daruigh
Member
Registered: Mar 2001
Location:
Posts: 8 |
Visor aluminum shells
Hi,
I'm the "Dave" from Dave Design. Several have commented on the high cost of our cases, asked about
casting and other alternative manufacturing techniques, etc., so I thought I'd comment.
With casting there are a couple of critical limitations. A common aluminum casting method is sand
casting. Unfortunately, this process is completely inappropriate for thin wall parts like our cases.
A local foundryman with about 50 years of experience suggested a minimum cast wall thickness close
to 1/8" (3.2mm), our cases have a wall of .04" (1mm), well below the practical limit for sand
casting aluminum. Die casting is a more complex process, involving a permanent mold made of die
steel. With this process, it's possible to approach our target thickness with hot runner dies (a
system of heating elements to allow the metal to flow into narrow cavities), but this would be
prohibitively expensive for our product. Jewelry is often made with still another process,
investment casting, which might be made to work and is very economical in small quantities, however,
I think the wall thickness limitations are the same as sand casting. Finally, surface finishing
options with any aluminum casting method are usually limited to paint or powder coating. Due to the
porosity of the cast material, it's virtually impossible to achieve the same luster as we can
achieve with color and clear anodizing. There are certainly many examples of cast products in
aluminum and even magnesium and titanium. The Nikon Coolpix camera is a mag casting, various
notebooks by IBM and Sony and the HP Jornada PDA I believe use a similar process (I think it's
called Thixomolding), but they are all painted. If we could achieve the volumes necessary to justify
the upfront tooling cost, there might be methods, such as stamping or forging that could get us the
wall, mechanical properties, and appearance we want, but having just about finished our 500th case
after a year of production, we don't really have the resources to pursue these, and frankly
speaking, our thing is machining!
Dave Ruigh
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