DFMEA – Detectability of the Failure Mode

Detectability or Probability of Detection of the Potential Failure Mode

* The probability that the failure mode caused by the design would be detected by the DV before the part is released to production on a 1 to 10 scale, where a 1 indicates a high probability and a 10 indicates a low probability.
* Ask  “If there is a design weakness, how likely is it to be detected by our current DVs before the part is released to production?”

FMEA-Process-Flow-Detectability

Detectability is the third of the 3 Risk Priority Number (RPN) rating criteria. It is an assessment of the ability of the DV program to identify a potential design weakness before release to production. It is a relative ranking (within the FMEA) of the ability of the DV to assure the design adequacy for the failure mode and/or cause or failure mechanism under study.

A high score means a low probability of detection, and a low score indicates a high probability of detection. Because of this possible confusion, some users call this criterion the Probability of Non-Detection.

A sample of a Probability of Detection ranking scale is shown on the next page.

Ranking Description
1-2 There is a very high probability that the design weakness, when it exists, will be detected before the part is released to production, usually by
the DV program. A very low probability of non-detection.
3-4 High probability that the design-based cause of the failure will be detected before the part’s release to production, usually by the DV program. A low probability of non-detection.
5-6 Moderate probability that the design-based cause of the failure will be detected before the part’s release to production, usually by the DV program. A moderate probability of non-detection
7-8 Low probability that the design-based cause of the failure will be detected before the part’s release to production. High probability of
non-detection.
9-10 Very low probability that the design-based failure will be detected before the part’s release to production. Very high probability of non-detection.

The company should adopt these sample rankings to their industry and include specific probability values. A low score means that there is a low probability that the failure mode or defect based on a design weakness, when the failure mode does exist*, will escape the DV controls before the design is released to Production and the defect has a chance to reach the customer. *Do not consider the likelihood that the defect will occur in scoring this criterion; this was evaluated in the second criterion (Occurrence).

A high score for Detectability means that there is a high probability that the failure mode or defect, when it exists, will escape the DV controls before the design is released to Production. If there is more than one design control that could prevent or detect a given failure mode or its cause under study, consider in the scoring the one that would provide the best prevention or detection.

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