Abstract:
A two-shot molding system with four independent molding positions at ninety degree intervals allow injection of the first shot, injection of the second shot, cooling, and ejection of the product to occur simultaneously while the mold is closed. Thus, the invention decreases cycle time, increases throughput, and allows for adequate cooling time without delaying injection and ejection.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
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     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
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     BACKGROUND OF THE INVENTION 
     The present invention relates to injection molding machines and methods and, in particular, to an injection molding system that allows for injecting, cooling, and ejecting plastic components in multi-shot injection molding of multicolored or multi-material parts. 
     Injection molding is a manufacturing process in which heated thermoplastic is forced under pressure into a mold. After the thermoplastic cools, the mold is separated along a part line and a molded thermoplastic part is ejected. With the proper mold, complex parts can be manufactured in extremely high volumes and low per-piece costs. 
     Many products that cannot be manufactured by injection molding in a single mold can be assembled from one or more separately molded parts. The step of assembling these parts can significantly increase the cost of the product and in certain cases decrease part volumes otherwise obtainable. 
     For this reason, there is considerable interest in so-called “in-mold” assembly techniques. In one such technique termed “two-shot” molding, a mold having replaceable portions allows different features to be added into one changing mold cavity over several sequential steps of plastic injection. The resulting product may be a single, fused structure or, by making the two shots of plastics that resist adhesion to each other, the resulting product may be an assembled collection of movable parts. 
     In conventional two-shot molding, portions of the mold are rotated. To produce a two-shot plastic part, first one shot of material is injected into a portion of the mold at a first molding station, the mold then opens and rotates portions of the mold 180° carrying parts to a second molding station, and the mold closes again. A second shot is then injected around the first shot at the second molding station to create a plastic part with two colors or materials. Simultaneously, the first shot is injected again at the first molding station. When the mold opens this time, the complete part is ejected at the second molding station. The mold will then rotate and close to repeat the cycle again. The rotary mold technique permits parallel simultaneous injection at the first and second molding stations of both shots. This results in relatively short cycle times, so that production is optimized. 
     To further reduce cycle times, it is known to permit simultaneous injecting and ejecting of plastic components, as described in U.S. Pat. No. 6,790,027 assigned to the assignee of the present invention and incorporated herein by reference. This injection mold provides a three-position, rotary indexing plate assembly which permits simultaneous injecting and ejecting of plastic components. The three stations of injection positions and ejection position are spaced apart in 120° increments and are in a plane perpendicular to the axis along which the molds separate. Core pins, forming the movable part of the molds, rotate along an axis parallel to the separation axis of the molds are also spaced apart in 120° increments and are in the same plane as the mold and ejection positions and rotate to carry parts between the mold positions. 
     This molding technique allowing simultaneous two-shot injecting and ejecting provides only limited cooling in between the time of the second injection until the ejection of the finished product as determined by the time it takes to open the mold, rotate the parts carriers, and close the mold. If additional cooling time is required, the ejection may be delayed until after injection of the subsequent first and second shots, but this negatively impacts cycle time, hence throughput and production efficiency. 
     A significant limitation to this technique described above of multi-station multi-shot injection, is that increasing the number of parts carriers required a significant increase in the mold size. Conventional injection molding machines may not be large enough to house such a mold and may not exert enough pressure on such a mold. 
     SUMMARY OF THE INVENTION 
     The present inventors have realized that for some molded items, additional molding stations and core pins can be accommodated without unduly increasing press size, by rotating the core pins perpendicularly to the axis of mold separation through four positions and by injecting at two successive molding stations separated by 90°. The third molding station can then be used for cooling and the fourth molding station will be advantageously positioned for ejection. Press area is more efficiently used. 
     Specifically, the present invention provides an injection molding system having a turret supporting parts carriers at 90-degree intervals about a longitudinal axis. A first and second mold portion close together along a transverse axis substantially perpendicular to the longitudinal axis to interfit around the turret when the turret is rotated to any of four positions. At each of the four positions, the first and second mold portions interfit with at least two parts carriers on the turret separated by 90 degrees to form corresponding first and second molding cavities for receiving injected plastic. 
     At least one part carrier at each of the four positions may be received by a cooling cavity in at least one of the first and second mold portions. 
