3D printing is capturing the attention of a lot of people these days, with promises to disrupt the manufacturing process. Devices that can produce finished objects from malleable substrates conjure up utopian visions of Star Trek-like replicators. The promise: We will eventually build anything we want at the touch of a button.

But like many promises of technology that will usher in a golden age, the reality is far less shiny. 3D printing will change the way goods are manufactured, but the old ways will still essentially remain in play, albeit with some changes.

In other words, don't count out the Rust Belt quite yet.

Inside 3D Printing

Whether you call it 3D printing or additive manufacturing, the process of creating objects by layering material in precise ways to build goods is nothing new. The core technologies behind it have been around for a couple of decades.

What's changed is the availability of sturdier materials used to create printed objects, better software to design the objects, and the general decrease in costs of hardware. These factors have combined to make 3D printing much more affordable.

And analysts are noticing: Last week, Gartner released its first forecast on 3D printing, which predicted that global shipments of 3D printers in the sub-$100,000 range will grow by 49% to 56,500 units by the end of 2013, and then jump up another 75% to just over 98,000 units in 2014. Here's how Gartner research director Pete Basiliere put it:

The 3D printer market has reached its inflection point. While still a nascent market, with hype outpacing the technical realities, the speed of development and rise in buyer interest are pressing hardware, software and service providers to offer easier-to-use tools and materials that produce consistently high-quality results.

With so much growth potential, it is easy to see a world where additive-manufacturing machines start replacing factories that use assembly lines and injection-molding to create products. But there are some good reasons why this won't happen on a large scale.

What 3D Printing Can't Do

Right now, the biggest limitation for 3D-printed goods is their lack of complexity. While 3D-printed objects can be very intricate in their designs, they are still essentially built in one piece. If you want moving parts, you can create them, but you will nearly always have to remove any rafts or supports that will turn the single-piece printed object into something with movable components.

That's a big deal, because it places limitations on what can be made. Yes, there are a lot of single-piece items to be manufactured, but in order to create items with more than one part, a manufacturer will have to introduce some sort of assembly system, either human-driven or automated. This assembly process will either involve printing separate parts and snapping them together, or removing the supports from a single printed device to create something that moves.

At this point, more limitations come into play. Once assembly processes are introduced, labor has to be managed, as will supply chain—components have to be ready for each stage of assembly. You can have 3D-printed components at the ready, but right now 3D printing is slower than molding methods. The biggest advantage to 3D-printed objects—customizability—is minimized when it comes to assembly. After all, customize a part too much, and it won't fit with other parts.

In the case of converting a single printed object to something that is movable, supply chain isn't as much of a problem, but labor time and expertise will still have to be taken into account.

This is mostly a question of economics. Unless some truly artisan products are being created, any sort of assembly process will need to rely on a supply chain. And 3D printing, by its nature, will have trouble keeping up with demand.

Mass production of products still favors the assembly line and molding processes, because the economics will support the upfront expense of creating molds and other fabrication techniques. This is why, unless 3D printing radically improves, it will not be involved in mass-produced goods.

What 3D Printing Can Do

Though factories won't be closing due to 3D printing, there will still be some interesting additions to the world of manufacturing now and in the near future.

Smaller-batch production is what 3D printing will excel in, with products that will better serve the needs to the customer. Like micropublishing, which prints and binds books on demand for self-published authors, small-batch products can serve niche customers with much greater efficiency.

Developing markets will also gain some benefit from 3D printing. In areas of the world where infrastructure is poor and hence labor, materials or distribution channels are difficult to obtain, 3D printing could help get products to market far less expensively than traditional manufacturing processes. One key area where 3D printing could help: printing agricultural tools to make them more readily available for small-farm workers.

3D printing will also be indispensable in prototyping and design testing, enabling designers to get their finished products to market a lot faster and with presumably better quality.

Perhaps, one day, you will be able to print your new tablet computing device, or that ham and Swiss on rye. But for now, 3D printing will thrive in the niches of manufacturing that large-scale production has trouble filling.

Image courtesy of Shutterstock.