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1、库存决策CR 2004 Prentice Hall,Inc.Chapter 9每一个管理上的失误最后都会变成库存。“Every management mistake ends up in inventory.Michael C.Bergerac Former Chief Executive Revlon,Inc.1产品方案三角形产品方案三角形Product in the Planning TriangleCR 2004 Prentice Hall,Inc.PLANNINGORGANIZINGCONTROLLINGTransport Strategy Transport fundamentals
2、 Transport decisionsCustomer service goals The product Logistics service Ord.proc.&info.sys.Inventory Strategy Forecasting Inventory decisions Purchasing and supply scheduling decisions Storage fundamentals Storage decisionsLocation Strategy Location decisions The network planning process 计划计划 组织组织
3、控制控制Transport Strategy Transport fundamentals Transport decisionsCustomer service goalsThe product Logistics service Ord.proc.&info.sys.Inventory Strategy Forecasting Inventory decisions Purchasing and supply scheduling decisions Storage fundamentals Storage decisionsLocation Strategy Location decis
4、ions The network planning process 库存战略 预测客户效劳目标采购和供给时间决策存储基础知识存储决策产品物流效劳订单管理和信息系统 库存决策 运输战略 运输基础知识 运输决策 选址战略 选址决策 网络规划流程2Inventory Decisions in StrategyCR 2004 Prentice Hall,Inc.PLANNINGORGANIZINGCONTROLLINGTransport Strategy Transport fundamentals Transport decisionsCustomer service goals The produ
5、ct Logistics service Ord.proc.&info.sys.Inventory Strategy Forecasting Inventory decisions Purchasing and supply scheduling decisions Storage fundamentals Storage decisionsLocation Strategy Location decisions The network planning processPLANNINGORGANIZINGCONTROLLINGTransport Strategy Transport funda
6、mentals Transport decisionsCustomer service goals The product Logistics service Ord.proc.&info.sys.Inventory Strategy Forecasting Inventory decisions Purchasing and supply scheduling decisions Storage fundamentals Storage decisionsLocation Strategy Location decisions The network planning process3CR
7、2004 Prentice Hall,Inc.什么是库存什么是库存What are Inventories?库存就是在企业生产和物流渠道中各点堆积的原材料、供给品、零部件、半成品和成品。4CR 2004 Prentice Hall,Inc.Where are Inventories?MaterialsourcesInboundtransportationProductionOutboundtransportationFinished goodswarehousingCustomersInventory locationsFinished goodsShippingInventoriesin-p
8、rocessReceivingProductionmaterials9-4原料来源生产内向运输外向运输成品储存 客户原材料半成品成品库存选址5CR 2004 Prentice Hall,Inc.9.1对库存的评述对库存的评述9.1.1库存原因库存原因Reasons for Inventories1.改善客户效劳2.降低成本首先，保有库存可以使生产的批量更大、批次更少，运作水平更高，因而产生经济效益其次，保有库存有助于实现采购和运输中的成本节约第三，先期购置可以在当前交易的低价位购置额外数量的产品。第四，抵销生产和运输过程中的不确定性第五，应付突发事件。6CR 2004 Prentice Hal
9、l,Inc.9.1对库存的评述对库存的评述9.1.1库存原因库存原因Reasons for InventoriesImprove customer service-Provides immediacy in product availabilityEncourage production,purchase,and transportation economies-Allows for long production runs-Takes advantage of price-quantity discounts-Allows for transport economies from large
10、r shipment sizesAct as a hedge against price changes-Allows purchasing to take place under most favorable price termsProtect against uncertainties in demand and lead times-Provides a measure of safety to keep operations running when demand levels and lead times cannot be known for sureAct as a hedge
