外文翻译机械设计及加工工艺精品.docx
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外文翻译机械设计及加工工艺精品
附录
英文原文
MechanicalDesignandManufacturingProcesses
Mechanicaldesignistheapplicationofscienceandtechnologytodeviseneworimprovedproductsforthepurposeofsatisfyinghumanneeds.Itisavastfieldofengineeringtechnologywhichnotonlyconcernsitselfwiththeoriginalconceptionoftheproductintermsofitssize,shapeandconstructiondetails,butalsoconsidersthevariousfactorsinvolvedinthemanufacture,marketinganduseoftheproduct.
Peoplewhoperformthevariousfunctionsofmechanicaldesignaretypicallycalleddesigners,ordesignengineers.Mechanicaldesignisbasicallyacreativeactivity.However,inadditiontobeinginnovative,adesignengineermustalsohaveasolidbackgroundintheareasofmechanicaldrawing,kinematics,dynamics,materialsengineering,strengthofmaterialsandmanufacturingprocesses.
Asstatedpreviously,thepurposeofmechanicaldesignistoproduceaproductwhichwillserveaneedforman.Inventions,discoveriesandscientificknowledgebythemselvesdonotnecessarilybenefitpeople;onlyiftheyareincorporatedintoadesignedproductwillabenefitbederived.Itshouldberecognized,therefore,thatahumanneedmustbeidentifiedbeforeaparticularproductisdesigned.
Mechanicaldesignshouldbeconsideredtobeanopportunitytouseinnovativetalentstoenvisionadesignofaproduct,toanalyzethesystemandthenmakesoundjudgmentsonhowtheproductistobemanufactured.Itisimportanttounderstandthefundamentalsofengineeringratherthanmemorizemerefactsandequations.Therearenofactsorequationswhichalonecanbeusedtoprovideallthecorrectdecisionsrequiredtoproduceagooddesign.
Ontheotherhand,anycalculationsmademustbedonewiththeutmostcareandprecision.Forexample,ifadecimalpointismisplaced,anotherwiseacceptabledesignmaynotfunction.
Gooddesignsrequiretryingnewideasandbeingwillingtotakeacertainamountofrisk,knowingthatifthenewideadoesnotworktheexistingmethodcanbereinstated.Thusadesignermusthavepatience,sincethereisnoassuranceofsuccessforthetimeandeffortexpended.Creatingacompletelynewdesigngenerallyrequiresthatmanyoldandwell-establishedmethodsbethrustaside.Thisisnoteasysincemanypeopleclingtofamiliarideas,techniquesandattitudes.Adesignengineershouldconstantlysearchforwaystoimproveanexistingproductandmustdecidewhatold,provenconceptsshouldbeusedandwhatnew,untriedideasshouldbeincorporated.
Newdesignsgenerallyhave"bugs"orunforeseenproblemswhichmustbeworkedoutbeforethesuperiorcharacteristicsofthenewdesignscanbeenjoyed.Thusthereisachanceforasuperiorproduct,butonlyathigherrisk.Itshouldbeemphasizedthat,ifadesigndoesnotwarrantradicalnewmethods,suchmethodsshouldnotbeappliedmerelyforthesakeofchange.
Duringthebeginningstagesofdesign,creativityshouldbeallowedtoflourishwithoutagreatnumberofconstraints.Eventhoughmanyimpracticalideasmayarise,itisusuallyeasytoeliminatethemintheearlystagesofdesignbeforefirmdetailsarerequiredbymanufac-turing.Inthisway,innovativeideasarenotinhibited.Quiteoften,morethanonedesignisdeveloped,uptothepointwheretheycanbecomparedagainsteachother.Itisentirelypossiblethatthedesignwhichisultimatelyacceptedwilluseideasexistinginoneoftherejecteddesignsthatdidnotshowasmuchoverallpromise.
Psychologistsfrequentlytalkabouttryingtofitpeopletothemachinestheyoperate.Itisessentiallytheresponsibilityofthedesignengineertostrivetofitmachinestopeople.Thisisnotaneasytask,sincethereisreallynoaveragepersonforwhichcertainoperatingdimensionsandproceduresareoptimum.
Anotherimportantpointwhichshouldberecognizedisthatadesignengineermustbeabletocommunicateideastootherpeopleiftheyaretobeincorporated.Communicatingthedesigntoothersisthefinal,vitalstepinthedesignprocess.Undoubtedlymanygreatdesigns,inventions,andcreativeworkshavebeenlosttomankindsimplybecausetheoriginatorswereunableorunwillingtoexplaintheiraccomplishmentstoothers.Presentationisasellingjob.Theengineer,whenpresentinganewsolutiontoadministrative,management,orsupervisorypersons,isattemptingtosellortoprovetothemthatthissolutionisabetterone.Unlessthiscanbedonesuccessfully,thetimeandeffortspentonobtainingthesolutionhavebeenlargelywasted.
Basically,thereareonlythreemeansofcommunicationavailabletous.Thesearethewritten,theoral,andthegraphicalforms.Thereforethesuccessfulengineerwillbetechnicallycompetentandversatileinallthreeformsofcommunication.Atechnicallycompetentpersonwholacksabilityinanyoneoftheseformsisseverelyhandicapped.Ifabilityinallthreeformsislacking,noonewilleverknowhowcompetentthatpersonis!
