Experimental Study On Grinding Process Of Electrostatic Minimal Quantity Lubricantion

The minimum quantity lubrication(MQL)is a novel green machining technology,in which by the use of compressed air,micro-size oil mists are effectively sprayed to the cutting zone in a high velocity to achieve the lubrication and cooling.However,due to the low usage of lubricants,the heat transfer performance of oil mists is poor,which is therefore not suitable for grinding processes.To improve the cooling and lubricating effects of MQL in grinding,an electrostatic minimum quantity lubrication(EMQL)was proposed in this study.As grinding lubricant was charged,the surface tension and wetting angle of lubricant droplets were reduced,thus increasing their permeability and wettability.At the same time,the electrostatic field produced by the charged gas mists could affect the micro-hardness of work-piece materials during the grinding process.A systematical experimental investigation on the grinding performance of EMQL was performed,and the main work and results were concluded as follows:(1)The wetting and permeating property of charged droplet was studied,which reflected the cooling and lubricating ability of EMQL.A comparison of charge characteristics using oil-based grinding lubricants and aqueous grinding lubricants was conducted,and the effect of high-voltage on the charge-mass ratio,surface tension,and wetting angle of oil mists,jet port voltage,as well as on the electrostatic field strength of the processing area were investigated in order to reveal its influence on the physical properties of the grinding lubricants.The results showed that EMQL reduced the surface tension and wetting angle of droplets and improved the spreading and permeating ability of charged droplet.The droplet charge-mass ratio,jet port voltage and the electric field strength of the processing area increased with the increase of the absolute value of the output voltage.(2)The effect of EMQL grinding on the surface properties of 45 steel was studied.The mechanism on the electrostatic field in EMQL grinding process was discussed.The effect of electrostatic field on the metallurgy and micro-hardness of the sub-surfaces of work-piece lubricated with EMQL was investigated.The results showed that the electrostatic field promoted the diffusion of carbon atoms and the dissolution of cementite,which improved the relative content of ferrite in the metallographic structure of the workpiece surface and reduced the micro-hardness of the workpiece surface.(3)The grinding performance of EMQL was systematically studied in terms of grinding forces,friction coefficient,grinding temperatures,grinding G ration,and surface quality.The results indicated that as the grinding lubricant was charged,the permeation and wetting properties of the droplets were improved,and the cooling and lubrication at the contact interface of the grinding wheel-workpiece was enhanced as well.This therefore led to the reduction in the grinding forces and the grinding heat,with a higher service life for the grinding wheel.Compared with the negative charge,positive charge EMQL could produce a better grinding performance.(4)Through the comparison of grinding performance under different conditions,the best experimental condition was obtained using the water-based grinding lubricant.An orthogonal experiment in terms of air pressure,flow rate and voltage,was conducted to optimize the EMQL grinding technology.