foam to conform intimately to the components and structurally bond directly to a predominant area of the inside surface covers, eliminating the need for and the associated weight and cost of a secondary adhesive for structural rigidity. This method results in a tray table that is light, requires less labor, and improves the manufacturing process by a simplification and reduction of the assembly steps. The foam density can also be further refined or reduced, and thus potentially eliminate even more weight, by simply reducing the amount of foam mixture poured into the cavity or processing temperature. This is contrary to the state of the art wherein industry standard foam densities are currently used and have relatively large steps between available foam densities. The assembly can also be post cured, a process where the assembly is placed at an elevated temperature to further complete the chemical reaction of the foam chemistry. 
         [0007]    By allowing for specific tailoring of foam density, providing a conformable foam medium, and eliminating the structural adhesive, a superior tray table is produced. 
         [0008]    The method for making the tray table excludes the primary use of an additional adhesive for the purpose of bonding the internal components of to the tray table covers for structural rigidity. This is accomplished by proper preparation of the skins for foam in place sandwich medium in a contained fixture to pressurize the foam during processing resulting in the necessary integral bonding of the assembly. Thus the foam in place medium is used not only for bonding the covers to make a sandwich structure, but also integrating the foam and foaming process as a locating and bonding material and method for the components and the covers of the tray table assembly. 
         [0009]    Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The disclosed tray table system and methods and method for fabrication can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. 
           [0011]      FIG. 1  is a view of a tray table connected to a vehicle seat. 
           [0012]      FIG. 2A-B  are views of the assembled and unassembled components of a tray table without foam. 
           [0013]      FIG. 3A-D  are views of edge sealing methods. 
           [0014]      FIG. 4  is a view of the foam cream mixture being poured into the lower cover. 
           [0015]      FIG. 5A-C  are views of the assembly of the tray table during the foaming process being loaded into a press for curing of the foam. 
           [0016]      FIG. 6A  and  FIG. 6B  are cross sections of an assembled tray table including the foam. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    As described in the foregoing, it is difficult to produce a lightweight tray table without adhesive liquid or film as the primary bonding component using foam in place material. Previous efforts have been unable to create sufficient bond strength, contain the foam, or produce a homogenous foam density without excess entrapped gases and provide a resulting tray table that will withstand a service environment. 
         [0018]    Described in the following is a system and method for manufacturing a lightweight structural seatback tray table. Although specific embodiments are presented, those embodiments are mere example implementations and it is noted that other embodiments are possible. All such embodiments are intended to fall within the scope of this disclosure. 
         [0019]    Turning to the figures, in which like numerals identify corresponding components,  FIG. 1  illustrates an embodiment of the tray table assembly  110  attached to the back of a vehicle seat  120 . 
         [0020]      FIG. 2A-B  illustrates an embodiment of the tray table assembly  210  and the minimum components necessary for assembly. The tray table assembly  210  is comprised by a lower cover  230  (or skin) and an upper cover  220 . These covers fit together to encapsulate a cavity which will contain the foam core material and a means for mechanical attachment, in this view there are two guide tubes  250 . The inner surface of these covers must be cleaned and prepared for bonding. This requires lightly abrading the internal cover surface with a scuffing pad or sandpaper like substance, flame treatment or other similar methods to create a physical or chemical propensity to bond and may further include cleaning with a solvent wipe. The means for attaching must be sealed to the internal cavity if they are hollow, however it may have an opening to allow the connecting rod, hinges or other connecting means to slide inside the means for attaching at the point of attachment. The means for attaching must be sealed, other than this open end, to eliminate foam from entering the inner part of the tube during the foaming process. 
         [0021]    This process requires that the edges of the cavity formed by the top cover  330  and the bottom cover  320  are sealed to contain the foam from blowing out of the mold through the seams between the covers and the openings of the guide tubes or other means for attaching. Although a perfectly trimmed pair of covers can seal intimately  370 , as in  FIG. 3A , and may not need an additional sealing method beyond the contacting perimeter of the covers. But multiple alternate methods for sealing the edges are envisioned. Examples of these methods include, but are not limited to solvent bonds, tape sealant and foam sealants. 
