Additive manufacturing is all the rage, but why?

Additive manufacturing, or 3D printing, gets people--and the Army is no exception--very excited because of its apparent potential to make virtually anything, even body parts or replacement organs.

But how? What makes it so special?

Imagine a baker decorating a cake, using a bag with a nozzle to squeeze out a fine line of frosting in a pattern. But the baker keeps adding lines on top of existing lines, eventually building up the layers into a form.

That, in a basic sense, is how additive manufacturing works: A machine deposits material sequentially, layer upon layer, or slice by slice, hardening the material as it goes, until the object is finished. Sometimes, like the baker's method, there's a nozzle depositing each layer until the shape is complete. That's analogous to what's known as material extrusion, probably the most well-known technology in the additive manufacturing portfolio of technologies. A nozzle deposits a heated plastic polymer (which usually comes in spools of fat, colored fishing line) that cures as it cools. MakerBots do material extrusion.

With other processes--such as with powder-bed fusion, which constructs objects using metal or plastic dust and heat, or vat photopolymerization, which uses a light-sensitive liquid plastic polymer--there's no nozzle, but the layering process is essentially the same. (Vat photopolymerization, also known as stereolithography, was the first method of 3D printing. Seeing a video of the technique can make it appear truly magical: A form is created, almost invisibly, layer by layer, in a vat of liquid and, when complete, rises out of the liquid as if from some digital womb.)

This layer-by-layer approach enables the transformation of a virtual, 3D model into a physical object. In theory, that single design can be customized endlessly, depending on the need.

DESIGNING MAGIC

But how do we get from idea to design to magic?

Designs can begin with a 3D scanner, which works much like a 2D scanner you might use for a photograph but with an added dimension. Or a designer can build a virtual model entirely in computer-aided design (CAD) software. The resulting CAD file, which has the .STL file extension (for stereolithography or other unwieldy backronyms), then can be printed with the appropriate machine.

Software divides the design into slices, and each slice represents one pass on the machine. With hundreds or thousands of passes--or more--the machine assembles the object, slice by slice. Depending on the kind of process, that can done with wire, polymer filament, powders, liquids, gels, mixtures of glues and materials, and slurries. ASTM International (previously the American Society for Testing and Materials) notes seven primary manufacturing processes. Within those exists a growing list of more specialized methods. It is entirely possible that more have been developed since ASTM's survey of the state of the art. That's how fast the technology moves.

QUICK AND CUSTOM

Quick custom design and build is one of the great promises of additive manufacturing as a category. In theory, every pair of shoes that every Soldier wears could be custom fit and printed to match the contours of a Soldier's feet. Indeed, at least one major athletic shoe brand makes a shoe that's entirely additively manufactured, although it's not customized to each pair of feet. Yet.

That customization possibility extends to both very large objects, such as the buildings that the U.S. Army Corps of Engineers' Automated Construction of Expeditionary Structures program is making, to the extremely small, such as the 4D robots (the fourth dimension is motion) that the Institute for Soldier Nanotechnologies at the Massachusetts Institute of Technology (MIT) recently developed. Dr. Xuanhe Zhao and his team created "soft, magnetic, 3D-printed structures that can transform their shape almost instantaneously by the wave of a magnet."

That speed is the real breakthrough, Zhao said in an interview with Army AL&T, but the use of nanomaterials is nothing to sneeze at. Currently, he said, "the drawback of existing [4D] structures is that their movement [is] very slow."

Zhao, an associate professor at MIT and a researcher at the Institute for Soldier Nanotechnologies, said, "What we developed is basically a new material system for 3D printing." In additive manufacturing, conceptually, the process, the design and the materials are all equally important. Zhao's team's new method places nanomagnetic particles strategically within the soft plastic. The placement and orientation of the materials enable controlled, rapid movement. "We use a new stimulation method, which is magnetic." Watching video of the structures is a bit like watching muscles twitch.

Indeed, Zhao, said, that's the point. "You can reach the level of energy density and the power density of real muscles. So now, we can make it move very fast and forceful."

Zhao said the technology that he and his team invented has real promise for biomedical devices that can be customized, but neither the printer nor the ink for the method they used existed, so they had to invent them. "We invented a printing method and the ink so that … researchers can print structures that they want--different shapes of robots, different shapes of actuators--and when we apply a magnetic field, you can actuate it or you can move this object."

Watching the structures move, it's not hard to imagine why Zhao said the team envisions them in medical applications. "We are actually trying to simulate the functions of the heart, so the heart beating, and muscle contraction inside the human body. And also, we are making this kind of magnetic materials, 3D-printed into, for example, catheters. But those catheters, you know, are smart. … They can steer themselves inside the human body. For example, in the blood vessel, they can make turns. … So that indeed is one … project we are working on."

'ADDITIVE DOESN'T CARE'

Human beings have been making things for thousands of years. The word "manufacturing" actually means "handmade," coming from the Latin for hand (manu) and made (factum), despite current connotations of machine-made.

Doing something for thousands of years means that an almost intuitive understanding of the materials and processes has been passed down from generation to generation. Sloughing off the knowledge built from thousands of years of doing the same thing and perfecting it evolutionarily is not an easy task, and that can be a serious problem for designers--that and the addition of potentially millions more variables into the manufacturing process.

Most often, the complex objects that we manufacture today are made up of lots of smaller, much less complex parts made in bulk, then fastened together. Each of those pieces needs to be cast or machined or forged or milled, and then someone has to assemble them. Additive manufacturing is most intriguing because it makes things holistically, with all the parts built together as one, and can potentially transform hundreds or even thousands of parts into just a few. At the very least, this opens up the possibility of much quicker prototypes, which has the Army excited.

