Chapter 6-1: Failure Modes Effect Analysis...

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Islamic University of Gaza - Palestine

Chapter 6-1: Failure Modes Effect Analysis(FMCEA)


Learning Outcomes:

After careful studying this lecture You should be able:• To Define FMEA• To understand the use of Failure Modes Effect Analysis

(FMEA)• To be informed about the history of FMEA• To learn the steps to developing FMEA• To discuss benefits and pitfalls of FMEA• To summarize the different types of FMEA

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Key Definitions

• Customer: persons and organizations that are affected by the process.

• Failure: any malfunction, defect or error that causes the process not to perform its intended function(s) or meet requirements satisfactorily.

• Failure Mode: the appearance, manner or form in which the process failure manifests itself. (Short circuit or handling damage)

• Cause(s) of the Failure: Possible mechanism(s) and/or way(s) in which the failure mode can be produced.

• Effect(s) of the Failure: the experience the customer encounters as a result of the failure mode


What is FMEA?

A bottoms-up, iterative approach for analyzing a design of a product or process in order to determine– what could go wrong – how badly it might go wrong– and what needs to be done to prevent it

Another definition:Any formal, structured activity which is applied in developing something new to assure that as many potential problems as are reasonably possible to predict have considered, analyzed, and their causes improved before the item under development reaches the hands of the end user.

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What is it?

• Actions• Prevention / reduction of failures• Tool for risk reduction

What it is not ?

• The FMEA is not a stand-alone tool to be used to solve problems

• The FMEA presents the opportunities but does not solve the problems


What is FMEA? (cont.)

• FMEA--a tool to identify risks in your process

• Can be used in multiple places in process improvement– Determine where problems are– Help identify cause/effect relationships– Highlight risks in solutions and actions to take

• Starts with input from processes

• Identifies three risk categories– Severity of impact– Probability of occurrence– Ability to detect the occurrence

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When to Conduct an FMEA?

• Early in the process improvement investigation• When new systems, products, and processes are being

designed• When existing designs or processes are being changed• When carry-over designs are used in new applications• After system, product, or process functions are defined, but

before specific hardware is selected or released to manufacturing


When to Use?

• Early stages (Define) to understand process and identify

problem areas

• Analyze data (Analyze) to help identify root causes

• Determine best solutions (Improve) with lowest risk

• Close out stage (Control) to document improvement and

identify actions needed to continue reducing the risk

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Failure Mode, Effects, and Criticality Analysis (FMECA)

What’s a FMECA?

A more expanded version of FMEA includes a determination of the criticality or severity of a particular failure mode.


Failure Mode Effects and Criticality Analysis (FMECA)

• Another similar technique, extension of FMEA

• The FMECA is the result of two steps:

– Failure Mode and Effect Analysis (FMEA) – Criticality Analysis (CA) to evaluate the frequency of

occurrence of the problems identified.

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Why is FMEA / FMECA Important?

• FMEA provides a basis for identifying root failure causes and developing effective corrective actions

• The FMEA identifies reliability/safety of critical components

• It facilitates investigation of design alternatives at all design stages

• Provides a foundation for other maintainability, safety, testability, and logistics analyses

• A Pro-active engineering quality method


What’s In It for Me?

• Allows us to identify areas of our process that has most impact on our customers

• Helps us identify how our process is most likely to fail

• Points to process failures that are most difficult to detect

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What can FMEA be used for?

• Competing• Prevention of Litigation• Identify Weak areas of a process/product• A bottom-up approach• To evaluate the effectiveness of the current control plan• Prioritize tasks


Benefits

• Improved product or process functionality and safety• Reduced warranty and replacement costs• Improve product/process reliability and quality • Increase customer satisfaction • Early identification and elimination of potential

product/process failure modes • Prioritize product/process deficiencies • Capture engineering/organization knowledge • Emphasizes problem prevention • Documents risk and actions taken to reduce risk • Identify critical to quality (CTQs)

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Application Examples

• Manufacturing: A manager is responsible for moving a manufacturing operation to a new facility. He/she wants to be sure the move goes as smoothly as possible and that there are no surprises.

• Design: A design engineer wants to think of all the possible ways a product being designed could fail so that robustness can be built into the product.

• Software: A software engineer wants to think of possible problems a software product could fail when scaled up to large databases.


What Is A Failure Mode?

• A Failure Mode is:– The way in which the component, subassembly, product,

input, or process could fail to perform its intended function• Failure modes may be the result of upstream operations or

may cause downstream operations to fail– Things that could go wrong

What Can Go Wrong?

