Module-1

Introduction to Additive Manufacturing

Introduction to Additive Manufacturing: Introduction to AM, AM evolution, Distinction between
AM & CNC machining, Advantages of AM, AM process chain: Conceptualization, CAD,
conversion to STL, Transfer to AM, STL file manipulation, Machine setup, build , removal and
clean up, post processing

Classification of AM processes: Liquid polymer system Discrete particle system, Molten

material systems and Solid sheet system
Post processing of AM parts: Support material removal, surface texture improvement, accuracy
improvement, aesthetic improvement, preparation for use as a pattern, property enhancements
using non-thermal and thermal techniques.
Guidelines for process selection: Introduction, Selection methods for a part, challenges of
selection.
AM Application: Functional Models, pattern for investment and vacuum casting, Medical
models, art models, Engineering analysis models, Rapid tooling, new materials development, Bi-
metallic parts, Re-manufacturing Application examples for Aerospace, defence, automobile Bio-
medical and general engineering industries

1.1 Introduction
The evolution of ADDITIVE MANUFACTURING (rapid prototyping, 3d printing, free form
fabrication) has changed the face of direct, digital technologies for the rapid production of models,
prototypes, patterns, and fit & functional parts, since its introduction, AM technology has changed
design, engineering, and .manufacturing processes within the aerospace, automotive, electrical &
electronics, consumer industries, biomedical and dental devices & implants. Due to wide
applications, rapid prototyping technology has become a revolutionary field in manufacturing.

Additive Manufacturing (rapid prototyping, 3 D printing) can be defined as the layer-. by-
layer fabrication of three-dimensional physical models directly from a computer-aided design
(CAD) data.

This am technology known by many names such as:-

 3d printing
 Rapid prototyping and manufacturing.
 Free-form fabrication
 solid free-form fabrication

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  direct digital manufacturing
 Additive Manufacturing (AM) is the official term for the technology as per ASTM
international (American Society for Testing and Materials) & ISO.
1.2 Evolution of Additive manufacturing
Rapid prototyping started from meager beginnings, but today it has grown to be one of the best
technologies in the manufacturing sector. Basically, the origins of rapid prototyping have been
branched from the cad industry. Solid modeling which is a feature of cad which produces 3-d
objects in an electronic format was introduced in the 1980s.

Rapid prototyping technology was born in the late 1970s when scientists at ultra violet
products, Inc. worked to develop a technology that could build three-dimensional parts using
lasers. This technology worked by curing or hardening a thick liquid substance (photopolymer)
called resin in the shape of the required prototype. As the photopolymer was exposed to the
heat it became harder and eventually became completely rigid.

In 1986 Charles hull, of ultra violet products, Inc. Patented this technology, which is now
known as stereolithographic. Later on, Charles hull formed 3d systems, Inc. and
commercialized this technology.

In the years between 1988, when chuck hull's stereolithographic was first made available for
public purchase, until 1996, many incremental accomplishments further advanced the
commercialization of AM. In 1991, the following am technologies were commercialized:
laminated manufacturing (LOM), solid ground curing (SGC), and fused deposition modeling.
These achievements were all based on the principle of additive manufacturing but used different
materials and composition methods to develop the final object.

1.3 Difference between AM & CNC machining process

An important difference between additive manufacturing technology and CNC machining
process is that a prototype or model is. obtained by layer by layer addition process as opposed to
removing material from a 'block'.

1) Material difference:

Additive manufacturing: 3D Printed materials are mainly liquid resin (SLA), nylon powder
(SLS), metal powder, gypsum powder, sandstone powder, wire, sheet (LOM) and many more.
Liquid resins, nylon powders, and-metal powders account for the vast majority of industrial 3d
printing.

CNC machining: the materials. used for CNC machining are all one piece of sheet metal,
which is a plate-shaped material. By measuring the length. Width, height, and wear of the
parts, the corresponding size of the sheet is cut for processing.

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2) Structural difference:
Additive manufacturing: Its principle is to cut the model into ti lay -et-sin multi-points, and
then pile up one by one in order, just like building blocks, therefore, additive manufacturing
processes parts with complex structures, such as hollowed out parts

CNC machining: It is the reduction of material manufacturing. Through the various, tools
running at high speed, the required parts are cut according to the programmed tool path.
Therefore, CNC machining can only produce rounded corners with a certain degree of
curvature but cannot directly process the inner right angle which is realized by processes such
as wire cutting/sparking.

3) Operating software
Additive manufacturing: most of the 3d printed slicing software is easy to operate, even if
the layman can master the slicing software in the next two days of professional guidance.
Because the slicing software is currently optimized to be very simple, support can be
generated automatically, which is why 3d printing, can be popularized to individual users.

CNC : Programming software is much more complicated and requires professional personnel
to operate.

4) Post-processing difference
Additive manufacturing: There are not many post-processing options for 3d printed parts,
which are generally polished, sprayed, deburred, dyed, etc.

CNC: Machined parts have a variety of post-processing options, in addition to grinding, fuel
injection, deburring, as well as electroplating, silk screen, pad printing, metal oxidation, laser
engraving, sandblasting and so on.

Advantages

 Design Complexity and freedom: The 3d printing technology has been expanding
products, which involve levels of complexity. The advantage has been taken up by
designers and artists to the impressive visual effect. It has made a significant impact on
the industrial application. These applications are being developed to materialize complex
components that are proving to be both lighter and stronger than their
Predecessors.

 Speed: one can do complex parts within hours, with limited human resource. The only
machine operator is needed for loading the data and the powder material, start the
process and finally for the finishing. During the manufacturing process, no operator is
needed.

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  Customization: 3d printing processes allow for mass customization, personalize
products according to individual needs and requirements.
 Tool-less: In industrial manufacturing, for low volume to medium volume production it
is costlier, time-consuming and labor-intensive, thus additive manufacturing can
eliminate the need for tool production
 Extreme lightweight design: Additive manufacturing enable weight reduction via
topological optimization
 Sustainable / environmentally friendly: 3D printing technology provide
environmental efficiencies in terms of the manufacturing process by utilizing up to
900 of standard materials, and, therefore, creating less waste.
 No storage cost: since 3d printers can "print" products as and when needed, and does
not cost more than mass manufacturing, no expense on storage of goods is required.
 Increased employment opportunities: Widespread use of 3d printing technology
will increase the demand for designers and technicians to operate 3d printers and
create blueprints for products.
Disadvantages:

 Questionable accuracy: 3d printing is primarily a prototyping technology, meaning

that parts created are mainly test parts. For a test part, the dimensions have to be precise
to get an accurate reading to check whether a part is feasible or not.
 Support material removal: when production volumes are small, the removal of
support material is usually not a big issue. When the volumes are high, it becomes an
important consideration.
 Limitations of raw material: in traditional manufacturing, there are a wide range of
materials wherein an additive manufacturing technology-can work with only a few.
More research is required to devise methods to enable 3d printed products to be more
durable and robust.
 Good skills are required for application design and to set process parameters
 Material cost: cost of most materials of additive systems is greater than that of those
used for traditional manufacturing.
 Material properties: a limited choice of materials is available: Actually, materials and
their properties (e.g., tensile property, tensile strength, yield strength, and fatigue) have
not been fully characterized. Also, in terms of surface quality, even the best RM
processes need perhaps secondary machining and polishing to reach acceptable
tolerance and surface finish.
 Intellectual property issues: the ease with which replicas can be created using 3d
technology raises issues over intellectual property rights. The availability of blueprints

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 online free of cost may change with for-profit organizations wanting to generate profits
from this new technology.
 Limitations of size: 3d printing technology is currently limited by size constraints. Very
large objects are still not feasible when built using 3d printers.

