In situ x-ray observation of keyhole dynamics for laser beam welding of stainless steel with 16 kW disk laser

Focused laser is one of the highest power density sources available to industries such as automotive industry, heavy industry, and nuclear power plant industry because thermal influence is narrow and it is excellent in local workability. However, laser welding causes defects of cracks and pores. In particular, the formation of keyholes, which are factors for forming these welding defects, and the mechanism of spatter generation have not been sufficiently investigated. In this study, an x-ray phase contrast imaging technique was employed to investigate the keyhole welding with laser in order to clarify the spatter generation mechanism and keyhole formation mechanism in vacuum. Furthermore, the amount of spatter generated by vacuum laser welding was quantitatively analyzed, and the factors that suppress the spatter under vacuum were clarified. As a result, it was found that the penetration depth was dependent on the keyhole aperture.