Research On Polishing Zirconia Ceramic With Magnetorheological Finishing-Ultrasonic Composite Technology

Magnetorheological fluids(MRF),as a new type of intelligent material,can be converted to a reversible state in the in the instant:it presents a solid under the action of a magnetic field and presents a liquid in the absence of a magnetic field.Based on this special rheological property,magnetorheological fluids have many applications,and magnetorheological polishing is one of them.Magnetorheological polishing(MRFF)is a kind of flexible precision machining technology,which can significantly improve the surface quality after processing.The ultrasonic polishing is a non-contact processing method,which is easy to process brittle hard materials,and can also improve the efficiency of material removal.In order to be able to simultaneously remove material and surface quality,this paper combined magnetorheological finishing with ultrasonic polishing to polish zirconia ceramics(10mm?(37)34mm).The following results had been obtained for this purpose:Firstly,the composition,stability and preparation of magnetorheological fluid were studied and analyzed.The rheological properties of the magnetorheological fluid were studied by the rheometer,and the Bingham model curve,the H-B model curve and the Casson model curve of the magnetorheological fluid were obtained.It was found that the curves of H-B model and Casson model were more close to the measured,which could better characterize the rheology of the magnetorheological fluid.The effects of the magnitude of the current,concentration of hydroxy iron powder,temperature,etc.on shear stress?and viscosity?were studied.Secondly,the mechanism of magnetorheological-ultrasonic comprehensive polishing was studied.Two kinds of abrasive wear models were analyzed and established.The mechanical models(positive pressure P and shear force_sF)and Ra model for material removal in magnetorheological-ultrasonic comprehensive polishing process were estab-lished.Combined with experiments and mechanical models,the effect of experimental parameters on polishing effect was analyzed and the following rules were obtained in a certain range:Applying ultrasonic vibration and increasing ultrasonic amplitude all could increase the material removal rateR_r,but it had no obvious effect on the surface roughness Ra.Increasing the magnetic field strength H could increase the material removal rateR_r and the value of surface roughness Ra.Increasing the concentration of hydroxyl iron powder could increase the material removal rateR_r and reduce the value of surface roughness Ra.Increasing the abrasive concentration could increase the material removal rateR_r and reduce the value of surface roughness Ra.However,if the concentration exceeded a certain concentration,increasing the abrasive concentration reduced the material removal rateR_r and increases the value of surface roughness Ra.The removal rateR_r and the value of surface roughness Ra showed an increasing trend with the increase of abrasive size.The increase of rotational speed could increase the material removal rateR_r and reduce the value of surface roughness Ra.In order to get better surface finish,it could increase the speed slightly.The increase of the working gap could simultaneously reduce the material removal rateR_r and the value of surface roughness Ra.Finally,based on the study of the polishing parameters,the experiment of polishing zirconia ceramics was performed.The surface roughness Ra was 0.096?m.