The oscillation arc assisted by an extra alternating longitudinal magnetic field (LMF) in narrow gap tungsten arc welding is proved to be effective in avoiding welding defects due to insufficient fusion at the side walls in joining thick wall plates. The behavior of the welding arc and molten pool under the LMF is simulated to reveal the influence of the LMF on the formation of a uniform penetration weld bead. A unified mathematical model was developed for the narrow gap tungsten arc welding including the plasma arc, molten pool, electrode, and their interactions. Under the LMF, the whole welding arc is deflected and oscillates between the two side walls. When the magnetic-field strength is larger than 6 mT, the axis of the arc deflects to the side wall; the max value of heat flux at the bottom decreases by one-half, and the max value at the side wall is increased by a factor of ten. On the other hand, under the LMF, the forces acting on the molten pool are changed; the fluid flow pattern is helpful to increase the heat transferred to the side walls. The model is validated by experimental results. Both the percentage deviations of the simulation weld penetration at the side wall and at the bottom from the experimental results are lower than 10%.

中文翻译：

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纵向磁场对窄间隙气体钨极氩弧焊中焊道形成的影响

事实证明，在窄间隙钨极电弧焊中，通过额外的交变纵向磁场（LMF）辅助的振荡电弧可有效避免由于连接厚壁板时侧壁熔化不足而引起的焊接缺陷。模拟了LMF下焊接电弧和熔池的行为，以揭示LMF对均匀熔透焊道形成的影响。针对窄间隙钨极电弧焊开发了统一的数学模型，包括等离子弧，熔池，焊条及其相互作用。在LMF下，整个焊接电弧会偏转并在两个侧壁之间振荡。当磁场强度大于6 mT时，电弧的轴会偏向侧壁。底部的热通量最大值减少了一半，侧壁的最大值增加了十倍。另一方面，在LMF的作用下，作用在熔池上的力发生了变化。流体流动方式有助于增加传递到侧壁的热量。通过实验结果验证了该模型。与实验结果相比，侧壁和底部模拟焊缝熔深的百分比偏差均低于10％。