Study On The Key Technology Of Nanoparticle Colloid Hydrodynamic Cavitation Jet Polishing

Ultra-smooth surfaces have been increasingly used in modern optics system, microelectronics industry and membrane science and other fields with the development of science and technology. Ultra-smooth surfaces, which require low roughness, less surface defect and sub-surface damage, are difficult to process. Meanwhile, ultra-smooth surfaces with complicated structure such as aspheric surfaces and concave surfaces have been so appreciated by the optical equipment in modern optics system. However, they can not be processed efficiently and quickly by existing machining methods for the machining condition are limited. Thus, the processing of these surfaces is a tough problem in modern precision machining industry. For the above-mentioned reasons, the present paper proposed the nano particle colloid hydrodynamic cavitation jet polishing technology to easily process the surfaces with complicated structure and meet the quality requirements of ultra-smooth surfaces.The present paper first designed the nano particle colloid hydrodynamic cavitation jet polishing system. The system is consisted of three modules, which are pressure generating system, cavitation generating system and machine tool Computerized Numerical Control (CNC) system. Two kinds of pressure generating system, the extrusion-type pressure generating system and the hydraulic-pneumatic supercharging system are developed in this paper. And the merits and demerits of the two kinds of pressure generating system have been evaluated. The pulse nozzle and swirling vane nozzle are selected as the cavitation generating nozzles, and the effect of cavitation of nozzles have been vertified. Vertified tests for the designed polishing systems show that the designed polishing systems can meet the requirements of processing the ultra-smooth surfaces.The fluid dynamic software was adopted to simulate flow field of the internal and external jet region for the conical nozzle, pulse nozzle and swirling vane nozzle. The distribution law of fluid pressure, velocity and cavitation effect on workpiece of each nozzle was obtained and the influence law of fluid field distribution on material removal was analysised. High speed photography of cavitation cloud and the profile of the polishing area for the three nozzles verified the rationality of simulated results. The law of cavitation intensity with pressure of system in flow field of swirling vane nozzle was obtained by the simulation and experiment.Using molecular dynamics theory, collision processes between the nano SiO2particle and monocrystalline silicon work piece under the velocity of common jet(v=50m/s) and micro-jet generated by cavitation(v=1000m/s) were studied, and then the mechanism of common jet effect and cavitation effect in nano particle colloid hydrodynamic cavitation jet polishing were obtained. The mechanical action of the nano SiO2particle can not exert an influence on the monocrystalline silicon work piece under the impact of jet flow of the nano particle colloid hydrodynamic cavitation jet polishing. The test results of laser Raman spectroscopy of the work piece after nano particle common jet polishing was correspondent with simulated results. The surface of monocrystalline silicon after nano particle colloid common jet polishing and nano particle colloid soaking effect are observed by X-ray photoelectron spectroscopy (XPS). XPS results show that the nano particle in the colloid can chemically bonded with the atom at the surface of the work piece after nano particle colloid common jet polishing. The results of simulation and experiments show that the mechanical effect of nanoparticle under impact effect of jet can not remove the material of workpiece, the removal of material depend on the bonding of nanoparticle and worpiece.The simulated results of contact of nano SiO2particle and monocrystalline silicon work piece under cavitation effect show that the nano SiO2particle under micro-jet effect generated by cavitation effect can exert an obvious influence on the lattice structure of the atoms, which make the atoms at the contacting surface take on amorphous lattice and the atom potential energy at the contacting area increase significantly. With the help of ultrasonic cavitation effect, the simulation results was vertified. The surface of monocrystalline silicon after nano particle colloid ultrasonic cavitation effect was observed by XPS. XPS results show that the work piece after nanoparticle colloid ultrasonic cavitation effect can chemically bonded with the atoms on the nanoparticles. The simulation and experiments show that the mechanical effect of nanoparticle under cavitation effect can improve the atom potential energy and the probability of occurrence of bonding, and then improve the material removal rate.Work pieces were vertically polished by nano particle colloid hydrodynamic cavitation jet polishing technology at a fixed location. Experimental results show that the polished zone present a ring-like shape, and the material removal depth at the center of the polished zone is lower than that around the center. The surface roughness at different position is somewhat different, and the lowest is at the ring with the biggest material removal depth. The result of experiment of cavitation effect under different pressure show that the powerful cavitation will case damage of workpiece. Then the range of pressure parameter to generate fit cavitation effect was obtained. In the experiment that the monocrystalline silicon obliquely polished by nano particle colloid hydrodynamic cavitation jet polishing technology, high quality surface with lowest roughness of Ra0.475nm (Rms0.594nm) was obtained. The factors that influence the machining efficiency for the nano particle colloid hydrodynamic cavitation jet polishing technology are studied by the polishing experiments. Results show that20%improvement in efficiency has been achieved by nano particle colloid hydrodynamic cavitation jet polishing while comparing the common jet polishing, and the efficiency of nano particle colloid hydrodynamic cavitation jet polishing increase with the pressure of the processing system and the concentration of the polishing liquid, but the change of the pH value has little influence on polishing efficiency.