Design for Six Sigma (DFSS) focuses on methodologies to ensure products meet customer needs and performance requirements through a structured process. Key concepts include defining customer requirements, design development, and quality function deployment. Innovation, creativity, and reliable design are emphasized, alongside tools like statistical modeling for performance prediction and design for manufacturability.

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Chapter 8
Design for Six Sigma
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Design for Six Sigma
Design for Six Sigma (DFSS) represents a set of tools and

2. methodologies used in product development 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 six sigma capability.
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DFSS Methodology: DMADV
Define – establish goals
Measure – identify voice of the customer and define CTQ
measures
Analyze – propose and evaluate high-level design concepts
Design – design the details of the product and processes used to
produce it
Verify – ensure that the product performs as expected and meets
customer requirements
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3. Features of DFSS
A high-level architectural view of the design
Use of CTQs with well-defined technical requirements
Application of statistical modeling and simulation approaches
Predicting defects, avoiding defects, and performance
prediction using analysis methods
Examining the full range of product performance using variation
analysis of subsystems and components
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Concept Development
Concept development – 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.
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4. Innovation
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 that results in new and unique goods and services that
delight customers and create competitive advantage.
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Types of Innovation
1. An entirely new category of product (for example, Twitter)
2. First of its type on the market in a product category already
in existence (for

5. example, the DVD player)
3. A significant improvement in existing technology (for
example, the Blu-ray
disc technology)
4. A modest improvement to an existing product (for example,
the latest iPad)
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Creativity
Creativity is seeing things in new or novel ways.
Creativity tools, such as brainstorming and “brainwriting,” are
designed to help change the context in which one views a
problem or opportunity, thereby leading to fresh perspectives.
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6. Understanding the Voice of the Customer
What is the product (good or service) intended to do?
Technical requirements, sometimes called design
characteristics, translate the voice of the customer into
technical language, specifically into measures of product
performance.
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Design Development
Design development - the process of applying scientific,
engineering, and business knowledge to produce a basic
functional design that meets all CTQs – both customer needs
and manufacturing or service delivery requirements.
Design development usually starts with a high-level design and
then moves toward more detail design of components or
subsystems.
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7. Axiomatic Design
Axiomatic design (developed by Dr. Nam Suh at MIT) is based
on the premise that good design is governed by laws similar to
those in natural science.
1. Independence Axiom: good design occurs when the
functional requirements of the design are independent of one
another.
2. Information Axiom: good design corresponds to minimum
complexity.
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Quality Function Deployment (QFD)
QFD is a planning process to guide the design, manufacturing,
and marketing of goods by integrating the voice of the customer
throughout the organization.

8. Through QFD, every design, manufacturing, and control
decision is made to meet the expressed needs of customers.
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The House of Quality
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Building the House of Quality
Identify customer requirements.
Identify technical requirements.
Relate the customer requirements to the technical requirements.

9. Conduct an evaluation of competing products or services.
Evaluate technical requirements and develop targets.
Determine which technical requirements to deploy in the
remainder of the production/delivery process.
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Example: Designing a Fitness Center
Identify customer requirements
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Example

10. Identify technical requirements
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Example
Relate customer requirements to technical requirements
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Example
Conduct competitive evaluation

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Example
Develop deployment targets
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The Four Linked Houses of Quality
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Detailed Design and Analysis
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.
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13. Tolerance Design
Tolerance design involves determining the permissible variation
in a dimension.
Narrow tolerances tend to raise manufacturing costs but they
also increase the interchangeability of parts within the plant and
in the field, product performance, durability, and appearance.
Wide tolerances increase material utilization, machine
throughput, and labor productivity, but have a negative impact
on product characteristics
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Traditional Economic View of Conformance to Specifications
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14. The Taguchi Loss Function
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.
Taguchi assumes that losses can be approximated by a quadratic
function so that larger deviations from target correspond to
increasingly larger losses.
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Nominal-Is-Best Loss Function
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15. Expected Loss
A measure of variation that is independent of specification
limits, showing the average loss over the distribution of output
the target.
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Design for Manufacturability (DFM)
Design for manufacturability (DFM) is the process of designing
a product for efficient production at the highest level of quality.
DFM is intended to prevent
product designs that simplify assembly operations but require
more complex and expensive components,
designs that simplify component manufacture while

16. complicating the assembly process, and
designs that are simple and inexpensive to produce but difficult
or expensive to service or support
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Design Reviews
Design review – a structured review of design progress intended
to stimulate discussion, raise questions, and generate new ideas
and solutions to help designers anticipate problems before they
occur
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17. DFMEA
Design failure mode and effects analysis (DFMEA) –
identification of all the ways in which a failure can occur, to
estimate the effect and seriousness of the failure, and to
recommend corrective design actions.
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DFMEA Elements
Failure modes
Effect of failures on customers
Severity, likelihood of occurrence, and detection rating (risk
priority)
Potential causes of failure
Corrective actions or controls
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18. Scoring Rubric for DFMEA
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Reliability Prediction
Reliability - the ability of a product to perform as expected over
time
Formally 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

