In other words, rather than merely trying to outdo other 3-D printers, Desktop Metal will have the tough task of converting manufacturers away from production methods that are at the heart of their businesses. But the very existence of this large, established market is what makes the prospect so intriguing. Making metal parts, says Fulop, “is a trillion-dollar industry.” And even if 3-D printing wins only a small portion of it, he adds, it could still represent a multibillion-dollar opportunity.

Too hot to print

Look around. Metals are everywhere. But whereas 3-D printing has been widely used in making plastics, the technology’s use in making metal parts “has been narrowly confined,” says Chris Schuh, head of materials science and engineering at MIT and cofounder of Desktop Metal. “Metal processing is more of an art. It’s a very challenging space.”

Making metal objects using 3-D printing is difficult for several reasons. Most obvious is the high temperature required for processing metals. The most common way to print plastics involves heating polymers and squirting the material out the printer nozzle; the plastic then quickly hardens into the desired shape. The process is simple enough to be used in 3-D printers that sell for around $1,000. But building a 3-D printer that directly extrudes metals is not practical, given that aluminum melts at 660 °C, high-carbon steel at 1,370 °C, and titanium at 1,668 °C. Metal parts also have to go through several high-temperature processes to ensure the expected strength and other mechanical properties.

To make a 3-D printer fast enough to be used in manufacturing metal objects, Desktop Metal turned to a technology that dates back to the late 1980s. That’s when a team of MIT engineers led by company cofounder Sachs filed a patent for “three-dimensional printing techniques.” It described a process of putting down a thin layer of metal powder and then using ink-jet printing to deposit a liquid that selectively binds the powder together. The process, which is repeated for hundreds or thousands of layers to define a metal part, can make ones with nearly unlimited geometric complexity. In the most common application of the technology, the binder acts like a glue. However, it can also be used to locally deposit different materials in different locations.

The MIT researchers knew their printing method could be used to make metal and ceramic parts, says Sachs. But they also knew it was too slow to be practical, and the metal powders required for the process were far too expensive at the time. Sachs turned to other research interests, including an effort to improve the manufacturing of photovoltaics (see “Praying for an Energy Miracle,”). In the next decades 3-D printing took off and captured the imagination of many product designers. Most famously, a cheap and easy-to-use 3-D printer from MakerBot was introduced in 2009, appealing to many self-styled inventors and tinkerers. But these affordable printers bumped up against the reality that they were limited to using a few cheap plastics. What’s more, though the machines can print complex shapes, the final product often isn’t as good as a plastic part made with conventional technology.

Close up of wing nut.

Desktop Metal printed the bolt and wing nut separately to demonstrate that it can fabricate parts with tight tolerances.

Meanwhile, researchers at industrial manufacturers like GE were busy advancing laser-based technologies invented in the late 1980s for printing metals. These machines use lasers—or, in some cases, high-power electron beams—to draw shapes in a layer of metal powder by melting the material. They repeat the process to build up a three-dimensional object out of the fused powders. The technique is impressive in its capabilities, but it’s slow and expensive. It is worthwhile only for extremely high-value parts that are too complex to make using other methods. Notably, GE’s new jet engine uses a series of sophisticated 3-D-printed fuel nozzles; they are lighter and far more durable because intricate cooling channels have been built into them.

The founders of Desktop Metal decided that to make 3-D metal printing more widely accessible, they would need to sell two different types of machines: a relatively inexpensive “desktop” model suitable for designers and engineers fabricating prototypes, and one that is fast and large enough for manufacturers. Luckily, several innovations have finally made Sachs’s original invention practical for mass production, including the development of very high-speed ink-jet printing for depositing the binder. Successively printing about 1,500 layers, each 50 micrometers thick and deposited in a few seconds, the production-scale printer can build up a 500-cubic-inch part in an hour. That’s about 100 times faster than a laser-based 3-D printer can make metal parts.

For its prototyping machine, Desktop Metal adopted a method from plastic-based 3-D printing. But instead of a softened polymer, it uses metal powders mixed with a flowable polymer binder. The formulation is extruded, using the printed binder to clump the metal powder into the intended shapes.

However, whether the part is printed with the prototyping machine or the production model, the resulting object—part plastic binder and part metal—lacks the strength of a metal one. So it goes into a specially designed microwave oven for sintering, a process of using heat to make the material more dense, producing a part with the desired properties. In a series of carefully calibrated steps during the sintering process, the polymer is burned off, and then the metal is fused together at a temperature well below its melting point.

The sales pitch

According to the promises of its enthusiasts, 3-D printing will reduce the need for industrial manufacturers and empower local artisan producers (see “The Difference Between Makers and Manufacturers,”). The reality is likely to be far different but nonetheless profound. Many sectors of industrial production increasingly use automation and advanced software, and 3-D printing enhances this ongoing move to digital manufacturing. In some ways, it is not unlike an automated machining process that works off a digital file to create a metal part. What’s different about 3-D printing is that it offers ways to make far more complex objects and removes many of the constraints that the production process puts on designers and engineers.