Process, Materials, Application Areas

Selective Laser Sintering (SLS) is a technique that uses laser as power source to form solid 3D
objects. This technique was developed by Carl Deckard, a student of Texas University, and his
professor Joe Beaman in 1980s. Later on they took part in foundation of Desk Top
Manufacturing (DTM) Corp., that was sold to its big competitor 3D Systems in 2001. SLS in
some way is very similar to Selective Laser Sintering. The main difference between SLS and
SLA is that it uses powdered material in the vat instead of liquid resin.
Unlike Stereolithography and Fused Deposition Modeling, Selective Laser Sintering does not
require the use of support structures, therefore cutting the amount of materials that one
needs to provide for the print. The object is, in fact, printed while being constantly surrounded
by not sintered powder.
The mere process involves a laser which is used to selectively sinter a layer of granules,
consequently binding together the material to create a solid form. At the end of the process,
the object can very hot and therefore it will be left to cool off before being removed from the
machine.

The use of SLS technology makes it possible to involve a variety of materials which range from
nylon, glass and ceramics, to aluminium, silver and even steel. However, some of them, like
ceramics, are not laser sintered. A binder, in this case, is used to glue parts together and this
is usually known as “Powder & Binder-based 3D Printing”.
The starting process of this technology is quite similar to Laser Sintering: a roller puts a thin
layer of powder on a platform. However, instead of a laser beam, a special print head places
a binding agent at specific points, printing a thin layer of your model that is able to bind to
subsequent layers. This process is then repeated over and over again until your model is
complete.
Since in this case the model was only "glued" together, some post processing is. The exact
post-processing steps heavily depend on the material: Multicolour models get a bath in
superglue, Ceramic prints are put in a drying oven and fired several times, High Detail Stainless
Steel and Steel objects are placed in an oven for fusing. Steel models are additionally infused
with Bronze for extra strength.

Areas of application of SLS technology range from the automotive sector to the consumer
goods sector. More specifically, it can be used in the case of product development and rapid
prototyping in a wide range of commercial industries, as well as limited-run manufacturing of
perfect for small batches production.
only
end-use parts. In the aerospace industry, for example, SLS is involved to build prototypes for
aircraft components. This represents a great advantage for companies because airplanes are
produced in small quantities since airlines companies, for example, use them for quite a long
time. Therefore, it is not cost-effective for production companies to build physical moulds for
airplane parts. In fact, these moulds would be too expensive to make and would then need to
be stored for long periods of time without being damaged or corroded.

Success with titanium would be one example of huge future opportunities with the military,
aerospace, medical and other industries looking to utilize titanium’s light weight, strength and
corrosion resistance. Much of the ground-breaking activity in 3D printing has utilized plastics
and moving from plastics into metals of all types is the next step.

Strengths and Weaknesses

One of the very first pros that Selective Laser Sintering presents is the fact that it makes no
use of support structures, as it is fully self-supporting. It therefore allows parts to be built
within other parts in a process called nesting. This has two main outcomes; the first one is that
it reduces the costs of the material which would therefore be used in order to provide support
structures, greatly used in the FDM technology. The second advantage in this case is that SLS
can handle a high complexity of geometry. Some products are that complex that without this
technology it would be complicated to produce them.
Generally, SLS is considered the 3D printing technology with the fastest additive
manufacturing process for printing functional, durable prototypes and end user parts.
Durability is, moreover, supported by the use of strong materials like nylon, which also allows
moulding plastics.
market.
a certain freedom in the functionality of the final 3D print. Besides, thanks to its excellent
mechanical properties, the material used in SLS is often a substitute of typical injection
At the same time, SLS produces parts which are generally rated to be very strong and stiff,
with good chemical resistance. Complex parts with interior components, channels, can be
built without trapping the material inside and altering the surface from support removal.
Accuracy is another important advantage of SLS technology. Final 3D prints present, usually,
a high accuracy. The required process is also fast, compared to the already analysed
technologies. At the same time, scalability allows to use SLS for a single part of component,
but also and easily for dozens of production pieces. Parts can be usually shipped between 1
and 4 days, which is a great advantage for companies who are required to be quick in the
However, usually SLS prints present a certain surface porosity hence why, just like in Fused
Deposition Modeling, post-processing is definitely required.