cqe经典复习资料2
Chapter 2 Basic Quality Concepts 11
CHAPTER 2
BASIC QUALITY CONCEPTS
1.0 The Nature of Variation
2.0 Quality
3.0 Quality Systems
4.0 Quality Systems Standards
5.0 Fundamental Principles
6.0 Human Factors
7.0 A Brief History of Quality
“Well! I've often seen a cat without a grin, but a grin without a
cat! It's the most curious thing I ever seen in all my life.”
Alice
Chapter 2 Basic Quality Concepts 13
BASIC QUALITY CONCEPTS
1.0 THE NATURE OF VARIATION
While standing on a street corner observing the passing traffic, two cars of the same make
and model stop at a traffic light. Both cars are the same color, have Goodyear tires and have
a luggage rack on the trunk. At first glance, the cars seem identical. Upon closer observation,
differences are detected. Both cars have Goodyear tires, but are the tires the same size?
Are the radios the same? Is the upholstery the same? There are many characteristics for
comparison.
The closer an item is examined, the more differences are found. No two objects are exactly
alike. All things differ by some degree. Some variation may be obvious, but other variation
may require precise measuring equipment to detect.
All manufactured parts exhibit variation. It is the concept of variation that forms the basis of
probability, statistics and quality control. Consider a part that is produced by a punch press.
As raw material is fed into the press, the machine punches out the parts. Eventually the
press will produce a large number of similar parts. A visual check of the diameters may
reveal no differences among the parts. If the diameter is measured with a scale, some
differences will be found. If the measurements are made with a micrometer, a greater
number of differences will be detected. Each level of comparison or method of measurement
reveals a greater amount of variation.
As the measurements increase in precision, the differences among the parts become
greater and greater until ultimately none of the parts would be the same. As the level of
comparison becomes more precise, the concept that no two objects are exactly alike is
realized.
2.0 QUALITY
The word quality is often used indiscriminately for many different meanings. Quality can be
defined as “fitness for use,” “customer satisfaction,” “doing things right the first time,” or
“zero defects.” These definitions are acceptable because quality can refer to degrees of
excellence. Webster’s dictionary defines quality as “an inherent characteristic, property or
attribute.” QReview will define quality as a characteristic of a product or process that can be
measured. Quality control is the science of keeping these characteristics or qualities within
certain bounds.
In a manufacturing or service environment, there are two major categories of quality: quality
of design and quality of conformance. A poorly designed product will not function properly
regardless of how well it meets its specifications. Conversely, a product that does not
conform to excellent design specifications will not properly perform its intended function.
QReview 14
2.1 Design Quality
Design quality refers to the level of characteristics that the designers specify for a
product. High-grade materials, tight tolerances, special features and high performance
are characteristics associated with the term, high quality product.
An example of design quality may be shown by the comparison between an expensive
automobile and an economy model. A Ferrari and a Ford Escort are compared. Both
cars will perform the same basic function of getting from point A to point B. Each will
generally conform to its design specification. The owners in both cases may be satisfied
with the way their cars are put together. However, that is where the similarity ends. The
Escort owner does not expect his car to go 150 mph, have leather seats and have twelve
coats of paint, or be highly responsive. The Ferrari owner expects these characteristics
or qualities.
The cost of making a product will usually rise as more characteristics are specified to
increase product performance, improve comfort, improve ease of use and make the
product look better. High-grade materials usually command a premium price. However, in
many cases, increased competition creates an atmosphere of finding ways to make
better and less expensive designs. This is true for products such as computers, VCRs
and televisions.
The reliability of a product must be considered in the design stage. Reliability is the
probability that a product will perform its intended function, without failure, for a specified
length of time. Reliability is dependent on the basic design, the quality of materials and
the quality of components that go into the final product. To achieve the required reliability,
designers may need to specify higher priced components. This may translate to higher
prices but also higher value for the consumer.
Many products command a premium price because they provide value to the consumer.
Others may be expensive because of their role as status symbols. Expensive products
do not always contribute to better product performance or customer satisfaction. This is
particularly true in the software industry. Many low priced applications work just as well
and sometimes better than expensive ones.
The designer may receive input from various sources when determining the level of
design quality. In addition to the designer’s own ideas, input concerning product
performance, materials to be used and various product characteristics may be received
from management, marketing, sales, other engineering organizations or directly from
customers. The final design specification may or may not be what the designer had in
mind.
Although some quality engineers and other quality professionals get involved with product
design, their time and effort is usually spent in designing and maintaining systems to
measure and control process and product characteristics after the design is complete. A
challenge to quality engineers is to implement the statistical techniques used in
manufacturing during the design stage. The goals would be to enhance product design
by eliminating problems early in the design process to ensure the ease of manufacturing.
Chapter 2 Basic Quality Concepts 15
2.2 Conformance Quality
After the level of design quality has been determined, the product characteristics are
formed into drawings and specifications. The manufacturing engineers will use the
drawings and specifications to develop manufacturing specifications and design the
operations necessary to produce the product. This includes the floor layout, machinery,
test sets, tools and other equipment. A plan for the number of employees required may
also be included. The quality engineer works with the manufacturing engineer to make
the quality system and maintenance of conformance quality an integral part of the
manufacturing process. Any product checks, process checks or quality improvement
activities should be an inherent part of the process. Conformance quality may be defined
as the degree of adherence of the product characteristics to the design drawings and
specifications. The objective of a quality program is to have a system that will measure
and control the degree of product and process conformance in the most economical
way.
The quality engineer will determine what product or process characteristics are to be
checked. The quality engineer will also determine the type of data to be collected, the
corrective actions required, and the statistical tools or other techniques to be used.
3.0 QUALITY SYSTEMS
A quality system is a mechanism that coordinates and maintains the activities needed to
ensure that the characteristics of products, processes or services are within certain
bounds. A quality system involves every part of an organization that directly or indirectly
affects these activities. Typically, the quality system is documented in a quality manual and
in the associated documents that specify procedures and standards.
3.1 Basic Elements in a Quality System
There are three basic elements in a quality system: Quality Management, Quality Control,
and Quality Assurance.
•Quality Management: Quality management is the means of implementing and
carrying out quality policy. They perform goal planning and manage quality control and
quality assurance activities. Quality management is responsible for seeing that all
quality goals and objectives are implemented and that corrective actions have been
achieved. They periodically review the quality system to ensure effectiveness and to
identify and review any deficiencies.
•Quality Control: The term quality control describes a variety of activities. It
encompasses all techniques and activities of an organization that continuously
monitor and improve the conformance of products, processes or services to
specifications. Quality control may also include the review of processes and
specifications and make recommendations for their improvement. Quality control
aims to eliminate causes of unsatisfactory performance by identifying and helping to
eliminate or at least narrow the sources of variation. Quality control has the same
meaning as variation control of product characteristics.
The objective of a quality control program is to define a system in which products
QReview 16
meet design requirements and checks and feedback for corrective actions and
process improvements. Quality control activities should also include the selecting
and rating of suppliers to ensure that purchased products meet quality requirements.
•Quality Assurance: The term quality assurance describes all the planned and
systematic actions necessary to assure that a product or service will satisfy the
specified requirements. Usually this takes the form of an independent final inspection.
The distinction between quality control and quality assurance is stated in an
ANSI/ASQ standard: “Quality control has to do with making quality what it should be,
and quality assurance has to do with making sure quality is what it should be.” The
quality assurance function should represent the customer and be independent of the
quality control function, which is an integral part of the manufacturing operation.
