TECHNICALLY SPEAKING the HYPE? Additive manufacturing is all the rage, but why? by Steve Stark A


dditive 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.


Tat, 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. Tat’s analo- gous 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 stereolithog- raphy, 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.)


Tis 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. Te resulting CAD file, which has the .STL file extension (for stereolithography or other unwieldy backronyms), then can be printed with the appropri- ate machine.


Software divides the design into slices, and each slice repre- sents 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


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