Numerical Investigation of Laser Absorption by Metal Powder Bed in Selective Laser Sintering Processes

Laser absorption by powder bed in selective laser sintering (SLS) processes remains a critical issue to be fully understood. This issue is important for the appropriate selection of processing parameters in practices as well as an accurate definition of the thermal input in numerical modeling. In this work, a ray tracing model is used to study this issue. In parametric studies, the effects of laser parameters and powder bed structures on the laser absorption are investigated. It is found that a top-hat laser produces a more uniform laser absorption within laser heated spots than a Gaussian laser. The absorption distribution generally does not follow an exponential decay; instead, it gradually increases to a “peak” and then decreases along the laser shooting direction. The absorption near the substrate can be enhanced when the powder bed thickness is reduced, which helps to bind the newly deposited layer with its substrate in SLS processes. Finally, using bimodal powder beds can reduce laser penetration and produce more uniform laser absorption in laser heated spots.