Glass Molding Process (GMP) is an effective method for producing precise optical elements such as lenses. This simulation study aimed to predict the distribution of temperature and stress within a lens during a multi-stage cooling process of GMP. To develop an accurate simulation model including molds and lens, thermal contact conductance and boundary conditions were determined by analyzing experimental and simulation results. The developed model was used to investigate changes in temperature and maximum principal stress within the lens, considering variations in cooling time, speed, and method at each cooling stage. Simulation results indicated that trends of maximum temperature difference and maximum principal stress within the lens were consistent over time. Results also showed that the maximum principal stress inside the lens increased significantly with additional cooling after uneven temperature distribution caused by a relatively short cooling time. Compared to simulation results of the cooling process involving contact only with bottom surface of the mold, contact cooling with both top and bottom surfaces showed decreased residual stress at the end of cooling and maximum temperature difference within the lens. However, the maximum principal stress could be higher during the cooling process involving both surfaces.

To monitor the stirring state by on-line estimation of liquid viscosity instead of stopping the stirring process and measuring the viscosity using viscometer, a basic study clarifying the effect of stirring conditions was carried out. For this purpose, the relationship between liquid viscosity and the stirring conditions, such as stirring torque, stirring speed, the duty ratio of PWM, impeller and beaker type, and the blade position in the beaker was analyzed. The second-order relationship between the stirring speed and torque, the linear relationship between viscosity and torque, and the linear relationship between duty ratio of PWM and stirring speed were observed, thereby indicating that the liquid viscosity could be estimated by an experimental formula based on the duty ratio and the stirring speed. In addition, the type of impeller and beaker was identified using the magnetic field inside impeller and RFID technology. For reducing the error in calculating the liquid viscosity, the employment of an impeller blade with a large rotational resistance and stirring with the blade at the center zone of the beaker were found to be necessary.