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CUTTING

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CUTTING

    CUTTING

    CHINESEJ0URNAL0FMECHANICALENGINEERING

    Vo1.21,No.5,2008?41?

    DOI:10.3901/CJME.2008.05.041,availableonlineatwww.cjmenet.com;www.cjmenet.com.cn

    LIUZhidong

    JiangsuProvinciaIKeyLaborato~of

    PrecisionandMicro-Manufacturing

    Technology,

    NanjingUniversityofAeronautics

    andAstronautics,

    Nanjing210016,China

    0INTRoDUCTIoN

    CUTTINGREGULARITYAND

    DISCHARGECHARACTERISTICS

    BYUSINGCOMPOSITECOOLING

    LIQUIDlNWIRECUTELECTRICAL

    DISCHARGEMACHINEWITHHIGH

    WIRETELINGSPEED

    Abstract:Theanalysisofcuttingregularityisprovidedthroughusingandcomparingtwotypical

    coolingliquids.Itisprovedthatcuttingregularityisgreatlyaffectedbycoolingliquid'swashing

    ability.Dischargecharacteristicsandtheoreticanalysisbetweentwoelectrodesarealsodiscussed

    basedondischargewaveform.Byusingcompositecoolingliquidwhichhasstrongwashingability,

    theefficiencyinthefirststablecuttingphasehasreachedmorethan200mmz/min,andtheroughness

    ofthesatfacehasreachedR<0.8

    afterthefourthcuttingwithmorethan50mm2/rainaverage

    cuttingefficiency.Itispointedoutthatcuttingsituationofthewirecutelectrica1dischargemachine

    wimhighwiretravelingspeed(HSWEDM)isbetterthanthewirecutelectricaldischargemachine

    with1owwiretravelingspeed(LSWEDM)intheconditionofimprovingthecoolingliquidwashing

    abiIity.ThemachiningindicesOfHSWEDMwil1beincreasedremarkablybyusingthecomposite

    coolingliquid.

    Keywords:Wirecutelectrica1dischargemachinewithhighwiretravelingspeed Compositecc~ing~iquidD~,sehargeckaracter~stieCuttingregutarity Thewirecutelectricaldischargemachinewithhiwire

    travelingspeedrHSWEDM1iswidelyusedinChina.AllOfthe

    HSWEDMmachinesinChinausedtouseakindofspecial

    emulsifiedoilascoolingliquidwhichisverydifferentfromthe

    liquidusedinthewirecutelectricaldischargemachinewithlow

    wiretravelingspeed(LSWEDM).Inthepast30years,the

    researchaboutthecuttingregularityonHSWEDMwasallbased

    onusingthiskindofliquid.Theresearchshowsthatbyusing

    thiskindofemulsifiedoi1.HSWEDMtechnologycannotreach

    theexpectedcuttingefficiencyandcuttingsurfacequality,andit alsolimitsthecuttingthicknessandproducesenvironment

    pollution.Theresearchhastriedtoreplacetheemulsifiedoil

    whichhasoi1inthecomponentswithwater.basedcoolingliquid

    whichhasnooi1inthecomponents.Byusingthewater.based

    coolingliquid.theprocessindicesofcutting.suchasthecutting

    efficiency,surfacequalityandthecuttingthickness,havebeen improvedtoacertainextent.Butthiskindofwater.based coolingliquidcallnotbewidelyusedintheproductionsinceit willcaRsetherustonthemachine,andgeneratealotoffoam whilecutting,makethecleaningofthemachinedifficult,and willfadethepaintofthemachine.Also.alltheresearch experimentsoncomparingtheemulsifiedoilcoolingliquidand water.basedcoolingliquidaredoneunderlowercuttingenergy whichusuallyusethecuttingcurrentlessthan3A.The experimentdoesnotshowremar

    

    kableimprovementofthe

    processindicesoftheHSWEDML.Themaximumcutting efficiencyinthefirstcuttingphaseofLSWEDMhasachieved about500mm2/minandthepracticalcuttingefficiencyisabout 15OrnlTl/minatpresentL.butthemaximumcuttingefficiencyin thefirstcuttingphaseOfHSWEDMlingeredatabout60-80 rrLm/minsincel980's.Thedifferenceisveryobviousandsome technologiessuchasmulti.cuttingtechnologycannotbe ThisprojectissupposedbyProvincialKeyLaboratoryofPrecisionand MicroManufacturingTechnologyofJiangsu,China(No.Z060105202).

