Stereo lithography - Report

SKIT,Jaipur
| S t e r i o l i t h o g r a p h y a n d i t s a p p l i c a t i o n i n M e d i c a l S c i e n c e
“Stereolithography & its application in Medical Science.”
A
Seminar Report
Submitted in partial fulfillment
For the award of the
Degree of Bachelor of technology
in Department of Mechanical Engineering
(Academic Session 2013-17)
ProjectGuide
Mr. Dheeraj Joshi
(Reader and Dept. Head)
ProjectCoordinators:
Mr. Dinesh Sharma
Mr. Ankit Agarwal
Department of Mechanical Engineering
Swami Keshvanand Institute of Technology, Management & Gramothan.
Submitted By:
Hitesh Sharma
[13ESKME036]

i
CERTIFICATE
This is to certify that the Seminar presentation entitled “Steriolithography and its application in
Medical Science” has been submitted to the Department of Mechanical Engineering, Swami
Keshvanand Institute of Technology, Management and Gramothan (Rajasthan Technical
University, Kota) for the fulfillment of the requirement for the award of the degree of Bachelor of
Technology in “Mechanical Engineering” by following student of final year B.Tech. (Mechanical
Engineering).
Student Name (with Roll no.)
 Hitesh Sharma (13ESKME036)
Project Guide Head of Department
Mr. Dheeraj Joshi Mr. N.K. Banthiya

ii
ACKNOWLEDGMENT
I like to share my sincere gratitude to all those who help us in completion of this report. During
the work I faced many challenges due to my lack of knowledge and experience but these people
help us to get over from all the difficulties and in final compilation of our idea to a shaped
sculpture.
I would like to thank Mr. Dheeraj Joshi sir for his governance and guidance, because of which I
was able to learn the minute aspects of the study.
I would also like to show mine gratitude to our Coordinators Mr. Dinesh Sharma and Mr. Ankit
Agarwal for their continuous help and monitoring during the work.
In the last I would like to thank the management of Swami Keshvanand Institute of Technology,
Management and Gramothan for providing me such an opportunity to learn from these
experiences.
I am also thankful to Mr. Narendra K. Banthiya Sir, Mr. Alok Mathur Sir and all the Faculties and
Staff of Department of Mechanical Engineering, SKIT, for their help and support towards this
study.
I am also thankful to my class and most of all to my parents who have inspired me to face all the
challenges and win all the hurdles in my life.
Thank you All.

iii
ABSTRACT
In the recent decades of development of manufacturing and production engineering, 3D printing
technology has emerged as one of the most promising area for research and development. With
the availability of flexible and user friendly manufacturing and interfacing system, the 3D printing
technology has attracted a lot of researchers form keen aspects of their field.
Medical Engineering is the branch of science that deal with the application of technological aspects
in solving medical problems. With the merger in these two vast fields a lot of problems has been
answered and the development of new things is on their verge of initiation.
In the recent decade both the engineers and medical researchers have worked on integration of
technologies to solve the medical problems globally. In the scenario, a lot of technology like 3D
printed Heart, Kidneys, etc., & physical implants like teeth’s, bones and medical support.
In this report, I have tried to acknowledge the work done in the field with their importance in the
ever changing scenario of the world.

iv
Table of Contents
Chapter 1: Introduction.......................................................................................................................1
1.1. Prototyping.........................................................................................................................1
1.2. Basic principle of rapid prototyping processes.......................................................................2
1.3. Rapid prototyping processes.................................................................................................4
1.3.1. Stereolithography .........................................................................................................4
1.3.2. Selective Laser Sintering...............................................................................................6
1.3.3. Fused Deposition Modeling...........................................................................................6
1.3.4. Laminated Object Manufacturing...................................................................................7
Chapter 2: Steriolithography................................................................................................................9
2.1. Introduction to Steriolithography ..........................................................................................9

v
Figure 1Typical process chain of various Rapid Prototyping systems .....................................................2
Figure 2 Generalized illustration of data flow in Rapid Prototyping.......................................................3
Figure 3. Classification of Rapid Prototyping Processes........................................................................4
Figure 4 Fine point structure for Stereolithography ...............................................................................5
Figure 5. Selective Laser Sintering System...........................................................................................6
Figure 6. Fused Deposition Modeling Process ......................................................................................7
Figure 7. Laminated Object Manufacturing Process..............................................................................8
Figure 8. Steriolithography Manufacturing Setup................................................................................10

vi
Table 1. Historical Development of Rapid Prototyping Technology .......................................................1

