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1、INVENTORY MANAGEMENT,Chapter Twenty,Copyright 2014 by The McGraw-Hill Companies, Inc. All rights reserved.,McGraw-Hill/Irwin,Learning Objectives,LO201: Explain how inventory is used and understand what it costs. LO202: Analyze how different inventory control systems work. LO203: Analyze inventory us
2、ing the Pareto principle.,20-2,Inventory,Inventory can be visualized as stacks of money sitting on forklifts, on shelves, and in trucks and planes while in transit. For many businesses, inventory is the largest asset on the balance sheet at any given time. Inventory can be difficult to convert back
3、into cash. It is a good idea to try to get your inventory down as far as possible. The average cost of inventory in the United States is 30 to 35 percent of its value.,20-3,Supply Chain Inventory Models,20-4,Inventory Models,20-5,Definitions,Inventory: the stock of any item or resource used in an or
4、ganization Includes raw materials, finished products, component parts, supplies, and work-in-process Manufacturing inventory: refers to items that contribute to or become part of a firms product Inventory system: the set of policies and controls that monitor levels of inventory Determines what level
5、s should be maintained, when stock should be replenished, and how large orders should be,20-6,Purposes of Inventory,20-7,Inventory Costs,20-8,Demand Types,20-9,Inventory Control-System Design Matrix,20-10,Inventory Systems Comparison,20-11,Single Period Inventory Model,20-12,Solving the Newspaper Pr
6、oblem,Consider how much risk we are willing to take of running out of inventory. Assume a mean of 90 papers and a standard deviation of 10 papers. Assume we want an 80 percent chance of not running out. Assume that the probability distribution associated of sales is normal, stocking 90 papers yields
7、 a 50 percent chance of stocking out.,20-13,Solving the Newspaper Problem,From Appendix E, we see that we need approximately 0.85 standard deviation of extra papers to be 80 percent sure of not stocking out. Using Excel, “=NORMSINV(0.8)” = 0.84162,20-14,Single-Period Inventory Models,20-15,Example 2
8、0.1,Excel: Overbooking,20-16,Example 20.1,From Appendix E, we see that our desired level falls about 0.55 standard deviations below the mean (z = -0.55) Using Excel, “=NORMSINV(0.2857)” = 0.56599,20-17,Example 20.1 Overbooking Table,If we overbook by 1 and we have zero no-shows, we incur the penalty
9、 of $200 one person must be compensated for having no room.,If we overbook by 1 and we have three no-shows, we have lost sales of $80.,Total cost of a policy of overbooking by 9 rooms is the weighted average of the events (number of no-shows) and the outcome of those events.,20-18,Single Period Mode
10、l Applications,20-19,Multi-Period Models,20-20,Multi-Period Models Comparison,Inventory remaining must be continually monitored Has a smaller average inventory Favors more expensive items Is more appropriate for important items Requires more time to maintain but is usually more automated Is more exp
11、ensive to implement,Counting takes place only at the end of the review period Has a larger average inventory Favors less expensive items Is sufficient for less-important items Requires less time to maintain Is less expensive to implement,Fixed-Order Quantity,Fixed-Time Period,20-21,Multi-Period Mode
12、ls Comparison,20-22,Multi-Period Models Process,20-23,Fixed-Order Quantity Models Assumptions,Demand for the product is constant and uniform throughout the period. Lead time (time from ordering to receipt) is constant. Price per unit of product is constant. Inventory holding cost is based on average
13、 inventory. Ordering or setup costs are constant. All demands for the product will be satisfied.,20-24,Fixed-Order Quantity Model,Always order Q units when inventory reaches reorder point (R).,Inventory arrives after lead time (L). Inventory is raised to maximum level (Q).,Inventory is consumed at a
14、 constant rate, with a new order placed when the reorder point (R) is reached once again.,20-25,Economic Order Quantity (EOQ),The optimal order quantity (Qopt) occurs where total costs are at their minimum,20-26,Example 20.2,Excel: Economic Order Quantity,20-27,Establishing Safety Stock Levels,20-28
15、,Fixed-Order Quantity Model with Safety Stock,Demand is variable, but follows a known distribution/,After the reorder is placed, demand during the lead time may be higher than expected, consuming some (or all) of the safety stock/,20-29,Example 20.4,Policy place a new order for 936 units whenever st
16、ock falls to 388 units on hand. This results in a 95% probability of not stocking out during the lead time.,For 95% probability, z = 1.64.,Excel: Reorder Point,20-30,Fixed-Time Period Model,20-31,Fixed-Time Period Model,Time periods are equal, but ending inventory varies.,Reorder quantity varies, depending upon ending inventory level. Beginning inventory is always the same.,20-32,Example 20.5,Excel: Fixed Time Period Model,20-33,Inventory Control and Supply Chain Management,