    ReceivedOctober24,2007;receivedinrevisedformJuly2,2008; acceptedJuly15,2008

    generallyusedinHSWEDMforimprovingtheprocessindices owingtotheunstableconditioninthedischargegapForthe purposeofimprovingthecuttingefficiencyandqualiitisvery importanttoanalyzethecoolingsituationindischargegapand systematicallystudytheprocessingregularityofHSWEDM.The researchshowsthatthegoalcanbereachedwithaninnovative byadoptingnewcoolingliquid.

1EXPERIMENTALCoNDITIoN

    Theexperimentstudiestheinfluenceofcoolingliquidon cuttingregularitybycomparingtwotypicalcoolingliquids.DX isakindofwidelyusedemulsifiedoilatpresent.AndJR1Aisa newcompositecoolingliquid.Differentcuttingsurfacefeatures withthesetwocoolingliquidsareshownonTable1.

    Table1Cuttingsurfacefeaturesafterusing

    differentcooBngliquids

    Cuttingconditions:Crl2,quenched,comparecuttingfeaturesunder conditionsofdifferentworkpiecethicknessandmachiningparameter 2ANALYSlSOFELECTRICALDISCHARGE

    CHARACTEIUSTlCS

    Beforethecompositecooling1iquidwasinvented.mostof theHSWEDMmachinesuseemulsion.whichismixedthe

    emulsifiedoilwithwaterwithratioabout1/10tO1/12.The componentsofemulsifiedoilandcompositecoolingliquidare showninTable2.Thestudyshowsthattheheattransfer coefficientofemulsionismuchlowerthanthatofcomposite coolingliquid.andalargeamountsofpolymerhydrocarbon ?42?

    LIUZhidong:Cuttingregularityanddishargecharacteristicbyusingcompositecoolingliqui

    dinwirecutelectrical

    dischargemachinewithhighwiretravelingspeed

    (machineoil.rosin,etc)willbegeneratedasverystickycolloidal materialwhichmightalsoincludealotofsolidparticle(shown inFig.11athighdischargetemperaturef>10000?)tmlinthe

    processofelectricaldischargemachining.Thestickymaterial willreducethecoolingeffectuponwireelecodeandevenmore

    itmightcauseaconaryeffectbyformingathermal-insulation aroundthewireelectrode,atthesametime,thestickymaterial

    wil1alsoblockfreshcoolingliquidfromenteringintothe dischargegaD.Thestudyalsodiscoveredthattheenduring abi1it,,fordischargeenergyofwireelectrodewilldecrease remarkablybyusingtheemulsionascoolingliquid.Undersuch coolingcondition.itbecomesverydimculttoimprovecutting efficiencybyincreasingcuttingenergyoradjustingdischarge wave:forlT1.

    Table2Componentsofemulsifiedoilandcompositecoolingliquid EmulsifiedoilCompositecoolingliquid

    Emulsifiedoilusingratio:emulsifiedoil/waterequals1/10to1/12; Compositecoolingliquidusingratio:liquid/waterequals1/I5to1/20 Thi

    and

    Fig1Gapsituationwithpoorwashingability

    Becauseerosionparticlesaredistributedinthedischarge gapunequallyandtherearelotsoferosionparticlesstayatthe exitofiointwhichblockthewireelectrodeatthisareatobe cooledandhencethepossibilityofwireelectrodebreakagenear exitregionisincreasedwhenthelargedischargeenergyisused inthecutting.

