This document provides an overview of selective laser sintering (SLS), including its definition, principles, procedures, applications, advantages/disadvantages, and future potential. SLS is an additive manufacturing technique that uses a high-power laser to fuse powdered materials like plastic, metal, ceramic, or glass into solid 3D objects by selectively melting layers of powder according to a CAD model. SLS can produce complex geometries without support structures and allows multiple parts to be built simultaneously.

1. Major Assignment
Sub – Production Engineering II
Topic – Laser Sintering
Session – 2015 - 2016
Submitted To –
Mr. Aditya Mishra
Asst. Proff.(Mech. Dept.)
Submitted By-
Kanishka Gaur
U.I.D.- K10805
B.tech, Civil Engg.
Sem - VI, Year - III

2. Index
 Introduction
 Definition
 Principle
 Procedure
 Industrial Application
 Advantages/Disadvantages
 Recent trends
 Future Scope
 Conclusion

3. Introduction
 Selective laser sintering (SLS) is an intelligent manufacturing
process based on the use of powder coated metal additives,
a process generally used for rapid prototyping and
instrumentation. A continuous Laser beams are used or
pulsating as heating source for scanning and aligning
particles in predetermined sizes and shapes of the layers.
 The geometry of the scanned layers corresponds to various
sections of the models established by computer-aided design
(CAD) or from files produced by stereo-lithography (STL).
After scanning the first layer, the scanning continues with the
second layer which is placed over the first, repeating the
process from the bottom to the top until the product is
complete.

4.  SLS is known also as solid free and open shape
manufacturing process, as a layer fabrication technology,
rapid prototyping technology, a selective sintering of metal
powders.
 SLS is reactive when using a chemical reaction of mixing
components in the presence of a laser and a selective laser
melting (SLM), a direct metal laser sintering (DMLS) or direct
metal laser re-melting, when the complete melting of
powders is pervasive over the solid state dust sintering. This
process was also used in manufacturing moulds, rapid
handling of electrodes manufactured, polymer moulds, die
casting, die casting of titanium zirconium, bio-medical
applications, pieces of zirconium-titanium (PZT) and sheet
metal parts.
 Currently, the experiments in the laboratory of INCDMTM and
dedicated magazines and articles draw attention to a new
comprehensive, integrated approach, of the SLS process

6. Definition
 One of the technologies used by today's 3D printers is called
selective laser sintering (SLS). During SLS, tiny particles of
plastic, ceramic or glass are fused together by heat from a
high-power laser to form a solid, three-dimensional object.
 The SLS process was developed and patented in the 1980s by
Carl Deckard — then an undergraduate student at the
University of Texas — and his mechanical engineering
professor, Joe Beaman.
Additive manufacturing, or 3D
printing, is the process of turning
digital designs into three-dimensional
objects. It is a convenient and
affordable way to make prototypes as
well as finished products, making it
popular with businesses, hobbyists and inventors.

7. Principle
 An additive manufacturing layer technology, SLS involves the
use of a high power laser (for example, a carbon dioxide 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 (for example from a CAD file or scan data) 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.

8.  In contrast with some other additive manufacturing processes,
such as stereolithography (SLA) and fused deposition modeling
(FDM), which most often require special support structures to
fabricate overhanging designs, SLS does not need a separate
feeder for support material because the part being constructed
is surrounded by unsintered powder at all times, this allows for
the construction of previously impossible geometries. Also, since
the machine's chamber is always filled with powder material the
fabrication of multiple parts has a far lower impact on the overall
difficulty and price of the design because through a technique
known as 'Nesting' multiple parts can be positioned to fit within
the boundaries of the machine. One design aspect which should
be observed however is that with SLS it is 'impossible' to
fabricate a hollow but fully enclosed element. This is because
the unsintered powder within the element can't be drained.
 Since patents have started to expire, affordable home printers
have become possible, but the heating process is still an
obstacle, with a power consumption of up to 5 kW and
temperatures having to be controlled within 2 °C for the three
stages of preheating, melting and storing before removal.

