Melt pool sensing and size analysis in laser powder-bed metal additive manufacturing

Process temperature measurement for selective laser melting (SLM) can provide critical information such as melt pool dimension for real-time part quality control. In this study, a LumaSense MCS640 thermal imager with a spectral range of about 670 nm wavelength was utilized to collect process radiant temperature information during SLM fabrication using Inconel 718 powder. Sharp transition of cooling curve in collected radiant temperature profile along scanning direction was considered as material phase transition, and it was identified by minimum secondary derivative values of each camera pixel from fitted polynomial functions. Obtained liquidus-solidus transition was used to calculate melt pool size. Speed effect on melt pool dimension has been investigated. The major findings are as follows. (1) At a beam power of 180 W, typical melt pool has average dimensions of about 0.39 mm and 0.23 mm in length and width for 400 mm/s scanning speed. (2) Similar melt pool sizes were observed at different build heights for a given scanning speed. (3) Melt pool width decreases with the increase of scanning speed while the trend for melt pool length is unclear; no significant difference was observed for melt pool length at different scanning speeds under a beam power of 180 W.