    However,Byusingcompositecoolingliquidcontaining fewerofoilascoolingfluid,thestabilityofcutting,theabilityof cuttingthickness,theprobabilityofwireelectrodeundamaged,

    andthecuttingsurfacequalitywillbeimprovedsignificantlyand thewearofwireismuchlowerthanusingemulsionascooling fluid.Thereasonistheerosionparticlesingapwillbemuchless whenthecompositecoolingliquidisused.Thecoolingliquid doesnotproducealargeamountofpolymercolloidalmaterial fshowninFig.2).Meanwhile,thecoolingliquidthatgenerates

hvaloidsmicroemulsionhasagoodabilityofwashingand

    osmosis,anditcontainsmoresurfactantassistedcomponentsto

    helpremovingtheerosionparticlesmoreeasily.Thespecial vegetableoi1usedinthecompositecoolingliquidformsalayer ofliquidprotectivefilmwhichactas"bulletproofvest''L"onthe wiresurface.Theprotectivefilmwil1volatileitselffirstwhenit iSbombedbycationsinordertoprotectthewire.Thedetected dischargewaveformshowsthatthewaveformofHSWEDMis similartothatofelectricaldischargemachining(EDM)byusing wellwashingabi1itycoolingliquid.Thewaveformwiththe characteristicsofthedischargebreakdownisdelayed.Fig.3a andFig.3bcomparedthedischargewaveformsbyusingDX emulsifiedoiland1Acompositecoolingliquid.Thefigures

    showthatthecharacteristicsofdischargebreakdownaredelayed insomedegreewhenJR1Acompositecoolingliquidisused. Sincethewirecanbecooleddownmoreevenlyandcompletely whileitisinthecuttinggaD,andmorepowerfuldischarge energycanbeusedwhencompositecoolingliquidisused.Inthe researchexperiment.wenoticethatbyusingthecoolingliquid whichhasbeRerwashingabilltyandproducelessstickcolloidal materia1.thecuttingefficiencyinHSWEDMcanbeimproved remarkably.

    l?U

    Fig.2Gapsituationwithwellwashingability

    ;l,.喜墨.

    Timet/ixs

    (a)UsingDX

    Timet/lxs

    (b)UsingJR1A

    Fig.3Waveformofcutting165rfmlworklcIiece

    Thedelayeddischargebreakdowncanbeviewedasoneof characterizationsthattheinter.electrodeofHSWEDMisingood washingcondition.Thedelayeddischargebreakdownindicates thatthetwoelectrodesareatgapstatetoacertainextent.Since thewireelectrodeinHSWEDMisrunningatveryhightraveling speedwhichwillcauseobviousvibration,itisalmostimpossible tokeepaverygoodgapstatusasextremelystabledischarge breakdowndelayedphenomenonasEDM.However,ifthe coolingliquidhasbetterwashingabilitytocleanthecuttinggap, thetendencyof2apmachiningwillbemoreobviously. Theanalysisoftheexperimentshowsthattheinter

    electrodeofHSWEDMisinverybadconditionwhenemulsion isused.Owingtothepoorcoolingcondition,onlylowcutting energycanbeusedinHSWEDMinordertoavoidthebreakage ofwireelectrode.andlesseffectisachievedinHSWEDMby improvingpulsepowerandwiretravelingsystemwhenthe cuttingemciencyistriedt0beimproved.Thisisoneofthemain reasonsthatHSWEDMcuttingindiceshavebeenlingeredata verylowlevelforalongtime.

    3MACHININGREGULAIUTY

    3.1Efleetonthecuttingefficiency

    Thehighcuttingefficiencyisthemostimportantaimfor WEDM.Thecuttingefficiencybyusingthetwokindsofcooling liquidsshowsdistinguishingdifference,theregularityofcutting efficiencywiththeincreasingofaveragecuttingcurrentisshown inFig.4whencutting60mlTlthicknessCr12stee1.

    CHINESEJOURNALOFMECHANICALENGINEERING?43?

    5

    Machiningcurrent//A

    Fig.4Relationbetweencuttingcurrentandefficiency

    FromFig.4wecanfindthatthecuttingefficiencyisno longertoincreasewhenthecuttingenergyincreasedtoacertain degreebyusingDXemulsifiedoil.Thereasonisthesituationof coolinginthecuttinggaDisworsenedandtheerosionproduction isnotabletoberemovedfromthegappromptlyL"J.However,by usingcompositecoolingliquidwithbetterwashingability.the cuttingefnciencyincreasesalongwithdischargeenergyalmost inalineardirection.Also.comparedwiththeDXemulsifiedoil. thedifferenceintheaspectofcuttingefciencybecomes

    significantwhenthedischargeenergyincreases.

