FIGURE 7.12 A stereolithographed chess piece. SOURCE: Courtesy of Potomac Photonics.
material is needed for the part. The laser wavelength and power can vary between manufacturers but is approximately 325 nm from a low-power He-Cd source. The part is built up in layers until the final geometry is completed.
On completion of the layering process, the part is subjected to high-intensity UV light for the postcuring process, which fully hardens the resin. A chess piece fabricated with stereolithography is shown in Figure 7.12.
Selective laser sintering (SLS) was developed in the mid-1980s and is capable of producing parts from thermoplastics, ceramics, or metals. Like stereolithography, SLS, shown in Figure 7.13, is a layering process that builds a part from a powder based on a three-dimensional CAD model. In the SLS process, a laser fuses the layers of powder in localized areas to create the final part geometry. Although systems vary between manufacturers, the laser used is approximately a 50-W CO2 laser. The process can yield very accurate parts with tolerances of ±0.05-0.25 mm. Components fabricated with SLS require no postprocessing. Figure 7.14 shows a replica of a violin produced with the SLS process.