3.2 The Quality Audit
A quality audit is an independent assessment comparing the various management and
quality activities to a standard. The word independent implies that the person performing
the audit is not associated with the activity being audited. There are two general types of
audits: management and quality system audits and product specific audits.
The types of quality audits:
•Management and Quality System Audit - Manufacturing
•Management and Quality System Audit - Software
•Management and Quality System Audit - Service
•Product Specific Audit - Manufacturing
•Product Specific Audit - Software
•Activity Specific Audit - Service
Companies use first-party audits to evaluate their own performance. Second-party
audits are conducted by a customer on a supplier. Audits conducted by completely
separate companies, with no personal stake in the audited company, are labeled thirdparty
audits. Auditors in a third-party audit are usually registrars that audit to international
standards such as the ISO 9000 series.
A customer will usually combine a quality system audit with a product-specific audit.
Third-party audits are usually reviews of the management and quality system and not
product specific.
Quality audits assess that:
•Quality plans and procedures are in place
•Documents are controlled to avoid misuse
•Standards and regulations are being followed
•The data system provides accurate and adequate information
•Problems are addressed and corrective action is taken
•Products conform to requirements
Audits should be conducted on a scheduled basis. There should be no surprises to the
organization being audited. This policy enables all those involved to organize their
workloads and assign personnel to assist in the audit. The audit should not disrupt any
processes or work being done.
Chapter 2 Basic Quality Concepts 17
3.3 Quality Systems Diagram
Incoming
Materials
Incoming
Materials
Inspection?
Inspection
Inspection
Make
Operation
Quality
Control
Quality
Control
Make
Operation
Feedback Loop Feedback Loop
Manufacturing Department
Manufacturing Department
Report Quality Level
Quality
Assurance
Customer
Supplier Certification,
Supplier Rating Program
Quality Management Documentation
Corrective Action
4.0 QUALITY SYSTEMS STANDARDS
4.1 The International Organization for Standardization (ISO)
The International Organization for Standardization (ISO) was founded in 1946 to develop
a common set of manufacturing, trade, and communications standards. It is based in
Geneva, Switzerland. ISO promotes standards to facilitate international trade. The
American Standards Institute (ANSI) is the United States representative to ISO. ISO has
a full time staff plus technical committees, subcommittees, working groups and ad hoc
groups. ISO receives input from governments, industry and other interested parties. ISO
develops and promotes but does not implement or enforce international standards.
Quality systems or quality programs in one form or another have existed since the
beginning of factories. Companies developed and implemented a quality system that
worked for them. Although there was an abundance of literature on quality system
elements, quality tools and statistical techniques, a standard did not exist until 1987. In
that year, an ISO technical committee developed and published the ISO 9000 series of
standards that define the minimum requirements for an adequate quality system. The
ISO 9000 series standards were revised in 1994.
QReview 18
The ISO 9000 series and the joint ANSI/ASQ Q9000 series of standards are used as a
tool to establish whether companies are using a quality system that will ensure their
ability to meet product quality and service performance requirements. The ISO 9000
series and the ANSI/ASQ Q9000 series of standards are technically identical.
The ISO 9000 series standards are intended to assure that a company has at least a
minimum adequate management and quality system in place. These generic standards
provide quality management guidance as well as quality assurance guidance and
requirements that apply to all types and sizes of companies. An ISO registration does not
necessarily mean that a company produces products that always meet their design
intent. The ISO audit is an assessment of the management and quality system and does
not address product issues. There are no standards for product quality in the ISO 9000
series standards.
Over eighty countries have adopted the ISO 9000 series as a national standard. All
standards developed by ISO are voluntary. There are no legal requirements to adopt
them. However countries and companies often adopt and attach legal requirements to
ISO standards. Each member country has an accreditation board that adopts the ISO
9000 series standards and certifies independent registrars. The Registrar Accreditation
Board (ANSI/RAB) is the USA-recognized accreditation board.
Registrars are third party companies that evaluate quality systems for conformity to ISO
9000 standards. The registrars conduct audits and issue certificates to organizations that
conform to the standards. The audit will involve most departments and functions in an
organization. The focus of the audits is on documentation, implementation and
effectiveness. Organizations are certified by the registrars and not by ISO or an
accreditation board. ISO-conforming companies are allowed to display the registrar’s
mark on advertising and stationary as evidence of registration. Unfortunately, not all
registrars are created equal so there may be significant differences in the way audits are
conducted and findings assessed.
The ANSI/RAB sets standards and specifies training for registrars but does not maintain
a list of registered companies. There are private companies that maintain lists with
voluntary information provided by registrars.
4.2 The ISO 9000 (ANSI/ASQ Q9000) Series Standards
Five sets of ISO 9000 series standards are currently published:
•ISO 9000 (ANSI/ASQ Q9000): Quality Management and Quality Assurance
Standards. This standard explains fundamental concepts and defines key terms.
•ISO 9001 (ANSI/ASQ Q9001): Quality Systems - Model for Quality Assurance in
Design, Development, Production, Installation and Servicing. ISO 9001 is the most
comprehensive in the series.
•ISO 9002 (ANSI/ASQ Q9002): Quality Systems - Model for Quality Assurance in
Production and installation. This standard is identical to ISO 9001 except that it does
not address Design Control.
Chapter 2 Basic Quality Concepts 19
•ISO 9003 (ANSI/ASQ Q9003): Quality Systems - Model for Quality Assurance in
Final Inspection and Test. This is the least comprehensive standard in the series.
•ISO 9004 (ANSI/ASQ Q9004): Quality Management and Quality System Elements.
This standard provides guidelines for a company to use in developing and
implementing a quality system. It is not used to conduct audits.
ISO 9001 or 9002 registration provides confidence to customers and potential customers
that an adequate quality system is in place and that quality and service requirements will
likely be met. An ISO auditor will gather preliminary information on the company to be
audited and then determine if the company is actually doing what it has documented.
Except for certain requirements, such as a quality manual, ISO 9000 audits are not
prescriptive. Organizations determine for themselves the best way to comply with the
standards.
4.2 ISO 9001 (ANSI/ASQ Q9001) Quality System Standards
Quality systems elements per ISO 9001 (ANSI/ASQ Q9001) are outlined below:
(The numbers, 4.1, 4.2, etc. are the ISO 9001 element numbers)
•4.1 Management responsibility: Management shall define and document quality
policy, objectives and goals for, and commitment to, quality. Responsibilities and
authority for various functions shall be defined. Management shall review the quality
system at appropriate intervals.
•4.2 Quality System: The establishment and maintenance of a documented quality
system as a means of ensuring that product conforms to specified requirements.
This includes work instructions, inspection and test instructions, and also a quality
manual.
•4.3 Contract review: Contract review includes determining and documenting
customer requirements and ensuring that contract requirements are met.
•4.4 Design control: The establishment and maintenance of procedures to control
and verify the design of the product in order to ensure that the specified requirements
are met.
•4.5 Document and Data control: The establishment and maintenance of
procedures to control all documents and data. This includes periodic reviews and
removal of obsolete documents. Appropriate documents must be made available to
those needing them.
•4.6 Purchasing: The purchasing organization shall ensure that purchased product
conforms to specified requirements. This includes the maintenance of an approved
supplier list and a procedure for qualifying and disqualifying suppliers.
•4.7 Control of Customer Supplied Product: The establishment and maintenance
of procedures for verification, storage, and maintenance of customer supplied
product provided for incorporation into the final product.
QReview 20
•4.8 Product Identification and Traceability: The establishment and maintenance of
procedures for identifying product from applicable drawings, specifications or other
documents, during all stages of production, delivery and installation.
