Tesla decided to use large aluminum castings (“gigacastings”) for the frame of many of its vehicles, including the Model Y and Cybertruck. This approach and the “Giga Press” used for it have been praised by many articles and youtube videos, repeatedly called revolutionary and a key advantage.
Most cars today are made by stamping steel sheets and spot welding them together with robotic arms. Here’s video of a Honda factory. But that’s outdated: gigacasting is the future! BYD is still welding stamped steel sheets together, and that’s why it can’t compete on price with Tesla. Hold on, it seems...BYD prices are actually lower than Tesla’s? Much lower? Oh, and Tesla is no longer planning single unitary castings for future vehicles?
I remember reading analysis from a couple people with car manufacturing experience, concluding that unitary cast aluminum bodies could have a cost advantage for certain production numbers, like 200k cars, but dies for casting wear out sooner than dies for stamping steel, and as soon as you need to replace them the cost advantage is gone. Also, robotic arms are flexible and stamped panels can be used for multiple car models, and if you already have robots and panels you can use from discontinued car models, the cost advantage is gone. But Tesla was expanding so they didn’t have available robots already. So using aluminum casting would probably be slightly more expensive, but not make a big difference.
“That seems reasonable”, I said to myself, “ふむふむ”. And I previously pointed that out, eg here. But things are actually worse than that.
aluminum die casting
Die casting of aluminum involves injecting liquid aluminum into a die and letting it cool. Liquid aluminum is less dense than solid aluminum, and aluminum being cast doesn’t all solidify at the same time. Bigger castings have aluminum flowing over larger distances. The larger the casting, the less evenly the aluminum cools: there’s more space for temperature differences in the die, and the aluminum cools as it’s injected.
As a result, bigger castings have more problems with warping and voids. Also, a bigger casting with the same curvature from warping has bigger position changes.
Tesla has been widely criticized for stuff not fitting together properly on the car body. My understanding is that the biggest reason for that is their large aluminum castings being slightly warped.
As for voids, they can create weak points; I think they were the reason the cybertruck hitch broke off in this test. Defects from casting are the only explanation for that cast aluminum breaking apart that way. If you want to inject more aluminum as solidification and shrinkage happens, the distance it has to travel is proportional to casting size—unless you use multi-point injection, which Tesla doesn’t, and that has its own challenges.
Somehow I thought Tesla would have only moved to its “Giga Press” after adequately dealing with those issues, but that was silly of me.
One approach being worked on to mitigate warping of large aluminum castings is “rheocasting”, where a slurry of solid aluminum in liquid aluminum is injected, reducing the shrinkage from cooling. But that’s obviously more viscous and thus requires higher injection pressures which requires high die pressures.
aluminum vs steel
Back when aluminum established its reputation as “the lightweight higher-performance alternative” to steel, 300 MPa was considered a typical (tensile yield) strength for steel.
Typical cast aluminum can almost match that, and high-performance aluminum for aircraft can be >700 MPa. Obviously there are reasons it’s not always used: high-strength aluminum requires some more-expensive elements and careful heat-treatment. Any hot welds will ruin the heat-treatment and thus be weaker.
But now, 1000+ MPa steel is common and used in many cars, and it’s possible to get higher strengths than that. Aluminum alloys have had much less progress. I suppose that’s because a lot of research went into aircraft materials in the past, and because steels are overall more complex.
Aluminum also has worse heat & fatigue resistance than steel, but it resists corrosion as well as stainless steel (which is weaker and more expensive than normal steel). Steel exposed to water needs to be painted. On the other hand, aluminum is more expensive, and most people want it painted anyway.
When a car is made from stamped steel sheets welded together, if one area gets dented, it’s sometimes possible to cut that part off and weld on a replacement. People don’t do such repairs as much as they used to, due to the relative cost of manufacturing vs labor changing, and design changes that make repair harder, but it’s at least a theoretical advantage.
