4QA3 F12 Week 10 Lecture Notes

Gandomi at j4 41 uncertainty mrp ignores demand

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ignores demand uncertainty, supply uncertainty, and internal uncertainties that arise in the manufacturing process. ●  Capacity Planning. Basic MRP does not take capacity constraints into account. ●  Rolling Horizons. MRP is treated as a static system with a ^ixed horizon of n periods. The choice of n is arbitrary and can affect the results. ●  Lead Times Dependent on Lot Sizes. In MRP lead times are assumed ^ixed, but they clearly depend on the size of the lot required. ●  Quality Problems. Defective items can destroy the linking of the levels in an MRP system. ●  Data Integrity. Real MRP systems are big (perhaps more than 20 levels deep) and the integrity of the data can be a serious problem. ●  Order Pegging. A single component may be used in multiple end items, and each lot must then be pegged to the appropriate item. 4QA3 F12 A. Gandomi 42 ●  JIT (Just In Time) is an outgrowth of the Kanban system developed by Toyota. Source: Hiezer & Render (2006) 4QA3 F12 A. Gandomi 43 ●  Kanban is the Japanese word for card, ●  Kanban authorizes production from downstream operations, o  ‘Pulls’ material through plant ●  Kanban may be a card, ^lag, verbal signal, etc., ●  Kanban is often used with ^ixed- size containers. ●  So in JIT systems, supplies and components are “ pulled ” through system to arrive where they are needed when they are needed. 44 4QA3 F12 A. Gandomi ●  MRP is the classic push system. The MRP system computes production schedules for all levels based on forecasts of sales of end items. Once produced, subassemblies are pushed to next level whether needed or not. ●  JIT is the classic pull system. The basic mechanism is that production at one level only happens when initiated by a request at the higher level. That is, units are pulled through the system by request. 4QA3 F12 A. Gandomi 45 ●  JIT systems reduce the work- in- process (WIP) inventory to a bare minimum. Inventory level Inventory level Scrap Setup time Process downtime Quality problems Scrap Setup time Late deliveries 4QA3 F12 Source: Hiezer & Render (2006) Process downtime Quality problems Late deliveries A. Gandomi 46 ●  Small lot sizes are optimal only if the setup cost is small. ●  The most signi^icant component of the cost of setting up for a new operation in a plant is the time required to change over the machinery for the operation. ●  The idea behind SMED is that a signi^icant portion of the die- changing operation can be done off- line while the previous dies are still in place. Source: Hiezer & Render (2006) 4QA3 F12 A. Gandomi 47 Suppliers Employee Empowerment Layout Quality Inventory Preventive Maintenance 4QA3 F12 Scheduling A. Gandomi 48 ●  ●  ●  These methods offer two completely different approaches to basic production planning in a manufacturing environment. Main advantage of MRP over JIT: MRP takes forecasts for end product demand into account. In an environment in which substantial variation of sales are anticipated (and can be forecasted accurately), MRP has advantage. Main advantage of JIT over MRP: JIT reduces inventories to a minimum. In addition to saving direct inventory carrying costs, there are substantial side bene^its, such as improvement in quality and plant ef^iciency. 4QA3 F12 A. Gandomi 49 ●  Course textbook o  Chapter 7: Ch. 7: 7.1–7.3; 7.5- 7.8, Appendix 7–A. ●  Suggested problems o  Chapter 7: 4, 5, 41, 42, 43. ●  Further Readings o  Jay Heizer & Barry Render, Operations Management (Prentice Hall): Chapter 14 and Chapter 16. o  William Stevenson, Operations Management (McGraw- Hill): Chapter 13, Chapter 14. ●  Next lecture readings: o  Chapter 8: 8.1–8.7; 8.10. 4QA3 F12 A. Gandomi 50...
View Full Document

This document was uploaded on 04/01/2014.

Ask a homework question - tutors are online