Fundamental Research on Fluctuating Wire Electrochemical Machining
Author:Zou Xiang He
Supervisor:zhu zuo fang xiao long
Ruled surface is widely used in aerospace,ocean engineering and mould making areas.Tenon and mortise structure of the aeroengine blade is a typical one.Its high demand of fatigue life and reliability forbids any recast layer and micro cracks on the working surface.If adopting wire discharge machining or laser cutting,a subsequent process of recast layer removal is required to ensure the fatigue life.Wire electrochemical machining(WECM)is a kind of ECM process in which a metallic wire is used as the tool electrode.It is convenient to fabricate complex structures using a wire tool through the numerical controlled relative movement between the electrodes.However,when the workpiece becomes thick,it is difficult to expel the electrolysis product out of the gap,which significantly affects the machining accuracy and surface quality and the electrode feed rate is limited.This paper proposes a method of fluctuating wire electrochemical machining to improve the removal of electrolysis products and the renewal of electrolyte.The following contributions have been made by this paper.(1)A mathematical model of WECM process has been established,and the WECM process under ideal state was simulated.The simulation results comfired that a pulse voltage could lead to a decrease of the machining gap compared to a direct voltage.Additionally,the effects of electrolyte flow field on the the machining under non-ideal state were discussed.(2)A method of WECM using a cutting edge tool has been proposed.The flow model of machining gap was established.The simulation results showed only electrolyte in the vicinity of the surface of the tool can be recycled when the cylindrical tool is used,whereas most of the electrolyte in the front gap is involved in the circulation when a cutting edge tool is used.The volume flow rate of side gap is larger than that of cylindrical tool,and it varies dynamically.Besides,the electric field simulation results showed that current density distribution changes dynamically as the cutting edge tool rotates.The effects of tool cross-sectional geometry on slit width and maximum feed rate,and effect of rotation speed on slit width were investigated experimentally.The results showed that the machining accuracy can be improved using a 1/2 cutting edge tool compared to that of a cylindrical wire electrode.At spindle speed of 15000 rpm,the maximum feed rate was 0.09 mm/min when machining a stainless steel block of 5 mm thickness by using a cylindrical wire electrode,while it increased to 0.144 mm/min when a 1/2 cutting edge tool was applied,which is 1.6 times of the former.(3)A method of WECM using a ribbed wire tool assisted with large-amplitude vibration has been proposed.Firstly,the current density distribution was calculated and the removal of electrolysis product particles was simulated.The results showed that ribbed wire tool assisted with large-amplitude vibration was beneficial for the removal of the electrolysis product.Then the effects of vibration amplitude,frequency and feed rate on the slit width were experimentaly investigated,and the results showed that the machining accuracy could be improved by using the ribbed wire tool.A mortise structure of 20 mm thickness was successfully fabricated by WECM assisted with large-amplitude vibration.At vibration amplitude of 5 mm and frequency of 1.5 Hz,the maximum feed rate was 0.08 mm/min when machining a stainless steel block of 5 mm thickness by using a cylindrical wire tool,while it increased to 0.1 mm/min when a ribbed wire tool was applied.(4)An electrolytic machine for WECM has been established,including X-Y-Z axes driven by linear motor,clamping fixture,electrolyte recycling system,high speed rotation unit,air pressure system,numberic control system,and machining current monitoring system,et al.(5)Cutting edge tool has been in situ fabricated by using block electrochemical machining and wire electrochemical micromachining method,respectively.A model for reciprocating block electrochemical machining was proposed,and verified by experiments.Moreover,the ribbed wire tool was fabricated by using wire electrochemical micromachining method and the effects of pulse voltage,frequency,duty cycle,and electrolyte conductivity on the annual groove width were studied.(6)A method for recast layer removal using WECM has been proposed.With orthogonal experiments,the effects of pulse voltage,feed rate,cutting edge engagement and combination of tool and motion on the surface roughness and cutting depth were studied.In experiments,a stainless steel block of 10 mm thickness was used as the workpiece,and cylindrical wire,cutting edge wire tool and ribbed wire tool were used as the tool electrode,repectively.The results showed that the recast layer could be removed quickly and effectively using proper machining parameters.The optimum parameters that give the best performance are as follow: pulse voltage of 20 V,electrode feed rate of 20μm/s,cutting edge engagement of 0.1mm,and cylindrical wire tool assisted with large-amplitude vibration.