机械工程专业英语 第一课文及阅读材料Word文档下载推荐.docx

机械工程专业英语 第一课文及阅读材料Word文档下载推荐.docx

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Itisalsoimportanttoconsiderhowthedesignprocessfitswithallfunctionsthatmusthappentodeliverasatisfactoryproducttothecustomerandtoservicetheproductthroughoutitsliftcycle.infact,itisimportanttoconsiderhowtheproductwillbedisposedofafterithasserveditsusefullife.thetotalofallsuchfunctionthataffecttheproductissometimescalledtheproductrealizationprocessorPRP.someofthefactorsincludedinPRPareasfollows:

1marketingfunctionstoassesscustomerrequirements

2researchtodeterminetheavailabletechnologythatcanreasonablybeusedintheproduct

3availabilityofmaterialsandcomponentsthatcanbeincorporatedintotheproduct

4productdesignanddevelopment

5performancetesting

6documentationofthedesign

7vendorrelationshipsandpurchasingfunctions

8work-forceskills

9physicalplantandfacilitiesavailable

10capabilityofmanufacturingsystems

11productionplanningandcontrolofproductionsystems

12productionsupportsystemsandpersonnel

13qualitysystemsrequirements

14salesoperationsandtimeschedules

15costtargetsandothercompetitiveissues

16customerservicerequirements

17environmentalconcernsduringmanufacture,operationanddisposaloftheproduct

18legalrequirements

19availabilityoffinancialcapital

Canyouaddtothislist?

Youshouldbeabletoseethatthedesignofaproductisbutonepartofacomprehensiveprocess.inthistext,wewillfocusmorecarefullyonthedesignprocessitself,buttheproducibilityofdesignsmustalwaysbeconsidered.thissimultaneousconsiderationofproductdesignandmanufacturingprocessdesignisoftencalledconcurrentengineering.

2skillsneededinmechanicaldesign

Productengineersandmechanicaldesignersuseawiderangeofskillsandknowledgeintheirdailywork.theseskillsandknowledgeareincludedinthefollowing:

1sketching,technicaldrawing,andcomputer-aideddesign

2propertiesofmaterials,materialsprocessing,andmanufacturingprocesses

3applicationsofchemistry,suchascorrosionprotection,plating,andpainting

4statics,dynamics,strengthofmaterials,kinematics,andmechanisms

5fluidmechanics,thermodynamics,andheattransfer

6fluidpower,thefundamentalsofelectricalphenomena,andindustrialcontrols

7experimentaldesignandperformancetestingofmaterialsandmechanicalsystems

8stressanalysis

9specializedknowledgeofthebehaviorofmachineelements,suchasgears,beltdrives,chaindrives,shafts,bearings,keys,splines,couplings,seals,spring,connections（bolted,riveted,welded,adhesive）,electricmotors,linearmotiondevices,clutches,andbrakes

10creativity,problemsolving,andprojectmanagement

11oralcommunication,listening,technicalwriting,andteamworkskills

3functions,designrequirementsandevaluationcriteria

Section1emphasizedtheimportanceofcarefullyidentifyingtheneedsandexpectationsofthecustomerpriortobeginningthedesignofamechanicaldevice.youcanformulatethesebyproducingclear,completestatementsoffunctions,designrequirements,andevaluationcriteria:

1Functionstelluswhatthedevicemustdo,usinggeneral,nonquantitativestatementsthatemployactionphrasessuchas“tosupportaload”,“toliftacrate”,“totransmitpower”,or“toholdtwostructuralmemberstogether”,etc

2Designrequirementsaredetailed,usuallyquantitativestatementsofexpectedperformancelevels,environmentalconditionsinwhichthedevicemustoperate,limitationsonspaceorweight,oravailablematerialsandcomponentsthatmaybeused

3Evaluationcriteriaarestatementsofdesirablequalitativecharacteristicsofadesignthatassistthedesignerindecidingwhichalternativedesignisoptimum-thatis,thedesignthatmaximizesbenefitswhileminimizingdisadvantages

Togethertheseelementscanbecalledthespecificationsforthedesign

Mostdesignsprogressthroughacycleofactivitiesareoutlinedinfigure1.1.youshouldtypicallyproposemorethanonepossiblealternativedesignconcept.Thisiswherecreativityisexercisedtoproducetrulynoveldesigns.Eachdesignconceptmustsatisfythefunctionsanddesignrequirements.acriticalevaluationofthedesirablefeatures,advantages,anddisadvantagesofeachdesignconceptshouldbecompleted.thenarationaldecisionanalysistechniqueshouldusetheevaluationcriteriatodecidewhichdesignconceptistheoptimumand,therefore,shouldbeproduced.

