Chapter 7
Just-In-Time and Lean
Systems
Just-In-Time (JIT)
• Getting the right goods to the right place
at the right time.
• In an ideal JIT system, inventory = ??
• JIT is a goal and a philosophy.
Lean System:
A Broad View of JIT
• Extending JIT philosophy to the entire
organization, it is the Lean System.
• In a lean system, everything is “right”,
therefore no waste existing.
What are “Wastes”?
• Waste is anything that doesn’t add value:
time, money, resource, material, space,
energy, labor activity, …
• What may cause wastes?
– Inventory
– Unsynchronized production
– Unstreamlined layouts
– Unnecessary material handling
– Scrap & rework
–…
Central Beliefs of Philosophy of
JIT / Lean System
•
•
•
•
•
•
Elimination of waste
Broad view of operations
Simplicity
Continuous improvement
Visibility
Flexibility
Eliminate Waste
• Anything in an operation that does not add
value is waste.
• Method A and method B can both get a task
done. If A can do it better, or faster, or in a
cheaper way, then there exist wastes in
method B.
Everyone Has a Broad View of
Organization
• Instead of focusing on the assigned jobs
only, a worker has a broad view of the
organization: its mission and goals, and
place his job in that big picture.
Simplicity
• If a problem can be solved in a simple
way, do not go complicate.
Continuous Improvement
• Good enough is not good enough.
• “Kaizen blitz” is a Japanese way of
implementing continuous improvement
idea. It is a few day’s intensive work of a
cross-functional team aiming at resolving
a bite-size chunk of a problem.
Visibility
• Visibility is to make waste visible.
• Waste can only be eliminated after it’s
discovered.
• Clutter and inventory hide waste.
• JIT requires clean facilities and open
space so that no waste can be hidden.
Flexibility
• Flexible so as to adapt to changes in the
demand and environment.
– Volume flexibility
– Variety flexibility
Three Elements that Make JIT
Work
• Just-in-time manufacturing
• Total quality management
• Respect for people
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JIT Manufacturing
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•
•
•
•
Kanbans & pull production systems
Quick setups & small lots
Uniform plant loading
Flexible resources
Efficient facility layouts
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Pull Production
• Process is driven by real demands
(rather than demand forecasts).
• Doing nothing unless a real demand
calls (demand pull).
• All work stations are “demand pull”.
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Kanban Production System
• A “pull production” system.
• Real demand information is passed in relay
backward from the last work station by using
‘kanbans (cards)’.
• Each work station works according to the
kanbans passed from the next station.
• Each work station is responsible to pass
proper kanbans to the previous station.
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Illustration of Kanban in Textbook
© Wiley 2010
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Number of Kanbans in a Withdraw Work
Station
DT  S
N
C
N = number of containers in a withdraw station
D = demand rate at the withdraw station
T = lead time from supply station
C = container size
S = safety stock to protect against uncertainty
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Quick Setups & Small Lots
• Setup times = time required to get the
machine ready
– cleaning, calibrating, changing tools, ...
• Internal setups
– The machine must stop when doing setup.
• External setups
– Setup can be performed when machine is
running.
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Uniform Plant Loading
• “Leveling” of the production
schedule so that the production of a
product is evenly spread over the
planning horizon in small batches.
• Leveling the schedule can have big
impact along whole supply chain.
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An Example of
Uniform Plant Loading
Weekly Production Required
A
B
C
D
E
Traditional Production Plan
Monday
Tuesday
AAAAA
BBBBB
AAAAA
BBBBB
JIT Plan with Level Scheduling
Monday
Tuesday
AABBBB
AABBBB
CDEE
CDEE
10 units
20 units
5 units
5 units
10 units
Wednesday
BBBBB
BBBBB
Thursday
DDDDD
CCCCC
Friday
EEEEE
EEEEE
Wednesday
AABBBB
CDEE
Thursday
AABBBB
CDEE
Friday
AABBBB
CDEE
© Wiley 2010
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Flexible Resources
• General purpose equipment:
– E.g.: drills, lathes, printer-fax-copiers, etc.
– Capable of being setup to do many different
things
• Multifunctional workers:
– Cross-trained to perform several different
duties
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Efficient Facility Layouts
• Workstations in close physical
proximity to reduce transport &
movement
• Streamlined flow of material
• Often uses:
– Cellular Manufacturing (instead of job shops)
– U-shaped lines: (allows material handler to
quickly drop off materials & pick up finished
work)
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Cellular Manufacturing
(Group Technology)
• Components are grouped according to their
similarities.
• Machines are grouped in cells so that a cell
can complete the processing of some groups
of components
• Similar components are processed completely
in a cell composed of dissimilar machines.
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Job Shop Layout
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Cellular Manufacturing
(Group Technology)
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TQM & JIT
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•
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Quality at the Source
Jidoka (authority to stop line)
Poka-yoke (foolproof the process)
Preventive maintenance
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Respect for People:
The Role of Workers
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•
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Cross-trained workers
Actively engaged in problem-solving
Workers are empowered
Everyone responsible for quality
Workers gather performance data
Team approaches used for problem-solving
Decision made bottom-up
Workers responsible for preventive
maintenance
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Respect for People:
The Role of Management
• Responsible for culture of mutual trust
• Serve as coaches & facilitators
• Support culture with appropriate
incentive system
• Responsible for developing workers
• Provide multi-functional training
• Facilitate teamwork
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Supplier Relations & JIT
•
•
•
•
•
Use single-source suppliers
Build long-term relationships
Co-locate facilities to reduce transport
Stable delivery schedules
Share cost & other information
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Benefits of JIT
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•
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Smaller inventories
Improved quality
Reduced space requirements
Shorter lead times
Lower production costs
Increased productivity
Increased machine utilization
Greater flexibility
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Implementing JIT Manufacturing
• Identify & fix problems
• Reorganize workplace
– Remove clutter & designate storage
• Reduce setup times
• Reduce lot sizes & lead times
• Implement layout changes
– Cellular manufacturing & close proximity
• Switch to pull production
• Extend methods to suppliers
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Implementing JIT Is a Process of
Continuous Improvement
© Wiley 2010
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JIT in Services
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•
•
•
•
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Multifunctional workers
Reduce cycle times
Minimize setups
Parallel processing
Good housekeeping
Simple, highly-visible flow of work
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