•4.9 Process Control: The establishment of procedures for monitoring and control of
process and product characteristics. Also, identify those special processes whose
results cannot be verified by subsequent operations.
•4.10 Inspection and Testing: The verification of incoming products, in-process and
final inspection and testing. Identification of nonconforming product and the
maintenance of records is also included.
•4.11 Inspection, Measuring and Test Equipment: Identify, control, calibrate and
maintain appropriate inspection, measuring and test equipment. Establish, document,
and maintain calibration procedures and records.
•4.12 Inspection and Test Status: The inspection and test status of product shall be
identified by using markings, authorized stamps, tags, labels, routing cards,
inspection records, computer databases or other suitable means.
•4.13 Control of Nonconforming Product: The establishment and maintenance of
procedures to ensure that product that does not conform to specified requirements is
prevented from inadvertent use or installation.
•4.14 Corrective and Preventive Action: The establishment and maintenance of
procedures to investigate causes of nonconforming product and prevent recurrences.
This also includes the application of controls to ensure that corrective actions are
taken and that they are effective.
•4.15 Handling, Storage, Packaging, Preservation and Delivery: The
establishment and maintenance of procedures to prevent damage and deterioration,
provide storage security, and proper transportation.
•4.16 Control of Quality Records: The establishment and maintenance of
procedures for identification, collection, indexing, filing, storage, maintenance and
disposition of quality records. Quality records are maintained to demonstrate
achievement of the required quality and the effective operation of the quality system.
•4.17 Internal Quality Audits: The implementation of an internal quality audit
program to verify whether quality activities comply with planned arrangements and to
determine the effectiveness of the quality system. A schedule of audit activities is part
of the requirements.
•4.18 Training: The establishment and maintenance of procedures for identifying the
training needs and provide for the training of all personnel performing quality related
activities. Establish curriculum of required courses and maintain records.
Chapter 2 Basic Quality Concepts 21
•4.19 Servicing: Where appropriate, establish and maintain procedures for
performing and verifying that servicing meets the specified requirements.
Responsibilities are to be clearly assigned and agreed upon by suppliers, distributors
and users.
•4.20 Statistical Techniques: Applications may include market analysis, product
design, process control, inspection and test procedures, data analysis and
performance assessment. Statistical quality and process control activities within the
manufacturing departments include designing the facilities to make it easy to produce
defect-free products. Also included are definitions of the characteristics to check,
how to check, what to do if a defect is found and how to record data. The creation of
a feedback loop to generate problem awareness and prevent future occurrences is
an important part of the process. Various statistical techniques are used to control
both the process and product characteristics.
5.0 FUNDAMENTAL PRINCIPLES
5.1 Statistical Quality Control and Statistical Process Control
Statistical quality control (SQC) and statistical process control (SPC) are scientific
methods for analyzing data and keeping the process within certain boundaries. Many
statistical tools, such as control charts, Pareto analysis, design of experiments,
regression analysis and acceptance sampling may be used. SQC methods can be
applied to anything that is possible to express in the form of numbers. SQC is concerned
with product characteristics and SPC is concerned with process characteristics.
The word statistical means having to do with numbers, or more specifically, with drawing
conclusions from numbers. The word quality means much more than the goodness or
defectiveness of the product. It refers to the qualities or characteristics of the product or
process being studied. The word control means to keep something within boundaries or
to regulate it so that its outcome may be predicted with some degree of accuracy. In a
manufacturing operation, conformance quality characteristics are to be kept within
certain bounds. Taken together, the words Statistical Quality Control or Statistical
Process Control mean:
Statistical - With the help of numbers or data,
Quality or Process - The characteristics of a product or process are studied,
Control - To make them behave the way they are intended to behave.
The most important element in statistical quality control is the feedback loop between the
quality control function and the make operation. In statistical process control, the
feedback loop is between the process control function and the device that regulates the
process or the person responsible for adjustments. Continuous feedback and the
appropriate corrective action drive statistical quality control and statistical process control
to achieve the desired results. Both SQC and SPC seem to work best when the checks
and feedback loops are automated and human intervention is minimized.
QReview 22
5.2 The Law of Large Numbers
The law of large numbers is a mathematical concept that says: Individual occurrences
are unpredictable and group occurrences are predictable. The number of marriages,
births and deaths in the United States next year can be predicted with some degree of
accuracy, but exactly who will get married, who will be born or who will die cannot be
predicted. This concept can be applied to a manufacturing process. For example, a
statistical study can determine that products from a certain process are on average two
percent defective. However, in any sample, the specific parts that will be defective cannot
be predicted.
5.3 Central Limit Theorem
The central limit theorem states that a group of averages of sample size 4, 5 or 6 units
always tends to follow the pattern of a normal distribution. If the population distribution
leans to one side or the other, the distribution of sample averages from that population
will tend to be symmetrical and have normal variation. The central limit theorem is what
legitimizes the use of variables control charts regardless of the actual population
distribution. The normal distribution and control charts will be reviewed in a subsequent
chapter.
5.4 Data
Webster's dictionary defines the word data as a plural noun portraying factual
information such as measurements or statistics used as a basis for reasoning,
discussion, or calculation. Data are categorized in two ways: attribute data and variables
data. Data classified as good/bad, pass/fail, go/no-go, etc., are called attribute or
discrete data. When actual measurements are taken and recorded, the data are called
variables or continuous data. In many cases (but not all cases), variables data will be
distributed in a symmetrical bell-shaped curve called the normal curve. The known
areas under the curve allow for inferences to be made about the process with relatively
small amounts of information. By using the known areas under the curve, the fraction of
measurements that will lie between, above, or below certain values can be predicted
with a high degree of accuracy.
5.5 Distributions
Because of variation between measurements of individual parts, data when plotted will
form a distribution. A distribution model describes how the data are dispersed. A plot of
the distribution will show a center value and the range of measurements. The variation
between data values will usually be quite small and follow a natural pattern. Large
variation indicates that the pattern is unnatural. This may be attributed to external or
assignable causes. When a pattern is unnatural, the cause should be investigated and
eliminated. Statistical techniques such as control charts are used to identify the
unnatural patterns. A plot of the actual data showing the data values versus the number
of occurrences is called a histogram. A mathematical estimate of the shape of the
histogram is called a frequency distribution. Distributions are formed because everything
in the world that can be measured exhibits variation. If the measuring instrument is very
precise, it will be discovered that like the snowflake, no two measurements are exactly
the same.
Chapter 2 Basic Quality Concepts 23
5.6 Precision and Accuracy
In addition to the objects that are measured, the measuring instrument itself has
variability. Two different instruments may measure the same parts and yield different
results. In many cases, measuring parts a second time with the same instruments will
give a different result. A low value of the instrument’s standard deviation indicates
greater precision. When an instrument is accurate but not precise, the measurements
are distributed about the true value within the acceptable range. When an instrument is
precise but not accurate, the measurements are clustered close together but at a
distance from the true value. When an instrument is both accurate and precise, the data
are clustered close together around the true value.
5.7 Statistical Techniques
Many statistical techniques are used in quality control and inspection. Listed below are
the most widely used statistical methods.
•Histograms •Acceptance Sampling
•Statistical Inference •Process Capability Analysis
•Hypothesis Testing •Reliability
•Decision Errors •Regression & Correlation
•Statistical Process Control •Design of Experiments
•Control Charts •Pareto Analysis
Basic probability is the foundation of statistical methods. Its importance cannot be
understated. To really understand statistical methods, an understanding of probability
concepts is essential.
