  3D printing is rapidly becoming an effective means of prototyping and
creating custom consumer goods. The most common method for printing a polymer
melt is fused filament fabrication (FFF), and involves extrusion of a
thermoplastic material through a heated nozzle; the material is then built up
layer-by-layer to fabricate a three-dimensional object. Under typical printing
conditions the melt experiences high strain rates within the FFF nozzle, which
are able to significantly stretch and orient the polymer molecules. In this
paper, we model the deformation of an amorphous polymer melt during the
extrusion process, where the fluid must make a 90$^\text{o}$ turn. The melt is
described by a modified version of the Rolie-Poly model, which allows for
flow-induced changes in the entanglement density. The complex polymer
configurations in the cross-section of a printed layer are quantified and
visualised. The deposition process involving the corner flow geometry dominates
the deformation and significantly disentangles the melt.
