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Determining the "Detection" Number Component of the FMEA RPN

G

GoKats78

#1
Here's the scenario...

Failure Mode: Cap Weld Bead Off Center
Effect of Failure: Damper Leak
Potential Cause: Torch Position Off Location
Prevention: Torch Position Check (at Start up and Re-Teach)
Detection: Leak Test
Visual Check of work piece (100%)
Tensile Strength Test (at Start up and Re-Teach)
Weld Penetration (at Start up and Re-Teach)

The Question is what is the "Detection" component of the RPN?


The are multiple checks for this cause...how do you determine the number when that is the case?
 

Miner

Forum Moderator
Staff member
Admin
#2
A typical approach is to determine the Detection rating of the most effective test and use that value. You must be careful to distinguish between Preventive tests and Detection tests. Preventive tests reduce the Occurrence rating while Detection tests change the Detection rating.
 

Jim Wynne

Super Moderator
#3
Here's the scenario...

Failure Mode: Cap Weld Bead Off Center
Effect of Failure: Damper Leak
Potential Cause: Torch Position Off Location
Prevention: Torch Position Check (at Start up and Re-Teach)
Detection: Leak Test
Visual Check of work piece (100%)
Tensile Strength Test (at Start up and Re-Teach)
Weld Penetration (at Start up and Re-Teach)

The Question is what is the "Detection" component of the RPN?


The are multiple checks for this cause...how do you determine the number when that is the case?
This is a good example of why I think that in most cases it's better to characterize the potential failure mode as the process failure and not the NC condition in the product:

Potential Process Failure Mode: Torch position off location
Potential Effect: Cap weld bead off-center
Potential Cause: ???

Look for what might cause the torch position to be wrong, and how to prevent that condition from happening. You can then have as many detection controls as you think might be appropriate, with the Detection RPN value simply reflecting the likelihood--given all of the detection controls--that a defective product will escape.
 
I

iamtroll

#4
I think that you have to use common sense and look at all of the components of detection. Then using whatever system of detection levels evaluation you use apply a number. Remember, this is not science, this is a tool to establish a pareto of issues that need to be addressed so if your a little off, you may work on one issue before another issue. I have attached a FMEA RPN evaluation that I like to use, maybe it will help you.
 

Attachments

Apoch

Starting to get Involved
#5
The detection should be rated based on the the capability of the control to detect the cause or the subsequent failure mode.

If the detection control is a mere visual inspection, then this should be rated as 8. If the error can be detected during setup, this is rated as 5 (gauging performed on setup or first-piece check).

I would recommend that you obtain the latest edition of the AIAG FMEA manual.
 
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