# Castings and Structural battery packs - what does it get us?



## GDN

I'm not sure I've seen views on this lately - but what are these new huge castings and the structural battery backs getting us or Tesla?

Do the large castings make the car much easier to assemble? Do they protect the occupants much more during a wreck? Do they make them much cheaper to build and assemble? Then on the flip side - what are they going to cost the consumer and the insurance industry to repair? Will they make them unrepairable driving costs way up because they just get totaled? Or will they be simpler to repair? Will they save more lives?

The same for the structural battery pack? Is it driving down cost of building the car? We won't see price drops. Is it making the car less safe and possibly unrepairable or just moving cost of owning the car to the consumer and insurance once again if you have a major wreck or problem?

I love innovation, but I'm just not sure that we aren't seeing some really big costs being lined up for the consumer and insurance when something goes wrong. I doubt the trade off for large castings and structural battery packs will be worth it, they just sound cool.


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## android04

The castings are definitely a time and cost reduction measure in assembling. One giant piece replaces hundreds of others that had to be aligned, glued, riveted, and welded together. It's also supposed to help with panel alignment issues that some vehicles have due to stacking tolerances of putting all those pieces together. The castings will allow Tesla to make vehicles faster to meet demand, save money, and have better quality. I'm unsure of the effects on repairability or insurance premiums, and am guessing that would depend on how much time it takes to disassemble the vehicle enough to replace the cast parts. It might actually be less time to replace the cast parts than to repair the unibody the previous way, where cutting, welding, riveting, and bonding had to be done.

The structural battery pack saves weight and space, which will help efficiency and range. I don't know how it will affect repairability yet, but it's not like the internal battery pack of the Model 3/Y is easily repairable right now either. If anything, since the pack will be structural, it might just involve extra precautions if service needs to separate the body and battery pack to avoid the body from flexing too much.

My only wish is that Tesla does not cut any corners in the quality and longevity of affected components that might become more difficult or impossible to get to with the new changes.


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## GDN

android04 said:


> ..... One giant piece replaces hundreds of others that had to be aligned, glued, riveted, and welded together. It's also supposed to help with panel alignment issues that some vehicles have due to attacking tolerances of putting all those pieces together.......


Hoping it definitely helps with this, however it is a lousy excuse based on the fact that no other manufacture has had the issue Tesla has had with this. All get a mis-aligned panel once in a while, but Tesla has just been lazy and sloppy.


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## TrevP

The huge casting reduce the complexity of assembly and cost to Tesla. Not only are there less parts there are less tools and dies to make for the parts (very expensive) as well as a drastic reduction in capital costs such as robotic stations.


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## GDN

TrevP said:


> The huge casting reduce the complexity of assembly and cost to Tesla. Not only are there less parts there are less tools and dies to make for the parts (very expensive) as well as a drastic reduction in capital costs such as robotic stations.


And what about the likely huge cost to the consumer to get it fixed? There has to be a trade off somewhere. Passing on huge repair bills to the aftermarket won't get them too far after a while.

Truly I'm open to the conversation and that is what this thread is about, but if they are impossible to repair or very hard to repair there will be huge insurance bills.


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## B_E_V

GDN said:


> And what about the likely huge cost to the consumer to get it fixed? There has to be a trade off somewhere. Passing on huge repair bills to the aftermarket won't get them too far after a while.
> 
> Truly I'm open to the conversation and that is what this thread is about, but if they are impossible to repair or very hard to repair there will be huge insurance bills.


Modern cars are designed to give their lives to save our lives when involved in high speed collisions. Insurance companies are fine with that, because even a Model S Plaid costs a lot less than a serious personal injury case.

My vague memory, though I cannot find the source, is that some provisions have been made in the design of the castings to allow cutting some parts off and welding replacements on when dealing with low speed collision damage.

I have not encountered any reliable data about repairing the structural battery pack. On the plus side, using 4680s will mean significantly fewer individual cells in the pack, so the odds of a bad cell may go down if the 4680s prove as reliable as the old cells on a per cell basis. However, the main reassurance for most customers is simply Tesla's 8 year warranty on the battery.

When thinking long term, I would prefer a car with NIO style battery swaps. So that as battery technology improves and my original battery ages I could easily update my car for increased range, or to reduce its weight for increased efficiency. However, in the short term, a structural battery pack should be lighter, and thus the car should be more efficient. A car with a structural battery pack is also probably cheaper to build than an equivalent car with NIO style batteries.


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## garsh

B_E_V said:


> My vague memory, though I cannot find the source, is that some provisions have been made in the design of the castings to allow cutting some parts off and welding replacements on when dealing with low speed collision damage.


This.

This is often how repairs are made to structural portions of a car today, especially in the rear-quarter-panel area. If there's not a convenient place to undo spot-welds, then pieces are simply cut & welded together.

I would guess that bumper extensions will still be used to allow those to be unbolted from the casting and replaced due to a less severe impact. Most impacts that are severe enough to damage one of these castings are probably going to cause the vehicle to be declared totaled anyhow.


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## JasonF

The pros and cons I can see so far are as follows:

- I'm not an engineer, but it looks to me like using a chunky battery pack as a structural member will give the cars the benefits that body-on-frame cars used to have before they all went to unibody. The structure of the car might be able to shrug off most minor impacts. It also could mean the rest of the car's structure can be all aluminum because it wouldn't need the steel substructure for rigidity anymore. It could mean crashes that don't touch the passenger cabin won't total the car anymore. It also could mean that it's possible to build a convertible Model 3!

