1. Design Failure Mode and Effects Analysis(DFMEA)
Purpose:
- is to identify all the ways in which a
failure can occur, to estimate the effect
and seriousness of the failure, and to
recommend corrective design actions.
2. Elements of DFMEA
• Failure modes – these modes are ways in which
each element or function can fail.
• Effect of the failure on the customer- failure includes
dissatisfaction, potential injury or other safety issue,
and downtime.
• Severity, likelihood of occurrence and detection
rating – severity might be measured on a scale of 1
to 10, where a “1” indicates that the failures is so
minor that the customer probably would not notice
it, and a “10” might mean that the customer might
be endangered.
3. • Potential causes of failure – often failure is
the result of poor design.
• Corrective actions or controls- these controls
might include design changes, “mistake
proofing”, better user
instructions, management
responsibilities, and target completion
dates.
4. Reliability Prediction
Reliability
- ability of a product to perform as
expected over time.
- one of the principal dimension of
quality.
- Essential aspect of both product
and process design.
5. Reliability Measurement
- is determined by the number of failures
per unit time during the duration under
consideration (called the failure rate.)
Failure rate= λ = Number of failures
Total unit operating hours
Or
λ=
Number of failures
(Units tested)x (Number of hours tested)
6. Predicting System Reliability
• The reliability data of individual
components can be used to predict
the reliability of the system at the
design stage. Systems of components
may be configured in series, in parallel,
or in some mixed combination.
7. The Taguchi Loss Function
• As opposed to “goalpost”
specifications, Taguchi suggest that no strict
cut-off point divides good quality from poor
quality. Rather, Taguchi assumes that losses
can be approximated by a quadratic
function so that larger deviations from target
correspond to increasingly larger losses.
•
L(x) = K(x-T)²
8. Optimizing Reliability
Techniques:
Standardization – one method of ensuring high
reliability is to use components with proven track
records of reliability over years of actual use.
Redundancy – provides backup components that
can be used when the failure of any one component
in a system can cause a failure of the entire system.
9. Tools for Design Verification
-the final phase of DFSS is verification of
product and process designs. Some
verification is required by government
regulation or for legal concerns.
10. Reliability Testing
The reliability of a product is determined
principally by the design and the reliability of
the components of the product.
Testing- is useful for a variety of other reasons.
11. Measurement System Evaluation
• Accurately assessing Six Sigma performance
depends on reliable measurement systems.
Measuring quality characteristics generally
requires the use of the human senses –
seeing, hearing, tasting and smelling and
the use of some types of instrument or
gauge to measure the magnitude of the
characteristics.
12. Types of Measuring Instruments
• Low technology instruments – are
primarily manual devices that have
been available for many years.
• High technology instruments- describe
those that depend on modern
electronics, microprocessors, lasers, or
advanced optics.
13. Accuracy
- is defined as the difference between the
true value and the observed average of a
measurement.
- is measured as the amount of error in a
measurement in proportion to the total size of
the measurement.
14. Precision
• - is defined as the closeness of repeated
measurements to each other.
• -relates to the variance of repeated
measurements.
15. Repeatability or Equipment Variation
• is the variation in multiple
measurements by an individual
using the same instrument. This
measure indicates how precise
and accurate the equipment is.
16. Reproducibility(operator variation)
• -is the variation in the same measuring
instrument when it is used by different
individuals to measure the same parts
and indicates how robust the
measuring process is to the operator
and environmental conditions.
17. Calibration Measurement
• Are only useful if they have sufficient
accuracy and precision for the task and are
repeatable and reproducible.
18. Typical Calibration system:
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Evaluation of equipment to determine its capability
Identification of calibration requirements
Selection of standards to perform the calibration
Selection of methods and procedures to perform
the calibration
Establishment of calibration frequency and rules for
adjusting this frequency
Establishment of a system to ensure that instruments
are calibrated according to schedule
Implementation of a documentation and reporting
system
Evaluation of the calibration system through an
established auditing process
19. Process Capability Evaluation
• Process capability is important to both
product designers and manufacturing
engineers and is critical to achieving
Six Sigma performance.
20. Process Capability Studies
• Is a carefully planned study designed to yield
specific information about the performance of a
process under specified operating conditions.
Typical questions asked in a process capability:
• Where is the process centered?
• How much variability exists in the process?
• Is the performance relative to specifications
acceptable?
• What proportion of output will be expected to meet
specifications?
• What factors contribute to variability?
21. 6 Steps in Process Capability
1. Choose a representative machine or segment of
the process.
2. Define the process conditions.
3. Select a representative operator.
4. Provide materials that are of standard grade, with
sufficient materials for uninterrupted study.
5. Specify the gauging or measurement method to
be used.
6. Provide for a method of recording measurements
and conditions, in order, on the units produced.
