Company to 3D print a steel pedestrian bridge in mid-air


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World of Goo IRL?


I, for one, welcome our new 3D steel, eh, bridge printing, um, overlord thing, yeah.


Oh, sure, they run along tracks, FOR NOW.


I spent far too long reading this headline trying to figure out why a company would print a floating pedestrian badge…


“First, we’ll need a large scaffolding that…uh, that spans the area between the two points that the bridge we will build will connect…”


…which we can print. If designed correctly, the whole thing can be grown from one side to another and be its own scaffolding.

In the initial version, all it has to be able to carry is its own weight and the weight of the printer. A design can be made to satisfy this.

And the printer can potentially even print additional scaffolding as a temporary support, if needed. Or a temporary tensioned-rope structure can be erected for a while.

The printer can also print the bridge in a different orientation, e.g. vertically, to be lowered into position once finished enough to support the printer. The rest of the load-bearing structure then can be added.

So many possibilities!


That you’re incorrect about that is what makes the post interesting in the first place.

I do wonder if these bots could ultimately print custom scaffolding? And then take it down after?


LoL, I saw the pictures, read the article, it was just too humorous a thought, had to comment


But a lot of the strength of steel depends on the pattern of crystalization. How do you get that from a 3-d printer? Now I’d like to see a little 3-d printer-bot with its own little built-in hammer and anvil, though I don’t know how well cold-hammering compares to hot.


Here’s what I read in lieu of watching a video, I find videos don’t hold my attention for some stuff especially when it has a sell format.


By choosing the alloy that has good mechanical properties from the kind of thermal history that comes from this kind of 3d printing. Only some alloys are sensitive enough to heat treatment; these are not so suitable for this application.

As this is a modified welding technology, all the materials behavior is already well described in the relevant literature.

Also, for surface treatment, you don’t really need a hammer.

And with selective laser melting, layer by layer, every part of the volume was once a surface. This would however work only for relatively small parts.
Even with the big application, if it is for surface-only, I can imagine the tool head equipped also with a pulsed laser and peen the part shortly after printing a segment. Same, just with a different head, for plasma coating or thermal spray.


I’m not asking about heat treatment, though it can be useful. I’m asking about the pattern of crystalization. I don’t know how else to explain it. Choosing the right allow doesn’t create the right pattern of crystalization. When steel crystalizes, it tends to form cells of with little carbon bounded by strips with more carbon. That’s why some steel objects, such as road barriers, have that blocky appearance. Hammering can affect the shape of the cells, and give more resistance to bending on one direction than in another. 3-d printing seems to sacrifice that advantage.


The blocky appearance of the road barriers is zinc, crystallized on the surface from dip coating in bath of molten zinc.

The crystallization you mention is relevant only for certain low-alloy steels, with high enough carbon to matter. The heat treatment then gets highly relevant for the mechanical properties. But there’s a large number of ferrous and nonferrous alloys that are way less sensitive to heat treatment, or where the relatively fast cooling from this kind of welding-deposition produces the right microstructure.

3d printing is unsuitable for some steels. The remedy is easy - use a more suitable alloy.


The post emphasizes the robotic 3D printing. But, based on the presentation I saw on this at Autodesk University, one of the more interesting aspects of this project is that it was using “generative design”- that is, taking the design problem to be solved (bridge), the dimensions and required loads, the materials available (including the new materials science, layering of alloys and disparate materials that 3D technology makes possible), and having the computer independently create an efficient design based on those parameters. That’s where the latticed, organic shape comes from, from not putting materials where they don’t contribute to strength. This is something that cloud computing, with nearly infinite resources, makes possible. This could potentially make structures far more material and energy efficient. I found that aspect to be more revolutionary than the 3D printing technology.


It’s the “in mid-air” part that impresses me most. I mean, I’d probably start from one end or the other but if they want to build the middle first and span outward from there then who am I to discourage them?


Now, correct me if I am wrong, but wouldn’t this be more impressive if it used solar power to take carbon from the air and made the bridge out of pure diamond? Certainly 3d printing will be able to accomplish this by tomorrow afternoon.

The future is . . . sparkling!


It would. Especially if you could address the inherent brittleness of the diamond. (Nanotubes instead, maybe?)

However, the metal printer wins the awesomeness test in this round by default, by the virtue of actually being there.


You’re talking about grain structure I assume? Which elemental composition does affect, but the main factor is thermal history: was it fully or only partially melted, how fast did it cool, etc.

For laser melting and electron beam melting (powder feedstock) 3D printers, some companies are starting to add thermal imaging cameras that monitor the thermal profile during printing and dynamically modify the beam power and scan rate to ensure each point has the right thermal profile/history to result in the grain structure you want. You can use heat treatments after the fact to alleviate unwanted residual strains, and if the shape allows I guess you could still do work hardening. In some cases aerospace companies have reported that 3D printed parts can be made with better mechanical performance than the same alloys made with conventional means.

For this process, I have no idea what the feedstock is or how it is melted and cooled, so I can’t say. I assume it is less precise since if seems to be done in air under ambient conditions.


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