Effect of extrusion–quenching pretreatment of PEEK feedstock on porosity and mechanical reproducibility in Arburg Plastic Freeforming

Additive manufacturing of polyetheretherketone (PEEK) is limited as much by the scatter of part properties as by their mean level. We examined whether the crystalline state of the feedstock affects the defects and reproducibility of parts made by Arburg Plastic Freeforming (APF), a granulate-fed droplet-deposition process scarcely characterised for PEEK. Extrusion and water quenching lowered the crystallinity of PEEK 450 G from 33.9% to 10.9%, and both feedstocks were printed under identical conditions. After the ≈17 h in-chamber dwell at 200 °C, the crystallinity of the co-printed base pads did not differ (24.2 vs 25.4%); the threefold difference in feedstock crystallinity was not retained. On the lateral faces the largest void per image averaged 60 µm (quenched) and 108 µm (semi-crystalline), and the area-weighted void aspect ratio was 2.4 and 3.1, respectively; because the fields of view of the two groups were not identical, these differences are indicative. Tensile strength at three build positions was 93.9 ± 2.4 MPa (CV 2.5%) for the quenched and 83.0 ± 18.7 MPa (CV 22.5%) for the semi-crystalline feedstock, whose strength fell from 103 to 66 MPa from rear to front. With three specimens per feedstock (from one build job per feedstock), the means did not differ significantly; the narrower distribution of the quenched feedstock is an observation whose origin remains open. External roughness did not differ between the feedstocks (S a ≈ 40 µm). The feedstock state is thus a candidate variable for more reproducible APF processing of PEEK.