How do 3d printers work

How do 3D printers work?

by Chris Woodford. Last updated: April 24, 2021.

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: 3D printing in action: this is the printhead of an Invent3D printer, slowly building up an object, layer by layer, by squirting molten blue plastic out of its precisely moving nozzle. Photo by Cpl. Justin Updegraff courtesy of US Marine Corps.

From hand-made prototypes to rapid prototyping
How does a 3D printer work?
Q: What kind of "ink" does a 3D printer use? A: ABS plastic!
Advantages and disadvantages
Applications
- Medicine
- Aerospace and defense
- Visualization
- Personalized products
The future of 3D printing
Find out more

From hand-made prototypes to rapid prototyping

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).

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.

How does a 3D printer work?

Artwork: One of the world's first three-dimensional FDM printers, developed by S. Scott Crump in the 1980s. In this design, the model (pink, 40) is printed on a baseplate (dark blue, 10) that moves in the horizontal (X–Y) directions, while the print head and nozzle (2 and 4, orange) move in the vertical (Z) direction. The raw material for printing comes from a plastic rod (yellow, 46), melted by the print head. The heating process is carefully regulated by a thermocouple (electrical heat sensor) connected to a temperature controller (purple, 86). The rod is extruded using compressed air from the large tank and compressor on the right (green, 60/62). Things have changed a bit since then, but the basic principle (of building up an object by melting and depositing plastic under three-dimensional control) remains the same. Artwork from US Patent 5,121,329: Apparatus and method for creating three-dimensional objects by S. Scott Crump, Stratasys Ltd, June 9, 1992, courtesy of US Patent and Trademark Office.

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: 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.

Photo: A Lulzbot 3D printer. You can see the little reel of raw, red plastic (the "filament") that feeds into the print head from the top. Photo by Stephane Belcher courtesy of US Navy.

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 either ABS (acrylonitrile butadiene styrene), PLA (polylactic acid), or PETG (polyethylene gerephthalate glycol).

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). 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).

PLA is easier to use than ABS and a little more environmentally friendly, though it's softer and less durable. PETG is a halfway house, closer to the strength of ABS, easy to shape, and relatively easy to recycle.

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

Photo: A B9Creator™—a typical low-cost, DIY 3D printer. It was originally available in kit form, priced at $2495; now it comes ready-assembled in three different versions priced from $6000–12000. Photo by courtesy of Windell H. Oskay, www.evilmadscientist.com, published on Flickr in 2012 under a Creative Commons Licence.

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.

Applications

What can you use a 3D printer for? It's a bit like asking "How many ways can you use a photocopier?" In theory, the only limit is your imagination. In practice, the limits are the accuracy of the model from which you print, the precision of your printer, and the materials you print with. Modern 3D printing was invented about 25 years ago, but it's only really started to take off in the last decade. Much of the technology is still relatively new; even so, the range of uses for 3D printing is pretty astonishing.

Medicine

Photo: 3D-printed plastic hearts make it possible for surgeons to practise operations with no risk. Model by Dr. Matthew Bramlet. Public domain photo published on Flickr courtesy of US NIH Image Gallery and 3D Print Exchange.

Life's a one-way journey; fallible, aging humans with creasing, crumbling bodies naturally see great promise in a technology that has the potential to create replacement body parts and tissue. That's why doctors were among the earliest people to explore 3D printing. Already, we've seen 3D printed ears (from Indian company Novabeans), arms and legs (from Limbitless Solutions, Biomechanical Robotics Group, and Bespoke), and muscles (from Cornell University). 3D printers have also been used to produce artificial tissue (Organovo), cells (Samsara Sciences), and skin (in a partnership between cosmetics giant L'Oreal and Organovo). Although we're some way away from having complete 3D printed replacement organs (such as hearts and livers), things are rapidly moving in that direction. One project, known as the Body on a Chip, run by the Wake Forest Institute for Regenerative Medicine in North Carolina, prints miniature human hearts, lungs, and blood vessels, places them on a microchip, and tests them out with a kind of artificial blood.

Apart from replacement body parts, 3D printing is increasingly being used for medical education and training. At Nicklaus Children's Hospital in Miami, Florida, surgeons practise surgery on 3D-printed replicas of children's hearts. Elsewhere, the same technique is used to rehearse brain surgery.

Aerospace and defense

Designing and testing airplanes is a complex and expensive business: a Boeing Dreamliner has about 2.3 million components inside it! Although computer models can be used to test quite a few aspects of how planes behave, accurate prototypes still need to be made for things like wind-tunnel testing. And 3D printing is a simple and effective way to do that. While commercial airplanes are built in quantity, military planes are more likely to be highly customized—and 3D printing makes it possible to design, test, and manufacture low-volume or one-off parts both quickly and cost-effectively.

