Abstract:
A method and system for producing an article using a thermoplastic sandwich material such as, for example, a 3-D deep-drawn article is disclosed. In accordance with an aspect of the present invention, two reinforced thermoplastic skins surround a generally planar honeycomb structure. During the manufacturing process, the skins and the honeycomb structure are bonded together by means of a thermocoupling process.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to thermoplastic sandwich materials and, more particularly, to a method and system for producing a 3-D deep-drawn article using a thermoplastic sandwich material. 
     BACKGROUND OF THE INVENTION 
     A process for producing a thermoplastic sandwich material that includes a honeycomb structure is disclosed in U.S. Pat. No. 5,683,782. Referring to FIG. 1 of U.S. Pat. No. 5,683,782, a greatly enlarged sectional representation of a honeycomb segment with a cover layer is shown. In accordance with the invention disclosed in this patent, a thermoplastic sandwich material is made from two outer reinforced thermoplastic skins with a cellular core at the center that is molded by a thermocompression process. The skins are formed from polypropylene with continuous glass mats or are formed by woven glass with polypropylene fibers. The content of U.S. Pat. No. 5,683,782 is incorporated by reference into this application as if fully set forth herein. 
     Thermoplastic sandwich materials such as those disclosed in U.S. Pat. No. 5,683,782 have been utilized in a variety of different applications. For example, U.S. patent application Ser. No. 09/451,970, filed Nov. 30, 1999 discloses a method for molding an impact resistant automotive part such as a bumper beam. A thermoplastic reinforced fiber structure at least partially forms a pair of attachment portions of the automotive part and continuously extends between the attachment portions to link the attachment portions. The content of the Ser. No. 09/451,970 patent application is incorporated by reference into this application as if fully set forth herein. 
     In another example, U.S. patent application Ser. No. 09/445,356, filed Dec. 10, 1999 discloses a method of making a composite panel that has a sandwich structure and that is provided with a hinge. The panel comprises a stack that includes at least one first skin of a reinforced thermoplastic material and a second skin of a thermoplastic material. The panel is formed by preheating the first and second skins to a softening temperature, and then pressing the stack of skins at a pressure that lies in a predetermined range. The content of the Ser. No. 09/445,356 patent application is incorporated by referenced into this application as if fully set forth herein. 
     Yet another exemplary use of thermoplastic sandwich material is disclosed in U.S. patent application Ser. No. 09/485,142, filed Feb. 4, 2000. This application discloses a method of making a reinforced composite panel of the sandwich type having a cellular-core. The content of the Ser. No. 09/485,142 application is incorporated by reference into this application as if fully set forth herein. 
     U.S. patent application Ser. No. 09/525,346, filed Mar. 15, 2000 discloses the utilization of thermoplastic sandwich material in a certain application. In particular, this application discloses a method and system for co-molding a thermoplastic material with a thermoplastic sandwich material to form a thermoplastic sandwich article. The article has a thermoplastic inner portion. The content of Ser. No. 09/525,346 patent application is incorporated by reference into this application as if fully set forth herein. 
     U.S. patent application Ser. No. 09/525,785 entitled “Method and System For Molding Thermoplastic Sandwich Material and Deep-Drawn Article Produced Thereby,” filed Mar. 15, 2000 discloses a method and system for molding a thermoplastic sandwich material to form a deep-drawn article. In particular, an inner portion of a blank of thermoplastic sandwich material is forced into a female die along a vertical axis to form a deep-drawn article. A step of clamping may be performed at a plurality of spaced outer portions of the blank immediately adjacent the female die. The content of the above-referenced “Method and System” patent application is incorporated by reference into this application as if fully set forth herein. 
     In use of such processes to form 3-D deep-drawn articles from a thermoplastic sandwich material, sometimes visual defects such as puckering, wrinkling, and the like may occur in the finished article, especially at the comer areas of the article. Visual defects of this sort may render the article visually unacceptable for commercial purposes. 
     In some applications, carpet has been utilized as a surface finish to render the article usable for commercial purposes. However, carpet is not suitable for use as an exterior finish in every application. Furthermore, in an application where an article is deep-drawn to a relatively large size such as over 18 inches, prior processes for forming thermoplastic sandwich materials may not allow “Class A” surfaces to be defined on the article that are visually acceptable for commercial purposes. 
