Investigation of the humping formation in the high power and high speed laser welding

High power and high speed laser welding is as an attractive way to achieve the higher productivity in practical production. The weld periodical appearance defect, humping, is frequently generated in the high speed welding process. The weld quality is sequentially deteriorated severely due to the formed humping defect, which greatly limits the improvement of welding efficiency. In this paper, the keyhole and weld pool dynamic behaviors in the normal welding and high power high speed welding are investigated in the welding process of 304 stainless steel using 3-9 kW fiber laser at different welding speeds. The complex keyhole evolution, metal flow and metallic vapor are recorded by the high speed video camera and described in schematic illustration. The weld pool behaviors in normal welding and high power welding are compared and their effects on the humping formation are discussed in details. The results show that the tilted angle of keyhole, narrow and long molten pool, collision of fluid flow are the main factors for humping formation. Moreover, both of the microstructure characteristics of pre-humping and humping welds induced by molten pool behaviors are further analyzed and compared based on the SEM images, which is essential for reducing welding defects and achieving high quality welding with high efficiency.