Abstract:
An adjustable mold is provided for vacuum assisted drawing of a thermoplastic material into the mold to form a dunnage tray, the mold being water cooled and allowing adjustment of the mold sides and surface topography to allow rapid and inexpensive user adjustment of the mold to from a variety of dunnage tray sizes and shapes as selected by a user.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to molding thermoplastic devices, and in particular, to an adjustable mold which can be used to make variously sized and shaped thermoplastic objects. 
     In the course of shipping and handling small parts and other objects, it is often desirable that multiple parts be placed into a tray for convenient handling. These trays generally are referred to as “dunnage trays.” They typically provide a molded depression which conforms to the shape of the part being handled or shipped. Using a dunnage tray, each part can be placed into its own shape-conforming depression in order to securely hold the part and to protect the part from jostling and damage during the shipment process. Typically dunnage trays are filled by the manufacturer of a small part, and then shipped to a second location where the part is withdrawn from the dunnage tray and used in a manufacturing application. Therefore, the dunnage tray serves not only as a reasonable protective packaging for the small part, but also serves as a transportation vehicle and storage compartment for the small part. Since dunnage trays are most efficiently maintained as a reusable item, it is necessary that they be constructed of a resilient material, and it is helpful if the material is also relatively lightweight so as not to add to shipping costs. In view of these requirements, thermoplastic material has developed as an ideal construction material for dunnage trays and a substantial amount of time and effort and expense is devoted to the designing of efficient dunnage trays which permit safe and secure housing for the parts to be shipped and which conform very closely to the shape of the particular part. Therefore, it will be appreciated that a dunnage tray of a standard shape is of little use to a wide variety of manufacturers. Rather, it is necessary that dunnage trays be specifically designed and produced to hold a particularly shaped part of a single manufacturer. Such individual design and construction of molds to produce dunnage trays is an expensive aspect of dunnage tray production. In the case where a manufacturer is producing a large volume of parts over a significant amount of time, the cost of the dunnage trays becomes an acceptable level of expense which can be amortized over a number of years. However, in the case of a small manufacturer or a limited production of a particular part, it is very difficult to justify the high expense of producing an individual mold for a production of a particular part which may not justify the expense of the dunnage tray over the long term. 
     Therefore, a need has long existed for a means for reducing the cost of production of dunnage trays by reducing the cost of producing a dunnage tray mold which is particularly suited to an individual part. In order to produce a dunnage tray mold which can be reconfigured easily and conveniently to different parts and different manufacturers, it is necessary that the dunnage tray mold be adaptable to change not only the length, width, and depth of the dunnage tray, but also, the shaping of the interior surface of the dunnage tray so that the interior surface of the tray can conform to whatever part is being shipped in the tray. 
     An additional problem presented by this art is the need for a vacuum to be applied by the mold form to draw the sheet of thermoplastic material into close contact with the mold to take on the shape presented by the mold. This requires that apertures be incorporated in the mold which allow an applied vacuum to be pulled against the plastic sheet. In the case of an adjustable mold, a substantial difficulty is presented as to how to provide sufficient vacuum ports for large size molds while eliminating those vacuum ports when they are not required for molding smaller pieces. In addition, a further difficulty is presented in that the vacuum must be communicated through the mold form in order to draw down the plastic sheet. 
     In view of the foregoing difficulties it will be appreciated that a substantial problem is presented in the industry of reducing the cost of production of dunnage trays by reducing molding costs while satisfying the very specific and particularized shape requirements of both the manufacturer and the manufacturer&#39;s particular part. 
     SUMMARY OF THE INVENTION 
     The above-identified problems are solved in the present invention which provides a mold for the creation of dunnage trays which permits rapid and inexpensive modification of the length, width, and height of the exterior dimensions of the dunnage tray and which allows the interior surface of the dunnage tray to be shaped to the particular specifications of a particular manufacturer&#39;s small part or other object which is to be transported in the dunnage tray. Therefore, it is an object of the present invention to provide a mold for a dunnage tray which can be varied in its overall dimensions of the length, width, and height of the outer perimeter of the dunnage tray and which can be used with conventional rotary and single station thermal forming equipment. 
     Another object of the present invention is to provide a dunnage tray which can easily and inexpensively have the interior surface of the dunnage tray shaped to conform to a particular manufacturer&#39;s part-shape or quantity of parts to be shipped in each tray. 
