电弧特性及其对熔池形貌影响的数值模拟

通过电弧模型与熔池模型耦合数值模拟，研究了氩弧和氦弧特性及其对SUS304不锈钢钨极惰性气体保护（TIG）焊熔池形貌的影响.通过比较氩弧和氦弧的温度轮廓线以及阳极表面电流密度和热流密度分布发现，氦弧的径向距离比氩弧收缩明显，导致更多热量传递给阳极.模拟了氩弧和氦弧下浮力、电磁力、表面张力和气体剪切力分别对熔池形貌的影响.结果表明：不论是在氩弧还是在氦弧下熔池中表面张力是影响熔池形貌的最主要驱动力.在氩弧下，影响熔池形貌的另一个重要的驱动力是气体剪切力，而氦弧下则是电磁力.由于电磁力引起的内对流运动增加了熔深，从而导致相同氧含量时氦弧下的熔深和焊缝深宽比要高于氩弧下的熔深和焊缝深宽比.随着氧含量的增加，氩弧和氦弧下的焊缝深宽比均先增加而后保持不变.焊缝深宽比的模拟结果与实验结果符合较好. 关键词： 氩弧 氦弧 电弧特性 熔池形貌

Numerical simulation of arc properties and their effects on the weld shape

A mathematical model of mutually coupled welding arc and weld pool is established for moving tungsten inert gas welding process on SUS304 stainless steels to investigate the argon and the helium arc properties and their effects on the weld shapes. The comparisons of the temperature contour, the current density and the heat flux on the anode surface between the argon and the helium arcs show that the helium arc is more constricted than the argon arc and transfers more heat fluxes to the anode. The effects of buoyancy, electromagnetic force, Marangoni force and drag individually on the weld pool are simulated, and simulation results show that the Marangoni force on the pool surface is one of the main forces affecting the weld shape, independent of shielding gases. Under argon arc, an other dominant force is the plasma drag force. However, the effect of electromagnetic force is stronger than that of the plasma drag force in helium arc. The inward convection induced by the electromagnetic force increases the weld depth, thereby leading the weld depth and the D/W ratio in helium arc to be larger than the ones in argon arc under the same oxygen content. The weld D/W ratio increases first and then maintains a constant with the increase of oxygen content for both argon arc and helium arc. The weld D/W ratio obtained by simulation is in good agreement with experimental results.