Coupled thermomechanical finite element models were developed in ABAQUS to simulate the precision glass lens molding process, including the stages of heating, soaking, pressing, cooling and release. The aim of the models was the prediction of the deviation of the final lens profile from that of the mold, which was accomplished to within one-half of a micron. The molding glass was modeled as viscoelastic in shear and volume using an n-term, prony series; temperature dependence of the material behavior was taken into account using the assumption of thermal rheological simplicity (TRS); structural relaxation as described by the Tool-Narayanaswamy-Moynihan (TNM)-model was used to account for temperature history dependent expansion and contraction, and the molds were modeled as elastic taking into account both mechanical and thermal strain. In Part I of this two-part series, the computational approach and material definitions are presented. Furthermore, in preparation for the sensitivity analysis presented in Part II, this study includes both a bi-convex lens and a steep meniscus lens, which reveals a fundamental difference in how the deviation evolves for these different lens geometries. This study, therefore, motivates the inclusion of both lens types in the validations and sensitivity analysis of Part II. It is shown that the deviation of the steep meniscus lens is more sensitive to the mechanical behavior of the glass, due to the strain response of the newly formed lens that occurs when the pressing force is removed.

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In this paper, we report the development of a kinetic model for precisely predicting glass material property response to a defined molding profile. The glass viscosity, thermal expansion, and specific heat properties for two commercial optical glasses, P‐SK57 and L‐BAL35 were measured and are reported in this paper. These data were used with the Tool–Narayanaswamy–Moynihan (TNM) model for glass structural relaxation in order to develop a thermal expansion model that simulates the glass workpiece changes through the critical cooling profile where the final workpiece shape is determined. The results show a structural relaxation model incorporated into an ABAQUS FEM code that precisely models the thermal expansion behavior acknowledging that the theory of structural relaxation is a critical element in predicting the final size and shape of a molded lens.