US 4,828,769 A · Method for injection molding articles

Abstract

Method and apparatus for injection compression molding of thermoplastic parts. A preferred apparatus (100) includes a platen assembly 106, a toggle clamp assembly 102, a screw injection assembly 101, a hydraulic system suitable for providing power to the toggle clamp assembly 102 and the screw injection assembly 101, and a control system 88 for operatively controlling the various hydraulic devices associated with the molding apparatus. The platen assembly 106 provides for a plurality of variable-volume mold cavities 7. In one embodiment, enlarged mold cavities 7 receive plasticized resin from the screw injection assembly 101, and compression of the injected resin is provided by the toggle clamp assembly 102. In another embodiment, the platen assembly 106 includes a floating die assembly wherein pressure created by injected resin causes die inserts 5 and support pillars 15 to slide relative to a molding plate 74. Compression in this embodiment is also preferably provided by the main toggle clamp assembly 102. Preferably, the toggle clamp assembly 102 provides multiple-stage compression of the resin to first redistribute the resin and vent the cavities and, second, compress the resin to compensate for cooling-induced shrinkage thereof. In the multiple cavity embodiment, because all cavities 7 are equally compressed simultaneously, control of the molding process and balancing of the mold are readily accomplished. The method and apparatus are particularly well suited for molding optical lenses and disks. Printed circuit substrates can also be molded thereby.

Claims31

Dependent claims

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.

2 more elements

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.

2 more elements

Dependencies are inferred from the claim text.

Method for injection molding articles

Life of this patent

Method for injection molding articles

Life of this patent

Abstract

Claims31