Mechanics of nozzle clogging during direct ink writing of fiber-reinforced composites

Nozzle clogging frequently occurs while printing fiber-filled polymer inks with extrusion-based additive manufacturing processes, which limits the quantity of fibers that can be added to the matrix, part fidelity, and geometric accuracy of the printing process. Both in situ X-ray radiography and ex situ X-ray computed tomography were used to explore the mechanisms that contribute to nozzle clogging. Three inks were considered, with fiber volume fractions ranging from 1% to 5.75%, and nominal fiber lengths from 150 to 470 mu m. These results showed that the specific mechanisms that produced the clog depended substantially on the fiber volume fraction, fiber length and nozzle geometry. Specific clogging mechanisms included the log-jam pileup of misoriented fibers near the nozzle tip, the lodging of a fiber entanglement in the nozzle tip, and the accumulation of misoriented fibers at step-like reductions in the nozzle profile. Suggestions to reduce the prevalence of nozzle clogging are presented.