Investigation on arc plasma, droplet, and molten pool behaviours in compulsively constricted WAAM

In order to study the special constriction effect and physical process features during compulsively constricted WAAM (CC-WAAM), the dynamic behaviours of arc, droplets, and molten pool were visually investigated. Possible interactions inside the narrow space were discussed to explain the mechanism of the compulsive constriction on ejected plasma and droplets. Based on the captured images, the strong radiative emission indicates that the ejected plasma was at high temperature at least 6000 K. As the current increases higher-temperature plasma jets were expected, which would lead to a larger plasma volume in the absence of constriction. The relationship between current and droplet diameters was preliminarily established to enable prediction of the droplet size. An important feature of small-size droplets (as low as 0.89 mm) offered CC-WAAM a great potential to improve the precision of the additive manufacturing layers, although the minimum width of the deposited layer is much larger than the droplet diameter due to liquid spreading and accumulation. The droplets were found to have a slight impact on the molten pool behaviours, which produces stable molten pool shapes. Under the wide-range parameters, the deposited layers showed good appearances, which indicates the good adaptability of this novel technology.