数控机床外文翻译 刀具和刀夹.docx
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数控机床外文翻译 刀具和刀夹.docx
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数控机床外文翻译刀具和刀夹
CUTTINGTOOLSANDTOOLHOLDERS
Tomachineaworkpiecesuccessfullyyoumusthave:
1.thecorrectkindofcuttingtoolortoolbit
2.therighttypeoftoolholder
3.atoolwithasharpcutting-edge
4.thecuttingtoolsetoradjustedtothecorrectheightandposition.
Cutting-toolmaterials
Toolbitsusedonthelathearemadeformoneofsixbasicmaterials:
water-hardeningsteels,high-speedsteels,hard-cast,nonferrousalloys,sintered(cemented)carbides,ceramics,anddiamonds.Theselectionofthematerialuseddependsuponmanyfactorsincluding:
toolcost,sizeanddesignoftool,metal-removalrate,lengthofrun,finishandtoleranceofpart,andconditionandcapabilityofthemachinetool.Becauseofthesefactors,materialselectionismoreoftenbasedongeneralexperiencethanonpreciseevaluation.Thereare,however,certaingeneralcharacteristicsofthedifferentcutting-toolmaterialsyoushouldunderstand.
Water-hardeningSteels.Theseincludethehigh-carbontoolsteels(eitherplaincarbonorthosewithminoradditionsofchromium,vanadium,ortungsten).Thedifferentgradesofwater-hardeningtoolsteelsareclassedasWsteelsinAmericanIronandSteelInstitute’ssystemofclassification.Toolsmadefromthesematerialshaveverysharp,smoothcutting-edgeswhenproperlyheat-treated.Theyareadequateforlimitedturningatarelativelylowcuttingspeedorwhenold,low-speedequipment,suchasaflat-beltlathe,isused.
Themainlimitationoftoolsmadeformwater-hardeningsteelsisthattheysoftenifthecutting-edgetemperatureexceedsapproximately300-400Fduringsharpeningorcutting.Aseconddisadvantageislowresistancetoedgewear.
High-speedSteels.High-speedsteelsoffergreatimprovementincuttingefficiencyoverwater-hardeningtoolsteels.Toolsmadefromhigh-speedsteelsretainenoughhardnesstomachineatrapidratesevenwhenthetooltemperaturereaches1050F.Theycanbeusedeventhoughtheybecomedullredwithheat.Uponcoolingtoroomtemperature,theoriginalhardnessofthesesteelsdoesnotchange.
Wearresistanceofhigh-speedsteelsismuchbetterthanthatofthecarbonoralloysteels.Thisisduetothehighcarbidecontent,especiallyinthehigher-alloytypesofhigh-speedsteel.Fullyhardened,high-speedsteelshavegreaterresistancetoshockthancarbidesorhard-castalloys.
Therearetwomaintypesofhigh-speedsteelsdesignatedintheAmericanIronandSteelsInstitutesystem,Msteels(molybdenumbaseandTsteelstungstenbase.Toolbitsmadefromthesematerialscanbepurchasedalreadygroundtovariousshapes.Ungroundtoolbitscalledtool-bitblankscanalsobepurchased.Thesetool-bitblanksaremadeinstandardsizetofitthecommonlyusedlathes.Thecommonsizesare3/16insquareby1inlong,1/4insquareby2inlong,5/16insquareby2-1/2inlong,and3/8insquareby3inlong.High-speedsteeltoolbitsarethetypemostusedintheschoolmachineshop.
Hard-castAlloy.Thesematerialsdonotcontainsufficientirontobeclassedassteels.Rather,theyaremainlyalloysofcobalt,chromium,andtungstenwithotherelementsaddedforspecialpurpose.Theyreachfullhardnessintheas-castcondition,withoutheattreatment.Themustbegroundtosizeaftercasting.Intermsofresistancetoheat,wear,shock,andinitialcost,castalloysrankbetweenhigh-speedsteelsandcarbides.
Hard-castalloysareweakerintensionandmorebrittlethanhigh-speedsteelsandthusarenotsuitableforsevereshockloads.Theyareknownbysuchcommercialnamesasstellite,Rexalloy,andtantung.
SinteredCarbides.Forefficientandhigh-speedmachining,bestresultscanbeobtainedwithsinteredcarbidetools.Carbidetoolsareavailableinsolidformandasinsertswhichareeitherbrazedorclampedintoolholders.Clampedinsertsareusuallyround,square,ortriangularinshapeandhavealledgeisalwaysavailable.Theseinsertscanberotatedsothatasharpedgeisalwaysavailable.Withmodernmachinetoolsandthepropergradeofcementedcarbide,itispossibletousecuttingspeeds10to30timefasterthanthosefeasiblewithhigh-speedsteels.
Carbidesaresuitableformostmachiningoperationssuchassingle-pointturning,drilling,milling,threadcutting,andreaming.Carbidesshouldbeusedonlywhentheycanbesupportedrigidlyandwhenthemachinetoolhasadequatepowerandspeedtoenabletheirefficientuse.
Ceramic.Withtheexceptionofindustrialdiamonds,ceramicinsertsarethehardestandstrongestinsertsavailable.Theyresistabrasivewear,chipping,andbreakage.Theseinsertsworkbestonveryrigidmachinetoolsandonwell-supportedworkpieces.Formostoperations,cuttingfluidsarenotneeded.
