Laser energy absorption and distribution behaviors of randomly packed powder bed using ray tracing method during laser powder bed fusion of metallic materials

Laser energy absorption of powder layer and melting behavior during laser powder bed fusion (LPBF) are vital for the subsequent metallurgical behavior. In this chapter, a randomly packed powder bed model was established, and the ray tracing calculation was developed to simulate the condition of the interaction between laser beam and powder particles. The influence of the particle size distribution, reinforcement type and contents on the laser absorptivity, irradiance distribution and track surface morphology were revealed. The results showed that the powder bed absorptivity and irradiance of the central powder particle were sensitive to the powder particle sizes. The laser energy absorptivity increased with a decrease in particle size, caused by the laser multiple reflection phenomenon. Adding ceramic reinforcement particles can significantly improve the absorption irradiance. However, with the excessive addition of ceramics, balling phenomenon and trapped unmelted particles deteriorated the surface morphology of the melted track. It could be attributed to the high required energy for completely melted ceramic particles and the elevated difficulty of thoroughly wetting the unmelted particles. These results provided a physical basis of high-quality and defect-free components fabricated by LPBF process.