iSixSigma

Gage RR

Viewing 15 posts - 1 through 15 (of 15 total)
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  • #45449

    E. Johnson
    Participant

    I am in heated discussions with a customer concerning Gage R&R’s.  The customer is demanding that before a gage can be used to measure a part, a Gage R&R is required on the gage measuring the part being produced.  My position is that a Gage R&R is independent of Part Variation.  To isolate the variation due to the MSA, the Gage R&R should be performed measuring gage blocks or a part with known characteristics.
    I am all messed up or is the customer correct?
    Eric

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    #148527

    The Force
    Member

    Probably your customer is pertaining to the calibration (e.g. bias, linearity, stability) of the gage because prior to MSA, the gage should be calibrated.

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    #148529

    E. Johnson
    Participant

    I believe the customer is looking for the Total Variation (TV) of the process.  TV is a function of Gage R&R and Part Variation.  The customer is not separating the Gage R&R, which is a function of Equipment Variation (EV) and Appraiser Variation (AV), from the Total Variation.  What do you think?
    Eric

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    #148531

    The Force
    Member

    Pls. clarify things with your customer. if you have validated that it’s more on TV — Then TV is part of the GR&R study already.

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    #148533

    Mikel
    Member

    Your customer is right – he has a right to know if the SYSTEM used to measure his parts is accurate and precise.

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    #148540

    Mike Carnell
    Participant

    E. Johnson,
    I do not understand why you would get into a heated discussion with a customer and jeopardize a customer relationship over this. If you are calibrated you have a sticker on the gage so everyone can see that it is calibrated – including the customer. Why would the R&R issue be any different? TV, AV, PV etc. what a stupid discussion to get into. It doesn’t matter.
    I would view a customer that is astute enough to ask for the R&R numbers as a good thing. They want to know about your ability to determine fitness for use. It is a much better place to be than Source Inspection where they bring their own tools so that they know what the R&R is because you won’t give them yours.
    You have put yourself in a bad situation and are making it worse.
    Just my opinion.

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    #148543

    Monk
    Participant

    E. Johnson
    If it is a production part, you must have alredy done the part approval process, which checks for your process capability and fitness to use.
    Customer is right in asking for Gauge R&R report before they start using the part at their production line. THINK from the customer perspective. How do they be confident of your process capability, if the measurement system is not validated. Customer is right in asking for gauge R&R.
    Only thing that you can do now, is to apologize to the customer and do the gauge R&R if you want to save your job!. In future be careful…..seek information when in doubt about what to Do!
    Hope this help.
    Monk

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    #148547

    BTDT
    Participant

    E. Johnson:Have there been any issues in the past where the customer has a problem where the company claims nothing is wrong?I worry that the customer is trying to get some resolution to a past problem where data reliability has come into question.Is this a “blame storming” session?Cheers, BTDT

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    #148551

    chhabra
    Participant

    Eric,
    Gage R&R is not independent of part variation. If  you refer to any typical gauge R&R analysis output, you will come across the “percentage contribution to total variation” section. which is nothing but the contribution due to the measurement system (Total Gage R&R) and part to part variation. It is Ideal to have less the 7% as total gage R&R and consequently 93% or more part-to- part variation.
    Also, while performing gage R&R its imperative that we should include the actual parts to be measured (and not measuring gage blocks). One should include the parts from entire range to capture the total part variation.
    So, I would say that the customer is correct when he is asking you to measure the actual part being produced.
    Hope this helps..
    Amit
     
     
     
     

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    #148559

    E. Johnson
    Participant

    Amit,
    Your response is very helpful.  My situation is difficult in that one measuring device is utilized to measure over 1000’s of part numbers.  Should it be anticipated that a Gage R&R is performed utilizing each part number?  That would seem to be overkill.  The devices I am talking about are CMM’s, CLM’s, paint mil thickness meters, and paint gloss meters.  I do not have a problem utilizing a part that would incorporate the range of the inspection envelope to encompass the variation in measuring over the entire equipment range.  My understanding of Gage R&R is to determine if the equipment is capable of measuring numerous parts without proving out the capability of the equipment on a part by part basis.
    Thanks for the input and I look forward to your response.
    Eric

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    #148561

    Haugen
    Participant

    E,
    You have to conduct a gage R&R on each part and every part feature that is different.  The measurement can be affected by part geometry, surface roughness, differences in datum interface with mounting surface, etc.
    I ran a whole plant worth of CMMs, and the first time through an inspect routine (program) usually about half the feature Gr&Rs would fail.  The probe would hang up on a chamfer, or the probe tip would be to big/small for the surface finish, etc.
    You don’t know what you don’t check.

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    #148780

    DA
    Participant

    Since the objective here is to check the creditability of the measuring system, i think performing the gage r&r over the operating range of the gauge should work absolutely fine, i dont see the need to do it on each part …

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    #148785

    RS
    Member

    Hi Eric. .. I think what Amit suggested is right. Gage variation is not independent of the part variation. It is a subset of the total variation which could be due to part-to-part, equipment, or operator.
    You need to measure actual parts across the product range to capture variation. For that you can take samples for the entire product range and determine if the equipment is capable of measuring numerous parts. When you analyze the data it will give you R&R output showing percent contribution to TV.
    Cheers!!!
    RS

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    #148827

    argon
    Participant

    Eric,
    as much as possible, never use gage blocks when performing GR&R. remember, you are assessing the measuring system’s ability to perform it’s ACTUAL job–to measure whatever it is you are ACTUALLY measuring in the process. you don’t need standards here. you are not measuring accuracy. use actual parts.

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    #149155

    hitesh
    Participant

    Eric,
    Your customer is very right in demanding a GR & R for a gage before it being used fot measurements more specifically if it is an critical charatcteristic.
    Here in you look for repeatability & reproduceability of your measurement system with the sample size with part variation w.r.t. characteristic of 95%.
     
    MSA may be done using some seletced parts or gage blocks, condition being 95% of the tolerance band is covered during analysis.

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