臺灣博碩士論文加值系統

本文主要利用ANSYS Fluent建立三維暫態數值模型，模擬選擇性雷射熔融法(Selective Laser Melting, SLM)以多重軌跡掃描(Multi-track)不鏽鋼316L粉末，考慮馬蘭戈尼效應，比較不同雷射功率、掃描速率下對粉末溫度及熔池尺寸之影響，並根據能量利用性與製程時間定義熔融效益參數進行雷射參數篩選，以探討改變掃描間距及掃描方式的影響，最後再針對基板與粉末預熱對溫度梯度、冷卻速率作進一步的分析。根據模擬結果顯示，當掃描速率640mm/s下，馬蘭戈尼效應對粉末溫度的影響會隨著雷射功率的增加而明顯變大。而固定雷射功率150W時掃描速率愈小，馬蘭戈尼效應對熔池影響會愈劇烈，造成熔池發展較為深、窄，故SLM使用此參數時應不可忽略此效應的影響。而透過參數篩選雷射功率200W，掃描速率800mm/s為粉末熔融效益最佳的參數，由此探討不同掃描間距發現，軌跡重疊率超過50%時，會使雷射作用區域的溫度梯度過大，而易造成熱應力集中，對於零件製造相當不利，相較下軌跡重疊率30%時溫度梯度較低，其熔池也具有良好的結合性。基板預熱能有利於降低溫度梯度及冷卻速率，其降低幅度會隨著預熱溫度的增加而變大，但為了避免材料過度蒸發，故此預熱溫度控制為700K內較佳。而粉末預熱由於雷射加工時粉末原先預熱的熱量已被大量散失，故造成其對溫度梯度、冷卻速率以及熔池尺寸皆無明顯改變，也無法有效改善零件品質。

In this study, a numerical model is established to investigate the molten pool of stainless steel 316L metal powder by multi-track scanning in Selective Laser Melting (SLM). The results show that the influence of Marangoni effect on the temperature field becomes greater with increasing laser power at scanning speed 640mm/s. When laser power maintains 150W, the decrease of scanning speed makes the shape of molten pool much deeper and narrower. Based on the results, it is inappropriate to neglect Marangoni effect during SLM simulation with these laser parameters. According to parameters analysis with energy utilization and manufacturing time, laser power 200W and scanning speed 800mm/s are more suitable parameters for melting effectiveness of powder. Through the analysis of hatch spacing which is found, if the overlapping rate exceeds 50%, it makes temperature gradient too large and is easy to cause thermal stress concentration, which is unfavorable for the manufacturing parts. Compared to the overlapping rate 30%, the temperature gradient is lower and molten pools show good bonding. We have also researched the implementation of two preheating methods to improve SLM process. Substrate preheating can help to have the lower temperature gradient and cooling rate. To avoid causing excessive the evaporation of material, it is better that the preheating temperature is controlled under 700K. Powder preheating shows no significant change in reducing the temperature gradient and the cooling rate. Therefore, it couldn’t improve the quality of the parts effectively.

摘要 I
誌謝 XI
目錄 XII
表目錄 XVI
圖目錄 XVII
符號說明 XXII
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 5
1-2.1 金屬粉末顆粒研究 5
1-2.2 馬蘭戈尼效應研究 9
1-2.3 選擇性雷射熔融法數值研究 11
1-2.4 零件表面品質研究 16
1-3 研究動機與目的 20
1-4 全文架構 21
第二章 基礎理論 22
2-1 雷射基礎理論 22
2-1.1 雷射基本原理 22
2-1.2 Nd-YAG雷射 23
2-1.3 高斯熱源能量分佈 27
2-2 熱傳理論介紹 34
2-2.1 相變化 34
2-2.2 熱對流與熱輻射 37
2-2.3 馬蘭戈尼效應 38
第三章 數值分析 41
3-1 物理模型 41
3-1.1 統御方程式 44
3-1.2 邊界條件 45
3-1.3 初始條件 47
3-2 數值方法 48
3-3 金屬材料熱物理性質 51
3-3.1 不鏽鋼316L(SS316L)材料性質 51
3-3.2 金屬粉末層等效熱物理參數 51
3-4 數值計算求解流程 59
3-5 物理模型測試 61
3-5.1 網格獨立測試 61
3-5.2 時間步階測試 63
第四章 結果與討論 65
4-1 熔池尺寸實驗比較 65
4-2 馬蘭戈尼效應分析 71
4-2.1 粉末溫度之影響 72
4-2.2 熔池尺寸之影響 82
4-3 雷射製程參數分析 84
4-3.1 雷射多重軌跡掃描分析 85
4-3.2 雷射參數熔融效益分析 89
4-4 掃描間距之探討 97
4-4.1 溫度梯度之影響 97
4-4.2 熔池尺寸之影響 100
4-5 掃描方式之探討 104
4-6 基板預熱之探討 110
4-6.1 溫度梯度之影響 110
4-6.2 冷卻速率之影響 112
4-6.3 熔池尺寸之影響 114
4-7 粉末預熱之探討 116
4-7.1 溫度梯度之影響 116
4-7.2 冷卻速率之影響 116
4-7.3 熔池尺寸之影響 119
4-8 預熱方式之比較 121
第五章 結論與未來工作 124
5-1 結論 124
5-2 未來工作 126
參考文獻 127

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