Just-In-Time Philosophy
The philosophy of JIT can be traced back to Henry Ford,
but formalized JIT originated in Japan as the Toyota
Production System. W. Edwards Deming’s lesson of
variability reduction was a huge influence.
JIT is a long-term approach to process improvement. It uses
timeliness as a lever to lower costs, improve quality and improve
responsiveness. However, JIT requires enormous commitment. It
took Toyota more than 25 years to get right!
The focus of JIT is to improve the
system of production by eliminating
all forms of WASTE.
Just-in-Time
• Downstream processes take parts from
upstream as they need.
– Get what you want
– when you want it
– in the quantity you want.
4. Just In Time-- What is It?
• Just-in-Time: produce the right parts, at the
right time, in the right quantity
– Requires repetitive, not big volume
– Batch size of one
– Short transit times, keep 0.1 days of supply
Characteristics of Just-in-Time
 Pull method of materials flow
 Consistently high quality
 Small lot sizes
 Uniform workstation loads
 Standardized components and work methods
 Close supplier ties
 Flexible workforce
 Line flows
 Automated production
 Preventive maintenance
Push versus Pull
• Push system: material is pushed into
downstream workstations regardless of
whether resources are available
• Pull system: material is pulled to a workstation
just as it is needed
From a a « push » to a « pull »
System
Work is pushed to the next station as it is
completed
S
U
P
P
L
I
E
R
S
C
U
S
T
O
M
E
R
S
From a a « push » to a « pull »
System
A workstation pulls output as needed
S
U
P
P
L
I
E
R
S
C
U
S
T
O
M
E
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S
Here the customer starts the
process, pulling an inventory item
from Final Assembly…
JIT Demand-Pull Logic
Then sub-assembly work
is pulled forward by that
demand…
Fab
Vendor
Fab
Vendor
Fab
Vendor
Fab
Vendor
Sub
Customers
Final
Assembly
The process continues throughout
the entire production process and
supply chain
Sub
Pull Versus Push Systems
 A pull system uses signals to request
production and delivery from upstream
stations
 Upstream stations only produce when
signaled
 System is used within the immediate
production process and with suppliers
Pull Versus Push Systems
 By pulling material in small lots, inventory
cushions are removed, exposing problems
and emphasizing continual improvement
 Manufacturing cycle time is reduced
 Push systems dump orders on the
downstream stations regardless of the
need
Waste in Operations
1. Waste from overproduction
2. Waste of waiting time
3. Transportation waste
4. Inventory waste
5. Processing waste
6. Waste of motion
7. Waste from product defects
8. Underutilization of people
Streamlined Production
Traditional Flow
Production Process
(stream of water)
Suppliers
Flow with JIT
Suppliers
Customers
Inventory (stagnant
ponds)
Material
(water in
stream)
Customers
Lowering Inventory Reduces Waste
WIP hides problems
Lowering Inventory Reduces Waste
WIP hides problems
Lowering Inventory Reduces Waste
Reducing WIP makes
problem very visible
STOP
Lowering Inventory Reduces Waste
Reduce WIP again to find
new problems
Reduce Variability
Inventory level
Process
downtime
Scrap
Setup
time
Quality
problems
Late deliveries
Reduce Variability
Inventory
level
Process
downtime
Scrap
Setup
time
Quality
problems
Late deliveries
Causes of Variability
1. Employees, machines, and suppliers produce
units that do not conform to standards, are
late, or are not the proper quantity
2. Engineering drawings or specifications are
inaccurate
3. Production personnel try to produce before
drawings or specifications are complete
4. Customer demands are unknown
Variability Reduction
 JIT systems require managers to reduce
variability caused by both internal and
external factors
 Variability is any deviation from the
optimum process
 Inventory hides variability
 Less variability results in less waste
Performance and WIP Level
• Less WIP means products go through system faster
• reducing the WIP makes you more sensitive to
problems, helps you find problems faster
• Stream and Rocks analogy:
– Inventory (WIP) is like water in a stream
– It hides the rocks
– Rocks force you to keep a lot of water (WIP) in the stream
Reduce Lot Sizes
Inventory
200 –
Q1 When average order size = 200
average inventory is 100
Q2 When average order size = 100
average inventory is 50
100 –
Time
Reducing Lot Sizes Increases the
Number of Lots
Customer
orders 10
Lot size = 5
Lot 2
Lot 1
Lot size = 2
Lot 1 Lot 2 Lot 3 Lot 4 Lot 5
Reduce Lot Sizes
 Ideal situation is to have lot sizes of one
pulled from one process to the next
 Often not feasible
 Can use EOQ analysis to calculate
desired setup time
 Two key changes
 Improve material handling
 Reduce setup time
Reduce Setup Times
Initial Setup Time
Step 1
90 min —
Separate setup into preparation and actual setup, doing
as much as possible while the machine/process is
operating
(save 30 minutes)
Move material closer and
improve material handling (save
20 minutes)
Step 2
Standardize and
improve tooling (save
15 minutes)
Step 3
Step 4
Step 5
Use one-touch system to eliminate
adjustments (save 10 minutes)
Training operators and standardizing work
procedures (save 2 minutes)
Repeat cycle until subminute
setup is achieved
60 min —
45 min —
25 min —
15 min —
13 min —
—
Kanban
• Japanese for ‘signboard’
• Method for implementing JIT
• In order to produce, you need both material
to work on, and an available kanban.
• Each work station has a fixed # kanbans.
