臺灣博碩士論文加值系統

本研究是以ANSYS Fluent 15.0作為數值分析模擬軟體，研究重點在於建立三維暫態的三層掃描DED數值熱分析模型，並藉由三層的DED加工來探討多層加工之情形，該模型之材料主要是以航太零組件中常見的修復材料 Inconel 718進行分析，由國立成功大學機械加工廠中的DED機台進行實驗驗證，證明該數值模型具有準確性。研究中先探討了雷射功率與雷射掃描速率對於三層金屬沉積物的幾何尺寸及冷卻速率的影響，再依據最佳平均節省製程時間、最佳平均節省能源消耗、降低冷卻速率這三個層面去衡量不同製程參數之組合，進而歸納出最佳製程參數，並建立光斑半徑與避免蒸發的極限雷射功率之關係式。最後以最佳製程參數探討保護氣體預熱、基板預熱、逐層調降雷射功率、基板預熱結合逐層調降雷射功率、加工停滯時間、單雙向加工掃描方式的影響性。
從研究結果可以得知，利用固定製程參數進行多層掃描加工時，則沉積物高度會逐層增加，但冷卻速率則反之；當光班半徑為2 mm且雷射功率2500 W、雷射掃描速率 8 mm/s最能節省製程時間與能源且能得到更佳的成品的結構與金相；可利用光斑半徑與避免蒸發的極限雷射功率之關係式作為不同光斑半徑下選用雷射功率進行分析的依據；保護氣體預熱對於多層掃描加工的影響有限；基板預熱能有效增加金屬沉積物之幾何尺寸，並可有效降低冷卻速率和溫度梯度改善結構品質；雷射功率隨著層數調降可以獲得較穩定的堆疊外形，亦可得到逐層平均化之冷卻速率；基板預熱結合逐層調降雷射功率能夠得到更佳的結構品質；加工停滯時間對於多層掃描加工的影響有限；單向加工較有利於維持沉積物的堆疊外型之一致性。

In this research, a numerical model for multi-layer scanning of Directed Energy Deposition (DED) process for Inconel 718 is established to investigate transient thermal phenomenon of process parameters. The study first investigated the effects of laser power and scanning speed on the geometry and cooling rate of multi-layer metal depositions, and then based on the optimal average process time-saving, optimal average energy-saving, and reducing cooling rates, the optimal combination of process parameters is determined.
According to research results when multi-layer scanning processing is performed by using fixed process parameters, the deposited height will increase layer-by-layer, but the cooling rate is reversed. It is found that spot sizes of 2 mm and the laser power of 2500 W and scanning speed of 8 mm/s can save the process time and energy and get a better structure and metallography. The relationship between the spot sizes and the limit laser power of avoid evaporation is established as the basis for the analysis of laser power under different spot sizes. To improve DED process problems induced by thermal field, the influences of shielding gas preheating and substrate preheating and reduce laser power layer-by-layer and substrate preheating combined with layer-by-layer reduction of laser power and idle time and scanning direction are studied. Shielding gas preheating has little influence on multi-layer scanning processing. Substrate preheating can effectively increase the geometrical size of deposition, and can effectively reduce the cooling rate and temperature gradient to improve the structural quality. The laser power can be reduced with the number of layers to obtain a more stable stacked shape, and the cooling rate of layer-by-layer averaging can also be obtained. Substrate preheating combined with layer-by-layer reduction of laser power can obtain better structural quality. The results show that idle time has the limited impact on multi-layer scanning processing. The same direction scanning is more conducive to maintain the consistency of the stacked appearance of deposition.

目錄
摘要 i
誌謝 xix
目錄 xx
表目錄 xxiv
圖目錄 xxv
符號表 xxxii
第一章 緒論 1
1-1 前言 1
1-1-1 積層製造的發展與應用 1
1-1-2 積層製造技術方法 4
1-1-3 定向性能量沉積技術 6
1-2 文獻回顧 8
1-2-1 DED加工技術之發展 8
1-2-2 DED加工之數值模擬方法 8
1-2-3 DED製程參數對成品品質之影響性 13
1-2-4 DED加工熔池中馬蘭格尼效應之影響性 18
1-3 研究背景與目的 20
1-4 全文架構 21
第二章 基礎理論 22
2-1 雷射理論 22
2-1-1 雷射工作原理 22
2-1-2 二極體雷射介紹 23
2-1-3 雷射種類與能量分布 26
2-2 鎳基(Inconel)超合金介紹 36
2-3 金屬固化理論與金相名詞介紹 42
第三章 研究方法 45
3-1 物理模型 45
3-1-1 基本假設 47
3-1-2 統御方程式 48
3-1-3 初始條件與邊界條件 48
3-2 Inconel 718熱物理性質 51
3-3 數值模擬流程 56
3-3-1 基板熔池模擬 56
3-3-2 預估金屬沉積物之堆疊幾何尺寸方法 58
3-3-3 DED製程之溫度場模擬方法 64
3-4 物理模型測試 67
3-4-1 網格獨立測試 67
3-4-2 時間步伐測試 71
3-5 實驗驗證 73
3-5-1 溫度場驗證 76
3-5-2 金屬沉積物幾何尺寸驗證 79
第四章 結果與討論 83
4-1 探討多層固定製程參數之影響 84
4-1-1 金屬沉積物幾何尺寸之變化 84
4-1-2 金屬沉積物冷卻速率之影響 90
4-2 製程參數最佳化分析 95
4-3 光斑半徑與極限雷射功率之關係 110
4-4 進階優化製程探討 112
4-4-1 保護氣體預熱之影響 112
4-4-2 基板預熱之影響 119
4-4-3 逐層調降雷射功率的影響 124
4-4-4 基板預熱結合逐層調降雷射功率的影響 129
4-4-5 加工停滯時間的影響 131
4-4-6 單向與雙向掃描方式的影響 136
第五章 結論與未來工作 140
5-1 結論 140
5-2 未來工作 142
參考文獻 143

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