Welcome back everyone!
I’m Jordan Giesige and this is The Limiting Factor.
This is the 4th video of the gigacasting series.
Today we’re gonna look at the challenges of gigacasting and the engineering solutions
Tesla has in place to ensure that their gigapresses are consistently pumping out high quality,
intricate die cast parts at high speed.
Most of the engineering solutions I’ll be covering today aren’t necessarily unique
to Tesla, but I felt they were too interesting to be left out of the gigacasting series.
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.
As always, the links for support are in the description.
Let’s dive right into the challenges of gigacasting and how they’re solved.
Depending on how you slice it, there are at least a dozen ways to cast molten aluminum.
Tesla’s gigapresses use high pressure die casting.
High pressure die casting can fill the die cavity in a tenth of a second, which allows
for faster production rates.
Additionally, due to the high injection velocity, it can produce intricate shapes because the
molten aluminum can be injected before the metal’s had a chance to cool.
However, it does come with drawbacks.
Or, if you think like an engineer, fun challenges.
This brings us to the first challenge of gigacasting.
The rapid injection of high pressure die casting combined with rapid cooling causes air that’s
in the die cavity to become trapped in cast part, creating porosity.
Porosity weakens the die cast part because where there should be solid metal, there’s
a void filled with air which can lead to weak parts that crack easily.
Furthermore, the porosity is random and therefore leads to inconsistent strength across castings.
When part strength is inconsistent, there are two options: Scrap the parts that aren’t
up to spec and/or make the parts thicker and heavier so that fewer parts need to be scrapped.
That is, porosity generates waste through scrap, extra mass through overengineered parts,
and heavy inefficient vehicles.
Was Tesla able to somehow reduce the porosity of their gigacastings?
In short, yes.
Let’s take a closer look.
The first source of gas and therefore porosity in aluminum castings is that molten aluminum
readily reacts with atmospheric water vapor and water in or on the raw materials to form
hydrogen gas that becomes dissolved in the molten aluminum.
The aluminum industry solves this problem by injecting argon gas into the molten aluminum.
The hydrogen gas preferentially diffuses into the argon gas, and as the argon bubbles out
of the molten aluminum, it takes the hydrogen gas with it.
Alex Voigt has confirmed that Tesla is using this Argon gas process and credit him for
bringing this to my attention.
Bubbling argon gas through the molten aluminum appears to be common in the casting industry
and not unique to Tesla.
How else might Tesla be reducing the porosity of gigacastings?
In this paper, titled “Effect of super vacuum assisted high pressure die casting on cast
alloys”, the researchers used a vacuum system to remove air from the die cavity before the
injecting the molten aluminum.
There was one vacuum channel at the top of the die cavity and one near the shot sleeve.
The shot sleeve is where the molten aluminum is injected.
As discussed earlier, the rapid injection and cooling of molten aluminum involved in
gigacasting causes air that’s in the die cavity to become trapped in cast part, creating
porosity.
Applying a vacuum to the die cavity before injection sucks out the air and therefore
reduces porosity.
The end result?
The image on the left didn’t use vacuum assisted die casting, and the image on the
right did.
I’ve marked some of the porosity in red to make the difference clear.
The reduction in porosity was drastic and as you’d expect, significantly improved
strength and elongation results.
Let’s do a quick refresher on stress and strain to understand what’s meant by strength
and elongation.
As this video by Real Engineering shows, ultimate strength measures the maximum amount of stress
a metal can handle before fracturing.
Elongation measures strain, which is a measure of how far a metal can stretch before fracturing.
Looking at the test results, the green circles are from conventional, non-vacuum assisted
high pressure die cast parts.
The red hexagons are the test results from the parts formed with vacuum assisted high
pressure die casting.
What the graph is telling us is that the vacuum formed parts were, on average, 5.6% stronger
and could stretch 43% farther before fracturing.
Furthermore, because the red hexagons are clustered in a tighter pattern, it means the
test results were more consistent.
The researchers found that the consistency for the elongation measurements improved by
71%.
Meanwhile, the consistency of strength improved by 86%.
This means that not only is vacuum cast aluminum stronger and has better elongation characteristics;
engineers can have more confidence that the parts will perform as expected.
This allows the engineers to design thinner parts and/or reduce scrap.
Is Tesla using super vacuum?
Yes, it appears so.
I’ll explain why later in the video.
The second challenge of gigacasting is wear and tear on the casting dies.
Aluminum alloys that contain silicon, like Tesla is using, react with steel.
That is, the skin of the aluminum casting likes to stick to or eat away at the steel
walls of the die cavity, causing wear and tear.
This is a big deal because large machine parts like dies can cost over a $1 million dollars.
If the casting eats away at or sticks to the die, each time a casting is removed it takes
some of the million dollar plus die with it, meaning the die needs to be replaced more
frequently, meaning higher production costs.
From what I can see, there are three ways to deal with this kind of wear and tear on
the die.
First, in the alloy video I advised that Tesla is using several elements that act as die
release agents which have a non-stick effect.
Second, Tesla is quite likely using vegetable oil to coat the die cavity between presses.
This oil is the same as the cooking oil you use at home, except Tesla is making 70 kilogram
metal pancakes.
Third, die surface treatments like nitriding or carbonitriding can make the die more robust.
All three of these solutions appear to be common in the industry.
The next challenge for Tesla is the thermal regulation of the gigacasting machine.
High pressure die casting has two thermal requirements:
First, that the die is hot enough so that the molten aluminum doesn’t solidify too
quickly as it flows through the die cavity.
