Real Time Monitoring of Electron Emissions during Electron Beam Powder Bed Fusion and Process Control for Arbitrary Geometries and Toolpaths

Manufacturing processes that utilize electron beams (EB) as a directed energy source often benefit from enhanced process monitoring and control opportunities. Electron interactions lead to a spread of energy over a region larger than the beam diameter, and this provides a wealth of near instantaneous spatio-temporal process data through the collection of secondary electrons, backscattered electrons, x-rays, photons and the like. These data are processed to measure localized geometric, topographic and compositional variations over a wide range of process temperatures, conditions, and length scales.

Real time monitoring of electron emissions during the operable processing steps of electron beam powder bed fusion (preheating, melting, post heating, etc.) provides a wealth of in-process data across multiple length scales. In this paper we present a methodology for collecting both real time beam positional data and electron emissions as a function of time for arbitrary component geometries and complex toolpaths. To demonstrate this, we collected these data during the melting steps of EB-PBF of pure copper and quantitatively compared electron images generated with this approach to both µCT data and optical micrographs of the same specimens. These results show a strong mathematical correlation between the location of loss of signal events observed in electron images and observed defects in µCT. At the same time, the collection of beam positional information facilitates the calculation of beam velocities, and hence local energy inputs. We also demonstrate a to methodology visualize process data from a wide variety of sources and map these over the 3D geometries as a function of time and position and to link these spatiotemporal data to structure observed in the in the electron imaging and energy input maps. Ultimately we have leveraged this new electron imaging approach to defect detection into a rudimentary control strategy to eliminate porosity in a copper sample.