Abstract: Carbon fiber reinforced polymer/plastic (CFRP) composites are widely used in aerospace industry because of high specific strength, corrosion resistance, fatigue resistance and other excellent properties. However, as typical anisotropic difficult-to-cut material, damage easily occurred in the hole-making of CFRP. This work focused on the quality of hole-making process, kinematic equations for ultrasonic vibration assisted helical milling (UVHM) are established, and the movement trajectory, cutting speed and equivalent rake angle of peripheral edge are studied. Fiber damage and material removal mechanism with or without ultrasonic vibration in HM is investigated. It is found that within the range of 0-45° cutting angle, fibers mainly bear the tensile stress in helical milling, while in UVHM, fibers bear mainly shearing stress with variable directions, which make the fiber fracture easily and the debonding between the fiber and resin is reduced accordingly. The effects of spindle speed, axial and tangential feeds on the cutting temperature and forces in UVHM are also investigated. Based on the variation of cutting force, temperature, the relative movement, speed between the cutting edge and fibers, and the equivalent rake angle, the influence mechanism of process parameters on the bur formation, delamination, and hole diameter was investigated. Due to ultrasonic vibration, the processing parameters affect the tool-workpiece contact behaviors, tool equivalent rake angle, leading to the variation of outting heat, forces, and finally, the quality of machined holes.

Key words: CFRP composites, ultrasonic vibration, helical milling, process parameters, hole quality