Presentation on theme: "Managing Inventory throughout the Supply Chain"— Presentation transcript:
1Managing Inventory throughout the Supply Chain Chapter 11
2Chapter Objectives Be able to: Describe the various roles of inventory, including the different types of inventory and inventory drivers.Distinguish between independent demand and dependent demand inventory.Calculate the restocking level for a periodic review system.Calculate the economic order quantity (EOQ) and reorder point (ROP) for a continuous review system.Determine the best order quantity when volume discounts are available.Calculate the target service level and target stocking point for a single-period inventory system.Describe how inventory decisions affect other areas of the supply chain. In particular, describe the bullwhip effect, inventory positioning issues, and the impacts of transportation, packaging, and material handling considerations.
3Introduction: A Balancing Act for Management Both the presence and absence of inventory contribute to value and to costs.Too much inventory is an investment that will provide no return.Too little inventory results in missed or late sales and deliveries.Carrying the correct amount of inventory is a difficult balancing act.
7Why Should Businesses Carry Inventory? Decoupling: Reducing the direct dependency of a process step on its predecessor. This could be in a process or in the supply chain.Decouple customer from supplier and machine from machineDisruptions, if decoupled, don’t have as serious of an impactDecoupling enhances reliability and response time
8Why Should Businesses Carry Inventory? DecouplingMeeting DemandEmergency Situations
93. Why should business avoid carry too much inventory?
10Why Should Businesses Avoid Carrying Too Much Inventory? No Financial returns - Inventory is an investment that should provide a financial return; excess inventory is an investment that provides no return.Associated costs - In addition to the cost of purchasing it, inventory also has other “carrying” costs: Cost of storage, Cost of insurance, Reduction in flexibility
11Why Should Businesses Avoid Carrying Too Much Inventory? Reduces management’s ability to make quick decisions (reduces flexibility)Less adaptability to changing market conditions
14Types of InventoryCycle stock – Components or products that are received in bulk by a downstream partner, gradually used up, and then replenished again in bulk by an upstream partner.Safety stock – Extra inventory that a company holds to protect itself against uncertainties in either demand or replenishment time.
16Types of InventoryTransportation inventory – Inventory that is moving from one link in the supply chain to another.Smoothing inventory – Inventory that is used to smooth out differences between upstream production levels and downstream demand.
18Costs and BenefitsOrder cost: The fixed cost associated with ordering inventory.Changeover (setup) cost: The cost of changing equipment from producing one product or service to another. Analogous to order cost.Carrying cost: Costs associated with carrying inventory. Insurance, storage, opportunity cost of money tied up in inventory.Stockout cost: Costs associated with not having inventory when a customer wants it.Purchasing cost: Cost of purchasing the actual inventory. Sometimes quantity discounts lower this cost, but this comes at the expense of raising carrying costs.Buying in Bulk (discounted)…..
19Inventory DriversInventory drivers – Business conditions that force companies to hold inventory.Table 11.2
206. Distinguish between independent and dependent demand inventories.
21Independent vs. Dependent Demand Inventory Independent demand inventory – Inventory items whose demand levels are beyond a company’s complete control.Dependent demand inventory – Inventory items whose demand levels are tied directly to a company’s planned production of another item.
22Independent vs. Dependent Demand Inventory Example:Independent demand:Kitchen table – Need 500 tables five weeks from nowDependent demand:Kitchen table legs – Need 4 per table or 2,000 legsCalculation of dependent demand (Chapter 12)
237. What are the two general approaches to managing independent demand inventory?
24Inventory Control Systems Continuous Review System – An inventory system used to manage independent demand inventory where the inventory level for an item is constantly monitored and when the reorder point is reached, an order is released.Periodic Review System – An inventory system that is used to manage independent demand inventory where the inventory level for an item is checked at regular intervals and restocked to some predetermined level.
25Continuous Review System Key features:Inventory levels are monitored constantly, and a replenishment order is issued only when the reorder point is reached.The size of a replenishment order is typically based on the trade-off between holding costs and ordering costs.The reorder point is based on both demand and supply considerations, as well as on how much safety stock managers want to hold.
26Continuous Review System Assumptions:Constant demand and lead timeHolding and Ordering cost known and fixedPrice of each unit is fixed.
27Continuous Review System When the demand rate and lead time are constant:Reorder point = demand x lead timeR = dLFigure 11.7
28Economic Order Quantity Economic Order Quantity (EOQ) – The order quantity that minimizes annual holding and ordering costs for an item.Holding costs (H)– The cost to hold a single unit in inventory for a year.Ordering costs (S) – The cost of placing an order regardless of the order quantity.
29Re-Order Point (ROP): The impact of varying demand rates and lead time Figure 11.10
30Causes of Variability The variability of demand The variability of lead timeThe average length of lead timeThe desired service level
31ROP ProblemFor men’s size XL Trevecca T-shirts at the bookstore, the average weekly demand is 7, with a standard deviation of 3. the replenishment lead time is 1 week. What should the re-order point be to maintain a 99% confidence of satisfying the demand during the lead time?
32Quantity DiscountsQuantity Discounts – Price reductions for ordering larger quantities.
33Quantity Discounts Two-step process: Calculate the EOQ. If the EOQ represents a quantity that can be purchased for the lowest price, stop – we have found the lowest cost order quantity. Otherwise, go to Step 2.Compare total holding, ordering, and item costs at the EOQ quantity with total costs at each price break above the EOQ. There is no reason to look at quantities below the EOQ, as these would result in higher holding and ordering costs, as well as higher item costs.
35Example 11.4 – Hal’s Magic Shop Because 115 is not eligible for the lowest price, calculate total cost at 115:
36Example 11.4 – Hal’s Magic Shop And compare to total cost at next price break or 201.Price is cheaper at the 201 price break.
37Periodic Review System Calculating the order quantity (Q)Q = R-IwhereR = restocking levelI = inventory level at the time of review.Figure 11.6
38Periodic Review System Calculating the restocking level (R)
39Calculating Service Level Service Level – A term used to indicate the amount of demand to be met under conditions of demand and supply uncertainty.Assumes that the demand during the reorder period and the order lead time is normally distributed.
40Single-Period Inventory System When excess inventory cannot be held in the future, firms must weigh the cost of being short against the cost of holding excess units.Examples:Fresh fish, magazines, newspapers, Christmas trees
41Single-Period Inventory System Single-period inventory system – A system used when demand occurs in only a single point in time.Goals:Determine a target service level (SLT) that strikes the best balance between shortage costs and excess costs.Use the target service level to determine the target stocking point (TS) for the item.
42Single-Period Inventory System Target service level – The service level at which the expected cost of a shortage equals the expected cost of having excess units.Target stocking point – The stocking point at which the expected cost of a shortage equals the expected cost of having excess units.
48Demand vs. Order Size The Bullwhip Effect Figure 11.12
49Managing Inventory Case Study Northcutt Bikes: The Service Department
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