> moving to plastic for the body
Some of those $10k cars in the 90s had more plastic in the bodies than cars today, e.g. Saturn S-series, where all body panels below the belt-line were plastic.
It isn't necessarily the cost savings one might expect though, because steel panels can also be load bearing and part of the crash structure, which is not really practical with plastic panels.
With plastic panels, that means they're replaceable. Possibly even swappable (custom 3D printing?). This just adds to the "modding platform" they could be marketing to.
Steel panels can also be made to be replaceable. Plastic has to be because it can't be welded to the frame.
In fact, on modern cars many times these panels are replaced.
If you get a big enough dent in a door, a good body shop will offer to replace the outer skin instead of filling with bondo. They cut the weld on the inside of the door all the way around, take off the shell, and epoxy a new one on. The body shop owner told me that the epoxy is actually stronger than the factory weld.
Yes, bodywork is quite a mature discipline. I was presuming the parent commenter meant user-replaceable, i.e. bolted on.
> The body shop owner told me that the epoxy is actually stronger than the factory weld.
Often this is because the special high strength steels used in vehicles today depend on proper heat treating to attain their strength, and welding can compromise this. Many OEMs even specify panel bonding for repairing particular crash-critical parts of vehicles now because of this.
It's mostly because the factory welds are the result of someone running numbers until they find the bare minimum whereas the autobody guy would rather not risk it.
The OEMs have proper repair procedures that are the correct way to fix the vehicle, and if the autobody shop is reputable, they follow them. And the stated reason OEMs specify panel bonding instead of welding is:
1. because UHSS is sensitive to heat, and robots are much more accurate in how they heat than Jimmy with a tig torch, and they were programmed by a process engineer, where as Jimmy welds until 'it looks good'.
2. welding may compromise anti-corrosive treatments on the inside of inaccessible cavities, which can lead to corrosion issues
e.g. https://rts.i-car.com/crn-24.html
A crappy shop will certainly just weld panels in without any regard for materials engineering, but it results in a crappy repair.
Cost savings wasn't the reason for the Saturn plastic panels, IIRC -- they were intended to make the car more durable; they were hard to dent. Some Saturn salespeople would kick the side of the car, hard, to demonstrate their resilience.
Those cars always looked great on the used car lot because they never had any door dings.