A Study On Ultrasonic Vibration Aided Micro-milling Of Hard And Brittle Materials

With the development of the aerospace, microelectronics and laser technology, hard and brittle materials with their excellent material properties, have been widely used in more and more fields of science. Because of its high hardness and brittleness, it is difficult to realize the machining of complicated shape micro parts in ductile regime by the conventional machining method. Therefore, the precision machining technology of hard and brittle materials needs further development.In this study, micro-milling of the hard and brittle materials is aided by ultrasonic vibration. Firstly, the processing mechanism of hard and brittle materials in the plastic domain is studied theoretically.Then, through the establishment of tool trajectory model, the influence of ultrasonic vibration direction on the milling process is researched. Finally,combining the cutting edge model of ball end mill and the removal manner of hard and brittle materials with the ultrasonic vibration, the ultrasonic vibration aided micro milling force model is established. In addition, the experimental system of ultrasonic vibration micro-milling is developed to complete the related experiments. By comparing the experimental results of conventional milling and ultrasonic vibration milling, the influence of ultrasonic vibration aided milling for the cutting force and machined surface quality of the hard and brittle materials is investigated.It shows that the periodic separation between the cutter and workpiece in the cutting process it achieved when ultrasonic vibration is working along the direction of feed,thereby the instantaneous cutting thickness is changed effectively. The high frequency intermittent cutting process can also be more conducive to chip discharge and reduction of cutting temperature, and thus, the service life of cutter can be improved. According to the experiment results, the fracture phenomenon on the machined surface is reduced, and the reciprocating extrusion effect of the cutter can remove the tooth mark on the machined surface effectively, so better surface quality can be machined. Using single factor analysis by comparing influences of different parameters on the machined surface quality, the best parameter combination can be is obtained. By comparing the milling forces of two kinds of processing methods, the milling force and its components in the X, Y and Z directions by ultrasonic vibration milling are smaller than those by conventional milling. From the waveform diagram of cutting force collected by dynamometer, it shows that the peak valueof the components by ultrasonic vibration milling is also lower than conventional milling,and the components reduce periodically along with the frequency of ultrasonic vibration.These are consistent with the above theoretical research.