| Electrical discharge machining(EDM)has been widely used in the processing of deep small holes because of its advantages such as bringing no cutting force and processing high-hard materials easily.In the traditional EDM hole machining using cylinder electrode,electrolytic corrosion products are accumulated at the bottom of the hole,which will seriously affect the machining ability.In recent years,some researchers have machined helical grooves on the cylinder electrode to obtain the ability to make the working fluid in the axial direction move during high-speed rotation,thereby promoting chip removal and increasing the processing speed.However,there are few research results in this area,especially the lack of clear conclusions on the influence of the helical groove structure on processing.Therefore,this paper mainly studies the influence of helical groove which is in the counterclockwise moving left-handed helical electrode structure on deep hole processing from the perspectives of its processing technology,simulation and experiment.To machine the electrodes and drill holes by them in the same machine tool,this paper selects micro-EDM milling to process helical electrodes.So a clamping movement device for assisting electrode processing has been developed on the basis of a three-axis micro-EDM machine tool,which realizes high-efficiency processing of brass helical electrodes with a diameter of 1 mm at low cost.According to the characteristics of the processed helical groove,the quadratic curve is selected to fit the groove shape,and the three parameters "lift angle,groove width,groove depth" that affect the structure of the helical groove and their restrictive relationship are defined and clarified mathematically.On this basis,a mathematical model of the helical groove was established.Combining the characteristics of processing technology and mathematical theory,through the experiment of EDM milling micro groove on the brass plane,the relevant factors affecting the structure of the micro groove are studied to improve the processing quality of the helical groove.To study the mechanism of the helical electrode's benefit in machining,the flow field simulation software of ANSYS FLUENT is used to simulate and analyze the working fluid state in the machining process.First,from the perspective of steady state,analyze the corresponding motion law of the working fluid when the electrode rotates,and explain its mechanism of promoting in removing electrolytic corrosion products from the three perspectives of pressure,flow velocity,and streamline trajectory;then from the perspective of transient state,the solid phase gathered at the bottom of the flow field model is used to simulate the electrical corrosion products during processing,and the distribution changes caused by the flow field in a specific time are studied.Both results fully proved the promotion effect of the helical electrode on the processing.Then,by extracting the characteristic values related to pressure and speed in the steady-state flow field,as the main basis for judging its ability to promote processing,the influence of spindle speed,helical groove's lift angle,groove width,and groove depth on processing is comparatively studied.Finally,the EDM drilling experiment was carried out on the Ti6Al4 V material.First,the cylinder electrode is used for processing,and the obtained data is used as a reference.To study the influence of structural parameters on processing,the L16(4^3)orthogonal experiment was carried out,and it was found that the influence of groove width and groove depth basically accorded with the results obtained by simulation,but the effect law of rising angle was more complicated.Therefore,a single-factor experimental study was carried out on the lift angle,and the difference in the processing effect at different depths was found from the results.Based on this,a variable-lift angle helical electrode was designed and used to achieve high-efficiency machining of small holes with a diameter of 1 mm and a depth-to-diameter ratio greater than 10. |
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