Machinability characteristics evolution of CFRP in a continuum of fiber orientation angles

Abstract

ABSTRACTCircular orthogonal milling tests on unidirectional carbon fiber reinforced polymer (UD-CFRP) laminate disks were conducted to investigate the machinability characteristics evolution in a continuum of fiber orientation angles (β). Experimental results show that surface cavities are the main machined surface damages, which elevate the surface roughness Ra. The surface cavities systematically appear between angles β = 25° and β = 75° for down-milling and β = 20° and β = 50° for up-milling and their occurrence may not be influenced by the cutting velocity and the feed rate. In the surface cavity region, low-level cutting forces are generated, which is highly correlated with the occurrence of fiber–matrix debonding for both down-milling and up-milling. SEM micrographs show that the formation of the surface cavities is mainly caused by the occurrence and propagation of fiber–matrix debonding, followed by bending-induced fiber fractures and compression-induced fiber fractures. Based on those observations, a novel milling strategy taking the fiber orientation angle into consideration is proposed to avoid the surface cavities; this unique approach provides a new way to milling typical aerospace CFRP laminates with high machined surface quality.