Are MSA?s (Measurement System Analysis) Process or Gage Based?

[tluker]

Are MSA’s (Measurement System Analysis) Process or Gage Based?

I’ve searched through all of the threads and have read the MSA book, but I can’t find a clear answer. The book would seem to indicate that it is process based, but all actual applications seem to be gage based. I am currently organizing our MSA’s. If they are process based then we would need an MSA for each process using a gage in the control plan. If they are gage based then we would need an MSA for each type of gage listed in our control plans and organize them according to gage types. Would an auditor ask for an MSA for calipers because they are listed in a control plan, or would an auditor ask for the MSA of a process (including GR&R of the calipers)?

I’m also interested on a personal level. If MSA’s are process based then it would be very useful although time consuming. If MSA’s are gage based then they are an absolute waste of time. There is no need to have an MSA for calipers (gage based). All good calipers on the face of the planet are going to perform the same. The only variation is going to be in the application they are used for (process based).

Any help will be appreciated.

 

[Miner]

Re: Are MSA’s (Measurement System Analysis) Process or Gage Based?

This is discussed in the following threads.

1. Do I Need To Do Gage R&r On Each Device Or Just Each Family?
2. MSA (Measurement Systems Analysis) - Where to begin when setting up a system?

 

[tluker]

Re: Are MSA’s (Measurement System Analysis) Process or Gage Based?

Thanks for the links. This is sill a murky area though. There is no end to what could be considered similar features, parts, and/or processes. Maybe this will be cleared up one day?

 

[bobdoering]

Re: Are MSA’s (Measurement System Analysis) Process or Gage Based?

MSA is the overall analysis of gage usage. Two key facets of the MSA is calibration and gage R&R (there are other analyses).

Calibration is individual gage-based: does the specific gage measure to a standard within accepted tolerance.

Gage R&R fundamentally determines if a gage is an appropriate gage for measuring a particular feature. It seeks to capture the gage system which is the gage, the product and the operator. Consideration of the process come into play when you analyze the amount of error in relationship to the process requirements - tolerance or control limits. GRR in % Tolerance. GRR % Control Limits, ndc as a function of tolerance or ndc as a function of control limits bring the process into play.


MSA does not think for you, though. It helps you justify your decision. So, some effects of the process, such as the environment that the gage will see in the process, will have to be considered prior to purchasing the gage. MSA will not sort that out for you.

Does that help any?

 

[bobdoering]

Re: Are MSA’s (Measurement System Analysis) Process or Gage Based?

Would an auditor ask for an MSA for calipers because they are listed in a control plan, or would an auditor ask for the MSA of a process (including GR&R of the calipers)?

An auditor should ask for calibration records of every specific gage used to perform measurements a control plan. So, all calipers used for a measurement calling out for the use of calipers.

An auditor should ask for a Gage R&R for a representative gage (a caliper of all cailpers in use) used to perform measurements a control plan. If it calls out a caliper, than a gage R&R using a caliper, the associated part. Using gage R&R for more than one feature or more than one part needs to be justified that the dimensions are similar (in size, location, access, etc.)

Here is the real questions the auditor is asking: "How do you know the gage is reading correctly?" (calibration) and "How do you know this is the correct gage for the job?" (gage R&R). Answer those questions will logical support, and you have a darn good start.

 

[tluker]

Re: Are MSA’s (Measurement System Analysis) Process or Gage Based?

Thanks Bob, that helped!

 

[Caster]

Re: Are MSA’s (Measurement System Analysis) Process or Gage Based?

If MSA’s are gage based then they are an absolute waste of time. There is no need to have an MSA for calipers (gage based). All good calipers on the face of the planet are going to perform the same. The only variation is going to be in the application they are used for (process based).

Ah, sounds like me years ago. I can recall saying a caliper is a caliper is a caliper.

Just to have some "easy" GRRs on file I did some studies on my calipers.

They were done "right", on real parts (limited to normal process variation), with all previous measurement results hidden from the operator (blind).

Wow, what I learned. Machinists with the "feel" get close to each other. Machine tenders hired off the street to load/unload struggle to just turn the thing on.

I still don't care much for MSA, but always find the studies show me previously unknown and unsuspected problems.

 

[bobdoering]

Re: Are MSA’s (Measurement System Analysis) Process or Gage Based?

Just to have some "easy" GR&Rs on file I did some studies on my calipers.

I swear. These days I have to ponder GR&R on destructive measurement, such as tensile testers and weld depth monitors.

Wow, what I learned. Machinists with the "feel" get close to each other. Machine tenders hired off the street to load/unload struggle to just turn the thing on.

One of my favorite demonstrations of GR&R that I use in metrology class is to have the students tell me what gage is best: steel rule, caliper or micrometer.

Then I have them do GR&R with the three gages on marshmallows. Guess which one wins...

I still don't care much for MSA, but always find the studies show me previously unknown and unsuspected problems.

At a minimum, it does make you think about the measurement system...gets you out of the 10:1 backyard thinking.

 

[roder - 2012]

Re: Are MSA’s (Measurement System Analysis) Process or Gage Based?

One of my favorite demonstrations of GR&R that I use in metrology class is to have the students tell me what gage is best: steel rule, caliper or micrometer.

Then I have them do GR&R with the three gages on marshmallows. Guess which one wins...

I guess its the steel rule...am I right?

 

[bobdoering]

Re: Are MSA’s (Measurement System Analysis) Process or Gage Based?

I guess its the steel rule...am I right?

Yep. Rarely matches what the first claimed was "the best gage". OK...it is also a good demo on gage pressure.

It also supports my general rule: The best answer to any question is 'it depends'.