Burrs affecting measurements and Process Capability

A

Ajgupta

#1
Hello all,

I was hoping to get some clarification in an issure regarding process capability for a part with burrs affecting measurements. We machine a Cam with a critical dimension for the Cam width. The cam has ears on its sides with burrs between the face and the ear after the milling operation. Our operators check the part straight after machining and send it to Heat treat. Parts are deburred after Heat Treat and then used.

The issue I have is regarding the treatment of these burrs for a capability analysis. An IE is adamant that we should deburr the pre-heat treated parts before conducting any GRR or Process Capability studies. My objection is that our process requires the operator to accept parts as good right after machining. We do not check parts once they come back from heat treat and are deburred. We measure the width using a shadow gage block and I know from a previous study that the burrs on the part edges cause a higher than actual reading for the part.

Any thoughts on how I should proceed with this situation. Thanks.
 
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K

kaushikb

#3
I would suggest you do deburr pre-heat treat, because deburring after heat treat is not effective to remove the burrs. I agree with your IE. Also, I would suggest incorporating in-process check by the operators to check for burrs after the machining process.

As you have mentioned "My objection is that our process requires the operator to accept parts as good right after machining. We do not check parts once they come back from heat treat and are deburred." I completely disagree with you. When you are not checking if your making good parts and your assuming them to be good and you catch the problem at final, then I suggest stop production. There is no point making parts when they are not good.

I don't know what you mean by your process requires the operator to accept parts as good right after machining. So my question to you here is "if your operator doesn't check the parts for its features or burrs, but parts are bad do you mean they still have to pass the parts even without inspecting?

Also, I am wondering hoe come your company does not check parts post heat treat. According to me your process lacks inspection, if you incorporate in-process inspection I am pretty sure your operators will be able to adjust the process. Also, for the burrs better check your tool life. Perform a study over a period of time to check burrs.

You will never show capable if you do not make extra effort to adjust your process.
 
Last edited by a moderator:

Golfman25

Trusted Information Resource
#4
Could you set an interm production parameter to measure to, which would include the burr and its variablitly? I see it as two parts. The WIP part which is fresh off the machine and the finished part after heat treat and deburing. If your looking at the capability of the machining process only, then it seems to me you need a dimension to hit which will be different then the dimension after the entire compeleted process. Good luck.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#5
Generally I see two approaches - measure the dimension in an area where the burr is not present or deburr prior to measuring. Since the final dimension is a deburred dimension, MMC including the burr is not relevant - the base material dimension is. If there was not deburring anywhere in the process, then the burr would count.

Since you are heat treating, data on the base dimension before and after is key. The burr holds no valuable data to gage pre- and post-heat treat results.

As far as deburring before or after heat treat - it depends. There is no one answer. Depends on the material, how hard it is, how large the burrs are. Some burrs break off better brittle after heat treat, some become so strong they are a permanent part of the piece.
 
A

Ajgupta

#6
Re: Burrs and Process Capability

Yes. GRR was conducted before and after deburring. 1st GRR was inadequate due to additional variability of burrs on readouts. Deburring and then conducting GRR was needed to prove parts out.
 
A

Ajgupta

#7
The disagreement was over whether we should check machine capability or process capability. Deburring the parts before HT for the capability study negates the alpha and beta risks associated with the parts production. I want to include that in the capability study and the IE doesnt.

I understand how the process is inadequate in its current stage. I will be conducting a before and after deburr capability study pre heat treat and then compare it to post heat treat. In a nutshell, the argument was over whether we should take best case scenario for a capability analysis or conduct it in real life conditions.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#8
I understand how the process is inadequate in its current stage. I will be conducting a before and after deburr capability study pre heat treat and then compare it to post heat treat. In a nutshell, the argument was over whether we should take best case scenario for a capability analysis or conduct it in real life conditions.
Is the process inadequate because you want to machine a burr-free product and eliminate deburring? Or, do you always expect your process to include deburring?

As far as alpha and beta risks, those are primarily judged after the final state - heat treat and deburred. Now, at that point you deburring process capability is key, and measure over any remaining burrs after deburring is recommended as an MMC condition (especially if fit is an issue) - unless the print states otherwise.
 
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