Flowability of SLS powders at elevated temperature

The development cycle of a Selective Laser Sintering (SLS) material incorporates many aspects that must be fulfilled before it can be satisfactory processed. Among these properties the polymer flowing behavior in its powder state is of primary importance. A lack of a suitable powder spreading quality during SLS processing leads to inhomogeneity of part density and reduced mechanical properties. However, none of the available powder characterization methods attempts to simulate the powder flowability at effective SLS processing temperatures. Therefore this investigation characterizes the powder flowing dynamics at higher temperature for commercially available materials and research powders. A measuring system with a rotating drum emulates the stress state of the material during the SLS deposition. New insights regarding the spreading conditions are presented, particularly above the glass transition point were the viscous part of the polymer becomes more relevant. In particular the dynamic avalanche angle, volume expansion ratio and surface fractal distributions represent suitable parameters to characterize the different powders in terms of the flowing behavior and its correlation to the final sintered density. This system is proposed as a SLS quality control and screening tool during the early stages of powder development.