In accordance with AIAG approach (detectability table), this detector controls the cause from DET=2. It is not preventive – it does not prevent non-assembly of the tool but detects this problem instead.
Generally speaking, SEV values in PFMEA must arise directly from DFMEA. For sure you cannot understate SEV values. The only result of overstating SEV in PFMEA is that during the process analysis the effect for the internal process emerges (e.g. the operator may cut himself/herself), and this kind of effects are not considered by a constructor with regard to DFMEA. Therefore in DFMEA the specific fault may have SEV=4, that is insignificant effects for the user, but in the process (PFMEA) cause the operator to cut himself/herself, that is SEV=10.
Practical use of the requirements stipulated in the AIAG and VDA manuals show a range of customers, starting from internal customers and ending up with final user (for more about this, see CSRs of particular OEM customers).
Implemented actions are transferred to the taken-actions column. In turn new actions add a new line with actions entered in the same or other fault cause.
New RPN values are entered in two cases:
a) When actions are recommended – you enter the goal you wish to achieve.
b) When actions are implemented – you enter the real result of the actions after efficacy has been assessed (the goal is not always achieved!)
OCC stands for occurrence which means occurrence of fault cause.
In accordance with AIAG terminology, you can describe detection as:
„Detection assured through prevention (1)”.
The general rule is that when you describe effects of the failure, you should assume that it goes through internal and external processes without any control, and „goes” towards the final customer. If the failure does not cause the process to stop (e.g. because it is impossible to mount a part due to too small diameter of the hole), you should not describe the so-called internal effects (in the process). Such approach prevents the risk analysis from showing all problems which may be relevant to the company adopting FMEA. For this reason it is a „good practice” to enter an internal effect (for the company) in the form of increased defectiveness, a need to repair, etc. In this case FMEA will demonstrate problems arising from a specific failure more comprehensively.
If lowering arises from previous high internal effects which had an impact on the ultimate value in SEV column, then the answer is yes; nevertheless two cases are taken into consideration:
- DFMEA was not available and Unknown Function (10) was entered; during further revisions there was an update to include available data from the existing DFMEA.
- During tests and validation, previously assessed effects turned out to be too strict and thus overstated SEV value.
Please remember: at present the ultimate SEV value in PFMEA is affected by results from at least three effect fields: internal, external and user.