本研究主要分為三個部分，第一部分針對送粉型直接式能量沉積製程(Directed Energy Deposition , DED)，在燒熔過程前先加入預熱雷射進行加熱，使基板先升溫再進行DED送粉燒熔過程。本研究以套裝軟體ANSYS Fluent進行數值模擬，將預熱雷射熱源以熱通量的形式加入基板上邊界條件，模擬預熱雷射對基板的加熱現象，並將此結果套入DED無因次經驗方程式，用以預測經過預熱之後的燒熔成形結果，並透過接觸角(wetting angle , θc）和接合度(dilution , Dc)分析最佳的預熱溫度。
第二部分同樣是針對送粉型直接式能量沉積製程，在同一基板相鄰位置燒熔多道熔覆層，其熔覆層表面不平整，因此我們針對熔覆層掃射五道雷射重新熔化表面，希望能整平熔覆層表面，以利於後續二次加工。本研究以套裝軟體ANSYS Fluent建立雷射重熔的二維數值模型，運用多相流模型(Volume of Fluid , VOF)將計算域分為氣體相(Argon)與金屬相(Inconel 625)，將模擬結果針對熔覆層表面進行表面粗糙度θ_Rq的定量分析，以及每一道雷射的熔池分析和不同道雷射間的熔池重覆區域。
第三部分針對同軸送線型直接式能量沉積製程，以開源軟體Openfoam進行數值模擬，運用大渦模型(Large eddy simulation, LES)和次網格尺度模型（Sub-Grid Scale Model , SGS）模擬紊流現象，研究目的為重點區域，即基板雷射光斑和靠近光斑之線材高溫區域的保護氣體含量，透過數值模擬改良噴嘴機構的幾何設計，以達到提升保護氣體含量之目的。

This study focuses on powder-fed and wire-fed Directed Energy Deposition (DED) processes, combining numerical simulations and experimental analyses to investigate the effects of laser preheating, laser remelting, and shielding gas on the process. The research is divided into three main sections:

Part 1: Laser Preheating

Before the DED melting process, a preheating laser is used to heat the substrate, raising its temperature prior to powder deposition and melting. Numerical simulations are conducted using ANSYS Fluent, where the preheating laser heat source is applied as a heat flux boundary condition on the top surface of the substrate to simulate the heating phenomenon. The results are incorporated into a dimensionless empirical equation for DED to predict the melting and formation outcomes after preheating. The optimal preheating temperature is analyzed based on the wetting angle (θc) and dilution (Dc).

Part 2: Laser Remelting

In the same powder-fed DED process, multiple cladding tracks are deposited on adjacent areas of the substrate, resulting in an uneven cladding surface. To smooth the cladding surface and facilitate subsequent secondary processing, five laser tracks are scanned to remelt the surface. A two-dimensional numerical model of laser remelting is developed using ANSYS Fluent, employing the Volume of Fluid (VOF) multiphase flow model to distinguish the computational domain into gas phase (argon) and metal phase (Inconel 625). The simulation results are used to quantitatively analyze the surface roughness (θ_Rq) of the cladding layer and evaluate the melt pool for each laser track, as well as the overlap regions between adjacent laser tracks.

Part 3: Shielding Gas in Wire-fed DED Nozzle

In the wire-fed DED process, numerical simulations are conducted using the open-source software OpenFOAM, employing the Large Eddy Simulation (LES) and Sub-Grid Scale (SGS) models to simulate turbulent flow phenomena. The research focuses on the critical area, specifically the laser spot on the substrate and the high-temperature region near the wire close to the spot, to analyze the shielding gas content. The numerical simulations aim to optimize the nozzle geometry to improve shielding gas coverage and effectiveness.

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