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Is a CF Model 3 frame possible?

tga

Supporting Member
Apr 8, 2014
3,922
2,764
New Hampshire
(Mods: feel free to move this thread if this is the wrong forum. I was going back and forth between Model 3, Technical, and Cars and Transportation, but went with here because I'm thinking about it in the context of the Model 3)

I was watching "How It's Made Dream Cars - Porsche 918 Spyder" (see below). There was a section describing the fabrication of the car's carbon fiber monocoque, and I noticed the high level of labor involved. I've done a little bit of CF and fiberglass repair and fabrication, but one-off hobby stuff is way different than high volume manufacturing using prepreg, autoclaves, etc.

That got me thinking - it there any way to automate CF layup? ie, using robots? Anyone know what process BMW uses with the i3? Lamborghini's use of CF is pretty advanced, but they don't need to worry about high volume, low cost manufacturing.

How Lamborghini Became The King Of Carbon Fiber

 
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strider

Active Member
Oct 20, 2010
3,527
772
NE Oklahoma
I don't know of a way to "automate" traditional carbon fiber pre-preg lay-up. IIRC BMW isn't using traditional woven carbon fiber. As I understand it it's more like a composite-reinforced plastic.

But to answer your question I think the probability is very low. With commodity prices in the toilet I'm thinking it would be cheaper to go ahead and make Model 3 out of aluminum since Tesla already owns all the equipment (and knowledge) needed to work with it.

This article talks about the i3: http://www.compositesworld.com/blog/post/the-making-of-the-bmw-i3
 

ratsbew

Active Member
Mar 3, 2012
1,282
947
O'Fallon, IL
Carbon fiber is out for the Model 3. My guess is the unibody is made from steel and the body panels will be aluminum, but that's just a guess.
 

Evbwcaer

Member
Jun 21, 2014
741
329
Minnesota
Here is a video of i3 production.

BMW i3 Production - Part 1 - YouTube

About 5 minutes in you can see what looks like a robot doing some layup.

I had been thinking the same thing, CF for the 3.

The I3 starts at $42k I think, so that demonstrates that it is no out of the real of possibility for the Model 3 cost wise.

Anybody know if you can injection mold CFRP, that would be great.

CF vs. steel means smaller battery, smaller motor, more safety, lighter wheels/tires....does offset some costs.
 

jaguar36

Active Member
Apr 10, 2014
2,055
1,524
NJ
You certainly can automate composite layup. The aerospace industry frequently uses a methodology called fiber placement. In this method a robot uses spools of carbon fibers (called tow)and lays it down over a form. Works great, although you can't do as complex shapes as with a hand-layup. Only problem is that its still very very slow compared to just stamping or welding up a frame. For this reason its always going to be way too expensive to use for a mass market car.

They are going to be looking to cut costs everywhere they can on the Model 3, no way it'll have a carbon fiber frame.
 

Bangor Bob

Member
Jan 5, 2015
670
486
Bangor, ME
Well... Expensive is a relative thing. Getting set up to build a unibody out of steel requires a LOT of heavy equipment. It takes a lot of stampings and a lot of equipment and tooling to make all those individual stampings. A lot of single-widget equipment runs in parallel to meet "line speed." With automated CF tape + thermoplastic layup you can build your unibody with order-of-magnitude fewer pieces, so possibly 10x less equipment, most of which doesn't need to run at the tonnage steel stamping does - so your individual presses are cheaper too. Maybe you need 2 sets to meet the speed needed, but then you're still talking 5x less equipment. Most pieces will be light enough to move by a worker's single hand - material handling costs go down because you don't need lifts every time you need to move each damned piece.

If you already have a 100 years worth of fully-amortized metal stamping equipment laying around then steel is always going to be cheaper. If you're starting from scratch, it's not so clear-cut.

No idea what equipment Tesla got when they bought NUMMI, maybe they already have everything needed to handle steel in M3 volumes...
 

