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河南科技学院机电学院-1-EnglishTranslationMaterial1.TransferMachineThehighestdegreeofautomationwithspecial-purpose,multifunctionmachinesisachievedbyusingtransfermachines.Transfermachineareessentiallyacombinationofindividualworkstationsarrangedintherequiredsequence,connectedbyworktransferdevices,andintegratedwithinterlockedcontrols.Workplacesareautomaticallytransferredbetweenthestations,whichareequippedwithhorizontal,vertical,orangularunitstoperformmachining,gaging,workplacerepositioning,assembling,washing,orotheroperation.Thetwomajorclassesoftransfermachinesarerotaryandin-linetypes.Animportantadvantageoftransfermachinesisthattheypermitthemaximumnumberofoperationstobeperformedsimultaneously.Thereisrelativelynolimitationonthenumberofworkplacesurfaceorplanesthatcanbemachined,sincedevicescanbeinterposedintransfermachinesatpracticallyanypointforinverting,rotating,ororientingtheworkplace,soastocompletethemachiningoperations.Workrepositioningalsominimizestheneedforangularmachiningheadsandallowsoperationstobeperformedinoptimumtime.Completeprocessingfromroughcastingorforgingtofinishedpartsisoftenpossible.Oneormorefinishedpartsareproducedonatransfermachinewitheachindexofthetransfersystemthatmovesthepartsfromstationstostations.Productionefficienciesofsuchmachinesgenerallyrangefrom50%foramachinevarietyofdifferentpartsto85%foramachineproducingonepart,inhighproduction,dependingupontheworkplaceandhowthemachineisoperated(materialhandlingmethod,maintenanceprocedures,etc.)Alltypesofmachiningoperations,suchasdrilling,tapping,reaming,boring,andmilling,areeconomicallycombinedontransfermachines.Lathe-typeoperationssuchasturningandfacingarealsobeingperformedonin-linetransfermachine,withtheworkplacebeingrotatedinselectedmachiningstations.Turningoperationsareperformedinlathe-typesegmentsinwhichtoolholdersarefedonslidesmountedontunnel-typebridgeunits.Workplacearelocatedoncentersandrotatedbychucksateachturningstation.TurningstationswithCNCareavailableforuseonin-linetransfermachine.TheCNCunitsallowthemachinecyclestobeeasilyalteredtoaccommodatechangesinworkplacedesignandcanalsobeusedforautomatictooladjustments.Maximumproductioneconomyontransferlinesisoftenachievedbyassembling河南科技学院机电学院-2-partstotheworkplacesduringtheirmovementthroughthemachine.suchitemsasbushings,seals,welchplugs,andheattubescanbeassembledandthenmachineortestedduringthetransfermachiningsequence.Automaticnuttorquingfollowingtheapplicationofpartsubassembliescanalsobecarriedout.Gundrillingorreamingontransfermachinesisanidealapplicationprovidedthatpropermachiningunitsareemployedandgoodbushingpracticesarefollowed.Contourboringandturningofsphericalseatsandothersurfacecanbedonewithtracer-controlledsingle-pointinserts,thuseliminatingtheneedforcostlyspecialformtools.In-processgagingofreamedorboredholesandautomatictoolsettingaredoneontransfermachinestomaintainclosetolerances.Lessconventionaloperationssometimesperformedontransfermachinesincludegrinding,inductionheatingofringgearsforshrink-fitpressingonflywheels,inductionhardeningofvalveseats,deeprollingtoapplycompressivepreloads,andburnishing.Transfermachineshavelongbeenusedintheautomotiveindustryforproductionrateswithaminimumofmanualparthandling.Inadditiontodecreasinglaborrequirements,suchmachinesensureconsistentlyuniform,high-qualitypartsatlowercost.Theyarenolongerconfinedjusttoroughmachiningandnowofteneliminatetheneedforsubsequentoperationssuchasgrindingandhoning.Morerecently,therehasbeenanincreasingdemandfortransfermachinestohandlelowervolumesofsimilarorevendifferentpartsinsmallersizes,withmeansforquickchangeoverbetweenproductionruns.Built-inflexibility,theabilitytorearrangeandinterchangemachineunits,andtheprovisionofidlestationsincreasesthecostofanytransfermachine,butsuchfeatureareeconomicallyfeasiblewhenproductredesignsarecommon.Manysuchmachinesarenowbeingusedinnonautomotiveapplicationsforlowerproductionrequirements.Specialfeaturenowavailabletoreducethetimerequiredforpartchangeoverincludestandardizeddimensions,modularconstruction,interchangeablefixturesmountedonmasterpalletsthatremainonthemachine,interchangeablefixturecomponents,theabilitytolockoutcertainstationsfordifferentpartsbymeansofselectorswitches,andprogrammablecontrollers.Productdesignisalsoimportant,andcommontransferandclampingsurfacesshouldbeprovidedondifferentpartswheneverpossible.2.ProgrammableLogicControllersAprogrammablelogiccontroller(PLC)isasolid-statedeviceusedtocontrolmachinemotionorprocessoperationbymeansofastoredprogram.ThePLCsendsoutputcontrolsignalsoutputandreceiveinputsignalsthroughinput/output(I/O)devices.APLCcontrolsoutputinresponsetostimuliattheinputsaccordingtothelogicprescribedbythestoredprogram.Theinputsaremadeupoflimitswitches,pushbuttons,thumbwheels,switches,pulses,analogsignal,ASCIIserialdata,andbinaryorBCDdatafromabsolutepositionencoders.Theoutputarevoltageorcurrent河南科技学院机电学院-3-leveltodriveenddevicessuchassolenoids,motorstarters,relays,lights,andsoon.Otheroutputdeviceincludeanalogdevices,digitalBCDdisplays,ASCIIcompatibledevices,servovariable-speeddrives,andevencomputers.Programmablecontrollersweredeveloped(circain1968)whenGeneralMotorsCorps,andotherautomobilemanufacturerswereexperimentingtoseeiftheremightbeanalternativetoscrappingalltheirhardwiredcontrolpanelofmachinetoolsandotherproductionequipmentduringamodelchangeover.Thisannualtraditionwasnecessarybecauserewritingofthepanelswasmoreexpensivethanbuyingnewones.Theautomotivecompaniesapproachedanumberofcontrolequipmentmanufacturersandaskedthemtodevelopacontrolsystemthatwouldhavealongerproductivelifewithoutmajorrewriting,butwouldstillbeunderstandabletoandrepairablebytheplantpersonnel.Thenewproductwasnameda“programmablecontroller”.TheprocessorpartofthePLCcontainsacentralprocessingunitandmemory.Thecentralprocessingunit(CPU)isthe“trafficdirection”oftheprocessor,thememorystoresinformation.Comingintotheprocessoraretheelectricalsignalsfromtheinputdevices,asconditionedbytheinputmoduletovoltagelevelsacceptabletoprocessorlogic.TheprocessorscansthestateofI/OandupdatesoutputsstoredinthememoryofthePLC.Forexample,theprocessormaybeprogrammedsothatifaninputconnectedtoalimitswitchistrue(limitswitchclosed),thenacorrespondingoutputwiredtoanoutputmoduleistobeenergized.Thisprocessorremembersthiscommandthroughitsmemoryandcomparesoneachscantoseeifthatlimitswitchis,infact,closed.Ifitisclosed,theprocessorenergizesthesolenoidbyturningontheoutputmodule.Theoutputdevice,suchasasolenoidormotorstarter,iswiredtoanoutputmodulesterminal,anditreceivesitsshiftsignalfromtheprocessor,ineffect,theprocessorisperformingalongandcomplicatedseriesoflogicdecisions.ThePLCperformssuchdecisionssequentiallyandinaccordingwiththestoredprogram.Similarly,analogI/Oallowstheprocessortomakedecisionsbasedonthemagnitudeofasignal,ratherthanjustifitisonoroff.Forexample,theprocessormaybeprogrammedtoincreaseordecreasethesteamflowtoaboiler(analogoutput)basedonacomparisonoftheactualtemperatureintheboiler(analoginput)Thisisoftenperformedbyutilizingthebuilt-inPID(proportional,integral,derivative)capabilitiesoftheprocessor.BecauseaPLCis“softwarebased”,itscontrollogicfunctionscanbechangedbyreprogrammingitsmemory.Keyboardprogrammingdevicesfacilitateentryoftherevisedprogram,whichcanbedesigntocauseanexistingmachineorprocesstooperateinadifferentsequenceortodifferentlevelof,orcombinationsofstimuli.Hardwaremodificationsareneededonlyifadditional,changed,orrelocatedinput/outputdeviceareinvolved.河南科技学院机电学院-4-3.AutomatedAssemblyAssemblyinthemanifacturingprocessconsistsofputtingtogetherallthecomponentpartsandsub-assembliesofagivenproduct,fastening,performinginspectionsandfunctiontests,labeling,separatinggoodassemblyfrombad,andpackagingandorpreparingthemforfinaluse.Assemblyisuniquecomparedtothemethodsofmanufacturingsuchasmachining,grinding,andweldinginthatmostoftheseprocessesinvovleonlyafewdisciplinesandpossiblyonlyone.Mostofthesenonassemblyoperationscannotbeperformedweithouttheaidofequipment；thusthedevelopmentofautomaticmethodshasbeennecessaryratherthanoptional.Assembly,ontheotherhand,mayinvolveinonemachinemanyofthefasteningmethods,suchasriveting,welding,screwdriving,andadhesiveapplication,aswellasautomaticpartsseletion,proding,gaging,functionaltesting,labeling,andpackaging.Thestateoftheartinassemblyoperationshasnotreachedthelevelofstandardization；muchmanualworkisstillbeingperformedinthisarea.Assemblyhastraditionallybeenoneofthehighestareasofdirectlaborcosts.Insomecases,assemblyaccountsfor50%ormoreofmanufacturingcsostsandtypically20%50%.However,closercooperationbetweendesignandmanufacturingengineershasresultedinreducingandinafewcaseseliminatingaltogethertheneedforassembly.Whenasssemblyisrequired,improveddesignorproductshassimplifiedautomated(semiautomaticorautomatic)assembly.ConsiderationsforAutomatedAssemblyBeforeautomatedassemblyisadopted,severalfactorsshouldbeconsiderd.Theseincludepracticalityoftheprocessforautomation,simulationforeconomicconsiderationsandjustification,managementinvolvement,andlaborrelations.Determiningthepracticalityofautomatedassemblyrequiredcarefulevaluationofthefollowing:a)Thenumberofpartsinassembly.b)Designofthepartswithrespecttoproducibility,assembility,automatichandling,andtestability(materials,forms,dimensionaltolerances,andweights).c)Qualityofpartstobeassembled.Out-of-toleranceordefectivepartscancauseproductionlossesandincreasecostsbecauseofstoppages.d)Availablityofqualiyied,technicallycompetentpersonaltoberesponsibleforequipmentoperation.e)Totalproductionandproduction-raterequipments.Productvariationsandfrequencyofdesignchanges.f)Joiningmethodsrequired.g)Assemblytimesandcosts.h)Assemblylinesorsystemconfiguration,usingsimulation,includingmaterialhandling.