Abstract:
A support for rotating molds used in multi-shot injection molding provides for platen mounting of a support track that may extend beneath the molds to support the rotating mold portion. The extensible track provides a telescoping configuration that allows a long support span independent of the mold width improving mold stability and increasing potential mold separation for easy access to the mold portions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       BACKGROUND OF THE INVENTION  
         [0001]    In injection molding, a molten thermal plastic or similar material is injected into a mold having a closed cavity having outer surfaces conforming to the shape of the desired part. After injection, the mold may be separated along a parting line to release the molded part and then closed again so that the injection process may be repeated.  
           [0002]    In multi-shot injection molding, a first shot of injected plastic is delivered to the mold and then a portion of the mold cavity is changed and a second shot of plastic is injected into the changed cavity. Multi-shot injection molding may be used to create parts having two or more different thermoplastic materials that are joined as an integral unit or that are separable after molding is complete. In this latter case, the molding process effectively pre-assembles the separate plastic components in the mold.  
           [0003]    The reconfiguration of the mold, in between the separate injections of plastic (shots), is easily performed by rotating a portion of the mold. The rotation may bring successive portions of the mold into alignment with different injector units so that the multiple shots may be accomplished simultaneously on different portions of the mold, thereby improving machine throughput. A well known technique for mold rotation involves rotating a center portion of a three part mold along an axis perpendicular to the direction in which the mold portions separate (the mold separation direction).  
           [0004]    During a first stage, a first material may be injected into a front cavity at the interface of a front and center portion of the mold to create a base part. At the same time, a second material may be injected into a rear cavity formed by the interface of the center and rear portions of the cavity. This rear cavity contains a base part previously molded in the front cavity and the second material over molds the part.  
           [0005]    In a second stage, the mold portions are separated and the over molded part is ejected from the rear cavity and the mold rotated 180°. The molds portions are closed again and the process is repeated.  
           [0006]    Rotation of the center portion of the mold about an axis perpendicular to the direction of mold separation reduces the required clamping pressure on the molds and may be contrasted to a system that rotates the molds about an axis parallel to the mold separation direction. This latter system increases the total area of the molds over which the injected plastic presses, requiring additional clamping pressure and possibly a larger injection-molding machine.  
           [0007]    While rotating the center mold portion perpendicularly to the mold separation direction requires less total clamping pressure, greater separation of the machine platens is required to provide for mold rotation and part removal. The center mold portion is supported during separation by the tie rods, which join the platens of the injection-molding machine. The location and size of these tie rods varies between machines and thus such an approach requires that the molds be designed for a specific machine.  
           [0008]    A variation on this approach holds the rotatable mold portion within a frame held by cantilevered lead pins extending from the front and rear mold portions and received by this frame. This approach is limited to relatively small molded parts using lightweight molds that separate only the short distance supportable by the cantilevered pins. One drawback is that the frame limits the area of the platens that may be used for the mold and thus the size of the molded part.  
           [0009]    What is needed is a mold support system adaptable to arbitrarily large molds that does not require the use of a specific injection-molding machine.  
         BRIEF SUMMARY OF THE INVENTION  
         [0010]    The present invention provides a mold support for a rotating central mold portion that is supported solely through the platen mold mounts and thus does not require extensive modification of an injection-molding machine or the use of an injection-molding machine having its tie rods in a particular location. The invention provides a frameless design in which the mold is supported from beneath on a rotating table held by rails attached to the platens. Positioning of the rails below the mold allows the rail to present a support span in the mold separation direction substantially wider than the mold itself allowing improved stability, greater mold sizes, and greater clearance when the molds are separated.  
           [0011]    Specifically, the present invention provides a rotating mold support having a first and second platen mount attachable to the opposed platens of a standard injection molding machine and providing opposed mold attachment surfaces for first and second mold portions, respectively, and adjacent track attachment surfaces. At least one extensible support track is attached to extend between the track support areas of the first and second platen mount to span the distance between the first and second platen mount for a plurality of separations of the first and second platen mounts along a mold separation axis. A rotatable mold stage is attached to a middle part of the extensible support track and has an upper surface supporting a third mold portion for rotation about an axis perpendicular to the mold separation axis.  
           [0012]    It is thus one aspect of the invention that it allows the frameless support of the center portion of the mold improving the capacity of an injection-molding machine to mold large parts.  
           [0013]    It is another aspect of the invention that it allows the mold to be supported on a wide variety of different injection molding machines without extensive modification to those machines. Because the rotatable mold stage is supported by tracks held by the platen mounts, only platen mounting is required to attach the mold to a given machine.  
           [0014]    The track attachment surfaces may be below the mold attachment surfaces so that the track is below the third mold portion. The third mold portion may be supported solely by the upper table surface during rotation.  
           [0015]    Thus it is another aspect of the invention that it provides an extremely simple mechanism for supporting a mold portion for rotation such that allows ready access to the third mold portion.  
