Impact of tool wear and fiber orientation on CFRP surface integrity: an experimental study with pre-wear PCD tools

Abstract

The machining of Carbon Fiber Reinforced Polymers (CFRP) presents substantial challenges in preserving surface integrity due to the material's pronounced anisotropy, high stiffness, and low thermal conductivity. These characteristics lead to significant tool wear, considerable thermal damage, and pronounced surface defects during the machining process. To assess the machining performance of Polycrystalline Diamond (PCD) tools under different wear conditions and fiber orientations, this article introduces an experimental study on the milling of T700 / epoxy CFRP components using pre-wear PCD tools. The CFRP workpieces were specially designed in a gear shape to minimize tool wear progression and facilitate subsequent measurements. The results, observed using a Scanning Electron Microscope (SEM), indicated variations in surface integrity related to tool wear progression. At zero Fiber Cutting Angles (FCAs), worn tool causes severer matrix peel up from the fiber. At acute FCAs, slightly worn tools produced a better surface finish than fresh tools due to matrix smearing, whereas severely worn tools resulted in chip adhesion and degraded surface quality. Down milling achieved greater surface integrity than up milling. Additionally, surface integrity was found more critical at low feed rates with severely worn tool. At obtuse FCAs, surface integrity was highly dependent on the feeding orientation, and was sensitive to tool wear. Up milling produced saw-tooth surface cavities at 150°FCA, while down milling showed significant cracks at 120° and 150°FCAs. The cutting force was more sensitive to tool wear progression at 30°, 60° and 90°FCAs, and less sensitive at 120° and 150°FCAs. Additionally, cutting forces were higher in up milling than in down milling, especially as tool wear progressed. These findings provide valuable insights for further research on optimizing CFRP machining processes to reduce tool wear and enhance component quality.