根据小孔壁面上的力学平衡条件, 建立了穿孔等离子弧焊(PAW)的小孔模型. 利用该模型, 对6 mm厚不锈钢板PAW准稳态小孔的形成过程进行了数值计算, 得到了不同工艺参数下准稳态小孔的形状和尺寸. 根据达到准稳态时小孔壁面的受力状态, 对PAW过程中小孔从盲孔到穿孔的转变机制进行了探讨, 分析计算了小孔壁面上各区域的作用力大小. 随着焊接电流的升高, 小孔的深度呈现非线性增大; 存在一个小孔在熔池内由盲孔突然转变为穿孔状态的焊接电流临界值; 等离子弧力在小孔底部急剧集中是导致小孔深度突变的主要原因. 通过穿孔PAW焊接工艺实验, 对数值计算结果进行了实验验证.

It is of great significance to develop a mathematical model of keyhole shape and dimension in order to widen the process parameter window and improve the process stability in keyhole plasma arc welding (PAW). In this study, a keyhole model was developed according to the force–balance conditions on the keyhole wall. The establishing process of quasi–steady state keyhole was numerically simulated for stainless steel plates of 6 mm thickness, and the keyhole shapes and dimensions were obtained under different welding process parameters. The transformation mechanism of the keyhole from blind (partial) to open (complete) states in PAW process was analyzed based on the calculated action forces on the keyhole wall. The values of action forces at different locations on the keyhole wall were calculated. With increasing of welding current, the keyhole depth rised in a nonlinear way. There existed a critical value of welding current, i.e., if welding current was a little bit hgher than this value, the keyhole inside the weld pool would suddenly transform from partial state (blind keyhole) ino complete state (open keyhole). The fast centralization of the plasma arc force at the keyhole bottom region resulted in the sudden transformation from a partial keyhole to an open keyhole. The keyhole PAW experiments were conducted to validate the numerical analyss results.