针对穿孔等离子弧焊接工艺, 建立了定点焊的二维轴对称非稳态数理模型, 描述高温流动的电弧与工件熔池的耦合输运过程, 通过数值模拟获得了电场、磁场、流场与温度场的演变规律. 模拟焊缝熔合线与实验结果吻合较好, 验证了数学模型的合理性. 研究结果表明: W阴极尖端附近的电流密度与温度是最高的; 等离子弧在工件上部呈现出“钟形”, 而在中心轴线处因进入小孔呈细长的“锥形”; 高速Ar气等离子体冲击到小孔壁面时速度急剧降低, 小孔内出现高压区和Ar气等离子体的返流现象; 熔池内流动与传热的综合作用使焊缝熔合线呈倒“喇叭形”. 进一步对焊接的操作参数及焊枪结构参数进行了影响因素的正交试验模拟. 极差分析表明, 焊枪的结构因素比焊接操作参数更重要, 即对电极间距、电极内缩量、喷嘴孔径需予以重点考虑, 以获得良好的焊缝形状.

A 2D axial symmetrical mathematical model was developed for stationary keyholing plasma arc welding (PAW), to describe the transport process in coupled high-temperature flow arc and molten pool in the workpiece. The evolutions of electric, magnetic, velocity and temperature fields were simulated. The simulated fusion line of the weld bead is in quite good agreement with the experimental results, validating the mathematical model. It turns out that, both the current density and the temperature reach the maximum values near the tip of the tungsten cathode. The arc displays a typical bell-shape above the workpiece, but becomes slim cone-shape near the central axis as the arc enters the keyhole. The argon plasma slows down sharply when it strikes the inner wall of the keyhole, so high pressure appears in the keyhole and some argon plasma flows back. The combination of fluid flow and heat transfer contributes to the reversed bugle shaped fusion line. The simulation of orthogonal test was further conducted to study the effects of operational and structural parameters of the weld torch. The range analysis shows that the structural parameters of weld torch are more influential than the operational parameters. That is, more attention should be paid to control the gap between two electrodes, the electrode shrinkage and the nozzle diameter to guarantee the welding quality.