Pneumatically driven, pin velocity controlled injection molding apparatus and method

Abstract

An injection molding apparatus comprising: a pneumatically driven actuator, the piston forming first and second drive chambers, a source of pressurized gas that generates gas flow to the drive chambers, a gas metering mechanism, a controller including programmable instructions that: automatically controllably positions the gas metering mechanism such that the piston or valve pin is disposed or held in one or more selected intermediate positions for a selected period of time during the course of an injection cycle where the tip end of the valve pin restricts flow of injection fluid through the gate to the mold cavity.

What is claimed is: 
     
         1 . A method for molding a plastic part, the method comprising:
 providing a valve gated nozzle including a valve stem interconnected to an actuator movable between an open position and a closed position and one or more intermediate positions between open and closed wherein flow of injection fluid is restricted or reduced to entry into a mold cavity;   the valve gated nozzle comprising a gas metering mechanism comprising one or more shutters or adjustable aperture devices that are mounted on or to or are integral with the actuator and are adjustable to one or more selectable positions that controllably vary the degree of openness of the fluid flow ports,   wherein the one or more shutters or adjustable aperture devices are interconnected to one or more electric motors which are interconnected to a controller and controllable to selectively adjust the shutters or adjustable aperture devices to the one or more selectable positions that correspond to restricted or reduced injection fluid flow rates during the course of at least a selected portion of the stroke length of the valve pin between the open position and the closed position,   controllably operating the gas metering mechanism to cause the valve pin to be disposed or held in one or more selected intermediate positions for a selected period of time during the course of an injection cycle where the tip end of the valve pin restricts flow of injection fluid through the gate to the mold cavity.   
     
     
         2 . The method of  claim 1  wherein the one or more selected intermediate positions are selected to cause the injection fluid to either fill the mold cavity on an upstream cycle of movement of the valve pin or to pack the mold cavity on a downstream cycle of movement of the valve pin. 
     
     
         3 . An injection molding apparatus for controlling velocity or volume of delivery of an injection fluid material through a gate to a cavity of a mold, the apparatus comprising:
 a pneumatically driven actuator comprising a fluid sealed chamber in which a piston is mounted, the piston being interconnected to a valve pin having a tip end,   the piston forming first and second drive chambers within the fluid sealed chamber, each drive chamber having respective fluid flow ports, the piston and valve pin being drivable along a reciprocal path of axial travel having a stroke length that extends between a fully upstream gate open position where unrestricted flow of injection fluid material is enabled through a gate to a mold cavity and a fully downstream gate closed position where the valve pin stops flow of the injection material through the gate to the mold cavity and one or more intermediate positions where flow of injection fluid to the mold cavity is restricted or reduced to entry to a mold cavity,   a source of pressurized gas that generates gas flow at a selected maximum pressure or flow rate,   a gas metering mechanism comprising one or more shutters or adjustable aperture devices that are mounted on or to or are integral with the actuator and are adjustable to one or more selectable intermediate positions that controllably vary the degree of openness of the fluid flow ports,   wherein the one or more shutters or adjustable aperture devices are interconnected to one or more electric motors which are interconnected to a controller and controllable to selectively adjust the shutters or adjustable aperture devices to the one or more selectable positions that correspond to one or more intermediate positions of the valve pin during the course of travel of the valve pin through at least a selected portion of the stroke length,   the controller including programmable instructions that:   automatically controllably positions the gas metering mechanism such that the piston or valve pin is disposed or held in a selected intermediate position for a selected period of time during the course of an injection cycle where the tip end of the valve pin restricts flow of injection fluid through the gate to the mold cavity.   
     
     
         4 . The apparatus of  claim 3  wherein the one or more selected intermediate positions are selected to cause the injection fluid to either fill the mold cavity on an upstream cycle of movement of the valve pin or to pack the mold cavity on a downstream cycle of movement of the valve pin. 
     
     
         5 . A method for controlling velocity or volume of delivery of an injection fluid material through a gate to a cavity of a mold in an injection molding apparatus wherein the apparatus comprises:
 a pneumatically driven actuator comprising a fluid sealed chamber in which a piston is mounted, the piston being interconnected to a valve pin having a tip end,   the piston forming first and second drive chambers within the fluid sealed chamber, each drive chamber having respective fluid flow ports, the piston and valve pin being drivable along a reciprocal path of axial travel between a fully upstream gate open position where unrestricted flow of injection fluid material is enabled through a gate to a mold cavity and a fully downstream gate closed position where the valve pin stops flow of the injection material through the gate to the mold cavity and one or more intermediate positions where flow of the injection fluid is restricted or reduced to the mold cavity,   a source of pressurized gas that generates gas flow at a selected maximum pressure or flow rate,   a gas metering mechanism disposed between the source and one or the other or both of the fluid flow ports of the drive chambers, the gas metering mechanism comprising one or more shutters or adjustable aperture devices that are mounted on or to or are integral with the actuator and are adjustable to one or more selectable positions that controllably vary the degree of openness the fluid flow ports,   the method comprising:   automatically controllably positioning the gas metering mechanism such that the piston or valve pin is driven to be disposed or held in a selected intermediate position for a selected period of time during the course of an injection cycle where the tip end of the valve pin restricts flow of injection fluid through the gate to the mold cavity.   
     
     
         6 . The method of  claim 5  further comprising automatically positioning the gas metering mechanism at a position that effects a high or maximum flow rate or pressure of the pressurized gas that drives the valve pin at a high or maximum pin velocity and automatically positioning the gas metering mechanism at a position that effects a reduced flow rate or pressure of the pressurized gas that drives the valve pin at a reduced pin velocity during the course of at least a selected portion of the stroke length on either an upstream or downstream cycle of travel of the valve pin between the fully upstream gate open position and the fully downstream gate closed position. 
     
     
         7 . The method of  claim 5  wherein the one or more selected intermediate positions are selected to cause the injection fluid to either fill the mold cavity on an upstream cycle of movement of the valve pin or to pack the mold cavity on a downstream cycle of movement of the valve pin.