机械毕业设计英文外文翻译279锯削Word格式.docx

机械毕业设计英文外文翻译279锯削Word格式.docx

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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,whicharedefinedbyahelixanglethatisgenerallyabout30º

butcanvarydependingonthematerialpropertiesoftheworkpiece.Thepointofthedrill（seeFig.12-3）generallyforma118º

angleandincludesa10clearanceangleandchiseledge.Thechiseledgeisflatwithawebthicknessofapproximately0.015*drilldiameter.Thisedgecancauseproblemsinholelocationowingtoitsabilityto“walk”onasurfacebeforeengagingtheworkpiece.Inthecaseofbrittlematerials,drillpointanglesoflessthan118º

areused,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