Research On Modeling Aspect Ratio Of A Micro Hole Drilling Aided With Planetary Movement Of Electrode By EDM

As one of the nontraditional machining technology,micro electrical discharge machining(micro EDM)has the advantages of no mechanical contact between the electrode and workpiece and machining any conductive material regardless its hardness and strength.Micro EDM can drill micro holes and micro cavities.Therefore,micro EDM is widely used in the fuel injection nozzle,inkjet printer orifice plate and gas holes of engine blade.However,in the process of micro holes drilled by micro EDM,the bubble cannot overcome the viscous resistance and surface tension of liquid medium to remove from hole when the aspect ratio of micro holes reach a certain value.Abnormal discharge appears frequently due to the accumulation of bubbles,which cause the machining speed slow down and excessive electrode wear.Therefore,the aspect ratio of micro holes drilled by micro EDM is limited.The planetary movement of electrode provides an unevenly flow field in the machining gap.The viscous resistance of the dielectric in the maximum gap is minimum,which can increase the aspect ratio of micro holes duo to improving machining debris removal ability.It is important to choose an appropriate eccentric radius in machining of micro holes.If the eccentric radius is small,the effect of electrode planetary movement is not obvious.If the eccentric radius is large,the efficiency of drilling become slower and electrode wear become serious.Although some scholars have proposed modeling aspect ratio of micro holes without planetary movement of electrode,the factors of aspect ratio of the holes with planetary movement of electrode and how to choose eccentric radius are unknown.In this paper,the NC program of planetary movement of electrode in the vertical MicroEDM machine tool is developed by LabVIEW based on the existing horizontal Micro-EDM machine tool,and it is well integrated with the micro hole machining module.The experiments of micro holes machining indicate the NC program can meet the needs of experiments.Based on the above problem,first of all,the impact factors of the planetary movement parameters and electrical parameters on the aspect ratio of micro holes drilled by micro EDM are studied,experimental results indicate that the aspect ratio of micro hole increases along with the increase of eccentric radius and capacitor under different machining conditions.The planetary movement speed is irrelevant to the aspect ratio of micro hole.Then a theoretical model of aspect ratio of micro hole in the normal discharge state is proposed based on the fluid mechanics and surface tension.The model illustrates that aspect ratio of micro hole is proportional to 1.5 times the square of eccentricity ratio.45 holes in deionized water and 40 holes in oil are drilled under different machining conditions to verify the model.Experimental results agree with the theoretical values,the error ratio in deionized water is 6.66% and the error ratio in oil is 5.94%,these two error ratio are both less than 10%.Finally,the optimal eccentric radius can be obtained under the condition of a certain diameter and aspect ratio of micro hole based on this model.9 holes in deionized water and 9 holes in oil are drilled to verify the optimal eccentric radius,experimental results indicate error ratio between experimental results and theoretical values are within 3%,which indicates the validity of the model.