同步生产和限制条件的理论（英文）

同步生产和限制条件的理论（英文）Goldratt’sRulesofProductionSchedulingDonotbalancecapacitybalancetheflow.Thelevelutilizationofanonbottleneckresourceisnotdeterminedbyitsownpotentialbutbysomeotherconstraintinthesystem.Utilizationandactivationofaresourcearenotthesame.Anhourlostatabottleneckisanhourlostfortheentiresystem.Anhoursavedatanonbottleneckisamirage.

Goldratt’sRulesofProductionScheduling(Continued)Bottlenecksgovernboththroughputandinventoryinthesystem.Transferbatchmaynotandmanytimesshouldnotbeequaltotheprocessbatch.Aprocessbatchshouldbevariablebothalongitsrouteandintime.Prioritiescanbesetonlybyexaminingthesystem’sconstraints.Leadtimeisaderivativeoftheschedule.Goldratt’sTheoryofConstraints(TOC)Identifythesystemconstraints.Decidehowtoexploitthesystemconstraints.Subordinateeverythingelsetothatdecision.Elevatethesystemconstraints.If,intheprevioussteps,theconstraintshavebeenbroken,gobacktoStep1,butdonotletinertiabecomethesystemconstraint.Goldratt’sGoaloftheFirmThegoalofafirmistomakemoney.PerformanceMeasurement:

FinancialNetprofitanabsolutemeasurementindollars

Returnoninvestmentarelativemeasurebasedoninvestment

Cashflowasurvivalmeasurement

PerformanceMeasurement:

Operational1.Throughputtherateatwhichmoneyisgeneratedbythesystemthroughsales2.Inventoryallthemoneythatthesystemhasinvestedinpurchasingthingsitintendstosell3.OperatingexpensesallthemoneythatthesystemspendstoturninventoryintothroughputProductivityDoesnotguaranteeprofitabilityHasthroughputincreased?Hasinventorydecreased?Haveoperationalexpensesdecreased?UnbalancedCapacityInearlierchapters,wediscussedbalancingassemblylines.Thegoalwasaconstantcycletimeacrossallstations.Synchronousmanufacturingviewsconstantworkstationcapacityasabaddecision.TheStatisticsofDependentEventsRatherthanbalancingcapacities,theflowofproductthroughthesystemshouldbebalanced.ProcessTime(B)ProcessTime(A)CapacityRelatedTerminologyCapacityistheavailabletimeforproduction.Bottleneckiswhathappensifcapacityislessthandemandplacedonresource.Nonbottleneckiswhathappenswhencapacityisgreaterthandemandplacedonresource.Capacity-constrainedresource(CCR)isaresourcewherethecapacityiscloseto

demandplacedontheresource.CapacityExampleSituation1XYMarketCaseAThereissomeidleproductioninthissetup.Howmuch?25%inYCapacityExampleSituation2YXMarketCaseBIsthereisgoingtobeabuildupofunnecessaryproductioninY?Yes,25%inY.CapacityExampleSituation3XYAssemblyMarketCaseCIstheregoingtobeabuildupinunnecessaryproductioninY?Yes,25%inY.CapacityExampleSituation4XYMarketMarketCaseDIfwerunbothXandYforthesametime,willweproduceanyunneededproduction?Yes,25%inY.TimeComponentsofProductionCycleSetuptimeisthetimethatapartspendswaitingforaresourcetobesetuptoworkonthissamepart.Processtimeisthetimethatthepartisbeingprocessed.Queuetimeisthetimethatapartwaitsforaresourcewhiletheresourceisbusywithsomethingelse.TimeComponentsofProductionCycle(Continued)Waittimeisthetimethatapartwaitsnotforaresourcebutforanotherpartsothattheycanbeassembledtogether.

Idletimeistheunusedtime.Itrepresentsthecycletimelessthesumofthesetuptime,processingtime,queuetime,andwaittime.SavingTimeBottleneckNonbottleneckWhataretheconsequencesofsavingtimeateachprocess?

Rule:Bottlenecksgovernboththroughputandinventoryinthesystem.Rule:Anhourlostatabottleneckisanhourlostfortheentiresystem.Rule:Anhoursavedatanonbottleneckisamirage.Drum,Buffer,RopeABCDEFBottleneck(Drum)Inventorybuffer(timebuffer)Communication(rope)MarketExhibit17.9QualityImplicationsMoretolerantthanJITsystemsExcesscapacitythroughoutsystem.

ExceptforthebottleneckQualitycontrolneededbeforebottleneck.BatchSizesWhatisthebatchsize?One?Infinity?BottlenecksandCCRs:

Flow-ControlSituationsAbottleneck(1)withnosetuprequiredwhenchangingfromoneproducttoanother.(2)withsetuptimesrequiredtochangefromoneproducttoanother.Acapacityconstrainedresource(CCR)(3)withnosetuprequiredtochangefromoneproducttoanother.(4)withsetuptimerequiredwhenchangingfromoneproducttoanother.InventoryCostMeasurement:

DollarDaysDollarDaysisameasurementofthevalueofinventoryandthetimeitstayswithinanarea.DollarDays=(valueofinventory)(numberofdayswithinadepartment)ExampleBenefitsfromDollarDayMeasurementMarketingDiscouragesholdinglargeamountsoffinishedgoodsinventory.PurchasingDiscouragesplacinglargepurchaseordersthatonthesurfaceappeartotakeadvantageofquantitydiscounts.ManufacturingDiscouragelargeworkinprocessandproducingearlierthanneeded.ComparingSynchronousManufacturingtoMRPMRPusesbackwardscheduling.Synchronousmanufacturingusesforwardscheduling.ComparingSynchronousManufacturingtoJITJITislimitedtorepetitivemanufacturingJITrequiresastableproductionlevelJITdoesnotallowverymuchflexibilityintheproductsproducedComparingSynchronousManufacturingtoJIT(Con