光學玻璃模造成形之有限元素分析

Abstract

玻璃模造技術為一適合用於大量製造內嵌在3C產品中的光學元件(如手機相機模組中的光學玻璃透鏡)之量產方式。儘管此技術具備許多優勢，在實際製造上仍有許多困難需克服。其中最關鍵的問題為歷經製程後的透鏡成品與原始設計值之間存在誤差。為解決此問題，本研究以詳盡的材料模型建立有限元素分析模型，並以此模型預測光學玻璃模造後之透鏡成品外型，期能藉此分析指出此問題關鍵處並加以改善。 為建構一完整的光學玻璃模造成形之有限元素分析模型，本研究一開始即針對玻璃進行材料實驗以取得詳盡的材料性質。研究裡採用的是低玻璃轉移溫度之玻璃L-BAL42 (Low Tg glass, Tg=506°C, Ohara Co.)。藉由熱膨脹實驗，得到玻璃在液體和玻璃態下的熱膨脹係數。接著利用掃描式熱差分儀（DSC）和單軸壓縮應力鬆弛實驗，分別取得玻璃之結構鬆弛性質以及應力鬆弛性質。另在成形溫度（568℃，At + 30℃）下進行單軸壓縮試驗，驗證牛頓流體確實能夠準確地代表玻璃在成形階段的流動行為。最後進行一非球面光學玻璃透鏡成形實驗，並以此實驗之成形參數代入分析中。分析模型以商用有限元素軟體MARC建立，並代入玻璃材料實驗所得之材料性質。藉由模擬和實驗結果比對一致性與準確性，確認了本研究提出之光學玻璃模造成形有限元素分析模型。

Glass molding is a high-volume fabrication method suitable for producing optical components embedded in 3C products, such as optical glass lenses in the camera modules of mobile phones, digital cameras and projectors, etc. Despite the advantages of glass molding, several difficulties encountered in the manufacturing process have yet to be overcome. The most critical issue is the deviation between the formed lens and the original lens shape design. Thus, to overcome this obstacle, the focus of this dissertation is to introduce finite element analysis (FEA) into the prediction of the molded lens shape with detailed material models of the optical glass. To construct a comprehensive finite element (FE) model for the optical glass molding process, this study firstly performed experiments on the optical glass to obtain detailed material properties. Low Tg optical glass, L-BAL42 (Tg=506°C, Ohara Co.), was used in this research. Detailed thermal expansion coefficients including liquid and glassy states are obtained by thermal expansion experiment. Followed by using differential scanning calorimetry (DSC) and uniaxial compressive stress relaxation experiments, the structural relaxation property and the stress relaxation property were obtained respectively. Uniaxial compression test was also performed at the molding temperature (568°C, 30°C above At) to verify that the Newtonian fluid could accurately represent the glass flow behavior at molding stage. An aspherical optical glass lens molding experiment was then performed and the FEA with the same forming parameters was also conducted by using the commercial finite element program, MARC, incorporating these obtained material properties and the proposed material model. After verifying the consistency of simulated and experimental results, a comprehensive FE model for optical glass lens molding process was assured.