供应链管理(第13讲1)

1、9-2Learning Objectivesl To determine the costs of holding inventory.l To identify the costs associated with a stockout.l To understand the EOQ concept.l To differentiate the various inventory flow patterns.l To appreciate the contemporary approaches to managing inventory.9-3Overview of Inventory Man

2、agementlInventories are stocks of goods and materials that are maintained for many purposes, the most being to satisfy normal demand patterns.lInventory management is a key component of supply-chain management, in part because inventory decision are often a start point, or driver, for other business

3、 activities such as warehousing, transportation, and materials handling.lDifferent functional areas have different inventory objectives.l Marketing tends to want to ensure that sufficient inventory is available for customer demand in order to avoid potential stockout situations higher inventory leve

4、ls.l Finance group generally seeks to minimize the costs associated with holding inventory lower inventory levels.lOne of the most prominent concerns about inventory is its cost, which is presented in greater detail later in this chapter.l Finished goods inventories are much more expensive to hold t

5、han raw materials or work in process.l The focus on inventory costs has intensified in recent years because of concern with inventory turnover.9-7l Inventory turnover is the number of times that inventory is sold in a 1-year period.l Inventory turnover: cost of goods sold divided by average inventor

6、y at cost.cost of goods sold = inventory turnoveraverage inventory $200,000 = inventory is sold 4 times per year. $ 50,000l Inventory turnover figures can provide important insights about an organizations competitiveness and efficiency. 9-8lCompare with competitors or benchmarked companies.lLow inve

7、ntory turnover = high inventory carrying costs, little (or no) stockout costs.lHigh inventory turnover = low inventory carrying costs, high stockout costs.lIts easy to say that organizations should strive for a proper balance of inventory; actually achieving it can be quite difficult because of trad

8、e-offs that are involved. Managing the tradeoff is important to maintain service levels.9-10Inventory ClassificationslIts important to know the key classifications of inventory because the classification influences the way that inventory is managed.lInventory is most frequently classified as Psychic

9、 stock ; Cycle or base stock; Safety or buffer stock; Pipeline or in-transit stock; Speculative stock.lWhile inventory generally exists to service demand, in some situations inventory is carried to stimulate demand, also known as psychic stock. Retail stores stock huge amounts of certain merchandise

10、.lCycle, or base, stock refers to inventory that is needed to satisfy normal demand during the course of an order cycle. We use one egg per day and we buy eggs every 12 days.lSafety, or buffer, stock refers to inventory that is held in addition to cycle stock to guard against uncertain in demand and

11、/or lead time. making a three-egg omelet; buying eggs every 14 days.lPipeline, or in-transit, stock is inventory that is en route between various nodes (i.e., fixed facilities such as a plant, warehouse, store) in a logistics system. eggs in transit between the retail store and your kitchen.lSpecula

12、tive stock refers to inventory that is held for several reasons, including seasonal demand, projected price increases, and potential shortages of product. Spring Festival, tends to cause an increase in demand for eggs. 9-17Inventory-Related CostslInventory-related costs are most frequently classifie

13、d as Inventory carrying (holding) costs; Stockout costs.lInventory carrying (holding) costs including:l Obsolescencel Inventory shrinkagel Storage costs and handling costsl Taxes l Interest chargesl Opportunity costlIn general, inventory carrying costs are expressed in percentage terms, and this per

14、centage is multiplied by the inventorys value. However, the calculation of a carrying cost percentage can be quite unstructured.lStockout costs: Such costs can accrue during stockouts, when customers demand items that arent immediately available.lAlthough calculation of stock costs can be difficult

15、and inexact, it is important for organization to do so because such knowledge can be beneficial when determining how much inventory to hold.lEstimating the costs or penalty for a stockout involves an understanding of customer reaction to a company being out of stock when a customer wants to buy an i

16、tem. (Page 273 )9-23Table 9-1: Determination of the Average Cost of a StockoutAlternativeLossProbabilityAverage Cost1. Brand-loyal customer $00.00.10 $00.002. Switches and comes back$37.00.65 $24.053. Lost customer$1,200.25 300.00Average cost of a stockout1.00$324.05These are hypothetical figures fo

