Research On The Mechanism Of Ultrasonic-assisted ELID Grinding Wheel Sharpenin

Ultrasonic assisted ELID grinding technology(UAEG)is a combination of ultrasonic vibration grinding technology(UVG)and ELID grinding technology.The technology is expected to be a solution for high-efficiency and precision grinding of hard-to-machine materials such as high-speed steel rolls.In this paper,UAEG grinding of high speed steel is taken as the research object,and the purpose is to reveal the mechanism of ultrasonic vibration,ELID and grinding wheel sharpening and to evaluate the sharpening effect.The grinding wheel sharpening mechanism was revealed by combining finite element numerical simulation with experimental study.The relationship between surface topography parameters of grinding wheel and grinding force and grinding surface roughness was studied by using grey relational analysis method,and the key indexes of grinding wheel sharpening effect evaluation were proposed.The specific work is as follows:(1)The sharpening mechanism,sharpening effect evaluation method and sharpening effect evaluation index of ultrasonic vibration grinding wheel were studied.Firstly,by comparing the cavitation threshold value of electrolyte with the simulation results of flow field pressure in single abrasive region,it is proved that the electrolyte excited by ultrasonic vibration can produce cavitation effect.Secondly,the results of UVG and ordinary grinding experiments show that the maximum normal grinding force of UVG is reduced by about 28%and the maximum tangential grinding force is reduced by about 36%.The maximum roughness reduction of grinding surface is about 4.2%.Thirdly,the grinding wheel surface topography parameters Spk,Svk,Sk,Sds,Ssc,Sq,Sa,Ssk and Sku were selected as the investigation parameters to evaluate the grinding wheel sharpening effect.The grinding wheel surface topography after UVG and ordinary grinding experiments were compared and analyzed,revealing the grinding wheel sharpening mechanism of ultrasonic vibration.The surface roughness of grinding wheel is reduced,the chip tolerance space is increased,the number of abrasive particles per unit area is increased,and the high concentration of abrasive particles is improved.Finally,based on the grey correlation analysis method,the correlation degree between grinding wheel surface topography parameters,grinding force and grinding surface roughness was studied,and the grinding wheel topography parameters Spk,Sds,Ssc,Sq,Sa and Svk were determined as the indexes to evaluate the grinding wheel sharpening effect.(2)The sharpening mechanism and evaluation index of sharpening effect of ELID grinding wheel were studied.Firstly,the main parameters affecting the oxide film thickness were simulated and analyzed based on the oxide film formation rate model.Secondly,the experimental results of ELID and ordinary grinding show that,compared with ordinary grinding,the maximum ELID normal grinding force is reduced by 90%,and the maximum tangential grinding force is reduced by 86%.The maximum roughness of the grinding surface is reduced by about 44%.Thirdly,the grinding wheel surface topography after ELID and ordinary grinding experiments was compared and analyzed to reveal the grinding wheel sharpening mechanism.After ELID sharpening,the grinding wheel surface topography parameters changed significantly.The electrolysis of the grinding wheel metal binder made the passivation abrasive particles fall off,and the new abrasive particles were constantly exposed.The number of abrasive particles per unit area of shallow layer is significantly increased,and the protruding height and sharpness of abrasive particles are improved,which is helpful to reduce grinding force.The elastic deformation of oxide film improves the concentration of grain protrusion height,which is beneficial to reduce grinding surface roughness.The oxidation film of ELID grinding wheel is too thick due to high voltage and duty ratio,which leads to large surface roughness of grinding wheel.Excessive shedding grains are difficult to discharge from the grinding area in time,which has adverse effects on grinding surface roughness.Finally,the grinding wheel morphology parameters Sds,Spk,SK,Sa and Sq were determined as the indexes to evaluate the sharpening effect of ELID grinding wheel.(3)The cooperative sharpening mechanism and evaluation indexes of ultrasonic assisted ELID grinding wheel were studied.Firstly,the influence of ultrasonic vibration on the compactness of ELID electrolytic oxide film was studied experimentally,and it was found that ultrasonic vibration was beneficial to improve the compactness of ELID electrolytic oxide film.Secondly,the grinding experiments of UVG,ELID and UAEG showed that the grinding force and surface roughness of UAEG were the smallest,followed by ELID and UVG.The normal grinding force of UAEG decreased about 37.1% compared with UVG,and the shear grinding force of UAEG decreased about 34.8%.The grinding surface roughness is reduced by 20.1% compared with UVG.Again,the comparison and analysis the UVG,ELID and UAEG after grinding experiment of the grinding wheel surface topography,reveals the mechanism of ultrasonic assisted ELID grinding wheel sharpening,namely on the basis of ELID grinding wheel sharpening,reducing the grinding wheel surface roughness,chip increased capacity space,highlight the high degree of concentration and improve the grits is beneficial to reduce the surface roughness of grinding and grinding force;On the basis of ultrasonic vibration grinding wheel sharpening,the number of abrasive particles per unit area is increased,and the protruding height and sharpness of abrasive particles are improved,which is beneficial to reduce grinding force.After ultrasonic assisted ELID grinding wheel sharpening,grinding wheel surface topography parameters are neutralized,such as Spk,Ssc,Sku,etc.,which further reduces grinding force and grinding surface roughness.Firstly,the mechanism of ultrasound-assisted ELID grinding was studied,that is,ultrasonic vibration increased the furrow travel of the abrasive grain,and the elasticplastic deformation of the oxide film with a certain thickness increased the cutting depth of the single abrasive grain.The joint action of the two improved the material removal rate.Finally,the grinding wheel topography parameters Sq,Sa,Sds and SK were determined as indexes to evaluate the ultrasonic assisted ELID grinding wheel sharpening effect.