Effects of welding parameters on weld geometry during high-power laser welding of thick plate

During high-power deep-penetration laser welding of thick plate, the geometrical characteristics of weld cross section were investigated under different welding conditions. The molten metal behaviors were observed by using the highspeed camera and X-ray imaging system to study the formation mechanism of weld cross section. With the increase of welding speed, the width and depth of weld seam decreased, and the geometry of weld cross section changed from bighead shape to needle-like shape. The change of focal position of laser beam led to the variation of molten metal behavior which thus resulted in different geometries of weld cross sections during laser welding. The accumulation of high-temperature molten metal at both the top surface of molten pool and the middle depth of molten pool could lead to a higher heat-transferring efficiency of the molten metal which could lead to a wider weld width. The stable molten metal behavior on the molten pool surface resulted in a low heat-transferring efficiency, and the sound appearance of weld seam could be obtained when the focal position was inside the metal.