| Minimum Quantity Lubrication(MQL)is a new method of clean,efficient,low consumption and low-carbon cooling lubricant supply.It avoids the high cost of using mineral cutting fluid in traditional flood lubrication,which threatens the natural environment and the health of operators.It has been widely used in the field of mechanical parts processing and manufacturing.Although the MQL realizes the reduction of lubricant supply by pneumatic atomization,there are still the following technical bottlenecks: MQL lubricants depend on high pressure gas atomization,and the droplet size,distribution and transportation flow field disturbance are difficult to be controlled accurately.PM10 and PM2.5 can be inhaled small droplets.It not only reduces the effective utilization rate of lubricants,but also threatens the environment and human health,and cannot be applied to grinding difficult materials in aerospace and other fields.Based on the above urgent needs and technical bottlenecks,the research team of the author took the lead in proposing a new process of electrostatic atomization minimum quantity lubrication(EMQL)in China.The new process adopts the collaborative atomization of electrostatic field and airflow field,which can effectively reduce the average particle size and distribution span of atomized droplets,and improve their deposition and permeability.Before the work of dissertation is carried out,the advantage of electrostatic atomization has been confirmed by processing verification experiments.However,the scientific essence of the atomization mechanism of the electrostatic nozzle under the coupling effect of multi physical fields,the atomization droplet transport and interface impact dynamics mechanism,and the multi field cooperative cooling and lubrication mechanism in the cutting area have not been revealed,so it is impossible to realize the accurate and controllable supply of MQL parametrically.Aiming at the original scientific problems such as the atomization characteristics of the EMQL nozzle and the mechanism of grinding zone,the theoretical research work of annular liquid film tearing atomization and small liquid mass breaking atomization driven by the multi energy field of the electrostatic atomizer is carried out.The dynamic behavior of charged droplet interface impact is studied,the mechanism of heat transfer enhanced by electric field is revealed,and the cooling and lubrication mechanism of EMQL grinding zone is explored.On this basis,the droplet average size for annular film tearing atomization and small droplet breakup atomization of electrostatic nozzle mathematical model is established,and the numerical simulation and grinding experiment are carried out.The main research contents are as follows:(1)The primary atomization mechanism of annular liquid film breakup in EMQL charged nozzle is studied.The influence of electric field parameters and air flow parameters on the annular liquid film thickness,transverse wavelength and longitudinal wavelength at the nozzle outlet is revealed.The K-H and R-T fluctuations of annular liquid film under charged condition are studied,and the mathematical model of average volume and particle size of primary atomized droplets is established.The effects of electric field parameters and flow field parameters on average particle size,droplet size distribution span R.S value and PM10/PM2.5 percentage concentration are studied.The theoretical model was verified by experiments.(2)The experiment of droplet size measurement on EMQL nozzle at different interception intervals is carried out.The influence of gas field parameters and electric field parameters on the average particle size of aerosol is analyzed.A mathematical model of the volume average particle size of small liquid mass crushing atomization is established,which includes the initial gas velocity,nozzle voltage and jet distance.The kinetic energy loss of gas,the potential energy change of liquid surface tension and the work law of electric field force in the process of electrostatic atomization are studied,and the energy distribution proportion model of electrostatic atomization system is established.(3)The evolution models of droplet velocity under different pressure and voltage conditions are established,and the initial velocity and particle size before droplet impacting the liquid film are obtained.The dynamic numerical calculation model of charged droplet impacting the liquid film is established,and three kinds of droplet impacting the liquid film,including rebound,spreading and splash breaking,are analyzed,and the influence mechanism of external electric field on droplet impacting the liquid film is revealed.The variation of velocity field,pressure field and space charge density in the process of impact between charged droplet and liquid film is studied.The formation mechanism of liquid crown and the dynamic mechanism of droplet springback,spreading and splashing are revealed.(4)The corona discharge process of needle plate electrode structure in air medium is studied.The motion and collision law of charged particles in positive corona discharge and negative corona discharge are analyzed.Combined with the electrochemical reactions such as ionization,recombination and adsorption between micro particles under high voltage,a simplified model of corona discharge in air medium is established.Combined with the actual heat exchange space of electrostatic atomization grinding area,according to the control equation of electrostatic field,two-phase flow field and multi physical field coupling equation,a mathematical model of temperature field based on EHD electric field strengthening heat exchange effect is established,and the distribution characteristics of electric field,velocity and pressure in the heat exchange space of the model are explored.(5)The surface grinding experiments of titanium alloy Ti-6Al-4V under dry grinding,flood,pneumatic MQL and EMQL are carried out.The grinding force,friction coefficient,grinding specific energy and workpiece surface morphology under different lubrication conditions are analyzed,and the lubrication mechanism of external electric field in the grinding zone is revealed.Combined with the orthogonal experiment method and S/N analysis,the optimization experiment of MQL jet parameters of electrostatic atomization is carried out,and the optimal gas supply pressure,nozzle voltage and nozzle angle are determined.The fragmentation atomization process of MQL and the impact behavior of charged droplet and liquid film are verified.(6)An experimental study on EMQL grinding of titanium alloy based on the gain of bioactive agent is carried out.The effects of lecithin addition on the surface tension,dynamic viscosity,electrical conductivity and charge mass ratio of soybean oil are analyzed.The surface morphology and surface roughness of the workpiece under different lecithin mixing ratios are studied,and the mechanism of lubrication gain in grinding zone of lecithin is revealed.The experiments of dry grinding,flood,MQL and EMQL are carried out.The temperature of grinding zone is measured by thermocouple method,and the cooling mechanism of external electric field on grinding zone is analyzed. |
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