考虑熔滴和小孔对熔池的影响, 建立了基于FLUENT软件的激光+熔化极电弧(GMAW)复合热源焊三维瞬态熔池流体流动数值分析模型. 利用双椭球体热源描述电弧热输入, 将激光热输入视为热流峰值可调节的双曲线旋转体热源, 其热源分布参数通过简化的小孔形状尺寸模型确定; 将熔滴过渡过程视为从熔池上部特定区域流入熔池高温液态金属的过程, 并通过建立液态金属流速对时间的周期函数表征熔滴过渡频率; 将小孔视为由激光致蒸汽反作用力引起的熔池表面变形, 以简化计算过程, 重点考虑小孔的存在对熔池流体流态的主要影响. 利用所建模型对不同焊接条件下的激光+GMAW复合热源焊小孔形态、熔池流体流动和温度场进行模拟计算, 分析了激光+GMAW复合热源焊流场特征, 探讨了激光功率对复合焊熔池动态行为的影响规律. 结果表明, 在1 m/min 焊速条件下, GMAW焊(激光功率为0 W)出现驼峰缺陷; 当激光功率为500 W时, 驼峰缺陷消失, 但熔池中无小孔产生, 且流体流动模式与GMAW焊相近; 而当激光功率增至2000 W, 熔池中出现小孔, 使得流体流动模式更为复杂. 将焊缝横断面形状尺寸的计算结果与实验结果进行比较, 2者吻合较好, 从而证明了模型的准确性和适用性.

Laser+gas metal arc welding(GMAW) hybrid welding fully combines the merits of both laser welding and GMAW, which can achieve high quality, high efficiency and comparatively low-cost welding of thin and thick plate, thus having great application prospect in manufacturing industry. However, compared with single heat source welding, hybrid welding involves more welding parameters and more complicated physical process, leading to difficult process optimization. When mismatching the process parameters, welding defects can still appear in high-speed welding, which affects the reliability of hybrid welding. Therefore, it is necessary to study the physical mechanism in hybrid welding deeply for suppressing welding defects and improving welding stability. In hybrid welding, fluid flow in weld pool has a critical influence on the weld formation. So, modeling and simulating the fluid flow is helpful for understanding the process mechanism completely. To date, however, there is only little study on velocity field in hybrid welding due to its complexity. In this work, with considering the effects of droplet and keyhole on weld pool, a three dimensional transient model is developed to numerically analyze fluid flow in weld pool of laser+GMAW hybrid welding based on FLUENT software. Arc heat input is modeled using an double-ellipsoid heat source; laser heat input is regarded as a hyperbolic curve-rotated heat source with changing peak power density, its distribution parameters being determined based on the simplified model for keyhole geometry and size. Droplet transfer is described as the process of high temperature liquid metal flowing into weld pool from the certain domain above the weld pool. Using the built model, the keyhole behavior, fluid flow and temperature distribution in laser+GMAW hybrid welding under different welding conditions are calculated. The features of velocity field in hybrid welding are analyzed and the effect of laser power on the weld pool dynamic behavior is discussed. The results show that, in the case of 1 m/min, weld bead hump is generated in single GMAW (laser power 0 W); when laser power is 500 W, bead hump disappears in welding, but there is no keyhole emerging in hybrid weld pool and fluid flow pattern is close to that in GMAW. When increasing laser power to 2000 W, keyhole is formed, which makes the fluid flow in weld pool more complicated. The predicted weld geometries and dimensions for varied laser powers are compared with the measured data, which are in good agreement, thereby indicating accuracy and applicability of the established model.