ZigZagZ: Improving mechanical performance in extrusion additive manufacturing by nonplanar toolpaths

Abstract

This study investigates the effect of novel non-planar deposition methods in fused filament fabrication (FFF) additive manufacturing. A range of non-planar geometries were developed including a ZigZagZ sequence in which filaments were deposited as the nozzle moved in the X or Y direction while simultaneously zigzagging up-and-down i.e. in the Z direction. As a result, repeating non-planar layers were generated throughout the specimen’s geometry. The use of the ZigZagZ toolpath to deposit the material significantly improved the mechanical performance of parts manufactured by FFF in the Z-direction by up to 62% in strength, 123% in strain-at-fracture and 245% in toughness compared to an optimised conventional planar geometry. All specimens in the study had only a single filament through their thickness; they were specially developed to enable precise mechanical characterisation. This is the first work to have developed and analysed nonplanar deposition with cyclic nonplanar nozzle movement of a geometric length scale similar to the nozzle diameter. Three novel toolpath designs were developed for this study: (i) zigzag (ZZ), based on the aforementioned ZigZagZ deposition; (ii) up-down (UD) involving vertically deposited nonplanar bulges with interconnecting planar sections; (iii) forward-back (FB) employing the nozzle’s movement forward and backward during planar deposition to enhance the nozzle’s contact and promote the ploughing of the deposited filament. These designs - along with the conventional planar toolpath designs (original (OR)) - were characterised and their mechanical properties compared to generate new understanding about the impact of deposition with the Z coordinate varying along the path on performance. The geometrical outcomes of these different deposition strategies were analysed microscopically to assess the effects of nonplanar toolpaths on the filament-scale geometry. It was established that the ZZ strategies resulted in higher extruded-filament thickness compared to OR. Additionally, various ZZ designs were developed to understand the impact of the zigzag height-to-width ratio and size not only on mechanical properties, but also geometry and fracture path. Fractographic analysis indicated that nonplanar FFF extrusion promoted through-filament fracture, suggesting a reduced concentration of stresses at interlayer bonds by redirecting the load into the filament; this could contribute to the increased level of toughness observed in ZZ specimens. The understanding developed in this study is readily adaptable for the use in both single-wall and infill geometries to provide their improved mechanical performance. A broad range of potential industrial applications and research relevance resulting from the findings is discussed in addition to future development opportunities. • Zigzag interfaces improved load-bearing capacity, strain-at-fracture and toughness. • Interfacial weakness is caused by filament-scale geometry, not the bond. • Nonplanar geometry overcame geometric vulnerabilities of the interface in FFF. • Zigzag nonplanar unit can be used for both thin-walled and infilled structures. • Zigzag geometry redirected the load into the filament, increasing plasticity.