How a 3D Printer Works

What is a 3D printer?

3D printers are a new generation of machines that can make everyday things. They’re remarkable because they can produce different kinds of objects, in different materials, all from the same machine.

A 3D printer can make pretty much anything from ceramic cups to plastic toys, metal machine parts, stoneware vases, fancy chocolate cakes or even (one day soon) human body parts.

They replace traditional factory production lines with a single machine, just like home inkjet printers replaced bottles of ink, a printing press, hot metal type and a drying rack.

How does a 3D printer work?

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 in a method known as fused depositional modeling (FDM). 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.

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. 

Advantages and disadvantages

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 vastly cheaper machines are also available (you can buy a Tronxy 3D printer kit for around $100–200). 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.