Six Sigma – iSixSigma Forums Old Forums General MEASUREMENTS VS TEMPERATURE

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    I’m currenlty working on a BB project that is measuring a machined cylinder that is 20″ in diameter and 10″ in length (laminations welded together).  The diameter has a tolerance .003″.  Ambient temperature of our Snap Gage vs the part and standard are causing issues with the measurement system.  Ex. A part that is cold is in tolerance and as it warms it is out.  Or when the snap gage is cold the part is good and when it heats up it is out.  Has anyone seen a similar effect with machined parts?  If so, how you handle the temp differences?



    When do measurements of the part really matter? When does
    contraction or expansion have the biggest impact:1. Before the weld or after the weld?
    2. What happens if the part heats up or gets cold in the field?
    3. What is the impact on laminates when you heat them after it
    cools. Your measurement system should address when the part should be
    measured and in what state of temperature and material state.
    Once you answer that, then you can work on your gage issue.



    I worked on a project that had a plastic part inside a metal cylinder.  The requirement that we measured was how far the plastic part was recessed inside the metal cylinder.  Because these two materials have different coeffecients of thermal expansion we had to condition the assembly overnight at 65-70 degrees F.   Conditioning the part and taking measurements at a specific temperature should always be a consideration when developing a measurement system.  It may turn out that temperature is not a critical parameter but it should be considered.

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