Investigation of Causal Relationships between Printing Parameters, Pore Properties and Porosity in Laser Powder Bed Fusion

Abstract

This work reports on employing X-ray computed tomography (XCT) and optical microscopy to investigate the causal relationships between printing parameters, pore properties, and porosity in 316L stainless steel samples additively manufactured by Laser Powder Bed Fusion (LPBF). The porosity is very similar for both investigation methods. XCT provides more accurate results for large lack of fusion pores, while optical results are more accurate for small keyhole pores. These results were employed to develop mathematical models to determine how printing parameters influence pore properties and overall porosity. The developed optical and XCT mathematical models reveal that power is the most significant factor affecting pore properties and overall porosity. Pore number and mean diameter decrease and sphericity increases with increasing power. Overall porosity is negatively correlated with power, indicating that the higher the power, the lower the overall porosity. Attention should also be paid to the quadratic effects of power, velocity and hatch spacing on porosity, revealing an inverse change in porosity after a certain threshold. Power interacts with velocity and hatch spacing, suggesting that changes in power affect the influence of velocity and hatch spacing on porosity, and vice versa. The interaction of velocity and hatch spacing is not significant. Both models successfully predicted optimal printing parameter sets as validated by experimental measurements.