Study On High Efficiency Acoustic Assisted Shear Thickening Polishing Method

In recent years,with the rapid development of world economy,science and technology are advancing with each passing day.The surface shape of all kinds of technology products is tending to curved surface and even complex surface,which increases the difficulty of the ultra-precision machining.Complex curved surface,which consists of various radius curve surface,is widely used in many areas such as vehicle transportation,marine,aerospace,energy,mould and medical equipment.How to obtain high quality complex curved surface with high efficiency and low cost has become a research focus.A new polishing method,acoustic assisted shear thickening polishing(ASTP)based on the shear thickening polishing(STP),which could actively control the strength of shear thickening effect by the assisted acoustic action,was proposed in this paper.A high efficient and high quality polishing results with low cost can be achieved in this polishing method.The main aspects of the study are including:The principle of ASTP was explained,and the motion equation of the acoustic wave in the viscous medium are derived based on the three basic equations of the acoustic wave in the ideal medium,and then the effects of transmission characteristic of acoustic wave on the slurry viscosity distributions are obtained.The influences of acoustic properties including frequency,power and waveform on the rheological properties of shear thickening polishing slurry(STPS)were investigated.The influences of acoustic direction for polishing effect were analyzed by the verified experiment of ASTP,the results reveal that the best polishing effect was obtained when the acoustic direction parallel to the workpiece surface.The experimental equipment of ASTP was developed,which included acoustic generator,4-axis linkage device,circulating cooling system and viscosity control system of STPS.The equipment is the basis for further processing experiments.A signal detector was developed to test the performance of acoustic generator,so as to verify the reliability of acoustic generator.According to the constitutive equation of non-Newtonian fluid and hydromechanics,a mechanical model formula is derived which is used for force calculation of workpiece surface,and then the mathematical model of material removal was obtained.The comparison of theoretically predicted results and experimental results proves the model is correct,and the error within 9%.The influences of acoustic properties including frequency,power and waveform on the polishing efficiency and quality were investigated through single factor experiments.Through the orthogonal experiment analysis,it is concluded that,when the material removal rate(MRR)is used as the evaluation indicator,acoustic frequency(50%)is the most significant followed by acoustic power(31%)and then acoustic waveform(11%).While surface roughness(Ra)is used as the indicator,acoustic waveform(36%)is the most significant followed by acoustic frequency(33%)and acoustic power(28%).Based on the analysis results,MRR reaches highest value 11.32μm/h,under the conditions with 20 Hz acoustic frequency,25 W acoustic power and sine wave acoustic waveform.On the other hand,the surface quality of the workpiece is best under the conditions with 60 Hz acoustic frequency,25 W acoustic power and sine wave acoustic waveform.The average surface roughness is reduced rapidly from Ra 110 nm to Ra 7nm after 1 hour’s processing,and the best surface quality reaches Ra 3.6nm;Better results than that of the shear thickening polishing without acoustic aid were achieved.