Abstract:
An injection molding system includes a manifold and a valve gated hot runner nozzle. The gating mechanism includes an actuated valve pin, where the mold gate orifice is open when the valve pin is in a first position to allow melt to flow there through. The mold gate orifice is closed when the valve pin is in a second position to prevent melt from flowing there though. A flow control pin is disposed within the melt stream, either coaxially with the valve pin within the melt channel of the nozzle or within the manifold melt channel. The flow control pin has a head with a complementary geometry with that of the melt channel at a flow control surface. The flow control pin is raised and lowered by an actuation mechanism to constrict or release the flow of the melt stream independent from the movement of the valve pin.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of provisional application 60/446,997, filed Feb. 13, 2003, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to injection molding technology, and more particularly to the dynamic control of the amount of plastic injected per injection cycle. 
     2. Background of the Invention 
     Injection molding of plastic parts is a common manufacturing practice. Various articles of commercial value such as plastic bottles, toothbrushes, and children&#39;s toys, are made using well-known injection molding techniques. Injection molding generally involves melting plastic then forcing the melt stream at high temperatures and pressures through one or more gates into a mold cavity. The melt cools in the shape of the mold cavity, which is opened to eject the finished part. 
     A valve gated injection molding apparatus is well known, as shown and described in U.S. Pat. No. 4,380,426 to Gellert, incorporated herein in its entirety by reference thereto. Usually a valve pin has a cylindrical or tapered front end and reciprocates between a retracted open position and a forward closed position in which the front end is seated in a gate. In some applications, the valve pin functions in the reverse direction and closes in the retracted position. 
     Valve-gated mechanisms are, however, typically designed to open and close the gates in a binary fashion, i.e., the gate is either opened or it is closed without allowing for a partially opened scenario in which the melt flow rate or amount is controlled through the gate. In some manufacturing processes, the ability to control the melt stream during the shot is highly desirable. For example in a multi-gated system in which a single mold cavity is fed melt through multiple gates, a common manifold serves all of the gates. However, a “knit line” is formed at the interface where melt flowing from one gate meets melt flowing from another gate. Even though all of the gates are commonly fed, the ability to control the flow rate through each gate individually allows the designer to control the location of the knit line for structural or aesthetic purposes. 
     Another instance in which control over the melt stream flow is desirable is when a number of parts are simultaneously molded. Each mold cavity is fed melt by an individual gate. However, the mold cavities are not necessarily all the same size, such as when components of an interlocking piece are simultaneously molded, as in the sections of a cellular telephone casing or the base and cover of a packaging system. The common melt stream is important so that the plastic characteristics are as uniform as possible between the mold cavities; however, as the mold cavities are not of a uniform size, one mold cavity customarily takes longer to fill than the other(s). However, if the larger mold cavity is filled more quickly, then both molded parts would be ready for ejection from its respective mold cavity at the same time. 
     Various methods exist in the art to provide this type of control over the melt stream. The gates could be individually re-tooled for every new product, but this is expensive and time-consuming. U.S. Pat. No. 5,556,582 to Kazmer et al., incorporated herein in its entirety by reference thereto, describes a system wherein multiple adjustable valve pins are located each in its respective gate within a manifold, wherein each gate is fluidly connected to a common mold cavity. Each valve pin can be dynamically adjusted by a computer according to pressure data read at or near the injection point into the mold. Each valve pin has a tapered head and each melt channel has a complementary geometry, such that the melt stream is slowed to an eventual full stop. 
     Another system is described in U.S. Patent Application Publication No. 2002/0121713 to Moss et al., incorporated herein in its entirety by reference thereto. In this publication, a valve pin is located in the manifold, with a tapered valve pin head disposed at the inlet point to a hot runner nozzle. The melt channel at the inlet point has a corresponding geometry to the tapered pin head, such that when the pin head is pushed into the inlet, the melt stream slows to an eventual stop. 
