Liquid Based and Solid Based Additive Manufacturing systems

DEPARTMENT OF INDUSTRIAL & PRODUCTION ENGINEERING www. jssstuniv.in
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ADDITIVE MANUFACTURING
(20IP653)
Module-2
Liquid based & Solid based AM systems
Course Instructor
Vijay Praveen P M
Assistant Professor
Department of I&P Engg.

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SYLLABUS
Liquid based additive Manufacturing systems: Classification
– Liquid based system – Stereolithography Apparatus (SLA)-
Principle, process, advantages and applications – Solid
based system –Fused Deposition Modeling – Principle,
process, advantages and applications, Laminated Object
Manufacturing.
Solid based AM Systems: Laminated Object Manufacturing
(LOM): Models and Specifications, Process, working
principle, Applications, Advantages and Disadvantages,
Case studies. Fused Deposition Modeling (FDM): Models
and specifications, Process, working principle,
Applications, Advantages and Disadvantages, Case studies.

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Introduction
➢Most liquid-based rapid prototyping systems build
parts in a vat of photo-curable liquid resin, an
organic resin that cures or solidifies under the
effect of exposure to laser radiation, usually in the
UV range.
➢The laser cures the resin near the surface, forming
a hardened layer. When a layer of the part is
formed, it is lowered by an elevation control
system to allow the next layer of resin to be
similarly formed over it.
➢This continues until the entire part is completed.
The vat can then be drained and the part removed
for further processing, if necessary

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Laser Stereolithography
Apparatus(SLA)
Stereo Lithography (SL) is the first process ever
developed in rapid prototyping field with the meaning
of .3-dimensional printing. Charles Hull developed and
patented the completed system in 1986. Then he
founded 3D Systems, inc. to develop commercial
applications of the process.
Stereo lithography builds plastic parts or objects a
layer at a time by tracing a laser beam on the surface
of a vat of liquid photopolymer. This class of materials
originally developed for the printing and packaging
industries, quickly solidifies wherever the laser beam
strikes the surface of the liquid.

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Principle of Stereo Lithography:
The SLA process is based
fundamentally on the following
principles:
(1) Parts are built from a photo-
curable liquid resin that
cures when exposed to a
laser beam which scans
across the surface of the
resin.
(2) The building is done layer by
layer, each layer being. scanned
by the optical scanning system
and controlled by an elevation
mechanism which lowers at the
completion of each layer.

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Working process of Stereo Lithography:
➢ SLAs have four main parts: a tank that can be filled with liquid plastic (photopolymer),
a perforated platform that is lowered into the tank, an ultraviolet (UV) laser and a
computer controlling the platform and the laser,
➢ In the initial step of the SLA process, a thin layer of photopolymer (usually between
0.05- 0.15 mm) is exposed above the perforated platform. The UV laser hits the
perforated platform, "painting" the pattern of the object being printed. Its scan at a
speed of 500 to 2500mm/sec
➢ The UV-curable liquid hardens instantly when the UV laser touches it, forming the first
layer of the 3D-printed object.
➢ Once the initial layer of the object has hardened, the platform is lowered, exposing a
new surface layer of liquid polymer. The laser again traces a cross section of the object
being printed, which instantly bonds to the hardened section beneath it.
➢ This process is repeated again and again until the entire object has been formed and is
fully submerged in the tank.
➢ The platform is then raised to expose a three-dimensional object. After it is rinsed with
a liquid solvent to free it of excess resin, the object is baked in an ultraviolet oven to
further cure the plastic.
➢ Objects made using stereo lithography generally have smooth surfaces, but the
quality of an object depends on the quality of the SLA machine used to print it.
➢ The amount of time it takes to create an object with stereo lithography also depends
on the size of the machine used to print it. Small objects are usually produced with
smaller machines and typically take between six to twelve hours to print. Larger
objects, which can be several meters in three dimensions, take days.

