Improving process stability of electron beam directed energy deposition by closed-loop control of molten pool

Abstract

As regards wire-based additive manufacturing technologies, including electron beam directed energy deposition (EB-DED), it is imperative to improve their process stability to promote their wide application. In the extreme non-equilibrium EB-DED process, the molten pool, a key factor for the stability and continuity of deposition, is susceptible to interference. The unique vacuum condition resulting in strong metal evaporation and adverse heat dissipation also brings challenges in introducing auxiliary means for enhancing its stability. In this study, we developed a real-time closed-loop control method to improve the stability of molten pool size by manipulating the electron beam current. We initially focused on investigating the behavior of molten pool width under different beam current variation laws and developed a relationship model between them for controller design. We then proposed a segmented control strategy considering the relationship model, the nonlinear process, the natural fluctuation of the molten pool, and the response capability of the EB-DED equipment. Our strategy and controller were tested and optimized through resisting interference and tracking input changes experiments. We further analyzed the mechanism of molten pool size variation under interferences and controlling, the origin of the natural fluctuation, and the influence of the droplet transfer. Our study improves the stability of the molten pool under potential interferences by closed-loop control, promotes the understanding of the interaction between the molten pool and electron beam, and lays the groundwork for enhancing the consistency and repeatability of the EB-DED process.