3英文翻译珩磨.docx

3英文翻译珩磨.docx

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3英文翻译珩磨

FundamentalsofMechanicalDesign

Mechanicaldesignmeansthedesignofthingsandsystemsofamechanicalnature—machines,products,structures,devices,andinstruments.Forthemostpartmechanicaldesignutilizesmathematics,thematerialssciences,andtheengineering-mechanicssciences.

Thetotaldesignprocessisofinteresttous.Howdoesitbegin?

Doestheengineersimplysitdownathisdeskwithablanksheetofpaper?

And,ashejotsdownsomeideas,whathappensnext?

Whatfactorsinfluenceorcontrolthedecisionswhichhavetobemade?

Finally,then,howdoesthisdesignprocessend?

Sometimes,butnotalways,designbeginswhenanengineerrecognizesaneedanddecidestodosomethingaboutit.Recognitionoftheneedandphrasingitinsomanywordsoftenconstituteahighlycreativeactbecausetheneedmaybeonlyavaguediscontent,afeelingofuneasiness,orasensingthatsomethingisnotright.

Theneedisusuallynotevidentatall.Forexample,theneedtodosomethingaboutafood-packagingmachinemaybeindicatedbythenoiselevel,bythevariationinpackageweight,andbyslightbutperceptiblevariationsinthequalityofthepackagingorwrap.

Thereisadistinctdifferencebetweenthestatementoftheneedandtheidentificationoftheproblemwhichfollowsthisstatement.Theproblemismorespecific.Iftheendisforcleanerair,theproblemmightbethatofreducingthedustdischargefrompower-plantstacks,orreducingthequantityofirritantsfromautomotiveexhausts.

Definitionoftheproblemmustincludeallthespecificationsforthethingthatistobedesigned.Thespecificationsaretheinputandoutputquantities,thecharacteristicsanddimensionsofthespacethethingmustoccupyandallthelimitationsonthesequantities.Inthiscasewemustspecifytheinputsandoutputsoftheboxtogetherwiththeircharacteristicsandlimitations.Thespecificationsdefinethecost,thenumbertobemanufactured,theexpectedlife,therange,theoperatingtemperature,andthereliability.

Therearemanyimpliedspecificationswhichresulteitherfromthedesigner’sparticularenvironmentorfromthenatureoftheproblemitself.Themanufacturingprocesseswhichareavailable,togetherwiththefacilitiesofacertainplant,constituterestrictionsonadesigner’sfreedom,andhenceareapartoftheimpliedspecifications.Asmallplant,forinstance,maynotowncold-workingmachinery.Knowingthis,thedesignerselectsothermetal-processingmethodswhichcanbeperformedintheplant.Thelaborskillsavailableandthecompetitivesituationalsoconstituteimpliedspecifications.

Aftertheproblemhasbeendefinedandasetofwrittenandimpliedspecificationshasbeenobtained,thenextstepindesignisthesynthesisofanoptimumsolution.Nowsynthesiscannottakeplacewithoutbothanalysisandoptimizationbecausethesystemunderdesignmustbeanalyzedtodeterminewhethertheperformancecomplieswiththespecifications.

Thedesignisaniterativeprocessinwhichweproceedthroughseveralsteps,evaluatetheresults,andthenreturntoanearlierphaseoftheprocedure.Thuswemaysynthesizeseveralcomponentsofasystem,analyzeandoptimizethem,andreturntosynthesistoseewhateffectthishasontheremainingpartsofthesystem.Bothanalysisandoptimizationrequirethatweconstructordeviseabstractofthesystemwhichwilladmitsomeformofmathematicalanalysis.Wecallthesemodelsmathematicalmodels.Increatingthemitisourhopethatwecanfindonewhichwillsimulatethephysicalsystemverywell.

Evaluationisasignificantphaseofthetotaldesignprocess.Evaluationisthefinalproofofasuccessfuldesign,whichusuallyinvolvesthetestingofaprototypeinthelaboratory.Herewewishtodiscoverifthedesignreallysatisfiestheneedorneeds.Isitreliable?

Willitcompetesuccessfullywithsimilarproducts?

Isiteconomicaltomanufactureandtouse?

Isiteasilymaintainedandabjusted?

Canaprofitbemadefromitssaleoruse?

Communicatingthedesigntoothersifthefinal,vitalstepinthedesignprocess.Undoubtedlymanygreatdesigns,inventions,andcreativeworkshavebeenlosttomankindsimplybecausetheoriginatorswereunableorunwillingtoexplaintheiraccomplishmentstoothers.Presentationisasellingjob.Theengineer,whenpresentinganewsolutiontoadministrative,management,orsupervisorypersons,isattemptingtosellortoprovetothemthatthissolutionisabetterone.Unlessthiscanbedonesuccessfully,thetimeandeffortspentonobtainingthesolutionhavebeenlargelywasted.

Basically,thereareonlytheremeansofcommunicationavailabletous.Thesearethewritten,theoral,andthegraphicalforms.Thereforethesuccessfulengineerwillbetechnicallycompetentandversatileinallthreeformsofcommunication.Atechnicallycompetentpersonwholacksabilityinanyoneoftheseformsisseverelyhandicapped.Ifabilityinallthreeformsislacking,ononewilleverknowhowcompetentthatpersonis!