SKIT,Jaipur
1 | S t e r i o l i t h o g r a p h y a n d i t s a p p l i c a t i o n i n M e d i c a l S c i e n c e
Chapter 1: Introduction
1.1. Prototyping
Prototyping or model making is one of the important steps to finalize a product design. It helps in
conceptualization of a design. Before the start of full production a prototype is usually fabricated
and tested. Manual prototyping by a skilled craftsman has been an age-old practice for many
centuries. Second phase of prototyping started around mid-1970s, when a soft prototype modeled
by 3D curves and surfaces could be stressed in virtual environment, simulated and tested with
exact material and other properties. Third and the latest trend of prototyping, i.e., Rapid
Prototyping (RP) by layer-by-layer material deposition, started during early 1980s with the
enormous growth in Computer Aided Design and Manufacturing (CAD/CAM) technologies when
almost unambiguous solid models with knitted information of edges and surfaces could define a
product and also manufacture it by CNC machining. The historical development of Rapid
Prototyping and related technologies is presented in table 1.
Table 1. Historical Development of Rapid Prototyping Technology
Year of Inception Technology
1770 Mechanization
1946 First Computer
1952 First NC Machine Tool
1960 First Commercial LASER
1961 First Commercial Robot
1963 First Version of CAD (Early Version)
1988 First Rapid Prototyping Machine

2
1.2. Basic principle of rapid prototyping processes
The process belong to the generative (or additive) production processes unlike subtractive or
forming processes such as lathing, milling, grinding or coining etc. in which form is shaped by
material removal or plastic deformation. In all commercial rapid prototyping processes, the part
is fabricated by deposition of layers contoured in a (x-y) plane two dimensionally. The third
dimension (z) results from single layers being stacked up on top of each other, but not as a
continuous z-coordinate. Therefore, the prototypes are very exact on the x-y plane but have stair-
stepping effect in z-direction. If model is deposited with very fine layers, i.e., smaller z-stepping,
model looks like original. Rapid prototyping can be classified into two fundamental process steps
namely generation of mathematical layer information and generation of physical layer model.
Typical process chain of various rapid prototyping systems is shown in figure 1.
Figure 1. Typical process chain of various Rapid Prototyping systems
It can be seen from figure 1 that process starts with 3D modeling of the product and then STL file
is exported by tessellating the geometric 3D model. In tessellation various surfaces of a CAD
model are piecewise approximated by a series of triangles (figure 2) and co-ordinate of vertices of
triangles and their surface normal are listed. The number and size of triangles are decided by facet
deviation or chordal error as shown in figure 2. These STL files are checked for defects like flip

3
triangles, missing facets, overlapping facets, dangling edges or faces etc. and are repaired if found
faulty. Defect free STL files are used as an input to various slicing software. At this stage choice
of part deposition orientation is the most important factor as part building time, surface quality,
amount of support structures, cost etc. are influenced. Once part deposition orientation is decided
and slice thickness is selected, tessellated model is sliced and the generated data in standard data
formats like SLC (stereolithography contour) or CLI (common layer interface) is stored. This
information is used to move to step 2, i.e., generation of physical model. The software that operates
rapid prototyping systems generates laser-scanning paths (in processes like Stereolithography,
Selective Laser Sintering etc.) or material deposition paths (in processes like Fused Deposition
Modeling). This step is different for different processes and depends on the basic deposition
principle used in rapid prototyping machine. Information computed here is used to deposit the part
layer-by-layer on rapid prototyping system platform. The generalized data flow in rapid
prototyping is given in figure 2.
Figure 2 Generalized illustration of data flow in Rapid Prototyping

