Quantification of supplied laser energy and its relationship with powder melting process in PBF-LB/P using near-infrared laser

Abstract

This study discusses the quantitative understanding of the laser input energy considering the optical properties and its effect on the melting process of powder materials in PBF-LB/P using a near-infrared laser. With the increased use of near-infrared lasers for PBF-LB/P in recent years, the influence of the input energy loss due to transmission and reflection on the powder melting process must be considered. Therefore, the modified energy melt ratio (Modified EMR), which is the ratio of the input energy to the energy required to melt the powder material, was proposed as a new energy supply index in this study. The energy absorbed by the powder layer was estimated from the transmission and diffuse reflection properties obtained in a previous study and the specular reflection properties obtained in this study. The powder layer thickness was determined by considering the consolidation of the powder layer, which affected the optical properties. The parts were fabricated with various optical properties, powder bed temperatures, and input energies to evaluate part density, which is closely related to the melting process. Compared to conventional indices, such as the energy density or EMR, the relationship between the Modified EMR and part density was more consistent, regardless of the optical properties and powder bed temperature. This study also investigated the effect of the laser heating of the layer below the powder layer on the melting process of the powder layer. The optical properties of a thin plate simulating the underlying layer were obtained, and the temperature increase in the underlying layer was determined from the known transmittance of the powder layer. It was concluded that heating the underlying layer does not accelerate the melting of the powder layer even at low powder bed temperatures, which require the highest laser energy for melting the powder material.