itroduction to cal quality control
TRANSCRIPT
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Introduction to Statistical
Quality Control
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Chapter 1
Quality Improvement in the
Modern Business Environment
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1-1. The Meaning of Quality and
Quality Improvement
1-1.1 Dimensions of Quality
1-1.2 Quality Engineering Technology
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1-1.1 Dimensions of Quality
Performance
Reliability
Durability
Serviceability
Aesthetics
Features
Perceived Quality
Conformance to
standards
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Performance Will the product perform its intended
function?
Will this industrial scale measure up to 4000
pounds in 5 pound graduations?
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Reliability How often does the product fail?
How often do I have to take this Toyota Camry
to the service department?
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Durability How long will the product last?
The product should perform satisfactorily over
a long period of life
If I buy that 1999 Toyota 4Runner when the
lease expires, will it give me good service for
10 more years?
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Serviceability How easy is it to repair the product?
If amazon.com sends the wrong book, how hard
is it to get this error corrected?
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Aesthetics Is the product pleasing to the senses?
Do you like the box in which Timberland Shoes
are packaged?
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Features What will the product do beyond the basics?
Does the new Ford Focus come with a CD
changer, or do you have to pay extra for that?
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Perceived quality What is the reputation of the company
selling this product?
Is Delta really ready when you are?
Why do people buy Gucci handbags?
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Conformance to standards
Is the product made as designed?
Why do they have to beat on those Ford Taurus
bodies when they are being assembled in
Hapeville?
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1-1.1 Dimensions of Quality Definitions of Quality
Quality means fitness for use- quality of design
- quality of conformance
Quality is inversely proportional tovariability.
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Quality of design Automobile differences
Materials used in construction
Specifications of the components
Reliability of drive train components
Reliability of accessories
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Quality of conformance How well does the product conform to the
specifications required by the design?
Choice of manufacturing processes
Training of the workers
Supervision of the workers
Motivation of the workers
Quality-assurance procedures that were used
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Quality is inversely proportional to variability
Toyota Lexus versus Ford Taurus
That transmission noise (or lack of it) is wasted
energy caused by components that dont fit
precisely
Imprecise components lead to wear and tear
Ford Taurus/Mercury Sable transmission lastsfor 64,000 miles
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1-1.1 Dimensions of Quality
Transmission Example
N(100,10)
vsN(100,4)
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1-1.1 Dimensions of Quality
Quality Improvement
Quality improvementis the reduction of
variability in processes and products.
Alternatively, quality improvementis also
seen as waste reduction.
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1-1.2 Quality Engineering
Terminology
Quality engineeringis the set of operational,
managerial, and engineering activities that acompany uses to ensure that the quality
characteristics of a product are at the
nominal or required levels.
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Inherent variability No two products are ever identical
Slight differences in materials
Slight differences in machine settings
Slight differences in operators
Slight differences in ambient temperature
during production Papermate Pens not much different
Fins on a turbine engine quite a lot
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1-1.2 Quality Engineering
Terminology
Two types of data:
Attributes Data - discrete data, often in theform of counts
Variables Data - continuous measurementssuch as length, weight
Both types will be discussed in the course
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1-1.2 Quality Engineering
TerminologySpecifications
Quality characteristics being measured are often
compared to standards orspecifications.Desired measure for the quality characteristic
Example: Shaft and bearing
Too loose the assembly will wobble causing
wearToo tight, and the assembly can not be made,
no clearance
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1-1.2 Quality Engineering
TerminologySpecifications
Nominal or target value
Desired value for a quality characteristic
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1-1.2 Quality Engineering
TerminologySpecifications
UpperSpecification Limit (USL)
LowerSpecification Limit (LSL)
Largest and smallest allowable values
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1-1.2 Quality Engineering
TerminologySpecifications
UpperSpecification Limit (USL)
LowerSpecification Limit (LSL) One-sided
The compression strength of a Coke bottle must begreater than a given psi value
Two-sided
The weight of potato chips in the bag can bebetween 7.8 and 8.3 ounces
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Design specifications Over the wall
From design to manufacturing
Cooperatively
Between design and manufacturing
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1-1.2 Quality Engineering
Terminology
When a component or product does not
meet specifications, it is considered to benonconforming.
A nonconforming product is considered
defective if it has one or more
nonconformities that may seriously affect
the safe or effective use of the product.
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1-1.2 Quality Engineering
Terminology
A new car is purchased
A bubble in the paint on the door is noticedNonconformity yes
Defective car - no
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1-1.2 Quality Engineering
Terminology
Concurrent Engineering
Team approach to design. Specialists frommanufacturing, quality engineering,
management, etc. work together for product
or process improvement.
