Light absorption of W-Cu powders in laser powder bed fusion

The intensity absorbed by particles is a crucial requirement in the simulation of manufacturing W-Cu composites by laser powder bed fusion. The ray-tracing method can be used to calculate the absorbed intensity accurately, but it is very time-consuming. To simplify the calculation of the absorbed intensity, models of W-Cu powders consisting of hard spheres were established. The absorptance and the absorbed intensity of these spheres were calculated numerically with the ray-tracing method and analytically based on Lambert's law and Fresnel's formulas. While the first method accounts for multiple reflections, the second does not. The results were compared to evaluate the influence of multiple reflections on the light absorption. With increasing Cu content in the powder, the ratio of total absorptance to the first reflection increases due to the high reflectivity of Cu. In addition, more intensity is transferred to deeper powder layers. Based on these findings, an analytical expression of the absorbed intensity within the powders was derived. It was validated by using it as a heat source for temperature field calculation in LPBF heat conduction models. The calculated temperatures agree well with those obtained by using ray-tracing results as a heat source.