Mike Nikodinovski, mechanical engineer and additive manufacturing expert in the Materials Division at the U.S. Army Tank Automotive Research, Development and Engineering Center, said that an example he often uses to demonstrate the difference between legacy manufacturing and additive is a hole.

"If you drill a hole in a part," he said, "usually it's in a straight line because that's the only thing that you can do with a drill," he said, "But additive doesn't care about that. If I want that hole to be twisty and do different things, now, designers … can design for something different, because the limitations of traditional manufacturing are gone. Now they can say, 'I can do all these crazy different things.' " That's one of the benefits, but also one of the problems. Sometimes it makes sense to do something completely outside any box ever made, but other times, not so much.

It's more than a radical change when everything you know about how to design and build an object are out the window.

"When you deal with a material that's been forged or cast for centuries, there are a lot of assumptions built into the selection of the material and the manufacturing method," said Dr. William Benard, senior campaign scientist in materials development with the U.S. Army Research Laboratory (ARL) in Adelphi, Maryland. According to Benard, ARL's research and development portfolio is divided into campaigns that reflect the Army's priorities. Senior campaign scientists work across the organization to develop and coordinate research strategy and to communicate and interface with the broader research communities--DOD, national labs, industry and academia.

That deep institutional and engineering muscle memory in manufacturing simply does not exist in additive, which has only been with us since the mid-1980s. That's not much more than a couple of ticks of the historical clock compared with the thousands of years that humans have been casting, forging, cutting, milling and drilling.

"That's where we really have to do the research to understand how the materials behave differently," Benard said. "It's not that they're so fundamentally different, it's just building up the knowledge base that we have with other manufacturing methods."

Not only that, said Benard, "I think the scale of the design space that is opened up makes it very challenging to develop good intuition. This is one of the areas we are working on--design tools to manage complexity and help identify non-intuitive optimal designs. The tools have to address the complexity of selecting and placing different materials in a volume, or modulating the material properties, to satisfy constraints and performance objectives that exist in multiple intersecting fields and dimensions--for example, looking at thermal, mechanical and electrical performance of high-power electronics packaging."

Same Technology, Different Result

Part of the potentially endless advantages of additive is the capability to easily produce dead-simple to ragingly complex objects. So, while we would seem to be a long way from printing a new human heart, the Rapid Equipping Force's Expeditionary Lab (Ex Lab) in Afghanistan recently designed and printed a specialized tourniquet component to help stanch blood flow from a Soldier's groin wound in the field.

This junctional tourniquet is just one of the hundreds of projects that the Ex Lab, which is essentially an engineering and fabrication facility in a box--in this case, a 20-foot shipping container--has created as the result of Soldiers' requests. "Among other fabrication processes, we use four additive manufacturing machines, which we run 24 hours a day, and what we're building is going right into the hands of U.S. Soldiers. That's a small piece of where the Army is with additive manufacturing in the deployed environment," said Angel Cruz, the U.S. Army Research, Development and Engineering Command (RDECOM) project lead, REF Ex Lab, in an interview.

"Everything that Ex Labs build is custom. A Soldier comes in with a mission-capability shortfall that can be solved by a materiel solution, and then the engineers we have downrange brainstorm with the Solider and build the custom solution on-site. If we can't build it there, we have it built somewhere within RDECOM and ship it forward. Ex Labs provide a truly unique and powerful capability accessed directly by deployed Soldiers."

There are probably too many advantages to the Ex Lab approach to list, but at the very top is the capacity to get unique equipment that does not currently exist to Soldiers very quickly. The Soldier brings an idea or a problem directly to the engineers, and they collaborate on a design that can be hammered out right then and there. The junctional tourniquet originated with special operations medics, Cruz said. They found it very difficult to stanch blood flow with the standard tourniquet in groin wounds. These medics were using chewing tobacco containers and applying them with ace bandages.

The medics brought the tobacco container method to the Ex Lab engineers and within hours had several printed prototypes to test and select the best one. And that's just one of the many solutions that's come out of the Ex Lab.

Similarly, according to Tim Phillis, the U.S. Army Armament Research, Development and Engineering Center's Rapid Fabrication via Additive Manufacturing on the Battlefield (R-FAB) is a factory in a box. "R-FAB only has additive with 3D scanning capability, as well. It's only polymer printing because that technology and those pieces of equipment were the ones we felt were the most ready for expeditionary use. And that's the whole thing: How do we get this technology to the tactical level?"

CONCLUSION

Additive's seemingly endless possibilities mean that the Army has a lot of work to do in figuring out what capabilities make sense to take forward, what capabilities to develop, and where they all belong. That's the focus of a lot of the Army's efforts, from building nanorobotic components to aircraft engines, to standing up the Additive and Advanced Manufacturing Center of Excellence at the Rock Island Arsenal Joint Manufacturing and Technology Center.

We are not yet--nor likely will be ever be--to the point where we will have the Replicator from "Star Trek." But additive has opened, and continues to open, a host of possibilities for the Army to explore.

STEVE STARK is senior editor of Army AL&T magazine. He holds an M.A. in creative writing from Hollins University and a B.A. in English from George Mason University. In addition to more than two decades of editing and writing about the military and S&T, he is the best-selling ghostwriter of several consumer health-oriented books and an award-winning novelist. He is Level II certified in program management.

This article is published in the January -- March 2019 issue of Army AL&T magazine.