Research On Mechanism And Application Of Powder Electrical Discharge Machining

The surface microstructure is referred to a structure machined on the surface of the material with different features,different dimensions and different functions.As the development of science and technology and continuous research,non-smooth surfaces with surface microstructures on the micro scale show excellent performances in terms of surface wetting,lubrication,thermal properties,optical properties,friction properties,and coating bond strength compared to smooth surfaces.Therefore,the microstructures of surface have extremely broad application prospects in aviation,aerospace,biomedical and many other fields,which is the key technology for manufacturing products with high performance.With the continuous deepening of the research on surface micro-structures and its increasingly widespread application,the rapid development of processing methods has followed.The main methods currently of processing surface with micro-structures include micro-electrolysis,UVLIGA,imprinting,laser texturing,ion beam texturing,and electric spark texturing.Most of the existing methods for fabricating surface micro-structures are complicated in processes,possess expensive equipment and need to make specific tool tips,etc.Therefore,this paper proposes a method of fabricating micro-structures inside microchannels employing the electrode with a hedgehog-like magnetic powder,aiming to simplify the process,improve efficient and reduce the cost of manufacturing surface micro-structures.The research completed in this paper mainly includes the following sections:(a)The electrode with a hedgehog-like magnetic powder were designed based on magnetic induction lines and magnetic field intensity distribution around the magnet.Through comparative experiments,it can be seen that the magnetic powder EDM whose the processed microstructure can fill the entire groove,has obvious advantages when compared with the traditional EDM machining microstructure in the groove.(b)The micro-structures were fabricated on the inner wall of the copper tube using the designed electrode.The experimental results show that the designed tool tip possesses the ability to process micro-structure on the inner wall of the copper tube.(c)By analyzing the waveform of the discharge collected by the oscilloscope and the surface morphology of the pits on the workpiece surface,it can be seen that the magnetic powder EDM with single-pulse penetrates the surface of the workpiece once,forming multiple electric pits.The spark discharge process of the magnetic powder EDM was observed by a high-speed camera,showing that there are multiple discharge channels in the electrical process of the powder EDM and the end times of the channels are not the same.From the above experimental results,this paper put forward a reasonable suppose on the magnetic powder discharge process.(d)The influence of the peak current,pulse width and magnetic powder size on the diameter and depth of pits under the magnetic powder EDM with single pulse was studied.The average diameter of the pits of electric corrosion increases first and then stabilizes with the increase of the peak current and pulse width.While with the increase of the magnetic particle diameter,the average diameter of the electric pit shows a continuous increase trend,but the growth rate gradually decreases.From the average depth of the pit,the average depth of the pit increases with the addition of the peak current,pulse width,and particle size.However,as the pulse width and peak current increases,the average depth of electric pit growth gradually decreases.(e)The effects of continuous current,peak current,pulse width,duty cycle,magnetic particle size,and processing time on the surface roughness of the specimen were investigated.The results show that the surface Ra and Rz values increase with the addition of peak current,pulse width,magnetic particle size and processing time,but the change of the duty cycle has no significant effect on the surface roughness of the specimen.Subsequently,the influence degree of each factor on the Ra and Rz values of the surface of the specimen after processing was studied by response surface methodology,showing the order of influencing factors from big to small was that peak current,pulse width,magnetic particle size and processing time.(f)The microstructure of the microfluidic channel on the bottom of the liquid-cooled heatsink was fabricated by means of EDM with the electrode of hedgehog-like magnetic powder,which verified the ability ofthe electrode of hedgehog-like magnetic powder to texture the micro-grooves of the array.What's more,it was found that the processed area at the bottom of the flow channel was mainly concentrated in the middle of the flow channel.Through testing the heat dissipation performance of the flow path before and after processing,the peak cooling rate of the treated liquid cooling radiator was significantly improved compared to that before treatment,verifying the improvement of the heat dissipation performance of the microstructure within the flow channel.