Transcript Introduction to Statistical Quality Control, 5th edition

Process Capability
Natural tolerance limits are defined as follows:
Chapter 7
Introduction to Statistical Quality Control, 5th Edition by Douglas C. Montgomery.
Copyright (c) 2005 John Wiley & Sons, Inc.
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Uses of process capability data:
Chapter 7
Introduction to Statistical Quality Control, 5th Edition by Douglas C. Montgomery.
Copyright (c) 2005 John Wiley & Sons, Inc.
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Reasons for Poor Process Capability
Process may have good
potential capability
Chapter 7
Introduction to Statistical Quality Control, 5th Edition by Douglas C. Montgomery.
Copyright (c) 2005 John Wiley & Sons, Inc.
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Chapter 7
Introduction to Statistical Quality Control, 5th Edition by Douglas C. Montgomery.
Copyright (c) 2005 John Wiley & Sons, Inc.
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Chapter 7
Introduction to Statistical Quality Control, 5th Edition by Douglas C. Montgomery.
Copyright (c) 2005 John Wiley & Sons, Inc.
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Practical interpretation – relationship of PCR to the proportion of the
tolerance interval used by the process:
For the hard bake process:
Chapter 7
Introduction to Statistical Quality Control, 5th Edition by Douglas C. Montgomery.
Copyright (c) 2005 John Wiley & Sons, Inc.
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One-Sided PCR
Chapter 7
Introduction to Statistical Quality Control, 5th Edition by Douglas C. Montgomery.
Copyright (c) 2005 John Wiley & Sons, Inc.
7
Interpretation of the PCR
Chapter 7
Introduction to Statistical Quality Control, 5th Edition by Douglas C. Montgomery.
Copyright (c) 2005 John Wiley & Sons, Inc.
8
Assumptions for Interpretation of
Numbers in Table 7-2
• Violation of these assumptions can lead to big trouble in using the
data in Table 7-2.
Chapter 7
Introduction to Statistical Quality Control, 5th Edition by Douglas C. Montgomery.
Copyright (c) 2005 John Wiley & Sons, Inc.
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Chapter 7
Introduction to Statistical Quality Control, 5th Edition by Douglas C. Montgomery.
Copyright (c) 2005 John Wiley & Sons, Inc.
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• Cp does not take
process centering into
account
• It is a measure of
potential capability, not
actual capability
Chapter 7
Introduction to Statistical Quality Control, 5th Edition by Douglas C. Montgomery.
Copyright (c) 2005 John Wiley & Sons, Inc.
11
A Measure of Actual Capability
Chapter 7
Introduction to Statistical Quality Control, 5th Edition by Douglas C. Montgomery.
Copyright (c) 2005 John Wiley & Sons, Inc.
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Normality and Process Capability
Ratios
•
The assumption of normality is critical to the
usual interpretation of these ratios (such as
Table 7-2)
For non-normal data, options are
•
1. Transform non-normal data to normal
2. Extend the usual definitions of PCRs to handle
non-normal data
3. Modify the definitions of PCRs for general
families of distributions
Chapter 7
Introduction to Statistical Quality Control, 5th Edition by Douglas C. Montgomery.
Copyright (c) 2005 John Wiley & Sons, Inc.
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