Is aluminum more dimensionally stable than steel?

[chimpera]

Is aluminum more dimensionally stable than steel? I understand that machining precision parts in steel is challenging because internal stresses cause warping whenever material is removed. Is the same true of aluminum?

If this is a stupid question feel free to make fun.

[Janos]

I do plenty of aluminum, P20 and A2. (Injection mold stuff) The aluminum stays put really nice. the only time it seems to move is when you take out a bunch of material and then have to get it annealed before final finish. Of all the materials that I do brass is the worst. I had a new programmer make a part aprox. 1.500 x 2.500 and .187 thick out of .375 stock. He did a face cut then the profile of the part, then flip and face off the rest. It had a .015 bow in the part over 2.5"

Asking questions is how you learn. Keep asking.

[Geof]

No such thing as a stupid question.

The answer(s) to your question are yes and no. Internal stresses in (CRS) will make it warp and twist whenever it is machined. Hot rolled steel (HRS) does not have internal stresses so it does not move when machined.

Cast aluminum may have low internal stresses so it will not move when machined. Extruded and tempered aluminum and aluminum plate may move like crazy due to lots of internal stresses. Cast aluminum tooling plate is very stable.

It depends entirely on the state of the metal and whether it has been cold worked, worked at a high temperature or annealed.

[RotarySMP]

Aluminium is less dimensionally stable than steel, with respect to thermal expansion. It has nearly twice the thermal expansion coefficient.

http://www.engineeringtoolbox.com/li...ents-d_95.html

[Janos]

Originally Posted by Geof No such thing as a stupid question. The answer(s) to your question are yes and no. Internal stresses in (CRS) will make it warp and twist whenever it is machined. Hot rolled steel (HRS) does not have internal stresses so it does not move when machined. Cast aluminum may have low internal stresses so it will not move when machined. Extruded and tempered aluminum and aluminum plate may move like crazy due to lots of internal stresses. Cast aluminum tooling plate is very stable. It depends entirely on the state of the metal and whether it has been cold worked, worked at a high temperature or annealed.

Originally Posted by RotarySMP Aluminium is less dimensionally stable than steel, with respect to thermal expansion. It has nearly twice the thermal expansion coefficient.

Yeah, What they said.

[Mcgyver]

Originally Posted by Janos Yeah, What they said.

ditto

i'd add that its probably not the fundamental criteria in most cases, lots of other factors would drive the decision on bar stock AL vs steel as you could see movement in either. Cold rolled mild steel is particularly bad, however you can get steels that won't move (much), you can heat treat the steels prior to machining to remove the stresses or there are machining techniques to deal with it.

When i used CRS i either have a part that is balanced (ie its when you take a strip off one side that it turns into a banana) or is completely machined all over or has minimal machining to be done

btw, getting something really, really flat, is not trivial, especially if its not a boxy shape. if its not flat to start with, just about no matter how you hold it, clamping it (whether vise, table or mag chuck) changes its shape such that after machining it will spring back toward its pre-machined shape and not be flat. keep that in mind the metal is not a geometric solid on a cad proggy...it moves when you clamp it, and moves when you machine it...and this has to often be taken into consideration to get the results you want