mcgraw-hill/irwin copyright © 2007 by the mcgraw-hill companies, inc. all rights reserved. 15 lean...

McGraw-Hill/Irwin Copyright © 2007 by The McGraw-Hill Companies, Inc. All rights reserved.

1515

Lean Operations

15-2

JIT/Lean ProductionJIT/Lean Production

Just-in-time (JIT): A highly coordinated processing system in which goods move through the system, and services are performed, just as they are needed,

JIT lean production

JIT pull (demand) system

JIT operates with very little “fat”

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GoalsGoals

Eliminate disruptions

Make system flexible

Eliminate waste, especially excess inventory

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Sources of WasteSources of Waste

Overproduction

Waiting time

Unnecessary transportation

Processing waste

Inefficient work methods

Product defects

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Kaizen PhilosophyKaizen Philosophy

Waste is the enemy Improvement should be done gradually and

continuously Everyone should be involved Built on a cheap strategy Can be applied anywhere

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JIT Building BlocksJIT Building Blocks

Product design

Process design

Personnel/organizationalelements

Manufacturing planning and control

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Product DesignProduct Design

Standard parts

Modular design

Concurrentengineering

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Process DesignProcess Design

Small lot sizes

Setup time reduction

Limited work in process

Quality improvement

Balanced system

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Personnel/Organizational Personnel/Organizational ElementsElements

Workers as assets

Cross-trained workers

Continuous improvement

Leadership/project management

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Manufacturing Planning and Manufacturing Planning and ControlControl

Pull systems

Visual systems

Close vendor relationships

Preventive maintenance

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Pull/Push SystemsPull/Push Systems

Pull system: System for moving work where a workstation pulls output from the preceding station as needed. (e.g. Kanban)

Push system: System for moving work where output is pushed to the next station as it is completed

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Kanban Production Control Kanban Production Control SystemSystem

Kanban: Card or other device that communicates demand for work or materials from the preceding station

Kanban is the Japanese word meaning “signal” or “visible record”

Paperless production control system

Authority to pull, or produce comes from a downstream process.

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Kanban FormulaKanban Formula

N = DT(1+X)Q

N = Total number of containers

D = Planned usage rate of using work center

T = Average waiting time for replenishment of parts plus average production time for a container of parts

X = Policy variable set by management - possible inefficiency in the system

Q = Capacity of a standard container (C in Book)

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KANBAN policy KANBAN policy

A KANBAN policy uses N containers, each containing Q units of the item and with a card on the bottom. When a container becomes empty, the card (a KANBAN) is used as an order for Q units.

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KANBAN policy (Q=4, N=8)KANBAN policy (Q=4, N=8)

Supply / production

productcard

Stock

Cards and empty containers

Full containers with cards

Demands

Card send first to avoid delays

Machine

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KANBAN versus (R,Q) KANBAN versus (R,Q)

A KANBAN policy is very similar to an (R, Q) policy with R = (N - 1)Q. But if there are already N outstanding orders, i.e., no stock on hand, no more orders can be triggered since no KANBANs are available. We can therefore interpret a KANBAN policy as an (R, Q) policy where backorders are not subtracted from the inventory position.

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Comparison of JIT and Comparison of JIT and TraditionalTraditional

Factor Traditional JIT

Inventory Much to offset forecast errors, late deliveries

Minimal necessary to operate

Deliveries Few, large Many, small

Lot sizes Large Small

Setup; runs Few, long runs Many, short runs

Vendors Long-term relationships are unusual

Partners

Workers Necessary to do the work Assets

Table 15.3

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JIT II: a supplier representative works right in the company’s plant, making sure there is an appropriate supply on hand.

JIT IIJIT II