Dennis Bricker
Dept of Mechanical & Industrial Engineering
The University of Iowa
JIT --Intro
02/11/03
page 1 of 28
Pull/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 (e.g MRP)
JIT --Intro
02/11/03
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“Pull” system Production Control
Send more widgets
Send more widgets
Information Flow
Material Flow
Production
Step 2
Information Flow
Material Flow
Last Step of
Production
Here they come
Here they come
Production at Step “2” in controlled by step “3”
JIT --Intro
02/11/03
page 3 of 28
“Pull” system Production Control
Send more widgets
First Step of
Production
Information Flow
Material Flow
Here they come
Send more widgets
Production
Step 2
Information Flow
Material Flow
Here they come
Production at Step “1” in controlled by step “2”
JIT --Intro
02/11/03
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§ a simple implementation of fixed-orderquantity/re-order point policy
§ uses two bins for storage of an item.
§ bottom bin contains items equal to the reorder point, together with an order form for
the replenishment.
JIT --Intro
02/11/03
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§ when top bin becomes empty, worker removes it, sends the
order form for the replenishment, and begins withdrawing
from the bottom bin.
§ when replenishment arrives, the bottom bin is refilled and the
remainder placed in the top bin.
This is a “PULL” system.
JIT --Intro
02/11/03
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Kanban System
• Kanban is the Japanese word for card.
• Paperless production control system
• Authority to pull, or produce comes from a downstream
process.
• A physical (visual) control system
• Composed of cards (production card and withdrawal card)
and containers
• rd)
JIT --Intro
02/11/03
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Kanban Cards
§ the Kanban number (card ID)
§ the part number
§ the name & description of the part
§ the place where the card is used
§ the two work centers if a withdrawal card
§ a single work center if a production card
§ the number of units in the standard container
JIT --Intro
02/11/03
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Three Rules:
§ A standard container must always be filled with the prescribed
number of parts.
§ A container must not be moved forward until authorized by receiving
a withdrawal card.
§ A container of parts must not be produced until authorized by a
detached production card.
JIT --Intro
02/11/03
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JIT --Intro
02/11/03
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I
A
a
nb
ka
al
aw
dr
ith
W
With
dr
kanb awal
ans
Work
center
ns
O
outbound
stockpoint
O
Inbound
stockpoint
Withdrawal
kanbans
O
Inbound
stockpoint
Production
kanbans
B
Production
kanbans
I
Withdrawal
kanbans
Inbound
stockpoint
outbound
stockpoint
Work
center
I
Final Assembly
Example: Kanban Flow Paths
outbound
stockpoint
supplier
JIT --Intro
02/11/03
page 11 of 28
Sequence of Kanban Flows
1.Each container at an Inbound stockpoint has a withdrawal kanban
attached.
2.When this container is selected for use in production at workcenter A, the
worker detaches the withdrawal kanban and attaches it to an empty
container.
3.This empty container is then sent to the Outbound stockpoint of B.
4.The withdrawal kanban is detached from the empty container and placed
on a full container, leaving the empty container without a kanban.
5.The production kanban is removed from the full container and placed in a
collection box.
6.The full replacement container (with only a withdrawal kanban) is sent to
the Inbound stockpoint of A.
7.Regularly a worker at workcenter B collects the production kanbans from
the collection box, and for each card, parts are produced and put into an
empty container.
8.The filled container then has a production kanban attached to it and placed
in the Outbound stockpoint of B.
9.Whenever worker at workcenter B selects a container of raw materials from
its Inbound stockpoint, he attaches its withdrawal kanban to an empty
container and sends to supplier.
JIT --Intro
02/11/03
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Waste in Operations
♦ Waste
from overproduction
♦ Waste
of waiting time
♦ Transportation
♦ Inventory
waste
waste
♦ Processing
waste
♦ Waste
of motion
♦ Waste
from product defects
JIT --Intro
02/11/03
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Some Examples of Waste
l Watching a machine run
l Waiting for parts
l Counting parts
l Over-runs in production
l Moving parts over long distances
l Storing inventory
l Looking for tools
l Machine breakdown
l Rework
JIT --Intro
02/11/03
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Before JIT… (material flow)
Final
Assembly
Work Centers
Stockrooms
Supplier A
Supplier B
Initial Layout
JIT --Intro
02/11/03
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After JIT… (material flow)
Supplier A
Final
Assembly
Supplier B
JIT Layout
JIT --Intro
02/11/03
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Benefits of JIT Systems
1.
