MM4 RPD RAPID PRODUCT DEVELOPMENT

GROUP 2: SELECTIVE LASER SINTERING

MODULE CONVERNER

DR. MD ENAMUL HOQUE (PHD; NUS, SINGAPORE)

GROUP MEMBERS

AMMIR IYLIA BIN AHMAD NASIR 004618

DANIAL IRFAN BIN BAHARUDDIN 004639

FARWA BINTI MOHAMED KAMAL 004917

MUHAMMAD DOM ASHAARI BIN MUHAMAD 004812

ZARITH SUHAILA BINTI ABD AZIZ 006547

1 Introduction of Selective Laser Sintering (SLS)

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The selective laser sintering (SLS) prototyping methods are usually used to make

complex structure parts for loading test. It was developed by The University of Texas in Austin,

and was commercialized in 1987 as well as was firstly shipped in 1992 (Cooper, 2001). The

basic concept of this technology is it uses a moving laser beam to trace and selectivity sinter

powdered polymer and/or metal composite materials into successive cross-sections of a three-

dimensional part (CUSTOMPART.NET, 2009).

The use of sintering enables people to eliminate tooling cost and drastically reduce the

time and cost of the product development or production. It also is an additive manufacturing

technique that uses a high power laser to fuse a small particles of plastic, metal, ceramic or

glass powder into a mass representing a desired 3-D object (RPWORLD.NET, 2011). This 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 (RPWORLD.NET, 2011). This prototyping can be

used in every stage of the product development cycle, from the production of one-shot models

to functional test parts and small production series (Materialise, 2012). Furthermore, the laser

sintering is suitable for larger amounts components, even for series of 50 to 100 pieces and

more (Materialise, 2012).

Selective laser sintering is reaching new dimensions with the development and

introduction of 3-D systems’ latest DuraForm flame retardant and polypropylene plastics

(3Dproparts, 2011). Parts produced are capable of withstanding harsh test conditions or meet

the toughness requirements of direct manufacturing applications without the need for tools and

fixtures and was acknowledged stronger than Stereolithography (SLA) (eFunda, 2012). This is

because the SLA process is limited to photosensitive resins which are typically brittle compared

to the SLS process which can utilize polymer powders that, when sintered, approximate

thermoplastics quite well (eFunda, 2012).

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2 Description of Selective Laser Sintering (SLS) technology

Rapid product development concept is not a new phenomenon in this contemporary era

of global market. The urge of compromising the demands of the ever-growing consumers has

lead to many positive measures for companies globally to compete in the market. Thus, to meet

the trend, many researches and developments effort were implemented to improve the

traditional way of producing products in terms of not only quality, but also quantity. As to achieve

the realisation of the concept, rapid production technology is recommended and many studies

have further develop the technology itself to introduced a vary type of manufacturing and

fabrication techniques.

Among such technique that is to be highlighted is the Selective Laser Sintering process

as it is one of the most rapidly growing prototyping techniques. It is known to be suitable to

process vary of materials available. Such materials are composites, metals, ceramics and many

more (Kruth et al., 2003).

The process of Selective Laser Sintering starts with the computer-aided designs (CAD)

introduced on the physical and geometrical approach of the prototype desire. The prototype

model produced is then graphically cut into thin layers before sent to the sintering laser where it

is processed to create a ceramic prototype (Heinrich et al., 2002).

The main process concern in this rapid prototyping technology is called sintering. Kang

(2005, pp3) states: “Sintering is a processing technique used to produce density-controlled

materials and components from metal or ceramic powders by applying thermal energy.” He

further said the process is categorized in the synthesis/process element among the well-known

four basic elements of materials science and engineering. In simpler and specifically term,

sintering is a process of creating objects from powder.

According to Materialise.com (2012), the parts of the prototype model are built layer by

layer. Powder layers, of particle sizes in the order of magnitude of 50 µm, are dispersed evenly

on top of one another. Examples of the heat-fusible powder deposited are ceramic powders,

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metal powders, polymer powders and also plastics (Deckard et al., 1992). Powder layers are

then scanned on the surface and the powder particles are bind selectively by a computer

controlled carbon dioxide laser beam. The exposure of the laser will cause rise of temperatures

exceed the glass transition point which leads adjacent particles to flow together

(Materialise.com, 2012). As the laser outline the design specified by the CAD on the layer of

powder across the cross-section, the particles of the powder is sintered when in contact with the

laser beam. The outlined layer is then lowered and new layer of powder is deposited and spread

equally on top of the old layer (PADT.com, 2012). The process is repeated until a final part of a

successive is formed.

