Tesla has switched their newer lines to casting. It seems like it's mostly about manufacturing efficiency rather than strength -- they can cast the whole underbody of the vehicle as a single piece rather than having dozens of stamped pieces that need to be welded or riveted together. Initially they were doing the front half as one piece and the back half as another, but they've needed to get bigger and bigger (higher- and higher-force) machines as they've gone from two-piece to single-piece construction.

When die casting, you inject semi-molten metal into a cold mould.

The mould must be held closed while metal is being injected. The "9100 tons" refers to the force keeping the mould closed. That force is approximately proportional to the surface area of the object being cast.

Some details about their "Super Large Die Casting Machine":

https://proleantech.com/xiaomis-super-large-die-casting-tech...