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      06-21-2012, 05:22 AM   #56
swamp2
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Quote:
Originally Posted by mkoesel View Post
As compared to traditional materials such as aluminum and steel, I still do suspect that materials costs are only a small consideration when weighed against fabrication and engineering costs. Hypothetically, what if we wanted to build a carbon fiber Hot Wheels car today? Let's say it cost $5 to produce where the current die-cast metal car might cost $1. In my mind, materials cost would account for perhaps $1 in the increase while R&D, manufacturing would account for the other $3. That's a silly example with some major SWAGs, but you can hopefully see what I am trying to say here.
You have this quite backwards.

Particularly with carbon fiber, as opposed to other composites such as glass fibers or others, material costs are almost for sure going to dominate total body manufacturing cost.

See the following from a pretty good MIT PhD thesis from 2006. Although you could certainly argue/debate/refute some specifics, the overall result that costs are material driven are clear and the ratio is not close nor small. Reference: fuchs.pdf. This is assuming 100k units/year which is right in line with the M3's target volume. It is key to note that the author assumes CF prices of right about $10/lb. Even if BMW reached their goal of $5/lb my conclusion is still valid but it is much closer to break even. Surprise, surprise... This observation dovetails very nicely with this $5/lb goal stated by BMW&SGL. Similar results should follow for components as well as long as aerospace type manufacturing methods are not used. The results may or may not follow for radically different manufacturing methods such as pultrusion or filament winding, etc. that might be used for non BIW type shapes. My gut tells me though that the same conclusion would still follow.

One other relevant data point is that McLaren can now manufacture the MP4-12C composite body in just 4 hours. Your thoughts may be guided by examples like an F1 car taking 3000 hours to manufacture or a MB SLR McLaren at 500 hours.

Lastly this work fully validates my "back of the envelope" estimates that it would cost around $1000 to save around 300 lb although this work seems to puts the 300 lb estimate closer to 500 lb, but again this is at the higher $10/lb figure. I'll easily take 50% or so accuracy for 5 minutes of work vs. perhaps 80% accuracy for many years of work (on a PhD...)
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Last edited by swamp2; 06-21-2012 at 05:36 AM..
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