CFD simulation and experimental studies of suspension flow field in ultrasonic polishing

Abstract

With the rapid development of science and technology, hard and brittle materials with high performance have been widely used. Meanwhile, it necessitates the development of compatible machining techniques. As the final processing step of precision component, polishing plays a decisive role. Ultrasonic polishing is a powerful method for improving polishing efficiency and surface quality, especially for hard and brittle materials. In this paper, effects of ultrasonic vibration on suspension flow field have been specifically studied in ultrasonic polishing. At micro level, a mathematical model for analyzing the effects of ultrasonic vibration on the velocity and stress of the inner microelement in polishing suspension flow filed was established. CFD simulation was adopted to study the behavior of polishing suspension flow filed under the action of ultrasonic vibration. It was proved that periodic dynamic changes occur and turbulence form in suspension flow field which are positive for polishing, suspension flow field velocity in x direction near workpiece surface could reach a maximum of about 2.3 m/s, while that in z direction is 0.13 m/s. Material removal thus mainly depends on generated transverse shear flow. And a surface rough change rule was summarized. At macro level, monocrystalline silicon polishing experiments have verified the positive role of ultrasonic vibration, within the same polishing time and polishing head rotation velocity, the surface roughness without ultrasonic vibration reduced from 102 nm to 15 nm, while that with ultrasonic vibration reduced from 109 nm to a minimum of 4 nm, only with ultrasonic amplitude of 15 μm, surface roughness reduced from 98 nm to 27 nm, with the rotation of polishing head and ultrasonic amplitude of 9 μm, 15 μm and 21 μm respectively, the surface roughness reduced to 6 μm, 4 μm and 4 μm respectively. The changes of surface roughness in all experiments were consistent with the summarized rule.