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,high-velocityjetsofliquidsandabrasives.Materialsthatinthepasthavebeenextremelydifficulttoform,arenowformedwithmagneticfields,explosives,andtheshockwavesfrompowerfulelectricsparks.Material-joiningcapabilitieshavebeenexpandedwiththeuseofhigh-frequencysoundwavesandbeamsofelectrons.Inthepast50years,over20differentnontraditionalmanufacturingprocesseshavebeeninventedandsuccessfullyimplementedintoproduction.Thereasontherearesuchalargenumberofnontraditionalprocessesisthesamereasontherearesuchalargenumberofconventionalprocesses；eachprocesshasitsowncharacteristicattributesandlimitations,hencenooneprocessisbestforallmanufacturingsituations.Inothercases,nontraditionalprocessesareusedtoreducethenumberofrejectsexperiencedbytheoldmanufacturingmethodbyincreasingrepeatability,reducingin-processbreakageoffragileworkpieces,orbyminimizingdetrimentaleffectsonworkpieceproperties.Asstatedpreviously,thepurposeofmechanicaldesignistoproduceaproductwhichwillserveaneedforman.Inventions,discoveryandscientificknowledgebythemselvesdonotnecessarilybenefitpeople；onlyiftheyareincorporatedintoadesignedproductwillabenefitbederived.Itshouldberecognized,therefore,thatahumanneedmustbeidentifiedbeforeaparticularproductisdesigned.Mechanicaldesignshouldbeconsideredtobeanopportunitytouseinnovativetalentstoenvisionadesignofaproduct,toanalyzethesystemandthenmakesoundjudgmentsonhowtheproductistobemanufactured.Itisimportanttounderstandthefundamentalsofengineeringratherthanmemorizemerefactsandequations.Therearenofactsorequationswhichalonecanbeusedtoprovideallthecorrectdecisionsrequiredtoproduceagooddesign.Ontheotherhand,anycalculationsmademustbedonewiththeutmostcareandprecision.Gooddesignrequiretryingnewideasandbeingwillingtotakeacertainamountofrisk,knowingthatifthenewideanotworktheexistingmethodcanbereinstated.Thusadesignermusthavepatience,sincethereisnoassuranceofsuccessforthetimeandeffortexpended.Creatingacompletelynewdesigngenerallyrequiresthatmanyoldandwell-establishedmethodsbethrustaside.Thisisnoteasysincemanypeopleclingtofamiliarideas,techniquesandattitudes.Adesignengineershouldconstantlysearchforwaystoimproveanexistingproductandmustdecidewhatold,provenconceptsshouldbeusedandwhatnew,untriedideasshouldbeincorporated.Duringthebeginningstagesofdesign,creativityshouldbeallowedtoflourishwithoutagreatnumberofconstraints.Eventhoughmanyimpracticalideasmayarise,itisusuallyeasytoeliminatethemintheearlystagesofdesignbeforefirmdetailsarerequiredbymanufacturing.Inthisway,innovativeideasarenotinhibited.Quiteoften,morethanonedesignisdeveloped,uptothepointwheretheycanbecomparedagainsteachother.Itisentirelypossiblethatthedesignwhichisultimatelyacceptedwilluseideasexistinginoneoftherejecteddesignsthatdidnotshowasmuchoverallpromise.Anotherimportantpointwhichshouldberecognizedisthatadesignengineermustbeabletocommunicateideastootherpeopleiftheyaretobeincorporated.Initially,thedesignermustcommunicateapreliminarydesigntogetmanagementapproval.Thisisusuallydonebyverbaldiscussionsinconjunctionwithdrawinglayoutsandwrittenmaterial.Tocommunicateeffectively,thefollowingquestionsmustbeanswered:(1)Doesthedesignreallyserveahumanneed?(2)Willitbecompetitivewithexistingproductsofrivalcompanies?(3)Isiteconomicaltoproduce?(4)Canitbereadilymaintained?(5)Willitsellandmakeaprofit?Besides,fortheproducersandadministrativepersonneloftheproducts,mechatronicshasmanyadvantagesasfollows:(1)HighCapitalEquipmentUtilizationTypically,thethroughputforasetofmachinesinamechatronicssystemwillbeuptothreetimesthatforthesamemachinesinastand-alonejobshopenvironment.(2)ReducedCapitalEquipmentCoststhehighutilizationofequipmentresultsintheneedforfewermachinesinthemechatronicsystemtodothesameworkasinaconventionalsystem.(3)ReducedDirectLaborCostsSinceeachmachineiscompletelyundercomputercontrol,full-timeoversightisnotrequired.(4)ReducedWork-in-ProcessInventoryandLeadTimeThereductionofwork-in-processinaisquitedramaticwhencomparedtoajob-shopenvironment.(5)ResponsivenesstoChangingProductionRequirementsAmechatronicsystemhastheinherentflexibilitytomanufacturedifferentproductsasthedemandsofthemarketplacechangeorasengineeringdesignchangesareintroduced.(6)AbilitytoMaintainProductionManymechatronicsystemsaredesignedtodegraderationallywhenoneormoremachinesfail.(7)HighProductQualitySometimes,anoverlookedadvantageofamechatronicsystemespeciallywhencomparedtomachinesthathavenotbeenfederatedintoacooperativesystem,isimprovedproductquality.(8)OperationalFlexibilityOperationalflexibilityoffersasignificantofproductivity.(9)CapacityFlexibilityWithreasonableplanningforavailablefloor,amechatronicsysteminitiallycanbedesignedforlowproduction,andprovidenecessaryadditionalproductivityaswell.Onlytimewillprovidethetrueanswerstotheprecedingquestions,buttheproductshouldbedesigned,manufacturedandmarkedonlywithinitialaffirmativeanswers.Thedesignengineeralsomustcommunicatethefinalizeddesigntomanuf