本研究利用計算流體力學套裝軟體，建立三維圓形擺盪焊接數值模擬，使用英高鎳合金(Inconel 718)金屬基板，採用可調型體熱源(Adaptive volumetric heat source)進行燒熔，重現出焊接過程中產生鎖孔(keyhole)之暫態流場，且觀察圓形擺盪焊接暫態燒熔之流場流動、熱傳機制、最終成型尺寸。為了更符合實際物理現象，本研究採用多相流模型捕捉自由液面形貌，考慮表面張力(Surface tension)、馬倫格尼力(Marangoni force)、反衝壓力(Recoil force)使燒熔中內部流場更真實呈現。考慮熔化潛熱、蒸發潛熱、熱對流及熱輻射散失計算出溫度分布及相變化時機點。
本研究經數值模擬所得結果與實驗之成型尺寸比較，熔池深寬尺寸平均誤差於10%內，冷卻率(cooling rate)之模擬與實驗結果平均誤差於20%內，二次枝晶臂間距(SDAS) 平均誤差於30%內，表示暫態溫度場具參考價值，由暫態流場觀察可了解鎖孔之生成與擺盪效應劇烈影響流場流動，不同擺盪位置亦影響鎖孔深度。熔池之形貌亦隨擺盪路徑重疊情況與重疊率不同產生差異，且建立雷射作用於Inconel 718金屬表面上之能量分布與表面冷卻率之關係。

In this study, computational fluid dynamics software was used to establish a three-dimensional circular oscillation welding numerical simulation. Inconel 718 was used as a metal substrate with an adjustable volume heat source to melt and reproduce the welding flow field. During this process, a keyhole transient flow field was generated, and the heat transfer mechanism, final forming size, and transient flow in the molten pool were observed. To be more in line with actual physical phenomena, this study uses a multiphase flow model to capture the shape of the free liquid surface, while considering surface tension, Marangoni force, and recoil force to make the melting process more realistic. Considering the latent heat of melting, latent heat of evaporation, heat convection, and heat radiation loss, calculate the temperature distribution and phase transition time.

The numerical simulation results of this study are compared with experimental data. The average error of the depth and width of the molten pool is within 10%. The average error of the cooling rate simulation and experiment results is about 20%. The average error of the distance between the secondary dendrite arms (SDAS) is about 30%, indicating that the transient temperature field is reliable. The observation of the transient flow field shows that the generation of keyhole and the effect of oscillation seriously affect the flow field, and different oscillation positions also affect the depth of the keyhole. The shape of the molten pool also changes with the number of overlaps of the oscillation path and the overlapping rate. The relationship between the energy distribution of the laser acting on the metal surface of Inconel 718 and the surface cooling rate is established.

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