Characterizing gas flow in the build chamber of laser powder bed fusion systems utilizing particle image velocimetry: A path to improvements

Laser Powder Bed Fusion (L-PBF) is increasingly being utilized for the manufacture of structural components for the aerospace industry. In L-PBF an inert gas is used to protect the melt pool from contamination by reactive elements in the build chamber and to carry away by-products generated by the laser-powder interaction, including soot, condensate, etc. Spatial variations or other undesirable characteristics (e.g., turbulence, dead zones, etc.) in the gas flow distribution could enable build defects to develop that cause spatial variability in metal quality and microstructure, as well as variability in the mechanical properties. This investigation analyzed the gas flow in a full-scale model of the build chamber for a commercial system utilizing high-fidelity Particle Image Velocimetry (PIV). Planar mode views showed that the gas flow within the build chamber is not uniform and that the flow distribution across the build plate undergoes a reduction in velocity laterally of nearly 50 %; the reduction in flow downstream from the gas inlet to the exit reaches nearly 70 %. Serial views involving multiple planes of evaluation revealed regions of stagnation as well as recirculation zones that could entrain soot and metal vapor condensate. Lastly, a modified Y-Duct design is conceived and shown through analysis performed using PIV to substantially improve the flow field distribution across the build plate. Details of the flow fields, locations of concern, and benefits of the PIV approach to assess and inform improvements in the gas flow distribution are discussed. These findings can lead to improvements in quality realized by part placement and distinguish opportunities for further tuning of the gas flow overall.