Ewwww. So those are MIG welding robots. They've been around for... 50 years? What's new is the idea that you could build a structure out of MIG wire, because the minute you bring steel up to molten and then air cool it, you have induced three properties: 1) It has deplorable yield strength (once you bend it, it's bent) 2) It has negligible corrosion resistance (it will turn brown with rust in a week in the Nevada desert) 3) It is fundamentally devoid of tensile strength (it might as well be coat hanger wire) Their process also allows it to have a crappy, porous finish, too. When one MIG welds, the parent metal is an important part of the process because you're only fucking with its metallurgy, rather than annihilating it. When you're just making a bead, you're basically making slag. I have no doubts that they will successfully construct a bridge. I also have no doubts that they will construct a bridge for a great deal more expense a great deal slower than a conventionally-made bridge. There are better choices for 3d printing bridges...
I agree that the material is pretty sketchy. If this is supposed to last any more than 5 minutes there must be some sort of tempering mechanic happening - Steel is just too brittle otherwise. It says on the website that they can print in steel, stainless steel, aluminium, bronze or copper, all of which are going to have the same problem. I guess we'll have to wait and see. Either we're missing some information, or it's not going to last very long.
Similar problems, not the same problem. There's nothing you can do to get aluminum's yield strength above zero; steel and iron can bend without damage, aluminum can't. Steel, meanwhile, can end up anywhere between "lead" and "glass" as far as hardness depending on how you temper and alloy it. Bronze and copper are actually easier to work with because they don't require an inert atmosphere. They're using MiG welding robots. That means they can do anything that can be wire-fed. You can wire-feed stainless, but it's much better TiG welded than MiG welded. Also worth noting: most every bridge, aircraft, car frame, etc you've ever seen is riveted, not welded because when you care about the strength, welding really fucks with your mojo. You can weld something and then re-temper it if it's steel, but everything else is tricky. I used to be a "weld everything" kinda guy until I discovered that you can really break things a lot by heating them up to molten. heating them up to molten in a reducing atmosphere? Yeah, asking for trouble.
I figured I had good reason to be skeptical when this video was posted the other day.