Methods and apparatuses for injection molding walled structures

A method for forming a medical barrel having a bypass groove within an inner wall of the medical barrel and an undistorted outer wall such that the medical barrel can be removed axially from the injection molding apparatus, the method comprising:

• providing a unitary inseparable mold block defining a mold cavity and adapted to receive molten thermoplastic material in the mold cavity and wherein the mold block comprises a cylindrical opening at one end;
• inserting an inner core that is adapted to pass through the cylindrical opening and to occupy a portion within the mold cavity to define a molding space that is outside of the inner core but within the mold cavity for forming the medical barrel therein and wherein the inner core comprises a longitudinal space therein;
• positioning an actuator within the longitudinal space and which is axially displaceable therein;
• monitoring at least one parameter within the mold cavity using a sensor that transmits a signal representative of the at least one parameter, the at least one parameter corresponding to a substantial, but not complete, filling of the molding space with the molten thermoplastic material, wherein the sensor is positioned so as not to directly contact the molten thermoplastic material and thereby not distort the medical barrel;
• displacing the actuator axially using a drive in response to the signal received from the sensor;
• and
• displacing an impression member orthogonally from the actuator to form the bypass groove within the inner wall of the medical barrel when the molding space is substantially, but not completely, filled with the molten thermoplastic material and when the actuator is axially displaced.