IE 482 Quality Engineering Course
Lecture Notes #3
Spring’06-07
Prepared by Elif Binboga
1
Juran’s Contribution to Quality
• Many books on the subjects of quality planning, quality
control,
quality
management,
and
quality
improvement
• Adapted the Pareto chart, a bar graph that ranks
problems in decreasing order of frequency, to quality
control
• Founded Juran Institute, which still offers consulting on
quality improvement practices and management
training
• Proposed a universal way of thinking about quality,
quality trilogy: quality planning, quality control, and
quality improvement
2
1
Juran’s Contribution to Quality…
• According to Juran, primary concern should be on
9 Quality planning
1.
2.
3.
4.
5.
Determine quality goals
Develop plans to meet those goals
Identify the resources to meet those goals
Translate goals into quality
Prepare a quality plan summarizing 1 to 4
9 Quality control
1. Evaluate performance
3
Juran’s Contribution to Quality…
2. Compare performance with set goals
3. Take action on the difference
9 Quality improvement
1.
2.
3.
4.
5.
Reducing wastage
Improving delivery
Enhancing employees’ satisfaction
Becoming more profitable
Ensuring greater customer satisfaction
4
2
Some of other Leaders in Quality
• Kaoru Ishikawa
– promoted widespread use of basic tools like cause and
effect diagram
• Armand Feigenbaum
– author of Total Quality Control,
organizational involvement in quality
promoted
overall
• Genichi Taguchi
– devised a methodology for testing multiple variables in the
manufacturing process
– engineering in quality through product design
– poor quality is a loss to society
5
Total Quality Management
• is a set of management practices throughout
the organization
• geared
to
ensure
the
organization
consistently meets or exceeds customer
requirements
• through the continual improvement of the
quality of the products, services, people,
processes, and environments
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3
Total Quality Management
• A more formal definition from International
Organization for Standrardization (ISO):
– "TQM is a management approach for an
organization, centered on quality, based on the
participation of all its members and aiming at
long-term success through customer satisfaction,
and benefits to all members of the organization
and to society."
7
Total Quality Management…
• Two aspects to total customer satisfaction
– The external customer
• The one who ultimately receives the company’s
products or services
– The internal customer
• The next person in any sequential process
– e.g. Manager is the customer of the secretary
• Don’t forget that when the total customer
satisfaction is accomplished internally, the end
result will satisfy the external customer as well
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4
Total Quality Management…
• Prior to the first change toward TQM
– Train everyone involved in quality concepts
– Establish clear definitions of quality for every job
– Statistical Quality Control (SQC) analysis should be
used to identify which measurements and/or
services are Critical To Quality (CTQ)
– Measure the status of quality in the specific jobs
using flowcharts, checksheets etc.
– Use SPC charts to determine special cause
variation and common cause variation
9
Total Quality Management…
– Form teams
• to formulate mission statements
• to decide on the procedures to be used to achieve
the goals set in the mission statements
• Gap Analysis
– Taking measures to eliminate discrepancies
– Monitoring
customer
expectations
and
product/services provided and work to decrease
the gap in between
• Customer surveys may help management to learn
customer expectations and satisfaction
10
5
Elements of TQM
• Continuous improvement
• Competitive Benchmarking
– a process that views other companies who have
become experts in a function that another
company would like to study and initiate for
themselves in order to improve their quality
• Employee empowerment
– giving more responsibility to employees who make
or serve products so that management needs less
time to supervise the lines (allows management to
do other important tasks)
11
Elements of TQM…
– encourages employee moral and gives employees
much more discretion over their own assigned
positions
• Team approach
– to encourage all group participants to be
involved, cooperate, and develop a team spirit
that will improve employee development,
motivation, product quality, and company moral
• Decisions based on facts rather than opinion
– helps operate an organization more efficiently and
effectively because more accurate decisions are
made
12
6
Elements of TQM…
• Knowledge of tools
– Employees and management should
knowledge of tools (at their usage)
– Results in a better product
also
have
the
• Supplier quality
– develop relationships with suppliers who have similar goals in
quality
13
FEATURES OF A TQM MODEL
Source: Adapted from Quality Control and
Improvement, A. Mitra 2nd Edition
14
7
Why Total Customer Satisfaction
is so important?
