CAVITY PRESSURE DYNAMICS AND SELF-TUNING CONTROL FOR FILLING AND PACKING PHASES OF THERMOPLASTICS INJECTION-MOLDING

Because of its versatility, cost effectiveness, and ability to produce intricate shapes to tight specifications, the injection molding proce ss is widely used in plastics processing. Mold cavity pressure plays a n important role in determining the quality of the molded articles. Th e dynamic behavior and control of cavity pressure were studied for the filling and packing phases. The dynamics of cavity pressure during fi lling were investigated and found to be both nonlinear and time-varyin g in relation to the hydraulic servo-valve opening, which is the manip ulated variable. A self-tuning control system was designed and tested for a wide range of conditions. The transition from filling to packing was best detected by the change in the derivative of cavity pressure. The dynamics of cavity pressure during packing were studied and model ed similarly as for filling. The self-tuning technique was successfull y extended and implemented in the packing phase.