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1、AnoverviewofmechanicaldesignThefirststepinthemanufactureofanyproductisdesign.Mechanicaldesignistheapplicationofscienceandtechnologytodeviseneworimprovedproductsforthepurposeofsatisfyinghumanneeds.Itisavastfieldofengineeringtechnologywhichnotonlyconcernsitselfwiththeoriginalconceptionoftheproductinte

2、rmsofitssize,shapeandconstructiondetails,butalsoconsidersthevariousfactorsinvolvedinthemanufacture，marketinganduseoftheproduct.Peoplewhoperformthevariousfunctionsofmachinedesignaretypicallycalleddesigners,ordesignengineers.Mechanicaldesignisacreativeactivity.However,inadditiontobeinginnovative,adesi

3、gnengineermustalsohaveasolidbackgroundintheareasofmechanicaldrawing,kinematics,dynamics,materialsengineering,strengthofmaterialsandmanufacturingprocesses.Herewetaketheselectionofmaterialsasanexample.Duringrecentyearstheselectionofengineeringmaterialshasassumedgreatimportance.Moreover,theprocessshoul

4、dbeoneofcontinualreevaluation.Newmaterialsoftenbecomeavailableandtheremaybeadecreasingavailabilityofothers.Concernsregardingenvironmentpollution,recyclingandworkerhealthandsafetyoftenimposenewconstraints.Thedesireforweightreductionorenergysavingsmaydictatetheuseofdifferentmaterials.Pressuresfromdome

5、sticandinternationalcompetition,increasedserviceabilityrequirements,andcustomerfeedbackmayallpromotematerialsreevaluation.Theextentofproductliabilityactions,oftentheresultofimpropermaterialuse,hashadamarkedimpact.Inaddition,theinterdependencebetweenmaterialandtheirprocessinghasbecomebetterrecognized

6、.Thedevelopmentofnewprocessesoftenforcesreevaluationofthematerialbeingprocessed.Therefore,itisimperativethatdesignandmanufacturingengineersexerciseconsiderablecareinselecting,specifying,andutilizingmaterialsiftheyaretoachievesatisfactoryresultsatreasonablecostandstillassurequality.Inmechanicsprocess

7、ing，millingandgrindingarealwaysundertheconsiderationofthedesigners.Withtheexceptionsofturninganddrilling,millingisundoubtedlythemostwidelyusedmethodofremovingmetal.Wellsuitedandreadilyadaptedtotheeconomicalproductionofanyquantityofparts,thealmostunlimitedversatilityofthemillingprocessmeritstheattent

8、ionandconsiderationofdesignersseriouslyconcernedwiththemanufactureoftheirproduct.Grindingisoneofthemostwidelyusedmethodsoffinishingpartstoextremelyclosetolerancesandlowsurfaceroughness.Currently,therearegrindersforalmosteverytypeofgrindingoperation.Particulardesignfeaturesofapartdictatetoalargedegre

9、ethetypeofgrindingmachinerequired.Whereprocessingcostsareexcessive,partsredesignedtoutilizealessexpensive,higheroutputgrindingmethodmaybewellworthwhile.Forexample,whereverpossibletheproductioneconomyofcenterlessgrindingshouldbetakenadvantageofbyproperdesignconsideration.Althoughgrindingisusuallycons

10、ideredafinishingoperation,itisoftenemployedasacompletemachiningprocessonworkwhichcanbegrounddownformroughconditionwithoutbeingturnedorotherwisemachined.Thusmanytypesofforgingsandotherpartsarefinishedcompletelywiththegrindingwheelatappreciablesavingsoftimeandexpense.Besides,theapplicationofnontraditi

11、onalmanufacturingprocesseswillbringmoreboldandinnovativedesign.Theconventionalmanufacturingprocessesinusetodayformaterialremovalprimarilyrelyonelectricmotorsandhardtoolmaterialstoperformtaskssuchassawing,drilling,andbroaching.Conventionalformingoperationsareperformedwiththeenergyfromelectricmotors,h

12、ydraulics,andgravity.Likewise,materialjoiningisconventionallyaccomplishedwiththermalenergysourcessuchasburninggasesandelectricarcs.Incontrast,nontraditionalmanufacturingprocessesharnessenergysourcesconsideredunconventionalbyyesterdaysstandards.Materialremovalcannowbeaccomplishedwithelectrochemicalre

13、actions,high-velocityjetsofliquidsandabrasives.Materialsthatinthepasthavebeenextremelydifficulttoform,arenowformedwithmagneticfields,explosives,andtheshockwavesfrompowerfulelectricsparks.Material-joiningcapabilitieshavebeenexpandedwiththeuseofhigh-frequencysoundwavesandbeamsofelectrons.Inthepast50ye

14、ars,over20differentnontraditionalmanufacturingprocesseshavebeeninventedandsuccessfullyimplementedintoproduction.Thereasontherearesuchalargenumberofnontraditionalprocessesisthesamereasontherearesuchalargenumberofconventionalprocesses；eachprocesshasitsowncharacteristicattributesandlimitations,hencenoo

15、neprocessisbestforallmanufacturingsituations.Inothercases,nontraditionalprocessesareusedtoreducethenumberofrejectsexperiencedbytheoldmanufacturingmethodbyincreasingrepeatability,reducingin-processbreakageoffragileworkpieces,orbyminimizingdetrimentaleffectsonworkpieceproperties.Asstatedpreviously,the

16、purposeofmechanicaldesignistoproduceaproductwhichwillserveaneedforman.Inventions,discoveryandscientificknowledgebythemselvesdonotnecessarilybenefitpeople；onlyiftheyareincorporatedintoadesignedproductwillabenefitbederived.Itshouldberecognized,therefore,thatahumanneedmustbeidentifiedbeforeaparticularp