     Yet another system is described in WIPO PCT publication WO 01/21377 to Kazmer et al., incorporated herein in its entirety by reference thereto. In this publication, the manifold includes “shooting pot” technology. A portion of the melt stream is diverted from the manifold melt channel into a separate compartment or “well”. Disposed within this well is an actuated ram, which can be positioned to seal the opening of the well. A nozzle is located downstream of the well. The flow of melt through a mold gate orifice is controlled by an actuated valve pin. When the melt stream is introduced into the manifold melt channel, the valve pin is seated within the mold gate orifice to prevent flow into a mold cavity. The ram is located in a retracted position so that a volume of melt from the melt stream may be diverted into the well and contained therein. To start the shot, a gating mechanism located upstream from the well closes the melt channel, thereby preventing the introduction of new melt into the well. The valve pin is unseated from the mold gate orifice, and the ram is moved forward at a first velocity to force melt into the mold cavity. A system of pressure sensors measures the pressure in the system and compares that pressure reading to a target pressure profile. If greater pressure is required, the ram velocity is increased. Alternatively, if lesser pressure is required, the ram velocity is slowed. When the ram reaches its lowermost position, the mold cavity is full, and the mold gate orifice is closed. Through this manipulation of the ram velocity, the flow rate of the melt stream can be controlled. This control over the melt stream requires completely closing off one portion of the melt channel in order to manipulate the melt stream in another portion thereof. 
     However, none of these systems provides the ability to control the melt stream such that the flow rate and amount are controlled separately from the traditional gating shut-off functions without causing a secondary interruption of the melt stream. A simplified mechanism to achieve a finer gradation of control over the flow of melt can improve the efficiency of the system, saving the manufacturer time and money. 
     SUMMARY OF THE INVENTION 
     The present invention is an injection molding apparatus including an injection molding manifold having a plurality of melt channels that are in communication with a plurality of hot runner nozzles. Each hot runner nozzle has a melt channel and communicates with a mold cavity or a portion of a mold cavity via a mold gate. A movable valve pin is used in cooperation with each nozzle to either permit or prevent the transfer of a molten material from the nozzle melt channel into the mold cavity. The valve pins further function to regulate the amount of molten material entering each mold cavity. An additional flow control pin is used to independently regulate the amount of molten material injected into each mold cavity when the valve pin is in the open position. The flow control pin is located in the melt channel of either the nozzle or the manifold. Injection molding processing sensors such as thermocouples and pressure sensors are placed along the manifold melt channels, the nozzle melt channels and/or in the mold cavity to provide temperature, viscosity and/or pressure information to a mold controller linked to the actuation mechanisms of the valve pins and the flow control pins. The position of the flow control pin is adjusted before or during the injection molding process based on processing data gathered by the processing sensors. 
     In one embodiment, of the present invention, each mold cavity is fluidly connected to only one hot runner nozzle wherein each mold cavity has substantially the same size and shape. In another embodiment, each mold cavity is fluidly connected to one hot runner nozzle wherein each mold cavity is not of the same size and shape. In yet another embodiment, several nozzles are fluidly connected to the same mold cavity via separate mold gates. In each of these embodiments, there is a need to control independently the amount of melt fed through each nozzle and through each mold gate to produce better molded parts in terms of weight and/or knit lines. 
     Accordingly, disclosed herein is an injection molding system wherein multiple levels of control can be attained over the melt stream. In an embodiment, a valve-gated nozzle is fed melt from a manifold. The gating mechanism includes an actuated valve pin, where the mold gate orifice is open when the valve pin is in a first position to allow melt to flow there through. The mold gate orifice is closed when the valve pin is in a second position to prevent melt from flowing there through. In addition, a flow control pin is disposed coaxially with the valve pin within the melt channel of the nozzle. The flow control pin has a head with a complementary geometry with that of the melt channel. The flow control pin is raised and lowered by an actuation mechanism to constrict or release the flow of the melt stream. The movement of the flow control pin could be pre-programmed or could be dynamically triggered using pressure and temperature sensors at or near the nozzle. The valve pin and the flow control pin are independently actuated. 