Aluminum is less dense than steel, which at the same strength-weight ratio increases bending strength, but casting also can’t produce thin walls or the complex ridge patterns that stamped steel can. Aluminum is also harder to weld, and die casting can’t produce hollow tubes like stamp + weld can.
this shouldn’t be a thing
The chassis of cars is a relatively small fraction of their cost. The cost of aluminum die casting and stamped steel is, on Tesla’s scale, similar. Yet, there were so many articles saying gigacasting was a major advantage of Tesla over other companies.
I don’t really care if Tesla cars have some panel gaps or some cars cost 3% more to make. If you’re interested in minor improvements to car manufacturing, my friends have thought of more interesting ones, such as:
Tires are filled with carbon black, so tire wear produces a significant amount of particulate pollution. There’s a way to precipitate CaCO3 so it can be a nontoxic and slightly-better-performing alternative.
Tires use vulcanized rubber. Most thermoplastic elastomers have too low a melting point and higher losses than that rubber, but there’s a novel thermoplastic elastomer with slightly lower tan δ than polybutadiene rubber, much better wear resistance, and sufficient heat resistance. That would make tires longer-lasting and somewhat recyclable.
A cost-effective active suspension, which would greatly reduce vibration and bumps while driving.
A better electric motor driver design for (car-sized) axial-flux motors (which have low inductance).
Oh yeah, the battery chemistry that I have a patent for.
As for how my car-manufacturing-related predictions have gone so far, some years back, I remember being optimistic about the practicality of:
factories using AGVs instead of conveyor belts
using high-strength boron steels with hot stamping in cars
power skiving of internal gears for planetary gearsets
DLC coating of gears and engine components
oil-soluble ionic liquids for lubricants for steel
using ball screws instead of hydraulics for some presses
EconCore-type panels for trucks
electric motors on turbochargers (“e-turbos”)
So, the reason I’m writing about this isn’t because of how much I care about die casting vs stamping. What concerns me is the failure of institutions and cultural systems.
When magazines talked about, say, “microservices” or “the cloud” being the future, it actually made them happen. There are enough executives that are gullible or just want to be given something to talk about and work on that it established an environment where everyone wanted to get “microservices” or whatever on their resume for future job requirements, and it was self-sustaining. Gigacasting isn’t at that self-sustaining point, but it’s another example of how shallow the analysis behind the decision-making processes of American businesses is.
What’s worse is that something actually good could’ve gone in that cultural space. MIT press releases full of BS, Forbes 30 lists full of scammers, stupid TED talks...these things occupy the spaces that actually-good ideas needed to succeed.
why was this a thing
Why were there so many articles that wrongly decided the Giga Press was of paramount importance and wrongly assessed its relative advantages vs existing systems? I think there were a few reasons.
Money is a factor, of course; PR agencies drive a lot of the articles in media. I assume Tesla pays some PR firms and people there presumably decided to push the Giga Press.
There are many fans of Tesla in general and Elon Musk personally. They want to see positive news about Tesla—especially news about Tesla pushing technology forwards, because that’s what they like about Elon. In the current American economy, where the limiting factor for a lot of investment is the legibility of technical expertise to investment managers, someone like Elon provides what’s missing.
The theory behind managers specializing in “management in general” was that business executives don’t need technical understanding because they can get expert advisors, but it doesn’t work. Elon actually provides some examples of why: there were engineers at SpaceX and Tesla who knew why the Hyperloop concept was flawed and the Giga Press would be somewhat worse, but did they go tell Elon that? I don’t think so. Elon, despite understanding engineering much better than the median US executive, wasn’t able to cut through the sycophancy and BS.
Even having the decisions made by people with PhDs doesn’t always work. I’ve talked to a number of business executives with scientific PhDs, and I’d sometimes look up their thesis and figure I’d make some brief but intelligent comment to show a basic level of scientific understanding. Some of them forgot everything about the topic they studied, and some of them...in retrospect, I think they had their thesis ghostwritten.
the Giga Press was a mistake
Link post
the giga press
Tesla decided to use large aluminum castings (“gigacastings”) for the frame of many of its vehicles, including the Model Y and Cybertruck. This approach and the “Giga Press” used for it have been praised by many articles and youtube videos, repeatedly called revolutionary and a key advantage.
