FMEA Thoughts
I am sitting at a major manufacturer of farm machinery (typically painted green) listening to a discussion about Failure Modes, and it occurs to me that there is a general misunderstanding of Failure and how to mitigate risks. I am writing this initial entry into the FMEA Blog to take the opportunity to clarify some key items about Failure and subsequent causes. In an FMEA, it is fairly common to get the causes, Failure modes and effects all mixed up. I like to follow a simple set of rules to make this easier.
- Get the function in a verb noun combination with a measurement defined.
- Simply reverse the Function into a failure mode.
- E.g Must dry clothes within 15 minutes (verb/noun underlined) Failure modes become: does not dry, takes too long to dry, uneven drying
- Effects are limited to customer effects in this order: Regulatory, Consumer/User, and assembly and manufacturing customers. Keep these words in the context of a non engineer. This means how would your mother or uncle describe the failure and rate how bad each is.
- Severity is assigned to each effect but only 1 severity number matters and the rest of the FMEA is driven from this one severity number. Remember that for each Failure Mode there is only 1 Severity or a 1 to 1 relationship. We do not look at Causes of each Effect.
- Causes must be associated with:
- individual components or subsystems, specifically things like geometry, materials, fatigue and other physics of failure.
- Interfaces of other systems and their impact on your design.
- Noise factors, or items that can affect performance but are outside the control of the team doing the FMEA
These are best understood by using Boundary diagrams and P diagrams. By clearly defining the differences between Failure Modes, Effects and Causes, the FMEA experience will be much more palatable for the team members. Remember the F in FMEA still does not stand for Fun. If you have any comments or wish to add something, please go the comments section and/or email me with your suggestions.
Lee