Chapter 7 Review Questions
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Chapter 7:
Design for Quality and Product Excellence
Review Questions
1.
Describe the steps of the product design and development process
Idea Generation: New or redesigned product ideas should incorporate
customer needs and expectations. However, true innovations often transcend
customers’ expressed desires, simply because customers may not know what
they like until they have it.
Preliminary Concept Development: In this phase, new ideas are studied for
feasibility, addressing such questions as: Will the product meet customers’
requirements? Can it be manufactured economically with high quality?
Objective criteria are required for measuring and testing the attributes
associated with these questions.
Product/Process Development: If an idea survives the concept stage—and
many do not—the actual design process begins by evaluating design
alternatives and determining engineering specifications for all materials,
components, and parts. This phase usually includes prototype testing, in
which a model (real or simulated) is constructed to test the product’s
physical properties or use under actual operating conditions, as well as
consumer reactions to the prototypes. Concurrently, companies develop, test,
and standardize the processes that will be used in manufacturing the product
or delivering the service, which includes selecting the appropriate
technology, materials, and suppliers and performing pilot runs to verify
results.
Full-Scale Production: Once the design is approved and the production
process has been set up, the company releases the product to manufacturing
or service delivery teams.
Market Introduction: The product is distributed to customers.
Market Evaluation: Deming and Juran both advocated an ongoing product
development process that relies on market evaluation and customer feedback
to initiate continuous improvements.
2.
Discuss the importance of and impediments to reducing the time for product
development.
Define Opportunities: Understand the purpose of the process to be
developed by goal statements, generation plans, and resource identification.
Measure Customer Needs: Understand the outputs required of the new
process by examining customer needs and competitive analysis.
Explore Design Concepts: Use creative techniques to develop alternative
concepts and evaluate those ideas by validating customer requirements.
Develop Detailed Design: Turn the concept into reality by the use of process
and product designs, pilot programs, and testing.
Implement Detailed Design: Fully deploy the new process and assess its
value against the desired outcome.
3.
What is concurrent engineering? What benefits does it have?
A process in which all major functions involved with bringing a product to
market are continuously involved with product development from
conception through sales. decreases product development time and also the
time to market, leading to improved productivity and reduced costs.
4.
What is Design for Six Sigma (DFSS)? Explain the four basic elements of
DFSS and the various tools and methodologies that comprise this body of
knowledge.
Design for Six Sigma (DFSS) represents a structured approach to product
development and a set of tools and methodologies for ensuring that goods
and services will meet customer needs and achieve performance objectives
and that the processes used to make and deliver them achieve high levels of
quality.
Concept Development: Concept development focuses on creating and
developing a product idea and determining its functionality based on
customer requirements, technological capabilities, and economic realities.
Detailed Design: Detailed design focuses on developing specific
requirements and design parameters such as specifications and tolerances to
ensure that the product fulfills the functional requirements of the concept.
Design Optimization: Design optimization seeks to refine designs to identify
and eliminate potential failures, achieve high reliability, and ensure that it
can be easily manufactured, assembled, or delivered in an environmentally
responsible manner.
Design Verification: Design verification ensures that the quality level and
reliability requirements of the product are achieved.
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5.
Explain concept development and innovation. Describe the importance of
innovation and creativity in concept development.
Concept development is the process of applying scientific, engineering, and
business knowledge to produce a basic functional design that meets both
customer needs and manufacturing or service delivery requirements.
Developing new concepts requires innovation and creativity. Innovation
involves the adoption of an idea, process, technology, product, or business
model that is either new or new to its proposed application. The outcome of
innovation is a discontinuous or breakthrough change and results in new and
unique goods and services that delight customers and create a competitive
advantage.
They support the development of novel and distinctive solutions that address
market demands.
6.
What is the purpose of detailed design?
Detailed design focuses on establishing technical requirements and
specifications, which represent the transition from a designer’s concept to a
producible design, while also ensuring that it can be produced economically,
efficiently, and with high quality.
7.
Explain the concept and the principal benefits of QFD.
A powerful tool for establishing technical design requirements that meet
customer needs and deploying them in subsequent production activities is
quality function deployment. QFD is simply a planning process to guide the
design, manufacturing, and marketing of goods by integrating the voice of
the customer throughout the organization. Through QFD, every design,
manufacturing, and control decision is made to meet the expressed needs of
customers. QFD benefits companies through improved communication and
teamwork between all constituencies in the value chain, such as between
marketing and design, between design and manufacturing, and between
manufacturing and quality control.
8.
Outline the process of building the House of Quality. What departments and
functions within the company should be involved in each step of the
process?
Building the House of Quality consists of six basic steps:
Identify customer requirements.
