机械毕业设计英文外文翻译279锯削.docx
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机械毕业设计英文外文翻译279锯削
[英文资料]
.Sawing
Sawingisthepartingofmaterialbyusingmetaldisks,blades,bands,orabrasivedisksasthecuttingtools.Sawingapiecefromstockforfurthermachiningiscalledcutoffsawing,whileshapingofformingapieceisreferredtoascontoursawing.
Machinesawingofmetalisperformedbyfivetypesofsawsorprocesses:
hacksawing,babdsawing,coldsawing,frictionsawing,andabrasivesawing.
Hacksawsareusedprincipallyascutofftools.Thetoothedblade,heldintension,isreciprocatedacrosstheworkpiece.Aviseholdsthestockinposition.Thebladeisfedintotheworkbygravityorspring.Sometimesamechanicalorhydraulicfeedisused.Automaticmachines,handlingbar-lengthstock,areusedforcontinuousproduction.
Bandsawscutrapidlyandaresuitedforeithercutofforcontoursawing.Theplaneinwhichthebladeoperatesclassifiesthemachineasbeingeitherverticalorhorizontal.Bandsawsarebasicallyaflexibleendlessbandofsteelrunningoverpulleysorwheels.Thebandhasteethononesideandisoperatedundertension.Guideskeepitrunningtrue.Theframeofthehorizontaltypeispivotedtoallowpositioningoftheworkpieceinthevise.Horizontalmachinesareusedforeitherstraightorangularcuts.Atablethatsupportstheworkpieceandthewidethroatbetweentheuprightportionsoftheblademakestheverticalbandsawidealforcontourwork.Bandsawsoperatingathighspeedarefrequentlyusedasfrictionsaws.
Coldsawingisprincipallyacutoffoperation.Thebladeisacirculardiskwithcuttingteethonitsperiphery.Bladesrangeinsizefromafewinchestoseveralfeetindiameter.Thecuttingteethmaybecutintotheperipheryofthediskortheymaybeinsertsofahardermaterial.Theblademovesintothestockwithapositivefeed.Stockispositionedmanuallyinsomecold-sawingmachines,whileothermodelsareequippedforautomaticcyclesawing.
Frictionsawingisarapidprocessusedtocutsteelaswellascertainplastics.Thisprocessisnotsatisfactoryforcastironandnonferrousmetals.Cuttingisdoneasthehigh-speedbladewipesthemetalfromthekerfaftersofteningitwithfrictionalheat.Circularalloy-steelbladesperformcutoffwork,thilefrictionalbandsawsdobothcutoffandcontoursawing.Circularbladesarefrequentlycooledbywaterorair.Circularbladesareadcancedintothework,thilethickwork-piecesrequirepower-tablefeedthenfriction-cutonabandsaw.
Abrasivesawingisacutoffprocessusingthinrubberorbakelitebondedabrasivedisks.Inadditiontosteel,othermaterialssuchasnonferrousmetals,ceramics,glass,certainplastics,andhardrubberarecutbythismethod.Cuttingisdonebytheabrasiveactionofthegritinthedisk.
Abrasivedisksareoperatedeitherwetordry.Forheavycuttingacoolingagentisgenerallyused.Theworkpieceisfirmlyheldwhilethewheeltraversesthroughit.Machinesaremadeinmanuallyoperatedandautomaticmodels.
Drilling
Holesareoneofthemostcommonfeaturesinproductsmanufacturedtoday.There-fore,drillingandotherrelatedprocessesandtoolsareextremelyimportant.Holesassmallas0.005in.maybedrilledusingspecialtechniques.Ontheotherhand,holeslargerthan2to2
in.indiameterareseldomdrilled,becauseotherprocessesandtechniquesarelessexpensive.
Thetwistdrill(showninFig.12-3)isthemostcommontypeofdrill.Theshankofthedrillisheldbythemachinetool,whichinturnimpartsanrotarymotion.Thisshankofthedrillisheldbythemachinetool.Whichinturnimpartsarotarymotion.Thisshankmaybestraightortapered.Thebodyofthedrillistypicallymadeupoftwospiralgroovesknownasflutes,whicharedefinedbyahelixanglethatisgenerallyabout30ºbutcanvarydependingonthematerialpropertiesoftheworkpiece.Thepointofthedrill(seeFig.12-3)generallyforma118ºangleandincludesa10clearanceangleandchiseledge.Thechiseledgeisflatwithawebthicknessofapproximately0.015*drilldiameter.Thisedgecancauseproblemsinholelocationowingtoitsabilityto“walk”onasurfacebeforeengagingtheworkpiece.Inthecaseofbrittlematerials,drillpointanglesoflessthan118ºareused,whileductilematerialsuselargerpointsanglesandsmallerclearanceangles.
Complexholeconfigurationsmayoftenbecalledfor;theseincludemultiplediameters,chamfers,countersinks,andcombinationsofthese,asillustratedinFig.12-4.Ineachofthesecasesinispossibletomakespecialcombinationdrillsthatcanproducetheconfigurationsshowninasingleoperation.Althoughexpensive,theycanbeeconomicallyjustifiedforsufficientvolume.