It must be stressed that the application of statistical techniques alone will not fix any
problems or improve product or process quality. Statistical techniques are tools to
identify problems and provide data for decisions. For problems to be fixed or
improvements to be made, some action must be taken. The action may be automated
or conducted by humans, but nevertheless, action must be taken. Automated actions
work best in manufacturing situations.
The chapters that follow cover the essential elements of the various statistical
techniques. QReview presents the material from an engineering point of view and
assumes that the student has some previous background in statistical concepts and
methodology. Mathematical derivations and in-depth explanations are not included.
These are tasks for textbooks on mathematical statistics. The subject of metrology and
calibration is covered in chapter twelve.
6.0 HUMAN FACTORS
Human factors focuses on human beings and how they interact with equipment, products,
environments, other people and day to day activities. The goal of human factors in a
company is to match the workplace and management approach to the capabilities, needs
and limitations of people. The part of human factors addressing human and machine
interactions is called ergonomics.
QReview 24
The first thrust of human factors was to study the workplace and design the environment and
machinery to better accommodate the person doing the job. This goal has been expanded to
include the way management manages and the involvement of employees in the decision
making process.
In the 1930s, a study was conducted at Western Electric’s Hawthorne Works in Chicago,
Illinois. Employees complained of bad lighting in an assembly area. New lighting was
installed that brightened the area. The employees seemed to be much happier and as
expected, productivity increased. It was decided to increase the light intensity and measure
productivity. As the intensity increased, productivity increased. The first assumption was that
brighter lights contribute to employee morale and higher productivity. One day the lights were
dimmed; however, productivity did not drop. Productivity kept increasing as the light intensity
decreased. The study team concluded that it was not the lighting that contributed to
increased productivity, but the mere fact that somebody was paying attention to them. This
study is called the Hawthorne study and the conclusion is referred to as the Hawthorne
effect.
In an authoritarian company, the boss gives orders and the employees carry them out. In
these situations, employees often complain about job satisfaction. In recent years, some
companies are shedding the boss-worker image by allowing managers to assume the
responsibility of coach. Workers are referred to as production associates. The coach’s job is
to coordinate the work and motivate employees. The employees, whether they are engineers
or production associates, become part of the team, not just someone who carries out
orders. This approach yields significant rewards for the company and the employee.
Company objectives and tasks are carried out in an efficient manner and the employee, by
making a contribution, feels good about a job well done.
Human conflict can be minimized but never eliminated. There may be times when
engineering decisions are overruled or employee suggestions not adopted. In these cases,
the findings should be documented for possible review at a later date, then the engineer or
employee can move on to the next assignment. In any conflict, whether it is between
management and employees, between management and unions, or between employees,
good judgement must be used.
Juran and Deming agree that the majority of problems arise from flaws in the system and not
because of employee motivation or employee errors. Deming has stated that 80% of
problems are management or system related. When the system is the problem, the output
will not meet specifications regardless of employee effort. The outcome is substandard
products and employee dissatisfaction. The situation is changing as management
approaches are changing. In many companies, management and system problems are
being addressed and the outcome is very positive. Management is investing in new
equipment, advanced employee training and respect for employee judgement. This results in
employee satisfaction, high quality products and increased productivity.
In recent years, computers have changed the way people work. The computer has become
an indispensable tool. Former mundane tasks are easier to accomplish and in some cases
even fun. In addition to increasing productivity at the workplace, computers and the computer
industry have made a significant impact in all areas of human activity.
Chapter 2 Basic Quality Concepts 25
7.0 A BRIEF HISTORY OF QUALITY
1550 BC - Egyptian royal cubit was standardized. It was about 20.63'' ±.02''.
1654 - Blaise Pascal with Pierre de Fermat developed the theory of probability. They were
prompted by the inquiries of gamblers seeking inside information to help them win at
cards and dice.
Early 1800's - Concepts of tolerances and gauging were developed in American armories.
1861-1865, Civil War - Tolerance and gauging concepts were used to mass produce arms
with interchangeability of parts.
After the Civil War - Tolerance and gauging concepts were used and improved by
companies such as Singer and McCormick.
1916 - Ford Motor Company developed systematic material handling, machine tool design,
factory layout and final inspection. Automobile production went from ten thousand
cars in 1909 to sixty thousand in 1916. The price decreased from $850 to $350 per
car.
1917 - The first published use of the term Control of Quality appeared in Industrial
Management in an article by G. S. Radford.
1922 - G. S. Radford published the first book on Quality Control: The Control of Quality of
Manufacturing.
1924 - Dr. Walter A. Shewhart of AT&T developed the concept of control charts. Dr.
Shewhart is referred to as the father of statistical quality control.
1925 - Harold F. Dodge of AT&T developed sampling concepts and terminology used in
acceptance sampling.
1931 - Dr. Walter A. Shewhart published Economic Control of Manufactured Product. This
was the first in-depth book on statistical quality control.
1941-1945 - The United States was involved in World War II. The war generated the first
extensive use of statistical concepts. U.S. Government suppliers were required to
use statistical quality control. The government sponsored many statistics and quality
control training classes.
1941 - Harold F. Dodge and Harry G. Romig published a unique book on sampling
procedures. Single and Double Sampling Inspection Tables. These tables were the
forerunners of the military standard sampling tables.
1944 - The Dodge-Romig Sampling Tables were published. OC curves, lot sizes and
sample sizes are given by AOQL. The tables include single and double sampling
plans.
1946 - The ASQC was organized and George Edwards of AT&T became the first president.
1947 - ASQC created the Shewhart medal to recognize outstanding contributors to the
QReview 26
quality profession.
1950 - Joseph M. Juran and W. Edwards Deming taught statistical methods and statistical
quality control to the Japanese.
1950 - Military Standard for Sampling by Attributes was published as Mil-Std 105A.
1951 - Joseph M. Juran published the first edition of Quality Control Handbook.
1968 - ASQC administers the first examination for Certified Quality Engineer. There were
147 successful candidates.
1970's - The focus was on continuous improvement and employee involvement.
1980's - The emphasis was on quality of design and design for manufacturability. Computers
were used extensively in all aspects of quality.
1987 - The International Organization for Standardization (ISO) establishes ISO 9000 Series
Quality System Standards.
1987 - Congress established the Malcolm Baldrige National Quality Award to promote quality
awareness, to recognize significant quality achievements of U.S. companies, and to
call public attention to successful quality strategies. The award is not for specific
products or services.
1988 - The first Baldrige award winners were announced. They were Globe Metallurgical Inc.
(small business), Motorola Inc. (manufacturing) and Westinghouse Electric
Corporation’s Commercial Nuclear Fuel Division (manufacturing).
1989 - Military Standard for Sampling by Attributes is reissued as Mil-Std 105E.
1990's - Quality Concepts were extended to service industries. Emphasis is on total quality
management (TQM) and customer satisfaction.
1993 - ANSI/ASQC Z1.4 Sampling Tables and Procedures replaced Mil-Std 105E.
1994 - ISO 9000 Standards were revised (for clarification?). ANSI/ASQC series standards
renamed from Q90 series to Q9000 series.
1996 - Eight thousand U.S. companies have achieved ISO registration since its inception.
Eight percent of all companies that are ISO registered are located in North America.
Forty six percent are located in the United Kingdom.
1996 - Since the ASQC certification program began, more than 55,000 people have become
certified in one or more of the certification areas.
1997 - The American Society for Quality Control (ASQC) officially changed its name to the
American Society for Quality (ASQ).