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Types of Failures
Functional failure – failure that occurs at the start of product
life due to manufacturing or material detects
Reliability failure – failure after some period of use
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Types of Reliability
Inherent reliability – determined by product design
Achieved reliability – observed during use
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20. Mathematics of Reliability
Reliability is determined by the number of failures per unit time
during the duration under consideration (called the failure
rate,λ).
For items that must be replaced when a failure occurs, the
reciprocal of the failure rate (having dimensions of time units
per failure) is called the mean time to failure (MTTF).
For repairable items, the mean time between failures (MTBF) is
used.
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Computing the Failure Rate
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21. Product Life Characteristics Curve
Many electronic components commonly exhibit a high, but
decreasing, failure rate early in their lives, followed by a period
of a relatively constant failure rate, and ending with an
increasing failure rate.
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Reliability Function
The reliability function, R(T), characterizes the probability of
survival to time T.
Properties:
1. R(0) = 1
2. As T becomes larger, R(T) is non-increasing

22. 3. R(T) = 1 - F(T), where F(T) is the cumulative probability
distribution of failures
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Exponential Reliability
Exponential probability density function of failures
f(t) = le-lt for t ≥ 0
Probability of failure from (0, T)
F(t) = 1 – e-lT
Probability of failure during the interval (t1 , t2)
F(t2) - F(t1) = e-λ(t2 –t1)
Reliability function (probability of survival)
R(T) = 1 – F(T) = e-lT
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23. Hazard Function
The hazard function is the probability that an item that has not
failed up to time t will fail immediately after time t .
For the exponential distribution, the hazard function is
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System Reliability
Series system: all components must function or the system will
fail.
the reliability of the system is the product of the individual
reliabilities
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24. Series Systems with Exponential Reliability
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System Reliability
Parallel system: uses redundancy.
The system will successfully operate
as long as one component functions.
The reliability is calculated as

25. If all components have identical reliabilities R, then
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Series-Parallel Systems
To compute the reliability of systems with both series and
parallel components, decompose the system into smaller series
and/or parallel subsets of component, compute the reliabilities
of these subsets, and continue until you are left with a simple
series or parallel system.
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26. Series-Parallel Example
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Design Optimization
Robust design refers to designing goods and services that are
insensitive to variation in manufacturing processes and when
consumers use them.
Robust design is facilitated by design of experiments and
alternative Taguchi methods

27. Design for Reliability
Reliability requirements are determined during the product
design phase.
Techniques used to improve designs and optimize reliability
include:
Standardization
Redundancy
Physics of failure
Design Verification
Design verification is necessary to ensure that designs meet
customer requirements and can be produced to specifications.
The purpose of verification is to validate product and process
designs and to prepare procedures and documentation for full-
scale production rollout.
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28. Reliability Evaluation
Life testing – running devices until they fail, is designed to
measure the distribution of failures to better understand and
eliminate their causes.
Accelerated life testing involves overstressing components to
reduce the time to failure and find weaknesses.
Environmental testing involves testing products for temperature,
shock-resistance, and other environmental conditions.
Burn-in, (component stress testing), involves exposing
integrated circuits to elevated temperatures in order to force
latent defects to occur.
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Simulation
Simulation is an approach to building a logical model of a real

29. business system and experimenting with it to obtain insight
about the behavior of the system or to evaluate the impact of
changes in assumptions or potential improvements to it.
Process simulation models the dynamics and behavior over time
of interacting elements in a system such as a manufacturing
facility or a call center.
Monte-Carlo simulation is based on repeated sampling from
probability distributions of model inputs to characterize the
distributions of model outputs, usually in a spreadsheet
environment.
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13 Statistical Thinking and Applications
MGMT 434/534: Quality Management
Chapter 8 Assignment; 10 points
Due: Monday, April 30, 6:15 pm
DIRECTIONS: Answer the following questions, TYPED, on
separate paper.
In order to receive full credit, you must show or explain how

30. you got your answers. Use complete sentences when
appropriate. Summarizing extensive results in lists or tables
may also be useful. All graphics/characters are to be computer
generated.
You may include the assignment questions along with your
answers, but this is not required. You may work alone or with
up to two classmates (but turn in one set of answers).
1) (2 points) An electronic component at Eltcomp has a
specification of 250.0 ± 7.5 ohms. Scrapping a defective
component results in a $135 loss.
a) Determine the Taguchi loss function.
b) If the process is centered at 248.6 ohms with a standard
deviation of 1.7 ohms, what is the expected loss per unit?
2) (2 points) At Elektroparts Manufacturers’ integrated
circuit business, it was found that any output voltage that
exceeds 255.0 ± 0.5 volts was unacceptable to the customer.
Exceeding these limits results in an estimated loss of $30.
a) Determine the Taguchi loss function.
b) The voltage of the integrated circuit can be corrected in
the plant by changing a resistor that costs $2.00. At what
tolerance should the integrated circuit be manufactured?
3) (2 points) Ten transformers were each tested for 720 hours,
four of which failed; at 297, 401, 422, and 457 hours. Once a
transformer fails, it cannot be restarted.

31. a) What is the failure rate for these transformers?
b) What is the MTTF?
4) (2 points) A particular type of light bulb has a mean life of
only 40 hours. Use the exponential distribution to answer the
following questions.
a) What percentage of light bulbs will fail within 50 hours?
b) When is it expected that 50% of the light bulbs will have
failed?
c) When is it expected that 95% of the light bulbs will have
failed?
5) (2 points) In a complex manufacturing process, three
operations are performed in series. Because of the nature of the
process, machines frequently fall out of adjustment and must be
repaired. To keep the system going, two identical machines are
used at each stage; thus, if one fails, the other can be used while
the first is repaired (see accompanying figure).
The reliabilities of the machines are as follows:
Machine Reliability
A 0.975
B 0.999
C 0.825

32. a) What is the system reliability, assuming only one machine
at each stage?
b) What is the system reliability when there are two machines
at each stage?