Effect of molten pool behaviors on welding defects in tandem NG-GMAW based on CFD simulation

The simulation of tandem narrow-gap GMAW based on computational fluid dynamics (CFD) was carried out to establish the relationship between the molten pool behaviors and weld bead formation under different wire feed rates (v(f)) and welding speed (v(w)). Inclined arcs were considered in the model by a novel rotated coordinate system. The variation of effective arc radius with welding current was also taken into consideration in the model. The experimental results illustrate that small v(f) or large v(w )easily leads to lack-of-fusion (LOF) defect. However, large v(f )also causes finger penetration. The simulation results indicate that a clockwise vortex in the right sidewall and an anticlockwise vertex in the left sidewall enhance the transverse transmission of fluid and heat, which is conducive to forming a concave weld bead. When v(f) is small or v(w) is large, due to low arc heat input, the groove sidewall cannot be melted and the transverse flow in the molten pool is weak. Furthermore, owing to the small flow velocity and large solidification rate of molten metal, the preferentially solidified metal further hinders the spreading of liquid metal to the sidewalls. As a result of high v(f), the droplet that has high transition frequency and velocity transfers the arc heat and the high momentum to the molten pool bottom. The downward flow in the molten pool center is enhanced and its velocity is also increased, resulting in finger penetration. (C) 2022 Elsevier Ltd. All rights reserved.

Automated summary

The relationship between molten pool behaviors and weld bead formation under different wire feed rates and welding speeds was studied using a computational fluid dynamics model. The results showed that low wire feed rates or high welding speeds can result in lack-of-fusion or finger penetration defects. The simulation results indicated that vortex flows on the sidewalls enhance the transverse transmission of fluid and heat, leading to the formation of a concave weld bead. Additionally, low wire feed rates or high welding speeds weaken the transverse flow in the molten pool, hindering the melting of groove sidewalls and the spreading of liquid metal.