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Aluminum arc thermal expansion

Aluminum arc thermal expansion

Aluminum arc thermal expansion

(OP)
This may be easy for some of you, but I have a question regarding a peice made from aluminum and what happens as a result of thermal expansion.  The part is machined from stock and is approx 6" X 2.5" x40"  It is also cut in an arc.  It is the radius of a 40" circle.

If specified to be machined to tolerances at 68 deg. F  what will happen as the temp rises and falls?  I know a circle will grow with the same coefficient of linear expansion as the material it is punched through, but what happens to a semi-circle?  Can it be expected to hold shape?  Does it wander?  I know if I heat and cool a piston NOT placed inside a bore it will no longer be round when I am done, so I wonder does a "Banana" of aluminum expand uniformly or not?

I'm curious if I can expect my CMM to measure correct inner and outer radius with thermal compensation activated or does that go out the window since the part is not a complete circle?

RE: Aluminum arc thermal expansion

Unless there are external forces acting on the part (or internal residual stresses), the expansion will be uniform provided the temperature is uniform and there are no phase transformations involved.

I am not sure why you think a piston that is heated and cooled NOT placed inside a bore will not be round when you are done.  Provided the heating and cooling is uniform, so will any expansion/contraction.

rp

RE: Aluminum arc thermal expansion

(OP)
Thanks for the answer.  That helps.

The piston thing?  I learned that at a much younger age.  Heated a piston in the same oven as my freshly painted cylinder for my dirt bike. I wanted to see how much it actually grew when heated to 550 deg F.  I found out.  It also wasn't round when cooled back to room temp.  I had to by a fresh piston with paper route money.

RE: Aluminum arc thermal expansion

Aluminum alloy heat treatment will be altered at temperatures above 350F. Grain size in the metal will grow.

RE: Aluminum arc thermal expansion

I agree with redpicker, the semi-circular/banana shaped piece should expand when heated and contract when cooled, provided that the temperature change is uniform.  There may be some amount of non-uniform distortion if there are residual stresses that have not been relieved during the manufacturing of the piece.

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