Date of Award

12-2009

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

Blouin, Vincent

Committee Member

Joseph , Paul

Committee Member

Miller , Richard

Committee Member

Richardson , Kathleen

Committee Member

Xuan , Xiangchun

Abstract

The lens molding process is a relatively new technique used to manufacture lenses, in particular, high precision aspheric lenses. In order to achieve the desired size and shape of the lens, the cooling process after pressing must be controlled precisely because of the time and temperature dependent viscoelastic behavior of glass near and below the molding temperature. This thesis gives a detailed description of a three-dimensional computational model for analyzing the cooling phase of the lens molding process. Conduction, convection and radiation are considered in the model by coupling a computational fluid dynamics analysis of the flow of nitrogen through the system and a transient heat transfer finite element analysis of the assembly. An iterative process between the fluid flow analysis and the thermal analysis is used to account for their interdependency. The model is calibrated and validated by direct comparison with the experimental results. Various parametric studies are performed to study the effect of several unknown parameters and design parameters on the accuracy of the numerical model. It was found that the model depends significantly on the unknown properties such as thermal contact conductance values and radiation properties, which should therefore be the subject of further investigation. This three-dimensional model can be used to extract the boundary conditions for a parallel study involving a more detailed two-dimensional axisymmetric sub-model of the lens and molds. The validity of two-dimensional axisymmetry assumption is verified from the results obtained through the three-dimensional model's simulations.

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