Physical mechanism of material flow and temperature distribution in keyhole plasma arc welding at initial unstable stage
Physical mechanism of material flow and temperature distribution in keyhole plasma arc welding at initial unstable stage
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DOI：
10.1063/5.0141776
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发表时间：
2023-03
影响因子：
4.6
通讯作者：
Jingbo Liu;F. Jiang;Bin Xu;Guokai Zhang;Shujun Chen
中科院分区：
文献类型：
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作者：
Jingbo Liu;F. Jiang;Bin Xu;Guokai Zhang;Shujun Chen
小孔等离子弧焊接的初始不稳定阶段严重影响焊接的稳定性和质量，特别是在非垂直焊接位置，难以控制，制约了工艺的发展和应用。本文利用红外热像仪和高速摄像系统，研究了从小孔挖掘阶段到小孔稳定运动阶段的温度分布和流动特性。实验结果表明，小孔后侧的熔融金属逐渐在小孔出口侧和后壁积聚并凝固。当足够的熔融金属积聚在小孔后侧壁上时，它在表面张力的作用下关闭。锁孔后侧壁形成的角度（86°-90°）可用于确定锁孔后侧是否闭合并达到锁孔稳定运动阶段。同时，研究了重力方向的改变对小孔熔池温度分布、流动行为和凝固形态的影响，进一步揭示了焊接过程的初始不稳定阶段。在平坦位置，在该阶段，小孔后侧壁表面内的高温区域逐渐积聚在靠近焊接熔池的出口侧。更多的熔融金属通过重力和剪切力流到小孔出口侧，这导致在小孔后侧上的分离区域更靠近焊池的出口侧。这使得在初始不稳定阶段期间当其处于平坦位置时更难闭合锁孔壁。此外，小孔后侧的温度分布和流动行为可以作为表征焊接过程中所有位置和阶段的熔池流动状态的另一个因素。
The initial unstable stage associated with keyhole plasma arc welding affects the stability and quality heavily, especially in the non-vertical welding position, which is difficult to control and restricts the process development and application. This work clarifies the temperature distribution and flow behavior of the process from the digging keyhole stage to the keyhole stable movement stage via an infrared thermography system and high-speed camera system. The experimental results showed that the molten metal on the rear side of the keyhole gradually accumulates and solidifies on the exit side and rear wall of the keyhole. When enough molten metal accumulates on the keyhole rear sidewall, it closes under the action of surface tension. The angle (86°–90°) of the keyhole rear sidewall formation can be used to determine whether the keyhole rear side is closed and reached the keyhole stable movement stage. Simultaneously, the influence of the shifting direction of gravity on the temperature distribution, flow behavior, and solidification morphology of the keyhole weld pool was investigated, which further revealed the initial unstable stage of the welding process. In the flat position, at this stage, the high-temperature area within the keyhole rear sidewall surface gradually accumulates close to the exit side of the weld pool. More molten metal flows to the keyhole exit side by gravity and shear forces, which causes a separation area on the keyhole rear side that is nearer to the exit side of the weld pool. This makes it harder to close the keyhole wall when it is in a flat position during the initial unstable stage. Furthermore, the temperature distribution and flow behavior of the keyhole rear side can be used as another factor to characterize the flow state of the weld pool in all positions and stages of welding.