     Thus, it is one object of at least one embodiment of the invention to provide a molding system that may cool parts at the same time the plastic is injected. 
     The cooling cavity may provide channels for circulating cooling medium. 
     Thus, it is one object of at least one embodiment of the invention to provide a cooling cavity that may have a cooling medium circulating through it in order to cool the parts and/or the molding system. 
     At least one part carrier at each of the four positions may be exposed outside of the first and second mold portions. 
     Thus, it is one object of at least one embodiment of the invention to provide a position where the parts may be ejected at the same time the plastic is injected. 
     A parts extractor may engage and remove at least one part on a part carrier at each of the four positions of the parts carrier at which the part carrier is exposed outside of the first and second mold portions. 
     Thus, it is one object of at least one embodiment of the invention to allow the parts to be removed by a parts extractor. 
     At least one parts carrier at each of the four positions may be received by a cooling cavity and at least one parts carrier at each of the four positions may be exposed outside of the first and second mold portions for ejection. 
     Thus, it is one object of at least one embodiment of the invention to allow for simultaneous cooling, plastic injection, and ejection, the latter, free from interference with mold structure. 
     The first molding cavity may be formed within the first mold portion only while the second molding cavity may be formed within the first and second mold portions. 
     Thus, it is one object of at least one embodiment of the invention to provide two different station of molding with only a 90-degree separation along an axis perpendicular to the separation of the molds. 
     The turret may support a plurality of parts carriers spaced about a longitudinal axis at 90-degree intervals. 
     Thus, it is one object of at least one embodiment of the invention to allow multiple parts to be molded at each station. 
     The parts carriers may be pins. 
     Thus, it is one object of at least one embodiment of the invention to provide pins that form the inner portion of a part. 
     A first and second runner for transporting plastic may be formed in the mold portions. The first runner may connect to the first molding cavity and the second runner path may connect to the second molding cavity. 
     Thus, it is one object of at least one embodiment of the invention to provide runner paths for transporting plastic to the molding cavities required by the present invention. 
     A second turret may support parts carriers spaced at 90-degree intervals about a longitudinal axis. The longitudinal axis of the second turret may be parallel to the longitudinal axis of the first turret. The first and second mold portions may close together along a transverse axis substantially perpendicular to the longitudinal axis of the second turret to interfit around the second turret when the second turret is rotated to any of four positions. At each of the four positions of the second turret, the mold portions may interfit with at least two parts carriers on the second turret separated by 90 degrees to form corresponding third and fourth molding cavities for receiving injected plastic. 
     Thus, it is one object of at least one embodiment of the invention to provide increased production efficiencies. 
     The direction of rotation of the first turret may be opposite to the direction of rotation of the second turret. 
     It is thus an object of at least one embodiment of the invention to provide symmetrical mold portions, simplifying the construction of runners. 
     A first runner for transporting plastic may connect to the first and third molding cavities and a second runner for transporting plastic may connect to the second and fourth molding cavities. 
     Thus, it is one object of at least one embodiment of the invention to minimize the number of runners and injection nozzles needed to transport plastic to the molding cavities. 
     At least two parts carriers of the first and second turrets may be received by cooling cavities in at least one of the first and second mold portions at each of the four turret positions. The cooling cavities may be in the same mold portion. 
     Thus, it is one object of at least one embodiment of the invention to cool the parts and/or molding apparatus of both turrets. Additionally, it is another object of at least on embodiment of the invention to simplify the cooling structure and provide enhanced cooling properties and possibly thermal balance. 
     At least two parts carriers may be exposed on opposite sides of the first and second mold portions outside of the first and second mold portions at each of the four turret positions. 
     Thus, it is one object of at least one embodiment of the invention to maximize the number of parts exposed outside the mold portions for ejection. 
     The parts carriers may be threaded, the first molding cavity may form an inner portion of a twist-on wire connector, and the second molding cavity may form an outer gripping surface of the twist-on wire connector. 
     Thus, it is one object of at least one embodiment of the invention to provide a mold system that particularly suited to twist-on wire connectors and similar components that have at least one component that may be molded with a two part mold cavity consisting of a core pin and surrounding mold block. 