Bangor Bob

Member
Jan 5, 2015
670
486
Bangor, ME
One more: Automotive doesn't need aerospace-level performance. Cheaper (shorter) fiber can be used, and the compositing agent doesn't need to be epoxy. Thermoplastic can be fine and that can speed things up immensely. One option is to have a robot lay out a rough blank made of layers of carbon tape (many of the tow bundles mentioned above arranged side-by-side) along with layers of thermoplastic tape - nylon, PEEK, UHMW Poly, etc. to get the rough shape and fiber alignment, then transfer to a heated press which moulds the shape and melts and fuses the plastic, then cools it to set the shape. Cycle times on the press can be 90-seconds or so. Trim the excess and you have a whole finished floorpan, or A-hoop, B-hoop, or whatever, ready for gluing to the rest of the unibody.

Not TOO far from what BMW is doing with the i3 and 8, although they're using epoxy which needs to cure in the mold - cycle times for that are much longer.

- - - Updated - - -

They got many tons of presses and stampers. One is 5 stories tall, part below the floor. It was, after all, a Toyota / GM automotive plant.

Take the tour some time.

I'm in the opposite corner of the country, but thanks for the info. Had no idea what got left and what was sold off prior to Toyota/GM pulling the plug...
 

Cobbler

Paranoid T.E.S.L.A Bull
Sep 22, 2015
476
4,534
België
For a base price of 35000$, why would Tesla do so much efforts in decreasing the mass of the vehicle?

Generally speaking, mass requires only a lot of energy if you want to accelerate it fast. If the base model would accelerate from 0 to 60mph in 8 seconds, wouldn't that be already great? So the energy drain for accelerating a rather heavy car, would be limited.
When cruising highways, the "biggest" energy consumer for the range, would be friction. Air friction & tyre friction, so the aerodynamics would be the biggest parameter to determine how much energy is needed to get a 200+ mile range.
 

jkk_

Member
Nov 16, 2015
356
139
Finland
If the base model would accelerate from 0 to 60mph in 8 seconds, wouldn't that be already great? .

I wouldn't call that great... That's not significantly better than what my ICE diesel achieves and a massive let-down if that somehow happens. For me "Tesla" signifies ecological performance with a real world range that is sufficient for me, and that is why I'm waiting so eagerly for M3. So I can get the same (same in this case means that for 0-60mph I'm assuming <6s depending on model) performance as Model S in price range that is suitable for me.
 

Ardie

Member
Oct 4, 2009
202
44
I would hazard a guess that Tesla is going to use the same kind of construction materials and methods that have served them well for the Model S and Model X. Any change to other material, even if it is steel, would be needlessly expensive if Tesla would have to obtain completely different tooling and machining equipment. Maybe more expensive machinery can be amortized over the expected production run, or the less costly materials would offset the tooling cost, but somehow I don't really expect to see any new or breathtaking production methods or materials from Tesla. Not now, anyway.

Oh, wait. It is just possible that the "other" company (SpaceX) might have some space-age materials and machinery lying around that it could lend to Tesla. I can see it now: Milled beryllium wheels. Carbon fiber wiper blade arms. Transparent aluminum windshield, sunroof, and headlight lenses. Titanium key fobs. Niobium dashboard overlay.

With a starting price in the mid-to-high $30,000's.


-- Ardie
 

Bangor Bob

Member
Jan 5, 2015
670
486
Bangor, ME
For a base price of 35000$, why would Tesla do so much efforts in decreasing the mass of the vehicle?

Generally speaking, mass requires only a lot of energy if you want to accelerate it fast. If the base model would accelerate from 0 to 60mph in 8 seconds, wouldn't that be already great? So the energy drain for accelerating a rather heavy car, would be limited.
When cruising highways, the "biggest" energy consumer for the range, would be friction. Air friction & tyre friction, so the aerodynamics would be the biggest parameter to determine how much energy is needed to get a 200+ mile range.

