17. fmea - akshay
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Failure Mode and Effects
Analysis
(FMEA)
AKSHAY .D. PAWAR
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Learning Objectives
To understand what is FMEA and its history.
To understand the use of Failure Modes EffectAnalysis (FMEA).
To learn the steps for developing FMEA.
Example.
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What is FMEA?
Failure Mode and Effects Analysis(FMEA) is a systematic team driven approach
to analyze and discover:1. All potential failure modes of a system.2. The effects these failures have on the system.
3. How to correct the failures or the effects on the
system. [The correction usually based on aranking of the severity and probability of thefailure]
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History of FMEA
FMEA was formally introduced in US Army in thelate 1940s with the introduction of the military
standard.
By the early 1960s, contractors for the U.S.National Aeronautics and SpaceAdministration (NASA) were using FMEA foravoiding failure in rocket and other space crafts.
Ford Motor Company introduced FMEA toautomotive in the late 1970s for safety and
regulatory consideration after the disastrous"Pinto" affair.
http://en.wikipedia.org/wiki/National_Aeronautics_and_Space_Administrationhttp://en.wikipedia.org/wiki/National_Aeronautics_and_Space_Administrationhttp://en.wikipedia.org/wiki/National_Aeronautics_and_Space_Administrationhttp://en.wikipedia.org/wiki/National_Aeronautics_and_Space_Administrationhttp://en.wikipedia.org/wiki/National_Aeronautics_and_Space_Administrationhttp://en.wikipedia.org/wiki/National_Aeronautics_and_Space_Administration -
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"A large safety factor does not necessarily translate
into a reliable product. Instead, it often leads toan overdesigned product with reliabilityproblems."
-Failure Analysis Beats Murphey's Law
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Why to use FMEA? Contributes to improved designs for products and
processes. Higher reliability Better quality Increased safety Enhanced customer satisfaction
Contributes to cost savings. Decreases development time and re-design
costs Decreases warranty costs Decreases waste, non-value added operations
Contributes to continuous improvement. Improve internal and external customer
satisfaction. Focus on prevention.
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Cost benefits associated with FMEA areusually expected to come from the ability to
identify failure modes earlier in the process,when they are less expensive to address. rule of ten If the problem costs Rs.100 when it is
discovered in the field, then It may cost Rs.10 if discovered during the
final testBut it may cost Rs.1 if discovered during
an incoming inspection.Even better it may cost Rs.0.10 if
discovered during the design or processengineering phase
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FMEA: A Team Tool
A team approach is necessary.
Team should be led by the Black Belt, aresponsible manufacturing engineer or technicalperson, or other similar individual familiar withFMEA.
The following should be considered for teammembers:
Design Engineers Operators Process Engineers Reliability
Materials Suppliers Suppliers
Customers
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Steps to conduct a FMEA
1. Identify components and associated functions.
2. Identify failure modes.
3. Identify effects of the failure modes.
4. Determine severity of the failure mode.5. Determine probability of occurrence.
6. Assign detection rating
7. Calculate RPN.
8. Develop an action plan to address high RPNs.9. Take action.
10. Reevaluate the RPN after the actions arecompleted.
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Step 1: Identify components andassociated functions
The first step of an FMEA is to identify all of thecomponents to be evaluated. This may include allof the parts that constitute the product or, if the
focus is only part of a product, the parts thatmake up the applicable sub-assemblies. Thefunction(s) of each part within in the product arebriefly described.
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Step 2: Identify failure modes
The potential failure mode(s) for each part areidentified. Failure modes can include but are notlimited to followings:
1. complete failures
2. intermittent failures
3. partial failures
4. failures over time
5. incorrect operation
6. premature operation7. failure to cease functioning at allotted time
8. failure to function at allotted time
It is important to consider that a part may have
more than one mode of failure.
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Step 3: Identify effects of the failuremodes
For each failure mode identified, theconsequences or effects on product, property andpeople are listed. These effects are bestdescribed as seen though the eyes of the
customer.
Here the brainstorming is used to find theconsequences.
