A real thing: 3D printing with metal – how it works
3D printing things out of plastic is all very good, but 3D Printing wouldn’t be nearly such as big a thing if there were no way to 3D print things out of metal. Metal is very durable and is often the only choice when it comes to materials. In the last few years 3D printing has been developing with breathtaking speed, and without doubt, the most dramatic and challenging was development of metal 3D printing. In this article we’ve gathered some interesting information and incredible videos that demonstrate the power and flexibility of metal 3D printing.
The first attempts at what can be categorized as metal 3D printing can be traced back to 1880s when welders who used twin-carbon arc welding discovered that one can lay down bids of metal if he inserts a sacrificial metal rod between the two electrodes.
Laser deposition welding
The technological breakthrough that has made 3D printing with metal possible was invention of laser. By that time people had been using spray welding for decades to repair worn motor shafts by adding metal to them, but the technology was too crude to use it for printing. Spray welding uses a special oxygen-acetylene torch that melts the incoming powdered metal that is being fed into the flame. Swap a torch for a laser and you get a powerful tool that can be used for 3D printing. Trumpf is an example of such devices:
The whole process is carried out in inert gas atmosphere (shielding gas on the picture on the right), which ensures fine-grained structure and very high metallurgic purity of the produced layer. The process is always carried out automatically by a robot.
Laser deposition technology applied to reconditioning metal components of machines:
Aside from repairing metal parts that had been worn down, the process is used to apply coating resistant to, among other things: wear, erosion, corrosion, cavitation, improving performance and lengthening lifetime of various mechanisms.
Binding powdered metal
Unlike printing with molten thermoplastic, it usually takes a very high temperature to melt metals. That and some other properties of metal make it much harder to print things out of metal than out of plastic. And while there are printers that print things by extruding liquid metal from the nozzle as it’s done with plastic in FDM 3D printers, most metal 3D printers use completely different approaches.
One such approach is as follows: as in other 3D printing techniques, the process starts with obtaining a CAD 3D model of the thing to be printed and slicing the model into fine layers. Then a very thin (a fraction of a millimeter) layer of fine metal powder is rolled on a build platform, after which a printing head sprays the powder with binder (glue), binding together metal particles of the current layer of the future object. Then the build platform is lowered just enough to make room for the next layer, and the cycle begins anew: another thin layer of metal powder is deposited atop the previous one and the binder is sprayed where needed to from the second layer of the future object atop the first one, and so on. When this is done, we are left with a metal structure buried in a cake of metal powder. At this point the object is very fragile, since it’s very porous, so the next step is to infuse it with metal to make it a solid metal part. This is done in a separate chamber where bronze powder melts and gets sucked into the 3D printed part like water into a sponge.
Direct Metal Laser Sintering (DMLS)
A more direct approach is a technology known as Direct Metal Laser Sintering (DMLS). Here metal powder is also deposited in thin layers one atop another, but instead of spraying it with binder, the printer sinters the powder with a powerful laser beam, drawing layers of the future object on the surface of the powder, building it layer by layer, from the bottom up. Unlike as it was in the case of binder, the piece is already solid metal, although various methods can be used to further strengthen it.
Another interesting solution is to print out a sand casting mold using the same process, only using sand instead of metal powder, and then use it to cast the detail in metal.
Dynamic Gas Cold Spray
Dynamic Gas Cold Spray a very technologically advanced metal 3D printing technology. Extremely fine metal powder is injected into a supersonic gas jet. The gas accelerates the metal particles and propels them towards the object that is being printed. The shear velocity at which these particles move (500-1000 meters per second) causes them to undergo plastic deformation and the particles adhere to the surface. This technology can be used both to produce new parts, and to add material to an already existing part.
Cold spray technology is currently used to repair machine parts in a matter of a few minutes. Metal particles travel at high speed in a blend of helium and nitrogen gas and gradually stack up on the surface of the damaged part, recreating the desired shape. The movement of the sprayer is controlled by a robot. The U.S. army is already using this technology to repair a component in Blackhawk helicopters, while General Electric is working on adapting the technology for civilian applications.
Printing with gallium and indium alloy at room temperature
Printing with metal does not always mean high temperatures. For instance, at the North Carolina State University a team of researches has developed a process that can be classified as 3D printing with metal at room temperature. They use gallium and indium alloy, an alloy that remains liquid at room temperature, but develops a thin hard skin when in contact with air. Thanks to this skin, the printed structure can maintain its shape while remaining liquid on the inside.
In future this technology could be used for building microcircuits and wearable stretchable electronics.
Michael Dikey who heads the team, said: “It’s an additive manufacturing technique, so you’re basically directly printing the material in 3D space. The resulting structures are soft, and if you embed them in, say, rubber, for example, you can create structures that are deformable and stretchable.”
We live in an age when wearable deformable electronics start to emerge, and companies like Samsung, Nokia and LG are experimenting with all sorts of possibilities. It might be that this technology will turn out revolutionary.
Currently, there are no decent quality consumer grade metal 3D printers, as the technology is still quite expensive. However, if you need to have something printed in metal, you can make use of services of one of the many (and the number continues to grow) 3D Printing services, which are a good solution for those who need something 3D printed with good quality but aren’t ready to buy their own 3D printers and spend quite a lot of time fine-tuning them and learning to use them.
It turns out that quite aside from the obvious advantage metal 3D printing has in terms of being able to manufacture custom and very complex shapes, some metal 3D printing technologies produce metal parts that are much more durable and resistant to various external influences than their machined equivalents. This means 3D printing with metal has bright future in many industrial applications, including, for instance, aerospace. Here is an interesting video that demonstrates among other things how aerospace engines benefit from 3D printing with metal, expanding on what I’ve already mentioned in my previous article.
On September 5, 2013 Elon Musk published an image of SpaceX’s SuperDraco rocket engine chamber being printed on an EOS 3D metal printer, noting that it was printed of the Inconel superalloy. SpaceX surprised many people in May 2014 by announcing that the flight-qualified version of the SuperDraco engine is fully printed, and that it was the first fully printed rocket engine. Printed with Inconel, an alloy of iron and nickel, via direct metal laser sintering technology, the engine operates at a chamber pressure of 6,900 kilopascals (1,000 psi) and at a very high temperature besides. The engines are encapsulated in a DMLS-printed protective nacelle to prevent fault propagation if an engine failure occurs. In May 2014 the engine completed a full qualification test, and now it is slated for its first orbital spaceflight in 2015 or 2016.
Thank you for reading this article! If you have any questions, suggestions or comments, let me know in the comments section.