FMEA: Failure Mode and Effects Analysis
FMEA is a theoretical cause and effect study with theoretical solutions. 7FM uses the the time sequence of functions to ensure that nothing is missed and that requirements and functions are in agreement from start to finish.
- A failure mode is a poor quality function and each function can fail in one of seven ways that are useful for conversation.
- Failure modes have three categories which are magnitude, variation, and time response.
- Risks are assessed as Severity with numbers between 1 and 10 with 10 being the most severe.
- Severity is the result of a failure mode of a function and as such cannot be reduced.
- Severity be eliminated if a function can be eliminated.
- To reduce severity to an acceptable level, its hazard rate (occurrence) of the function’s failure mode must be reduced.
- Occurrence also has numbers ranging from 1 to 10 with 10 being the worst.
- The hazard rate can only be reduced by changing design parameters so causes occur less frequently.
- Design parameters are the requirements that the function requires and also the design parameters that reduce the impact of degradation factors (e.g. temperature, vibration, chemicals, debris, radiated energy, etc.)
- In design and in process FMEAs the most important risk is called criticality.
- Criticality is the product of the worst severity for a failure mode multiplied by the worst occurrence.
- Criticality is the risk of creating a hazard
- RPN stands for Risk Priority Number and is the most widely known risk number. It is the product of the worst severity, occurrence, and best detection.
- RPN is the risk of escape and just because a problem was not found in detection does not mean that quality is good and the product is safe.
- RPN is worked on after all important criticalities have been addressed.