Effect of molding machine's stiffness on the thickness of molded glass rings

Ensuring the final center thickness of molded optics within specified tolerance is one standard requirement for precision glass molding. In this study, we mainly discuss why and how the machine's stiffness affects the final thickness of molded glass rings. To this end, molding experiments using displacement control mode are performed at different molding temperatures. Additionally, tailored tests are conducted to determine the mechanical stiffness and thermal deformation of the molding machine. Thermo-displacement coupled finite element simulations are employed to reveal how the molding behaviors and the thickness evolution depend on the machine's stiffness. Results show that the final thickness deviation is mainly related to the maximum generated machine deformation during pressing, and thus decreases with the machine's stiffness. The influence extent of the machine's stiffness remarkably decreases with the molding temperature, which explains why the experimental final thickness results decrease as well. Besides, compared to the rigid machine assumption, the simulated thickness results under the real machine's stiffness, are well coherent with the experiments, which proves the importance of considering the machine's stiffness. Finally, it is demonstrated that applying a period of position holding after pressing at molding temperature, can effectively reduce the final thickness deviation.