3 legged 5 Why - Hole diameter Oversize caused by Gauging

I

ImagineThat

#1
Hello Folks,


We had an issue with a stamped part in which the hole diameter was oversize. We found out that the gauge we are using to verify the hole was giving us false readings. We found this out by taking a 3 point Mauser bore gauge and measuring the hole diameter vs the two point bore gauge that was giving us false reasons. In my opinion, we have found the root cause by using a different gauge and verifying the results of that gauge to a CMM.
The customer wants me to do up a 3 legged 5 why, but I'm not sure on how to tackle the on why is was not caught or the systemic issues associated with the defect. Has anyone had any experience with an oversized hole diameter in which the gauge was the direct result?. The team here is stumped on the next process and non of us have been through a 5 why.

Any help would be greatly appreciated!

Thanks,

IT
 
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hogheavenfarm

Quite Involved in Discussions
#2
Sounds like the customer is trying to insure that you do not just replace the gauge, but understand the underlying issues that led to its use, and the fact that it continued to be used without question.
A 3 leg will verify that you have covered all the bases.
There are validation/calibration issues raised here, as well as scheduling those, which may extend to other areas as well.
 
T

tonefordays

#3
This can be a bit tricky,
I don't think that the method of inspection would be considered the root cause for the hole being oversize. Although the method of inspection may not have adequately detected the oversize hole, it didn't actually cause the hole to become oversize. You could however include that as part of improving the process. Using a different inspection process only detects the problem differently, and and won't directly fix the problem........hope this makes sense.

I think to find the root cause of the oversize hole, you should also be looking at the process used to make the hole. ie: machine tooling, fixtures, setup, planning, etc...This is where the 5 why could help.

Hope this helps.
 

Michael_M

Trusted Information Resource
#4
Hello Folks,


We had an issue with a stamped part in which the hole diameter was oversize. We found out that the gauge we are using to verify the hole was giving us false readings. We found this out by taking a 3 point Mauser bore gauge and measuring the hole diameter vs the two point bore gauge that was giving us false reasons. In my opinion, we have found the root cause by using a different gauge and verifying the results of that gauge to a CMM.
The customer wants me to do up a 3 legged 5 why, but I'm not sure on how to tackle the on why is was not caught or the systemic issues associated with the defect. Has anyone had any experience with an oversized hole diameter in which the gauge was the direct result?. The team here is stumped on the next process and non of us have been through a 5 why.

Any help would be greatly appreciated!

Thanks,

IT
I am still struggling with Corrective Actions myself, but I am going to ask a few questions I can image someone helping me asking me:

1. What was the cause of the false readings?
---a. Was the instrument bad, how was it allowed to be used?
---b. Was the instrument not 'set' correctly, how can you prevent this from happening again (say in 3 years as an example)?
---c. Was the instrument being used correctly, what allowed the instrument to be used incorrectly?
2. Did you make any other parts with this same gage, if so, did you review the parts to verify they are conforming?
3. Was the hole out-of-round, what can be done in the future to verify holes are not out-of-round (not just with this part).

I had someone helping me with CA's and they gave me a fairly good description:

Immediate action applies to the specific event or part. Answering this says what are you doing to the parts and what did you do to check 'other' parts that may have the same issue (because it used the same gage for example).

Root Cause applies to the system failure. What within the system you use has allowed the event to happen. This is more 'global' in that it applies to more than just the part or event that was used to create the CA. For example, if the hole is out-of-round, what system change are you implementing to check all holes for out-of-round. What are you going to do to remove out-of-round holes?

Of coarse, this is just a tip of a VERY large iceberg but I hope it might help.
 

Golfman25

Trusted Information Resource
#5
Please answer some questions:

Is it a punched hole?
Shaved?
Type of material?
Thickness of material?
Are there any bends close to the hole?
Dia and tolerance of the hole?

The gage is not your root cause. Under normal circumstances a punched hole is relatively round and should be ok if checked with a two point measuring device. That you got a different reading with a three point device indicates that they hole may not be round. Your root cause is part of your stamping process -- you need to determine what is happening to the hole. The gage is only relevant to why the condition was missed.
 

Ron Rompen

Trusted Information Resource
#6
I have to agree with Golfman and tonefordays; the root cause of the failure (hole diameter oversize) is not the gauge, it is somewhere in the process that was used to make the hole.

On your 3x5, the gauging method failure would fall under the 2nd WHY (why was it not detected/why was it shipped).

You still need to focus on the first WHY (why did it happen).
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#7
agree with Ron and Golfman, you are not at the cause of the oversized hole.
the escape cause(s) are that he wrong gage was used in inspection, this is what allowed the oversized hole to escape undetected. I would branch this error into two different whys:
  1. why wasn't the defect caught at the process? setup or in process inspection?
  2. why wasn't the original two point gage validated as being appropriate to measure the feature? this is an overlooked part of MSA that isn't covered by either calibration or gage R&R methods. physical features and properties are particularly susceptible to this error
 

AgnieszkaSz

Involved In Discussions
#8
Hello,
1. why the possibility of making wrong size hole was NOT PREDICTED at the stage of manufacturing proces planning?
2. why have you PRODUCED the wrong size hole? why have you not prevented it?
3. why HAVEN'T you CAUGHT the mistake before sending the product to customer?
 
#9
I'm reading this a little differently than most people here; before moving on, I'd like to rephrase the problem as I read it.

Problem statement:
A conforming part was measured non-conforming with a 2-point bore gage; the part was confirmed to be conforming after additional inspection with a 3-point bore gage and a CMM.

OP, is this correctly stated? If so, the corrective action and 5-why will be much different from a case where we're talking about a nonconforming part.
 
Last edited:

Golfman25

Trusted Information Resource
#10
I'm reading this a little differently than most people here; before moving on, I'd like to rephrase the problem as I read it.

Problem statement:
A conforming part was measured non-conforming with a 2-point bore gage; the part was confirmed to be conforming after additional inspection with a 3-point bore gage and a CMM.

OP, is this correctly stated? If so, the corrective action and 5-why will be much different from a case where we're talking about a nonconforming part.
I read it the opposite but you could be right. Unfortunately, it seems the OP has disappeared.
 
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