In television’s “Star Trek,” the crew used “replicators” to instantly create anything from Earl Grey tea to engine parts. For modern science, that remains something of a frontier. But Z Corporation in Burlington, Mass., is working on a real-world variation that comes stunningly close.

The company stands among the early players in 3-D printing, in which engineers load up a schematic of what they want, feed in some plastic, and watch a machine print out a fully formed model – complete with moving parts.

At its heart, this style of “rapid prototyping” relies on a simple concept: building an object one cross section at a time, similar to laying down LEGO bricks to make a larger shape.

The field is still very young, says Scott Harmon, vice president of business development at Z Corporation. Several companies make these three-dimensional printers, the cheapest of which sells for about $10,000.

Despite a wide array of potential uses, interest and investment has been slow because “even designing a door hinge is pretty difficult,” says Mr. Harmon. What’s missing is the “killer app” – the thing that will give 3-D printing companies a reason to mass-produce. “You’d need to have some reason to want to make something you couldn’t get in a store.”

Z Corporations’ printers use a powder as the basis for the things it builds. The powder is laid down in a thin layer. When the printer head passes over it, the nozzle sprays out a glue-like substance instead of ink. The bed on which the powder is laid then moves down 4/10000ths of an inch, another layer of powder is put down and the process repeats. Making a small part can take a few hours – and the current generation of 3-D printers can produce parts up to about 640 cubic inches, somewhat bigger than a basketball.

The advantage to Z Corp.’s method – and other systems that use powder – is that hollow spaces can exist in the model, saving on material. The powder also acts as a support. The downside is that the model isn’t as strong, unless you dip it into a resin, which soaks into the tiny pores on the surface.

Harmon says that, besides industry, there is a market for making one-off models that Z Corp serves. One big application: wedding-cake toppers.

Other companies, notably Dimension in Eden Prairie, Minn., make machines that use plastic. The machine works in a similar fashion, laying down plastic layer by layer. The difference is that the print head alternates between the plastic used in the model and a support material, which helps keep the shape for overhangs and hollow forms. The supporting material can be chipped off the finished models.

An Israeli company, Objet, has a version that can make a wider variety of shapes and uses a resin. As each layer prints, the resin is dried and cured with an ultraviolet lamp.

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