Method and apparatus to injection co-mold and assemble plastic material objects

A method for injection molding synthetic plastics objects including a first piece having a hinge pin and a second piece having an annular element coupled with said hinge pin to provide articulation between the first and second pieces, comprising the steps of:

• a) providing a mold with a first molding member defining an impression for said hinge pin and a second molding member defining an impression for said annular element, said first molding member and said second molding member being coaxially movable relative to one another;
• b) configuring said first and second molding members to provide first and second pin elements, respectively, which are coaxial and slidable relative to each other, said first and second pin elements comprising a first molding end and a second molding end for molding said hinge pin and said annular element, respectively;
• c) providing a cooling channel within and extending along an axis of the first pin element to an internal zone of said first pin element in the vicinity of said first molding end;
• d) providing a tubular cooling element within and coaxial with said cooling channel which extends to said internal zone, said cooling channel and said tubular cooling element defining an annular cooling gap;
• e) delivering cooling fluid into said tubular cooling element in the vicinity of said internal zone and along said annular cooling gap to cool said first and second pin elements, said hinge pin and said annular element;
• f) selectively moving said first and second molding members with first and second drive cams, respectively;
• g) upon opening of the mold, partially extracting a molded object from the mold by selective axial movement of said first and second mold members;
• h) assembling the molded object by coupling said annular element of said second piece with said hinge pin of said first piece via a snap engagement;
• and
• i) completely extracting the molded object by disengaging said first molding member from said annular element and said second molding member from said hinge pin.

An apparatus for injection molding synthetic plastic objects including a first piece comprising a container having a hinge pin and a second piece comprising a handle having an annular element, the hinge pin and annular element being connected for articulated movement relative to each other, comprising:

• an injection mold including a first molding member and a second molding member, the first and second molding members defining impressions of the hinge pin and the annular element, respectively, wherein the first molding member includes a first pin element and the second molding member includes a second pin element, the first and second pin elements being slidably and coaxially movable together, wherein the first molding pin comprises a first molding end for molding said hinge pin and wherein the second molding pin comprises a second molding end for molding said annular element;
• an extracting device movable linearly in an axial direction to assemble the container hinge pin and handle annular element during an initial extraction movement of the molded object, wherein said first molding member and said second molding member are supported by said extracting device;
• first and second drive cams for selectively moving said first and second molding members, respectively, between an advanced molding condition, an assembly condition and a retraction condition to disengage the hinge pin and the annular element;
• a cooling system for cooling said first and second pin elements with a cooling fluid, said cooling system including a channel within said first pin element and a tubular element extending coaxially in a longitudinal direction within the channel.