The Importance of Material Compaction in Extrusion Deposition Additive Manufacturing

Conference Abstract: The reduction in coefficient of thermal expansion gained by adding carbon fiber to printing polymers has enabled printing geometries of meters in length. The large-scale additive manufacturing process that has emerged utilizes single-screw extruders to efficiently melt pelletized feedstock. The suspension of fibers in molten polymer is deposited in the form of beads to form a three-dimensional geometry on a layer-by-layer basis. Multiple flow mechanisms including shear, stretch, and squeeze flow develop as the material flows through the printing nozzle, exits the nozzle, turns ninety degrees, and is compressed with the action of a compacter. Further, these flow mechanisms affect the orientation of fibers within the printed bead.
This presentation focuses on a virtual study carried out on the effects of active material compaction through a roller or a tamper on the fiber orientation within the printed bead, the mitigation of inter-bead voids, and the heat removed through the compacter. The results showed the effect of the squeeze flow developed during compaction on the reorientation of the fibers from the print direction to the direction transverse to the print. Similarly, the effectiveness of the compacter in mitigating the inter-bead voids increased with the aspect ratio (width to height) of the printed bead and with the overlap between adjacent beads. Finally, the influence of the compacter on the transient temperature history developed during the printing process of a part was investigated.