机械专业英文翻译.docx
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机械专业英文翻译.docx
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机械专业英文翻译
Designofmachineandmachineelements
Machinedesign
Machinedesignistheartofplanningordevisingneworimprovedmachinestoaccomplishspecificpurposes.Ingeneral,amachinewillconsistofacombinationofseveraldifferentmechanicalelementsproperlydesignedandarrangedtoworktogether,asawhole.Duringtheinitialplanningofamachine,fundamentaldecisionsmustbemadeconcerningloading,typeofkinematicelementstobeused,andcorrectutilizationofthepropertiesofengineeringmaterials.Economicconsiderationsareusuallyofprimeimportancewhenthedesignofnewmachineryisundertaken.Ingeneral,thelowestover-allcostsaredesigned.Considerationshouldbegivennotonlytothecostofdesign,manufacturethenecessarysafetyfeaturesandbeofpleasingexternalappearance.
Theobjectiveistoproduceamachinewhichisnotonlysufficientlyruggedtofunctionproperlyforareasonablelife,butisatthesametimecheapenoughtobeeconomicallyfeasible.
Theengineerinchargeofthedesignofamachineshouldnotonlyhaveadequatetechnicaltraining,butmustbeamanofsoundjudgmentandwideexperience,qualitieswhichareusuallyacquiredonlyafterconsiderabletimehasbeenspentinactualprofessionalwork.
Designofmachineelements
Theprinciplesofdesignare,ofcourse,universal.Thesametheoryorequationsmaybeappliedtoaverysmallpart,asinaninstrument,or,toalargerbutsimilarpartusedinapieceofheavyequipment.Innoease,however,shouldmathematicalcalculationsbelookeduponasabsoluteandfinal.Theyareallsubjecttotheaccuracyofthevariousassumptions,whichmustnecessarilybemadeinengineeringwork.Sometimesonlyaportionofthetotalnumberofpartsinamachinearedesignedonthebasisofanalyticcalculations.Theformandsizeoftheremainingpartsaredesignedonthebasisofanalyticcalculations.Ontheotherhand,ifthemachineisveryexpensive,orifweightisafactor,asinairplanes,designcomputationsmaythenbemadeforalmostalltheparts.
Thepurposeofthedesigncalculationsis,ofcourse,toattempttopredictthestressordeformationinthepartinorderthatitmaysagelycarrytheloads,whichwillbeimposedonit,andthatitmaylastfortheexpectedlifeofthemachine.Allcalculationsare,ofcourse,dependentonthephysicalpropertiesoftheconstructionmaterialsasdeterminedbylaboratorytests.Arationalmethodofdesignattemptstotaketheresultsofrelativelysimpleandfundamentaltestssuchastension,compression,torsion,andfatigueandapplythemtoallthecomplicatedandinvolvedsituationsencounteredinpresent-daymachinery.
Inaddition,ithasbeenamplyprovedthatsuchdetailsassurfacecondition,fillets,notches,manufacturingtolerances,andheattreatmenthaveamarketeffectonthestrengthandusefullifeofamachinepart.Thedesignanddraftingdepartmentsmustspecifycompletelyallsuchparticulars,mustspecifycompletelyallsuchparticulars,andthusexercisethenecessaryclosecontroloverthefinishedproduct.
Asmentionedabove,machinedesignisavastfieldofengineeringtechnology.Assuch,itbeginswiththeconceptionofanideaandfollowsthroughthevariousphasesofdesignanalysis,manufacturing,marketingandconsumerism.Thefollowingisalistofthemajorareasofconsiderationinthegeneralfieldofmachinedesign:
①Initialdesignconception;
②Strengthanalysis;
③Materialsselection;
④Appearance;
⑤Manufacturing;
⑥Safety;
⑦Environmenteffects;
⑨Reliabilityandlife;
Strengthisameasureoftheabilitytoresist,withoutfails,forceswhichcausestressesandstrains.Theforcesmaybe;
①Graduallyapplied;
②Suddenlyapplied;
③Appliedunderimpact;
④Appliedwithcontinuousdirectionreversals;
⑤Appliedatloworelevatedtemperatures.
Ifacriticalpartofamachinefails,thewholemachinemustbeshutdownuntilarepairismade.Thus,whendesigninganewmachine,itisextremelyimportantthatcriticalpartsbemadestrongenoughtopreventfailure.Thedesignershoulddetermineaspreciselyaspossiblethenature,magnitude,directionandpointofapplicationofallforces.Machinedesignismot,however,anexactscienceanditis,therefore,rarelypossibletodetermineexactlyalltheappliedforces.Inaddition,differentsamplesofaspecifiedmaterialwillexhibitsomewhatdifferentabilitiestoresistloads,temperaturesandotherenvironmentconditions.Inspiteofthis,designcalculationsbasedonappropriateassumptionsareinvaluableintheproperdesignofmachine.
