초록 ▼

In critical surface quality plastic molded articles, especially in optical lenses and disks, an “adaptive”mold cavity is used to automatically control melt pressure and densification during mold packing to within a predetermined range of acceptable values, while normal cycle-to-cycle molding process

In critical surface quality plastic molded articles, especially in optical lenses and disks, an “adaptive”mold cavity is used to automatically control melt pressure and densification during mold packing to within a predetermined range of acceptable values, while normal cycle-to-cycle molding process variations produce a corresponding minor but acceptable change in the molded-part thickness. In multicavity “adaptive”moldsets, permissible cavity-to-cavity imbalance without an overfilled cavity flashing at the parting line is increased. A resilient member (mechanical steel spring or elastomer or hydraulic cylinder) is interposed between the part-forming mold insert surface and the associated clamp plate for that half of the moldset. When the mold is initially closed, a separation distance between the A and B mold insert is less than the molded product specification\s minimum acceptable part thickness. Sufficient volume of injected plastic melt must enter the adaptive mold cavity to cause at least some minimum spring deflection, and thus assure that the resulting molded-part thickness will be somewhere between minimum and maximum thickness tolerances. At maximum acceptable volume of the injected melt, the resilient member is still incompletely compressed. This A-B mold insert second separation distance must also be less than or equal to the maximum acceptable molded-part thickness. The adaptive cavity\s proper self-adjusting performance may be verified by an LVDT.

대표청구항 ▼

An injection molding method of producing plastic molded products having consistently high replication of at least one partforming surface of an adaptive mold cavity enclosed within a moldset wherein first and second opposing mold insert partforming surfaces are wetted by an injected plastic melt, th

An injection molding method of producing plastic molded products having consistently high replication of at least one partforming surface of an adaptive mold cavity enclosed within a moldset wherein first and second opposing mold insert partforming surfaces are wetted by an injected plastic melt, the first mold insert surface located on a stationary half of the moldset and the second mold insert surface located on a movable half of the moldset, the first and second mold insert surfaces forming the mold cavity having a first volume, the first and second mold insert surfaces being separated in a first position by a predetermined first distance which is slightly less than a sum of a desired final part thickness measured at room temperature plus a thermal shrinkage factor characteristic of the plastic, the first mold insert surface being separated a second distance away from a stationary-half clamp plate, and the second mold insert surface being separated a third distance from a movable-half clamp plate while the first and second mold insert surfaces are still in the first position, at least one of the second and third distances being measurably shortened in direct proportion to a melt volume of the injected plastic melt, wherein a resilient member is interposed between at least one of the first and second mold insert surfaces and its clamp plate, the resilient member having a length L2 when mounted in the moldset with inserts in the first position and having a length L4 when fully compressed, and a spring constant which determines its relationship of length to force is unchanged throughout the molding cycle for the resilient member, the method comprising the steps of: a. injecting a greater volume of plastic melt than the first volume into the mold cavity in the first position to partially compress the resilient member to a length L3 which is less than the length L2 but greater than the length L4, at which length L3 the melt packing force onto the second insert equals the opposing spring force of the resilient member; b. holding within the mold cavity substantially all the injected volume and cooling the plastic melt to solidification, thereby reducing its volume and melt packing force, causing reduction in spring force and increase in length, until the moldset is opened for ejection.