A study which appeared on the ScienceDirect Journal describes the development of a geometry based model for predicting lack of fusion during metal powder bed fusion processes (SLM, DMLS, EBM). The model relies on melt pool dimension, hatch spacing and layer thickness. The porosity (or density) predicted with the model agrees well with reported literature data on PBF processes.
The Carnegie Mellon University (located in Pittsburgh, PA) study was conducted by Ming Tang and P.Chris Pistorius (both from the Department of Materials Science and Engineering) and Jack L. Beuth, of the Department of Mechanical Engineering. In their research the scientists used a geometry-based simulation to predict porosity caused by insufficient overlap of melt pools (lack of fusion), a common and dire issue in powder bed fusion AM processes.
The inputs into the simulation are hatch spacing, layer thickness, and melt pool cross-sectional area. Melt pool areas used in the simulations can be obtained from experiments, or estimated with the analytical Rosenthal equation. The necessary material constants, including absorptivity for laser-based melting, have been collated for alloy steels, aluminum alloys and titanium alloys.
Comparison with several data sets from the literature shows that the simulations correctly predict process conditions at which lack-of-fusion porosity becomes apparent, as well as the rate at which porosity increases with changes in process conditions such as beam speed, layer thickness and hatch spacing.