The first attempt at this type of printing was done by someone on the Lulzbot forum back in 2013. Back then they didn't give any particular consideration to the material properties of the molten metal, which is why they couldn't get past the clogging issues they were having.

Later on in 2013 or 2014, some high school student who's name I forget tried semisolid metal printing with an antimony alloy. Were they the one who eventually went on to start Vader Systems? I forget but if anyone still knows where that info is, please do mention it in the comments.

In 2015 I started a project at WPI which over the following years became a full scale collaboration with Lawrence Livermore National Lab and produced some papers. But the technology was abandoned: they attempted to print in the semisolid state, but semisolid metals undergo granular jamming under compression and shear, because they are not one homogenous phase. This meant that either the nozzle had to be very wide as with a concrete printer, or they had to implement something complicated to avoid granular jamming. Ultrasonic, induction and direct mechanical stirring were proposed, but each had its pitfalls, either making the system more expensive than other metal printing technologies, or outright not being feasible. I've heard whispers that Desktop Metal also attempted Semisolid Metal Printing, but evidently they got no further than LLNL.

While at Voxel8 in 2015 and again in 2016, I attempted to further develop semisolid metal printing in order to print traces for use in 3d printed circuit boards. This time, it was abandoned by a fluke more than any engineering bottleneck: the company pivoted to printing shoes, and therefore didn't need the capability to print metal anymore. I learned what I could from that last prototype, and continued thinking of a way to solve all of its flaws.

And so we find ourselves at today, with this project. I've iterated a few more times on my own, and we're finally closing in on a real engineering solution. It's been a long road.

Many thanks to Ninja-Robot for their affordable and customer-focused CNC machining service! Go get your stuff machined with him

Shoutout to Johnny at Ultimachine: I've never managed to brick a RAMBO dude, and I know a ton of that is thanks to your diligence.