 Cost of printers: The cost of a 3d printer is not feasible for purchase by the average
householder. Also, different 3d printers are required in order to print different types of
objects.

1.5 Additive Manufacturing Process

Nowadays many rapid prototyping techniques are available even however all employ the
following Process.

The steps are:

1. Conceptualization
2. CAD
3. Conversion to STL
4. Transfer to additive manufacturing
5. STL file manipulation
6. Machine setup
7. Build removal and clean up
8. Post processing

1.5.1 Conceptualization
The first step in an additive manufacturing process is that one needs to imagine and also
develop a thought about the function and appearance of the product. This may be in the form of
textual descriptions, sketches, 3-dimensional computer models. Conceptualization is done through
making 3d cad model using cad programs.

1.5.2 CAD
After conceptualizing object to be built, modeling is done using a computer-aided design
software packages. Solid modeling packages like solid works, pro/engineer, catia, and
unigraphics are used to represent 3-d objects more accurately than 2-d wireframe modeling
packages and gives better results. The pre-existing cad file is used to create prototypes.

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1.5.3 Conversion to STL
Additive manufacturing technology uses the stereo lithographic (standard triangulation language (STL)
file format. The STL format of a 3D cad model captures all surfaces of the 3D model by means of
stitching triangles of various sizes on its surfaces. The spatial locations of the vertices, the vectors
normal to triangle combined, allows additive manufacturing pre-process 'programs to determine the
spatial locations, of surfaces of the part in a building envelope and locate the surface of the interior of
the part. The limitation here in STL is only geometry information is stored in files while all other
information that a cad model can contain is eliminated such as unit, color, material, etc. which plays a
critical role in the functionality of the built part and effects finished parts

The "AMF" format was developed specifically to address limitations of STL format and is
now the ASTM/ISO standard format. This format addresses dimensions, color, material, and
additional information with a file format.

Though currently, the predominant format of a file used by additive manufacturing systems
and supported by cad modeling programs is still the STL format. An increasing number of CAD
program companies, including several major programs, have included support of AMF file
formats. Currently, actual use of the information stored in the AMF file is still limited due to the
capabilities of current am systems and the state of current technology development.

1.5.4 Transfer to additive manufacturing

Once a correct STL file is available, a series of steps is required to transfer the information
to start the build. The needed information varies, depending on the technology but in general,
these steps start with repairing any errors within the STL file such as gaps between surface
triangle facets, inverted normal where the "wrong side" of a triangle facet is identified as the
interior of the part.

Once the errors have been repaired, proper orientation of the 3d model with respect to the
build platform is- decided. Following the orientation, the geometry, density, geometry of support
structures are decided and generated in 3d model space and assigned to the part model.

1.5.5 STL File Manipulation

The CAD model preparation starts with importing an STL, or other compatible file formats,
into the 'pre-process software program (e.g., magic's). Once imported, the dimensions can be
modified if needed. Series of steps is carried out to correct possible errors in the model file.
These errors can include missing triangles, inverted or double triangles, transverse triangles,
open edges and contours, and shells. Each type of error can cause issues in the building process
or result in incorrect parts and geometries.

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1.5.6 Machine Setup
Machine preparation can roughly be divided into two groups of tasks such as machine
hardware set up and process control.

1) Machine hardware setup: Hardware setup entails cleaning of build chamber from the
previous build, loading of powder material, a routine check of all critical build settings and
process controls such as gas pressure, flow rate, oxygen sensors, etc.
2) Process control; The tasks in the, process control group allow an additive
manufacturing system
 To accept and process the build files
 Start the build
 Interrupt the build at any given time if desired or required,
 Preparing the machine for finished part extraction,
 Unloading of material.
After physical locations of parts are decided, it is followed by a series of steps of defining the

 Build process parameters,

 Material parameters, and
 Part parameters.

1) The build process parameter controls machine level parameter that is applied to
the entire build.
2) Material parameters control powder dosing behaviors and chamber environment
control through inert gas injection.
3) Part parameters are assigned to each and every component/part to be built. These
parameters are taken into account in the slicing process that takes place in the previous step of
the process chain

1.5.7 Support generation

The primary function of the "support" structure is to extract heat from the model and
to provide anchor surfaces and features to the build plate to avoid warpage due to thermal
stresses during and after the build.

Generation of support structures in powder bed processes can be accomplished in by

two different ways. The first way is to generate the support structures during cad modeling
and design the support to be features of the geometry of the part. The other way is that the
support structures can be generated in the STL preprocess software program.

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1.5.8 Build file preparation
In this step slicer program is used to divide the models into layers in the build
direction based on the desired layer thickness. Ideally, the layer thickness would be slightly
larger than the mean diameter of powder to achieve high coupling of laser energy input
into the absorption, heating, and melting of powder.

Parameters which determine an amount of energy incident onto the powder bed per unit
time, are energy input, beam power, scan speed, and focus move.

Once the slice information is generated, it is transferred into the interface program that
runs on am systems. The interface program serves as the interface between information of
the build and machine controls that carry out the actual build process.

1.5.9 Build removal

The build time of the powder bed process depends on a number of factors the main
factor here we see is the height of the entire build which has an effect on the total time. It
can take anywhere from minutes to days.

Once the build completes, unpacking of the build chamber is done and retrieves finished
part. The unpacking process typically involves raising the platform in the build chamber and
removing loose powder at the same time. Once the loose powder is removed from the finished
part, the build is ready for post-process.

The finished parts at this point for powder based polymer metals are removed by
chemical technique and for metal powder, we use cutting tools such as band saws, or wire
EDM for higher fidelity and flexibility.

1.5.10 Post processing

Depending on additive manufacturing technology post-processing techniques can be varied
in a wide range. It can require anything from no post process to several additional steps of
processing to change the surface, dimensions, or material properties of the built part.

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 Fig 1.1 Additive Manufacturing Process

1.6 Classification of Additive Manufacturing

There are numerous ways to classify additive manufacturing technologies.

 According to baseline technology, like whether the process uses lasers, printer
technology, extrusion technology, etc.

 According to processes and the type of raw material input. The problem with these
classification methods is that some processes get grouped together in what seems to be odd
combinations (like selective laser sintering (SLS) being grouped together with 3d printing)
or that some processes that may appear to produce similar results end up being separated
(like stereolithographie and material jetting with photopolymers). It is probably
inappropriate, therefore, to use a single classification approach.
A popular way of classifying is ,a two-dimensional classification method as shown in fig.

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 Fig 1.2 Classification of Additive Manufacturing

From the above diagram thus, additive manufacturing can be classified as follows

 Liquid'polymer system,
 Discrete particle system,
 Molten material systems and
 Solid sheet system.

1.6:1 Liquid polymer systems

As liquid polymers is widely and popularly used material. Using these liquid polymer 3d
systems developed a first commercial system using stereolithographic process (SLA). Let us
understand the working of the SLA system. The detail working principal of SLA is explained
below.

Stereo Lithography (SLA or SL) Systems

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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 Fig 1.3 Stereo Lithography

Fig 1.4 Stereo lithography apparatus

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.

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
(basically, undergoing the photo polymerization process) which scans across the
surface of the resin.

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 (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.

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, as shown in figure 7.
 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.
 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.
Photopolymers (material used in SLA for manufacturing the model):

There are many types of liquid photopolymers that can be solidified by exposure to
electro-magnetic radiation, including wavelengths in the gamma rays, X-rays, UV and
visible range, or electron-beam (EB). The vast majority of photopolymers used in the
commercial RPsystems, including 3D Systems' SLA machines are curable in the UV range.
UV-curable photopolymers are resins which are formulated from photo initiators and
reactive liquid monomers.

