Abstract: Most of the energy of the coaxial electron beam wire additive manufacturing (C-EBAM) acts on the wire can avoid the adverse effect of the axial side wire feeding mode on the forming quality. In order to further improve the forming accuracy and efficiency of the C-EBAM, and optimize the electron beam quality, the work of factors analysis on the electron beam waist position of gas discharger electron beam gun of coaxial beam wire is carried out. Difficulties in characterizing the structure of plasma anode lenses for C-EBAM electron beam sources. Based on the theoretical analysis of the electron beam waist position parameters, a method combining numerical simulation and experimental analysis is adopted. The influence of cathode-anode electrode structure, working voltage, discharge gas type and gas pressure on the beam waist position characteristic parameters is investigated. The numerical simulation results show that the current density at the beam waist is affected by the cathode spherical radius and the anode inclination on the electrostatic convergence ability of the beam, which first increases and then decreases. The experimental analysis shows that the working voltage, the type of discharge gas and the gas pressure affect the plasma ionization degree and the particle velocity, and change the characteristic parameters of the waist position, i.e., with the increase of the working voltage and the gas flow rate, the distance from the bottom end surface of the electron gun to the axial center of the beam waist and the beam waist length increase respectively.

Key words: wire-fed electron beam additive manufacturing, coaxial beam wire, electron gun structure, CST electromagnetic simulation, waist position