Identify technical requirements.
Relate the customer requirements to the technical requirements.
Conduct an evaluation of competing products or services.
Evaluate technical requirements and develop targets.
QFD uses a set of linked matrixes to ensure that the voice of the customer is
carried throughout the production/delivery process (see Figure 7.2). Because
of the visual structure, these are called “houses of quality.” The first house of
quality relates the voice of the customer (customer requirements) to a
product’s overall technical requirements; the second relates technical
requirements to component requirements; the third relates component
requirements to process operations; and the final one relates process
operations to quality control plans. In this fashion, every design and
production decision, including the design of production processes and the
choice of quality measurements, is traceable to the voice of the customer. If
applied correctly, this process ensures that the resulting product meets
customer needs
9.
Determine which technical requirements to deploy in the remainder of the
production/delivery process.
The characteristics that have strong relationships to customer needs, have
poor competitive performance or have strong selling points are selected.
These critical characteristics are to be translated into the language of each
function in design and production processes so that proper actions are taken
and controls are maintained to meet the customer's needs. Other
characteristics, which are not so critical to quality, do not need special
attention to that extent.
10.
Explain and give an example of nominal specifications and tolerances in
both manufacturing and service.
Manufacturing specifications consist of nominal dimensions and tolerances.
Nominal refers to the ideal dimension or the target value that manufacturing
seeks to meet; tolerance is the permissible variation, recognizing the
difficulty of meeting a target consistently. Tolerances are necessary because
not all parts can be produced exactly to nominal specifications because of
natural variations (common causes) in production processes due to the “5
Ms”: men and women, materials, machines, methods, and measurement. The
“ratio” notation (0.514/0.588) denotes the permissible range of the
dimension. Unless otherwise stated, the nominal dimension is the midpoint.
Thus, the specification of 0.514/0.588 may be interpreted as a nominal
dimension of 0.551 with a tolerance of plus or minus 0.037. Usually, this is
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written as 0.551 ± 0.037. The manufacturing-based definition of quality
conformance to specifications is based on such tolerances.
11.
Explain the Taguchi loss function and how it is used in process and tolerance
design.
An equation used to quantify the financial loss incurred due
to deviations in product quality from the target value. It is
based on the principle that any deviation from the ideal or
target value increases costs associated with poor quality,
customer dissatisfaction, or product failures. Taguchi
measured quality as the variation from the target value of a
design specification and then translated that variation into
an economic “loss function” that expresses the cost of
variation in monetary terms. In mathematical terms, Taguchi
assumes that losses can be approximated by a quadratic
function so that larger deviations from the target correspond
to increasingly larger losses. where x is any actual value of
the quality characteristic and k is some constant. Thus, (x −
T) represents the deviation from the target and the loss
increases by the square of the deviation. This is called the
Taguchi loss function
12.
Define reliability. Explain the definition thoroughly.
is defined as the probability that a product, piece of equipment, or system
performs its intended function for a stated period of time under specified
operating conditions. This definition has four important elements:
probability, time, performance, and operating conditions.
First, reliability is defined as a probability, that is, a value between 0 and 1.
Thus, it is a numerical measure with a precise meaning. Expressing
reliability in this way provides a valid basis for the comparison of different
designs for products and systems. For example, a reliability of 0.97 indicates
that, on average, 97 of 100 items will perform their function for a given
period of time and under certain operating conditions. Often reliability is
expressed as a percentage simply for descriptive purposes.
The second element of the definition is time. Clearly, a device having a
reliability of 0.97 for 1,000 hours of operation is inferior to one having the
same reliability for 5,000 hours of operation, assuming that the mission of
the device is long life.
Performance is the third element and refers to the objective for which the
product or system was made. The term failure is used when expectations of
performance of the intended function are not met. Two types of failures can
occur: functional failure at the start of product life due to manufacturing or
material defects such as a missing connection or a faulty component, and
reliability failure after some period of use.
13.
What is the difference between a functional failure and a reliability failure?
A functional failure happens at the start of product life due to manufacturing
or material defects as reliability failure is a failure after some period of use.
Reliability failure could include a device not working, the operation of the
device is not stable, or the performance of a device worsening. The failure
must be clearly defined in order for it to be fixed because the type of failure
can vary greatly.
14.
What is the difference between inherent reliability and achieved reliability?
Reliability engineers distinguish between inherent reliability, which is the
predicted reliability determined by the design of the product or process, and
achieved reliability, which is the actual reliability observed during use.
Achieved reliability can be less than the inherent reliability due to the effects
of the manufacturing process and the conditions of use.
15.
What is the definition of failure rate? How is it measured?
