Frequently Asked Questions
Failure Mode and Effects Analysis is a systemised approach used for eliminating failure during product development or for quality improvement activities. As such it is an integral part of Advanced Quality Planning, and is often a pre-requisite for automotive and aerospace manufacturers and their supply chain. It may be focused on the design (DFMEA) or process (PFMEA). In most cases the DFMEA feeds into the PFMEA and this determines the order in which the two are addressed.
FMEA has also been used successfully to defend product liability claims in court, and many organisations have taken up the approach due to the protection that it can provide in this area.
As with many powerful techniques the strength of FMEA is derived from a cross-functional, team-based approach. The word potential is often placed ahead of FMEA in order to highlight that the tool is best utilised early in a product's concept/development phase, in order that failure is averted in service or during manufacture.
The objective of FMEA is to capture the following aspects of product or process failure:
- What might go wrong (the failure mode)
- What might the result of that failure be (the effect of failure)
- How serious could the result of the failure be (the severity of failure), S.
A numerical value is assigned to the severity of the failure, S.
With the above variable identified the process asks what might cause the failure and how likely, or often, it is that the cause will occur.
A numerical value is also assigned to the occurrence of the failure, O.
Finally the question is asked of the existing design controls, QA systems, process controls or inspection procedures, how likely it is that a given failure mode will be detected or predicted. This aspect of the process is known as the detection effectiveness of current controls.
The likelihood of detection D is assigned the final numerical value.
All of the values assigned are in the range 1 to 10, 1 being the lowest impact on product function or process output, 10 being the highest. The values are specific to each business and based on volumes of manufacture and other historical information.
The product of S x O x D is called the Risk Priority Number (RPN), this is the basis for planned changes to product or process designs. The RPN is used to prioritise work and may be re-calculated to ensure that actions taken have had the desired effect.
High severity ratings found during DFMEA (above 8 or 9) are highlighted for action regardless of the total RPN, and are considered critical or significant product characteristics. The minimum action would be to conduct PFMEA to ensure adequate QA or QC controls are in place to prevent users experiencing these failure modes.
The FMEA document co-exists with the product and its manufacturing process, and as new data on performance, or new controls are added, it can be updated. The live FMEA document is useful when derivative products need to be introduced, and as a store for organisational design and process knowledge.
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