Numerical analysis of arc welding phenomena from a unified arc-electrodes model

由于电弧等离子体与熔池之间存在复杂的相互作用现象，因此建立焊接过程的数值模型对于理解焊接现象中质量、能量和力平衡的量化值是非常有用的，因为由于电弧等离子体与熔池之间存在复杂的相互作用现象，因此仍有机会在实验上理解它们的量化值。为简化起见，本文采用静态钨极惰性气体保护焊(TIG)焊接过程，但由于考虑了电弧等离子体与熔池之间的密切相互作用，TIG焊的整个区域，即钨阴极、弧等离子体、工件和熔池，都被用统一的数值模型处理。对150A电流下的固定TIG焊接进行了计算，阳极被假定为不锈钢SUS304。预测了TIG焊接全过程的二维温度和速度分布。并对焊缝熔深形状进行了预测。此外，还给出了不同等离子体和电极区的能量平衡的量化值。电弧等离子体和钨阴极表面温度的预测值与实验值吻合较好。焊缝形状与实验结果基本吻合。计算得到的熔池内的对流流动主要由阴极射流的阻力和Marangoni力所主导，而另外两种驱动力即浮力和电磁力是主要的驱动力。结果表明，焊接熔池内再循环流动方向的改变导致了明显不同的焊缝熔深形状。

The development of a numerical model of the process is quite useful for understanding quantitative values of the balances of mass, energy and force in the welding phenomena, because there is still luck of experimentally understanding the quantitative values of them due to the existence of complicated interactive phenomena between the arc plasma and the weld pool. This study was focused on a stationary tungsten inert gas (TIG) welding process for simplification, but the whole region of TIG arc welding, namely, tungsten cathode, arc plasma, work-piece and weld pool was treated in a unified numerical model because of taking the close interaction between the arc plasma and the weld pool into account. Calculations were made for stationary TIG welding at a current of 150 A. The anode was assumed to be a stainless steel, SUS304. The two-dimensional distributions of temperature and velocity in the whole region of TIG welding process were predicted. The weld penetration geometry was also predicted. Furthermore, quantitative values of the energy balance for the various plasma and electrode regions were given. The predicted temperatures of the arc plasma and the tungsten cathode surface were in good agreement with the experiments. There was also approximate agreement of the weld shape with experiment. The calculated convective flow in the weld pool was mainly dominated by the drag force of the cathode jet and the Marangoni force as compared with other two driving forces, namely, the buoyancy force and the electromagnetic force. It was shown that change in the direction of re-circulatory flow in the weld pool led to dramatically different weld penetration geometry.