Machinability analysis of carbon fibre reinforced PET-Glycol composites processed by additive manufacturing

Fused filament fabrication (FFF) is one of the most widely used additive manufacturing (AM) techniques, which has enabled a simpler, more flexible, and low-cost processing procedure for obtaining functional fibre reinforced composite products. However, one of the shortcomings of AM processing is its poor geometric and dimensional behaviour that hinders the manufacture of high-quality functional parts. Though this limitation can be overcome with surface post-processing machining, the machining of composites is complex due to their non-homogeneous microstructure producing delamination, splintering, and fractures. In this study, the machinability of short carbon fibre reinforced glycol-modified polyethylene terephthalate (CF-PETG) processed by FFF additive manufacturing was assessed in face milling and edging peripheral milling operations by analysing the AM process parameters layer thickness (Lt) and build orientation (Bo). This machinability analysis was based on energy consumption and geometric properties. The former was assessed by measuring cutting forces, and the latter involved examining dimensional accuracy, flatness and surface roughness measurements, combined with 3D-topography and SEM microscope images. PETG processed by FFF showed good machinability in both machining operations with acceptable energy consumption and surface texture, with no significant effect of Lt or Bo. The addition of carbon fibre reinforcement to PETG improved energy consumption in both operations, and enhanced the surface texture in face milling. However, machinability worsened in terms of geometric properties for peripheral milling with the addition of carbon fibre and increased Lt, exhibiting substantial surface defects such as tearing and burrs.