Different types of Fmea and Procedures- Failure mode effect analysis

Failure mode effect analysis – FMEA

 

There are a lot of examples of vehicle recalls due to quality or safety related issues. so Fmea helps one to make the vehicle more safe with following different steps and procedures.


Failure mode effect analysis

Failure mode effect analysis:

According to the definition by wikipedia,  Failure mode effect analysis [FMEA] is one of the first highly structured, systematic techniques for failure analysis. It was developed by reliability engineers in the late 1950’s to study problems that might arise from malfunctions of military systems.

An Failure mode effect analysis [FMEA] is often considered the first step of a system reliability study.

There are a lot of examples of vehicle recalls due to quality or safety related issues.

Failure mode effect analysis [FMEA] is a methodology aimed at allowing companies to anticipate failure during the product designed stage and manufacturing process design stage by identifying all the possible failures. This mentioned image above is a sample template of the FMEA offered by Systemstowin. 

BENEFITS OF FMEA

  • Allows us to identify areas of our process that most impact our customers
  • Helps us identify how our process is most likely to fail
  • Points to process failures that are most difficult to detect
  • Following up action
  • Providing documentation for quality audit
  • Checking on the decisions +ve / -ve
  • Making clear the accountability
  • Continuous improvement
  • Part of the validation or verification

Let’s see about the Different types of fmea in the upcoming paragraphs

Different types of fmea

There are mainly two categories of FMEA.

1.DFMEA – DESIGN FAILURE MODE EFFECT ANALYSIS

2.PFMEA – PROCESS FAILURE MODE EFFECT ANALYSIS

1.DFMEA-DESIGN FAILURE MODE EFFECT ANALYSIS

Design:

  • Analyzes product design before release to production, with a focus on product function
  • Analyzes systems and subsystems in early concept and design stages

DESIGN FAILURE MODE AND EFFECT ANALYSIS was first used in space research programs. The rocket development process in the 1950’s didn’t go well due to continuous failures.Root cause analysis (RCA) was used to investigate all these failures .But, didn’t went well due to no evidence were remaining because of explosion happened during failure provided rocket scientist a platform to prevent failures.A similar platform is used today in many industries to identify risk.

DFMEA is a methodological approach used for identifying potential risk on a new design of a product.

This DFMEA initially identifies design functions failure modes and their effect on customer with severity ranking or danger of the effect then the possible causes of these failures are identified and fixed.

DFMEA tracks improvement through  RPN ( Risk priority number) by comparing before and after RPN.

2.PFMEA-PROCESS FAILURE MODE EFFECT ANALYSIS

process:
  • Used to analyze manufacturing and assembly processes after they are implemented

PROCESS FAILURE MODE AND EFFECT ANALYSIS looks at each process step to identify risk and possible errors from many different sources. PFMEA is a methodological approach used for identifying risk on manufacturing process.

PROCESS FAILURE MODE AND EFFECT ANALYSIS initially identifies process functions,failure modes ,their effects on the product and process.The severity ranking is determined for each effect of failure,then causes and their mechanism of failure mode are identified .

The PFMEA also tracks improvements through RPN reductions ,by comparing the before and after RPN, where RPN is the Risk Priority Number.

 

STEPS IN MAKING FMEA:

FMEAs are an analytical way of identifying how a process can fail and the consequences of that failure.  FMEAs are best used prior to implementing a new process, or prior to modifying an existing process.  This type of analysis is an organized way of discovering what could go wrong, and planning what we can do to eliminate such potential problems.

FMEAs evaluate three key dimensions of process failure; severity, occurrence frequency and detectability on a scale of 1 to 10 (1 lowest, 10 highest).  Severity is a measure of how damaging a failure would be.  Occurrence frequency tells us how often this type of failure might occur.  A problem that occurs several times a day rates high on the occurrence scale while something that happens once every few years rates very low on the occurrence scale

Detectability is an estimate of how likely it is that you will detect the failure prior to its having a harmful effect.  A failure mode that would be obvious for a long time prior to any harmful effects happening rates a low detectability score.  Failure modes that are essentially undetectable prior to the effects taking place rate high on this scale.

Step 1: What Is the Process?

A process is a naturally occurring or designed sequence of changes of properties or attributes of an object or system.

