Welcome back everyone!
I’m Jordan Giesige and this is The Limiting Factor.
Three months ago I did a video on Tesla Gigacasting, and there were a lot of comments on that video
ranging from genuine concern to criticism of Tesla’s gigacasting approach.
I started digging into those concerns and criticisms and found most of them to be unfounded,
so it’s time to do a series of deep dive videos to address the question marks around
Tesla Gigacasting.
I’ll be doing these gigacasting deep dives between other videos on batteries to keep
the channel content balanced.
The series will build 4 additional videos on top of the original video.
Today we’re going to start with crashworthiness and repair because it was the most common
comment on the original video.
The too long; didn’t watch here is that Tesla’s engineers have designed around the
potential pitfalls of a giant casting.
The crashworthiness and repairability should be similar to conventional, unibody vehicles
that use advanced high strength steels.
Before we begin, a special thanks to my Patreon supporters and YouTube members.
This is the support that gives me the freedom to avoid chasing the algorithm and sponsors,
and I hope will eventually allow me to do this full time.
As always, the links for support are in the description.
Back to QuantumScape.
First, as I mentioned in the previous video, I’m not a vehicle structural engineer.
I’m doing the best with the limited information available to me.
If I misstep in the video, let me know with some constructive feedback in the comments
below.
Let’s get into it.
The main concern with Tesla’s gigacastings in my last video was repairability.
The theory is that if a giant piece of cast aluminum is used, repair costs will be sky
high or repair will be simply impossible.
Let’s look at a picture of a vehicle body to understand whether this is the case.
As we see in this image from Tesla’s Q1 2020 investor slide deck, the gigacasting
is buried under a good 10-15cm of rocker, wheel wells, and bumper.
Additionally, the wheel wells will also house wheels that absorb impact before intruding
into the gigacasting.
That is, at low speed, the exterior of the body and wheels should absorb the impact of
fender benders before intruding into the underbody gigacasting.
For a side impact at moderate speed, the gigacasting might be damaged, and that might result in
the car being a write off.
However, when the wheel does contact the gigacasting it’ll be met with the broad side of the
gigacasting and the structural webbing we see here.
My guess is that the wheel and tire would act as a crush can, dissipating and distributing
the energy across a pretty massive chunk of aluminum.
But let’s say that’s not the case, and the gigacasting is damaged beyond repair.
Would a typical vehicle with unibody construction also be a write off under similar circumstances?
The move from body-on-frame construction years ago to a unibody design resulted in lower
production costs for high volume vehicles, but also reduced repairability.
This is because, as the name suggests, a unibody is a single moulded unit formed from many
smaller pieces, and significant damage to any part of the unibody can result in damage
to the broader unibody structure.
Furthermore, in the last 10-15 years, auto OEM’s have migrated away from conventional
steel to advanced high strength steel to reduce vehicle weight.
Repairs with advanced or ultra-high strength steel involve ordering a factory replacement
part because they have reduced repairability.
My assumption is that the same would be true for a gigacasting.
In a worst case scenario, a replacement gigacasting might be required, increasing the odds of
a write off.
In my view, in the event of a wreck that damages the casting, the most likely scenario is that
the alloy would crack.
If that is the case, according to thefabricator.com the casting should be weldable because of
the 3 series aluminum alloy that Tesla’s using.
But, even if my assumption is true and cracking is more likely than warping or bending, would
the gigacasting actually crack in a moderate speed accident?
After reviewing the features of Idra and LK Machinery’s Giga Presses and Tesla’s alloy,
I think the gigacasting’ll hold up well.
We’ll get into the materials science of the reasons why in later videos of this gigacasting
series.
At high speeds, like on the highway or fast city driving, the equation for side impacts
completely changes.
Vehicles are designed to be as expendable as possible to absorb energy from the impact,
which reduces the energy that’s transferred to the humans they’re carrying.
This is because the cost of any vehicle repair is dwarfed by the cost of medical care for
people injured in the accident.
For this reason, my guess is that most vehicles are written off when they get in accidents
at high speed, regardless of whether it’s a side impact, front, or rear impact.
This means that in the next class of accidents we’re going to cover, front and rear collisions,
I won’t devote more time to high speed front and rear collisions.
I’ll focus on just low and moderate speed collisions.
Let’s take a look, starting with the rear of the vehicle.
As we can see in this image, there appears to be about 30cm at the rear of the vehicle
between the bumper and the rear underbody casting.
