Strengthening ABS, Nylon, and Polyester 3D Printed Parts by Stress Tensor Aligned Deposition Paths and Five-Axis Printing

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.