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[Random_Dragon]

Yeah uh...consider the work that goes into casting metal. Consider the importance of eliminating air bubbles impurities and other irregularities, especially if it's something that's going to take a lot of stress. Consider how fiddly this is with basically any casting, investment, even 3D printing can be finicky unless things are config'd right. Even the article brings it up:

So far, automakers have shied away from casting ever-bigger structures because of the "gigacast dilemma": creating molds to make parts of 1.5 metres squared or more boosts efficiency but is expensive and comes with myriad risks.

In case the story of the sub implosion hasn't already illustrated what tends to happen when some big-shot corporate fuckwit says they can handle, take all the above considerations and filter them through Tesla's level of trustworthiness. Add a dash of scummy practices like handing control of self-driving cars back to the user when it detects a collision is imminent so they can escape liability, in case you needed your memory to be freshened up a bit there.

Now consider that their intent is to use this known-to-be-risky casting method with the parts that hold up the battery and engine, and also the part that's going to be quite important in a collision, something that rather obviously puts metal through a very sudden and intimate stress-test...

[Mech#4]

One big mould would also cause problems with form rigidness, wouldn't it? You want something in multiple pieces so there's give and take between different sections of a vehicle while it's in motion. Absorbing shock and vibration and all that.

[Starver]

You could design in any allowable vibration modes. Though I'd (not as a car designed, just going on general materials science principles) be worried about introducing weaknesses where the flexing is allowed.

But surely rigidity of (composite or monocoque) bodywork is more desirable, anyway, leave all the shock-absorbing[1] to the... shock-absorbers and similarly sprung attachment points? An everyday flexing chassis seems to be undesirable, and they must take great pains to reduce that, from what I (think I) know about the industry.


[1] Save for the crumple-zones, in a one-time sacrificial act to (hopefully) render the occupied bits of the car still survivable even as stress limits are exceeded in the peripheral structure.

[anewaname]

You want form rigidness in the structure, with absolutely no flexing on the 2-dimensional plane. This is better for the occupants and the cosmetics of the vehicle (interior/exterior trim, etc). The wheel assemblies are designed to move in response to shock and vibration using the spring coils, the shock absorbers, and torsion bars; all to keep the base of the vehicle on the 2-dimention plane.

What Tesla is doing in that article is advertising an improvement in the design; because fewer parts usually mean easier repair. This isn't a first in manufacturing as the article suggests, it is just an improvement of sorts that benefits Tesla and their repair franchises, not the consumer.

[Frumple]

What Tesla is doing in that article is advertising an improvement in the design; because fewer parts usually mean easier repair. This isn't a first in manufacturing as the article suggests, it is just an improvement of sorts that benefits Tesla and their repair franchises, not the consumer.

I... don't think that's actually true? Like, more parts doesn't necessarily mean easier repair, but fewer, especially as the individual parts get bigger or more involved due to it, often makes things harder to repair. You can't remove and replace just one damaged component, you need more specialized tools to handle larger pieces, so on and so forth. It makes repair more difficult, not less.

Tesla being tesla, I'd expect that to be fairly intentional, trying to fuck over smaller, less specialized repair services so they can force their car owners to funnel more money into company affiliated repair franchises, even if it makes the process of repair and maintenance harder and more expensive

[Starver]

If you can replace a structural member with just about any bit of right-sized tubing (suitably machined, of course, by someone who knows enough about what they're doing), there's no intrinsic lock-in to the manufacturer. But when you have to replace something that's basically the whole footprint of the vehicle (and manufactured with cutting-edge fabrication techniques, not just any old cutting edge) then you'rectying your customere in.

It's the "IBM-compatible" vs "Apple product" dichotomy, of yesteryear (and, as far as I know, pretty much still). And the next step is when the vehicle refuses to start if the front-left suspension coil hasn't announced itself as being an Authorised Replacement (the Authorised Replacer having had to register the change in the Black Box, via their two-part key and a phone-home connection)

[anewaname]

Spoiler (click to show/hide)

from this article:

For context, that image where the colorful 70 parts would be replaced with one part, is why it would be easier to build, and why I expect it would be easier to repair. That section of the underbody isn't likely to ever need replacement outside of a collision which likely would send the vehicle to the franchises that would strip it of parts and discard the body.

EDIT: Where I do agree that sometimes one part is more difficult to replace than a group of parts. Often it depends on how many fasteners are involved.

[Lord Shonus]

Expecting to scrap an entire car because of damage to a portion of that area is ludicrously bad design. It isn't just major collisions that can do it - having to make an emergency swerve (such as for a sudden kid in the road), and hitting a curb could do it. On any normal car, such a repair would be a few hundred dollars in parts and labor.