A Failure Mode and Effects Analysis (FMEA) begin by specifying the process to be studied.  You should have a process flow diagram (PFD) of the process. Record what the process is in the first column on the top half of the FMEA sheet.

Step 2: What Is the Potential Failure Mode?

As a group, brainstorm all possible ways that this process could fail. These are the “potential failure modes.” Write these ideas on a flip chart in a fishbone format. Look at the process using 4Ms, P and E – Methods, Materials, Measurement, Machinery, People, and Environment – in the “fishbone” format. From the brainstormed list, choose the most significant failure mode and write it in Column 2 on the FMEA form. You can repeat this process for different failure modes.

 Step 3: What Are The Potential Effects Of The Failure Mode?

Write down the effects that would happen if the potential failure was a real failure. How would the failure impact your company? Your suppliers? Your customers? What would be the worst possible outcomes?

 Step 4: What is the Severity of the Failure Mode to the Customer, Product, or Service?

The Severity Rate (S) is the “best guess” of how serious it would be to the customers, the product, or the service if the failure really occurred. A rating of 1 would mean the effect of the failure is considered minor; a rating of 10 would indicate that the effect of the failure would be very severe. Using the information in Step 2, your “best guess,” and the scale below, assign one overall severity rate to the failure mode identified in Step 2.

Severity Scale: 

9 – 10: With potential safety risk or legal problems – potential loss of life or major dissatisfaction

7 – 8: High potential customer dissatisfaction – serious injury or significant mission disruption

5 – 6: Medium potential customer dissatisfaction – potential small injury, mission inconvenience, or delay

3 – 4: The customer may notice the potential failure and may be a little dissatisfied – annoyance

1 – 2: The customer will probably not detect the failure – undetectable

 Step 5: What Are the Possible Causes of the Failure? Why Does It Happen?

For the failure mode listed in Step 2, write down all factors the team can think of that could cause the failure to occur. Number the causes. Be creative in trying to determine why the failure would occur. Talk to your internal and external suppliers of the process, your internal and external customers, and the “natural team” involved. A fishbone is, again, a helpful SPC tool to use with this step. Failure modes always have more than one cause.

 

Step 6: How Often Does the Cause of Each Failure Occur?

The Occurrence Rate (O) is an estimate of how often the failure happens due to each specific cause listed in Step 5. A rating of 1 or 2indicates the failure very rarely happens; a rating of 10 indicates it happens very frequently. (For example, a specific stock item may require a “buy out” virtually every week; thus, the occurrence rate for this cause of a failure mode could be a 10.) For each of the numbered causes in Step 5, assign an occurrence rate from the scale below.

Occurrence Scale: 

9 – 10: Very high probability of occurrence

7 – 8: High probability of occurrence

5 – 6: Moderate probability of occurrence

3 – 4: Low probability of occurrence

1 – 2:  Remote probability of occurrence

 Step 7: How Do We Currently Prevent Each Listed Cause of Failure from Happening?

For each of the failure mode causes in Step 5, write down current ways you prevent the situation from occurring. Number each of these current ways to correspond with the cause number in Step 5. If no current way exists, state “none.” Each potential “cause” should have at least one current prevention method or a response of “none.” Take time to identify current ways of prevention. Decide if you need a control chart to monitor how the current way of preventing the failure is working.

Step 8: How Easy Is It to Detect the Failure Before the Customer Sees It?

The Detection Rate (D) is an estimate of how difficult it is to detect the failure before the customer sees it. A rating of 1 would indicate that it is obvious right away to anyone that the failure is occurring; a rating of 10 would indicate that the failure will go undetected until the effect is felt by the customer. (For example, over billing a customer’s account might not be detected until the customer gets it. The detection rate for this failure mode would be a10.) For each of the current ways (Step 7) being used to prevent the cause of a failure mode (Step 5), assign a Detection Rate (D) using the scale below.

 Detection Scale: 

9 – 10: Zero probability of detecting the potential failure cause

7 – 8: Close to zero probability of detecting potential failure cause

5 – 6: Not likely to detect potential failure cause

3 – 4: Good chance of detecting potential failure cause

1 – 2:  Almost certain to identify potential failure cause

 

 

 Step 9: Scoring Summary

Enter the brutality rate from Step 4 for each cause from Step 5. There is only on severity rating, so it will be the same number for each cause.