11、 against contingencies-Buffers against such events as strikes,fires,and disruptions in supply7CR 2004 Prentice Hall,Inc.9.1.2反对保有库存的原因反对保有库存的原因Reasons Against Inventories第一，库存被认为是一种浪费第二，库存可能掩盖质量问题第三，保有库存鼓励人们以独立的观点来看待物流渠道整体的管理问题8CR 2004 Prentice Hall,Inc.9.1.2反对保有库存的原因反对保有库存的原因Reasons Against Invento
12、riesThey consume capital resources that might be put to better use elsewhere in the firmThey too often mask quality problems that would more immediately be solved without their presenceThey divert managements attention away from careful planning and control of the supply and distribution channels by
13、 promoting an insular attitude about channel management9流通渠道流通渠道Pipeline Inventories in transit投机投机Speculative-Goods purchased in anticipation of price increases定期性或周期性特征定期性或周期性特征Regular/Cyclical/Seasonal-Inventories held to meet normal operating needs安全安全Safety-Extra stocks held in anticipation of
14、demand and lead time uncertainties仓耗仓耗Obsolete/Dead Stock-Inventories that are of little or no value due to being out of date,spoiled,damaged,etc.9.2库存类型库存类型Types of Inventories10持久性需求持久性需求Perpetual demand-Continues well into the foreseeable future季节性需求季节性需求Seasonal demand-Varies with regular peaks
15、and valleys throughout the year尖峰需求尖峰需求Lumpy demand-Highly variable 规律性需求规律性需求Regular demand-Not highly variable 3 Mean终端需求终端需求Terminating demandDemand goes to 0 in foreseeable future派生需求派生需求Derived demandDemand is determined from the demand of another item of which it is a part9.3库存管理类型的分类库存管理类型的分类
16、9.3.1需求特点需求特点Nature of DemandAccurately forecasting demand is singly the most important factor in good inventory management11CR 2004 Prentice Hall,Inc.拉动式库存管理法拉动式库存管理法Pull-基于每个仓库的特定需求以一定的订货批量补足库存-每一个存储点独立Each stocking location is considered independent-最大化控制库存Maximizes local control of inventories推动
17、式库存管理法推动式库存管理法Push根据总需求分配产品到库存点鼓励规模生产准时生产制准时生产制Just-in-time同步库存流量以满足需求Attempts to synchronize stock flows so as to just meet demand as it occurs最小化库存Minimizes the need for inventory9.3.2管理思想管理思想Inventory Management Philosophies12CR 2004 Prentice Hall,Inc.拉动式库存管理法拉动式库存管理法Pull-Draws inventory into the
18、 stocking location-Each stocking location is considered independent-Maximizes local control of inventories推动式库存管理法推动式库存管理法PushAllocates production to stocking locations based on overall demandEncourages economies of scale in production准时生产制准时生产制Just-in-timeAttempts to synchronize stock flows so as t
19、o just meet demand as it occursMinimizes the need for inventory9.3.2管理思想管理思想Inventory Management Philosophies13CR 2004 Prentice Hall,Inc.供给驱动供给驱动Supply-Driven-供给量和时间未知Supply quantities and timing are unknown-所有的供给必须接受和处理All supply must be accepted and processed-通过需求控制库存Inventories are controlled thr
20、ough demand联合控制联合控制Aggregate Control工程分类工程组根据基于80-20法则确定的销售水平为3个或以上的产品组合允许不同的库存策略9.3.2管理思想管理思想Inventory Management Philosophies14PlantWarehouse#1Warehouse#2Warehouse#3A1A2A3A=Allocation quantity to each warehouseQ=Requested replenishment quantity by each warehouseQ1Q2Q3DemandforecastDemandforecastDe
