The Failure Mode and Effects Analysis, FMEA, is a subjective screening tool that uses numerical assignments to determine the risk associated with each input (failure mode). The highest scored items add the highest risk to the problem or present the highest risk to the process, design, or function.
Assign a level of risk for each input as in impacts the output by determining the severity, frequency of occurrence, and ability to detect the failure mode for each input. A Risk Priority Number (RPN) is calculated and corrective action emphasis is given to those inputs with the highest RPN. Any input with a high severity (such as 9-10) should be given attention regardless of RPN.
The figure below shows the linkage of the subjective screening tools in a DMAIC project.
Before you and the team jump into assigning values remind everyone that assigning ratings is subjective. Companies have different interpretations of each value and its meaning and many have developed tables and guides for each number 1-10 on what they represent.
It is more important that the scale applied is linear and well understood by each appraiser to minimize error from interpretation. The appraisers in this application are the team members, each one gets has input. Take time to review the meaning of each value for:
Each person can explain their score too and this helps the others on the team understand their perspective on the problem. Eventually the team leader needs to decide on one value and move on....don't let this process drag out too long, keep the team moving forward. It's easy to get derailed and begin great debates. Be careful for this!
Completing the FMEA:
Keep in mind, none of the scores can be a zero or the RPN will be zero. Therefore, to make the list on the FMEA as a Failure Mode, there must be a score >0 assigned to each the Severity, Occurrence, and Detection score.
The goal is to reduce the highest
RPN’s. It’s a never ending cycle and not all of the failure modes have to be
addressed and re-scored at once.
ü Sort the Failure Modes in descending order with the highest RPN’s at the top. These are the modes to focus on reducing the Severity, Occurrence, and Detection.
ü Complete any easy improvement actions regardless of RPN.
ü Target any Failure Modes with a high severity value inputs regardless of RPN.
After an improvement is done, rescore the failure mode and continue on the journey of reducing other RPN’s. Often times an improvement can be applied to other failure modes...find all those you can!
This tool is widely used in quality control organizations across
all industries and segments to improve customer satisfaction.
They are used for design, processes, services, and more. It is
recommended to become very familiar with this tool and how it works.
Click here to purchase the FMEA and REVISED FMEA template.
This module provides more detail about the development of a FMEA.
All Six Sigma project managers need to be
familiar with this tool as it applies to almost every project.
What is the Risk Priority Number (RPN) of a particular failure mode where the team assigned the following values?
Severity = 5, Detection = 3, and Occurrence = 9
RPN = Severity * Detection * Occurrence = 5*3*9 = 135
Next, assume the team implemented a few poka-yokes and other improvements. Therefore the revised FMEA now has the following scores assigned by the team:
Severity = 5 (usually the severity of the failure mode stays the same but not always)
Detection = 2
Occurrence = 4
What is the RPN for the Revised FMEA? The answer is 5*2*4 = 40
Therefore the RPN for that failure mode was reduced from 135 to 40. This is obviously a significant improvement but it may not be enough depending on the customer needs.
The idea is to go after the highest RPN on a regular basis. The process never stops in the world of quality control. There will always be a failure mode(s) with a higher score than others. Never stop pursuing the ability to reduce the RPN's.
Think about the three categories.....usually ANY failure mode with a Severity of 5 or higher automatically gets attention. A failure mode with a high severity should be addressed vigorously to somehow reduce the severity, perfect the detection, or eliminate the possibility of it occurring.
The example below shows a Six Sigma team's initial FMEA for a few process steps involving setting up and forming a widget.
Notice the right side of the FMEA is not yet complete. This portion is completed after the improvements are in place and verified.
You can see the highest RPN is delivering of wire to the machine with a potential failure mode of "Wrong Material".
The RPN is 243 followed by others of lower RPN. The team decides to implement a series of improvements (actions) to address the highest RPN's.
Often times simple improvements such as improving the quality of work instructions (SOP's) and advanced training are common improvements for almost any failure mode. Many improvements apply to more than one failure mode as well.
Some improvements require money, testing, trials, or other resources. Remember you may not be able to do them all but at least get the ideas on paper and discuss them with the leadership of the company.
Below you can see the improvements and the impact of the RPN on the failure modes. All of them were reduced except for one that the team decided not to address.
What is that worth to the company? You will want to quantify those risk reductions with your Finance representative.
Now the cycle continues and the relentless pursuit for improvement never ends.
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