Why RPN was replaced by AP in AIAG+VDA FMEA?
First we should know what is RPN and AP (Action Priority). Then we will see what was problem with previous FMEA? Mainly here i am going to discuss about PFMEA (Process failure mode and effect analysis).
What was RPN in AIAG-FMEA?
RPN stand for Risk Priority Number. It is product of S, O & D. S is severity, O is occurrence and D stand for detection.
If we multiply this 3 number we will get RPN value. Here S value could be between 1-10 similarly O, D value will also vary between 1-10 number.
So maximum RPN value could be 1000 and minimum value could be 0, ZERO. So we can say RPN value could be any number between 0 to 10000.
In previous edition of AIAG-FMEA (4th edition) guidelines for recommended action were not clear. Companies decided there RPN limit, so were taking action on the basis of that. Actually same thing is with new edition.
Below picture is an example of recommended action as per RPN which is decided by a company.
FMEA manual never say company should follow this guidelines for recommended action. Every company has to set its own guidelines for recommended action as per FMEA manual. So here problem was with FMEA 4th edition, which is replaced by introducing new AIAG+VDA FMEA.
This new AIAG+VDA FMEA make easy the decision making.
What was problem with RPN in 4th edition of FMEA?
Because RPN could be same for different-different S,O& D, which leave the team in confusion for taking decision for action.
Let’s understand it with an example, suppose we have fix RPN -150 for action.
Severity is 8 and O, D value is 3 and 6 respectively. Then RPN will be 144, that mean we don’t need action. But actually we should take.
Severity is 3 (Which not high) and O, D value is 7,7. RPN is 147, we don’t need action here also. But we should take.
previous PFMEA more emphasis was given on severity first, then occurrence, then
In new edition of FMEA , AP (Action priority) is system to prioritize the recommended action. This improved prioritization process will enable the team to clearly identify action for improvement.
How AP (Action Priority) is better than RPN?
Action Priority (AP) defines the actual need of action to reduce the risk. Action priority is system to prioritize the recommended action. With AP system decision making become simple.
Action priority is divided into 3 categories:-
Medium Action Priority
Low Action Priority
High Action Priority
Medium Action Priority
For medium AP team should identify appropriate action to improve the prevention and detection control. Or at discretion of company justify with proper documents why this current control is adequate. That mean for medium AP there should be an action to improve the process further.
Low Action Priority
AP system, for severity 9-10 failure effect AP will be either High or medium.
Then there will be requirement one recommended action at least. But
it not mean we always have to check AP as High, medium & Low. Apart from it
if severity number is not big but AP is High due to O & D then recommended
action will be required.
Below is Action Priority Table as per AIAG+VDA
If we have to decide guidelines for recommended action as per new FMEA edition (AIAG+VDA). Then you can add following lines in your decision making condition:-
severity is 9-10 or Action priority is H & M then team need to identify
appropriate action to improve prevention or detection control.
2. If Action priority is high due to
occurrence & Detection rating then
team need to identify appropriate action to improve prevention or detection
3. If Action priority is medium due to occurrence
& Detection rating then team should identify appropriate action to improve prevention or detection control,
or, at discretion of company justify with document why current control is
4. If Action Priority is Low then team could identify action to improve
prevention or detection control.
The above mentioned guidelines will completely replace RPN system of risk action prioritization.
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