Study On Features Of Grinding White Layer And Spectrum Characteristics Of Acoustic Emission Signal Of Hardened GCr15 Bearing Steel

Hardened GCr15 bearing steel has been widely used in vehicles of aerospace,automobile and architectural engineering,as a kind of high-carbon chromium steel with superior performance.As an important precision machining method,grinding determines the dimensional accuracy and surface quality of workpiece,but the "white layer" appearing in the grinding process of hardened GCr15 bearing steel reduces wear resistance and fatigue life of the workpiece,it is of great significance to study the essential characteristics of white layer and explore the influence of grinding conditions on white layer to guide the grinding of bearing workpiece.Therefore,hardened GCr15 bearing steel was taken as the experimental object in this paper,the grinding force,grinding temperature and acoustic emission signal were analyzed and studied,combined with the microstructure and morphology of white layer,the characteristics of white layer were discussed.The main research contents are as follows:(1)Experiments on surface grinding of hardened GCr15 bearing steel were carried out,the influence of grinding parameters on grinding force and grinding temperature was studied.The results show that the grinding force increases with the increase of cutting depth,the effect of cutting depth on normal grinding force is significantly greater than that of tangential grinding force.Under condition of dry grinding,the grinding temperature increases at a rate of 104℃/s and decreases at a rate of 103℃/s.The cutting depth significantly affects the grinding temperature,high grinding temperature causes the burning of workpiece surface and makes surface roughness increase sharply.(2)The microstructure of white layer was observed,the characteristics of white layer were studied,and the influence of grinding parameters on white layer was analyzed.Research shows that the structure of white layer is dense with many dislocations.The microhardness of white layer is much higher than that of dark layer and bulk material,the variation law of microhardness is the same as the distribution law of the microstructure of cross section in workpiece.Grinding temperature is the main factor affecting the thickness of white layer,when the grinding temperature exceeds phase transition temperature of materials,the thickness of white layer largely changes.(3)The spectrum characteristics of acoustic emission signal were analyzed,the spectrum regularities of acoustic emission signal under the coupling effect of mechanical extrusion and grinding heat were clarified.Studies show that the acoustic emission signal in the process of grinding is affected by mechanical compression and the thermal stress,the formation of white layer relates to the effect of thermal stress,the white layer forms with strong effect of thermal stress.The high-frequency amplitude of acoustic emission signal is mainly affected by thermal stress effect.When the thermal stress effect is enhanced,the high-frequency amplitude also increases.Based on the effect of thermal stress,the correlation between the high-frequency amplitude and the thickness of white layer is established.There is a positive correlation between the high-frequency amplitude of acoustic emission signal and the thickness of white layer in grinding process.