This Article is the third in a four part series to show you “How to Complete a Six Sigma Root Cause Analysis.” The series covers four tools:
- The SIPOC(R) Diagram
- The Input (or Variables) Map
- The C&E Matrix
- The FMEA (Failure Modes and Effects Analysis)
In this article, we will be discussing the FMEA or the Failure Modes and Effects Analysis
Every product or process is subject to different types or modes of failure and the potential failures all have consequences or effects.
The FMEA is used to:
- Identify the potential failures and the associated relative risks designed into a product or process
- Prioritize action plans to reduce those potential failures with the highest relative risk
- Track and evaluate the results of the action plans
The Steps to Complete a FMEA:
Step #1: Review and label the Process Steps (using your process map) and the intended function or functions of those steps
Step #2: Consider the Potential Failure Modes for each component and its corresponding function
- A potential failure mode represents any manner in which the component or process step could fail to perform its intended function or functions.
Step #3: Determine the Potential Failure Effects associated with each failure mode. The effect is related directly to the ability of that specific component to perform its intended function
- The effect should be stated in terms meaningful to the product or system performance.
- If the effects are defined in general terms, it will be difficult to identify (and reduce) true potential risks.
Step #4: For each failure mode, determine all the Potential Root Causes
- Use tools classified as Root Cause Analysis tool, as well as the best knowledge and experience of the team.
Step #5: For each cause, identify Current Process Controls. These are tests, procedures or mechanisms that you now have in place to keep failures from reaching the customer
Step #6: Assign a Severity Ranking to each effect that has been identified
- The Severity Ranking is an estimate of how serious an effect would be should it occur.
- To determine the Severity, consider the impact the effect would have on the customer, on downstream operations, or on the employees operating the process.
- The Severity Ranking is based on a relative scale ranging from 1 to 10.
- A “10” means the effect has a dangerously high severity leading to a hazard without warning.
Step #7: Assign the Occurrence Ranking
- The Occurrence Ranking is based on the likelihood, or frequency, that the cause (or mechanism of failure) will occur.
- Once the cause is known, capture data on the frequency of causes. Sources of data may be scrap and rework reports, customer complaints, and equipment maintenance records.
Step #8: Assign the Detection Rankings
- To assign detection rankings, identify the process or product related controls in place for each failure mode and then assign a detection ranking to each control. Detection rankings evaluate the current process controls in place.
- A control can relate to the failure mode itself, the cause (or mechanism) of failure, or the effects of a failure mode.
- To make evaluating controls even more complex, controls can either prevent a failure mode or cause from occurring or detect a failure mode, cause of failure, or effect of failure after it has occurred.
Step #9: Calculate the Risk Priority Number (RPN)
- The RPN is the Risk Priority Number. The RPN gives us a relative risk ranking. The higher the RPN, the higher the potential risk.
- The RPN is calculated by multiplying the three rankings together. Multiply the Severity ranking times the Occurrence ranking times the Detection ranking.
- Calculate the RPN for each failure mode and effect.
Prioritize the Risks by Sorting the RPN from Highest Score to Lowest Score. This will help the team determine the most critical inputs and the causes for their failure.
Step #10: Develop Action Plan
- Taking action means reducing the RPN. The RPN can be reduced by lowering any of the three rankings (severity, occurrence, or detection) individually or in combination with one another.
Step #11: Who is Responsible
- This is a very important step in Taking Action!
- Be sure to include person(s) responsible and the deadline
Step #12: Take Action
- The Action Plan outlines what steps are needed to implement the solution, who will do them, and when they will be completed.
- Most Action Plans identified during a PFMEA will be of the simple “who, what, & when” category.
- Responsibilities and target completion dates for specific actions to be taken are identified.
Step #13: Recalculate the Resulting RPN
- This step in a PFMEA confirms the action plan had the desired results by calculating the resulting RPN.
- To recalculate the RPN, reassess the severity, occurrence, and detection rankings for the failure modes after the action plan has been completed.