Warpage evaluation and mechanical characterisation of modified polyamide-6 specimens produced by Arburg plastic freeformer

Abstract In injection moulding and additive manufacturing processes, it is common for the final product to exhibit warpage induced by a non-uniform cooling rate after material deposition. Residual stresses can be generated in the built parts, with a volume shrinkage that leads to dimensional inaccuracy and reduced usability. This phenomenon is even amplified in the presence of semi-crystalline polymers, which still need to be more widespread among additive manufacturing processes despite their capacity to show better mechanical properties when compared to amorphous ones. This study evaluates the degree of deformation and subsequently characterises the mechanical properties of a novel modified Polyamide 6 formulation (i.e., RADILON® S X21351 NT) printed through the Arburg Plastic Freeforming process. This new proprietary formulation modified the crystallisation behaviour during cooling. The whole exothermic crystallisation peak was shifted to lower temperatures, allowing the processing envelope of the modified formulation to widen. More specifically, after preliminary polymer characterisation analyses and after evaluating the warpage, a mechanical characterisation was performed using tensile tests on specimens (dry-as-moulded and conditioned) printed with different filling strategies on the build platform (XY-0°; XY- ± 45°; XY-90°; ZX-0°). Measured mechanical properties were ultimately compared to those achieved by applying the injection moulding technique on the same non-modified material. The specimens produced through the Arburg Plastic Freeforming process showed brittle behaviour that was more marked than those obtained by injection moulding. Moreover, the infill direction and water content significantly influenced the mechanical properties of specimens.