Most cars today are made by stamping steel sheets and spot welding them together with robotic arms. Here’s video of a Honda factory. But that’s outdated: gigacasting is the future! BYD is still welding stamped steel sheets together, and that’s why it can’t compete on price with Tesla. Hold on, it seems...BYD prices are actually lower than Tesla’s? Much lower? Oh, and Tesla is no longer planning single unitary castings for future vehicles?
I remember reading analysis from a couple people with car manufacturing experience, concluding that unitary cast aluminum bodies could have a cost advantage for certain production numbers, like 200k cars, but dies for casting wear out sooner than dies for stamping steel, and as soon as you need to replace them the cost advantage is gone. Also, robotic arms are flexible and stamped panels can be used for multiple car models, and if you already have robots and panels you can use from discontinued car models, the cost advantage is gone. But Tesla was expanding so they didn’t have available robots already. So using aluminum casting would probably be slightly more expensive, but not make a big difference.
“That seems reasonable”, I said to myself, “ふむふむ”. And I previously pointed that out, eg here. But things are actually worse than that.
aluminum die casting
Die casting of aluminum involves injecting liquid aluminum into a die and letting it cool. Liquid aluminum is less dense than solid aluminum, and aluminum being cast doesn’t all solidify at the same time. Bigger castings have aluminum flowing over larger distances. The larger the casting, the less evenly the aluminum cools: there’s more space for temperature differences in the die, and the aluminum cools as it’s injected.
As a result, bigger castings have more problems with warping and voids. Also, a bigger casting with the same curvature from warping has bigger position changes.
Tesla has been widely criticized for stuff not fitting together properly on the car body. My understanding is that the biggest reason for that is their large aluminum castings being slightly warped.
As for voids, they can create weak points; I think they were the reason the cybertruck hitch broke off in this test. Defects from casting are the only explanation for that cast aluminum breaking apart that way. If you want to inject more aluminum as solidification and shrinkage happens, the distance it has to travel is proportional to casting size—unless you use multi-point injection, which Tesla doesn’t, and that has its own challenges.
Somehow I thought Tesla would have only moved to its “Giga Press” after adequately dealing with those issues, but that was silly of me.
One approach being worked on to mitigate warping of large aluminum castings is “rheocasting”, where a slurry of solid aluminum in liquid aluminum is injected, reducing the shrinkage from cooling. But that’s obviously more viscous and thus requires higher injection pressures which requires high die pressures.
aluminum vs steel
Back when aluminum established its reputation as “the lightweight higher-performance alternative” to steel, 300 MPa was considered a typical (tensile yield) strength for steel.
Typical cast aluminum can almost match that, and high-performance aluminum for aircraft can be >700 MPa. Obviously there are reasons it’s not always used: high-strength aluminum requires some more-expensive elements and careful heat-treatment. Any hot welds will ruin the heat-treatment and thus be weaker.
But now, 1000+ MPa steel is common and used in many cars, and it’s possible to get higher strengths than that. Aluminum alloys have had much less progress. I suppose that’s because a lot of research went into aircraft materials in the past, and because steels are overall more complex.
Aluminum also has worse heat & fatigue resistance than steel, but it resists corrosion as well as stainless steel (which is weaker and more expensive than normal steel). Steel exposed to water needs to be painted. On the other hand, aluminum is more expensive, and most people want it painted anyway.
When a car is made from stamped steel sheets welded together, if one area gets dented, it’s sometimes possible to cut that part off and weld on a replacement. People don’t do such repairs as much as they used to, due to the relative cost of manufacturing vs labor changing, and design changes that make repair harder, but it’s at least a theoretical advantage.
