When you think about 3-D printing, chances are you think of little plastic doodads created by desktop devices like those made by MakerBot. Computing and printer giant HP wants you to think about metal.

Today the company announced the Metal Jet printer, an industrial-scale 3-D printer that builds items not of plastic but of steel.

3-D plastic printing is widely used for custom items such as prosthetics and hearing aids, and by product designers for prototyping. But it's still a relatively small part of overall manufacturing. That's because, compared with more traditional mass-production techniques, 3-D printing is relatively slow and expensive and can be used with a more limited range of materials.

HP is trying to change that. In 2016, it launched its Jet Fusion plastic 3-D printer, designed for mass production rather than one-off printing. Now with the Metal Jet, it wants to get into big manufacturing sectors such as automobiles and medical devices. The company has partnered with Parmatech, which manufactures components for healthcare devices, and GKN, a supplier of automotive and aerospace parts. Those companies in turn will work with customers like Volkswagen to experiment with 3-D-printing metal. The partners will be able to get Metal Jets this year; others will have to wait until 2020.

For now, many of the products printed by the Metal Jet may be cosmetic---key fobs with custom engravings, for example. It will likely be years before you can buy a car with 3-D-printed metal parts under the hood. But Tim Weber, HP's head of 3-D metals, says 3-D printing will save manufacturing costs for certain product parts and enable companies to create new products faster. In some cases, companies will be able to use the same designs for prototyping and then for production. "A lot of parts take months to prototype. We can now do in days what it took months or years to do," he says. "It will increase the pace of innovation."

Others have been 3-D printing metal for years. GE Aviation, for example, produced a fuel nozzle for one of its jet engines using a process known as selective laser sintering. But that process is, like other 3-D printing techniques, slow and expensive. It might work for extremely expensive jet engine components, but it's not practical for the countless other metal items manufactured every day around the world.

HP is using a different process, known as binder-jet printing, which Weber says is cheaper and more efficient. The Metal Jet printer, which looks a bit like a washing-machine-sized photocopier, spreads layers of metal powder and then sprays it with a binding agent to solidify it in a process not unlike layer-by-layer 3-D printing. These items, essentially made of glued-together metal dust, aren't very sturdy; you can break thin pieces with your bare hands. So the initial pieces are then placed in an furnace---imagine placing cookie sheets in an oven, but instead of cookies you have a tray of car parts---where the extreme heat solidifies the powder. The final results are relatively light, smooth, and can include surprisingly fine details.