CHAPTER 2
BASIC QUALITY CONCEPTS
1.0 The Nature of Variation
2.0 Quality
3.0 Quality Systems
4.0 Quality Systems Standards
5.0 Fundamental Principles
6.0 Human Factors
7.0 A Brief History of Quality
“Well! I've often seen a cat without a grin, but a grin without a
cat! It's the most curious thing I ever seen in all my life.”
Alice
Chapter 2 Basic Quality Concepts 13
BASIC QUALITY CONCEPTS
1.0 THE NATURE OF VARIATION
While standing on a street corner observing the passing traffic, two cars of the same make
and model stop at a traffic light. Both cars are the same color, have Goodyear tires and have
a luggage rack on the trunk. At first glance, the cars seem identical. Upon closer observation,
differences are detected. Both cars have Goodyear tires, but are the tires the same size?
Are the radios the same? Is the upholstery the same? There are many characteristics for
comparison.
The closer an item is examined, the more differences are found. No two objects are exactly
alike. All things differ by some degree. Some variation may be obvious, but other variation
may require precise measuring equipment to detect.
All manufactured parts exhibit variation. It is the concept of variation that forms the basis of
probability, statistics and quality control. Consider a part that is produced by a punch press.
As raw material is fed into the press, the machine punches out the parts. Eventually the
press will produce a large number of similar parts. A visual check of the diameters may
reveal no differences among the parts. If the diameter is measured with a scale, some
differences will be found. If the measurements are made with a micrometer, a greater
number of differences will be detected. Each level of comparison or method of measurement
reveals a greater amount of variation.
As the measurements increase in precision, the differences among the parts become
greater and greater until ultimately none of the parts would be the same. As the level of
comparison becomes more precise, the concept that no two objects are exactly alike is
realized.
2.0 QUALITY
The word quality is often used indiscriminately for many different meanings. Quality can be
defined as “fitness for use,” “customer satisfaction,” “doing things right the first time,” or
“zero defects.” These definitions are acceptable because quality can refer to degrees of
excellence. Webster’s dictionary defines quality as “an inherent characteristic, property or
attribute.” QReview will define quality as a characteristic of a product or process that can be
measured. Quality control is the science of keeping these characteristics or qualities within
certain bounds.
In a manufacturing or service environment, there are two major categories of quality: quality
of design and quality of conformance. A poorly designed product will not function properly
regardless of how well it meets its specifications. Conversely, a product that does not
conform to excellent design specifications will not properly perform its intended function.
QReview 14
2.1 Design Quality
Design quality refers to the level of characteristics that the designers specify for a
product. High-grade materials, tight tolerances, special features and high performance
are characteristics associated with the term, high quality product.
An example of design quality may be shown by the comparison between an expensive
automobile and an economy model. A Ferrari and a Ford Escort are compared. Both
cars will perform the same basic function of getting from point A to point B. Each will
generally conform to its design specification. The owners in both cases may be satisfied
with the way their cars are put together. However, that is where the similarity ends. The
Escort owner does not expect his car to go 150 mph, have leather seats and have twelve
coats of paint, or be highly responsive. The Ferrari owner expects these characteristics
or qualities.
The cost of making a product will usually rise as more characteristics are specified to
increase product performance, improve comfort, improve ease of use and make the
product look better. High-grade materials usually command a premium price. However, in
many cases, increased competition creates an atmosphere of finding ways to make
better and less expensive designs. This is true for products such as computers, VCRs
and televisions.
The reliability of a product must be considered in the design stage. Reliability is the
probability that a product will perform its intended function, without failure, for a specified
length of time. Reliability is dependent on the basic design, the quality of materials and
the quality of components that go into the final product. To achieve the required reliability,
designers may need to specify higher priced components. This may translate to higher
prices but also higher value for the consumer.
Many products command a premium price because they provide value to the consumer.
Others may be expensive because of their role as status symbols. Expensive products
do not always contribute to better product performance or customer satisfaction. This is
particularly true in the software industry. Many low priced applications work just as well
and sometimes better than expensive ones.
The designer may receive input from various sources when determining the level of
design quality. In addition to the designer’s own ideas, input concerning product
performance, materials to be used and various product characteristics may be received
from management, marketing, sales, other engineering organizations or directly from
customers. The final design specification may or may not be what the designer had in
mind.
Although some quality engineers and other quality professionals get involved with product
design, their time and effort is usually spent in designing and maintaining systems to
measure and control process and product characteristics after the design is complete. A
challenge to quality engineers is to implement the statistical techniques used in
manufacturing during the design stage. The goals would be to enhance product design
by eliminating problems early in the design process to ensure the ease of manufacturing.
Chapter 2 Basic Quality Concepts 15
2.2 Conformance Quality
After the level of design quality has been determined, the product characteristics are
formed into drawings and specifications. The manufacturing engineers will use the
drawings and specifications to develop manufacturing specifications and design the
operations necessary to produce the product. This includes the floor layout, machinery,
test sets, tools and other equipment. A plan for the number of employees required may
also be included. The quality engineer works with the manufacturing engineer to make
the quality system and maintenance of conformance quality an integral part of the
manufacturing process. Any product checks, process checks or quality improvement
activities should be an inherent part of the process. Conformance quality may be defined
as the degree of adherence of the product characteristics to the design drawings and
specifications. The objective of a quality program is to have a system that will measure
and control the degree of product and process conformance in the most economical
way.
The quality engineer will determine what product or process characteristics are to be
checked. The quality engineer will also determine the type of data to be collected, the
corrective actions required, and the statistical tools or other techniques to be used.
3.0 QUALITY SYSTEMS
A quality system is a mechanism that coordinates and maintains the activities needed to
ensure that the characteristics of products, processes or services are within certain
bounds. A quality system involves every part of an organization that directly or indirectly
affects these activities. Typically, the quality system is documented in a quality manual and
in the associated documents that specify procedures and standards.
3.1 Basic Elements in a Quality System
There are three basic elements in a quality system: Quality Management, Quality Control,
and Quality Assurance.
•Quality Management: Quality management is the means of implementing and
carrying out quality policy. They perform goal planning and manage quality control and
quality assurance activities. Quality management is responsible for seeing that all
quality goals and objectives are implemented and that corrective actions have been
achieved. They periodically review the quality system to ensure effectiveness and to
identify and review any deficiencies.
•Quality Control: The term quality control describes a variety of activities. It
encompasses all techniques and activities of an organization that continuously
monitor and improve the conformance of products, processes or services to
specifications. Quality control may also include the review of processes and
specifications and make recommendations for their improvement. Quality control
aims to eliminate causes of unsatisfactory performance by identifying and helping to
eliminate or at least narrow the sources of variation. Quality control has the same
meaning as variation control of product characteristics.
The objective of a quality control program is to define a system in which products
QReview 16
meet design requirements and checks and feedback for corrective actions and
process improvements. Quality control activities should also include the selecting
and rating of suppliers to ensure that purchased products meet quality requirements.
•Quality Assurance: The term quality assurance describes all the planned and
systematic actions necessary to assure that a product or service will satisfy the
specified requirements. Usually this takes the form of an independent final inspection.
The distinction between quality control and quality assurance is stated in an
ANSI/ASQ standard: “Quality control has to do with making quality what it should be,
and quality assurance has to do with making sure quality is what it should be.” The
quality assurance function should represent the customer and be independent of the
quality control function, which is an integral part of the manufacturing operation.