Diamonds.Industrialdiamondsthathaveeithercircularorfacetedcutting-edgesareusedforlightfinishingcutswhenanextremelyhigh-qualitysurfacefinishrequired.Althoughaverysmoothfinishcanbeachievedusingothercutting-toolmaterials,diamondturningcanprovideevensmootherfinisheswithverysmalltolerances.
TOOLHOLDERS
Thetoolholderholdsthecuttingtoolrigidduringcuttingoperations.Fourtypesoftoolholdersareingeneraluse.
1.Thetoolpostwithstandardtoolholders.Thetooltoopostiscomprisedofthepost,screw,washer,collar,androcker.Thewasherfitsthetopslideepieceslot.Thecollarandtherockerelevateorlowerthepointoftoo.Thescrewclampsthetoolholderinplace.
Thestandardtoolholderforhigh-speedsteelcutterbitscomesinthreecommonshapes:
straight,right-handoffsetorshank,andleft-handoffsetorshank.Youcanidentifyright-handandleft-handoffsetholdersbyholdingthesetscrewendinyourhand.Iftheshankbendstotheright,itisaleft-handoffsetholder.
Thestraighttoolholderisfusedformostwork.Theleft-handtoolholderisusedwhenyouneedtocutclosetothechuckorlathedog.Theright-handholderisusedwhenfeedingtowardthetailstockofthelathe.Thecutting-toolbitisheldineachofthesetoolholdersatanangleof14to16.5degrees.Thisiscalledthetoolholderangle.
Carbidetoolholdersalsocomeinthreestylesandaresimilarinappearancetothosementionedabove.Theholeforthecutterbit,however,isparalleltothebottomedgeoftheholder.
2.Theopen-sideorheavy-dutytoolblockholdsonetoolatatimeandconsistsofaT-slotclamp,aC-shapedblock,andtwoormoretoolclampingscrews.Becausethisunitisveryrigid,itisespeciallyusefulforheavycuts.Atoolbitcanbemounteddirectlyinthetoolblockorsometypeofcarbidetooolholdercanbeused.
3.Theturrettoolblockorfour-waytoolholderconsistsofaswivelingblockinwhichthetoolsareclampedCommonturretblockholdfourtools.Eachcanbequicklyswiveledintocuttingpositionandclampedinplace.Someturretblockshaveeighttoolstations.Frequently,anopen-side-typetoolblockisalsomountedontherearofthecrossslidetoaddoneadditionalcuttingoperation.Withthisarrangement,anywhereformfivetoninedifferentkindsoftoolscanbemountedandoperatedinsequenceforturning,forming,facing,knurling,andcuttingoffduplicateparts.
4.Thequick-change-typetoolsystemholdsonlyonetoolatatime,butthreedifferentsidescanbeusedtopositionthetool.Itconsistsofaquick-changetoolpostwithaclampingleverandaseriesoftoolholdersforturning,facing,boring,cuttingoff,threading,knurling,andthreadcutting.
Single-pointCuttingTools
ToolParts.Beforeyoucangrindatoolbit,youmustbecomeacquaintedwithsomeofthetermsusedtodescribethevariouspartsofthecuttingtool.
1.Thefaceisthetopofthetoolbit.Itisthesurfaceonwhichapartofthechipattachesasitiscutawayformtheworkpiece.
2.Thecutting-edgeisthatpartofthecutterbitwhichactuallydoesthecutting.
3.Thenoseisthecornerorareformedbythesideandendcutting-edge.
4.Theflankisthesurfacebelowthecutting-edge.
5.Thepointisthepartofthetoolbitwhichisshapedtoformthecutting-edgeandface.
ToolAngles.Thefollowingareimportanttoolanglesusedforallsingle-pointcuttingtools.
1.Thesidereliefangleistheanglebetweenthegroundsurfaceandtheverticalsideofthetoolbitbeforeitisground.Thisanglewasformerlycalledsideclearance,andmanymachinistsstillusethisterm.Thesidereliefangleprovidesclearancebetweenthecutsurfaceoftheworkandtheflankoftool.Toolwearreducestheeffectivesideclearanceangle.Iftheangleistoosmall,thecutterwillrubandheat.Iftheangleistoolarge,thecutting-edgewillbeweakandthetoolwillhaveatendencytodigintotheworkpiece.
2.Theendreliefangleistheangleformedbetweentheendofthecutting-edgeandaverticalline.Itwasformerlycalledfrontclearance.Theendreliefangleprovidesclearancebetweenthefinishedsurfaceoftheworkandthetool.Ifthisangleistoosmall,thetoolwillrubonthefinishedsurfaceandproduceapoorfinish.Weartendstoreducethisangle.Iftheangleistoolarge,thetoolmaydigintothework,chatter,andfailthroughchipping.Anangleof8to15isrecommenedforsteeltoolsand6to8forcarbidetools.Ifthetoolissetabovethecenterofrotation,theeffectiveclearanceangleisreduce.Thismustbeconsideredinchoosingtheproperangle.
3.Theendcutting-edgeangleprovidesclearancebetweenthecutterandthefinishedsurfaceofthework.Ifthisangleistoosmall,itmaycausechatter.Asmallangleofabout6isdesirableonlightfinishingcuts,however,inordertoproduceasmoothfinish.
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