Research On Ultrasonic High-speed Milling Technology Of Carbon Fiber Reinforced Composites

Carbon fiber reinforced composites(CFRC), as a kind of advanced compositematerials with carbon matrix, have been widely employed in the advanced fields for theirexcellent properties such as light weight, high specific strength, high specific modulus andlow heat expansion coefficient. However, because of its anisotropic mechanical properties,high hardness, high strength, and poor thermal conductivity, the machining difficultiesbecome the bottleneck of its wide application. Therefore, it is promising to explore thepost-processing technology of CRFC.According to the particular advantages of ultrasonic vibration in machiningdifficult-to-cut materials, a new machining method, combining ultrasonic vibration andhigh-speed milling, was discussed to seek the effective way to improve machiningefficiency and surface quality. Based on vibration theory, the special acoustic system ofmilling setup with longitudinal vibration was designed for high-speed CNC, and thetwo-dimensional ultrasonic vibration system applied to workpiece was also designed. Thetwo systems can be combined freely in different vibration directions. There are someproblems for electricity transmission in high-speed processing, so that the contactlesspower transfer system was developed. And the influences of load, frequency, gap size andcompensation on the transmission performance were studied.The acoustic characteristics and stability of the system were studied through thevibration tests. The results showed that he tool diameter, tool length and the slot numbershad significantly influences on the resonant frequency of the acoustic system. Accordingto the resonance test results of planar systems in which the two identical one-dimensionalultrasonic vibration systems designed by Lissajous theory, were applied in theperpendicular directions of the workpiece, the workpiece vibrated elliptically. The steadystate amplitude of the acoustic system was more than10μm and the resonant frequencywas20.6kHz, which can meet the machining requirements.The average force cutting model was discussed in ultrasonic vibration milling. Themilling force can be reduced obviously by employing ultrasonic vibration. According tothe orthogonal milling tests of CFRC, the cutting force decreased against the spindle speed,and it increased along with the axial radial cutting depth and feed rate. Under the samemilling parameters, the milling forces were different from the vibration modes. The morethe vibration dimension, the smaller the milling force. The fibers were mainly sniped in ultrasonic milling, while they were mostly pulledout and pressed in matrix in ordinary milling from the SEM observation. The peaks andvalleys of grooves distributed unevenly in ordinary milling, and there were lots of holes inthe surface. The sine waveforms were appeared clearly on the one-dimensional vibrationmilled surface of the workpiece. Under two-dimensional ultrasonic vibration, themachined surface was flatter in the whole, and the small peaks and valleys weredominated. For three-dimensional ultrasonic vibration milling, the surface is relatively flat,and the peak is low, and the valley is not deep and the structure is meticulous. Finally, thethree-dimensional assessment and analyses were conducted on the machined CFRCsurface, and the tool wear were briefly discussed in ultrasonic milling process.Studies showed CFRC can be processed under ultrasonic vibration with high-speed,high quality and high efficiency.