确定需求下的库存管理

Ch12InventoryManagementwithKnownDemand第10章确定需求下的库存管理Teachingaims1.Formulateamathematicalmodeldescribingthebehavioroftheinventorysystem.2.Seekanoptimalinventorypolicywithrespecttothismodel.Primarycoverage1.Scientificinventorymanagement2.TheBasicEconomicOrderQuantity(EOQ)Model（经济订购批量模型）3.TheEOQmodelwithplannedshortages4.TheEOQModelwithquantitydiscounts5.TheEOQmodelwithgradualreplenishmentFocusanddifficulty1.TheEOQModelwithQuantityDiscounts2.TheEOQmodelwithplannedshortages§12.1Scientificinventorymanagement科学库存管理12.1InventoryManagementManufacturersneedinventoriesofthematerialsrequiredtomaketheirproducts.Theyalsoneedinventoriesofthefinishedproductsawaitingshipment.Bothwholesalersandretailersneedtomaintaininventoriesofgoodstobeavailableforpurchasebycustomers.Thecostsassociatedwithstoringinventoryareverylarge,perhapsaquarterofthevalueoftheinventory.Just-in-timeinventorysystem(准时化库存系统)emphasizesplanningandschedulingsothattheneededmaterialsarrivejust-in-timefortheiruse.JIT的思想可以概括为“在需要的时候，按需要的量生产需要的产品”12.1InventoryManagement12.1ScientificinventorymanagementManagersusescientificinventorymanagementtoimprovetheirinventorypolicyforwhenandhowmuchtoreplenish（补充）theirinventory.§12.2ACaseStudyTheAtlanticCoastTireCorp.(ACT)Problem大西洋海岸轮胎公司（ACT）问题BackgroundofACT•ACTisthedistributor（分销商）ofEversafetires.Whentheinventoryleveloftiresgetlow,ACTplacesalargeorderwithEversafetoreplenishtheinventory.Eversafeshipsthetirestoarrivenineworkingdaysaftertheplacementoftheorder.•Thetireshavebeensellingataregularrateofabout500permonth.Manager’spolicyhasbeentoplaceanorderwithEversafefor1,000tiresasneededeverycouplemonths.Theorderisplacedjustintimetohavethedeliveryarriveastheinventoryrunsout.(因此库存用完之前的第九天就开始订货)BackgroundofACT024681012InventoryLevelMaximum=1000Average=500Minimum=0Time(Months)Areyousure?•Is1,000theoptimalamountfortheorderquantity?IFhighinventorylevelTHENloworderfrequencyIFLowinventorylevelTHENhighorderfrequency§12.3CostComponentsofInventoryModels库存模型中的成本构成Costcomponent1:Acquisitioncost(获得成本)1.Retailersandwholesalers(suchasACT)replenishtheirinventorybypurchasingtheproduct.（购买）2.Manufacturers(suchasEversafe)replenishtheirinventoryoffinishedproductsforsubsequentsaletotheircustomersbymanufacturingmoreoftheproductinvolved.（自己生产）•Acquisitioncost---whetheraproductispurchasedormanufactured,thereisadirectcostassociatedwithbringingitintoinventory.Thedirectcostofreplenishinginventoryisacquisitioncost.Costcomponent1:Acquisitioncost•Notation:c=unitacquisitioncost•ACTExample:–Purchaseprice=$20pertire–c=$20pertireCostcomponent1:Acquisitioncost•Thesetupcostconsistsofthevariousadministrativecosts(管理成本)associatedwithinitiatingandprocessingthepurchaseorder,receivingtheshipment,andprocessingthepayment.（准本成本由各种管理成本构成，包括准备和处理购货单、接收运抵的货物和处理付款手续等。）Costcomponent2:Setupcost（准备成本）Notation:K=setupcost•ACTExample:–Foreachorder,therewillbealaborcostof$90andalsoassociatedoverheadcosts(supervision,officespace,etc.)of$25.Thesumofthesetwofiguresis$115.–Administrationcostforplacinganorder=$115–k=$115Costcomponent2:Setupcost•Thesecostsrepresentsthecostsassociatedwithholdingtheitemsininventoryuntiltheyareneededelsewhere.FortheACTexample,thiskindofcostincludesthecostofcapitaltiedupininventory（库存占用资金的成本，比如利息）aswellasthecostofspace,insurance,protectionetc.Costcomponent3:Holdingcost（持有成本）(storagecost)•Notation:h=annualholdingcostperunitheld=unitholdingcost(h=每单位货物的年持有成本=单位持有成本)Costcomponent3:Holdingcost(storagecost)•缺货成本是指当需要从库存中取货而库存中已无货时发生的成本。不能立即满足客户订单的一种可能的结果是丢了这笔生意，或者降低客户满意度从而丢失未来的订单等。•Notation:p=annualshortagecostperunitshort=unitshortagecost（p=每单位货物的年短缺成本=单位货物短缺成本）Costcomponent4:Shortagecost（缺货成本）•Annualacquisitioncost=c*numberofunitsaddedtoinventoryperyear•Annualsetupcost=k*numberofsetupsperyear•Annualholdingcost=h*averagenumberofunitsininventorythroughoutayearTotalinventorycost•Annualshortagecost=p*averagenumberofunitsshortthroughoutayear•TC=totalinventorycostperyear=sumoftheabovefourannualcostsTotalinventorycostNO.CostUnitExample(ACT)Annual1获得成本c$20c*每年加入库存的数量2准备成本k$115K*每年准备的次数3持有成本h$4.20h*每年平均库存数量4缺货成本p$7.50p*每年平均缺货数量5库存成本41iCostTCTotalinventorycostFixedcost•Fixedcost---acostthatremainsthesameregardlessofthedecisionsmade.•Theannualacquisitioncostwillindeedbeafixedcostiftheunitacquisitioncostisfixed.Variablecosts•variablecosts---thosecoststhatareaffectedbythedecisionmade---sincethesearetheonlycoststhatcanbedecreasedbyimprovingthedecisions.•TVC=totalvariableinventorycostperyear=sumofthevariableannualcostsTheBasicEconomicOrderQuantity(EOQ)Model基本经济订购批量（EOQ）模型§12.3TheassumptionsoftheEOQmodel1.Aconstantdemandrate.（固定需求率）D=annualdemandrate=numberofunitsbeingwithdrawnfrominventoryperyear2.为补充库存而订购的货物能在需要时立即到达.3.不允许计划内的缺货.Leadtime（提前期）Leadtime---theamountoftimebetweentheplacementoftheorderanditsreceiptisreferredtoastheleadtime.（在下订单和收到货物之间的一段时间叫做提前期）如：ACT的提前期是9个工作日。Reorderpoint（再订购点）Reorderpoint---theinventorylevelatwhichtheorderisplacediscalledthereorderpoint.（下订单时的库存水平）Reorderpoint=(dailydemand)*(leadtime)Safetystock送货的延迟将导致库存短缺，因此库存经理有时会提高一点在订购点以在送货延迟时有