Effect of the ratio of cutting depth to edge diameter on chip formation mechanism in machining of CFRPs

Carbon fiber reinforced plastics (CFRPs) are used widely to reduce the structural weight. Drilling and milling processes are inevitable in order to satisfy the assembly requirements of CFRPs structure. However, the subsurface damage easily occurs due to the interface debonding under the cutting forces in machining of CFRPs, and severely reduces the mechanical properties of the structure. This paper studies the chip formation mechanism in machining of CFRPs. Firstly, the characteristic of cutting forces and the specific energy under different ratios of cutting depth to cutting edge diameter (RDD) are investigated by the orthogonal machining of CFRPs. Furthermore, the tool-material interactions are analyzed to investigate the chip formation mechanism. In addition, the fiber failure and the interface debonding are analyzed by the scanning electron microscope (SEM) of the machined surface. For 90° cutting angle, fiber failure mode is like microbuckling due to the insufficient support of the matrix for RDD=1, and the interface debonding does not extend to the subsurface. It changes into the kinkband formation with the increasing of the RDD. For 135° cutting angle, mode I fracture of the interface easily occurs due to the opening load with the increasing of the RDD. Thus, the RDD should be controlled to reduce the severe subsurface damage in machining of CFRPs.