Abstract:
An injection molding apparatus includes a fixed injection molding machine having a housing, a first injection molding unit and a mold associated therewith. A portable framework is removably attached to the platen and has at least a second injection molding unit operably aligned with the mold and cooperable with the first injection molding unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation-in-part of U.S. application Ser. No. 09/543,805 filed Apr. 6, 2000 now U.S. Pat. No. 6,352,427. 

   FIELD OF THE INVENTION 
   This invention relates broadly to thermoplastic injection molding apparatus and, more particularly, pertains to the enhancement of a commercially available injection molding machine to increase production capability. 
   BACKGROUND OF THE INVENTION 
   Changes in plastics manufacturing strategies, particularly the growing emphasis on reducing in-process time and inventories, make multishot molding more viable and cost justifiable than single shot molding for a broader range of manufacturers. The multishot process allows multiple colors or materials to be sequentially injected in a single, continuous process to speed throughput, minimize production and assembly operations, improve part quality. and create innovative part features. 
   In most cases, a single injection molding machine with multiple injection units will cost less than separate machines with an equivalent number of single injection units. Likewise, a single two-color mold will usually cost less than two one-color molds. There is also a labor savings when using a multishot machine because only a single machine operator is required for the multi-step process. This can have major impact on payback calculations and life cycle costs. Floor space, electricity, and other utility costs are also reduced by consolidating operations on one machine. Faster inventory turns for savings on in-process inventory can be a critical factor in the decision matrix as well. 
   Despite their advantages, multishot injection molding machines are not readily available from the inventory of large press manufacturers and must often be custom built which results in several months of delay before the desired production can commence. Once the multishot machine is delivered and installed, the customer is locked into the particular arrangement of the multiple injection units on the machine. There is no interchangeability with another press manufacturer&#39;s machine or parts thereof. 
   Accordingly, it is desirable to provide an arrangement for removably mounting an injection molding unit on a commercially available injection molding machine in a manner which will produce all the advantages of a multishot machine without any of its drawbacks. It is also desirable to provide a flexible framework for retrofitting additional injectors onto standard injection molding machines. 
   SUMMARY OF THE INVENTION 
   It is a general object of the present invention to transform a standard single shot molding machine into a multishot molding machine. 
   It is one object of the present invention to provide a portable injection molding unit for expanding the flexibility of a standard injection molding machine. 
   It is another object of the present invention to provide a method of mounting an additional injector on a standard injection molding machine that will work with a wide variety of standard injection molding machines. 
   It is an additional object of one embodiment of the invention to minimize cantilever of the additional injector and material fatigue in the mounting of the injector by affixing the additional injector to the movable platen. 
   It is an additional object of another embodiment of the invention to accommodate large injectors by minimizing movement of the additional injector by affixing it to the stationary platen. 
   In one aspect of the invention, a kit is provided for converting an injection molding machine to multishot operation, where the injection molding machine has a first stationary platen holding a stationary mold portion in communication with an injection cylinder, and a second movable platen holding a movable mold portion joining with the stationary mold portion with movement of the movable platen along a closure axis, the injection cylinder, stationary platen and movable platen controlled by an injection molding controller. The kit includes a second injection cylinder having a mounting surface adapted to attach to one of the movable and stationary platens; and interface electronics providing an interface between the second injection cylinder and the injection molding controller. 
   In another aspect of the invention, the invention provides a method of retrofitting an injection molding machine to multishot operation, where the injection molding machine has a first stationary platen holding a stationary mold portion in communication with an injection cylinder and a second movable platen holding a movable mold portion joining with the stationary mold portion with movement of the movable platen, the injection cylinder, stationary platen and movable platen controlled by an injection molding controller. The method includes the steps of attaching a second injection cylinder to one of the movable and stationary platens; and connecting interface electronics to provide an interface between the second injection cylinder and the injection molding controller, to the injection molding controller to coordinate the operation of the second injection molding cylinder with the movement of the stationary and movable platens. 
