专业英语翻译.docx
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专业英语翻译.docx
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专业英语翻译
翻译资料:
Computer-aideddesign
Computer-aideddesignistheuseofcomputersystemstofacilitatethecreation,modification,analySIS,andoptimizationofadesign.Inthiscontextthetermcomputersystemmeansacombinationofhardwareandsoftware.Computer-aidedmanufacturingistheuseofacomputersystemtoplan,manage,andcontroltheopemtionofamanufacturingplant.AnappreciationofthescopeofCAD/CAMcanbeobtainedbyconsideringthestagesthatmustbecompletedinthedesignandmanufactureofaproduct,asillustmtedbytheproductcycleshowninFig.5.8.Theinnerloopofthisfigurein~ludesthevariousstepsintheproductcycleandtheouterloopshowssomeofthefunctionsofCAD/CAMsuperimposedontheproductcycle.
Basedonmarketandcustomerrequirements,aproductisconceived,whichmaywellbeamodificationofpreviousproducts.Thisproductisthendesignedindetail,includinganyrequireddesignanalysis,anddrawingsandpartslistsareprepared.Subsequently,thevariouscomponentsandassembliesareplannedforproduction,whichinvolvestheselectionofsequencesofprocessesandmachinetoolsandtheestimationofcycletimes,togetherwiththedeterminationofprocessparameters,suchasfeedsandspeedsCJJ.Whentheproductisinproduction,schedulingandcontrolofmanufacturetakeplace,andtheorderandtimingofeachmanufacturingstepforeachcomponentandassemblyisdetemnnedtomeetanoverallmanufacturingschedule.Theactualmanufacturingandcontrolofproductqualitythentakesplaceaccordingtothescheduleandthefinalproductsaredeliveredtothecustomers.
Computer-basedprocedureshavebeenorarebeingdevelopedtofacilitateeachofthesestagesintheproductcycle,andtheseareshownintheouterloopofFig.5.8.Computer-aideddesignanddraftingtechniqueshavebeendeveloped.Theseallowageometricmodeloftheproductanditscomponentstobecreatedinthecomputer.ThismodelcantlIenbeanalyzedusingspecializedsoftwarepackages,suchasthoseforfiniteelementstressanalysis,mechanismsdesign,andsoon.Subsequently,dmwingsandpartslistscanbeproducedwithcomputer-aideddraftingsoftwareandplotters.Computer-aidedprocess-planningsystems,includingtheprepamtionofNCprograms,areavailablethatproduceworkplans,estimates,andmanufacturinginstructionsautomaticallyfromgeometricdescriptionsofthecomponentsandassembliesCll•
r'orschedulingandproductioncontrol,largeamountsofdataandnumerousrelativelysimplecalculationsmustbecarriedout.Oneexampleisthedeterminationoforderquantitiesbysubtmctingstocklevelsfromforecastsofthenumberofitemsrequiredduringaparticularmanufacturingperiod®.Manycommercialsoftwarepackagesareavailableforscheduling,inventorycontrol,andshopfloorcontrol,includingmaterialsrequirementsplanning(MRP)systems.Attheshop-floorlevelcomputersareusedextensivelyforthecontrolandmonitoringofindividualmachines.
Thereisadifferenceinthetimescalerequiredforprocessingdataandtheissuingofinstructionsforthesevariousapplicationsofcomputersintheproductcycle.Forexample,designandprocess-planningfunctionsarecarriedoutonceforeachnewproductandthetimescalerequiredisontheorderofweekstoyearsforthecompetionofthetask.Schedulingandproductionperiodcusuallyoneweek,throughouttheyear.atthemachine-controllevelin-structionsmustbeissuedcontinuallywithatimescaleofmicro-ornanosecondsinmanycases.
OneofthemajorobjectivesofCAMistheintegrationofthevariousactivitiesintheproductcycleintooneunifiedsystem,inwhichdataistransfenedfromonefunctiontoanotherautomatically.Thisleadstothe
conceptofcomputer-integratedmanufacture(CIM),withthefinalobjectivebeingthe"paperless"factory.Severaldevelopmentshavetakenplace,butnototallyintegratedCIMsystemshaveyetbeenachieved.Sincethedesignandprocess-planningfunctionsarecarnedoutonceintheproductcycle,thesearethemostsuitablefunctionsforintegration.Thisintegrationisparticularlydesirablebecausethegeometricdatageneratedduringthedesignprocessisoneofthebasicinputsusedbyprocessplannipgwhendeterminingappropriatemanufacturingsequencesandworkplans®.Consequently,variousactivitiesindesilSllandprocessplanningcanshareacommondesignandmanufacturingdatabase,asillustratedinFig.5.9.Withsuchasystem,geometricmodelsoftheproductsandcomponentsarecreatedduringthedesignprocess.Thisdataisthenaccessedbyvariousdownstreamactivities,includingNCprogramming,processplanning,androbotprogramming.Theprogramsandworkplansgeneratedbytheseactivitiesarealsoaddedtothedatabase.Productioncontrolandinventorycontrolprogramscanthenaccesstheworkplans,timeestimates,andpartslists(billofmaterialsfile),inpreparingthemanufacturingschedules,forexample.
