7. Economic Order Quantity Model Assuming demand certainty Trade-offs between setup costs and inventory holding costs, but ignores issues such as demand uncertainty and forecasting . 1000 2000 3000 4000 5000 6000 0 50 100 150 200 250 300 350 Ordering (Acquisition)Costs Holding or Carrying Costs Total Costs Economic Order Quantity
23. Initial Inventory and Profit The case motivates a powerful ( s , S ) inventory policy (or a min max policy): s is the reorder point and S is the order-up-to-level
26. Variable Demand with a Fixed ROP Reorder point, R Q LT Time LT Inventory level 0 Result of uncertainty
27. Reorder Point with a Safety Stock The amount of safety stock needed is based on the degree of uncertainty in the lead time demand and desired customer service level Reorder point, R Q LT Time LT Inventory level 0 Safety Stock
44. Advantages / Disadvantages large costs to have flexibility accommodate demand uncertainty Capacity Pooling reduce inventory investment additional transportation costs keep inventory closer to customer extra costs of operating distribution center decrease lead time Lead Time Pooling better performance in terms of matching supply and demand potentially degrades product functionality reduction in demand variability Product Pooling reduce expected inventory investment needed to achieve a target service level creates distance between inventory and customers reduce demand variability Location Pooling Disadvantages Advantages
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46. Example Decentralized system: total SS = 47.88 total avg. invent. = 179 Safety Stock SS = z · STD · Reorder Point R = AVG · L + SS Order Quantity Q = sqrt(2* C 0 *AVG/h ) Order-up-to-level R + Q Average Inventory SS + Q/2 Service Level:97% k=1.88 Lead Time= 1 week Q/2+SS AVG STD SS R Q Order- up-to Level Average Inventory Warehouse 1 39.3 13.2 25.08 65 132 197 91 Warehouse 2 38.6 12.0 22.8 62 131 193 88 Centralized Warehouse 77.9 20.7 39.35 118 186 304 132
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50. Decentralized Centralized Inbound transportation cost (from factories to warehouses) Facility/Labor cost Outbound transportation cost (from warehouses to retailers) Safety Stock Responsiveness to customers (lead time) Centralized vs. Decentralized Overhead Costs Service Level