Laser beam absorptance effects during wire directed energy deposition

Laser energy absorption plays an important role in determining process stability and energy efficiency in wire Directed Energy Deposition using a laser beam. However, the combined influence of wire geometry, beam positioning, and temperature-dependent optical properties on absorbed laser power remains insufficiently understood. This work presents an analytical framework for predicting the absorptance and absorbed power during the processing of Inconel 718. The model combines Monte Carlo ray tracing, Fresnel reflection theory, and a temperature-dependent Drude formulation in which the optical properties are related to electrical resistivity. A parametric investigation was conducted to evaluate the effects of wire-feeding angle, beam-wire offset, melt pool temperature, and wire temperature. The results showed that increasing the wire feeding angle altered the incidence-angle distribution of laser rays on the wire surface, resulting in non-monotonic variations in wire absorptance and absorbed power despite increasing beam interception. Furthermore, the interaction between wire and melt pool temperatures revealed three operating regimes governing the response of absorbed power to beam-wire offset. When the wire absorptance was lower than that of the melt pool, absorbed power increased with increasing offset, whereas the opposite trend occurred when the wire absorptance exceeded that of the melt pool. Between these regimes, a compensation condition was identified in which absorbed power remained nearly independent of beam-wire offset. This behavior occurred when the wire absorptance approached that of the melt pool, minimizing the influence of laser-energy redistribution between both surfaces. For the investigated geometry and optical assumptions, the compensation condition was associated with an approximately constant electrical-resistivity ratio and a constant relationship between the compensation wire temperature and melt pool temperature.