In situ monitoring of beam current in electron beam directed energy deposition based on adsorbed electrons

Abstract

Electron beam directed energy deposition (EB-DED) is a promising and efficient additive manufacturing technology, but the vacuum environment challenges the in situ parameters monitoring. In this paper, an in situ beam current monitoring method is developed based on the absorbed electrons. A series of experiments show that there is a linear relationship between the absorbed electron current and the impinging beam current. However, this relationship only holds when the beam power density is relatively low. When the power density is high, the absorbed electron current will be lower than the theoretical value determined by the linear relationship. This is mainly due to the massive generation and ionization of metal vapor. The critical power density depends on the melting point of the material. Nonetheless, the deviation of the absorbed electron current at high power density can roughly determine the relative position between the focal spot and the workpiece surface. In addition, the slope of the linear relationship is material-dependent, so this method can also distinguish different materials.