Binder jetting is a 3D printing process that uses inkjet print heads to deposit a liquid binding agent onto a powder bed. A thin layer of powder is spread across the build platform, and the printhead makes a pass over it, squirting its goo with precision.
Then the build platform drops down a smidgen, a recoating blade spreads a new layer of powder across it, and the process repeats.
Layer by layer, the object is built up.
At the end you've got what looks like a box full of powder, with your unseen part(s) curing inside of it. The loose powder is blown or shaken off, and retrieved, as it can be used for the next print.
If the process sounds slow, it's only because my description was clumsy. Binder jetting can be "as much as 100 times faster than laser powder bed fusion systems," according to Desktop Metal, a company at the forefront of binder jetting, and whose images and videos are used here. As an example, their video below shows a laser on the left, and their binder jetting printhead on the right:
Their printhead can deliver up to 670 million drops of binder per second, and they can print at a resolution of 1200 dpi, yielding extraordinarily detailed objects.
Additive Manufacturing points out another benefit of binder jetting: Stacking parts for greater production speed. "Binder jetting machines offer larger build volumes than many powder-bed 3D printing technologies and make it possible to stack multiple layers of parts on top of each other in the build box. Parts made this way can be nested within all three dimensions of the printer's build volume, enabling parallel manufacturing of multiple parts at the same time."
The process also yields a costs savings versus other methods:
"Materials used in binder jetting tend to be more affordable and more easily recycled than those used in other powder-based AM processes, which translates to cost savings and competitive part pricing. The technology is also accurate and repeatable, making it suitable for serial production of small, precise parts."
To throw it back to Desktop Metal: "The result is a system that is not only accurate enough to print a watch bezel with precise detailing around its edge," DM writes, "but also fast enough to produce as many as 1,200 of them in a single build, at a cost of just $1.06."
Here's what all this means: The high quality of the part, the ability to quickly produce complex geometry, the competitive cost, the repeatability and the speed mean that this digital fabrication technology--we're well beyond "rapid prototyping" here--mean that they can begin to compete with traditional mass production techniques. "Binder jetting systems," DM says, "[can] deliver per-part costs that can compete with traditional processes like casting and forging."
You can learn more about the production method here.