How 3-D Printing Works


3-D human heart
A 3-D printed heart made from human tissue is processed at Tel Aviv University, Israel in 2019. Israeli scientists have, for the first time, created an entire heart with cells, blood vessels, ventricles and chambers using a 3-D printer. Amir Levy/Getty Images

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Not too long ago, the idea of 3-D printing – creating three-dimensional objects using machines that add layers of material on top of one another – seemed novel. If you say you're going to print something from your computer, most people still think of two-dimensional printing, putting toner or ink on a piece of paper. Now, although many people may not have experienced 3-D printing themselves, they may very well know what you're talking about. And 3-D printers have become affordable enough to start showing up in homes, makerspaces and classrooms.

3-D printing uses a family of manufacturing technology called additive manufacturing (AM). AM is the means of creating an object by adding material to the object layer by layer. AM is the current terminology established by ASTM International (formerly the American Society for Testing and Materials) [source: Gibson, et, al.]. Throughout its history, additive manufacturing in general has gone by various names: stereolithography, 3-D layering and 3-D printing. This article uses the term 3-D printing because it's more well known.

You can see some of the basic principles behind AM in caves; over thousands of years, dripping water creates layers and layers of mineral deposits, which accumulate to form stalagmites and stalactites. Unlike these natural formations, though, 3-D printing is much faster and follows a predetermined plan provided by computer software. The computer directs the 3-D printer to add each new layer as a precise cross-section of the final object.

Additive manufacturing and 3-D printing specifically, continues to grow. Technology that started out as a way to build fast prototypes is now a means of creating products for the medical, dental, aerospace and automotive industries. 3-D printing is also crossing over into toy and furniture manufacturing, art and fashion.

This article looks at the broad scope of 3-D printing, from its history and technologies to its wide range of uses, including printing your own 3-D models at home. First, let's take a look at how 3-D printing got its start and how it is developing today.

History of 3-D Printing

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 3-D printing.

The earliest development of 3-D 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 3-D 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].

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3D Systems, based in Rock Hill, South Carolina, has pioneered and used a variety of 3-D 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 3-D printing, other companies have also brought innovative new products to the professional market, building on these AM technologies.

Today, some of the same 3-D 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 subtractive, 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.

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

Direct and Binder 3-D Printing

illustration of 3-D binder printing
3-D binder printing
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One approach to 3-D printing is direct 3-D printing. Direct 3-D printing uses inkjet technology, which has been available for 2-D printing since the 1960s [source: Gibson, et al.]. As in a 2-D inkjet printer, nozzles in a 3-D printer move back and forth dispensing a fluid. Unlike 2-D 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 3-D object.

Rapid prototyping (RP), which we described earlier in the article, has been a major factor in the growth of direct 3-D 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. 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.].

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Binder 3-D printing, like direct 3-D 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 3-D 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 3-D printing has a few advantages over direct 3-D 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 and Sintering

illustration of selective laser sintering
Selective laser sintering
HowStuffWorks.com

Photopolymerization is a 3-D printing technology whereby drops of a liquid plastic are exposed to a laser beam of ultraviolet light. 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 3-D printing, the SLA repeats this process layer by layer until the print is finished.

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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 3-D printing. SLS relies on a laser to melt a flame-retardant plastic powder, which then solidifies to form the printed layer. This is similar to the mechanism behind 2-D 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 3-D printing has developed and four widely adopted 3-D printing technologies. Next, let's examine the general process of printing three-dimensional objects, which applies no matter what approach you're using.

The 3-D Printing Process

No matter which approach a 3-D 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:

  • Step 1: CAD – Produce a 3-D model using computer-aided design (CAD) software. The software may provide some hint as to the structural integrity you can expect in the finished product, too, using scientific data about certain materials to create virtual simulations of how the object will behave under certain conditions.
  • Step 2: Conversion to STL – Convert the CAD drawing to the STL format. STL, which is an acronym for standard tessellation language, is a file format developed for 3D Systems in 1987 for use by its stereolithography apparatus (SLA) machines [source: RapidToday.com]. Most 3-D printers can use STL files in addition to some proprietary file types such as ZPR by Z Corporation and ObjDF by Objet Geometries.
  • Step 3: Transfer to AM Machine and STL File Manipulation – A user copies the STL file to the computer that controls the 3-D printer. There, the user can designate the size and orientation for printing. This is similar to the way you would set up a 2-D printout to print two-sided or in landscape versus portrait orientation.
  • Step 4: Machine Setup – Each machine has its own requirements for how to prepare for a new print job. This includes refilling the polymers, binders and other consumables the printer will use. It also covers adding a tray to serve as a foundation or adding the material to build temporary water-soluble supports.
  • Step 5: Build – Let the machine do its thing; the build process is mostly automatic. Each layer is usually about 0.1 mm thick, though it can be much thinner or thicker [source: Wohlers]. Depending on the object's size, the machine and the materials used, this process could take hours or even days to complete. Be sure to check on the machine periodically to make sure there are no errors.
  • Step 6: Removal – Remove the printed object (or multiple objects in some cases) from the machine. Be sure to take any safety precautions to avoid injury, such as wearing gloves to protect yourself from hot surfaces or toxic chemicals.
  • Step 7: Postprocessing – Many 3-D printers will require some amount of post-processing for the printed object. This could include brushing off any remaining powder or bathing the printed object to remove water-soluble supports. The new print may be weak during this step since some materials require time to cure, so caution might be necessary to ensure that it doesn't break or fall apart.
  • Step 8: Application – Make use of the newly printed object or objects.