21、mandforecastPULL-Replenish inventory withorder sizes based on specific needsof each warehousePUSH-Allocate supply to eachwarehouse based on the forecastfor each warehouse拉动式或推动式库存管理思想拉动式或推动式库存管理思想Pull vs.Push Inventory PhilosophiesCR 2004 Prentice Hall,Inc.9-11推动式基于每个仓库的预测将供给分配给各个仓库拉动式基于每个仓库的特定需求以一定
22、订货批量补足库存A将产品分配到各个仓库Q每个仓库需要的补货量159.3.3产品汇总程度n多数库存管理是针对每一种产品的库存进行控制。自下而上法n另一种方法是管理一类产品而不是管理单独一种产品自上而下法169.3.4多层级库存n供给链管理鼓励管理者将供给渠道中更多的局部包括到方案过程中来，供给渠道中多个层级的库存也成为核心问题。179.3.5虚拟库存n虚拟库存即将自己将来所可能需要而又没有的东西的所有相关信息建立档案，包括品名规格价格数量等，在需要时能使用上。189.4库存目标库存目标Inventory Management ObjectivesGood inventory management
23、 is a careful balancing act between stock availability and the cost of holding inventory.Customer Service,i.e.,Stock AvailabilityInventory Holding costsService objectives-Setting stocking levels so that there is only a specified probability of running out of stockCost objectives-Balancing conflictin
24、g costs to find the most economical replenishment quantities and timingCR 2004 Prentice Hall,Inc.199.4.1产品的现货供给比率n效劳水平n=1-每年产品缺货件数的期望值/年需求总量 20CR 2004 Prentice Hall,Inc.采购成本采购成本Procurement costs-准备订单的成本Cost of preparing the order-订单传输成本Cost of order transmission-产品安装成本Cost of production setup if app
25、ropriate-接受地物料搬运或加工成本Cost of materials handling or processing at the receiving dock-商品价格Price of the goods9.4.2库存管理相关成本库存管理相关成本Costs Relevant to Inventory Management21CR 2004 Prentice Hall,Inc.Relevant Costs Contd采购成本采购成本Procurement costs-Cost of preparing the order-Cost of order transmission-Cost o
26、f production setup if appropriate-Cost of materials handling or processing at the receiving dock-Price of the goods22CR 2004 Prentice Hall,Inc.库存持有成本库存持有成本Carrying costs-空间成本。库存成本随时间推移-Cost for holding the inventory over time-资金成本。-库存效劳成本-库存风险成本23CR 2004 Prentice Hall,Inc.9.4.2库存管理相关成本库存管理相关成本Costs
27、Relevant to Inventory Management库存持有成本库存持有成本Carrying costs-Cost for holding the inventory over time-The primary cost is the cost of money tied up in inventory,but also includes obsolescence报废,insurance,personal property taxes,and storage costs-Typically,costs range from the cost of short term capita
28、l to about 40%/year.The average is about 25%/year of the item value in inventory.24CR 2004 Prentice Hall,Inc.Relevant Costs Contd缺货成本缺货成本Out-of-stock costs-销售损失成本Lost sales cost利润损失Profit immediately foregone商誉损失Future profits foregone through loss of goodwill-缺货成本Backorder cost额外订单处理费用Costs of extr
29、a order handling额外的运输和处理费用Additional transportation and handling costs可能的安装费用Possibly additional setup costs25Inventorys Conflicting Cost PatternsCost补给量Replenishment quantity缺货成本Stockout cost采购成本Procurement cost库存持有成本Carrying cost总成本Total cost最低订货成本最低订货成本Minimum costreorder quantityCR 2004 Prentice
30、 Hall,Inc.9-1626术语汇编术语汇编Glossary of TermssoldbeingunitsofyprobabilitCPtimeleadofdeviationstandardandaverage,demandannualtotalofpercentaaslevelservice$cost,relevanttotalunits,orstock,safetyondistributidemandcompoundonmeanfromdeviationsstandardofnumberordeviatenormalunitslevel,inventorytargetdayse.g.,
