存货管理 Inventory Management CHAPTER 8 存货管理 Inventory Management

Learning Objectives To determine the costs of holding inventory To identify the costs associated with a stockout To understand the EOQ concept To differentiate the various inventory flow patterns To identify several contemporary approaches to managing inventory To discuss special concerns with inventory management

Key Terms ABC analysis ABC分析法 Complementary products 补充产品 Cycle(base) Stock 周转库存 (基本库存) Dead inventory 呆滞存货 Economic order quantity(EOQ) 经济订货批量 Fixed order interval system 定期订货系统 Fixed order quantity system 定量订货系统 Inventory 存货 Inventory carrying(holding) costs 存货持有成本 Inventory flow diagram 存货流程图 Inventory shrinkage 存货收缩

Inventory turnover 存货周转率 Just-in-time(JIT) approach 及时制方法 Nodes 物流结点 Pipeline (in-transit) stock 管道库存 (在途库存) Reorder (trigger) point (ROP) 再订货点 Safety (buffer) stock 安全库存(缓冲库存) Speculative stock 投机性库存 Stockout costs 缺货成本 Substitute products 替代品 Vendor-managed inventory (VMI) 供应商管理存货

引例: 惠普喷墨系列打印机的库存问题 必须用更少的库存去满足顾客的需要 惠普当时主要存在的两个问题。 第一个问题是要找出一种好方法，既能随时满足顾客对各种产品的需求，又可尽量减少库存； 第二个问题是要在各部门之间，就正确的库存水平达成一致意见。 必须用更少的库存去满足顾客的需要

我们对存货又爱又恨！到底应该保持多少存货才合理？什么时间进行订货？每次订货量为多少？ 案例启示 一方面，人们设置库存的目的是防止短缺，这样便占用了企业大量的资金，减少了企业的利润； 另一方面，库存能保持生产的连续性，缓解供需矛盾，提高客户满意度，甚至有些时候，库存还有“居奇”的作用，使企业盈利。 我们对存货又爱又恨！到底应该保持多少存货才合理？什么时间进行订货？每次订货量为多少？

1. 关于存货 about Inventory Inventories are stocks of goods and materials that are maintained for many purposes, the most common being to satisfy normal demand patterns. 存货是为了达到多种目的而维持货物和物料,主要用于满足正常的需求 如: 原材料(raw materials);外购零件(purchased parts);在制品(work-in-process);产成品(finished-goods);商品(merchandies);机器工具等备用零件(spare parts)等

The reasons of holding inventories Act as a buffer between production and selling processes 生产和销售之间的缓冲 Unexpected changes in customer demand消费者需求的不确定性 The short life cycle of an increasing number of products. The presence of many competing products in the marketplace. Uncertainty in the quantity and quality of the supply, supplier costs and delivery times. 供应数量和质量,供应商的成本和交付时间的不确定性 Delivery Lead Time, Capacity limitations 交付提前期,容量限制 Economies of scale (transportation cost) 规模经济

The reasons not holding inventories It is not free! 成本 Carrying costs It is risky 风险 Short product life cycles increase risk of product obsolescence It may not be needed 不需要 Information substitution It hides other problems 隐藏另外的问题 It may not add value to the supply chain So, What can you do?

Inventory management Decisions drive other business activities 存货决策是企业活动的起点或驱动器 Different functional areas have different inventory objectives 企业不同的职能部门有不同的存货管理目标 Marketing: higher inventory levels to avoid potential stockout situations Finance: lower inventory levels to minimize the costs accosicated with holding inventory ...... Inventory costs are important to consider存货成本非常重要

Inventory costs are important to consider Inventory turnover(存货周转率), the number of times that inventory is sold in a one-year period 一年内存货销售的次数 存货周转率高，库存管理的效率高；反之，意味着库存占用资金量大 (一般而言,越高越好) But,并非周转率越高就越好， low inventory turnover = high inventory carrying costs, little (or no) stockout costs ，high inventory turnover = low inventory carrying costs, high stockout costs Managing the tradeoff is important to maintain service levels

2.库存类型 Inventory Classifications Psychic stock 心理库存 to stimulates demand Cycle or base stock 周转库存 to satisfy normal demand during the course of an order cycle Safety or buffer stock 安全库存（缓冲库存） to guard against uncertainty in demand and/or lead time Pipeline or in-transit stock管道库存（在途库存） en route between various nodes in a logistics system Speculative stock 投机性库存 for seasonal demand, projected price increases, and potential shortage of product

