中英文翻译--机械工程设计.doc

Mechanicalengineeringdesign1.ThemeaningofdesignThebeginningtheparticularneedtothesatisfiedmaybequitewell-defined.Herearetwoexamplesofwell-definedneeds.1.Howcanweobtainlargequantitiesofpowercleanly,safely,andeconomicallywithoutusingfossilfuelsandwithoutdamagingthesurfaceoftheearth?2.Thisgearshaftisgivingtrouble；therehavebeeneightfailuresinthelastsixweeks.Dosomethingaboutit.Ontheotherhandtheparticularneedtobesatisfiedmaybesonebulousandill-definedthataconsiderableamountofthoughtandeffortisnecessaryinordertostateitclearlyasaproblemrequiringasolution.Herearetwoexamples.1.Lotsofpeoplearekilledinairplaneaccidents.2.Inbigcitiestherearetoomanyautomobilesonthestreetsandhighways.Thissecondtypeofdesignsituationischaracterizedbythefactthatneithertheneednortheproblemtobesolvedhasbeenidentified.Note,too,thatthesituationmaycontainmanyproblems.Wecanclassifydesigntoo.Forinstance:1.Clothingdesign7.Bridgedesign2.Interiordesign8.Computer-aideddesign3.Highwaydesign9.Heatingsystemdesign4.Landscapedesign10.Machinedesign5.Buildingdesign11.Engineeringdesign6.Shipdesign12.ProcessdesignInfactthereareanendlessnumber,sincewecanclassifydesignaccordingtotheparticulararticleorproductoraccordingtotheprofessionalfield.Incontrasttoscientificormathematicalproblems,designproblemshavenouniqueanswers；itisabsurd,forexample,torequestthe“correctanswer”toadesignproblem,becausethereisnone.Infacta“good”answertodaymaywellturnouttobea“poor”answertomorrow,ifthereisagrowthofknowledgeduringtheperiodorifthereareotherstructureorsocietalchanges.Almosteveryoneisinvolvedwithdesigninonewayoranother,evenindailyliving,becauseproblemsareposedandsituationsarisewhichmustbesolved.Considerthedesignofafamilyvacation.Theremaybesevendifferentplacestogo,allthedifferentdistancesfromhome.Thecostsoftransportationaredifferentforeach,andsomeoftheoptionsrequireovernightstopsontheway.Thechildrenwouldliketogotoalakeorseashoreresort.Thewifewouldprefertogotoalargecitywithdepartmentstoreshopping,theatres,andnightclubs.Thehusbandprefersaresortwithagolfcourse.Whentheseneedsanddesiresarerelatedtotimeandmoney,varioussolutionsmaybefound.Ofthesetheremayormaynotbeoneormoreoptimalsolutions.Butthesolutionchosenwillincludethetravelroute,thestops,themodeoftransportation,andthenamesandlocationsofresorts,motels,campingsites,orotheraway-from-homefacilities.Itishardtoseethatthereisreallyaratherlargegroupofinterrelatedcomplexfactorsinvolvedinarrivingatoneofthesolutionstothevacationdesignproblem.Adesignisalwayssubjecttocertainproblem-solvingconstraints.Forexample,twooftheconstraintsonthevacationdesignproblemarethetimeandmoneyavailableforthevacation.Note,too,thattherearealsoconstraintsonthesolution,inthecaseabovesomeofthoseconstraintsarethedesireandneedsofeachofthefamilymembers.Finally,thedesignsolutionfoundmightwellbeoptimal.Inthiscaseanoptimalsolutionisobtainedwheneachandeveryfamilymembercansaythatheorshehadagoodtime.Adesignproblemisnotahypotheticalproblematall.Designhasanauthenticpurposethecreationofanendresultbytakingdefiniteactingorthecreationofsomethinghavingphysicalreality.Inengineeringtheword“design”conveysdifferentmeaningtodifferentpersons.Somethinkofadesignerasonewhoemploysthedrawingboardtodraftthedetailsofagear,clutch,orothermachinemember.Othersthinkofdesignasthecreationofacomplexsystem,suchasacommunicationsnetwork.Insomeareasofengineeringtheworddesignhasbeenreplacedbyothertermssuchassystemsengineeringorapplieddecisiontheory.Butnomatterwhatwordsareusedtodescribethedesignfunction,inengineeringitisstilltheprocessinwhichscientifictheprinciplesandthetoolsofengineeringmathematics,computers,graphics,andEnglishareusedtoproduceaplanwhich,whencarriedout,willsatisfyahumanneed.2.ThephasesofdesignThetotaldesignprocessisofinteresttous,howdoesitbegin?Doestheengineersimplysitdownathisorherdeskwithablanksheetofpaperandjotdownsomeideas?Whathappensnext?Whatfactorsinfluenceorcontrolthedecisions,whichhavetobemade?Finally,howdoesthisdesignprocessend?Thecompleteprocess,fromstarttofinish,isoftenoutlinedasinFigure.Theprocessbeginswitharecognitionofaneedandadecisiontodosomethingaboutit,aftermanyiterations,theprocessendswiththepresentationoftheplansforsatisfyingtheneed,weshouldexaminethesestepsinthedesignprocessindetail.3.MechanicalengineeringdesignMechanicaldesignmeansthedesignofthingsandsystemofamechanicalnaturemachines,products,structures,devices,andinstruments.Forthemostpart,mechanicaldesignutilizesmathematics,thematerialssciences,andtheengineeringmechanicalscience.Mechanicalengineeringdesignincludesallmechanicaldesign,butitisabroaderstudybecauseitincludesallthedisciplinesofmechanicalengineering,suchasthethermal-fluidssciences,too.Asidefromthefundamentalsciencesthatarerequired,thefirststudiesinmechanicalengineeringdesignareinmechanicaldesign,andhencethisistheapproachtakeninthisbook.4.DesignProcessandStagesMechanicaldesigniseithertoformulateallengineeringplanforthesatisfactionforthespecifiedneedortosolveanengineeringproblem.Itisvastfieldofengineeringtechnologywhichnotonlyconcernsitselfwiththeoriginalconceptionoftheproductintermsofitssize,shapeandconstructiondetails,butallconsidersthevariousfactorsinvolvedinthemanufacture,marketinganduseofproduct.Mechanicaldesigninvolvesarangeofdisciplinesinmaterials,mechanics,heat,flow,control,electronicsandproduction.Mechanicaldesignshouldbeconsideredtobeanopportunitytouseinnovativetalentstoenvisionadesignofaproduct,toanalyzethesystemandthenmakesoundjudgmentsonhowtheproductistobemanufactured.Itisimportanttounderstandthefundamentalsofengineeringratherthanmemorizemerefactsandequations.Therearenofactsorequationswhichalonecanbeusedtoprovideallthecorrectdecisionsrequiredtoproduceagooddesign.Ontheotherhand,anycalculationsmustbedonewiththeutmostcareandprecision.Forexample,ifadecimalpointismisplaced,anotherwiseacceptabledesignmaynotfunction.Mechanicaldesignmaybesimpleorenormouslycomplex,easyordifficult,mathematicalornonmathematical,itmayinvolveatrivialproblemoroneofgreatimportance.Gooddesignistheorderlyandinterestingarrangementofallideatoprovidecertainresultsandeffects.Awell-designedproductisfunctional,efficient,anddependable.Suchaproductislessexpensivethanasimilarpoorlydesignedproductthatdoesnotfunctionproperlyandmustconstantlyberepaired.Peoplewhoperformthevariousfunctionsofmechanicaldesignaretypicallycalleddesigners,ordesignengineers.Mechanicaldesignisbasicallyacreativeactivity.However,inadditiontobeinginnovative,adesignengineermustalsohaveasolidbackgroundintheareasofmechanicaldrawing,kinematics,dynamics,materialsengineering,manufacturingprocesses.Thedesignermustfirstcarefullydefinetheproblem,usinganengineeringapproach,toensurethatanyproposedsolutionwillsolvetherightproblem.Itisimportantthatthedesignerbeginbyidentifyingexactlyhowheorshewillrecognizeasatisfactoryalternative,andhowtodistinguishbetweentwosatisfactoryalternativesinordertoidentifythebetter.Soindustrialdesignersmusthavecreativeimagination,knowledgeofengineering,productiontechniques,tools,machines,andmaterialstodesignanewproductformanufacture,ortoimproveanexistingproduct.Inthemodernindustrializedworld,thewealthandlivingstandardsofanationarecloselylinkedwiththeircapabilitiesdesignandmanufacturingengineeringproducts.Itcanbeclaimedthattheadvancementofmechanicaldesignandmanufacturingcanremarkablypromotetheoveralllevelofacountrysindustrialization.Manycountriesareplayingmoreandmorevitalroleintheglobalmanufacturingindustry.Toacceleratesuchanindustrializingprocess,highlyskilleddesignengineershavingextensiveknowledgeandexpertiseareneeded.5.MechanicaldesignprocessProductdesignrequiresmuchresearchanddevelopment.Manyconceptofanideamustbestudied,tried,refined,andtheneitherusedordiscarded.Althoughthecontentofeachengineeringproblemisunique,thedesignersfollowthesimilarprocesstosolvetheproblems.Thecompleteprocessisoftenoutlinedasinfigures.Thedesignprocessusuallybeginswithaspecificationofasolution.Wesometimesalludetoadesigncycle,buttheprocessmaycontainadesigncycleplusdesignimplementation,whichinvolvesactualproductionbaseduponthedesign.Thedesigncyclecaninvolvetheoriginalthoughts,sketches,andknowledgethatinthespecificationstageproduceengineeringdrawings.Computer-aiddesignisnowemployedtoimplementacycleinwhichvariousdesignsordesignideasmaybetestedorsimulated.6.ContentsofMechanicalDesignMechanicaldesignisanimportanttechnologicalbasiccourseinmechanicalengineeringeducation.Itsobjectiveistoprovidetheconcepts,procedures,data,anddecisionanalysistechniquesnecessarytodesignmachineelementscommonlyfoundinmechanicaldevicesandsystems；todevelopengineeringstudentscompetenceofmechanicaldesignthatistheprimaryconcernofmachinerymanufacturingandthekeytomanufacturinggoodproducts.Mechanicaldesigncoversthefollowingcontents:1Providesanintroductiontothedesignprocess,p