3.2 The Quality Audit
A quality audit is an independent assessment comparing the various management and
quality activities to a standard. The word independent implies that the person performing
the audit is not associated with the activity being audited. There are two general types of
audits: management and quality system audits and product specific audits.
The types of quality audits:
•Management and Quality System Audit - Manufacturing
•Management and Quality System Audit - Software
•Management and Quality System Audit - Service
•Product Specific Audit - Manufacturing
•Product Specific Audit - Software
•Activity Specific Audit - Service
Companies use first-party audits to evaluate their own performance. Second-party
audits are conducted by a customer on a supplier. Audits conducted by completely
separate companies, with no personal stake in the audited company, are labeled thirdparty
audits. Auditors in a third-party audit are usually registrars that audit to international
standards such as the ISO 9000 series.
A customer will usually combine a quality system audit with a product-specific audit.
Third-party audits are usually reviews of the management and quality system and not
product specific.
Quality audits assess that:
•Quality plans and procedures are in place
•Documents are controlled to avoid misuse
•Standards and regulations are being followed
•The data system provides accurate and adequate information
•Problems are addressed and corrective action is taken
•Products conform to requirements
Audits should be conducted on a scheduled basis. There should be no surprises to the
organization being audited. This policy enables all those involved to organize their
workloads and assign personnel to assist in the audit. The audit should not disrupt any
processes or work being done.
Chapter 2 Basic Quality Concepts 17
3.3 Quality Systems Diagram
Incoming
Materials
Incoming
Materials
Inspection?
Inspection
Inspection
Make
Operation
Quality
Control
Quality
Control
Make
Operation
Feedback Loop Feedback Loop
Manufacturing Department
Manufacturing Department
Report Quality Level
Quality
Assurance
Customer
Supplier Certification,
Supplier Rating Program
Quality Management Documentation
Corrective Action
4.0 QUALITY SYSTEMS STANDARDS
4.1 The International Organization for Standardization (ISO)
The International Organization for Standardization (ISO) was founded in 1946 to develop
a common set of manufacturing, trade, and communications standards. It is based in
Geneva, Switzerland. ISO promotes standards to facilitate international trade. The
American Standards Institute (ANSI) is the United States representative to ISO. ISO has
a full time staff plus technical committees, subcommittees, working groups and ad hoc
groups. ISO receives input from governments, industry and other interested parties. ISO
develops and promotes but does not implement or enforce international standards.
Quality systems or quality programs in one form or another have existed since the
beginning of factories. Companies developed and implemented a quality system that
worked for them. Although there was an abundance of literature on quality system
elements, quality tools and statistical techniques, a standard did not exist until 1987. In
that year, an ISO technical committee developed and published the ISO 9000 series of
standards that define the minimum requirements for an adequate quality system. The
ISO 9000 series standards were revised in 1994.
QReview 18
The ISO 9000 series and the joint ANSI/ASQ Q9000 series of standards are used as a
tool to establish whether companies are using a quality system that will ensure their
ability to meet product quality and service performance requirements. The ISO 9000
series and the ANSI/ASQ Q9000 series of standards are technically identical.
The ISO 9000 series standards are intended to assure that a company has at least a
minimum adequate management and quality system in place. These generic standards
provide quality management guidance as well as quality assurance guidance and
requirements that apply to all types and sizes of companies. An ISO registration does not
necessarily mean that a company produces products that always meet their design
intent. The ISO audit is an assessment of the management and quality system and does
not address product issues. There are no standards for product quality in the ISO 9000
series standards.
Over eighty countries have adopted the ISO 9000 series as a national standard. All
standards developed by ISO are voluntary. There are no legal requirements to adopt
them. However countries and companies often adopt and attach legal requirements to
ISO standards. Each member country has an accreditation board that adopts the ISO
9000 series standards and certifies independent registrars. The Registrar Accreditation
Board (ANSI/RAB) is the USA-recognized accreditation board.
Registrars are third party companies that evaluate quality systems for conformity to ISO
9000 standards. The registrars conduct audits and issue certificates to organizations that
conform to the standards. The audit will involve most departments and functions in an
organization. The focus of the audits is on documentation, implementation and
effectiveness. Organizations are certified by the registrars and not by ISO or an
accreditation board. ISO-conforming companies are allowed to display the registrar’s
mark on advertising and stationary as evidence of registration. Unfortunately, not all
registrars are created equal so there may be significant differences in the way audits are
conducted and findings assessed.
The ANSI/RAB sets standards and specifies training for registrars but does not maintain
a list of registered companies. There are private companies that maintain lists with
voluntary information provided by registrars.
4.2 The ISO 9000 (ANSI/ASQ Q9000) Series Standards
Five sets of ISO 9000 series standards are currently published:
•ISO 9000 (ANSI/ASQ Q9000): Quality Management and Quality Assurance
Standards. This standard explains fundamental concepts and defines key terms.
•ISO 9001 (ANSI/ASQ Q9001): Quality Systems - Model for Quality Assurance in
Design, Development, Production, Installation and Servicing. ISO 9001 is the most
comprehensive in the series.
•ISO 9002 (ANSI/ASQ Q9002): Quality Systems - Model for Quality Assurance in
Production and installation. This standard is identical to ISO 9001 except that it does
not address Design Control.
Chapter 2 Basic Quality Concepts 19
•ISO 9003 (ANSI/ASQ Q9003): Quality Systems - Model for Quality Assurance in
Final Inspection and Test. This is the least comprehensive standard in the series.
•ISO 9004 (ANSI/ASQ Q9004): Quality Management and Quality System Elements.
This standard provides guidelines for a company to use in developing and
implementing a quality system. It is not used to conduct audits.
ISO 9001 or 9002 registration provides confidence to customers and potential customers
that an adequate quality system is in place and that quality and service requirements will
likely be met. An ISO auditor will gather preliminary information on the company to be
audited and then determine if the company is actually doing what it has documented.
Except for certain requirements, such as a quality manual, ISO 9000 audits are not
prescriptive. Organizations determine for themselves the best way to comply with the
standards.
4.2 ISO 9001 (ANSI/ASQ Q9001) Quality System Standards
Quality systems elements per ISO 9001 (ANSI/ASQ Q9001) are outlined below:
(The numbers, 4.1, 4.2, etc. are the ISO 9001 element numbers)
•4.1 Management responsibility: Management shall define and document quality
policy, objectives and goals for, and commitment to, quality. Responsibilities and
authority for various functions shall be defined. Management shall review the quality
system at appropriate intervals.
•4.2 Quality System: The establishment and maintenance of a documented quality
system as a means of ensuring that product conforms to specified requirements.
This includes work instructions, inspection and test instructions, and also a quality
manual.
•4.3 Contract review: Contract review includes determining and documenting
customer requirements and ensuring that contract requirements are met.
•4.4 Design control: The establishment and maintenance of procedures to control
and verify the design of the product in order to ensure that the specified requirements
are met.
•4.5 Document and Data control: The establishment and maintenance of
procedures to control all documents and data. This includes periodic reviews and
removal of obsolete documents. Appropriate documents must be made available to
those needing them.
•4.6 Purchasing: The purchasing organization shall ensure that purchased product
conforms to specified requirements. This includes the maintenance of an approved
supplier list and a procedure for qualifying and disqualifying suppliers.
•4.7 Control of Customer Supplied Product: The establishment and maintenance
of procedures for verification, storage, and maintenance of customer supplied
product provided for incorporation into the final product.
QReview 20
•4.8 Product Identification and Traceability: The establishment and maintenance of
procedures for identifying product from applicable drawings, specifications or other
documents, during all stages of production, delivery and installation.
