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Transcript of Fmea
Spring, 2005
FAILURE MODES AND EFFECTS ANALYSIS
(FMEA)
Julie VanLaanen
Failure Modes and Effects Analysis (FMEA)
Failure Mode and Effect Analysis is an analytical technique used by a product design team as a means to identify, define, and eliminate, to the extent possible, known or potential failure modes of a product or system.
How The FMEA Fits Into Your Final ProposalProposal Sections:
Letter of Intent ----------------->> TransmittalTitle Page
Executive Summary Table of Contents
List of FiguresLetter of Intent ------------------>> Introduction
QFD/House of Quality ------>> Design ObjectivesFMEA Analysis ----------------->> Product, System, or Process
Division of ResponsibilityProject Milestones------------- >> Project Schedule
Budget Resume -------------------------->> Qualifications BibliographyQFD/House of Quality ------>> Appendices
Detailed Project Schedule- >> Appendix Glossary
Was Failure a design requirement in your QFD?
Should it have been?
Can you design for failure?
Failure is ALWAYS a Design Constraint
All Products fail!
Determining how they fail, when they will fail, and why they are failing will allow a designer to incorporate failure as an acceptable design constraint.
Failure as an acceptable design constraint = Customer Satisfaction = Design Quality
From: “Inviting Disaster – Lessons From the Edge of Technology”
By James R. Chiles
Regarding the continuing failure of rear cargo door on a DC-10:
“ The design was originally going to use hydraulics, but under pressure from its client, American Airlines, to simplify and lighten the DC-10 equipment; McDonnell Douglas shifted to an electric door closer instead. This worried engineers working for the builder of the door assembly, Convair Division of General Dynamics. Convair engineers even sent McDonnell Douglas a formal document, called a “failure modes effects analysis,” describing the problem and the disastrous consequences.
How could your design fail?
Identify potential failure areas in your designDetermined analytically through models and
analysisDetermined empirically through stressed life
testingDetermined after product release through
customer warranties and failure reporting
When will my design fail?
Determining how my design might fail requires a through understanding of my design.
Part of answering this question is determining when my customer believes failure is acceptable.
When will my design fail?
Design failure is acceptable if customers perceive it as acceptable. Design Failure has a direct effect on Customer perceptions of Product Quality.
Periodic Maintenance (oil changes)Periodic Replacements (change tires)Acceptable End of Life (customer expectations –
car replacement every 8-10 years)
Reliability Curve
Time
FailureFrequency
ChanceInfantMortality
Wearout
Useful Life
Assuming a part/product is designed correctly, statistically it should follow a standard bath-tub curve
Infant Mortality – failures don’t usually affect the customer, except DOAUseful life – failures here are problemsWear Out – failures here are acceptable
Causes of Reliability Curve Failure
Early Failure(Infant Mortality)
Chance Failure Wear Out Failure
- Poor Quality Control
- Poor workmanship
- Insufficient Burn In
- Substandard Materials
- Contamination
- Human Error
- Incorrect Packaging
- Design Errors
- Insufficient SafetyMargins
- Undetected Defects
- Misapplication
- Abuse of Equipment
- Lack of PreventiveMaintenance
- Acts of God
- Stress Concentration
- Corrosion
- Fatigue
- Creep
- Abrasive Wear
- Wrong Environment
- Poor Maintenance
Tools used to Design for acceptable Product Failure
Failure Modes and Effects Analysis (FMEA): Method to identify and understand potential product failures and their severity
Mean Time Between Failures (MTBF) of individual parts. Determined by:
MIL Standards Testing Mathematical Predictions
Design of Experiments (DOE): Experimentally optimizing our design using physical models and optimized testing (Taguchi)
Tools to used to Design for acceptable Product Failure (cont.)
Statistical Process Control (SPC): Monitoring process failures through tight statistical control of process variables
Six-Sigma (6): Statistical repeatability to six standard deviations (in other words, 99.9999998% within design specifications!)