Theflatchiseledge,whichcan“walk”onthesurfaceoftheworkpiece,andthelong,slendershaftandbodyofthetwistdrill,whichcandeflect,makeitdifficulttomachineholestotighttolerances.Acombinationcenterdrillandcountersinkcanbeusedtoaccuratelystartahole,owingtoitssmallwebthicknessanditstendencytodeflectonlyverysmallamounts(becauseofarelativelylargediameter-to-lengthratio).Truingoftheholetomakeitstraightisaccomplishedbyboring.Reamingtheholeprovidesabetterfinishaswellasmoreaccuratesizing.
Thefeedrateofadrillisnormallyproportionaltoitsdiameter,becauseitdependsonthevolumeofchipstheflutescanhandle.Howeverthefeedisindependentofthecuttingspeed,whichisafunctionofthetool-workcombination.Aruleofthumbwouldgiveafeedrateasapproximatelyd/65,sothata3/4-in.-diameterdrillwouldhaveafeedrateofabout0.012in./rev.Althoughtheholewalltendstosupportthedrillwhentheholedepthexceedsthreetimesthedrilldiameter,thereisatendencyforbucklingtooccurandthefeedrateshouldbereduced.
Mostdrillsaremadefromhigh–speedsteelbecauseofitsrelativelylowcostandeaseofmanufacture.Sometypesofcarbidedrillsarenowavailablecommercially.Thedemandsofnumericallycontrolledmachinetoolshaveledtothedevelopmentofdrillsthatwillproduceporepreciseholesandthatwilloriginateaholeinlinewiththecenterlineofthedrill-pressspindle.Drillsthathaveheavierwebs,lessstickout,doublemargins,andaregroundwithaspiralpointhelpmeetthesenewdemands.
Reaming
Reamingisamachiningprocessforenlarging,smoothingand/oraccuratelysizingexistingholesbymeansofmeansofmultiedgeflutedcuttingtools(reamers).Asthereamersand/orworkpieceisrotatedandadvancedrelativetoeachother,chipsareproducedtoremoverelativelysmallamountsofmaterialfromtheholewall.Reamingmaybeperformedonthesametypeofmachinesusedfordrilling.
Accuracyoftheholeandqualityoffinishproducedbyreamingdependsprimarilyupontheconditionofthestartingbole,rigidityofthemachineandfixture,correctspeedsandfeeds,asuitableandproperlyappliedcuttingfluid,andpreciseresharpeningofdulltools.
Sincestockremovalissmallandmustbeuniforminreaming,thestartingholes(drilledorotherwiseproduced)musthaverelativelygoodroundness,straightness,andfinish.Reamerstendtofollowtheexistingcenterlineoftheholebeingreamed,andinlimitedinstancesitmaybenecessarytoboretheholespriortoreamingtomaintainrequiredtolerances.Withtheproperconditionsandoperatingparameters,reamingcanproduceclosetolerancesandsmoothfinishes.
Reamers
Areamerisarotarycuttingtool,generallyofcylindricalorconicalshape,intendedforenlargingandfinishingholestoaccuratedimensions.Itisusuallyequippedwithtwoormoreperipheralchannelsorflutes,eitherparalleltoitsaxisorinaright–orleft-handhelixasrequired.Thosewithhelicalflutesprovidesmoothshearcutting,arelesssubjecttochatter,andproduceabetterfinish.Theflutesformcuttingteethandprovidechannelsforremovingthechips.
KindsofReamers
Reamersaremadeinmanydifferentforms,includingsolidandinserted-bladetypes,adjustableandnonadjustable;theyareavailableforeithermanualoperation(handreamers)orformachineuse(chuckingreamers).Materialsfromwhichcuttingelementsofmostproductionreamersaremadeincludehigh-speedsteelandcementedcarbides.ofmostproductionreamersaremadeincludehigh-speedsteelandcementedcarbides.
CarbidereamersThesetoolsarebeingusedincreasinglybecauseoftheirlingerlife,improvedaccuracy,andresistance.
BorereamersThesetoolscombineboringandreaminginasingleoperationtominimizeproblemswithrespecttoholesize,straightness,andfinish.Single-pointborereamers,foruseinapplicationsforwhichguidebushingscanbeused,haveasingle-pointcuttingedgeontheendofthetool,followedbyareamingsection.Multipointborereamersareavailableforapplicationsforapplicationsforwhichbushingscannotbeused.
Coolant-fedreamersThesetools,havingmeans(usuallyinternalpassages)fordirectingcoolanttothecuttingedges,offeradvantagesforsomeapplications,particularlywhenreamingblindholes.Insuchapplications,reducedfrictionandtemperaturesatthereamer/workpieceinterfacedecreasewearandlengthentoollife.Insomecases,feedsandspeedscanbeincreasedandimprovedaccuraciesandsmootherfinishesobtained.Theinitialcostofcoolant-fedreamersishigher,butincreasedproductivityandimprovedqualityoftenmakethemeconomicallydesirable.
ReamerHolders/Drivers
Reamersarecommonlyheldanddrivenbythree-jawchucks,straightsleevesandsetscrews,and,fortapershanks,sleevesorsockets.Reamerswithadaptersforquick-changechucksareusedforproductionapplications.
Whenreamersmustguidethemselvesintopreviouslymadeholes,theyrequiregloating