本研究之目的為探討積層製造(Additive Manufacturing, AM)之定向能量沉積技術(Directed Energy Deposition, DED)，利用商用軟體ANSYS Fluent 18.0建構一個三維暫態之多層加工固態模型，選用不鏽鋼316L做為金屬基板及金屬粉末之材料，探討各項製程參數之組合、馬蘭格尼效應驅使熔池內部熔融態金屬流動對熔池外型之發展以及各層金屬薄層幾何尺寸之影響，透過建構之異向熱傳導模型考慮馬蘭格尼效應對熔池內部熔融態金屬所造成之流動，另外也會探討各項製程參數組合下對冷卻速率之影響與趨勢，並且更進一步探討加工停滯時間之長短、基板預熱與否對金屬薄層幾何尺寸與冷卻速率之影響，最後，比較異向與等效兩種熱傳導模型所模擬之金屬薄層之幾何尺寸、熔池外型發展趨勢與冷卻速率之差異。
研究結果顯示，固定雷射掃描速率時，隨著雷射功率越大，金屬薄層冷卻速率則越慢，相較雷射功率1200 W，使用雷射功率1800 W可提升16 %左右的堆疊寬度，以及提升90 %左右的堆疊高度；固定雷射功率固定時，隨著雷射掃描速率越大，金屬薄層冷卻速率則越快，而雷射掃描速率每降2 mm/s可提升4 %左右的堆疊寬度，以及提升12~16 %左右的堆疊高度。在固定製程參數下之多層加工中，金屬薄層堆疊高度會隨加工層數增加而有不斷加高之趨勢，而冷卻速率則是減少。在進階製程分析中，過長的加工停滯時間無法有效改善製程品質，建議縮短加工停滯時間以提升加工效率；基板預熱對金屬薄層幾何尺寸有明顯的增加，並可以有效改善冷卻速率過快之問題，且有助於柱狀晶的形成與減少裂紋之產生。最後，在異向與等效兩種熱傳導模型之優劣分析中，無論是金屬薄層幾何尺寸或是熔池外型發展之趨勢，異向熱傳導模型所模擬之結果更優於等效熱傳導模型所模擬之結果，且使用等效熱傳所模擬之冷卻速率可能有高估之情形。

The purpose of this research is to develop a three-dimensional model of anisotropic heat conduction for directed energy deposition (DED) process. In this research, 316L stainless steel is used as material, and the study focuses on the fluid flow of melt pool is affected by the Marangoni effect. The Marangoni effect is simulated by the anisotropic enhanced thermal conductivity coefficient. The geometric sizes and cooling rate of metal layers are investigated under various combination of laser power and laser scanning speed.
In order to promote the growth of columnar grains and reduce cracking possibility, the effect of idle time and substrate preheating are studied. Moreover, the geometric sizes, melt pool, and cooling rate of metal layers simulated by two kinds of heat conduction models, namely equivalence and anisotropy, are compared in this study.
The research results indicate that when a fixed laser scanning speed is compared, using a laser power of 1800 W instead of 1200 W can lead to an increase in stack height by around 90%. When the laser power is fixed, decreasing the laser scanning speed by 2 mm/s can increase the stack height by around 12-16 %. Moreover, the cooling rate increases when laser scanning speed increases or laser power decreases but decreases with an increase in layer number.
The results also show that idle time has no obvious effects on process. Substrate preheating can increase the geometric sizes of metal layers and significantly reduce the cooling rate. The geometric sizes, melt pool, and cooling rate of metal layers simulated by the anisotropic heat conduction model are better than those simulated by the equivalent heat conduction model. Furthermore, using the equivalent heat conduction model may lead to an overestimation of the cooling rate.

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