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１[英文资料].SawingSawingisthepartingofmaterialbyusingmetaldisks,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,２certainplastics,andhardrubberarecutbythismethod.Cuttingisdonebytheabrasiveactionofthegritinthedisk.Abrasivedisksareoperatedeitherwetordry.Forheavycuttingacoolingagentisgenerallyused.Theworkpieceisfirmlyheldwhilethewheeltraversesthroughit.Machinesaremadeinmanuallyoperatedandautomaticmodels.DrillingHolesareoneofthemostcommonfeaturesinproductsmanufacturedtoday.There-fore,drillingandotherrelatedprocessesandtoolsareextremelyimportant.Holesassmallas0.005in.maybedrilledusingspecialtechniques.Ontheotherhand,holeslargerthan2to221in.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,３drillpointanglesoflessthan118ºareused,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.４ReamingReamingisamachiningprocessforenlarging,smoothingand/oraccuratelysizingexistingholesbymeansofmeansofmultiedgeflutedcuttingtools(reamers).Asthereamersand/orworkpieceisrotatedandadvancedrelativetoeachother,chipsareproducedtoremoverelativelysmallamountsofmaterialfromtheholewall.Reamingmaybeperformedonthesametypeofmachinesusedfordrilling.Accuracyoftheholeandqualityoffinishproducedbyreamingdependsprimarilyupontheconditionofthestartingbole,rigidityofthemachineandfixture,correctspeedsandfeeds,asuitableandproperlyappliedcuttingfluid,andpreciseresharpeningofdulltools.Sincestockremovalissmallandmustbeuniforminreaming,thestartingholes(drilledorotherwiseproduced)musthaverelativelygoodroundness,straightness,andfinish.Reamerstendtofollowtheexistingcenterlineoftheholebeingreamed,andinlimitedinstancesitmaybenecessarytoboretheholespriortoreamingtomaintainrequiredtolerances.Withtheproperconditionsandoperatingparameters,reamingcanproduceclosetolerancesandsmoothfinishes.ReamersAreamerisarotarycuttingtool,generallyofcylindricalorconicalshape,intendedforenlargingandfinishingholestoaccuratedimensions.Itisusuallyequippedwithtwoormoreperipheralchannelsorflutes,eitherparalleltoitsaxisorinaright–orleft-handhelixasrequired.Thosewithhelicalflutesprovidesmoothshearcutting,arelesssubjecttochatter,andproduceabetterfinish.Theflutesformcuttingteethandprovidechannelsforremovingthechips.KindsofReamersReamersaremadeinmanydifferentforms,includingsolidandinserted-bladetypes,adjustableandnonadjustable；theyareavailableforeithermanualoperation(handreamers)orformachineuse(chuckingreamers).Materialsfromwhichcuttingelementsofmostproductionreamersaremadeincludehigh-speedsteelandcementedcarbides.ofmostproductionreamersaremadeincludehigh-speedsteelandcementedcarbides.CarbidereamersThesetoolsarebeingusedincreasinglybecauseoftheirlingerlife,improvedaccuracy,andresistance.BorereamersThesetoolscombineboringandreaminginasingleoperationtominimizeproblemswithrespecttoholesize,straightness,andfinish.Single-pointborereamers,foruseinapplicationsforwhichguidebushingscanbeused,haveasingle-pointcuttingedgeontheendofthetool,followedbyareamingsection.Multipointborereamersareavailableforapplicationsforapplicationsforwhichbushingscannotbeused.

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