Abstract: A method and assembly for injection molding a part. The injection molding assembly has a frame and a core back assembly on the frame with a material controlling region. The core back assembly has first and second states with the material controlling region: i) in a first position with the core back assembly in the first state; and ii) in a second position with the core back assembly in the second state. First and second mold units are configured to be placed in operative relationship on the frame wherein the first and second mold units cooperate to form a mold cavity on the frame. The frame, core back assembly, and first and second mold units are configured so that the state of the core back assembly is changed as an incident of the first and second mold units being placed in the operative relationship.