   The second injection cylinder may be attached to the stationary platen and include at least one positioning actuator for moving the second injection cylinder along its axis. The interface electronics in this case allows the injection molding controller to control the positioning actuator in coordination with movement of the stationary and movable platens to engage by axial movement with the movable mold portion when the movable mold portion is joined with the stationary mold portion and to disengage by axial movement with the movable mold portion prior to separation of the movable mold portion and the stationary mold portion. The second injection molding cylinder may be attached to the top of the stationary platen or to a front surface of the stationary platen holding the stationary mold portion or to the stationary mold portion itself. 
   Alternatively, the second injection cylinder may be attached to the movable platen to engage with the movable mold portion and move therewith. The attachment point may be the top of the movable platen, a front surface of the movable platen holding the movable mold portion, or the movable mold portion itself. 
   Various other features, objects, and advantages of the invention will be made apparent from the following description taken together with the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will become better understood by reference to the following detailed description of the preferred exemplary embodiment when read in conjunction with the appended drawings, wherein like numerals denote like elements and: 
       FIG. 1  is an elevational view of a portable injection molding arrangement removably mounted to an injection molding machine in accordance with the invention; 
       FIG. 2A  is a left side perspective view of a portable injection molding arrangement removably mounted to a standard injection molding machine in accordance with the invention; 
       FIG. 2B  is a right side perspective view of the arrangement shown in  FIG. 1 ; 
       FIG. 3  is a left side perspective view of the framework in the arrangement with various components removed for clarity; 
       FIG. 4  is a right side perspective view of the framework shown in  FIG. 3 ; 
       FIG. 5  is a view of a portable injection molding arrangement having two injection molding units mounted to the upper housing of the injection molding machine; 
       FIG. 6  is a view of a portable injection molding arrangement having an injection molding unit removably mounted to the side housing of the injection molding machine; 
       FIG. 7  is a view similar to  FIG. 1  showing support of the portable injection molding arrangement on a stationary platen of the injection molding machine; 
       FIG. 8  is view similar to  FIG. 1  showing support of the portable injection molding arrangement on a movable platen of the standard injection molding machine; and 
       FIG. 9  is a detailed fragmentary view of the movable and stationary platens of  FIGS. 8 and 9  showing variations in the mounting locations of the portable injection molding arrangement to the platens and showing an adjustment bracket for controlling the amount of cantilever in the mounting arrangement. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIGS. 1–4 , a retrofit injection unit  10  is removably mounted on the platen  12  of a fixed, standard, or commercially available injection molding machine  14 . As is well known, standard injection molding machine  14  includes at least one injection molding unit  16  which cooperates with a mold  18  and injects heated pellets into a mold to produce plastic products of a desired structure. Such machines equipped with one injection molding unit  16  are referred to as single shot molding machines. As explained in the background of the invention, single shot molding machines are limited in their production capability and are being upstaged by multishot machines which are usually custom-built by large press manufacturers. 
   The present invention converts or transforms the standard injection molding machine  14  into a two-shot or multishot machine by means of a unique mounting arrangement in a shorter period of time, and without the enormous cost and long wait of a specially manufactured machine. 
   The retrofit injection unit  10  includes a frame  20  for adjustably supporting at least one commonly purchased injection molding unit  22  and an enclosure  24  for housing the various electrical controls therefore. As seen in  FIGS. 3 and 4 , frame  20  includes a pair of parallel side panels  26 , 28  interconnected by a front cross member  30 , an intermediate cross member  32  and a transverse support wall  34 . The bottom portions of the side panels  26 , 28  define respective longitudinal rails  36 , 38  which are slidably mounted in a set of four longitudinal linear bearings  40 , 42 , 44 , 46  anchored to a rectangular base plate  48 . Extending vertically upward from the side panels  26 , 28  immediately adjacent the support wall  34  is a pair of parallel uprights  50 , 52 . A cross piece  54  joins the uprights  50 , 52  at their upper ends and supports a pair of hydraulic manifolds  56 , 58  associated with the injection molding unit  22 . The electrical enclosure  24  is seated on the rear portions and top edges of the side panels  26 , 28  and behind the uprights  50 , 52 . It should be noted that the retrofit injection unit  10  is conveniently adapted to the standard injection molding machine  14  by removably securing the base plate  48 , such as by fasteners  60 , to the platen  12 . It should also be appreciated that base plate  48  spans the width of the frame  20 , and extends beyond the side panels  26 , 28  in order to provide stability to the add-on equipment. 
