New Ultrasonic Solidification Sensing Techniques for Injection Molding

An ultrasonic transducer installed facing a pressure transducer in the cavity of a rectangular plaque injection mold shows new sensitivities to the solidification of the polymer in the mold. Features of the amplitude variation of a pulse transmitted twice through the polymer are sensitive to the flow rate and solidification state of the polymer at the transducer face. The signal from a normal incidence shear transducer gives a direct indication of solidification. A model was developed to describe the changing amplitude of a pulse transmitted through the polymer. The model illustrates how temperature, pressure, flow rate, and signal frequency affect the measured echo amplitude.