           [0016]    The extensible support track may include a first and second parallel rail extending along the mold separation axis. The first parallel rail may be attached to the first platen mount and the second parallel rail may be attached to the second platen mount, and the first and second parallel rails may slidably engage with a support element over a support span, the support element forming the middle part of the extensible support track.  
           [0017]    Thus it is another aspect of the invention that the support track may provide for telescoping action increasing its usable range.  
           [0018]    The support span may have a width measured along the mold separation axis greater than the width of the third mold portion measured along the mold separation axis.  
           [0019]    Thus it is another aspect of the invention that it may provide an extremely sturdy extensible support track that can provide support points much exceeding the size of the mold for improved stability against torsion and the like.  
           [0020]    The parallel rails may have a cross-sectional height measured vertically that is more than twice their cross-sectional width measured horizontally.  
           [0021]    It is a feature of some embodiments of the invention to allow advantageous rail cross-sections by displacing the extensible track away from the mold area.  
           [0022]    The first and second parallel rails may include opposed racks and the support element may be positioned between the first and second parallel rails and include a gear simultaneously engaging both racks to cause the support element to move equally with respect to the first and second platen supports.  
           [0023]    It is thus another feature of at least one embodiment of the invention that the third mold portion may be positioned to remain centered between the first and second mold portions as the latter open.  
           [0024]    The first and second parallel rails may include opposed ways and the support element may be positioned between the first and second parallel rails and may include slides engaging the opposed ways of the first and second parallel rails to move freely along each.  
           [0025]    It is another aspect of the invention that it provides for an improved slider mechanism over that obtained by leader pins alone.  
           [0026]    The features and advantages may not apply to all embodiments of the inventions and are not intended to define the scope of the invention, for which purpose claims are provided. In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which there is shown by way of illustration, a preferred embodiment of the invention. Such embodiment also does not define the scope of the invention and reference must be made therefore to the claims for this purpose. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    [0027]FIG. 1 is a simplified perspective view of the rotating mold support of the present invention showing platen mounts holding a first and second mold portion on an upper surface and an extensible support track on a lower surface, the latter which holds a stage rotating a central mold portion about an axis perpendicular to the separation axis of the platens;  
         [0028]    [0028]FIG. 2 is a cross-section along lines  2 - 2  of FIG. 1 showing the multiple parallel rails which form the extensible support track of FIG. 1 and showing an upper table surface being part of the rotatable stage and showing a motor positioned between the rails beneath the stage to rotate the table;  
         [0029]    [0029]FIG. 3 is a fragmentary plan view of a gear mechanism joining racks attached to the rails of FIG. 2 and operating to position the rotatable stage equally between the platens regardless of their separation; and  
         [0030]    [0030]FIG. 4 is a plan view of a single rail of FIGS. 1 and 2 in full extension showing the support span over which the rails engage each other in telescoping fashion compared to the maximum mold width and such as provides improved stability to the mold portions. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0031]    Referring now to FIG. 1, the present invention provides a rotating mold support  10  suitable for use with multi-shot molding as described above and uses a front mold portion  12 , a central mold portion  14  and a rear mold portion  16 . During operation, front mold portion  12  and rear mold portion  16  are closed upon either side of central mold portion  14  along a mold separation axis  24  as indicated by arrows  18  so that central mold portion  14  is sandwiched between mold front mold portion  12  and rear mold portion  16 .  
         [0032]    Cavities  20  in the abutting faces of each mold portion  12 ,  14  and  16  define a first injection cavity between front mold portion  12  and central mold portion  14  and a second injection cavity between central mold portion  14  and rear mold portion  16 . Thermoplastic may be injected into these cavities when mold portions  12 ,  14  and  16  are in closed configuration.  
         [0033]    After injection, mold portions  12 ,  14  and  16  are opened and a part is ejected from the second mold cavity. Central mold portion  14  then rotates by 180° as indicated by arrow  22  and the mold portions  12 ,  14  and  16  are again closed together along arrows  18 . The first shot may be supplied by a first injector nozzle  26  and the second shot may be provided by a second injection nozzle  28  shown positioned axially along axis  24  but subject to a number of different variations well known in the art. The passages through which the thermoplastic is conducted from the injection nozzles  26  and  28  through the front mold portion  12  and rear mold portion  16  are not shown for clarity.  
         [0034]    The invention provides a movable support for the mold portions  12 ,  14  and  16  held solely by the stationary front machine platen  30  and a movable rear machine platen  32 . The stationary front machine platen  30  and movable rear machine platen  32  present relatively standard mounting surfaces and include a clamping mechanism (not shown) providing a closing pressure for the mold portions  12 ,  14  and  16 .  
         [0035]    Referring still to FIG. 1, the invention provides a front and rear mold platen mount  34  and  36 , respectively, consisting generally of plates of metal having an outer surface attachable to the front machine platen  30  or rear machine platen  32  and an opposite inner surface providing an upper area attachable to one of front mold portion  12  or rear mold portion  16 .  
