论文翻译《材料的选择》.docx

论文翻译《材料的选择》.docx

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论文翻译《材料的选择》

SelectingMaterials

Anever-increasingvarietyofmaterialsisnowavailable,eachhavingitsowncharacteristics,applications,advantages,limitations,andcosts.Thefollowingarethegeneraltypesofmaterialsusedinmanufacturing,eitherindividuallyorincombinationwithothermaterials:

•Ferrousmetals:

carbon,alloy,stainless,andtoolanddiesteels.

•Nonferrousmetals:

aluminum,magnesium,copper,nickel,titanium,superalloys,refractorymetals,beryllium,zirconium,low-meltingalloys,andpreciousmetals.

•Plastics（polymers）:

thermoplastics,thermosets,andelastomers.

•Ceramics,glasses,glassceramics,graphite,diamond,anddiamond-likematerials.

•Compositematerials:

reinforcedplastics,metal-matrixandceramic-matrixcomposites,alsoknownasengineeredmaterials.

•Nanomaterials,shape-memoryalloys,amorphousalloys,semiconductor,superconductors,andvariousotheradvancedmaterialswithuniqueproperties.

Asnewmaterialsaredeveloped,theselectionofappropriatematerialsbecomesevenmorechallenging.Aerospacestructures,automotiveapplications,militaryequipment,andsportinggoodshavebeenattheforefrontofnew-materialusage.Therearecontinuallyshiftingtrendsintheuseofmaterialsinallproducts,trendsthataredrivenprincipallybyeconomicconsiderations,butalsobyotherconsiderations,aswillbedescribedbelow.

Propertiesofmaterials

Whenselectingmaterialsforproducts,wefirstconsidertheirmechanicalproperties:

strength,toughness,ductility,hardness,elasticity,fatigue,andcreep.Themechanicalpropertiesspecifiedforaproductanditscomponentsshould,ofcourse,beappropriatetotheconditionsunderwhichtheproductisexpectedtofunction①.Nextthephysicalpropertiesofmaterialsareconsidered:

density,specificheat,thermalexpansionandconductivity,meltingpoint,andelectricalandmagneticproperties.Acombinationofmechanicalandphysicalpropertiesisthestrength-to-weightandstiffness-to-weightratiosofmaterials,particularlyimportantforaerospaceandautomotiveapplications,aswellasforsportsequipment.Aluminum,titanium,andreinforcedplastics,forexample,generallyhavehighersuchratiosthansteelsandcastirons.

TABLE3.1.1GeneralManufacturingCharacteristicsofVariousAlloys

Alloy

Castability

Weldability

Machinability

Aluminum

E

F

E-G

Copper

G-F

F

G-F

Graycastiron

E

D

G

Whitecastiron

G

VP

VP

Nickel

F

F

F

Steels

F

E

F

Zinc

E

D

E

Note:

E,excellent;G,good;F,fair;D,difficult;VP,verypoor.

Chemicalpropertiesalsoplayasignificantrole,bothinhostileandinnormalenvironments.Oxidation,corrosion,generaldegradationofproperties,toxicity,andflammabilityofmaterialsareamongtheimportantfactorstobeconsidered.Insomecommercialairlineaccidents,forexample,manydeathshavebeencausedbytoxicfumesfromburningnonmetallicmaterialsintheaircraftcabin.

Themanufacturingpropertiesofmaterialsdeterminewhethertheycanbecast,formed,machined,joined,andheat-treatedwithrelativeease（Table3.1.1）.Themethodormethodsusedtoprocessmaterialstothedesiredfinalshapescanaffecttheproduct'sperformance,servicelife,andcost.

Costandavailability

Costandavailabilityofrawaswellasprocessedmaterialsandofmanufacturedcomponentsaremajorconcernsinmanufacturing.Theeconomicaspectsofmaterialselectionareasimportantastechnologicalconsiderationsofthepropertiesandcharacteristicsofmaterials.Ifraworprocessedmaterialsormanufacturedcomponentsarenotavailableinthedesiredshapes,dimensions,andquantities,substitutesand/oradditionalprocessingwillberequired,andthesecancontributesignificantlytoproductcost②.Forexample,ifweneedaroundbarofacertaindiameteranditisnotavailableinstandardform,thenwehavetopurchasealargerrodandreduceitsdiameterbysomemeans（suchasmachining,drawingthroughadie,orgrinding）.However,aproductdesigncanoftenbemodifiedtotakeadvantageofstandarddimensionsofrawmaterialsand,thus,avoidextramanufacturingcosts.

Reliabilityofsupply,aswellasdemandforthematerial,affectscost.Mostcountriesimportnumerousrawmaterialsthatareessentialformanufacturing.Formanufacturingpurposes,theUnitedStates,forexample,importsmostofthefollowingmaterials:

naturalrubber,diamond,cobalt,titanium,chromium,aluminum,andnickel.Thebroadgeopoliticalimplicationsofsuchrelianceonothercountriesareself-evident.Reliabilityofsupplyisalsoimportantinindustries,especiallyautomotive,whenitiscrucialformaterialsandcomponentstoarriveattheplantatthepropertimeintervals.

