Given the high cost of repairs for the aluminium body panels, what would be the weight increase if the body were made of steel or some other composite? (I'm not talking about the underlying structure). What might be the cost differential? Surely, it would make it cheaper to produce and I would think given the already heavy battery packs, I don't think it would be all that much more heavy. Anything that I'm not considering in all of it - forming the shapes, etc?
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Model S and X aluminium body thoughts
- Thread starter TrevTremaine
- Start date
I don't know the cost differential (it would be pure speculation) but you answered your own question...it's the weight.
I've soured on aluminum over time. I mean, it's lovely that it's light and doesn't rust (*if* you properly prevent galvanic corrosion - if you don't it can go very quickly).I have an old / high mileage Gen1 insight (all-aluminum body) and for the past couple years it's been with a water leak. "Couple years" because three separate garages tried to fix it and failed. The most recent one took all of the trim off.... and found that there's two cracks running the entire length of the roof on each side. Steel would never do that; aluminum fatigues and becomes brittle.
And yes, there's not as many people with experience welding aluminum, so there's that. One of the challenges with aluminum is that if you want it strong, it has to be tempered; annealed aluminum has a vastly lower tensile strength than tempered. When you weld aluminum, it heats up the metal around the weld and causes it to lose its temper. There are ways around this, but... yeah, there are issues.
And yes, there's not as many people with experience welding aluminum, so there's that. One of the challenges with aluminum is that if you want it strong, it has to be tempered; annealed aluminum has a vastly lower tensile strength than tempered. When you weld aluminum, it heats up the metal around the weld and causes it to lose its temper. There are ways around this, but... yeah, there are issues.
Barklikeadog
Active Member
Isn't 1 ton of aluminum 10x dirtier to produce than 1 ton of steel?
I never understood how shedding a few pounds can make up for this. If every car were made from aluminum we would be in a far worse situation in terms of greenhouse gases.
I never understood how shedding a few pounds can make up for this. If every car were made from aluminum we would be in a far worse situation in terms of greenhouse gases.
dhrivnak
Active Member
True Al production uses a lot of electricity. But due to that fact most Al smelting is done where electricity is very cheap. Which happens to be hydro or wind energy which are essentially carbon free.
Yes weight would go up, but I also asked by how much? I admit it's all speculation in the end, but I'm just trying to understand the approximations or guesstimates.
The savings can be justified. Aluminum smelters in China use about 15 MWh of electricity per tonne to produce (less in the developed world), so for a vehicle like a Model X, a tonne of aluminum is equivalent to maybe 40000 miles of driving, or about 4 years for your typical American driver. However, recycling recaptures about 95% of the energy that goes into making it, and for a large object like a car, it will almost certainly be recycled because that's a lot of money (even aluminum cans have a 65% recycling rate). So that's about 2000 miles of driving to equal the energy. If the vehicle lives for, say, 12 years before being recycled (4 years after the battery warranty), and is driven 10k miles per year, then that's 120k miles total. Versus 2000, it's easy to see how a small energy savings could make up for that cost (even ignoring the energy that goes into steel).
And yes, aluminum is made wherever power is cheapest. Which is usually hydroelectric. In my country, we have three smelters, and each one uses more power than all homes and businesses combined. It really depends on what you think of hydropower. Personally I'm quite against it, I wish we'd focus more on our geo and crazy-abundant wind, even if they cost a couple more krónur per kWh.
Steel production is a bit different in that most of the energy that goes into it is not electricity but coke; most coke (70%) used in steel production is a processed form of coal (heated up to drive off volatile compounds... sort of like making charcoal). So while the total energy consumption is lower (iron oxide isn't tightly bound to its oxygens like aluminum oxide is), you are burning coal to make it. Also, while it's also extensively recycled, its lower value per tonne makes it not quite as valuable of a recycling product, and thus one can expect somewhat lower of a recovery rate.
So from a production side, overall I don't have anything against aluminum. But mechanically.... I mean, it's wonderful when it's function at its design specs, but keeping it that way (no fatigue, no galvanic corrosion, etc), that's the hard part.
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Petra
Member
Yeah, this sort of thing is why I occasionally wonder if BWM's approach with CFRP is better long term...
Yeah, composites are really interesting. It's producing them affordably in mass production that's always been the challenge, but I think they're the future. The strength to weight ratios are incredible.
One of my favorite new composite techs I've seen is a mixed weave of carbon and spectra/dyneema (UHMWPE). Carbon has a very high strength to weight ratio but is brittle and has poor energy absorption. UHMWPE isn't as strong per unit mass but has excellent energy absorption. But there's a little side benefit to adding in the UHMWPE: its low density. Which means that it makes your panels thicker. And anyone with an engineering background knows, increasing the thickness of a plate vastly decreases its bending and stress (if I recall correctly, bending decreases proportional to thickness cubed and stress with thickness squared). That's why you use I-beams and rectangular profile (or better, trusses) rather than just solid rods: the further you have your loadbearing material from the center of the beam, the more strength it contributes.
Composites aren't perfect. They have finite lifespans (although better binders may help with this) due to UV degradation. They're also poorly recycleable. But nonetheless, the strength to weight ratios that they offer mean major energy savings / safety improvements.
Lex
Member
I do have one vague memory, perhaps from one of the documentaries, that it's equivalent to the weight of 1 person... ?? In any case that's my wild guess
at least 200 lbs. of savings courtesy the Al body and the other structural alternatives.
