Study On The Optimization Of Edm Parameters And Surface Integrity Of Super Alloy

As one of the key parts of aeroengine,aeroengine blade has an important influence on the performance of aeroengine.Nickel base superalloy and titanium alloy are widely used as aeroengine blade materials because of their excellent strength,hardness,high temperature resistance and creep resistance.Electrochemical machining(ECM)has become one of the main machining methods for blades because it is not limited by the mechanical properties of materials and has no tool wear.However,the complexity of flow field and electric field on the leading and trailing edges of the blade during ECM results in large dimensional and shape errors.As a key part of the blade,the leading and trailing edges of the blade are very important to the performance of the engine,it is very necessary to dress them.Electric discharge machining(EDM)is an effective way to machine difficult-to-machine materials with complex shape,which has the characteristics of high machining accuracy and no error reflection.In this paper,EDM aided by vibration is used to dress the leading and trailing edges of the blade.The dressing process mainly includes two steps: roughing(remove part of the material)and finishing(dressing the profile of the edges).In order to realize the above machining methods,a high-precision EDM device with auxiliary vibration is designed in this paper.The control program is developed by using NI LabVIEW software,which can realize three-dimensional machining,data acquisition,detection and other functions.In order to optimize the parameters such as peak current,pulse duration,vibration amplitude and vibration frequency,extensive experiments have been carried out based on Taguchi method.Thin sheets of nickel and titanium alloys with cross section of 29 mm × 0.5 mm are cut off 2mm in length,the optimal machining parameters were verified by confirmation experiments,at the same time,the corresponding electrode wear were analyzed.It was found that under optimal conditions and using graphite electrode,machining time of nickel alloy was 1.62 minutes and machining time of titanium alloy was 2.12 minutes.In addition,there will be a recast layer and heat-affect zone formed on the surface of the EDMed workpiece.Because of the existence of microcracks and residual stresses,the recast layer will have a great impact on the performance of the engine,which must be removed.However,the effect of the heat-affect zone on the workpiece has not been determined,and there is no basis for judgment.In this paper,the surface microstructure of the workpiece after machining is analyzed by means of nano indentation,metallographic microscope,scanning electron microscope and electron probe.It is found that the microhardness near the recast layer has increased.In addition,under the abnormal machining conditions of continuous short circuit or arcing,the electrode composition and oxide can be detected at the arcing position of the workpiece,and obvious fine grains appear near the machined surface of the workpiece.No significant metallographic changes were observed under normal conditions.