Which should be enough to absorb the impact from a vehicle travelling at low speeds, and
possibly moderate speeds of up to 20 mph or more.
Why do I say 20 mph?
In this video, a Mercedes at 25 and 12 mph rear-ends a Chevy Malibu.
The 12 mph impact does very little damage, whereas the 25 mph impact intrudes roughly
30 centimeters.
Doubling the impact speed from 12 to 25mph actually quadruples the impact energy, meaning
even a slight decrease in speed to 20mph will cause significantly less damage.
We also have to factor in that the Chevy Malibu has a massive rear overhang created by the
trunk that’s much larger than the rear overhang in the Model Y.
The trunk would be mostly empty space and probably doesn’t contain much structure.
I tried to verify this assumption, but I couldn’t find an image of the Malibu underbody.
Regardless, despite the smaller rear overhang of the Model Y, it has a trick up its sleeve.
This is the rear gigacasting of the Model Y.
On the left side you can see two structures that have been attached to the gigacasting.
What are these?
I think we can safely assume these are crash absorption rails mentioned in this tweet from
Elon.
These crash absorption rails are bolted to the Gigacasting and can be replaced if the
vehicle gets in a serious accident.
The same is true for the front of the vehicle.
This is the front casting of the Model Y with no crash absorption rails.
Returning to the image from the Q1 slide deck, we can see that there are also crash absorption
rails bolted to the front of the vehicle, forming a bull bar type structure at the front
of the vehicle.
What all this is telling us is that Tesla’s engineers appear to have embedded the underbody
castings deep in the vehicle to address issues with repairability.
They’ve purposely left a gap between the outer structures of the vehicle and the gigacastings.
Those outer structures include the bumpers, crash absorption rails, fenders, wheel wells,
and wheels.
This adds up to a vehicle that shouldn’t be more expensive to repair or more likely
to be written off.
But, let’s say that’s incorrect, and Tesla vehicles using a gigacasting are noticeably
more expensive to repair and are more likely to be written off.
When it comes to accidents, Tesla vehicles have benefits that other vehicles don’t.
They have some of the best drivers assist safety systems on the vehicle market, which
reduces the number of car wrecks that Tesla vehicles get into in the first place.
As a direct result of that, Tesla vehicles have a different risk profile than other vehicles
on the market.
Insurance companies haven’t given credit to Tesla vehicle owners for this and Tesla
has started their own insurance service, Tesla insurance, to drive down insurance costs for
Tesla owners.
It’s slowly being rolled out market by market, but hopefully it’ll eventually be available
to all Tesla owners.
This means that if Tesla’s with gigacastings do have higher repair costs, the accidents
are less likely and may be offset by Tesla’s cheaper insurance product.
In summary, the most likely scenario is that the crashworthiness and repairability of Tesla
vehicles with a gigacasting is similar to that of a conventional unibody vehicle.
At low speed, the car crash won’t intrude far enough into the structure of the vehicle
to cause issues.
At high speed, most vehicles, not just Tesla vehicles, are a write-off because they’re
designed to disintegrate to absorb the crash energy.
At moderate speed, for head on collisions or if the vehicle’s rear-ended, Tesla’s
engineers have incorporated crash absorption rails that can be replaced with a few bolts,
presumably making the gigacasting as repairable as any other vehicle.
Tesla gigacastings might be more susceptible to cracking, but Tesla is using an alloy and
casting process that should increase the strength and ductility of the casting.
If it does crack it should be weldable.
If it can’t be welded, then the repairability is similar to conventional, unibody vehicles
that use advanced high strength steels.
An aluminum replacement part will be more expensive due to the higher material cost
of aluminum.
With that said, a vehicle with aluminum giga castings should lower the price floor for
vehicles and reduce lifetime energy consumption, which reduces total cost of ownership.
We’ll get into this in the next video.
Add all that up, and I don’t think we’ll see a massive spike in insurance costs due
to gigacastings because Tesla’s engineers have engineered around the repairability problem
and because Tesla’s are involved in fewer accidents in the first place.
That is, I don’t think we’ll see junkyards filled with throw away vehicles that get into
one fender bender and had to be scrapped.
The next video will discuss the positive aspects of QuantumScape’s technology, and in the
video after that we’ll look at how Tesla’s shaken up the entire cost model of Aluminum
versus advanced high strength steel in vehicle bodies.
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