Does aluminum shrink when cast?

[hydin]

I am stumped on this one.

I know some metals shrink when they are being cast, but I can't seem to find any information on aluminum.

I figured someone here had to have made a metal casting of something, and would be able to tell me.

Any help is greatly appreciated
Chris

 

[Finhead]

Yes Aluminum shrinks approx 5-7% when cast.

I am stumped on this one.

I know some metals shrink when they are being cast, but I can't seem to find any information on aluminum.

I figured someone here had to have made a metal casting of something, and would be able to tell me.

Any help is greatly appreciated
Chris

 

[hydin]

Well poop.

Is there any metal that isn't crazy expensive, is lightweight, and won't shrink when cast?

The only other option is aluminum dust for cold casting, and that's just.. meh.

Chris

 

[Wolfdagon]

I have never done any casting, but I would asume that all metals will shrink. Metal expands when heated and contracts when cooled. It is heated to pour it into the mold and it cools of as it hardens so I don't see any way that you could keep it from contracting (shrinking).

 

[exoray]

I would asume that all metals will shrink.

Not all, some actually expand...

Gray cast iron (common cast iron) actually expands when it solidifies...

Is there any metal that isn't crazy expensive, is lightweight, and won't shrink when cast?

Short answer no, aluminum, copper, magnesium and zinc all have pretty high shrink ratios and are the main components in most light weight casting alloys...

You also have to factor in two shrinkage ratios when molding metal, the liquid to solid shrinkage and then the hot solid to room temperature solid cooling shrinkage... A metal like aluminum will shrink another 1% going from a hot solid to room temperature solid...

 

[micdavis]

Look for a copy of the Machinist and Pattern Makers' Handbook.

It has shrink rates of most metals.

Most are in % per linear foot.

Basically the bigger the part the more it will shrink. But boy I watched these pattern maker guys I worked with compensate for that and when parts would come back from the forge they'd be nuts on perfect.

 

[exoray]

But boy I watched these pattern maker guys I worked with compensate for that and when parts would come back from the forge they'd be nuts on perfect.

What a little math can do for you...

I have actually read about a 'newer' casting method using a twist on the lost wax technique and plaster slurry instead of using wax they use a proprietary blend of water and basically gelatin... With a little science and math they tailor the water gelatin mixture's freezing expansion ratio to the metal being cast shrinkage ratio and you get pretty close copies of an existing part without creating a new larger pattern...

 

[hydin]

The only real snag in the project is I have the master copy already done, so I wanted to just make a resin copy and hit the local metalworking places and see if they can replicate it.

Hmm... hell, it wouldn't be worth doing if it was easy.

Chris