Timing of FMEA
The FMEA should be updated whenever: At the beginning of a cycle (new product/process) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem
Uses of FMEA
Development of system requirements that minimize the likelihood of failures. Development of methods to design and test systems to ensure that the failures have been eliminated. Evaluation of the requirements of the customer to ensure that those do not
give rise to potential failures. Identification of certain design characteristics that contribute to failures, and minimize or eliminate those effects. Tracking and managing potential risks in the design. This helps avoid the same failures in future projects. Ensuring that any failure that could occur will not injure the customer or seriously impact a system.
Improve the quality, reliability and safety of a product/process Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures, capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasis problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions
If used as a top-down tool, FMEA may only identify major failure modes in a system. Fault tree analysis (FTA) is better suited for "top-down" analysis. When used as a "bottom-up" tool FMEA can augment or complement FTA and identify many more causes and failure modes resulting in top-level symptoms. It is not able to discover complex failure modes involving multiple failures within a subsystem, or to report expected failure intervals of particular failure modes up to the upper level subsystem or system. Additionally, the multiplication of the severity, occurrence and detection rankings may result in rank reversals, where a less serious failure mode receives a higher RPN than a more serious failure mode. The reason for this is that the rankings are ordinal scale numbers, and multiplication is not a valid operation on them. The ordinal rankings only say that one ranking is better or worse than another, but not by how much. For instance, a ranking of "2" may not be twice as bad as a ranking of "1," or an "8" may not be twice as bad as a "4," but multiplication treats them as though they are.