The final part formed is then cleaned from the un-sintered powder that surrounds the

prototype model by means of normal paint brush. By doing so, the complete mechanical

assemblies can be made mechanically functional. Based on graphically-computer design

desired, it is possible to obtain a model with trapped volumes that is not reachable by the means

of brush. To remove the powder trapped inside is possible by creating small windows or drain

holes (Paramount, 2012).

The prototype model produced from the Selective Laser Sintering process is well known

for its good attributes. The subject is possible to be in top form in terms of material durability and

resistible to heat and chemical, exceptionally reduction in weight, parts consolidation, quality

assurance, repeatable process controls and many more (Solid Concepts, 2012). Another unique

attributes that changed the rapid prototyping technology paradigms is that it supports models

that is mechanical functional which enables more freedoms in designing, as compared to

conventional technology (Paramount, 2012). Thus with the top attributes, it is widely used in

various types of fields. Such fields are medical, automotive, bioengineering, anatomy and also

many more industries (Berry et al, 1998).

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3 Advantages and limitations of Selective Laser Sintering (SLS) technologyOne of the advantages of Selective Laser Sintering (SLS) is it has a wide range of

material selection including nylon, metals and elastomers (Protocam, 2011). In fact, any

materials that soften due to heat can be used in the SLS process (Kimble, 1992). However, the

type of laser used in the process may be changed depending on the type of materials chosen.

For instance, to produce metal prototype parts, the machine uses a high powered watt fibre

optic laser along with the powder metal in the process (Rapidtoday, 2007).

Furthermore, by using the DuraForm or DuraForm Glass Filled material, the SLS

technology can produce the part of prototype with material properties similar to the injection

molded pieces (Protocam, 2011). The DuraForm material is used to for functional plastic parts

while DuraForm Glass Filled material is used for functional plastic parts with glass filled

(Protocam, 2011).

Another advantage of SLS prototype process is it has ability to produce complex parts

without external supporting structure such as clamping tools. This is possible because the SLS

part is created in a pool of powder material. The unsintered powder material will act as a

supporting structure to the sintered powder and hence will provide stability and firmness along

the SLS process. In addition, the unsintered powder material is easy to remove without

damaging the prototype part once the process is completed (Kimble, 1992).

Next, the SLS fabrication method needs lower maintenance and very cost efficient. The

prototype fabrication process is fully computational and easy to operate. The prototypes are

created directly from 3D Cad models and convert to it into. The cost to operate the process is

low since the materials that are not sintered can be recycled back to the fabrication chamber to

be re-used for the next process (Modelltechnik, 2010). However, the cost of the SLS computer

operated machine could be very high.

The SLS process has also the ability to produce very complex parts at a very high

precision (produce near net shape objects). The layered manufacturing technique used in the

SLS process allowed it to fabricate the part at each layer. Generally, the thickness of each layer

is in between of 0.005 inch to 0.01 inch depending on the complexity of the designed part

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(Kimble, 1992). It is because, the thinner the layer, the higher the precision of the SLS prototype

will be produced.

The other advantages of SLS process is the fabricated prototypes are porous or lower in

density. Typically, a fabricated prototype produced using the SLS technique is 60% lower in

density compare to the same fabricated prototype produced using molding technique

(Protosystech, 2005). Therefore, the fabricated prototype will be light in weight but impairing

their strength and surface finish.

However the uses of selective laser sintering technology also has its own limitations.

One of the disadvantages of Selective Laser Sentering (SLS) is it has a rough surface finish.

The SLS details are not as crispy and as sharp as fabricated prototype produced by Stereo

Lithography or molding process (Modelltechnik, 2010). This is because; the basic principal

behind the SLS process is the melting of powder bead material by laser beam to form a firm

layer (Kimble, 1992). However, a better surface finish of the prototype could be achieved by

increasing the sintering speed at each layer of the bead material (Taimisto, 2009).

Another disadvantage of Selective Laser Sintering is the accuracy of the fabricated

prototype is depending on the thickness of the layer (Kimble, 1992) and the size of the powder

particles (Taimisto, 2009). Therefore, to fabricate a complex designed prototype, the thickness

layer must be very thin and the size of the powder particle must be small. In addition, a smaller

size bead particle will have lower porosity and thus, the infiltration to fill the void by other bead

particles can be avoided (Oglemodels, 2011).

Generally, the mechanical properties achieved by the SLS fabricated prototype is below

than the injection molding method. The fabricated prototype using the SLS fabrication method

will be having more voids appearing in the prototype (the fabricated prototypes are porous).

