Active thermal control of melt flow in nozzles

Currently active control of the flow of plastic melt in injection molding machine nozzles relies on the use of mechanical means to seal the nozzle orifice and prevent leakage of the melt. The objective of this thesis was to control the flow of the melt in the nozzle by varying its temperature such that the transition from melt flow to freeze-off and freeze-off to melt flow occurs quickly with respect to the process dynamics. Finite element analysis of the temperature distribution of a nozzle contacting the mold showed a significant temperature distribution as a function of the axial and radial position in the metal and plastic. The temperature of the metal determines the viscosity of the plastic and subsequent flow through the nozzle. Numerical simulation and experimental investigation validated the analysis by characterizing the temperature and pressure changes needed to induce flow as a function of nozzle and mold temperature. Control of the polymer freeze-off and melt flow in injection molding machine nozzles is necessary for fully automatic production, as well as development of advanced molding processes.