How Does a 3D Printer Work?

The earliest use of additive manufacturing was in rapid prototyping (RP) during the late 1980s and early 1990s. Prototypes allow manufacturers a chance to examine an object's design more closely and even test it before producing a finished product. RP allows manufacturers to produce those prototypes much faster than before, often within days or sometimes hours of conceiving the design.

In RP, designers create models using computer-aided design (CAD) software, and then machines follow that software model to determine how to construct the object. The process of building that object by "printing" its cross-sections layer by layer became known as 3D printing.

The earliest development of 3D printing technologies happened at Massachusetts Institute of Technology (MIT) and at a company called 3D Systems. In the early 1990s, MIT developed a procedure it trademarked with the name 3D Printing, which it officially abbreviated as 3DP. As of September 2019, MIT has granted licenses to six companies to use and promote the 3DP process in its products [source: MIT].

3D Systems, based in Rock Hill, South Carolina, has pioneered and used a variety of 3D printing approaches since its founding in 1986. It has even trademarked some of its technologies, such as the stereolithography apparatus (SLA) and selective laser sintering (SLS), each described later in this article. While MIT and 3D Systems remain leaders in the field of 3D printing, other companies have also brought innovative new products to the professional market, building on these AM technologies.

Today, some of the same 3D printing technology that contributed to RP is now being used to create finished products. The technology continues to improve in various ways, from the fineness of detail a machine can print to the amount of time required to clean and finish the object when the printing is complete. Processes are getting faster, the materials and equipment are getting cheaper, and more materials can be used, including metals and ceramics. Printing machines now range from the size of a small car to the size of a microwave oven.

Additive manufacturing is often compared to, or even mistaken for, another common manufacturing process called computer numerical controlled (CNC) machining. However, CNC is an example of subtractive manufacturing, which is the opposite of AM. In CNC machining, material is removed from some pre-existing block until the finished product remains, much like a carving a statue from stone, one layer at a time.

Now that you have some background information about the field, let's explore some 3D printing technologies.

One approach to 3D printing is direct 3D printing. Direct 3D printing uses inkjet technology, which has been available for 2D printing since the 1960s [source: Gibson, et al.]. As in a 2D inkjet printer, nozzles in a 3D printer move back and forth dispensing a fluid. Unlike 2D printing, though, the nozzles or the printing surface move up and down so multiple layers of material can cover the same surface. Moreover, these printers don't use ink; they dispense thick waxes and plastic polymers, which solidify to form each new cross-section of the sturdy 3D object.

Rapid prototyping (RP), which we described earlier in the article, has been a major factor in the growth of direct 3D printing. In 1994, the ModelMaker, a machine produced by a company known as Solidscape, became the first commercially successful technology to apply the inkjet approach to RP [source: Gibson, et al.]. Other commercial RP products have followed, defying traditional manufacturing methods. For example, today's advanced rapid prototyping products use technologies such as multi-jet modeling (MJM), which creates wax prototypes quickly with dozens of nozzles working simultaneously [source: G.W.P.].

Binder 3D printing, like direct 3D printing, uses inkjet nozzles to apply a liquid and form each new layer. Unlike direct printing, though, binder printing uses two separate materials that come together to form each printed layer: a fine dry powder plus a liquid glue, or binder. Binder 3D printers make two passes to form each layer. The first pass rolls out a thin coating of the powder, and the second pass uses the nozzles to apply the binder. The building platform then lowers slightly to accommodate a new layer of powder, and the entire process repeats until the model is finished.

MIT's 3DP process, mentioned earlier, uses this binder approach. MIT licenses companies to develop products that use 3DP, but to qualify, the company must use some unique combination of powder and binder materials. Binder 3D printing has a few advantages over direct 3D printing. First, it tends to be faster than direct printing because less of the material is applied through the nozzles. Another advantage is that you can incorporate a wider variety of colors and materials in the process, including metals and ceramics.

Photopolymerization is a 3D printing technology whereby drops of a liquid plastic are exposed to an ultraviolet laser. During this exposure, the light converts the liquid into a solid. The term comes from the roots photo, meaning light and polymer, which describes the chemical composition of the solid plastic.

In the 2000s, the Piedmont Triad Center for Advanced Manufacturing (PTCAM) was a partnership of schools and businesses that provided hands-on training in metalworking skills in North Carolina. Some of PT CAM's training incorporated a stereolithography apparatus (SLA) by 3D Systems. SLA uses photopolymerization, directing a laser across a vat of liquid plastic called photopolymer. As with inkjet 3D printing, the SLA repeats this process layer by layer until the print is finished.

Sintering is another additive manufacturing technology that involves melting and fusing particles together to print each successive cross-section of an object. Selective laser sintering (SLS) is one form of sintering used in 3D printing. SLS relies on a UV laser beam to melt a flame-retardant powdered material, which then solidifies to form the printed layer. This is similar to the mechanism behind 2D printers: They melt the toner so that it will adhere to the paper and create the image.

Sintering is naturally compatible with building metal objects because metal manufacturing often requires some type of melting and reshaping. One example of using metal as a sintering material is from 3D Systems [source: 3D Systems]. The objects created with LaserForm A6 have several advantages over metal products made by other means, such as die-casting. One of the biggest advantages is the high level of precision that SLS can achieve.

So far, we've looked at how 3D printing has developed and four widely adopted 3D printing technologies. Next, let's examine the general process of printing three-dimensional objects, which applies no matter what approach you're using.

