数控机床的部分进行设计说明书论文.docx
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数控机床的部分进行设计说明书论文.docx
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数控机床的部分进行设计说明书论文
转塔式数控加工中心设计
摘要
数控机床是一种高科技的机电一体化产品,是现代制造技术中不可缺少的生产手段。
随着科技的不断发展,数控机床在国内也进入了实用化阶段,但在目前我国许多国营大厂都有一批老机床,若在老机床的基础上对其进行改造,配以数控技术,这样不仅可降低成本,而且可提高老机床的使用寿命。
因此,我们毕业设计的题目就是将普通铣床改为集镗、铣、钻为一体的八轴转塔式简易加工中心,实现不用人工换刀的情况下,短时间内进行镗、铣、钻的转换,这样不仅可以提高生产效率和加工精度,并且还可以降低成本。
我主要负责机床的整体布局和八轴转塔自动换刀装置的设计。
在机床的整体布局方面,我从人机工程学和产品造型两方面对机床进行设计。
八轴转塔自动装置的工作原理是在八个轴上事先根据工序的安排将加工中所需要的刀具装夹好,当将油注入中心油缸后,产生压力带动整个转塔头使八轴转塔旋转,使其实现自动换刀的功能。
这套简易的数控加工中心也应用了近年来才发展起来的变频技术,从而提高了其中的科技含量。
由于现在国内的国营大厂都面临老机床淘汰的情况,因此在老机床的基础上进行数控改造是很有市场前景的,从而进行这次毕业设计也是比较实用的。
关键词:
数控技术,八轴转塔头,变频技术,自动换刀
SLEEVEBEARINGS
BEARINGMATERIALS
Theantifrictionpropertiesofrubbingpairsareconsideredinconjunctionwiththematerialsoftheshaftandbearing,andthelubricant.
Bearingmaterialsarechosenforapplicationinapairwithasteelor,muchlessfrequently,castironshaftjournal.Owingtothefactthatthecostofshaftsis,asarule,higherthanthatofthebearingliners(especiallyinthecaseofcrankshaftsandothermainshafts),theirwearmustbelessthanthatoftheliners.Thehigherthehardnessoftheshaftjournals,themorereliabletheirperformance.Asarule,journalsarehardened.Journalsrunninginhigh-speedbearingsarehardenedtoahighhardness,55to60Rc(followingcarburizing).
Integratedrequirements,complyingwiththebasiccriteriaofbearingperformance,canbemadetobearingmaterials.Thus,theymust:
(a)beantifrictional,apropertycharacterizedbythecoefficientoffrictioninoperationinapairwiththematerialoftheshaftjournal,andbythetemperatureattheworkingsurface;(b)havehighwearresistance;and(c)havehighfatiguestrength.
Ofimportanceinmeetingtheseintegratedrequirementsarethefollowingbasicpropertiesofbearingmaterials:
(a)thermalconductivity,toprovideintensiveheatdisposalfromthefrictionsurfaces,andalowcoefficientoflinearexpansiontoavoidlargechangesintheclearancesinthebearingsduringoperation;
(b)capacityforbeingruninreadily,whichreducesedgeandlocalpressuresresultingfromelasticdeformationanderrorsinmanufacture;
(c)goodwettabilitywithoilandthecapacityforformingstableandrapidlyrestorableoilfilmsonitssurfaces;
(d)goodcorrosionresistance;
(e)lowmodulusofelasticity.
Alsoofbasicimportanceareprocessingproperties,suchascastability,machinability,etc.
Themostfavorablestructureforanantifrictionmaterialisonehavingaplasticmatrixintowhichhardcomponentsareembedded.
Withrespecttotheirchemicalcomposition,antifrictionbearingmaterialscanbeclassifiedintothefollowinglargegroups:
(a)metallicmaterials:
babbitts,bronzes,zinc-basealloys,aluminium-basealloysandantifrictioncastirons;
(b)sinteredmetalpowders;
(c)nonmetallicmaterials:
plastics,woodlaminates,rubbers,etc.
