Cutting tests and performance evaluation of recycled PET in fused filament fabrication

Fused Deposition Modelling (FDM) technology in 3D printing offers numerous advantages, such as cost-effectiveness, ease of use, and the ability to produce complex geometries with minimal material waste; however, surface quality remains a significant challenge. This study investigates how the hardness and melt flow properties of the raw material affect surface roughness and how this can be improved by post-machining. Modified recycled poly(ethylene terephthalate) (RPET) was used as the raw material in the experiments, considering aspects of the circular economy. The material properties were adjusted by varying the ratio of ethylene-butyl-acrylate-glycidyl-methacrylate (EBA-GMA) additive. It was demonstrated that a decrease in the melt flow rate (MFR) results in more uniform deposited layers, leading to smoother surfaces. By systematically varying turning parameters and applying statistical analysis, it was shown that feed rate has the most significant impact on surface roughness. Using a feed rate of 0.1 mm/rev reduced the average surface roughness from 13–25 μm to 2–4 μm. Scanning electron microscopy (SEM) revealed that the surface characteristics after post-processing were minimally influenced by material hardness. This suggests that the findings are likely applicable to 3D printing with other plastics as well. • Filaments were produced using varying RPET/EBA-GMA compositions for sample printing. • Melt flow index significantly influenced the surface roughness of printed specimens. • Machining process notably reduced surface roughness values after printing. • EBA-GMA content achieved a 57 % and 60 % reduction in Ra and Rz compared to OPET. • An optimal feed rate of 0.1 mm/rev yielded the best surface quality.