   The top portions of the front cross member  30  and intermediate cross member  32  form respective latitudinal rails  62 , 64  upon which a pair of respective latitudinal linear bearings  66 , 68  are slidably mounted. The bearings  66 , 68  underlie the injection molding unit  22  which includes a pair of hydraulic cylinder mounting blocks  70 , 72  coupled together by a tie bar  74  for a purpose to be more appreciated hereafter. The mounting blocks  70 , 72  support a main casting  76  movable upwardly and downwardly along respective cylinder rods  78 , 80  of a pair of carriage cylinders  82 ,  84 . The casting  76  includes a hydraulic motor  86  for driving an injection screw  88  used to deliver thermoplastic pellets through a hopper feed throat  90  to the heater bands  92  of an injection barrel  94 . Heated flowable plastic is periodically injected or “shot” by means of an injector cylinder  96  from a nozzle  98  which is directed to the mold  18  in the standard injection molding machine  14 . This additional “shot” supplied by retrofit injection unit  10  cooperates with the shot provided by the standard injection molding machine  14  to create a multishot machine having multicolor/material molding capability with more features, better quality and less cost than when using separate single shot machines. 
   A salient feature of the present invention resides in the adjustability of the injection barrel  94  along three (x, y and z) axes relative to the standard injection molding machine  14 . As described above, movement of the injection barrel  94  along a vertical or z-axis is provided by means of the carriage cylinders  82 , 84 . To enable adjustment along an x-axis or longitudinally of the standard injection molding machine  14 , a longitudinal lead screw  100  having a nut  102  fixed thereto is threadedly received in a pair of pillow block bearings  104 ,  106  joined to the side panel  26 . The nut  102  is captured in a support block  108  which is connected to the side panel  26  and slides on the linear bearings  40 , 42 . Because the side panels  26 , 28  are joined together, turning a handle  110  on lead screw  100  will move the side panels  26 , 28  and the remainder of frame  20  supporting injection barrel  94  forwardly and rearwardly in a horizontal plane parallel to the platen  12 . To enable adjustment along a y-axis or laterally of the standard injection molding machine  14 , a latitudinal lead screw  112  having a nut  114  fixed thereon is threadedly received in a pair of pillow block bearings  116 , 118  mounted on the top edges of side panels  26 , 28 . The nut  114  is joined directly with the mounting block  72  which is slidably mounted on rail  64 . Because the mounting blocks  70 , 72  are linked together by tie bar  74 , turning of a handle  120  on lead screw  112  will cause the mounting blocks  70 , 72  and the injection molding unit  22  including the injection barrel  94  to traverse from side-to-side in a horizontal plane parallel to its platen  12 . 
   When it is desired to enhance the molding capability of a standard injection molding machine  14 , a crane is used to lift the retrofit injection unit  10  to a flat plane of the platen  12 , and dispose the injection barrel  94  over the mold  18  of the standard injection molding machine  14 . The entire frame  20  is lowered so that the base plate  48  lies flush on the platen  12 , after which fasteners  60  are used to secure the base plate  48  to the housing of the standard injection molding machine  14 . At this point, the various electrical, hydraulic and plastic lines are connected to the injection molding unit  22  and the enclosure  24 . If necessary, the handles  110 , 120  are manipulated to locate the proper x and y coordinates for the injector barrel  94 . Then, the cylinders  82 , 84  are employed to lower the barrel  94  to the proper injection location relative to the die of the standard injection molding machine  14 . 
   Another attractive feature of the present invention is the ability of the retrofit injection unit  10  to be used on other brands of standard injection molding machine  14 . By simply removing the fasteners  60  from the base plate  48 , a crane can be employed to transfer the frame  20  from one standard injection molding machine  14  to another. 