4
1.3.Rapid prototyping processes
The professional literature in rapid prototyping contains different ways of classifying rapid
prototyping processes. However, one representation based on German standard of production
processes classifies rapid prototyping processes according to state of aggregation of their original
material and is given in figure 3.
Figure 3. Classification of Rapid Prototyping Processes
1.3.1. Stereolithography
In this process photosensitive liquid resin which forms a solid polymer when exposed to ultraviolet
light is used as a fundamental concept. Due to the absorption and scattering of beam, the reaction
only takes place near the surface and voxels of solid polymeric resin are formed. A SL machine
consists of a build platform (substrate), which is mounted in a vat of resin and a UV Helium-
Cadmium or Argon ion laser. The laser scans the first layer and platform is then lowered equal to
one slice thickness and left for short time (dip-delay) so that liquid polymer settles to a flat and

5
even surface and inhibit bubble formation. The new slice is then scanned. In new SL systems, a
blade spreads resin on the part as the blade traverses the vat. This ensures smoother surface and
reduced recoating time. It also reduces trapped volumes which are sometimes formed due to
excessive polymerization at the ends of the slices and an island of liquid resin having thickness
more than slice thickness is formed. Once the complete part is deposited, it is removed from the
vat and then excess resin is drained. It may take long time due to high viscosity of liquid resin.
The green part is then post-cured in an UV oven after removing support structures.
Overhangs or cantilever walls need support structures as a green layer has relatively low stability
and strength. These overhangs etc. are supported if they exceed a certain size or angle, i.e., build
orientation. The main functions of these structures are to support projecting parts and also to pull
other parts down which due to shrinkage tends to curl up (Gebhardt, 2003). These support
structures are generated during data processing and due to these data grows heavily specially with
STL files, as cuboid shaped support element need information about at least twelve triangles. A
solid support is very difficult to remove later and may damage the model. Therefore a new support
structure called fine point was developed by 3D Systems (figure 6) and is companys trademark.
Build strategies have been developed to increase build speed and to decrease amount of resin by
depositing the parts with a higher proportion of hollow volume. These strategies are devised as
these models are used for making cavities for precision castings. Here walls are designed hollow
connected by rod-type bridging elements and skin is introduced that close the model at the top and
the bottom. These models require openings to drain out uncured resin.
Figure 4 Fine point structure for Stereolithography

6
1.3.2. Selective Laser Sintering
In Selective Laser Sintering (SLS) process, fine polymeric powder like polystyrene, polycarbonate
or polyamide etc. (20 to 100 micrometer diameter) is spread on the substrate using a roller. Before
starting CO2 laser scanning for sintering of a slice the temperature of the entire bed is raised just
below its melting point by infrared heating in order to minimize thermal distortion (curling) and
facilitate fusion to the previous layer. The laser is modulated in such away that only those grains,
which are in direct contact with the beam, are affected. Once laser scanning cures a slice, bed is
lowered and powder feed chamber is raised so that a covering of powder can be spread evenly over
the build area by counter rotating roller. In this process support structures are not required as the
unsintered powder remains at the places of support structure. It is cleaned away and can be recycled
once the model is complete. The schematic diagram of a typical SLS apparatus is given in figure
5.
Figure 5. Selective Laser Sintering System
1.3.3. Fused Deposition Modeling
In Fused Deposition Modeling (FDM) process a movable (x-y movement) nozzle on to a substrate
deposits thread of molten polymeric material. The build material is heated slightly above

