熔滴短路过渡建模及熔池三维瞬态行为模拟

针对短路过渡CO2焊接的熔滴过渡随机性强、熔池动态行为复杂的特点，考虑熔滴与熔池短路时刻、短路时刻的熔滴半径、温度和中心位置等随机因素，提出了熔滴短路过渡行为模型.采用非对称高斯热源表征电弧热流密度沿焊接方向的非对称性，采用附加源项法处理熔池各动量源，采用VOF追踪熔池气-液界面，采用液相分数法和焓-孔隙度法处理液-固糊状区熔化金属凝固潜热及动量损失，建立了短路过渡焊接熔池的三维瞬态模型.基于FLUENT软件二次开发，模拟了熔池的动态行为，研究了熔池温度场和流场的瞬态变化.对比等速送丝和脉冲送丝情况，熔滴短路间隔时间的概率密度分布和焊缝成形的模拟与实验结果吻合良好，验证了熔滴短路过渡行为模型和熔池三维瞬态模型的有效性.
For CO2 arc welding with short-circuiting transfer, the droplet transfer and dynamic behavior of molten pool are complexity and have strong randomness. Considering the random factors, such as short-circuiting time between droplet and molten pool, radius, temperature and central position of droplet at short-circuiting time, the model of droplet short-circuiting transfer behavior is proposed and set up. The three-dimensional transient model of molten pool is established for arc welding with short-circuiting transfer, after the asymmetric Gauss heat source being adopted to characterize the asymmetry of arc heat flux density along welding direction, the additional source term method being used to deal with many momentum sources, the VOF model being adopted to realize the tracking of gas-liquid interface, and the liquid volume fraction method and enthalpy-porosity technique being used to compute the latent heat of molten metal solidification and the momentum loss in the liquid-solid mush zone. Based on the secondary development of FLUENT software, the dynamic behavior of molten pool is numerically simulated; the transient evolution of the temperature field and flow field in molten pool is acquainted. The simulation results of probability density distribution of short-circuiting time interval and final weld formation agree with experimental data well, the validation of the model of droplet short-circuiting transfer behavior and three-dimensional transient model of molten pool being demonstrated.