QUALITY MAPProcess Control to
Identify Possible Causes
SPC
6
Quantify Processesand Rank Suppliers
DOE
Model Variablesand InteractionsReduce Variance
Reliability Engr.
Evaluate ProductPerformance Predict
Product Life
FMEA
Prevent Failures fromReaching the Customer
Failure Modes and Effects Analysis (FMEA)
Begins at the initiation of a product design cycle
Seeks to identify potential failure modes before a actual failure occurs
Continues throughout product design cycle
Three Key Questions Posed by FMEA
What could fail in each component of my product?
To what extent might it fail and what are the potential hazards produced by the failure?
What steps should be implemented to prevent failures?
Design FMEA AnalysisItem andFunction
PotentialFailureMode
PotentialEffects of
Failure
SEV
PotentialCause(s)of Failure
OCC
DetectionMethod &
QualityControls
DET
RPN
RecommendedActions
List PartName,NumberandFunction
List thepossiblemodes offailure
List theconsequencesof failure onpart functionand on thenext higherassembly
List thosesuch as:inadequatedesign,impropermaterials,etc.
List thesemeasuresavailable todetectfailuresbefore theyreach thecustomer
List them foreach of thefailure modesidentified asbeingsignificant bythe RPN
= Critical characteristic which may effect safety, compliance with Gov. regulations, or require special controls.
SEV = Severity rating (1 to 10)
OCC = Occurrence frequency (1 to 10)
DET = Detection Rating (1 to 10)
RPN = Risk Priority Number (1 to 1000)
Rifle Bolt ExamplePart and Function
Potential Failure Mode
Potential Effects of Failure
S
E
V
Potential Cause(s) of Failure
O
C
C
Detection Method & Quality Controls
D
E
T
R
P
N
Recommended Actions
Item and FunctionList each subassembly and component, along with it’s basic
function. Example: Rifle Bolt
Part and Function
Potential Failure Mode
Potential Effects of Failure
S
E
V
Potential Cause(s) of Failure
O
C
C
Detection Method & Quality Controls
D
E
T
R
P
N
Recommended Actions
Rifle BoltChambers bulletLocks into receiverFires RoundSustains firing pressure on lugsProvides extraction of spent case
Identify and List Potential Failure Modes
For any failure mode, the idea is to identify what could occur, not that it will necessarily occur. Identify through:
BrainstormingAnalysisTestExperience
Example Failure Modes
Identify and List Potential Failure Modes
Part and Function
Potential Failure Mode
Potential Effects of Failure
S
E
V
Potential Cause(s) of Failure
O
C
C
Detection Method & Quality Controls
R
P
N
Recommended Actions
Rifle BoltChambers bulletLocks into receiverFires RoundSustains firing pressure on lugsProvides extraction of spent case
Fracture
Jamming
List Potential Effects from Failure
Impact on EnvironmentHazard to humansExcessive noisePoor AppearanceUnpleasant OdorErratic Operation
Potential Effects from Failure
Part and Function
Potential Failure Mode
Potential Effects of Failure
S
E
V
Potential Cause(s) of Failure
O
C
C
Detection Method & Quality Controls
R
P
N
Recommended Actions
Rifle BoltChambers bulletLocks into receiverFires RoundSustains firing pressure on lugsProvides extraction of spent case
Fracture Catastrophic failure with destruction of weapon and injury to personnel
Jamming Failure of weapon to function
Critical Potential Effects from Failure
Are the potential effects critical? Will they effect: Personal Safety Compliance with a Government Standard Compliance with a Government Regulation Require special controls
Identifying Critical Failures
Part and Function
Potential Failure Mode
Potential Effects of Failure
S
E
V
Potential Cause(s) of Failure
O
C
C
Detection Method & Quality Controls
R
P
N
Recommended Actions
Rifle BoltChambers bulletLocks into receiverFires RoundSustains firing pressure on lugsProvides extraction of spent case
Fracture Catastrophic failure with destruction of weapon and injury to personnel
Jamming Failure of weapon to function
Specifying Severity of Failure (SEV)Estimate potential severity (SEV) of failure and its effect
Ranking Effect Criteria: Severity of Effect1 None No effect2 Very Minor Very minor effect on product or system
performance.3 Minor Minor effect on product or system performance.4 Low Small effect on product performance.
