Module 8B Lean Systems

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8
Lean Systems
For Operations Management, 9e by
Krajewski/Ritzman/Malhotra
© 2010 Pearson Education
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall.
8–1
Lean Systems
 Lean systems affect a firm’s internal linkages
between its core and supporting processes and its
external linkages with its customers and suppliers.
 One of the most popular systems that incorporate
the generic elements of lean systems is the just-intime (JIT) system.
 The Japanese term for this approach is Kaizen.
The key to kaizen is the understanding that excess
capacity or inventory hides process problems.
 The goal is to eliminate the eight types of waste.
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall.
8–2
Eight Wastes
TABLE 8.1
|
THE EIGHT TYPES OF WASTE OR MUDA
Waste
Definition
1. Overproduction
Manufacturing an item before it is needed.
2. Inappropriate
Processing
Using expensive high precision equipment when simpler
machines would suffice.
3. Waiting
Wasteful time incurred when product is not being moved or
processed.
4. Transportation
Excessive movement and material handling of product between
processes.
5. Motion
Unnecessary effort related to the ergonomics of bending,
stretching, reaching, lifting, and walking.
1. Inventory
Excess inventory hides problems on the shop floor, consumes
space, increases lead times, and inhibits communication.
1. Defects
Quality defects result in rework and scrap, and add wasteful
costs to the system in the form of lost capacity, rescheduling
effort, increased inspection, and loss of customer good will.
1. Underutilization of
Employees
Failure of the firm to learn from and capitalize on its employees’
knowledge and creativity impedes long term efforts to eliminate
waste.
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8–3
Continuous Improvement
Figure 8.1 – Continuous Improvement with Lean Systems
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8–4
Supply Chain Considerations
 Close supplier ties

Low levels of capacity slack or inventory

Look for ways to improve efficiency and reduce
inventories throughout the supply chain

JIT II

In-plant representative

Benefits to both buyers and suppliers
 Small lot sizes

Reduces the average level of inventory

Pass through system faster

Uniform workload and prevents overproduction

Increases setup frequency
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall.
8–5
Process Considerations
 Pull method of work flow


