How 3-D Printing Works

Some day, you might be able to print out new house keys and other three-dimensional items on a printer like this one (or an even smaller version) from the comfort of your home office.
Some day, you might be able to print out new house keys and other three-dimensional items on a printer like this one (or an even smaller version) from the comfort of your home office.
Photo courtesy of Stratasys, Inc.

Imagine that you've decided to organize your closet, but instead of measuring containers at a store to make sure they will work, you just go to your office, enter the measurements you want your containers to be, and print them out right there. Now imagine that you have to build a diorama of a famous Civil War battle for a project at school, and you use that same printer to construct all the soldiers, cannons and trees in perfect detail.

This technology may be closer than you think thanks to 3-D printing. 3-D printing is making it easier and faster to produce complex objects with multiple moving parts and intricate design, and soon it will be affordable enough to have at home.

Additive manufacturing (AM) is the family of manufacturing technology that includes 3-D printing. 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 3-D printing because it seems to be the most common term used to describe AM products.

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 allowed 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 February 2011, 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, SC, 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 such as Z Corporation, Objet Geometries and Stratasys have also brought innovative new products to 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 [source: The Economist]. 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. The processes are getting faster, the materials and equipment are getting cheaper, and more materials are being used, including metals and ceramics. Printing machines now range from the size of a small car to the size of a microwave oven.

3-D printing and other forms of AM are still new players in the field of manufacturing. 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

3-D binder printing
3-D binder printing

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.]. Like 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, and all of them use waxy compounds. 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 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 [source: Gibson, et al.]. 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 materials in the process, including metals and ceramics, as well as color.

Photopolymerization and Sintering

Selective laser sintering
Selective laser sintering

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. For more details on this process, see our article How Stereolithography 3-D Layering Works.

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 a product called LaserForm A6 metal from 3D Systems [source: 3D Systems, "A6"]. The objects created by the 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:]. 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 2-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

An engine manifold prototype created by PTCAM using 3-D printing
An engine manifold prototype created by PTCAM using 3-D printing

If you do a Web search for 3-D printing, you'll notice that its uses are growing exponentially. One reason for this growth is that manufacturers are increasingly relying on 3-D printing to make prototypes and parts for large 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).

Another reason 3-D printing is growing is because innovative professionals outside of large industrial manufacturing have found ways to use it in their own fields. For example, Bespoke Prosthetics in San Francisco, CA, is using 3-D printing to create unique prosthetic limb coverings [source: Bespoke]. They're also experimenting with 3-D printing as a way to produce entire limbs that are much cheaper than conventional prosthetics and are even dishwasher-safe [source: Vance]. 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].

Engineers in the aerospace industry are incorporating 3-D printing for some large-scale product improvements. The industry is already using rapid prototyping to help test and improve its designs as well as to show off how well they work [source: Gordon]. Aerospace 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 [sources: Sauermann, Jotero GbR]. Freedom of Creation (FOC), a company in the Netherlands, sells several 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].

Costs of 3-D Printing

Historically, 3-D printing has been an expensive technology. PTCAM's SLA, described earlier in the article, cost in excess of $250,000; the liquid plastic cost 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 February 2011, 3D Systems' ProJet CPX 3000was selling for $79,999 and it could produce highly-detailed models up to 11.75 inches by 7.3 inches by 8 inches (298 millimeters by 185 millimeters by 203 millimeters) [sources: Rapid Direction, "ProJet", 3D Systems, "ProJet"]. That price doesn't include the required VisiJet CPX200 Wax Build Material, which costs $975 for a 4-cartridge case [source: Rapid Direction, "VisiJet"].

Dimension 3-D printers from Stratasys, Inc., demonstrate how 3-D printing can be even less expensive. The Dimension Elite printer, for example, can create production-grade plastic models up to 8 inches by 8 inches by 12 inches (203 millimeters by 203 millimeters by 305 millimeters) starting at $29,900 [source: Stratasys, "Elite"]. In addition, the ABS Plus plastic printing material, required for use in the Dimension Elite, comes in nine different colors and can be used even in Stratasys' desktop-sized uPrint printers, priced from $14,900 [source: Stratasys, "uPrint"].

Not only is 3-D printing getting cheaper within its own category, it's also a more cost-effective way to produce products previously made using other technologies. For example, Solidscape targets dental labs for some of its small 3-D printers [source: Solidscape]. These models cost $30,000 to $60,000, and build and support materials cost a few hundred dollars more [source: Esslinger]. These and other types of 3-D printers can craft molds for crowns, bridges and dentures faster and with greater accuracy than older methods, increasing a dental lab's productivity [source:].

3-D Printing at Home

Now that you're aware of common 3-D printing technologies and how different industries are employing them, you might be wondering how soon you can start printing a custom-designed computer mouse, toy trucks for the kids or the perfect toolbox from your home office. As we've seen, 3-D printing is expensive, both in terms of machinery and materials. Products like V-Flash however, are paving the way to affordable 3-D printing at home. The V-Flash Personal 3-D Printer weighs under 150 pounds, builds objects up to 9 inches by 6 and three-fourths inches by 8 inches (228 millimeters by 171 millimeters by 203 millimeters) and is small enough to sit on a table in your office [source: 3D Systems, "V-Flash"]. V-Flash is available from 3D Systems for $9,900, making it more affordable than other 3-D printers currently on the market. The building material for V-Flash is a durable plastic called film transfer resin (FTI); a 1.8 kg cartridge can be purchased for $850. In addition to the material, you'll need the build pads that the machine uses as the starting surface on which to print the first layer. These pads cost about $95 for a set of 20. [source: ProParts]

If the cost of V-Flash is out of reach for your home use, you have a few other options available to you. Some enthusiastic makers and do-it-yourself enthusiasts have come up with their own solutions. For example, physicist and blogger Windell Oskay built his own 3-D printer in 2007 that fabricates objects from sugar using a sintering approach [source: Oskay]. The project, called CandyFab, has a dedicated Web site at

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 develop and grow and is becoming an increasingly popular and more affordable way to produce prototypes and finished products. In the near future, a kid could be using 3-D printers in school to build miniature replicas of Mount Rushmore -- and you could be printing your own copies of your house key rather than making a trip to the hardware store.

For lots more information about 3-D printing, head on over to the next page.

Related Articles

More Great Links


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