3D Modeling of Additive Manufacturing Process: The Case of Polymer Laser Sintering

These last years, many industrial and academic interests concerning the additive manufacturing of materials are developed. Even the industry has made major advances in this area, it remains that several phenomena are still not well understood in order to properly model the process and propose quality improvement of tracks and parts made.

               The SLS process fabricates solid objects by means of a laser radiation, which depends on several parameters related to the laser beam: laser power, scanning velocity and wavelength. The energy input by laser is often assumed as a heat flux density with Gaussian distribution, when computing the temperature field      

Recently, several researchers developed models of heat diffusion for laser sintering process. The authors underestimated the effect of the air between grains in the laser sintering process. In fact, the powder bed is always treated as a homogeneous medium instead of discrete granular system, which is an assembly of many discrete solid particles interacting with each other due to dissipative collisions.

This work focus on studying multiphysical transient phenomena in polymer powders occurring during selective laser sintering in polymers powders. In such processes, the laser interacts with the polymer powder bed, allowing multiple phenomena: laser scattering and absorption, polymer heating, melting, coalescence, densification, and all the material parameters evaluate virus the temperature. To simulate all these phenomena, we chose using modified Monte Carlo-ray tracing method coupled with the Mie theory to simulate the laser power transfer in the powder bed. For the heat transfer after the laser sweep on the powder, a finite volume method is adopted. The model couples the heat diffusion, melting, coalescence and densifications of the polymers grains, and the crystallization kinetics during the cooling steps.  According to our molding, the laser intensity is more concentrated on the surface of the material, in discordance with the prediction when using the Beer-Lambert law. The laser applied on thermoplastic material caused the polymer powder melting, coalescence between melted grains, air diffusion versus densification, crystallization and volume shrinkage. All these processes are simulated by a series of multiphysical models, and numerical tools are based on the finite volume method (FVM). Further more, we tested the reliability of the modeling by comparing with other’s experiments result from the literature, and a parametric analysis is performed, based on the process characteristics as the laser sweep speed, its intensity and shape, the polymers grain size and so on. Many original recommendation on the process optimization where then proposed.