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1-2. A Brief History of Quality
Control and Improvement
(Refer to Table 1-1)
Frederick Taylor (1875) introduces theprinciples of scientific management;
dividing work into tasks with standardized
procedures
The Gilbreths developed standard times and
motions (1920s)
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1-2. A Brief History of Quality
Control and Improvement
(Refer to Table 1-1)
WalterShewhart (1924) introduced statistical
control chart concepts and QC begins
Dodge and Romig (1928), Bell Labs, develop
acceptance sampling as an alternate to 100%
inspection
During WW II the shells didnt fit the howitzers
leading to development of MIL-STDs
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1-2. A Brief History of Quality
Control and Improvement
(Refer to Table 1-1)
The
American
Society for Quality
Controlformed in 1946 [now known as the
American Society for Quality (ASQ)]
1950s and 1960s saw an increase in
reliability engineering, experimental design,
and statistical quality control
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1-2. A Brief History of Quality
Control and Improvement
(Refer to Table 1-1)
Competition from foreign industries (Japan)
increases during the 1970s and 1980s.
Statistical methods for quality improvement use
increases in the United States during the 1980s
Total Quality Management (TQM) emergesduring 1970s and into the 1980s as an important
management tool to implement statistical methods.
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1-2. A Brief History of Quality
Control and Improvement
Malcolm Baldrige National Quality Award is
established in 1988.
ISO 9000 certification activities increase in U.S.
industry in the 1990s.
Motorolas Six-Sigma initiative begins in the1990s.
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1-3. Statistical Methods for
Quality Control and Improvement
Three major areas:
Statistical process control (SPC)
Design of experiments (DOE)
Acceptance sampling
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1-3. Statistical Methods for
Quality Control and Improvement
Statistical ProcessControl (SPC)
Control charts are
used for process
monitoring and
variability reduction.
SPC is an on-line
quality control tool.
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1-3. Statistical Methods for
Quality Control and Improvement
Design of Experiments
Experimental design is an approach tosystematically varying the controllable input
factors in the process then determining the effect
these factors have on the output responses.
Experimental designs are off-line quality tools. Crucial for variability reduction.
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1-3. Statistical Methods for
Quality Control and ImprovementAcceptance Sampling
Acceptance samplingis the inspection and
classification of a sample of the product selectedat random from a larger batch or lot and theultimate decision about disposition of the lot.
Two types:
1. Outgoing inspection - follows production2.Incoming inspection - before use in
production
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Quality cannot be inspected into
the product When the organization realizes this, process
improvement efforts begin
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The objective Systematic reduction of variability
First, by using acceptance sampling
Then, by using SPCFinally, by using DOE
We dont stop when requirements are met
F
urther reductions in variability lead to betterperformance
Avoid the Taurus transmission
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1-4. Other Aspects of Quality
Control and Improvement
Total Quality Management (TQM)
TQM is a managerial framework to accomplishquality improvement.
Other names and related approaches:
Company-Wide Quality Control (CWQC) Total Quality Assurance (TQA)
Six-Sigma
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1-4. Other Aspects of Quality
Control and Improvement
1-4.1 Quality Philosophy and Management
Strategies
1-4.2 The Link Between Quality and
Productivity
1-4.3 Quality Costs
1-4.4 Legal Aspects of Quality
1-4.5 Implementing Quality Improvement
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1-4.1 Quality Philosophy and
Management StrategiesThree Important Leaders
W. Edwards Deming
- Emphasis on statistical methods in qualityimprovement
Joseph Juran
- Emphasis on managerial role in quality
implementation Armand V. Feigenbaum
- Emphasis on organizational structure
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1-4.1 Quality Philosophy and
Management Strategies
Total Quality Management (TQM)
Quality Standards and Registration
ISO 9000
Six Sigma
Just-In-Time, Lean Manufacturing,
Poka-Yoke, etc.
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TQM Began in the early 80s based on the
philosophies of Deming and Juran
Evolved into wide spectrum of ideasParticipation in quality groups
Work culture
Customer focus
Supplier quality improvement
Cross-functional teams concerned with quality
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TQM A success?
Moderately
Why not?
Not enough concern for reduction of variability
Ineffective training conducted by HRpeople
No knowledge of what is important
Success measured by % of workforce trained
Management not committed
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TQM More reasons for lack of success
Zero defects, value engineering, quality is free
Programs with no emphasis on reducing variability
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ISO 9000
Quality system oriented
Say what you do, do what you say
Much effort devoted to paperwork and
bookkeeping
Not much to reducing variability and improving
processes
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ISO 9000 paragraphs
1. Management responsibility for quality
2. Design control
3. Document and data control
4. Purchasing and contract management
5. Product identification and traceability
6. Inspection and testing, includingcontrol of measurement and inspectionequipment
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ISO 9000 paragraphs
7. Process control
8. Handling of nonconforming product
9. Handling, storage, packaging and delivery ofproduct
10. Control of quality records
11. Internal audits
12. Training
13. Statistical methodology
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ISO 9000
US$40 billion annual business worldwide
Registrars, auditors, consultants
Plus, 1000s of hours of internal costs
Effective?
Does it reduce variability?
