Correlation between the scan strategy, residing spatter distribution, and parts quality in laser powder bed fusion

Abstract

Spattering may cause defects in the Laser Powder Bed Fusion (LPBF) process, and the inert gas flow has been identified as an effective method for removing/mitigating the negative effects and preventing vapor interference in the melting process. Given the variability of scan strategies in LPBF, optimizing the scan strategy to minimize residing spatters on powder bed is challenging but important. This study focuses on the correlation between the distribution of residing spatters, parts quality, and scan strategies (particularly scan direction and scan sequence here) under the influence of inert gas flow. A single lens reflex camera and image processing are employed to detect the distribution of spatters residing on the powder bed, providng unprecedented insight and valuable guidance for the design of scan strategy. The results reveal that the scan sequence against the gas flow induces fewer spatters residing on the powder bed. The large size residing spatters, with the diameter ranging from 80 μm to 210 μm, are concentrated along the scan direction in close proximity to the melting area. Scan sequence along the gas flow leads to rougher surface of the part, and more defects are formed between layers caused by spatter inclusions, which deteriorates the tensile properties obviously. It is recommended to employ orthogonal S-scanning strategy (S-45° with 90° layerwise rotation, scan sequence against gas flow) during the LPBF process. The selection of scanning parallel or perpendicular to the gas flow is dependent on the distribution of the surrounding processing areas, to ensure consistency of the parts quality.