MS 401
Production and Service Systems Operations
Spring 2009-2010
Just-in-Time (JIT) Manufacturing
Slide Set #14
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What is Just-In-Time (JIT) ?
“The more a company has, … the less likely they will have what
they need”
Taiichi Ohno
• JIT is both a philosophy and a set of techniques
• An integrated system related to different aspects of operations
including manufacturing, scheduling, quality, product design,
supplier relations, human resources and innovation
• Related concepts
– Toyota Production System (TPS)
– Lean manufacturing
• Recommended book: “The Toyota Way” by Jeffrey Liker
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What is Just-In-Time (JIT) ?
• History: Japanese companies’ desire to catch-up with their
US competitors after WW II, with limited resources
Main concepts
• Production must flexibly adopt to
• Required items must be produced in required quantities in
required time
• Waste should be identified and eliminated. Waste includes
–
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Why Reduce Inventory?
Quality
issues
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Unreliable
suppliers
Capacity
imbalance
4
JIT Methods Summary-1
• Synchronizing product flow with demand
– pull system (kanban)
– synchronized production with suppliers
–
–
• Line balancing to reduce waste (Muda)
– cross-trained workers
–
–
Source: Cachon and Terwiesch 2006
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JIT Methods Summary-2
• Quality methods to reduce defects
–
–
– build in quality (tsukurikomi)
• at every step rather than relying on inspection steps
– worker involvement/ improvement (kaizen)
• quality circles
• structured problem solving (SPC, fish-bone diagrams etc.)
• Human resource practices
– lifetime employment
– skill-development
– empowerment
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Source: Cachon and Terwiesch 2006
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JIT Building Blocks
• Product design
• Process design
• Human / organizational elements
• Manufacturing planning and control
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Product Design
• Standard parts
• Modular design
• Quality
• Fewer bill of material (BOM) levels
• Manufacturability in production cells
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Process Design
• Small lot sizes / setup time reduction
– SMED:
• Manufacturing cells
• Limited work in process inventory
• Quality improvement
• Production flexibility
• Production bandwidth
– sufficient surge capacity
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Process Design: SMED
• Single Minute Exchange of Dies (SMED)
–
–
• Smaller lot sizes
– lower inventory
–
• The methods
– convert
as much as possible
• for example: pre-heat dyes
– eliminate the needs for adjustment
• for example, dies constructed to can fit only in the correct position
– standardize the external setup routine
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Process Design: U-type Manufacturing Cells
Inbound Stock
Outbound Stock
• Concentrate on material velocity
• smooth and fast flow from one machine to the next
• the aim is to make detailed tracking unnecessary
• Operator can monitor the cell without too much walking
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Human / Organizational Elements
• Workers as assets
• Whole person
– hiring “people”, not their “muscles”
• Cross-trained workers
– wider job definitions
• Flexible labor
• Continuous learning and improvement
• Accounting and performance measurement
• Leadership and project management
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Manufacturing Planning and Control
• Level loading
–
• Pull systems
• Visual systems
– kanban
• Close supplier relationships
– continuous delivery (supplier factories located nearby)
– tiered supplier network
• Reduced transaction processing
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MPC: Mixed Model Production
Model
Required Daily
Volume
A
100
B
200
C
400
TOTAL
700
Required Cycle
Time (minutes)
• Toyota: Operations are adjusted on a monthly basis such that the same
sequence of cars will be produced every day
–
–
•
A common part needs to be produced with a
•
A part used only in Model-A needs to be produced with
• Determine the number of workers and machines to achieve the required
cycle times in part production
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Source: Just in time production controlled by Kanban”, HBS
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Tiered Supplier Network
The Firm
First Tier Supplier
Supplier
Supplier
Second Tier Suppliers
Third Tier Suppliers
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Supplier
Supplier
Supplier
Supplier
Supplier
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Summary: JIT Goals and Building Blocks
Ultimate
Goal
Supporting
Goals
A
balanced
and rapid flow
Reduce setup and lead times
Eliminate disruptions
Make the system flexible
Building
Blocks
Product
Design
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Process
Design
Eliminate waste
Minimize inventories
Human
Factors
MPC
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Push vs. Pull Production Systems
• Push system: A workcenter pushes its part output to the
downstream workcenter as they are completed, according to
a production plan
–
–
• Pull system: When a workcenter needs parts for production,
it pulls them from its upstream workcenter
–
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Kanban Systems
• Kanban is the Japanese word for card
• Once a “balanced” production system is established, kanbans
are used to transmit information on
– when to transfer parts to the downstream workcenter
– when to produce a (small) lot of parts to replace the transferred parts
• Kanban does not have to be a card (can be any visual signal)
• A manual and visual production control system
– not production planning
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Two-card Kanban System
•
•
Each container must have a card
A container cannot be moved forward until authorized by
the receipt of a move card
•
A container of parts cannot be produced until authorized by
a production card
•
•
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Two-card Kanban System
6) Request of WC-2
is sent from stock,
production card is
detached
4) WC-2
production uses
raw materials from
stock, move card is
detached
WC-1
2) Request of WC-3
is sent from stock,
production card is
detached
WC-2
5) Detached move
card sent to WC-1
with an empty
container
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3) Detached
production card
authorizes
production at WC-2
1) Request of WC-3
arrives as a move
card with an empty
container
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How Many Kanban Card Sets?
• The trade-off:
– more kanbans mean
– fewer kanbans mean
• Number of kanbans can be decreased over time to
–
–
• The number of kanbans limit the “demand fluctuation” that one
workcenter can place on its upstream workcenter
–
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Heijunka Box with Kanbans
Time intervals
(such as 30 minutes)
Used to achieve
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Source: http://en.wikipedia.org/wiki/File:Heijunka_2.JPG
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Shortcomings of MRP
•
– costly to set up
– difficult to train workers
•
– realized lead time depends on the congestion in the system
– to be on the safe side, MRP considers a large leadtime
• causing the orders to be released too early, leading to high inventory
•
•
– the shop floor can be more flexible than MRP
– MRP promises more precision than it can provide
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Shortcomings of JIT
• Requires
– not applicable to job-shop or continuous production
• Practical issues
– setup times might be difficult to reduce
– suppliers may not be located close by
– moving products in small batches may not be possible
•
• Vulnerable to risks due to low inventory
– shutdowns, demand surges etc.
• Hybrid approach: MRP for planning, JIT for scheduling
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MPC and JIT
“production control”
rather than “production
planning”
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An Alternative: Optimized Production
Technology (OPT)
• Neither MRP nor JIT would be effective in the presence of
significant “bottlenecks”
• For such environments, Optimized Production Technology
(OPT) approach is applicable
–
–
• Popularized by the book “The Goal” by E. Goldratt
• The Theory of Constraints (TOC) philosophy
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