Electric current evaluation for process monitoring in electron beam directed energy deposition

Electrons, which carry abundant information, can be used for the in situ monitoring of electron beam additive manufacturing, such as in the emerging electron optics method for monitoring surface morphology. In electron beam directed energy deposition (EB-DED), droplet transfer, which affects the stability and quality of the deposition, is a unique and critical process. In this study, we developed a dual-channel absorbed current monitoring method based on absorbed electrons for the in situ monitoring of droplet transfer in the EB-DED process, which differs from the common vision-based monitoring technology. The ability to identify different droplet transfer modes and parameter changes was verified through a series of experiments. The results show that this method exhibited prominent signal characteristics corresponding to typical droplet transfer modes in EB-DED, accurately identified the droplet transfer mode during part fabrication, and provided a clear criterion for identifying the stability of the deposition process. It also distinguished changes in the droplet transfer distance and wire-feeding speed via a quantitative analysis of the signal variation caused by the corresponding droplet behavior. We also analyzed and explained the generation mechanisms of the signal characteristics. The dual channel absorbed current monitoring method exhibited high reliability and efficiency during the in situ monitoring of the droplet transfer of EB-DED. The proposed method represents a new tool for information sensing in closed-loop control and facilitates the study of droplet transfer behavior in EB-DED.