Mechanisms of variable polarity alternating arc based directed energy deposition with feedforward control of mass transfer and droplet kinetics

Abstract

Conventional DED-Arc processes suffer from heat and mass transfer instability due to thermomechanical coupling in an arc. This paper proposes a real-time feedforward control method using a variable-polarity alternating arc. The method decouples arc thermomechanical transmission and utilizes electrical signals of the arc to trigger piezoelectric ceramic forces. By combining droplet inertia with arc forces, it synergistically regulates droplet necking and detachment for stable deposition. The paper designed two control modes, M1 (falling-edge triggering) and M2 (rising-edge delayed triggering). A comparative analysis of droplet transfer under the two control modes at varying welding parameters revealed that at 80 A current, stable droplet transfer was achieved using the M2 control mode. The droplet transfer frequency underwent linear fitting with a determination coefficient (R²) of 0.99946, indicating a high linear correlation and stable droplet transfer frequency. In the M2 control mode under high-current conditions (≥100 A), the inertial driving effect became more pronounced, and the droplet transfer frequency increased significantly. Under low-current conditions (≤80 A), uniform and stable droplet transfer was maintained even with reduced wire feed speed. Compared to the original stable process window, the M2 control mode expanded the viable parameter range by 50 %. Formation experiments demonstrated that under the M2 control mode, single-pass formation continuity and uniformity were significantly superior to conventional modes, with deposition layer surface flatness improved by approximately 80 %. This paper provided both theoretical and practical foundations for droplet dynamics regulation and process optimization in variable-polarity arc additive manufacturing.