Surface-Ply Defect Quantification in Machined UD GFRP Composites

Fiber-reinforced polymers (FRPs) are high-performance materials used in lightweight and high-strength applications. Machining is often required because FRP manufacturing processes leave excess material that must be removed to meet final geometry, dimensional tolerances and surface quality requirements. The UD-GFRP laminates are produced by resin infusion and contain stitched plies for handling during manufacturing. A semi-automatic image processing method is proposed to separately quantify delamination and fluffing on surface plies. Slotting tests were conducted using a two-flute straight-tooth PCD cutter on a robotic machining setup, with fiber orientations of 0°, 45°, 90°, and 135° and four feed-per-tooth levels. Fiber orientation and milling strategy (up/down milling) strongly affect surface quality, while feed per tooth has a minor effect. Stitching threads also affect the formation of defects. The optimal configuration is up milling at θ = 0°, producing minimal delamination and reduced fluffing. These results show that delamination and fluffing must be evaluated separately for reliable surface characterization