[cg 2005]

I cast my first aluminum ingot today. The foundry worked well and the ingot looked good until I started to machine it in the mill.

The melt material was mostly aluminum floor drops, not cuttings or cans.

I used end mills, fly cutters, varied the speed and doc but all of the cuts looked bad. A lot of tool marks and ripped material. The fly cutter produced the best results, but not a mirror finish.

I did not notice any porosity of any visible size.

Is this what is expected from the DIY cast Al billets?

Any ideas?

[txcncman]

Cast aluminum is tricky. Did you alloy anything into it? What pickling or other treatment did you give it before machining? Did you chemically age it before machining?

[cg 2005]

Cast aluminum is tricky. Did you alloy anything into it? What pickling or other treatment did you give it before machining? Did you chemically age it before machining?

Pickling, treatment??? Just Al, unless the drops were alloys, which I doubt.

I let it cool and chucked it up. I did play with grinding some new bits to change the angles and finally got an acceptable finish.

I guess I need to do more research again, but now into aging the metal,etc.

Thanks

[awerby]

As-cast aluminum is soft and gummy. It's hard to get a good finish on it by machining. Heat-treating it would help harden it and make it cut better. But you've got another issue to confront as well.

An ingot isn't the same thing as a billet. It will often have porosity, since there's no reserve of hot metal for the cooling metal in the center to draw from, so the core, as it shrinks, will draw metal from closer to the surface. To avoid this effect, cast your billet the same as you'd cast any other part, inside a mold with a riser of sufficient thickness to allow it to draw metal from a reservoir of metal that remains liquid when the core of the billet is cooling.

Andrew Werby
www.computersculpture.com

[cg 2005]

Thanks for the help and insight. I needed a project like this to keep the gray matter from becoming septic.

[Me2]

What temperature did you cast at? Try and keep it below 750 degree C. To hot and you will get a lot of hydrogen precipitation, when machining you will get a poor finish. Try and cast as cool as possible. Inoculation tablets also help.

Cam

[Geof]

The material you used was almost certainly some alloy, pure aluminum is very rare because it is so soft.

All alloys need to be age hardened, also called tempering, to attain the best physical properties and machinability.

You could try doing your own age hardening; Heat the ingot to 75 - 80% of the melting point and quench it as rapidly as possible in a tank of cold water. This fully anneals it and gives it close to the same condition throughout.

For age hardening you can simply wait a long, long time like several decades and it will age harden at room temperature; but probably you are in a hurry. So you can age harden at an elevated temperature.

It is possible to do it in a normal domestic oven, particularly the self cleaning type that has the ability to get extra hot. Simple bake it at a temperature as high as the oven will go for several hours. It can take something like ten or more hours but if age hardening is overdone the material can become brittle.

One approach you could try is to anneal the ingot then cut it into several pieces and age harden these for different lengths of time and see if the machiniability differs.

Do not quench it after age hardening, let it cool down slowly.

You may not find any difference in the machinability after this because some alloys do not harden as much as others.