| The injection molding process, due to its versatility, cost effectiveness, and ability to produce intricate shapes to tight specifications, is widely used in plastics processing. Mold cavity pressure plays an important role in determining the quality of the molded articles. The dynamic behaviour and control of cavity pressure were studied in this research project. The work deals with all phases of the process: filling, packing, and cooling.;A real-time data acquisition and computer control system has been developed to assist the implementation of advanced control techniques for injection molding machine operation. Modularity and extensibility were emphasised in its development.;The dynamics of cavity pressure during filling were investigated and found to be both non-linear and time-varying in relation to the hydraulic servo-valve opening which is the manipulated variable. A self-tuning control system was designed and tested for a wide range of conditions.;The transition of the filling-to-packing was found to be best detected by the derivative of the cavity pressure. The dynamics of cavity pressure during packing were studied and modelled similarly as for filling. The self-tuning technique was successfully extended into the packing phase.;Cavity pressure is essentially independent of the hydraulic servo-valve opening once the cavity gate freezes and the process enters the cooling phase. A cooling system was designed to provide quick manipulation of coolant temperature. Controlled pressure cooling time (CPCT) was proposed to represent the behaviour of cavity pressure during the cooling phase. Its dynamics in relation to coolant temperature were found to be best described as a first order system. A control system for CPCT was designed and successfully tested. |
