Operations management, 9e by krajewski itzman malhotra chapter 08

8

Lean Systems

PowerPoint Slides
by Jeff Heyl

For Operations Management, 9e by
Krajewski/Ritzman/Malhotra
© 2010 Pearson Education
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 justin-time (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.

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.

8–3


Continuous Improvement

Figure 8.1 – Continuous Improvement with Lean Systems
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
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
8–6


Process Considerations
Standardized components and work
methods
Flexible workforce
Automation
Five S (5S) practices
Total Preventive Maintenance (TPM)

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.

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

8–9


Group Technology

Figure 8.2 – One-Worker, Multiple-Machines (OWMM) Cell
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

Receiving and
shipping

M

M

Assembly
A

A

A

A

G

G

G

G

G

G

(a) Jumbled flows in a job shop without GT cells
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

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

O1

Fabrication
cell

O3

O2

Assembly line 2
Full containers

Figure 8.4 – Single-Card Kanban System
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

O1

Fabrication
cell

O3

O2

Assembly line 2
Full containers

Figure 8.4 – Single-Card Kanban System
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

O1

Fabrication
cell

O3

O2

Assembly line 2
Full containers

Figure 8.4 – Single-Card Kanban System
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

O1

Fabrication
cell

O3

O2

Assembly line 2
Full containers

Figure 8.4 – Single-Card Kanban System
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

O1

Fabrication
cell

O3

O2

Assembly line 2
Full containers

Figure 8.4 – Single-Card Kanban System
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

O1

Fabrication
cell

O3

O2

Assembly line 2
Full containers

Figure 8.4 – Single-Card Kanban System

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

O1

Fabrication
cell

O3

O2

Assembly line 2
Full containers

Figure 8.4 – Single-Card Kanban System
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

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

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
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

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?

8 – 24


Determining the Appropriate
Number of Containers
SOLUTION
d a.
=
2,000 units/day,
p=
0.02 day,
α=
0.10,
w=
0.08 day, and
c=
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

= 22 = 10 containers

Figure 8.5 – OM Explorer Solver for
Number of Containers
8 – 25