         [0022]      FIG. 3B  depicts the location and effect of sealing of the cover edges accomplished by a solvent bond. This process uses a solvent, such as Tetrahydrofuran (THF), applied to the contact point  370  of the upper cover  320  and the lower cover  330  to effectively melt the plastic covers and join them when the solvent evaporates and leaves a plastic meniscus  375  at the contact point. This method is most difficult as it must be performed after pouring in the foam. 
         [0023]      FIG. 3C  depicts the application of a removable tape (or any conformable and removable outer seal)  395  on the outside of the seam of the covers. It is necessary and difficult to press the tape into the cavity between the covers to produce an aesthetically pleasing final part, and as such this is not the preferred method as it also must be performed after pouring in the foam. 
         [0024]    The preferred method shown in  FIG. 3D  employs a foam tape with pressure sensitive adhesive  390  applied to the inner cover (in the configuration as viewed this is the lower cover  330 , inner being defined as the cover with the edge residing in the internal cavity of the final assembly). The foam tape  390  is attached, protruding high enough above the edge of the cover such that when the opposing cover  320  is placed on top and the assembly is pressed into the molding fixture, the foam tape  390  will compress an create a seal for the cavity edge, thus preventing blow out during the structural foam expansion. The seal is made after the foam is poured into the lower cover  330  and when the upper cover is placed on top. 
         [0025]      FIG. 4  illustrates the preparation and locations of the components of the assembly for the foam installation. Guide tubes  450 , representing a means for attaching, are placed onto the fixture positioning rods  455  (or other appropriate mechanical means) and fitted into the lower cover cutout slot  435  for accurate positioning during the curing process. A measured amount of at least 2 part mixture of foam resin and catalyst is mixed together into a creamy liquid. The measured amount is determined by the size of the cavity, the predicted post expansion volume of the foam and the foam&#39;s desired density. This pre-foam liquid is called a foam cream  460 . This foam cream will rapidly catalyze and the foaming agents in the mixture will create tiny gas bubbles in the resin liquid and create a visco-elastic foam which will rapidly expand into the cavity formed by the covers. The catalyst in the mixture will cure the resin into a single piece of rigid foam. The cream is poured along the edge of a preheated lower cover  430  (as defined by gravity for pouring) at the side opposite the lower cover cutout slots  435 . This allows for the foam to expand and push the entrapped air in the cavity out of the small gap between the lower cover cutout slots  435  and the guide tubes  450 . 
         [0026]      FIG. 5A  illustrates the assembly  510  after the cream  560  is poured into the lower cover  530 , a preheated upper cover  520  is placed onto the lower cover and the assembly  510  is placed into a lower press fixture  580  such that the fixture positioning rods  555  are located into a designated position in the lower press fixture  580 . This fixture also has an upper section  585 , and both are shaped with an interior profile to support shape of the tray table assembly as the foam expands and cures. The cavity of the fixture is angled at least 10 degrees from horizontal, preferably 20 degrees, to assist in the foam filling the cavity from the bottom, using gravity, to push air, entrapped in the cavity that is not filled or being filled by the foam, out of the small gap between the lower cover cutout slots  535  and the guide tubes  550 . The fixtures are pre-heated to the proper foam cure temperature and a pressure of at least 350 Kpa (51 PSI) is employed to contain the outer surfaces of the assembly  510 . The upper  585  and lower  580  fixtures are not required to be at the same temperature. For ease of manufacturing and thermal control simplification, the temperatures may differ.  FIG. 5B  and  FIG. 5C  highlight the expanding foam  560  filling the internal cavity of the tray table. The foam cream expands and creates a hydrostatic pressure which not only fills the internal cavity but bonds to a preponderance of the internal cover surfaces creating a sandwich structure. 
         [0027]      FIG. 6A  and  FIG. 6B  illustrate a front and side cross section view of a completed tray table assembly  610 . The upper cover  620  is now bonded to the lower cover  630  by the cured foam  660 . The guide tubes  650  are now permanently located for attachment and the integrated seal  340  is encapsulated in the cavity. 
         [0028]    It is to be appreciated, however, that the concepts described in the following can be applied to substantially any vehicle tray table that requires a lightweight integrated assembly method; however, other tray tables aesthetic curves, thickness variations and configurations as well as guide tube shapes configurations are contemplated.