     In another embodiment of the present invention, a valve-gated nozzle is fed melt from a manifold. The mold gate orifice includes an actuated valve pin, where the mold gate orifice is open when the valve pin is in a first position to allow melt to flow there through. The mold gate orifice is closed when the valve pin is in a second position to prevent melt from flowing there through. A flow control pin is located in the manifold melt channel, offset from the melt channel of the nozzle. The flow control pin has a head with a complementary geometry with that of the manifold melt channel. The flow control pin is raised and lowered by an actuation mechanism to constrict or release the flow of the melt stream. The movement of the flow control pin could be pre-programmed or could be dynamically triggered using pressure and temperature sensors at or near the nozzle. The valve pin and the flow control pin are independently actuated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
       The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. 
         FIG. 1  shows a sectional schematic view of an injection molding system according to a first embodiment of the present invention, where the flow is constrained and the mold gate orifice is open. 
         FIG. 2  shows an enlarged view of the nozzle of  FIG. 1 . 
         FIG. 3  shows a sectional schematic view of an injection molding system according to a first embodiment of the present invention, where the flow is not constrained and the mold gate orifice is closed. 
         FIG. 4  shows an enlarged view of the nozzle of  FIG. 3 . 
         FIG. 5  shows a sectional schematic view of an injection molding system according to a second embodiment of the present invention, where the flow is constrained and the mold gate orifice is open. 
         FIG. 6  shows a sectional schematic view of an injection molding system according to the second embodiment of the present invention, where the flow is not constrained and the mold gate orifice is closed. 
         FIG. 7  shows a sectional schematic view of an injection molding system according to a third embodiment of the present invention, where the flow is constrained and the mold gate orifice is open. 
         FIG. 8  shows a sectional schematic view of an injection molding system according to the third embodiment of the present invention, where the flow is not constrained and the mold gate orifice is closed. 
         FIG. 9  shows a sectional schematic view of an injection molding system according to a fourth embodiment of the present invention, where the flow is constrained and the mold gate orifice is open. 
         FIG. 10  shows a sectional schematic view of the injection molding system according to the fourth embodiment of the present invention, where the flow is not constrained and the mold gate orifice is closed. 
         FIG. 11A  shows an enlarged view of the nozzles of the injection molding system according to the first embodiment of the present invention in a first application, where the nozzles are in a first configuration. 
         FIG. 11B  shows an enlarged view of the nozzles of the injection molding system according to the first embodiment of the present invention in a first application, where the nozzles are in a second configuration. 
         FIG. 12A  shows an enlarged view of the nozzles of the injection molding system according to the first embodiment of the present invention in a second application, where the nozzles are in a first configuration. 
         FIG. 12B  shows an enlarged view of the nozzles of the injection molding system according to the first embodiment of the present invention in a second application, where the nozzles are in a second configuration. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Specific embodiments of the present invention are now described with reference to the figures, where like reference numbers indicate identical or functionally similar elements. 
     Referring now to  FIG. 1 , a first embodiment of the invention is described. An injection molding system  100  includes a manifold  102  and a plurality of nozzles, such as nozzle  104 . Nozzle  104  is a valve-gated hot runner nozzle, with a heater  127  and a thermocouple  128 . 
     A manifold melt channel  106  is disposed within manifold  102  and conveys melt to a plurality of nozzle channels, such as for example nozzle melt channel  107 , which further conveys the melt through a gate  108  into mold cavity  109 . In this embodiment, there are several mold cavities, such as for example mold cavity  109 , of equal or almost equal size and shape in communication with several nozzles (not shown), such as nozzle  104 . Each cavity has a single mold gate  108 . The present invention allows multiple cavities of equal size to be filled in the same cycle or time period by “balancing” the melt flow through manifold  102 , as will be explained in further detail below. 
