Over the past decades Precision Glass Molding (PGM) technology has been used to manufacture high-quality infrared lenses with surfaces ranging from simple conics to complex aspheric. Since most of the infrared lenses utilize chalcogenide glasses including germanium, which is expensive as a raw material, the use of near net shape process like Precision Glass Molding Process as a cost effective process to eliminate material waste is necessary. In this case, Finite Element Analysis (FEM) is a tool that can simulate the PGM process and help designers to predict the appropriate mold geometry that can form the desire surface lens profile. This tool can also anticipate residual stress of the molded lens that can result in an inhomogeneous refractive index that directly affects the optical performance of the lens. As can be seen in the market, there is a lot of commercial FE software like ABAQUS, MSC MARC, ANSIS, DEFORM, and etc., that can be used to simulate the PGM process that each has its own advantages and disadvantages. In this case, a fair evaluation of software would be helpful for FEM users.
This thesis starts with an understanding of glass properties as a fundamental to establish a model by FE software. To have an understanding of glass behavior, glass properties like glass viscoelasticity, glass viscosity and glass transition temperature and other related glass properties should be studied.
The study of manufacturing process of an infrared lens by using a commercial glass molding machine, GP-10000HT, is the second step to figure out all the details of a real precision glass molding process that help us to provide a simulation that makes a better prediction of glass molding process.
By having a good understanding of material properties as well as manufacturing process of glass molding process, the numerical modeling of PGM process by using two commercial FE software, MSC MARC and ABAQUS, is another approach of this thesis. These two numerical modeling are designed with the same condition to help us evaluate and compare these two software at a fair situation. The simulation results that consist of molded glass geometry as well as residual von Mises stress, show that the maximum geometry (center thickness and diameter) deviation of 8 and 6 microns for MSC MARC and ABAQUS, respectively.
In the last chapter of this thesis, the simulation results, obtained by MSC MARC and ABAQUS, are evaluated based on seven parameters which are Overall dimensions, curvature of upper and lower molded glass, residual stress at each step software capability to introduce material properties, calculation Time, visualization capability, and being user-friendly. According to this evaluation, both software are able to have a good prediction of the final geometry of the lens as well as the residual stress, but ABAQUS because of its ability to converge to the solution in shorter time, better visualization and also being user-friendly would be preferred.
MSC MAC has also a built-in module to introduce the Narayanaswamy model to describe the structural relaxation behavior of the glass, which is not available in ABAQUS. This disadvantage of ABAQUS can be easily covered by running appropriate code that could be write in software like C++ or FORTRAN.
Keywords: Aspherical lens, lenses,precision glass molding, finite element method, chalcogenide glasses, molded infrared optics, viscosity, glass viscoelasticity, Glass transition temperature,ABAQUS, MSC MARC,