Physical Mechanism And Grinding Force Model Of Nanolubricant Traction By Magnetic Field

High-strength alloy materials have been applied to various key parts in the aerospace field for decades.For example,titanium alloy takes up almost 30% of the weight in an aerospace engine.With the increasingly rigorous requirement in precision and surface quality,grinding is attracting more interest as a vital process in manufacturing.During the grinding process of high-strength alloy materials,the temperature of the grinding zone always remains at a high level for the high strength and low thermal conductivity of the material characteristics,resulting in the deterioration of the workpiece surface roughness,and even burns.To overcome this problem,the traditional pouring flooding method has introduced a large amount of grinding fluid,where the low effective flow rate,unfortunately,leads to a significant difference between the grinding zone and the basic cooling environment of the workpiece.Especially,the surface integrity may easily deteriorate with a large grinding arc under this condition.In recent research,nanolubricant minimum quantity has been proven as an efficient and environment-friendly cooling lubrication method.The unique techniques in nano-lubricant minimum quantity,including atomizing jet and enhanced heat transfer mechanism,are becoming the most promising approach compared to flooding in the grinding process,and have been applied in the grinding of common materials preliminarily.Given this context,the insufficient infiltration problem of lubricant caused by the poor transport energy is still an unresolved challenge in the deep grinding and forming grinding of difficult-to-machine materials.To handle the challenge mentioned above,a novel nano-lubricant minimum quantity lubrication grinding assisted by the magnetic field is proposed for the first time,which aims to improve the infiltration and cooling lubrication properties of nano-lubricant in grinding zone with the utilization of magnetic field.To investigate the magnetic adsorption transport mechanism and the anti-friction mechanical behavior in the proposed method,the systematic theory is discussed,which is then verified by the experiments designed correspondingly.The main contents of the thesis are listed as follows:(1)A magnetic field auxiliary device grinding process equipment is invented,which employs the permanent magnet and the ferromagnetic wheel to apply a gradient magnetic field in the grinding area.The magnetization mechanism of the wheel in the magnetic field and its influence on the distribution of the magnetic inductance line are revealed,and the changing trend of magnetic field intensity and gradient is explored.The parameters setting range of the processing unit is obtained based on the force and transport of the lubricant droplets.(2)Three kinds of plant oil-based magnetic nano-lubricants are developed with the adoption of Fe3O4,Fe3O4 composite graphene,and Fe3O4 mixed graphene.The variation characteristics and quantitative relationship of physical properties of the developed nanolubricant including viscosity,density,saturation magnetization,and relative permeability,are investigated under the effect of the magnetic field.The kinematic behavior of the magnetic nano lubricant in the jet zone and the dynamic behavior of collision and adsorption on the workpiece surface of the grinding wheel are revealed.The effect of the magnetic field intensity and jet velocity on microdroplet sliding,film formation,and falling is studied.The collision-adsorption behavior map of microdroplets under the action of magnetic field intensity and jet velocity is obtained,which provides a theoretical basis for process optimization.(3)The film formation and antifriction,and anti-wear mechanism of nanoparticles at the wheel/titanium alloy interface under the magnetic field are revealed,and tribological experiments are carried out to simulate grinding conditions.The lubrication behavior of Fe3O4,graphene,Fe3O4 composite graphene,and Fe3O4 mixed graphene nano-lubricant under the magnetic field is studied by the coefficient of friction,abrasion morphology,and cross-sectional area.Furthermore,the optimization of the matching parameters of Fe3O4 mixed graphene nano-lubricant with excellent performance is studied,and the optimization scheme is obtained.(4)The mechanical behavior of magnetic field adsorption transport of magnetic nano-lubricant in the grinding zone is analyzed,the lubricant velocity and flow model considering the boundary slip of the interface is established,and the influence of magnetic field on the transport efficiency of lubricant is obtained.Combined with tribological experiments,the distribution law and expression of the coefficient of friction in the grinding zone under the influence of lubricant flow rate are obtained.In this thesis,a grinding wheel model based on truncated hexahedral grinding grains is constructed for grinding difficult-to-machine materials.On this basis,a magnetic field-assisted grinding force model is established and verified by experiments.(5)A magnetic field-assisted grinding device was established and experimental research on titanium alloy grinding is carried out.The excellent grinding performance of magnetic nano-lubricant under the action of the magnetic field was verified through grinding force and workpiece surface quality evaluation.The formation of lubricating oil film is found by EDS analysis of the workpiece surface.A large grinding length(25mm)experiment is carried out to observe the grinding temperature,surface roughness,and 3D morphology of the workpiece at different lengths.The significant effect of magnetic field adsorption on micro-interface lubricant transport in the grinding zone is verified.(6)Based on theoretical research and confirmatory experiments,considering the comprehensive effects of magnetic field-assisted grinding device parameters on magnetic field distribution and antifriction characteristics of lubricants,a three-factor and four-level optimization experiment is carried out.The influence weights of horizontal distance,vertical distance,and angle between the permanent magnet and wheel on grinding force and surface roughness are obtained,and the relatively optimized process parameter combination is obtained.Furthermore,the surface power spectral density function and surface morphology are used as characterization parameters to obtain the optimization process parameters of titanium alloy grinding.