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Comment by causi | 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.

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...

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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 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.

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.

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)

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