Differentcostsareinvolvedinprocessingmaterialsbydifferentmethods.Somemethodsrequireexpensivemachinery,othersrequireextensivelabor,andstillothersrequirepersonnelwithspecialskills,ahighlevelofeducation,orspecializedtraining.

Appearance,servicelife,andrecycling

Theappearanceofmaterials,aftertheyhavebeenmanufacturedintoproducts,influencestheirappealtotheconsumer.Color,feel,andsurfacetexturearecharacteristicsthatweallconsiderwhenmakingadecisionaboutpurchasingaparticularproduct.

Time-andservice-dependentphenomena,suchaswear,fatigue,creep,anddimensionalstability,alsoareimportant.Thesephenomenacansignificantlyaffectaproduct'sperformanceand,ifnotcontrolled,canleadtomalfunctionorfailureoftheproduct.Similarly,compatibilityofmaterialsusedinaproductisimportant.Frictionandwear,corrosion（includinggalvaniccorrosionbetweenmatingpartsmadeofdissimilarmetals）,andotherphenomenacanshortenaproduct'slifeorcauseittofailprematurely.

Aswehavebecomeincreasinglyconsciousoftheneedforconservingresourcesandformaintainingacleanandhealthyenvironment,recyclingorproperdisposalofcomponentmaterialsattheendofaproduct'susefulservicelifehasbecomeamajorconsideration.Note,forexample,theuseofbiodegradablepackagingmaterialsandofrecyclableplasticbottlesandaluminumbeveragecans.Thepropertreatmentanddisposaloftoxicwastesandmaterialsisalsoamajorconsideration.

EXAMPLE3.1.1MaterialselectionforU.S.pennies

Billionsofpenniesaremintedeachyear（FiG.3.1.1）.ThematerialsusedbytheU.S.Minttomakepennieshaveundergonesignificantchangesthroughouthistory,mainlybecauseofmaterialshortagesandthefluctuatingcostofrawmaterials.Thefollowingtableshowsachronologicaldevelopmentofmaterialsubstitutionsinpennies.Thesematerials,ortheircombinations,needtoimpartappropriatepropertiestothepenniesduringtheircirculationanduse.

1793-1837

100%copper

1837-1857

95%copper,5%tinandzinc（bronze）88%

1857-1863

copper,12%nickel（nickel-bronze）95%

1864-1962

copper,5%tinandzinc（bronze）Steel

1943（WWIIyears）

（platedwithzinc）95%copper,5%zinc

1962-1982

（bronze）97.5%zinc,platedwith2.5%

1982-present

copper

FIG.3.1.1U.S.pennies

38.3Computer-IntegratedManufacturing

Thevariouslevelsofautomationinmanufacturingoperations（describedinChapter37）havebeenextendedfurtherbyincludinginformationprocessingfunctionsandbyutilizinganextensivenetworkofinteractivecomputers.Thishasledtocomputer-integratedmanufacturing（CIM）,whichdescribesthecomputerizedintegrationofallaspectsofproductdesign,processplanning,production,anddistribution,aswellasthemanagementandoperationofthewholemanufacturingorganization.

Computer-integratedmanufacturingisamethodologyratherthananassemblageofmachines,equipment,andcomputers.TheeffectivenessofCIMcriticallydependsontheuseofalarge-scaleintegratedcommunicationssysteminvolvingcomputers,machines,andtheircontrols（describedinSection39.7）.BecauseCIMideallyshouldinvolvethetotaloperationofanorganization,itmusthaveanextensivedatabaseconcerningthetechnicalandbusinessaspectsoftheoperation.Consequently,ifplannedallatonce,CIMcanbeprohibitivelyexpensive,particularlyforsmall-andmedium-sizedcompanies.

ImplementationofCIMinexistingplantsmaybeginwithmodulesinvariousphasesofthetotaloperation.Fornewmanufacturingplants,ontheotherhand,comprehensiveandlong-rangestrategicplanningcoveringallphasesoftheoperationisessentialinordertofullybenefitfromCIM.Suchplanningmusttakeintoaccountthefollowingconsiderations:

•Themission,goals,andcultureoftheorganization.

•Availabilityoffinancial,technical,andhumanresources.

•Existingaswellasemergingtechnologiesintheareasoftheproductstobemanufactured.

•Thelevelofintegrationrequired.

SubsystemsofCIM.Computer-integratedmanufacturingsystemsconsistofsubsystemsthatareintegratedintoawhole.Thesesubsystemsconsistofthefollowing（seeFig.38.1）:

•Businessplanningandsupport

•Productdesign

FIGURE38.1Aschematicillustrationofacomputer-integratedmanufacturingsystem.ThemanufacturingcellsandtheircontrolsshownatthelowerleftaredescribedinSection39.2.Source:

AfterU.Rembold.

•Manufacturingprocessplanning

•Processautomationandcontrol

•Productionmonitoringsystems

Thesubsystemsaredesigned,developed,andimplementedinsuchamannerthattheoutputofonesubsystemservesastheinputofanothersubsystem.Organizationally,thesesubsystemsusuallyaredividedintotwofunctions:

•Businessplanningfunctions:

Theseincludeactivitiessuchasforecasting,scheduling,material-requirementsplanning,invoicing,andaccounting.

•Businessexecutionfunctions:

Includesproductionandprocesscontrol,materialhandling,testing,