Engineering 11
Design for X
Bruce Mayer, PE
Licensed Electrical & Mechanical Engineer
BMayer@ChabotCollege.edu
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
OutLine  Design for X
 Trade-offs in Satisfaction
 Robust design
 Failure Modes & Effects Analysis
 Tolerance design
Customer
Needs
(CN)
Engineering-11: Engineering Design
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Functional
Requirements
(FR)
Design
Parameters
(DP)
Process
Variables
(PV)
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Basic Design Engineering Goals
 Design Engineering Goals for Product:
• “performs as expected”
• “works all the time” & “lasts long”
• “is easy to maintain”
 and THAT
• no damage occurs to product
• no damage or harm to environment
• no harm or injury to operator or user
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Design for X (DfX)
 During design, we often focus on the final product,
and not its manufacture.
 The Design For X (DfX) philosophy suggests that a
design be continually reviewed from the start to the
end to find ways to improve production and other
non-functional aspects
 Advantages of DfX techniques include
•
•
•
•
•
•
shorter production times
fewer production steps
smaller parts inventory
more standardized parts
simpler designs that are more likely to be robust
they can help when expertise is not available, or as
a way to re-examine traditional designs
• proven to be very successful over decades of application
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
The “X” in DfX
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Design for Robustness
 Methods to reduce the sensitivity of product
performance to variations such as:
• manufacturing (materials & processes)
• wear
• operating environment
 Currently used methods
• Taguchi Method
• Probabilistic optimal design (Monte Carlo)
 Both Taguchi and Monte Carlo methods use
statistics and probability theory
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Failure Modes & Effects Analysis
 The FMEA Method seeks to
systematically identify and correct
potential product or process deficiencies
before they occur
 The Process
• Identify EVERY Way in Which Product Can
FAIL; i.e., determine the Failure MODES
• Analyze the CONSEQUENCES of Every
Failure; i.e., determine the EFFECTS
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Failure Modes & Effects Analysis
 After Completion of the FMEA Work to
REDUCE
• The NUMBER of
Failure MODES
• The SEVERITY
of the EFFECTS
 Prioritize Risk
Reduction using
“Risk Priority No.”
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
FMEA Example  Log Splitter
 FMEA considers Both DESIGN and
MANUFACTURING Deficiencies
 Example  Hydraulic Log Splitter
• Hydraulic hose, on a home-use log splitter,
begins to leak.
• The leak reduces the pressure to the
piston/ram resulting in poor splitting.
• The leak drips oil on ground, creating a
mess, costly too!
• Upon examination, a weak spot is found
on hose due to poor manufacturing!
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
FMEA Main Concepts
 Failure Mode: the “way” a part fails to perform
• e.g. failure mode: hose leaks
 Effect: adverse consequence of failure mode
• e.g. hose leak results in oil spills, refill costs
• Effects can be severe or hardly noticeable.
 Cause: why it fails (or may fail)
•
•
e.g. poor hose manufacturing, improper pressure
Causes occur with some likelihood or probability
 Dectectability: the ability to discover the cause
before the part is shipped from the factory.
•
e.g. conduct a pressure test to detect leaks?
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
FMEA Risk Metric  RPN
 Determine a rating for each mode of failure
…. using a “risk priority number” (RPN)
RPN = [Severity rating] x [Occurrence rating] x
[Detection rating]
RPN = (S)•(O)•(D)
 RPN will range from 1 to 1000
• Large RPN  “bad”
• Small RPN  “good”
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
RPN Calculation
 Step 1: determine the failure modes
• From:
– Engineering design specifications
– Function decomposition diagrams
– functions ---- matter, energy, signal
– HoQ
– free body diagrams
– force flow diagrams
– process flow diagrams
– configuration sketches / drawings
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
RPN Calculation
 Step 2: determine potential effects of
each failure mode
 Step 3: determine a severity (S) rating for
each effect from the Severity rating table.
 Step 4: determine an occurrence (O)
rating for each cause from the
Occurrence rating table.