     As gate  108  is a valve gate, the front portion of a valve pin  110  is disposed within nozzle melt channel  107 . Valve pin  110  extends through a portion of manifold melt channel  106  to a valve pin actuation mechanism  112 , which is disposed longitudinally above manifold  102 . Gate  108  allows the flow of melt into mold cavity  109 . In a first position, valve pin  110  is retracted from gate  108  by operation of valve pin actuation mechanism  112  to allow melt to flow through gate  108  into mold cavity  109 . In a second position, shown in  FIGS. 3 and 4 , valve pin  110  is seated within gate  108  by operation of valve pin actuation mechanism  112  to prevent the flow of melt into mold cavity  109 . 
     Valve pin actuation mechanism  112  includes a piston  113  driven by any of the various actuation driving mechanisms known in the art, including but not limited to pneumatic, hydraulic, or cam and lever devices. A pneumatic driving system operates by linking an external air source to the piston driving mechanism with valves controlled by a timing circuit which applies and releases the pressure in a repetitive timed sequence in conjunction with the application of pressure to the melt from the molding system. A hydraulic driving system operates in the same manner as the pneumatic system, only hydraulic fluid is substituted for air. 
     In an alternate embodiment, a bladder piston, as shown and described in the co-pending U.S. Appl. No. 60/363,891 filed on Mar. 14, 2002 by the same assignee which is incorporated herein in its entirety by reference thereto, may be used. A bladder piston is an expandable and elongated bag which shortens in length when filled with a pressurized fluid like air, water, or oil. One end of the bladder is affixed to a valve pin such that, as the bladder is pressurized, it contracts in length and the valve pin is unseated from the mold gate orifice, which allows the melt to flow into the mold cavity. Similarly, depressurizing the bladder causes the bladder to increase in length, which seats the valve pin in the mold gate orifice and stops the flow of the melt into the mold cavity. 
     Valve pin actuation mechanism  112  can be controlled in a variety of ways. Preferably, one or more pressure transducers  125  are linked to servo valve  123 . Servo valve  123  is linked to the driving mechanism (not shown). When the pressure inside the system, as measured by pressure transducers  125 , reaches a first level, servo valve  123  switches so that fluid or air from the driving mechanism can flow to valve pin actuation mechanism  112 , causing piston  113  to move valve pin  110  within gate  108 . When pressure in the system is measured by pressure transducers  125  to be a second level, servo valve  123  switches so that fluid or air from the driving mechanism is shut off, causing piston  113  to retract valve pin  110  from gate  108 . 
     Alternatively, valve pin actuation mechanism  112  may be controlled by mechanisms other than servo valve  123 . For example, in one embodiment, valve pin actuation mechanism  112  may be controlled by a computer that follows a pre-determined cycle. The computer signals circuitry connected to the driving mechanism according to the cycle, and the circuitry then triggers the driving mechanism, and piston  113  is driven up or down. Accordingly, rather than controlling valve pin  110  by servo valve  123  movement based on pressure readings, the computer controlled arrangement is based on the timing of each cycle. 
     Disposed within nozzle melt channel  107  is a flow control pin  114 . As with valve pin  110 , flow control pin  114  extends through a portion of manifold melt channel  106  to a flow control pin actuation mechanism  117 . Flow control pin actuation mechanism  117  is located between manifold  102  and valve pin actuation mechanism  112 , although the relative position of actuation mechanisms  112 ,  117  could easily be reversed. Flow control pin  114  is in one embodiment a sleeve which coaxially surrounds valve pin  110 , as shown in  FIG. 1 , although pins  110  and  114  could also simply run parallel to one another within a larger diameter nozzle melt channel  107 . 
     Flow control pin  114  enables control of the amount of melt passing through nozzle  104  independent of the functioning of valve pin  110 . To achieve this purpose, flow control pin  114  includes a flow control surface  116 , a head disposed at the terminal end of flow control pin  114  within nozzle  104 . In the embodiment of  FIG. 1 , flow control surface  116  has a larger diameter than that of the shaft of flow control pin  114 , and the distal end of flow control surface  116  has a tapered geometry. Nozzle melt channel  107  has a complementary geometry at a flow control surface  120 . 
