Selective laser sintering of a crystalline and a glass-filled crystalline polymer: Experiments and simulations

A previously developed two-dimensional, thermal finite element simulation of the selective laser sintering (SLS) of amorphous polymers has been extended to the study of crystalline and composite crystalline polymers. Three developments were needed: the inclusion of the latent heat of melting; modification of the amorphous viscous sintering law to allow for the crystalline fraction of material during melting; and allowance for the CO2 laser radiation to be absorbed over a finite depth of the powder bed. The simulation is based on a continuum view of heat conduction in the powder bed. When it is applied to the SLS of nylon-12 parts, its predictions of how density and size accuracy depend on the laser energy absorbed by the powder bed can be brought into agreement with experiments by appropriate choices of sintering and absorption law parameters. However, when the simulation is applied to SLS of glass-filled nylon-11 parts, its in-plane size accuracy predictions are incorrect. It is speculated (based on experimental observations of sintered microstructure) that the continuum view of heat conduction is inadequate and that consideration must be given to differential absorption of laser radiation in the glass and polymer fractions of the powder. A final application of the simulation suggests that the ambient temperature of the powder bed must be held to within 4degreesC of its set value to maintain process accuracy.