An efficient ray tracing methodology for the numerical analysis of powder bed additive manufacturing processes

This paper presents a ray tracing model to simulate the laser-powder bed interaction for additive manufacturing processes. Ray tracing is a technique that is able to accurately and efficiently capture the interaction of light with multiple objects with complex geometries made of different materials. In the proposed methodology the laser energy distribution is modelled by a finite number of rays which are traced through the powder bed that is modelled as stacked spherical particles. The proposed ray tracing methodology addresses the reflection and refraction of light using the Fresnel equations and its absorption using a Beer–Lambert law. Simulations of a stationary laser on a powder bed show that for metallic materials the effect of polarisation of the light on the energy distribution in the powder bed is negligible. In addition, it is demonstrated that the refracted rays are fully absorbed by single powder particles. The illumination results of a stationary polarised laser under a range of incident angles indicate a significant absorption difference at high angles. In order to increase computational efficiency, a closed form relation for an equivalent homogenised volumetric laser heat source has been derived, whereby the shape and power profile of the laser matches the ray tracing results. Simulating single scan lines by varying power, spot size and speed demonstrates that the model accurately captures a moving laser in a DEM simulation, revealing the relations between single scan line dimensions and printer settings.