确定需求下的库存管理培训教材

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1、Ch12 Inventory Management with Known Demand第第10章章 确定需求下的库存管理确定需求下的库存管理Teaching aims1.Formulate a mathematical model describing the behavior of the inventory system.2.Seek an optimal inventory policy with respect to this model.Primary coverage1.Scientific inventory managementScientific inventory mana

2、gement2.The Basic Economic Order Quantity(EOQ)Model（经济订购批量模型经济订购批量模型）3.The EOQ model with planned shortages4.The EOQ Model with quantity discounts5.The EOQ model with gradual replenishment Focus and difficulty1.The EOQ Model with Quantity Discounts 2.The EOQ model with planned shortages12.1Scientifi

3、c inventory management科学库存管理科学库存管理12.1 Inventory ManagementlManufacturers need inventories of the materials required to make their products.They also need inventories of the finished products awaiting shipment.lBoth wholesalers and retailers need to maintain inventories of goods to be available for

4、purchase by customers.lThe costs associated with storing inventory are very large,perhaps a quarter of the value of the inventory.lJust-in-time inventory system(准准时时化化库库存存系系统统)emphasizes planning and scheduling so that the needed materials arrive just-in-time for their use.JIT的的思思想想可可以以概概括括为为“在在需需要要

5、的的时时候候，按按需需要的量生产需要的产品要的量生产需要的产品”12.1 Inventory Management12.1 Scientific inventory managementlManagers use scientific inventory management to improve their inventory policy for when and how much to replenish（补充）（补充）their inventory.12.2 A Case StudyThe Atlantic Coast Tire Corp.(ACT)Problem大西洋海岸轮胎公司（大

6、西洋海岸轮胎公司（ACT）问题）问题Background of ACTACT is the distributor（分销商）（分销商）of Eversafe tires.When the inventory level of tires get low,ACT places a large order with Eversafe to replenish the inventory.Eversafe ships the tires to arrive nine working days after the placement of the order.The tires have been s

7、elling at a regular rate of about 500 per month.Managers policy has been to place an order with Eversafe for 1,000 tires as needed every couple months.The order is placed just in time to have the delivery arrive as the inventory runs out.(因此因此库存用完之前的第九天就开始订货库存用完之前的第九天就开始订货)Background of ACTAre you s

8、ure?Is 1,000 the optimal amount for the order quantity?IF high inventory level THEN low order frequency IF Low inventory level THEN high order frequency 12.3 Cost Components of Inventory Models库存模型中的成本构成库存模型中的成本构成 Cost component 1Cost component 1:Acquisition cost(获得成本获得成本)1.Retailers and wholesalers

9、(such as ACT)replenish their inventory by purchasing the product.（购买购买）2.Manufacturers(such as Eversafe)replenish their inventory of finished products for subsequent sale to their customers by manufacturing more of the product involved.（自己生产自己生产）Acquisition cost-whether a product is purchased or man

10、ufactured,there is a direct cost associated with bringing it into inventory.The direct cost of replenishing inventory is acquisition cost.Cost component 1:Acquisition cost Notation:c=unit acquisition cost ACT Example:Purchase price=$20per tirec=$20 per tire Cost component 1:Acquisition costThe setup

11、 cost consists of the various administrative costs(管理成本管理成本)associated with initiating and processing the purchase order,receiving the shipment,and processing the payment.（准本成本由各种管理成本构成，包括准备和处（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。）理购货单、接收运抵的货物和处理付款手续等。）Cost component 2:Setup cost（准备成本）（准备成本）Nota

12、tion:K=setup cost ACT Example:For each order,there will be a labor cost of$90 and also associated overhead costs(supervision,office space,etc.)of$25.The sum of these two figures is$115.Administration cost for placing an order=$115k=$115 Cost component 2:Setup costThese costs represents the costs ass

13、ociated with holding the items in inventory until they are needed elsewhere.For the ACT example,this kind of cost includes the cost of capital tied up in inventory（库存占用资金的成本，比如利息）（库存占用资金的成本，比如利息）as well as the cost of space,insurance,protection etc.Cost component 3:Holding cost（持有成本）（持有成本）(storage c

14、ost)Notation:h=annual holding cost per unit held =unit holding cost (h=每单位货物的年持有成本每单位货物的年持有成本 =单位持有成本单位持有成本 )Cost component 3:Holding cost (storage cost)缺货成本缺货成本是指当需要从库存中取货而库存是指当需要从库存中取货而库存中已无货时发生的成本。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=annual shortage cost per unit sh

