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Achieving Printable Filament Diameter Tolerance (FDT) for Fused Filament Fabrication (FFF) 3D Printing with Air Cooling

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Conference Abstract: The flow rate of a fused filament fabrication (FFF) printer is affected by filament diameter, with an inconsistent diameter resulting in irregular gaps between printed beads, poor surface quality, extruder jams, and excessive overlap. Filament diameter tolerance (FDT) has received limited research focus, though 1.75±0.05mm is the commonly accepted tolerance. To better understand the effect of the FDT on filament printability, filament made from RES4043D polylactic acid (PLA) and Prografen PLA with iron additive was produced using two extruder systems: a ThermoFischer Scientific Process 11 extruder and a Filabot EX2 extruder. Filament was cooled with a Filabot Airpath. Filament diameter was affected by extrusion speed, draw speed, nozzle temperature, and fan speed, with significant adjustment needed to achieve the desired filament extrusion. The FDT range was measured inline during extrusion and recorded. The fabricated filaments were then tested by printing test prints, with print failure type and filament diameter at point of failure recorded. The ThermoFischer Scientific-extruded Prografen PLA/Fe failed with a filament diameter of 1.90mm (+0.15mm) by jamming in the print head. The Filabot-extruded RES4043D PLA had a range of 1.61mm-1.85mm, with a nominal diameter around 1.8mm, and failed by jamming in the print head. The filament diameter at the jam varied by measurement location around the filament. The ThermoFischer Scientific-extruded RES4043D PLA had a range of 1.67mm-1.83mm, with nominal diameter range from 1.7mm-1.77mm and successfully printed multiple test prints. Maintaining a nominal tolerance of 1.75mm and maximum tolerance of ±0.08mm allowed for successful FFF prints. The extruded filament cross-section was not perfectly circular. Further work should consider the effect of FDT and cross-sectional filament aspect ratio on part strength and repeatability as well as the best FDT for repeatable parts.
  • Katie Martin
    Research Mechanical Engineer
    US Army Corps of Engineers (USACE) Engineer Research and Development Center (ERDC)