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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.
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.

1.6.2 Discrete particles systems

Discrete particles systems are also known as powders based systems. The system is
graded into a relatively uniform particle size and shape and narrow size distribution. The finer is
the particles the better will be the result, if too small powders are used there may be a case of
controlling the distribution and dispersion.

In a Id channel approach using a laser, produce thermal energy in a controlled manner

and, therefore, raise the temperature sufficiently to melt the powder. The polymer powders used

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should exhibit thermos elastic behavior so that they can be melted and re-melted to permit
bonding of one layer to another.

The two main polymer-based systems commercially available are the SLS technology
marketed by 3d systems and the FOS hit processes developed' by the German company EOS.

Let us understand the SLS process in detail,

The SLS process (Figure.l) creates three-dimensional objects, layer by layer by layer from
CAD-data generated in CAD software using powdered materials with heat generated by a CO 2
laser within the Vanguard system. CAD data files in the STL file format are first transferred to
the Vanguard system where they are sliced. From this point, the SLS process involves
following steps.

1. CAD data files are converted to STL file format are first transferred to the Vanguard
system where they are sliced.
2. A thin layer of heat-fusible powder is deposited . onto the part building chamber.
3. The bottom-most cross-sectional slice of the CAD part under fabrication is selectively
"drawn" (or scanned) on the layer of powder by a heat-generating CO2 laser. The
interaction of the laser beam with the powder elevates the temperature to the point of
Melting, fusing the powder particles to form a solid mass.' The intensity of the laser beam
is modulated to melt the powder only in areas defined by the part's geometry.
Surrounding powder remains a loose compact and serves as supports.
4. When the cross-section is completely drawn, an additional layer of powder is deposited
via a roller mechanism on top of the previously scanned layer. This prepares the next
layer for scanning.
5. Steps 3 and 4 are repeated, with each layer fusing to the layer below it. Successive layers
of powder are deposited and the process is repeated until the part is completed.
6. As SLS materials are in powdered form, the powder not melted or fused during
processing serves as a customized, built-in support structure. There is no need to create
support structures within the CAD design prior to or during processing and thus no
support structure to remove when the part is completed.
7. SLS parts may then require some post-processing or secondary finishing, such as
sanding, lacquering and painting, depending upon the application of the prototype

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Materials

In theory, a wide range of thermoplastics, composites, metals and ceramics can be used
in this process

 Polyamide. Trade named "DuraFonnTM", this material is used to create rigid

and rugged plastic parts for functional engineering environments.
 Thermoplastic elastomer. Flexible, rubber-like parts can be prototyped using
the SLS.
 Polycarbonate. An industry-standard engineering thermoplastic.
 Nylon. Another industry-standard engineering thermoplastic.
 Metal. This is a material where polymer coated stainless steel powder is
infiltrated with bronze.
Principle

The SLS process is based on the following ‘two principles:

 Parts are built by sintering when a CO2 laser beam hits a thin layer of powdered
material. The interaction of the laser beam with the powder raises the
temperature to the point of melting, resulting in particle bonding, fusing the
particles to them and the previous layer to form a solid.
 The building of the part is done layer by layer. Each layer of the building
process contains the Cross-sections of one or many parts. The next layer is then
built directly on top of the sintered layer after an additional layer of powder is
deposited via a roller mechanism on top of the previously formed layer.

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1.6.2.2 Direct Metal Laser Sintering (DMLS)
Direct Metal Laser Sintering (DMLS) was developed jointly by Rapid . Product innovation
(RPI) and EOS GmbH, starting in 1994, as the first commercial rapid prototyping method to
produce metal parts in a single process. With DMLS, metal powder (20 micron diameter), free
of binder or fluxing agent, is completely melted by the scanning of a high power laser beam to
build the part with properties of the original material. Eliminating the polymer binder avoids
the burn-off and infiltration steps, and produces a 95% dense steel part compared to roughly
70% density with Selective. Laser Sintering (SLS). An additional benefit of the DMLS process
compared to SLS is higher detail resolution due to the use of thinner layers, enabled by a
smaller powder diameter. This capability allows for more intricate part shapes. Material
options that are currently offered include alloy steel, stainless steel, tool steel, aluminum,
bronze, cobalt-chrome, and titanium. In addition to functional prototypes, DMLS is often used
to produce rapid tooling, medical implants, and aerospace parts for high heat applications.

The DMLS process can be performed by two different methods, powder deposition and
powder bed, which differ in the way each layer of powder is applied. In the powder deposition
method, the metal powder is contained in a hopper that melts the powder and deposits a thin
layer onto the build platform. In the powder bed method (shown below), the powder dispenser
piston raises the powder supply and then a recoated arm distributes a layer of powder onto the
powder bed. A laser then sinters the layer of powder metal, In both methods, after a layer is
built the build piston lowers the build platform and the next layer of powder is applied. The
powder deposition method offers the advantage of using more than one material, each in its
own hopper. The powder bed method is limited to only one material but offers faster build
speeds

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1.6.3 Molten material systems
Molten material systems also called solidly based systems are characterized by a pre-heating
chamber that raises the material temperature to melting point so that it can flow through a
delivery system. The most well-known method for doing this is the fused deposition
modeling (FDM) material extrusion technology developed by the US Company Stratasys.

Fused deposition modelling (FDM) process

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

Step 2: The 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. T he
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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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 extrudeson 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 RPsystems. Parameters which
affect performance and functionalities of the system are material column strength, materials
flexural modulus, material viscosity, positioning accuracy, road widths, deposition speed,
volumetric flow rate, tip diameter, envelope temperature, and partgeometry

Materials

Materials are available, such as

 Acrylonitrile Butadiene Styrene (ABS)- Standard prototyping plastic with

durability,
 Polycarboriate (PC),
 Polyamide (PA),

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  Polystyrene (PS),
 Lignin,
 Rubber, among many others, with different trade-offs between strength and
temperature properties.
Advantages

1. Fabrication of functional parts. FDM process is able to fabricate prototypes with

materials that are similar. to that of the actual molded product. With ABS, it is able to
fabricate fully functional parts that have 85% of the strength of the actual molded part.
This is especially useful in developing products that require quick prototypes for
functional testing.
2. Minimal wastage. The FDM process build parts directly by extruding semi-liquid
melt onto the model. Thus only those material needed to build the part and its support
are needed, and material wastages are kept to a minimum. There is also little need for
cleaning up the model after it has been built.
3. Ease of support removal. With the use of Break Away Support System (BASS) and
Waterworks Soluble Support System, support structures generated during the FDM
building process can be easily broken off or simply washed away. This makes it very
convenient for users to get to their prototypes very quickly and there is very little or
no post-processing necessary.
4. Ease of material change. Build materials, supplied in spool form (or cartridge form in
the case of the Dimension or Prodigy Plus), are easy to handle and can be changed
readily when the materials
Disadvantages

1. Restricted accuracy. Parts built with the FDM process usually have restricted
accuracy due to the shape of the material used, i.e., the filament form. Typically,
the filament used has a diameter of 1.27 mm and this tends to set a limit on how
accurately the part can be built.
2. Slow process. The building process is slow, as the whole cross-sectional area needs
to be filled with building materials. Building speed is restricted by the extrusion
rate or the flow rate of the build material from the extrusion head. As the build
material used is plastics and their viscosities are relatively high, the build process
cannot be easily speeded up.
3. Unpredictable Shrinkage. As the FDM process extrudes the build material from its
extrusion head and cools them rapidly on deposition, stresses induced by such rapid
cooling invariably are introduced into the model. As such, shrinkages and
distortions caused to the model built are a common occurrence and are usually
difficult to predict, though with experience, users may be able to compensate for
these by adjusting the process parameters of the machine.