No matter which approach a 3D printer uses, the overall printing process is generally the same. In their book "Additive Manufacturing Technologies: Rapid Prototyping to Direct Digital Manufacturing," Ian Gibson, David W. Rosen and Brent Stucker list the following eight steps in the generic AM process:

Increasing availability and affordability of 3D printing solutions has made the technology attractive to people across many industries. For example, the automotive industry has used 3D printing technology for many years for rapid prototyping of new auto part designs. The picture above shows a manifold prototype created by the Piedmont Triad Center for Advanced Manufacturing (PTCAM).

Medical Applications

The medical profession eagerly adopted 3D printing for a number of uses, such as printing prosthetics. Traditional professionally made prosthetics can be expensive, but a 3D printer could make a prosthetic hand for as little as $50 [source: Amputee Coalition]. Similarly, Walter Reed Army Medical Center has used 3D printing to produce models that surgeons can use as a guide for facial reconstructive surgery [source: King]. Several professional 3D printer manufacturers sell machines specifically designed for dental work.

Aerospace Engineering Applications

Engineers in the aerospace industry incorporate 3D printing to help test and improve its designs as well as to show off how well they work [source: Gordon]. Research company EADS has an even bolder ambition for 3D printing: to manufacture aircraft parts themselves, including an entire wing for a large airplane. EADS researchers see this as a green technology, believing 3D printed wings will reduce an airplane's weight and, thus, reduce its fuel usage. This could cut carbon-dioxide emissions and the airline around $3,000 over the course of a year. [source: The Economist]

Artistic Applications

3D printing also has some interesting aesthetic applications. Designers and artists are using it in creative ways to produce art, fashion and furniture. Graphic artist Torolf Sauermann has created colorful geometric sculptures using 3D printing [source: Jotero GbR].

Freedom of Creation (FOC), a company in the Netherlands, sold 3D printed products made from laser-sintered polyamide, including lighting with intricate geometric designs and clothing designs consisting of interlocking plastic rings that resemble chain mail. FOC also has a number of corporate clients using its design and print services, including Philips, Nokia, Nike, Asics, and Hyundai [source: FOC].

Culinary Applications

A tastier application of 3D printing technology comes from the chocolate industry, which has developed machines that can create unique confectionary items. Although unsuitable for mass production, 3D printers can make computer-designed objects as prototypes, or just as unique, customized treats [source: Ooi].

Looking for something a little more savory? You can use 3D printers to create many types of food — it has to be something you can puree to get it into the machine — but you can make burgers with 3D printing. One thing to note: Printed food has a different texture than traditional food [source: Houser].

Historically, 3D printing has been an expensive technology. PTCAM's SLA, described earlier in the article, cost more than $250,000; the liquid plastic costs about $800 per gallon. Organizations that owned this type of equipment might sell stereolithography services to others or allow companies to purchase blocks of time to use the equipment.

Today, many large industrial AM machines are still pricey, though less so than before. For example, in September 2019, 3D Systems' ProJet CPX 3000MJP 3600 was selling for less than $100,000 and could produce models in high definition up to 11.75 inches by 7.3 inches by 8 inches (298 millimeters by 185 millimeters by 203 millimeters) [sources: BasTech].

In addition to price, there are some other drawbacks with 3D printers. They use a lot of energy, about 100 times as much electrical energy as regular manufacturing. Researchers also found that they can emit a lot of carcinogenic particles and volatile organic compounds, particularly when used in a small space such as a home.

The plastic used for most 3D projects also has its own problems. Plastic remnants from 3D projects likely will end up in landfills and contribute to Earth's crisis with disposable plastic. Furthermore, plastic's strength varies and may not be best for all component parts of a project. 3D printers are also slow and a project could take several days or hours to print [source: 3-D Insider].

It is likely that many of these problems will be remedied over time, as the technology improves. But other problems may persist. For instance, people have already made guns using 3D printers, including one man who was denied a gun permit earlier. Can steps be taken to prevent people from using 3D printers to make guns, knives and other weapons?

There is also concern about copyright violations. People could get hold of blueprints and print an object rather than purchasing it from the patent or copyright holder. It may be difficult for a patent holder to track down the person (or hundreds of people) who print something patented and claim copyright infringements.

Although it's still not commonplace, 3D printers are showing up in more homes, libraries, schools, and makerspaces. Prices for these machines have also decreased as the technology matures. For example, as of 2024, a MakerBot Replicator Mini+ starts at $1,375. The company sells small spools of its PLA material in 12 standard and limited-edition colors (glow-in-the-dark, anyone?) for an extra charge.

If you don't want to splurge on a machine for home use, you could always build one yourself. For example, physicist and blogger Windell Oskay built his own 3-D printer in 2007 that fabricates objects from sugar using a sintering approach. The project, called CandyFab, has a dedicated website at CandyFab.org. Although the project has shut down, you can still read about it and how he made it work.

For a more professional approach, you can purchase 3D printing services instead. These services allow you to send in your own CAD file and get back a high-quality production of your object or objects created by an industrial 3D printer. Online companies that offer 3D printing services include Shapeways and Ponoko. These sites also give you the option of setting up an online store, allowing you to make money when others purchase 3D prints of your design. [source: Shapeways, Ponoko]

Although a low-cost version has yet to come about, 3D printing continues to offer better print quality at a cheaper price. Perhaps in the future these machines will be commonplace tools used to remedy everyday problems like printing a new house-key instead of driving to the hardware store for a replacement.