Detection Evaluation Criteria in the FMEA book is very vague

B

bturner

#1
To me, the Detection Evaluation Criteria in the FMEA book is very vague and I need some guidance for a specific operation in our company. We make fasteners on cold heading machines with involves thread rolling. Very few actual error proofing devices are available for these operations and most of our inspection, i.e. heading blank sizes and thread gaging is done by the operator on a regularly scheduled basis using micrometers and thread gages. Since no actual error proofing devices are used on the machine for this gaging and these features are only measured by a person, my first choice would be to give Detection a 5 ranking since the operator uses both visual and gages to measure the part after it has left the machine. But the 5 designation also mentions 100% Go/NoGO gaging. We do not measure every part. Is there any way I could give this a Detection of 3 since we have several steps after the part leaves the machine where the parts are measured (again not 100%) such as last off, final inspection and several lab tests that involve actually driving the bolt into a threaded plate? Detection of 3 states error detection "in-station" but does this always mean some sort of mechanical error proofing device on the machine or can it mean error detection in multiple layers of operator checking at the machine as I think it states in the OR section of the description?
 
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Jim Wynne

Staff member
Admin
#2
bturner said:
To me, the Detection Evaluation Criteria in the FMEA book is very vague and I need some guidance for a specific operation in our company. We make fasteners on cold heading machines with involves thread rolling. Very few actual error proofing devices are available for these operations and most of our inspection, i.e. heading blank sizes and thread gaging is done by the operator on a regularly scheduled basis using micrometers and thread gages. Since no actual error proofing devices are used on the machine for this gaging and these features are only measured by a person, my first choice would be to give Detection a 5 ranking since the operator uses both visual and gages to measure the part after it has left the machine. But the 5 designation also mentions 100% Go/NoGO gaging. We do not measure every part. Is there any way I could give this a Detection of 3 since we have several steps after the part leaves the machine where the parts are measured (again not 100%) such as last off, final inspection and several lab tests that involve actually driving the bolt into a threaded plate? Detection of 3 states error detection "in-station" but does this always mean some sort of mechanical error proofing device on the machine or can it mean error detection in multiple layers of operator checking at the machine as I think it states in the OR section of the description?
The information about enumeration of RPN factors in the AIAG manual is provided for guidance and is not prescriptive. You should do what makes sense. I advise suppliers to look at it as a simple 1-10 scale, with 1 meaning that there's no chance in he!! that a defect will go undetected, and 10 meaning that there's no known way to detect a defect should one occur. Look at it this way: if a given type of defect occurs, what the chances it will be detected before being shipped, or before more value is added?
 

Helmut Jilling

Auditor / Consultant
#3
bturner said:
...... Since no actual error proofing devices are used on the machine for this gaging and these features are only measured by a person, my first choice would be to give Detection a 5 ranking since the operator uses both visual and gages to measure the part after it has left the machine. But the 5 designation also mentions 100% Go/NoGO gaging. We do not measure every part. Is there any way I could give this a Detection of 3 since we have several steps after the part leaves the machine where the parts are measured (again not 100%) such as last off, final inspection and several lab tests that involve actually driving the bolt into a threaded plate? ....

In an audit, I would say that 3 or 5 would be too low for the situation you describe. The FMEA manual states these ratings, or something equivalent should be used. The Big 3 have at various times supported them as well. While I agree with Jim that they are not absolutes, drifting too far from the intent could result in nonconformities. The ratings became more stringent for a reason.
 

Jim Wynne

Staff member
Admin
#4
hjilling said:
In an audit, I would say that 3 or 5 would be too low for the situation you describe. The FMEA manual states these ratings, or something equivalent should be used. The Big 3 have at various times supported them as well. While I agree with Jim that they are not absolutes, drifting too far from the intent could result in nonconformities. The ratings became more stringent for a reason.
What if it can be demonstrated that there's only a {enter small number here} chance of undetected nonconformance based on documented past performance?
 

