In-situ monitoring and regulating of the molten pool during the laser powder bed fusion process and the positive effect on surface roughness

A high-resolution high-speed imaging system was used to capture mesoscopic non-stationary molten pool fluctuations during the laser powder bed fusion (LPBF) of high copper alloys. Varying the pre-fabricated contour tracks created different laser absorption and thermal conductivity conditions, allowing for the regulation of molten pool fluctuations. The increased contour tracks weakened the fluctuations of the molten pool. With the combined increase in the laser reflectivity and thermal conductivity, the droplet column surge was successfully eliminated under the condition of three pre-fabricated contour tracks. Multiple pre-fabricated contour tracks reduced the temperature accumulation at the filling track onset, which was validated by numerical simulations. The regulation significantly improves the LPBF specimens' side surface roughness, reducing Ra values from 16.02 µm to 8.61 µm by stabilising molten pool fluctuations and preventing surface 'island' formation. This study visualised the molten pool fluctuation effects on the side surface roughness and proposed an effective regulation method that is potentially applicable to diverse metallic materials.