【作者】 陶波；

【导师】 沈连婠； Allen Yi；

【作者基本信息】 中国科学技术大学 ， 精密仪器及机械， 2013， 博士

【摘要】 作为一种替代传统的光学玻璃透镜的制造方法,光学玻璃透镜的精密热压成型是一个有吸引力的工艺。它具有一次成型,高效率低成本,适应于玻璃透镜的规模生产,环境友好等优点。但是热压成型技术是一种在高温下对光学玻璃模压成型工艺,由于冷却过程中的温度不均匀,以及玻璃在其转变区域内的复杂状态变化,导致最后残余应力被冻结在玻璃透镜里。而残余应力的存在会使玻璃透镜产生双折射现象,以及折射率偏差,从而影响透镜的光学性能。为了研究热压成型透镜中的残余应力问题,本文分别采用实验和有限元仿真研究了玻璃透镜中的残余应力分布,并探索了利用退火工艺来改善玻璃透镜中的残余应力与折射率偏差的方法。为了理解玻璃透镜中的残余应力分布,实验搭建了圆偏光器(circular polariscope),分别对经过热处理后的圆柱透镜以及热压成型的非球面透镜进行了测量。测量过程中采取用六步左右相移法获得了被测透镜不同的光强图像,计算得到了被测透镜的等倾角与相位延迟。根据轴对称应力、以及弱双折射情况下的透镜中的应力与透镜等倾角与相位延迟关系,以及透镜的平衡方程以及一般性求和法则,利用编写的残余应力重建程序,重建了透镜中的残余应力分布。采用有限元仿真计算了圆柱透镜以及非球面透镜中的残余应力,并将仿真分析结果与实验测量计算进行了对比,研究表明,有限元仿真可以用来研究热压成型透镜中的残余应力。同时探讨了有限元计算仿真中玻璃材料的比热容,热膨胀系数对仿真结果的影响,对玻璃透镜冷却过程中的冷却速率进行了仿真研究,探索了冷却速率对透镜中残余应力以及透镜曲面形貌的影响。发现转折温度前的冷却速率对成型透镜的残余应力和曲面形貌影响较大,同时随着冷却速率的的减小,透镜中的残余应力在减小,但是曲面相貌偏差会变大。为了降低热压成型的非球面镜中的残余应力,本文还对非球面透镜进行了退火实验。并分别利用圆偏光器、基于Mach-Zehnder干涉仪的实验装置,以及轮廓仪测量了退火实验前、后透镜中的残余应力,折射率偏差以及透镜的非球面曲面形貌。研究表明,当退火温度在应变点附近时,能够减小透镜中的残余应力,但是对折射率偏差的影响不大；当退火温度在玻璃材料退火点附近时,透镜中的残余应力与折射率偏差都变小了；且在退火后透镜非球面的曲面形貌得到了较好的保存。最后根据文中的实验与仿真,提出了一种新的透镜热压成型工艺,即在透镜热压成型阶段针对透镜曲面面型进行优化工艺,透镜热压成型后,利用退火方式来降低透镜中的残余应力与折射率偏差,由于退火过程中只需要进行温度控制,因此可以对批量的透镜同时退火以提高生产效率。更多还原

【Abstract】 As an alternative method for fabricating glass lenses, compression molding is a very attractive process. Compared to the conventional glass fabrication techniques, compression molding is an environmentally conscience process since it is an near net-shape process, high productively and low cost, suitable for mass production of glass lenses in industry.Compression molding is a hot forming method in which a glass blank was pressed by molds to create the lens shape. Residual stresses were frozen in the glass lens due to the nonuniform of temperature and complicated process when the glass lens went through its glass transition region during the cooling process. The existence of residual stresses in glass lenses lead to birefringence and refractive index variation which affect the optical performance of the glass lens.In this research, both experimental and numerical simulation methods were employed to study the residual stresses inside compression molded glass lenses. And annealing experiments of molded aspherical glass lenses were investigated to reduce the residual stresses and refractive index variation in the glass lenses.Residual stresses inside a cylindrical glass lens and compression molded aspherical glass lenses were measured in this research. The residual stresses inside the glass lenses were measured by a circular polariscope. With six-step left right phase shifting technique, isoclinic angle and optical retardation of the glass lens under test can be measured. Taking advantage of axisymmetrical properties of the residual stresses and weak birefrignece of the glass lens, the residual stresses can be reconstructed using the relations between stresses and parameters of photoelasticity, equilibrium equation and generalized sum rule.Residual stresses inside the glass lenses were also studied by numerical simulation. The simulation results demonstrated a reasonable agreement with experiment results. It shows that numerical simulation can be used to predict the residual stresses of compression molded glass lenses.The influences of heat capacity and the coefficient of thermal expansion of the glass on residual stresses in numerical simulation were studied. The influences of cooling rates were also studied by numerical simulation. Based on the results, the cooling rate before break temperature of BK7Glass plays an important role in the cooling process. As the cooling rate decreased, the residual stresses became smaller but the surface deviation became bigger.In order to reduce the residual stresses inside the compression molded aspherical glass lenses, annealing experiments were conducted. The influence of annealing on the aspherical glass lenses was evaluated by the change of residual stresses, refractive index vaiation and aspherical surface curve deviation of the glass lens pre and post annealing experiement. The residual stresses were measured by the circular polariscope. The refractive index variation was measured by an optical setup based on Mach-Zehnder interferometer. And the aspherical surface curve deviation was measured by a profilometry. The results showed that the residual stresses can be reduced when the annealing temperature is lower than the glass’s strain point, however the refractive index experienced a minor change. If the annealing temperature is near the glass’s annealing point, both residual stresses and refractive index variation of the glass lens can be reduced. While the aspherical surface curve deviation has a minor change after annealing experiments.Based on the experiments and simulations shown in this research, a new compression molding process can be proposed. Once the glass lens was fabricated by compression molding, an annealing process could be used to reduce the residual stresses and the refractive index variation in the glass lens.更多还原