The role of horizontal gaps on metal flow and heat transfer in bottom-locking welding joints

Abstract

A validated numerical simulation model coupling multiple phases and physics is developed. The role of horizontal gaps in the laser-arc hybrid welded bottom-locking joints is focused. A new adjustment method for the surface tension momentum source is proposed to suppress the spontaneous closure of internal gaps. The weld profile, metal flows, keyhole dynamics and heat flux distribution under different gap sizes are compared. The results indicated that horizontal gaps deteriorated the weld formation. The weld depth was lower than 3 mm when the gap size reached 0.8 mm, which failed to meet the design requirements. In addition, horizontal gaps induced a split-flow once the molten metal penetrated the upper butt part. The split-flow reduced the density of upward back flows on the gap side while hardly affected that on the other side. Consequently, more keyhole wall humps formed under the unbalanced upward flows compared with gap-free conditions. Moreover, more severe keyhole fluctuations hindered the laser beam from reaching the keyhole bottom. The average keyhole depth was thus reduced with the increase of gap sizes. Correspondingly, the heat transfer was also affected. Higher heat flux was obtained when no gap existed while more heat energy was located at the keyhole wall under gap conditions, which was responsible for the reduction of the weld depth. This study clarifies weld pool dynamics of bottom-locking joints and will provide more modeling guidance on welding CFD analysis involving gap conditions.