Moreover,itisabsolutelyessentialthatadesignengineerknowshowandwhypartsfailsothatreliablemachineswhichrequireminimummaintenancecanbedesigned.Sometimes,afailurecanbeserious,suchaswhenatireblowsoutonanautomobiletravelingathighspeeds.Ontheotherhand,afailuremaybenomorethananuisance.Anexampleisthelooseningoftheradiatorhoseintheautomobilecoolingsystem.Theconsequenceofthislatterfailureisusuallythelossofsomeradiatorcoolant,aconditionwhichisreadilydetectedandcorrected.
Thetypeofloadapartabsorbsisjustassignificantasthemagnitude.Generallyspeaking,dynamicloadswithdirectionreversalscausegreaterdifficultiesthanstaticloadsand,therefore,fatiguestrengthmustbeconsidered.Anotherconcerniswhetherthematerialisductileorbrittle.Forexample,brittlematerialsareconsideredtobeunacceptablewherefatigueisinvolved.
Ingeneral,thedesignengineermustconsiderallpossiblemodesoffailure,whichincludethefollowing:
①Stress;
②Deformation;
③Wear;
④Corrosion;
⑤Vibration;
⑥Environmentaldamage;
⑦Looseningoffasteningdevices.
Thepartsizesandshapesselectedmustalsotakeintoaccountmanydimensionalfactorswhichproduceexternalloadeffectssuchasgeometricdiscontinuities,residualstressesduetoformingofdesiredcontours,andtheapplicationofinterferencefitjoint.
Selectedfrom”designofmachineelements”,6thedition,m.f.sports,prentice-hall,inc.,1985and“machinedesign”,AnthonyEsposito,charlese.,Merrillpublishingcompany,1975.
Qualityassuranceandcontrol
Productqualityisofparamountimportanceinmanufacturing.Ifqualityisalloweddeteriorate,thenamanufacturerwillsoonfindsalesdroppingofffollowedbyapossiblebusinessfailure.Customersexpectqualityintheproductstheybuy,andifamanufacturerexpectstoestablishandmaintainanameinthebusiness,qualitycontrolandassurancefunctionsmustbeestablishedandmaintainedbefore,throughout,andaftertheproductionprocess.Generallyspeaking,qualityassuranceencompassesallactivitiesaimedatmaintainingquality,includingqualitycontrol.Qualityassurancecanbedividedintothreemajorareas.Theseincludethefollowing:
①Sourceandreceivinginspectionbeforemanufacturing;
②In-processqualitycontrolduringmanufacturing;
③Qualityassuranceaftermanufacturing.
Qualitycontrolaftermanufactureincludeswarrantiesandproductserviceextendedtotheusersoftheproduct.
Sourceandreceivinginspectionbeforemanufacturing
Qualityassuranceoftenbeginslingbeforeanyactualmanufacturingtakesplace.Thismaybedonethroughsourceinspectionsconductedattheplantsthatsupplymaterials,discreteparts,orsubassembliestomanufacturer.Themanufacturer’ssourceinspectortravelstothesupplierfactoryandinspectsrawmaterialorpremanufacturedpartsandassemblies.Sourceinspectionspresentanopportunityforthemanufacturertosortoutandrejectrawmaterialsorpartsbeforetheyareshippedtothemanufacturer’sproductionfacility.
Theresponsibilityofthesourceinspectoristocheckmaterialsandpartsagainstdesignspecificationsandtorejecttheitemifspecificationsarenotmet.Sourceinspectionsmayincludemanyofthesameinspectionsthatwillbeusedduringproduction.Includedintheseare:
①Visualinspection;
②Metallurgicaltesting;
③Dimensionalinspection;
④Destructiveandnondestructiveinspection;
⑤Performanceinspection.
Visualinspections
Visualinspectionsexamineaproductormaterialforsuchspecificationsascolor,texture,surfacefinish,oroverallappearanceofanassemblytodetermineifthereareanyobviousdeletionsofmajorpartsorhardware.
Metallurgicaltesting
Metallurgicaltestingisoftenanimportantpartofsourceinspection,especiallyiftheprimaryrawmaterialformanufacturingisstockmetalsuchasbarstockorstructuralmaterials.Metalstestingcaninvolveallthemajortypesofinspectionsincludingvisual,chemical,spectrographic,andmechanical,whichincludehardness,tensile,shear,compression,andspectr5ographicanalysisforalloycontent.Metallurgicaltestingcanbeeitherdestructiveornondestructive.
Dimensionalinspection
Fewareasofqualitycontrolareasimportantinmanufacturedproductsasdimensionalrequirements.Dimensionsareasimportantinsourceinspectionastheyareinthemanufacturingprocess.Thisisespeciallycriticalifthesourcesuppliespartsforanassembly.Dimensionsareinspectedatthesourcefactoryusingstandardmeasuringtoolsplusspecialfit,form,andfunctiongagesthatmayrequired.Meetingdimensionalspecificationsiscriticaltointerchangeabilityofmanufacturedpartsandtothesuccessfulassemblyofmanypartsintocomplexassembliessuchasautos,ships,aircraft,andothermultipartproducts.
Destructiveandnondestructiveinspection
Insomecasesitmaybenecessaryforthesourceinspectionstocallfordestructiveornondestructivetestsonrawmaterialsorp0artsandassemblies.Thisisparticularlytruewhenlargeamountsofstockrawmaterialsareinvol
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