Reduced inventory
2.
Improved quality
3.
Lower costs
4.
Reduced space requirements
5.
Shorter lead time
6.
Increased productivity
7.
Greater flexibility
8.
Better relations with suppliers
9.
Simplified scheduling and control activities
10. Increased capacity
11. Better use of human resources
12. More product variety
JIT --Intro
02/11/03
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JIT Reduced Waste at Hewlett-Packard
Waste Reduction (%)
Setup
20%
Scra
30%
Finished Goods
Inventory
Spac
30%
40%
Lead
50%
Raw Material
Inventory
Work-in-Process
Inventory
0
JIT --Intro
50%
82%
20
40
60
02/11/03
80
100
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Basic Elements of JIT
l Pull (Kanban) production control system
l Small-lot production
l Quick setups
l Flexible resources
l Cellular layouts
l Uniform production
l Quality at the source
l Total productive maintenance
l Supplier networks
JIT --Intro
02/11/03
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Basic Elements of JIT
lPull (Kanban) production control system
Produce only what is needed - only when it is needed
lSmall-lot production
Faster through-put, greater flexibility
lQuick setups
Facilitates economical small-lot-size production
lFlexible resources
Facilitates cellular layouts, TPM, and Kaizen
lCellular layouts
Retain relevant flexibility of job shop, obtain efficiency of production line
lUniform production
Create and maintain a stable production system
lQuality at the source
Facilitates removal of “buffers” and contributes to stability of the “system”
lTotal productive maintenance
Contributes to stability of the “system”
lSupplier networks
Facilitates frequent, small quantity delivery of materials
JIT --Intro
02/11/03
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Inventory Hides Problems
Bad
Design
Poor
Quality
Lengthy
Setups
Inefficient
Layout
JIT --Intro
Machine
Breakdown
02/11/03
Unreliable
Supplier
page 21 of 28
To Expose Problems:
Reduce Inventory Levels
Bad
Design
Poor
Quality
Lengthy
Setups
Inefficient
Layout
JIT --Intro
Machine
Breakdown
02/11/03
Unreliable
Supplier
page 22 of 28
Remove Sources of Problems and Repeat the Process
Poor
Quality
Lengthy
Setups
Bad
Design
JIT --Intro
Machine
Breakdown
Inefficient
Layout
02/11/03
Unreliable
Supplier
page 23 of 28
Characteristics of JIT Vendor Partnerships
•
•
•
•
•
•
•
Few, nearby suppliers
Long-term contract agreements
Steady supply rate
Frequent deliveries in small lots
Buyer helps suppliers meet quality
Suppliers use process control charts
Buyer schedules inbound freight
JIT --Intro
02/11/03
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Supplier Networks: Goals of Just-in-Time Purchasing
q elimination of
unnecessary activities
q elimination of in-plant
inventory
q elimination of in-transit
inventory
q quality and reliability
improvement
JIT --Intro
02/11/03
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Supplier Networks: Trends In Supplier Policies
•
Locate near to the customer
•
Use small, side loaded trucks and ship mixed loads
•
Consider establishing small warehouses near to the customer
or consolidating warehouses with other suppliers
•
Use standardized containers and make deliveries according to
a precise delivery schedule
•
Become a certified supplier and accept payment at regular
intervals rather than upon delivery
JIT --Intro
02/11/03
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Potential Supplier Concerns with Just-in-Time Purchasing
l Desire for diversification. Supplier is concerned about all business
stemming from single customer.
l Poor customer scheduling. Supplier is concerned that customer will not
be able to develop smooth, consistent schedule.
l Engineering changes. Supplier is concerned that customer will
promulgate frequent engineering changes with inadequate lead time.
l Quality assurance. Supplier may consider production with zero defects
unrealistic.
l Small lot sizes. Many suppliers are unaccustomed to working with small
lot sizes.
l Proximity. Delivery of small lot sizes over long distances may not be
economical.
JIT --Intro
02/11/03
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Respect for People
• Level payrolls
• Cooperative employee unions
• Subcontractor networks
• Bottom-round management style
• Quality circles
JIT --Intro
02/11/03
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