# Introduction to Statistical Quality Control 1

```Introduction to Statistical
Quality Control
1
What is Statistical Quality Control?
 Statistical
 Quality
 Control
 Statistical Quality Control - SQC
2
“Statistical”
 What does the term statistical imply?
3
“Control”
 What does the term control imply?
4
What is Quality?
5
What is Quality?
 Traditional definition of Quality:
 Product focused
 Fitness of use - products must meet the
requirements of users.
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Dimensions of Quality (Products)






Performance – Will the product do the intended job?
Reliability – How often does the product fail?
Durability - How long does the product last?
Serviceability – How easy is it to repair the product?
Aesthetics – What does the product look like?
Features – What does the product do?
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Dimensions of Quality
 In addition to products there is
quality of:
 Dimensions
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Two Aspects of “Fitness for Use”
 Quality of design –


Products are designed to be in various grades of
quality. (e.g., Autos differ with respect to size,
options, speed, etc.)
Service systems are designed for different grades of
quality
 Quality of conformance –
 How well the product conforms to specifications.
(e.g., If diameter of a drilled hole is within
specifications then it has good quality.)
 Does the service representative follow guidelines?
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A General Definition of Quality
 Quality can viewed in multiple ways
 To study quality and develop quality analysis
approaches, a more general definition is
needed
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A General Definition of Quality
 Quality is inversely proportional to Variability
 If the variability of an important product
characteristic decreases  quality of product
increases
 Quality Improvement –
 Reduction of variability in processes and
products.
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Examples
12
A General Definition of Quality
 Characterizing variability is generally
quantitative and data driven.
 Reducing variability in some product/service
characteristic forces more in depth exploration
and knowledge of the design and production or
delivery processes.
13
Summary
 SPC embodies statistical methods
focusing on monitoring and reducing
variability.
 Our initial focus will be on basic
statistical concepts and analysis
methods.
14
Quality in Industry
 Terminology
 Where quality control is applied
 Six-Sigma
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Terminology
 Quality Engineering –
 Set of operational, managerial, and
engineering activities that a company
uses to ensure that quality
characteristics of a product/service are
at nominal levels
 Quality planning
 Quality assurance
 Quality control and improvement
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Terminology
 Quality planning
 Strategic: Customers and their needs, products,
measures,…
 Quality assurance
 Policies, procedures, work instructions,
specifications, records, etc. for making sure
products meet desired quality levels
 Quality control and improvement
 Monitoring specific results and identifying ways
to eliminate causes of unsatisfactory results
(reduce variability)
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Where Quality Control is Applied
 “An ounce of prevention is worth a
pound of cure”
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Acceptance Sampling
 Sample from lot to determine
acceptance
 More efficient than 100% inspection
 Reduces bad product sent to
consumer
 Dodge & Romig 1930s
 No feedback, prevention or
improvement
19
On-Line Process Control
 Monitoring of manufacturing process
measures with control charts
 Shewhart 1920s
 Sample & stop process if necessary
 No improvement, but maintains
current process
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Off-Line Improvement
 Designed experiments
 Taguchi & Classical Statistics 1980s
 Continuous improvement of product
designs and manufacturing processes
 Identification of “leverage” relative to
improvement
 Optimization of process parameters
21
Statistical Methods for Quality Control
& Improvement
 Method
-
Relative Savings
 Acceptance Sampling
(\$1)
 On-Line Process Control
(\$10)
 Off-Line Process Improvement
(\$100)
22
Six Sigma - Motorola
 Six Sigma = 2 defects per billion
opportunities!
 Applied ubiquitously (originally production
focused)


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identify problem;
develop measurement;
set goal;
close gap
 Utilizes statistical methods
 Training levels defined for personnel
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DMAIC – Chapter 2
 DMAIC is a structured problem-solving
technique consisting of the following
steps:
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
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Define
Measure
Analyze
Improve
Control
 DMAIC is usually associated with six
sigma.
 Text coverage of the introductory
material
 Chapter 1
 Chapter 2
 Chapter 3 – see syllabus
 Reminder:
 There is a lab this week.
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