Process for molding hollow workpieces

A method of releasing a workpiece having an undercut from a complementary core in an injection molding apparatus, having a longitudinal axis, said method comprising the steps of:

• providing an injection molding apparatus drive system comprising a stripper plate bilaterally movable back and forth in an axial direction and having a core pin protruding forwardly through a hole in said stripper plate, said core pin being usable to form a cavity in the workpiece, a core pin sleeve juxtaposed with said stripper plate, said core pin sleeve having a feature to form the undercut in the workpiece, a hollow stripper sleeve extending oppositely from said core pin, said hollow stripper sleeve being rigidly joined to said stripper plate and axially spaced from said core pin and circumscribing said longitudinal axis, said hollow stripper sleeve having at least one stripper sleeve cam therein providing for responsive motion of a respective stripper sleeve follower, a core pin base rigidly joined to said core pin and being axially spaced from said stripper plate opposite said core pin, said core pin base having at least one core pin base cam therein providing for motion of a respective core pin base follower, a stripper sleeve insert disposed intermediate said hollow stripper sleeve and said core pin base and being rigidly joined to said core pin sleeve, said stripper sleeve insert having an outwardly extending stripper sleeve follower cooperating with said at least one stripper sleeve cam and an inwardly extending core pin base follower cooperating with said at least one core pin base cam, the workpiece having the cavity being removably molded onto said core pin and onto said core pin sleeve whereby said workpiece has the undercut formed by said feature of said core pin sleeve;
• moving said stripper plate in rearwardly an axial direction away from a complementary mold half in a first predetermined path;
• moving said stripper plate forwardly in the axial direction towards the complementary mold half, wherein said stripper sleeve insert moves in a second predetermined path, said second predetermined path being opposite said first predetermined path;
• moving said core pin base follower within said at least one core pin base cam in a predominantly axial direction, then simultaneously in an axial and circumferential direction forming a spiral around said longitudinal axis;
• moving said stripper sleeve follower within said at least one stripper sleeve cam, so that said stripper sleeve follower and said core pin base follower superimpose respective motions thereof onto said stripper sleeve insert;
• and
• moving said core pin sleeve synchronously with said stripper sleeve insert;
• to thereby release the workpiece from said core pin sleeve and said core pin.

A method of driving a stripper plate in an injection molding apparatus for injection molding a workpiece having an undercut, said method releasing workpiece from said apparatus and comprising the steps of:

• providing an injection molding apparatus drive system comprising a stripper plate bilaterally movable back and forth in an axial direction and having a core pin protruding forwardly through a hole in said stripper plate and defining a longitudinal axis, said core pin being usable to form a cavity in the workpiece, a core pin sleeve juxtaposed with said stripper plate, said core pin sleeve having a feature to form the undercut in the workpiece, a hollow stripper sleeve extending oppositely from said core pin, said hollow stripper sleeve being rigidly joined to said stripper plate and axially spaced from said core pin and circumscribing said longitudinal axis, said hollow stripper sleeve having at least one stripper sleeve cam therein providing for responsive motion of a respective stripper sleeve follower, a core pin base rigidly joined to said core pin and being axially spaced from said stripper plate opposite said core pin, said core pin base having at least one core pin base cam therein providing for motion of a respective core pin base follower, a stripper sleeve insert disposed intermediate said hollow stripper sleeve and said core pin base and being rigidly joined to said core pin sleeve, said stripper sleeve insert having an outwardly extending stripper sleeve follower cooperating with said at least one stripper sleeve cam and an inwardly extending core pin base follower cooperating with said at least one core pin base cam, the workpiece having the cavity being removably molded onto said core pin and onto said core pin sleeve whereby said workpiece has the undercut formed by said feature of said core pin sleeve;
• moving said stripper plate in the axial direction;
• responsively moving said core pin base follower within said at least one core pin base cam;
• responsively moving said stripper sleeve follower within said at least one stripper sleeve cam, so that said stripper sleeve follower and said core pin base follower superimpose respective motions thereof onto said stripper sleeve insert;
• superimposing said movement of said core pin base follower and said stripper sleeve follower onto said stripper sleeve insert so that said hollow stripper sleeve moves in a path having combined motion thereof;
• and
• moving said core pin sleeve synchronously with said stripper sleeve insert to thereby release the workpiece from said core pin sleeve and said core pin,
• wherein said core pin sleeve rotates at least 90 degrees.