The product does not require repair.5 Moderate Moderate effect on product performance.
The product requires repair.6 Significant Product performance is degraded. Comfort or
convenience functions may not operate.7 Major Product performance is severely affected but
functions. The system may not be operable.8 Extreme Product is inoperable with loss of primary function.
The system is inoperable.9 Serious Failure involves hazardous outcomes and / or
noncompliance with govt. regulations or standards.10 Hazardous Failure is hazardous, and occurs without warning. It
suspends operation of the system an/or involvesnoncompliance with govt. regulations
Specifying Severity of Failure (SEV)
Part and Function
Potential Failure Mode
Potential Effects of Failure
S
E
V
Potential Cause(s) of Failure
O
C
C
Detection Method & Quality Controls
R
P
N
Recommended Actions
Rifle BoltChambers bulletLocks into receiverFires RoundSustains firing pressure on lugsProvides extraction of spent case
Fracture Catastrophic failure with destruction of weapon and injury to personnel
10
Jamming Failure of weapon to function
8
Potential Cause of Failure
List possible potential causes of failure Tolerance stack-up Assembly errors Poor maintenance Impact loading Overstressing Poor Design
These causes should indicate appropriate preventive measures that might be adopted
Potential Cause of Failure
Part and Function
Potential Failure Mode
Potential Effects of Failure
S
E
V
Potential Cause(s) of Failure
O
C
C
Detection Method & Quality Controls
R
P
N
Recommended Actions
Rifle BoltChambers bulletLocks into receiverFires RoundSustains firing pressure on lugsProvides extraction of spent case
Fracture Catastrophic failure with destruction of weapon and injury to personnel
10
ShrinkagePorosity caused by improper feed
Jamming Failure of weapon to function
8 Out of spec. DimensionChange in shell refractory
Likelihood of Occurrence (OCC)Estimate the potential occurrence of failure
Ranking PossibleFailure Rates
Probability of Failure
1 1 x 10-6 Nearly Impossible2 1 x 10-5 Remote3 1 x 10-4 Low4 4 x 10-4 Relatively Low5 2 x 10-3 Moderate6 1 x 10-2 Moderately High7 4 x 10-2 High8 0.2 Repeated Failures9 0.33 Very High10 0.55 Extremely High: Failure Almost
Inevitable
Likelihood of Occurrence (OCC)
Part and Function
Potential Failure Mode
Potential Effects of Failure
S
E
V
Potential Cause(s) of Failure
O
C
C
Detection Method & Quality Controls
R
P
N
Recommended Actions
Rifle BoltChambers bulletLocks into receiverFires RoundSustains firing pressure on lugsProvides extraction of spent case
Fracture Catastrophic failure with destruction of weapon and injury to personnel
10
ShrinkagePorosity caused by improper feed
6
Jamming Failure of weapon to function
8 Out of spec. DimensionChange in shell refractory
5
Detection Methods & Quality Controls
Develop Methods to detect and control the potential causes of failure Manufacturing tests Incoming Inspection SPC Methods Vendor/Supply Controls Dimension Inspection
Detection Methods & Quality Controls
Part and Function
Potential Failure Mode
Potential Effects of Failure
S
E
V
Potential Cause(s) of Failure
O
C
C
Detection Method & Quality Controls
R
P
N
Recommended Actions
Rifle BoltChambers bulletLocks into receiverFires RoundSustains firing pressure on lugsProvides extraction of spent case
Fracture Catastrophic failure with destruction of weapon and injury to personnel
10
ShrinkagePorosity caused by improper feed
6 Incoming Part InspectionDye penetrant testing
Jamming Failure of weapon to function
8 Out of spec. DimensionChange in shell refractory