     Yet another object of the present invention is to provide a variably-sized mold for creation of dunnage trays which allows the application of vacuum to that portion of the mold which is being utilized to form the dunnage tray and without loss of vacuum from portions of the mold or mold frame which are not being utilized. 
     The foregoing and other objects are not intended in a limiting sense as will be readily evident upon a study of the following specification and accompanying drawings comprising a part thereof. Other objects and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawings, wherein is set forth by way of illustration and example, an embodiment of this invention. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention, illustrative of the best modes in which the applicant has contemplated applying the principles, are set forth in the following description and are shown in the drawings and are particularly and distinctly pointed out and set forth in the appended claims. 
     FIG. 1 is a perspective view of a preferred embodiment of the present invention having a mold piece placed thereon; 
     FIG. 2 is an exploded view of the embodiment shown in FIG.  1  and having the mold piece and three of the cover plates removed for clarity; 
     FIG. 3 is a fragmentary top and end perspective view of an embodiment of a rail of a preferred embodiment of the present invention; 
     FIG. 4 is a cross-sectional view taken along line  4 — 4  of the rail shown in FIG. 3; 
     FIG. 5 is a top plan view of the rail shown in FIG. 3; 
     FIG. 6 is a fragmentary cross-sectional view taken along line  6 — 6  of FIG. 2; 
     FIG. 7 is a fragmentary cross-sectional view taken along line  7 — 7  of FIG. 2; 
     FIG. 8 is a perspective view of a mold plate and showing two side rails joined to the plate with the mold plate rim insert removed to allow connection of the mold plate to the side rails; and 
     FIG. 9 is a cross-sectional view of the mold plate taken along line  9 — 9  of FIG.  8 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, variable sized mold  10  is shown which is composed of base unit  12  and bottom plate  14 . As will be described in detail hereinafter, base  12  permits the securing of fixtures to the top surface of base  12  through the use of lock-down voids  16 . Base  12  also permits the transmission of reduced pressure or vacuum to the top surface  13  of base  12  by communication of the vacuum on reduced pressure through vacuum openings  20  on top surface  13  of base  12 . Vacuum openings  20  are in communication with vacuum tubes  21  (FIG. 6) which are drilled completely through base  12  to allow the communication of vacuum between the bottom surface of base  12  and base top surface  13 . In addition to communicating the reduced pressure or vacuum to top surface  13 , base  12  also allows for the circulation of a coolant. The circulation of water or other coolant is accomplished by cooling water circulation tubes  38  (FIG.  2 ), which are drilled horizontally, through base  12  to allow water circulation through base  12  for cooling of the mold during the molding process. Water enters the circulation tubes  38  (FIG. 2) through water entry port  36  (FIG.  1 ). As will be described hereinafter, the water or other coolant is passed from one circulation tube to the next circulation tube by water flow director  41  which allows water to exit a first water circulation tube  38  (FIG. 2) from circulation tube end  39  (FIG. 2) and to enter an adjacent circulation tube  38 . 
     The use of water or some other coolant to cool base  12  is particularly helpful during the molding process as a hot sheet of thermoplastic material is set on top of mold base  12 . Once it is properly in place, the reduced pressure or vacuum drawn on mold  10  through the various vacuum openings  20  pulls the hot thermoplastic sheet (not shown) into the mold and conforms the plastic sheet to the final shape which is dictated by the configuration to which the mold has been adapted. Once the hot sheet of thermoplastic material has been pulled against the shape of the mold, it is then necessary to cool the sheet of plastic so that it retains the shape in which it has been formed. This is accomplished through the transfer of heat from the plastic sheet to base  12 . The excess heat transferred to base  12  is drawn off by the circulating coolant within base  12 . While it will be appreciated that base  12  could simply be allowed to cool by dispersal of heat to the surrounding air, this would not be practical in a commercial circumstance and would require excessive time between molding operations. 
