Metal transfer behavior and its correlation with process parameters in coaxial wire laser directed energy deposition using an annular laser beam

Directed energy deposition – laser beam, wire feedstock (DED-LB/W) shows great promise for manufacturing near net-shape components by saving cost and time. Lateral wire feeding with a certain angle towards the workpiece is commonly used in DED-LB/W, which suffers from limited movement capability and reduced flexibility. In this work, a direction-independent coaxial wire laser directed energy deposition using an annular laser beam was proposed. Metal transfer behavior, which plays an important role in determining the process stability and quality, were investigated in the newly developed process using an annular laser beam with a specific position of wire to laser beam. The results showed that four metal transfer modes, i.e. unstable liquid bridge or pendant droplet, stable liquid bridge, stable wire penetration, and unstable process, were observed under various working distance. The power density and temperature field for the annular laser beam under various working distance were calculated. It was found the power density and the position of wire to laser determine the laser energy for melting the wire, which has a significant effect on the metal transfer mode. Furthermore, an easy-to-use parameter that involves common process parameters such as working distance, laser power and wire feeding speed is proposed for the practice use to predict the metal transfer mode for optimizing the deposition quality in coaxial DED-LB/W.