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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