臺灣博碩士論文加值系統

本文藉由Ansys Fluent R15.0建立二維軸對稱模型，模擬選擇性雷射熔融法定點加熱不鏽鋼316L金屬粉末，考慮熔池表面張力效應(馬蘭戈尼效應)，比較不同雷射能量、雷射半徑對金屬熔池發展的影響，並於最後與移動熱源做連結，討論在雷射高移動速度下，馬蘭戈尼效應影響的劇烈與否。
根據模擬結果顯示，在熔融不鏽鋼316L金屬粉末過程中，其熔池受到馬蘭戈尼效應的影響，其內部流動為逆時針方向之流動，產生一較深、較窄的熔池形狀。
固定雷射半徑，增加雷射能量會增加粉末融熔的效益，但在雷射能量大於30 W時其溫度會高於蒸發溫度，造成金屬粉末之損耗，亦會浪費能量，應盡量避免，故雷射能量應選用大於5 W及小於等於30 W之間；固定雷射能量，增加雷射半徑雖然會增加熔池寬，但是熔池深會隨著減少，且雷射半徑增加至 以上時，其熔池寬成長幅度會減緩，且有下降的趨勢，故雷射半經應選低於 。
在增加雷射移動速度下，即每單位點之照射時間越短，其馬蘭戈尼效應對熔池幾何、熔池體積影響較不顯著，但對表面溫度之影響較顯著，且增加雷射能量會使溫度差距更明顯，故即便在照射時間極短下，仍不宜忽略此效應。

In this study, a numerical model is developed to investigate the molten pool of stainless steel 316L metal powder by fixed- point heating in Selective Laser Melting (SLM). This model also considers the effects of buoyancy, Marangoni forces, radiation and convection heat losses. Furthermore, it relates to moving heat source to consider whether Marangoni effects highly affects molten pool or not in high laser scanning speed. The results show that Marangoni forces make the shape of molten pool much deeper and narrower. The benefits of powder melting will increase with increasing the laser power, but the temperature will be higher than the evaporation temperature if the laser energy greater than 30W. It will not only make metal powder mass loss but waste energy. So the laser energy should be chosen between 5 to 30 W. The increase of laser beam radius will decrease molten pool depth but increase molten pool width. When the beam radius increase to more than , the growth rate of molten pool width will slow down. So the beam radius should not be chosen greater than . Furthermore, the higher laser scanning speed means the shorter irradiation time per unit point, the effect of the Marangoni force is not significant on volume but on surface temperature of the molten pool. Based on the result, it is inappropriate to neglect the effect of Marangoni force during the SLM simulation even though the irradiation time is very short.

摘要 I
誌謝 VIII
目錄 IX
表目錄 XII
圖目錄 XIII
符號說明 XVII
第一章 緒論 1
1-1 研究背景 1
1-1.1 積層製造 1
1-1.2 選擇性雷射熔融法 2
1-2 文獻回顧 4
1-2.1 金屬粉末層之研究 4
1-2.2 數值模擬選擇性雷射熔融法 7
1-2.3 金屬熔池內流動之數值研究 10
1-3 研究目的及方法 12
1-4 全文架構 14
第二章 理論分析 15
2-1 雷射基礎理論 15
2-1.1 雷射輻射原理 15
2-1.2 Nd-YAG雷射 17
2-1.3 高斯雷射熱源 20
2-2 熱傳理論 26
2-2.1 相變化 26
2-2.2 表面張力 29
2-2.3 輻射熱傳及對流熱傳 30
第三章 數值模擬方法 31
3-1 數值方法 31
3-2 物理模型 34
3-3 統御方程式 36
3-4 初始條件 37
3-5 邊界條件 38
3-6 金屬材料熱物理性值 41
3-6.1 不鏽鋼金屬Stainless steel 316L(SS316L) 41
3-6.2 等效金屬層熱物理參數 41
3-7 計算求解流程 48
3-8 驗證 50
3-8.1 驗證一：數值方法驗證 50
3-8.2 驗證二：實驗溫度場驗證 50
第四章 結果與討論 57
4-1 物理模型測試 57
4-1.1 網格獨立測試 57
4-1.2 時間步階測試 60
4-2 探討馬蘭戈尼效應對粉末融熔的影響 60
4-3 定點加熱不鏽鋼316L金屬粉末之熱流演變現象 70
4-4 改變雷射能量之影響 76
4-5 改變雷射半徑之影響 80
4-6 SLM雷射移動速度下馬蘭戈尼效應之影響 83
第五章 結論與未來工作 95
5-1 結論 95
5-2 未來工作 96
參考文獻 97

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