This technology positions a perforated platform just below the surface of a vat of liquid photocurable polymer. A UV laser beam then traces the first slice of an object on the surface of this liquid, causing a very thin layer of photopolymer to harden. The perforated platform is then lowered very slightly and another slice is traced out and hardened by the laser. Another slice is created and then another, until a complete object has been printed and can be removed from the vat of photopolymer, drained of excess liquid, and cured. Stereolithographic printers remain one of the most accurate types of hardware for fabricating 3D output, with a minimum build layer thickness of only 0.06mm (0.0025 of an inch).
One of the appealing aspects about SL is that a functional part can be created in just one day. Most SL machines can produce parts with a maximum size of approximately 50 cm x 50 cm x 60 cm (20″ x 20″ x 24″). Prototypes made by stereolithography can be very beneficial as they are strong enough to be machined and can be used as master patterns for injection molding, thermoforming, blow molding, and also in various metal casting processes. Although stereolithography can produce a wide variety of shapes, the process is often expensive – the photo-curable resin costs anywhere from $80 to $210 per liter. A stereolithography machine can cost from about $100,000 to more than $500,000.
Fused Deposition Modeling (FDM)
Using this method, hot thermoplastic is extruded from a temperature-controlled print head to produce fairly robust objects to a high degree of accuracy. A key benefit of this technique is that objects can be made out of exactly the same thermoplastics used in traditional injection molding. Most FMD 3D printers can now print with both ABS (acrylonitrile butadiene styrene) plastics, as well as a biodegradable bioplastic called PLA (polylactic acid) that is produced from organic alternatives to oil.
Selective Laser Sintering (SLS)
This process builds objects by putting down a fine layer of powder and then using a laser to selectively fuse some of its granules together. At present, SLS 3D printers can output objects using a wide range of powdered materials. These include polystyrene, nylon, glass, ceramics, steel, titanium, aluminum and even sterling silver. During printing non-bonded powder granules support the object as it is constructed. Once printing is complete, most excess power is then recycled. (A closely related 3D printing technique to SLS is known as selective laser melting. This uses a laser to fully melt the powder granules that form a final object, rather than just heating them enough to fuse them together). Compared to other methods of additive manufacturing, SLS can produce parts from a relatively wide range of commercially available powder materials.
Multi-Jet Modeling (MJM – 3DP)
Similarly, this method builds up objects from successive layers of powder with an inkjet print head used to spray on a binder solution that selectively glues only the required granules together. Some MJM printers can spray on four different colors of binder solution. This allows them to create full-color 3D objects at up to 600x540dpi.
Top Image Courtesy of MakerBot