磁场对K-TIG电弧热力特性和小孔稳定性的调控机制

K-TIG (Keyhole Tungsten Inert Gas Welding) process is a novel welding process of high-productivity, can be used to join the mid-thick metal plate of low thermal conductivity in keyhole mode. However, the averaged energy density of the free-burning arc employed in present K-TIG is low, the arc force property is sensitive to the arc length, it is not so optimal to stabilize the keyholing process if the welded metal is of relative high level thermal conductivity. In the research project, in order to improve the heat density and force field of the arc, magnetic field is designed and employed to constrict the arc jet. Based on the weld pool and keyhole parameters extracted from weld pool images captured from the front side and back side of the workpiece, 3D model will be built to characterize the weld pool & keyhole. The coupling mechanism of the arc jet to the weld pool and keyhole will be investigated; the inducing affect of the weld pool and keyhole to the weld defects will be figured out. Dynamic keyhole welding experiments will be carried out to study the effecting mechanism of the arc heat-force property and base metal thermal conductivity property to the keyholing behavior. The constrict-arc property will be optimized to improve the keyhole stability. The project results will deepen the understanding of the coupling behaviors in the "welding arc - weld pool - keyhole - weld" in keyhole welding process, lay solid foundation to stabilize the keyholing process and improve the practical application of the K-TIG welding process.

K-TIG焊是一种新型高效焊接方法，能够对低热导率的中厚钢板实现穿孔焊接。但是，现有K-TIG采用自由电弧，平均能量密度低，电弧力对弧长变化敏感，焊接热导率较高的钢材时小孔稳定性差。本课题提出采用磁场压缩电弧柱，改善电弧的热源-力源特性；基于从熔池图像中提取的正反两面熔池和小孔形态参数，构造穿透小孔熔池的三维腔体模型；分析电弧热-力特性对小孔熔池行为的耦合作用机制；揭示小孔熔池行为与焊缝缺陷之间的联系；研究动态穿孔过程中，电弧热-力特性、工件热导率对熔池能量与小孔行为的影响机理，优化压缩电弧形态，提高穿孔稳定性。预期成果将为深入理解K-TIG焊接过程中“电弧-熔池-小孔-焊缝”的耦合作用机制、稳定K-TIG穿孔过程、拓宽工艺适用性奠定坚实基础。

K-TIG焊是一种新型高效焊接方法，能够对低热导率的中厚钢板实现穿孔焊接。但是，现有K-TIG采用自由电弧，平均能量密度低，电弧力对弧长变化敏感，焊接热导率较高的钢材时小孔稳定性差。本课题提出采用磁场压缩电弧柱，改善电弧的热源-力源特性，基于永磁铁设计了双尖角磁场增强，配合自主研发的K-TIG焊枪，构建了磁控K-TIG焊接系统。开展定点焊接工艺试验，发现熔化区域变为椭圆，电弧沿着N→S方向被压缩，沿着S→N方向被拉伸；从熔池图像中提取小孔形态参数，小孔形态随着正面电弧形态的变化也发生了变化；构造穿透小孔熔池的三维腔体模型，分析了小孔熔池的温度场、流场和受力状态。开展连续穿孔焊接实验，发现磁控K-TIG正面焊缝宽度减小，背面焊缝宽度增加，更多的热量传递到熔池底部，焊缝晶粒变化不明显，60°磁极角度下穿孔临界电流降低最有效（40A）。对于热导率较高的碳钢材料，磁场作用对穿孔电流降低不明显。本项目研究成果对稳定K-TIG穿孔过程、拓宽工艺适用性奠定坚实基础，磁控K-TIG能够有效地改善对低热导率材料的焊接性。