Process based modelling of power density for wire laser additive manufacturing using a coaxial head

Wire Laser Additive Manufacturing enables the production of near net shape parts at high deposition rates while reducing the risks due to metallic powder handling. Common configurations of this process use a single laser beam with lateral wire feeding, inducing a dependency on the feeding angle and direction relative to the travel direction. In contrast, coaxial configurations feed the wire along the direction of the energy input, which can be achieved by using a ring beam or multiple beams. In this case, the beams are placed so that they form a single spot on the focal plane. Varying the distance between the intersection point of the beams and the substrate allows for specific power densities with different spot sizes, resulting in varying bead geometries and penetrations. However, most models for process simulations consider a single equivalent beam or a single heat source to model the power input, which cannot accurately represent the obtained power densities. This article presents a modelling of power density inspired by the process for coaxial heads. The developed approach can be used to simulate the laser power density on any surface with any number of beams. It is applied to model the experimental setup using a three beam coaxial head with an identified laser beam model. The simulated power densities are compared to experimental results to validate the predictions of spot size and shape. To better represent process behaviour, both wire and bead are modelled and the power densities are simulated on these surfaces. Finally, the effect of the head rotation is investigated as it modifies the power density and geometry of the beads. The resulting power profiles are compared to the internal and external profiles of the manufactured beads to conclude on the effect of this parameter.