     These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
    
    
     
       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 top plan view of an injection molding system having two mold portions and two turrets in accordance with an embodiment of the invention; 
         FIG. 2  is a perspective view of the injection molding system of  FIG. 1 , showing positioning of two injection nozzles in accordance with an embodiment of the invention with turret supporting structure removed for clarity; 
         FIG. 3  shows a cross section along a horizontal plane through the injection molding system of  FIGS. 1 and 2 , when the mold portions are in the closed position; and 
         FIG. 4  is a timing diagram showing successive two-shot molding, cooling, and ejecting stages for a molding system in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIGS. 1 and 2 , the injection molding system  10  of the present invention includes a mold portion  12  and mold portion  14 . The mold portion  12  has a cavity side  16 , a left side  18 , a right side  20 , and a rear side  22 . The mold portion  14  has a cavity side  24 , a left side  26 , a right side  28 , and rear side  30 . 
     Generally, the cavity side  16  of mold portion  12  and the cavity side  24  of mold portion  14  close together along a transverse axis of separation  32  as supported by tie rods (not shown) according to methods well known in the art. 
     In the present invention, the mold portion  12  may be connected to a set of push rods  34  extending from hydraulic cylinders  19  attached to the mold portion  12  (or other stationary structure) and extending to attach to an upper turret support bar  36 . A similar structure is positioned below the mold portion  12  to support a lower turret support bar (not shown). 
     The turret support bars hold a left turret  38  rotatable about a vertical axis  39  and a right turret  40  rotatable about a vertical axis  43  as driven by hydraulic motors  44  and  46  respectively. Both turrets  38  and  40  support core pins  42  extending radially from the vertical axes  39  and  40  at 90 degree intervals about the vertical axes  39  and  40 . These core pins  42  are duplicated in vertical rows at each angle extending along the axes  39  and  40 . Importantly, the transverse axis of separation  32  of the mold portions  12  and  14  is perpendicular to the vertical axes of left turret  38  and right turret  40 . 
     A control system  48  is connected by a plurality of control signal lines  50  to the push rods  34  and to the motors  44  and  46  as well as to the other components of the injection molding system  10  to coordinate movement of the turrets  38  and  40  in rotation and translation toward and away from the mold portion  12  as will be described below. 
     Referring now to  FIG. 3 , the left turret  38  and right turret  40  may be incrementally moved to any of four rotation positions  41   a ,  41   b ,  41   c ,  41   d , each separated by 90 degrees. At each of these positions  41 , two core pins  42  (at positions  41   a  and  41   c  as shown) will be perpendicular to the transverse axis of separation  32  to lie along a part line between the stationary mold portions  16  and the mold portion  14 , while two core pins  42  (at positions  41   b  and  41   d  as shown) will extend into the mold portion  12  and mold portion  14  respectively aligned with the transverse axis of separation  32 . 
     Referring again to  FIG. 1 , in any one of these positions  41 , the first mold portion  12  and second mold portion  14  interfit around the left turret  38  and right turret  40  and with core pins  42  to form molding cavities for receiving injected plastic. A set of left first molding cavities  52  and a plurality of right first molding cavities  54  are formed completely within mold portion  14  corresponding to the core pins  42  at positions  41   a  on turrets  38  and  40  respectively. A plurality of left second molding cavities  56  and a plurality of right second molding cavities  58  are formed within both mold portion  14  and stationary mold portion  12  corresponding to the core pins  42  at positions  41   c  on turrets  38  and  40  respectively. 
     Referring also to  FIG. 2 , a first runner path  60  in mold portion  14  transports material from a first injector nozzle  62  positioned behind the movable mold portion and generally aligned with transverse the axis of separation  32  to left first molding cavities  52  and right first molding cavities  54 . A second runner path  64  formed at the interface of the mold portion  14  and mold portion  12  transports material from a second injector nozzle  66  to left second molding cavities  56  and right second molding cavities  58 . 
     Referring still to  FIGS. 1 and 2 , a left cooling cavity  68  and a right cooling cavity  70  are formed within stationary mold portion  12 . The cooling cavities may also be formed in both of the mold portions. In one embodiment of the invention, channel(s)  72  formed within mold portion  12  circulate a cooling medium through the mold portion  12  to aid cooling. A cooling medium may also be circulated through the cooling cavities to aid cooling. 
