Complex flow and temperature history during melt extrusion in material extrusion additive manufacturing

3D printing using the materials extrusion additive manufacturing (ME-AM) process is highly non-isothermal. In this process, a solid polymer filament is mechanically drawn into a heated hot end (liquefier) where the polymer is ideally melted to a viscous liquid. This melt is extruded through an orifice using applied pressure of the solid filament that is continuously being drawn into the extruder. The extruded filament melt is deposited to build up the desired part. The poor thermal conductivity of most polymers inevitably leads to temperature gradients, in both the radial and axial directions. Here we quantify the temperature evolution of the polymer filament in axial direction using embedded fine thermocouples as a function of process parameters. Information about the radial gradients is obtained by introducing dye markers within the filament through understanding the flow behavior through the extruder by the deformation of the dye from a linear to pseudo parabolic profile. The polymer is heated above the glass transition temperature for less than 30 s for reasonable print conditions with the center of the filament remaining cooler than the liquefier temperature throughout the process. These process measurements provide critical data to enable improved simulation and modeling of the ME-AM process and the properties of the printed parts.