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What kind of GRR study has to be performed?`

Discussion in 'Gage R&R and MSA - Measurement Systems Analysis' started by Ricardo Rodriguez M, Nov 6, 2018.

  1. Ricardo Rodriguez M

    Ricardo Rodriguez M New Member

    Mar 5, 2016
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    We build a system (gas analyzer) where the only CC is the torque value for the touchscreen since if too much torque is applied it will fail.

    The spec. is 23in-lb +/- 10%, the tool we use is a torque screwdriver set as close as possible to the nominal (required by the customer)

    In order to get the toque value we have a display torque meter where we get the value from to chart and record our readings.

    My question is, what kind of spc chart should I use (I-MR)?
    what GRR study (BIAS?) 3 readings (by nature of the product 3 readings are taken per day)

  2. ncwalker

    ncwalker Well-Known Member

    Sep 21, 2015
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    North Carolina
    I am understanding that you have a screwdriver with a torque setting (like a torque wrench) that you use on each and every part. You aren't measuring torque, you are just using this screwdriver until a clutch skips or it clicks (basically, stop tightening).

    What is confusing me, is you say you have a torque value for the touch screen. Which makes me think you are applying torque to the screen to see if it cracks. But you may be talking about the torque to mounting screws of the screen.

    In either case, from what you're saying, you tighten nuts with your screwdriver, then 3X a day, you actually MEASURE the torque you are getting. Are you measuring the torque of the actual screw? Or are you putting your screw driver in the gage and confirming it slips or stops at the specified torque?

    I can't help without those clarifications.

    I can tell you that BIAS is not an option for a GRR, but an OUTPUT of a GRR. So yes, you want to do a GRR to confirm your measurement device is repeatable and reproducible.

    I can also tell you that SPC isn't going to be valid because you are making one measurement 3X a day. For SPC to have value, you need to make 3 measurements in a row (at least, 5 would be better) to make a subgroup THEN take several subgroups. How often you do this depends on how much variation you see.

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