Extruded diameter dependence on temperature and velocity in the fused deposition modeling process

The use of fused deposition modeling has become increasingly widespread in additive manufacturing. This technique involves the extrusion of a polymer filament through a narrow hole with a given diameter on which the deposited raster characteristics depend. This paper presents an experimental study on the extrudate diameter variations in fused deposition modeling using polylactic acid (PLA). The main parameters influencing the diameter have been identified through a review of the literature. It is stated that the extruded diameter depends on the force applied to the polymer as it enters the extruder hole. This force in turn varies according to the operating temperature and velocity. Above a certain mass flow rate, the polymer filament did not melt enough and a slippage was noticed at the point where the rollers make contact with the filament, preventing the extruding motor from pushing the latter toward the outlet. As a result, the extruded filament had an irregular aspect showing split zones. At high temperatures and low velocities, the extruded filament shrinks due to natural flow under gravity. However, swelling occurs at the die outlet for higher extrusion velocities, i.e., when the extruding force increases. The maximum and minimum values of the extruded diameter are analyzed in relation to the velocity. Additional experiments consisting in printing single-walled parts have also allowed analyzing the effect of the diameter inconsistency on FDM part accuracy.