5 Measure patternsConfirm finished casting dimensions
Likelihood of Detection (DET)Estimate the likelihood that the detection method
in place will actually detect the fault
Ranking Detection Probability1 Almost Certain Detection2 Very High Chance of Detection3 High Probability of Detection4 Moderately High Chance of Detection5 Moderate Chance of Detection6 Low Probability of Detection7 Very Low Probability of Detection8 Remote Chance of Detection9 Very Remote Chance of Detection
10 Absolute Uncertainty – No Control
Likelihood of Detection (DET)
Part and Function
Potential Failure Mode
Potential Effects of Failure
S
E
V
Potential Cause(s) of Failure
O
C
C
Detection Method & Quality Controls
D
E
T
R
P
N
Recommended Actions
Rifle BoltChambers bulletLocks into receiverFires RoundSustains firing pressure on lugsProvides extraction of spent case
Fracture Catastrophic failure with destruction of weapon and injury to personnel
10 ShrinkagePorosity caused by improper feed
6 Incoming Part InspectionDye penetrant testing
5
Jamming Failure of weapon to function
8 Out of spec. DimensionChange in shell refractory
5 Measure patternsConfirm finished casting dimensions
3
Calculate a Risk Priority Number (RPN)
The RPN prioritizes the relative importance of each failure mode and effect on a scale of 1 – 1000. It is calculated as follows:
RPN = (SEV) x (OCC) x (DET)A 1000 rating implies a certain failure that is
hazardous and harmfulA 1 rating is a failure that is highly unlikely and
unimportantRatings above 100 will occurRating below 30 are reasonable for typical applications
Calculate a Risk Priority Number (RPN)
Part and Function
Potential Failure Mode
Potential Effects of Failure
S
E
V
Potential Cause(s) of Failure
O
C
C
Detection Method & Quality Controls
D
E
T
R
P
N
Recommended Actions
Rifle BoltChambers bulletLocks into receiverFires RoundSustains firing pressure on lugsProvides extraction of spent case
Fracture Catastrophic failure with destruction of weapon and injury to personnel
10 ShrinkagePorosity caused by improper feed
6 Incoming Part InspectionDye penetrant testing
5 300
Jamming Failure of weapon to function
8 Out of spec. DimensionChange in shell refractory
5 Measure patternsConfirm finished casting dimensions
3 1
2
0
Develop Recommended Actions
Based on your RPN number, develop recommended actions to solve failure modes Assign responsibilities Outline corrective actions Revise test plans, material specifications
These actions should be specific, not general action items
Develop Recommended ActionsPart and Function
Potential Failure Mode
Potential Effects of Failure
S
E
V
Potential Cause(s) of Failure
O
C
C
Detection Method & Quality Controls
D
E
T
R
P
N
Recommended Actions
Rifle BoltChambers bulletLocks into receiverFires RoundSustains firing pressure on lugsProvides extraction of spent case
Fracture Catastrophic failure with destruction of weapon and injury to personnel
10 ShrinkagePorosity caused by improper feed
6 Incoming Part InspectionDye penetrant testing
5 300
Initiate radiographic testing of all rifle bolts
Jamming Failure of weapon to function
8 Out of spec. DimensionChange in shell refractory
5 Measure patternsConfirm finished casting dimensions
3 1
2
0
Initiate SPC program to check and maintain bolt dimensions
Spring, 2005
Acknowledgement
Lecture taken from:Dr. Bob Frost of the Metallurgical Engineering Dept. from his course on Statistical Process Control (SPC)Dr. Munoz from the Mechanical Engineering Department.Product Design: Techniques in Reverse Engineering and New Product Development by Kevin Otto & Kristin Wood, pp 564-571.