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研究生:黃冠霖
研究生(外文):Guan-LinHuang
論文名稱:選擇性雷射熔融法應用於不鏽鋼316L金屬粉末之非等向增強性熱傳導模型建立及熔池熱分析
論文名稱(外文):Anisotropic Enhanced Thermal Conductivity Modeling and Thermal Analysis on Molten Pool of Stainless Steel 316L Metal Powder in Selective Laser Melting
指導教授:温昌達
指導教授(外文):Chang-Da Wen
學位類別:碩士
校院名稱:國立成功大學
系所名稱:機械工程學系
學門:工程學門
學類:機械工程學類
論文種類:學術論文
論文出版年:2020
畢業學年度:108
語文別:中文
論文頁數:134
中文關鍵詞:選擇性雷射熔融非等向增強熱傳導多層及多重軌跡掃描熔池分析
外文關鍵詞:Selective Laser Meltinganisotropic enhanced thermal conductivitymulti-layer and multi-track scanninganalysis of molten pool
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本研究主要是以ANSYS Fluent建立三維暫態數值模型,模擬選擇性雷射熔融法以多層及多重軌跡掃描不鏽鋼316L粉末。其中為了簡化和加快建模過程,在此研究中藉由非等向增強性熱傳導方法來解決熔池內對流的問題,並透過與實驗結果的比對,發現此方法與實驗結果具有很好的一致性。研究中亦利用所建立之模型比較雷射功率及掃描速度對熔池尺寸、溫度分佈及冷卻速率之影響,並透過能量利用性及冷卻速率進行雷射參數的篩選。最後以優化後之製程參數對基板預熱、掃描間距及單雙向加工掃描方式的影響做進一步的分析。
從研究結果可以得知,非等向增強性熱傳導模型對於熔池尺寸及溫度場具有一定的影響性,隨著增強因子的增加,熔池的深度及寬度會隨之增加,而熔池的最高溫度則會降低;在多層及多軌掃描中,當雷射功率愈大、掃描速度愈慢時,可以使熔池尺寸、熔池溫度及溫度梯度增加,但會降低冷卻速率;而透過製程參數優化分析發現,雷射功率200 W、掃描速度800 mm/s具有較好的加工效率及能源利用性,且所產生的零件品質較佳;在基板預熱方面,發現基板預熱可以有效降低溫度梯度及冷卻速率;在掃描間距的探討中得到,軌跡重疊率若超過50%,會使某區域容易產生局部熱堆積問題,此現象易造成熱應力集中,對於零件製造相當不利,在軌跡重疊率為30%時其熔池具有良好的結合性;單向掃描方式能避免端點處的能量堆積。
In this research, a three-dimensional transient numerical model is established by ANSYS Fluent to simulate multi-layer and multi-track scanning of Selective Laser Melting method for stainless steel 316L metal powder. To simplify and speed up the modeling process, the research uses the anisotropic enhanced thermal conductivity approach to account for melt pool convection. The effects of laser power and scanning speed on the geometry, temperature distribution, and cooling rate of the molten pool are investigated. The results show that anisotropic enhanced thermal conductivity has an effect on the molten pool dimensions and temperature field. According to the comparing results of different laser parameters, when the laser power is larger or scanning speed is slower, the size of the molten pool, melt pool temperature, and temperature gradient will increase. The microstructural and mechanical properties are mainly governed by the corresponding solidification parameters, including thermal gradient (G) and solidification rate (R), where the G/R ratio governs the solidification mode while their product (G × R) controls the scale of the solidification microstructure. When the laser power is larger or scanning speed is slower, the G/R ratio will increase and the cooling rate will decrease. Based on parameter analysis with energy utilization and cooling rate, it is found that the laser power of 200 W and the scanning speed of 800 mm/s can save the process time and energy and obtain a better structure. To further improve the manufacturing problems induced by thermal field, substrate preheating and hatch spacing are studied. The results indicate that substrate preheating can increase geometrical sizes of the molten pool, and obviously reduce temperature gradient and cooling rate. If the overlapping rate exceeds 50%, it is easy to cause thermal stress concentration, which is unfavorable for the manufacturing parts.
摘要 i
誌謝 xii
目錄 xii
表目錄 xvii
圖目錄 xviii
符號說明 xxiii
第一章 緒論 1
1-1 研究背景 1
1-1.1 積層製造 1
1-1.2 積層製造技術方法 2
1-1.3 選擇性雷射熔融法 3
1-2 文獻回顧 6
1-2.1 金屬粉末層之影響性 6
1-2.2 零件常見之缺陷成因 11
1-2.3 選擇性雷射熔融法數值研究 13
1-2.4 馬蘭戈尼效應之影響性 17
1-3 研究動機與目的 21
1-4 全文架構 23
第二章 基礎理論 24
2-1 雷射基礎理論 24
2-1.1 雷射作用原理 24
2-1.2 Nd-YAG雷射 27
2-1.3 高斯熱源能量分佈 29
2-2 不鏽鋼介紹 34
第三章 研究方法 37
3-1 物理模型 37
3-1.1 基本假設 37
3-1.2 統御方程式 39
3-1.3 初始條件與邊界條件 40
3-1.4 蒸發 41
3-2 金屬材料熱物理性質 45
3-2.1 不鏽鋼316L材料性質 45
3-2.2 非等向性增強熱傳導係數 51
3-2.3 金屬粉末層等效熱物理參數 52
3-3 數值方法 54
3-4 數值計算求解流程 57
3-5 物理模型測試 59
3-5.1 網格獨立測試 59
3-5.2 時間步階測試 61
第四章 結果與討論 63
4-1 非等向增強性熱傳導模型驗證 63
4-1.1 增強因子大小之影響 64
4-1.2 增強因子大小之探討 69
4-1.3 熔池尺寸驗證 72
4-2 雷射製程參數對於SLM加工的影響 76
4-2.1 熔池幾何變化 77
4-2.2 溫度場之變化 80
4-2.3 熔池熱行為之比較 85
4-2.4 G/R值之影響 92
4-3 雷射參數優化分析 99
4-4 進階優化探討 106
4-4.1 基板預熱之影響 106
4-4.2 掃描間距之影響 112
4-4.3 掃描方式之影響 118
第五章 結論與未來工作 123
5-1 結論 123
5-2 未來工作 125
參考文獻 126
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