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 Application

1. Models for conceptualization and presentation. Models can be marked, sanded,

painted and drilled and thus can be finished to be almost like the actual product.
2. Prototypes for design, analysis and functional testing. The system can produce a
fully functional prototype in ABS. The resulting ABS parts have 85% of the
strength of the actual moulded part. Thus actual testing can be carried out;
especially with consumer products.
Patterns and masters for tooling. Models can be used as patterns for investment
casting, sand casting and moulding.

Example

1, Toyota Uses FDM for Design and Testing

Toyota, the fourth-largest automobile manufacturer in the United States, produces more than
one million vehicles per year. Its design and testing of vehicles are mainly done at the
Toyota Technical Center(TTL) USA Inc.In 1997, TTL purchased the Stratasys' FDM 8000
fused deposition modeler (FDM) system to improve on their efficiency in design and testing.
The system, not only is able to produce excellent physical properties prototype, it is also
able to produce them fast. Furthermore, the system does not require any special environment
to be operated in. In the past, fabricating a prototype was costly and time consuming at TTL.
To manufacture a fully functional prototype vehicle, it required$10 000 to $100 000 to
manufacture a prototype injection mold and it took as long as 16 weeks to produce.
Furthermore, the number of parts required was around 20 to 50 pieces and thus, the
conventional tooling method is unnecessarily costly. In the Avalon 2000 project,. TTL,
replaced its conventional tooling method with the FDM system. Although a modest 35 parts
were being replaced by rapid prototypes, it was estimated that it saved Toyota more than $2
million in prototype tooling costs. Moreover, rapid prototyping also helped designers to
identify unforeseeable problems early. in the design stage. It would have added to the
production costs significantly if the problems were discovered during the production stage.
The physical properties of these prototypes are not identical to those made from the
conventional method, but nevertheless, as claimed by one of the staff in TTL, they are often
good enough. TTL plans to increase its rapid prototyping capacities by introducing
additional units of the FDM system. Its aim is to eliminate all conventional prototyping
tooting and go straight to production tooling in the near future.

1.6.4 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.

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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. Below, 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. As of 2001,
Helisys is no longer in business

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 Advantages:

 Multiple parts can be positioned within the entire working

envelop throughput
 No support structure is required as the wax support the structure in all (iii
 Each layer is fully cured resulting that the dimension is very stable
with no effect after the process and requires no post-curing process
 Capable to build even the most complicated parts without much difficulty
 Build session can be interrupted and erroneous layer can be
erased
Disadvantages

 Requires large Physical space. The size of the system is much larger than other
systems with a similar build volume size.
 Wax gets stuck in comers and crevices. It is difficult to remove wax from parts with
intricate geometry. Thus, some wax may be left behind.
 Waste material produced. The milling process creates shavings,which have -to be
cleaned from the machine.

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  Noisy. The Solider system generates a high level of noise as compared to other
systems.-
Applications

The applications of Cubital's system can be divided into four areas:

 General applications. Conceptual design presentation, design proofing, engineering

testing, integration and fitting, functional analysis, exhibitions and pre-production sales;
market research, and inter-professional communication.
 Tooling and casting applications. Investment casting, sand casting and rapid, tool-free
manufacturing of plastic parts.
 Mold and tooling. Silicon rubber tooling, epoxy tooling, spray metal tooling, acrylic
tooling, and plaster mold casting.
 Medical imaging. Diagnostic, surgical, operation and reconstruction planning and
custom prosthesis design.
Case Study

Cubital Prototyping Machine Builds Jeep in 24 Hours

Toledo Model and Die Inc. (TMD) of Toledo, Ohio, has used Cubital's Solider 5600 rapid
prototyping system to produce three design iterations of a toy jeep (Figure 3.2) in three days.
The plastic push toy is about 30 cm (12 in) long, 23 cm (9 in) wide and 23 cm (9 in) high.
Using the Cubital Solider 5600, TMD was able to produce each design iteration in 13 hours of
machine time. By using the Cubital front-end software, the parts were "nested-within a
working volume only 10 cm (4 in) deep, within the Solider's working area 50 cm x 35cm (20
in by 14 in). Initial file checking and post-production wax removal accounted for the rest of
the 24 hours.

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1.7 Post-processing of AM parts
Most additive manufacturing processes require post-processing after part building to
prepare the part for its intended form, fit and/or function. Depending upon the additive
manufacturing technique, the reason for post-processing varies. The various post-processing
techniques which are used to enhance components or overcome additive manufacturing
limitations are:

1. Support material removal

2. Surface texture improvements
3. Accuracy improvements
4. Aesthetic improvements
5. Preparation_ for use as a pattern
6. Property enhancements using non-thermal techniques
7. Property enhancements using thermal techniques

1.7.1 Support Material Removal

The most common type of post-processing in additive manufacturing is support removal.
The support material can be broadly classified into two categories:

(a) Natural supports

(b) Synthetic supports
(a) Natural support post-processing:

In processes where the part being built is fully encapsulated in the build material, the part
must be removed from the surrounding material prior to its use. Processes which provide
natural supports are primarily powder-based and sheet-based processes.

All powder bed fusion (PBF) and binder jetting processes require removal of the part
from the loose powder surrounding the part, and bond-then-form sheet metal lamination
processes require removal of the encapsulating sheet material.

The process of removal of support Materials

o In polymer powder bed fusion processes, after the part is built it is necessary to allow
the part to go through a cool-down stage.
o The part remains embedded inside the powder to minimize part distortion due to non-
uniform cooling.
o The cool-down time is dependent on the build material and the size of the part(s).
o Once cool-down is complete, there are several methods used to remove the part(s)
from the surrounding loose powder.

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 o Typically, the entire build (made up of loose powder - and fused parts) is removed
from the machine as a block and transported to a "breakout" station where the parts
are removed manually from the surrounding powdered material.
0 Brushes, compressed air, and light bead blasting are commonly used to remove loosely
adhered powder; whereas, wood-working tools and dental cleaning tools are
commonly used to remove powders which have sintered to the surface or powder
entrapped in small channels or features.

o Internal cavities and hollow spaces can be difficult to clean and may require

Fig 1.12 Automated powder removal using vibratory and vacuum

assist in a zcorp 450 machine

(b) Synthetic support removal:

,Processes which do not naturally support parts require synthetic supports for overhanging
features. In some cases, such as when using powder-based fusion. techniques for metals,
synthetic supports are also required to resist distortion.

Synthetic supports can be made from the build material or from, secondary material.

 Supports made from the build material

All material extrusion, material jetting, and vat photo polymerization processes require
supports for overhanging structures and to connect the part to the build platform. Since these
processes are used primarily .for polymer parts, the low strength- of the supports allows them
to be removed manually. These types of supports are also commonly referred to as breakaway
supports. The removal of supports from downward-facing features leaves witness marks where
the supports were attached. As a result, these -surfaces may require subsequent sanding and
polishing.

o Supports made from secondary materials

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 For polymers, the most common secondary support materials are polymer materials
which can be melted and/or dissolved in a water-based solvent. The water can be jetted or
ultrasonically vibrated to accelerate the support removal process. For metals, the most common
secondary support materials are lower melting- temperature alloys or alloys which can be
chemically dissolved in a solvent (in this case the solvent must not affect the build material).

1.7.2 Surface texture improvements

Additive manufacturing parts have common surface texture features that may need to be
modified for aesthetic or performance reasons. Common undesirable surface texture features
include: stair-steps, powder adhesion, fill patterns from material extrusion systems, and
witness marks-from support material removal.