         [0036]    A lower portion of the inner surface of the front and rear mold platen mount  34  holds opposite ends of an extensible support track assembly  37 . The extensible support track assembly  37  consists of two parallel rail pairs made up of rails  38   a  and  40   a , for one pair, and  38   b  and  40   b , for the second pair, each extending generally along the axis  24 . Each rail  38   a ,  38   b ,  40   a ,  40   b  has a length less than the closed separation between front machine platen  30  and rear machine platen  32  during clamping of the mold portions  12 ,  14 , and  16  and greater than half the separation of the front machine platen  30  and rear machine platen  32  during opening of the mold portions  12 ,  14  and  16 .  
         [0037]    Parallel rails  38   a  and  38   b  have one end attached to a lower part of the rear mold platen mount  36  and the other end extending toward front mold platen mount  34 . Similarly, parallel rails  40   a  and  40   b  have one end attached to the lower portion of front mold platen mount  34  and the remaining end extending toward rear mold platen mount  36 . Rails  40   a  and  40   b  are set horizontally closer to each other than rails  38   a  and  38   b  so that they pass by each other with movement of the front machine platen  30  and rear machine platen  32  toward and away from each other.  
         [0038]    Between rails  38   a  and  40   a , is a third rail  42   a  forming a support element supporting on its upper surface a stage base  44 . The rail  42   a  is generally parallel to rails  38   a  and  40   a . Similarly, between rails  38   b  and  40   b  is a support element  42   b  also parallel to rails  38   b  and  40   b  and positioned therebetween, and also supporting on its upper surface, the stage base  44 .  
         [0039]    Referring now to FIG. 2, each of rails  38   a  and  40   a  and  40   b  and  38   b  include inwardly extending ways  46   a  and  46   b , respectively. These ways  46   a  and  46   b  are in turn received by a pair of sliding collars  48   b  and  48   a , the collars of each pair attached on opposite sides of rails  42   b  and  42   a , respectively. Thus elements  42   a  and  42   b  may thus slide freely between rails  38   b  and  40   b  and rails  40   a  and  38   a , respectively.  
         [0040]    Referring now to FIG. 4, it will be understood that this arrangement provides for a telescoping action of rails  38   b ,  42   b , and  40   b , and the corresponding rails  40   a ,  42   a  and  38   a  (not shown in FIG. 4) that allows them to extend nearly twice the length of each of the rails  38   b  and  40   b  and to compress nearly to the length of one of rails  38   b  or  40   b . Further, however, it will be understood that the support span  50  defined as the outermost engagements between collars  48   b  extending between rails  38   b ,  42   b , and  40   b  (and that corresponding distance on  38   b ,  42   b , and  40   b ) may be substantially wider than the width  52  of the central mold portion  14  as shown also in FIG. 1. This allows for greater separation of the central mold portions  14  from front mold portion  12  and rear mold portion  16 , and for greater resistance to torsion, independent of the width of the central mold portion  14  which limits the length of received lead pins or the like.  
         [0041]    It will be understood that additional intermediate rails, slidably engaging with adjacent rails, may be added to the telescoping set of rails  38   b ,  42   b , and  40   b , and the corresponding rails  40   a ,  42   a  and  38   a  to provide for even greater extension.  
         [0042]    Referring again to FIGS. 1 and 2, the stage base  44  as held on the tops of rails  42   a  and  42   b  provides a turntable  54  supported for rotation about a vertical axis  56  by bearing  58  fitting between the base  44  and turntable  54 . The turntable  54  is disc-shaped and retained at its edges by gibs  60  and at its center by a shaft  63  driven by a motor  65 , the latter which effects rotation of the central mold portion  14 . Referring now to FIGS. 1, 2 and  3 , extending inward from each of the rails  38   b ,  40   b , and  40   a  and  38   a , respectively, below the ways  46   b  and  46   a , are racks  62 . These racks engage opposite edges of a gear  64  positioned at the bottom of the rails  42   b  and  42   a . This engagement causes any movement of rail  42   b  (or  42   a ) with respect to rail  38   b  ( 40   a ) to be equal to the movement between rail  42   b  ( 42   a ) and rail  40   b  ( 38   a ). In this way, the stage base  44  is always kept equidistant between the front machine platen  30  and rear machine platen  32 .  
         [0043]    As seen in FIGS. 1 and 2, the cross section of the rails  38   a ,  38   b ,  42   a ,  42   b ,  40   a , and  40   b  is substantially taller than it is wide providing for good resistance against downward bending of the rails while decreasing the total width of the support structure of extensible support track assembly  37 . Generally, the height will be more than twice the width of the rails.  
         [0044]    It will be seen from FIG. 1, that the central mold portion  14  is readily accessible from three sides. The present structure provides ample separation of the mold portion  12 ,  14 , and  16  so that parts can be ejected between mold portions, however, the elimination of the frame around the mold also allows a 90° rotation of the central mold portion  14 , and thus permits ejection of the parts to the side or the loading of inserts.  
         [0045]    It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but that modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments also be included as come within the scope of the following claims.