Research On Surface Quality And Function Properties Of The Micro Wire Electrical Discharge Machining

Micro Wire Electrical Discharge Machining,MWEDM for short,plays an significant role in the micro electro-mechanical system manufacturing field since its unique processing method.MWEDM surface quality directly impacts the performance and lifespan of the parts.Currently,the domestic and foreign researches of the micro wire electrical discharge machining mostly focus on the impulsing power source,the electrode wire wearing out,the cutting process,the controlling system and so on.Thus,the surface structure and characteristics research has not established a whole assessment system.The research of the functional properties such as the surface friction and wear properties and the corrosion resistance has not been systematically developed.Therefore,the surface quality study is not enough,which will inevitably affect its development and application.This paper firstly studies the MWEDM surface quality,which is the fundamental research to develop the study of functional properties.It also explores and assesses the relation between the surface micro topography and functional properties.The paper uses the mathematical morphology to study the MWEDM surface geometric structure.With the scanning electron microscope and atomic force microscope,it is confirmed that the surface consists of many approximate spherical peaks and pits and the peaks are hemispherical.It builds the discharge physical model and analyzes the thermal load mechanism of the peaks and pits formation,their distribution on the surface,and the changing rule of the peak height and the pit depth with the discharge energy.According to the MWEDM mechanism,it establishes the surface micro topography mathematical model and proves the validity of the method through the simulation.On the basis of the power spectral density function,the spectral distance,the surface height distribution function,it discusses the MWEDM statistical characteristics,and the results indicate that the amplitude distribution obeys the Gaussian distribution and has good isotropy and uniformity.Meanwhile,the paper mainly focuses on the research of the mechanical properties such as the surface metamorphic layer,microhardness,and residual stresses based on the thermal load-oriented characteristic.It also analyzes the surface metamorphic layer composition,metallurgical structure,and the variation of the layer thickness,and tests the microhardness and residual stresses from the surface metamorphic layer to the matrix.The research results demonstrate that the surface metamorphic layer consists of the melted-solidified layer(also called the white layer)and the thermal affected layer and has the residual tensile stress in the layer;as a result,there are many microcracks on the surface,and the white layer has high microhardness.It further sutdies the friction and wear process of two friction types,point-contracting and surface contracting,under the dry friction and lubrication status,thereby summing up the variation rule of the friction and wear properties with different load,frequency(speed),and time.It also establishes the models of the viscous effect,plowing effect,and mixed lubrication and derives the formulas between the friction coefficient and the abrasion.The results show that MWEDM surface has the smaller friction coefficient,the lower wear ratio,and more extended wear life than the superfinishing processing.Through analyzing different friction and wear behaviors,it recommends that adhesive wear and deformation are the main form under the dry friction situation while the lubrication friction mechanism is the mixed wear with asperity contact,boundary lubrication,and fluid lubrication.On the basis of the friction and wear mechanism,the paper studies the variation rule of the amplitude,function,and mixing parameters with different loads during the friction and wear process.In the amplitude parameter,the arithmetical mean deviation Sa is well correlated with the friction coefficient and the wear ratio;in the function parameter,the surface bearing index Sbi and the core fluid retention index Sci are the main parameters of the surface bearing property and the lubrication performance;the three surface roughness parameters,Sa?Sbi?Sci,are considered as the comprehensive index to assess the MWEDM wear resistance performance;with the unique surface geometric structure,it calculates and analyzes the curvature change validity of the 3D hemispherical peak and the variation rule of the gaussian curvature Sgc;the MWEDM assessment system is built based on the friction and wear correlation and the characterization comprehensiveness.To study the corrosion resistance,the paper conducts a comparative research between the MWEDM surface and the grinding machining surface by using the electrochemical method.The results show that the MWEDM corrosion resistance is better than the grinding machining process;the surface roughness value of the grinding machining is smaller,the corrosion resistance is better,while the MWEDM corrosion resistance is getting better with increasing discharge energy and gradually weaker after reaching a certain energy.Finally,the paper uses the analytic hierarchy process in order to comprehensively study the MWEDW surface and establishes the structure of the MWEDM surface analytic hierarchy process.Based on the weighted coefficient,it analyzes the surface roughness parameters and the performance index influencing the surface integrity and indicates that the MWEDM surface integrity has good performance index.