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FMEA

• Why– Methodology that facilitates process improvement– Identifies and eliminates concerns early in the development

of a process or design– Improve internal and external customer satisfaction– Focuses on prevention– FMEA may be a customer requirement– FMEA may be required by an applicable Quality System

Standard


FMEA

• A structured approach to:– Identifying the ways in which a product or process can fail– Estimating risk associated with specific causes– Prioritizing the actions that should be taken to reduce risk– Evaluating design validation plan (design FMEA) or current

control plan (process FMEA)

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Evolution

• 1960’s: NASA moon program engineers devised a method of forecasting problems.

• 1970’s: Method becomes known as FMEA and is adopted by various quality organizations.

• In the late 1970’s, the automotive industry was driven by liability costs to use FMEA

• Later, the automotive industry saw the advantages of

using this tool to reduce risks related to poor quality


Evolution (cont.)

• 1980’s: With increased emphasis on quality, method

spreads to large corporations.

• 1990’s: Large corporations are, in turn, pressing

suppliers to adopt the method.

• 2000’s: Method is being applied elsewhere such as

HealthCare.

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The FMEA Form

Identify failure modes and their effects

Identify causes of the failure modesand controls

Prioritize Determine and assess actions

A Closer Look


Types of FMEAs

• Design– Analyzes product design before release to production, with a

focus on product function– Analyzes systems and subsystems in early concept and

design stages

• Process– Used to analyze manufacturing and assembly processes

after they are implemented

• FMCEA

Specialized Uses

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Product versus Process

• Product or Design FMEA.– What could go wrong with a product while in service as a

result of a weakness in design.– Product design deficiencies

• Process FMEA.– What could go wrong with a product during manufacture or

while in service as a result of non-compliance to specification or design.

– Manufacturing or assembly deficiencies– Focus on process failures and how they cause bad quality

products to be produced


FMEA: A Team Tool

• A team approach is necessary.• Team should be led by the Process Owner who is the

responsible manufacturing engineer or technical person, or other similar individual familiar with FMEA.

• The following should be considered for team members:– Design Engineers – Operators– Process Engineers – Reliability– Materials Suppliers – Suppliers– Customers

Team Input Required

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FMEA Procedure

1. For each process input (start with high value inputs), determine the ways in which the input can go wrong (failure mode)

2. For each failure mode, determine effects– Select a severity level for each effect

3. Identify potential causes of each failure mode– Select an occurrence level for each cause

4. List current controls for each cause– Select a detection level for each cause

Process Steps


FMEA Procedure (Cont.)

5. Calculate the Risk Priority Number (RPN)

6. Develop recommended actions, assign responsible persons, and take actions– Give priority to high RPNs– MUST look at severities

7. Assign the predicted severity, occurrence, and detection levels and compare RPNs

Process Steps

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FMEA Inputs and Outputs

FMEA

BrainstormingCause & Effect Matrix (C&E)Process Map

Process HistoryProceduresKnowledgeExperience

List of actions to prevent causes or

detect failure modes

History of actions taken

InputsOutputs

Information Flow


Severity, Occurrence, and Detection

• Severity– Importance of the effect on customer requirements

• Occurrence– Frequency with which a given cause occurs and

creates failure modes

• Detection– The ability of the current control scheme to detect

or prevent a given cause

Analyzing Failure & Effects

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Rating Scales

• There are a wide variety of scoring “anchors” presenters, both quantitative or qualitative

• Two types of scales are 1-5 or 1-10• The 1-5 scale makes it easier for the teams to decide on

scores• The 1-10 scale may allow for better precision in estimates

and a wide variation in scores (most common)

Assigning Rating Weights


Rating Scales

• Severity– 1 = Not Severe, 10 = Very Severe

• Occurrence– 1 = Not Likely, 10 = Very Likely

• Detection– 1 = Easy to Detect, 10 = Not easy to Detect

Assigning Rating Weights

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Risk Assessment Factors

Severity (S): A number from 1 to 5 (10), depending on the severity of the potential failure mode’s effect 1 = no effect5 (10) = maximum severity

Probability of occurrence (O): A number from 1 to 5 (10), depending on the likelihood of the failure mode’s occurrence1 = very unlikely to occur5 (10) = almost certain to occur


Risk Assessment Factors

Probability of detection (D): A number from 1 to 5 (10), depending on how unlikely it is that the fault will be detected by the system responsible (design control process, quality testing, etc.)1 = nearly certain detention5 (10) = impossible to detect

Risk Priority Number (RPN): The failure mode’s risk is found by the formula RPN = S x O x D. RPN = Severity x Probability of Occurrence x Probability of Detection. RPN will be a number between 1 (virtually no risk) and 125 (1000) (extreme risk).

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Risk Priority Number (RPN)

ó RPN is the product of the severity, occurrence, and detection scores.

