Material removal mechanism of UD-C/C composites in ultrasonic-assisted vibration orthogonal cutting

To address the problems of severe machined surface defects and serious material breakage in unidirectional C/C composites (UD-C/C), this study investigates a UD-C/C composite removal mechanism using ultrasonic-assisted orthogonal cutting technology. A solid cemented carbide cutting edge is used. This study focuses on the chip formation, cutting forces, and morphology of the machined surface in different directions between the tool feed and fiber, including perpendicular to the fiber, along the fiber, along the fiber cross section, and different fiber orientation angles, recorded simultaneously using a high-speed camera. The experimental results indicated that, in the perpendicular direction, damage in the interfacial phase and crack extension in the matrix dominated the chip generation process. The cracks formed during cutting along the fiber direction were relatively short, thus producing continuous segmentation chips. Owing to the accumulation and extrusion of chips, the measured cutting force remained low rather than zero. In the fiber direction, the extension of interfacial cracks in the direction of the fiber and the bending fracture of the fiber dominate in the process of material removal. The matrix was first removed, and the fiber was bent and clung to the rank face, producing a continuous band of chips. The measured cutting force remained stable. In the cross-sectional fiber direction, crack propagation results from interlayer separation, fiber yield, and matrix breakage caused by tool extrusion. The cracks expanded along the interface to the inner part of the material, and discontinuous powders were formed during the cutting process. Moreover, for different fiber orientation angles, the machining quality of the acute cutting zone was significantly better than that of the obtuse cutting zone. Second, the surface topographies of the workpieces were evaluated using a 3D surface-measuring instrument and scanning electron microscopy (SEM). Owing to the occurrence of secondary cutting, the quality of surface topographies cutting perpendicular to the fiber direction improves with increasing cutting depths. The surface topographies cutting along the fiber direction present numerous craters on the surface of the specimen as well as regional surface damage. The surface topographies cutting along the fiber cross-sectional direction show relatively serious machining damage and poor surface machining quality.

Automated summary

This study investigates the removal mechanism of UD-C/C composites using ultrasonic-assisted orthogonal cutting technology. The experimental results show that different cutting directions lead to different machined surface defects and variations in cutting forces. The extension of cracks and fracture of fibers are the main material failure mechanisms during the removal process.