Selective laser melting of 316L stainless steel: porosity dependence on geometric feature size

This technical brief reports an experimental study on the effect of geometric feature size on the porosity in parts made via selective laser melting. Cylindrical features of different diameters were designed on a single part and printed using the same scan strategy. The resultant pores at different cylindrical feature diameters were captured by optical microscopy. The image processing results showed that as the cylindrical feature diameter decreased from 10 mm to 0.8 mm, the porosity increased from 0.11 % to 4.1 %, and the maximum pore size increased from 41.7 mu m to 102.2 mu m. To identify the reason for this interesting finding, the average areal energy density was calculated at each cylindrical feature diameter. The calculations showed that the different cylindrical feature diameters resulted in local energy density discrepancies. Because the scan strategy had a disparity for the border in comparison to the volume infill, and the areal ratio of the border to the volume infill naturally varied at different cylindrical feature diameters, the average areal energy density was found to vary significantly for cylindrical features of different diameters. The average areal energy density increased from 2.8 J/mm(2) to 5.9 J/mm(2) as the cylindrical feature diameter decreased from 10 mm to 0.8 mm. That change in the average areal energy density was identified as the cause for the porosity variation in this study.