Push method
Pull method
 Quality at the source



Jidoka
Poka-yoke
Anadon
 Uniform workstation loads




Takt time
Heijunka
Mixed-model assembly
Lot size of one
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall.
8–6
Process Considerations
 Standardized components and work
methods
 Flexible workforce
 Automation
 Five S (5S) practices
 Total Preventive Maintenance (TPM)
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8–7
Five S Method
TABLE 8.2
|
5S DEFINED
5S Term
5S Defined
1. Sort
Separate needed from unneeded items (including tools, parts,
materials, and paperwork), and discard the unneeded.
2. Straighten
Neatly arrange what is left, with a place for everything and everything
in its place. Organize the work area so that it is easy to find what is
needed.
3. Shine
Clean and wash the work area and make it shine.
4. Standardize
Establish schedules and methods of performing the cleaning and
sorting. Formalize the cleanliness that results from regularly doing
the first three S practices so that perpetual cleanliness and a state of
readiness are maintained.
5. Sustain
Create discipline to perform the first four S practices, whereby
everyone understands, obeys, and practices the rules when in the
plant. Implement mechanisms to sustain the gains by involving
people and recognizing them via a performance measurement system.
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall.
8–8
Designing Lean System Layouts
 Line flows recommended
 Eliminate
waste
 One worker, multiple machines (OWMM)
 Group technology
 Group
parts or products with similar
characteristics into families
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8–9
Group Technology
Figure 8.2 – One-Worker, Multiple-Machines (OWMM) Cell
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall.
8 – 10
Group Technology
Figure 8.3 – Process Flows Before and After the Use of GT Cells
Lathing
L
L
Milling
L
L
M
Drilling
M
M
D
D
D
D
M
Grinding
L
L
L
L
M
Receiving and
shipping
M
Assembly
A
A
A
A
G
G
G
G
G
G
(a) Jumbled flows in a job shop without GT cells
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8 – 11
Group Technology
Figure 8.3 – Process Flows Before and After the Use of GT Cells
L
L
M
L
G
M
Assembly
area
A
Cell 2
Cell 1
Receiving
D
G
A
G
Cell 3
L
M
D
Shipping
(b) Line flows in a job shop with three GT cells
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8 – 12
The Kanban System
Receiving post
Kanban card for
product 1
Kanban card for
product 2
Storage
area
Empty containers
Assembly line 1
O2
Fabrication
cell
O3
O1
Assembly line 2
Full containers
O2
Figure 8.4 – Single-Card Kanban System
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8 – 13
The Kanban System
Receiving post
Kanban card for
product 1
Kanban card for
product 2
Storage
area
Empty containers
Assembly line 1
O2
Fabrication
cell
O3
O1
Assembly line 2
Full containers
O2
Figure 8.4 – Single-Card Kanban System
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8 – 14
The Kanban System
Receiving post
Kanban card for
product 1
Kanban card for
product 2
Storage
area
Empty containers
Assembly line 1
O2
Fabrication
cell
O3
O1
Assembly line 2
Full containers
O2
Figure 8.4 – Single-Card Kanban System
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall.
8 – 15
The Kanban System
Receiving post
Kanban card for
product 1
Kanban card for
product 2
Storage
area
Empty containers
Assembly line 1
O2
Fabrication
cell
O3
O1
Assembly line 2
Full containers
O2
Figure 8.4 – Single-Card Kanban System
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall.
8 – 16
The Kanban System
Receiving post
Kanban card for
product 1
Kanban card for
product 2
Storage
area
Empty containers
Assembly line 1
O2
Fabrication
cell
O3
O1
Assembly line 2
Full containers
O2
Figure 8.4 – Single-Card Kanban System
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8 – 17
The Kanban System
Receiving post
Kanban card for
product 1
Kanban card for
product 2
Storage
area
Empty containers
Assembly line 1
O2
Fabrication
cell
O3
O1
Assembly line 2
Full containers
O2
Figure 8.4 – Single-Card Kanban System
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall.
8 – 18
The Kanban System
Receiving post
Kanban card for
product 1
Kanban card for
product 2
Storage
area
Empty containers
Assembly line 1
O2
Fabrication
cell
O3
O1
Assembly line 2
Full containers
O2
Figure 8.4 – Single-Card Kanban System
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8 – 19
The Kanban System
2. Assembly always withdraws from
fabrication (pull system)
KANBAN
Part Number:
Location:
Lot Quantity:
Supplier:
Customer:
1. Each container must have a card
3. Containers cannot be moved without a
kanban
1234567Z
Aisle 5
Bin 47
6
WS 83
WS 116
4. Containers should contain the same
number of parts
5. Only good parts are passed along
6. Production should not exceed
authorization
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8 – 20
Number of Containers
 Two determinations
 Number of units to be held by each container

Determines lot size
 Number of containers

Estimate the average lead time needed to produce a
container of parts
 Little’s law

