FMEA Visual Inspection Detection Rating

S

Sean Kelley

#1
Last week I had an interesting find in that one of our FMEAs lists a visual inspection of the process but rates it a 4 instead of the required 7 or higher. The intersting part is that this is a visual inspection of the process and not the product. We are a steel mill with a galanizing line. There is a dross build-up of oxidized zinc that naturally occurs and must be removed as part of the process. I just wanted to see what some others thought of this type of visual inspection as I cannot fault their thought process and that it is not a visual inspection of the product.

:thanx:
 
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Jim Wynne

Staff member
Admin
#2
Last week I had an interesting find in that one of our FMEAs lists a visual inspection of the process but rates it a 4 instead of the required 7 or higher. The intersting part is that this is a visual inspection of the process and not the product. We are a steel mill with a galanizing line. There is a dross build-up of oxidized zinc that naturally occurs and must be removed as part of the process. I just wanted to see what some others thought of this type of visual inspection as I cannot fault their thought process and that it is not a visual inspection of the product.

:thanx:
There is no "required" detection number unless the requirement comes from a customer. The reason for this is that detection can be very complex (think of very small surface defects on a cosmetically critical surface) or very simple, such as distinguishing one color from another. In the absence of customer requirements, it's usually best to use the 1-10 scale as 1= will always be detected and 10 = no chance in heck of detection. Nearly everything will fall somewhere between 2 and 9.
 

Kales Veggie

People: The Vital Few
#3
Last week I had an interesting find in that one of our FMEAs lists a visual inspection of the process but rates it a 4 instead of the required 7 or higher. The intersting part is that this is a visual inspection of the process and not the product. We are a steel mill with a galanizing line. There is a dross build-up of oxidized zinc that naturally occurs and must be removed as part of the process. I just wanted to see what some others thought of this type of visual inspection as I cannot fault their thought process and that it is not a visual inspection of the product.

:thanx:
I think that a 4 is hard to defend. Visual inspection is tough. I often see a 7 or 8 for visual inspection. Do you have evidence from actual quality data / process result that support a 4?

Process or product visual inspection does not make a difference, I think.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#4
no doubt visual inspection comes with it's own complexities. a targeted well designed MSA can help determine the ability of inspectors to detect...but detection is also effected by boredom. any inspector will miss the obvious if they don't look or if they are so distracted they don't process the image. this part is tough to rate and is a good reason for being cautious in rating detection.
 

TPMB4

Quite Involved in Discussions
#5
FWIW I tend to look at detection as a fixed scale with a ranking based on type of detection. For example visual is 6-10, gauging is say 2 or 3 to 6 and error proofed is 1 to 4. It was a detection rating I inherited and seems to satisfy all our customers through the PPAP process.

There is some cross over between the three detection types I've listed. For example the lowest gauging detection rating is for automatic gauges which has an automatic stop on it. We can't set that up with our production so the best (in our ranking) we can get for gauging is 4 or 3.

Not sure if this is any help but we fix our detection scale and stick to it. It may be we are wrong in certain cases and could argue for a lower figure but at the end of the day a higher RPN figure tends to trigger you to look at the process closer. In some ways that is no bad thing as it can force you towards making improvements, especially if customers have as their requirements that the RPN must be less than a certain figure. We've not had that but I understand some do. (I guess that could be called burning platform in a push/pull).
 
Z

Zbigniew Huber

#6
...
The intersting part is that this is a visual inspection of the process and not the product
...
I just wanted to see what some others thought of this type of visual inspection as I cannot fault their thought process and that it is not a visual inspection of the product.

:thanx:
In my opinion it is correct to visually inspect for cause (process)
The detection controls are related to failure mode detection (usually a product defect) or detection of cause (process).
AIAG FMEA manual, page 95 says:
----
"Detection:
Identify (detect) the cause of failure or the failure mode, leading
to the development of associated corrective action(s) or countermeasures.
"
----


Regarding visual inspection ranking = 4:

If typical AIAG FMEA rev.4 ranking scale is used then the detection should be 7 (visual inspection at source) not 4.
Det. ranking 4 means automatic detection of failure mode and part lock to prevent further processing (post processing, next op).

I believe that visual inspection detection should NOT be related to "how easy" is to see the problem. I saw several complaints where inspectors/operators inspected products for "small defects" and accidentally omitted "easy to see" defects. I also saw complaints where several layers of visual inspection were used and the defect still passed through. That's why the AIAG FMEA rev.4 Detection tables does not consider "multiple visual detection" as better control than single visual inspection.
 
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