Photo: The US Navy has been testing 3D printers on ships since one was installed on USS Essex in 2014. In theory, an onboard printer makes a ship more self-reliant, with less need to carry spare parts and materials, especially during wartime. This is a 3D-printed undersea wireless charger, typical of the objects that might be printed during a mission at sea. Photo by Devin Pisner courtesy of US Navy.

Spacecraft are even more complex than airplanes and have the added drawback that they are "manufactured" in tiny quantities—sometimes only one is ever made. Instead of going to all the expense of making unique tools and manufacturing equipment, it can make much more sense to 3D print one-off components instead. But why even make space parts on Earth? Shipping complex and heavy structures into space is difficult, expensive, and time-consuming; the ability to manufacture things on the Moon, or on other planets, could prove invaluable. It's easy to imagine astronauts (or even robots) using 3D printers to produce whatever objects they need (including spare parts), far from Earth, whenever they need them. But even conventional, Earth-spawned space projects can benefit from the speed, simplicity, and low-cost of 3D printing. The latest, human-supporting NASA Rover uses 3D-printed parts produced with help from Stratasys.

Photo: Spares and repairs are no problem. Closeup view of a Lulzbot Taz 6 3D printer being used to make spare parts onboard a US naval ship. Photo by Christopher A. Veloicaza courtesy of US Navy.

Visualization

Making prototypes of airplanes or space rockets is an example of a much broader use for 3D printing: visualizing how new designs will look in three dimensions. We can use things like virtual reality for that, of course, but people often prefer things they can see and touch. Increasingly, 3D printers are being used for rapid, accurate architectural modeling. Although we can't (yet) 3D print in materials such as brick and concrete, there's a wide range of plastics available and they can be painted to look like realistic building finishes. In the same way, 3D printing is also now widely used for prototyping and testing industrial and consumer products. Since many everyday things are molded from plastic, a 3D printed model can look very similar to the finished product—perfect for focus-group testing or market research.

Personalized products

From plastic toothbrushes to candy wrappers, modern life is here-today, gone-tomorrow—convenient, inexpensive, and disposable. Not everyone appreciates off-the-shelf mass production, however, which is why expensive "designer labels" are so popular. In the future, more of us are going to be able to enjoy the benefits of affordable, highly personalized products custom-made to our exact specification. Jewelry and fashion accessories are already being 3D printed. Just as the Etsy website created a worldwide community of artisan crafters , so Zazzy has now replicated that using 3D printing technology. Thanks to simple online services like Shapeways, anyone can make their own 3D printed nick-nacks, either for themselves or to sell to other people without the expense and hassle of using their own 3D printer (even Staples is now offering 3D printing services in some of its stores).

"Customized products" aren't simply things we buy and use: the food we eat can fall into that category too. Cooking takes time, skill, and patience, because preparing a mouthwatering meal goes far beyond mixing ingredients and heating them on a stove. Since most food can be extruded (squeezed through nozzles), it can (theoretically) also be 3D printed. A few years ago, Evil Mad Scientist Laboratories playfully printed some weird objects out of sugar. In 2013, New York Times columnist A.J. Jacobs challenged himself to print an entire meal—including the plate and cutlery. In the process, he chanced upon the work of Cornell University's Hod Lipson, who believes meals may one day be personally, 3D printed to match your body's exact nutritional needs. Which brings us neatly to the future...

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.

The future of 3D printing

Many people believe 3D printing will herald not merely a tidal wave of brash, plastic gimmicks but a revolution in manufacturing industry and the world economy that it drives. Although 3D printing will certainly make it possible for us to make our own things, there's a limit to what you can achieve by yourself with a cheap printer and a tube of plastic. The real economic benefits are likely to arrive when 3D printing is universally adopted by big companies as a central pillar of manufacturing industry. First, that will enable manufacturers to offer much more customization of existing products, so the affordability of off-the-shelf mass-production will be combined with the attractiveness of one-off, bespoke artisan craft. Second, 3D printing is essentially a robotic technology, so it will lower the cost of manufacturing to the point where it will, once again, be cost-effective to manufacture items in North America and Europe that are currently being cheaply assembled (by poorly paid humans) in such places as China and India. Finally, 3D printing will increase productivity (since fewer people will be needed to make the same things), lowering production costs overall, which should lead to lower prices and greater demand—and that's always a good thing, for consumers, for manufacturers, and the economy.

Photo: Two views of the printhead (sometimes called the "tool head") of a 3D printer. Photo by Ashley McLaughlin courtesy of US Marine Corps.