Process Capability Natural tolerance limits are defined as

Process Capability Natural tolerance limits are defined as follows: Chapter 7 Introduction to Statistical Quality Control, 5 th Edition by Douglas C. Montgomery. Copyright (c) 2005 John Wiley & Sons, Inc. 1

Uses of process capability data: Chapter 7 Introduction to Statistical Quality Control, 5 th Edition by Douglas C. Montgomery. Copyright (c) 2005 John Wiley & Sons, Inc. 2

Reasons for Poor Process Capability Process may have good potential capability Chapter 7 Introduction to Statistical Quality Control, 5 th Edition by Douglas C. Montgomery. Copyright (c) 2005 John Wiley & Sons, Inc. 3

Chapter 7 Introduction to Statistical Quality Control, 5 th Edition by Douglas C. Montgomery. Copyright (c) 2005 John Wiley & Sons, Inc. 4

Chapter 7 Introduction to Statistical Quality Control, 5 th Edition by Douglas C. Montgomery. Copyright (c) 2005 John Wiley & Sons, Inc. 5

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, 5 th Edition by Douglas C. Montgomery. Copyright (c) 2005 John Wiley & Sons, Inc. 6

One-Sided PCR Chapter 7 Introduction to Statistical Quality Control, 5 th Edition by Douglas C. Montgomery. Copyright (c) 2005 John Wiley & Sons, Inc. 7

Interpretation of the PCR Chapter 7 Introduction to Statistical Quality Control, 5 th 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, 5 th Edition by Douglas C. Montgomery. Copyright (c) 2005 John Wiley & Sons, Inc. 9

Chapter 7 Introduction to Statistical Quality Control, 5 th Edition by Douglas C. Montgomery. Copyright (c) 2005 John Wiley & Sons, Inc. 10

• 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, 5 th 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, 5 th Edition by Douglas C. Montgomery. Copyright (c) 2005 John Wiley & Sons, Inc. 12

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, 5 th Edition by Douglas C. Montgomery. Copyright (c) 2005 John Wiley & Sons, Inc. 13