Thecompetentengineershouldnotbeafraidofthepossibilityofnotsucceedinginapresentation.Infact,occasionalfailureshouldbeexpectedbecausefailureorcriticismseemstoaccompanyeveryreallycreativeidea.Thereisagreatdealtobelearnedfromafailure,andthegreatestgainsareobtainedbythosewillingtoriskdefeat.Inthefinalanalysis,therealfailurewouldlieindecidingnottomakethepresentationatall.

Machinedesignistheapplicationofscienceandtechnologytodeviseneworimprovedproductsforthepurposeofsatisfyinghumanneeds.Itisavastfieldofengineeringtechnologywhichnotonlyconcernsitselfwiththeoriginalconceptionoftheproductintermsoftermsofitssize,shapeandconstructiondetails,butalsoconsidersthevariousfactorsinvolvedinthemanufacture,marketinganduseoftheproduct.

Peoplewhoperformthevariousfunctionsofmachinedesignaretypicallycalleddesigners,ordesignengineers.Machinedesignisbasicallyacreativeactivity.However,inadditiontobeinginnovative,adesignengineermustalsohaveasoildbackgroundintheareasofmechanicaldrawing,kinematics,dynamics,materialsengineering,strengthofmaterialsandmanufacturingprocesses.

Asstatedpreviously,thepurposeofmachinedesignistoproduceaproductwhichwillserveaneedforman.Inventions,discoveriesandscientificknowledgebythemselvesdonotnecessarilybenefitpeople;onlyiftheyareincorporatedintoadesignedproductwillabenefitbederived.Itshouldberecognized,therefore,thatahumanneedmustbeidentifiedbeforeaparticularproductisdesigned.

Gooddesignsrequiretryingnewideasandbeingwillingtotakeacertainamountofrisk,knowingthatifthenewideadoesnotworktheexistingmethodcanbereinstated.Thusadesignermusthavepatience,sincethereisnoassuranceofsuccessforthetimeandeffortexpended.Creatingacompletelynewdesigngenerallyrequiresthatmanyoldandwell-establishedmethodsbethrustaside.Thisisnoteasysincemanypeopleclingtofamiliarideas,techniquesandattitudes.Adesignengineershouldconstantlysearchforwaystoimproveanexistingproductandmustdecidewhatold,provenconceptsshouldbeusedandwhatmew,untriedideasshouldbeincorporated.

Newdesignsgenerallyhave“bugs”orunforeseenproblemswhichmustbeworkedoutbeforethesuperiorcharacteristicsofthenewdesignscanbeenjoyed.Thusthereisachanceforasuperiorproduct,butonlyathigherrisk.Itshouldbeemphasizedthat,ifadesigndoesnotwarrantradicalnewmethods,suchmethodsshouldnotbeappliedmerelyforthesakeofchange.

Duringthebeginningstagesofdesign,creativityshouldbeallowedtoflourishwithoutagreatnumberofconstraints.Eventhoughmanyimpracticalideasmayarise,itisusuallyeasytoeliminatethemintheearlystagesofdesignbeforefirmdetailsarerequiredbymanufacturing.Inthisway,innovativeideasarenotinhibited.Quiteoften,morethanonedesignisdeveloped,uptothepointwheretheycanbecomparedagainsteachother.Itisentirelypossiblethatthedesignwhichisultimatelyacceptedwilluseideasexistinginoneoftherejecteddesignsthatdidnotshowasmuchoverallpromise.

Psychologistsfrequentlytalkabouttryingtofitpeopletothemachinestheyoperate.Itisessentiallytheresponsibilityofthedesignengineertostrivetofitmachinestopeople.Thisisnotaneasytask,sincethereisreallynoaveragepersonforwhichcertainoperatingdimensionsandproceduresareoptimum.

Anotherimportantpointwhichshouldberecognizedisthatadesignengineermustbeabletocommunicateideastootherpeopleiftheyaretobeincorporated.Initially,thedesignermustcommunicateapreliminarydesigntogetmanagementapproval.Thisisusuallydonebyverbaldiscussionsinconjunctionwithdrawinglayoutsandwrittenmaterial.Tocommunicateeffectively,thefollowingquestionsmustbeanswered:

Doesthedesignreallyserveahumanneed?

Willitbecompetitivewithexistingproductsofrivalcompanies?

Isiteconomicaltoproduce?

Canitbereadilymaintained?

Willitsellandmakeaprofit?

Onlytimewillprovidethetrueanswerstotheprecedingquestions,buttheproductshouldbedesigned,manufacturedandmarketedonlywithinitialaffirmativeanswers.Thedesignengineeralsomustcommunicatethefinalizeddesigntomanufacturingthroughtheuseofdetailandassemblydrawings.

Quiteoften,aproblemwilloccurduringthemanufacturingcycle.Itmaybethatachangeisrequiredinthedimensioningortelegrammingofapartsothatiscanbemorereadilyproduced.Thisfallsinthecategoryofengineeringchangeswhichmustbeapprovedbythedesignengin