牛头刨床钻床和铣削机械系论文外文翻译.docx
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牛头刨床钻床和铣削机械系论文外文翻译
译文
题目牛头刨床、钻床和铣削
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专业年级
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指导教师
Shapers,DrillingandMillingMachines
Ashapersutilizesasingle-pointtoolonatoolholdermountedontheendoftheram.Cuttingisgenerallydoneontheforwardstroke.Thetoolisliftedslightlybytheclapperboxtopreventexcessivedragacrossthework,whichisfedunderthetoolduringthereturnstrokeinpreparationforthenextcut.Thecolumnhousestheoperatingmechanismsoftheshaperandalsoservesasamountingunitforthework-supportingtable.Thetablecanbemovedintwodirectionsmutuallyperpendiculartotheram.Thetoolslideisusedtocontrolthedepthofcutandismanuallyfed.Itcanberotatedthrough90deg,oneithersideofitsnormalverticalposition,whichallowsfeedingthetoolatanangletothesurfaceofthetable.
TwotypesofdrivingmechanismsforshapersareamodifiedWhitworthquick-returnmechanismandahydraulicdrive.FortheWhitworthmechanism,themotordrivesthebullgear,whichdrivesacrankarmwithanadjustablecrankpintocontrolthelengthofstroke.Asthebullgearrotates,therockerarmisforcedtoreciprocate,impartingthismotiontotheshaperram.
Themotoronahydraulicshaperisusedonlytodrivethehydraulicpump.Theremainderoftheshapermotionsarecontrolledbythedirectionoftheflowofthehydraulicoil.Thecuttingstrokeofthemechanicallydrivenshaperuses220deg.Ofrotationofthebullgear,whilethereturnstrokeuses140deg.Thisgivesacuttingstroketoreturnstrokeratioof1.6to1.Thevelocitydiagramforahydraulicshapershowsthatformostofthetoolduringcuttingstrokeisneverconstant,whilethevelocitydiagramforahydraulicshapershowsthatformostofthecuttingstrokethecuttingspeedisconstant.Thehydraulicshaperhasanaddedadvantageofinfinitelyvariablecuttingspeeds.Theprincipaldisadvantageofthistypeofmachineisthelackofadefinitelimitattheendoftheramstroke,whichmayallowafewthousandthsofaninchvariationinstrokelength.
Aduplicatingdevicethatmakespossiblethereproductionofcontoursfromasheet-metaltemplateisavailable.Thesheetmetaltemplateisusedinconjunctionwithhydrauliccontrol.
Uprightdrillingmachinesordrillpressesareavailableinavarietyofsizesandtypes,andareequippedwithasufficientrangeofapindlespeedsandautomaticfeedstofitthenedsofmostindustries.Speedrangesonatypicalmachinearefrom76to2025rpm.,withdrillfeedfrom0.002to0.020in.perrevolutionofthespindle.
Radialdrillingmachinesareusedtodrillworkpiecesthataretoolargeorcumbersometoconvenientlymove.Thespindlewiththespeedandfeedchangingmechanismismountedontheradialarm;bycombiningthemovementoftheradialarmaroundcolumnandthemovementofthespindleassemblyalongthearm,itispossibletoalignthespindleandthedrilltoanypositionwithinreachofthemachine.Forworkthatistoolargetoconvenientlysupportonthebase,thespindleassemblycanbeswungoutoverthefloorandtheworkpiecesetonthebesidethemachine.
Plainradialdrillingmachinesprovideonlyforverticalmovementofthespindle;universalmachinesallowthespindletoswivelaboutanaxisnormaltotheradialarmandtheradialarmtorotateaboutahorizontalaxis,thuspermittingdrillingatanyangle.
Amultispindledrillingmachinehasoneormoreheadsthatdrivethespindlesthroughuniversaljointsandtelescopingsplinedshafts.Allspindlesareusuallydrivenbythesamemotorandfedsimultaneouslytodrillthedesirednumberofholes.Inmostmachineseachspindleisheldinanadjustableplatesothatitcanbemovedrelativetotheothers.Theareacoveredbyadjacentspindlesoverlapsothatthemachinecanbesettodrillholesatanylocationwithinitsrange.
Themillingoperationinvolvesmetalremovalwitharotatingcutter.Itincludesremovalofmetalfromthesurfaceofaworkspiece,enlargingholes,andformcutting,suchasthreadsandgearteeth.
Withinankneeandcolumntypeofmillingmachinethecolumnisthemainsupportingmemberfortheothercomponents,andincludesthebasecontainingthedrivemotor,thespindle,andthecutters.Thecutterismountedonanarborheldinthespindle,andsupportedonitsouterextremitybyabearingintheoverarm.Thekneeisheldonthecolumnindovetailslots,thesaddleisfastenedtothekneeindovetailslots,andthetableisattachedtothesaddle.Thus,thebuild-upthekneeandcolumnmachineprovidesthreemotionsrelativetothecutter.Afourmotionmaybeprovidedbyswivelingthetablearoundaverticalaxisprovidedonthesaddle.
