考虑金属蒸汽的钨极惰性气体保护焊电弧与熔池交互作用三维数值分析

Three-dimensional numerical analysis of interaction between arc and pool by considering the behavior of the metal vapor in tungsten inert gas welding

基于局域热平衡状态假设并考虑金属蒸汽的作用,建立了钨极惰性气体保护焊电弧与熔池交互作用的三维数学模型.电弧等离子体的热力学参数和输运系数由温度和金属蒸汽浓度共同决定,并使用第二黏度近似简化处理金属蒸汽在氩等离子中的输运过程.在考虑熔池流动时,主要考虑了浮力、电磁力、表面张力和等离子流拉力的作用.通过对麦克斯韦方程组、连续性方程、动量守恒方程、能量守恒方程和组分输运方程的耦合求解,得到了金属蒸汽在电弧中的空间分布、电弧和熔池的温度场、速度场和电流密度分布等重要结果.通过与未考虑金属蒸汽的结果对比,研究了熔池上表面产生的金属蒸汽对电弧等离子体行为的影响,以及电弧等离子对熔池行为的影响.结果表明,金属蒸汽主要富集在熔池上表面附近;金属蒸汽对电弧等离子体有明显的收缩作用,而对等离子速度和电势影响较小;金属蒸汽的出现对熔池上表面速度分布和剪切力分布以及熔池形貌并无明显影响.求解结果与已有的实验结果和计算结果符合良好.

A three-dimensional （3D） numerical analysis model of tungsten inert gas welding arc interacting with an anode material is presented based on the local thermodynamic equilibrium assumption and taking the behavior of metal vapor into account. The thermodynamic parameters and transport coefficients of plasma arc are dependent on the local temperature and metal vapor concentration. A second viscosity approximation is used to express the diffusion coefficient which describes the metal vapor diffuse in the argon plasma. The weld pool dynamic is described by taking into account the buoyancy, Lorentz force, surface tension, and plasma drag force. The temperature coefficient of the surface tension at the weld pool surface is considered in two ways： one is taken as a function of temperature with only oxygen being the active component, and the other is taken as a constant value. The distributions of temperature field and velocity field of arc plasma and weld pool, metal vapor concentration and current density in the arc plasma are investigated by solving the Maxwell equations, continuity equation, momentum conservation equation, energy conservation equation and the components of the transport equation. The influence of metal vapor on arc plasma behavior and that of arc plasma on the weld pool are studied and compared with the non-metal vapor results. It is shown that the distribution of Fe vapor concentrates around the weld pool surface. Metal vapor has obvious shrinkage effect on arc plasma, and weak influences on velocity and potential of the arc plasma. In addition, the metal vapor has a weak effect on the distributions of velocity and shear force on the weld pool surface and no obvious influence on the molten pool shape. We test two different methods to illustrate this point in the case with or without metal vapor. The method used for a variable temperature coefficient of surface tension allows the prediction of a depth-to-width ratio and weld pool shape in agreement with experimental result when taking the behavior of metal vapor into account. The results in this paper, obtained by simulation are in good agreement with experimental results and also with the simulation results by some other authors.