Thecompetentengineershouldnotbeafraidofthepossibilityofnotsucceedinginapresentation.Infact,occasionalfailureshouldbeexpectedbecausefailureorcriticismseemstoaccompanyeveryreallycreativeidea.Thereisagreatdealtobelearnedfromafailure,andthegreatestgainsareobtainedbythosewillingtoriskdefeat.Inthefinalanalysis,therealfailurewouldlieindecidingnottomakethepresentationatall.Tocommunicateeffectively,thefollowingquestionsmustbeanswered:
(1)Doesthedesignreallyserveahumanneed?
(2)Willitbecompetitivewithexistingproductsofrivalcompanies?
(3)Isiteconomicaltoproduce?
(4)Canitbereadilymaintained?
(5)Willitsellandmakeaprofit?
Onlytimewillprovidethetrueanswerstotheprecedingquestions,buttheproductshouldbedesigned,manufacturedandmarketedonlywithinitialaffirmativeanswers.Thedesignengineeralsomustcommunicatethefinalizeddesigntomanufacturingthroughtheuseofdetailandassemblydrawings.
Quiteoften,aproblemwilloccurduringthemanufacturingcycle[3].Itmaybethatachangeisrequiredinthedimensioningortolerancingofapartsothatitcanbemorereadilyproduced.Thisfailsinthecategoryofengineeringchangeswhichmustbeapprovedbythedesignengineersothattheproductfunctionwillnotbeadverselyaffected.Inothercases,adeficiencyinthedesignmayappearduringassemblyortestingjustpriortoshipping.Theserealitiessimplybearoutthefactthatdesignisalivingprocess.Thereisalwaysabetterwaytodoitandthedesignershouldconstantlystrivetowardsfindingthatbetterway.
Designingstartswithaneed,realorimagined.Existingapparatusmayneedimprovementsindurability,efficiently,weight,speed,orcost.Newapparatusmaybeneededtoperformafunctionpreviouslydonebymen,suchascomputation,assembly,orservicing.Withtheobjectivewhollyorpartlydefined,thenextstepindesignistheconceptionofmechanismsandtheirarrangementsthatwillperformtheneededfunctions.
Forthis,freehandsketchingisofgreatvalue,notonlyasarecordofone'sthoughtsandasanaidindiscussionwithothers,butparticularlyforcommunicationwithone'sownmind,asastimulantforcreativeideas.
Whenthegeneralshapeandafewdimensionsoftheseveralcomponentsbecomeapparent,analysiscanbegininearnest.Theanalysiswillhaveasitsobjectivesatisfactoryorsuperiorperformance,plussafetyanddurabilitywithminimumweight,andacompetitiveeast.Optimumproportionsanddimensionswillbesoughtforeachcriticallyloadedsection,togetherwithabalancebetweenthestrengthoftheseveralcomponents.Materialsandtheirtreatmentwillbechosen.Theseimportantobjectivescanbeattainedonlybyanalysisbasedupontheprinciplesofmechanics,suchasthoseofstaticsforreactionforcesandfortheoptimumutilizationoffriction;ofdynamicsforinertia,acceleration,andenergy;ofelasticityandstrengthofmaterialsforstressanddeflection;andoffluidmechanicsforlubricationandhydrodynamicdrives.
Finally,adesignbaseduponfunctionandreliabilitywillbecompleted,andaprototypemaybebuilt.Ifitstestsaresatisfactory,andifthedeviceistobeproducedinquantity,theinitialdesignwillundergocertainmodificationsthatenableittobemanufacturedinquantityatalowercost.Duringsubsequentyearsofmanufactureandservice,thedesignislikelytoundergochangesasnewideasareconceivedorasfurtheranalysisbasedupontestsandexperienceindicatealterations.Salesappeal,customersatisfaction,andmanufacturecostareallrelatedtodesign,andabilityindesignisintimatelyinvolvedinthesuccessofanengineeringventure.
Tostimulatecreativethought,thefollowingrulesaresuggestedforthedesigner.
1.Applyingenuitytoutilizedesiredphysicalpropertiesandtocontrolundesiredones.
Theperformancerequirementsofamachinearemetbyutilizinglawsofnatureorpropertiesofmatter(e.g.,flexibility,strength,gravity,inertia,buoyancy,centrifugalfor,principlesoftheleverandinclinedplane,friction,viscosity,fluidpressure,andthermalexpansion),alsothemanyelectrical,optical,thermal,andchemicalphenomena.
However,whatmaybeusefulinoneapplicationmaybedetrimentalinthenext.Flexibilityisdesiredinvalvespringsbutnotinthevalvecamshaft;frictionisdesiredattheclutchfacebutnotintheclutchbearing.Ingenuityindesignshouldbeappliedtoutilizeandcontrolthe
physicalpropertiesthataredesiredandtominimizethosethatarenotdesired.
2.Provideforfavorablestressdistributeandstiffnesswithminimumweight.Oncomponentssubjectedtofluctuatingstress,particularattentionisgivent