Detection method of filling imbalance in a multi-cavity mold for small lens

Due to the small product size, multi-cavity molds are used for the phone camera lenses. It is well known that filling imbalance often occurs in multi-cavity molds by shear heating in the runner. However, detecting the filling imbalance is not an easy task in the mold. In this work, we tried to detect filling imbalance by temperature sensors in the runner and indirect pressure sensors at the bottom of lens core. In order to confirm the filling imbalance, short shot tests were carried out at various injection speeds. Temperature and pressure signals were analyzed for a correlation with the short shot test. Temperature signal showed a reliable correlation with respect to the resin-arrival-time (RAT) difference, but pressure signal did not produce a reliable result.