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Advantages
➢ Round the clock operation. The SLA can be used continuously
and unattended round the clock.
➢ Good user support. The computerized process serves as a good
user support .
➢ Build volumes. The different SLA machines have builds volumes
ranging from small to large to suit the needs of different users.'
➢ Good accuracy. The SLA has good accuracy and can thus be
used for many application areas.
➢ Surface finish. The SLA can obtain one of the best surface
finishes amongst Rp technologies.
➢ Wide range of materials. There is a wide range of materials,
from general-purpose materials to specialty materials for
specific applications

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Disadvantages
➢ Requires support structures, Structures that have overhangs and undercuts
must have supports that are designed and fabricated together with the main
structure.
➢ Requires post-processing. Post-processing includes removal of supports and
other
unwanted materials, which is tedious, time-consuming and can damage the model.
➢ Requires post-curing. Post-curing may be needed to cure the object
completely and ensure the integrity of the structure.
Applications of SLA:
The SLA technology provides manufacturers with cost justifiable methods for
reducing time to market, lowering product development costs, gaining greater
control of their design
process and improving product design. The range of applications includes:
✓ Models for conceptualization, packaging and presentation.
✓ Prototypes for design, analysis, verification and functional testing.
✓ Parts for prototype tooling and low volume production tooling.
✓ Patterns for investment casting, sand casting and moulding.
✓ Tools for fixture and tooling design, and production tooling.

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Solid Based AM
• Solid-based rapid prototyping systems are
very different from the liquid-based photo-
curing systems.
• They are also different from one another,
though some of them do use the laser in the
prototyping process. The basic common
feature among these systems is that they all
utilize solids (in one form or another) as the
primary medium to create the prototype

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Classification

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Solid sheet systems
This is an obsolete technology which is not seen widely used
nowadays. Example of earliest solid sheet system is the laminated
object manufacturing (LOM) system from Helisys, USA. This
technology uses a laser to cut out profiles, from sheet paper, supplied
from a continuous roll, which formed the layers of the final part.
Laminated object Manufacturing (LOM) process:
This process is developed by Helisys of Torrance,
California: USA, in 1998 which is a layer additive process.
In this process, the Material consists of paper laminated
which is coated with thermoplastic adhesive and rolled
up on spools. As shown in the fig

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Principle
(1) Parts are built, layer-by-layer, by laminating each layer of paper or
other sheet-form materials and the contour of the part on that layer
is cut by a CO2 laser.
(2) Each layer of the building process contains the cross-sections of
one or many parts. The next layer is then laminated and built
directly on top of the laser-cut layer.
(3) The Z-control is activated by an elevation platform, which lowers
when each layer is completed, and the next layer is then laminated
and ready for cutting. The Z-height is then measured for the exact
height so that the corresponding cross sectional data can be
calculated for that layer.
(4) No additional support structures are necessary as the “excess”
material, which are cross-hatched for later removal, act as the
support.

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working
➢ a feeder mechanism advances
the sheet over the build platform,
where a base is made up from
paper and double-sided foam
tape.
➢ A heated roller applies pressure
to bond the paper to the base.
➢ Cot laser traces the outline of
the cad data fed in the computer.
After the laser cutting is
completed the platform moves
down and a fresh sheet of
laminated paper is rolled on. The
process is repeated as needed to
build the part. Lom process is
used in pattern making and toy
designing as this process is
cheaper and high volume
production can be achieved.

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Materials
Potentially, any sheet material with adhesive
backing can be utilized in Laminated Object
Manufacturing.
It has been demonstrated that plastics, metals,
and even ceramic tapes can be used. However,
the most popular material has been Kraft paper
with a polyethylene-based heat seal adhesive
system because it is widely available, cost-
effective, and environmentally begin

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Fused Deposition Modelling (FDM)
• Principle
• The principle of the FDM is based
on surface chemistry, thermal
energy, and layer manufacturing
technology..
• The material in filament (spool)
form is melted in a specially
designed head, which extrudes on the
model.
• As it is extruded, it is cooled and thus
solidifies. To form the model.
• The model is built layer by layer, like
the other RP systems.
• Parameters which affect performance
and functionalities of the system are
material column strength, material
viscosity, positioning accuracy, road
widths, deposition speed,
volumetric flow rate, tip diameter,
envelope temperature, and part
geometry

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Step 1: The Preparation
A geometric model of a conceptual design is created on
CAD software which uses IGES or STL formatted files, It
can then imported into the workstation where it is
processed Through The Quick Slice and Support Work
propriety software before loading to FDM systems.
The CAD file is sliced into horizontal layers after the part
is oriented for the optimum build position, and any
necessary support structures are automatically detected
and generated. The slice thickness can be set manually to
anywhere between 0.172 to 0.356 mm (0.005 to 0.014 in)
depending on the needs of the models

