3D Printing Metal from Rust

It seems backwards, but engineers from Northwestern University have made 3D printing metal easier (and eventually cheaper) by adding extra production steps to the procedure. (Paper available in PDF).

Laser sintering works by laying down a thin layer of metal powder and then hitting it with a strong enough laser to sinter the particles together. (Sintering sticks the grains together without getting the metal hot enough to melt it.) The rapid local heating and cooling required to build up 3D objects expands and cools the metal, and can result in stresses inside the resulting object.

The Northwestern team still lays down layers of powder, but glues the layers together with a quick-drying polymer instead of fusing them with a laser. Once the full model is printed, they then sinter it in one piece in an oven.

3D-printed copper lattice. Credit: Ramille Shah and David Dunand

The advantages of adding this extra step are higher printing speed — squirting the liquid out of syringe heads can be faster than fusing metal particles with a laser — and increased structural integrity because the whole model is heated and cooled at one time. A fringe benefit is that the model is still a bit flexible before firing, opening up possibilities for printing a flat model and then bending it into shape before sintering.

And if that weren’t enough, the team figured that they’d add a third step to the procedure to allow it to be used with rust (iron oxide) as the starting powder. They print the rust and polymer model, then un-rust the iron using hydrogen, and then fire it as before. Why rust? Do you know anything cheaper to use as a raw material?

What do you think? The basic idea may even be DIYable — glue metal particles together and heat them up enough to stick. Not in my microwave oven, though. We’d love to see a more energy-efficient 3D metal printer.

Thanks to [Joe] for the tip!

25 thoughts on “3D Printing Metal from Rust

    1. the data layer is under plastic so i doubt one could get access to it with hydrogen in any simple way.
      many polymers and metals also become brittle when subjected to hydrogen, especially liquid or at pressure.

    2. I’m not a chemist but presumably the process would be different for different materials – hydrogen may help with iron oxide but not other metals. There’s plenty of products that “kill” or “convert” rust but I’m fairly sure they don’t work on, for example oxidised aluminium, and may even harm other materials as they can contain nasty stuff.

      1. Aluminium oxide is a very strong bond. I don’t think that Hydrogen would be able to rip away the Oxygen. Aluminium production uses electrolysis of the molten oxidised ore. That would be rather radical on the data on the disc.

    3. If it is not a recordable CD, then remove the printed side with acetone and sticky tape. Reapply aluminium with a sputter gun. The data is actually pressed into the polycarbon, the aluminum is only needed to reflect the laser.

    1. You can only cold-weld surfaces that are very clean. Besides, the heating is required not so much to fuse the metal as to drive the reduction and get rid of the polymer.

      The objects shrink in the cooking process – note the scale on the images in the paper! The “before” are mostly 2x the linear size of the “after”.

    2. That would require very pure metals and a good vacuum but should work. However I think there could be a problem in making parts completely solid using that method, at least if using powdered metal – it’s easy to see that particles may be placed by chance so that there are gaps in the print. Using extremely fine wires instead may be a better solution however even then the solidity may suffer… But I guess the only way to know is to try it! :)

  1. If your going to mess around with a sintering oven, why not use MIM(Metal Injection Molding) feed stock via a FDM or SLS machine. The polymer de-binding is pretty straight forward and the process is well understood.

  2. For most people, using their printer to create a mold for casting seems to provide all the “complexity for free” of 3d printers without the inherent lack of structural integrity of the layering deposition processes. Yeah adding a foundry for casting is not an option for everyone,but

    1. Depends on the material being formed.

      Lead is pretty much just a cooking pot and a camping stove.

      something like steel you might need a clay or plaster lined pot and a kiln made of bricks to melt it.

      but its certainly doable. I have made many a zinc casting out of plaster and wax. (carve out the shape in wax, cast plaster around it, heat it to melt the wax, then pour in the molten zinc. you just heat the zinc with a torch inside a plant pot, works like a charm)

  3. I wonder how this could be used for 3d printing structures and devices on Mars if/when we get there. Then it becomes cheaper to send people there as they don’t need to bring as much with them. They bring hydrogen, use rust found on Mars, and get a structure and water out of the deal. Two very needed things for explorers on the red planet.

    1. There’s water on Mars, which you’d probably use if you were there, for growing food and drinking. So you won’t need to bring hydrogen with you.

      The idea of 3D printing will probably revolutionise manned exploration of moons and planets, when we eventually start doing it again. You’re probably better off machining things like air tanks, until 3D printing offers the same strength, but you can always 3D print the tools you use to make them. Or 3D print the tools you use to make the tools.

  4. there is a astroid mining company, that is doing laser sintering of nickle to 3d print.

    put in for a patent for using a “fog” of particles instead of trying to use wires or wipers

  5. Just a guess, but the material being used sounds a lot like a thinned version of Precious Metal Clay, a product used by amateur jewelers. It is available in silver, gold, copper and bronze and works roughly the same way except that the product is intended for hand forming rather than 3d printing. Maybe this has more DIY potential than meets the eye. Metal Clay generally fires between 800 and 1K Centigrade and copper and bronze need to be fired in a sealed tin of charcoal to eliminate oxygen.
    About the rust thing, I would be concerned that the hydrogen would need to reach all part of the model on a molecular level or you would be left with pockets of rust inside a shell of raw iron. Not good for structural integrity.

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