Study On Two Dimensional Ultrasonic Vibration Assisted Grinding Mechanism Of Nanocomposite Ceramics And Its Surface Quality

Currently single-phase ceramics does not meet the higher requirement of engineering application, so nanocomposite ceramics has attracted a lot of attention and has become one of the hot-points in the field of material research. On the other hand, it is hard to machine nanocomposite ceramics, especially surface microdefects of finished surface may lead to low reliability of ceramics parts, so its wide potential application brings great challenges to modern machining techniques. It is necessary to develop precise machining technology to raise working efficiency and improve surface quality.Based on the toughening and reinforcing mechanisms of ceramics, ultrasonic vibration theory, fracture mechanics and macro micro mechanics, it worked on surface formation mechanism, material removal mechanism and surface quality of nano zirconium toughening alumina ceramics (ZTA nanocomposite ceramics) under two-dimensional ultrasonic vibration assisted grinding (TDUVAG), and it analyzed how two-dimensional ultrasonic vibration has the effect on the processing characteristic of ZTA nanocomposite ceramics, which may reveal efficient precision finishing characteristic ZTA nanocomposite ceramics under TDUVAG and provide fundamental basis for the popularization of TDUVAG. The main research contents were listed as follow:1. New technique of two-dimensional ultrasonic assisted grinding (TDUVAG) for ZTA nanocomposite ceramics was put forward, the resonance vibration of the system was analyzed by the mechanical impedance theory, vibratory response of the system was deduced by elastic-plastic mechanics, and vibration characteristics of the system was measured by test. Based on ultrasonic vibration theory, microscopic cutting trace of abrasive particle under two dimensional ultrasonic vibrations were analyzed, and cutting trace formula of abrasive particle was built fistly, and the spiral cutting trace of single abrasice grain was defined, cutting time, ultrasonic vibration time, and cutting arc length of single abrasive grain in the cutting zone are deduced, and the critical frequency condition of ultrasonic vibration was given. Based on the series of research, surface formation mechanism of TDUVAG was established.2. Based on indentation fracture mechanics and plastic working theory, it worked on the removal mechanism of ZTA nanocomposite ceramics under TDUVAG,the critical cutting thickness of abrasive particle under TDUVAG was built, and the critical condition of brittle-ductile transition of ceramics under TDUVAG was given by plastic working theory, high efficient material removal rate model of ceramics under TDUVAG, and experiment results showed that the material removal rate under TDUAG is about twice as that under common grinding.3. Based on impulse theories and the grinding force model under common grinding, the mathematics grinding force model under TDUVAG was built, and the processing characteristic of TDUVAG was analyzed according to the characteristic of grinding force,and it analyzed how ultrasonic vibration and grinding parameters had affect grinding force and grinding force ratio by tests.4,How grinding parameters and ultrasonic vibration affect surface roughess Ra was analyzed by single-factor test of surface roughness Ra, experimental results showed that TDUVAG may obtain the less surface roughness Ra than common grinding. By means of adaptive-network-based fuzzy inference system, the prediction model of surface roughness of ZTA ceramics was built, and the model may obtain the higher precsion (81.25%) by dealing with nonlinear problem among grinding parameters, and fuzzy rule curved face formed by prediction model showed four input factors have different influence on surface roughness Ra, and they are abrasive grain size, grinding method (TDUVAG or common grinding), grinding depth, axial feed and speed of worktable from top to bottom.5,The surface/subsurface damages of ZTA ceramics under TDUVAG were observed by XRD,SEM,TEM and white light interferometer. The phase transformation, surface residual stress, microcrack and grinding badness layer in the grinding surface of ZTA nanocomposite ceramics under TDUVAG were analyzed by comparative trials,experimental results showed TDUVAG may form the higher compressive stree caused by martensitic transformation of zirconia grain, the microcracks in the grinding surface under TDUVAG differed from that under common grinding, and grinding badness layer of ZTA nanocomposite ceramics under TDUVAG is shallower than that under common grinding, as a result, TDUVAG may obain the better grinding surface integrity of ZTA ceramics.6,The fracture analog experiment was designed to study the fracture behaviour of ZTA ceramics under ultrasonic vibration. With the aid of the experiment, crack formation and its expand pattern of ZTA ceramics under ultrasonic vibration were analyzed, its fracture criterion was established and the experiment results showed that intercrystalline fracture is the main fracture pattern of ZTA ceramics under common grinding, and transcrystalline fracture is the main fracture pattern of ZTA ceramics under TDUVAG, and the finding add to evidence showing that TDUVAG has better material removal property.