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Step 4: Determine severity of thefailure mode
Definition: assessment of the seriousness ofthe effect(s) of the potential failure mode onthe next component, subsystem, or customerif it occurs
Severity ranking varies from 1 = Not Severe to10 = Very Severe
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Severity RankingEffect Rank Criteria
None 1 No effect
Very Slight 2 Negligible effect on Performance. Some users may notice.
Slight 3 Slight effect on performance. Non vital faults will be noticedby many users
Minor 4 Minor effect on performance. User is slightly dissatisfied.
Moderate 5 Reduced performance with gradual performancedegradation. User dissatisfied.
Severe 6 Degraded performance, but safe and usable. Userdissatisfied.
High Severity 7 Very poor performance. Very dissatisfied user.
Very High Severity 8 Inoperable but safe.
Extreme Severity 9 Probable failure with hazardous effects. Compliance withregulation is unlikely.
Maximum Severity 10 Unpredictable failure with hazardous effects almost certain.Non-compliant with regulations.
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Step 5: Determine probability ofoccurrence
This step involves determining or estimating theprobability that a given cause or failure mode willoccur. The probability of occurrence can bedetermined from field data or history of previous
products. If this information is not available, asubjective rating is made based on theexperience and knowledge of the cross-functionalexperts.
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Occurrence RankingOccurrence Rank Criteria
Extremely Unlikely 1 Less than 0.01 per thousand
Remote Likelihood 2 0.1 per thousand rate of occurrence
Very Low Likelihood 3 0.5 per thousand rate of occurrence
Low Likelihood 4 1 per thousand rate of occurrence
Moderately LowLikelihood
5 2 per thousand rate of occurrence
Medium Likelihood 6 5 per thousand rate of occurrence
Moderately HighLikelihood
7 10 per thousand rate of occurrence
Very High Severity 8 20 per thousand rate of occurrence
Extreme Severity 9 50 per thousand rate of occurrence
Maximum Severity 10 100 per thousand rate of occurrence
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Step 6: Assign detection rating
The detection effectiveness rating estimates howwell the cause or failure mode can be preventedor detected. If more than one detection techniqueis used for a given cause or failure mode, an
effectiveness rating is given to the group ofcontrols.
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Detection RankingDetection Rank Criteria
Extremely Likely 1 Can be corrected prior to prototype/ Controls will almostcertainly detect
Very High Likelihood 2 Can be corrected prior to design release/Very Highprobability of detection
High Likelihood 3 Likely to be corrected/High probability of detection
Moderately HighLikelihood
4 Design controls are moderately effective
Medium Likelihood 5 Design controls have an even chance of working
Moderately LowLikelihood
6 Design controls may miss the problem
Low Likelihood 7 Design controls are likely to miss the problem
Very Low Likelihood 8 Design controls have a poor chance of detection
Remote Likelihood 9 Unproven, unreliable design/poor chance for detection
Extremely Unlikely 10 No design technique available/Controls will not detect
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Step 7: Calculate Risk Priority
Number (RPN)
RPN is the product of the severity, occurrence,and detection scores.
Severity Occurrence Detection RPNX X =
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Selecting the vital problems
RPN is used for selecting vital problem by settingsome threshold limit and working on all potentialfailures above this limit.
Another approach is to arrange the RPN values ina Pareto plot and give attention to those potentialfailures with the highest ratings
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Compare failure modes A and B. A has nearlyfour times the RPN of B, yet B has a severity offailure that would cause safety risk and complete
system shutdown. Failure by A would cause onlya slight effect on product performance. It achievesits high RPN value because it is not possible todetect the defect that is causing the failure.
Certainly failure B is more critical than A andshould be given prompt attention.
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The FMEA Form
Identify failure modesand their effects
Identify causes of thefailure modesand controls
PrioritizeDetermine and assess
actions
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Example
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Applications for FMEA
Process - analyze manufacturing and assemblyprocesses.
Design - analyze products before they are
released for production. Equipment - analyze machinery and equipment
design before they are purchased.
Service - analyze service industry processes
before they are released to impact the customer.
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THANK YOU