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kenikh kenikh is offline
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Join Date: Feb 2005
Location: North of Exit 17
Posts: 7,729
Flieger, you misread me. I in now way meant to dimish the value of casting. I was simply saying that certain processes lend themselves better to some applications than other.

I know for certain that creating a wheel of equivalent weight and strength to a CNC built unit is possible. It is simply that given the extremely narrow cavities required to die cast identical parts to billet, it would require using technology at the extreme margins of casting process. You'd need to build a VERY expensive and complex die casting mold, most likely requiring the use of both vaccum assistance AND centrifugal assist to evenly populate the mold at the thicknesses required to match a machined part. The number of units required to amortize this tooling is only realistic for entities at the scale of your example: BMW, etc.

Next, casting is very hard to implement cost effectively for negative draft angles, requiring multi-part molds that at the scale of small parts like a compressor wheel is nearly impossible to achieve with acceptible fidelity. Die casting molds also have finite service life...they wear out, so you need to replenish molds regularly. The tighter the tolerances required, the more parts in the mold, the shorter the service life.

CNC processes are much easier to manage in small production runs, given the part. That said, CNC is not great for large runs as it is slow and doesn't scale well as to reach large capacity manufacturing runs, machine costs and space rapidly become unwieldy. The process used fits the scale of the market and application which is why BMW casts and Blouch CNCs.

These processes do have material benefits the other doesn't, though. Bleeding edge casting technology can align grain structure of metals along chosen planes of a part through mold design in ways billet can't. Billet gives you whatever you get from the stock you use.

In the end combining the process benefits of forging, casting and machining can give the best of all worlds, as long as economically feasible. Machining a forged or cast part can make a part that is superior to a single process part, no doubt.
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Old 06-11-2010, 01:15 PM
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