Error Proofing sensors in PFMEA

[jrgeerdz]

Hello to all,

I have some doubts regarding how some control methods should be declared in PFMEA.

Here is the context example as stated in the PFMEA:

- Failure mode:
Tube bent out of specification
- Cause of failure:
Tube placed incorrectly in Bending machine (incorrect position)
- Preventive control
Tube position sensor in bending machine.
- Detection control
Process gage with correct route after Bending process.


In order to validate that the sensor in question is working correctly, I have a Master dummy part that should be detected as NOK position.

So the question is:
In the PFMEA, in the same failure mode "Tube bent out of specification", should I add another cause of failure row stating "Position sensor not working properly" and input the Master dummy part validation as both Prevention/Detection controls?

Because in the control plan, I want to input both controls: the position sensor and it's validation method (Master dummy part).

Thanks in advance for any of your opinions/feedback.

 

[Jim Wynne]

I always encourage using the process failure as the failure mode, and the nonconforming condition as the effect. It is, after all, a Process Failure Mode and Effects exercise. Using your example:

- Failure mode:
Tube placed incorrectly in Bending machine (incorrect position)
- Effect of failure:
Tube bent out of specification

Then the prevention and detection controls that you cite. If you feel that adding to this would be helpful, do it.

 

[Sebastian]

IATF 16949 10.2.4 Error-proofing
The organization shall have a documented process to determine the use of appropriate error-proofing methodologies. Details of the method used shall be documented in the process risk analysis (such as PFMEA) and test frequencies shall be documented in the control plan.

Answer could be "No", because standard requires literally identifying error-proofing in PFMEA and setting its testing frequency in control plan.
It is assumed, that it won't work someday , therefore it needs to be tested, but ... what about other risks related to manufacturing equipment failures and maintenance as prevention, what about other risks related to unreliable inspection equipment and calibration as prevention? Do you have any? So, based on manufacturing experience some can decide, that maintenance and calibration should be there, then sensor failure deserves mentioning too, I think.
On other hand how often do we see maintenance and calibration in control plan?
In this case standard requires verification of error proofing, so it has to be there.

- Preventive control
Tube position sensor in bending machine.

Not so much details here, to be honest.
There is some imagination of error proofing and every PFMEA team member could have different.
1. Detection has to be ranked and it is directly connected to this imagination.
2. Follow up revision to verify, that it's implemented within process and expected rank can be kept, requires confrontation of imagination with reality.
So what is imagination of how tube position sensor works and prevents?

In my opinion, it was one of reasons why reverse PFMEA was created.
It can be opportunity to confront PFMEA team imaginations with real manufacturing conditions.
"It is not as we were expecting or not fully folloiwng our imaginations."
This is not a problem of big companies, where a lot people gets involved in process design beyond PFMEA team, but also small one.
"What exactly we were thinking writing it down this way? I don't remember, but I am in charge of this, so I will do it my way."