Stair-stepping is a fundamental issue in layered manufacturing, although one can choose

a thin layer thickness to minimize error at the expense of build time.

Powder adhesion is a fundamental characteristic of binder jetting and powder-based

processes. The amount of powder adhesion can be controlled, to some degree, by changing

part orientation, powder morphology, and thermal control technique.

The type of post-processing utilized for surface texture improvements is dependent upon
the desired surface finish outcome. If a matte surface finish is desired, a simple bead blasting
of the surface can help even the surface texture, remove sharp corners from stair-stepping, and
give an overall matte appearance.

If a smooth or polished finish is desired, then wet or dry sanding and hand-polishing are
performed.

In many cases, it is desirable to paint the sufface prior to sanding or polishing. Painting the
surface has the dual benefit of sealing porosity and, by viscous forces, smoothing the stair-
step effect, thus making sanding and polishing easier and more effective.

Several automated techniques have been explored for surface texture improvements. Two
of the most commonly utilized include tumbling for external features and abrasive now
machining for, primarily, internal features.

1.7.3 Accuracy Improvements

There is a wide range of accuracy capabilities between additive manufacturing processes.
Some processes are capable of submicron tolerances, whereas others have accuracies around 1
mm. typically, the larger the build volume and-the faster the build speed the worse the
accuracy.

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 Sources of inaccuracy

 Process-dependent — process dependent inaccuracy can be - improved by good

operator skill. By using automatic real-time control strategies to monitor and
control process one can increase accuracy. Integration of additive plus subtractive
processing method to be adapted for process accuracy improvement.

o Material-dependent - material-dependent inaccuracy includes shrinkage effects which can

be compensated by scaling the cad model, quantitative understanding of the effects of
process parameters, build style, part orientation, support structures, and other factors on
the magnitude of shrinkage, residual stress, and distortion is necessary to enhance
predictive capabilities.
o In order to meet the needs Of applications where the benefits of additive manufacturing
are desired with the accuracy of a CNC machined component, a comprehensive strategy
for achieving this accuracy can be adopted. One such strategy involves pre-processing of
the STL file to compensate for inaccuracies followed by finish machining of the final
part. The following sections describe steps to consider when seeking to establish a
comprehensive finish machining strategy.

Model pre-processing to compensate for inaccuracy

o For many additive manufacturing processes, the position of the part within the build
chamber and the orientation will influence part accuracy, surface finish, and build time.
Thus, translation and rotation operations are applied to the original model to optimize
the part position and orientation.
o To compensate for shrinkage variation, the highest shrinkage value is used then ribs and
similar features will always be at least as big as the desired geometry. However,
channels and holes will be too large. Thus, simply using the largest shrinkage value is
not an acceptable solution. In order to make sure that there is enough material left on the
surface to be machined, adding "skin" to the original model is necessary.
o This skin addition, such that there is material left to machine everywhere, can be referred
to as making the part "steel-safe." Many studies have shown that shrinkage variations are
geometry dependent, even when using the same additive manufacturing or furnace post-
processing parameters.
o Thus, compensating for shrinkage variation requires offsetting of the original model to
guarantee that even the features with the largest shrinkage levels and all channels and
holes are steel-safe.
 There are two primary methods for adding a skin to the surface of a part. The first is to
offset the surfaces and then recalculate all of the surface intersections.

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  This methodology, though the most common, has many drawbacks for STL files made
up of triangular facets. In answer to these drawbacks; an algorithm developed for
offsetting all of the individual vertices of an STL file by using the normal vector
information for the connected triangles, then reconstructing the triangles by using new
vertex values, has been developed. In an STL file, each vertex is typically shared by
several triangles whose unit normal vectors are different. When offsetting the vertices of
a model, the new value of each vertex is determined by the unit normal values of its
connected triangles.

Machining strategy

Machining strategy is very important for finishing additive manufacturing .parts and tools.
Considering both accuracy and machine efficiency, adaptive raster milling of the surface, plus
hole drilling and sharp edge contour machining can fulfill the needs of most parts.

1.7.4 Aesthetic Improvements:

Many times additive manufacturing is used to make parts which will be displayed for
aesthetic or artistic reasons or used as marketing tools. In these and similar instances, the
aesthetics of the part is of critical importance for its end application. Often the desired aesthetic
improvement is solely related to surface finish. In some cases, a difference in surface texture
between one region and another may be desired. In this case, the finishing of selected surfaces
only is required. In cases where the color of the additive manufacturing part is not of sufficient
quality, several methods can be used to improve the part aesthetics.

Some types of additive manufacturing parts can be effectively colored by simply dipping the
part into a dye of the appropriate color. This method is particularly effective for parts created
from powder beds, as the inherent porosity in these parts leads to effective absorption. If painting
is required, the part may need to be sealed prior to painting. Common automotive paints are quite
effective in these instances.

Another aesthetic enhancement (which also strengthens the part and improves wear
resistance) is chrome plating. Several materials have been electro less coated to additive
manufacturing parts, including ni, cu, and other coatings. In some cases, these coatings are
thick enough-that, in addition to aesthetic improvements, the parts are robust enough to use as
tools for injection molding.

1.7.5 Preparation for use as a pattern:

Often parts made using additive manufacturing have intended as patterns for investment
casting, sand casting, room temperature vulcanization molding, spray metal deposition, or other
pattern replication processes. In many cases, the use of an additive manufacturing pattern in a
casting process is the least expensive way to use additive manufacturing to produce a metal
part, as many of the metal-based additive manufacturing processes are still expensive to own

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and operate. The accuracy and surface finish of an additive manufacturing pattern will directly
influence the final part accuracy and surface finish. As a result, special care must be taken to
ensure the

Pattern has the accuracy and surface finish desired in the final part. In addition, the pattern
must be scaled to compensate for any shrinkage that takes place in the pattern replication steps.

Investment casting patterns

In the ease of investment casting, the additive manufacturing pattern will be consumed
during processing. In this instance, the residue left in the mold as the pattern is melted or
burned out is undesirable. Any sealants used to smooth the surface during pattern

Preparation should be carefully chosen so as not to inadvertently create unwanted

residue.

Additive manufacturing parts can be printed on a casting tree or manually added to a casting
tree after additive manufacturing. The figure shows rings made using a material jetting system.

Rings for . Investment casting

In the first figure, a collection of rings is shown on the build platform; each ring is
supported by a secondary support material in white. Itithe second picture, a close-up of the ring
pattern is shown. The third picture shows metal rings still .attached to a casting tree.
In this instance, the rings were added to the tree after additive manufacturing, but
before casting. When using the stereo lithography quick cast build style, the hollow, truss-
filled shell patterns must be drained of liquid prior to investment: The hole(s) used for draining
must be covered to avoid investment entering the interior of the pattern. Since photopolymer
materials are thermosets, they must be burned out of the investment rather than melted.
When powdered materials are used as investment casting patterns, such as polystyrene
from a polymer laser sintering process or starch from a binder jetting process, the resulting part
is porous and brittle. In order to seal the part and Strengthen it for the investment process, the
part is infiltrated with an investment casting wax prior to investment.

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 1.7.6 Property enhancements using non4hernial techniques
Powder-based and extrusion-based processes often create porous structures. In many cases,
that porosity can be infiltrated by a higher-strength material, such as cyanoacrylate. (super
glue®). Proprietary methods and materials have also been developed to increase , the strength,
ductility, heat deflection, flammability resistance, emit shielding, or other properties of additive
manufacturing parts using infiltrates and various types of Nano-composite reinforcements.

