Powder-Based Additive Manufacturing Systems

D Systems’ Selective Laser Sintering (SLS)

Selective laser sintering (SLS) was invented and patented by Dr. Carl Deckard and academic adviser Dr. Joe Beaman at the University of Texas, Austin, in the mid- 1980s, sponsored by DARPA. Deckard and Beaman participated in the resulting start-up company DTM, which was set up to design and manufacture SLS machines. In 2001, DTM was acquired by 3D Systems, the biggest competitor for DTM and SLS technology. The latest patent on Deckard’s SLS technology was issued on 28 January 1997 and expired on 28 January 2014.

Technology

Selective laser sintering (SLS) printers from 3D Systems can perform rapid prototyping and produce high-resolution nylon parts up to seven times quicker than competing SLS 3D printers. The ability of SLS to manufacture many parts at once also makes the process a good choice for products needing strength and heat resistance from direct digital manufacturing (DDM) products. Additive production layer technology SLS involves the use of a high-power laser (e.g. carbon dioxide laser) to fuse small particles of plastic, metal, ceramic, or glass powder into a mass that has the desired three-dimensional shape. The laser selectively fuses the powdered material to the surface of the powder bed by scanning cross-sections created from a 3D digital representation of the object (e.g. from a CAD file or scan data). Once each cross-section is checked, one layer thickness lowers the powder bed, a new layer of material is applied to the rim, and the process continues until the portion is finished. The SLS system usually uses a pulsed laser because the final component density depends on peak laser power rather than laser duration.

The SLS system heats the bulk powder content well below its melting point in the powder bed, making it much simpler for the laser to raise the temperature of the selected regions to the melting point the rest of the way. Figure 5.1 shows the process of selective laser sintering (SLS).

In comparison to some other additive manufacturing techniques, such as stereolithography (SLA) and fused deposition modeling (FDM), which most often require specific support structures for the manufacture of overhanging designs, SLS does not need a different feeder for supporting material because the part being constructed is surrounded by uninterrupted powder at all times, which allows for the construction of a previous feeder.

Selective laser sintering (SLS)

FIGURE 5.1 Selective laser sintering (SLS).

Also, since the chamber of the machine is always full of powder material, the manufacture of various parts has a much lower impact on the overall difficulty and price of the design because, by means of a method known as “Nesting,” various parts can be positioned to fit within the limits of the machine. One design feature that should be noted, however, is that it is “impossible” for SLS to produce a hollow but fully enclosed element. This is because the uninterrupted powder cannot be drained inside the element.

 
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