FMEA or PFMEA if you want to analyse a process is analysis tool that is used to identify and reduce potential risks. It was 1^st developed by the US Military in the 1940’s and has been widely (1) used in a variety of sectors in the modern era. FMEA stands for Failure, Mode, Effect, Analysis or also known as Five Men Eternally Arguing. The letter P stands for Process if you are using a PFMEA instead of a FMEA.

It’s good to start FMEA at the beginning of the design process as it can help develop concepts and prevent issues at the start. The FMEA tool should be reviewed and updated as the project progresses as more knowledge during the development is established. The biggest mistake when carrying out a FMEA is to do it in 1 or 2 all day meetings as it’s difficult to pay attention and do it properly. Plus carrying out an FMEA is boring and a very dry subject so it’s best to limit long sessions and just break it up. Another mistake is to treat a FMEA as a “tick the box” exercise where you carry out an analysis and then forget about it. This is as mentioned earlier that the whole purpose of this exercise is to prevent issues from appearing which could lead to expensive rework and delays but also part of the tool requires you to take up an action plan to resolve these potential risks and follow them up. In addition, whenever put in a new design or procedure in place to prevent a hazard to ever happen you may have inadvertently created new potential risks which will need reviewed.

Figure 1 Cubesat with HDRM (blue) for antenna

In our example on how to carry out a FMEA we will use a cubesat (Figure 1) with an HDRM that locks and releases and antenna.

An FMEA can be split into two halves. The 1^st half (Figure 2)  is where the team mapping out the design functions or process and identify the modes, failures, causes, current controls and the RPN ratings. The 2^nd half (Figure 3) focuses on coming up with solutions to these potential failures.

1^st Half

Figure 2 FMEA 1st half

Function/Process step

list out each feature of a design function or process step.

Potential Failure Mode

The failure mode is what can go wrong in your feature or process. In our example our HDRM can’t be mounted onto our satellite. If you have multiple potential failures in a design feature or mode, then make sure they are in a separate cell because these modes will have different RPN ratings.

Potential Effect of Failure

What will the impact of this failure mode be? Will it cause a delay? Damage your system? Cause injury to the operator? Make sure you list out multiple effects in a separate cell. Our failure is that the HDRM cannot be used therefore the antenna cannot be deployed properly.

Severity

Give the failure effect a severity rating of 1-10. 1 will be minimal adverse effects with 10 being catastrophic failure which could lead to mission failure, loss of equipment and severe injury or death to person. In our example our severity is 10 because the mission can’t go ahead as the antenna can’t be fixed and released.

Potential Causes of Failure

What are possible reasons as to why this failure occur? Incorrect instructions? Wrong parts? The mounting interface between our HDRM and satellite don’t match due to tolerance issues as the drawings weren’t updated due after some minor alterations. You can use Ishikawa and 5 whys analysis tools to help find the root cause.

Occurrence

How likely will this failure occur? Occurrence, severity, and detection usually use the 1-10 scale, in this case 1 is almost impossible to happen and 10 is inevitable. In our example the likelihood is 3 due to our current controls.

Current Controls

Current controls are methods that are currently in place to prevent the failure mode from occurring. This can be design reviews, tolerance stacks, adhering to standards, protocols, safety measures and equipment. For our HDRM issue we have implemented tolerance stacks and review sessions.

Detection

How easy is it to detect this failure mode? Can it be detected before it will occur, or will the fault occur as current controls are unable to detect the issues from arising. With our current measures it is not adequate to ensure design modifications are updated therefore its detection is 6.

RPN

Risk Priority Number or RPN is a rating system that can help you prioritise which issues to resolve as these will have the highest RPN ratings. The severity, occurrence and detection are multiplied to provide RPN. If you have modes with high severity ratings such as >7 then it is advisable to resolve them as well because even if you can detect them or are unlikely to occur, they can cause serious issues to your project, business, process or product.

In our cause our failed HDRM has an RPN rating of 80.

Figure 3 FMEA 2nd half

Once you identify which modes you should prioritise it is time to develop an action plan to resolve or prevent the issues from happening or repeating.

Recommended Actions

Provide recommended actions to resolve the issues. In future whenever we make a new design alternation to the HDRM, we will update the drawings immediately and roll out a version control process where current designs are given new versions when a change is made. Also, during the testing phase, a lesson learned exercise will be carried out and documented.

Responsibility

Who will oversee these changes and when will these changes be carried out?

Action taken

What has been carried out to resolve or prevent the issue from happening? In our HDRM example we implemented a new PDM software for our CAD system which helps improve version control and keeps all the documents up to date. Whenever a new version of a part is made the old version is locked and unavailable for export.

New RPN

Give new RPN ratings based on the new measures put in place. Do the changes reduce the severity, likelihood or improve detection? Our new measures increase the detection of incorrect versions of the HDRM design being sent out to machining with the new PDM in place old versions being locked.

Bibliography

1. History of FMEAs. Quality Training Portal . [Online] [Cited: May 11, 2023.] https://qualitytrainingportal.com/resources/fmea-resource-center/fmea-history/.