What foam for aluminum casting?

[biomed_eng]

In the past, we had parts aluminum sand cast using patterns hand shaped from mdf and bondo.

I now want to move to cnc'ing the patterns out of some type of foam. What foam should I use? Name brands? Types? I am totally new to foams.

I would like the foam to be as "light" as possible so that I can run the cnc faster than with "heavy" foam. However, I presume that the foam needs to be heavy/stiff enough so that when the foundry is pressing the pattern into the sand that the foam does not compress or break.

If you know of good foam suppliers for this kind of stuff in the Southern California are, please feel free to recommend them.

Thanks!

[Kipper]

Try a google of "lost foam casting" you'll then see the way to approach this method. The main difference being no binder in the sand and that the sand is usually dry. Most of the lost foam casting i've seen has been gated only at the top...you may want to look at traditional gating and risers as i'd think it would give a better finish and a closer grain in the casting. Never bothered with it myself but once you see it you'll know how it's done. Any pottery suppliers near you? they have nice slips you could use hth

[biomed_eng]

Thanks for your suggestions.

I am interested in using a regular sand casting process, not lost foam casting. I am only doing one-off projects.

I would like a foam that I can CNC and then give to the sand caster. Ideally, the foam would not be damaged by them pressing it into the sand.

[ViperTX]

Check buildyouridea.com he uses foam for aluminum casting forms.

[toneV8]

I have one question:

lost foam casting process, for example using 10mm foam sheet when cast aluminium how much is dimensions after 10mm aluminium sheet more or less.

[ViperTX]

I believe the shrinkage is about 10% for a cast aluminum part....break out the mechanics bible....

[RdHawg]

Originally Posted by ViperTX Check buildyouridea.com he uses foam for aluminum casting forms.

He does - but it's all 'lost' in the process. I believe the poster is looking for a foam that will be able to be re-utilized.

My question now is, if your only doing a one-off then why do you care if the foam goes away?

[acondit]

Patternmakers use 1/4" per foot shrink rules for aluminum (about 2%).

[schemo]

Originally Posted by ViperTX I believe the shrinkage is about 10% for a cast aluminum part....break out the mechanics bible....

it more like 1-2% for aluminum

for 10% you must be thinking of jello

[venomx999]

Best foam i've used are regular insulation foam.
They are thick and soft, when casted, take the perfect shape with 1-2% shrinkage.
Try to use a coating outside the foam. Home made formulas is dry wall paste mixed with masontry cement. Your casts will be as smooth as the foam you prepared.

[chuggins143]

Originally Posted by venomx999 Best foam i've used are regular insulation foam. They are thick and soft, when casted, take the perfect shape with 1-2% shrinkage. Try to use a coating outside the foam. Home made formulas is dry wall paste mixed with masontry cement. Your casts will be as smooth as the foam you prepared.

I too have seen several websites where the person casting just takes the foam part with risers and all, dips them in thinned out drywall compound (thinned out enough to flow into all the nooks and crannys) several times to get a good thick coating. Lets it dry and then pours dry sand around the whole thing to support it during the pour. This will be the route I go when I finally get my furnace fired and am ready to start pouring parts. ...just my .02