A common post-processing operation for photopolymer materials is. curing. During Processing,
many photopolymers do not achieve complete polymerization. As a result, these parts .are put
into a post-cure apparatus, a device that floods the part with UV and visible radiation in order to
completely cure the surface and subsurface regions of the Part. Additionally, the part can
undergo a thermal cure in a low-temperature oven, Which can help completely cure the
photopolyrner and in some cases greatly, enhance the part's mechanical properties .

1.7.7 Property enhancement's using thermal techniques,

After additive manufacturing processing, many parts are thermally processed to enhance their
properties. In the case of powder-based fusion techniques for metals, this thermal processing is
primarily heat treatment to form the desired microstructures and to relieve residual stresses. In
these instances, traditional recipes for heat treatment developed for the specific metal alloy
being employed are often used. In .some cases, however, special heat treatment methods have
been developed to retain the fine-grained microstructure within the additive manufacturing part
while still providing stress relief and ductility enhancement.

In order to prepare a green part for furnace processing, several preparatory steps are typically
done. The figure shows the steps for preparing a metal green part made from laser form st-100
for furnace infiltration.

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 The use of cooling channels which follow the contours of the surface (conformal cooling
channels) in an injection mold has been shown to significantly increase the productivity of
injection mold tooling by decreasing the cooling time and part distortion, the appropriate use of
conformal cooling channels enables many companies to utilize additive manufacturing-produced
tools to increase their productivity.

In addition to the thermal processes discussed earlier, a number of other procedures have been
developed over the years to combine additive manufacturing with furnace processing to produce
metal or ceramic parts.

One example approach utilized laser sintering to produce porous parts with gas impermeable
skins. By scanning only the outside contours of a part during fabrication by SLS, a metal "can"
filled with loose powder is made. These parts are then post-processed to full density using hot
isostatic pressing. This in situ encapsulation results in no adverse container—powder interactions
(as they are made from the same bed of powder), reduced pre-processing time, and fewer post-
processing steps compared to conventional

The selection method followed for an additive manufacturing part is

o Decision theory
o Approaches to determining feasibility
o Approaches to selection,
1) Decision theory
There are three elements for any decision, they are.

o Options—the items from which the decision maker is selecting

 Expectations—of possible outcomes for each option
o Preferences—how the decision maker values each outcome
 In an additive manufacturing selection, an outcome might consist of the time, cost,

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 and surface finish of a part built using a certain additive manufacturing process, while
the process itself is the option.

o Expectations of outcomes are modeled as functions of the options, x=g (a), and may be
modeled with associated uncertainties. (a- set of decision options, x- expectations)
o Preferences model the importance assigned to outcomes by the decision maker.
For example, a designer may prefer low cost and short turn-around times for a concept model,
while being willing to accept a poor surface finish. In many ad hoc decision support methods,
preferences are modeled as weights or impOrtance. For simple problems, the decision maker may
just choose weights, while for more complex decisions, more sophisticated methods are used, such
as pair-Wise comparison. In utility theory, preferences are modeled as utility functions on the
expectations. Expectations are then modeled as expected utility. The best alternative is the one with
the greatest expected utility.

F. Mistree, JIB. Allen, and their coworkers have been developing the decision support problem
technique over the last 20 years. The advantages of decision support problem, compared with other
decision formulations, are that they provide a means for mathematically modeling design decisions
involving multiple objectives and supporting a human judgment in designing systems. The
formulation and solution of decision support problem facilitate several types of decisions, including:

Selection—the indication of preference, based on multiple attributes, for one among several
alternatives,

Compromise—the improvement of an alternative through modification

Coupled and hierarchical—decisions that are linked together, such as selection–selection,

compromise–compromise, or selection–compromise.

The selection problems being addressed is divided into two.

First, it is necessary to generate feasible alternatives, which, in this case, include materials and
processes.

Second, given those feasible alternatives, a. quantification process is applied that results in
a rank-ordered list of alternatives.

The first sub problem is referred to as "determining feasibility," while the second is
simply called "selection."

2, Approaches to determining feasibility

Most approaches to determine feasibility are a knowledge-based approach to deal with

the qualitative: information related to am process capability.

Deglin and Bernard defined the problem as "to propose, from a detailed functional

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 specification, different alternatives of rapid manufacturing processes, which can be ordered
and optimized when considering a. combination of different specification criteria (cost,
quality, delay, aspect, material, etc.)." Their approach utilized two reasoning methods,
case-based and the bottom-up generation of processes; the strengths of each compensated
for the other's weaknesses. Their system was developed on the KADVISER. platform and
utilized a relational database system with extensive material, machine, and application -
information.

The problem of determining the process and material feasibility can be represented by
the preliminary selection decision support problem. The word formulation is given in the
table below, the decision support problem is a structured decision formulation and
corresponds to a formal decision method based on decision theory. Qualitative comparisons
among processes and materials, with respect to decision criteria, to identify feasible
alternatives and eliminate infeasible ones.

Given a set of concepts

Identify the principal criteria influencing selection. The relative importance of the criteria

Capture experience-based knowledge about the concepts with respect to a datum

and the established criteria

Rank the concepts in order of preference based on multiple criteria and their relative
importance

The key step here is how to capture and apply experience-based knowledge. One chooses a
datum concept against which all other ,concepts are compared.

Qualitative comparisons are performed, where a concept is judged as better, worse, or

about the same (+1, -1, 0, respectively) as the datum with respect to the principal criteria
for the selection. problem. Then, a weighted sum of comparisons with the datum is
computed. Typically, this procedure is repeated for several additional choices of datum's..
In this manner, one gets a good understanding of the relative merits and deficiencies of
each concept.

3. Approaches to selection

While the basic advantages. of using decision support problem of any type lie in providing
context and structure for engineering problems, regardless of complexity, they facilitate the
recording of viewpoints associated with these decisions, for completenes s and future
reference, and evaluation of results through post solution sensitivity analysis.

The standard selection decision support problem has been applied to many engineerin g
problems and has recently been applied-to am selection.

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 The word .formulation of the standard selection decision support problem is given in a
table, the decision options for additive manufacturing selection are feasible material-
process combinations. Expectations are determined by rating the options against the
attributes. Preferences are modeled using simple importance values. Rank ordering of
options is determined using a weighted-sum expression of importance and attribute
ratings. An extension to include utility .theory has recently been accomplished. For the
identify step, evaluation attributes are to be specified. For example," accuracy, cost, build
time, tensile strength‘ and feature detail (how small of a feature can be created) are typical
attributes. Scales denote how the attribute is to be measured.

Given set of additive. manufacturing processes machines and materials (alternatives)

1 identity set of evaluation attributes Create scales and determine importance.
Capture each alternative relative to each attribute. '
Rank. additive Manufacturing methods from most to least promising

1.8.1Chall enges of selection

The complex relationships among attributes, and the variations that can arise when
building a wide range of parts, make difficult to decouple decision attributes and
develop structured decision problems. Nonetheless, with a proper understanding of
technologies d attributes, and how to relate them together, meaningful information can
be gained.

For example, there are large, expensive machines that can fabricate parts using a
variety of materials with relatively good accuracy and/or material properties and with the
ability to fine-tune the systems to meet specific needs. In contrast, there are cheaper
systems, which are designed to have minimal setup and to produce parts of acceptable
quality in a predictable and. reliable manner. In this latter case, parts may not have high
accuracy, material strength, or flexibility of use. Different users will require different
things from an additive manufacturing machine.

Machines vary in terms of cost, size, a range of materials, an accuracy of a-part, time of
build, etc, it is not surprising to know that the more expensive machines provide the wider range
of options and, therefore, it is important for one looking to buy a new machine to be able to
understand the costs vs, the benefits so that it is possible to choose the best machine to suit their
needs.

