Transcript Managing Quality Integrating the Supply Chain - 4th Edition

Chapter 11
Statistically-Based
Quality Improvement
for Variables
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Chapter 11
Statistical
Fundamentals
Control Charts
Some Control Chart Concepts for
Variables
Process Capability for Variables
A Closer Look at Quality
Other Statistical Techniques in Quality
Management
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Statistical Fundamentals
Statistical Thinking
All
work occurs in a system of
interconnected processes
All process have variation (The amount
… tends to be underestimated)
Understanding variation and reducing
variation are important keys to success
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Statistical Fundamentals
Why do statistics sometimes fail in
the workplace?
Lack
of knowledge about the tools
General disdain for all things
mathematical
Cultural barriers in a company
Statistical specialists have trouble
communicating
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Statistical Fundamentals
Why do statistics sometimes fail in
the workplace?
Statistics
generally are poorly taught,
emphasizing mathematical development
rather than application
People have a poor understanding of
the scientific method
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Statistical Fundamentals
Why do statistics sometimes fail in
the workplace?
Organizations
lack patience in
collecting data. All decisions have to be
made “yesterday”
Statistics are viewed as something to
buttress an already-held opinion
People fear using statistics
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Statistical Fundamentals
Why do statistics sometimes fail in
the workplace?
Most
people don’t understand random
variation
Statistical tools often are reactive and
focus on effects rather than causes
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Statistical Fundamentals
Type I and Type II Errors
Type
I error
Producers
risk
Probability that a good product will be
rejected
Type
II error
Consumers
risk
Probability that a nonconforming product
will be available for sale
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Statistical Fundamentals
Understanding Process Variation
Random variation
Centered
around the mean
Consistent amount of dispersion
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Statistical Fundamentals
Understanding Process Variation
Nonrandom variation
“Special
Causes”
Results from some event
Dispersion and average of the process
are changing
Process that is not repeatable
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Statistical Fundamentals
Understanding Process Variation
Process stability
Random
Variation
Not nonrandom variation
Process Charts
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Statistical Fundamentals
Understanding Process Variation
Sampling Methods
Samples
are cheaper
Take less time
Less intrusive
Destructive tests may destroy the
sample
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Statistical Fundamentals
Random
Samples
Each
piece has an equal chance of
being selected for inspection
Systematic
According
Rational
Samples
to time or sequence
subgroups
A
group of data that is logically
homogeneous
Computing variation between
subgroups
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Statistical Fundamentals
Planning
for Inspection
What
type of planning will be used
Who will perform the inspection
What critical attributes to be inspected
are
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Control Charts
Variables and attributes control charts
1.
2.
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You must understand this generic
process for implementing process
charts
You must know how to interpret
process charts
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Control Charts
Variables and attributes control charts
3.
4.
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You need to know when different
process charts are used
You need to know how to computer
limits for the different type of process
chart
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Control Charts
A generalized procedure for developing
process charts
1. Identify critical operations in the
process
2. Identify critical product characteristics
3. Determine whether the critical
product characteristic is a variable or
an attribute
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Control Charts
A generalized procedure for developing
process charts
4. Select the appropriate process
control chart
5. Establish the control limits and use
the chart to continually monitor and
improve
6. Update the limits when changes have
been made to the process
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Control Charts
Understanding control charts
A control chart is an application of
hypothesis testing where:
The null hypothesis is that the process is
stable
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Some Control Chart Concepts for Variables
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Choosing the correct variables
control chart
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Are the data variable?
Is it homogeneous in nature or not
conducive to subgroup sampling?
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Some Control Chart Concepts for Variables
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1.
2.
3.
4.
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When a process is out of control
some corrective action is needed:
Identify the quality problem
Form the correct team to evaluate
and solve the problem
Use structured brainstorming
Brainstorm to identify potential
solutions
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Some Control Chart Concepts for Variables
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5.
6.
7.
8.
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When a process is out of control
some corrective action is needed:
Eliminate the cause
Restart the process
Document the problem, root cause
and solutions
Communicate the results
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Process Capability for Variables
A highly capable process produces
high volumes with few or no defects
World-class levels of process
capability are measured by parts per
million (ppm) defect levels
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Process Capability for Variables
Six Sigma
A design program which emphasized
engineering parts so that they are
highly capable
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Process Capability for Variables
Capability Studies
Two purposes to determine whether
a process is capable
1. To determine whether a process
consistently results in products that
meet specifications
2. To determine whether a is in need of
monitoring
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Process Capability for Variables
The difference between capability and
stability
A process is capable if individual
products consistently meet
specification
A process is stable only if common
variation is present in the process
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Strategic Quality Planning
Statistically-Based Quality Improvement for Variables
Summary
You need:
 To know the generic process for
developing charts
 To be able to interpret charts
 To be able to choose which chart to
use
 The formulas to derive the charts
 To understand the purposes and
assumptions underlying the charts
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Printed in the United States of America.
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