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Six Sigma
Developed by Motorola in the late 80s
Consider that + 3Wprovides 0.00135 in
each tail, or 0.00270 in the two tales
So, in 1 million parts, 2700 would be
defective
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Six Sigma
Consider an assembly of 100 parts that must
all function for the assembly to function
.9973 x .9973 x ..9973 = (.9973)100 = .7631
Thus, about 23.7% of the products under 3W
will fail
Not usually an acceptable situation
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Six Sigma
But, + 6W results in 0.999999998 inside
specs
(0.999999998)100 = .9999998
Or, 2 parts/billion defective
i.e., 0.2 ppm
Much better than + 3W
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Six Sigma
Has moved beyond Motorola
Has come to encompass much more
Has become a method for improving
corporate business performance
Companies involved in Six Sigma use
teams that work on projects involving
quality and costs
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Six Sigma
More successful than TQM
More managerial commitment
Involves costs
But, its still another slogan and program
Better to train everyone in quality tools and
make efforts to reduce variability
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JIT, Lean Manufacturing, etc.
Programs that devote too little attention to
variance reduction
For example, JIT
The variability in demand results in a need for
inventory
Reduce the variability and reduce the inventory
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1-4.2 The Link Between Quality
and Productivity
Effective quality improvement can be
instrumental in increasing productivity andreducing cost.
The cost of achieving quality improvements
and increased productivity is often
negligible.
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An example
Data
100 parts/day are manufactured
75% are conforming
60% of the nonconforming can be reworked for
a cost of$4
Remainder are scrapped Direct manufacturing cost is $20/part
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An example
Cost/conforming part
[$20 (100) + $4 (15)]/90 = $22.89
Note that the yield is 90 conforming/day
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An example
New process us introduced
Fallout is 5%
60% can be reworked
Cost/conforming part
[$20 (100) + $4 (3)]/98 = $20.53
Note that the yield is 98 conforming/day
Up from 90/day
And, costs are reduced by 10.3%
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1-4.3 Quality Costs
Quality Costs are those categories of costs that are
associated with producing, identifying, avoiding,
or repairing products that do not meetrequirements. These costs are:
Prevention Costs
Appraisal Costs
Internal Failure Costs
External Failure Costs
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Quality costs
Prevention costs
Quality planning and engineering
New products review
Product/process design
Burn-in
Training Quality data acquisition and analysis
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Appraisal costs
Inspection and test of incoming material
Product inspection and test
Materials and services consumed
Maintaining accuracy of test equipment
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Internal failure costs
Scrap
Rework
Retest
Failure analysis
Downtime
Yield losses
Downgrading (off-specing)
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External failure costs
Complaint adjustment
Returned product/material
Warranty charges
Liability costs
Indirect costs
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Pareto analysis
Cost reduction through identifying
improvement opportunities
Identifying quality costs by category, or by
product, or by type of defect or
nonconformity
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Monthly quality costs forPCB assembly
Type of defect % of total defects Scrap & rework costs
Insufficient solder 42 $37,500
Misaligned components 21 $12,000
Defective components 15 $8,000
Missing components 10 $5,100
Cold solder joints 7 $5,000
All other causes 5 $4,600
Total 100 $72,200
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Pareto analysis
Insufficient solder
42% of defects and 52% of scrap and rework
costs Work on that defect first
Most of the cost reductions will come fromattacking the few problems that are
responsible for the majority of the qualitycosts
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Appraisal or prevention
Many firms spend far too much of their
quality management budget on appraisal
and not enough on prevention Money spent on prevention has a much better
payoff than money spent on appraisal
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1-4.4 Legal Aspects of Quality
The re-emergence of quality assurance as
an important business strategy is in
part a result of
1. Consumerism
2. Product Liability
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Consumerism
Virtually every product line of today issuperior to that of yesterday
But, many consumers see it otherwise Consumer tolerance for minor defects &
aesthetic problems has decreasedconsiderably
Blemishes, surface-finish defects, noises,appearance problems
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Consumerism
Many manufacturers introduce new designs
before they are fully evaluated and tested
To remain competitive
Unproved designs
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Product liability
Manufacturers and sellers are likely to incur
a liability when they have been
unreasonably careless or negligent in whatthey have designed, or produced, or how
they have produced it
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More stringent: Strict liability
1. There is a strong responsibility for both
manufacturer and merchandiser requiring
immediate responsiveness to unsatisfactoryquality through product service, repair, or
replacement of defective product
Extends into the period of use by the consumer By producing the product, manufacturer and
seller must accept responsibility for use
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More stringent: Strict liability
2. All advertising statements must be
supportable by valid company quality or
certification data
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Introduction to Statistical Quality Control,
1-4.5 Implementing Quality
Improvement Strategic management of quality
Almost all successful efforts have been
management-driven. Too much emphasis on registration and
certification programs (ISO, QS)
Insufficient focus on quality planning and design,
quality improvement, overemphasis on qualityassurance
Poor use of available resources