應用大渦流模擬於雷射沉積製程中之多噴嘴粉末噴流

Abstract

雷射沉積製成是一種透過融化和固化金屬粉末來製造三維工件的工業打印製程技術。在過往的許多研究當中，幾乎都是使用雷諾平均納維-斯托克斯方程紊流模型(RANS)來進行計算流體力學(CFD)的模擬。但其限制是不能求解出流場中的紊流擾動量，而這卻是影響到金屬顆粒行為的一個潛在變因。再者，大部分有關熔池模擬的研究都是單純應用濃度數值模型來進行粉末質量輸入，進而忽略顆粒真實運動行為。因此，此研究目標為使用大渦流模擬紊流模型來求解分析流場與顆粒的運動現象，並藉由拉格朗日顆粒追蹤法實現更加真實的熔池濃度質量輸入。我們的分析重點也專注在流場與顆粒的運動和溫度，以及其之間的交互作用現象。透過使用大渦流模擬紊流模型，我們的模擬結果讓高解析度的瞬時流場特徵得以可視化。並且經由分析流場的紊流動能，我們證明了大渦流模擬此類能求解瞬時流場的模型之必要性。此外，我們也發現物體加工的基板很大程度地影響了流場結構，且也因為此特殊流場，粉末的聚焦點至少上移了1毫米。

The laser Direct Energy Deposition (DED) process is an additive manufacturing technique that utilizes the melting and solidification of metallic powder to create three-dimensional objects. In many research studies, the Reynolds-Averaged Navier-Stokes (RANS) turbulence model has commonly been used for Computational Fluid Dynamics (CFD) analysis of the powder stream in the DED process. However, a limitation of the RANS model is its inability to simulate turbulence fluctuations affecting the particles. Furthermore, many studies simulate the melting pool using only the concentration analytical model for mass input, which may not accurately capture the actual particle movement. Therefore, this study aims to investigate the flow field and particle movement in the DED process using the Large-Eddy Simulation (LES) method, while employing the Lagrangian particle method to achieve a more realistic concentration mass input for melting pool. Moreover, our analysis emphasizes on multiple aspects, including the flow, particles, coupling between the two phases, and temperature interaction. By employing LES, the simulation results demonstrate the high-resolution visualization of instantaneous flow field structure. The analysis of turbulent kinematic energy further confirms the necessity of employing LES models to solve transient flow fields in the DED process. Additionally, our findings reveal that the presence of a substrate for object processing significantly alters the flow structures compared to the case without a substrate. The convergence depth of the powder flow also moves upward at least 1 mm due to the unique flow structure induced by the substrate.