Electron-Optical In Situ Imaging for the Assessment of Accuracy in Electron Beam Powder Bed Fusion

Abstract

The current study evaluates the capabilities of electron-optical (ELO) in situ imaging with respect to monitoring and prediction of manufacturing precision in electron beam powder bed fusion. Post-process X-ray computed tomography of two different as-built parts is used to quantitatively evaluate the accuracy and limitations of ELO imaging. Additionally, a thermodynamic simulation is performed to improve the understanding of ELO data and to assess the feasibility of predicting dimensional accuracy numerically. It is demonstrated that ELO imaging captures the molten layers accurately (deviations <100 μm) and indicates the creation of surface roughness. However, some geometrical features of the as-built parts exhibit local inaccuracies associated with thermal stress-induced deformation (deviations up to 500 μm) which cannot be captured by ELO imaging. It is shown that the comparison between in situ and post-process data enables a quantification of these effects which might provide the possibility for developing effective countermeasures in the future.

A Ray Tracing Model for Electron Optical Imaging in Electron Beam Powder Bed Fusion

“…More details can be found in Section 2.1.3 and Appedix A. In the case of the 2nd scattering event, s 1,k replaces d which allows to compute N 1,k with the respective α 1,k and β 1,k as defined by Equation (7). All other dependencies of g BSE are omitted here for the sake of brevity.…”

“…Recently, Electron optical (ELO) imaging has been demonstrated to be a successful, reliable process monitoring method in electron beam powder bed fusion (PBF-EB), which has been used to develop process parameters [5], defection detection [6] or the assessment of dimensional accuracy [7]. After melting, the solidified build surface is scanned in a separate additional process step with a focused and low-power electron beam.…”

In Situ Inclusion Detection and Material Characterization in an Electron Beam Powder Bed Fusion Process Using Electron Optical Imaging

“…ELO imaging has been shown to provide excellent topographical information [ 2 , 3 , 5 , 6 ]. Applications include: developing process windows for new materials [ 7 ], developing part-specific scan strategies for complex geometries [ 8 , 9 ] and process monitoring for defect detection [ 10 ].…”