Failure Modes are actual or potential defects in a process or item. Generally these are limited to defects which affect the customer.
Failure Mode Effect Analysis (FMEA) analyzes the potential failure modes of a process, and classifies these modes by severity or the types of effects on the system.
FMEA is predictive: the analysis should begin in the product's design stage, in subsequent re-design stages, or when manufacturing processes are being revised.
The analysis does need historic data:
FMEA needs pre-work: in particular, the product must have enough documentation to let the review team know the valued functions, the components, how the components work together. The more known, the better the analysis can be.
This may be a familiar example. Consider the bathroom toilet with a tank to store clean water for flushing. A hollow metal float is attached to a lever which controls both a drain stopper and a cut-off valve. The user flushes by moving the lever to lift the stopper; this causes rapid drainage. This also opens the cut-off valve so fresh water begins to slowly refill the tank. When the tank's water level goes down, the float drops to permit the stopper to drop and stop the drainage. When the float rises high enough, then the cut-off valve stops refilling the tank.
Part of the worksheet might look like this:
Function | Failure Mode |
Effects | Severity Rating |
Cause(s) |
Refill tank |
Tank refills forever. Level is high. |
Wastes water. Noise. Possible overflow onto floor. |
5 |
Leaky float does not rise. Float detached from lever. |
Refill tank |
Tank refills forever. Level is low. |
Wastes water. Noise. |
4 |
Stopper is not water-tight. |
Refill tank |
Tank remains empty |
Cannot flush toilet next time. |
2 |
Plumbing leading to toilet. Cut-off valve is stuck. |
Tha Failure Mode Effect Analysis is, of course, more complex – even for a simple example like the one above.
An worksheet might include:
Some organizations use ratings from 1 to 4 rather than 1 to 10. Regardless of the ratings scale, the goal is to determine the RPN for each failure in order to prioritize the remediation efforts.
The risk-based analysis is very important in achieving higher quality by working toward:
By Oskar Olofsson
Making lean work for you
World-Class / Lean Manufacturing
5S Implementation
SMED Quick Change-over
TPM and Plant Maintenance
Succeeding With Standardized Work
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