Lens thickness adjustment method and apparatus in a thermoplastic injection mold for ophthalmic finished spectacle lenses

An injection mold apparatus for molding thermoplastic vision-corrective spectacle lens, said injection mold having a mechanism determining a preset fixed thickness of said lens being of a finished single vision family of differing optical magnification powers by precisely adjusting and then locking into a fixed position said mechanism without removing said injection mold mounted onto a clamping platen of an injection molding machine nor disassembling said injection mold, the apparatus comprising:

• a. said injection mold having a plurality of mold cavities formed between two moldhalves which open and close about a parting line, with each moldhalf housing a plurality of opposing pairs of curved optically polished mold inserts, each of said inserts having a curved optically polished surface facing into said mold cavity and each of said inserts having a substantially planar back surface which faces away from said mold cavity,
• said insert optically polished surface facing into said mold cavity being of specified surface curvatures and said opposing pair of mold inserts thereby forming partforming surfaces of said mold cavity,
• said insert back surface being mechanically supported against a substantially mating planar face of a loadbearing support assembly which in turn is capable of transmitting mechanical forces from said insert within said moldhalf to said clamping platen of said injection molding machine, such that melt pressures which may be exerted upon said partforming surfaces of said mold cavity after being filled by injection are ultimately supported by a countervailing clamping force applied by said injection molding machine,
• said inserts having a suitable pattern of cooling channels machined within said inserts so as to provide for internal circulation of a heat-transfer fluid within said insert being maintained in fluid communication with supply lines into said loadbearing support assembly,
• said inserts being made of a high thermal conductivity metal such as beryllium copper and having nickel or chromium plating onto said optically polished surface of said inserts;
• said mold having a plurality of pre-enlarged, variable-volume mold cavities oversized at the start of each injection cycle with sufficiently great cavity height that the meltflow path would be relatively nonconstrictive, and the compression stroke is applied to injected melt by creating a relative motion between said inserts with respect to the parting-line reference plane, by sliding forward motion of said inserts axially within concentric bores of said mold,
• b. an adjustable and lockable mated pair of opposing wedge blocks, each wedge having a specified inclined plane geometry such that a specified amount of linear displacement of one wedge block causes a correspondingly predetermined specified linear displacement of the opposing wedge block in a direction perpendicular to the parting line plane,
• said mated pair of opposing wedge blocks comprising said loadbearing support assembly which mechanically transmits forces between said inserts back surface and said clamping platen of said injection molding machine, said opposing wedge blocks having an angle of inclination of between 5 and 15 degrees;
• c. means for adjustment for determining said preset fixed thickness of said lens external to said injection mold, said means for adjustment being capable of being moved to a plurality of positions when the mold is not filled with plastic;
• d. means for mechanical linkage of motions of said mated pair of opposing wedge blocks in response to operator manually-driven motions of said means for adjustment external to said injection mold, by which motions a specified amount of linear displacement of one wedge block is produced when the mold is not filled with plastic, said means for mechanical linkage of motions of said mated pair of opposing wedge blocks and a means for adjustment being a rotatable threaded screw of known pitch fitted with an external head;
• e. means for locking said mated pair of opposing wedge blocks into a fixed position after said ajustment is made when the mold is not filled with plastic;
• such that there is substantially no slippage between said mated pair of opposing wedges during subsequent injection molding cycles, thereby determining a preset fixed thickness of said lens.

A method for adjustment of thickness of an injection molded thermoplastic vision-corrective spectacle lens being of a finished single vision family of differing optical magnification powers without removing an injection mold mounted onto a clamping platen of an injection molding machine nor disassembling said injection mold, the method being employed as part of setup procedures before start of injection, the method comprising:

• a. moving a means for adjustment external to said injection mold and accessible to an operator for manually driven motion to one of a plurality of positions, before starting injection molding cycles;
• b. sliding a wedge block mechanically linked to said means for adjustment,
• said wedge block being one of a slideably mated pair of opposing wedge blocks, each wedge having a specified inclined plane geometry such that a specified amount of linear displacement of one wedge block causes a correspondingly predetermined linear displacement of the opposing wedge block in a direction perpendicular to the parting line plane;
• c. locking in place said slideably mated pair of opposing wedge blocks so as to prevent slippage between said slideably mated pair of opposing wedges during injection molding cycles, said slideably mated pair of opposing wedge blocks comprising a loadbearing support assembly which mechanically transmits compressive forces between a substantially planar back surface of said insert and said platen of said injection molding machine,
• said insert and said loadbearing support assembly being mounted within one of two moldhalves which open and close about a parting line to form at least one mold cavity, said insert being one of an opposing pair of curved optically polished mold inserts surface facing into said mold cavity
• such that said correspondingly predetermined linear displacement of the opposing wedge block in a direction perpendicular to the parting line plane advances or retracts said insert optically polished surface facing into said mold cavity in at least one of said two moldhalves, thereby increasing or decreasing thickness of said injection molded thermoplastic vision-corrective spectacle lens.