Patent Publication Number: US-6991446-B2

Title: Multiple density interior trim substrate and method and system for making same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. application Ser. No. 09/560,233 filed Apr. 28, 2000, now U.S. Pat. No. 6,379,595. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a multiple density substrate for selective impact energy absorption, and a method and system for making the same. 
     BACKGROUND ART 
     There is a growing need to improve the energy absorption properties of automotive interior trim substrates which also provide structural support to the sheet metal structure of a vehicle. Such sheet metal structures include pillars, side rails, and roof structures. However, the industry has been challenged in determining a cost effective way of manufacturing interior trim substrates and interior components in order to meet industry demands. For example, manufacturers continue to search for ways of improving the properties of substrates for absorbing energy in a cost effective manner while providing structural support. 
     One challenge that manufacturers are faced with is that energy absorption throughout the passenger compartment, such as on pillars, side rails, or the roof structure of a vehicle, requires different amounts or different densities of energy absorption material, including molded foam or beads. This is due to the vehicle structure design which typically includes a plurality of sheet metal pieces that form the passenger compartment of a vehicle. The thickness and geometric stiffness of the sheet metal typically determine the amount of energy absorption material required. That is, the thicker and/or stiffer the sheet metals is, the more absorption material is required to meet industry demands. Thus, materials of different amounts of energy absorption and/or different densities would be useful to have in interior trim substrates. 
     Although current energy absorbing parts may be adequate, improvements can be made thereupon. Currently, multi-density component parts are manufactured for energy absorbing purposes. Some multi-density component parts are separately manufactured and then combined to comprise an energy absorbing part which is fastened to an area of a vehicle compartment, such as a pillar. More specifically, single density foam or beads are molded to form a shape of a vehicle component. The molded foam or beads are then attached to a predetermined area on an interior trim material or a shell which then fastens onto the structure of a vehicle. The separate manufacturing processes used in forming the molded foam or beads and the interior trim substrates result in additional manufacturing time and costs. 
     U.S. Pat. No. 5,700,050 to Gonas discloses an energy absorbing interior automotive trim part. The part has a shell made from polypropylene sections is divided via partitions to extend from the outer wall of the shell. The shell is then filled with structurally engineered energy absorbing foam. 
     Thus, what is needed is an improved system and method of making an integrally formed substrate that more efficiently meets the industry demands for energy absorption on collision impacts. 
     DISCLOSURE OF INVENTION 
     An object of the present invention is to provide for an improved method of manufacturing a multiple density substrate for impact energy absorption with a mold having a mold cavity of a predetermined shape. The method includes providing a first set of unbonded beads of a first density and a second set of unbonded beads of a second density, loading the mold cavity with the first set of unbonded beads at a predetermined location in the mold cavity sufficiently to leave a void in the mold cavity, and separately injecting a sufficient amount of the second set of unbonded beads into the void. The method further includes bonding the first and second sets of beads together with heat to define a molded set of bonded beads having the predetermined shape, and cooling the molded set of bonded beads sufficiently to define the multiple density substrate. 
     Another object of the present invention is to provide an improved method of manufacturing a multiple density substrate for impact energy absorption with a mold of a predetermined shape. The method includes providing a bag containing a first set of unbonded pre-expanded beads of a first density and providing a second set of unbonded pre-expanded beads of a second density, loading a portion of the mold with the bag including the first set of unbonded beads at a predetermined location on the mold, and injecting the second set of unbonded beads into the mold. The method further includes bonding the first and second set of beads together with heat to define a molded set of bonded beads having the predetermined shape and cooling the molded set of bonded beads sufficiently to define the multiple density substrate. 
     Another object of the present invention is to provide an improved system for manufacturing a multiple density substrate for differential impact energy absorption with a mold of a predetermined shape, a first set of unbonded beads having a first density, and a second set of unbonded beads having a second density. The system includes a mechanism for loading a portion of the mold with the first set of unbonded beads at a predetermined location in the mold sufficiently to leave a void in the mold, and a mechanism for injecting the loaded mold portion with a sufficient amount of the second set of unbonded beads into the void. The system further includes a mechanism for bonding the first and second sets of beads together with steam to define a molded set of bonded beads having the predetermined shape. 
     Yet another object of this invention is to provide for an improved multiple density substrate for impact energy absorption. The substrate is a molded set of bonded beads manufactured by a steam heating process and has a predetermined shape. The substrate comprises a first set of expanded bonded beads of a first density to define a first density level, a second set of expanded bonded beads of a second density integrally disposed adjacent the first set of expanded bonded beads, and a casing device of the first set of expanded bonded beads disposed between the first and second sets to sufficiently separate the first and second density levels to define the multiple density substrate of the predetermined shape. 
