Tashiro Shinichi
Joining and Welding Research Institute, Osaka University, Osaka 567-0047, Japan.
Materials (Basel). 2024 Mar 15;17(6):1348. doi: 10.3390/ma17061348.
The Keyhole Plasma Arc Welding (KPAW) process utilizes arc plasma highly constricted by a water-cooled cupper nozzle to produce great arc pressure for opening a keyhole in the weld pool, achieving full penetration to the thick plate. However, advanced control of welding is known to still be difficult due to the complexity of the process mechanism, in which thermal and dynamic interactions among the arc, keyhole, and weld pool are critically important. In KPAW, two large eddies are generally formed in the weld pool behind the keyhole by plasma shear force as the dominant driving force. These govern the heat transport process in the weld pool and have a strong influence on the weld pool formation process. The weld pool flow velocity is much faster than those of other welding processes such as Tungsten Inert Gas (TIG) welding and Gas Metal Arc (GMA) welding, enhancing the heat transport to lower the weld pool surface temperature. Since the strength and direction of this shear force strongly depend on the keyhole shape, it is possible to control the weld pool formation process by changing the keyhole shape by adjusting the torch design and operating parameters. If the lower eddy is relatively stronger, the heat transport to the bottom side increases and the penetration increases. However, burn-through is more likely to occur, and heat transport to the top side decreases, causing undercut. In order to realize further sophistication of KPAW, a deep theoretical understanding of the process mechanism is essential. In this article, the recent progress in studies regarding the interaction mechanism of arc, keyhole, and weld pool in KPAW is reviewed.
小孔等离子弧焊（KPAW）工艺利用由水冷铜喷嘴高度约束的电弧等离子体，产生巨大的电弧压力以在熔池中打开一个小孔，从而实现对厚板的全熔透。然而，由于工艺机制的复杂性，先进的焊接控制仍然困难，其中电弧、小孔和熔池之间的热和动态相互作用至关重要。在KPAW中，作为主要驱动力的等离子体剪切力通常会在小孔后方的熔池中形成两个大涡旋。这些涡旋控制着熔池中的热传输过程，并对熔池形成过程有很大影响。熔池流速比其他焊接工艺（如钨极惰性气体保护焊（TIG）和熔化极气体保护电弧焊（GMA））快得多，增强了热传输以降低熔池表面温度。由于这种剪切力的强度和方向强烈依赖于小孔形状，通过调整焊枪设计和操作参数来改变小孔形状，就有可能控制熔池形成过程。如果下部涡旋相对较强，向底部的热传输增加且熔深增加。然而，更有可能出现烧穿，并且向顶部的热传输减少，导致咬边。为了实现KPAW的进一步完善，对工艺机制有深入的理论理解至关重要。在本文中，回顾了关于KPAW中电弧、小孔和熔池相互作用机制研究的最新进展。