     Referring now to FIG. 2, bottom plate  14 , which is attached to base  12  of mold  10  in operation, is shown separated from base  12 . Bottom plate  14  is a flat block of aluminum or other machinable material. Bottom plate  14  is provided with a vacuum entry port  32  which is in the center of a machined-out depression or vacuum chamber  30  in bottom plate  14 . This depression provides a void of approximately one-eighth to one-quarter inch extending fully across the surface of bottom plate  14  and terminating in an outside rim  34  of bottom plate  14 . Rim  34  provides a secure and air-tight connection of bottom plate  14  against the bottom surface of base  12 . In this manner, a vacuum chamber  30  is provided on the bottom side of base  12  which allows the vacuum or low pressure which enters through vacuum connection port  32  to be spread across the entire bottom surface of base  12  and to be communicated to each of vacuum tubes  21  (FIG. 6) extending vertically through base  12 . It will be appreciated that bottom plate  14  securely fastens to the bottom of base  12 , and that use of a gasket on bottom plate rim  34  may assist in maintaining the low pressure or vacuum state created in vacuum chamber  30  of bottom plate  14  when mold  10  is in use. 
     Referring again to FIG. 1, additions to base  12  are shown which operate to reduce the exposed surface area of base top surface  13  when a mold dimension smaller than the full area of base top surface  13  is required. When it is desired to reduce the amount of exposed base top surface  13 , such as when small dunnage trays are being molded, cover plates  26  are installed across portions of base top surface  13 . Cover plates  26  are fastened in place by use of lock-down voids  16  which are machined into top surface  13  of base  12 . To maintain the low pressure or vacuum which is used to operate mold  10 , a gasket (not shown) is applied to the bottom surface of each of cover plates  26  to fully seal the covered area of top surface  13  and to reduce loss of vacuum in the unused portions of top surface  13  of base  12 . 
     Referring again to FIG. 2, the assembly of the railing  22  and attachment of railing  22  to base  12  will be described. Railing  22  is a segment of a mold form which is attached to base  12  in order to create an outside rim for the molded object, in the case shown, a side of a dunnage tray. As can be seen in FIG. 1, a portion of the top surface of base  13  has been sealed using cover plates  26  to reduce the total area of top surface  13  of base  12 . Just inside cover plates  26 , rails  22  have been assembled and affixed to base  12  by insertion of a bolt through bolt void  61  (FIG. 3) of rail  22  of lock-down voids  16  in base  12 . Rails  22  join together to form an outside perimeter for the mold piece. In the particular case shown in FIG. 1, the corner rail segments  22  have been joined together at their mitered corners to form each of the four corners of the outside perimeter of the rail. In FIG. 8, the area of the rail between corner segments  22  has been filled with extension rail units  24  to connect to the mitered corner rail units while extending the length of the railing. By use of extension rail units  24 , a complete perimeter of any size up to the full perimeter of base  12  can be established on top surface  13 . As the length of extension rails or rail extension segments  24  can be varied according to the size of the mold piece intended to be constructed, a mold perimeter of any size which can be fit onto top surface  13  of base  12  can be constructed in this fashion. 
     Referring now to FIGS. 3,  4  and  5 , the construction of corner rail  22  and extension rail  24  will be discussed in greater detail. FIG. 3 shows a typical rail  22 ,  24  in fragmentary perspective view. Rail segment  22 ,  24  is provided with an inner side  23   a  and an outer side  23   b.  Trough  25  is provided between inner side  23   a  and outer side  23   b  which allows formation of an outer parameter lip of the molded piece. To draw the heated sheet of thermoplastic material down into trough  25  of rail segment  22 , 24 , vacuum holes or ports  59  are provided in rail segments  22 , 24  to draw the thermoplastic material down and against rail segments  22 , 24 . To securely fasten rail segments  22 ,  24  to base top surface  13 , bolt voids  61  (FIG. 4) are provided in rail segments  22 ,  24  to permit fastening of the rail segments onto base  12 . In FIG. 4, a cross-section view of rail  22 ,  24  shows the passage of vacuum ports  59  and bolt voids  61  through rail segments  22 ,  24 . 
     Referring now to FIG. 4, a cross-sectional view of rail segment  22 ,  24  is shown. It will be appreciated that for vacuum ports  59  of rail segments  22 ,  24  to be effective, they must be in communication with the vacuum which is being applied to top surface  13  of base  12  (FIG.  1 ). The communication of vacuum to vacuum ports  59  of rail segments  22 ,  24  is accomplished by milling out of a depression or rail vacuum chamber  56  in the bottoms of segments  22 ,  24 . Depression or rail vacuum chamber  56  allow communication of the vacuum from vacuum opening  20  (FIG. 2) in base top surface  13  to rail vacuum ports  59 . Also shown in FIG. 4 is bolt void  61  for securing rail segments  22 ,  24  to lock-down voids  16  of base  12 . 
