Method for injection molding articles

Claim 1

A method of forming an article from a molten plasticized thermoplastic resin using an injection molding machine capable of producing a main clamp force, comprising the steps of: (a) forming a mold cavity by adjusting relative positions of an opposing pair of inserts upon which the molded plastic article will be formed, at least one insert being capable of movement relative to the other insert within settable mechanical limits, wherein the dimensions of said mold cavity are determined by the combination of the distance between the machine's movable platen and its fixed platen and said settable mechanical limits, and said inserts are initially separated within the mold cavity to form a pre-enlarged cavity volume greater than a maximum volume occupied at atmospheric pressure by the molten plastic resin to be injected into the cavity, thereby being suitable for receiving the plastic resin without introducing significant back pressure therein since at least some gas volume is provided for in addition to the volume to be occupied by the plastic molten resin; (b) injecting into the mold cavity a volume of the plasticized resin slightly larger than the volume of the article to be formed but insufficient to fill said pre-enlarged mold cavity, said injected resin volume being of at least equal mass as the final molded article at desired dimensions; (c) applying the main clamp force of the injection molding machine before completion of said injection, so as to reduce the volume of the mold cavity, thereby filling said reduced-volume mold cavity and driving out gases through vent means; and (d) maintaining the applied main clamp force until a final clamp lock-up position is reached, thereby compressing the resin until any slight excess resin is forced into pressure relief means and the resin within the further reduced-volume mold cavity solidifies, such that final molded article's desired dimensions are determined by said settable mechanical limits.

Claim 2

A method of forming an article from a molten plasticized thermoplastic resin using an injection molding machine capable of producing a main clamp force, comprising the steps of: (a) forming a mold cavity by adjusting relative positions of an opposing pair of inserts upon which the molded plastic article will be formed, at least one insert being capable of movement relative to the other insert within settable mechanical limits, wherein the dimensions of said mold cavity are determined by the combination of the distance between the machine's movable platen and its fixed platen and said settable mechanical limits, and said inserts are initially separated within the mold cavity to form a pre-enlarged cavity volume greater than a maximum volume occupied at atmospheric pressure by the molten plastic resin to be injected into the cavity, thereby being suitable for receiving the plastic resin without introducing significant back pressure therein since at least some gas volume is provided for in addition to the volume to be occupied by the plastic molten resin; (b) injecting into the mold cavity a volume of the plasticized resin slightly larger than the volume of the article to be formed but insufficient to fill said pre-enlarged mold cavity, said injected resin volume being of at least equal mass as the final molded article at desired dimensions; (c) applying the main clamp force of the injection molding machine before completion of said injection, so as to reduce the volume of the mold cavity, thereby filling said reduced-volume mold cavity and driving out gases through vent means; and (d) maintaining the applied main clamp force until a final clamp lock-up position is reached, thereby compressing the resin until any slight excess resin is forced into pressure relief means and the resin within the further reduced-volume mold cavity solidifies, such that final molded article's desired dimensions are determined by said settable mechanical limits.

Claim 11

A method of forming a plurality of articles from a molten plasticized thermoplastic resin using an injection molding machine having first and second mold platens, first and second parting line mold plates, a plurality of first mold inserts operatively disposed within the first parting line mold plate, and a plurality of second mold inserts operatively disposed within the second parting line mold plate, wherein the first and second mold plates and first and second mold inserts are respectively commonly supported by the first and second mold platens, the method comprising: (a) forming a plurality of mold cavities by adjusting relative positions of opposing pairs of inserts upon which the molded plastic article will be formed, at least one insert being capable of movement relative to the other insert within settable mechanical limits, wherein the dimensions of said mold cavities are determined by the combination of the distance between the machine's movable platen and its fixed platen and said settable mechanical limits, and said inserts are initially separated within the mold cavities to form pre-enlarged cavity volumes greater than a maximum volume occupied at atmospheric pressure by the molten plastic resin to be injected into the cavities, thereby being suitable for receiving the plasticized resin without introducing significant back pressure therein since at least some gas volume is provided for in addition to the volume to be occupied by the plastic molten resin; (b) injecting into each mold cavity a a volume of the plasticized resin slightly larger than the volume of the article to be formed but insufficient to fill said pre-enlarged mold cavities, said injected resin volume bing of at least equal mass as the final molded article at desired dimensions; (c) commonly and simultaneously applying the main clamp force of the injection molding machine before completion of said injection, so as to reduce the volumes of the mold cavities, thereby filling said reduced-volume mold cavities and driving out gases through vent means; and maintaining the applied main clamp force until a final clamp lock-up position is reached, thereby compressing the resin until any slight excess resin is forced into pressure relief means and the resin within the further reduce-volume mold cavities solidifies, such that final molded article's desired dimensions are determined by said settable mechanical limits.

Claim 12

A method of forming a plurality of articles from a molten plasticized thermoplastic resin using an injection molding machine having first and second mold platens, first and second parting line mold plates, a plurality of first mold inserts operatively disposed within the first parting line mold plate, and a plurality of second mold inserts operatively disposed within the second parting line mold plate, wherein the first and second mold plates and first and second mold inserts are respectively commonly supported by the first and second mold platens, the method comprising: (a) forming a plurality of mold cavities by adjusting relative positions of opposing pairs of inserts upon which the molded plastic article will be formed, at least one insert being capable of movement relative to the other insert within settable mechanical limits, wherein the dimensions of said mold cavities are determined by the combination of the distance between the machine's movable platen and its fixed platen and said settable mechanical limits, and said inserts are initially separated within the mold cavities to form pre-enlarged cavity volumes greater than a maximum volume occupied at atmospheric pressure by the molten plastic resin to be injected into the cavities, thereby being suitable for receiving the plasticized resin without introducing significant back pressure therein since at least some gas volume is provided for in addition to the volume to be occupied by the plastic molten resin; (b) injecting into each mold cavity a a volume of the plasticized resin slightly larger than the volume of the article to be formed but insufficient to fill said pre-enlarged mold cavities, said injected resin volume bing of at least equal mass as the final molded article at desired dimensions; (c) commonly and simultaneously applying the main clamp force of the injection molding machine before completion of said injection, so as to reduce the volumes of the mold cavities, thereby filling said reduced-volume mold cavities and driving out gases through vent means; and maintaining the applied main clamp force until a final clamp lock-up position is reached, thereby compressing the resin until any slight excess resin is forced into pressure relief means and the resin within the further reduce-volume mold cavities solidifies, such that final molded article's desired dimensions are determined by said settable mechanical limits.