Enter the Occurrence rate from Step 6 for each cause from Step 5.

Enter the Detection rate from Step 8 for each prevention method listed in Step 7.

Multiply the “S” times the “O” times the “D” for each cause to get an initial Risk Priority Number (RPN).

S x O x D = RPN

 

The highest RPN possible is 1000. Such a high RPN would indicate a mode of failure that is very severe (S = 10), occurs frequently (O = 10), and is almost impossible to detect with the current systems (D = 10). The lowest possible RPN is 1; such a mode of failure would not have a severe impact (S =1), would occur very infrequently (O = 1), and would be very easy to detect (D =1).

  Step 10: Review if Management Involvement Is Needed.

At this point, before time is spent determining how to revise the process, teams can review their Failure Mode and Effects Analysis (Fmea) with management if necessary. It is probably good to do this if it appears that great costs will be incurred should a major change in process be made. If management is not in agreement with the team’s calculations, the two groups should discuss the rating system until they reach a consensus. Then, the team can return to Step 4 and revise its calculations.

If management is in agreement with the team’s calculations, then management and the team need to decide whether or not the Risk Priority Numbers are high enough to warrant doing something about the process right away.

  Step 11: Action Steps: What needs to be done?

For each cause with a high RPN, brainstorm ways that the RPN can be reduced. Remember, RPNs can only be reduced by revising the process. Normally, the Occurrence Rate (O) must be lowered or the ability to detect the failure (D) must be increased. The Severity of the failure (S) usually cannot be reduced.

To lower the RPN, brainstorm ideas that will address the occurrence rate or the detection rate. Discuss these ideas as a team and reach a team consensus for best ideas for process improvement or process revisions. The team will find that some recommendations are general for all potential causes of a failure mode; other recommendations should be assigned to a specific potential cause of failure.Take the best ideas for improvement and recommend action steps. State what needs to be done, who needs to be responsible for doing it or seeing that it gets done, and when it should be started and finished.

Step 12: Implement Action Steps.

Once agreement is reached on the specific recommended action steps, the Action Plan should be implemented. This involves reviewing the steps in Step 11, including who is responsible for each step, and when each step will be completed. Input from management may be required.

 Step 13: Recalculate and Adjust New RPNs after Strategy Intervention

Once the action steps have been implemented and new control data are generated that accurately reflect the impact of implemented changes, the team should recalculate the Risk Priority Numbers for each process by determining Severity Rate (S), Occurrence Rate (O) and Detection Rate (D) for the revised process for each cause listed in Step 5. RPN is then calculated (see Step 9). Projected RPNs in Step 12 should be adjusted accordingly. Results should be shared.

 Conclusions:

The failure mode and effects analysis (Fmea) tool provides a method of looking at potential ways a process can fail and then implementing plans to prevent the most likely causes of failure.  A few general comments are given below on Failure mode effect analysis.

High severity, which often indicates a potential catastrophe, can capture total attention and too much time when O&D are rated as a “1.”

Occurrence is not usually subjective; it can be measured in terms of frequency.

Detection is also typically data-based in terms of how often that failure cause has been detected before the customer reports it.

People can spend a lot of time on a high O with low D&S.  It is easy to see such a failure, and it can be tempting to spend too much time on a problem that is not important (low S) and easy to detect (low D).

When the problem occurs frequently, but is not severe, and the detection is easy, we are usually dealing with common cause variation.

Management needs to consider making systemic modifications and/or changes.

Look for root causes of high RPNs before deciding on recommended action steps.

Review the draft Failure mode effect analysis with those closest to the job before deciding on recommended action steps; they may have additional input.

Use Failure mode effect analysis prior to implementing a new process (Design FMEA) and prior to modifying an existing process (Process FMEA).

Comment:

Failure mode effect analysis are an analytical way of identifying how a process can fail and the consequences of that failure.

Failure mode effect analysis’s are best used prior to implementing a new process, or prior to modifying an existing process.

This type of analysis is an organised way of discovering what could go wrong, and planning what we can do to eliminate such potential problems.

Reference

Definition: FMEA : wikepedia

image credit: systems2win

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