Monitoring melt pool dynamics using multi-detector electron optical imaging

Experimental observation of the dynamic melt pool evolution in advanced powder bed fusion processes is a challenging endeavor. The main challenge is that the small melt pool dimensions and its fast dynamic evolution require high spatial and temporal resolution of the monitoring equipment. Only dedicated, often costly experimental setups like high-resolution imaging or synchrotrons enable close-up views of the melt pool behavior. Multi-detector electron optical imaging enabled recently to determine the build surface topography in situ in layer-based monitoring scenarios in electron beam powder bed fusion. This study applies the method to study melt pool evolution. Detector signals during melting are recorded, with and without applied bias voltages on the detector plates. Furthermore, the dynamically evolving melt pool surface of single points is captured by fast electron optical imaging sweeps after beam is turned off. The imaging scan is also modelled using a mesoscopic Lattice-Boltzmann simulation tool to rule out possible melt pool distortions caused by scanning. Differences in melt pool evolution between experiment and model are observed. The developed method allows for observing melt pool dynamics with a previously unknown level of detail. It is envisioned that the method will allow for calibrating mesoscopic simulation models with experimentally measured dynamic melt pool properties. • Dynamic melt pool surface topography evolution observable with multi-detector Electron Optical operando imaging. • Detector bias voltages suppress thermionic contributions to detector signals during melting. • Backscattered electron dominated detector data usable for surface gradient computation. • Modelling confirms melt pool dynamics remain unchanged by observation.