積層製造技術中的定向能量沉積系統（DED）在製造與修復零件方面皆具有很大的潛力。DED製程使用高能量雷射熔化金屬基板以在基板表面上形成熔池，接著將金屬粉末同時注入熔池中以進行材料沉積，將上述過程多次重複以製造複雜的3D部件。DED製程中包含的物理現象是高度複雜的，其中包含的有雷射輻射在粉末集中性區域與基板中金屬粉末的吸收和散射特性，熱傳導性質，熔池的形成與凝結等物理現象。
　　本研究提出了一種新方法來分析金屬粉末與雷射交互作用後之能量吸收率並提供於構建體積熱源以應用於DED製程的傳熱模擬。為了達成此目的，首先執行計算流體力學（CFD）模擬以估計粉末集中性區域的尺寸和位置。另外，亦可獲得粉末集中性區域中的粉末集中性分佈曲線。接著，執行蒙特卡羅射線追踪(Monte Carlo ray tracing)模擬以計算粉末集中性區域的總粉末能量吸收率。且經過實驗與模擬比對，平均粉末濃度區域和總吸收率的模擬結果與實驗結果相當接近並得到良好驗證。最後，此研究討論了粉末質量流量與粉末氣體流速對於金屬粉末和金屬基板的能量吸收率的影響。據我們所知，此模擬方法為DED過程中不透過任何估計的情況下，能夠直接由金屬粉末與雷射交互作用模擬直接求得能量吸收率。

　　Additive Manufacturing such as Directed Energy Deposition (DED) process has strong potential in manufacturing parts. DED uses thermal energy of laser beam to fuse the metal substrate for creating the molten pool on the surface of the substrate and then Multiple streams of metal powders are simultaneously injected into the molten pool for material deposition. The procedure described above is repeated line by line, layer by layer to manufacture complex 3D parts. Physical phenomenon associated with DED process is highly complex including absorption and scattering of laser radiation with powder particles in the concentration region and substrate, thermal conduction, the formation and solidification of the melt pool, and so on.
　　The present study proposes a new methodology to construct the volumetric heat source for heat transfer simulation of DED process. For modeling the volumetric heat source, computational fluid dynamics (CFD) simulation is first performed to estimate dimensions and location of the powder concentration region. Additionally, the powder mass distribution in the concentration region is also attained. Subsequently, Monte Carlo ray tracing simulation is performed to calculate the total powder energy absorptivity of the concentration region. It is shown that the simulated results of the average powder concentration region and total absorptivity are in good agreement with the experimental results. Finally, the effects to the average absorptivity of the metal powder and substrate regarding to the powder mass flow rate and powder-gas flow rate are discussed. To the best of our knowledge, this is the first finding in the total laser absorptivity of the concentration zone in DED process without any fitting estimation.

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