7
(approximately 0.5 C) its melting temperature so that it solidifies within a very short time
(approximately 0.1 s) after extrusion and cold-welds to the previous layer as shown in figure 6.
Various important factors need to be considered and are steady nozzle and material extrusion rates,
addition of support structures for overhanging features and speed of the nozzle head, which affects
the slice thickness. More recent FDM systems include two nozzles, one for part material and other
for support material. The support material is relatively of poor quality and can be broken easily
once the complete part is deposited and is removed from substrate. In more recent FDM
technology, water-soluble support structure material is used. Support structure can be deposited
with lesser density as compared to part density by providing air gaps between two consecutive
roads.
Figure 6. Fused Deposition Modeling Process
1.3.4. Laminated Object Manufacturing
Typical system of Laminated Object Manufacturing (LOM) has been shown in figure 9. It can be
seen form the figure that the slices are cut in required contour from roll of material by using a 25-
50 watt CO2 laser beam. A new slice is bonded to previously deposited slice by using a hot roller,
which activates a heat sensitive adhesive. Apart from the slice unwanted material is also hatched
in rectangles to facilitate its later removal but remains in place during the build to act as supports.
Once one slice is completed platform can be lowered and roll of material can be advanced by
winding this excess onto a second roller until a fresh area of the sheet lies over the part. After

8
completion of the part they are sealed with a urethane lacquer, silicone fluid or epoxy resin to
prevent later distortion of the paper prototype through water absorption.
Figure 7. Laminated Object Manufacturing Process
In this process, materials that are relatively cheaper like paper, plastic roll etc. can be used. Parts
of fiber-reinforced glass ceramics can be produced. Large models can be produced and the building
speed is 5-10 times as compared to other rapid prototyping processes. The limitation of the process
included fabrication of hollow models with undercuts and reentrant features. Large amount of
scrap is formed. There remains danger of fire hazards and drops of the molten materials formed
during the cutting also need to be removed.

9
Chapter 2: STERIOLITHOGRAPHY
2.1. Introduction to Steriolithography
The manufacturing of 3D objects by stereolithography is based on the spatially
controlled solidification of a liquid resin by photo-polymerization. Using a computer-
controlled laser beam or a digital light projector with a computer-driven buildi ng
stage, a pattern is illuminated on the surface of a resin. As a result of this, the resin in
the pattern is solidified to a defined depth, causing it to adhere to a support platform.
After photo-polymerization of the first layer, the platform is moved away from the
surface and the built layer is recoated with liquid resin. A pattern is then cured in this
second layer. As the depth of curing is slightly larger than the platform step height, good
adherence to the first layer is ensured (unreacted functional groups on the solidified
structure in the first layer polymerize with the illuminated resin in the second layer) .
These steps (the movement of the platform and the curing of an individual pattern in
a layer of resin) are repeated to construct a solid, three-dimensional object. After
draining and washing-off like most solid freeform fabrication techniques, stereo-
excess resin, an as-fabricated (or green) structure is obtained. In lithography is an
additive fabrication process that allows the fabrication of parts from a computer-
aided design (CAD) file. The designed external and internal (pore) geometry of the
structure that is to be built can either be devised using 3D drawing computer software,
be described using mathematical equations, or be derived from scanning data of
(clinical) imaging technologies such as magnetic resonance imaging (MRI), or
tomography techniques. The possibility to use data from scans makes these
manufacturing technologies particularly useful for many applications in biomedical
engineering, as it enables to fabricate patient-specific models or implants. The CAD-
file describes the geometry and size of the parts to be built. For this, the STL file
format was developed; an STL file lists the coordinates of triangles that together
make up the surface of the designed 3D structure. This designed structure is
(virtually) sliced into layers of the thickness that is used in the layer-by-layer
fabrication process (usually in the range of 25e100 mm). These data are then uploaded
to the stereolithography apparatus (SLA) and the structure is fabricated. This

10
structure, the conversion of reactive groups is usually incomplete, and post-curing
with (stroboscopic) ultraviolet light is often done to improve mechanical properties of
the structures.
To date, most SLA setups in use resemble the ones ﬁrst developed. Using a computer-
controlled laser beam to draw a pattern, structures are built bottom-up from a support
platform that rests just below the resin surface. Only a thin layer of resin is illuminated
from above, and cured on top of the structure as it is built in a layer-by-layer manner.
A top-down approach is increasingly being applied in stereolithography. In such
setups, light is projected on a transparent, non-adhering plate from underneat h
(the transparent plate forms the bottom of the vessel that contains the resin), and the
support or build platform is dipped.
Figure 8. Steriolithography Manufacturing Setup
2.2. Resins used in stereolithography
The limited number of resins that are commercially available for processing by stereolithography
has often been considered the main limitation of the technique. The resin should be a liquid that
rapidly solidifies upon illumination with light. The first resins developed for use in
stereolithography were based on low-molecular weight polyacrylate or epoxy macromers that form
glassy networks upon photo-initiated polymerization and crosslinking. Several resins have been

