A computational fluid dynamics model was established to investigate the undercut formation in high speed gas metal arc welding (GMAW). A double-ellipse integrated "arc current density-arc pressure-electromagnetic force-arc heat" distribution model, which could be self-adaptive to weld pool surface evolution, was developed. The multi-coupling transport phenomena in weld pool were simulated, and the effect of driving forces on the behaviors of molten metal and the formation of undercut was analyzed quantitatively. The results show that the high-velocity backward molten metal flow, large-size gouging region and prematurely solidified thin metal layer at weld toe were typical processes that initiated undercut. The evolution of undercut morphology was determined by the characteristics of inertia force, hydrostatic pressure and arc pressure in the different stages. Based on Buckingham-π theorem, the dimensionless growth rate of undercut area was a parabolic function of a dimensionless group including characteristics of stress state, molten metal flow and morphology of weld pool. This study clarified the physical origin of undercut defect in GMAW and might also provide some basic guidelines for its suppression.

建立了计算流体动力学模型来研究高速气体保护金属电弧焊 (GMAW) 中咬边的形成。建立了一种可自适应熔池表面演化的双椭圆集成“电弧电流密度-电弧压力-电磁力-电弧热”分布模型。模拟了熔池中的多耦合输运现象，定量分析了驱动力对熔融金属行为和咬边形成的影响。结果表明，高速逆流、大尺寸气刨区域和焊趾处过早凝固的薄金属层是引发咬边的典型过程。底切形态的演变由惯性力的特性决定，不同阶段的静水压力和电弧压力。基于白金汉——根据π定理，咬边区的无量纲增长速度是一个无量纲群的抛物线函数，包括应力状态、金属液流动和熔池形态特征。该研究阐明了 GMAW 中底切缺陷的物理起源，并可能为其抑制提供一些基本指南。