     In a first position, shown in  FIGS. 1 and 2 , flow control surface  116  is positioned at or near flow control surface  120 . Due to the complementary geometry of surface  116  and nozzle melt channel  107  at surface  120 , surface  116  constricts the flow of melt through nozzle melt channel  107  to decrease the volume of melt thereby decreasing the flow of material to gate  108 . In a second position, shown in  FIGS. 3 and 4 , flow control surface  116  is positioned away from flow control surface  120  so that the flow of melt through nozzle melt channel  107  is not constricted. Intermediate positioning of flow control surface  116 , where the flow of melt through nozzle melt channel  107  is only partly constricted, is also possible. 
     Flow control pin actuation mechanism  117 , like valve pin actuation mechanism  112 , is a piston  118  driven by any of the actuation driving mechanisms known in the art, such as pneumatic, hydraulic, cam and lever devices, or bladder pistons. Flow control actuation mechanism  117  is controlled as described above with respect to valve pin actuation mechanism  112 . Flow control actuation mechanism  117  can be controlled in a variety of ways. Preferably, one or more pressure transducers  124  are linked to servo valve  122 . Servo valve  122  is linked to the driving mechanism (not shown). When the pressure inside the system, as measured by pressure transducers  124 , reaches a first level, servo valve  122  switches so that fluid or air from the driving mechanism can flow to flow control actuation mechanism  117 , causing piston  118  to move flow control pin  110  towards flow control surface  120 . When pressure in the system is measured by pressure transducers  124  to be a second level, servo valve  122  switches so that fluid or air from the driving mechanism is shut off, causing piston  118  to retract flow control pin  114  away from flow control surface  120 . 
     Alternatively, flow control actuation mechanism  117  may be controlled by mechanisms other than servo valve  122 . For example, in one embodiment, flow control actuation mechanism  117  may be controlled by a computer that follows a pre-determined cycle. The computer signals circuitry connected to the driving mechanism according to the cycle, and the circuitry then triggers the driving mechanism, and piston  118  is driven up or down. Accordingly, rather than controlling flow control pin  114  by servo valve  122  movement based on pressure readings, the computer controlled arrangement is based on the timing of each cycle. 
     In addition to pressure information controlling flow control pin  114 , in another embodiment of the present invention temperature information may also be used to control flow control pin  114  and therefore adjust the position of flow control pin  114 . Further, in addition to thermocouple  128 , injection molding system  100  may include additional temperature sensors (not shown) to help control of melt flow. 
     The geometry of nozzle melt channel  107  is shown in  FIGS. 1 and 2  to have a slightly larger diameter in the region of flow control surface  116 , i.e., the nozzle melt channel expands and then tapers back to the original diameter at a lower end of flow control surface  120 . This geometry allows flow control surface  116 , which has a larger diameter than the rest of flow control pin  114 , to move freely within nozzle melt channel  107 . However, many different geometries are contemplated by the present invention. For example, the nozzle melt channel  107  may have a first diameter which is greater than the diameter of the flow control surface  116  which tapers at flow control surface  120  to a second diameter. 
     Referring now to  FIGS. 5–6 , a second embodiment of the present invention is shown. Injection molding system  500  includes a manifold  502  and a nozzle  504 . Nozzle  504  is a valve-gated hot runner nozzle. Injection molding system  500  further includes a thermocouple  528 . 
     A manifold melt channel  506  is disposed within manifold  502  and conveys melt to a nozzle melt channel  507 , which further conveys the melt through gate  508  into mold cavity  509 . 
