Droplet spatter suppression in laser lap welding of galvanized sheets using additional coaxial annular laser source

•The eddy and reflux of molten metal pool are primary factors for impact force on the keyhole oscillation.•Polymorphic superimposed laser source well balanced the impact force and improved the welding stability, which is significant to prevent droplet spatter. This study is to prevent droplet spatter in laser welding of galvanized sheets. Three-dimensional welding simulation model is also established and analyzed to reveal the relationship between keyhole oscillation and flow behavior. It is found major reason for droplet spatter is the impact force of the reflux and eddy of the metal pool toward the keyhole. Keyhole oscillates seriously and reflux impact causes energy exchange discontinuity, making the keyhole opening intermittent closed in traditional Gaussian laser source alone. While certain output proportion of coaxial annular and Gaussian laser source could considerably improve impact resistance on the reflux and suppress droplet spatter obviously. Weld appearance is relatively beautiful and harmonious, with few undercuts, collapses and humps.