确定需求下的库存管理培训教材.ppt

1、,Ch12 Inventory Management with Known Demand,第10章 确定需求下的库存管理,Teaching aims,1. Formulate a mathematical model describing the behavior of the inventory system. 2. Seek an optimal inventory policy with respect to this model.,Primary coverage,Scientific inventory management The Basic Economic Order Quan

2、tity (EOQ) Model（经济订购批量模型） The EOQ model with planned shortages The EOQ Model with quantity discounts The EOQ model with gradual replenishment,Focus and difficulty,1.The EOQ Model with Quantity Discounts 2.The EOQ model with planned shortages,12.1,Scientific inventory management,科学库存管理,12.1 Inventor

3、y Management,Manufacturers need inventories of the materials required to make their products. They also need inventories of the finished products awaiting shipment. Both wholesalers and retailers need to maintain inventories of goods to be available for purchase by customers.,The costs associated wi

4、th storing inventory are very large, perhaps a quarter of the value of the inventory. Just-in-time inventory system (准时化库存系统) emphasizes planning and scheduling so that the needed materials arrive just-in-time for their use. 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”,12.1 Inventory Management,12.1 Scientific

5、inventory management,Managers use scientific inventory management to improve their inventory policy for when and how much to replenish（补充） their inventory.,12.2 A Case Study,The Atlantic Coast Tire Corp. (ACT) Problem,大西洋海岸轮胎公司（ACT）问题,Background of ACT,ACT is the distributor（分销商） of Eversafe tires.

6、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 selling at a regular rate of about 500 per month. Managers policy has been to place

7、 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.(因此库存用完之前的第九天就开始订货),Background of ACT,Are you sure?,Is 1,000 the optimal amount for the order quantity? IF high inventory level THEN low order

8、 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,Cost component 1: Acquisition cost (获得成本),Retailers and wholesalers (such as ACT) replenish their inventory by purchasing the product. （购买） Manufacturers (such as Eversafe) replenish their

9、 inventory of finished products for subsequent sale to their customers by manufacturing more of the product involved. （自己生产）,Acquisition cost-whether a product is purchased or manufactured, there is a direct cost associated with bringing it into inventory. The direct cost of replenishing inventory i

10、s acquisition cost.,Cost component 1: Acquisition cost,Notation: c=unit acquisition cost ACT Example: Purchase price=$20per tire c=$20 per tire,Cost component 1: Acquisition cost,The setup cost consists of the various administrative costs (管理成本) associated with initiating and processing the purchase

11、 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）,Notation: 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

12、. The sum of these two figures is $115. Administration cost for placing an order = $115 k=$115,Cost component 2: Setup cost,These costs represents the costs associated with holding the items in inventory until they are needed elsewhere. For the ACT example, this kind of cost includes the cost of cap

13、ital tied up in inventory（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） (storage cost),Notation: h=annual holding cost per unit held =unit holding cost (h=每单位货物的年持有成本 =单位持有成本 ),Cost component 3: Holding cost (storage cost),缺货成本是指当需要从库存

14、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=annual shortage cost per unit short =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 4: Shortage cost（缺货成本）,Annual acquisition cost = c*number of units added to inventory per year Annual setup cost = k*number o

15、f setups per year Annual holding cost = h*average number of units in inventory throughout a year,Total inventory cost,Annual 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 cost,Total inventory co

16、st,Fixed cost,Fixed 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 costs,variable costs-those costs that are affected by the decision made-since these are the only costs that

17、 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（EOQ）模型,12.3,The assumptions of the EOQ model,A constant demand rate.（固定需求率） D=annual demand rate =number of units being wi

18、thdrawn from inventory per year 为补充库存而订购的货物能在需要时立即到达. 不允许计划内的缺货.,Lead time（提前期）,Lead time-the amount of time between the placement of the order and its receipt is referred to as the lead time.（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。,Reorder point（再订购点）,Reorder point-the inventory level at which the

19、order is placed is called the reorder point.（下订单时的库存水平） Reorder point=(daily demand)*(lead time),Safety stock,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些回旋余地。这种额外的防止送货延迟的库存叫做安全库存（safety stock）,33,EOQ model,Number of setups per year = ( annual demand rate) / (order quantity) =D/Q Average inventory level

20、=(max. level + Min. level)/2 =(Q+0)/2=Q/2 TVC=annual setup cost + annual holding cost = k(D/Q)+h(Q/2),ACT Inventory Cost,准备成本,持有成本,年总成本,Summary,With different Q, TVC is different. There exists optimal Q making TVC minimum. How to find the optimal Q?,10.4,the optimal inventory policy for the basic EOQ model,基本EOQ模型的最优库存策略,Optimal order quantity,Min TVC=k(D/Q)+h(Q/2) Let Then, Q*=,Result Analysis,Original Q=1000 tires, no