工艺规程制订与并行工程外文文献翻译.docx

工艺规程制订与并行工程外文文献翻译.docx

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工艺规程制订与并行工程外文文献翻译

ProcessPlanningandConcurrentEngineering

工艺规程制订与并行工程

ProcessPlanningandConcurrentEngineering

T.RamayahandNorainiIsmail

ABSTRACT

Theproductdesignistheplanfortheproductanditscomponentsandsubassemblies.Toconverttheproductdesignintoaphysicalentity,amanufacturingplanisneeded.Theactivityofdevelopingsuchaplaniscalledprocessplanning.Itisthelinkbetweenproductdesignandmanufacturing.Processplanninginvolvesdeterminingthesequenceofprocessingandassemblystepsthatmustbeaccomplishedtomaketheproduct.Inthepresentchapter,weexamineprocessingplanningandseveralrelatedtopics.

ProcessPlanning

Processplanninginvolvesdeterminingthemostappropriatemanufacturingandassemblyprocessesandthesequenceinwhichtheyshouldbeaccomplishedtoproduceagivenpartorproductaccordingtospecificationssetforthintheproductdesigndocumentation.Thescopeandvarietyofprocessesthatcanbeplannedaregenerallylimitedbytheavailableprocessingequipmentandtechnologicalcapabilitiesofthecompanyofplant.Partsthatcannotbemadeinternallymustbepurchasedfromoutsidevendors.Itshouldbementionedthatthechoiceofprocessesisalsolimitedbythedetailsoftheproductdesign.Thisisapointwewillreturntolater.

Processplanningisusuallyaccomplishedbymanufacturingengineers.Theprocessplannermustbefamiliarwiththeparticularmanufacturingprocessesavailableinthefactoryandbeabletointerpretengineeringdrawings.Basedontheplanner’sknowledge,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. Workmeasurementtechniquesareusedtosettimes

tandardsforeachoperation.

 .Cuttingtoolsandcuttingconditions. Thesemustbespecifiedformachiningoperations,oftenwithreferencetostandardhandbookrecommendations.

Processplanningforparts

Forindividualparts,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,itisusuallythefinalstepintheprocessingsequen

ce.

ProcessingPlanningforAssemblies

Thetypeofassemblymethodusedforagivenproductdependsonfactorssuchas:

（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.

MakeorBuyDecision

Animportantquestionthatarisesinprocessplanningiswhetheragivenpartshouldbeproducedinthecompany’sownfactoryorpurchasedfromanoutsidevendor,andtheanswertothisquestionisknownasthemakeorbuydecision.Ifthecompanydoesnotpossessthetechnologicalequipmentorexpertiseintheparticularmanufacturingprocessesrequiredtomakethepart,thentheanswerisobvious:

Thepartmustbepurchasedbecausethereisnointernalalternative.However,inmanycases,thepartcouldeitherbemadeinternallyusingexistingequipment,oritcouldbepurchasedexternallyfromavendorthatprocesssimilarmanufacturingcapability.

Inourdiscussionofthemakeorbuydecision,itshouldberecognizedattheoutsetthatnearlyallmanufacturesbuytheirrawmaterialsfromsupplies.Amachineshoppurchasesitsstartingbarstockfromametalsdistributoranditssandcastingsfromafoundry.Aplasticmoldingplantbuysitsmoldingcompoundfromachemicalcompany.Astampingpressfactorypurchasessheetmetaleitherfroadistributorordirectfromarollingmill.Veryfewcompaniesareverticallyintegratedintheirproductionoperationsallthewayfromrawmaterials,itseemsreasonabletoconsiderpurchasingatleastsomeofthepartsthatwouldotherwisebeproducedinitsownplant.Itisprobablyappropriatetoaskthemakeorbuyquestionforeverycomponentthatisusedbythecompany.

Thereareanumberoffactorsthatenterintothemakeorbuydecision.Onewouldthinkthatcostisthemostimportantfactorindeterminingwhethertoproducethepartorpurchaseit.Ifanoutsidevendorismoreproficientthanthecompany’sownplantinthemanufacturingprocessesusedtomakethepart,thentheinternalproductioncostislikelytobegreaterthanthepurchasepriceevenafterthevendorhasincludedaprofit.However,ifthedecisiontopurchaseresultsinidleequipmentandlaborinthecompany’sownplant,thentheapparentadvantageofpurchasingthepartmaybelost.ConsiderthefollowingexamplemakeorBuyDecision.

Thequotedpriceforacertainpartis$20.00perunitfor100units.Thepartcanbeproducedinthecompany’sownplantfor$28.00.Thecomponentsofmakingthepartareasfollows:

                   Unitrawmaterialcost=$8.00perunit

                   Directlaborcost=6.00perunit

                   Laboroverheadat150%=9.00perunit

                   Equipmentfixedcost=5.00perunit

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