Study On Ultrasonic Grinding Mechanism For Engineering Ceramics

Nowadays, engineering ceramics becomes more and more important as a kind of new engineering materials while the application of hard brittle materials has been involved into every field of technology and people's livings. Engineering ceramics has many good characteristics, for example high-intensity, high hardness, low density, low expansion, etc., and has been widely applied to airspace, petrochemical industry, instruments and meters, mechanical manufacturing and nuclear industry. But to machining them is difficult, inefficient and high-cost for them good performance. As a result, their extensive user is limited. With the development of science and technology, non-conventional machining methods emerge as the times require and their development is all right. Ultrasonic vibration machining is one of non-conventional machining and it has been effective means to machining hard and brittle materials. At present its field of application is wider and wider. In contrast with conventional ultrasonic machining, its machining efficiency and machining surface quality are increased.According to the difficult-to-machining of engineering ceramics, this thesis worked on engineering ceramics removing mechanism under rotational ultrasonic vibration grinding (RUG) that combined ultrasonic vibration with common grinding.Based on the characteristic of ultrasonic machining system and the connected experience of the system cooperation, the grinding head of RUG was designed. Because of its simple structure, small volume and low cost, this grinding head can be assembled on the numerical control machine, drill machine and vertical milling machine, so that it can gain its end of rotational ultrasonic grinding.It abstractly analyzed the surface production mechanism of ceramics by means of indentation fracture mechanics, obtained its critical grinding depth. The grinding mechanism in RUG was analyzed, and there were many actions which acted on together in RUG. The kinematics models of RUG were founded. Based on the models of grinding process, the kinematics characteristics and the relative movement trace between the single abrasive grit and the workpiece were researched, and the correlative geometry parameters were analyzed and calculated. The critical conditions of the abrasive grit apart from the workpiece were also analyzed in RUG. The theoretical model of materials removing rate was founded under RUG and plain grinding. The materials removal rate in RUG was higher than that in plain grinding with the same grinding machining condition from the analysis in the model. In addtion, the model showed that any increase of static load, grain diameter, work speed, the amplitude and frequency of tool or any decrease of fracture toughness property and hardness would result in the increase of the materials removal rate of RUG. Base on the mathematic model and emulated results of grinding force, we can gain the follow conclusion that:the grinding force increased with larger grinding depth and workpiece speed, while the increase of the grinding velocity led to a decrease of the grinding force; however, the higher grinding velocity weakened the contributiveness of ultrasonic vibration to the decrease of the grinding force. The grinding force in RUG was higher than that in plain grinding under the same grinding parameters in the theoretical formula model.