Average work-in-process inventory equals the average
demand rate multiplied by the average time a unit spends
in the manufacturing process
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall.
8 – 21
Number of Containers
WIP = (average demand rate)
 (average time a container spends in the manufacturing process)
+ safety stock
WIP = kc
kc = d (w + p )(1 + α)
d (w + p )(1 + α)
k=
c
where
k=
d=
w=
p=
c=
α=
number of containers
expected daily demand for the part
average waiting time
average processing time
number of units in each container
policy variable
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8 – 22
Number of Containers
 Formula for the number of containers
Average demand during lead time + Safety stock
k=
Number of units per container
WIP = (average demand rate)(average time a container
spends in the manufacturing process) + safety stock
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8 – 23
Determining the Appropriate
Number of Containers
EXAMPLE 8.1
 The Westerville Auto Parts Company produces rocker-arm
assemblies
 A container of parts spends 0.02 day in processing and 0.08
day in materials handling and waiting
 Daily demand for the part is 2,000 units
 Safety stock equivalent of 10 percent of inventory
a. If each container contains 22 parts, how many containers
should be authorized?
b. Suppose that a proposal to revise the plant layout would
cut materials handling and waiting time per container to
0.06 day. How many containers would be needed?
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall.
8 – 24
Determining the Appropriate
Number of Containers
SOLUTION
a. If
d=
p=
α=
w=
c=
2,000 units/day,
0.02 day,
0.10,
0.08 day, and
22 units
b. Figure 8.5 from OM
Explorer shows that
the number of
containers drops to 8.
2,000(0.08 + 0.02)(1.10)
k=
22
220
=
= 10 containers
22
Figure 8.5 – OM Explorer Solver for
Number of Containers
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8 – 25
Other Kanban Signals
 Cards are not the only way to signal need
 Container system
 Containerless system
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8 – 26
Value Stream Mapping (VSM)
 Value stream mapping
is a qualitative lean
tool for eliminating
waste
 Creates a visual “map”
of every process
involved in the flow of
materials and
information in a
product’s value chain
Product
family
Current state
drawing
Future state
drawing
Work plan and
implementation
Figure 8.6 – Value Stream Mapping Steps
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8 – 27
Value Stream Mapping
Figure 8.7 – Selected Set of Value Stream Mapping Icons
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8 – 28
Value Stream Mapping
Figure 8.8 – A Representative Current State Map for a Family of
Retainers at a Bearings Manufacturing Company
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8 – 29
House of Toyota
 A key challenge is to bring underlying
philosophy of lean to employees in an
easy-to-understand fashion
 The house conveys stability
 The roof represents the primary goals of
high quality, low cost, waste elimination,
and short lead-times
 The twin pillars, which supports the roof,
represents JIT and jidoka
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8 – 30
House of Toyota
Highest quality, lowest cost,
shortest lead time by eliminating
wasted time and activity
Just in Time (JIT)
Culture of
Continuous
Improvement
 Takt time
 One-piece flow
Jidoka
 Manual or automatic
line stop
 Separate operator and
machine activities
 Pull system
 Error-proofing
 Visual control
Operational Stability
Heijunka
Standard Work
TPM
Supply Chain
Figure 8.9 – House of Toyota
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8 – 31
Operational Benefits and
Implementation Issues
 Organizational considerations
 Human
costs of lean systems
 Cooperation
 Reward
and trust
systems and labor classifications
 Process considerations
 Inventory and scheduling
 Schedule
stability
 Setups
 Purchasing
and logistics
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8 – 32
Solved Problem
A company using a kanban system has an inefficient machine
group. For example, the daily demand for part L105A is 3,000
units. The average waiting time for a container of parts is 0.8
day. The processing time for a container of L105A is 0.2 day,
and a container holds 270 units. Currently, 20 containers are
used for this item.
a. What is the value of the policy variable, α?
b. What is the total planned inventory (work-in-process and
finished goods) for item L105A?
c. Suppose that the policy variable, α, was 0. How many
containers would be needed now? What is the effect of the
policy variable in this example?
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8 – 33
Solved Problem
SOLUTION
a. We use the equation for the number of containers and then
solve for α:
d (w + p )(1 + α)
k=
c
3,000(0.8 + 0.2)(1 + α)
=
270
so
20(27)
(1 + α) =
= 1.8
3,000(0.8 + 0.2)
α = 1.8 – 1 = 0.8
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8 – 34
Solved Problem
b. With 20 containers in the system and each container holding
270 units, the total planned inventory is 20(270) = 5,400 units
c. If α = 0
3,000(0.8 + 0.2)(1 + 0)
k=
270
= 11.11, or 12 containers
The policy variable adjusts the number of containers. In this
case, the difference is quite dramatic because w + p is fairly
large and the number of units per container is small relative to
daily demand.
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8 – 35
Application 8.1
Item B52R has an average daily demand of 1000 units. The
average waiting time per container of parts (which holds 100
units) is 0.5 day. The processing time per container is 0.1 day. If
the policy variable is set at 10 percent, how many containers
are required?
d (w + p )(1 + α)
k=
c
1,000(0.05 + 0.01)(1 + 0.1)
=
100
= 6.6, or 7 containers
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8 – 36
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall.
8 – 37
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