| As the application field of hard and brittle difficult-to-machine materials becomes more and more extensive,such as sapphire,monocrystalline silicon and other materials with high hardness in nature,the traditional grinding and polishing technology can no longer meet the requirements for their surface grinding and processing quality.In recent years,with the vigorous support of the state policy for science and technology industry,the panel,smart wear,VR and LED industries have ushered in the spring of vigorous development,which brings a huge demand for sapphire industry market.Due to its excellent physical and chemical properties,sapphire is widely used in various industries,and the largest proportion of demand is as LED substrate material.With the emergence of new technologies such as Mini Led and Micro Led,the surface quality of sapphire has become more demanding,so it is extremely important to explore high quality and high efficiency precision processing of sapphire.Piezoelectric ultrasonic transducers are widely used in various ultrasonic-assisted processing fields because of their simple structure,easy fabrication,electromechanical coupling coefficient and high electromechanical conversion efficiency.Therefore,this paper had been proposed to apply the piezoelectric ultrasonic vibration to the traditional grinding and polishing process,designed a longitudinal resonant piezoelectric ultrasonic vibration system,built an ultrasonic grinding experimental platform,and conducted ultrasonic grinding experimental research on sapphire to investigate the effect of non-contact free abrasive ultrasonic grinding on the surface morphology,surface roughness value and material removal of sapphire,laying the foundation for further improvement of grinding and polishing efficiency and surface quality of hard and brittle materials.The research work of this paper can be divided into the following parts:(1)The system composition and classification of ultrasonic-assisted grinding and polishing technology were introduced,and the research status of grinding and polishing technology and the application of ultrasonic processing technology were outlined.(2)The basic principles of ultrasonic processing were described,the characteristics of ultrasonic waves and their applications were summarized,and the factors affecting ultrasonic processing were outlined.(3)Based on the ultrasonic vibration equation and resonance design theory,the longitudinal resonant piezoelectric ultrasonic vibration system was constructed,the transducer and the variable amplitude rod were preferentially selected,and the piezoelectric ultrasonic vibration grinding system was constructed based on this,the ultrasonic grinding experimental platform was built,the three-dimensional geometric model of the grinding tool head was established,the characteristic frequency of the tool head was solved by simulation software,and the resonant frequency of the piezoelectric system was satisfied by optimizing the structural design,so that the system met the requirements of frequency consistency.(4)The constructed longitudinal resonant piezoelectric ultrasonic vibration system was tested for impedance using an impedance analyzer.The test results were as follows: the resonant frequency of the transducer-variable rod was 19.912 k Hz and the anti-resonant frequency was 19.992 k Hz;the resonant frequency value of the ultrasonic grinding system was measured to be 19.732 k Hz and the anti-resonant frequency value was 19.75 k Hz,with a resonant frequency error of 0.9%.The vibration characteristics of the ultrasonic grinding system were tested by laser vibrometer,and the average amplitude of the longitudinal amplitude was 6-7 μm under 220 V voltage condition,which satisfied the experimental requirements.(5)For the above designed piezoelectric ultrasonic vibration grinding system,the ultrasonic grinding experimental was conducted on single crystal sapphire to investigate the effect of non-contact free abrasive ultrasonic grinding on the surface roughness value,material removal and surface morphology of sapphire,compared with the mechanical grinding experiments,ultrasonic grinding significantly improved the surface quality and processing efficiency of sapphire wafers,and did not cause secondary damage or less secondary damage to sapphire chips,suppressing the grinding edge effect.The surface finish tended to be uniform with the processing time,and the surface finish was also greatly improved.The roughness value of the sapphire chips after ultrasonic grinding was around sixty nanometers,and some could reach a dozen or even a few nanometers,which verified the feasibility of the designed ultrasonic grinding system and it had certain significance for ultra-precision processing of sapphire. |
