Thermal forming process for precision freeform optical mirrors and micro glass optics.

摘要

Glass thermal forming processes are an emerging industrial techniques that can be adopted for high volume manufacturing of common size spherical, aspherical, and freeform glass optics, as well as micro glass optical components. Thermal forming processes discussed in this dissertation include compression molding and thermal slumping. The thermal forming processes are net shape, environment friendly and high volume production manufacturing techniques. However, there are still quite a few technical challenges associated with these new processes which include proper curvature compensation, mold design and mold life issues, residual stresses in the molded lenses, and refractive index variation after molding. These difficulties must be overcome before glass thermal forming processes can be readily implemented in industry.;This dissertation research seeks a fundamental understanding of the thermal forming process for both freeform glass mirrors and glass micro optical lenses by adopting a combined experimental, analytical and numerical Finite Element Method (FEM) approach. Preliminary investigation was conducted on the optical design for beam shaping reflector and freeform two-stage solar concentrator. The freeform primary mirrors were used as thermal slumping test samples. Thermal slumping experiments were performed to determine the effects of different molding parameters i.e. the slumping temperature, holding time and cooling rate on the final thermal formed glass mirrors' quality. The surface roughness and contour error were evaluated based on the requirement of freeform solar concentrator. The manufacturing tolerance analysis of the freeform solar concentrator system was also performed. Numerical modeling was utilized to compensate the curvature deviation during a thermal forming process, and evaluated using experimental results with matching process conditions. Moreover, in compression molding of precision glass lens experiments were also performed to study the residual stresses under different cooling rate. An FEM simulation model was developed and predictions were compared with the actual experimental results. Based on the comparison, FEM simulation can be used to predict and optimize cooling rate in the thermal forming process.;Finally, compression molding experiments were performed to fabricate glass microlens arrays and diffractive optical elements (DOEs). The molded glass micro optical lenses were measured with AFM/SEM, and the optical performance of the molded lens was also evaluated by using a home-built optical metrology setup. Experimental results have showed that the thermal forming processes are capable of producing precision freeform glass mirrors and glass micro optics with shape and surface quality within the tolerance requirement.