A viscous sintering model for pore shrinkage in packings of cylinders

The process of particle coalescence due to surface tension, usually referred to as sintering, is very important in processes involving polymer, ceramic, or metal aggregates, especially in additive manufacturing. A model was developed for part shrinkage by determining the rate of void and volume reduction of a square unit cell in a lattice arrangement of cylindrical particles. Neck growth between cylinders in contact is determined by assuming planar extensional flow for a Newtonian fluid. The model provides growth of neck width, which is easily converted to void area reduction and relative density, as a function of dimensionless time. The results obtained were compared to previously published numerical simulations of shrinkage and to experimental data available in the literature, involving polypropylene (PP) particles from one study and liquid glass particles from two others. Also, predictions of neck width were compared to experimental data in fused filament fabrication (FFF) of PLA.