     SUMMARY OF THE INVENTION 
     It is desirable to provide an improved method and system for producing articles from a thermoplastic sandwich material such as, for example, a 3-D deep-drawn article in which the exterior surface of the article has a “Class A” surface. According to an aspect of the present invention, such articles include a generally planar layer of a honeycomb material that is sandwiched between two thermoplastic skins. The portions of the article that extend away from the generally planar layer of honeycomb material are formed only from the two thermoplastic skins, not the honeycomb material. 
     Providing such a method and system has a number of distinct advantages. For example, forming the third dimensional aspect of an article generally only from thermoplastic skin material allows articles having relatively large deep-draws to be manufactured with a minimum of visual defects. In some applications, according to an aspect of the invention, articles with a deep-draw on the order of well beyond forty-eight inches can be made. Furthermore, in an exemplary automotive application of the present invention where the article to be formed is a truck box, the costs of manufacturing the truck box are significantly reduced because, for example, the labor costs associated with the application of a plastic liner to the metal truck box are totally eliminated. 
     Other features and advantages of the invention will become apparent from the description that follows. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an exemplary 3-D deep-drawn article that is formed from a thermoplastic sandwich material and that is manufactured in accordance with a number of aspects of the present invention; 
     FIG. 2 is a sectional view of the 3-D deep-drawn article shown in FIG. 1 taken along lines  2 — 2 ; 
     FIG. 3A is a plan view of a sheet of thermoplastic material; 
     FIG. 3B is a plan view of the thermoplastic sheet shown in FIG. 3A that has been die-cut to form a number of slits and fold lines; 
     FIG. 3C is a plan view of the die-cut thermoplastic sheet shown in FIG. 3B that has been folded along the fold lines shown in FIG. 3B; and 
     FIG. 4 is an exploded view of a section of the 3-D deep-drawn article shown in FIG. 1 taken along lines  4 — 4 , wherein the article is shown in a partially manufactured state and positioned to be surrounded by two mold halves. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a perspective view of an exemplary 3-D deep-drawn article  10  that is formed from a thermoplastic sandwich material in accordance with a number of aspects of the present invention is shown. In the illustrated embodiment of the present invention, 3-D deep-drawn article  10  forms a truck box that is utilized in conventional pick-up trucks in place of a standard metal box that typically is used in conjunction with a plastic liner. Manufacturing truck boxes from a thermoplastic sandwich material in accordance with a number of aspects of the present invention provides for significant cost savings for a number of reasons. For example, the labor costs associated with the application of a plastic liner to a conventional metal truck box are totally eliminated by the utilization of the present invention. 
     It should be appreciated by those of ordinary skill in the relevant art that article  10  can be any article that is formed, for example, in a deep-drawn manner. In a number of exemplary automotive applications of the present invention other than that discussed above, article  10  is a low cost floor panel, a removable hard top, a fixed hard top, or the like. It also should be appreciated that the present invention is suitable for use in non-automotive applications to manufacture articles such as 3-D deep-drawn parts. Examples of such articles include, but are not limited to, counter tops, cubical dividers, low cost headliners, or the like. 
     Referring to FIGS. 1 and 2, truck box  10  includes two side walls  12 , a front wall  14 , and a bottom wall  16 . In the illustrated embodiment of the present invention, side walls  12 , front wall  14 , and bottom wall  16  are formed from first and second reinforced thermoplastic skins  18  and  20  as shown in FIG.  2 . Bottom wall  16  includes a layer of honeycomb material  22  that is sandwiched between thermoplastic skins  18  and  20 . Reference is made to U.S. Pat. No. 5,683,782 that is incorporated by reference into this application as noted above for a complete discussion of the construction of the honeycomb material  22 . 
     In the illustrated embodiment of the present invention, front wall  14  is located adjacent to the cab of a pickup truck when truck box  10  is mounted on a pick-up truck. A rear wall surface  21  is formed by juxtaposed portions of skins  18  and  20  at a distal end of side walls  12  and a distal end of bottom wall  16  at a location opposite front wall  14 . Rear wall surface  21  covers a distal end of the honeycomb structure  22 . 
