In most fused filament fabrication systems, all filament laydown paths are at constant Z
height. This creates a weak direction in the resulting parts, as the interlayer adhesion between
melted and solidified material is much weaker than the tensile strength of the bulk
material. For example, a hemispherical dome pressure vessel endcap will fail easily along
these Z=constant cleavage planes. We resolve this problem by proposing a 3D printing system
that does not limit the nozzle positioning to a single Z layer at a time, or to constant
pitch and yaw angle, but instead lay down extrusions more closely aligned with the stress
tensor within the part (but requiring 5 simultaneous axes of motion). To verify this, we have
constructed a working 5-axis fused-filament fabrication 3D printer and produced a number of
test parts in ABS, nylon 645, and T-glase polyester. Using a commercial hydrostatic pressure
system, we have tested these parts to destruction and find a typical strength improvement
of 3x to 5x over conventional 3-axis parts printed to the same specification, in the same machine,
from the same spool of polymer; the only thing changed was the extrusion pattern. An
approximate calculation to translate this into the material’s ultimate tensile strength shows
that the 5-axis FFF parts are within a factor of two of the ultimate tensile strength of typical
professionally injection-molded ABS material.