Research On Machining Mechanism And Experiment Of Ultrasonic Electrochemical Hybridized Grinding Of Bearing Raceway

In the machinery and high-end equipment manufacturing industry,bearing,as a core basic component,plays an irreplaceable important role.Raceway is an important working surface in rolling bearings,and its the grinding accuracy and surface quality have an important impact on the accuracy,performance and reliability of mechanical products and equipment.As one of the key manufacturing processes of rolling bearing,the grinding of bearing raceway has a decisive impact on the manufacturing cost and efficiency of rolling bearing.For the precision machining of rolling bearing raceways,it is of great significance to develop new grinding technology and realize the efficient shape and performance collaborative machining of raceway surfaces for promoting the capacity and technological progress of bearing manufacturing industry.Ultrasonic vibration assisted machining is a mechanical processing method that precisely regulates the interface energy in the processing area by regulating the external ultrasonic energy field and energy input,to realize the efficient removal of the machined surface materials and the precise creation of the surface.Electrochemical grinding(ECG)is an electrochemical-mechanical hybridized grinding technology that combines electrochemical machining with traditional mechanical grinding.It has excellent machining performance because of its high machining efficiency,good surface quality,and minor grinding wheel wear.Combined with the advantages of ultrasonic vibration assisted machining and ECG,ultrasonic electrochemical hybridized grinding(UECHG)is firstly proposed based on the characteristics of plunge grinding of bearing raceways in this dissertation.And the material removal mechanism,machining stability and machining surface quality of the bearing raceway UECHG under the condition of multi-energy field coupling are studied.The specific contents of this work are as follows:(1)Based on the principle of bearing raceway UECHG,the material removal mechanism was studied from the passivation characteristics of GCr15 bearing steel,the ultrasonic cavitation effect of electrolyte,the passivation film characteristics under ultrasonic vibration,and the removal states of workpiece material during the machining process.The research shows that the negative pressure value caused by the ultrasonic vibration of the conductive grinding wheel on the electrolyte is far greater than the cavitation sound pressure threshold of the electrolyte.And the crumble and vibration of the ultrasonic cavitation bubble have impact and influence on the passivation film formed in the bearing raceway UECHG,which can cause the local peeling of the passivation film,which help to improve the material removal rate(MRR)and processing efficiency in the machining process.With the change of electrolytic voltage and grinding feed rate,there are four states of workpiece material removal,which affect the machining efficiency and accuracy.(2)Basing on the theory of electrochemical shaping and grinding kinematics,the MRRs of bearing raceway UECHG are modeled and studied.Firstly,according to the characteristics of the internal cylindrical plunge ECG of the bearing outer ring,the MRRs,overcut depths,and the critical machining parameter conditions for generating overcutting are modeled and studied by using equivalent plane ECG.And the rigid differential equation is numerically solved by variable substitution.The results show that the electrolytic voltage,the circumferential feed speed of the workpiece,and the radial feed speed of the grinding wheel have different effects on the MRR,the proportion of electrochemical anode dissolution in it,and the overcut depths.Then,the effect of ultrasonic vibration on the material removal rate of bearing raceway UECHG is studied through electrochemical anodic dissolution experiments and modeling of material removal rate in single abrasive mechanical grinding.The results indicate that the ultrasonic vibration will lead to an increase in both electrolytic current and current efficiency,resulting in an increase in the material removal rate of electrochemical anodic dissolution during the machining process.Under the action of ultrasonic vibration,it can effectively reduce mechanical grinding force and grinding heat,thus achieving greater material removal rate by using larger cutting amounts under the same grinding force.(3)The influence of multi energy field coupling on the UECHG process of bearing raceways was studied through the simulation of electrolyte flow and electric field in the machining area,as well as the simulation experiment of machining stability.According to the coupling relationship of multi-energy fields in the machining area,under the condition of considering electrochemical polarization and concentration polarization,the three-dimensional model simulations of the flow field and electric field distribution in the process of bearing raceway UECHG are carried out by using the tertiary current distribution.The results show that the ultrasonic vibration of the conductive grinding wheel makes the electrolyte more sufficient and the current density distribution more uniform in the machining area.The simulation experiment of machining stability shows that this is conducive to ensuring the machining stability of bearing raceway UECHG,thus improving the electrolytic voltage,the grinding wheel’s radial feed rate and MRR.(4)The relevant models and research conclusions are experimentally verified.Firstly,the MRRs,and the overcut models of the internal cylindrical plunge ECG are verified by experiment.The results show that the experimental value of the total MRR under each machining condition is close to the theoretical value,and the change trend is generally consistent.The maximum relative deviation between the two is 4.8%.The machining condition that produces overcut,and the and the critical machining parameter conditions for generating overcut are completely consistent with the theoretical research results.(5)On the basis of research on specialized machine tool and on-machine dressing of the conductive grinding wheel,the experiments of bearing raceway UECHG are carried out.And the effect of ultrasonic vibration of the grinding wheel on the the machined surface quality is studied through four aspects of the machined surface morphology,roughness,residual stress,and microscopic structure.The research shows that the ultrasonic vibration applied to the conductive grinding wheel can effectively improve the micro-topography of the machined surface,reduce the roughness,increase the residual compressive stress,reduce the thickness of surface deterioration layer during machining,and thus improve the machined surface quality of the workpiece.