    3.2Effectonthequalityofcattingsurfaee

    Theinfluenceonthecuttingsurfacequalitycausedby differentcoolingliquidsismainlydeterminedbythesize.depth andtheedgesituationofelectricaldischargecrater.Theprimary factoractingontheedgesituationofcrateriswhethererosion productioncouldbepromptlycarriedawaybyliquidafter elecicaldischarge.Thecoolingliquidwithbetterwashing abilitycankeepthe1iquidflowinginthegapthenmakethe electricdischargesurfacetogetunceasinglywashingandcooling, evenifenergyoftheelectricdischargeisveryhuge,thecutting surfaceisstillmaintainedquitesmoothly(showninFig.5a). Butwimthepoorwashingabilityliquid.underthesimilar curingparameters.thecuttingsurfaceisrough.Becauseofpoor washingabi1itytheerosionparticleaswellasthecarbidewhich formedbytheemulsioncannotbecarriedawaypromptlyby cooling1iquid.Theparticleremainedingapandstuckinthe cuttingsurfacewhichwillformanenvironmentofmixed,sticky 1iquid,andsometime,evenlikeajellyforthe1aterdischarge. Thekindofenvironmentwillnotbeabletocoolthecuring

surfacecompletely,andtheelecicdischargewil1bumthe

    curingsurfaceseriously.Thiscausesmassiveburnonthecuring surfaceanddegradestheintegrityofworkpiecesurface(shown inFig.5b).

    (a)UsingJR1A

    (b)UsingDX

    Fig.5Cuttingsurfaceappearance

    withdifferentworkingliquid

    3.3Effectonthecuttingthickness

    Thecomparisonoftherelationshipbetweencutting eciencyandthicknessbyusingtwokindsofcoolingliquids underthesameelecicalparameterisshowninFig.6.Fromthe figure,wecanfindthatthetopofthecuttingefficiencyisinthe region0f150-200i/IrathicknessusingJRlA.meanwhile.by usingDXemulsifiedoilthetopeffectiveregionisinlessthan75 rnrnarea西encuringthicknessexceedsthisregionbecauseof thedecreasingofwashingabilithecuringeciencywill

    graduallydrop.Ifthecuringicknessexceeds10O1TIITI.the

    decreasingofcuttingefficiencywillbecomemoreremarkably andwhenthecuttingthicknessexceedsover350mm,thecuring stabilitytendsworse.Thereareobviousdifferentindetected waveformsfromthememoryoscilloscopewhencuttinghigh thicknessworkpiecebyusingdifferentcooling1iquids.Using DXemulsifiedoil,thewaveformiumpsbetweentheopen.circuit toshort.circuitmorefrequently(showninFig.7a).Thismeans thedischargeisunderthenonstableprocessingsituation.This

    situationwillbecomemorestablyusingJR1Aasthecooling liquid(showninFig.7b).Itisobviousthatthecuringefficiency, theregionofhighestcuttingefficiencyandthecuttingstability ofthethickworkpieceareaffectedseriouslybythecooling

    1iquid'swashingability.Thecooling1iquidwithpowerful washingabilityshouldhavethecharacteristicsthattheCutting emciencywon'tberemarkablydecreasedwhenthethicknessof theworkpieceisincreased.

    l

    

    

    

    050150250350450550

    Thicknessofworkpiece///mm

    Fig.6Relationbetweenthicknessandefficiency .

    lU

    Timet/us

    fa1UsingDX

    l?u

    0

    Timet/gs

    (b)UsingJRIA

    Fig.7Waveformofcutting410rniTlworkpiece

    3.4Effectofthewiretravelingspeedonthecutting efficiency

    ThetravelingspeedofwireinHSWEDMwasgenerally consideredtobehigherthan8m/s.Lowerspeedwillseriously affectthecuttingeciencyandcuringstability,aswirecannot besufficientlycooleddowningap.thusincreasingthe probabilltyofwirebreaking.ThisconclusioniSsuitableforthe coolingliquidasemulsion.Theexperimentshowsthat.byusing thecompositecoolingliquidwhichhasmorepowerfu1washing abi1itthetravelingspeedofthewiremayactuallybedecreased

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