Hence, the voids that exist in the prototype will weaken its mechanical properties (Protosystech,

2005). In order to increase the strength of the prototype, the infiltration of other particles to fill

the void is usually implemented (Oglemodels, 2011).

The other disadvantage of selective laser sintering technology is the involvement of nitrogen in

the SLS process. In order to avoid oxidation of the material, inert gases are usually inserted into

the fabrication chamber of the SLS machine (Taimisto, 2009). Usually, nitrogen gas is selected

to fill the fabrication chamber. If not properly maintained and supervised, explosion could

happen when high volume of powder material is involved (Ferris, 2011). Due to that, expertise

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and professional supervision on the SLS operation is necessary to avoid this incident from

occur.

Besides, the limitation in SLS technology is its speed to complete a process. A SLS

fabrication method is actually a fairly fast build time method (Protosystech, 2005). However, the

speed to complete a process is depending on the complexity and the thickness of the powder

material. As mentioned before, the range of thickness of each layer is in between of 0.005 inch

to 0.01 inch. A 0.005 inch layer thickness will take twice the time needed for a 0.01 inch to

complete excluding the geometry (complexity) factor (Kimble, 1992). So, as the size, thickness

and complexity increase, the time needed to finish as process will be increased too.

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4 Recent case studies using Selective Laser Sintering (SLS) technology

The selective laser sintering have been developed since the mid of 1980's and the

technology grew rapidly over the years. The selective laser sintering have been use in many

applications be it in architecture, medical, automotive, manufacturing, additive manufacturing

and art and sculpture models.

One of the latest applications of the selective laser sintering is the SULSA (Southampton

University Laser Sintered Aircraft) which is an unmanned air vehicle. This is the first aircraft

made entirely with 3D printing and it was made within a week time. The entire structure of the

aircraft was printed using the laser sintering machine including wings, integral control surfaces

and access hatches which fabricates plastic or metal objects building up the item layer by layer.

It has been said that no fasteners were used and all the parts and equipment was attached

using snap fit techniques which allowed the entire craft to be put together without tools in

minutes. The electric-powered aircraft has a 2 meters wingspan, top speed of nearly 100mph

which glides silently in a cruise mode. It is also equipped with a miniature autopilot. The method

of creating this aircraft is by producing a computerized design first. It was then fed to a 3D

printer which cut up the model into ultra thins slices. The layers were then build up from plastic

powder using laser (selective laser sintering) to carve up and fused each one's shape. Laser

sintering gives an advantage of allowing designers to create shapes, structures of a highly-

tailored aircraft that would normally involve costly traditional manufacturing techniques in a short

period of time. The using of snap fit allows a changes in the structure and design of the craft be

made with no extra cost. (Southampton, 2011)

Another latest invention of selective laser sintering is the precise fabrication of dental

components such as the crowns, bridges, bridges framework, dental restorations and implants.

Similar to the SULSA creation, the set of geometric data for the dental components is provided

for 3D description and a 3D CAD model is created. The CAD model then is processed in the

form of layered data to generate numerous layers. The laser sintering process is carried out

according to the data layer for each CAD model layer where along with the assistance of a

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computer, the powdered material used for laser sintering is correspondingly applied in layers on

a fabrication platform. The body of the dental component is then transferred to a heat treatment

oven, heated and then cooled. The advantage of using this SLS is that it can further minimize

the currently existing production tolerances at the same time increasing the efficiency of the

fabrication. This invention allows the material structure of the body to undergo relaxation on the

fabrication platform, where the surface after treatment of the body can be carried out straight

away while it is still on the platform automatically with precisions once more using the 3D data

that has already present when creating the CAD model with the assistance of the computer.

(Hintersehr, 2010)

Another use selective laser sintering is the creation of grids for selective transmission of

electromagnetic radiation (X-ray) which is important in medical imagining devices such as

computed tomography scanners (CT), standard X-ray scanners, mammography, single photon

emission computed tomography devices (SPECT) or positron emission tomography scanner

(PET). These grids can be found placed in between a source of electromagnetic radiation and a

radiation-sensitive detection device. The grid is use to selectively reduce the content of a certain

kind of radiation that must not impinge onto the radiation-sensitive detection device. The

advantages of using selective laser sintering in creating these grids is that it allows a large

design freedom which has a complex 3D structure that is not easily achievable by conventional

molding techniques. The creation of these grids starts by providing the 3D data, followed by the

CAD model for the grid for selective transmission of electromagnetic radiation. The structural

elements comprising a plurality of the particles are provided where then the particles/powder is

sintered together creating pores in between the neighbouring particles. A liquid is then inserted

into the pores to solidify the materials. (Vogtmeier & Dorscheid, 2011)

These are only a few recent invention of the application of selective laser sintering.

