Investigating the generation process of molten droplets and arc plasma in the confined space during compulsively constricted WAAM

Abstract

Wire arc additive manufacturing (WAAM) has unmatched efficiency and cost advantages in the formation of large-scale structural parts while the forming accuracy and forming quality deteriorate due to the increase of heat accumulation during the forming process. The authors have proposed a variant technology called compulsively constricted WAAM (CC-WAAM) trying to solve the problem of excessive heat input. The present study focuses on the physical generating process of arc and droplets in the confined space during CC-WAAM using high speed photography. The results revealed that arc behaviors and droplets transfer were very unstable at low-level electrical parameters with the feature that the droplets transfer diameters were large (1.8–5.3 mm), the droplets transfer frequencies were low (2–23 Hz), and the arc phenomena were complicated. While the opposite phenomena were obtained at high-level electrical parameters, achieving a droplet of 0.8 mm and a transfer frequency 300 Hz. Further experiments were conducted to study the influences of the shielding gas flow on arc behaviors and droplets transfer. The gas made arc disperse at low-level electrical parameters and promoted the arc plump at high-level electrical parameters. Preliminary force analysis of the droplets was made to explain the droplets transfer trajectories. And optimized parameters setup has been obtained to produce stable arc burning and predictable small-size droplet transfer.