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A typical 3D printer: a B9Creator.

3D printers

by Chris Woodford. Last updated: September 29, 2014.

Even the best artists struggle to show us what real-world objects look like in all their three-dimensional (3D) glory. Most of the time that doesn't matter—looking at a photo or sketch gives us a good-enough idea. But if you're in the business of developing new products and you need to show them off to clients or customers, nothing beats having a prototype: a model you can touch, hold, and feel. Only trouble is, models take ages to make by hand and machines that can make "rapid prototypes" cost a fortune (up to a half million dollars). Hurrah, then for 3D printers, which work a bit like inkjets and build up 3D models layer by layer at up to 10 times the speed and a fifth the cost. How exactly do they work? Let's take a closer look!

Photo: A B9Creator™—a typical low-cost, DIY 3D printer. Other popular 3D printer makes include Z Corporation, Stratasys, Objet Geometries, and Dimension uPrint. Photo by courtesy of Windell H. Oskay, www.evilmadscientist.com, published on Flickr in 2012 under a Creative Commons Licence.

From hand-made prototypes to rapid prototyping

A wax prototype of a NASA model plane.

Before there were such things as computer-aided design (CAD) and lasers, models and prototypes were laboriously carved from wood or stuck together from little pieces of card or plastic. They could take days or even weeks to make and typically cost a fortune. Getting changes or alterations made was difficult and time-consuming, especially if an outside model-making company was being used, and that could discourage designers from making improvements or taking last-minute comments onboard: "It's too late!"

With the arrival of better technology, an idea called rapid prototyping (RP) grew up during the 1980s as a solution to this problem: it means developing models and prototypes by more automated methods, usually in hours or days rather than the weeks that traditional prototyping used to take. 3D printing is a logical extension of this idea in which product designers make their own rapid prototypes, in hours, using sophisticated machines similar to inkjet printers.

Photo: A high-quality rapid prototype of a space plane made in wax from a CAD drawing by NASA. Photo courtesy of NASA Langley Research Center (NASA-LaRC).

How does a 3D printer work?

Designing an object on a computer screen with CAD software.

Imagine building a conventional wooden prototype of a car. You'd start off with a block of solid wood and carve inward, like a sculptor, gradually revealing the object "hidden" inside. Or if you wanted to make an architect's model of a house, you'd construct it like a real, prefabricated house, probably by cutting miniature replicas of the walls out of card and gluing them together. Now a laser could easily carve wood into shape and it's not beyond the realms of possibility to train a robot to stick cardboard together—but 3D printers don't work in either of these ways!

A typical 3D printer is very much like an inkjet printer operated from a computer. It builds up a 3D model one layer at a time, from the bottom upward, by repeatedly printing over the same area. Working entirely automatically, the printer creates a model over a period of hours by turning a 3D CAD drawing into lots of two-dimensional, cross-sectional layers—effectively separate 2D prints that sit one on top of another, but without the paper in between. Instead of using ink, which would never build up to much volume, the printer deposits layers of molten plastic or powder and fuses them together (and to the existing structure) with adhesive or ultraviolet light.

Photo: A computer-aided-design (CAD) drawing like this is the starting point for a 3D print. Photo courtesy of NASA Glenn Research Center (NASA-GRC).

Q: What kind of "ink" does a 3D printer use? A: ABS plastic!

Where an inkjet printer sprays liquid ink and a laser printer uses solid powder, a 3D printer uses neither: you can't build a 3D model by piling up colored water or black dust! What you can model with is plastic. A 3D printer essentially works by extruding molten plastic through a tiny nozzle that it moves around precisely under computer control. It prints one layer, waits for it to dry, and then prints the next layer on top. Depending on the quality of the printer, what you get is either a stunning looking 3D model or a lot of 2D lines of plastic sitting crudely on top of one another—like badly piped cake icing! The plastic from which models are printed is obviously hugely important.

A basic computer mouse

When we talk about plastic, we generally mean "plastics": if you're a diligent recycler, you'll know there are many types of plastic, all of which are different, both chemically (in their molecular makeup) and physically (in the way they behave toward heat, light, and so on). It's hardly surprising that 3D printers use thermoplastics (plastics that melt when you heat them and turn solid when you cool them back down), and typically one called ABS (acrylonitrile butadiene styrene). Perhaps most familiar as the material from which LEGO® bricks are made, ABS is also widely used in car interiors (sometimes in outside parts such as hubcaps too), for making the insides of refrigerators, and in plastic computer parts (it's quite likely the mouse and keyboard you're using right now are made from ABS plastic).

Photo: A computer mouse made from black ABS plastic.

So why is this material used for 3D printing? It's really a composite of a hard, tough plastic (acrylonitrile) with a synthetic rubber (butadiene styrene). It's perfect for 3D printing because it's a solid at room temperatures and melts at a little over 100°C (220°F), which is cool enough to melt inside the printer without too much heat and hot enough that models printed from it won't melt if they're left in the Sun. Once set, it can be sanded smooth or painted; another useful property of ABS is that it's a whiteish-yellow color in its raw form, but pigments (the color chemicals in paint) can be added to make it virtually any color at all. According to the type of printer you're using, you feed it the plastic either in the form of small pellets or filaments (like plastic strings).

You don't necessarily need to print in 3D with plastic: in theory, you can print objects using any molten material that hardens and sets reasonably quickly. In July 2011, researchers at England's Exeter University unveiled a prototype food printer that could print 3D objects using molten chocolate!

Advantages and disadvantages

Two 3D printed objects made from granulated sugar by Evil Mad Scientist Laboratories.

Makers of 3D printers claim they are up to 10 times faster than other methods and 5 times cheaper, so they offer big advantages for people who need rapid prototypes in hours rather than days. Although high-end 3D printers they are still expensive (typically about $25,000–$50,000), they're a fraction the cost of more sophisticated RP machines (which come in at $100,000–$500,000), and cheaper machines are now beginning to appear (the B9Creator™ in our top photo comes in kit form, priced at $2495). They're also reasonably small, safe, easy-to-use, and reliable (features that have made them increasingly popular in places such as design/engineering schools).

On the downside, the finish of the models they produce is usually inferior to those produced with higher-end RP machines. The choice of materials is often limited to just one or two, the colors may be crude, and the texture may not reflect the intended finish of the product very well. Generally, then, 3D-printed models may be better for rough, early visualizations of new products; more sophisticated RP machines can be used later in the process when designs are closer to finalization and things like accurate surface texture are more important.

Photo: In theory, you can make 3D prints from any raw material you can feed into your printer. Here are some fantastic 3D objects printed with granulated sugar by a "CandyFab 4000" (a hacked old HP plotter) by the always entertaining folk at Evil Mad Scientist Laboratories. Photo by courtesy of Windell H. Oskay, www.evilmadscientist.com, published on Flickr in 2007 under a Creative Commons Licence.

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Text copyright © Chris Woodford 2010, 2011. All rights reserved. Full copyright notice and terms of use.

B9Creator is a trademark of B9Creations, LLC.

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Woodford, Chris. (2010) 3D printers. Retrieved from http://www.explainthatstuff.com/how-3d-printers-work.html. [Accessed (Insert date here)]

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