How to Cast Aluminium Heat Sink Fins

I have a read a few books on metal casting but I haven't read any information of how to cast aluminium heat fins like those found on
small air cooled engines. I know for larger air cooled engines the heat fins are machined but believe small engine heat fins are cast. Thanks for any information.
Brock
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mattathayde had written this in response to http://polytechforum.com/metalworking/how-to-cast-aluminium-heat-sink-fins-207451-.htm :
------------------------------------- durabol wrote:

ive never cast AL but i have done non ferrous (mostly silver and pewter) in my jewelry/metalsmithing classes. if you just want to make one or 2 you probably are better off machining or fabricating them. the small ones are probably made either in a steel mould or maybe by lost wax depending on the shape/design of them. im not sure how easily such a small pieces in AL. for production they surely use a high tech casting set up.
-matt
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On Tue, 10 Nov 2009 04:15:38 +0000, mattathayde wrote:

Fins-207451-.htm
Dunno what the OP counts as 'small', but there were any number of model airplane engines in years past that had sand cast crank cases with fins. You have to be _good_ at sand casting.
I suspect that plaster investment casting would be more than good enough, but I've never tried it.
--
www.wescottdesign.com

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mattathayde had written this in response to http://polytechforum.com/metalworking/re-how-to-cast-aluminium-heat-sink-fins-207483-.htm :
------------------------------------- Tim Wescott wrote:

o i totally forgot about some of the technical issues with investment casting, i am not sure how it will translate to AL since it has a lower melting temp but when investment casting most nonferrous you cannot go thinner than 1mm with good consistent results (you could taper at the end of the metals path to it but you still might have issues). note though that i am used to casting very small things and the investment/scale means we dont even need vent holes
-matt
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durabol wrote:

One-off or production? Production would be die cast. One-off would depend upon what you mean by "small". For a model aircraft engine, lost wax is probably the only feasible technique. For lawn mower engine, sand or lost foam. I tried lost foam for an electronics heat sink & was only moderately successful. Mostly a matter of my low experience level.
Bob
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I first want to cast a rectangular heat sink for an amplifier. This would be an open face plaster casting using a wax model of the heat sink. I have tried this before and had troubles with air bubbles in the plaster and getting the aluminium into the fin slots. I am just doing this for fun as I know it would be better just to buy extruded.
Brock
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