3D Printing of Metals: Is It Really Printing, and Does That Matter?
While visiting the Fabrisonic booth at the IDTechEx Show recently, I was compelled to ask whether a process that welds thin metal foils together should really be called 3D printing. The question is, what defines 3D printing? It's a buzzword that gets attention and sounds a lot more exciting than "additive manufacturing," even though additive manufacturing is technically a more correct phrase for the variety of methods through which 3D objects are being "printed."
Fabrisonic creates 3D parts using ultrasonic welding. Ultrasonic vibration effectively scrubs the oxides off the surface of metals, allowing foils of the same or different metals to bond automatically without added heat. The process does operate at a slightly elevated temperature, but far below the normal melting point of any of the metals involved. The ability to weld dissimilar metals enables structures that wouldn't be able to be made using conventional machining.[caption id="" align="alignnone" width="300.0"] Individual layers of metal foil bond together to form a 3D part. Photo courtesy of Fabrisonic. [/caption]
Fabrisonic takes advantage of a huge CNC milling machine that the company modified to add ultrasonic welding capability. CNC stands for computer numerical control. Users upload designs to the machine and the internal computer controls the motion of the cutting tools to create the desired shape. The Fabrisonic process combines additive and subtractive manufacturing. Layers of metal foil are welded together and built up additively, and grooves are machined out before welding additional layers. This approach enables structures with internal cavities. The sample products in the photos below contain an embedded curved groove (into which I inserted a paper clip) and a hidden cavity containing BB pellets that rattle when the piece is shaken. That's just for fun, but the process can be used to embed useful things like wires or electronic components.[caption id="" align="alignnone" width="400.0"] Giveaway from Fabrisonic booth. Logo shows ability to co-print copper and aluminum. The side view shows the layers of dissimilar metals and the groove through which I threaded a paper clip. [/caption]
A more typical method of 3D printing metal, selective laser sintering (SLS), starts with metal powders and uses a laser to sinter (melt) them so that they fuse together into solid metal layers. 3D inkjet printing with metallic inks, also known as functional fluids, is the technique that is most like standard printing. It produces relatively flat structures, such as printed antennas, that are much thinner in one dimension than in the other two and therefore not as obviously 3-dimensional. I discussed both SLS and inkjet printing in my recently published article in Screen Printing Magazine, “The Migration of Printed Electronics to 3D.”
MX3D in the Netherlands has developed an impressive method of creating 3D metal structures. Its website features a video of one of its industrial robots drawing metal ropes in the air. It looks like the metal strands appear from nowhere. The process relies on welding, as welding tips at the ends of the robotic arms bond one drop of metal at a time. They build structures with remarkable speed.
When MX3D says it is thinking outside the box, the company means this in a literal sense. Every other 3D printing technique that I’ve heard of creates objects within a box-shaped machine. Whether the box fits on a table or is over 10 feet high, like Fabrisonic’s machine, objects still need to be built in a confined space. The 6-axis industrial robots, however, can travel to a job site.
MX3D’s most ambitious project is a 3D bridge, to be built on-site over a canal in Amsterdam. The project is currently scheduled to be completed in 2017. The concept envisions the robots starting the build on one side of the canal and walking across the bridge segments they have just built to create more of the bridge. That should be quite something to see. Perhaps I should plan a trip to Amsterdam next summer.
As Laurie Winkless pointed out in her book Science and the City, it is hard to feel confident that a bridge printed in this manner will be sufficiently strong and durable for its intended purpose. Do the welds formed by fusing individual droplets of metal really have a uniform internal structure with enough strength and toughness? Still, the MX3D website does show a photo of an employee walking on a much smaller bridge-like structure build by its robots, and it doesn’t seem to be bending under the man’s weight.
Regardless of the technique and whether it looks like what we traditionally associate with printing, companies are developing some amazing techniques to create 3D structures that can’t be made with traditional methods like casting parts from molten metal and machining them. Companies are also printing 3D structures from a variety of other materials, including silicones, but that’s a story for another time.