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MechanicalDesignJohnErnstAbstract：Amachineisacombinationofmechanismsandothercomponentswhichtransformstransmits.Examplesareengines,turbines,vehicles,hoists,printingpresses,washingmachines,andmoviecameras.Manyoftheprinciplesandmethodsofdesignthatapplytomachinesalsoapplytomanufacturedarticlesthatarenottruemachines.Thetermmechanicaldesignisusedinabroadersensethanmachinedesigntoincludetheirdesign.Themotionandstructuralaspectsandtheprovisionsforretentionandenclosureareconsiderationsinmechanicaldesign.Applicationsoccurinthefieldofmechanicalengineering,andinotherengineeringfieldsaswell,allofwhichrequiremechanicaldevices,suchasswitches,cams,valves,vessels,andmixers.Keywords:MechanicalDesign；MechanismsDesignProcess；Application1.TheDesignProgressDesigningstartswithaneedreal.Existingapparatusmayneedimprovementsindurability,efficiency,weight,speed,orcost.NewapparatusmaybeneededtoperformafunctionpreviouslyDonebymen,suchascomputation,assembly,orservicing.WiththeobjectivewhollyorpartlyInthedesignpreliminarystage,shouldallowtodesignthepersonnelfullytodisplaythecreativity,noteachkindofrestraint.Evenifhashadmanyimpracticalideas,alsocaninthedesignearlytime,namelyinfrontoftheplanblueprintiscorrected.Onlythen,onlythendoesnotsendtostopsuptheinnovationthementality.Usually,mustproposeseveralsetsofdesignproposals,andthenperformthecomparison.Hasthepossibilityverymuchintheplanwhichfinallydesignated,hasusedcertainnotinplansomeideaswhichaccepts.Whenthegeneralshapeandafewdimensionsoftheseveralcomponentsbecomeapparent,analysiscanbegininearnest.Theanalysiswillhaveasitsobjectivesatisfactoryorsuperiorperformance,plussafetyanddurabilitywithminimumweight,andacompetitivecost.Optimumproportionsanddimensionswillbesoughtforeachcriticallyloadedsection,togetherwithabalancebetweenthestrengthsoftheseveralcomponents.Materialsandtheirtreatmentwillbechosen.Theseimportantobjectivescanbeattainedonlybyanalysisbasedupontheprinciplesofmechanics,suchasthoseofstaticforreactionforcesandfortheoptimumutilizationoffriction;ofdynamicsforinertia,acceleration,andenergy;ofelasticityandstrengthofmaterialsforstressanddeflection;ofphysicalbehaviorofmaterials;andoffluidmechanicsforlubricationandhydrodynamicdrives.Theanalysesmaybemadebythesameengineerwhoconceivedthearrangementofmechanisms,or,inalargecompany,theymaybemadebyaseparateanalysisdivisionorresearchgroup.Designisareiterativeandcooperativeprocess,whetherdoneformallyorinformally,andtheanalystcancontributetophasesotherthanhisown.Productdesignrequiresmuchresearchanddevelopment.ManyConceptsofanideamustbestudied,tried,andtheneitherusedordiscarded.Althoughthecontentofeachengineeringproblemisunique,thedesignersfollowthesimilarprocesstosolvetheproblems.Productliabilitysuitsdesignersandforcedinmaterialselection,usingthebestprogram.Intheprocessofmaterial,themostcommonproblemsforfive(a)don'tunderstandornotuseaboutthelatestapplicationmaterialstothebestinformation,(b)failedtoforeseeandconsiderthereasonableusematerialmay(suchaspossible,designersshouldfurtherforecastandconsiderduetoimproperuseproducts.Inrecentyears,manyproductsliabilityinlitigation,theuseofproductsandhurttheplaintiffaccusedmanufacturer,andwonthedecision),(c)ofthematerialsusedallorsomeofthedata,data,especiallywhentheuncertaintylong-termperformancedataisso,(d)qualitycontrolmethodisnotsuitableandunproven,(e)bysomecompletelyincompetentpersonschoosematerials.Throughtotheabovefivequestionsanalysis,mayobtainthesequestionsisdoesnothavethesufficientreasonexistencetheconclusion.Mayforavoidthesequestionstothesequestionsresearchanalysestheappearanceindicatingthedirection.Althoughusesthebestchoiceofmaterialmethodnottobeabletoavoidhavingtheproductresponsibilitylawsuit,designsthepersonnelandtheindustrycarriesonthechoiceofmaterialaccordingtothesuitableprocedure,maygreatlyreducethelawsuitthequantity.Mayseefromtheabovediscussion,thechoicematerialpeopleshouldtothematerialnature,thecharacteristicandtheprocessingmethodhavecomprehensiveandthebasicunderstanding.Finally,adesignbaseduponfunction,andaprototypemaybebuilt.Ifitstestsaresatisfactory,theinitialdesignwillundergocertainmodificationsthatenableittobemanufacturedinquantityatalowercost.Duringsubsequentyearsofmanufactureandservice,thedesignislikelytoundergochangesasnewideasareconceivedorasfurtheranalysesbasedupontestsandexperienceindicatealterations.Salesappeal.2.SomeRulesforDesignInthissectionitissuggestedthat,appliedwithacreativeattitude,analysescanleadtoimportantimprovementsandtotheconceptionandperfectionofalternate,perhapsmorefunctional,economical,anddurableproducts.Tostimulatecreativethought,thefollowingrulesaresuggestedforthedesignerandanalyst.Thefirstsixrulesareparticularlyapplicablefortheanalyst.（1）Acreativeuseofneedofphysicalpropertiesandcontrolprocess.(2）Recognizefunctionalloadsandtheirsignificance.(3)Anticipateunintentionalloads.(4)Devisemorefavorableloadingconditions.(5)Provideforfavorablestressdistributionandstiffnesswithminimumweight.(6)Usebasicequationstoproportionandoptimizedimensions.（7）Choosematerialsforacombinationof