Machinability and Geometric Evaluation of FFF-Printed PLA-Carbon Fiber Composites in CNC Turning Operations

Fused Filament Fabrication enables the manufacturing of complex polymer components. However, surface finish and dimensional accuracy remain key limitations for their integration into functional assemblies. This study explores the potential of conventional turning as a post-processing strategy to improve the geometric and surface quality of PLA reinforced with carbon fiber parts produced by FFF. Machinability was evaluated through the analysis of cutting forces, thermal behaviour, energy consumption, and surface integrity under varying cutting speeds, feed rates, and specimen slenderness. The results indicate that feed is the most influential parameter across all performance metrics, with lower values leading to improved dimensional accuracy and surface finish. Nevertheless, the surface roughness is higher than that of metals, and deviations in geometry along the length of the specimen have been observed. A critical shear stress of 0.237 MPa has been identified as the limit for interlayer failure, defining the boundary conditions for viable cutting operation. Compared to long printing times in high-resolution FFF, the addition of machining step significantly reduced fabrication time while enhancing part quality. These findings support the use of machining operations as a viable and efficient post-processing method for improving the functionality of polymer-based components produced by additive manufacturing.