Research On Grinding Mechanism Of Ultrasonic Assisted CBN Grinding Wheel For ZrO₂ Biological Materials

With the rapid development of material science and technology,the research on the precision and ultra-precision grinding technology of hard brittle materials and various kinds of toughened and strengthened composite materials has become a hot topic all over the world.Among them,the application of oxide ceramic materials has been widely concerned.These oxide ceramic materials are not only widely used in industry,manufacturing and aerospace,but also applied to biomedicine due to their good biocompatibility.In particular,with the development of all-ceramic dental biotechnology,zirconia ceramic teeth technology is widely used in the field of dental prosthetics due to their good aesthetic characteristics,biocompatibility,stable chemical performance and abrasion resistance.However,zirconia ceramic restorations are difficult to be processed directly because of its high hardness and low fracture toughness.At present,the traditional processing method is that the pre-sintered zirconia porcelain is machined by high speed milling and then sintered at high temperature.The result is that there are differences in the thickness of the pre-sintered zirconia ceramic dentures at different locations,and the quality and precision of the zirconia ceramic dentures are affected.In view of the above problems,the promotion of zirconia ceramic dentures will be severely restricted.And this is very difficult to avoid the problem of secondary sintering and shrinkage accuracy during the preparation process.Therefore,the ultrasonic vibration assisted grinding technology is introduced into the field of oral remediation to achieve direct processing of fully sintered zirconia ceramics.As a result,the processing accuracy and processing quality of the zirconia crown can be improved,and the patient's waiting time can be shortened.This study includes the removal mechanism,kinematics,grinding force,and surface quality of ultrasonic vibration assisted grinding,which will provide some theoretical guidance for the application of the technology in the field of dental restoration.The specific research content is as follows:(1)The one-dimensional ultrasonic vibration trajectory model along tangential direction and normal direction of workpiece feed and the two-dimensional ultrasonic vibration trajectory model of a single abrasive particle were established respectively by the research of grinding trajectory of the ultrasonic vibration assisted CBN grinding head,and the matching problem of each parameter in ultrasonic vibration assisted interrupted machining process was also analyzed.In addition,a dynamic grinding contact rate model was established,which based on this foundation and combined with the established mathematical model of one-dimensional ultrasonic vibration grinding trajectory,then the influence of processing parameters and vibration parameters on the contact rate was obtained through the combination of theoretical analysis and experiment.(2)Based on the aforementioned contact rate model,the surface removal mechanism of ultrasonic vibration assisted grinding was analyzed from two aspects of plastic removal and brittle removal,and a mathematical model of single abrasive grinding force in the side grinding process was established.Then the influence of each factor on the grinding force was analyzed to find a method for predicting the grinding force in the ultrasonic vibration assisted machining process.The rationality and effectiveness of the model are verified by the experiments.(3)For the grinding process of ceramic thin-walled parts,on the one hand,the negative impact of vibration on the grinding process was analyzed from the mechanism of vibration generation(chatter).On the other hand,the regenerative chatter suppression process with adding ultrasonic vibration was analyzed from the perspective of the use of vibration(ultrasonic vibration).Then the dynamic model of zirconia brittle-hard material grinding with ultrasonic vibration-assisted CBN grinding head was established.And the modal experiment was conducted and the modal parameters were measured.Then the reasonable processing plan of the zirconia brittle hard material thin wall was finally formulated by combining with the theoretical analysis and modeling simulation prediction.At the same time,the regenerative chatter suppression of ultrasonic vibration assisted grinding was analyzed.(4)The model of surface topography with the grinding head was established,and then the surface topography models of the workpiece in the ordinary machining and ultrasonic vibration machining process were established respectively by analyzing the ultrasonic vibration-assisted grinding process of zirconia ceramic brittle-hard material.In addition,the influence of each factor on the surface topography was analyzed,and then a surface roughness prediction model based on linear regression was established.Finally,combined with the experimental results,genetic algorithm was used to optimize the parameters of ultrasonic vibration assisted grinding.