1Computer-AidedDesign
Computer-aideddesign,orCADasitismorecommonlyknown,hasgrownfromanarrowactivityandconceI;>ttoamethodologyofdesignactivitiesthatincludeacomputerorgroupofcomputersusedtoassistintheanalysis,development,anddraw-ingofproductcomponents.TheoriginalCADsystemsdevelopedandusedinindustrycouldmorerealisticallybeclassifiedascomputer-aideddraftingsystems.However,thebenefits,ofusingbasicgeometricinformationforstructuralanalysisandplanningformanufacturingwerequicklyrecognizedandincludedinmanyCADsystems.Today,asinthepast,thebasisforCADisstillthedraftingfeaturesorinteractivecomputergraphics(ICG)thatthesesystemswereoriginallydesignedtoperform.However,thescopeofthesesystemshastakenonanewmeaning.
Ingeneral,therearefourbasicreasonsforimplementingCADsystems.
1.Areductionindesigntime.Thetotaltimerequiredfrominceptionofanideatoitscompletespecificationcanbereducedbyanorderofmagnitudebyusingeasilyalterablegeometricmodels.Designperturbations/changescanbecompletedinminimaltime.Wholescenariosofdesignpossibilitiescanbeconstructedquickly.
2.Improvedproductdesign.BecauseCADsystemsallowthedesignertoaltertheproductwithoutmajorredrav-ringwithconsiderabletimecommitment,manyfinaldesignscanbeconstructedinareasonableperiodoftime.Similarly,thesedesignscanbeautomaticallyanalyzedforstlUCturalcharacteristicsbyusingcomputer-aidedengineering(CAE)softwaresuchasfinite-elementmodeling(FEM).
3.Improvedinformationaccess.BecauseCADdrawingsarestoredinalargecomputerdatabase,theycanbeaccessedquicklyandeasily.Partscanbecodedonthebasisofgeometricshape,andsimilarpartscanbecalleduptoassistinthedesignandspecificationofnewparts."Standardparts"canbeemployedwheneverpossible,ratherthanhavingtore-inventthewheeloverandagain.
4.Manufacturing,datacreation.Withtheadventofnumericalcontrol(NC)carnetheneedtoautomaticallygeneratethetoolpathrequiredformachining.Sincethepartgeometrydictatesthemachiningrequired,kno,,-ingthepartshapecanallowfor(semi-)automaticpart-prograrnpreparation.CADdatacanalsobeusedforautomatedprocessplanning.
Itisinterestingtonotethattwentyyearsagoifapartofreasonablegeometricandmanufacturingsophisticationwascreated,hundredsofdesignanddraftinghourswouldberequired.Afterthepartwasspecified,marlufacturewouldbegin.ll1isplanningwouldnormallyrequiresomeminordesignchanges(backtothedesigneranddraftsman),andmighttakeaslongastheoriginaldesignprocess.Specialtooling,fixturing,etc.,mightalsobespecifiedduringtheplarmingformanufacture.Inall,theentireprocessofproductandprocessdesigncouldtakeseveralweeksormonths.Withtoday'sCADsystems,designing(againgarea.'\onablysophisticatedcomponent)andgeneratingmanufacturingplans,preparing
paItprogramsandproducingthepmispossibleindaysratherthanweeks.Ingeneral,thetatalen!
?
ineeringaI1dmanufacturingtimehasbeenmarkedlyusingintegratedCAD/CAMmethodalogies.
2Computer-AidedlVIanufacturing
Thescientificstudyofmetal-cuttingandautamatiantechniquesarepnxluctsafthetwentiethcentury.Two.pianeersofthesetechniqueswereFrederickTaylarandHenryFord.Duringtl1eearly1900s,theimprovingU.S.standardaflivingbroughtanewhighinpenlOnalwealth.'Illemajarresultwa<;theincreaseddemandfardurablegoods.Thisincreaseddemandmeantthatmanufacturingcauldno.longerbetreatedasablacksmithtrade,aIldtheuseafscientificstudywasemplayedinmanufacturinganalysis.Taylarpianeeredstudiesin"scientificITlaI1agement"inwhichmethodsfarproductianbybothmenandmachineswerestudied.Taylaralsoconduetedmeatal-cuttingexperimentsattheMidvaleSteelCampai1ythatlasted26yeaI"Sandproduced400tansafmetalchips.TheresultafTaylar'smetal-cuttingexperimentswasthedevelapmentaftheTaylartool-lifeequationthatisstillusedinindustrytoday.Thistoollifeequatianisstillthebasisafdetenniningecanamicmetalcuttingandhasbeenusedinadaptivecanhulledmachining.
HenryFord'scontributionstookadifferentturnfromTaylor's.Fordrefinedanddevelopedtheuseofassemblylinesforthemajorcomponentmanufacturerofhisautomobile.FordfeltthateveryAmericanfamilysh~dhaveanautomobile,andiftheycouldbemanufacturedinexpensivelyenoughtheneveryfamilywouldbuyone.SeveralmechanismsweredevelopedatFordtoaccommodateassemblylines.TheautomationthatForddevelopedwasbuiltintothehardware,andFordrealizedthatsignificantdemandwasnecessarytooffs
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