  We present a field-based method of toolpath generation for 3D printing
continuous fibre reinforced thermoplastic composites. Our method employs the
strong anisotropic material property of continuous fibres by generating
toolpaths along the directions of tensile stresses in the critical regions.
Moreover, the density of toolpath distribution is controlled in an adaptive way
proportionally to the values of stresses. Specifically, a vector field is
generated from the stress tensors under given loads and processed to have
better compatibility between neighboring vectors. An optimal scalar field is
computed later by making its gradients approximate the vector field. After
that, isocurves of the scalar field are extracted to generate the toolpaths for
continuous fibre reinforcement, which are also integrated with the boundary
conformal toolpaths in user selected regions. The performance of our method has
been verified on a variety of models in different loading conditions.
Experimental tests are conducted on specimens by 3D printing continuous carbon
fibres (CCF) in a polylactic acid (PLA) matrix. Compared to reinforcement by
load-independent toolpaths, the specimens fabricated by our method show up to
71.4% improvement on the mechanical strength in physical tests when using the
same (or even slightly smaller) amount of continuous fibres.
