Influence of head orientation on bead geometry and penetration in wire laser additive manufacturing with coaxial technology

Wire laser additive manufacturing (WLAM) distinguishes itself from other wire based processes by its stability and repeatability of deposited geometry, even at high deposition rates, leading to near net shape parts. While the most common configuration of head technology consists of a single laser beam and wire feeding along two different orientations, other technologies align the feed direction with the energy resulting in a coaxial configuration. This can be achieved by the use of several laser beams placed on a cone around the wire to focus on the virtual tool centre point. Although wire feed angle and direction have been linked to variations in bead dimensions and penetration with a single laser, few articles investigated the head orientation effects with coaxial technologies. This study focuses on the effect of the head orientation to the substrate on bead and penetration profiles using a three lasers coaxial head. The head rotation around its own axis results in varying shapes and penetration profiles and leads to production defects in some configurations. Asymmetrical beads with non-centred penetrations are observed experimentally and linked to the beam's positions relative to the bead direction. A symmetrical arrangement with one laser to the front of the wire and two lasers at the back produces a symmetrical bead with minimal penetration, while an asymmetrical configuration with two lasers on one side of the wire and one on the other results in a displacement of the bead geometry toward the higher irradiance area, with a greater bead penetration. Therefore, the rotation of the coaxial head around its own axis relatively to the travel direction needs to be considered to maintain the control of the deposited material and the stability of the process during the manufacturing of the part.