• It is a measure of quality
– If a customer sets the specifications for a product
and is completely satisfied, then quality has been
achieved
• It makes sense economically
Pete Babich, “Customer Satisfaction: How
good is good enough?” (Quality Progress,
January 1994)
– 5 times costly to have a new customer than to
keep the current one
– A company with a 99% customer satisfaction rate
would end up with more than five times the market
share of a competitor with a 95% rate
15
Costs of Quality
A measure of performance of the TOTAL
QUALITY SYSTEM is cost associated with it
• Prevention Costs
–
–
–
–
New product quality planning
Product improvement
Process improvement
Staff training and development
• Appraisal Costs
– Incoming materials
inspection
– Monitoring production for
quality issues
– Customer surveys
– Quality laboratories
– Finished goods inspection
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8
Costs of Quality…
• Internal Failure Costs
Scrap
Reworking / correcting
Downgrading
Retest
Plant downtime
Investigation /
troubleshooting
–
–
–
–
–
Warranty / guarantees
Returned goods
Handling complaints
Allowances / litigation
Loss of goodwill
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Cost of Quality Model
Costs
–
–
–
–
–
–
• External Failure Costs
Total Cost
Prevention + Appraisal costs
Internal + External Failure Costs
Quality
Improvement
18
9
ISO – 9000 series
• Quality
system
standards
adopted
by
International Organization for Standardization in
1987; revised in 1994 and 2000
– Globally accepted quality standards
– Requires regular re-certification
• Briefly, require firms to document their qualitycontrol systems at every step so that they’ll be
able to identify those areas that are causing
quality problems and correct them
19
ISO – 9000 series…
• ISO 9000
• ISO 9001
Quality management and quality
assurance standards: This provides
guidelines for the selection and use
of the standards
Quality systems: The model for quality
assurance in design, development,
production, installation, and servicing
(most inclusive of the external quality
assurance standards, i.e. 9001, 9002,
9003 – are used in contractual
situations to provide confidence to
the purchaser)
20
10
ISO – 9000 series…
• ISO 9002
• ISO 9003
• ISO 9004
Quality systems: The model for quality
assurance in production, installation,
servicing
Quality systems: The model for quality
assurance in the final inspection and
testing
Guide organizations in quality
management to assist them in
developing and implementing a
quality system (internal quality
assurance)
21
Introduction to Variation and Statistics…
Measurement Concepts
• No two products or characteristics are same
• Any measurement is only as good as the
measuring device and the person’s reading of
the measuring device
• What is accuracy?
– The smallest unit
measuring device
of
measurement
on
the
• The maximum error of a measurement is half
the accuracy
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11
Introduction to Variation and Statistics…
Measurement Concepts
• If length of a door is measured to the nearest
tenth of a centimeter, what is the maximum
error can measurement have?
– 0.05 centimeter
– When the measurement is to the nearest tenth of a
centimeter, any length between 102.45 and 102.54
will be called 102.5
• A measurement is an approximate number
because it has been rounded off to the
accuracy
23
Introduction to Variation and Statistics…
Measurement Concepts
• When a measurement is written
– Its accuracy is implied by the number of place
values
– Zeros cannot be dropped
– 0.3 cm and 0.300 cm are significantly different
• 0.3 cm measurement would lie between 0.25 cm &
0.34 cm
• 0.300 cm measurement would lie between 0.2995 cm
& 0.3004 cm
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12
Introduction to Variation and Statistics…
Measurement Concepts
• When measurements for length of two sections
of an item are taken separately with different
measuring devices with different accuracies
(e.g. ruler and meter stick) How you calculate
the total length of the item?
• The correct way in this kind of calculations is
1. add the measurements
2. then round off the answer to match the accuracy
of the least accurate number used in the
calculations
25
Introduction to Variation and Statistics…
Measurement Concepts
• Round-off Rules
– Round up
• 153.45 to the nearest tenth Æ153.5
• 23.4556 to the nearest thousandth Æ 23.456
• 8.384 to the nearest tenth Æ 8.4
– Truncate
• 18.544 to the nearest hundredth Æ 18.54
• 2839 to the nearest hundred Æ 2800
• 4.1454 to the nearest thousandth Æ 4.145
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13
Introduction to Variation and Statistics…
Measurement Concepts
• What does tolerance mean?
