Selective laser sintering is an additive manufacturing technique that uses a laser as the power source
to sinter powdered material, aiming the laser automatically at points in space defined by
a 3D model, binding the material together to create a solid structure. It is similar
to direct metal laser sintering; the two are instantiations of the same concept but differ
in technical details. Selective laser melting uses a comparable concept, but in SLM the
material is fully melted rather than sintered, allowing different properties. SLS is a relatively
new technology that so far has mainly been used for rapid prototyping and for low-volume
production of component parts. Production roles are expanding as the commercialization
of AM technology improves.
History Selective laser sintering was developed and
patented by Dr. Carl Deckard and academic adviser, Dr. Joe Beaman at the University
of Texas at Austin in the mid-1980s, under sponsorship of DARPA. Deckard and Beaman were
involved in the resulting start up company DTM, established to design and build the SLS
machines. In 2001, 3D Systems the biggest competitor of DTM and SLS technology acquired
DTM. The most recent patent regarding Deckard's SLS technology was issued 28 January 1997
and expired 28 Jan 2014. A similar process was patented without being
commercialized by R. F. Housholder in 1979. Technology
An additive manufacturing layer technology, SLS involves the use of a high power laser
to fuse small particles of plastic, metal, ceramic, or glass powders into a mass that
has a desired three-dimensional shape. The laser selectively fuses powdered material
by scanning cross-sections generated from a 3-D digital description of the part on the
surface of a powder bed. After each cross-section is scanned, the powder bed is lowered by one
layer thickness, a new layer of material is applied on top, and the process is repeated
until the part is completed. Because finished part density depends on peak
laser power, rather than laser duration, a SLS machine typically uses a pulsed laser.
The SLS machine preheats the bulk powder material in the powder bed somewhat below its melting
point, to make it easier for the laser to raise the temperature of the selected regions
the rest of the way to the melting point. Unlike some other additive manufacturing processes,
such as stereolithography and fused deposition modeling, SLS does not require support structures
due to the fact that the part being constructed is surrounded by unsintered powder at all
times, this allows for the construction of previously impossible geometries.
Materials and applications Some SLS machines use single-component powder,
such as direct metal laser sintering. Powders are commonly produced by ball milling. However,
most SLS machines use two-component powders, typically either coated powder or a powder
mixture. In single-component powders, the laser melts only the outer surface of the
particles, fusing the solid non-melted cores to each other and to the previous layer.
Compared with other methods of additive manufacturing, SLS can produce parts from a relatively wide
range of commercially available powder materials. These include polymers such as nylon or polystyrene,
metals including steel, titanium, alloy mixtures, and composites and green sand. The physical
process can be full melting, partial melting, or liquid-phase sintering. Depending on the
material, up to 100% density can be achieved with material properties comparable to those
from conventional manufacturing methods. In many cases large numbers of parts can be packed
within the powder bed, allowing very high productivity.
SLS technology is in wide use around the world due to its ability to easily make very complex
geometries directly from digital CAD data. While it began as a way to build prototype
parts early in the design cycle, it is increasingly being used in limited-run manufacturing to
produce end-use parts. One less expected and rapidly growing application of SLS is its
use in art.
See also 3D printing
Desktop manufacturing Digital fabricator
Direct digital manufacturing Fab lab
Instant manufacturing, also known as "direct manufacturing" or "on-demand manufacturing"
Rapid manufacturing Rapid prototyping
RepRap Project Solid freeform fabrication
Von Neumann universal constructor References
External links DMLS – DEVELOPMENT HISTORY AND STATE OF
THE ART Selective Laser Sintering, Birth of an Industry