Fixed-bedmillingmachinesaredesignedtoprovidemorerigiditythanthekneeandcolumntype.Thetableismounteddirectlyonthemachinebase,whichprovidestherigiditynecessaryforabsorbingheavycuttingload,andallowsonlylongitudinalmotiontothetable.Verticalmotionisobtainedbymovingtheentirecuttinghead.
Tracermillingischaracterizedbycoordinatedorsynchronizedmovementsofeitherthepathsofthecutterandtracingelements,orthepathsoftheworkpieceandmodel.Inatypicaltracermillthetracingfingerfollowtheshapeofthemasterpattern,andthecutterheadsduplicatethetracermotion.
Thefollowingaregeneraldesignconsiderationsformilling:
1.Whereverpossible,thepartshouldbedesignedsothatamaximumnumberofsurfacescanbemilledfromonesetting.
2.Designfortheuseofmultiplecutterstomillseveralsurfacessimultaneously.
3.Thelargestflatsurfacewillbemilledfirst,sothatalldimensionsarebestreferredtosuchsurface.
4.Squareinsidecornersarenotpossible,sincethecutterrotates.
GrindingMachinesandSpecialMetal-removalProcess
Randompoint-cuttingtoolsincludeabrasivesintheshapeofawheel,bondedtoabelt,astick,orsimplysuspendedinliquid.Thegrindingprocessisofextremeimportanceinproductionworkforseveralreasons.
1.Itismostcommonmethodforcuttinghardenedtoolsteelorotherheat-treatedsteel.Partsarefirstmachinedintheun-heat-treatedcondition,andthengroundtothedesireddimensionsandsurfacefinish.
2.Itcanprovidesurfacefinishto0.5µmwithoutextremecost.
3.Thegrindingoperationcanassureaccuratedimensionsinarelativelyshorttime,sincemachinesarebuilttoprovidemotionsinincrementsoften-thousandthsofaninch,insteadofthousandthsasiscommoninothermachines.
4.Extremelysmallandthinpartscanbefinishedbythismethod,sincelightpressureisusedandthetendencyfortheparttodeflectawayfromthecutterisminimized.
Onacylindricalgrindingmachinethegrindingwheelrotatesbetween5500and6500rpm.,whiletheworkrotatesbetween60and125rpm...Thedepthofcutiscontrolledbymovingthewheelhead,whichincludesboththewheelanditsdrivemotor.Coolantsareprovidedtoreduceheatdistortionandtoremovechipsandabrasivedust.
Materialremovalfromductilematerialscanbeaccomplishedbyusingatoolwhichisharderthantheworkpiece.HoweverduringWordWarⅡthewidespreaduseofmaterialswhichwereashardorharderthancuttingtoolscreatedademandfornewmaterial-removalmethods.Sincethenanumberofprocesseshavebeendevelopedwhich,althoughrelativelyslowandcostly,caneffectivelyremoveexcessmaterialinapreciseandrepeatablefashion.Therearetwotypesofprocesses.Thefirsttypeisbasedonelectricalphenomenaandisusedprimarilyforhardmaterials;theseconddependsuponchemicaldissolution.
Chemicalmillingiscontrolledetchingprocessusingstrongalkalineoracidetchants.Aluminum,titanium,magnesium,andsteelaretheprincipalmetalsprocessedbythismethod.Theareatoremainuntouchedbytheetchantaremaskedwithaprotectivecoating.Forexample,theentirepartmaybedippedinthemaskingmaterialandthemaskremovedfromthoseareastobeetched,orachemicallyresistantprescribedtime,afterwhichthepartisrinsedincoldwater,themaskingremoved,thepartinspected,andthoroughlycleaned.
Therearecertaindisadvantagestoconsider.Metalwillerodeequallyinalldirections,sothatwallsoftheetchedsectionwillhavearadiusequaltothedepthofetch.Aseconddisadvantageisthatabetterfinishisobtainedonsurfacesparalleltothedirectionofrollingofasheetthanonsurfaceperpendiculartothedirectionofrolling.Thiscanbecomparedtothesurfaceobtainedwhenworkingwoodparallelto,oracrossthegrain.Athirddisadvantage,notuniquewiththisprocess,isthewarpagethatwilloccurinthin,previouslystressedsectionsetchedonjustoneside.
Chemicalmilling,however,hasmanyadvantagesoverconventionalmetal-removalmethods.Thereisnowarpageofheavysectionssuchasforgingsorextrusionswhentheetchantisappliedsimultaneouslytoallsidesforreductionofsectionthickness.Inconventionalmillingonlyonesidecanbeworkedatatime,andfrequentturningofapartisnecessarytopreventwarpage.Chemicalmillingcanbeappliedtopartsofirregularshapewhereconventionalmillingmaybeverydifficult.Light-weightconstructioncanbeobtainedwithchemicalmillingbytheeliminationofwelding,riveting,andstiffeners;partscanbecontouredtodistributetheloadinthemostsuitablemanner.Asanexampleofthepotentialsavingsofthisprocess,ascomparedtomachinemilling,onecompanyreportsthatthecostofremovingaluminumbychem.-millingis$0.27perpoundascomparedto$1.00perpoundbyconventionalmilling.Therateofmetalremovalforchem.-millingis0.001in.foraluminum.
Electric-dischargemachiningisaprocessinwhichanelectricalpot