Approaching a manufacturer or distributor of additive manufacturing equipment is one way

to get information concerning the specification of their machine.

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Conventions exhibitions are a good way to make Comparisons, but it is not necessarily easy to
identify the usability of machines.

Contacting existing users is sometimes difficult and time-consuming, but they can give
very. honest opinions. This approach works best if you are already equipped with
background information concerning your proposed use of the technology. When looking for
advice about suitable selection methods or systems, it is useful to consider the following
points.

o The information in the system should be unbiased wherever possible. .

o The system should provide support and advice rather than just a quantified result.
o The system should provide an introduction to additive manufacturing to equip the
user with background knowledge as well as advice on different additive
manufacturing technologies.
o A range of options should be given to the user in order to adjust requirernents and
show how changes in requirements may affect the decision.
o The system should be linked to a comprehensive and up-to-date database of additive.
Manufacturing machines.
o After the search process has completed, the system should give guidance on where to
look next for additional information.
If it were possible to decouple the attributes of the system from the user specification,
then it would be a relatively simple task to select one machine against another. To illustrate
that this is not always possible, consider the following scenarios:

I. In a powder bed fusion machine, warm up and cool down are important stages during the
build cycle that do not directly involve parts being fabricated, This means that large parts do
not take proportionally longer times to build compared with smaller ones: Large builds are
more efficient than small ones. In vat photo polymerization and material extrusion machines,
there is a much stronger correlation between part size and build time.. Small parts would;
therefore, take less time on a vat photo polymerization and material extrusion machines
machine than when using powder bed fusion machine if considered in isolation. Many users,
however, batch process their builds and the ability to vertically stack parts in a powder bed
fusion machine, makes it generally possible to utilize the available space more efficiently.
The warm-up and cool down overheads are less important for larger builds and the time per
layer is generally quicker than most SL and material extras machines. As a result of this is
not easy to see Which machine would be quicker without carefully analyzing the entire
process plan for using a new machine.

2. Generally, it costs less to buy a dimension or other low-end material extrusion machine
compared to a binder jetting (BJ) machine. There are technical differences between -these
machines that make them suitable for different potential applications. However, because they'

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 are in a similar price bracket, they are often compared- for similar applications. Dimension
Material extrusion machines use a cartridge-based material delivery system that requires a
complete replacement of the cartridge when empty. This makes material use much more
expensive when compared with the 3d systems bj (aka "zcorp") machine. For occasional use,
it is therefore perhaps better to use a dimension machine when all factors are equal. On the
other hand, the more parts you build, the more cost-effective the 133 machine becomes.

These examples indicate that selection results depend to a large extent on the users
knowledge of additive manufacturing capabilities and applications. Selection tools that include
expert systems may have an advantage over tools based on straightforward decision methods
alone. Expert systems attempt to embody the expertise resulting from extensive, use of additive
manufacturing technology into a software package that can assist the user in overcoming at
least some of the learning curve quickly and in a single stage.

1:9 Applications of additive manufacturing

1.9.1 Functional models
There are a number of RP technologies that meet the need for building functional
prototypes with material properties close to those of production parts. One of the RP
processes that are widely used for producing models for functional tests is SLS. Initially,
four nylon-based materials (standard nylon, fine nylon, fine nylo medical grade, nylon
composite) were available commercially for this process. Later Duraform PA and glass
reinforced Duraform GF were added to this. iluraform prototypes can be relatively easily
finished to a smooth appearance. The production of nylon parts is generally cost-effective
when a small number (1-5) of parts is required. Before the introduction of Duraforrn pa, a
nylon composite known as the proto-form composite was used widely for producing
functional parts.

A case study of protoform- building a functional model

Proto form is a bleld of 50% by weight nylon powder and 50% by weight spherical
glass beads. This SLS glass-filled nylon processed to near full density which has a high
modulus and good heat and chemical resistance. The housing in figure is a test part and is
built in proto form composite because it is required to withstand harsh testing conditions
including temperatures of about 100°c. As a base part for mounting precision
components, it has to keep its dimensions within close limits. The geometry of the
housing prevented the downdraft, leaving a hot area inside the part and causing post-build
warping of the walls.

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 Fig 1.15 Composite nylon housing: without ribs (left) - with ribs (right)
The first part manufactured suffered from much distortion: there was vertical growth and
"wash out" (loss of definition and rounding of edges) on the downward facing surfaces and
the external dimensions of the sidewalls varied. This problem was solved by making the wall
thickness uniform and reducing its dimension. The non-functional ribs were added across the
housing to stiffen it. Two ribs were positioned vertically and two others horizontally as shown
in figure the number and size of the ribs were determined from experience to constrain post
process distortion in the x and y directions without adding too much build time. The ribs were
also located so that they could easily be removed by machining after completing the build.
Subsequently manufactured parts had much better .dimensional accuracy. The main
functional dimensions were measured but no

Form or geometrical accuracy measurements were taken. To evaluate the influence of the ribs,
the accuracy in the build direction (z direction) and the x-y plane. was studied. The results
showed that the ribs improved the accuracy consistently but had different effects in each
direction. Also, there was reduced post-process distortion due to the added ribs. Another
indicator of the quality of a part produced by RP is the international tolerance grade established
by the ISO-ANSI standards which showed good results in nylon.

1.9.2 Patterns far investment and Vacuum casting

RP technologies are widely used for building patterns for investment and vacuum casting. For
example, models built employing SLA, SLS, and FDM can be used as patterns for both casting
processes. A case study is presented below that discusses some accuracy aspects of producing
SLS patterns and also addresses general issues regarding the technological capabilities of the
process.

Two SLS materials are currently available for producing casting patterns, cast form and true
form. In this case study, true form; which is an acrylic-based powder, is used to build casting

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patterns. It is processed at relatively low temperatures, good accuracy but moderate strength.
The density of true form parts can vary from 70 to 90% depending on build parameters and
they can be polished to a mirror-like finish. Dense parts are used as patterns for vacuum
casting while rather porous parts are better suited for investment casting; unlike dense
models, they do not expand to cause shell cracking during the burning out of the patterns.

The figure shows a to BS 199 aluminum housing (195x145x250mm) made by investment

casting from a true form pattern.

Fig 1.16 BS 199 aluminum housing (195x145x250mm) made by

investment casting from a true form pattern.

True form housing pattern. (Right) and aluminum investment casting (left)

True form behaves like an injection molded plastic and thick sections may be subjected to
sinking or sagging. Part orientation must, where possible, be selected to prevent sagging. This may
not always be practicable and in such cases shelling of the model (i.e. Converting a solid model
into a hollow part) can significantly reduce part distortion. Trueform normally gives good
accuracy.

If a larger SLS machine such as the Sinterstation 200 had been used this would. h4ve
allowed the part to be oriented horizontally in the build area. In this way, the accuracy would
certainly have been much closer to±0.12snain which is the accuracy quoted for the trueform
Material by the machine manufacturer.

However, even if some dimensions were out of the required general tolerance (0.1
2smin) the aluminum castings were fully satisfactory as any deviations were able to be
corrected when some of the features were machine-finished afterward. Trueform patterns
become cost-effective when a small number of parts, say up to 50, of complex design are
required and the cost of a mold for wax patterns is prohibitive.

1.9.3 Engineering analysis models

Computer aided engineering (CAE) analysis is an -integral part of time compression
technologies. Various software tools exist, mainly based on finite element analysis (FEA), to

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speed up the development of new products by initiating design optimization before physical
prototypes are available. However, the creation

Of accurate FEA models for complex engineering objects sometimes requires significant
amounts of time and effort. By employing RP techniques it is possible to begin test
programmes on physical models much earlier and complement the CAE data. Two applications
of RP models for engineering analysis are described below.

