气流再压缩等离子弧热-力特性对焊接熔池和小孔行为的影响机制

The gas focusing plasma arc welding with arc column secondly constricted by focusing gas, can increase the arc penetrability significantly and improve the welding speed. Therefore, the gas focusing plasma arc welding has potential application prospect in thick plate welding. However, the overlarge arc penetrability will easily cause the molten metal being blown down, which will disrupt the stability of weld pool and keyhole, and influence the weld formation, and even make the weld bead discontinuous. So far, the influence mechanism of the arc penetrability to the stability of weld pool and keyhole is unclear, while the quantitative relationship between the arc penetrability and focusing gas flow rate also lacks a further profound study. In this project, the arc plasma theory and hydrodynamic theory are applied to study the constricting mechanism of focusing gas to arc, and the relationship between focusing gas flow rate and the characteristic of arc heat and pressure is quantitatively described. With consideration of the couple relationship among “heat transfer—fluid flow—keyhole”, the model of gas focusing plasma arc welding process is established. The dynamic evolution of weld pool and keyhole is numerically simulated, while the stability of weld pool and keyhole is analyzed. And finally, the quantitative relationship among “welding parameters—arc heat density and arc pressure—stability of weld pool and keyhole—weld” is obtained. The expected achievement will enrich and develop the theory of gas focusing plasma arc welding, and lay a theory foundation for making gas focusing plasma arc welding process high quality and high efficiency.

气流再压缩等离子弧焊接通过聚焦气实现对电弧弧柱的“二次压缩”，可显著增强电弧穿透能力并提高焊接速度，在厚板焊接领域具有潜在的应用前景。但电弧穿透能力过大容易导致熔池金属被吹落，破坏熔池和小孔的稳定，影响焊缝成形甚至不能形成连续的焊缝。迄今，电弧穿透能力对熔池和小孔稳定性的影响机制尚不清晰，电弧穿透能力与聚焦气流量之间的定量关系也缺乏深入的研究。本项目拟基于电弧等离子体理论和流体动力学理论，深入研究聚焦气对电弧的压缩机理，定量描述聚焦气流量与电弧热-力特性之间的关系；考虑“传热—熔池流动—小孔”之间的相互耦合关系，构建气流再压缩等离子弧焊接过程数理模型，定量分析熔池和小孔的动态演变过程及其稳定性条件，获取“焊接工艺参数—电弧热流密度和电弧压力—熔池和小孔稳定性—焊缝成形”之间的定量关系。预期成果将丰富和发展气流再压缩等离子弧焊接工艺理论，为实现优质高效的气流再压缩等离子弧焊接奠定理论基础。

提高电弧穿透能力，是维护焊接穿孔过程稳定、提高焊接速度、增大常规PAW 最大可焊接厚度的有效途径。本项目针对气流再压缩等离子弧焊接工艺开展研究具有重要的意义。本研究搭建了气流再压缩等离子弧焊接实验平台，开展了焊接实验，研究了不同焊接工艺参数条件下的气流再压缩等离子弧焊接工艺，分析了压缩气对电弧形态、电弧电压、焊缝成形的影响。研究发现，相同电流条件下，与常规PAW相比，气流再压缩等离子弧焊接电弧电压升高、熔深增大。.建立了气流再压缩等离子弧焊接电弧热源模型和电弧压力分布模型，构建了考虑“传热-熔池流动-小孔演变”的三维数值分析模型，模拟了气流再压缩等离子弧焊接穿孔过程，模拟结果与实验结果基本吻合。初步建立了“焊接工艺参数—电弧热流密度和电弧压力—熔池和小孔稳定性—焊缝成形”之间的关系。.建立了气流再压缩等离子弧数理分析模型，计算了等离子弧温度分布、流场分布，结果表明，压缩气对喷嘴内的等离子弧温度分布基本没有影响，对喷嘴外部的等离子弧温度分布影响较大；压缩气对喷嘴外的等离子弧具有一定的拘束压缩作用；压缩气对等离子弧速度分布基本没有影响。模拟结果与实验结果基本吻合。.研究发现，电流（150A，155A，160A）改变时，喷嘴内部电弧温度场和喷嘴外部电弧温度场都会发生变化，电弧电压、电弧压力随焊接电流增加而增大；离子气流量（2.5L/min，3.0L/min，3.5L/min）改变时，喷嘴内部电弧温度场和喷嘴外部电弧温度场都会发生变化，电弧电压、电弧压力随离子气流量增加而增大；压缩气流量（1.0L/min，1.5L/min，2.0L/min）改变时，喷嘴内部电弧温度场没有变化，喷嘴外部电弧温度场发生变化，电弧电压随压缩气流量增加而增大，压缩气流量增加时电弧压力没有变化；保护气流量（15L/min，20L/min，25L/min）改变时，喷嘴内部电弧温度场和喷嘴外部电弧温度场都基本没有变化，电弧电压基本没有变化。.本研究丰富了气流再压缩等离子弧焊接理论体系，为指导气流再压缩等离子弧焊接工艺提供了基础数据。