<VV> casting aluminum

[JVHRoberts at aol.com]

You're absolutely WRONG!! This is the PERFECT job for investment casting.  
Turbocharger impellers are made by this process, and these are a LOT thinner  
than a fan blade. 
 
Also, small runs are perfect for investment casting. And there are LOTS of  
precision investment casting shops out there. I've used them, they do great 
work  on intricate parts with wildly varying profiles. Also, investment casting  
typically gives VERY high yields, and VERY few flaws if done correctly. And  
quite frankly, I don't know of any investment casting shops that do sloppy work 
 in aluminum. Also, every investment casting shop I've dealt with has the 
post  casting ovens, etc, to get the right temper, etc. 
 
CNC is capable of a lot, but thin sections require a LOT of time in the  mill 
so the thin sections don't get bent by the machining forces. Also, on  
something like a fan impeller, well over 95% of the metal will be scrapped. 
 
The only way I'd do a CNC impeller is to make the first test part. After  
that, I'd send it off for casting if I thought the market was there. 
 
In a message dated 8/6/2007 7:46:50 A.M. Eastern Daylight Time,  
jekepler at amplex.net writes:

Bottom  line, if you were to do this, you would have them cast by a casting   
house.They know all these details. 

Just to inject a touch of  economic reality into this, and explain a couple
of problems with all of  this talk of casting a fan.  

First, a fan impeller is NOT a type  of investment casting that is going to
be easy to make....the low mass  requires VERY thin web-thicknesses, as well
as extreme dimensional  consistency.  These requirements will generate high
reject rates,  which will raise cost considerably.  Second, the low-volumes
for an  aftermarket part will force anyone contemplating this into the realm
of the  "Low-Volume Job-Caster".....the bottom-feeders of the metal
fabrication  world!  These guys are great for making belt-buckles and cute
little  yard ornaments....but not so good for a critical  high-speed/high-load
automotive part that will require precise alloy  integrity (which also
implies things like engineering and laboratory  support that they usually
don't have!), as well as some pretty good  equipment and a high-degree of
casting expertise that is HIGHLY uncommon in  that group of firms (I'm being
generous....I've never found ANY low-volume  job-caster that could make a
consistently decent product, but I suppose  there HAS to be one out there!)

At the end of the day, and in the  volumes that are reasonable to
expect.....it'll be easier and cheaper to  CNC mill the fan out of billet
than cast it, with one hell of a lot better  fan out the door!

John


 



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