That's a secondary issue, though. That area takes an enormous amount of the stresses on the body. Even if you assume that the current construction is connected together in a solid immovable block rather than having some flex room built into it (there are pros and cons to both) it will be taking enormous forces when the car is in motion. A small void or stress fracture? Your car might literally snap apart while you're accelerating onto the highway. Guess what issues become more likely the larger and more complex a casting or stamping gets.


People don't avoid doing things that way because it is technically impossible, or because they'd really like to do it but it is prohibitively expensive. It isn't done that way because trying to make that as one part is so mindblowingly stupid that anybody who doesn't happen to own the company would be fired for the mere suggestion.

[McTraveller]

Spoiler: Because engineering is not politics (click to show/hide)

Making things easier for serial production is generally in conflict with post-production repair.  Bolts in strange places, needing to remove a bunch of parts to get at the part you're trying to repair, etc.

"Design for assembly" vs "Design for repair."

Things like this actually don't facilitate repair - they end up requiring replacement instead.

Personally I'd be worried about the yield on such a large casting: casting voids, anisotropy due to nonuniform cooling, casting flow effects, and numerous other factors.

UAW stuff: seems like they really are pushing the 4-day workweek issue, based on the headlines from the weekend.  Interesting.

[Lord Shonus]

Spoiler: Because engineering is not politics (click to show/hide)

Making things easier for serial production is generally in conflict with post-production repair.  Bolts in strange places, needing to remove a bunch of parts to get at the part you're trying to repair, etc.

"Design for assembly" vs "Design for repair."

Things like this actually don't facilitate repair - they end up requiring replacement instead.

Personally I'd be worried about the yield on such a large casting: casting voids, anisotropy due to nonuniform cooling, casting flow effects, and numerous other factors.

UAW stuff: seems like they really are pushing the 4-day workweek issue, based on the headlines from the weekend.  Interesting.

Spoiler (click to show/hide)

You're 100% spot on. If you don't put every single casting through an X-ray or even fancier imaging, you're probably going to make cars that would make Nader decide that he was too harsh on the Pinto.

4 day workweeks have been hugely beneficial to a lot of companies that have tried it, as well as massively improving the lives of employees. Lower fatigue makes everybody significantly more productive.

[hector13]

Sometimes.

[anewaname]

Expecting to scrap an entire car because of damage to a portion of that area is ludicrously bad design. It isn't just major collisions that can do it - having to make an emergency swerve (such as for a sudden kid in the road), and hitting a curb could do it. On any normal car, such a repair would be a few hundred dollars in parts and labor.

That's a secondary issue, though. That area takes an enormous amount of the stresses on the body. Even if you assume that the current construction is connected together in a solid immovable block rather than having some flex room built into it (there are pros and cons to both) it will be taking enormous forces when the car is in motion. A small void or stress fracture? Your car might literally snap apart while you're accelerating onto the highway. Guess what issues become more likely the larger and more complex a casting or stamping gets.


People don't avoid doing things that way because it is technically impossible, or because they'd really like to do it but it is prohibitively expensive. It isn't done that way because trying to make that as one part is so mindblowingly stupid that anybody who doesn't happen to own the company would be fired for the mere suggestion.

When there is significant damage to the body, the insurance companies routinely declare a car as "totalled" and offer the owner blue book value in exchange for the title and car, and the car is either fixed and sold, or scrapped for parts. If the owner wants to keep the damaged car, they get less from the insurance company. Just a couple months ago a neighbor got hit in the front right fender, hard enough to shove the right front wheel well a bit, but not hard enough to stop her from driving 25 miles to get home, and the insurance company paid her the max blue book of $11k in exchange for the car. This is routine.

The wheel assemblies all put the stress into the main unibody frame, and neither the 72 pieces or the 1 replacement piece are involved in absorbing those stresses.

If your car snaps apart on the highway, it is precisely because you slammed curbs too often and bent some components of the wheel assembly enough to put it under additional friction or load stress, or someone took two damaged cars and cut and welded the unibodies together without regard for their role in load-bearing.

So, you really think that the engineers who designed and validated the new part design, and programmed the machines to stamp the piece, are so mindblowingly stupid? They probably just cut 30 minutes off production times per vehicle and removed the need for 150 fasteners.

[hector13]

Still not Ameripol…

[Lord Shonus]

So, you really think that the engineers who designed and validated the new part design, and programmed the machines to stamp the piece, are so mindblowingly stupid? They probably just cut 30 minutes off production times per vehicle and removed the need for 150 fasteners.

The only "engineer" involved in this decision is a drug addict who used the profits from a slave-labor emerald mine to make some lucky investments in the 90s and crown himself as the Genius Savior Of Mankind.

[Starver]

(Amerisomething, but at least it isn't car design.)

Stealth jet so stealthy that apparently not even the pilot who was flying it now knows where it is...

(Someone remind me how Wonder Woman managed it. Something to do with WW having gods-given telepathy and the jet having intrinsic (alien?) intelligence of its own, wasn't it?)