Aluminum is less dense than steel, which at the same strength-weight ratio increases bending strength, but casting also can’t produce thin walls or the complex ridge patterns that stamped steel can. Aluminum is also harder to weld, and die casting can’t produce hollow tubes like stamp + weld can.
this shouldn’t be a thing
The chassis of cars is a relatively small fraction of their cost. The cost of aluminum die casting and stamped steel is, on Tesla’s scale, similar. Yet, there were so many articles saying gigacasting was a major advantage of Tesla over other companies.
I don’t really care if Tesla cars have some panel gaps or some cars cost 3% more to make. If you’re interested in minor improvements to car manufacturing, my friends have thought of more interesting ones, such as:
Tires are filled with carbon black, so tire wear produces a significant amount of particulate pollution. There’s a way to precipitate CaCO3 so it can be a nontoxic and slightly-better-performing alternative.
Tires use vulcanized rubber. Most thermoplastic elastomers have too low a melting point and higher losses than that rubber, but there’s a novel thermoplastic elastomer with slightly lower tan δ than polybutadiene rubber, much better wear resistance, and sufficient heat resistance. That would make tires longer-lasting and somewhat recyclable.
A cost-effective active suspension, which would greatly reduce vibration and bumps while driving.
A better electric motor driver design for (car-sized) axial-flux motors (which have low inductance).
Oh yeah, the battery chemistry that I have a patent for.
As for how my car-manufacturing-related predictions have gone so far, some years back, I remember being optimistic about the practicality of:
factories using AGVs instead of conveyor belts
using high-strength boron steels with hot stamping in cars
power skiving of internal gears for planetary gearsets
DLC coating of gears and engine components
oil-soluble ionic liquids for lubricants for steel
using ball screws instead of hydraulics for some presses
EconCore-type panels for trucks
electric motors on turbochargers (“e-turbos”)
So, the reason I’m writing about this isn’t because of how much I care about die casting vs stamping. What concerns me is the failure of institutions and cultural systems.
When magazines talked about, say, “microservices” or “the cloud” being the future, it actually made them happen. There are enough executives that are gullible or just want to be given something to talk about and work on that it established an environment where everyone wanted to get “microservices” or whatever on their resume for future job requirements, and it was self-sustaining. Gigacasting isn’t at that self-sustaining point, but it’s another example of how shallow the analysis behind the decision-making processes of American businesses is.
What’s worse is that something actually good could’ve gone in that cultural space. MIT press releases full of BS, Forbes 30 lists full of scammers, stupid TED talks...these things occupy the spaces that actually-good ideas needed to succeed.
why was this a thing
Why were there so many articles that wrongly decided the Giga Press was of paramount importance and wrongly assessed its relative advantages vs existing systems? I think there were a few reasons.
Money is a factor, of course; PR agencies drive a lot of the articles in media. I assume Tesla pays some PR firms and people there presumably decided to push the Giga Press.
There are many fans of Tesla in general and Elon Musk personally. They want to see positive news about Tesla—especially news about Tesla pushing technology forwards, because that’s what they like about Elon. In the current American economy, where the limiting factor for a lot of investment is the legibility of technical expertise to investment managers, someone like Elon provides what’s missing.
The theory behind managers specializing in “management in general” was that business executives don’t need technical understanding because they can get expert advisors, but it doesn’t work. Elon actually provides some examples of why: there were engineers at SpaceX and Tesla who knew why the Hyperloop concept was flawed and the Giga Press would be somewhat worse, but did they go tell Elon that? I don’t think so. Elon, despite understanding engineering much better than the median US executive, wasn’t able to cut through the sycophancy and BS.
Even having the decisions made by people with PhDs doesn’t always work. I’ve talked to a number of business executives with scientific PhDs, and I’d sometimes look up their thesis and figure I’d make some brief but intelligent comment to show a basic level of scientific understanding. Some of them forgot everything about the topic they studied, and some of them...in retrospect, I think they had their thesis ghostwritten.