The 3-D Printing Revolution

3-D printed violin, Laurent Bernadac
Laurent Bernadac plays a 3-D printed violin during the 2017 NAMM Show in Anaheim, California. Jesse Grant/Getty Images for NAMM

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Increasing availability and affordability of 3-D printing solutions has made the technology attractive to people across many industries. For example, the automotive industry has used 3-D 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).

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

Engineers in the aerospace industry incorporate 3-D 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 3-D printing: to manufacture aircraft parts themselves, including an entire wing for a large airplane. EADS researchers see this as a green technology, believing 3-D 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]

3-D 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 3-D printing [source: Jotero GbR]. Freedom of Creation (FOC), a company in the Netherlands, sold 3-D 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].

A tastier application of 3-D printing technology comes from the chocolate industry, which has developed machines that can create unique confectionary items. Although unsuitable for mass production, 3-D 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 3-D 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 3-D printing. One thing to note: Printed food has a different texture than traditional food [source: Houser].

Downsides of 3-D Printing

Historically, 3-D 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].

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In addition to price, there are some other drawbacks with 3-D 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 3-D projects also has its own problems. Plastic remnants from 3-D projects likely will end up in landfills and contribute to the Earth crisis with disposable plastic. Further plastic's strength varies and may not be best for all component parts of a project. 3-D 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 3-D printers, including one man who was denied a gun permit earlier. Can steps be taken to prevent people from using 3-D 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.

3-D Printing at Home

homemade 3-D printer, CeBit fair, Germany
Students from the Goethesschule High School present their homemade 3-D printer at the 2015 CeBIT technology trade fair in Hanover, Germany. Sean Gallup/Getty Images

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Although it's still not commonplace 3-D printers are showing up in more homes, libraries, schools and makerspaces.

Prices for these machines have also declined as the technology matures. For example, as of 2019, a MakerBot Replicator Mini+ starts at $1,299 [source: MakerBot]. The company sells small spools of its PLA material in 12 standard colors starting at $18, 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 3-D printing services instead. These services allow you to send in your own CAD files and get back a high-quality production of your object or objects created by an industrial 3-D printer. Online companies that offer 3-D 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 3-D prints of your design. [source: Shapeways, Ponoko]

3-D printing continues to improve as its cost comes down. Perhaps in the future these machines will be commonplace tools used to remedy everyday problems like printing out school projects or printing a new housekey instead of driving to the hardware store for a replacement.

Last editorial update on Sep 25, 2019 05:01:14 pm.

