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Analyze

Failure Mode and Effects Analysis



Introduction

Failure Mode and Effects Analysis (FMEA) is an industrial strength risk

assessment tool which

• Gives a step-by step approach to recognize and evaluate all potential

failures in a design manufacturing or assembling process of a product

or a process

• Identifies actions that could eliminate or reduce the chances of the

occurrence of the potential failure

• Tracks the corrective actions and their effects

• Document the entire decision process

FMEA can be viewed

• As an assessment tool, as it is used to diagnose the opportunities

• As a prevention tool, as it used to prevent high level risks



Purpose of FMEA

• To recognize and evaluate the failure and the effects that failure has on

the system

• To take actions to eliminate or reduce failures, starting with the highest-

priority ones

• To reduce the time and cost of the operation

• To improve the teamwork

• To promote accountability



Elements of FMEA

Severity(S):

• Severity is the worst potential outcome of a failure, which is determined by the degree of injury, system damage etc.

• Severity is the impact of failure, numbers from 1 to 10 are assigned to each failure effect, where 1 refers to the failure with no/slight effect and 10 refers to that failure with most critical effect

• The range of Severity is 1 < S <10

The following table gives the different values in the Severity scale and

corresponding effects

Rank Effect

10 Hazardous without warning

9 Hazardous with warning

8 Very High

7 High

6 Moderate

5 Low

4 Very Low

3 Minor

2 Very Minor

1 None



Occurrence (O):

• Occurrence refers to the number of times a cause of a failure will

occur.

• Occurrence is considered to be a design weakness, numbers from 1 to

10 are assigned to each failure, where 1 refers to that failure which is

unlikely to occur and 10 refers to that failure which is most likely to

occur

• The range of Occurrence is 1 < O < 10

The following table represents the different values in occurrence scale

and the corresponding effect

Rank Effect

10 Very High (1 in 2)

9 Very High (1 in 3)

8 High (1 in 8)

7 High (1 in 20)

6 Moderate (1 in 80)

5 Moderate (1 in 400)

4 Moderate (1 in 2,000)

3 Low (1 in 15,000)

2 Low (1 in 150,000)

1 Remote (1 in 1,500,000)



Detection (D):

• Detection refers to the ability of designed checks and inspections to

detect and remove defects of failure modes.

• Numbers from 1 to 10 are assigned to each failure effect, where 1

refers to that failure which is easy to detect and 10 refers to that failure

which is almost certain that we can’t detect

• The range of detection is 1 < D < 10

The following table represents the different values in the detection

scale and the corresponding effect

Rank Effect

10 Absolute Uncertainty

9 Very Remote

8 Remote

7 Very low

6 Low

5 Moderate

4 Moderately High

3 High

2 Very High

1 Almost Certain



Risk Priority Numbers (RPN):

• RPN is the product of severity(s), Occurrence (O) and Detection (D)

• The range of RPN is 1 < RPN < 1000

Failure effect:

Failure effect refers to the consequence of a failure mode on the part of the product/process as perceived by the internal and external customers

Failure mode:

Failure mode refers to the manner in which a component, subsystem,

system, process, etc. probably fails to adhere to the design intent.

Failure cause:

Defects in plan, process, quality, etc. that result in a failure or initiate a

process that leads to failure.

RPN = Severity × Occurrence × Detection



Corrective actions

• RPN has to be calculated for the entire process

• Highest priority is given to that failure with highest RPN, Since higher

the RPN values higher the risks involved

• We should consider the less RPN values in some cases, because there

can be some failures which are less severe and less detective but

occurs most often.



Procedures involved in conducting FMEA

The basic procedures involved in FMEA are listed below:

1) The first step in the FMEA methodology is to describe the

product/process and its functions.

2) Create a block diagram which includes all major components of the

product/process. Connect the blocks logically.

3) Identify the failure modes in terms of component, subsystem, system,

process, etc.

4) Identify the effects of failure mode on the product/process as

perceived by the internal and external customers.



5) Assign severity: Numbers from 1 to 10 can be used to rank the

severity of the effects.

6) Brainstorm the root causes of the failure: the sources for each failure mode have to be discovered and recorded.

7) Occurrence: This is followed by entering the probability factor, which is

the numerical weight assigned to each failure mode effect cause, indicating ‘the probability that the failure mode effect cause may occur’.

8) The next step is to identify the current controls. Current Controls are the devices that detect and check the failure mode causes from occurring before the customer gets access to the product or service.

9) Detection: Likelihood of detection has to be ascertained in this step.

Detection refers to the probability that the current controls will detect the cause of the failure mode before the customer gets access to the product.



10) Calculate RPN: After ascertaining the likelihood of detection, the

Risk Priority Number (RPN) has to be created and reviewed. RPN is

the product obtained after multiplying severity, probability, and

detection ratings.

RPN = (Severity) x (Probability) x (Detection)

The RPN is used to rank the items that require supplementary quality

planning or corrective measures.

11) Recommend actions: This is followed by determination of

recommended actions to deal with potential failures that have a high

RPN.

12) Document changes of RPN: After the recommended actions are implemented, the implemented actions have to be documented. This can be used to reassess the severity, probability, and detection and review the revised RPNs. This is done to explore the possibility of the requirement of supplementary actions. 13) Review Periodically: Finally, the FMEA has to be updated as and

when the design or process changes or the assessment changes or

new information becomes known.

