CMM operators who measure sheet metal parts...Question for you

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  • rebeldude
    replied
    We dont do it for QS9000 either. I agree with Matt. Your auditor makes the standards. Get a new auditor!!!

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  • Andrew Gardner
    replied
    I had asked the question about a "calibrated" thermometer for my inspection lab. The new standard does not require it. I try to keep the room about 70 deg. The only time I have a problem, is on close tolerance grinding work. But hey, what's a couple of tenths between friends, right?

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  • Hilton Roberts
    replied
    Temperature

    Here is another quick tip you can use to see if temperature variation is affecting your measurements.

    If you use the dual sphere artifact and it is aligned along Y axis, measure the thing and set zeroes in the sphere. Periodically measure the location and watch where the Y and Z coordinates go. It is pretty amazing what happens to those two values if temperature in you CMM room is unstable.

    H

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  • Hilton Roberts
    replied
    Matt,

    One thing he also told me about the machine in Mexico was the cleaning folks came through and climbed up on the machine with a bucket of dirty water and began mopping the surface plate.......makes you cringe doesn't it?

    I really am thinking about retirement. I will be 64 in June and have been with Boeing 37 years. That is a long time anyway you look at it but I still have a pretty good time here at work and I like what I do.

    I would like to part-time it for a while but do not know if I am really ready to take the plunge. The cost of medical insurance is scary and you need something in case your health takes a dump.

    It is refreshing to see how much knowledge is dispensed on this forum.

    I get new ideas almost daily....they usually come to me when my eyes are closed......

    H

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  • Matthew D. Hoedeman
    replied
    YEP, put high technology in the hands of the un-trained and you might as well give them a tape measure and a hammer. Hey, maybe when you retire, Hilton, you could go there and train their QC workforce. Probably get lots of good TEQUILA that way!

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  • kbotta
    replied
    DANG!!!!!

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  • Hilton Roberts
    replied
    temperature compensation

    A few years ago a DEA tech., the late Kurt Burrell, was in here to work on our machine and he had just gotten back from a repair in Mexico.

    He said he had to do major replacement of PH9 heads and cartridges.

    The machine was located in an aluminum foundry and they were bringing castings to be checked right as soon as they could get the castings out of the molds.

    Kurt told them the parts could not be checked in that condition and they responded they had purchased a machine with thermal compensation.......

    Turns out the castings were so hot they fried the PH9 head........

    True story.

    Hilton

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  • Matthew D. Hoedeman
    replied
    HEY WINSTON, you are right in that you have to follow those guidlines, but they are VERY loose in scope for the most part and allow a LOT of leeway.

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  • Matthew D. Hoedeman
    replied
    And yet another reason that (so far) I have not worried about temp variation in our parts. Heck, ya know that if you even take the die out of one press and put it in another that you get a different part, sometimes REALLY different. We were doing 3rd party tryout not too long ago for someone who had a die built in (gasp) Korea and we used the stock they gave us. We got it to draw and form and trim like it should (we were NOT responsible for dimensional, we just had to get the die to run without splitting, so I didn't check any parts) and then THEY, the customer bought it off and we shipped it back to them. We used all the stock they gave us running the die off to prove that it no longer split, etc. Then they got it back to their shop, used a different coil from a different batch of steel and all the splits came right back. Both coils of stock were well within the required specs for the production of the part, thickness, composition, etc., yet one coil worked wonderfully, the other was a disaster. This is why production is so much harder in some cases than construction. Every time a new coil from a new batch is put into the die, changes may need to be made to get a functional part. Thus the reason for SPC and continuous monitoring of the process, hour after hour, day after day, week after week, month after month, year after year, well, you get the idea. And this says nothing about shop temps from build source to production source or from winter to summer in the same shop. Not many automotive shops have that kind of climate control (none that I have ever seen). That is a major reason I am SO GLAD I am not in a production shop.

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  • kbotta
    replied
    Advocates devil...Your funny Matt!

    My bad for semi Thread-jacking...
    Kev

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  • Guest's Avatar
    Guest replied
    you still have to conform to the QS guidelines which is why they have those nice pretty blue books for you to follow.