     A plan view of a sheet of thermoplastic material  24  is shown in FIG.  3 A. Two of such sheets  24  are utilized to form the thermoplastic skins  18  and  20 . Referring to FIG. 3B, in order to make the thermoplastic sheet  24  into the box shape shown in FIG. 1, two slits  26 ,  28  as well as fold lines  30 ,  32 ,  34 , and  36  are formed in the thermoplastic sheet  24  by, for example, a die-cutting process. A conventional folding station is utilized to fold the die-cut sheet  24  into the folded form  56  shown in FIG.  3 C. 
     Referring to FIG. 3B, fold lines  30 - 36  define a bottom portion  38  in sheet  24 . Bottom portion  38  forms a part of the bottom wall  16  of truck box  10  (FIG.  1 ). 
     Fold line  30  and slit  28  define a side foldable portion  40 . Similarly, fold line  32  and slit  26  form a side foldable portion  42 . Fold line  36  defines first and second portions  48  and  50  as well as  52  and  54  in the side foldable portions  40  and  42 , respectively. The side foldable portions  40  and  42  are folded by the folding station as shown in FIG. 3C so that the second portions  50  and  54  form a portion of the sidewalls  12  of truck box  10  (FIG.  1 ). 
     Fold line  36  and slits  26 ,  28  define a front foldable portion  44 . The front foldable portion  44  and the first portions  48  and  52  of side foldable portions  40  and  42 , respectively, are folded by the folding station as shown in FIG. 3C to form the front wall  14  of truck box  10  (FIG.  1 ). It should be appreciated that, in accordance with a further aspect of the present invention, side foldable portions  40  and  42  are folded by the folding station so that an inner surface of portions  48  and  52  are in contact with an outer surface of portion  44 . It also should be appreciated that complex shapes such as, for example, wheel wells can be formed in skins  18  and  20  when the skins are manufactured by, for example, a die-cutting operation. 
     Fold line  34  defines a rear foldable portion  46  in sheet  24 . Rear foldable portion  46  is folded in the manner shown in FIG. 3C by the folding station to form a rear end surface  21  of the truck box  10  (FIG.  1 ). 
     Referring to FIG. 4, an exploded view of a section of the 3-D article shown in FIG. 1 taken along lines  4 — 4 , wherein the truck box  10  is shown in a partially manufactured state. In accordance with one embodiment of the present invention, mold halves  58  and  60  form first and second mold halves of a typical compression mold that are movable relative to each other. In this example, skins  18  and  20  are formed by placing two folded forms  56  (FIG. 3C) on vacuum preforms that hold the portions  44 ,  48 , and  52  of each folded form  56  together. The vacuum preform and folded form  56  are heated to a softening temperature to caused portions  44 ,  48 , and  52  to be bonded together. 
     In some applications, it is desirable to provide texture on the exterior surface of an article that is produced in accordance with this aspect of the present invention. In this case, folded forms  56  are subject to a known texturizing process. 
     After skins  18  and  20  are formed, then a stack is made as shown in FIG. 4 relative to mold halves  58  and  60 . Mold halves  58  and  60  are then pressed together to seal the truck box  10  by a known thermocompression process. After the molding process is completed, truck box  10  is removed from the mold and any flash thereon truck box  10  is removed. 
     In accordance with a second embodiment of the present invention, first and second mold halves  58  and  60  form first and second mold halves of a typical vacuum compression mold that are movable relative to each other. In accordance with this aspect of the present invention, first and second folded forms  56  (FIG. 3C) are placed in the first and second mold halves  58  and  60 . The vacuum provided in each mold half  58  and  60  holds the portions  44 ,  48 , and  52  of each folded form together. 
     In some applications, it is desirable to provide texture on the exterior surface of an article that is manufactured in accordance with this aspect of the present invention. In this case, mold halves  58  and  60  form textured vacuum compression mold halves, and a relatively high vacuum is used during the molding process to provide the desired texture. 
     Thereafter, a layer of honeycomb material  22  is stacked on top of the folded form  56  on mold half  58  that is shown as skin  20  in FIG.  4 . Then, the first and second mold halves  58  and  60  are closed, and the stack is pressed to subject the stack to a predetermined pressure that is sufficient to cause the skins  18  and  20  as well as the honeycomb material  22  to be bonded together. After the molding process is completed, truck box  10  is removed from the mold and any flash is removed. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is considered as illustrative and not restrictive in character, it being understood that all changes and modification that come within the spirit of the invention are desired to be protected.