Title: Design for
1Chapter 12
2DFSS ActivitiesFour Principal Activities
- Concept development, determining product
functionality based upon customer requirements,
technological capabilities, and economic
realities - Design development, focusing on product and
process performance issues necessary to fulfill
the product and service requirements in
manufacturing or delivery - Design optimization, seeking to minimize the
impact of variation in production and use,
creating a robust design - Design verification, ensuring that the capability
of the production system meets the appropriate
sigma level
3Key Idea
Like Six Sigma itself, most tools for DFSS have
been around for some time its uniqueness lies in
the manner in which they are integrated into a
formal methodology, driven by the Six Sigma
philosophy, with clear business objectives in
mind.
4Tools for 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. - Quality function deployment (QFD)
- Concept engineering
5Key IdeaConcept Development
Developing a basic functional design involves
translating customer requirements into measurable
technical requirements and, subsequently, into
detailed design specifications.
6Key IdeaQFD
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 purchasing and
suppliers.
7House of Quality
8(No Transcript)
9Quality Function Deployment
10Building the House of Quality
- 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. - Determine which technical requirements to deploy
in the remainder of the production/delivery
process.
11Tools for Design Development
- Tolerance design
- Design failure mode and effects analysis
- Reliability prediction
12Key IdeaTools for Design Development
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.
13Tolerance Design
- Determining permissible variation in a dimension
- Understand tradeoffs between costs and
performance
14Key IdeaTolerance Design
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.
15DFMEA
- 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.
16DFMEA
- Failure modes
- Effect of the failure on the customer
- Severity, likelihood of occurrence, and detection
rating - Potential causes of failure
- Corrective actions or controls
17Reliability Prediction
- Reliability
- Generally defined as 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
18Types 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
19Types of Reliability
- Inherent reliability predicted by product
design - Achieved reliability observed during use
20Reliability Measurement
- Failure rate (l) number of failures per unit
time - Alternative measures
- Mean time to failure (MTTF)
- Mean time between failures (MTBF)
21Cumulative Failure Rate Curve
22Failure Rate Curve
Infant mortality period
23Average Failure Rate
24Key IdeaReliability Prediction
Many electronic components commonly exhibit a
high, but decreasing, failure rate early in their
lives (as evidenced by the steep slope of the
curve), followed by a period of a relatively
constant failure rate, and ending with an
increasing failure rate.
25Product Life Characteristic Curve
- Three distinct time period
- Early failure
- Useful life
- Wearout period
26Predicting System Reliability
- Series system
- Parallel system
- Combination system
27Series Systems
RS R1 R2 ... Rn
28Parallel Systems
RS 1 - (1 - R1) (1 - R2)... (1 - Rn)
29Series-Parallel Systems
C
RA
RB
RD
RC
A
B
D
C
RC
- Convert to equivalent series system
RA
RB
RD
A
B
C
D
RC 1 (1-RC)(1-RC)
30Tools for Design Optimization
- Taguchi loss function
- Optimizing reliability
31Key IdeaTools for Design Optimization
Design optimization includes setting proper
tolerances to ensure maximum product performance
and making designs robust, that is, insensitive
to variations in manufacturing or the use
environment.
32Loss Functions
Traditional View
Taguchis View
33Loss function
34Taguchi Loss Function
- No strict cut-off point divides good quality from
poor quality. Rather, losses can be approximated
by a quadratic function so that larger deviations
from target correspond to increasingly larger
losses.
35Optimizing Reliability
- Standardizationuse components with proven track
records - Redundancyprovide backup components
- Physics of failureunderstand physical properties
of materials
36Tools for Design Verification
- Reliability testing
- Measurement systems evaluation
- Process capability evaluation
37Key IdeaTools for Design Verification
Design verification is necessary to ensure that
designs will meet customer requirements and can
be produced to specifications.
38Reliability testing
- Life testing
- Accelerated life testing
- Environmental testing
- Vibration and shock testing
- Burn-in (component stress testing)
39Measurement System Evaluation
- Whenever variation is observed in measurements,
some portion is due to measurement system error.
Some errors are systematic (called bias) others
are random. The size of the errors relative to
the measurement value can significantly affect
the quality of the data and resulting decisions.
40Metrology - Science of Measurement
- Accuracy - closeness of agreement between an
observed value and a standard can lead to
systematic bias. - Precision - closeness of agreement between
randomly selected individual measurements can
lead to random variation.
41Accuracy vs. Precision
42Repeatability and Reproducibility
- Repeatability (equipment variation) variation
in multiple measurements by an individual using
the same instrument. - Reproducibility (operator variation) - variation
in the same measuring instrument used by
different individuals
43Key IdeaCalibration
One of the most important functions of metrology
is calibrationthe comparison of a measurement
device or system having a known relationship to
national standards against another device or
system whose relationship to national standards
is unknown.
44Process Capability
- The range over which the natural variation of a
process occurs as determined by the system of
common causes - Measured by the proportion of output that can be
produced within design specifications
45Process Capability StudyTypical Questions Asked
- Where is the process centered?
- How much variability exists in the process?
- Is the performance relative to specs acceptable?
- What proportion of output will be expected to
meet the specs? - What factors contribute to variability?
46Types of Capability Studies
- Peak performance study - how a process performs
under ideal conditions - Process characterization study - how a process
performs under actual operating conditions - Component variability study - relative
contribution of different sources of variation
(e.g., process factors, measurement system)
47Process Capability
48Process Capability
Process is capable
49Process Capability
Process is not capable
50Effects of Reducing Variability on Process
Capability
51Key IdeaProcess Capability
The process capability index, Cp (sometimes
called the process potential index), is defined
as the ratio of the specification width to the
natural tolerance of the process. Cp relates the
natural variation of the process with the design
specifications in a single, quantitative measure.
52Process Capability Index
UTL - LTL 6s
Cp
UTL - m 3s
Cpu
m - LTL 3s
Cpl
Cpl, Cpu
Cpk min