FMEA

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. FMEA identifies actions that could eliminate or reduce the chances of the occurrence of the potential failure and tracks the corrective actions and their effects. It also document the entire decision process

FMEA can be viewed as an assessment tool, as it is used to diagnose the opportunities or as a prevention tool, as it used to prevent high level risks.

Purpose of FMEA

The purpose of FMEA is to recognize and evaluate the failure and the effects that failure has on the system and take actions to eliminate or reduce failures, starting with the highest-priority failures. FMEA also aims to reduce the time and cost of the operation by improving the teamwork and promoting accountability.

Elements of FMEA

FMEA consists of following elements, as

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 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 form 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 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(1in 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 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

Important FMEA Terms

• Risk Priority Numbers (RPN) – RPN is the product of severity(s), Occurrence (O) and Detection (D). The range of RPN is 1 <RPN <1000. It is calculated as

RPN = Severity x Occurrence x Detection

• 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.

Important Measures

• 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.

FMEA Procedure

The basic procedures involved in FMEA are listed below

• The first step in the FMEA methodology is to describe the product/process and its functions.
• Create a block diagram which includes all major components of the product/process. Connect the blocks logically.
• Identify the failure modes in terms of component, subsystem, system, process, etc.
• Identify the effects of failure mode on the product/process as perceived by the internal and external customers.
• Assign severity – Numbers from 1 to 10 can be used to rank the severity of the effects.
• Brainstorm the root causes of the failure – the sources for each failure mode have to be discovered and recorded.
• 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’.
• 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.
• 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.
• 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.

• Recommend actions – This is followed by determination of recommended actions to deal with potential failures that have a high RPN.
• 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.
• 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

FMEA Types

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

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. It highlights the area of improvement. It helps to improve the system safely in accordance with the priority by eliminating unsafe conditions. DFMEA is mainly used to analyze product or component designs

Process FMEA (PFMEA) – PFMEA is mainly used to assess transactional processes. 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

FMEA Advantages

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

FMEA Disadvantages

The major disadvantages for an organization due to usage of FMEA are as

• 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.