   It should be understood that the retrofit injection unit  10  can be readily supplied to the owner of a standard injection molding machine  14  to increase the versatility of the standard injection molding machine  14 . The present invention has a universal or modular design which permits the retrofit injection unit  10  to be easily installed on any standard injection molding machine  14  regardless of its particular manufacture. As a result, mold changeover is made remarkably convenient and enables the molder to meet the changing demands of customers with superior quality and high production volumes. The present invention creates valuable multishot capabilities which can be used to sequence molding and thus overmold an array of plastic components with various colors, materials, and properties for greater appearance and perceived value. In addition to consolidating several molding operations on one machine, multishot molding can be employed to eliminate assembly operations. For example, a rigid automotive housing can be molded with a soft gasket eliminating secondary handling and assembly. 
   While the invention has been described with reference to a preferred embodiment, those skilled in the art will appreciate that certain substitutions, alterations, and omissions may be made without departing from the spirit thereof. For example, it should be understood that the invention further contemplates that a second injection molding unit  22 ′ ( FIG. 5 ) may be removably mounted to the platen  12  of the standard injection molding machine  14 . In addition, an injection molding unit  22 ″ can be removably mounted to another housing portion such as a side portion  13  of the standard injection molding machine  14 , as shown in  FIG. 6 . In each adaptation, the additional injection molding unit is arranged to cooperate with the mold  18  of the standard injection molding machine  14  to increase the productivity thereof. 
   Referring now to  FIG. 7 , the mold  18  may include a stationary mold portion  18   a  and a movable mold portion  18   b  separable along a parting line  200  through which an injected part is removed. 
   The stationary mold portion  18   a  may be held on a stationary platen  12   a  and the movable mold portion  18   b  may be held on a movable platen  12   b . As is understood in the art, the movable platen  12   b  opposes the stationary platen  12   a  and may be moved as indicated by arrows  202  toward the stationary platen  12   a  so as to position itself, as shown in phantom lines, so that mold portions  18   b  and  18   a  close together. 
   The retrofit injection unit  10  of the present invention may be advantageously mounted on the upper flat surface of the stationary platen  12   a  with the frame  20  positioned so as to locate the injector cylinder  96  and nozzle  98  over the movable mold portion  18   b  when the platens  14   a  and  14   b  are in the closed position with mold portions  18   a  and  18   b  closed. 
   After the mold portions  18   a  and  18   b  closed, the main casting  76  supporting the injector cylinder  96  may be moved downward (as shown in phantom line) by carriage cylinders  82  and  84  so that the nozzle  98  may be engaged with a port in mold  18   b  allowing injection of plastic material into the movable mold portion  18   b  and thus into the mold  18  generally. The hydraulic carriage cylinders  82  and  84  may alternatively be electric drives as is known in the art. 
   Frame  20  may be adjustable using lead screws, as taught above, or may be adjustable by other means, for example, through the use of a set of standard brackets of different sizes, or screws engaging with ones of multiple alignment holes (as will be described below) or by a machinable spacer plate or the like. Critically, the frame  20  allows control of the amount by which the injection cylinder  96  is cantilevered over the mold portions  18   b  and  18   a.    
   In this case, the injector cylinder  96  is cantilevered by the distance necessary to reach over mold portion  18   a  to mold portion  18   b . The electrical enclosure  24  and upright  52  may be positioned above the platen  12   a  so as to counterbalance this cantilever torque. 
   During each cycle of the standard injection molding machine  14 , the injection cylinder must be withdrawn by carriage cylinders  82  and  84  so that the nozzle  98  may disengage from the movable mold portion  18   b , prior to the movable mold portion  18   b  separating from the stationary mold portion  18   b  and the stationary platen  12   a . In addition, the operation of the internal screw of the injection cylinder  96 , which rotates to plasticize the injected material and fill the barrel, and moves axially to effect the injection process, must be controlled in coordination with movement of the mold portions  18 . 
   In this regard, control signals for the hydraulic motor  86  controlling the injection screw of the injector cylinder  96  and the carriage cylinders  82  and  84  are processed by the electronic enclosure  24  which provides interface electronics and communicates standard signals known in the art over an interface cable  210  that may join with a common controller  199  of injection molding unit  16  of the standard injection molding machine  14 . A program running on the common controller  199  (normally custom written for the application) coordinates the actions of the injector cylinder  96  and carriage cylinders  82  and  84  with other components of the standard injection molding machine  14 . 
