供应链管理-2

Chapter2InventoryManagement,SupplyContractsandRiskPoolingZhangYuhuaProfessorofGuangdongUniversityofForeignStudiesTel:020-39328850E-mail:[e-mail]ion2.1IntroductiontoInventoryManagement2.2SingleWarehouseInventory(1)EOQ(2)DemandForecast(3)SupplyContracts(4)Amulti-PeriodInventoryModel(5)PeriodicReviewPolicy2.3RiskPooling2.4Centralizedvs.DecentralizedSystems2.5ManagingInventoryintheSC2.6PracticalIssuesinInventoryManagement2.1InventoryWheredoweholdinventory?SuppliersandmanufacturerswarehousesanddistributioncentersretailersTypesofInventoryWIPrawmaterialsfinishedgoodsWhydoweholdinventory?UnexpectedchangesincustomerdemandThepresenceinmanysituationsofasignificantuncertaintyEconomiesofscaleofferedbytransportationcompaniesLeadTime,CapacitylimitationsUnderstandingInventoryTheinventorypolicyisaffectedby:DemandCharacteristicsLeadTimeNumberofProductsObjectives•Servicelevel•MinimizecostsCostStructureCostStructureOrdercostsFixedVariableHoldingCostsInsuranceMaintenanceandHandlingTaxesOpportunityCostsObsolescence2.2.1EOQ:ASimpleModel*ACase:BookStoreMugSalesDemandisconstant,at20unitsaweek(Dforayear)Fixedordercostof$12.00,noleadtime(k)Holdingcostof25%ofinventoryvalueannually(H)Mugscost$1.00,sellfor$5.00QuestionHowmany(Q),whentoorder?EOQillustratesthetrade-offsbetweenorderingandstoragecosts.EOQ:AViewofInventory*TimeInventoryOrderSizeNote:•NoStockouts•Orderwhennoinventory•OrderSizedeterminespolicyAvg.InvenEOQ:CalculatingTotalCost*PurchaseCostConstantHoldingCost:(Avg.Inven)*(HoldingCost)Ordering(SetupCost):NumberofOrders*OrderCostGoal:FindtheOrderQuantitythatMinimizesTheseCostsEOQ:TotalCost*020406080100120140160050010001500OrderQuantityCostTotalCostOrderCostHoldingCostEOQ:OptimalOrderQuantity*OptimalQuantity=(2*Demand*SetupCost)/holdingcostQ=Sqrt((2*D*K)/H)=Sqrt(2*20*52*12)/25%)=316Soforourproblem,theoptimalquantityis316EOQ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：12DTCQHKcDQ2()2dTCHKDdQQEOQ令为0，可求出最优的Q*为dQTCd/)(*2DkQH每年的订货次数为***1DNtQ两次订货之间最佳的时间间隔为**2QktDHDEOQ:ImportantObservations*Tradeoffbetweenset-upcostsandholdingcostswhendeterminingorderquantity.TotalCostisnotparticularlysensitivetotheoptimalorderquantityOrderQuantity50%80%90%100%110%120%150%200%CostIncrease125%103%101%100%101%102%108%125%TheEffectofDemandUncertaintyMostcompaniestreattheworldasifitwerepredictable:ProductionandinventoryplanningarebasedonforecastsofdemandmadefarinadvanceofthesellingseasonCompaniesareawareofdemanduncertaintywhentheycreateaforecast,buttheydesigntheirplanningprocessasiftheforecasttrulyrepresentsrealityRecenttechnologicaladvanceshaveincreasedthelevelofdemanduncertainty:ShortproductlifecyclesIncreasingproductvariety2.2.2DemandForecastThethreeprinciplesofallforecastingtechniques:ForecastingisalwayswrongThelongertheforecasthorizon,theworsttheforecastAggregateforecastsaremoreaccurateCase:SnowTimeSportingGoodsFashionitemshaveshortlifecycles,highvarietyofcompetitorsSnowTimeSportingGoodsNewdesignsarecompletedOneproductionopportunityBasedonpastsales,knowledgeoftheindustry,andeconomicconditions,themarketingdepartmenthasaprobabilisticforecastTheforecastaveragesabout13,000,butthereisachancethatdemandwillbegreaterorlessthanthis.Case2SupplyChainTimeLinesJan00Jan01Jan02Feb00Sep00Sep01DesignProductionRetailingFeb01ProductionSnowTimeDemandScenariosDemandScenarios0%5%10%15%20%25%30%80001000012000140001600018000SalesProbabilitySnowTimeCostsThevariableProductioncostperunit(C):$80Sellingpriceperunit(S):$125Salvagevalueperunit(V):$20Fixedproductioncost(F):$100,000Tostartproduction,themanufacturerhastoinvest$100,000independentoftheamountproduced.Qisproductionquantity,DdemandProfit=Revenue-VariableCost-FixedCost+SalvageSnowTimeScenariosScenarioOne:Supposeyoumake12,000jacketsanddemandendsupbeing13,000jackets.Profit=125(12,000)-80(12,000)-100,000=$440,000ScenarioTwo:Supposeyoumake12,000jacketsanddemandendsupbeing11,000jackets.Profit=125(11,000)-80(12,000)-100,000+20(1000)=$335,000Profit=Revenue-VariableCost-FixedCost+SalvageSnowTimeBestSolutionFindorderquantitythatmaximizesweightedaverageprofit.Question:Willthisquantitybelessthan,equalto,orgreaterthanaveragedemand?WhattoMake?Question:Willthisquantitybelessthan,equalto,orgreaterthanaveragedemand?Averagedemandis13,100LookatmarginalcostVs.marginalprofitifextrajacketsold,profitis125-80=45ifnotsold,costis80-20=60SowewillmakelessthanaverageSnowTimeExpectedProfitExpectedProfit$0$100,000$200,000$300,000$400,0008000120001600020000OrderQuantityProfitThequantitythatmaximizesaverageprofit,isabout12,000.WhattoMake?Ifthecostofnotsellinganadditionalunitislargerthantheprofitfromsellinganadditionalunit,theoptimalquantityingeneralwillbelessthanaveragedemand,whileifthereverseistrue,theoptimalorderquantityingeneralwillbegreaterthanaveragedemand.SnowTimeExpectedProfitEx