31、interval,orderunitsquantity,pointreorderquantityordersystem-(Ptimecycleorderplustimeleadduringorsystem)-(Qtimeleadduringstock-inbeingofyprobabilitintegrallossnormalunitornexpectatiopartialondistributidemandcompoundofdeviationstandardpricepurchaseunitper$cost,stock-of-outunits(d),demandofdeviationsta
32、ndardunitper$value,productyearper%value,productofpercentaascostscarrying$/orderorder,percosttprocuremenunitsdemand,periodaverageunitsdemand,annualaveragen)(nsLTSLTCz x srzMAXTROPQPEspksCISdDLTzd=279.5推动式库存管理n1.通过预测或其他手段确定从现在到下一次生产或采购期间的需求量n2.找出每个存储点现有的库存量n3.设定每个存储点库存的现货供给水平n4.计算总需求n5.计算净需求n6.在平均需求速率
33、的基础上，将超过总净需求的局部分配到各存储点n7.在净需求加上分配的超量局部得到需分配到每个存储点的货物总量289.6基本的拉动式库存管理n1需求是一次性的、高季度性的或持续性的情况n2订货程序在某一库存水平上启动或由库存盘点程序启动n3需求和补货提前期存在不同程度不确定性的情况29CR 2004 Prentice Hall,Inc.9.6.1一次性订货量一次性订货量Single Order PurchasingMake a one-time purchase of an item.How much to order?Procedure:平衡利润增加额与损失增加额利润=单位价格-单位成本损失=
34、单位成本-单位残值如果考虑一定量产品被售出的概率 CPn，预期收益和预期损失在以下点得到平衡 CPn x 损失=1-CPn x 利润or CPn=利润/利润+损失CPn代表至多售出n个单位产品的累积概率Daily stocking of newspapers in vending machines is a good example9-1830CR 2004 Prentice Hall,Inc.9.6.1一次性订货量一次性订货量Single Order PurchasingMake a one-time purchase of an item.How much to order?Procedu
35、re:Balance incremental profit against incremental loss.Profit=Price per unit Cost per unitLoss=Cost per unit Salvage value per unitIf CPn is probability of n units being sold,then CPn x Loss=1 CPn x Profitor CPn=Profit/Profit+LossNow,increase order quantity until CPn just matches cumulative probabil
36、ity of selling additional units.Daily stocking of newspapers in vending machines is a good example9-1831CR 2004 Prentice Hall,Inc.Single Order Purchasing ContdExample A clothing item is purchased for a seasonal sale.It costs$35,but it has a sale price of$50.After the season is over,it is marked down
37、 by 50%to clear the merchandise.The estimated quantities to be sold are:Number ofitems,nProbability ofselling exactly nitemsCumulativeprobability100.150.15150.200.35200.300.65250.200.85300.100.95350.051.001.009-1932CR 2004 Prentice Hall,Inc.9.6.1一次性订货量一次性订货量Single Order Purchasing ContdSolutionProfi
38、t=$50-35=$15Loss=$35-0.550=$10CPn=15/15+10=0.60CPn is between 15 and 20 items,round up and order 20 items.339.6.2重复订货量重复订货量1.即刻补货即刻补货TC每年总的相关成本美元Q补充存货的订单批量件D对库存产品的年需求量件S采购成本美元/订单C库存产品的价值美元/件I库存持有成本占产品价值的比例%/年Develop a simple control system by finding the replenishment quantity Q and the reorder poin
39、t ROP.The relevant total cost is:总成本=采购成本和库存成本注注:需求和提前期确定需求和提前期确定周期性的库存管理周期性的库存管理9-21349.6.2重复订货量重复订货量1.即刻补货即刻补货TC每年总的相关成本美元Q补充存货的订单批量件D对库存产品的年需求量件S采购成本美元/订单C库存产品的价值美元/件I库存持有成本占产品价值的比例%/年Develop a simple control system by finding the replenishment quantity Q and the reorder point ROP.The relevant to
40、tal cost is:总成本=采购成本和库存成本Note:No uncertainty in demand or lead timemanage regular cycle stock only9-2135CR 2004 Prentice Hall,Inc.0TimeLead timeLead timeOrder PlacedOrder PlacedOrder ReceivedOrder ReceivedInventory LevelReorder point,RQReorder Point Method Under Certaintyfor a Single ItemQuantity on