     Referring again to  FIG. 3 , in one embodiment of the invention, two-shot twist-on wire connectors  74  may be produced having an inner threaded portion  76  of a relative hard plastic material intended to thread onto and twist wire conductors together and an outer grip portion  78  surrounding the inner threaded portion  76  of an elastomeric material intended to provide an improved gripping surface. For this purpose, the core pins  42  have threaded tips defining the threads on the inner threaded portion  76   
     The twist-on wire connectors  74  are produced in four steps corresponding to four molding stations  79   a ,  79   b ,  79   c , and  79   d  defined when the mold portions  12  and  14  are closed along an axis of separation  31 . The first molding station  79   a  is formed by core pins  42  inside of first molding cavities  52  and  54 . The inner portions  76  of the wire-twist-on wire connectors  74  are injected at the first molding station  79   a . Because the core pins  42  must be able to remove the inner portions  76  of the twist-on wire connectors from the unitary molding cavities, sufficient relief must be incorporated into the outer surface of the inner portions  76  of the twist-on wire connectors to allow the molded parts to be withdrawn axially. 
     The second molding station  79   b  is formed by core pins  42 , carrying inner portions  76 , inside of molding cavities  56  and  58 . The outer portions  78  of the twist-on wire connectors  74  are formed at the second molding station  79   b . Here, the molding cavities  56  and  58  are formed from separating parts of mold portions  12  and  14  so axial relief requirements are relaxed. 
     The third molding station  79   c , does not in fact provide molding although this could optionally be performed, and is formed by core pins  42 , carrying completed twist-on wire connectors  74 , inside of cooling cavities  68  and  70 . The completed twist-on wire connectors  74  are cooled at the third molding station  79   c.    
     The fourth molding station  79   d  is formed by core pins  42 , carrying cooled-completed twist-on wire connectors  74 , exposed outside of the mold portions  12  and  14 . The cooled-completed twist-on wire connectors  74  are extracted at the fourth molding station  79   d . Parts extractors  80  (not shown) may remove twist-on wire connector  74  from the core pins  42  by twisting them off. 
     Referring to  FIGS. 3 and 4 , the molding of a given twist-on wire connector  74  associated with a given core pin  42  is completed in a four step cycle  82 ,  84 ,  86 , or  88  comprising the above described steps of a first molding shot step  90   a  at station  79   a , a second molding shot step  90   b  at station  79   b , a cooling step  90   c  at station  79   c  and a ejection step  90   d  at station  79   c . As shown in  FIG. 4  each cycle  82 , associated with a different position  41   a - 41   c  on the turrets  38  and  40  is staggered so that at any given time the first injector nozzle  62  injects material through the first runner path  60  to the molding cavities  52  and  54  to form a plurality of inner portions  76  and a second injector nozzle  66  injects material through second runner path  64  into second molding cavities  56  and  58  to form a plurality of outer portions  78 . 
     In between each step  90 , mold portion  12  moves away from mold portion  14  and push rods  34  extend to move the turrets  38  and  40  away from mold portions  12  and  14 . This removes core pins  42  carrying inner portions  76  from first molding cavities  52  and  54  and core pins  42  carrying inner portions twist-on wire connectors  74  from molding cavities  56  and  58 . 
     Left motor  44  rotates left turret  38  ninety degrees and right turret  40  ninety degrees and push rods  34  retract to move the turrets  38  and  40  towards mold portion  12 . Mold portion  12  moves towards mold portion  14  and closes the mold portions together along axis of separation  31 . 
     In the preferred embodiment of the present invention, injection of inner portions  76 , injection of second outer portion  78 , cooling of twist-on wire connector  74 , and ejection of twist-on wire connector  74  occur simultaneously. Cooling could alternatively occur between the first and second shots. Additionally, a third shot of material could be provided by third molding cavities in place of the cooling cavities  68  and  70 . In another embodiment of the present invention, parts carriers may not be core pins  42  other mold elements well known in the art. 
     The above description of an embodiment of the present invention describes two turrets but the injection molding system  10  may have only one turret. 
     It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.