Qualification Vs Verification

[[Do...]]

Hi all,
I have been reviewing various posts and polls related to the topic and am interested in obtaining additional information. Currently, our nightly routine involves running a probe re-qualification program, followed by a morning verification. The verification process generates reports highlighting X and Z deviations, along with sphere diameter and form.

We are stuck in an ongoing cycle of re-runs, with operators mandated to verify that all probes adhere to the designated tolerances for these parameters. Consequently, this situation has resulted in extended periods of machine downtime and incurred costs for replacing probes that might actually be in proper working condition.

I've come across comments suggesting that the XYZ values should never be "0" during this test. While I agree with this perspective, I am curious if there should be a consistent tolerance that we can anticipate hitting, or if these values are arbitrary and do not necessarily correlate with the probe's quality. Should we really only be looking at sigma values, diameters, etc.?

Ideally, I feel we should be running re-qualification on Mondays and only running verifications during the week, with exceptions for incidents like collisions. What specific targets should we aim for on a daily basis, and what standards do you typically adhere to in your operations?

Also, should there be additional consideration given to CAA calibrated probes as they typically have a higher sigma value during calibration?

We are primarily operating XXT probes running on 2014 Conturas. Any insight would be greatly appreciated.

Cheers,
Don

[[Mi...]]

XYZ mean very little and honestly won't mean anything meaningful to your standard operator. You can use them to compare new values to old, or current vs expected. You can use them to judge how well you build a stylus system etc...

This sounds like a training and cleanliness issue more than anything.

We have 33 CMMs, 2 programmers and half a dozen people that will calibrate. 9/10 times somebody is struggling with calibration myself or the other programmer will redo it with no issues. We take the probes they say are no good and run them somewhere else with no issues.

We set limits of 0.001 for Sigma on Direkt XXT, 0.0003 for XT and 0.003 for our RDS (With Renishaw probing - yuck). But I hold myself to half those and extremely rarely have any issues meeting it. We don't use CAA calibration on our RDS Machines... we calibrate in all the angles used... but we only have about 30 angles.

They think they are cleaning well enough - they aren't. At the very least don't let anybody but your most experienced decide a probe is no good. I bet you've got a person who has no issues, find out their cleaning method and adopt it as a standard practice.

[[Ow...]]

Michael Shultze is right on track regarding cleanliness. Just a hair or spec of anything will throw the standard deviation/sigma out and temperature fluctuations will alter sphere size recorded. Isopropyl alcohol works best for cleaning to ensure there is no sticky residue left on the probe or sphere as most common household cleaners will leave a residue and then everything will stick to it.

Regarding xyz numbers, I believe they are irrelevant most of the time, maybe excluding cracked carbon shafts or flat spots but , if you're concerned about them, create a program that will scan the reference sphere with the master-probe to set location and size and then scan it with each probe used and report the size and location.

If they’re just wanting to ensure the CMM is repeating as it should, you might just need a known ‘Master’ part that covers the majority of the axis’s, probes, size and form of the features/characteristics commonly checked on the CMM. For instance, maybe keep the largest or average size part you make or check routinely in the CMM room and check it before calibration, after calibration (to see changes, if any) and ESPECAIALLY after a significant crash because even a good probe calibration WILL NOT detect if the CMM has been knocked out of square.

[[Mi...]]

You can accomplish a good chunk of the verification with a ring gauge or two as well. We have a program to check the same circle with multiple probes/probe systems as an indicator of needing calibration. Depending on what parts you run, this may be enough.

For us, we have so many CMMs with the same programs it's easier to run the same part 3 places and then calibrate the one that doesn't agree.

[[Cl...]]

We do a verification with several Master Parts. Ensuring all styli are used.
Then Applying a tolerance to the actuals average gathered from historical
data. Then a tolerance is applied based on the (min/max) range.

[[Do...]]

I appreciate all of the feedback so far. I had also failed to mention in the original post that we are using the Zeiss reference sphere for both qualification and verification. The verification program checks probes in the cardinal directions as well as A0B0 and A180B0.

When verifying a stylus system via ring gage, are you measuring just one orientation or at multiple angles? I can look into a master part option as well.

Cleanliness has not been our strong suite and I've requested that operators wipe down guideways, probes, adapter plates, etc. on a daily basis. In the past, operators had a general housekeeping checklist, which was filled out half-heartedly and/or when someone remembered do it. I am looking into creative ways to ensure compliance with these PMs and if anyone has a process that works for them and their team, please chime in.

