Bubble characteristics and bubble volume fraction have significant effects on crater morphology and machining efficiency during electrical discharge machining (EDM) in liquid. Therefore, there is a need to elucidate the mechanism of bubble characteristics in EDM and analyze the mechanism of crater formation based on these bubble characteristics. However, since EDM is a transient multiphysics process, it is extremely difficult to understand bubble characteristics using experimental methods. Therefore, the generation, expansion, explosion, and disappearance of bubbles during EDM were simulated based on a three-phase flow model in this study. The model used the phase field method to track the boundary motion, judged the existence mode of each phase according to the order parameter gradient function, and analyzed the formation of crater morphology by the gradient of surface tension in the molten pool. The motion process of bubbles, the material removal mode, and the formation mechanism of crater morphology during the pulsed discharge were analyzed using the model. The results revealed that the periodic motion of the plasma channel would drive the molten pool to produce the corresponding periodic motion, and the bubbles would grow following the periodic motion of the molten pool. The material was removed in different ways in different periods, among which the removal mode of molten splash was predominant. The surface tension gradient inside the molten pool, the periodic motion of the molten pool, and the hydrostatic pressure in the molten region had a combined effect on bubble motion, the flow of the molten pool, and the formation of the crater morphology.

中文翻译：

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基于三相流模型的电火花加工中气泡特征和熔池动力学机制分析

气泡特性和气泡体积分数对液体放电加工（EDM）过程中的凹坑形态和加工效率有显着影响。因此，有必要阐明电火花加工中气泡特性的机理，并根据这些气泡特性分析缩孔形成的机理。然而，由于电火花加工是瞬态多物理场过程，因此使用实验方法了解气泡特性极其困难。因此，本研究基于三相流模型模拟了电火花加工过程中气泡的产生、膨胀、爆炸和消失。该模型采用相场法跟踪边界运动，根据序参梯度函数判断各相的存在模式，并通过熔池表面张力梯度分析弹坑形貌的形成。利用该模型分析了脉冲放电过程中气泡的运动过程、材料去除方式以及弹坑形貌的形成机制。结果表明，等离子体通道的周期运动会带动熔池产生相应的周期运动，气泡会随着熔池的周期运动而长大。不同时期材料的去除方式不同，其中以熔飞溅去除方式占主导地位。熔池内部的表面张力梯度、熔池的周期性运动以及熔区的静水压力共同影响气泡的运动、熔池的流动以及火山口形貌的形成。