•4.9 Process Control: The establishment of procedures for monitoring and control of
process and product characteristics. Also, identify those special processes whose
results cannot be verified by subsequent operations.
•4.10 Inspection and Testing: The verification of incoming products, in-process and
final inspection and testing. Identification of nonconforming product and the
maintenance of records is also included.
•4.11 Inspection, Measuring and Test Equipment: Identify, control, calibrate and
maintain appropriate inspection, measuring and test equipment. Establish, document,
and maintain calibration procedures and records.
•4.12 Inspection and Test Status: The inspection and test status of product shall be
identified by using markings, authorized stamps, tags, labels, routing cards,
inspection records, computer databases or other suitable means.
•4.13 Control of Nonconforming Product: The establishment and maintenance of
procedures to ensure that product that does not conform to specified requirements is
prevented from inadvertent use or installation.
•4.14 Corrective and Preventive Action: The establishment and maintenance of
procedures to investigate causes of nonconforming product and prevent recurrences.
This also includes the application of controls to ensure that corrective actions are
taken and that they are effective.
•4.15 Handling, Storage, Packaging, Preservation and Delivery: The
establishment and maintenance of procedures to prevent damage and deterioration,
provide storage security, and proper transportation.
•4.16 Control of Quality Records: The establishment and maintenance of
procedures for identification, collection, indexing, filing, storage, maintenance and
disposition of quality records. Quality records are maintained to demonstrate
achievement of the required quality and the effective operation of the quality system.
•4.17 Internal Quality Audits: The implementation of an internal quality audit
program to verify whether quality activities comply with planned arrangements and to
determine the effectiveness of the quality system. A schedule of audit activities is part
of the requirements.
•4.18 Training: The establishment and maintenance of procedures for identifying the
training needs and provide for the training of all personnel performing quality related
activities. Establish curriculum of required courses and maintain records.
Chapter 2 Basic Quality Concepts 21
•4.19 Servicing: Where appropriate, establish and maintain procedures for
performing and verifying that servicing meets the specified requirements.
Responsibilities are to be clearly assigned and agreed upon by suppliers, distributors
and users.
•4.20 Statistical Techniques: Applications may include market analysis, product
design, process control, inspection and test procedures, data analysis and
performance assessment. Statistical quality and process control activities within the
manufacturing departments include designing the facilities to make it easy to produce
defect-free products. Also included are definitions of the characteristics to check,
how to check, what to do if a defect is found and how to record data. The creation of
a feedback loop to generate problem awareness and prevent future occurrences is
an important part of the process. Various statistical techniques are used to control
both the process and product characteristics.
5.0 FUNDAMENTAL PRINCIPLES
5.1 Statistical Quality Control and Statistical Process Control
Statistical quality control (SQC) and statistical process control (SPC) are scientific
methods for analyzing data and keeping the process within certain boundaries. Many
statistical tools, such as control charts, Pareto analysis, design of experiments,
regression analysis and acceptance sampling may be used. SQC methods can be
applied to anything that is possible to express in the form of numbers. SQC is concerned
with product characteristics and SPC is concerned with process characteristics.
The word statistical means having to do with numbers, or more specifically, with drawing
conclusions from numbers. The word quality means much more than the goodness or
defectiveness of the product. It refers to the qualities or characteristics of the product or
process being studied. The word control means to keep something within boundaries or
to regulate it so that its outcome may be predicted with some degree of accuracy. In a
manufacturing operation, conformance quality characteristics are to be kept within
certain bounds. Taken together, the words Statistical Quality Control or Statistical
Process Control mean:
Statistical - With the help of numbers or data,
Quality or Process - The characteristics of a product or process are studied,
Control - To make them behave the way they are intended to behave.
The most important element in statistical quality control is the feedback loop between the
quality control function and the make operation. In statistical process control, the
feedback loop is between the process control function and the device that regulates the
process or the person responsible for adjustments. Continuous feedback and the
appropriate corrective action drive statistical quality control and statistical process control
to achieve the desired results. Both SQC and SPC seem to work best when the checks
and feedback loops are automated and human intervention is minimized.
QReview 22
5.2 The Law of Large Numbers
The law of large numbers is a mathematical concept that says: Individual occurrences
are unpredictable and group occurrences are predictable. The number of marriages,
births and deaths in the United States next year can be predicted with some degree of
accuracy, but exactly who will get married, who will be born or who will die cannot be
predicted. This concept can be applied to a manufacturing process. For example, a
statistical study can determine that products from a certain process are on average two
percent defective. However, in any sample, the specific parts that will be defective cannot
be predicted.
5.3 Central Limit Theorem
The central limit theorem states that a group of averages of sample size 4, 5 or 6 units
always tends to follow the pattern of a normal distribution. If the population distribution
leans to one side or the other, the distribution of sample averages from that population
will tend to be symmetrical and have normal variation. The central limit theorem is what
legitimizes the use of variables control charts regardless of the actual population
distribution. The normal distribution and control charts will be reviewed in a subsequent
chapter.
5.4 Data
Webster's dictionary defines the word data as a plural noun portraying factual
information such as measurements or statistics used as a basis for reasoning,
discussion, or calculation. Data are categorized in two ways: attribute data and variables
data. Data classified as good/bad, pass/fail, go/no-go, etc., are called attribute or
discrete data. When actual measurements are taken and recorded, the data are called
variables or continuous data. In many cases (but not all cases), variables data will be
distributed in a symmetrical bell-shaped curve called the normal curve. The known
areas under the curve allow for inferences to be made about the process with relatively
small amounts of information. By using the known areas under the curve, the fraction of
measurements that will lie between, above, or below certain values can be predicted
with a high degree of accuracy.
5.5 Distributions
Because of variation between measurements of individual parts, data when plotted will
form a distribution. A distribution model describes how the data are dispersed. A plot of
the distribution will show a center value and the range of measurements. The variation
between data values will usually be quite small and follow a natural pattern. Large
variation indicates that the pattern is unnatural. This may be attributed to external or
assignable causes. When a pattern is unnatural, the cause should be investigated and
eliminated. Statistical techniques such as control charts are used to identify the
unnatural patterns. A plot of the actual data showing the data values versus the number
of occurrences is called a histogram. A mathematical estimate of the shape of the
histogram is called a frequency distribution. Distributions are formed because everything
in the world that can be measured exhibits variation. If the measuring instrument is very
precise, it will be discovered that like the snowflake, no two measurements are exactly
the same.
Chapter 2 Basic Quality Concepts 23
5.6 Precision and Accuracy
In addition to the objects that are measured, the measuring instrument itself has
variability. Two different instruments may measure the same parts and yield different
results. In many cases, measuring parts a second time with the same instruments will
give a different result. A low value of the instrument’s standard deviation indicates
greater precision. When an instrument is accurate but not precise, the measurements
are distributed about the true value within the acceptable range. When an instrument is
precise but not accurate, the measurements are clustered close together but at a
distance from the true value. When an instrument is both accurate and precise, the data
are clustered close together around the true value.
5.7 Statistical Techniques
Many statistical techniques are used in quality control and inspection. Listed below are
the most widely used statistical methods.
•Histograms •Acceptance Sampling
•Statistical Inference •Process Capability Analysis
•Hypothesis Testing •Reliability
•Decision Errors •Regression & Correlation
•Statistical Process Control •Design of Experiments
•Control Charts •Pareto Analysis
Basic probability is the foundation of statistical methods. Its importance cannot be
understated. To really understand statistical methods, an understanding of probability
concepts is essential.