(FMEA is an ongoing activity)



• Example of FMEA work sheet

No

Function

Potential failure mode

Potential failure effect

Severity

Class


Occurrence

Current controls

Detection

RPN

Recommended action

Severity

Occurrence

Detection

RPN



Types of FMEAs

There are various types of FMEAs available for organizations. They can

make use of these FMEAs in accordance with their requirements. The major

types of FMEAs are as follows:

1) Design FMEA (DFMEA):

DFMEA is mainly used to analyze product or component designs

2) Process FMEA (PFMEA):

PFMEA is mainly used to assess transactional processes



Design FMEA (DFMEA):

• DFMEA is mainly concentrating on identifying the weakness in the design of a product or its components, that may cause the failure of the total system while the product is in service total system while the product is in service

• It highlights the area of improvement

• It helps to improve the system safely in accordance with the priority by eliminating unsafe conditions



Worked Example for DFMEA on a common defect in the mobiles

No

Function



Severity


Occurrence

Current controls

Detection

RPN Recommended action

Severity

Occurrence

Detection

RPN

1

Mobile handset

No display

Customer dissatisfaction

8 8

Presence of moisture in the circuit Improper connection between circuit and display flip models

5 3

None

7 2

280 48

Usage of thin plastic layer between the circuit and keypad Ensure proper connection and usage of good materials

2 2

1 1

2 1

4 2



Process FMEA (PFMEA):

• PFMEA helps to identify the deficiencies of the process in the early

stage of production

• It gives an organized and systematized approach to reduce the

potential process deficiencies in a accordance with the priority

• It helps to improve the future process by taking necessary action to reduce deficiencies



Worked Example For FMEA on fire in the residential buildings

No

Function



Severity


Occurrence

Current controls

Detection


Severity

Occurrence

Detection

RPN

1

Provides safety and protection

Flammable

Residents’ displeasure

8 7 4

Leakage of gas Short circuit Carelessness

5 6 4

None

7 6 6

336 252 96

Usage of quality pipelines and ensure closure of pipes after use Usage of quality wires Avoid flammable things

2 2 3

3 2 3

2 3 2

18 12 18



Worked example of FMEA

• Assume that a bank wants to conduct a failure mode effects analysis on

the working of its ATM units. By using the steps mentioned earlier, a

failure mode effects analysis is conducted. The analysis, depicted in the

FMEA worksheet, appears as follows:



• Worked example of FMEA

No

Function



Severity


Occurrence

Current controls

Detection


Severity

Occurrence

Detection

1

Dispense the cash in 30 seconds.

Takes more than 30 seconds to dispense the cash

Customer dissatisfaction

8

Intermittent power supply

4

None

4

128

Usage back-up power supply

2

1

1



Advantages of using FMEA

1) FMEA captures the collective knowledge of the team. This will direct the total efforts of the team toward a common goal.

2) FMEA improves the quality, reliability, and safety of the process as it identifies the possible failure modes. Thus, it enables the personnel to plan for the future while it remedies the present hindrances.

3) FMEA helps to identify design qualities that are responsible for failures and minimizes or eliminates them from the system. Thus, it allows for creation of a logical structured process.

4) FMEA cuts down process improvement time and cost as it optimizes the ability to transmit structured information from one project to another. Thus, it drives the qualities of repeatability and reproducibility across the system.

5) FMEA records and monitors the activities aimed at reducing the potential risks in the design. This helps in the expansion of corporate database and leads to the success of future products as well.



6) FMEA helps to identify critical-to-quality characteristics (CTQs) as they

evaluate the requirements obtained from the customer or other

participants in the design process.

7) As FMEA is constantly updated with anticipated failure modes, it

provides a baseline for the future design. Thus, it not only provides

historical records but also helps in establishing the future baseline.

8) FMEA evaluates the functions and the form of products and processes. It provides safety factors to make sure that the design succeeds and keeps crucial elements of the project from slipping away. Thus, it protects the customer against product or process failure and helps to increase customer satisfaction and safety.



Disadvantages of using FMEA

The major pitfalls that an organization can face because of using FMEA are

as follows:

• The FMEA is limited to the experience of previous failures because FMEA is purely dependent on the team members who analyze the product failures. So, if a failure mode is not identified then the organization may have to seek external help which will increase the costs.

• If FMEA is used only as a top-down tool, the probability of identifying minor failure modes in a system is remote. So, it may ignore the minor failure modes which in the course of time may develop into a major failure mode.

• If FMEA is used only as a top-down tool, it will be able to identify most of the major and minor causes of failure modes in the system. But, at times, it will not be able to identify some of the complex failure modes that comprise manifold failures within a subsystem. Thus, it will not be able to report probable failure intervals of particular failure modes up to the upper level subsystem or system.

• Another drawback of using FMEA is that the multiplication of the

severity, occurrence, and detection rankings may result in rank

reversals. ‘Rank reversal’ means a serious failure mode is attributed a

lower RPN, whereas a less severe failure mode is given a higher RPN.

‘Rank reversals’ may result in the organization facing major problems

in the current and future scenarios.



Conclusion

• Introduction

• Purpose and elements of FMEA

• Types of FMEAs

• Procedure Involved in FMEA with Example

• Advantages of using FMEA

• Disadvantages of using FMEA

Documents

Six Sigma Black Belt Study Guides - PMTUTOR · PDF fileSix Sigma Black Belt – Study Guides . ... • As a prevention tool, ... • Detection refers to the ability of designed checks