17、r illustration.l As a general rule, the higher the average cost of a stockout, the better it is for the company to hold some amount of inventory (safety stock) to protect against stockouts. The higher the probability of a delayed sale, the lower the average stockout costsand the lower the inventory

18、that needs to be held by a company.9-25lTrade-offs exist between carrying and stockout costs.l Marginal analysis focuses on the trade-off between carrying and stockout costs, allow a company to determine an optimum level of safety stocks.l Marginal analysis helps define the point at which the costs

19、of holding additional safety stock are equal to the savings in stockout costs avioded.9-26Table 9-2: Determination of Safety Stock LevelNumber of Units of Safety StockTotal Value of Safety Stock ($480 per Unit)25% Annual Carrying CostCarrying Cost of Incremental Safety StockNumber of Additional Orde

20、rs FilledAdditional Stockout Costs Avoided10$4,800$1,200$1,20020$6,481.0020 9,600 2,400 1,20016 5,184.803014,400 3,600 1,20012 3,888.604019,200 4,800 1,2008 2,592.405024,000 6,000 1,2006 1,944.306028,800 7,200 1,2004 1,296.207033,600 8,400 1,2003 972.159-27When to OrderlFixed order quantity system;

21、Fixed order interval system (Page 276 )lReorder point (ROP) (Page 276 )ROP = DD x RC under certaintyROP = (DD x RC) + SS under uncertaintyWhere DD = daily demandRC = length of replenishment cycleSS = safety stock9-28How Much to ReorderlThe typical inventory order size problem, referred to as the eco

22、nomic order quantity (EOQ), deals with calculating the proper order size with respect to two costs: the costs of carrying the inventory and the costs of ordering the inventory. lEQQ determines the point at which the sum of carrying costs and ordering costs is minimized, or the point at which carryin

23、g cost equal ordering cost .9-30Figure 9-1: Determining EOQ by Use of a Graphl Economic order quantity (EOQ) in dollarsEOQ = 2AB/C (Page 278 )WhereEOQ = the most economic order size, in dollars A = annual usage, in dollars B = administrative costs per order of placing the order C = carrying costs of

24、 the inventory (%)9-32l Economic order quantity (EOQ) in unitsEOQ = 2DB/IC (Page 278 )WhereEOQ = the most economic order size, in units A = annual demand, in units B = administrative costs per order of placing the order C = carrying costs of the inventory (%) I = dollar value of the inventory, per u

25、nit9-33Table 9-3: EOQ Cost CalculationsNumber of orders per yearOrder size ($)Ordering cost ($)Carrying cost ($)Total cost (sum of ordering and carrying cost) ($)11,000 251001252 500 50 501003 333 75 331084 250 100 251255 200 125 20145lThe figures from the fixed order quantity (e.g., EQQ) and the sa

26、fety stock calculations can be used to develop an inventory flow diagram, which graphically depicts the demand for, and replenishment of, inventory.Inventory Flows9-35Figure 9-2: Inventory Flow Diagram9-36lSafety stock can prevent against two problem areas.l Increased rate of demandl Longer-than-nor

27、mal replenishmentlWhen fixed order quantity system like EOQ is used, time between orders may vary.lWhen reorder point is reached, fixed order quantity is ordered.9-37Contemporary Approaches to Managing InventorylSeveral of the more prominent approaches are presented in this section: ABC Analysis; Ju

28、st-in Time (JIT) Approach; Vendor-Managed Inventory (VMI); Inventory Tracking.l ABC Analysis of inventory recognizes that inventories are not of equal value and that all inventory should not be managed in the same way. l Measures used to determine ABC status include sales volume, the fastest-selling

29、 items, item profitability, or item importance.l In terms of item importance, ABC might be operationalized as follows: A the highest criticality; B moderate criticality; C low criticality.l Just-in Time (JIT) Approach: From an inventory perspective, the JIT approach seeks to minimize inventory by re

30、ducing 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.l The JIT approach has a number of important implications for supply-chain efficiency.l Collaboration among supply-chain participants is key to successf

31、ul JIT initiatives.l Vendor-Managed Inventory (VMI): Under VMI, the size and timing of replenishment orders are the responsibility of the manufacturer.l VIMs benefits for distributors and retailers tend to involve a reduced number of stockouts and higher inventory turns, while manufacturer benefits include improved demand forecasting.l