things cast in aluminum

[davidh]

besides being interested in hobby machining, i am also into hobby casting of aluminum and even did some brass, plus trying my hand at powder coat painting.

yesterday i poured a couple aluminum things using the "lost foam" method. its easy to do, you can make many things that are only limited by the amount of metal you can melt and your creative juices. i only wish i was a semi talented or even just a tad talented in the artist imagination regime.

a few years ago i hot-wired a bunch of character deer, poured them and gave away to my kids etc along with their xmas gifts. . . last weekend my granddaughter and her friend were here for a picnic (13 yrs old or so) and bored like crazy. city kids without target or the mall can't seem to be terribly creative when in the country. . . . so i had them hot wire "something" out of foam and i told them i would pour it for them. . . they got busy letter plaques, animals, a cross. . . then coated them with a goopy mixture. i was amazed. so yesterday i did my melt, buried the foam things in the buckets of sand i have, and poured.

after about 2 hours of warming and melting a bunch of oxygen bottles i got from the medical oxy supply folks (im told it was 6061 and not a good thing for structural castings) and did my messy / stinky thing.

most of the items came out fine. i forgot the importance of "vents" attached to the foam on one item to allow the outgassing of the burning foam so that item did a short pour. my handwheel i was making for my milling machine vice ended up pretty dang good except the 6061 was really gummy to machine and i had a heck of a time getting a decent finish on it. but, in the long run, it will work. i pressed in an old socket and i gues it was a bit too tight as the side of of bore that was poorly supported in the press kinda tore itself out. but it works. im going to attempt to put a few pictures on this post and another one if anyone is interested. . . . another post will follow about the powder coating endevor.

[lynnl]

Regarding this "lost foam" method: Do you leave the foam in place, and let the molten metal melt it out of the cavity? Or is there some other process that's used to get rid of the foam?

(added) I guess I didn't really read your account closely enough. I understand now.

[Dr Stan]

Regarding this "lost foam" method: Do you leave the foam in place, and let the molten metal melt it out of the cavity? Or is there some other process that's used to get rid of the foam?

(added) I guess I didn't really read your account closely enough. I understand now.

You burn out the foam with the molten metal. BTW make sure you have plenty of ventilation as the fumes from styrofoam are not exactly healthy. Its a really good process to make "one-off's" since you can just make the pattern in foam instead of going to all the work of making a wooden or metal pattern. You do not even have to concern yourself with the draft angle since you're not pulling the pattern out of the sand.

Lost foam is also used in production, especially automotive engine blocks, heads, etc. They make the foam block, etc using the same process as making the cheap styrofoam coolers. They include the sprue, risers and the gating system and just burn it out with the molten aluminum. It makes for much more precise castings than the traditional sand casting methods thus reducing the amount of machining and improves fuel mileage by reducing the weight of the vehicle. Next time you pop the hood of your car/truck look closely at the engine and you'll probably see the pattern of the styrofoam retained in the casting.

[philbur]

Been there, done that. If you throw it under the bench for a few weeks or artificially age it by heating it in an oven for a few hours it will machine just fine.

Phil

my handwheel i was making for my milling machine vice ended up pretty dang good except the 6061 was really gummy to machine and i had a heck of a time getting a decent finish on it. but, in the long run, it will work.