3.存货相关成本 Inventory-Related Costs Inventory carrying (holding) costs 存货持有成本：企业因持有存货而发生的一切费用 (存货成本=年库存持有成本百分比*平均库存价值） Obsolescence 过时成本 Inventory shrinkage 存货损耗 Storage costs 仓储成本 Handling costs 搬运费用 Insurance costs 保险费用 Taxes 税金 Interest charges 利息 Opportunity cost 机会成本

Stockouts costs 缺货成本：当顾客需要或需求时没有产品供应而产生成本 Lost Sales Costs 失销成本 Back Order Costs 延期交货成本 Determination of the Average Cost of a Stockout Alternative Loss Probability Average Cost 1. Brand-loyal customer $00.00 .10 2. Switches and comes back $37.00 .65 $24.05 3. Lost customer $1,200 .25 300.00 Average cost of a stockout 1.00 $324.05 缺货成本的高低与储备量的大小有关，储备量大时，缺货的次数和数量相对就较少，缺货成本可能较低，但库存持有成本必然升高；储备量小时，缺货成本可能很高，但库存持有成本却可能降低。由于客户的反应随机性很大，缺货成本的具体衡量比较困难。

Customer Decisions Regarding a Stockout Stockout Occurs Option Option Option Wait Substitute Product Substitute Store Priority Backorder Normal Replenishment This Occasion Forever This Occasion Forever Product Selection Brand Price Location Customer Decisions Regarding a Stockout Brand Price Same Product Different Product

Determination of Safety Stock Level Trade-offs exist between carrying and stockout costs 库存持有成本与缺货成本之间的权衡 Marginal analysis Determination of Safety Stock Level Number of Units of Safety Stock Total Value of Safety Stock ($480 per Unit) 25% Annual Carrying Cost Carrying Cost of Incremental Safety Stock Number of Additional Orders Filled Additional Stockout Costs Avoided 10 $4,800 $1,200 20 $6,481.00 9,600 2,400 1,200 16 5,184.80 30 14,400 3,600 12 3,888.60 40 19,200 4,800 8 2,592.40 50 24,000 6,000 6 1,944.30 60 28,800 7,200 4 1,296.20 70 33,600 8,400 3 972.15

Order costs 订购成本:为了订购货物而产生的成本，它的大小基本上与每批产品的订购数量无关，而只与订货次数有关。 Fixed 订购的固定成本 Variable 订购的变动成本 检查库存水平 编制并提出订购申请 对多个供应商进行调查比较，选择最合适的供货商 填写并发出订购单 填写、核对收货单 验收发来的商品 筹备资金并进行付款

4. 存货策略 Inventory strategy Inventory strategy is the guidelines concerning what to purchase or manufacture, when to take action, and it what quantities Book Store Mug Sales Demand is constant, at 2400 units a year Fixed order cost of $19.00, no lead time Holding cost of 20% of inventory value annually Mugs cost $5.00, sell for $8.00 Question When to order? How many? 确定什么时候订货?每次订货多少?

(1)When to Order Fixed order quantity system（定量订货系统）

Fixed order interval system （定期订货系统） （库存策略就是要解决订货点的策略。订货点是用于确定再补给库存应该在何时启动，补货多少）

Reorder point (ROP)订货点（产品单位） ROP = DD x RC under certainty （补货订购按时进行） e.g.：假设需求量为20件/天，交货期为10天，则ROP为200件（或10天） ROP = (DD x RC) + SS under uncertainty（产品需求和运作周期不确定） e.g.：假设当需求或使用速度为每周100件，交货期为3周，安全库存为200件时，ROP为500件 Where DD = daily demand 平均的日需求量（产品单位） RC = length of replenishment cycle 交货期（天） SS = safety stock （安全库存）

(2)How Much to Reorder 模型假设：（1）缺货费用无穷大；（2）货物储存量减少到0时，可以立即得到补充；（3）货物需求是连续、均匀的，即货物消耗速率为常数；（4）每次进货量不变，订货费不变；（5）单位存储费用不变 Inventory Demand Speed R Order Size ROP Avg. Inven Time Cycle Time =T

Economic Order Quantity Model (EOQ) (Ford W. Harris, 1915) 取一阶导数为0 总成本 持有成本 订购成本 最为经济的订单数量

EOQ：A simplistic policy to determine order size Economic order quantity (EOQ) in units EOQ = √2DB/IC Where EOQ = the most economic order size, in units 每次定货 的经济批量大小（单位） D = annual demand, in units 年需求量（单位） B = administrative costs per order of placing the order 每次订购费用或准备成本（以美元表示） C = carrying costs of the inventory (%) 按每单货存货价值计算的每年库存持有成本（产品价值百分比%） I = dollar value of the inventory, per unit 每单位存货的价值或费用（以美元表示） t*= Q*/D=√2B/ICD 订购次数

年需求量 2400个单位 产品单位成本 5美元 库存持有成本百分比 20%/年 订购费用 19美元/订单 年需求量 2400个单位 产品单位成本 5美元 库存持有成本百分比 20%/年 订购费用 19美元/订单 EOQ=√（2*19*2400）/（0.2*5）=302 （产品单位）-----为方便计算，取约值为300 则，总的订购费用=2400/300*19=152美元 ； 库存持有成本=[300/2*（5*0.2）]=150美元 因此，每次订购的数量应该为300个单位，而最经济的订购次数为一年8次（2400/300），平均基本库存为150个单位

5.存货流 Inventory Flows Safety stock can prevent against two problem areas Increased rate of demand Longer-than-normal replenishment When fixed order quantity system like EOQ is used, time between orders may vary When reorder point is reached, fixed order quantity is ordered

6.现代库存管理方法 Contemporary Approaches to Managing Inventory ABC Analysis ABC分类法 Just-in Time (JIT) Approach 准时制方法 Vendor-Managed Inventory (VMI) 供应商管理存货 Inventory Tracking 存货跟踪 214800 232087768

（1）ABC分类法 分类系统 由GE的H. Ford Dicky在1951所发展出来。

帕累托定律（Parato’s Law)或“80-20法则”(“80-20” rule) 80%的销售來自于20%的存货。 20%的销售來自于80%的存货。 80-20法则已经被用來解释许多令管理者感到有兴趣的现象。 例如，80%的销售來自于20%的顾客，反之亦然

100% 90 80 70 60 50 40 30 20 10 销售额百分比 10 20 30 40 50 60 70 80 90 100% 产品项的百分比 A　　　　B 　　　　　C

不同类型库存的管理策略 库存类型 特点（按货币量占用） 管理方法 A 品种数约占库存总数的15%，成本约占70%-80% 进行重点管理。现场管理要更加严格，应放在更安全的地方；为了保持库存记录的准确要经常进行检查和盘点；预测时要更加仔细 B 品种数约占库存总数的30%，成本约占15%-25% 进行次重点管理。现场管理不必投入比A类更多的精力；库存检查和盘点的周期可以比A类要长一些 C 成本也许只占5%，但品种数量或许是库存总数的55% 只进行一般管理。现场管理可以更粗放一些；但是由于品种多，差错出现的可能性也比较大，因此也必须定期进行库存检查和盘点，周期可以比B类长一些

（2）JIT (Just In Time) Approach 概念来自于美国的看板(Kanban)系统，但是，是Toyota开发的。 JIT系统设计用于管理提前期和消除浪费 (JIT approach views inventory as waste) JIT approach seeks to minimize inventory by reducing safety stock, as well as by having the required amount of materials arrive at the production location at the exact time that they are needed. JIT approach requires smaler, more frequent shipments and close supplier location 有效地实施JIT理念能显著地降低零件和物料存货、在产品和产成品.

（3）VMI (Vendor Managed Inventory) 遵循合作、目标一致、互惠和持续改进原则 供应商 零售商 RMI模式 基于预期的订单 货物送达 VMI模式 客户需求信息 按需求发货

7.特殊的存货管理问题 Inventory Management: Special Concerns Complementary items 互补产品 Dead Inventory 呆滞库存 Deals 交易 Defining Stock-Keeping Units(SKUs)确定存货单位 Informal arrangements outside the distribution channel 分销渠道以外的非正式安排 Repair/replacement parts 维修和更换零部件 Reverse logistics逆向物流 Substitute Products替代产品