介绍,operation,management,项目管理17

12 InventoryManagement 12 2 LearningObjectives Definetheterminventory listthemajorreasonsforholdinginventories andlistthemainrequirementsforeffectiveinventorymanagement DiscussthenatureandimportanceofserviceinventoriesDiscussperiodicandperpetualreviewsystems Discusstheobjectivesofinventorymanagement DescribetheA B Capproachandexplainhowitisuseful 12 3 LearningObjectives DescribethebasicEOQmodelanditsassumptionsandsolvetypicalproblems Describetheeconomicproductionquantitymodelandsolvetypicalproblems Describethequantitydiscountmodelandsolvetypicalproblems Describereorderpointmodelsandsolvetypicalproblems Describesituationsinwhichthesingle periodmodelwouldbeappropriate andsolvetypicalproblems 12 4 Inventory astockorstoreofgoods Inventory 12 5 InventoryModels Independentdemand finishedgoods itemsthatarereadytobesoldE g acomputerDependentdemand componentsoffinishedproductsE g partsthatmakeupthecomputer 12 6 TypesofInventories RawmaterialsandpurchasedpartsPartiallycompletedgoodscalledwork in processFinished goodsinventories manufacturingfirms ormerchandise retailstores 12 7 TypesofInventories Replacementparts tools andsuppliesGoods in transittowarehousesorcustomers 12 8 FunctionsofInventory TomeetanticipateddemandTosmoothproductionrequirementsTodecoupleoperationsToprotectagainststockouts 12 9 FunctionsofInventory TotakeadvantageofordercyclesTohelphedgeagainstpriceincreasesTopermitoperationsTotakeadvantageofquantitydiscounts 12 10 ObjectiveofInventoryControl ToachievesatisfactorylevelsofcustomerservicewhilekeepinginventorycostswithinreasonableboundsLevelofcustomerserviceCostsoforderingandcarryinginventory Inventoryturnoveristheratiooftheaveragecostofgoodssoldtotheaverageinventoryinvestment 12 11 AsystemtokeeptrackofinventoryAreliableforecastofdemandKnowledgeofleadtimesReasonableestimatesofHoldingcostsOrderingcostsShortagecostsAclassificationsystem EffectiveInventoryManagement 12 12 InventoryCountingSystems PeriodicSystemPhysicalcountofitemsmadeatperiodicintervalsPerpetualInventorySystemSystemthatkeepstrackofremovalsfrominventorycontinuously thusmonitoringcurrentlevelsofeachitem 12 13 InventoryCountingSystems Two binsystem Twocontainersofinventory reorderwhenthefirstisemptyUniversalProductCode UPC Barcodeprintedonalabelthathasinationabouttheitemtowhichitisattached 12 14 Leadtime timeintervalbetweenorderingandreceivingtheorderHolding carrying costs costtocarryanitemininventoryforalengthoftime usuallyayearOrderingcosts costsoforderingandreceivinginventoryShortagecosts costswhendemandexceedssupply KeyInventoryTerms 12 15 ABCClassificationSystem Classifyinginventoryaccordingtosomemeasureofimportanceandallocatingcontroleffortsaccordingly A veryimportantB moderatelyimportantC leastimportant Figure12 1 12 16 CycleCounting AphysicalcountofitemsininventoryCyclecountingmanagementHowmuchaccuracyisneeded Whenshouldcyclecountingbepered Whoshoulddoit 12 17 Economicorderquantity EOQ modelTheordersizethatminimizestotalannualcostEconomicproductionmodelQuantitydiscountmodel EconomicOrderQuantityModels 12 18 OnlyoneproductisinvolvedAnnualdemandrequirementsknownDemandiseventhroughouttheyearLeadtimedoesnotvaryEachorderisreceivedinasingledeliveryTherearenoquantitydiscounts AssumptionsofEOQModel 12 19 TheInventoryCycle Figure12 2 12 20 TotalCost Annualcarryingcost Annualorderingcost Totalcost TC 12 21 CostMinimizationGoal OrderQuantity Q TheTotal CostCurveisU Shaped OrderingCosts QO AnnualCost optimalorderquantity Figure12 4C 12 22 DerivingtheEOQ Usingcalculus wetakethederivativeofthetotalcostfunctionandsetthederivative slope equaltozeroandsolveforQ 12 23 MinimumTotalCost Thetotalcostcurvereachesitsminimumwherethecarryingandorderingcostsareequal D Q S 12 24 ProductiondoneinbatchesorlotsCapacitytoproduceapartexceedsthepart susageordemandrateAssumptionsofEPQaresimilartoEOQexceptordersarereceivedincrementallyduringproduction EconomicProductionQuantity EPQ 12 25 OnlyoneitemisinvolvedAnnualdemandisknownUsagerateisconstantUsageoccurscontinuallyProductionrateisconstantLeadtimedoesnotvaryNoquantitydiscounts EconomicProductionQuantityAssumptions 12 26 EconomicRunSize 12 27 TotalCostswithPurchasingCost 12 28 TotalCostswithPD Figure12 7 12 29 TotalCostwithConstantCarryingCosts Figure12 9 12 30 WhentoReorderwithEOQOrdering ReorderPoint Whenthequantityonhandofanitemdropstothisamount theitemisreorderedSafetyStock Stockthatisheldinexcessofexpecteddemandduetovariabledemandrateand orleadtimeServiceLevel Probabilitythatdemandwillnotexceedsupplyduringleadtime 12 31 DeterminantsoftheReorderPoint TherateofdemandTheleadtimeDemandand orleadtimevariabilityStockoutrisk safetystock 12 32 SafetyStock Figure12 12 12 33 ReorderPoint Figure12 13 12 34 OrdersareplacedatfixedtimeintervalsOrderquantityfornextinterval SuppliersmightencouragefixedintervalsMayrequireonlyperiodicchecksofinventorylevelsRiskofstockoutFillrate thepercentageofdemandfilledbythestockonhand Fixed Order IntervalModel 12 35 TightcontrolofinventoryitemsItemsfromsamesuppliermayyieldsavingsin O