Because it makes the rest of the car better and cheaper. Because the vehicle is lighter, the suspension springs can be wound at a lower spring rate and still control the vehicle. Which makes them cheaper and lighter. Less vehicle mass means the brake discs and calipers and pads can be smaller for the same target performance. Which makes them lighter. And the wheel hubs and wheels and A-arms and don't have to be as beefy because the forces are smaller due to the lower mass. And now there is less unsprung weight, so the suspension doesn't have to work as hard to control the wheels. So the suspension gets smaller and lighter and cheaper, the dampers can have more forgiving valving and the ride and handling gets better.

Because the forces are smaller, we can go to a smaller, lighter, cheaper steering rack with a smaller cheaper motor providing the power assist/autosteer.

Now that the suspension and steering is smaller and lighter, we've dropped a whole bunch more weight, and we're getting more performance than the design targets called for, so the motors can be smaller with lower-power inverters and smaller wiring and we're dropping yet more weight and cost. Oops, now the half-shafts and CV-joints are heavier than needed - let's downspec those.

Rolling resistance is proportional to load, so we're reducing a constant parasitic propulsion load the entire time as well - so the battery can get smaller, lighter, cheaper...

Reducing mass is a virtuous cycle. Done properly, it makes cars better and cheaper and even... Safer. Carbon/thermoplastic apparently has GREAT crash characteristics - crash structures can crumple sort of like steel but with fantastic energy absorption/mass performance.

BMW went with Carbon for the i-series vehicles for a reason, and in the i3 it wasn't for supercar cachet.

FIAT is experimenting here too. Their Alfa Romeo 4C is a carbon monoque coming in at around $54k. Yes, nearly double the base target for the 3, but there is a huge production volume difference as well, FIAT aren't planning to make many 4C's so unit costs will be much higher.

I know in my heart that Tesla won't do carbon for the 3. But they should...

[ edit ] Additional 4C data. 3500 chassis/year production rate. The passenger cell weighs 143lbs for the Coupe, 236lbs for the convertible. 0-60 in 4.5 seconds from just 240hp... More at Wikipedia [ /edit ]
 
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wdolson

Supporting Member
Jul 24, 2015
7,535
10,071
Clark Co, WA
Unless you treat the carbon fiber with some kind of metal, the Faraday Cage effect from the metal body of the car is gone. BMW disabled the AM radio on the i3 because the electrical noise in the cabin was so high it swamped the radio. PWM motors are electrically extremely noisy and I have done some reading on the health effects from exposure to that electrical noise. The results are inconclusive, but I've seen enough that I wouldn't want to be exposed to it on a regular basis. There are people who have reported getting sick after a PWM motor was installed nearby such as a pump motor for a water well. It's possible that the cause and effect were happenstance and something else was making them sick, but I have enough first hand experience getting sick from something that is claimed to be "safe". In my case, I can't have anything with GMO corn in it. I get punched in the gut about 1/2 hour later. I have no issues with non-GMO corn and I've had a reaction only to find out something had some kind of corn in it after reading the ingredients after it was too late.

In my case, I'm going to do my best to remain isolated from noisy electricity until there is more data. It is possible it's a not problem, but I'll prefer to err on the side of caution.

Now carbon fiber that is treated with some kind of metal, often nickel plated will have many of the same electrical shielding properties of traditional metal materials, but that extra step would have to be taken. Tesla has done surprising things in the past, so I wouldn't rule out a carbon fiber body, but I expect the Model 3 will be made with more conventional materials.
 

RobStark

Well-Known Member
Jul 2, 2013
10,483
54,110
Los Angeles, USA
i3 starts at $42k with a 22 kWh battery pack and its Carbon Fiber Reinforced Plastic is proprietary. Tesla would need to pay a pretty premium over BMW cost to get it. M3 battery pack will be at least 48 kWh to get to 200 EPA miles.

Tesla's current lines will be used exclusively for S and X.

The 7 story stamping press was used for steel and is now used for aluminum. It can handle 500k cars per year.

Robots and equipment for Model 3 above and beyond that stamping press and paint boot will be purchased in the future.

Those purchases can be optimized for whatever material Tesla chooses.

I can see Tesla using a CF roof panel but not the entire car or monocoque.

Most likely is a combination of high strength steel and aluminum.

Tesla will solicit bids and look at counteroffers before making a decision.
 

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