Research On Microstructure Of The Inner Wall Surface In Small Hole By Electrochemical Machining With Low-frequency Vibration

With the progress of scientific research,new studies show that the cooling tube/hole with characteristics of enchanced surface(surface having a turbulent microstructure)instead of a normal smooth tube/hole,the heat transfer efficiency of cooling tubes/hole increased obviously.The enhanced surface including some turbulent microstructure machined in the inner hole surface wall,such as grooves,concave pit,convex rib and so on.Experimental datas show that the enchanced surface can strengthen the heat transfer efficiency in some heat transfer equipment.The heat transfer efficiency will increased by 35%-300% than the smoth bore.Therefore,it is an important research topic to study the micro machining method of the micro structure on the small hole wall with high efficiency,low cost and competitive.The micro electrochemical machining(EMM)is a technology,where material was removed in the form of ions.There is non-contact between workpiece and the tool during the procesing,no residual stress and recast layer on the processed workpiece surface.Therefore,metal micro structure in the inner wall surface could be machined by EMM.But,there are still some technical problems when machining microstucture on the small hole wall,such as the electrolyte refresh in the machining gap,the sludge and heat discharge.When add low-frequency vibration in the electrolyte steady flow,it will form a disturbed flow field in the machining gap,and this can improve flow field and products discharge in the narrow gap.Focus on the spiral hole of machining in EMM,the experiments and simulations were done in this study.The main contents consist of tool(cathode)fabrication,the design of low frequency vibration platform,the simulation of flow characteristics in the gap,effects of the processing parameters and low-frequency vibration on microstructure forming on the inner wall surface inEMM.The main research works are as follows:(1)Successfully built the experimental equipment used for micro-spiral hole machining on the inner wall surface in ECM.(2)Developed the process method to improve the life of the tool electrode.The binding force of the insulation adhesive and tool electrode could improve by adding 15% SiC to the photosensitive resin,controlling the curing temperature,the curing time.Meanwhile,the modified photosensitive resin enhance the thermal conductivity and strength,it makes the service life of the tool electrode increased significantly.(3)According to the Computational Fluid Dynamics(CFD),fluent software was applied to simulate and analyze the field flow in the machining gap of electrolysis process with low frequency vibration.Results show that the amplitude and speed of vibration influence the flow field of the machining gap and disturbed flow field may formed.(4)Experimental study of ECM technology on microstructure of the inner wall surface in small hole.The improved tool electrode was used to machine the spiral hole.Influences of factors of low-frequency vibration on the process stability and processing efficiency are analized.Results show that the uniformity of the hole becoming better with the increase of vibration amplitude,and the material removal rate was also improved;The greater the vibration acceleration,the more contribute to removal of the material,but has less impact to uniformity of the hole.The higher the vibration frequency,the electrolyte was updated more frequently,and that is better to uniformity of rib on the hole wall,however the material removal rate decreases.