Coalescence Behavior of Polyamide 12 as Function of Zero-Shear Viscosity and Influence on Mechanical Performance

The favored material for powder bed fusion of polymers (PBF-LB/P) is polyamide-12. Its molecular weight increases from post-condensation at elevated temperatures in the building chamber, consequently having different properties when reused. An important aspect of PBF directly affected hereby is the coalescence behavior, as it significantly determines the surface quality, porosity, and thus the component’s mechanical properties. However, detailed studies on coalescence are limited to virgin powders with low viscosity; therefore, coalescence behavior of polyamide-12 with different molecular weights is investigated using hot stage microscopy. Additionally, the zero-shear viscosity is determined using the Carreau model, allowing comparison of experimental results to sintering models. Furthermore, the mechanical properties and surface qualities are analyzed, and components with adequate values are made with two-cycle reprocessed powder. Since surface flaws do not exist uniformly across all components, the orange peel effect is not attributed solely to the increased viscosity of the reused powder.