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GRR for troque driver.

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  • #50855

    Wilson
    Member

    Hi,
    Good morning/afternoon.  I had six manual type torque drivers and one torque checker, customer requested me to perform variable GR&R and it should be at 0.3 or below, could someone help how to do it?  Thank you very much for kind help.
    Best regards
    Wilson (Sept.1,2008)(Mon.)

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    #175362

    Michael Mead
    Participant

    Hello Wilson, this seems to be a common topic here. I suggest you go to “search by keyword” in the upper right corner and enter  “GR&R” and “Torque”. I just did it  and found 13 threads.
    Good luck,

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    #175372

    Craig
    Participant

    We just did one and used 5 torque wrenches of the same nominal value, 3 operators, and 3 replicates. In the GRR platform, substitute “torque wrench” for “part”. Our wrenches have a +/- 6% tolerance so we translated this to in-lbs and plugged this in as the upper minus lower in Minitab. Our R&R / Tol was horrendous. We did a what-if, and used a wider tolerance based on drawing requirements for the screws we are torquing. Even using this tolerance, the R&R/Tol was real bad. We have a new torque analyzer on order.
     

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    #175385

    Robert Kluttz
    Member

    Are you doing a GR&R just because someone asked you, or are you actually trying to solve a production problem? 
    You can do a fantastic GR&R and still not know why you’re getting loose terminations.  Torque drivers are only one small contributor to termination integrity.  So I’d take a step back and figure out what you’re trying to accomplish – do you want a kappa score or do you want a root cause of why you’re getting loose terminations?  If it’s the latter, a 8D problem-solving exercise would be more beneficial than a GR&R. 

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    #175437

    Wilson
    Member

    Hi Michael.
    Good morning and thanks for the information.  Have a great day.
    best regards
    wilson

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    #175494

    Wilson
    Member

    Hi Robert,
    Yes you are correct, I’m doing this just because customer ask us to do so.  we had nearly 500 pieces of manual type driver (brands name as ‘mountz’) and we picked 6 and select 3 operators to perform GR&R in excel spreadsheet format and observe the result is not good, I got P/total tolerance ratio as 0.8 and P/total SD as 1.  I knew that if I would like to see both at 0.3 or less, I should have part-to-part variation in a very distinct or obvious stage while for the rest should have less distinct.  Anyway may I know whetehr you have any successful example and story about the GR&R which can be shared.  Thank you.
    best regards
    wilson

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    #176138

    Robert Kluttz
    Member

    A few questions;

    How did you verify the resultant torque from each of the 3 operators?
    What was the range of torque values that you have them tighten to?
    How did you select the 6 tools & 3 operators? 
    I would set it up as follows;
    Select ten torque values representative of the range used in your shop (if you torque from 1 – 10 in lbs, use 1, 2, 3, 4, 5, 6…… 10).  Select 3 operators and 3 tools.  Using a desktop torque tester, have each operator use each tool (twice) to tighten to each of the ten settings.  record the actual values from the torque tester. 
    With this method, most of your variation should be part-part.  If it’s not, then I’d bet that you’d have some operator variation (applied torque would vary by how fast torque is applied, where on the shaft the driver is held, environmental conditions, etc).  If you’re seeing a lot of operator variation, I’d recommend refresher training followed by a repeat of the GR&R

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    #176142

    Taylor
    Participant

    Wilson
    Just a word to the wise, from my experience torque is a Destructive test and replicates will inflate the Repeatability

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    #176148

    Robert Kluttz
    Member

    Its only destructive if you’re using actual fasteners and mating surfaces.  Using a desktop torque tester allows you to avoid that.

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    #176149

    Taylor
    Participant

    I dont disagree, but thats not what the Poster is doing, he specifically stated pulling 6 samples from a 500 part lot

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    #176150

    Robert Kluttz
    Member

    I may be wrong, but I believe the “500” reference was to the number of torque drivers being used on the floor rather than the number of fasteners.  Mountz is a brand of drivers.

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    #176152

    Taylor
    Participant

    ok, seems silly to perform R&R on just 6 units out of 500 then. From a customer stand point I would be more interested in a Change out/PM schedule and/or calibration/performance test plan rather than a random R&R.

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    #176156

    Wilson
    Member

    Hi Chad,
    Yes, we have 500 units of the torque.  I do agree with you point that we should be more focus on calibration and PM schedule rather than random R&R.  Thanks for your response.
    best regards
    wilson

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    #176157

    Wilson
    Member

    Hi Robert,
    Yes, 500 is refer to number of torque use in the production area.
    regards
    wilson

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    #176162

    Craig
    Participant

    the GRR applies to the measurement system. (the torque analyzer).
    It is not intended to assess the capabilities of the torque wrenches.
    is the customer interested in how well you torque things, or how well you measure torque?

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    #176166

    Robert Kluttz
    Member

    In this case, the torque analyzer would be the prime standard. 
    The Mountz torque drivers are pre-set to the desired value (5 in-lbs for example).  The operator would apply the driver to the torque checker and turn in the tightening direction until the driver clicks.  The difference between specified torque (5 in-lbs) and actual torque (the reading on the torque checker) would equal the sum of the variation contributed by the tool, the operator and the process. 
    So it would most certainly assess the capability of the torque driver (as well as the operator and the process). 

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