Method of and apparatus for injection molding with pressurized fluid assist

A method for the injection molding of a plastic article in an injection molding system including a resin injection nozzle and a mold having an injection aperture for receiving molten resin from the nozzle at an upstream position, a mold cavity at a downstream position and a resin flow path for fluidly communicating the injection aperture and the mold cavity between the upstream and downstream positions, the method comprising the steps of:

• pressurizing a charge of fluid at a predetermined pressure level;
• injecting a quantity of molten plastic from the injection nozzle through the injection aperture and the flow path and into the mold cavity at a nominal plastic injection pressure;
• communicating the charge of pressurized fluid to an orifice opening to the resin flow path in the mold between the upstream and downstream positions;
• introducing the fluid charge into the flow path from the orifice to distribute the molten plastic within the mold cavity;
• preventing the introduced fluid charge from traveling from the flow path, through the injection aperture and into the injection nozzle;
• containing the fluid under pressure within the article until it has set up in the mold cavity;
• and
• venting the fluid to ambient wherein the mold includes valve means movable between fluid open and fluid closed positions, the valve means allowing the fluid charge to travel through the orifice and into the flow path in the fluid open position and preventing the flow of the fluid charge through the orifice and into the flow path in the fluid closed position.

An injection molding system for the injection molding of plastic articles comprising:

• an injection molding machine including an injection nozzle for injecting molten plastic through the nozzle;
• a mold having a resin injection aperture for receiving the molten plastic at an upstream position, a cavity defining the shape of the molded article at a downstream position and a plastic flow path for fluidly communicating the injection aperture and the cavity between the upstream and downstream positions;
• fluid charge means for pressurizing a charge of fluid at a predetermined level;
• and
• fluid circuit means interconnecting the flow path and the fluid charge means between the upstream and downstream positions at an orifice opening to the flow path for introducing the fluid charge into the flow path so that the fluid charge distributes the molten plastic in the mold cavity;
• said fluid means including means for preventing the introduced fluid charge from traveling from the flow path, through the injection aperture and into the nozzle wherein the mold includes a sprue, the sprue having the injection aperture and at least part of the flow path and wherein the fluid circuit means is contained within the sprue and wherein the sprue includes a bushing having the orifice and wherein the injection nozzle communicates with the bushing and the fluid charge is communicated to the orifice in the bushing.