《機械工程專業(yè)英語》課件-機械工程專業(yè)英語課件-PART4

PART4MachiningToolsUnit16LathesUnit17DrillsandDrillingMachinesUnit18Milling,Shaper,PlanerandGrindingMachinesUnit19MachineToolTests,AccuracyCheckingandMaintenanceUnit20NontraditionalManufacturingProcessesUnit16LathesNewwordsandexpressionsUnit16LathesLathesaremachinetoolsdesignedprimarilytodoturning,facing,andboring.Verylittleturningisdoneonothertypesofmachinetools,andnonecandoitwithequalfacility.Becauselathesalsocandodrillingandreaming,theirversatilitypermitsseveraloperationstobedonewithasinglesetupoftheworkpiece.Consequently,morelathesofvarioustypesareusedinmanufacturingthananyothermachinetool.Theessentialcomponentsofalathearethebed,headstockassembly,tailstockassembly,carriageassembly,andtheleadscrewandfeedrod.Thebedisthebackboneofalathe.Itisusuallymadeofwell-normalizedoragedgrayornodularcastironandprovidesaheavy,rigidframeonwhichalltheotherbasiccomponentsaremounted.Twosetsofparallel,longitudinalways,innerorouter,arecontainedonthebed,usuallyontheupperside.SomemakersuseaninvertedV-shapeforallfourways,whereasothersutilizeoneinvertedVandoneflatwayinoneorbothsets.Theyareprecision-machinedtoassureaccuracyofalignment.Onmostmodernlathesthewaysaresurface-hardenedtoresistwearandabrasion,butprecautionshouldbetakeninoperatingalathetoassurethatthewaysarenotdamaged.Anyinaccuracyinthemusuallymeansthattheaccuracyoftheentirelatheisdestroyed.Theheadstockismountedinafixedpositionontheinnerways,usuallyattheleftendofthebed;itprovidesapoweredmeansofrotatingtheworkatvariousspeeds.Essentially,itconsistsofahollowspindle,mountedinaccuratebearings,andasetoftransmissiongears-similartoatrucktransmission-throughwhichthespindlecanberotatedatanumberofspeeds.Mostlathesprovideform8to18speeds,usuallyinageometricratio,andonmodernlathesallthespeedscanbeobtainedmerelybymovingfromtwotofourlevers.Anincreasingtrendistoprovideacontinuouslyvariablespeedrangethroughelectricalormechanicaldrives.Becausetheaccuracyofalatheisgreatlydependentonthespindle,itisofheavyconstructionandmountedinheavybearings,usuallypreloadedtaperedrollerorballtypes.Thespindlehasaholeextendingthroughitslength,throughwhichlongbarstockcanbefed.Thesizeofthisholeisanimportantdimensionofalathebecauseitdeterminesthemaximumsizeofbarstockthatcanbemachinedwhenthematerialmustbefedthroughspindle.Thetailstockassemblyconsists,essentially,ofthreeparts.Alowercastingfitsontheinnerwaysofthebedcanslidelongitudinallythereon,withameansforclampingtheentireassemblyinanydesiredlocation.Anuppercastingfitsontheloweroneandcanbemovedtransverselyuponit,onsometypeofkeyedways,topermitaligningthetailstockandheadstockspindles.Thethirdmajorcomponentoftheassemblyisthetailstockquill.Thisisahollowsteelcylinder,usuallyabout51to76mmindiameter,thatcanbemovedseveralincheslongitudinallyinandoutoftheuppercastingbymeansofahandwheelandscrew.Thesizeofalatheisdesignedbytwodimensions.Thefirstisknownastheswing.Thisisthemaximumdiameterofworkthatcanberotatedonalathe.Itisapproximatelytwicethedistancebetweenthelineconnectingthelathecentersandthenearestpointontheways.Thesecondsizedimensionisthemaximumdistancebetweencenters.Theswingthusindicatesthemaximumworkpiecediameterthatcanbeturnedinthelathe,whilethedistancebetweencentersindicatesthemaximumlengthofworkpiecethatcanbemountedbetweencenters.Enginelathesarethetypemostfrequentlyusedinmanufacturing.Theyareheavy-dutymachinetoolswithallthecomponentsdescribedpreviouslyandhavepowerdriveforalltoolmovementsexceptonthecompoundrest.Theycommonlyrangeinsizefrom305to610mm(12to24inches)swingandfrom610to1219mm(24to48inches)centerdistances,butswingsupto1270mm(50inches)andcenterdistancesupto3658mm(12feet)arenotuncommon.Mosthavechippansandabuilt-incoolantcirculatingsystem.Smallerenginelathes——withswingsusuallynotover330mm(13inches)——alsoareavailableinbenchtype,designedforthebedtobemountedonabenchorcabinet.Althoughenginelathesareversatileandveryuseful,becauseofthetimerequiredforchangingandsettingtoolsandformakingmeasurementsontheworkpiece,theyarenotsuitableforquantityproduction.Oftentheactualchip-productiontimeislessthan30%ofthetotalcycletime.Inaddition,askilledmachinistisrequiredforalltheoperations,andsuchpersonsarecostlyandofteninshortsupply.However,muchoftheoperation’stimeisconsumedbysimple,repetitiousadjustmentsandinwatchingchipsbeingmade.Consequently,toreduceoreliminatetheamountofskilledlaborthatisrequired，turretlathes,screwmachines,andothertypesofsemiautomaticandautomaticlatheshavebeenhighlydevelopedandarewidelyusedinmanufacturing.Unit17DrillsandDrillingMachinesNewwordsandexpressionsUnit17DrillsandDrillingMachinesThetwistdillisaveryefficienttool.Itisgenerallyformedbyforgingandtwistinggroovesinaflatstripofsteelorbymillingacylindricalpieceofsteel,high-speedsteelbeingcommonlyused[1].High-speedsteelcostsmorebuttoolsmadeofitwithstandheatmuchbetterthanthosemadeofordinarytoolsteel[2].Thetwistdrillmaybedividedintothreeprincipalparts:body,shank,andpoint.Theflutesarethespiralgroovesthatareformedonthesideofadrill,drillsbeingmadewithtwo,orfourflutes.Thosehavingthreeorfourflutesareusedforfollowingsmallerdrillsorforenlargingholesalreadydrilled,andarenotsuitedfordrillingintosolidstock.Spiralfluteshavefourmainadvantages:(1)Theygivethecorrectraketothelipofadrill.(2)Theycausethechiptocurlsotightlythatitoccupiestheminimumamountofspace[3].(3)Theyformchannelsthroughwhichchipsescapefromthehole.(4)Theyallowthelubricanttofloweasilydowntothecuttingedge.Themarginisthenarrowstriponthecuttingedgeoftheflute.Itispracticallythefulldiameterofthedrillandextendstheentirelengthoftheflute,itssurfacebeingapartofacylinder[4].Theportionofthebodynexttothemarginisoflessdiameterthanthemargin.Thislesseneddiameter,calledbodyclearance,reducesthefrictionbetweenthedrillandthewallsofthehole,whilethemargininsurestheholebeingofaccuratesize.Theshankistheendofthedrillwhichfitsintothesocket,spindle,orchuckofthedrillpress.Thetangisusuallyfoundonlyontaperedshanktools.Thedrillingmachineisthesecondoldestmachinetools,havingbeeninventedshortlyafterthelathe,andisoneofthemostcommonandusefulmachines.Thedrillingmachinesmaybeclassifiedintothreegeneraltypes:verticalspindle,multiplespindle,andradialspindlemachines.Theverticalspindledrillingmachinecomesinthreetypes:heavyduty,plain,andsensitive.Besidesthedrillingofholes,suchoperationsmaybeperformedonthedrillingmachine:drilling,tapping(internalthreading),reaming(finishingtheholewithareamer),countersinking,counterboringboring,boringandspot-facing.Unit18Milling,Shaper,PlanerandGrindingMachinesNewwordsandexpressionsmillingmachine銑床millingcutter銑刀Unit18Milling,Shaper,PlanerandGrindingMachinesMillingMachinesThemillingmachineisamachinethatremovesmetalfromtheworkwitharevolvingmillingcutterastheworkisfedagainstit[1].Themillingcutterismountedonanarborwhereitisheldinplacebyspacersorbushings[2].Thearborisfixedinthespindlewithoneend,whiletheotherendofthearborrotatesinthebearingmountedonthearboryoke.Themostimportantpartsofthemillingmachineare:1)startinglevers;2)spindle;3)column;4)knee;5)elevatingscrew;6)table;7)indexhead;8)speedlevers;9)feedlevers;10)tablemovementlevers;11)footstock;12)arboryoke.Thespindleofthemillingmachineisdrivenbyanelectricmotorthroughatrainofgearsmountedinthecolumn.Thetableoftheplainmillingmachinemaytravelonlyatrightanglestothespindlewhiletheuniversalmillingmachineisprovidedwithatablethatmaybeswiveledonthetransverseslideformillinggearteeth,threads,etc.SharperandPlanerThemachinetoolsofthisgrouparegenerallyused,formachiningflatsurfaces,whichisusuallyperformedbyacutterthatpee1sthechipfromthework.Themainmotionisreciprocatingandthefeedisnormal(perpendicular)tothedirectionofthemainmotion.Thetoolandtheapronofashaperarelocatedontheram.Achipispeeledofftheworkontheforwardstroke.Anadjustabletablewith“T”-slotsholdsthework,vise,andotherfixturesforholdingthework.Theshaperhasarockerarmwhichdrivestheram,andamechanismforregulatingthelengthofthestroke.Theramsupportsthetoo1head.Theheadcarriesthedownfeedmechanismandwillswivelfromsidetosidetopermitthecuttingofangles.Thisisgenerallyahandfeed,butsomeshapersareequippedwithapowerdownfeedinadditiontotheregularhanddownfeed.Thetableoftheshaperisofboxformwith“T”-slotsonthetopandsidesforclampingthework.Thecrossrailisbolteddirectlytotheframeorcolumnoftheshaperwithbolts.Theautomaticfeedorpowerfeedisobtainedbyapawlwhichengagesinawheelorratchet.Unit19MachineToolTests,AccuracyCheckingandMaintenanceNewwordsandexpressionsUnit19MachineToolTests,AccuracyCheckingandMaintenanceMachineToolTestsandAccuracycheckingAftermanufactureorrepairs,eachmachinetoolshouldmeettherequirementsofspecifications.Accordingtotheapprovedgeneralspecifications,acceptancetestsofmachinetoolsshouldinclude:(a)idle-runtests,mechanismsoperationchecks,certificatedatechecks;(b)loadtestsandproductiveoutputtests(forspecialmachinetools);(c)checksofthegeometricalaccuracy,surfaceroughness,andaccuracyoftheworkpiecebeingmachined;(d)rigiditytestsofmachinetools;(e)testsforvibration-proofpropertiesofmachinetoolscutting.Theshaperhasarockerarmwhichdrivestheram,andamechanismforregulatingthelengthofthestroke.Theramsupportsthetoo1head.Theheadcarriesthedownfeedmechanismandwillswivelfromsidetosidetopermitthecuttingofangles.Thisisgenerallyahandfeed,butsomeshapersareequippedwithapowerdownfeedinadditiontotheregularhanddownfeed.Thetableoftheshaperisofboxformwith“T”-slotsonthetopandsidesforclampingthework.Thecrossrailisbolteddirectlytotheframeorcolumnoftheshaperwithbolts.Theautomaticfeedorpowerfeedisobtainedbyapawlwhichengagesinawheelorratchet.Thesetestsofmachinetoolsshouldbeconductedintheabovesequence.Theaccuracyoftheworkpiecebeingmachinedanditssurfaceroughnessmaybecheckedduringtheloadtestsofthemachinetoolandbeforethegeometricalaccuracyofthelatterischecked.Accuracychecksareconsideredbelow.Theseincludethecheckingofthemachinetoolgeometricalaccuracy,theaccuracyoftheworkpiecemachinedanditssurfaceroughness.Machinetoolgeometricalaccuracytestsinclude:thecheckingofguidewaysforstraightness;worktablesforflatness;columns,uprights,andbaseplatesfordeviationfromtheverticalandhorizontalplanes;spindlesforcorrectlocationandaccuracyofrotation;relativepositionofaxesandsurfacesforparallelismandsquareness;leadscrewsandindexingdevicesforspecificerrors;etc.ThesechecksareconductedinaccordancewiththeGOSTsforagiventypeofmachinetool.Geometricalaccuracytestsaloneareinadequatetojudgethemachine-toolperformancebecausetheydonot(orinadequately)revealvariationsinrigidityofmachine-toolcomponents,thequalityoftheirmanufactureandassembly,andespecially,theinfluenceofthemachine-fixture-cuttingtool-workpiecesystemrigidityontheaccuracyofmachining.ThatiswhythecorrespondingStateStandardsstipulatecompulsoryaccuracytestsofmachinetoolsbymachiningworksamplesincludingacheckoftheirsurfaceroughness.Thesetestsshouldbecarriedoutafterthepreliminaryidlerunningofthemachinetooloritsloadtests,withessentialpartsofthemachininghavingastabilizedworkingtemperature[1].Thekingofworksample,itsmaterial,andthecharacterofmachiningforvarioustypesofmachinetoolsaregivenincorrespondingstandards.MachineToolMaintenanceThemaintenanceofmachinetoolsintheUSSRisaccomplishedinaccordancewithaplannedmaintenancesystem(PMS).Thissystemprovidesforcomplexmeasuresforservicing,inspection,andrepairsofequipment,whichpreventthewearofequipmentandhelptokeepitingoodorder[2].ThePMSsystemcanbeaffectedbymeansofthefollowingmethods:(1)Post-inspectionsrepairs.Thismethodinvolvestheplanningofperiodicinspectionstathetthanrepairs.Thetimeintervalbetweensuccessiveinspectionsisdeterminedaccordingtotheminimumservicelifeofrapidlywearingcomponents.Ifaninspectionconfirmsthatthereisnoneedforrepairsandthatthemachinecanoperatewithouttheseuntilthenextinspection,therepairsarepostponed.Thismethodpreventsanysuddenbreakdownofequipment.(2)Themethodofperiodicrepairsconsistsinrepairsbeingdoneafteragivenrunningtime.Themethodofsrandard(compulsory)repairsinvolvescompulsoryrepairsofequipmentatplannedintervals,whicharestandardforeachpieceofequipment.ThePMSsystemincludes:(1)Routineservicing,whichprovidesfornormaleverydayrunningofmachines,minorrepairsand,whenevernecessary,adjustmentofseparateunitsormembersofthemachinetool.(2)Periodicinspections,whichareconductedaccordingtoscheduleandinvolvevisualinspectioncleaning,andaccuracychecks.(3)Inspectionsassuchconsistinexteriorchecksaccompaniedbypartialdisassembly.Allthemechanismsarecheckedinoperationandregulated,fastenersarerepairedorreplaced,thestateandwearofthemachinetoolasawholeanditsindividualunitsareassessed.Theinspectionresultedarerecordedinareportonthemechanicalconditionofthemachine.Thedateforthenextrepairsisdefinedinaccordancewiththisreport,Theaccuracycheckofthemachinetoolisconductedaccordingtoapprovedstandards.(4)Scheduledrepairsaredividedintominor(orroutine),medium,andgeneralrepairs.Inroutinerepairs,sepatatecomponentsorunitsofthemachinearerepairedorreplacedwithoutthoroughdisassemblyofthemachine.Mediumrepairsincludealltheelementsofroutinerepairswiththeadditionalrestorationoftherelativepositionoftheprincipalunitsandwithpartialrepairstobasiccomponents.Generaloverhaulinvolvesthecompletereplacementorrepairsofallthebasiccomponents,fullrestorationoftherelativepositionoftheprincipalunitsandtherequiredaccuracyofthemachinetool.Unit20NontraditionalManufacturingProcessesNewwordsandexpressionsThehumanracehasdistinguisheditselffromallotherformsoflifebyusingtoolsandintelligencetocreateitemsthatservetomakelifeeasierandmoreenjoyable.Throughthecenturies,boththetoolsandtheenergysourcestopowerthesetoolshaveevolvedtomeettheincreasingsophisticationandcomplexityofmankind’sideas.Intheirearliestforms,toolsprimarilyconsistedofstoneinstruments.Consideringtherelativesimplicityoftheitemsbeingmadeandthematerialsbeingshaped,stonewasadequate.Whenirontoolswereinvented,durablemetalsandmoresophisticatedarticlescouldbeproduced.Thetwentiethcenturyhasseenthecreationofproductsmadefromthemostdurableand,consequently,themostdifficult-to-machinematerialsinhistory.Inanefforttomeetthemanufacturingchallengescreatedbythesematerials,toolshavenowevolvedtoincludematerialssuchasalloysteel,carbide,diamond,andceramics.Asimilarevolutionhastakenplacewiththemethodsusedtopowerourtools.Initially,toolswerepoweredbymuscles;eitherhumanoranimal.Howeverasthepowersofwater,wind,steam,andelectricitywereharnessed,mankindwasabletofurtherextendedmanufacturingcapabilitieswithnewmachines,greateraccuracy,andfastermachiningrates.Everytimenewtools,toolmaterials,andpowersourcesareutilized,theefficiencyandcapabilitiesofmanufacturersaregreatlyenhanced.Howeverasoldproblemsaresolved,newproblemsandchallengesarisesothatthemanufacturersoftodayarefacedwithtoughquestionssuchasthefollowing:Howdoyoudrilla2mmdiameterhole670mmdeepwithoutexperiencingtaperorrunout?Isthereawaytoefficientlydeburrpassagewaysinsidecomplexcastingsandguarantee100%thatnoburrsweremissed?Isthereaweldingprocessthatcaneliminatethethermaldamagenowoccurringtomyproduct?Sincethe1940s,arevolutioninmanufacturinghasbeentakingplacethatonceagainallowsmanufacturerstomeetthedemandsimposedbyincreasinglysophisticateddesignsanddurable,butinmanycasesnearlyunmachinable,materials.Thismanufacturingrevolutionisnow,asithasbeeninthepast,centeredontheuseofnewtoolsandnewformsofenergy.Theresulthasbeentheintroductionofnewmanufacturingprocessesusedformaterialremoval,forming,andjoining,knowntodayasnontraditionalmanufacturingprocesses.Theconventionalmanufacturingprocessesinusetodayformaterialremovalprimarilyrelyonelectricmotorsandhardtoolmaterialstoperformtaskssuchassawing,drilling,andbroaching.Conventionalformingoperationsareperformedwiththeenergyfromelectricmotors,hydraulics,andgravity.Likewise,materialjoiningisconventionallyaccomplishedwiththermalenergysourcessuchasburninggasesandelectricarcs.Incontrast,nontraditionalmanufacturingprocessesharnessenergysourcesconsideredunconventionalbyyesterday’sstandards.Materialremovalcannowbeaccomplishedwithelectrochemicalreactions,high-temperatureplasmas,andhigh-velocityjetsofliquidsandabrasives[2].Materialsthatinthepasthavebeenextremelydifficulttoform,arenowformedwithmagneticfields,explosives,andtheshockwavesfrompowerfulelectricsparks.Material-joiningcapabilitieshavebeenexpandedwiththeuseofhigh-frequencysoundwavesandbeamsofelectrons.Inthepast50years,over20differentnontraditionalmanufacturingprocesseshavebeeninventedandsuccessfullyimplementedintoproduction.Thereasontherearesuchalargenumberofnontraditionalprocessesisthesamereasontherearesuchalargenumberofconventionalprocesses;eachprocesshasitsowncharacteristicattributesandlimitations,hencenooneprocessisbestforallmanufactu