确定需求下的库存管理

1、确定需求下的库存管理确定需求下的库存管理 ssss1. Formulate a mathematical model describing the behavior of the inventory system. 2. Seek an optimal inventory policy with respect to this model. 1.The EOQ Model with Quantity Discounts 2.The EOQ model with planned shortageslManufacturers need inventories of the materials r

2、equired 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 purchase by customers. lThe costs associated with storing inventory are very large, perhaps a quarter of the

3、 value of the inventory.lJust-in-time inventory system (准时化库存系准时化库存系统统) emphasizes planning and scheduling so that the needed materials arrive just-in-time for their use.l JIT的思想可以概括为的思想可以概括为“在需要的时候，按需在需要的时候，按需要的量生产需要的产品要的量生产需要的产品l lManagers use scientific inventory management to improve their inven

4、tory policy for when and how much to replenish补充补充 their inventory.l ACT 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

5、of the order. The tires have been selling 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

6、前的第九天就开始订货) 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 库存模型中的本钱构成库存模型中的本钱构成 Cost component 1: Acquisition cost (获得本钱获得本钱)Retailers and wholesalers (such as ACT) replenish their inventory by pur

7、chasing the product. 购置购置 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 manufactured, there is a direct cost associated

8、with bringing it into inventory. The direct cost of replenishing inventory is acquisition cost. : Acquisition cost Notation: c=unit acquisition cost ACT Example: Purchase price=$20per tire c=$20 per tire : Acquisition cost The setup cost consists of the various administrative costs (管理本钱管理本钱) associ

9、ated with initiating and processing the purchase order, receiving the shipment, and processing the payment. 准本本钱由各种管理本钱构成，包括准备和准本本钱由各种管理本钱构成，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。处理购货单、接收运抵的货物和处理付款手续等。 Notation: K=setup cost ACT Example: For each order, there will be a labor cost of $90 and also associated ove

10、rhead costs (supervision, office space, etc.) of $25. The sum of these two figures is $115. Administration cost for placing an order = $115 k=$115 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 i

11、ncludes the cost of capital tied up in inventory库存占用资金的本钱，比方利息库存占用资金的本钱，比方利息 as well as the cost of space, insurance, protection etc. Notation: h=annual holding cost per unit held =unit holding cost (h=每单位货物的年持有本钱每单位货物的年持有本钱 =单位持有本钱单位持有本钱 ) : Holding cost (storage cost) 缺货本钱是指当需要从库存中取货而库存缺货本钱是指当需要从库

12、存中取货而库存中已无货时发生的本钱。中已无货时发生的本钱。 不能立即满足客户订单的一种可能的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，或者降低客户满意结果是丢了这笔生意，或者降低客户满意度从而丧失未来的订单等。度从而丧失未来的订单等。 Notation: p=annual shortage cost per unit short =unit shortage cost p=每单位货物的年短缺本钱每单位货物的年短缺本钱 =单位货物短缺本钱单位货物短缺本钱 Annual acquisition cost = c*number of units added to inventory per

13、 year Annual setup cost = k*number of setups per year Annual holding cost = h*average number of units in inventory throughout a year 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 NO.CostUnitExample (ACT)

14、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41iCostTCFixed 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

15、 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 can be decreased by improving the decisions. TVC=total variable inventory cost per year =sum of the variable annual costs A constant demand rate.

16、固定需求率固定需求率 D=annual demand rate =number of units being withdrawn from inventory per year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. 不允许方案内的缺货不允许方案内的缺货. lLead time-the amount of time between the placement of the order and its receipt is referred to as the lead time.在下订单和收在下订单和收到货物之间的一段时间叫做提前期到货物之间的一段时间

17、叫做提前期l l 如：如：ACT的提前期是的提前期是9个工作日。个工作日。l 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l lReorder point=(daily demand)*(lead time)l l 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盘时会提高一点在订购点以在送货延迟时有些盘旋余地。这种额外的防止送货延迟的库存叫做旋余地

18、。这种额外的防止送货延迟的库存叫做平安库存平安库存safety stockl 33 Number of setups per year = ( annual demand rate) / (order quantity) =D/Q Average inventory level =(max. level + Min. level)/2 =(Q+0)/2=Q/2 lTVC=annual setup cost + annual holding cost = k(D/Q)+h(Q/2) DQK($) h ($)k (D/Q) ($)h (Q/2) ($)TVC ($)600010001154.2069021002790600015001154.204603100356060005001154.20138010502430准备本钱准备本钱持有本钱持有本钱年总本钱年总本钱lWith different Q, TVC is different.lThere exists optimal Q making TVC minimum.lHow to find the optimal Q? 根本EOQ模型的最优库存策略l Min TVC=k(D/Q)+h(Q/2) Let lThen, Q*=hKD2022hQkD