- If the structural battery design hasn't been altered since testing, there is a strong possibility that the failure of too many cells in the pack would cause the car to be totaled because the labor involved to replace it would amount to the sort of body work that normally goes into replacing the entire front end or rear end of a car after a collision. After thinking some more on this, it could be that battery failures are now mitigated by individual control circuits on each battery rather than "neighborhood" blocks. If this is indeed the case (and I'm hoping so, because it would be so risky otherwise!), it could become virtually impossible for the entire battery pack to fail. A shorted/dead cell would be isolated, and wouldn't affect more than a tiny bit of capacity. As the battery ages, you lose more cells, but not enough to fail the entire pack. Of course, this means the cells placed in them would have to have extremely low failure rate, because the cost of "oops" is far too high.


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## slacker775

That’s an interesting notion about the batteries. If that is in fact the case, that would put an end to the EV-age-old question of ‘how much does it cost to replace the battery?’ If a few cells die but they are isolated, you lose some overall capacity but otherwise you are still fine. Too many go, and you are getting a new car. Realistically, that’s not much different for most people than an ICE car. Most folks don’t go around replacing their engine during the life of a car.


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## JasonF

slacker775 said:


> That's an interesting notion about the batteries. If that is in fact the case, that would put an end to the EV-age-old question of 'how much does it cost to replace the battery?' If a few cells die but they are isolated, you lose some overall capacity but otherwise you are still fine. Too many go, and you are getting a new car. Realistically, that's not much different for most people than an ICE car. Most folks don't go around replacing their engine during the life of a car.


That was just a guess on my part, but it's probably not too far off. Small electronics batteries are being manufactured with each one having its own control circuit. Obviously they're individually more expensive to make that way, but if you're basically trying to manufacture a battery that's integral to the structure of a car, it could be the line between it being viable and an incredibly expensive mistake.

I'm thinking of it like the micro inverters that modern solar panels use. If you total up the cost of all of those, they are probably more expensive than one single inverter to install. But before those existed, you could have a solar panel or two fault and take down the entire array with it because they were not individually controllable (unless you wire each one up separately, which would be expensive). Having micro inverters is more attractive for an out of warranty system because if a panel or two dies it will impact your production but not stop it entirely, so you can get away with ignoring it.


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## TrevP

GDN said:


> And what about the likely huge cost to the consumer to get it fixed? There has to be a trade off somewhere. Passing on huge repair bills to the aftermarket won't get them too far after a while.
> 
> Truly I'm open to the conversation and that is what this thread is about, but if they are impossible to repair or very hard to repair there will be huge insurance bills.


If the damage is sufficient enough insurance will write it off. Cars are very expensive to fix these days, not just Teslas. Most "fender benders" are relegated to the front or rear of the car where the crush cans are located. Those are bolted into the castings and are designed to the replaceable, this is covered in the Tesla body shop repair manual










You can clearly see the front crush cans in the traditional Model Y non-structural body in white (notice it doesn't have the front Giga casting) in this video time stamp:






And then compare it to the new Model Y with structural pack (notice the massive front Giga casting) in the same video at this time stamp:






They both same the same type of crush cans and they're bolted to the subframe.

Also notice how few parts there are in the front Giga casting! I count 6 parts (not including cross-members or outer body steel stampings) that make up the front. If you ever pull out the frunk tub in your Model 3 or Y try and count how many various steel parts make up the whole front end. You'll soon understand why this is a game changer


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## JasonF

TrevP said:


> Also notice how few parts there are in the front Giga casting! I count 6 parts (not including cross-members or outer body steel stampings) that make up the front. If you ever pull out the frunk tub in your Model 3 or Y try and count how many various steel parts make up the whole front end. You'll soon understand why this is a game changer


While I don't think it was Tesla's primary intention, it's quite possible the new assembly methods could mean in the future if your car is damaged in the front or rear (as long as the passenger cabin is intact) Tesla would just ship a new front third or rear third to the body shop, and they would just replace the damaged section all at once instead of ordering a bunch of structural and body pieces. That could keep labor costs down for body work, which could mean less totaled cars in the long run, and lower insurance rates.


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## mrwug

android04 said:


> It's also supposed to help with panel alignment issues that some vehicles have due to attacking tolerances of putting all those pieces together.


Color me skeptical. It's not like the rear castings eliminated (or even effectively mitigated) rear hatch alignment issues. Just glad my car built in November 2021 didn't have any significant issues.


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## garsh

mrwug said:


> Color me skeptical. It's not like the rear castings eliminated (or even effectively mitigated) rear hatch alignment issues. Just glad my car built in November 2021 didn't have any significant issues.


That casting will always have the same exact dimensions. When you attempt to create an equivalent piece of structure out of 40+ parts being welded and glued together, your tolerances are nowhere near as good, and then it becomes more difficult to hang body panels off of that piece precisely.


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## mrwug

garsh said:


> That casting will always have the same exact dimensions. When you attempt to create an equivalent piece of structure out of 40+ parts being welded and glued together, your tolerances are nowhere near as good, and then it becomes more difficult to hang body panels off of that piece precisely.


I understand the concept but, as I noted above, rear castings didn't exactly eliminate gap issues on the rear of the vehicle.


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