It must be stressed that the application of statistical techniques alone will not fix any
problems or improve product or process quality. Statistical techniques are tools to
identify problems and provide data for decisions. For problems to be fixed or
improvements to be made, some action must be taken. The action may be automated
or conducted by humans, but nevertheless, action must be taken. Automated actions
work best in manufacturing situations.
The chapters that follow cover the essential elements of the various statistical
techniques. QReview presents the material from an engineering point of view and
assumes that the student has some previous background in statistical concepts and
methodology. Mathematical derivations and in-depth explanations are not included.
These are tasks for textbooks on mathematical statistics. The subject of metrology and
calibration is covered in chapter twelve.
6.0 HUMAN FACTORS
Human factors focuses on human beings and how they interact with equipment, products,
environments, other people and day to day activities. The goal of human factors in a
company is to match the workplace and management approach to the capabilities, needs
and limitations of people. The part of human factors addressing human and machine
interactions is called ergonomics.
QReview 24
The first thrust of human factors was to study the workplace and design the environment and
machinery to better accommodate the person doing the job. This goal has been expanded to
include the way management manages and the involvement of employees in the decision
making process.
In the 1930s, a study was conducted at Western Electric’s Hawthorne Works in Chicago,
Illinois. Employees complained of bad lighting in an assembly area. New lighting was
installed that brightened the area. The employees seemed to be much happier and as
expected, productivity increased. It was decided to increase the light intensity and measure
productivity. As the intensity increased, productivity increased. The first assumption was that
brighter lights contribute to employee morale and higher productivity. One day the lights were
dimmed; however, productivity did not drop. Productivity kept increasing as the light intensity
decreased. The study team concluded that it was not the lighting that contributed to
increased productivity, but the mere fact that somebody was paying attention to them. This
study is called the Hawthorne study and the conclusion is referred to as the Hawthorne
effect.
In an authoritarian company, the boss gives orders and the employees carry them out. In
these situations, employees often complain about job satisfaction. In recent years, some
companies are shedding the boss-worker image by allowing managers to assume the
responsibility of coach. Workers are referred to as production associates. The coach’s job is
to coordinate the work and motivate employees. The employees, whether they are engineers
or production associates, become part of the team, not just someone who carries out
orders. This approach yields significant rewards for the company and the employee.
Company objectives and tasks are carried out in an efficient manner and the employee, by
making a contribution, feels good about a job well done.
Human conflict can be minimized but never eliminated. There may be times when
engineering decisions are overruled or employee suggestions not adopted. In these cases,
the findings should be documented for possible review at a later date, then the engineer or
employee can move on to the next assignment. In any conflict, whether it is between
management and employees, between management and unions, or between employees,
good judgement must be used.
Juran and Deming agree that the majority of problems arise from flaws in the system and not
because of employee motivation or employee errors. Deming has stated that 80% of
problems are management or system related. When the system is the problem, the output
will not meet specifications regardless of employee effort. The outcome is substandard
products and employee dissatisfaction. The situation is changing as management
approaches are changing. In many companies, management and system problems are
being addressed and the outcome is very positive. Management is investing in new
equipment, advanced employee training and respect for employee judgement. This results in
employee satisfaction, high quality products and increased productivity.
In recent years, computers have changed the way people work. The computer has become
an indispensable tool. Former mundane tasks are easier to accomplish and in some cases
even fun. In addition to increasing productivity at the workplace, computers and the computer
industry have made a significant impact in all areas of human activity.
Chapter 2 Basic Quality Concepts 25
7.0 A BRIEF HISTORY OF QUALITY
1550 BC - Egyptian royal cubit was standardized. It was about 20.63'' ±.02''.
1654 - Blaise Pascal with Pierre de Fermat developed the theory of probability. They were
prompted by the inquiries of gamblers seeking inside information to help them win at
cards and dice.
Early 1800's - Concepts of tolerances and gauging were developed in American armories.
1861-1865, Civil War - Tolerance and gauging concepts were used to mass produce arms
with interchangeability of parts.
After the Civil War - Tolerance and gauging concepts were used and improved by
companies such as Singer and McCormick.
1916 - Ford Motor Company developed systematic material handling, machine tool design,
factory layout and final inspection. Automobile production went from ten thousand
cars in 1909 to sixty thousand in 1916. The price decreased from $850 to $350 per
car.
1917 - The first published use of the term Control of Quality appeared in Industrial
Management in an article by G. S. Radford.
1922 - G. S. Radford published the first book on Quality Control: The Control of Quality of
Manufacturing.
1924 - Dr. Walter A. Shewhart of AT&T developed the concept of control charts. Dr.
Shewhart is referred to as the father of statistical quality control.
1925 - Harold F. Dodge of AT&T developed sampling concepts and terminology used in
acceptance sampling.
1931 - Dr. Walter A. Shewhart published Economic Control of Manufactured Product. This
was the first in-depth book on statistical quality control.
1941-1945 - The United States was involved in World War II. The war generated the first
extensive use of statistical concepts. U.S. Government suppliers were required to
use statistical quality control. The government sponsored many statistics and quality
control training classes.
1941 - Harold F. Dodge and Harry G. Romig published a unique book on sampling
procedures. Single and Double Sampling Inspection Tables. These tables were the
forerunners of the military standard sampling tables.
1944 - The Dodge-Romig Sampling Tables were published. OC curves, lot sizes and
sample sizes are given by AOQL. The tables include single and double sampling
plans.
1946 - The ASQC was organized and George Edwards of AT&T became the first president.
1947 - ASQC created the Shewhart medal to recognize outstanding contributors to the
QReview 26
quality profession.
1950 - Joseph M. Juran and W. Edwards Deming taught statistical methods and statistical
quality control to the Japanese.
1950 - Military Standard for Sampling by Attributes was published as Mil-Std 105A.
1951 - Joseph M. Juran published the first edition of Quality Control Handbook.
1968 - ASQC administers the first examination for Certified Quality Engineer. There were
147 successful candidates.
1970's - The focus was on continuous improvement and employee involvement.
1980's - The emphasis was on quality of design and design for manufacturability. Computers
were used extensively in all aspects of quality.
1987 - The International Organization for Standardization (ISO) establishes ISO 9000 Series
Quality System Standards.
1987 - Congress established the Malcolm Baldrige National Quality Award to promote quality
awareness, to recognize significant quality achievements of U.S. companies, and to
call public attention to successful quality strategies. The award is not for specific
products or services.
1988 - The first Baldrige award winners were announced. They were Globe Metallurgical Inc.
(small business), Motorola Inc. (manufacturing) and Westinghouse Electric
Corporation’s Commercial Nuclear Fuel Division (manufacturing).
1989 - Military Standard for Sampling by Attributes is reissued as Mil-Std 105E.
1990's - Quality Concepts were extended to service industries. Emphasis is on total quality
management (TQM) and customer satisfaction.
1993 - ANSI/ASQC Z1.4 Sampling Tables and Procedures replaced Mil-Std 105E.
1994 - ISO 9000 Standards were revised (for clarification?). ANSI/ASQC series standards
renamed from Q90 series to Q9000 series.
1996 - Eight thousand U.S. companies have achieved ISO registration since its inception.
Eight percent of all companies that are ISO registered are located in North America.
Forty six percent are located in the United Kingdom.
1996 - Since the ASQC certification program began, more than 55,000 people have become
certified in one or more of the certification areas.
1997 - The American Society for Quality Control (ASQC) officially changed its name to the
American Society for Quality (ASQ).
没有找到相关结果
已邀请:
RSS Feed
0 个回复