Readingmaterial

Mechanicaldesignistheprocessofdesigningand/orselectingmechanicalcomponentsandputtingthemtogethertoaccomplishadesiredfunction.Ofcoursemachineelementsmustbecompatible,mustfitwelltogether,andmustperformsafelyandefficiently.Thedesignermustconsidernotonlytheperformanceoftheelementbeingdesignedatagiventime,butalsotheelementswithwhichitmustinterface.

Toillustratehowthedesignofmachineelementsmustbeintegratedwithalargermechanicaldesign,letusconsiderthedesignofaspeedreducerforthesmalltractor.supposethat,toaccomplishthespeedreduction,youdecidetodesignadouble-reduction,spurgearspeedreducer.Youspecifyfourgears,threeshafts,sixbearings,andahousingtoholdtheindividualelementsinproperrelationtoeachother.Theprimaryelementsofthespeedreducerare:

1theinputshaftistobeconnectedtothepowersource,agasolineenginewhoseoutputshaftrotatesat2000rpm.aflexiblecouplingistobeemployedtominimizedifficultieswithalignment.

2thefirstpairofgears,aandb,causesareductioninthespeedoftheintermediateshaftproportionaltotheratioofthenumbersofteethinthegears.Gearbandcarebothmountedtointermediateshaftandrotateatthesamespeed.

3akeyisusedattheinterfacebetweenthehubofeachgearandtheshaftonwhichitismountedtotransmittorquebetweenthegearandtheshaft.

4thesecondpairofgears,candd,furtherreducesthespeedofgeardandtheoutputshafttotherangeof290rpmto295rpm.

5theoutputshaftistocarryachainsprocket.thechaindriveultimatelyistobeconnectedtothedrivewheelofthetractor.

6eachofthethreeshaftsissupportedbytwoballbearings.makingthemstaticallydeterminateandallowingtheanalysisofforcesandstressesusingstandardprinciplesofmechanics.

7thebearingsareheldinahousingthatistobeattachedtotheframeofthetractor.notethemannerofholdingeachbearingsothattheinnerracerotateswiththeshaftwhiletheouterraceisheldstationary.

8sealsareontheinputandoutputshaftstoprohibitcontaminantsfromenteringthehousing.

9detailsofhowtheactiveelementsaretobeinstalled,lubricated,andalignedareonlysuggestedatthisstageofthedesignprocesstodemonstratefeasibility.onepossibleassemblyprocesscouldbeasfollows.

Startbyplacingthegearingthegears,keys,spacers,andbearingsontheirrespectiveshafts

Theninsertinputshaftintoitsbearingseatontheleftsideofthehousing.

Inserttheleftendofintermediateshaftintoitsbearingseatwhileengagingtheteethofgearsaandb.

Installthecenterbearingsupporttoprovidesupportforthebearingattherightsideofinputshaft.

Installoutputshaftbyplacingitsleftbearingintotheseatonthecenterbearingsupportwhileengaginggearscandd.

Installtherightsidecoverforthehousingwhileplacingthefinaltwobearingsintheirseats.

Ensurecarefulalignmentoftheshafts.

Placegearlubricantinthelowerpartofhousing.

Thearrangementofthegears,theplacementofthebearingssothattheystraddlethegears,andthegeneralconfigurationofthehousingarealsodesigndecisions.thedesignprocesscannotrationallyproceeduntilthesekindsofdecisionsaremade.whentheoveralldesignisconceptualized,thedesignoftheindividualmachineelementsinthespeedreducercanproceed.youshouldrecognizethatyouhavealreadymademanydesigndecisionsbyrenderingsuchasketch.first,youchoosespurgearsratherthanhelicalgears,awormandwormgear,orbevelgears.infact,othertypesofspeedreductiondevices–beltdrives,chaindrives,ormanyothers—couldbeappreciate.

1gears

forthegearpairs,youmustspecifythenumberofteethineachgear,thepitch（size）oftheteeth,thepitchdiameters,thefacewidth,andthematerialanditsheattreatment.thesespecificationsdependonconsiderationsofstrengthandwearofthegearteethandthemotionrequirements（kinematics）.Youmustalsorecognizethatthegearsmustbemountedonshaftsinamannerthatensuresproperlocationofthegears,adequate