BearingMetals.Babbittsarehigh-qualitybearingalloysthathavebeenusedformanyyearsinengineering.Theyarebasedontinorleadandarecharacterizedbytheirlowhardness(theyareusedforcastingintoasupportorhousing),goodrunning-inproperties,andrelativelylowerrequirementsastothehardnessoftheshaftjournalsandtothestateoftherubbingsurfaces.
High-tinbabbitts,gradesB83,B89,etc.aretobeappliedforhighrunningspeedsandhighpressures.Theyallowoperationatpressuresuptop=200kgf/cm2andpv=1000kgf-m/cm2-s.To
avoidburning-out,babbittsareusedfortemperaturesupto110°Conly.Typicalapplicationsareinthebearingsofsteamturbines,andofpowerfulelectricgeneratorsandmotors.Theuseofhigh-tinbabbittsleadstominimumwearoftheshaftjournals.
Shortcomingsofhigh-tinbabbittsaretheirrelativelylowfatiguestrength,whichrestrictstheirapplicationinimpact-typemachineryandhigh-speedpistonmachines,andtheimpossibilityofapplyingtheminthinlayersbecauseoftheirlargecrystals.
Sovietautomobilesusebearinglinerswithalayerofbabbitt,gradeCOC6-6(88%lead,6%tinand6%antimony),andacermetsublayer,sinteredofapowderwith40%Niand60%Cu,onasteelbacking.Thereisexcellentcohesionbetweenthelayersbecausethesublayerisimpregnatedwiththebabbittwhichforms,withthesinteredmetal,asubstantiallyincreasedcohesionsurface.Ontheotherside,thesublayerdiffusesintothesteelbacking.Thisgradeofbabbitthasanincreasedfatiguestrengthand,owingtotheabsenceofhardcomponents,itsuseleadstolessshaftwear.Anotheradvantageisthatitlendsitselftohigh-productionmanufacturingtechniques(pressformingfromstripstock).
Acalciumbabbitt,gradeBR2,isusedindieselenginemanufacture.Amongthoselonginuseintheengineeringindustriesarethetin-leadbabbitts,gradesB16andBH,whichhavepropertiesclosetothoseofthehigh-tinbabbitts(p<=150kgf/cm2andpv<=500kgf-m/cm2-s).
Calciumbabbitt,gradeBK,findsapplicationformediumduty.Itcontainsnotinandisused,forinstance,forbabbittingthebearingsofrailwayrollingstock.Alessexpensivebabbitt,gradeBC,isusedforlightdutyapplications.
Bronzes.Athighspeedsandpressures(uptop=300kgf/cm2)and,inparticular,forvariableloadstypicalofinternal-combustionengines,aleadedbronze,gradeBp.C-30,isused.Ithasahigherfatiguestrengththanthehigh-tinbabbitts.Leadedbronzemakeshigherrequirementsthanthebabbittsdotothehardnessoftheshaftjournals(hardeningiscompulsory),tothesurfacefinishofthejournalsandliners,andalsotothelubricantssinceoxidizedoilscausecorrosion.
Shaftwearishigherthanthatwithbabbittliners.Iftheleadcontentisincreasedto35%,thewearcanbereduced.Leadedbronzeisappliedtostripstockfromwhichthelinersarepressformedoritiscastintotheliner.Owingtothedangerofcorrosion,theuseofleadedbronzehasbeencurtailedinrecentyears.
Theworkingsurfaceofthelinersofcriticalbearingsiscoatedwithathinrunning-inlayerofanalloyofleadwithtin,orofindiumortin.
UniversaltinbronzesoftheBp.OΦ10-1typeprovideforefficientperformanceathighpressuresandmediumspeeds.However,owingtothehightincontent,theirapplicationislimited.Thisbronzeisnottoberecommendedforuseinbimetallicbearingliners.