     An improved integrally formed substrate implementing a single method of manufacturing such substrate aids in reducing current manufacturing time and costs. Moreover, integrally formed, multiple density energy absorbing materials aid in improving the manufacture of interior substrates in meeting industry demands to absorb energy on collision impacts while providing adequate support. 
     Other objects, features, and advantages of the present invention will be apparent from the ensuing description in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a mold drawn partially in phantom which may be used in carrying out the present invention; 
         FIG. 2   a  is a plan view of the mold of  FIG. 1  with a cut-away portion to depict a first set of unbonded beads loaded in a recess formed on the mold; 
         FIG. 2   b  is a plan view of the mold with a cut-away portion to depict a second set of unbonded beads injected into the recess adjacent the first set of unbonded beads; 
         FIG. 3  is a flow chart of one method implemented in making a multiple density interior trim substrate with the mold of  FIG. 1 ; 
         FIG. 4  is a cross-sectional view of a multiple density interior trim substrate formed in accordance with the method of  FIG. 3 ; and 
         FIG. 5  is a cut-away perspective view of the substrate of  FIG. 4 . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
       FIG. 1  illustrates a mold  10  drawn partially in phantom. Mold  10  may be used for manufacturing a multiple density interior trim substrate in accordance with one embodiment of the present invention. As shown, mold  10  includes lower portion  12  and upper portion  14  (drawn in phantom). Lower portion  12  includes recess or cavity  16  formed thereon. Lower portion also includes injection hole  18  and steam holes  20 , as further described below. 
       FIG. 2   a  illustrates a plan view of mold  10  in an open position. As shown, first set  22  of pre-expanded unbonded beads is placed in package casing or bag  23  which is loaded into recess  16  to define a first area in which bag  23  occupies. Bag  23  may be loaded into recess  16  automatically, e.g., by robotics, or manually, e.g., by hand.  FIG. 2   b  depicts a second set  24  of pre-expanded unbonded beads which may then be loaded into a remaining portion of recess  16  to define a second area or a void in which bag  23  does not occupy. As further shown in  FIGS. 2   a  and  2   b , lower portion  12  includes injection hole  18  through which nozzle  26  may insert. Nozzle  26  injects second set  24  of unbonded beads into mold  10  in a closed position as shown in  FIG. 2   b . Lower portion  12  further includes steam holes  20  which receive steam lines (not shown) to admit steam to the unbonded beads. 
     Mold  10  may include conventional controls, plumbing, and mold-actuating mechanisms to allow proper operation of lower portion  12  and upper portion  14 . For example, portions  12 ,  14  of mold  10  may be attached to two platens mounted on tie-rods. One platen may be stationary, while the other may be movable to permit opening and closing of portions  12  and  14 . Platen actuation may be by hydraulic or air cylinder. Steam may be supplied to mold  10  via conventional manifolding and individual lines. 
       FIG. 3  illustrates one method  110  implemented to manufacture a multiple density interior trim substrate with mold  10  of  FIGS. 2   a  and  2   b . As shown in box  112 , the method includes providing the first set  22  of unbonded pre-expanded beads of a first density and the second set  24  of unbonded pre-expanded beads of a second density. In this embodiment, each bead of first set  22  has a greater density than each bead of second set  24 . However, each bead of first set  22  may be less than each bead of second set  24 . Preferably, densities of the each bead is between 10 kg/m 3  and 120 kg/m 3 . 
     The beads may be pre-expanded by any suitable means, such as by continuous steam, conveyor and steam chamber, steam pressure chamber (batch), continuous hot air, conveyor/radiant heater, hot water (batch), and oven (batch). In this embodiment, the beads are pre-pressurized with hot compressed air for several hours. The beads used may also include a conductive material, such as carbon powder, to provide the resulting molded part with conductive properties. This may be accomplished by loading bag  23  with beads having a conductive material, e.g., carbon powder. During the admission of steam, the beads will be concentrated at the location at which bag  23  was loaded to provide conductive properties for applications such as heating pads, electrical line, or any other suitable use. 