41、-hand plus on-order9-22369.6.2重复订货量重复订货量Given:d=50 units/week I=10%/year S=$10/order C=$5/unit LT=3 weeksNote:No uncertainty in demand or lead timemanage regular cycle stock only9-212.有提前期的补货有提前期的补货37CR 2004 Prentice Hall,Inc.Using differential calculus,the optimal value for Q will be:The reorder po
42、int is:ROP=dLT=350=150 unitsFamous EOQformulaRule When the inventory level drops to 150 units ROP then reorder 322 units Q*.9-23383.对不准确数据的敏感性n尽管我们不一定总能知道需求和成本确实切水平，经济订货批量的计算对估计错误的数据并不敏感。394.非即刻补货nEOQ模型中有一个基本假设，即任何订货批量都可以及时补进。在有些制造和再供给环节中，生产要持续一定时间，并且可能和需求同步进行。np是生产速率，d是需求速率40CR 2004 Prentice Hall,I
43、nc.9.7高级拉动式库存管理高级拉动式库存管理9.7.1需求不确定下的再订货点模型需求不确定下的再订货点模型1.计算计算Q*和和ROPGood method for products:1.Of high value2.That are purchased from one vendor or plant3.Having few economies of scale in production,purchasing,or transportation9-24Find Q*and ROP41CR 2004 Prentice Hall,Inc.9.7高级拉动式库存管理高级拉动式库存管理9.7.1需
44、求不确定下的再订货点模型需求不确定下的再订货点模型Given:d=50 units/week C=$5/unit sd=10 units/week LT=3 weeks I=10%/year P=99%during lead time S=$10/orderFind Q*and ROPFrom the EOQ formulaGood method for products:1.Of high value2.That are purchased from one vendor or plant3.Having few economies of scale in production,purcha
45、sing,or transportation9-2442CR 2004 Prentice Hall,Inc.Reorder Point Control for a Single ItemROPQuantity on hand0QQReceive orderPlace orderStockoutLTTimeLTDDLTP9-2543CR 2004 Prentice Hall,Inc.ROPQ0Inventory levelLTLTTimeSafety stockReorder Point Control for a Single ItemActual on handQuantity on han
46、d+on order backordersQuantity for control9-2644Weekly demand is normally distributed with a mean of d=100 and a standard deviation of sd=10Lead time is 3 weeksReorder Point Control ContdFinding the reorder point requires an understanding of the demand-during-lead-time distributionsd=10d=100sd=10d=10
47、0sd=10d=100+=Week 3Week 2Week 1zPDDLTX=300 ROPS=17.39-2745CR 2004 Prentice Hall,Inc.Reorder Point Control Contdwhere 2.33 is the normal deviate at a probability of 0.01 taken from a normal distribution table.462.平均库存成本n平均库存=经常性库存+安全库存nA/L=Q/2+zsdn在前例中，n平均库存=322/2+2.33*17.32=201个47Reorder Point Contr
48、ol Contd3.总相关成本Total relevant cost The total relevant cost equation is now extended to include the costs of safety stock as well as out-of-stock.The out-of-stock cost k is$2/unit.The price term is dropped.Hence,where Ez=0.0034 from a unit normal loss table at a z value of 2.339-29484.效劳水平n效劳水平n=1-每年
49、产品缺货件数的期望值/年需求总量49CR 2004 Prentice Hall,Inc.9.7.2缺货成本情况下的再订货成本缺货成本情况下的再订货成本With known stockout costs k如果缺货成本，就没必要规定客户效劳水平了，可以将效劳和成本的最正确平衡点计算出来。可用反复迭代的方法1 利用基本EOQ公式得出订货量的近似值Solve initially for Q2 通过下式计算提前期内现货供给的概率Using Q,find如果缺货允许If backordering is allowedor如果销售出现损失If sales are lost50CR 2004 Prentic
50、e Hall,Inc.Reorder Point Control Contd3 计算Q的修正值Using P,find revised Q4 重复2,3步直到P和Q不再变化Repeat steps 2 and 3 until no further change5 计算ROP和其他所需的统计值 pute ROP and other statistics51CR 2004 Prentice Hall,Inc.Reorder Point Control ContdExample Given:每月需求预测,d 11,107 units预测标准差,sd 3,099 units补货提前期,LT 1.5 m