 Step 5: determine a detection (D) rating
for each cause from the Detection rating
table
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Severity Rating Criteria
Severity (S)
Rating
10
9
8
7
6
5
4
3
2
1
Type of effects
Causes injury to people, property and or the
environment
Causes damage to product, property or
Extremely Harmful
environment
Very Harmful
Causes damage to product
Major degradation of function
Harmful
Moderate
Causes partial malfunction of product
Significant
Performance loss causes customer complaints
Loss of function is annoying, cannot be overcome
Annoying
Minor
Some loss of performance, but can be overcome
Insignificant
Very little function degradation
No noticeable effects in function or harm to others
None
Catastrophic
Engineering-11: Engineering Design
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Description
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Occurrence Rating Criteria
Occurence (O)
Rating
10
9
8
7
6
5
4
3
2
1
Likelihood
Expected
Very likely
Probable
Occasional
More plausible
Plausible
Remote
Unlikely
Very unlikely
Improbable
Engineering-11: Engineering Design
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Description
> One per day
>30 %
30 % (3 per 10)
5 % (5 per 100)
1 % ( 1 per 100)
0.3 % (3 per 1,000)
One per week
One per month
One per three months
5
0.006 % (6 per 10 )
One per year
7
0.00006 % (6 per 10 ) One per three years
9
< 2 per 10 events
> five years per failure
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Detection Rating Criteria
Detection (D)
Rating
10
9
8
7
6
5
4
3
2
1
Detectability
Impossible
Very rare
Rare
Possible
Quite possible
Somewhat likely
Likely
Quite likely
Almost certain
Certain
Engineering-11: Engineering Design
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Description
Impossible to detect, or no inspection
Some chance of detecting, or 50% inspection
Quite likely to detect, or 75% inspection
Will be detected, or 100% inspection
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
RPN Calculation & Reduction
 Step 6: calculate the risk priority number
for each effect
 Step 7: prioritize or rank the failure
modes for action
 Step 8: take action to eliminate the
failure mode or reduce its severity
 Step 9: recalculate the risk priority
number as failure modes are reduced or
eliminated
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
RPN Calculation Summary
 RPN Calculations are Usually Tabulated
or put in a SpreadSheet
Severity (S)
Failure mode
S
Effects Rating
Engineering-11: Engineering Design
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Occurrence (O)
Causes
Detection (D)
O
controls
Rating tests
D
Recommended
Rating RPN
Action
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
RPN Example  Hose Failure
 Log-Splitter RPN & Remediation
Severity (S)
Failure mode
hydraulic
hose
leaks
Effects
S
Rating
Occurrence (O)
Causes
poor log
7
splitting (harmful) weak spot
O
Rating
7
(1%)
Detection (D)
controls
tests
D
Recommended
Rating RPN
Action
10
490
none
oil mess
costs to
refill
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
implement
pressure test
Design for Safety Issues
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
Injury
Hazards
Conditional Circumstances
Legal Responsibilities
Guidelines for Safe Products/Systems
Safety Hierarchy
Safe Design Principles
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Define Safe Product/System
 No injury to user, (products liability)
 No injury to consumer/society
 No injury to production worker
 No damage to personal property
 No damage to real property or the
environment
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Hazards
 Hazard ≡ a source of danger which has
the potential to injure people or damage
property or the environment
 Partial Hazard List
•
•
•
•
•
•
Entrapment – pinch, crush
Contact – heat, sharp edges, electric
Impact – hammer, robot arm
Ejection – grinder sparks, saw dust
Entanglement – hair, clothing
Noise & Vibration – hearing loss, HAVS
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Conditional Circumstances
 hazard is inherent during normal use
 hazard originates from a component
failure
 hazard caused by user misuse
 hazard exists during normal maintenance
 hazard created by improper maintenance
 hazard stems from lack of maintenance
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Product Legal-Liability
 Plaintiff’s attorney will try to prove that the company
or its employees failed to:
• perform “appropriate analyses.”
• comply with published standards.
• make use of state-of-the-art technology, due to ignorance.
•
•
•
•
include reasonable safety features or devices.
take into account how the user might misuse the product.
consider hidden dangers that might surprise the user.
consider variations in materials, mfg processes,
or effects of wear.
• carry out appropriate testing, or interpret results correctly.
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Guidelines for Safe Products
1.
2.
3.
4.
Perform appropriate analyses
Comply with published standards
Use state-of-the-art technology
Include reasonable safety features or
devices
5. Take into account how the user might
misuse the product
6. Consider hidden dangers that might
surprise the user
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Guidelines for Safe Products
7. Consider variations in materials or
manufacturing processes, or effects of
wear
8. Carry out appropriate testing and
interpret results correctly
9. Provide adequate warnings
10. Implement superior quality control
11. Document everything
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Safety Hierarchy Method
1. Eliminate the hazard - ProActive approach,
“design-out” the hazard (eliminate any
moving parts, hot or sharp surfaces)
2. Protect against the hazard with passive
approach, (machine guards, seat belts)
3. Warn against the hazard - weak remedy
(warning labels, alarms)
4. Provide Training - Provide and require
operating training.
5. Provide Personal Protection - LEAST
effective, (safety glasses, gloves, shoes)
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Safe-Design Principles
 Safe-Life  Good
• entire predicted useful life without malfunction.
• designers to identify all operating conditions, misuses
and abuses
• design appropriate maintenance and repair schedules.
 Fail-Safe  Better
• upon failure of a component, product/system
SHUTS DOWN safely,
• critical functions are sometimes still performed
– e.g. boiler feed-water valve failing in the open position
 Redundant design  Best (but EXPENSIVE)
• additional product components or systems are designed
to take over the principle function of the failed component
or system.
– e.g., multi-engine airplanes, emergency brakes, BackUp
pumps in nuclear PowerPlants
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
All Done for Today
Environmental
Tolerance
Zone
 The ETZ is the
Limits of SURVIVAL
• Well Beyond the Comfort Zone
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Engineering 11
Appendix
Bruce Mayer, PE
Registered Electrical & Mechanical Engineer
BMayer@ChabotCollege.edu
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Method 6-3-5 (Brain-Writing)
 The traditional brainstorming relies on verbal
communications.
• Idea generation may be dominated by a small
number of aggressive members.
 Guidelines for 6-3-5 method
 Team members are arranged around a
circular table to provide continuity. Six (6)
members are ideal.
 Each member sketches three (3) ideas for the
product configuration or functions. Sketches
should be the focus of this activity. The top
five product functionswith respect to the
customer needs are considered.
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt
Engineering-11: Engineering Design
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-11_Lec-12_Chp10_Design_for_X.ppt