Abstract

Direct ink writing enables deposition of multiphase filaments with designed microstructures. Using acoustophoresis, we establish a narrow distribution of microparticles at the center of a direct-write nozzle. The distribution shifts and widens after deposition depending on the printing direction. We use particle image velocimetry and digital image analysis to identify flows transverse to the printing direction and characterize particle distributions in the printed filament. Sources of direction-dependent effects include square nozzles, co-deposition of support material, a rotationally asymmetric microstructure established in the nozzle, and speed inaccuracies that occur in 3-axis gantries. We propose an analytical model for predicting print direction-dependent flows and particle distributions as a function of anisotropy of the particle distribution in the nozzle, a disturbed zone near the nozzle, fluid reshaping of the print bead, uniform rotation of the print bead, calibration of the ink and support nozzle positions, and 3D printer motor error. Using the model, we propose strategies for controlling direction-dependent microstructures in direct ink writing. The analytical model can be easily adapted to similar direct-write applications to diagnose sources of direction-dependent microstructures.