Understanding temperature and it its effect on CMM measurement can be very confusing to most people. There are many things to consider when deciding how this effects your measurement. How does it affect the part, how does it affect the machine?
There are some major components to temperature,
Ambient Temperature
Rate of change
Drafts or localized effects
Ambient Temperature is the general room temperature that the machine is occupying. The CMM manufacturer will specify and ambient and with a nominal deviation A typical statement would be 68 degrees F plus or minus 2 degrees, some machines will allow a larger spread such as +/- 4 degrees or tighter spread such as +/- 1 degree. The Key in this statement is the spread not really the nominal. For instance, if the machine is calibrated at 70 degrees in the +/- 2degree spread you can expect it to measure parts effectively from 68 to 72 degrees F, you might incur issues if you were to run the machine at 66 degrees
Rate of change is important as rapid changes in temperature even when within the specification can cause an issue. If your temperature is changing quickly over a short period the machine will be moving during the periods of change and more importantly the part you are measuring due to is smaller mass or different material will be moving at a faster rate due to its reduced mass
Drafts are another cause measurement issues, because they can cause localized cold or hot spots on the CMM or part, deforming the part or machine until it stabilizes
Localized affect that can exist is divergent temperature between the manufacturing and the quality environments. An example of this would be taking, a part sample from the manufacturing area to the quality room and measuring it immediately. If the manufacturing area is 2 degrees warmer then the QA area on a 10-inch steel part this could be an error of 0.00018 in the measurement and on a tight tolerance part this could consume a large portion of your manufacturing tolerance
(calculation based on a general specification for thermal coefficient of expansion for steel)
There are many other effects such as gradient temperature, humidity and others that can cause issues to measurement values, these are some of the most common ones that are over looked when using a CMM or other measurement device. If further information is required please contact Masters Precision at sales@mastersprecision.com
There are some major components to temperature,
Ambient Temperature
Rate of change
Drafts or localized effects
Ambient Temperature is the general room temperature that the machine is occupying. The CMM manufacturer will specify and ambient and with a nominal deviation A typical statement would be 68 degrees F plus or minus 2 degrees, some machines will allow a larger spread such as +/- 4 degrees or tighter spread such as +/- 1 degree. The Key in this statement is the spread not really the nominal. For instance, if the machine is calibrated at 70 degrees in the +/- 2degree spread you can expect it to measure parts effectively from 68 to 72 degrees F, you might incur issues if you were to run the machine at 66 degrees
Rate of change is important as rapid changes in temperature even when within the specification can cause an issue. If your temperature is changing quickly over a short period the machine will be moving during the periods of change and more importantly the part you are measuring due to is smaller mass or different material will be moving at a faster rate due to its reduced mass
Drafts are another cause measurement issues, because they can cause localized cold or hot spots on the CMM or part, deforming the part or machine until it stabilizes
Localized affect that can exist is divergent temperature between the manufacturing and the quality environments. An example of this would be taking, a part sample from the manufacturing area to the quality room and measuring it immediately. If the manufacturing area is 2 degrees warmer then the QA area on a 10-inch steel part this could be an error of 0.00018 in the measurement and on a tight tolerance part this could consume a large portion of your manufacturing tolerance
(calculation based on a general specification for thermal coefficient of expansion for steel)
There are many other effects such as gradient temperature, humidity and others that can cause issues to measurement values, these are some of the most common ones that are over looked when using a CMM or other measurement device. If further information is required please contact Masters Precision at sales@mastersprecision.com
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