     Referring again to FIG. 3B, additional aspects of rail segments  22 ,  24  will be discussed. It will be appreciated by those skilled in the art that for mold  10  to be effective, it is useful for mold insert pieces  53  (FIG.  1 ), or a mold plate  51  (FIG.  8 ), to be included in order to shape the otherwise flat top surface  13  (FIG. 1) of base  12  into a desired mold configuration. In the case of a dunnage tray, in particular, it is desirable to shape the top surface  13  of base  12  in order that depressions may be created in the plastic material molded by mold  10 . It is useful that the final molded thermoplastic material have depressions therein which conform to the shape of a particular part or other object so that the part or object is securely held within the dunnage tray. This is accomplished by the attachment of a mold insert  53  (FIG. 1) to top surface  13  of base  12 , or by the insertion of mold plate  51  (FIG. 8) across the top surface  13  of base  12 . 
     When mold insert  53  (FIG. 1) is used, mold insert  53  may be directly attached to base top surface  13  by bolting mold insert  53  into lock-down voids  16  drilled into top surface  13  of base  12 . Alternatively, it may be more efficient to cast an entire mold plate  51  (FIG. 8) to cover top surface  13  of base  12 . Plate  51  is provided with a series of perforations or voids  52  to allow the communication of vacuum from vacuum openings  20  (FIG. 1) through mold plate  51  to draw a thermoplastic sheet against mold plate  51 . 
     In FIG. 9, a vertical cross section of a rail segment  22  in connection with insert mold plate  51  is shown. To provide a tight-fitting connection between rail  22 ,  24  (FIG. 8) and mold plate  51  (FIG.  8 ), rail segments  22 ,  24  have been provided with a detachable mold plate rim insert  49  (FIG. 3) which can be released from rail segments  22 ,  24  to accommodate the insertion of the edge of mold plate  51 . In this manner, as shown in FIG. 9, a tight fitting alignment between rail segments  22 ,  24  and insert plate  51  is provided. A gasket may be used therebetween to preserve the integrity of the vacuum being pulled on mold  10  which communicates through mold plate  51  and rail segment  22 ,  24  in order to draw the thermoplastic material down and into place. 
     Referring now to FIGS. 6 and 7, the alignment between cooling water circulation tubes  38  and lock-down voids  16  and vacuum openings  20  and vacuum tubes  21 , all of which are contained within base  12 , will be discussed. As is shown in FIG. 7, water circulation tubes  38  are drilled horizontally completely through base  12  and reach from side-to-side. It is also shown in FIG. 6 that vacuum tubes  21  are drilled vertically through base  12  to allow communication of vacuum from vacuum chamber  30  up through vacuum tubes  21  and to vacuum opening  20 . Vacuum openings  20  in top surface  13  of base  12  are arranged in alternate rows with respect to lock-down voids  16 . To accommodate all of these features within base  12 , the arrangement is configured such that lock-down voids  16  are generally above cooling water circulation tubes  38 . Since lock-down voids  16  extend only one or two inches vertically into base  12 , they do not closely approach cooling water circulation tube  38 . This vertical alignment between lock-down void  16  and cooling water circulation tubes  38  permits vacuum tubes  21  to be drilled in between water circulation tubes  38  thereby allowing vacuum tubes  21  to reach from top surface  13  of base  12  downwardly to vacuum chamber  30  without interfering with cooling water circulation tubes  38 . 
     Referring now to FIG. 2, the manner in which water is transferred from one circulation tube  38  to an adjacent circulation tube  38  will be discussed. As previously described, water circulation tubes  38  are horizontally drilled completely across base  12 . Water entering one side of a circulation tube  38  would simply drain out on the other side of water circulation  38  without the addition of a means for directing the water flow from one circulation tube  38  to an adjacent circulation tube  38 . This directing of water flow is accomplished by water flow director  41  which is attached to the side of base  12  to cover circulation tube ends  39 . Face  44  of water flow director  41  contacts the side of base  12 . Face  44  is provided with milled-out depressions  43  which align with two adjacent circulation tube ends  39  when water flow director  41  is bolted to the side of base  12 . Director bolt voids  42  are shown in FIG.  2  through which a bolt may be inserted to attach water flow director  41  to the side of base  12 . When flow director  41  is in place, water will exit from a circulation tube end  39  and will be directed laterally by depression  43  of water flow director  41 , and the water will then enter circulation tube end  39  of an adjacent water circulation tube  38 . In this manner, water is allowed to enter water cool entry ports  36  (FIG. 1) and circulate throughout an entire set of adjacent cooling water circulation tubes  38  and finally exit from the end of the last circulation tube  38  on the side of base  12  that is opposite the side having entry ports  36 . 
