电火花复习

1、什么是EDMElectricalDischargeMachining(EDM)istheprocessofmachiningelectricallyconductivematerialsbyusingpreciselycontrolledsparksthatoccurbetweenanelectrodeandaworkpieceinthepresenceofadielectricfluid,sotomakethesize,theshapeandthesurfacequalitymeetthepredeterminedrequirements.2、EDM与传统加工方法的差异1）electrodedoesnotmakephysicalcontactwiththeworkpieceformaterialremoval.2）EDMhasnotoolforce.3）electrodemustalwaysbespacedawayfromtheworkpiecebythedistancerequiredforsparking,knownasthesparkinggap.4）onlyonesparkoccursatanyinstant.(exceptforHSWEDM)(frequencyrangefrom2,000to500,000sparkspersecond)3、绝缘工作液（dielectricmaterialordielectricfluid）1）、EDMisathermalprocess;materialisremovedbyheat.2）、wherethesparkoriginatesandterminates,areheatedtothepointwherethematerialvaporizes.3）、Thisdielectricmaterialisnormallyafluid.4）、Die-sinkertypeEDMmachinesusuallyusehydrocarbonoil,whilewire-cutEDM(LSWEDM)machinesnormallyusedeionizedwater.4、绝缘工作液的主要特点（maincharacteristicofdielectricfluid）1）、Controllingthesparking-gapspacingbetweentheelectrodeandworkpieceasaninsulator;2）、CoolingtheheatedmaterialtoformtheEDMchip;3）、RemovingEDMchipsfromthesparkingarea;4）、Compressdischargechannel&causeexplosioninchannel.5、电火花加工的必要条件（necessaryconditionsforEDM）1）、Sparkgap2）、Dielectricfluid3）、Powerfulpulsepower4）、Sparkontimeisveryshort5）、Enoughsparkofftime6、EDM的发展历史EDMoriginatedfromtheneedtoperformmachiningoperationsondifficulttomachinemetals.TheprocesswasdevelopedalmostsimultaneouslyintheUSSRandtheUSAatthebeginningofWorldWarII.In1943，theFirstEDMIntheWorldIn1943,theLazarenkosdevelopedasparkmachiningprocesswithanelectricalcircuitthatusedmanyofthesamecomponentsastheautomobileignitionsystem.ThisprocessbecameoneofthestandardEDMsystemsinusethroughouttheworld.SincetheLazarenkoEDMsystemusedresistorsandcapacitors,itbecameknownasaresistor-capacitor(R-C)circuitforEDM.7、WEDM机床的的发展历史约在1960年,前苏联的科学院中央电工实验室,首先研制出第一台低速走丝靠模仿形电火花线切割机床,以后二三年中,从靠模仿形又发展到光电跟踪,1962年前后瑞士阿奇公司开始研究电火花线切割加工的数字控制技术,但在五六年后才达到实用化程度。我国科学院电子研究所1964年研制出光电跟踪线切割机床,这又是思维和技术上的一次飞跃。可较大地提高工作效率、缩短制造周期和降低加工成本,增加了切割更复杂型面的可能性,提高了工艺的适应性和“柔性”。由于第一代线切割机床的丝速很低,在煤油工作液中切缝较窄,排屑不畅,所切割速度很低,只有2～5mm2/min,且电极丝一次性使用也很浪费。上海电表厂张维良工程师对此作了创新性改进,在阳极机械切割工艺和机床的基础上,采用了往复、高速走丝和水基工作液(乳化液),使切割速度成倍、数十倍提高(大于10mm2/min),且可进行大厚度切割。此后上海机床电器厂又和复旦大学数学系联合研制出线切割简易数控系统,后经用户、生产厂、科研院所、高校等的技术工人和科技人员多方面改进和完善,形成了具有我国自主知识产权和中国特色的数控高速走丝电火花线切割机床品种。Thefirstmajoreventintheevolutionofwire-cutEDMwasnumericalcontrol(NC)in1960s.In1967,awire-cutEDMmachineproducedintheUSSRwasdisplayedatamachineexpositioninMontreal,Quebec,Canada.Thismachinefeaturednumericalcontrolwithpositioningbysteppingmotors.TheUSSRwire-cutEDMmachinewasprobablythefirstcommerciallyavailableunittobemarketed.8、电火花与线切割的比较(comparisonofdie-sinkerandwire-cutmachines)Bothdie-sinkerandwire-cutEDMmachinesusesparkstoremoveelectricallyconductivematerial.Butwhilebothtypesareelectricaldischargemachines,therearedifferencesintheiruseandoperation.Dielectricfluid:die-sinkerEDMmachinesusehydrocarbonoilandsubmergetheworkpieceandsparkinthefluid;wire-cutEDMmachinesnormallyusedeionizedwaterandcontainonlythesparkingareainthefluid.Applications：die-sinkerEDMmachinesarenormallyusedforproducingthree-dimensionalshapes;wire-cutEDMmachinesarealwaysusedforthroughholemachining,sincetheelectrodewiremustpassthroughtheworkpiecebeingmachined.Sparking:die-sinkermachinesproducesparksthaoccurbetweentheelectrodeendandtheworkpiece.wire-cutmachinesproducesparksthatoccurbetweentheelectrode-sidesurfaceandtheworkpiece.9、EDM的部件以及EDM与WEDM两者之间的差异（缺）Ofthemajorassembliesrequiredtocompletethedie-sinkerandwire-cutEDMmachinesystems,theonlycomparableitemisthepowersupply.Themachinetool,dielectricunit,servocontrol,andCNC-controlassembliesforthetwomachineshavedifferentrequirementsandmustbeevaluatedseparately.ThreeMajorAssembliesAretheMachineTool,PowerSupply,andDielectricUnit.10、电离的解释ExplanationofIonization1）Electricityflowsbetweentheelectrodeandtheworkpiecethroughtheionizeddielectricfluid.2）Afterionizationofthedielectricfluid,electricitycontinuestoflowthroughthefluiduntilthepoweristurnedOFF.3）OnceOFF,thedielectricfluiddeionizesandthefluid,again,becomesanelectricalinsulator.4）WhileEDMmachiningisinprogress,dielectricfluidionizationanddeionizationtakesplacethousandsoftimeseachsecond.11、放电的四个过程MicrocosmicProcessofDischarge1）Dielectricfluidionizesandchangesfromanelectricalinsulatorintoanelectricalconductor;2）Energytransferandtransmit;3）Electrodematerialremoval;4）Dielectricfluiddeionizationandcomebackinsulator.12、极性效应PolarityEffectPolarityeffect：thephenomenathatdifferentpositiveandnegativepolarityleadtodifferentelectricalcorrosionamount.Generally,whentheworkpieceisconnectedtothepositiveelectrodeofthepulsepowersupply,themachiningisdefinedas“positivepolaritymachining”,whereaswhentheworkpieceisconnectedtothenegativeelectrodeofthepulsepowersupply,themachining(toolelectrodeisconnectedtothepositiveelectrode)isdefinedas“negativepolaritymachining”.Duringthesparkdischarge,surfacesofthepositiveelectrodeandthenegativeelectrodearerespectivelybombardedandinstantlyheatedbythenegativee