Quantitative characterization of keyhole absorption mechanisms in 20 kW-class CO2 laser welding processes

Deep penetration laser welding is associated with the deposition of very high irradiation of a laser beam to a workpiece to form a slender capillary into the workpiece, denoted as a keyhole , as well as violent plasma generation which consists of metal vapour, ionized atoms, and free electrons. Plasma resides both outside and inside the keyhole, known as plasma plume and keyhole plasma , respectively. In this paper, we quantitatively characterize the plasma absorption of a laser beam inside the keyhole based on photodiode measurements and spectroscopic measurements in 20 kW-class CO 2 laser welding processes. The results show that the plasma absorption of a laser beam cannot be neglected in certain welding conditions. Furthermore, this plasma absorption mainly occurs in the top portion of the keyhole, resulting in a wider weld shape in the top portion of the weld bead.