Geometry and Surface Feature Evaluation in E-PBF Process Using In-Operando Electron Emission Signal

Electron beam powder bed fusion (E-PBF) requires reliable in situ process monitoring, and electron emission signals offer a promising avenue for this purpose. Most prior studies have relied on dedicated beam scans performed before or after melting, leaving open the question of whether the signal acquired during the melt itself can directly indicate geometric and topographical features of the fabricated part. In this work, the in-operando electron emission signal was recorded during spot-melting of a Ti-6Al-4V spur gear and evaluated for its ability to reconstruct geometric features and surface topography, with optical microscopy and profilometry serving as ground truth. A melt-pool dilation correction was applied to compensate for the geometric expansion of individual melt spots. After correction, the in-operando reconstruction reached agreement deviation values below 2.2% across the tooth tips, tooth bases, and chord widths, which are comparable to or better than those obtained from post-melt ELO imaging. Comparison with profilometer height profiles confirmed strong correlation with surface topography (Pearson 0.67-0.87 across all four profiles, p < 0.05 for all), indicating that the signal captures meaningful surface-topography variation in addition to geometric boundaries. The results demonstrate that the in-operando electron emission signal shows strong potential for in situ geometric and topographical assessment of complex parts in E-PBF, supporting its future integration into closed-loop process monitoring.