11
developed over the past two decades, and the mechanical properties of the networks obtained after
curing cover a wide range. The properties of parts built by stereolithography are continuously
improving, making them not only useful as prototypes but also as functional parts for more
demanding end-use applications. Resins that can be used to create biodegradable devices for
application in medicine are being developed as well, see below.
Most of the available stereolithography resins are based on low molecular weight, multi-functional
monomers, and highly cross-linked networks are formed. These materials are predominantly
glassy, rigid and brittle. Only few resins have been described that allow the preparation of
elastomeric objects by stereolithography. These resin formulations include macromers with low
glass transition temperatures and relatively high molecular weights (1e5 kg/mol), often in
combination with non-reactive diluents such as Nmethylpyrrolidone (NMP) or water to reduce the
viscosity of the resin.
To create polymer-ceramic composite objects, ceramic particles (e.g. alumina or hydroxyapatite)
are homogeneously suspended in the stereolithography resin and photo-polymerized in the SLA.
Processing of the resin is more difficult, as the viscosity of the resin can significantly increase
upon addition of the powder. Maximum ceramic contents of up to 53 wt% have been reported.
Furthermore, the ceramic particle size should be smaller than the layer thickness in the building
process to prepare the objects accurately. The fabricated composite structures are in general,
stiffer and stronger than the polymeric structures. Starting from these composite structures, all-
ceramic objects have been made by first fabricating a composite structure by stereolithography
and then burning out the polymer (pyrolysis) and sintering the ceramic particles.
Different resins have been processed using stereolithography, leading to objects with widely
differing characteristics. Although the number of resins that is available continues to increase, the
technique is still limited to the use of a single resin at a time. (Note that 3D printing and plotting
techniques related to fuse deposition modelling allow the use of multiple cartridges to prepare
structures using different materials simultaneously.) The ability to pattern multiple resins in a
construct (and even within a single layer) is possible in stereolithography too, but complex
sequential polymerization and rinsing steps are required for each layer built. A major technological
challenge lies in developing an automated system to remove uncured resin and exchange resin

12
reservoirs. The restriction to use one resin in stereolithography is perhaps the true major limitation
of the technique.
2.3.New developments in stereolithography and related technologies
Two-photon polymerization is increasingly used in stereo-lithographic fabrication. In two-
photon polymerizations, the photo initiator is excited by the (nearly) simultaneous absorption of
two photons with relatively low intensity, which together introduce enough energy to break the
labile bond and initiate the polymerizations reaction. As a result, two-photon polymerizations is
a non-linear optical process in which the polymerizations rate is proportional to the square of the
laser intensity, as opposed to a linear relationship as is the case for single-photon
polymerizations. This leads to a more localized initiation of the polymerizations, and therefore
to higher resolutions. Using stereolithography setups based on two-photon absorption,
resolutions as high as 200 nm can be obtained.
Holography or interference lithography is a technique in which two or more light sources are
used to create an interference pattern. By superposition of the light waves, regular patterns with
locally varying light intensities are obtained. It is a well-known process for the creation of micro-
and nanostructures like nanopillars, nanostructured substrates, micro frames, 3D photonic
crystals and micro sieves. Interference holography provides a faster and more accurate method
to solidify patterns in a photo-curable resin than can be achieved with stereolithography, and
although it is restricted to a limited number of patterns it could be of interest to prepare repetitive
porous structures for tissue engineering.

Stereo lithography - Report

More Related Content

What's hot

Similar to Stereo lithography - Report

More from Hitesh Sharma

Recently uploaded

Stereo lithography - Report