     The shaft of a valve pin  510  extends through a portion of manifold melt channel  506  to a valve pin actuation mechanism (not shown), which is disposed longitudinally above manifold  502 . Gate  508  controls the flow of melt into mold cavity  509 . In a first position, valve pin  510  is unseated from gate  508  by operation of the valve pin actuation mechanism to allow melt to flow through gate  508  into mold cavity  509 . In a second position, shown in  FIG. 6 , valve pin  510  is seated within gate  508  by operation of the valve pin actuation mechanism to prevent the flow of melt into mold cavity  509 . 
     The actuation of valve pin  510  and the functioning, variations, and control of the valve pin actuation mechanism may be any of the systems as described above with respect to the first embodiment, for example utilizing a transducer  524  and a servo valve  523 . 
     Disposed within manifold melt channel  506  is a flow control pin  514 . The shaft of flow control pin  514  extends through a portion of manifold melt channel  506  to a flow control pin actuation mechanism  517 . Flow control actuation mechanism  517  is located between manifold  102  and the valve pin actuation mechanism (not shown), although their relative positions could easily be reversed. 
     Flow control pin  514  enables control of the flow of melt passing through nozzle  504  independent of the functioning of valve pin  510 . To achieve this purpose, flow control pin  514  includes a flow control surface  516 , a head disposed at the terminal end of flow control pin  514  within manifold  502 . Flow control surface  516  has a larger diameter than that of the shaft of flow control pin  514 , and the distal end of flow control surface  516  has a tapered geometry. Manifold melt channel  507  has a complementary geometry at a flow control surface  520 . 
     In a first position, shown in  FIG. 5 , flow control surface  516  is positioned at or near flow control surface  520 . Due to the complementary geometry of surface  516  and manifold melt channel  506  at surface  520 , surface  516  constricts the flow of melt through manifold melt channel  507 . In a second position, shown in  FIG. 6 , flow control surface  516  is positioned away from flow control surface  520  so that the flow of melt through manifold melt channel  506  is not constricted. Intermediate positioning of flow control surface  516 , where the flow of melt through manifold melt channel  506  is only partially constricted, is also possible. 
     As shown in  FIG. 5 , manifold melt channel  506  leads away from flow control surface  520  at an angle. This offset configuration allows for an optional second manifold melt channel  506 A to be added to the system so that a second nozzle ( 504 ) may be flow controlled simultaneously with nozzle  504 . However, the present invention is not limited to this geometry, and nozzle melt channel  507  may be disposed in a collinear arrangement with manifold melt channel  506 . With this arrangement, flow control pin  514  would have the sleeve-like configuration as described above with respect to the first embodiment. 
     As described above with respect to the first embodiment, flow control pin actuation mechanism  517 , is a piston  518  driven by any of the actuation driving mechanisms known in the art, such as pneumatic, hydraulic, cam and lever devices, or bladder pistons. Flow control actuation mechanism  517  is controlled as described above with respect to the first embodiment. 
       FIGS. 7 and 8  show another embodiment of the present invention, depicting another possible arrangement of a valve pin  710  and an independently actuated flow control pin  714  within an injection molding system  700 . In this embodiment, valve pin  710  is laterally offset with respect to actuated flow control pin  714  and at an angle α therewith.  FIG. 7  shows valve pin  710  in a first position, unseated from gate  708  to allow melt to flow through gate  708  into mold cavity  709 .  FIG. 8  shows valve pin  710  seated within gate  708  to prevent the flow of melt into mold cavity  709 . System  700  functions similarly as described above with respect to the first and second embodiments, for example utilizing transducers  724  and  725 , a servo valve  722 , and a thermocouple  728 . 
       FIGS. 9 and 10  show another embodiment of the present invention, depicting another possible arrangement of a valve pin  910  and an independently actuated flow control pin  914  within an injection molding system  900 . Valve pin  910  and independently actuated flow control pin  914  are positioned in the same configuration as shown in  FIG. 1 , except that the servo valve ( 922 ) for controlling valve pin  910  has been eliminated.  FIG. 9  shows valve pin  910  in a first position, unseated from gate  908  by operation of valve pin actuation mechanism  912  to allow melt to flow through gate  908  into mold cavity  909 .  FIG. 10  shows valve pin  910  seated within gate  908  by operation of valve pin actuation mechanism  912  to prevent the flow of melt into mold cavity  909 . 