Secondarytin-zinc-leadbronzes(i.e.onesobtainedbyremelting),forinstance,gradeBp.OЦC6-6-3,havefoundextensiveapplicationandhaveprovedquitesatisfactoryformediumduty.
Aluminium-ironbronzesareusedtosomeextentforbearingssubjecttoconsiderablepressuresatlowspeedsandoperatingwithahardenedshaftjournal.
Inrecentyears,aluminium-basebearingalloyshavecomeintousebecausetheyaremoreeconomicalduetothelowcostofthebasicmaterial.Thesealloyshavelowdensity,lowcorrosionresistance,highthermalconductivity,lowmodulusofelasticityandahighfatiguestrength.Theuseofthesealloysincreasedconsiderablyafteratechniquewasdevelopedforapplyingthemtoasteelbackingbyarollingprocess.
Tinlessaluminiumbearingalloyshavesufficientlyhighantifrictionproperties,butathighspeedstheirresistancetoscoringisnotveryhigh;theyaresensitivetodirtintheoilandhaveahighcoefficientoflinearexpansion.ThemostwidelyusedofthesealloysintheUSSRisgradeACMwhichisfoundinthebearingsoftractorengines.Nofavorableresultswereobtained,however,whenattemptsweremadetoapplytheminthebearingsofautomobileengines
whichrunathigherspeeds.
Themostpromisingbearingmaterialsarethealuminium-tinantifrictionalloyswhichhavehighantifrictionpropertiesandhighfatiguestrength.InusearealloysgradeAO9-2(9%tin,2%copper,castinandusedasamonometal),AO9-2B(castinandusedasabimetal),AO9-1(madebyrollingandusedasabimetal).andAO20-1(madebyrollingandusedasabimetal).Thesealloyshaveoptimalstructureandarecapable,incasesofoilstarvation,offormingaprotectivefilmoftinonthejournal.AlloysAO9-1andAO9-2,forexample,arebeingefficientlyemployedinthebearingsofinternal-combustionenginesofdiesellocomotives,shipsandheavy-dutytractors.
Ofthezincbearingalloys,thebestknownisgradeЦAM10-5(10%aluminium,5%copperandtheremainderzinc),Owingtoitssatisfactoryantifrictionproperties,abundancyofitsconstituentmaterials,lowcostandsimplemanufacture,thisalloyiswidelyusedinplaceoftypeБ16babbittsandbronzes.
Shortcomingsofthisalloyareitspoorrunning-inproperties,andtheconsequentlyhigherrequirementsmadetotheaccuracyofthebearingsurfaces,andthehighcoefficientoflinearexpansion.Thehighestpermissibletemperatureofsuchbearingsis80°C.Thealloyisusedeitherforcast-inorforpressfittedliners.
AnewbearingalloyisgradeЦAM9-1.5;atechniquehasbeendevelopedformakingbimetallicstripstock.Testsshowthatithashighwearresistance.
Polymetallicmultiple-layerbearingsarebeingemployedtoanever-increasingextent.Bearingsareused,forexample,inautomobileenginesthatconsistofasteelbacking,a0.25-mmlayerofleadedbronze,servingasacompliantcushionwithgoodthermalconductivityandfatiguestrength,anextremelythinlayerofnickeloracopper-zincalloywhichpreventsdiffusionofthetin,and,finally,asurfaceantifrictionlayerofatin-leadalloy,25micronsthick,whichhasexcellentrunning-inproperties.
Antifrictioncastiron(USSRStdGOST1585-70)canbeappliedforlow-speedmoderatelyloadedbearings.Thehardnessoftheshaftjournalsmustbehigherthanthatofthecastironliners.Theworkingsurfacesshouldbecarefullyruninusingacolloidalmixtureofgraphiteinoil.Thepermissiblepressuresinthesebearingsdropsharplywithanincreaseinrunningspeed
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