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Step 2: T he Build
The nozzle is heated to melt the plastic filament and is mounted to a
mechanical stage which can be moved in both horizontal directions.
As the nozzle is moved over the table in the required geometry, it
deposits a thin bead of extruded plastic to form each layer and create
a two-dimensional cross section of the model.
The plastic hardens immediately after being squirted from the nozzle
and bonds to the layer below.
The platform then descends where the next layer is extruded upon the
previous. This continues until the model is completed,. The entire
system is contained within a chamber which is held at a temperature
just below the melting point of the plastic.
Step 3: Post -processing
Once all the layers are drawn and the model is complete, the model is
then removed from the platform, and the support structures are
removed from the part

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Materials
Materials are available, such as
➢ Acrylonitrile Butadiene Styrene (ABS)- Standard
prototyping plastic with durability,
➢ Polycarborate (PC),
➢ Polyamide (PA),
➢ Polystyrene (PS),
➢ Lignin,
➢ Rubber, among many others, with different
trade-offs between strength and temperature
properties.

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Case study-1
1. National Aeronautical and Space Administration (NASA) and Boeing
Rocketdyne Uses LOM TM to Create Hot Gas Manifold for Space
Shuttle Main Engine
One successful example of how an organization implements LOMTM
systems into their design process would be from the Rapid Proto- typing
Laboratory, NASA’s Marshall Space Flight Center (MSFC), Huntville, AL.
The laboratory was set up initially to conduct research and
development in different ways to advance the technology of
buildingparts in space by remote processing methods. However, as
MSFC engineers found a lot more useful applications, i.e., production of
concept models and proof-out of component designs other than
remote processing when rapid prototyping machines were installed, the
center soon became a rapid prototyping shop for other MSFC groups, as
well as other NASA locations and NASA subcontractors.

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The center acquired the LOM-1015TM machine from Helisys in 1999
to add on their existing rapid prototyping systems and the machine
was put through its first challenge when MSFC’s contractor, Boeing/
Rocketdyne designed a hot gas manifold for the space shuttle’s main
engine.
The part measured 2.40 m (8 ft) long and 0.10 m (4 in) in diameter
and was complex in design with many twists and turns and “tee”
junction connectors. If the conventional method of creating the
prototype were employed, it would require individual steel parts to be
welded together to form the prototype.
However, there was always a potential of leakage at the joint part and
thus, an alternate method was considered. The prototype was to be
made from a single piece of steel and such a solution was not only
expensive, the prototype built did not fit well to the main engine of
the space shuttle.

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Eventually, engineers at Boeing decided to build the part using the
LOMTM process at MSFC. They prepared a CAD drawing of the design and
sent it over to MSFC.
The design was sectioned into eight parts, each with the irregular boss-
and-socket built in them so as to facilitate joining of the parts together
upon completion.
The whole building process took ten days to complete, including three
days of rework for flawed parts.
It was worked on continuously. One advantage of using the LOMTM
machine is that the system can be left unattended throughout the
building process and if the system runs out of paper or the paper gets
jammed while building, it is able to alert the operator via a pager. The
prototype was then mounted onto the actual space shuttle for final fit
check analysis.
It was estimated that the company saved tens of thousands of dollars,
although Boeing declined to reveal the actual cost saving. The whole
process also drastically reduces the building time from two to three
months to a mere ten days.

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Case study-2
• STRATASYS’ FUSED DEPOSITION MODELING (FDM)
Stratasys Inc. was founded in 1989 and has developed most of the
company’s products based on the Fused Deposition Modeling (FDM)
technology.
The technology was first developed by Scott Cramp in 1988 and the patent
was awarded in the U.S. in 1992.
FDM uses the extrusion process to build 3D models. Stratasys introduced its
first rapid prototyping machine, the 3D modeler® in early 1992 and started
shipping the units later that year. Over the past decade, Stratasys has grown
progressively, seeing her rapid prototyping machines’ sales increase from six
units in the beginning to a total of 1582 units in the year 2000 [9].

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Important Questions
• 1. Explain with a neat sketch SLA AM process
and also state its advantages, disadvantages and
applications of it.
• 2. Explain with a neat sketch LOM AM process
and also state its advantages, disadvantages and
applications of it.
• Explain with a neat sketch FDM AM process and
also state its advantages, disadvantages and
applications of it

Liquid Based and Solid Based Additive Manufacturing systems

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