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Chapter 8. Inventory Management. Introduction. Radio Frequency Identification (RFID) . Conventional bar codes are replaced with computer chips or smart tags. Use wireless technology to track inventory. Wal-Mart RFID. Early adopter of RFID is Wal-Mart.
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Chapter 8 Inventory Management
Radio Frequency Identification (RFID) • Conventional bar codes are replaced with computer chips or smart tags. • Use wireless technology to track inventory. Chapter 8 - Inventory Management
Wal-Mart RFID • Early adopter of RFID is Wal-Mart. • By January 2005, 53 of its top 100 suppliers were sending RFID-tagged goods to its three distribution centers in the Dallas, Texas area. • Wal-Mart’s goal is to have all top 100 suppliers shipping RFID-tagged goods by the end of February 2005 in addition to 37 other suppliers. Chapter 8 - Inventory Management
Wal-Mart RFID continued • The impetus for Wal-Mart’s investment in RFID was the lack of visibility it had into its backroom storage areas. • The major drawback to RFID is its cost. • In 2005, the cost of smart tags was $0.25 each if purchased in volume, and $0.75 if purchased in smaller quantities. • The stated goal in the industry is to get the price of smart tags down to $.05 Chapter 8 - Inventory Management
Vendor-Managed Inventory (VMI) • With VMI, suppliers are given responsibility for managing the inventory carried by their retail or wholesale customers. • Rich Products, a $2 billion family-owned food company headquartered in Buffalo, NY, has a partnership with IBM to provide VMI services to the grocery industry for its frozen food items. Chapter 8 - Inventory Management
Functions of Inventories • Transit Inventories • Buffer Inventories (safety stocks) • Anticipation Inventories • Decoupling Inventories • Cycle Inventories Chapter 8 - Inventory Management
Forms of Inventories • Raw materials • Maintenance, repair, and operating supplies • Work-in-process (WIP) • Finished goods Chapter 8 - Inventory Management
Inventory-Related Costs • Ordering or setup costs • Inventory carrying or holding costs • Stockout costs • Opportunity costs • Cost of goods Chapter 8 - Inventory Management
Decisions in Inventory Management • When to order? • How much to order? Chapter 8 - Inventory Management
Types of Inventory Management Systems • Reorder point systems • time between orders varies • constant order quantity • Periodic review systems • time between orders fixed • order quantity varies • Material requirements planning (MRP) • dependent demand items Chapter 8 - Inventory Management
Fluctuations in Inventory Chapter 8 - Inventory Management
Reorder Point Systems • Reorder point • Lead time • Two-bin system • Perpetual inventory system Chapter 8 - Inventory Management
A Reorder Point System Chapter 8 - Inventory Management
Periodic Review System • maximum inventory level • - on-hand inventory • - on-order quantity • + demand over lead time • reorder quantity Chapter 8 - Inventory Management
Periodic Review System Without Considering On-Order Quantity Chapter 8 - Inventory Management
Periodic Review System (Assumes None On Order at Time of Reorder) Chapter 8 - Inventory Management
Priorities for Inventory Management: The ABC Concept • A items • 15-20% of items that account for 75-80% of annual inventory value • B items • 30-40% of items that account for 15% of annual inventory value • C items • 40-50% of items that account for 10-15% of annual inventory value Chapter 8 - Inventory Management
ABC Inventory Categories Chapter 8 - Inventory Management
Assumptions • Constant rate of demand • Shortages not allowed • Stock replenishment can be scheduled to arrive exactly when inventory drops to zero • Purchase price, ordering cost, and per unit holding cost are independent of quantity ordered • Items are ordered independently of each other Chapter 8 - Inventory Management
Notation • Q = order quantity • U = annual usage • CO = order cost per order • CH = annual holding cost per unit Chapter 8 - Inventory Management
Water Distributor’s Inventory Pattern Chapter 8 - Inventory Management
Water Distributor’s Inventory Graph Chapter 8 - Inventory Management
Annual Order Cost $ Q Chapter 8 - Inventory Management
Annual Holding Cost $ Q Chapter 8 - Inventory Management
Graph of Annual Inventory Costs Chapter 8 - Inventory Management
Finding an Optimal Policy Chapter 8 - Inventory Management
Alternative Way of Deriving EOQ Chapter 8 - Inventory Management
Alternative Way of Deriving EOQ continued Chapter 8 - Inventory Management
EOQ Example • Given: • 25,000 annual demand • $3 per unit per year holding cost • $100 ordering costs Chapter 8 - Inventory Management
Cautions Regarding EOQ • GIGO • Exclude “sunk” costs • Very small EOQ values my not be valid Chapter 8 - Inventory Management