Establishment of the Model Widely Valid for the Melting and Vaporization Zones in Selective Laser Melting Printings Via Experimental Verifications

The thermally affected material properties operating in the three phases and porosity variations in the SS316L steel powder have been introduced to the numerical analyses for the transient volumetric heat source (Q) models developed for the solid powder, melting, and vaporization regions in the selective laser melting (SLM). The bulk Q is thus a function of these heat sources and their ratio defined for the liquid and vapor phases. The heat conduction developed for the solid powders with porosity strings the heat convection with Q as the moving heat source to solve two-dimensional temperature distributions efficiently without the confinement of operating conditions and phase presumption. The specimens with single- and multiple-track printings are prepared to investigate the effects of incident energy density (E) and power intensity (I-o) on the geometries of single-track printings and the areal surface roughness (Sa) values of the multiple-track printings with 0 and 50% overlap ratios. Laser power and scanning velocity are the controlling factors for the melting pool depth D and width W. D and W become the governing factors for the keyhole with evaporations, which affects the height H of single track after solidification. The W and D results predicted by the theoretical models developed in this study have an error range, 5-20%, compared to the experimental ones, which is much lower than those reported in the literatures (Gusarov et al. in J Heat Transf 131(7):072101, 2009. ; Hussein et al. in Mater Des 52:638-647, 2013. ; Yin et al. Int J Adv Manuf Technol 83(9-12): 1847-1859, 2016. ; Andreotta et al. in Finite Elem Anal Des 135: 36-43, 2017. ). The contact angle (phi*) is defined as a function of single-track width (W) and solidification height (H). phi* and Sa are significantly reduced as an E is applied beyond its critical value (47.62-57.14 J/mm(3)). Significant change in Sa is ascribed to the big difference in the morphology and its surface pattern when E or I-o reaches its critical value.

Automated summary

Thermally affected material properties and porosity variations were introduced into numerical analyses for selective laser melting, and a transient volumetric heat source model was developed. The study investigated the effects of laser power and scanning velocity on printing geometry and surface roughness, with theoretical predictions showing a 5-20% error range compared to experimental results.