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Tolerances differences in temperature change

  1. Jul 17, 2008 #1
    Does anyone out there know if there are any published studies which have tested the tolerance changes in steel and aluminum machined components when they are manufactured in one (temperature) environment and moved to different (temperature) environment.

    Anything would help.

    Thanks,
     
  2. jcsd
  3. Jul 17, 2008 #2

    Mech_Engineer

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    Assuming the part is the same temperature as its environment in each case, moving it from one temperature to another will cause it to shrink or expand according to its coefficient of thermal expansion. Tolerances would essentially stay the same.

    If the part has some unknown temperature distribution (say hotter where the machining operation took place) the part will end up slightly changing shape as it cools. how the tolarance changes would be material and geometry dependent, but generally a material with a very low coefficient of thermal expansion (and hopefully a high thermal conductivity) will probably fare better than one with a large CTE and low thermal conductivity.
     
  4. Jul 18, 2008 #3

    FredGarvin

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    What tolerances are you referring to? Are you looking at single parts or an assembly? Ideally, the tolerances on a part don't change due to thermals. Simply the overall size does (like ME already mentioned). Now, if you're talking about stack ups between parts, then those tolerances may change and often do. We use different stack ups based on assembly, high and low temp conditions.

    It would help if you explained what you are looking for a bit better, i.e. what is your scenario?
     
  5. Jul 22, 2008 #4
    OK, situation is as follows:

    We store raw material in an area about 95 degrees F.
    Raw material is loaded into a machine, and machined with coolant.
    The final part comes out and is inspected. The area where the part comes out of the machine is about the same 95 degree F atmosphere. Parts are inspected in this location for some critical tolerances.
    The part is then transfered to a room which is controlled to about 70 degrees F. The same critical tolerances are inspected as well as a few others.
    Parts are then sent out for finishing.
    Received back in, inspected, then shipped.

    This is not an assembly, piece part only. The material is steel bar.

    Thanks,
     
  6. Jul 23, 2008 #5

    FredGarvin

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    Unless your machinists are taking huge cuts that build up a very large amount of heat, there should be no issues.
     
  7. Jul 24, 2008 #6
    By taking huge cuts, I am guessing that you are suggesting that the part will heat up to a very high temperature, then might have the possibility of being cooled quickly... Yeah, I guess in this situation, it really won't make a difference.

    Thanks all...
     
  8. Jul 26, 2008 #7
    The Average coefficient of expansion, (μm/m · K, at °C) is typically between 12 and 15,
    for the ranges 20 - 100 and 20 - 700 C for carbon and low alloy steels. Cutting which produces most heat is typically not the most accurate. Milling large pieces is usually cooled.
     
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