To Owen's point, we are scanning the sphere with the masterprobe and then reporting the XYZ values, size and form for all of our high running styli. We had at some point settled on ±.0004" tolerances for the positional values, which is where we are having the most trouble. We maintain tighter tolerances for the form and diameter to .0002" and rarely have issues there.

With that in mind, should values be expected to meet that tolerance given the method described or is it common to see results that exceed .0004" in a single direction? I will look into pulling historical data to see what our range is and determine if an increase to the tolerances is required.

Thanks everyone!

[[Si...]]

Hi,

Does anyone mind to share how you made your verification program on the reference sphere. Do you guys use 2 spheres or just move one around to get all the axis. 

Thanks. - Simon

[[Cl...]]

We perform a weekly inspection and cleaning and qualification of all stylus. We also have numerous "Master Parts". These parts were initially measured the first time right after the machine has had its annual calibration. Then each day these master parts are measured and the results compared against the original master data. We use SPC from this data to establish a LCL and UCL. The numbers must fall withing this spec. Any deviations outside of these control limits would flag us to a potential problem with either the CMM or the stylus.

[[Da...]]

My CMM measures mostly positions of punched or laser-cut holes on sheetmetal and/or PEMs inserted into those holes, so most of our work is dimensioned no tighter than ±.005" or a position of .010", so we aren't nearly as "picky" as some of you guys making flight-critical aerospace pieces. Cleaning of probes is something we do about once a month (if we remember..), and the calibration ball gets a wipe-down once a week when I do the weekly calibration. for us, we consider ±.0002" a passing calibration, although I have a "super-calibration program where we do a full re-qualification to ±.00005" (which I do periodically; usually when a probe is replaced, or there had been a machine collision. 

[[Si...]]

Okay, I made a program that measure the Ø30 ref. sphere. Datum is made with the masterprobe. I then compare the other stylus systems to the masterprobe. If you then get a difference in XYZ and diameter. What do you do? do you chance the geometry of the stylus?

[[Ke...]]

I don't discard any probe as "damaged" without doing a visual inspection, under magnification. It can be very beneficial to know *why* the probe is bad...If it is worn, then you definitely got your moneys worth out of it. Collisions can happen to the best of us, but if you are finding impact damage on probes and collisions have not been reported, then that could be an issue as well. Probes with material buildup can often be cleaned and put back into circulation.

 

[[Do...]]

Zeiss has an excellent article on a verification program. I have used this format for testing and it appears to work well. We are waiting to implement SPC tracking on it before releasing to the floor.

Not sure if this link will take to you the exact article so I'll include the title to search for as well.

 

Diagnose Potentially Damaged Probes with a Verification Program

ZEISS Portal

[[Ri...]]

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I have been doing something similar since 2003. I base it on the standard 5 articulations. 

1. Place the Reference sphere in the middle of the CMM.

2. Run CMM program that uses the 5 standard articulations.

3. I report Diameter, Form, and True Position (spherical).

4. Diameters are set to ±.0001"

5. Form to max .0001"

6. True position is .0003".

7. Once a month run the program at one of the 5 different locations (See image: Locations)

8. At the 6th month, place the reference sphere on a riser (I use an 6-inch riser).

9. Run the program once a month thru the 5 locations using the riser.

10. Go back to #1, wash, rinse, repeat.

11. Add data to an MSA for the duration of the current calibration.

This not only can help detect an issue, it also checks a good range of the working volume.

This has never failed to find an issue if there is one, it was about 8 months ago when this plan found an issue with a 1 1/2-year-old Contura 2014, it was the XTR sensor.

The same program is edited for our XXT sensor now.

 

You can also perform this same test with raw data, no filters, no outliers turned on.

I make charts of refined measurements and Raw measurements, if I over lay these and they do not appear to be very similar, you can start to look at why?

 

Edited Wednesday at 06:50 PM

[[Si...]]

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I cant seem to find the article on zeiss portal, where is it located?

[[Do...]]

Zeiss Portal > Knowledge Base > Diagnose Potentially Damaged Probes with a Verification Program

I tried copying the link a different way and I think it works now.

https://portal.zeiss.com/knowledge-base?id=2437337

[[Si...]]

Can you send a screen print?, i got no tap called knowledge base.