Experimental and numerical studies of nozzle effect on powder flow behaviors in directed energy deposition additive manufacturing

The spatial distribution of the flying powder particles was simulated by the established integrated model, in which computational fluid dynamics and discrete element methods were combined. In addition to the finite element model of heat transfer, the influences of the defocused amount, gas flow rate, and nozzle diameter on the DED-AM process were studied. Comparison with experimental observations can validate the proposed models. The results indicate that the negative defocused amount is benefit for powder particles to fly on the melt pool center and higher laser energy can be applied to the deposition layer. The powder particle speeds can be accelerated by increasing both the carrier gas and shield gas flow rates. As a result, the laser energy attenuation and the average temperature rise of powder particles decrease. However, the shield gas can lead to scattering of the powders, which causes the higher average temperature rise. When the carrier gas velocity remains constant, an excessively high or low nozzle diameter can lead to an increase in the divergence angle. The divergence angle can be minimized by the optimal selection of nozzle diameter.