考虑小孔后向偏移的等离子弧焊接热过程模型

Thermal Process Model of Plasma Arc Welding with Considering the Backside Keyhole Deviation

在穿孔等离子弧焊接过程中,背面小孔中心相对于焊枪轴线存在一定的偏移。深入研究小孔孔道后向偏移时所涉及的熔池与小孔瞬态演变行为和传热过程,对于优化以背面小孔中心偏移量为控制参数的控制方法,保证焊缝成形质量具有重要意义和实用价值。针对穿孔等离子弧焊接中小孔的形成特点,建立随小孔形状动态调整的组合式体积热源模型,并在热源模型中引入热源中心向后偏移的参量,间接反映背面小孔后向偏移对穿孔等离子弧焊接热过程的影响。在小孔形状方程中,增加等离子流后推力,间接描述等离子流对熔池流体的后推作用。利用建立的三维瞬态熔池与小孔的数学模型,分析等离子弧焊接过程中温度场和小孔形状的瞬时演变过程。将工件背面小孔形状尺寸和穿孔时间等模拟结果与试验结果进行对比,两者基本吻合,对所建立的数学模型进行验证。

When the plasma torch and the work-piece move relatively in keyhole plasma arc welding（PAW）, it is found that there is a keyhole exit deviation distance between the keyhole center point and the welding torch axis. Considering the keyhole deviation, studying the interaction of weld pool and keyhole is of great theoretical as well as practical significance to obtain the high-quality welds. In addition, the research can also provide guidelines to optimize the control method, on the basis of taking the backside keyhole deviation distance as the controlled variable. A combined volumetric heat source model is established to reveal the dynamic interaction between heat transfer process and keyhole evolution. Along the thickness of the test plate, a deviation parameter of the volumetric heat source center is set in the model, which describes the thermal effect of the keyhole deviation in the PAW. In the keyhole shape equation, the backward pushing force of plasma jet is taken into account, which reflects the influence the plasma jet on the weld pool. The thermal conduction process and keyhole evolution in PAW are numerically simulated. The predicted and measured keyhole exit sizes and keyhole establishment time agree with each other.