Effects of Bimodal Beam Shaping on Melting And Resolidification of Stainless Steel

Laser processing offers precise control over conventional techniques, but the lack of control over microstructure. Traditional single-mode beam strategies often result in steep thermal gradients and columnar grain growth. In this study, we introduce a bimodal beam scanning approach in which one laser beam scans steadily while a second laser beam oscillates perpendicularly to the scan direction at a controlled frequency and amplitude. By modulating the spatial distribution of the energy input during scanning, this technique enables dynamic shaping of the melt pool geometry. Cross-sectional analysis reveals that while unmodulated tracks exhibit elongated columnar grains, modulated tracks display more equiaxed grains. Differences observed in both melt pool geometry and microstructure between the steady single-mode and the bimodal laser scan prompted three-dimensional thermal simulations to investigate the underlying thermal mechanisms. These simulations were used to examine how beam modulation affects temperature profiles and gradients, helping to explain the resulting variations microstructure. This dynamic beam shaping approach offers a promising pathway for laser-based metal processing, to achieve a more equiaxed microstructure.