If the aluminum solidifies too quickly, it can create casting defects like cold shut.
Cold shut is where two flows of molten aluminum meet and form a seam, which is a weakness.
The second thermal requirement is that the die cools quickly and evenly after the aluminum
is injected.
If the aluminum doesn’t cool quickly, it can slow down the production rate.
If it doesn’t cool evenly, the part can warp.
As a side note, Tesla noted at battery day that their castings don’t warp.
This would be due to both the thermal regulation system and the fact that Tesla developed their
own in house alloy that doesn’t require heat treatments.
Heat treatments are often used to strengthen parts and can warp the parts if they’re
not cooled evenly.
Check out my alloy video if you’d like to know more.
In one of their promotional videos, LK machinery points out the thermal regulation and vacuum
units for their gigacasting machine, the Impress-Plus.
The thermal regulation units are also visible in this photo from Giga Shanghai, and each
machine appears to use about 20.
Tesla purchases gigapress from both LK Machinery in China and Idra in Italy, so I also contacted
Idra to check if they offered both vacuum casting and thermal regulation units for their
machines.
They do, and the contact pointed out that the machines are visible in a three story
structure.
I’m assuming the contact is referring to this image from battery day, where again,
there are about 20 thermal regulation units.
Like the other technologies we’ve discussed so far today, thermal regulation isn’t unique
to Tesla.
However, I do wonder if Tesla is using more cooling units to push their machines to the
limit, as Tesla often does.
As we’ll discuss in the final video of the series, Tesla’s goal for their gigapresses
exceeds the factory specs for the gigapress.
With the challenges and solutions out of the way, let’s look at a key benefit of gigacastings
that I missed in the original video.
In the Third Row Tesla podcast interview with Elon he advised that the gigacasting doesn’t
need machining and doesn’t use datums.
Let’s look at each.
In my view, there appears two things that Elon could be referring to with machining.
First, deburring and trimming off material such as the sprue, biscuit, runners, and flash,
which are excess material left from the casting process.
Can Tesla avoid this?
It doesn’t appear so.
In this render, there’s massive biscuit where the molten aluminum is injected along
with some fine runs on the opposite end of the casting which may not be functional.
But is the rendering accurate?
Footage from battery day confirms the biscuit and the fine runs, so they are there in the
cast part.
Do the biscuit and fine runs make it into the final casting?
It doesn’t appear so.
So, to me, it looks like the biscuit and fine runs are trimmed away in the final product.
In this image, the biscuit would have been on the left and the fine runs would have been
on the right.
In other words, it appears that Tesla’s castings do need to be trimmed up before being
sent to the assembly line.
This brings us to what I’m calling the second step of machining, which is what Elon was
probably referring to when he said machining.
I think he’s referring to boring out larger holes for mounting points or milling fine
features like screw threads.
I couldn’t confirm whether Tesla was able to do away with milling and boring because
I’d either need enough detail from the battery day images to see things like screw threads
or I’d need to see a final product to look for marks made by milling and boring.
What about datums?
Datums are markings either cast in place or machined into a part that that are used for
quality control and for robots to orient themselves with a part.
I don’t understand the full implications of a part without datums, but I’m assuming
it means that the parts are of such high consistency that dimensional quality checks aren’t needed
or that the parts are so precise that the robots can use the features of the part to
orient themselves rather than a datum.
If you know something about machining or datums, let me know if I’ve gone astray in the comments
below.
Overall, even if Tesla still needs to do the first machining step, which is trimming and/or
deburring, eliminating boring and milling would be a big win for their production process.
It would eliminate at least part of one of the major production steps for aluminum castings.
Which of Tesla’s innovations allows them to skip some of the machining steps and datums?
Based on what I’ve learned doing this series, it looks like Tesla unlocked the ability to
skip machining through a combination of the casting alloy covered in the past video and
the massive forces involved in gigacasting.
The alloy appears to provide the necessary flow characteristics to form intricate part
features while the gigapress punches the slug of molten aluminum into the die cavity at
extreme pressures and speeds, allowing all the die features to completely fill before
the molten aluminum solidifies.
In summary, the giga press isn’t just one machine.
It’s a bundle of machines that work in concert to produce parts with a high degree of consistency
and quality at a high rate with minimal maintenance while reducing production steps.
All of which drive down production cost.
The high consistency and quality are provided by vacuum casting technology that reduces
the porosity of the cast parts.
The importance of this can’t be overstated.
High part quality and consistency reduces waste and allows for thinner, lighter weight
parts to be used.
The thermal management system ensures the conditions before, during, and after casting
are ideal, which maximises throughput and reduces the chances of flow defects and warping
in the castings.
Replacement of the casting die is kept to a minimum by Tesla’s casting alloy recipe,
spraying the die with cooking oil to create a thin, cheap, and expendable barrier between
the aluminum alloy and the steel die, and by using hardened steel dies.
Finally, the gigacasting process removes production steps such as machining.
Eliminating production steps reduces cost and makes gigacasting a viable alternative
to steel bodies.
If you’d like to know more about the economics of gigacasting, check out my gigacasting economics
video.
The next video of the gigacasting series will be my speculation on how the gigacasting will
marry with the exoskeleton of the Cybertruck.
The Cybertruck won’t be using a traditional body-on-frame design or a unibody design,
it’s something new altogether, so how will it come together in the factory?
If you enjoyed this video, please consider supporting me on Patreon with the link at
the end of the video or as a YouTube member.
You can find the details in the description.
A special thanks to my YouTube members, and all the patrons listed in the credits.
I appreciate all your support, and thanks for tuning in.