An action shot of the welder-powered printer, courtesy Michigan Tech
Dazzle someone with a tale of the 3D-printed future, where everyone, everywhere prints their own goods at home, and after the initial surprise that you can print anything from math tools to body parts wears off, you'll hear the same question: This is cool, but does it only print plastic?
Plastics may be the future, but they're not the perfect materials for everything we need. The holy grail of 3D printers is a model that can print a multitude of materials at once—imagine printing a working cell phone—but for now, it'd be nice to be able to print some good old-fashioned metal. Extremely costly options exist, but engineers at Michigan Technological University have developed a metal 3D printer that can be built for less than $2000.
"Metal was the last class of material that the low-cost open-source 3D printing community needed to complete their collection," Joshua Pearce, an associate professor at Michigan Tech's Open Sustainability Tech Lab and a co-author of a paper outlining the work to be published in IEEE Access, wrote in an email. "This helps us take one more step down the path to 'printing everything.'"
Metal parts are largely shaped by one of a trio of processes—casting, forging, and machining—or some combination of all three. Printing metal—that is, building a structure by fusing layer after layer of material—is more difficult than plastic largely because plastics can have lower melting points. Working with rapidly heated and cooled ABS plastic is less of an endeavor than developing a printer head that can work with molten iron.
The welder lays down material on the 3-axis stage, via the paper
But an off-the-shelf machine that spits out clean lines of molten metal already exists: a MIG welder, which spools out a wire electrode that's melted as part of the welding process. The team developed a system for automatically controlling the arc and speed of the welder's electrode, which is laid down in beads that act as the printed layers.
Rather than moving the welder like a print head, the team developed a computer-controlled platform that moves in three axes. (The analogy that comes to mind is moving an ice cream cone under a soft-serve nozzle to build up a massive swirl.) By moving the stage under the bead laid down by the welder, the printer is able to build up layer after layer of printed metal.
The team demonstrated the printer's viability with a water-tight cup design—which showed that the metal indeed fused together—as well as a sprocket shape. While the final results of durability tests aren't yet in, initial measurements show the team's printed products are far from flimsy.
"We haven't completed the full gauntlet of mechanical tests yet, but they are solid steel objects you are printing," Pearce said. "You would not want to print a ball and play catch, as it would certainly hurt to get hit with it."
Better yet, the design is open-source and runs on Linux-powered microcontrollers. To make things even easier, the printer adheres to RepRap self-replicating standards, which means the printer "runs on free software, has free and open hardware designs, requires no specialized training in welding and existing self-replicating rapid prototypers can print the primary custom components necessary for its fabrication," the team wrote.
"Utilizing the open-source hardware concept used in the RepRap community enabled us to develop the metal 3D printer in weeks rather than years," Pearce said. "Under this paradigm we are obligated to share our improvements back to the community."
"This is something we are happy to do because we can be assured that the global maker community is already hacking the concept and developing improvements on our design or applying the concept to other types of RepRaps," he added. "Making a technology open source simply helps it develop faster."
Instructions for the design, including a shopping list and open-source firmware for the various controllers needed, is available on Appropedia. The hope is that just about any hobbyist with a modicum of hacking experience, access to a 3D printer to print the specialized parts, and a couple grand sitting around could build the MTU team's design. Compared to commercial metal 3D printers that cost hundreds of thousands of dollars or an equally-costly 5-axis CNC machine, it's a much lower barrier to entry to creating custom, complex metal parts.
"I see three core applications: First, small businesses will finally have access to metal prototyping and small batch production of metal 3D printed products, which will radically drop costs while also likely reducing environmental impact similarly to what we have seen for plastic RepRaps," Pearce wrote. "Second, the developing world can use the printers to fabricate appropriate technology for sustainable development at extremely low costs. Finally, scientists will be able to digitally fabricate metal components of low-cost scientific equipment making 'open source labs.'"
Behold a cheaply printed sprocket. Via the paper
In the paper, the team notes that the concept isn't perfect just yet. Aside from needing to develop built-in safety features—with a full-on welder in play, it's far from a self-contained desktop system like a MakerBot—there are some practical hurdles to clear.
For one, the system can't yet print horizontal holes, which requires a method for building a "bridge" across gaps in layers. There may be a firmware solution, but it also relates to a second problem: the printer's resolution is limited by how thin the welder's wire material is. The team plans on moving to the thinnest commercially available wire, which will allow for finer details, but the design means that the precision of decisions is limited by how thin the wire material is.
The team does state that multiple metal alloys could be used with their method. One particularly interesting alloy they suggest is that of aluminum beverage cans, which are widely abundant, accessible, and offer a nice weight-to-strength ratio. Actually utilizing that aluminum stock would likely require creating a more pliable alloy, but for 3D-printing enthusiasts looking to get metal stock on the cheap without buying in bulk, it's an attractive option.
That last point offers a nice glimpse into the 3D-printed future. Today, our manufacturing is locked up in factories, where bulk shipments of raw materials are delivered, transformed, and distributed. But the hope is that a distributed manufacturing network powered by 3D printers could ultimately be more efficient.
"Many of the products we use are dominated by plastic," Pearce said. "It is easy for me to envision us moving to a society where we all have polymer RepRaps in our homes. For metals we would probably rely on a local business or community centers for the few times we needed metal components."
So instead of getting your spork shipped from China and stored in a warehouse, you print it when you need it. And instead of ordering a replace sprocket for your bike, your neighborhood metal printer could produce it with material from your local aluminum recycler. It's a fascinating concept, and one that continues to inch closer to reality.