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This work establishes a geometric model and a numerical model of the L-PBF printer. To simulate the scanning laser and spatter particles in the printing process，it develops UDFs for two models: a movable Gaussian heat source model and a movable particle-release source model. It performs calculations，including grid-independent verification and gas-solid two-phase flow coupling simulation. The flow field in the printer chamber，temperature distribution in the heated area，and final distribution of the spatter particles are studied under different conditions. It performs a quantitative analysis of the impact of the particle distribution using the laser power，particle injection velocity，and direction. The following results are obtained:
（1） The gas flow within 30 mm above the workbench is uniform. Thus，argon is linearly distributed from the lower inlet to the outlet. However，in the upper area，the flow field is disorderly，and there are several cyclonic gas flows.
（2） The laser can only induce high temperature and upward gas flow in a small area close to the workbench （at an observation height less than 1.6 mm） and the effects on the flow field are more severe when the laser power is high.
（3） The deposition of particles inside the printer chamber is significantly affected by the initial velocity，injection direction of the particles，and laser power.Particles injected along the flow direction are mostly blown toward the outlet.However，a large percentage of the other particles are deposited inside the printer chamber and on the workbench.
In subsequent studies，it will explore methods for controlling particle deposition on the workbench.