Characterization of Die-Swell in Thermoplastic Material Extrusion
Austin Colon, David Kazmer, Amy Peterson, Jonathan Seppala
Die-swell is a flow effect that occurs in polymer extrusion whereby the material experiences rapid stress and dimensional changes upon exiting the nozzle orifice. Material extrusion additive manufacturing is no exception, and this effect influences the final dimensions of the printed road and imparts residual stresses. Die-swell is measured via a custom test cell that uses optical and infrared cameras and an instrumented hot end with an infeed pressure load cell. The instrumented hot end is mounted onto a stationary extruder above a conveyor to simulate printhead translation at steady state conditions for a wide range of volumetric flow rates. Investigated factors for an acrylonitrile butadiene styrene (ABS) filament include volumetric flow rate (0.9 mm3/s to 10.0 mm3/s), hot end temperature setpoint (200 °C to 250 °C), and nozzle orifice diameter (0.25 mm to 0.60 mm). The die-swell increases as a function of the volumetric flow rate and shear stress but decreases as a function of the hot end temperature setpoint and nozzle orifice diameter. For modelling, an implementation of the Tanner model for die-swell displays good agreement with experimental results. The model also demonstrates that the same proportionality constant, k_(N_1 ), which relates first normal stress difference to shear stress, can be used for different nozzle orifice diameters with the same length to diameter ratios, and that k_(N_1 )increases as a function of hot end temperature setpoint as expected with the rheological concept of time temperature superposition.
, Kazmer, D.
, Peterson, A.
and Seppala, J.
Characterization of Die-Swell in Thermoplastic Material Extrusion, Additive Manufacturing, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=936015
(Accessed September 25, 2023)