摘要
本研究主要以建立不鏽鋼(SS 304L)之三維數值模型探討銲接的流場狀況及成型，其中考慮反衝壓力(Recoil force)、馬倫格尼力(Marangoni force)、表面張力(Surface tension)對於熔池流動的影響，以及固液化模型、蒸發潛熱、雙相流模型以貼近真實銲接過程之物理現象，且在鎖孔(Keyhole)條件下，由於雷射於鎖孔內部進行多重反射(Multiple reflections)，以雷射體熱源模型(Body heat source)描述材料對於雷射能量之吸收率隨鎖孔深度增加而有變化。
過去研究若計算銲接模擬，需要因應銲接工況而調整許多數值參數且需要實驗參數進入模型中，而本研究藉由實驗加工參數進行無因次化，透過無因次參數與熔池成型之理論及本研究數值實驗之配合，可歸納出直掃式銲接模型與實際銲接成型之經驗資料，不僅減少模型中變動參數，且後人可透過本研究之經驗曲線所對應之無因次參數查表可得其模擬參數進行預測熔池成型，減少時間成本及數值實驗，且於模擬結果中分析鎖孔銲接所造成流場內部之氣泡型成與流動現象。

The purpose of this study is to establish a three-dimensional numerical welding model to evaluate the flow dynamics, which considers the effects of recoil force, Marangoni force, and surface tension. The model consists of the solidification/melting process, latent heat, interfacial forces, and two-phase flow model, which can describe the physical phenomena of the real welding process both quantitively and qualitatively. Under the condition of the keyhole, the laser performs multiple reflections inside the keyhole. The body heat source model is used to describe the change in the absorptivity of the material for laser energy as the depth of the keyhole increases.
In the previous studies, the simulation of welding requires many empirical parameters in advance of the experiments, which could vary according to the working conditions of the welding. This study utilizes dimensionless parameters that predict the width and depth of the welding pool based on experimental literature to determine the empirical parameters in the volumetric body heat source of the numerical model. As a result, this study provides a systematic framework to avoid the trial-and-error process to select the parameters in the model, which has also been validated through experiments with all kinds of working conditions for welding. Through the results, when the recoil pressure is stronger than the surface tension at the tip of the keyhole, the keyhole becomes deeper. When the surface tension is stronger than the recoil pressure at the tip of the keyhole, the free surface rises. In the stable keyhole mode, the location of the collapse of the keyhole becomes shallower without the Marangoni effect, but there is no significant difference in the size of the molten pool. In the unstable keyhole mode, due to the instability of the keyhole welding, the Marangoni effect cannot be ignored.

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