10. Procedure
 Just like the Stereolithography (SLA) technology, Selective
Laser Sintering is an additive manufacturing technique which
can be used to turn digital CAD designs into 3-Dimensional
objects.
 The printing process in Selective Laser Sintering (SLS) is
however not quite the same as that used in
Stereolithography.
 In SLA, an ultraviolet curable photopolyme resin is used
instead of powder and an ultraviolet laser is used to cure the
liquid into a solid object.
 When it comes to SLS on the other hand, powdered is
heated by a high powered laser at just below its melting
point. This causes the powders to sinter together forming the
solid 3D model which was intended to be made.

12. Industrial Application
 Digital Manufacturing
Produce models directly from digital files. Any deviations form
the ideal model can be easily corrected and applied to
your next SLS prototype.
 High-Temperature Resistance
High temperatures often ruin prototypes. They are typically
unable to withstand the additional stress, causing issues in
testing as well as R&D. With SLS prototypes, high
temperatures can be tolerated to enhance the realness of your
prototype.
 Complex, Thin-Wall Ductwork
SLS prototyping technologies can produce large, durable
models. They are also capable of delivering miniscule, intricate
prototypes, with no deviation in quality or durability.

13.  Rapid Manufacturing
The material selection of SLS technology provide a whole
array of rapid manufacturing possibilities, including aerospace
hardware, medical and healthcare products, military hardware,
and consumer goods.
 Concept Models
A concept model is used when time and cost effectiveness
constraints are more important than cosmetics and accuracy.
We can develop CAD files.
 Production Parts Without Tooling
The durability of the materials, as well as the ability to
prototype metal mean the tooling step can be skipped with an
SLS production process.

14. Advantages/Disadvantages
 First of all, there is no need for supports when printing
overhanging, unsupported structures (e.g. the horizontal
parts of a capital letter F). The powder itself provides the
necessary support. Second, parts can be created out of a
wide selection of materials. And lastly, complexity isn’t an
issue as long as you can remove the not sintered powder.
 Next are some of the disadvantages of SLS. The biggest
problem of the technology is that the fabricated parts can be
porous and/or have a rough surface depending on the used
materials. Another problem, mainly for polymer parts, is
thermal distortion. This can cause shrinking and warping of
fabricated parts. These are two things to keep in mind when
designing products to be fabricated using SLS printers.

15. Recent trends
 3D printing is an additive technology in which objects are
built up in a great many very thin layers. The first commercial
3D printer was based on a technique
called stereolithography. This was invented by Charles Hull
in 1984. Stereo lithographic 3D printers (known as SLAs or
stereolithography apparatus) position a perforated platform
just below the surface of a vat of liquid photopolymer. 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 then 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. Stereo lithographic 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).

16. Future Scope
 Imagine a future in which a device connected to a computer can
print a solid object. A future in which we can have tangible
goods as well as intangible services delivered to our desktops or
high-street shops over the Internet. And a future in which the
everyday "atomization" of virtual objects into hard reality has
turned the mass pre-production and stock-holding of a wide
range of goods and spare parts into no more than an historical
legacy.
 Such a future may sound like it is being plucked from the worlds
of Star Trek. However, while transporter devices that can
instantaneously deliver us to remote locations may remain a
fantasy, 3D printers capable of outputting physical objects have
been in both development and application for over three
decades, and are now starting to present a whole host of new
digital manufacturing capabilities. 3D printing may therefore
soon do for manufacturing what computers and the Internet
have already done for the creation, processing and storage of
information.

17. Conclusion
 Since its emergence, the SLS has attracted attention from
both researchers and users. As a result, various aspects of
the processes and materials used for SLS sintering have
been studied and there have been established that this is a
modern and at the same time also a rapid means for
prototyping and manufacturing.