外文翻译--工艺规程制订与并行工程.doc

ProcessPlanningandConcurrentEngineeringT.RamayahandNorainiIsmailABSTRACTTheproductdesignistheplanfortheproductanditscomponentsandsubassemblies.Toconverttheproductdesignintoaphysicalentity,amanufacturingplanisneeded.Theactivityofdevelopingsuchaplaniscalledprocessplanning.Itisthelinkbetweenproductdesignandmanufacturing.Processplanninginvolvesdeterminingthesequenceofprocessingandassemblystepsthatmustbeaccomplishedtomaketheproduct.Inthepresentchapter,weexamineprocessingplanningandseveralrelatedtopics.ProcessPlanningProcessplanninginvolvesdeterminingthemostappropriatemanufacturingandassemblyprocessesandthesequenceinwhichtheyshouldbeaccomplishedtoproduceagivenpartorproductaccordingtospecificationssetforthintheproductdesigndocumentation.Thescopeandvarietyofprocessesthatcanbeplannedaregenerallylimitedbytheavailableprocessingequipmentandtechnologicalcapabilitiesofthecompanyofplant.Partsthatcannotbemadeinternallymustbepurchasedfromoutsidevendors.Itshouldbementionedthatthechoiceofprocessesisalsolimitedbythedetailsoftheproductdesign.Thisisapointwewillreturntolater.Processplanningisusuallyaccomplishedbymanufacturingengineers.Theprocessplannermustbefamiliarwiththeparticularmanufacturingprocessesavailableinthefactoryandbeabletointerpretengineeringdrawings.Basedontheplannersknowledge,skill,andexperience,theprocessingstepsaredevelopedinthemostlogicalsequencetomakeeachpart.Followingisalistofthemanydecisionsanddetailsusuallyincludewithinthescopeofprocessplanning.Interpretationofdesigndrawings.Thepartofproductdesignmustbeanalyzed(materials,dimensions,tolerances,surfacefinished,etc.)atthestartoftheprocessplanningprocedure.Processandsequence.Theprocessplannermustselectwhichprocessesarerequiredandtheirsequence.Abriefdescriptionofprocessingstepsmustbeprepared.Equipmentselection.Ingeneral,processplannersmustdevelopplansthatutilizeexistingequipmentintheplant.Otherwise,thecomponentmustbepurchased,oraninvestmentmustbemadeinnewequipment.Tools,dies,molds,fixtures,andgages.Theprocessmustdecidewhattoolingisrequiredforeachprocessingstep.Theactualdesignandfabricationofthesetoolsisusuallydelegatedtoatooldesigndepartmentandtoolroom,oranoutsidevendorspecializinginthattypeoftooliscontacted.Methodsanalysis.Workplacelayout,smalltools,hoistsforliftingheavyparts,eveninsomecaseshandandbodymotionsmustbespecifiedformanualoperations.Theindustrialengineeringdepartmentisusuallyresponsibleforthisarea.Workstandards.Workmeasurementtechniquesareusedtosettimestandardsforeachoperation.Cuttingtoolsandcuttingconditions.Thesemustbespecifiedformachiningoperations,oftenwithreferencetostandardhandbookrecommendations.ProcessplanningforpartsForindividualparts,theprocessingsequenceisdocumentedonaformcalledaroutesheet.Justasengineeringdrawingsareusedtospecifytheproductdesign,routesheetsareusedtospecifytheprocessplan.Theyarecounterparts,oneforproductdesign,theotherformanufacturing.Atypicalprocessingsequencetofabricateanindividualpartconsistsof:(1)abasicprocess,(2)secondaryprocesses,(3)operationstoenhancephysicalproperties,and(4)finishingoperations.Abasicprocessdeterminesthestartinggeometryoftheworkparts.Metalcasting,plasticmolding,androllingofsheetmetalareexamplesofbasicprocesses.Thestartinggeometrymustoftenberefinedbysecondaryprocesses,operationsthattransformthestartinggeometry(orclosetofinalgeometry).Thesecondarygeometryprocessesthatmightbeusedarecloselycorrelatedtothebasicprocessthatprovidesthestartinggeometry.Whensandcastingisthebasicprocesses,machiningoperationsaregenerallythesecondprocesses.Whenarollingmillproducessheetmetal,stampingoperationssuchaspunchingandbendingarethesecondaryprocesses.Whenplasticinjectionmoldingisthebasicprocess,secondaryoperationsareoftenunnecessary,becausemostofthegeometricfeaturesthatwouldotherwiserequiremachiningcanbecreatedbythemoldingoperation.Plasticmoldingandotheroperationthatrequirenosubsequentsecondaryprocessingarecallednetshapeprocesses.Operationsthatrequiresomebutnotmuchsecondaryprocessing(usuallymachining)arereferredtoasnearnetshapeprocesses.Someimpressiondieforgingsareinthiscategory.Thesepartscanoftenbeshapedintheforgingoperation(basicprocesses)sothatminimalmachining(secondaryprocessing)isrequired.Oncethegeometryhasbeenestablished,thenextstepforsomepartsistoimprovetheirmechanicalandphysicalproperties.Operationstoenhancepropertiesdonotalterthegeometryofthepart；instead,theyalterphysicalproperties.Heattreatingoperationsonmetalpartsarethemostcommonexamples.Similarheatingtreatmentsareperformedonglasstoproducetemperedglass.Formostmanufacturedparts,theseproperty-enhancingoperationsarenotrequiredintheprocessingsequence.Finallyfinishoperationsusuallyprovideacoatontheworkparts(orassembly)surface.Examplesincludedelectroplating,thinfilmdepositiontechniques,andpainting.Thepurposeofthecoatingistoenhanceappearance,changecolor,orprotectthesurfacefromcorrosion,abrasion,andsoforth.Finishingoperationsarenotrequiredonmanyparts；forexample,plasticmoldingrarelyrequirefinishing.Whenfinishingisrequired,itisusuallythefinalstepintheprocessingsequence.ProcessingPlanningforAssembliesThetypeofassemblymethodusedforagivenproductdependsonfactorssuchas:(1)theanticipatedproductionquantities；(2)complexityoftheassembledproduct,forexample,thenumberofdistinctcomponents；and(3)assemblyprocessesused,forexample,mechanicalassemblyversuswelding.Foraproductthatistobemadeinrelativelysmallquantities,assemblyisusuallyperformedonmanualassemblylines.Forsimpleproductsofadozenorsocomponents,tobemadeinlargequantities,automatedassemblysystemsareappropriate.Inanycase,thereisaprecedenceorderinwhichtheworkmustbeaccomplished.Theprecedencerequirementsaresometimesportrayedgraphicallyonaprecedencediagram.Processplanningforassemblyinvolvesdevelopmentofassemblyinstructions,butinmoredetail.Forlowproductionquantities,theentireassemblyiscompletedatasinglestation.Forhighproductiononanassemblyline,processplanningconsistsofallocatingworkelementstotheindividualstationsoftheline,aprocedurecalledlinebalancing.Theassemblylineroutestheworkunittoindividualstationsintheproperorderasdeterminedbythelinebalancesolution.Asinprocessplanningforindividualcomponents,anytoolsandfixturesrequiredtoaccomplishanassemblytaskmustbedetermined,designed,built,andtheworkstationarrangementmustbelaidout.MakeorBuyDecisionAnimportantquestionthatarisesinprocessplanningiswhetheragivenpartshouldbeproducedinthecompanysownfactoryorpurchasedfromanoutsidevendor,andtheanswertothisquestionisknownasthemakeorbuydecision.Ifthecompanydoesnotpossessthetechnologicalequipmentorexpertiseintheparticularmanufacturingprocessesrequiredtomakethepart,thentheanswerisobvious:Thepartmustbepurchasedbecausethereisnointernalalternative.However,inmanycases,thepartcouldeitherbemadeint