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机械外文翻译--机械设计概述.doc

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机械外文翻译--机械设计概述.doc

AnoverviewofmechanicaldesignThefirststepinthemanufactureofanyproductisdesign.Mechanicaldesignistheapplicationofscienceandtechnologytodeviseneworimprovedproductsforthepurposeofsatisfyinghumanneeds.Itisavastfieldofengineeringtechnologywhichnotonlyconcernsitselfwiththeoriginalconceptionoftheproductintermsofitssize,shapeandconstructiondetails,butalsoconsidersthevariousfactorsinvolvedinthemanufacture,marketinganduseoftheproduct.Peoplewhoperformthevariousfunctionsofmachinedesignaretypicallycalleddesigners,ordesignengineers.Mechanicaldesignisacreativeactivity.However,inadditiontobeinginnovative,adesignengineermustalsohaveasolidbackgroundintheareasofmechanicaldrawing,kinematics,dynamics,materialsengineering,strengthofmaterialsandmanufacturingprocesses.Herewetaketheselectionofmaterialsasanexample.Duringrecentyearstheselectionofengineeringmaterialshasassumedgreatimportance.Moreover,theprocessshouldbeoneofcontinualreevaluation.Newmaterialsoftenbecomeavailableandtheremaybeadecreasingavailabilityofothers.Concernsregardingenvironmentpollution,recyclingandworkerhealthandsafetyoftenimposenewconstraints.Thedesireforweightreductionorenergysavingsmaydictatetheuseofdifferentmaterials.Pressuresfromdomesticandinternationalcompetition,increasedserviceabilityrequirements,andcustomerfeedbackmayallpromotematerialsreevaluation.Theextentofproductliabilityactions,oftentheresultofimpropermaterialuse,hashadamarkedimpact.Inaddition,theinterdependencebetweenmaterialandtheirprocessinghasbecomebetterrecognized.Thedevelopmentofnewprocessesoftenforcesreevaluationofthematerialbeingprocessed.Therefore,itisimperativethatdesignandmanufacturingengineersexerciseconsiderablecareinselecting,specifying,andutilizingmaterialsiftheyaretoachievesatisfactoryresultsatreasonablecostandstillassurequality.Inmechanicsprocessing,millingandgrindingarealwaysundertheconsiderationofthedesigners.Withtheexceptionsofturninganddrilling,millingisundoubtedlythemostwidelyusedmethodofremovingmetal.Wellsuitedandreadilyadaptedtotheeconomicalproductionofanyquantityofparts,thealmostunlimitedversatilityofthemillingprocessmeritstheattentionandconsiderationofdesignersseriouslyconcernedwiththemanufactureoftheirproduct.Grindingisoneofthemostwidelyusedmethodsoffinishingpartstoextremelyclosetolerancesandlowsurfaceroughness.Currently,therearegrindersforalmosteverytypeofgrindingoperation.Particulardesignfeaturesofapartdictatetoalargedegreethetypeofgrindingmachinerequired.Whereprocessingcostsareexcessive,partsredesignedtoutilizealessexpensive,higheroutputgrindingmethodmaybewellworthwhile.Forexample,whereverpossibletheproductioneconomyofcenterlessgrindingshouldbetakenadvantageofbyproperdesignconsideration.Althoughgrindingisusuallyconsideredafinishingoperation,itisoftenemployedasacompletemachiningprocessonworkwhichcanbegrounddownformroughconditionwithoutbeingturnedorotherwisemachined.Thusmanytypesofforgingsandotherpartsarefinishedcompletelywiththegrindingwheelatappreciablesavingsoftimeandexpense.Besides,theapplicationofnontraditionalmanufacturingprocesseswillbringmoreboldandinnovativedesign.Theconventionalmanufacturingprocessesinusetodayformaterialremovalprimarilyrelyonelectricmotorsandhardtoolmaterialstoperformtaskssuchassawing,drilling,andbroaching.Conventionalformingoperationsareperformedwiththeenergyfromelectricmotors,hydraulics,andgravity.Likewise,materialjoiningisconventionallyaccomplishedwiththermalenergysourcessuchasburninggasesandelectricarcs.Incontrast,nontraditionalmanufacturingprocessesharnessenergysourcesconsideredunconventionalbyyesterdaysstandards.Materialremovalcannowbeaccomplishedwithelectrochemicalreactions,highvelocityjetsofliquidsandabrasives.Materialsthatinthepasthavebeenextremelydifficulttoform,arenowformedwithmagneticfields,explosives,andtheshockwavesfrompowerfulelectricsparks..Materialjoiningcapabilitieshavebeenexpandedwiththeuseofhighfrequencysoundwavesandbeamsofelectrons.Inthepast50years,over20differentnontraditionalmanufacturingprocesseshavebeeninventedandsuccessfullyimplementedintoproduction.Thereasontherearesuchalargenumberofnontraditionalprocessesisthesamereasontherearesuchalargenumberofconventionalprocesseseachprocesshasitsowncharacteristicattributesandlimitations,hencenooneprocessisbestforallmanufacturingsituations.Inothercases,nontraditionalprocessesareusedtoreducethenumberofrejectsexperiencedbytheoldmanufacturingmethodbyincreasingrepeatability,reducinginprocessbreakageoffragileworkpieces,orbyminimizingdetrimentaleffectsonworkpieceproperties.Asstatedpreviously,thepurposeofmechanicaldesignistoproduceaproductwhichwillserveaneedforman.Inventions,discoveryandscientificknowledgebythemselvesdonotnecessarilybenefitpeopleonlyiftheyareincorporatedintoadesignedproductwillabenefitbederived.Itshouldberecognized,therefore,thatahumanneedmustbeidentifiedbeforeaparticularproductisdesigned.Mechanicaldesignshouldbeconsideredtobeanopportunitytouseinnovativetalentstoenvisionadesignofaproduct,toanalyzethesystemandthenmakesoundjudgmentsonhowtheproductistobemanufactured.Itisimportanttounderstandthefundamentalsofengineeringratherthanmemorizemerefactsandequations.Therearenofactsorequationswhichalonecanbeusedtoprovideallthecorrectdecisionsrequiredtoproduceagooddesign.Ontheotherhand,anycalculationsmademustbedonewiththeutmostcareandprecision.Gooddesignrequiretryingnewideasandbeingwillingtotakeacertainamountofrisk,knowingthatifthenewideanotworktheexistingmethodcanbereinstated.Thusadesignermusthavepatience,sincethereisnoassuranceofsuccessforthetimeandeffortexpended.Creatingacompletelynewdesigngenerallyrequiresthatmanyoldandwellestablishedmethodsbethrustaside.Thisisnoteasysincemanypeopleclingtofamiliarideas,techniquesandattitudes.Adesignengineershouldconstantlysearchforwaystoimproveanexistingproductandmustdecidewhatold,provenconceptsshouldbeusedandwhatnew,untriedideasshouldbeincorporated.Duringthebeginningstagesofdesign,creativityshouldbeallowedtoflourishwithoutagreatnumberofconstraints.Eventhoughmanyimpracticalideasmayarise,itisusuallyeasytoeliminatethemintheearlystagesofdesignbeforefirmdetailsarerequiredbymanufacturing.Inthisway,innovativeideasarenotinhibited.Quiteoften,morethanonedesignisdeveloped,uptothepointwheretheycanbecomparedagainsteachother.Itisentirelypossiblethatthedesignwhichisultimatelyacceptedwilluseideasexistinginoneoftherejecteddesignsthatdidnotshowasmuchoverallpromise.Anotherimportantpointwhichshouldberecognizedisthatadesignengineermustbeabletocommunicateideastootherpeopleiftheyaretobeincorporated.Initially,thedesignermustcommunicateapreliminarydesigntogetmanagementapproval.Thisisusuallydonebyverbaldiscussionsinconjunctionwithdrawinglayoutsandwrittenmaterial.Tocommunicateeffectively,thefollowingquestionsmustbeanswered1Doesthedesignreallyserveahumanneed2Willitbecompetitivewithexistingproductsofrivalcompanies3Isiteconomicaltoproduce4Canitbereadilymaintained5WillitsellandmakeaprofitBesides,fortheproducersandadministrativepersonneloftheproducts,mechatronicshasmanyadvantagesasfollows1HighCapitalEquipmentUtilizationTypically,thethroughputforasetofmachinesinamechatronicssystemwillbeuptothreetimesthatforthesamemachinesinastandalonejobshopenvironment.2ReducedCapitalEquipmentCoststhehighutilizationofequipmentresultsintheneedforfewermachinesinthemechatronicsystemtodothesameworkasinaconventionalsystem.3ReducedDirectLaborCostsSinceeachmachineiscompletelyundercomputercontrol,fulltimeoversightisnotrequired.4ReducedWorkinProcessInventoryandLeadTimeThereductionofworkinprocessinaisquitedramaticwhencomparedtoajobshopenvironment.5ResponsivenesstoChangingProductionRequirementsAmechatronicsystemhastheinherentflexibilitytomanufacturedifferentproductsasthedemandsofthemarketplacechangeorasengineeringdesignchangesareintroduced.6AbilitytoMaintainProductionManymechatronicsystemsaredesignedtodegraderationallywhenoneormoremachinesfail.7HighProductQualitySometimes,anoverlookedadvantageofamechatronicsystemespeciallywhencomparedtomachinesthathavenotbeenfederatedintoacooperativesystem,isimprovedproductquality.8OperationalFlexibilityOperationalflexibilityoffersasignificantofproductivity.9CapacityFlexibilityWithreasonableplanningforavailablefloor,amechatronicsysteminitiallycanbedesignedforlowproduction,andprovidenecessaryadditionalproductivityaswell.Onlytimewillprovidethetrueanswerstotheprecedingquestions,buttheproductshouldbedesigned,manufacturedandmarkedonlywithinitialaffirmativeanswers.Thedesignengineeralsomustcommunicatethefinalizeddesigntomanufacturingthroughtheuseofdetailandassemblydrawings.Quiteoften,aproblemwilloccurduringthemanufacturingcycle.Itmaybethatachangeisrequiredinthedimensioningortoleranceofpartsothatitcanbemorereadilyproduced.Thisfallsinthecategoryofengineeringchangeswhichmustbeapprovedbythedesignengineersothattheproductfunctionwillnotbeadverselyaffected.Inothercases,adeficiencyinthedesignmayappearduringassemblyortestingjustpriortoshipping.Theserealitiessimplybearoutthefactthatdesignisalivingprocess.Thereisalwaysabetterwaytodoitandthedesignershouldconstantlystrivetowardsfindingthatbetterway.Thecompetentengineershouldnotbeafraidofthepossibilityofnotsucceedinginapresentation.Infact,occasionalfailureshouldbeexpectedbecausefailureorcriticismseemstoaccompanyeveryreallycreativeidea.Thereisagreatdealtobelearnedformafailureandthegreatestgainsareobtainedbythosewillingtoriskdefeat.Inthefinalanalysis,therealfailurewouldlieindecidingnottomakethepresentationatall.

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