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.