Severity Occurrence Detection RPNX X =

Calculating a Composite Score


Difficulties in Implementation

• Time and resource constraints• Lack of understanding of the purpose of FMEA• Lack of management commitment• Employee training requirements• Initial impact on product and manufacturing schedules• Financial impact required to upgrade design,

manufacturing, and process equipment and tools

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FMEA Cycle


Extend to FMECA

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IN-CLASS PROBLEM 1

For Change Oil in Car generate a partial FMEA.


IN-CLASS PROBLEM 2

For the cordless screwdriver generate a partial FMEA.

a) List the three most significant functions of the case.

b) For most potentially difficult function, name Potential

Failure Modes

c) For each Potential Failure Mode, name Potential Effects

d) For each Potential Failure Mode, name Potential Causes

e) For each Potential Failure Mode, assign Severity, Occurrence,

and Detection values

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Summary

• An FMEA:– Identifies the ways in which a product or process can fail– Estimates the risk associated with specific causes– Prioritizes the actions that should be taken to reduce risk

• FMEA is a team tool• There are two different types of FMEAs:

– Design– Process

• Inputs to the FMEA include several other Process tools such as C&E Matrix

Key Points


END of the Chapter

Key Points

A collection of information including links to examples, guides, standards, etc.

http://www.fmeainfocentre.com/index.htm

http://www.fmeainfocentre.com/index.htm

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RPN is a quantitative measure to evaluate and assess the failure modeThe RPN is comprised of the following three criteria:

S = Severity or seriousness of the failure modeO = Probability of the occurrence of the failure modeD = Probability that a potential failure will be detected before it can have any consequences

The ranking system for each criterion is typically based on a linear scale:

1-10 ranking scale, 1-5 ranking scale depending on team preferenceLow number corresponds to low risk High number corresponds to high risk


Severity Rating Scale (1-10 Scale)

Rating Description Definition

10 Extremely Dangerous Failure could injure the patient

98

Very Dangerous Failure could cause major or permanent injury

7 Dangerous Failure causes minor to moderate injury with a high degree of patient dissatisfaction

65

Moderate Danger Failure cause minor injury with some customer dissatisfaction

43

Low to Moderate Danger Failure causes very minor or no injury but annoys customers

2 Slight Danger Failure causes no injury and customer is unaware

1 No Danger Failure causes no injury and has no impact on system

Adapted from: The Basics of FMEA, Productivity, Inc. Copyright 1996 Resource Engineering, Inc.

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Occurrence Rating Scale (1-10 Scale)Rating Description Potential Failure Rate

10 Certain probability Failure occurs at least once a day; or, failure occurs almost every time

9 Failure is almost inevitable

Failure occurs predictably; or, failure occurs every 3 or 4 days

87

Very high probability Failure occurs frequently; or. Failure occurs about once per week

65

Moderately high probability

Failure occurs about once per month

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Moderate probability Failure occurs occasionally; or, failure occurs once every 3 months

2 Low probability Failure occurs rarely; or, failure occurs about once per year

1 Remote probability Failure almost never occurs; no one remembers last failure

Adapted from: The Basics of FMEA, Productivity, Inc. Copyright 1996 Resource Engineering, Inc.


Detection Rating Scale (1-10 Scale)Rating Description Definition

10 No chance of detection

There is no known mechanism for detecting the failure

98

Very Remote/Unreliable

The failure can be detected only with thorough inspection and this is not feasible or cannot be readily done

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Remote The failure can be detected with manual inspection but no process is in place so that detection is left to chance

5 Moderate chance of detetion

There is a process for double-checks or inspection but it is not automated an/or is applied only to a sample and/or relies on vigilance

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High There is 100% inspection or review of the process but it is not automated

2 Very High There is 100% inspection of the process and it is automoated

1 Almost certain There are automatic “shut-offs” or constraints that prevent failure

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Risk Priority Number (1-5 Scale)Rating Severity (S) Occurrence (O) Detection

(D)1 Failure did not reach

pt.1 failure per year 100% of the time

2 Failure reached pt. 1 failure per quarter Almost always

3 Failure requires monitoring

1 failure per month 75% of the time

4 Failure requires intervention

1 failure per week 50% of the time

5 Failure results in death

1 failure per day Not detectable

Severity: Assessment of the seriousness of the effect Occurrence: Estimation of likelihood that a failure will occur.Detection: How likely will the failure be detected



• RPN = Severity Rank x Occurrence Rank x Detection Rank• The highest RPN’s and Occurrence Ranking should be given

the first consideration for corrective actions.

• As a general rule, special attention should be given when the severity ranking is high, regardless of the resultant RPN.

Chapter 6-1: Failure Modes Effect Analysis...

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