Research On Wettability Of EDM Surface And Fabrication Technology Of Functional Superhydrophobic Surface

Surface strengthening on physical and chemical properties has become an inevitable trend in machining approach development,and the research on the high performance and efficient machining process of functional surface is of great significance to improve the product effect and productivity.At present,the excellent anti wetting ability of superhydrophobic surface makes it play an important role in fluid drag reduction and droplet manipulation,which has broad prospects for product improvement and upgrading.During EDM,rough surface is formed due to the superposition of discharge craters,the unique micro morphological characteristics of the surface affect the wettability,it is significative to adopt it in superhydrophobic surface fabrication and further in wide application.This thesis focuses on the rough EDM surface,evaluates and fits the surface micro morphology,then analyzes its wettability.In addition,a method of high performance superhydrophobic surface preparation is proposed,which is applied to the fabrication and practical application of functional superhydrophobic surface and wettability pattern.Three-dimensional morphologies of EDM surface are evaluated and reconstructed here,it’s expected to establish the function between morphology characteristics and machining parameters.The shape and size of single pulse discharge craters are simulated and experimentally analyzed,the response surfaces are established from machining current and pulse width to craters size.Statistical operation and power spectral density analysis are carried out on the data matrix obtained by morphology measurement,the characteristics in Z direction and X-Y plane are summarized,and the surface height distribution,spatial frequency distribution are related to the size of single pulse discharge crater.According to the fractal theory,the signal component are separated through wavelet decomposition method,and the two characteristic parameters,namely spatial characteristic frequency and amplitude are extracted.A large number of experiments and characterization are carried out,and the functions of characteristic parameters and machining current and pulse width are obtained.Using the extracted five groups of parameters,the contour is reconstructed by curve equations,and extended to the mathematical expression of three-dimensional surface,so as to realize the prediction of surface morphology through machining parameters.The surface wettability is studied based on the reconstructed surface of EDM with specified parameters.The theoretical model of water droplet contact angle on the surface with ideal array microstructure is established depending on force balance principle,and then introduced into the prediction of water droplet contact angle on reconstructed surface.Firstly,according to Wenzel and Cassie-Baxter theory,the solid fraction and contact line density are calculated from the surface equation and the mechanical analysis of threephase contact line,therefore,the contact angle is solved.Two kinds of dual frequency ripple surfaces,which include surfaces with fractal characteristics and non fractal characteristics,are used for wettability analysis,the transformation conditions and critical state of the composite wetting model under different characteristic parameters are explored,so as to realize the prediction of the contact angle of water droplets on the hydrophobic treated surfaces.Under the verification of experimental tests and modification for model,surface wettability is constructed numerical relationship with parameters of EDM.Based on the above contact angle model of water droplets on EDM surface,superhydrophobic surface fabrication processing is explored.A method of combining EDM with electrochemical technique is proposed to realize hierarchical micro nano structure superhydrophobic surface,in which nano or submicron particles formed of electrochemical etching and deposition further enhance the superhydrophobic ability of the surface.The composite wettability model of these fractal surfaces is studied theoretically,which provides theoretical support for the machining parameters adjustment,in order to prepare superhydrophobic surfaces of high performance.EDM combined with electrochemical etching approach is employed on copper,the contact angle reaches167.1±2.6°,its excellent anti wetting and anti-corrosion ability of superhydrophobic surface was proved by morphology characterization and electrochemical corrosion test.The superamphiphobic of water and kerosene on aluminum surface was obtained by EDM and electrodeposition under nano titanium fluoride treatment,the water contact angle is169.8±3.0°.Through the wear resistance test and drag reduction performance test,it is proved that the EDM technology plays an important role in improving the wear resistance and stability of superhydrophobic surface.Since theory and experiment of EDM and electrochemical combination finished,the design and manufacture of functional wettability pattern are carried out.The droplet storage device is fabricated by EDM circular array on electrochemical deposited zinc coating,which the diameter is 500μm.The practicability of this method is proved through theoretical calculation of droplet contact angle and contact angle hysteresis on the pattern and the droplet experiment on as-prepared sample.Based on mask electrochemical deposition technology,functional patterns are designed and tested on EDM surface substrate according to different pattern scales.Copper foil masks are used in large size non-uniform wettability patterns,which is effective in water mist collection and wedgeshaped droplet self-driven directional transport.High precision functional wettability texture is prepared by lithography mask technology,then patterns with anisotropic droplet drag reduction function such as fish scale and arrow are designed.The experiments show them valuable on the devices for droplet unidirectional drag reduction function.In this thesis,the surface morphology and wettability of EDM are studied in detail by theoretical research and experimental exploration,the controllable fabrication of superhydrophobic surface and functional wettability pattern is realized with the assistance of characterization test.This innovation transforms surface defects into process advantages.Therefore,the application value of EDM process is expanded,it also adds new idea to superhydrophobic surface and fluid manipulation technology.