Corrective Actions Priority - Process FMEA (PFMEA) RPN Limits - Recommended Actions

B

brutas

#1
Hello,

Currently I am trying to make a PFMEA Guidelines for our company (automotive microelectronics).
Here is my suggestion about how to give priorities of the corrective actions:

Recommended actions

Prioritize recommended/ corrective actions in the following order:

A. Actions are mandatory for ALL Failure modes resulting in a Severity of 9 or 10
B. By the “Seriousness” = Severity x Occurrence
High Severity values, coupled with high Occurrence values merit special attention (require Recommended actions). Actions are recommended for any Severity of 5 or higher with an Occurrence of 4 or higher
C. Actions recommended for any failure modes resulting in a high RPN regardless of Severity X Occurrence combination (Use Pareto technique to prioritize the highest RPNs).
Apply Pareto principle 30/70 which means:
30% of causes produce 70% of the troubles.

You should work towards RPN reductions until RPN became to be lower than 32. If RPN < 32, and A and B cases are not valid, then Corrective actions are not required anymore.

So, my question is regarding this RPN limit (<32) from which applying corrective actions is not feasible anymore.

How this number was obtained:
8x2x2 = 32 => Severity 8 combined with Occurrence 2 and Detection 2 I consider to be no more danger. The other variant is 8x1x2 = 16.

What is your opinion? What is the practice in your companies? Although PFMEA is continual improvement process it is not feasible to try to reduce the RPNs at any cost. We should stop at certain point.

Thank you,
:)
 
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M

Michael Walmsley

#2
Re: Corrective actions priority. RPN limits

Brutas,

Keep it simple.

For sure,maintain "A" & "B".

"B" is also known as "criticality" in the auto industry.

If criticality >/= 18 , a mandatory redesign (or plans for) is needed.

Since "A" feeds "B",you can pareto within this group.

Other than that, simply state that you need to work on the top 5 RPNs
at any given time.

As one is resolved, another one is moved up onto the list. This supports the "continuous improvement process".
 
M

Michael Walmsley

#4
Re: Corrective actions priority. RPN limits

18 = Sev 9 X Occ 2.
NHTSA is operating on a safety defect rate of 1/800,000 over the product life for new products (to begin inquiries that could potentially lead to recalls). This figure was obtained several years ago when I called their Chicago office. It was reinforced when I visited them in Washington to promote Electronic stability control with a group from Bosch.



Daimler Chrysler , Ford and GM have provided the Top 5 argument.
If you think about it, the FMEA is meant to be a dynamic document.
eg, continually upgraded.


ps I have a tool that might be helpful to you if you have some basic background in Reliability.

It provides a means to add a cost to the issue (so that you have half of the cost benefit done).

If you want a copy of it e-mail me at michael[DOT]walmsley[DOT]b[AT]bayer[DOT]com.
 
Last edited by a moderator:
B

brutas

#5
Re: Corrective actions priority. RPN limits

Thank you very much Michael,
but I need a limit. This is what our management wants and what some of the Customer require.
I know that this is a living document and continual improvement philosophy should be in place but I also know that many of the companies use such limit (arround 50~60).

You will agree with me thah RPN < 16 is not needed to be decrease (or < 32).

I just want to know your practice and your arguments but I need a limit :)

Thank you.
:rolleyes:
 
M

Michael Walmsley

#6
Re: Corrective actions priority. RPN limits

36 = Sev X Occ X Det = 6 X 3 X 2.


In the auto industry, safety issues / concerns initiate with severity level >/= 7.

Occ level of 4 is associated with a Ppk process of 1.33.


I would use the 36 level from my perspective as a cutoff point.
 
B

brutas

#7
Re: Corrective actions priority. RPN limits

Thank you Michael.
It will be interesting to see other opinions also...
 
C

ChuckHughes

#8
Re: Corrective Actions Priority - RPN limits

Hello Brutas

A different approach in setting priorities:cool:

Prepare a second FMEA document and align the failure modes with the cost of occurance instead of the severity. The failure mode may not injure or cause annoyance to the customer/user, but if it occurs once, the cost of correction may be significant. Both internal and external costs should be used.

This new FMEA will give you more benefit to your business by prioritizing the higher failure costs. The decision to "fix or monitor" can be made more clearly, especially if the return on investment is low.
 
T

tac123

#9
Re: Corrective Actions Priority - RPN limits

Why have mandatory action for severity 9 or 10? If OCC is 1 and DET is 1 it is likely that you cannot reduce risk further.

Do not work to thresholds (max rpn) as engineers whom are good at math will modify the numbers to reach the threshold. Instead work on reducing the high risk numbers that can be reduced with given available resources.
 
B

brutas

#10
Re: Corrective Actions Priority - RPN limits

Do not work to thresholds (max rpn) as engineers whom are good at math will modify the numbers to reach the threshold. Instead work on reducing the high risk numbers that can be reduced with given available resources.
I agree with you but this process is not endless. The reducing of the RPNs should stop at certain level.
 
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