17、roductisdesigned.Mechanicaldesignshouldbeconsideredtobeanopportunitytouseinnovativetalentstoenvisionadesignofaproduct,toanalyzethesystemandthenmakesoundjudgmentsonhowtheproductistobemanufactured.Itisimportanttounderstandthefundamentalsofengineeringratherthanmemorizemerefactsandequations.Therearenofa

18、ctsorequationswhichalonecanbeusedtoprovideallthecorrectdecisionsrequiredtoproduceagooddesign.Ontheotherhand,anycalculationsmademustbedonewiththeutmostcareandprecision.Gooddesignrequiretryingnewideasandbeingwillingtotakeacertainamountofrisk,knowingthatifthenewideanotworktheexistingmethodcanbereinstat

19、ed.Thusadesignermusthavepatience,sincethereisnoassuranceofsuccessforthetimeandeffortexpended.Creatingacompletelynewdesigngenerallyrequiresthatmanyoldandwell-establishedmethodsbethrustaside.Thisisnoteasysincemanypeopleclingtofamiliarideas,techniquesandattitudes.Adesignengineershouldconstantlysearchfo

20、rwaystoimproveanexistingproductandmustdecidewhatold,provenconceptsshouldbeusedandwhatnew,untriedideasshouldbeincorporated.Duringthebeginningstagesofdesign,creativityshouldbeallowedtoflourishwithoutagreatnumberofconstraints.Eventhoughmanyimpracticalideasmayarise,itisusuallyeasytoeliminatethemintheear

21、lystagesofdesignbeforefirmdetailsarerequiredbymanufacturing.Inthisway,innovativeideasarenotinhibited.Quiteoften,morethanonedesignisdeveloped,uptothepointwheretheycanbecomparedagainsteachother.Itisentirelypossiblethatthedesignwhichisultimatelyacceptedwilluseideasexistinginoneoftherejecteddesignsthatd

22、idnotshowasmuchoverallpromise.Anotherimportantpointwhichshouldberecognizedisthatadesignengineermustbeabletocommunicateideastootherpeopleiftheyaretobeincorporated.Initially,thedesignermustcommunicateapreliminarydesigntogetmanagementapproval.Thisisusuallydonebyverbaldiscussionsinconjunctionwithdrawing

23、layoutsandwrittenmaterial.Tocommunicateeffectively,thefollowingquestionsmustbeanswered:(1)Doesthedesignreallyserveahumanneed?(2)Willitbecompetitivewithexistingproductsofrivalcompanies?(3)Isiteconomicaltoproduce?(4)Canitbereadilymaintained?(5)Willitsellandmakeaprofit?Besides,fortheproducersandadminis

24、trativepersonneloftheproducts,mechatronicshasmanyadvantagesasfollows:(1)HighCapitalEquipmentUtilizationTypically,thethroughputforasetofmachinesinamechatronicssystemwillbeuptothreetimesthatforthesamemachinesinastand-alonejobshopenvironment.(2)ReducedCapitalEquipmentCoststhehighutilizationofequipmentr

25、esultsintheneedforfewermachinesinthemechatronicsystemtodothesameworkasinaconventionalsystem.(3)ReducedDirectLaborCostsSinceeachmachineiscompletelyundercomputercontrol,full-timeoversightisnotrequired.(4)ReducedWork-in-ProcessInventoryandLeadTimeThereductionofwork-in-processinaisquitedramaticwhencompa

26、redtoajob-shopenvironment.(5)ResponsivenesstoChangingProductionRequirementsAmechatronicsystemhastheinherentflexibilitytomanufacturedifferentproductsasthedemandsofthemarketplacechangeorasengineeringdesignchangesareintroduced.(6)AbilitytoMaintainProductionManymechatronicsystemsaredesignedtodegraderati

27、onallywhenoneormoremachinesfail.(7)HighProductQualitySometimes,anoverlookedadvantageofamechatronicsystemespeciallywhencomparedtomachinesthathavenotbeenfederatedintoacooperativesystem,isimprovedproductquality.(8)OperationalFlexibilityOperationalflexibilityoffersasignificantofproductivity.(9)CapacityF

28、lexibilityWithreasonableplanningforavailablefloor,amechatronicsysteminitiallycanbedesignedforlowproduction,andprovidenecessaryadditionalproductivityaswell.Onlytimewillprovidethetrueanswerstotheprecedingquestions,buttheproductshouldbedesigned,manufacturedandmarkedonlywithinitialaffirmativeanswers.The

29、designengineeralsomustcommunicatethefinalizeddesigntomanufacturingthroughtheuseofdetailandassemblydrawings.Quiteoften,aproblemwilloccurduringthemanufacturingcycle.Itmaybethatachangeisrequiredinthedimensioningortoleranceofpartsothatitcanbemorereadilyproduced.Thisfallsinthecategoryofengineeringchanges

30、whichmustbeapprovedbythedesignengineersothattheproductfunctionwillnotbeadverselyaffected.Inothercases,adeficiencyinthedesignmayappearduringassemblyortestingjustpriortoshipping.Theserealitiessimplybearoutthefactthatdesignisalivingprocess.Thereisalwaysabetterwaytodoitandthedesignershouldconstantlystri

31、vetowardsfindingthatbetterway.Thecompetentengineershouldnotbeafraidofthepossibilityofnotsucceedinginapresentation.Infact,occasionalfailureshouldbeexpectedbecausefailureorcriticismseemstoaccompanyeveryreallycreativeidea.Thereisagreatdealtobelearnedformafailureandthegreatestgainsareobtainedbythosewillingtoriskdefeat.Inthefinalanalysis,therealfailurewouldlieindecidingnottomakethepresentationatall.