     In operation the use of the inventive mold is as follows. The user, attaches water flow directors  41  into place and connects a stream of coolant to entry ports  36 . The user then arranges and attaches the proper molding parts onto top surface  13  of base  12 . The arrangement of molding parts is, of course, necessary in order to provide a surface topography on top surface  13  to provide a molding form to shape a hot sheet of thermoplastic material as it is applied to variably sized mold  10 . 
     The arrangement and attachment of molding parts is accomplished by selecting a mold insert  53  (FIG. 1) or a mold plate  51  (FIG. 8) for use on mold  10  and attaching the mold piece  53  or mold plate  51  to top surface  13 . The attachment is accomplished, as previously described by inserting bolts through the mold piece  53  or mold plate  51  and securing the bolts in the available lock-down voids  16  machined into the top surface  13  of base  12 . Once this is accomplished, a perimeter rail formed by rail segments  22 ,  24  may be established around the mold insert  53  or mold plate  51 . 
     When rail segments  22 ,  24  are to be bolted to top surface  13 , bolt void  61  is used to pass the bolt through rail segments  22 ,  24  to connect the bolt into bolt void  16  of top surface  13 . This last secure contact of rail segments  22 ,  24  with top surface  13  and allows the transfer of the applied vacuum or reduced pressure through vacuum ports  59  of rail segments  22 ,  24  in order to draw the thermoplastic material down against rail segments  22 ,  24 . When rail segments  22 ,  24  are applied around the perimeter of mold plate  51 , it is first necessary that rim inserts  49  (FIG. 4) be removed from rail segments  22 ,  24  so that insertion of the edge of mold plate  51  closely against rail segments  22 ,  24  may be provided. In the case in which mold inserts  53  (FIG. 1) are utilized on top surface  13  of base  12 , it is not necessary to remove rim inserts  49  from rail segments  22 ,  24  to preserve the integrity of the vacuum being pulled on mold  10 . 
     When the position of rail segments  22 , 24 , or other final mold plate or mold insert  53  has been attached to top surface  13 , it is necessary to seal off any vacuum openings  20  which are outside the molding area. This is done to reduce the loss of vacuum that is being pulled on mold  10  during operation. This is simply accomplished by application of cover plates  26  (FIG. 1) across the unused portion of top surface  13  of base  12  in order to seal vacuum openings  20  which are not needed in order to pull a heated sheet of thermoplastic material against mold  10 . 
     Once the mold plate or mold insert  53  and rail segments  22 ,  24  have been secured to top surface  13  of base  12 , the mold  10  is prepared for use. The operator then applies the vacuum or reduced pressure to opening  32  of bottom plate  14  (FIG. 2) to provide vacuum to vacuum chamber  30  so that vacuum is distributed across the entirety of base  12  and communicated to vacuum tubes  21  which pass through base  12  to provide vacuum or reduced pressure to vacuum openings  21  and top surface  13  of base  12 . The operator establishes the flow of coolant through openings  36  (FIG. 1) of base  12  in order to maintain mold  10  at proper operating temperature. Once this has been accomplished, mold  10  is now prepared to have heated thermoplastic sheets applied to the top of mold  10  so that the applied vacuum or reduced pressure to mold  10  may pull the heated thermoplastic sheet against mold plate  51  or mold insert  53  and rail segments  22 ,  24  in order to form the desired molded part on mold  10 . 
     In the foregoing description, certain terms have been used for brevity, clearness and understanding; but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such terms are used for descriptive purposes and are intended to be broadly construed. Moreover, the description and illustration of the inventions is by way of example, and the scope of the inventions is not limited to the exact details shown or described. 
     Certain changes may be made in embodying the above invention, and in the construction thereof, without departing from the spirit and scope of the invention. It is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not meant in a limiting sense. 
     Having now described the features, discoveries and principles of the invention, the manner in which the improved dunnage tray mold is constructed and used, the characteristics of the construction, and advantageous, new and useful results obtained; the new and useful structures, devices, elements, arrangements, parts and combinations, are set forth in the appended claims. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.