Just-In-Time (JIT) Motivation JIT Philosophy JIT Procedure - - PowerPoint PPT Presentation

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Just-In-Time (JIT) Motivation JIT Philosophy JIT Procedure - - PowerPoint PPT Presentation

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Just-In-Time (JIT) Motivation JIT Philosophy JIT Procedure Toyota Kanban Systems MRP vs. JIT Summary Reading: Page 678 707 Learning Objectives Understand the philosophy of Just-In- Time (JIT) Learn

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SLIDE 1

Just-In-Time (JIT)

  • Motivation
  • JIT Philosophy
  • JIT Procedure – Toyota Kanban Systems
  • MRP vs. JIT
  • Summary
  • Reading: Page 678 – 707
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SLIDE 2

Learning Objectives

  • Understand the philosophy of Just-In-

Time (JIT)

  • Learn the working procedure of JIT
  • Know the differences between the two

production-control systems, MRP (the push system) and JIT (the pull system)

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SLIDE 3

Inventory Models Revisited

h KD EOQ 2 =

  • EOQ model:

Cycle stock =

  • Reorder point system:

Safety stock =

  • What if K and σd are large?

d

L z σ

β

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SLIDE 4

Inventory & Process Improvement

  • Short-term responses:

– Large order size (large production batch) – More safety stock (just in case)

  • Long-term (JIT) responses:

– Reduce setup cost K – Reduce variability σd – Reduce lead-time

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SLIDE 5

Inventory Masks Problems

Excessive inventory masks problems (water covers rocks) Reduced inventories reveal problems (rocks becomes visible) excessive inventory low forecasting accuracy low product quality low productivity long leadtime … …

large volume of capital Marketing risk

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SLIDE 6

History of JIT

  • Origin of JIT: The idea and the practice of Just-in-time

(JIT) were initiated in 1970’s at Toyota, the leading automobile manufacturer of Japan

  • Characteristics of Manufacturing Environment in Japan

– Limited working space – Closeness to suppliers and consumers – Small economy scale – Relatively uniform taste of consumers – Eastern culture (well organized, system-oriented, etc.)

⇒ Improving productivity and reducing inventory become necessary and possible

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SLIDE 7

The Concept of JIT

  • JIT (lean operations): an operations

system in which materials are moved through the system and services are delivered with precise timing so that they are delivered at each step of the process just as they are needed

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SLIDE 8

Goals of JIT

  • Eliminate disruptions
  • Make the system flexible
  • Eliminate waste, especially excess

inventory

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SLIDE 9

Other aspects of JIT

  • Less worker specialization
  • Autonomation
  • Worker cooperation
  • Quality circles
  • Integrated production
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SLIDE 10

Benefit of Small Lot Size

  • Demand variation

Mode Old Monthly New Monthly Daily A 600 600 60 B 200 600 60 C 800 400 40 D 200 200 20 E 300 300 30 F 300 300 30 2,400 for half month .

Assume 400C changed to 400B at the middle of the month

  • Of the 24 units, we can sequence as follows

A A A A A A B B C C C C C C C C D D E E E F F F

  • r A C A E C F B C A C D A E F C B C A D C F E A C ?

Which is better?

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SLIDE 11

Environments Suited to JIT

  • JIT is only one mechanism of production control.

It should not be viewed as an all-purpose solution for all manufacturing systems. Characteristics of environments that are well suited to the JIT idea should include

– Discrete parts produced in highly repetitive manner – Fairly smooth demand pattern throughout the time horizon – Small product line diversity – Setup time/costs can be greatly reduced – High worker flexibility – Closeness with suppliers – High level of quality management

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SLIDE 12

Toyota Kanban System

  • The Kanban system is a manual realization of the JIT idea
  • Two Kanban systems are often used in practice:

1) One-card Kanban system (only production cards) is suitable for the situation where workstations are close 2) Two-card Kanban system (both production and move cards) is suitable when workstations are not close

  • The production of cards is authorized only with available

production cards. So is the movement of the parts in the two-card system

  • The number of parts associated with a workstation is limited

by the number of cards associated with that workstation

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SLIDE 13

One-Card Kanban System

Workstation Inventory buffer Card box Work- station

1: demand occurs ⇐

Part Production card

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SLIDE 14

One-Card Kanban System

Workstation Inventory buffer Card box Work- station Part Production card

2: one part meets demand, releasing production card ⇐

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SLIDE 15

One-Card Kanban System

Workstation Inventory buffer Card box Work- station Part Production card

3: production is authorized

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SLIDE 16

One-Card Kanban System

Workstation Inventory buffer Card box Work- station Part Production card

4: production is completed

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SLIDE 17

Two-Card Kanban System

Workstation Inventory buffer 2 Move-card box

1: demand occurs ⇐

Production-card box Production card Inventory buffer 1 Part Move card

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SLIDE 18

Two-Card Kanban System

Workstation Inventory buffer 2 Move-card box Production-card box Production card Inventory buffer 1 Part Move card

2: one part meets demand, releasing move card ⇐

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SLIDE 19

Two-Card Kanban System

Workstation Inventory buffer 2 Move-card box Production-card box Production card Inventory buffer 1 Part Move card

3: movement is authorized, releasing production card

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SLIDE 20

Two-Card Kanban System

Workstation Inventory buffer 2 Move-card box Production-card box Production card Inventory buffer 1 Part Move card

4: movement is completed

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SLIDE 21

Two-Card Kanban System

Workstation Inventory buffer 2 Move-card box Production-card box Production card Inventory buffer 1 Part Move card

5: production is authorized

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SLIDE 22

Two-Card Kanban System

Workstation Inventory buffer 2 Move-card box Production-card box Production card Inventory buffer 1 Part Move card

6: production is completed

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SLIDE 23

Kanban Formula

N = DT(1+X) C

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

C = Capacity of a standard container

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SLIDE 24

Example

Suppose the usage at a work center is 300 parts per day, and a standard container holds 25 parts. It takes an average of 0.12 day from the time a withdraw Kanban is issued until a full container is received. Compute the Kanban cards needed if the efficiency factor is X=0.2.

Solution:

D=300/day, T=0.12 day, C=25 parts per day, X=0.2

⇒ N= 300(0.12)(1+0.2) / 25 = 1.728 ≈ 2.

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SLIDE 25

MRP VS. JIT Production System

MRP

  • Developed first in US
  • Schedule-based
  • “Push” system
  • Often computer-based, may be

complicated

  • Typically with centralized control

JIT

  • Developed first in Japan
  • Authorization-constrained
  • “Pull” system
  • Does not need computers,

simple to understand

  • Often with decentralized

control

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SLIDE 26

Push & Pull Production Systems

1 2 3 1 2 3 Push sytem (MRP) Pull system (JIT) Schedule Demand ⇐ Demand ⇐ workstation Inventory material flow information flow

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SLIDE 27

Centralized & Decentralized Control

1 2 3 1 2 3 Cenralized control Decentralized control Central control

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SLIDE 28

Summary

  • JIT is another basic philosophy of production

control and is “pull” system

  • JIT is less complex than MRP, but it works well only

in certain environments

  • The Kanban system is a manual realization of the

JIT idea

  • There are significant differences between MRP and

JIT

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SLIDE 29

Review Problems

  • Page 709, Problems 1, 2, 3.