   The retrofit injection unit  10  may be readily added to any existing machine and quickly integrated into the control process. 
   The kit for adding the retrofit injection unit  10  may optionally include a power source  207  (pump, regulator, and accumulator) for the hydraulic motor  86  and carriage cylinders  82  and  84  (or a stabilized electrical power source for electrical drive equivalents) positioned off the frame  20  (as shown) or over platen  12   a  for additional compactness and to provide counterbalancing torque. The power source  207  may be connected by cable  209  with the electronic enclosure  24  and ultimately with the carriage cylinders  82  and  84  and hydraulic motor  86  associated with the injector cylinder  96 . 
   The platen  12   a  forms a common location to which an additional injection molding unit  22  may be attached for most standard injection molding machines  14  without requiring modification of the underlying standard injection molding machine  14  or additional structure. While the top of the platen  12   a  is a convenient location, other attachment points are also possible. For example, the frame  20  may be attached to a front vertical side of the platen  12  or to the mold  18   a  communicating in turn with the platen  12   a . Because the platen  12  is generally simple and unobstructed, to facilitate attachment of various kinds of molds and runner systems to the platens  12 , the retrofit injection unit  10  can normally be attached to it with very little modification. 
   Attaching the frame  20  to the stationary platen  12   a  eliminates movement of the mass of the retrofit injection unit  10  along the closure axis  206 . Thus, the mass of the retrofit injection unit  10  is of little consequence. However, a disadvantage is that the injector cylinder  96  must be raised and lowered on each cycle of the injection molding machine to allow retreat of the movable mold portion  18   b  from stationary mold portion  18   a . This axial vertical movement of the injector cylinder  96  places repetitive stresses on the attachment of the frame  20  to the platen  12   a  such as may produce fatigue on those elements. In addition, removal of the injector nozzle  28  from the mold portion  18   b  allows excess plastic to encrust the injector nozzle  98  requiring periodic cleaning of the injector nozzle  98  and creating a chance that a molten plastic filament extending from injector nozzle  98  to the mold  18   b  will be drawn, with separation of mold portions  18   b  and  18   a , across the finished part, marring or damaging it. 
   Accordingly, in an alternative embodiment shown in  FIG. 8 , the retrofit injection unit  10  may be affixed to the movable platen  12   b  to move therewith. In this case, the injector nozzle  98  may be continuously engaged with the movable portion of the mold  18   b  during normal cycling of the injection molding machine, reducing the encrusting of the nozzle  98  with plastic, and substantially decreasing the chance that a molten plastic filament would fall across the finished part  212  prior to the part  212  being injected from mold  18   a.    
   Referring now to  FIG. 9 , the frame  20  may include a mounting plate  201  having regularly spaced index holes, selected ones of which are attached to a mounting block  203  by screws  209  to control the cantilever of the injection cylinder and/or its right to left offset. The retrofit injection unit  10  may be attached to the top, or front of the platen  12   b  (or  12   a ), or directly to the mold  18   b  (or  18   a ) as indicated by blocks  203 ,  203 ′ and  203 ″, respectively. In the former cases, for mounting to the movable platen  12   b , the mold  18   b  provides an additional point of stability between itself and the injector nozzle  98  whose continued downward force stabilizes the injector cylinder  96  and does not produce the fatigue associated with varying pressures found in the embodiment of  FIG. 7 . The mass of the retrofit injection unit  10  which must move along the closure axis  206  as indicated by arrows  202  with movement of the platen  12   b  is minimized by placement of the power source  207  off the movable platen  12   b , and also by movement of other components including possibility the electronics enclosure  24  off the movable platen  12   b . Again, the frame  20  may be adjustable as described above, or may be a replaceable or machinable component being part of the retrofitting kit. 
   The foregoing description is meant to be exemplary only, and should not be deemed limitative on the scope of the invention set forth with the following claims.