ИСТИНА

The deep penetration mode is widely used in laser welding, and it has begun to be used in additive manufacturing by melting powder layers with a laser beam in recent years. In contrast to conduction mode with its characteristic shallow melt pool, a deep penetration regime differs by a significant surface depression as a cavity, due to which the beam penetrates deep into the metal, forming a melting zone narrow and deep. The unstable cavity behavior causes defects (pores), which significantly degrade the structural integrity and performance of products, limiting the potential of technologies. A fundamental understanding of pore formation is key to a practical pore reduction strategy. The report presents a study of capillary oscillations inside a cavity leading to pores formation. The amplitude and frequency of these oscillations determine the volume and frequency of pore appearance. The change of pores volume and appearance frequency depending on the beam scanning speed is analyzed. Scanning speed values at which the amplitude and frequency of capillary oscillations (i.e., the pores volume and frequency of pores appearance) reach their maximum values are obtained. The correspondence between the calculated curves and experimental data confirms the capillary nature of cavity oscillations leading to pores formation, as well as the predictive capabilities of presented analysis.