     System  900  functions similarly as described above with respect to the first and second embodiments, for example utilizing a transducer  924 , a servo valve  922 , and a thermocouple  928 , except that valve pin actuation mechanism  912  is controlled by a method other than a servo valve. As previously mentioned, valve pin actuation mechanism  912  may be controlled by a computer that follows a pre-determined cycle. The computer would signal circuitry connected to the driving mechanism according to the cycle, and the circuitry would trigger the driving mechanism, and piston  913  would be driven up or down. Alternatively, valve pin actuation mechanism  912  may be controlled by an operator who manually triggers the driving mechanism. 
       FIGS. 11A and 11B  show an application of the present invention wherein multiple nozzles  1104   a  and  1104   b  are feeding one large mold cavity  1109 . Valve pins  1110   a  and  1110   b  and independently actuated flow control pins  1114   a  and  1114   b  are positioned in the same configuration as shown in  FIG. 1 , and function similarly as described above with respect to the first and second embodiments. In this embodiment of the present invention, the positions of valve pins  1110   a  and  1110   b  and flow control pins  1114   a  and  1114   b  are controlled in such as manner to produce an acceptable knit line where the melt from each nozzle  1104   a  and  1104   b  meets within mold cavity  1109 .  FIG. 11A  shows valve pin  1110   a  unseated from gate  1108   a  to allow melt to flow through gate  1108   a  into mold cavity  1109 , while valve pin  1110   b  is seated within gate  1108   b  to prevent flow of melt into mold cavity  1109 . In  FIG. 11B , valve pin  1110   a  is seated within gate  1108   a  to prevent the flow of melt into mold cavity  1109 , while valve pin  1110   b  is unseated from gate  1108   b  to allow melt to flow through gate  1108   b  into mold cavity  1109 . It would be understood to one of ordinary skill in the art that each valve pin and flow control pin are independently actuated to controllably regulate the flow of the melt to achieve optimal molding conditions within the mold cavity and thereby produce an improved molded part. 
       FIGS. 12A and 12B  show another application of the present invention wherein a first nozzle  1204   a  is feeding a first mold cavity  1209   a  and a second nozzle  1204   b  is simultaneously feeding a second cavity  1209   b  of a different size than first cavity  1209   a.  Valve pins  1210   a  and  1210   b  and independently actuated flow control pins  1214   a  and  1214   b  are positioned in the same configuration as shown in  FIG. 1 , and function similarly as described above with respect to the first and second embodiments. Multiple cavities of different sizes may be filled in the same cycle or time period due to the flow control provided by valve pins  1210   a  and  1210   b  and flow control pins  1214   a  and  1214   b.  Each of the valve and flow control pins are independently actuatable to provide balancing of the melt flow from manifold  102  through each respective nozzle and into the respective mold cavities. 
       FIG. 12A  shows valve pin  1210   a  unseated from gate  1208   a  to allow melt to flow through gate  1208   a  into first cavity  1209   a,  while valve pin  1210   b  is seated within gate  1208   b  to prevent flow of melt into second cavity  1209   b . In  FIG. 12B , valve pin  1210   a  is seated within gate  1208   a  to prevent the flow of melt into first cavity  1209   a,  while valve pin  1210   b  is unseated from gate  1208   b  to allow melt to flow through gate  1208   b  into second cavity  1209   b.    
     While in  FIGS. 11A ,  11 B,  12 A, and  12 B, one valve pin is shown seated and the other valve pin is shown unseated, it should be understood that both valve pins may simultaneously be seated or unseated dependent on the molding conditions, and that each valve pin is actuatable to control flow of melt from the nozzle channel to the mold cavity at various intermediate positions. 
     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.