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基于磁流体动力学及Maxwell方程组,建立了变极性等离子电弧的三维瞬态计算模型,依据变极性等离子弧焊对铝合金板材穿孔焊接过程的物理特性,提出了随电弧极性变化的分时导电模型,通过计算得到了变极性等离子电弧的温度场、流场、电流密度和电弧压力的分布情况,以及电弧压力随时间的变化过程。通过实验测量了工件表面电弧中心压力,得到了不同极性时的电弧形态。结果表明:相同电流条件下,正极性时电弧温度场分布比反极性时更加分散,但正极性时电弧最高温度范围小于反极性时;反极性电弧压力和电流密度在电弧中心处均大于正极性,在径向距电弧中心一定距离处,2种极性时的电弧压力和电流密度的大小出现反转;电弧压力对焊接电流响应迅速,正极性电弧压力小于反极性电弧压力,焊接电流过零时,电弧压力会降低到较低的值,电流增加时电弧压力变化存在“过冲”现象;对实验与计算得到的变极性等离子电弧正反极性时电弧图像和工件表面电弧中心压力进行了对比,结果吻合良好。
Based on the magnetohydrodynamics and Maxwell’s equations, a three-dimensional transient model of variable polarity plasma arc was established. According to the physical characteristics of variable-polarity plasma arc welding on the process of perforation welding of aluminum alloy plate, Time-dependent conduction model, the distribution of the temperature field, the flow field, the current density and the arc pressure of the arc plasma with variable polarity and the variation of the arc pressure with time are calculated. The arc center pressure on the workpiece surface was measured experimentally, and the arc shape at different polarities was obtained. The results show that under the same current conditions, the distribution of arc temperature field is more dispersed than that of the opposite polarity at positive polarity, but the maximum temperature range of the arc is less than that at the opposite polarity at the same current. Both the arc voltage and the current density at the arc center Is greater than the positive polarity, at a certain distance from the center of the arc in the radial direction, the magnitude of the arc pressure and the current density in the two kinds of polarity are reversed; the arc pressure quickly responds to the welding current, the positive arc pressure is less than the reverse arc voltage, When the welding current zero crossing, the arc pressure will be reduced to a lower value, the current increase in the arc pressure changes exist “overshoot” phenomenon; experimental and calculated variable polarity plasma arc positive and negative arc image and Workpiece surface arc center pressure were compared, the result is in good agreement.