Metal and other materials thermal expansion

litlerob1 · Nov 15, 2014

Well instead of bumping the Temperature and Measuring thread all the way off topic, I thought I would start a new one. Are there formulas for calculating the thermal expansion or contraction of materials? Obviously (for me), I would think based on material type-mass-time to acclimate-similarity of inspection equip. to material being measured.

But really the question is; Are there formulas for calculating this? I as the machinist would like to know especially since I gotta check a first article before it comes out of the machine and sometimes find myself pulling my hair out, because of thermal issues and waiting for a sign off for "go ahead". Not saying I would go ahead anyway, just be nice information (I think, maybe not). :hole:

Robert

6061Mike · Nov 15, 2014

Yes, google it. Sorry, not being an ass, but there is alot of information out there. You should easily find the thermal coefficients of different materials without too much trouble. Not that I know if you will find specifically what you are looking for, i.e. different expansion rates based on mass, etc...
Someone here most likely has some numbers off the top of their head, I do not. Are you trying to hold very tight tolerances, or is your work environment having wild temperature shifts? I think most of the thermal stuff is related to engineering and/or extreme temp variances, not every day machining/inspecting, unless youa re doing very tight tolerances...

FWIW, Sometimes I see a difference in the machine as the coolant brings the part down a few degrees vs it sitting in the air for a day or so, but this is in the tenth range...

Derek Smalls · Nov 15, 2014

Sure are. They are expressed usually as: How much a material expands per inch of length per degree. So for example, steel expands @ about .000006"/inch/1*F, varies slightly depending on particular alloy and condition, but 6 millionths is close enough for me. A 10" long bar will grow .00006" if heated 1*F, .0006" if heated 10*F. There is a table with the expansion rates of all commonly used materials in the Machineries Handbook.

bryan_machine · Nov 15, 2014

The magic phrase is "coefficient of thermal expansion" - that's the name of the quantity Derek Smalls describes, and it would ineed be X-length expansion per Y-length of object per unit of temp.

So you want to search (google, bing, etc) for (say) "coefficient of thermal expansion for steel" you'll get charts that show it at 6.7 millionths of an inch per inch of length per degree F.

Note that it's expansion per unit length - so the effective growth a of a large object (say a 10 foot long machine bed) will much large in absolute terms than say a 1" long gage block.
This effect becomes important with thing like large machine tools working on close tolerance parts.

gvidas · Nov 15, 2014

For the lazy folks:

Coefficients of Linear Thermal Expansion

Milland · Nov 16, 2014

gvidas said:
For the lazy folks:

Coefficients of Linear Thermal Expansion

And for the really lazy, take those numbers and plug them into this calculator, along with the final difference in temperature:

Thermal Expansion Calculator [metric units]

Heavey Metal · Nov 16, 2014

No work that is produced in a lathe has anything to do with linear expansion.

It is subject to volumetric expansion.

Something that is affected by many forces including stress

The reason gageing is calibrated at a specific temp.

If you are doing enough parts you will get a feel for the temp effects, kind of worthless for a first article though.

Milland · Nov 16, 2014

I'd go with volumetric expansion follows (is a function of) linear expansion of a material subjected to changes in temperature. Stress or other actors on the form or volumne of the material are separate, but must be dealt with to meet performance (tolerance) criteria.

Heavey Metal · Nov 16, 2014

Linear expansion is a concept that dosnt exist but in theory.

Eaver tried to chuck up a line?

opscimc · Nov 16, 2014

Heavey Metal said:
Linear expansion is a concept that dosnt exist but in theory.

Eaver tried to chuck up a line?

No, I've never tried to chuck up a line. But, micrometers measure linear dimensions, not area or volume, which is why linear thermal expansion very much exists in practice and not just in theory. If a round rod heats up by a certain amount in a lathe the change in its (linear) diameter is given by tabulated values of linear thermal expansion coefficients and confirmed by a measurement made by a (linear) micrometer.

litlerob1 · Nov 16, 2014

6061Mike said:
Yes, google it. Sorry, not being an ass, but there is alot of information out there. You should easily find the thermal coefficients of different materials without too much trouble. Not that I know if you will find specifically what you are looking for, i.e. different expansion rates based on mass, etc...
Someone here most likely has some numbers off the top of their head, I do not. Are you trying to hold very tight tolerances, or is your work environment having wild temperature shifts? I think most of the thermal stuff is related to engineering and/or extreme temp variances, not every day machining/inspecting, unless youa re doing very tight tolerances...

FWIW, Sometimes I see a difference in the machine as the coolant brings the part down a few degrees vs it sitting in the air for a day or so, but this is in the tenth range...

Sorry but yes you are being an ass,

how much effort did it take you to post?

What is tight? A mold that is turned to about 3' diameter with a true position callout of .005" from 4 bolt hole pattern about 2" square to 3 datums OD, ID and a face groove? I call that damn tight. And with that size of material QC wants to wait on it, which is totally understandable. Obviously that one needs to go to CMM I have to get it out of the machine, but in other cases... And my next part I need to pull a 20" chuck and put on a collet closer to do some small work. (Jobbing shops) :crazy:

So I wait, and pull my hair out. And I work in sub .001" all day everyday.

Robert

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Metal and other materials thermal expansion

litlerob1

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6061Mike

Hot Rolled

Derek Smalls

Stainless

bryan_machine

Diamond

gvidas

Aluminum

Milland

Diamond

Heavey Metal

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Milland

Diamond

Heavey Metal

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opscimc

Stainless

litlerob1

Diamond

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