超声空化对软性磨粒流切削效率和质量的影响

Effect of ultrasonic cavitation on maching efficiency and quality of soft abrasive flow

为提高软性磨粒流切削的效能,研究了利用超声空化作用加快材料去除的方法。在分析磨粒抛光试验和计算流体动力学仿真结果的基础上,提出并验证磨粒碰撞壁面的动能是影响切削效率主要因素的假设;根据对超声空化气泡溃灭,及其在外围水域中冲击波形成与传播的研究结果,分析气泡溃灭在推动磨粒改变其动能时所起的增强湍流效果的作用。在此基础上搭建了超声辅助磨粒流试验装置,以表面覆有氧化层的硅片为试验对象,根据其表面氧化层的去除情况,分析超声空化对硅片表面材料去除能力的影响,并在磨粒流加工无氧化层硅片表面的试验中,观察到超声空化对磨粒流切削的显著影响。验证了超声空化能使磨粒流中的磨粒的动能发生改变,从而起到提高切削效率和提高表面质量的作用,以期为超声波作用下磨粒流加工工艺的改进提供参考。

The method of material removal by ultrasonic cavitation was studied to improve the efficiency of soft abrasive flow machining. Soft abrasive flow machining uses water as the carrier, and the actual processing effect is achieved by abrasive. The uneven peak and valley structure of the machined surface is impacted by a large number of abrasive particles. Those molecules at the high positions of the workpiece surface are more likely to slip or fall apart after collision. First of all, because of the probability of its impact, the molecule of the top in the collision will get more energy to escape from the original position. After a large amount of impact, the structure of the peak and valley tends to be smooth and the surface roughness decreases. The processing efficiency is determined by the kinetic energy of abrasive particles impinging on the wall of the workpiece. Based on the analysis of the abrasive particle polishing experiments and computational fluid dynamics simulation, it was proposed and verified that the kinetic energy of abrasive grain impacting the wall was the main factor affecting the cutting efficiency. When the ultrasonic wave passes through the water, the liquid is no longer a kind of incompressible fluid, and the density of particles varies with sound waves. Bubbles will appear in the water, and the size of bubble will be changed by the ultrasonic wave. The modified Rayleigh-plesset equation with time. Ultrasonic cavitation occurs when the bubble of motion can be used to calculate the variation of bubble diameter diameter is reduced to zero. The actual observation and theoretical calculation indicate that the collapse of the bubble in its interior will produce high temperature and pressure, which triggers a series of complex physical and chemical phenomena. According to the study of ultrasonic cavitation bubble collapse, and the research results of the peripheral water shock wave formation and its propagation, the role of bubble collapse in the change of abrasive particle kinetic energy was analyzed. When the bubble collapses, high-pressure area formed on the periphery of bubbles is thin, and the high-pressure area then spreads outward to form a shock wave. The amplitude of shock wave is attenuated with a speed of the reciprocal of propagation distance. The kinetic energy of the abrasive particles in the vicinity of the bubble due to shock wave can be analyzed. Strong ultrasonic wave can destroy the surface of parts. In order to make the cavitation bubble collapse caused by the ＂shock wave＂ and ＂micro jet＂ reasonably affect the machining process, the cavitation intensity must be controlled reasonably, so as to promote the acceleration of the abrasive particles as much as possible without hurting the machined surface. A large number of experiments have been carried out to obtain a reasonable ultrasonic intensity. The experimental device was set up to observe the effect of ultrasonic cavitation on the removal of SiO2 on the surface of silicon wafer. Significant effect of ultrasonic cavitation was observed in the process of abrasive particle flow machining on the silicon wafer surface. The results show that the ultrasonic cavitation can change the kinetic energy of the abrasive particles in the particle flow, which can improve the cutting efficiency and improve the surface quality. When the frequency of ultrasonic wave is 20 kHz, the ultrasonic intensity is 92 W/cm2, the abrasive particle velocity reaches 21 m/s, and the size of the abrasive particles is above 13μm, it can significantly improve the abrasive flow to remove the surface material under the action of ultrasonic wave.