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在本研究中,採用由加權函數推導出之有限差分法來分析塑膠鏡片在模穴
中的冷卻現象,並以含冷卻速率效應的非平衡態P-V-T方程式來描述塑膠鏡
片在冷卻過程中的比容變化,進而由此來預測成品之熱收縮現象.基於考量
鏡片的邊界為一具有曲率的表面,本研究採用座標轉換(邊界重合座標轉
換)將具有曲率的物理曲面轉換至一正交的計算曲面,以利計算時網格的配
置.此外,本研究所採用的多區塊網格亦可用來處理具有較複雜外形的工程
問題.在對射出成型中之冷卻階段模擬時,能量方程式中的比熱與熱傳導係
數也以溫度的函數描述,以期能更精確地模擬射出成型之冷卻階段的實際
情況.藉由此一數值系統,鏡片各部位在冷卻過程的溫度分佈,熱收縮現象
與熱殘餘應將可預測.In this study, a finite difference method(
FDM) based on weighting function scheme is developed to study
the cooling process of a plastic lens inside the cavity. Non-
equilibrium P-V-T equation is introduced to describe the
volumetric change of plastic lens during the cooling stage of
injection molding process. Thermal shrinkage of the part is also
predicted from the calculated volumetric variation. To take care
the curved shape of lens in this study, a boundary-conforming
curvilinear coordinate system transformation technique is
develope to transform the irregular physical domain into a
rectangular one. In this way, computational grid can be
generated quickly and the numerical solution is reliable.
Multiple-block grid generation method introduced in this work
can be extended to more comloicated geometry encountering in
other engineering problem. Temperature effect is also considered
in the heat capacity and thermal conductivity in order to
accurately simulate the thermal behavior of plastic lens during
the cooling process. By mean of methodology developed in this
study,the cooling behavior, thermal shrinkage and thermal
residual stress of injection-molded lens can be predicted.
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