A vacuum laser powder bed fusion (L-PBF) method incorporating beam profile control was developed to fabricate high-quality three-dimensional (3D) objects.To evaluate the quality of 3D fabrication, the denudation zone (DZ) was analyzed as a key quality indicator during the formation of a single bead.The primary objective of this study was to elucidate the correlation between the DZ and beam profiles.Beam profiles, including Gaussian, ring, and flat-top modes, were generated using a dioptric system equipped with a beam shaper.Single beads were formed by irradiating stainless steel 316L (SS316L) powder under various pressure conditions, followed by measurement of the DZ.The results demonstrated that the flat-top mode achieved the smallest DZ under atmospheric pressure.To further investigate this phenomenon, the dynamics of metal vapor during laser irradiation were observed using the Schlieren imaging technique under atmospheric conditions.It was determined that the average velocity of the metal vapor in the flat-top mode was the slowest, measured at 199 mm/s.These findings indicate that the size of the DZ is influenced by the dynamics of metal vapor.Furthermore, the ambient pressure was reduced to 300 Pa to minimize gas movement, thereby providing additional insights into the relationship between pressure conditions and DZ characteristics.
SATO et al. (Mon,) studied this question.