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Sources

  • 3D Systems. "Safety Data Sheet: LaserForm A6 Metal." Jan. 25, 2006. (Sept. 18, 2019) http://infocenter.3dsystems.com/materials/sites/default/files/sds-files/production/sls/Laser_Form_A6_Metal/24123-S12-00-B%2CSDS%2CEU%2CEnglish%2CA6%2C042406.pdf
  • 3D Systems. "ProJet CPX 3000: 100% Real Wax Pattern Production System." 2009. (Sept. 18, 2019) https://web.archive.org/web/20100331113449/http://www.3dsystems.com/products/datafiles/projet/ProJet_CPX_3000.pdf
  • Amputee Coalition. "3=D Printed Prosthetics: Where We Are Today." Feb. 8, 2019 (Sept. 18, 2019) https://www.amputee-coalition.org/3d-printed-prosthetics/
  • Bardwell, Thomas. "ObJet30 Pro 3D Printer Review." 3D Beginners. March 20, 2019 (Sept. 17, 2019) https://www.3dbeginners.com/objet30-pro-3d-printer-review/
  • BasTech. "3D Systems Multijet Plastic Printers." BasTech. (Sept. 16, 2019) http://bastech.com/wp-content/uploads/2017/11/3D-Systems_MJP-Printers-Brochure_201705_BasTech.pdf
  • Economist, The. "3D printing: The printed world." The Economist Newspaper Limited. Feb. 10, 2011. (Sept. 18, 2019) https://www.economist.com/briefing/2011/02/10/the-printed-world
  • Esslinger and Company. "Solidscape Rapid Prototype." 2008. (Sept. 18, 2019) https://web.archive.org/web/20140413152446/http://www.esslinger.com/solidscaperapidprototype.aspx
  • Freedom of Creation (FOC). "About." 2011. (Sept. 18, 2019) https://www.3dsystems.com/blog/foc
  • Gibson, Ian, Rosen, David W., and Stucker, Brent. "Additive Manufacturing Technologies: Rapid Prototyping to Direct Digital Manufacturing." Springer Science+Business Media. 2010. (Sept. 19, 2019) https://doi.org/10.1007/978-1-4419-1120-9
  • Gordon, Leslie. "Designing and 3D Printing a New Kind of Turboprop." Machine Design. Feb. 17, 2010 (Sept. 18, 2019) https://www.machinedesign.com/archive/designing-and-3d-printing-new-kind-turboprop
  • Grimm, Todd. "Fused Deposition Modelling: A Technology Evaluation." T.A. Grimm & Associates. April 2003. (Sept. 18, 2019) http://www.trosol.com/fortus/downloads/WPGrimm.pdf
  • G.W.P. Manufacturing Services AG. "Multi-jet Modeling (MJM)." 2011. (Sept. 18, 2019) https://www.gwp-ag.com/services/prototyping/rapid-prototyping/multijet-modeling/index.html
  • Houser, Franklin. "3D Printed Food: A Culinary Guide to 3D Printing Food." All3DP. (Sept. 16, 2019) https://all3dp.com/1/3d-printed-food-3d-printing-food/
  • Jotero GbR. "Gallery." 2008. (Sept. 18, 2019)http://www.evolution-of-genius.de/gallery/default.htm
  • King, Rachael. "Printing in 3D Gets Practical." Bloomberg Businessweek. Bloomberg L.P.October 6, 2008. (Sept. 18, 2019) https://www.bloomberg.com/news/articles/2008-10-06/printing-in-3d-gets-practicalbusinessweek-business-news-stock-market-and-financial-advice
  • Massachusetts Institute of Technology (MIT). "Licensees of 3D Printing Technology." (Sept. 18, 2019) http://web.mit.edu/tdp/www/licensees.html
  • Ooi, Tian. "Chocolate 3D Printer – All You Need to Know in 2019." All3DP. Jan. 25, 2019 (Sept. 16, 2019) https://all3dp.com/2/chocolate-3d-printer-all-you-need-to-know/
  • Oskay, Windell H. "Sneak Preview: The Evil Mad Scientist 3-D Printer Project." Feb. 24, 2007. (Sept. 18, 2019) http://www.evilmadscientist.com/article.php/3printerpreview
  • Ponoko. "How it works." 2019. (Sept. 18, 2019) http://www.ponoko.com/make-and-sell/how-it-works
  • RapidToday.com. "STL 2.0 May Replace Old, Limited File Format." Rapid Publishing, LLC. 2009. (Sept. 18, 2019) http://www.rapidtoday.com/stl-file-format.html
  • Sauermann, Torolf. "YouTube Channel: Math Art of Torolf Sauermann." (Sept. 18, 2019) http://www.youtube.com/user/torolf44
  • Shapeways. "Shapeways Custom 3D Printing Service." (Sept. 18, 2019) https://www.shapeways.com/create
  • Solidscape. " 3D Printers." (Sept. 17,, 2019) https://www.solidscape.com/products/3d-printers/
  • Stevenson, Kerry. "Solidscape's New S390 High-Rez Jewelry 3D Printer." Fabbaloo. March 14, 2018 (Sept. 17, 2019) https://www.fabbaloo.com/blog/2018/3/14/solidscapes-new-s390-high-rez-jewelry-3d-printer
  • Stratasys, Inc. "PolyJet 3D Printers Systems and Materials." 2018. (Sept. 17, 2019) https://www.stratasys.com/-/media/files/printer-spec-sheets/polyjet-systems-and-materials-overview-en-a4.pdf
  • Whitwell, Tom. "Microtrends: Printing in 3D." Times Online. Times Newspapers, Ltd.. (Sept. 18, 2019)https://www.thetimes.co.uk/article/microtrends-printing-in-3d-zqp736c76kl
  • Wohlers, Terry. "Additive Manufacturing 101: Part I." Time Compression. Gardner Publication, Inc. January/February 2010. (Sept. 17, 2019) http://www.wohlersassociates.com/JanFeb10TC.htm