Helmut Jilling

Auditor / Consultant
#5
Jim Wynne said:
What if it can be demonstrated that there's only a {enter small number here} chance of undetected nonconformance based on documented past performance?
That's a fair question. I'll give two answers.

1. Past performance would generally be addressed by the occurance number. That addresses how the process performs.

2. Your question is a little different, though, in that you specifically asked about historical ability to "detect" with data to back it up. The FMEA Reference Manual mentions the possibility that other similar systems could be used, if it meets the intent. I believe it allows room for other approaches. That is why it is not completely prescriptive. However, I strongly believe that alternative approaches must have a legitimate basis. Data could perhaps meet that test. But, arbitrarily picking an easier scale to achieve a lower number would probably not pass the smell test, however.

I have written a number of nonconformities on this item. But, never when presented with an attempt at a legitimate alternate system. It was usually just the older 2nd ed scoring system, without any adjustment.

PS: I heard a rumor that Ford recently issued a new scoring system with significantly different values, but I have not seen evidence of that yet. Wouldn't understand why they would. They used to mirror these scores pretty closely. Anyone know for sure?
 
Last edited:

Jim Wynne

Staff member
Admin
#6
hjilling said:
The FMEA Reference Manual mentions the possibility that other similar systems could be used, if it meets the intent. I believe it allows room for other approaches. That is why it is not completely prescriptive.
It's not even partially prescriptive; the tables for RPN factors are clearly marked as "suggested," and "guideline." What is prescriptive are customer requirements, although that gets to be murky as well. If a customer says that FMEA must be done in accordance with the AIAG manual, how are "suggestions" within the manual to be dealt with?

Two things:
  • If straying from the S-O-D determination methods in the manual, the customer should be made aware of it.
  • There is no reason whatsoever, from an auditing standpoint, that any method for determining S-O-D factors that makes good sense should be penalized so long as there are no contrary explicit customer requirements.
 
G

Gilberto - 2009

#7
bturner said:
To me, the Detection Evaluation Criteria in the FMEA book is very vague and I need some guidance for a specific operation in our company. We make fasteners on cold heading machines with involves thread rolling. Very few actual error proofing devices are available for these operations and most of our inspection, i.e. heading blank sizes and thread gaging is done by the operator on a regularly scheduled basis using micrometers and thread gages. Since no actual error proofing devices are used on the machine for this gaging and these features are only measured by a person, my first choice would be to give Detection a 5 ranking since the operator uses both visual and gages to measure the part after it has left the machine. But the 5 designation also mentions 100% Go/NoGO gaging. We do not measure every part. Is there any way I could give this a Detection of 3 since we have several steps after the part leaves the machine where the parts are measured (again not 100%) such as last off, final inspection and several lab tests that involve actually driving the bolt into a threaded plate? Detection of 3 states error detection "in-station" but does this always mean some sort of mechanical error proofing device on the machine or can it mean error detection in multiple layers of operator checking at the machine as I think it states in the OR section of the description?



The criteria of detention of the Manual of FMEA are not obligator to follow, the manual says that it would have and does not have.
Advice, adapte one detention table more agreement to its process.
In the Manual of PPAP 3º edition - appendix F in bulk material to gives some table suggestions.
 
B

bturner

#8
Bulk materials

Could fasteners be considered bulk materials? It's not like we are making assemblies or specific parts for the car. We make bolts in hoppers, millions at a time.
 
B

bturner

#9
Question answered

I just looked up bulk material in the PPAP manual glossary and it states that bulk material are non-dimensional. So I guess fasteners do not fall in that category.
 

Jim Wynne

Staff member
Admin
#10
bturner said:
I just looked up bulk material in the PPAP manual glossary and it states that bulk material are non-dimensional. So I guess fasteners do not fall in that category.
No, fasteners are not considered bulk materials. The designation applies to commodities such as paint, oil and gases.
 
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