Help needed concerning a destructive Gage RR

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    Hi all,
    I need to do a Gage R&R on an SAE spec’d (possibly destructive) test.
    I’ve done many ‘normal’ GR&Rs, but this is a bit confusing.  In this particular test, the sample is held at a certain voltage for a period of time.  If the part passes it can be tested again, but it is unknown if multiple testing can lead to failure.  If a part fails at a certain voltage it will definately fail if retested… and at a much lower voltage.
    I question whether or not that a GR&R really is applicable here.  The machine that does the testing is up to date in calibration.  All the operator must do is load the parts and press a button.  If the part fails he must record the voltage and/or the time.
    Any ideas? comments? suggestions?


    Erik L

    We conduct MSAs if there are concerns over the precision and accuracy of the measurement process.  Are either of those a concern (I’m assuming time to failure and the voltage that the instrument is set at)? 
    Based on the information that you’ve provided, there is certainly a nice opportunity to conduct some logistic regression around time, stratified by various voltages.  This would allow you to see how you’re doing relative to the specification limit for test time.  Or, alternatively, you could use that analysis to set a max eposure time at a ceratain % failure rate.



    This is for my greenbelt certification project.
    Maybe I am trying to make this more difficult than it really needs to be.  All I need to do is verify the measurement system.  GR&R is only one tool that can be used to do this. 
    Here is a more detailed look at the testing process.
    1) The operator loads (5) assemblies into a tank of water and attaches a clip to the stripped end of each while the other end is submerged in water.
    2) The operator flips the main power switch and energizes the tester.
    4) The operator presses and holds the ramp up button. The voltage then increases at a rate of 500 volts per second until the test voltage is reached.
    5) Once the test voltage is reached, the operator releases the button and starts a timer.  The assemblies remain submerged for a period of (5) mins.  If no failures occur during ramp up or within the hold time the assembly has passed the test.
    6) If at any point during this test an assembly fails (di-electric failure which trips the machine) the operator records the voltage (or the time if the test voltage was achieved).
    What would you do to verify this measurement system?



    What you need to do is to find reference samples that are known to fail.  You have a couple of options here.  If you’re interested in only pass/fail, then run the test with samples that will and will not fail (approximately 50/50 mix of each).  Don’t use “basket case” failures as that will bias your results.  You want “borderline” failures; ones you suspect the test may or may not be able to detect.  More samples is better.
    Your other option is if you are running this as a variable MSA.  Your Y is either voltage to failure or time to failure.  Again, taking samples that are known to fail, you compare your tester results with the standards and run your analysis.
    What are samples “known to fail?”  That is where you have some latitude.  They do not necessarily need to be representative of your actual products under test.  Work with your engineers/scientists to come up with a set of standards you can use for this investigation.
    Good luck!

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