– An acceptable range of measurements on a
specific dimension
• Tolerance is usually set at the design stage of
the product
• It is simply a target measurement plus or minus
the variation that is acceptable
• Any item that has its measurement beyond the
tolerable range is said to be unacceptable or
defective
27
Introduction to Variation and Statistics…
Causes of Variation
– Variability is a part of any process, no matter how
sophisticated
– As mentioned before
• Common causes of variation (random-chance variation)
– Inherent in the process, therefore the only way to decrease
common cause variation is to make improvements in
process
– If a common cause variation is misinterpreted as
special cause
• extensive local action work will be wasted because local
action does not involve changes in the process
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14
Introduction to Variation and Statistics…
Causes of Variation
• Special causes
variation)
of
variation
(assignable-cause
– Affects the process in unpredictable ways and can be
detected by simple statistical techniques
– Can be eliminated from the process by the worker or
process control team in charge (local action)
– If a source of special-cause variation is incorrectly
classified as common-cause variation
• Expensive changes to the process may be
undertaken
• Will probably worsen the quality of output because
problem is not eliminated
29
Introduction to Variation and Statistics…
Causes of Variation
Common cause variation
Special cause variation
30
15
Case study 3.1, on Page 51
The Ace Machining Company experienced excessive variation among
products from one of its machines. Ace decided that since it was an old
machine, it must need an overhaul. It was taken out of service, torn done to
replace worn parts, and reassembled for in-service operation. The overhaul cost
exceeded $10,000 in worker hours and lost production time. One bearing
seemed to be worn and it was replaced. When the machine was back in
service, the excessive variation in its output was virtually the same. The real
problem in that case was in the process. In company-wide downsizing change,
the operators on each shift had been laid off and their responsibilities for running
the machine were now shared by two other operators on each shift. The two
operators were instructed to check the machine each half hour in turn. One
checked it on the hour and the other checked it on the half hour. They were
instructed to adjust the machine if the critical measurements on the part being
produced were more than .005 inch from the target measurement. Each
operator silently blamed the other each time they adjusted the machine and,
consequently, the machine was adjusted every half hour. Overadjustment was
the true source of the excessive variation and was due to the process that was
established by management as part of the company downsizing. Without the
use of control charts to identify the type of variation, it was misdiagnosed as
special-cause variation. The mistake cost the company a large amount of
money and a morale problem with the machine operators
31
Introduction to Variation and Statistics…
Causes of Variation
• The effect of Overadjustment
32
16
Introduction to Variation and Statistics…
The Variation Concepts
• What is a distribution?
– Any large set of measurements will form a graphical
pattern when the frequency of each measurement is
charted, that pattern is called a distribution
– It is an ordered set of numbers that are grouped in some
manner (in table/graph/picture form)
• Why the concept of distributions is important in
quality control?
– Because all Statistical Process Control techniques use the
distribution of a limited number of measurements to
imply the “true” distribution of all measurements
33
Introduction to Variation and Statistics…
The Variation Concepts
• Suppose you measure the diameter of the items
you produce, if you chart the frequency of (the
day’s) measurements then the pattern of the
curve is the distribution of a day’s production of
items’ diameters
The day’s distribution curve with tailed
measurements
34
17
Introduction to Variation and Statistics…
The Variation Concepts
• Every distribution has the following measurable
characteristics
– Location
– Spread
35
Introduction to Variation and Statistics…
The Variation Concepts
–Shape
36
18
Introduction to Variation and Statistics…
The Variation Concepts
• Which one of the following
indicates the poorest quality?
distributions
The widest pattern belongs to the
distribution in the middle and it
indicates a large amount of variation
in the measurements. Please note that
since all three distributions are on target, the figure in the middle
indicates the poorest quality. The one with narrowest distribution
indicates the one with the smallest amount of variation and the highest
quality
37
Introduction to Variation and Statistics…
The Variation Concepts
• If the plotted statistic is sample average, the underlying
distribution is usually normal (central limit theorem Æ will be covered later)
•Skewed left
•Problem with excessively small
measurements
•Special cause variation
•When problem is found and
eliminated, the shape of the
distribution should return to
normal pattern
38
19
Introduction to Variation and Statistics…
The Variation Concepts
•Two distinct high picks
•Bimodal
•Special cause variation
•When problem is found and
eliminated, the shape of the
distribution should return to
normal pattern
39
Introduction to Variation and Statistics…
Distributions and SPC Goals
Special cause
variation affects
the process in
UNPREDICTABLE
ways
Special causes of variation are present
When special causes of variation is eliminated and the
process is in statistical control than day-to-day production
will be as follows:
When process is in
statistical control
production is
PREDICTABLE
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