Adaptive online quality control for injection-molding by monitoring and controlling mold separation

This paper presents a unique method that makes use of a small signal (of the magnitude of microns) measured by a precision linear displacement transducer mounted on the outside of mold plates to monitor the momentary separation of the core and cavity plates. The maximum value of the separation is found to be highly correlated with part weight, one of the important quality indices. The whole profile of the mold separation (MS) is monitored and used in order to control the process adaptively and to keep the part quality consistent. Adaptive algorithms are developed to control the switchover point from filling to packing in terms of hydraulic pressure from shot to shot. Within a shot, the hydraulic pressure during the holding stage is manipulated to control the MS profile. The experimental results with different resins and mold geometries show that the variation of part weight is reduced significantly as compared to the conventional hydraulic pressure control.