Kanban
Flow of work
2
3
• Worker 2 finishes a part, outbound moves over
• 2 has a blue tag avaliable, so 2 gets another part to
work on:
– 2 takes off 1’s green tag giving it back to 1, and
– puts on her blue tag and moves it into position.
Kanban
Flow of work
2
3
• When 3 finishes a part,
– Finished parts move over one spot
– He has to have a red tag available to put on,
– He gets a part from 2’s outbound pile,
– And gives the blue back to 2
Kanban
Flow of work
2
3
• When 3 finishes a part,
–
–
–
–
Finished parts move over one spot
He has to have a red tag available to put on,
He gets a part from 2’s outbound pile,
And gives the blue back to 2
• 3’s production will be taken by 4, offstage right.
– Tag goes back into 3’s bin
Kanban
2
3
• Red finishes his part next.
2
3
• But 4 hasn’t freed up any of the red kanbans, so there is
nothing for 3 to work on now.
• 3 could maintain his machine, or see if 4 needs help
The Number of Cards
or Containers


Need to know the lead time needed to produce a container of parts
Need to know the amount of safety stock needed
Number of kanbans =
Demand during
Safety
lead time
+ stock
Size of container
Number of Kanbans Example
Daily demand
Production lead time
(wait time +
material handling time +
processing time)
Safety stock
Container size
= 500 cakes
= 2 days
= 1/2 day
= 250 cakes
Demand during lead time = 2 days x 500 cakes = 1,000
Number of kanbans = 1,000 + 250 = 5
250
Example
•
•
•
•
A switch is assembled in batches of 4 units at an
“upstream” work area.
delivered in a bin to a “downstream” control-panel
assembly area that requires 5 switch
assemblies/hour.
The switch assembly area can produce a bin of
switch assemblies in 2 hours.
Safety stock = 10% of needed inventory.
k=
=
Expected demand during lead time + safety stock
size of container
dL (1+S)
C
5(2)(1.1)
=
= 2.75 or 3
4
Scheduling Small Lots
JIT Level Material-Use Approach
A A
B
B
A A A A A A
B
B
C
A A
B
B
B
C
B
C C C
Large-Lot Approach
B
B
B
Time
B
B
B
B
Minimizing Waste:
Uniform Plant Loading
Suppose we operate a production plant that produces a single product.
The schedule of production for this product could be accomplished using
either of the two plant loading schedules below.
Not uniform
Jan. Units
Feb. Units
Mar. Units
Total
1,200
3,500
4,300
9,000
or
Uniform
Jan. Units
Feb. Units
Mar. Units
Total
3,000
3,000
3,000
9,000
How does the uniform loading help save labor costs?
Mixed Batch Example
• Company produces
three products with a
mixed model assembly
line.
– Operates 16 hours per
day for 250 days/yr.
– Determine the mixed
model MPS for a daily
batch.
– Determine minimum
batch MPS and the mix
schedule for a day.
Products
Forecasts
(year)
1
20,000
2
10,000
3
5,000
Calculations
Year Forecast
#1
#2
#3
20000
10000
5000
Daily Batch
divide by 250
80
40
20
Hourly Batch
divide by 16
5
2.5
1.25
4
2
1
Minimum Batch
MPS
For every unit of #3 (minimum batch), we need twice as many #2 and 4 times
As many #1 so for minimum batch:
Produce during each day produce #1,1,1,1,2,2,3 - repeated 20 times
Characteristics of JIT Partnershps
•
•
•
•
•
•
•
•
Few, nearby suppliers
Supplier just like in-house upstream process
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
Cellular Layout
• Promote flow with little WIP
• Facilitate workers staffing multiple machines
• U-shaped cells
• Maximum visibility
• Minimum walking
• Flexible in number of workers
• Facilitates monitoring of work entering and leaving cell
• Workers can conveniently cooperate to smooth flow and
address problems
Inbound Stock
Outbound Stock
Group Technology
An engineering and manufacturing philosophy that identifies
physical similarities of parts and establishes their effective
production.
Assignment of individual products to
product families
Cellular Manufacturing
Assignment of product families to
manufacturing cells
Group Technology (Part 1)
Note how the flow lines are going back and forth
• Using Departmental Specialization for plant layout can cause a lot of
unnecessary material movement
Saw
Saw
Saw
Grinder
Grinder
Heat Treat
Lathe
Lathe
Lathe
Press
Press
Press
Group Technology (Part 2)
• Revising by using Group Technology Cells can reduce movement and improve
product flow
Grinder
Saw
1
2
Lathe
Lathe
Press
Lathe
Press
Heat Treat
Grinder
Saw
Lathe
A
B
Group Technology (con’d)
• A set of machines dedicated to processing one or more family
• Arrange machines in a narrow U
• Workers rotate among several machines
Group Technology (con’d)
Advantages
 Reduce cycle time
Move time
Queue time
Set up time
 Adjust the output rate by increasing or decreasing the
number of workers in a cell
 Facilitate job training
 Promote job satisfaction
Typical Benefits of JIT
• Cost savings: inventory reductions, reduced scrap, fewer
defects, fewer changes due to both customers and
engineering, less space, decreased labor hours, less rework.
• Revenue increases: better service and quality to the customer.
• Investment savings: less space, reduced inventory, increased
the volume of work produced in the same facility.
• Workforce improvements: more satisfied, better trained
employees.
• Uncovering problems: greater visibility to problems that JIT
allows, if management is willing to capitalize on the
opportunity to fix these problems.