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Comment by kjksf | Hacker News Reader

Munroe addressed this complaint and his point was: if the collision is bad enough that it damages that cast, it would total a non-cast car as well.

Plus you have to reason on the level of systems, not components.

Single-piece rear casting replaces 70+ parts.

Those parts have to be welded together by robots.

Each weld is a potential failure point.

Casting produces more reliable car with less variances which ends up lowering repair costs on global (system) level.

https://twitter.com/Tesla/status/1513886756923445254

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Munroe addressed this complaint and his point was: if the collision is bad enough that it damages that cast, it would total a non-cast car as well.

I don't see how that's possible. Grain structure and alignment make forged parts much stronger than cast for a given weight.

http://www.expansion-parts.com.tw/upload/web/MetalPowderPart...

Very few parts of any automobile are forged. Even then it's usually high performance variants of ICE vehicles, limited to the engine internals, and transmission/differential internals.

Having said that though, the sheet metal used in unibody construction is far more ductile than usually brittle castings. If they've developed new alloys making the large castings more ductile than previous castings, it might not be a problem.

It's mostly going to be internal engine/gearbox parts that are forged, and possibly wheels.

Forged suspension arms are uncommon but not unheard of. They are becoming more common as cars get bigger and heavier, though most manufacturers are going to extruded aluminum since it keeps costs down.

Forged wheels. Pretty damn expensive. Posh race cars use them. A cheapest set I was looking at some years ago was €6.5k.

IIRC RAYS / Volk Racing produced forged alloy aftermarket wheels at an affordable price. The TE-37 was a model back when I was modding RX7s and MX5s...

No one uses forged wheels for regular production cars, unless they're extremely high-end. All those alloy wheels you see on sub-$50k cars are all cast.

All those Alcoa style rims Ford used in the 80s and 90s were forged. It has only gotten more prevalent since.

Should this not be a comparison to stamped /welded metal since that’s what car manufacturing generally uses?

The structural part of cars, at least any in the under $100k range, are not made of forged parts.

Sure various high stress suspension pieces are forged, but those aren't the ones being replaced by die cast assemblies.

That's not at all true. Critical structural parts, such as B-pillars, are almost always made of forged or hot-stamped high-strength steels. And this is true even in cheap vehicles like the 2007 Dodge Caliber. See, e.g.: https://i.imgur.com/N399WLV.png

I think that the casting technique mentioned in the article is primarily, or entirely, for non-structural parts that would otherwise be made of something akin to mild steel.

No, the aluminum injection castings are structural. Using high pressure injection helps keep the voids low or non-existent compared to atmospheric pressure sand casting, for instance, which significantly improves performance (improving strength and toughness).

No part of significant size will be forged in a sub $100k car. As another user mentioned, even the cheapest forged wheels are >>$1k each.

Can one align the grains by magnetizing the cast (aluminum is para magnetic)

It’s pretty funny seeing a post from Tesla right after a line about „less variances“. It’s a common knowledge by now, posted many times here, that Tesla build quality and parts passing depend on the phase of the Moon and the menu at the factory.

>if the collision is bad enough that it damages that cast, it would total a non-cast car as well.

This is just lunacy.

It's absolutely possible to locally damage a cast item in a manner in which a welded/bolted steel assembly would also be locally damaged. And the cast is going to be harder to repair.

Who's going to do that weld and then take liability for the safety of the car after?

The people performing their work and their insurer, just like literally every other case where skilled labor is bought.

Contrary to internet screeching welding the kind of cast alloys used on cars isn't really a big deal especially the aluminum ones (iron is harder). If the business case materializes I'm it will become common just like aluminum body repair.

But almost nobody does it and insurance companies just total cars that have this kind of damage. Yes, in theory, it can be repaired but it's too expensive and because it's hard to guarantee the correctness of the repair, insurance companies don't do it and most consumers wouldn't stand for it.

It's the labor cost that makes it non-viable in most cases. If it penciled out economically then all the people who are outsourcing their thinking to their insurance company would automatically become fine with it.

There is nothing about it harder to guarantee than anything else in the autobody business. How do you know they're applying panel bonding adhesive properly? You don't.

Lots of older cars are rolling around with suspect welds today, often times performed by amateur welders. Everyone understands a repaired car might be be exactly same as new.

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