Milling Characteristics and Damage Assessment of Ultrasonic Vibration-Assisted End Milling Cf/SiC Composites

C-f/SiC composites are characterized as anisotropic, heterogeneous, brittle, and hard materials. The process of manufacturing C-f/SiC composites using traditional machining techniques is prone to edge chipping damage and tool wear, which makes it difficult to meet the machining quality and machining accuracy. The purpose of this paper is to investigate the milling characteristics and damage assessment during ultrasonic vibration-assisted end milling (UVAEM) of C-f/SiC composites. Firstly, UVAEM experiments on C-f/SiC composites were carried out at different ultrasonic amplitudes and comparative experiments with conventional milling (CM). In addition, tool wear, surface roughness, surface micromorphology, milling force and subsurface damage (SSD) were measured and analysed. Finally, the SSD factors of C-f/SiC composites were established to quantify machining damage, and analyzed the effect of ultrasonic amplitude on SSD. Furthermore, the formation mechanism of SSD was investigated and discussed. The findings indicate that appropriate ultrasonic amplitude improves the surface quality by UVAEM, while excessive amplitude deteriorates the surface quality. During the UVAEM, micro/macro brittle fracture of the fibers on the surface occurs, leading to machining defects such as fiber breakage, fiber-interface debonding and pits. The milling force gradually decreases with the increase of ultrasonic amplitude. On the other hand, the forms of SSD in CM and UVAEM are mainly fiber pullout, subsurface crack, crack extension and machining pits. Matrix cracking and fiber pullout in SSD were affected by fiber orientation. Moreover, the introduction of ultrasonic vibration plays a significant contribution in the inhibition of the SSD in C-f/SiC composites.