供应链管理-2.ppt

Chapter2InventoryManagement,SupplyContractsandRiskPooling,ZhangYuhuaProfessorofGuangdongUniversityofForeignStudiesTel-mail:zhyh58,OutlineofthePresentation,2.1IntroductiontoInventoryManagement2.2SingleWarehouseInventory(1)EOQ(2)DemandForecast(3)SupplyContracts(4)Amulti-PeriodInventoryModel(5)PeriodicReviewPolicy2.3RiskPooling2.4Centralizedvs.DecentralizedSystems2.5ManagingInventoryintheSC2.6PracticalIssuesinInventoryManagement,2.1Inventory,Wheredoweholdinventory?SuppliersandmanufacturerswarehousesanddistributioncentersretailersTypesofInventoryWIPrawmaterialsfinishedgoodsWhydoweholdinventory?UnexpectedchangesincustomerdemandThepresenceinmanysituationsofasignificantuncertaintyEconomiesofscaleofferedbytransportationcompaniesLeadTime,Capacitylimitations,UnderstandingInventory,Theinventorypolicyisaffectedby:DemandCharacteristicsLeadTimeNumberofProductsObjectivesServicelevelMinimizecostsCostStructure,CostStructure,OrdercostsFixedVariableHoldingCostsInsuranceMaintenanceandHandlingTaxesOpportunityCostsObsolescence,2.2.1EOQ:ASimpleModel*,ACase:BookStoreMugSalesDemandisconstant,at20unitsaweek(Dforayear)Fixedordercostof$12.00,noleadtime(k)Holdingcostof25%ofinventoryvalueannually(H)Mugscost$1.00,sellfor$5.00QuestionHowmany(Q),whentoorder?,EOQillustratesthetrade-offsbetweenorderingandstoragecosts.,EOQ:AViewofInventory*,Time,Inventory,OrderSize,Note:NoStockoutsOrderwhennoinventoryOrderSizedeterminespolicy,Avg.Inven,EOQ:CalculatingTotalCost*,PurchaseCostConstantHoldingCost:(Avg.Inven)*(HoldingCost)Ordering(SetupCost):NumberofOrders*OrderCostGoal:FindtheOrderQuantitythatMinimizesTheseCosts,EOQ:TotalCost*,TotalCost,OrderCost,HoldingCost,EOQ:OptimalOrderQuantity*,OptimalQuantity=(2*Demand*SetupCost)/holdingcostQ=Sqrt(2*D*K)/H)=Sqrt(2*20*52*12)/25%)=316Soforourproblem,theoptimalquantityis316,EOQ,总成本用如下公式表示：等式右边的第一项表示的是库存持有成本。右边的第二项表示的是订货成本或者生产准备成本，R/Q表示每年向供货点发出订货定单的次数。由此可见，如果Q增加，而每年的需求固定，那么每年的订货的次数就相应减少。第三项是货物自身的成本，它不影响最优订货批量和最优订购周期的确定。为获得使总成本最低的最优订货批量Q*，总成本TC看作以Q为自变量的函数，将TC函数对Q微分：,EOQ,令为0，可求出最优的Q*为,每年的订货次数为,两次订货之间最佳的时间间隔为,EOQ:ImportantObservations*,Tradeoffbetweenset-upcostsandholdingcostswhendeterminingorderquantity.TotalCostisnotparticularlysensitivetotheoptimalorderquantity,TheEffectofDemandUncertainty,Mostcompaniestreattheworldasifitwerepredictable:ProductionandinventoryplanningarebasedonforecastsofdemandmadefarinadvanceofthesellingseasonCompaniesareawareofdemanduncertaintywhentheycreateaforecast,buttheydesigntheirplanningprocessasiftheforecasttrulyrepresentsrealityRecenttechnologicaladvanceshaveincreasedthelevelofdemanduncertainty:ShortproductlifecyclesIncreasingproductvariety,2.2.2DemandForecast,Thethreeprinciplesofallforecastingtechniques:ForecastingisalwayswrongThelongertheforecasthorizon,theworsttheforecastAggregateforecastsaremoreaccurate,Case:SnowTimeSportingGoods,Fashionitemshaveshortlifecycles,highvarietyofcompetitorsSnowTimeSportingGoodsNewdesignsarecompletedOneproductionopportunityBasedonpastsales,knowledgeoftheindustry,andeconomicconditions,themarketingdepartmenthasaprobabilisticforecastTheforecastaveragesabout13,000,butthereisachancethatdemandwillbegreaterorlessthanthis.,Case2,SupplyChainTimeLines,Jan00,Jan01,Jan02,Feb00,Sep00,Sep01,Design,Production,Retailing,Feb01,Production,SnowTimeDemandScenarios,SnowTimeCosts,ThevariableProductioncostperunit(C):$80Sellingpriceperunit(S):$125Salvagevalueperunit(V):$20Fixedproductioncost(F):$100,000Tostartproduction,themanufacturerhastoinvest$100,000independentoftheamountproduced.Qisproductionquantity,DdemandProfit=Revenue-VariableCost-FixedCost+Salvage,SnowTimeScenarios,ScenarioOne:Supposeyoumake12,000jacketsanddemandendsupbeing13,000jackets.Profit=125(12,000)-80(12,000)-100,000=$440,000ScenarioTwo:Supposeyoumake12,000jacketsanddemandendsupbeing11,000jackets.Profit=125(11,000)-80(12,000)-100,000+20(1000)=$335,000,Profit=Revenue-VariableCost-FixedCost+Salvage,SnowTimeBestSolution,Findorderquantitythatmaximizesweightedaverageprofit.Question:Willthisquantitybelessthan,equalto,orgreaterthanaveragedemand?,WhattoMake?,Question:Willthisquantitybelessthan,equalto,orgreaterthanaveragedemand?Averagedemandis13,100LookatmarginalcostVs.marginalprofitifextrajacketsold,profitis125-80=45ifnotsold,costis80-20=60Sowewillmakelessthanaverage,SnowTimeExpectedProfit,Thequantitythatmaximizesaverageprofit,isabout12,000.,WhattoMake?,Ifthecostofnotsellinganadditionalunitislargerthantheprofitfromsellinganadditionalunit,theoptimalquantityingeneralwillbelessthanaveragedemand,whileifthereverseistrue,theoptimalorderquantityingeneralwillbegreaterthanaveragedemand.,SnowTimeExpectedProfit,Itindicatesthatproducing9,000unitsorproducing16,000unitswillleadtoaboutthesameaverageprofitof$294,000.,SnowTime:ImportantObservations,TradeoffbetweenorderingenoughtomeetdemandandorderingtoomuchSeveralquantitieshavethesameaverageprofitAverageprofitdoesnottellthewholestoryQuestion:9000and16000unitsleadtoaboutthesameaverageprofit,sowhichdoweprefer?,SnowTimeExpectedProfit,ProbabilityofOutcomes,Whentheproductionquantityis16,000units,thedistributionofprofitisnotsymmetrical.Lossesof$220,000happenabout11%,whileprofitsofatleast$410,000happen50%.Whentheproductionquantityis9,000units,thedistributionhasonlytwopossibleoutcomes.Profitiseither$200,000withprobabilityofabout11%,or$305,000withprobabilityofabout89%.,KeyInsightsfromthisModel,Theoptimalorderquantityisnotnecessarilyequaltoaverage,orforecastdemandTheoptimalquantitydependsontherelationshipbetweenmarginalprofitandmarginalcostAsorderquantityincreases,averageprofitfirstincreasesandthendecreasesAsproductionquantityincreases,riskincreases.Inotherwords,theprobabilityoflargegainsandoflargelossesincreases,SnowTimeCosts:TheEffectofInitialInventory,Productioncostperunit(C):$80Sellingpriceperunit(S):$125Salvagevalueperunit(V):$20Fixedproductioncost(F):$100,000Qisproductionquantity,DdemandProfit=Revenue-VariableCost-FixedCost+Salvage,SnowTimeExpectedProfit,InitialInventory,Supposethatoneofthejacketdesignsisamodelproducedlastyear.SomeinventoryisleftfromlastyearAssumethesamedemandpatternasbeforeIfonlyoldinventoryissold,nosetupcostQuestion:Ifthereare5000unitsremaining,whatshouldSnowTimedo?Whatshouldtheydoifthereare10,000remaining?,InitialInventoryandProfit,InitialInventoryandProfit,InitialInventoryandProfit,Ifthemanufacturerdoesnotproduceanyadditionalsuits,nomorethan5,000unitscanbesoldandnoadditionalfixedcostwillbeincurred.However,itthemanufacturerdecidestoproduce,afixedproductioncostischargedindependentoftheamountproduced.,InitialInventoryandProfit,Averageprofitexcludingfixedproductioncost,Averageprofitincludingfixedproductioncost,(1)thereare5000unitsremainingIfnothingisproduced,averageprofitisequalto625000.Productionshouldincreaseinventoryfrom5,000unitsto12,000units.Thus,averageprofitisequalto771000(fromthefigure).(2)thereare10,000unitsremainingItiseasytoseethatthereisnoneedtoproduceanythingbecausetheaverageprofitassociatedwithaninitialinventoryof10,000islargerthanwhatwewouldachieveifweproducetoincreaseinventoryto12,000units.Ifweproduce,themostwecanmakeonaverageisaprofitof$375,000.Thisisthesameaverageprofitthatwewillhaveifourinitialinventoryisabout8,500units.Hence,ifourinitialinventoryisbelow8,5000units,weproducetoraisetheinventorylevelto12,000units.Ifinitialinventoryisatleast8,5000units,weshouldnotproduceanything.,Analysis,(s,S)Policies,Forsomestartinginventorylevels,itisbettertonotstartproductionIfwestart,wealwaysproducetothesamelevelThus,weusean(s,S)policy.Iftheinventorylevelisbelows,weproduceuptoS.sisthereorderpoint,andSistheorder-up-tolevelThedifferencebetweenthetwolevelsisdrivenbythefixedcostsassociatedwithordering,transportation,ormanufacturing,WholesalePrice=$80,2.2.3SupplyContracts,Whotakestherisk?Whatwouldthemanufacturerlike?,DemandScenarios,DistributorExpectedProfit,DistributorExpectedProfit,470,000,SupplyContracts(cont.),Distributoroptimalorderquantityis12,000unitsDistributorexpectedprofitis$470,000Manufacturerprofitis$440,000SupplyChainProfitis$910,000,Isthereanythingthatthedistributorandmanufacturercandotoincreasetheprofitofboth?,SupplyContracts,Buy-BackContractsTheselleragreestobuybackunsoldgoodsfromthebuyerforsomeagreed-uponpricehigherthanthesalvagevalue,WholesalePrice=$80,SupplyContracts(betweenmanufacturerandretailer),Inthepreviousstrategy,theretailertakesalltheriskandthemanufacturertakeszerorisk.Thisiswhytheretailerhastobeveryconservativewiththeamountheorders.Iftheretailercantransfersomeoftherisktothemanufacturer,theretailermaybewillingtoincreasehisorderquantityandthusincreasebothhisprofitandthemanufacturerprofit.,RetailerProfit(BuyBack=$55),RetailerProfit(BuyBack=$55),*假定制造商同意以55美元的价格从零售商处购买销售不了的衣服，则零售商愿意增加订货量到14000件，并获得513800美元的利润，而制造商的平均利润增加到471900,ManufacturerProfit(BuyBack=$55),ManufacturerProfit(BuyBack=$55),$471,900,SupplyContracts,Revenue-SharingContractsThebuyersharessomeofitsrevenuewiththeseller,inreturnforadiscountonthewholesaleprice,WholesalePrice=$?,SupplyContracts(betweenmanufacturerswholesalepriceandretailer),Whatdoeswholesalepricedrive?Howcanmanufacturerbenefitfromlowerprice?,RetailerProfit(WholesalePrice$70,Retailersback15%tomanufacturer),RetailerProfit(WholesalePrice$70,RS15%),$504,325,ManufacturerProfit(WholesalePrice$70,RS15%),ManufacturerProfit(WholesalePrice$70,RS15%),$481,375,SupplyContracts,WholesalePrice$70,RS15%,SupplyContracts,GlobalOptimizationContractsThisunbiaseddecisionmakerwouldconsiderthetwosupplychainpartners,thesupplierandthebuyer,astwomembersofthesameorganization.Thatis,thetransferofmoneybetweenthepartiesisignoredandtheunbiaseddecisionmakerwillmaximizesupplychainprofit,WholesalePrice=$80,SupplyContracts,Whatisthemaximumprofitthatthesupplychaincanachieve?Toanswerthisquestion,oneneedstoforgetaboutthetransferofmoneyfromtheretailertothemanufacturer.,SupplyChainProfit,SupplyChainProfit(Globaloptimization),SupplyContracts,SupplyContracts:KeyInsights,EffectivesupplycontractsallowsupplychainpartnerstoreplacesequentialoptimizationbyglobaloptimizationBuyBackandRevenueSharingcontractsachievethisobjectivethroughrisksharing,SupplyContracts:CaseStudy,Example:DemandforamovienewlyreleasedvideocassettetypicallystartshighanddecreasesrapidlyPeakdemandlastabout10weeksBlockbusterpurchasesacopyfromastudiofor$65andrentfor$3Hence,retailermustrentthetapeatleast22timesbeforeearningprofitRetailerscannotjustifypurchasingenoughtocoverthepeakdemandIn1998,20%ofsurveyedcustomersreportedthattheycouldnotrentthemovietheywanted,SupplyContracts:CaseStudy,Startingin1998BlockbusterenteredarevenuesharingagreementwiththemajorstudiosStudiocharges$8percopyBlockbusterpays30-45%ofitsrentalincomeEvenifBlockbusterkeepsonlyhalfoftherentalincome,thebreakevenpointis6rentalpercopyTheimpactofrevenuesharingonBlockbusterwasdramaticRentalsincreasedby75%intestmarketsMarketshareincreasedfrom25%to31%(The2ndlargestretailer,HollywoodEntertainmentCorphas5%marketshare),OtherContracts,QuantityFlexibilityContractsSupplierprovidesfullrefundforreturneditemsaslongasthenumberofreturnsisnolargerthanacertainquantitySalesRebateContractsSupplierprovidesadirectincentivetotheretailertoincreasesalesbymeansofarebatepaidbythesupplierforanyitemsoldaboveacertainquantity,Contractsformake-to-stock/make-to-ordersupplychains,Pay-backContractsInthiscontract,thebuyeragreestopaysomeagreed-uponpriceforanyunitproducedbythemanufacturerbutnotpurchasedbythedistributor.Cost-sharingContractsInacost-sharingcontracts,thebuyersharessomeoftheproductioncostwiththemanufacturer,inreturnforadiscountonthewholesaleprice.,Contractswithasymmetricinformation,CapacityreservationcontractsManufacturerpaystoreserveacertainlevelofcapacitywiththesupplier.AdvancepurchasecontractsSupplierchargestheadvancepurchasepriceforfirmsordersplacedpriortobuildingcapacityandadifferentpriceforanyadditionalorderplacedwhendemandisrealized.,Contractsfornonstrategiccomponents,Long-termContractsAlsocalledforwardorfixedcommitmentcontracts,thesecontractsspecifyafixedamountofsupplytobedeliveredatsomepointinthefuture.Thesupplierandthebuyeragreesonboththepriceandquantitytobedeliveredtothebuyer.Flexible,oroption,ContractsThebuyerprepaysarelativelysmallfractionoftheproductpriceupfront,inreturnforacommitmentfromthesuppliertoreservecapacityuptoacertainlevel.,Contractsfornonstrategiccomponents,SpotpurchaseBuyerslookforadditionalsupplyintheopenmarket.PortfolioContractTofindaneffectivecontracts,thebuyerneedstoidentifytheappropriatemixoflow-priceyetlow-flexibility(Long-term)contracts,reasonablepricebutbetterflexibility(option)contracts,orunknownpriceandquantitysupplybutnocommitment(Spotmarket).,2.2.4AMulti-PeriodInventoryModel,Often,therearemultiplereorderopportunitiesConsideracentraldistributionfacilitywhichordersfromamanufactureranddeliverstoretailers.Thedistributorperiodicallyplacesorderstoreplenishitsinventory,TheDCholdsinventoryto:,SatisfydemandduringleadtimeProtectagainstdemanduncertaintyBalancefixedcostsandholdingcosts,Reminder:TheNormalDistribution,Average=30,StandardDeviation=5,StandardDeviation=10,TheMulti-PeriodContinuousReviewInventoryModel,NormallydistributedrandomdemandFixedordercostplusacostproportionaltoamountordered.InventorycostischargedperitemperunittimeIfanorderarrivesandthereisnoinventory,theorderislostThedistributorhasarequiredservicelevel.Thisisexpressedasthethelikelihoodthatthedistributorwillnotstockoutduringleadtime.Intuitively,howwillthiseffectourpolicy?,AViewof(s,S)Policy,Time,InventoryLevel,S,s,0,LeadTime,LeadTime,InventoryPosition,The(s,S)Policy,(s,S)Policy:Whenevertheinventorypositiondropsbelowacertainlevel,s,weordertoraisetheinventorypositiontolevelS.Thereorderpointisafunctionof:TheLeadTimeAveragedemandDemandvariabilityServicelevel,Notation,AVG=averagedailydemandSTD=standarddeviationofdailydemandLT=replenishmentleadtimeindaysh=holdingcostofoneunitforonedayK=fixedcostSL=servicelevel(forexample,95%).Thisimpliesthattheprobabilityofstockingoutis100%-SL(forexample,5%)Also,theInventoryPositionatanytimeistheactualinventoryplusitemsalreadyordered,butnotyetdelivered.,Analysis,Thereorderpoint(s)hastwocomponents:Toaccountforaveragedemandduringleadtime:LTAVGToaccountfordeviationsfromaverage(wecallthissafetystock)zSTDLTwherezischosenfromstatisticaltablestoensurethattheprobabilityofstockoutsduringleadtimeis100%-SL.Sincethereisafixedcost,weordermorethanuptothereorderpoint:Q=(2KAVG)/hThetotalorder-up-tolevelis:S=Q+s,Example,Thedistributorhashistoricallyobservedweeklydemandof:AVG=44.6STD=32.1Replenishmentleadtimeis2weeks,anddesiredservicelevelSL=97%Averagedemandduringleadtimeis:44.62=89.2SafetyStockis:1.8832.12=85.3Reorderpointisthus175,orabout3.9weeksofsupplyatwarehouseandinthepipeline,WhatisReorderpoint?whatistheorder-up-to-level?,Example,Cont.,Weeklyinventoryholdingcost:.87Therefore,Q=679Order-up-tolevelthusequals:ReorderPoint+Q=176+679=855,2.2.5PeriodicReview,SupposethedistributorplacesorderseverymonthWhatpolicyshouldthedistributoruse?Whataboutthefixedcost?,Base-StockPolicy,PeriodicReviewPolicy,Eachreviewechelon,inventorypositionisraisedtothebase-stocklevel.Thebase-stocklevelincludestwocomponents:Averagedemandduringr+Ldays(thetimeuntilthenextorderarrives):(r+L)*AVGSafetystockduringthattime:z*STD*r+L,2.3RiskPooling,CoefficientofvariationCoefficientofvariation=Standarddeviation/AveragedemandTheStandarddeviationmeasurestheabsolutevariabilityofcustomerdemands,thecoefficientofvariationmeasuresvariabilityrelativetoaveragedemand.,2.3RiskPoolingExample,Considerthesetwosystems:SomeproblemsfacedbyACME,acompanythatproducesanddistributeselectronicequipmentintheNortheastoftheUnitedStates.(1)ThecurrentdistributionsystempartitionstheNortheastintotwomarkets,eachofwhichhasasinglewarehouse.Retailersreceiveitemsdirectlyfromthewarehouses;eachretailerisassignedtoasinglemarketandreceivesdeliveriesfromthecorrespondingwarehouse.,RiskPoolingExample(cont),(2)Replacethetwowarehouseswithasinglewarehouse.Thesameservicelevel,97%,bemaintainedregardlessofthelogisticsstrategyemployed.ThissystemallowsACMEtoachieveeitherthesameservicelevelof97%withmuchlowerinventoryorahigherservicelevelwiththesameamountoftotalinventory.,RiskPoolingExample(cont),Forthesameservicelevel,whichsystemwillrequiremoreinventory?Why?Forthesametotalinventorylevel,whichsystemwillhavebetterservice?Why?Whatarethefactorsthataffecttheseanswers?,RiskPoolingExample(cont),Comparethetwosystems:twoproducts(A,B)maintain97%servicelevel$60ordercost$.27weeklyholdingcost$1.05transportationcostperunitindecentralizedsystem,$1.10incentralizedsystem1weekleadtime,Table1HistoricalDataforProductAandB,RiskPoolingExample,Thetablesincludeweeklydemandinformationforeachproductforthelasteightweeksineachmarketarea.ObservethatProductBisaslow-movingproductthedemandforProductBisfairlysmallrelativetothedemandforProductA.,RiskPoolingExample,Table2SummaryofHistoricalData,RiskPoolingExample,Table3InventoryLevels,RiskPooling:ImportantObservations,Centralizinginventorycontrolreducesbothsafetystockandaverageinventorylevelforthesameservicelevel.Thehigherthecoefficientofvariation,thegreaterthebenefitobtainedfromcentralizedsystems;thatis,thegreaterthebenefitfromriskPooling.Highcoefficientofvariation,whichincreasesrequiredsafetystock.Negativelycorrelateddemand.Why?ThebenefitsfromriskPoolingdependonthebehaviorofdemandfromonemarketrelativetodemandfromanother.,RiskPooling:TypesofRiskPooling*,RiskPoolingAcrossMarketsRiskPoolingAcrossProductsRiskPoolingAcrossTimeDailyorderuptoquantityis:LTAVG+zAVGLT,10,12,11,13,14,15,Demands,Orders,2.4ToCentralizeornottoCentralize,Whatarethetrade-offsthatweneedtoconsiderincomparingcentralizeddistributionsystemswithdecentralizeddistributionsystems?Whatistheeffecton:Safetystock?Servicelevel?Overheadcosts?CustomerLeadtime?TransportationCosts?,CentralizedvsDecentralizedsystem,Safetystock.Clearly,safetystockdecreasesasafirmmovesfromadecentralizedtoacentralizedsystem.Servicelevel.Whenthecentralizedanddecentralizedsystemshavethesametotalsafetystock,theservicelevelprovidedbythecentralizedsystemishigher.Leadtime.Sincethewarehousesaremuchclosertothecustom