15、ort =unit shortage cost （p=每单位货物的年短缺成本 =单位货物短缺成本 ）Cost component 4Cost component 4:Shortage cost（缺货成本）（缺货成本）Annual acquisition cost=c*number of units added to inventory per year Annual setup cost=k*number of setups per year Annual holding cost=h*average number of units in inventory throughout a year

16、 Total inventory costAnnual shortage cost=p*average number of units short throughout a year TC=total inventory cost per year =sum of the above four annual costs Total inventory costNO.CostUnitExample(ACT)Annual1获得成本获得成本 c$20c*每年加入库存的数量每年加入库存的数量2准备成本准备成本 k$115K*每年准备的次数每年准备的次数3持有成本持有成本 h$4.20h*每年平均库存数

17、量每年平均库存数量4缺货成本缺货成本 p$7.50p*每年平均缺货数量每年平均缺货数量5库存成本库存成本Total inventory costFixed costFixed cost-a cost that remains the same regardless of the decisions made.The annual acquisition cost will indeed be a fixed cost if the unit acquisition cost is fixed.Variable costsvariable costs-those costs that are a

18、ffected by the decision made-since these are the only costs that can be decreased by improving the decisions.TVC=total variable inventory cost per year =sum of the variable annual costs The Basic Economic Order Quantity(EOQ)Model基本经济订购批量（基本经济订购批量（EOQ）模型）模型12.3The assumptions of the EOQ model 1.A con

19、stant demand rate.（固定需求率）（固定需求率）D=annual demand rate =number of units being withdrawn from inventory per year2.为补充库存而订购的货物能在需要时立即到达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不允许计划内的缺货.Lead time（提前期）（提前期）lLead time-the amount of time between the placement of the order and its receipt is referred to as the lead

20、time.（在下订单和（在下订单和收到货物之间的一段时间叫做提前期）收到货物之间的一段时间叫做提前期）如：如：ACT的提前期是的提前期是9个工作日。个工作日。Reorder point（再（再订购点）点）lReorder point-the inventory level at which the order is placed is called the reorder point.（下订单时的库存水平）（下订单时的库存水平）lReorder point=(daily demand)*(lead time)Safety stock l送货的延迟将导致库存短缺，因此库存经理有送货的延迟将导致库

21、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些回时会提高一点在订购点以在送货延迟时有些回旋余地。这种额外的防止送货延迟的库存叫做旋余地。这种额外的防止送货延迟的库存叫做安全库存安全库存（safety stock）33EOQ modelNumber of setups per year =(annual demand rate)/(order quantity)=D/Q Average inventory level =(max.level+Min.level)/2 =(Q+0)/2=Q/2 TVC=annual setup cost+annual holding cost =k(

22、D/Q)+h(Q/2)ACT Inventory CostDQK($)h($)k(D/Q)($)h(Q/2)($)TVC($)600010001154.2069021002790600015001154.204603100356060005001154.20138010502430准备成本准备成本持有成本持有成本年总成本年总成本Summary lWith different Q,TVC is different.lThere exists optimal Q making TVC minimum.lHow to find the optimal Q?10.4 the optimal inven

23、tory policy for the basic EOQ model基本EOQ模型的最优库存策略Optimal order quantityl Min TVC=k(D/Q)+h(Q/2)Let lThen,Q*=Result AnalysislOriginal Q=1000 tires,now Q*=573 lNearly 43 percent reduction in average inventory levels.l14 percent reduction in the total variable cost.（original$2790,now$2407）准备次数由原来的准备次数由原

24、来的6次升到了次升到了10.47Sensitivity AnalysisThe accuracy of optimal order quantity depends on the accuracy of the data that went into the analysis.Each of these data(k,h)could be off by as much as 10 percent in either direction.Setup cost:$103.50 to$126.50 Unit holding cost:$3.78 to$4.62 Q*=573The EOQ model with planned shortages有计划缺货的有计划缺货的EOQ模型模型12.542The EOQ model with planned shortagesTVC=年准备成本+年持有成本+年缺货成本 年准备成本=年持有成本=h(库存水平为正时的平均库存水平)(正库存水平所占时间比例)=年缺货成本=p(当缺货出现时的平均缺货水平)(缺货所占的时间比例)=The EOQ model with planned shortages演讲完毕，谢谢观看！