There are a lot more new application of SLS technology as the technology is still rapidly grow

for years to come. The use of selective laser sintering helps to create parts/ structures in less

time and costs and very helpful in creating structures that is complex using conventional

techniques.

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5 Future Directions of Selective Laser Sintering (SLS) technology

Laser sintering technology is a new technology which enables complex design of a

product simply through a software without any need for expensive tooling. The reliability of this

technology coupled with its cost effectiveness had lead manufacturers to believe that laser

sintering would have a bright implication in the future of manufacturing industries (Nobert S.,

2011)

One of the future directions of laser sintering is its application in the manufacture of

medical equipment. Medical equipment such as a retractor requires very particular design and

has very complex geometries as well as hollow channels which are difficult to be design using

normal manufacturing tools. Thus by using laser sintering technology, manufacturers are able to

draw the 3D prototype with ease without having any problems with the complexity of the medical

equipment designs. Medical equipment are required to be sterilized and cleaned after each use,

which makes the implementation of RFID chips into medical equipment as the best option to

monitor the processing of the equipment (Nobert S., 2011). By using normal mechanical design,

the RFID chips usually needs to have an opening above them when layered with a metal cast in

order for the signal to be read. This however is not ideal for surgical instrument since opening

may cause fluid to enter the opening during use of the instrument. Laser sintering in the other

hand enables RFID chips to be fully covered by metal cast without having the problem to

receive and transmit data from the chip (Imgrund P. 2011) .The RFID chips are also permanently

imbued into the instrument without having any risk of being removed.

Besides being useful in the developing 3D prototypes, research on laser sintering

technology had shown that the technology may also be able to develop finish product by using

direct metal laser sintering (DMSL) in which metal are sintered into the product directly with

laser. This future application not only saves the cost of developing new equipment, it also saves

a lot of time used in development as well as improving the quality of the developed products

(The Economist, 2011). The quality of developed products directly from laser sintering

technology is enhanced as there are no manufacturing constraints as opposed by normal

manufacturing method. Andy Hawkins, lead engineer of EADS projects says that by using laser

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sintering, the development of finish product is easier as you can accurately allocate the where a

certain material is needed and where it is not . This helps develop a product which uses just the

right amount of material and would efficiently save raw materials since it eliminates the excess

use of material. The problem of excess use of material causes the product developed to look

bulky which may not be aesthetically appealing, but by using DMSL technology, the excess

material is not present thus producing a more elegant and appealing product (FILTON, 2011).

Developers also predict laser sintering to heavily affect the development of bio-material

used in medicine. Research had shown that by laser sintering technology, implants as well as

bone scaffold are able to be directly fabricated using bio-composite material such as bio-

degradable polycarbonate and bioactive ceramic composites (Paulo B., 2008). Laser sintering is

also able to perfectly develop an established bio-composite material known as HAPEX. In

addition, the research on this technology also shows potential in developing bioactive implants

which is used in bone replacement as well as tissue growth. There are also possibilities of

creating hybrid biological/artificial materials which may enable the control of bone growth as well

as regeneration mechanisms (Bidanda B. 2008)

Laser sintering future direction shows the wide spectrum of advantages it may lead to in

the manufacturing of different type of equipment. Research had also been done on the

technology itself to further improvise laser sintering technology in the future. An example on the

future improvisation includes the use of different types of laser to enhance the control of the

machinery as well as minimizing the thermal damage upon material worked on (Kooper G.

2001). Some of the lasers types that are anticipated to be develop are chemical oxygen-iodine,

diode-pumped Nd-Yag, crystal generated harmonics, direct diode and copper vapor lasers.

These different types of lasers may also improve the dimensional accuracy and tolerance of the

product as they have smaller wavelengths which enable the focusing of the laser diameter to

design small and complex features.

There are a lot of researches on the endless possibilities of laser sintering in the future.

This research covers not only the basic mechanical manufacturing enhancement, but it also

covers the development of manufacturing in the field of bio-medical, agriculture and

architecture. Thus, laser sintering shows a bright promising future in the field of manufacturing

and enables the development of ideas without constraint while also improving quality, cost

effectiveness as well as productivity of the product (EOS, 2012).

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WORDS COUNT: 3450

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Number of references: 34

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