A new design of continuous coaxial nozzle for direct metal deposition process to overcome the gravity effect

In the metal deposition process, the performance of the nozzle is crucial to the quality of clad. Continuous coaxial nozzles are broadly used in this process for repairing two- and three-dimensional parts, because it can create a homogeneous distribution of powder particles. In addition, an inert gas can be applied using this type of nozzles which shields powder particles and laser interaction zone, and prevents the surface from oxidizing at high process temperatures. However, when this type of nozzle is tilted from the vertical axis for cladding non-horizontal surfaces, the effect of gravity on powder particles affects the uniformity of powder distribution at the nozzle outlet. This matter limits the application of the nozzle at non-zero inclination angles in multi-axis cladding. The purpose of this paper is to present a new design for continuous coaxial nozzles which is less sensitive to gravity, and thus, improves the performance of the nozzle at non-zero inclination angles. The new design is based on changing the configuration of nozzle inlets and partitioning powder flow in existing continuous coaxial nozzles. The powder flow is divided into eight parts before entering the nozzle, each part passing through one of the eight radially symmetrical grooves embedded in the inner cone of the nozzle. The performance of the new design is investigated through numerical simulation of powder flow in the nozzle. Improved values for the parameters affecting the powder flow distribution, including the velocity of carrier gas and the geometric dimensions of powder inlet and outlet sections, is also extracted. The simulation results show that using the new design, the deviation of the powder focal point from the nozzle axis is decreased. It is observed that at inclination angles of 0, 20, 30 and 45 degrees, the powder passing through a circle of 2.5 mm diameter is 90%, 89%, 87% and 86%, respectively. This indicates that tilting the nozzle has a small influence on the amount of powder delivered at the nozzle focal plane. Consequently, by reducing the effect of gravity on the powder flow distribution, the new nozzle can be used in a wide range of inclination angles.