In practice, reliability is determined by the number of failures per unit time
during the duration under consideration (called the failure rate, λ). Some
products must be scrapped and replaced upon failure; others can be repaired.
16.
Explain the product life characteristics curve and its implications for
reliability and quality control.
Product life characteristics curve, and shows the instantaneous failure rate at
any point in time. (This is often referred to as a “bathtub” curve for obvious
reasons.) We see that the failure rate is rather high at the beginning of
product life, then levels out over a long period of time, and then eventually
begins to increase. This is a typical phenomenon for electronic components
such as semiconductors and consumer products such as light bulbs.
17.
What is a reliability function? Explain how to determine it.
Reliability is the probability that an item will not fail over a given period of
time. We express this using the reliability function, R(T), which
characterizes the probability of survival to time T. It has the following
properties:
R(0) = 1
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As T becomes larger, R(T) is non-increasing
R(T) = 1 − F(T), where F(T) is the cumulative probability
distribution of failures
Thus, to tabulate a reliability function, we simply need to know the
cumulative probability distribution of failures over time.
18.
Explain how to compute the reliability of series, parallel, and series-parallel
systems.
Systems of components may be configured in series, in parallel, or in some
mixed combination. Block diagrams are useful ways to represent system
configurations where blocks represent functional components or subsystems.
Engineers can use reliability calculations to predict performance and
evaluate alternative designs to optimize performance within cost, size, or
other constraints. Redundant components are designed in a parallel system
configuration as illustrated in Figure 7.21. In such a system, failure of an
individual component is less critical than in series systems; the system will
successfully operate as long as one component functions.
19.
What is robust design? Explain why it is important for both consumers and
manufacturers.
. Robust design refers to designing goods and services that are insensitive to
variations in manufacturing processes and when consumers use them.
Robust design is facilitated by the design of experiments to identify optimal
levels for nominal dimensions and other tools to minimize failures, reduce
defects during the manufacturing process, facilitate assembly and
disassembly (for both the manufacturer and the customer), and improve
reliability.
20.
What is design failure mode and effects analysis (DFMEA)? Provide a
simple example illustrating the concept.
Design failure mode and effects analysis (DFMEA), often simply called
failure mode and effects analysis (FMEA). DFMEA was used by NASA in
the 1960s and became popular in the automotive industry in the 1980s.
Recently, it has found increasing application in health care. A Joint
Commission for Accreditation of Healthcare Organizations standard lists
DFMEA as a risk assessment tool, referring to it as “fault mode and effect
analysis.”
21.
What is fault tree analysis? How does it differ from DFMEA?
Fault Tree Analysis (FTA), sometimes called cause and effect tree analysis,
is a method to describe combinations of conditions or events that can lead to a
failure. In effect, it is a way to drill down and identify causes associated with
failures and is a good complement to DFMEA. It is particularly useful for
identifying failures that occur only as a result of multiple events occurring
simultaneously. A cause and effect tree is composed of conditions or events
connected by “and” gates and “or” gates
22.
How can product design affect manufacturability? Explain the concept and
importance of design for manufacturability.
It involves optimizing the design of your product for its manufacturing and
assembly process and merging the design requirements of the product with
its production method. Employing Design for Manufacturing tactics reduces
the cost and difficulty of producing a product while maintaining its quality.
23.
Summarize the key design practices for high quality in manufacturing and
assembly.
Placing all components on the topside of the board
Grouping similar components whenever possible
Maintaining a 0.60-inch clearance for insertable components
24.
Discuss environmental responsibility issues relating to product design facing
businesses today.
Environmental concerns have an unprecedented impact on product and
process designs. Hundreds of millions of home and office appliances are
disposed of each year. The problem of what to do with obsolete computers is
a growing design and technological waste problem today. Pressures from
environmental groups clamoring for “socially responsive” designs, states
and municipalities that are running out of space for landfills, and consumers
who want the most for their money all cause designers and managers to look
carefully at the concept of design-for-environment, or DFE.
25.
Describe the basic approach to design for excellence (DFX)
DFE is the explicit consideration of environmental concerns during the
design of products and processes and includes such practices as designing
for recyclability and disassembly.
26.
Explain the purpose of design reviews and how they facilitate product
development.
The purpose of a design review is to stimulate discussion, raise questions, and
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generate new ideas and solutions to help designers anticipate problems before they
occur. Generally, a design review is conducted in three major stages: preliminary,
intermediate, and final. The preliminary design review establishes early
communication between marketing, engineering, manufacturing, and purchasing
personnel and provides better coordination of their activities. It usually involves
higher levels of management and concentrates on strategic issues in design that
relate to customer requirements and thus the ultimate quality of the product.
27.
Describe different forms of product testing.
accelerated life testing
high accelerated life testing