     It is to be noted that other beads may be used which would not fall beyond the scope or spirit of the present invention. Other beads may include but are not limited to polyethylene beads, polystyrene beads, other thermoplastic beads and mixtures thereof. Moreover, the beads may have heat expanding components to aid in varying the density between a plurality of set of beads. For example, in one embodiment, the beads may be polystyrene beads having a predetermined amount of a heat expanding component, such as pentane or any other suitable component. A difference in amount of heat expanding component between a plurality of sets of beads provides a difference in density between each bead of each respective set. Additionally, other beads may include the product of the trade name GECET™ manufactured by Huntsman Chemical Corporation of Chesapeake, Virginia and the product of the trade name NEOPOLEN-P™ manufactured by BASF Corporation of Wyandotte, Mich. It is also to be noted that the material comprising the beads, e.g., polypropylene, may be recycled material or virgin (non-recycled) material. 
     In this embodiment, a predetermined amount of the first set  22  of unbonded pre-expanded beads are placed in a package casing, such as a low melt polymer bag. Low melt polymer bag  23  may be made of a polymer, such as polypropylene. As shown in box  114 , bag  23  having first set  22  of unbonded beads is then loaded into lower recesses  16 . In this embodiment, bag  23  is sized to fit into the first area. However, bag  23  may be larger or smaller in volume to include a greater or lesser amount of beads therein. Thus, bag  23  may be a pre-molded bag of a predetermined shape to fit a certain shape of a recess in a mold. Bag  23  acts to separate set  22  from set  24  during further steps of the method of the present invention. 
     As mentioned above, portions  12  and  14  are then engaged to close mold  10 . One of the portions may be stationary as the other moves to place mold  10  in a closed position. As shown in box  116 , second set  24  is injected into mold  10  in its closed position, as shown in  FIG. 2   b , by conventional air conveying systems. More specifically, second set  24  is injected in mold  10  by nozzle  26  through injection hole  18 . 
     Then, steam may be admitted into mold  10  through steam holes  20  when mold  10  is in its closed position to bond sets  22 ,  24  of beads together, as shown in box  120 . Preferably, the steam is admitted into mold  10  at 40 to 60 pounds per square inch gauge (psig) and 230° F. for 1.0 to 3.0 minutes and then at 40 to 60 psig and 120° F. for 1.0 to 3.0 minutes. This causes sets  22 ,  24  of beads to bond together, creating an integral molded set. The steam causes further expansion of the beads and forces them to conform to the shape of recess  16 . The expanding beads close off steam holes  20  in mold  10 , cutting off the admission of steam. In this embodiment, with admitted steam, low melt polymer bag  23  melts to allow contact of sets  22  and  24 . However, separation is maintained between first set  22  and second set  24  to define the first and second areas having different densities. 
     Alternatively, bag  23  may be a mesh bag that sufficiently holds first set  22  of unbonded beads. However, the bag is made of a material in a mesh form to allow second set  24  to partially contact first set  22  through the mesh bag and allow for steam flow therethrough. Mesh bag  23  may be a net or screen formed material having a higher melting point than the polypropylene beads. In this embodiment, mesh bag  23  does not melt during heating of the beads. Thus, mesh bag  23  acts to continually separate first set  22  from second set  24  through heating, yet allow partial contact of sets  22  and  24  in order to sufficiently bond sets  22  and  24  together. 
     Next, as shown in box  122 , the mold with a resulting part or interior trim substrate therein is cooled by water and/or by conventional vacuum techniques (not shown) until the resulting part stabilizes. This is done in order to prevent the part from collapsing by trapped condensing steam during handling of the part. Then, the part is ejected by any suitable means. 
     As shown in  FIGS. 4 and 5 , interior trim substrate  210  includes inner portion  212  of the first density and outer portion  214  of the second density. If desired, outer layer  216  may be attached thereto in order to provide a more aesthetic look. Alternatively, outer layer  216  may be placed in mold  10  prior to placing beads in mold  10 , eliminating the need of attaching an outer layer after heating. Outer layer  216  may be any conventional show surface material such as polyolefin, vinyl, or other suitable materials. Additionally, although  FIGS. 4 and 5  depict inner portion  212  flanking sheet metal structure  215 , it is to be noted that portion  212  may be configured adjacent only one side of structure  215 , as desired. 
     One or a plurality of conventional fasteners may be disposed within the mold in order to be bonded to the beads to provide an interior trim substrate having integral fasteners that may be directly attached to the structure of the vehicle. This eliminates the need of adhesives used to glue the fasteners onto the substrate. 
     It is to be noted that, as areas on a substrate may have different densities, such areas may then have different shades of colors as a result. As desired, the integrally formed multiple density interior trim substrate may have multiple locations rather than multiple layers of different densities without falling beyond the scope or spirit of this invention. For instance, a headliner (not shown) made from the methods of this invention may be formed simply by changing the mold to the shape of the desired headliner having multiple locations in which different sets of beads having different densities may be placed for energy absorption and/or structural purposes. 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.