Mechanism and feasibility of ultrasonic-assisted milling to improve the machined surface quality of 2D Cf/SiC composites

For C-f/SiC composites, obtaining high-quality surface by machining is a great challenge. In this paper, the PCD tool was used for ultrasonic-assisted milling experiments of C-f/SiC composites. The machined surface integrity was evaluated based on the surface roughness obtained by three-dimensional topography and the residual stress obtained by Raman spectroscopy. The machined surface roughness had a strong negative correlation with specific milling energy. When the feed rate was small, micro brittle fracture occurred under tool extrusion, resulting in large cutting energy, but small roughness. Increasing the feed rate induced transformation of material removal mechanism. Macro brittle fracture resulted in small specific milling energy, but large roughness. The appropriate tool amplitude promoted the initiation and propagation of micro-cracks, thus promoting the material to be removed by micro brittle fracture and effectively reducing the machined surface roughness. But an excessive tool amplitude had the opposite effect. When the material was removed by micro brittle fracture, the residual tensile stress was small. The longitudinal vibration of the tool reduced the residual tensile stress and even produced residual compressive stress.