Peeling off behavior of centimeter-level molten pool subjected to subsonic tangential airflow during laser ablation process

In this paper, a computational fluid dynamics model considering the interaction between subsonic tangential airflow and centimeter-level molten pool was established to investigate the melt peeling off behavior during laser ablation process. The results showed that the airflow resulted in violent fluctuations on the surface of molten pool and then flowed upward at a velocity of 2–10.5 m/s, accelerating the surface melt to move upward. A liquid column was formed and elongated slender along the metal surface pushed by the subsonic tangential airflow. An upward-bending tail appeared at the end of the liquid column, which was accelerated up to 6 m/s and then cut off by the airflow, making the melt peel away from the molten pool. Compared with the partial melt peeling off at 0.3 Ma, almost all of the melt was pushed out of the molten pool to peel off when the airflow velocity was increased to 0.5 Ma. When the airflow velocity was further increased to 0.8 Ma, the metal on the surface was accelerated in short time, leading to the peel-off occurring in advance. In addition, the melt temperature decreased due to the forced convection cooling effect of airflow. When the melt solidified, the solid-liquid interfacial tension generated in the liquid column provided tangential force conducive to cutting off the liquid column and peeling off. The decrease rate of the melt temperature with time accelerated significantly and then expedited the melt solidifying and peeling off when the airflow velocity was increased to 0.5 Ma. The decrease rate further accelerated and the temperature decrease occurred earlier at 0.8 Ma, reaching a stable state in a shorter time.