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  • ag162
    replied
    Temps that affect stampings:
    I've had one part that was severly affected by a changing environment and it was a very thin part that went into a transmission. It was just a small thin shield. Just falling off of the press shute, made physical changes, then add a change of 10 - 20 degrees in temp and you had a cmm disaster. Therefore if your lab is controlled and production is not, my question:
    What is the true representation for layout purposes?
    Right off of the press - like the customer will receive or a chilled deviation of the sample?
    Then, will the sample be the same in the summer as in the winter?
    Oh yeah, then take in the material range. One composition ran today, may not be the same next run, but still within the spec, so what is the environment going to do to the dimensions then? Now I remember the reason I like beer,,,,,,,..........
    A.Gore

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  • Matthew D. Hoedeman
    replied
    AH, but that is not what we are talking about, now is it? QS9000 has nothing to do with that, UNLESS YOU INCLUDE IT IN YOUR STANDARDS. Now, I am not say YEA or NAY to it, I am mearly pointing out what QS9000 requires, which is basically NOTHING!

    If I set my QS9000 standard to say, "I will make reports that show all parts good, no matter what they actually measure." and as long as I do exactly that, and document that I did exactly that, then I am certified as QS9000. Now, I am not saying that will get me a lot of work, but it CAN get me my QS9000 certification.

    Now, this IS way over the top, but that is really what QS9000 boils down to. You can DO whatever you want, as long as your standards SAY that is what you will do and then you document that you did do it.


    As for compensating for tempurate, Hilton said "You can figure 6.5 ppm times the number of degrees from 68 times the number of inches to get an idea of the effect of thermals on your parts if you are checking steel."

    So, 6.5ppm is part per million or .0000065 X 10 (we will use 10 degrees of temp variation) X 72" (my machine travel) = 0.00468". Now, that is if the part is as long as my machine, 90% (100% right now) are under 48" so that lowers it to 0.00312" TOTAL error. That is as 10 degrees change. I can use my calibration record for temp changes over the last 10 years, fo a total temp range of 5 degrees, max to min. So, that changes it down to 0.00156" for a 48" part. The machine specs are +/-0.0007" both accuracy AND repeatability for a total 'tolerance' of 0.0014". Not much difference than the temperature, now is it?

    Now, I AM NOT SAYING that tempurature does not need to be monitored. IT WILL all depend on the applications and parts and tolerances you are running. Hilton, I imagine, needs to run a much TIGHTER tolerance so temperature will play a HUGE roll in what he does. I am running +/-0.020" for the tight tolerance and +/-0.080" or more for the loose tolerances. With a 5 degree temp range and the average size of the parts, that is a 5% error, and you remember the 10% rule? The measurement device SHOULD be accurate to 10% of the tolerance being used. The machine is another 5% so that gives me the required 10% accuracy.

    See, you can be the devil's advocate, and I'll the the advocate's devil!

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  • Don Henger
    replied
    We have a SOP here (standard operating procedure) booklet that Inspection made for this kind of audit. In the SOP there is a statment that parts have to soak in our room for 24 hrs before measurement. When the fire comes from the floor of having problems that goes right out the window. Yes we also have a locked thermostat and a temp gage. Ours is the same as most 68 degrees +-2. As for the sheet metal stamped parts we make the heatercores and evaporator coils which are .020"material and I have done them right off the press. I do not see a differance in a 24 hour soak period.

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  • jmgreen
    replied
    No problem, I have similar experiences and I do not disagree with you. Went thru the exact same argument about GRR. We compromised and did a GR&R on one micrometer, one indicator etc. I put them in a file and have only had to show them once since. We were fortunate in that the auditor we had first and for a few years after was really quite reasonable and knowledgeable. We've had some since that would fit your description to a tee.
    I even had one who wanted all our GR&R files moved from the file cabinet in our CAD room onto the computer where we keep all the certification data. This after the auditor before had said everything was fine. I refused and never heard anymore about it. To this day I believe he was too lazy to get up and walk 30 feet. We could probably devote several pages of this thread to audit horror stories.
    The only reason I mentioned about customer requirements is that we are also audited occasionally by our customers such as GM or Nissan. So if you can incorporate some of their requirements in yours then it doesn't hurt. Did not mean to imply that it has to be part of YOUR procedure.

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