Development of a transducer for in-line and through cycle monitoring of key process and quality variables in injection molding

Injection molding, a key polymer processing technique, transforms plastic granules into various plastic parts. The requirements of quality injection molded part have been significantly increased in the past decade. The quality of molded part for a given material, mold and machine highly depends on the processing conditions and this creates a continuous demand of developing advanced sensors for monitoring and controlling the process. The traditional temperature and pressure transducers have been widely employed in the industry; however, the measurements do not have a direct correlation to the product quality. Soft sensor, which in a degree estimates certain product quality through soft computing, often has limited accuracy over the range of conditions of how the sensor is developed. In view of these shortcomings, a novel capacitive transducer is designed for real time and continuous monitoring of injection molding. This paper demonstrates that the proposed sensor has excellent ability of detecting start/end of mold filling, and tracing the melt flow position in the mold cavity. The sensor outputs can be further correlated to online part weight prediction, and also the measurement of part solidification rate. The ability to monitor the entire injection cycle makes the transducer a cost effective and robust technique for process and quality control.