1. Visualization of flow patterns. For example, SLA models were used to optimize the cross-
flow jacket of a v6 high-performance racing engine (figure). 60 sensors were installed in the
model to monitor local flow temperature and pressure conditions. The coolant flow patterns were
visualized by accurately injecting very small air bubbles. The flow patterns were recorded by
high-speed video. The analysis conducted provided valuable data about stagnation zones and
insufficiently cooled sections. This data allowed the critical sections to be redesigned and. SLA
models of the modified components were produced. Each design iteration took one week. This
enabled the testing of flow channel variations in a very short time. The accuracy and surface
quality of the SLA models are more than adequate to reproduce complex flow behaviors,

Fig 1.17 Assembly of the cross -flow water jacket of a v6 high-performance

2. Photo elastic stress analysis. Photo elastic testing can be used to determine the stresses and
strains within physical parts under specific conditions. This analysis is based on the temporary
birefiingence of a transparent material subjected to a specific load. Sla models fabricated using the
aces build style exhibit the required birefringence that can be illustrated by irradiating the test
samples with polarized white and monochromatic light. Results from photo elastic analysis of SLA
models can be transferred to functional metal parts by employing fundamental similarity laws. This
allows predictions to be made rapidly at a low cost regarding the actual stress distributions
anticipated in functional parts. By using SLA models for photo elastic stress analysis, it is also
possible to "freeze" the stresses and strains by warming the loaded model to a level above the resin
glass transition temperature and then gradually cooling the model back to room temperature

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 Fig 1.18 The frozen stress distribution for a model of an aero engine turbine rotor

1.9.4 Artistic industry

The use of additive manufacturing technology in jewelry and arts offers new possibilities
to design most complex designs or shapes as shown in figure SLA (from 3d systems) has
been used successfully to develop fine jewelry models because of the high printing
resolution. Models fabricated by SLA were used as master patterns to create the rubber
molds for manufacturing wax patterns. These were later used in the investment casting
process to fabricate the functional end-user product.

Fig 1.19 An investment cast silver alloy prototype of a broach (right), a

wax pattern created from the Silicon rubber molding (center), and the
two-time scaled SL built model (left)
Additive manufacturing technologies can provide a powerful tool to the jewelers and
artists for their work, which will allow them to fabricate unique shaped parts in just a few
hours rather than days or weeks. Systems manufacturer Solidscape division of Stratasys in
the united states, have shown much interest in this particular area and have reported the most
work in this area

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 The other example of a work of art produced employing RP techniques is a bracelet
designed by m. Woolner and t. Cook. The bracelet is designed in such a way that it can be
produced only by using RP technologies. The artifact is a complex trajectory extrusion
starting at one end as an ellipse with.a star-shaped internal form and finishing at the other
end with a star-shaped section having an ellipse as an internal 'form. The RP model was built
using an SLA system. Both models are shown in figure, the intention was to cast the bracelet
in silver after making minor modifications to the design.

Fig 1.20 3d cad model and the SLA art prototype

Medical industry:

RP technologies are applied in the medical domain for building models that provide visual
and tactile information. In particular, RP models can be employed in the following medical
applications

 Operation planning. Using real size RP models of patients pathologic regions,

surgeons can much more easily understand physical problems and gain a better insight
into the operations to be performed. RP models can also assist surgeons in
communicating the proposed surgical procedures to the patients.
 surgery rehearsal. RP models offer unique opportunities for surgeons and surgical
teams to rehearse complex operations using the same techniques and tools as during
actual surgery. Potentially, such rehearsals can lead to changes in surgical procedures
and significantly reduce risk.

 Training. RP models of specimens of unusual medical deformities can be built

to facilitate the training of student surgeons and radiologists: Such models can also be
employed for student examinations.
 Prosthesis design. RP models can be used to fabricate master patterns which are
then replicated using a bio-compatible plastic material. Implants produced in this way
are much more accurate and cost-effective than those produced employing conventional
techniques.

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 A study considered 47 mandibular reconstruction cases (between 2003 and 2009) to evaluate
the feasibility of applying am built 3d models, in the medical field, concluded that c5.7% of the
patients were found to have at least a satisfactory result and the majority (38 out of 47) of
patients were in a good and the very good end result categories.

Recently this technology was used for the separation of Siamese twins by performing , precise
pre-surgical planning on additive manufacturing built models as shown in figure. It is a very
significant discovery in the medical sector, which opened the way for creating other complex
human organs or tissues with the help of additive manufacturing technology.

But still, this technology cannot be used in daily practices due to the presence of current
issues like cost, time, suitable material etc. For biomedical applications, further research is.
required to reduce the overall cost (virtual planning and fabrication cost), development of
suitable biomaterials.

Fig 1.21 Additive manufacturing model of congenital scoliosis, (b) pre-

surgical planning on the additive manufacturing model before total hip
replacement, (c) presurgical planning on additive manufacturing built
models to separate Siamese twins.

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1.9. 6 Architectural Industry
Another interesting field whereof this emerging technology has been used is an
architectural industry. As we know architects usually make their models by performing
manual tasks (hand techniques). It consumes a lot of time and sometimes it's a hard task to
create a complex shape model or to present their ideas in physical shape. Similar to the
jewelry industry, additive manufacturing technology is capable to create complex shapes
quickly and accurately, also it saves time in designing and developing complex shaped
architectural models. Exceptional shapes become a reality with the use of additive
manufacturing processes.

Stereo lithography process is very suitable for architectural modeling because of its
printing resolution and materials availability. Furthermore, designs can be improved easily by
simply additive manufacturing ending the cad model. Additive manufacturing technology
provides a better resolution than other processes used in architecture. Models such as presented
in figure can only be fabricated by additive manufacturing processes.

Fig 1.22 Artistic models fabricated by additive manufacturing technology

1.9.7 Rapid tooling

Prior to 1992, Chrysler experimented with a. variety of rapid tooling processes with stereo
lithography master patterns. This included vacuum forming, resin transfer molding, sand casting,
squeeze molding, and silicone molding. Here we realize how early in the additive manufacturing
field's development :these applications were investigated. An area of significant effort in both the
aerospace and automotive industries was the use. of SL parts as investment casting patterns. Early
experiments used thinly walled SL patterns or hollow parts. Because SL resins expand more than
investment casting wax, when used as patterns, the SL part tended to expand and crack the ceramic
shell. This led to the development of the quick cast pattern style in 1992, which is a type of lattice
structure that was added automatically to hollow part STL Files by SL machine pre-processing
software.

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 The quick cast. style was designed to support thin walls but not to be too strong. Upon
heating and thermal expansion, the quick cast lattice struts were designed to flex, collapse
inward, break, but not transfer high loads to the part skins which could crack the shell which,
revolutionized the investment casting industry.

Another interesting development in the early 2000s was the large-frame binder jetting
technology by Exone, where a sand material was developed that was suitable for use as sand
casting dies. Exone marketed the s15 binder jetting machine for several years (the technology
was purchased from a German company generis GMBH in 2003).

As one example, two of these sand machines were operating at the ford Dunton technical center
in England in the mid-2000s (they may still be operational) to support their design and
development activities. Much of the ford of Europe operations are housed here, including - small
car design, power train 'design and development, and some commercial vehicles.

As of the end of 2005, Exone had reportedly sold 19- s15 machines, each of which cost over
$1m. More recently, Boeing,.Northrop-Grumma4 and other aerospace companies have used
material extrusion technology to fabricate tooling. They developed -tooling designs for
composite part lay-up that was suitable for me fabrication., Other reported tooling applications
included drill guides and various assembly tools.

1.9.8 Aerospace
The primary advantage for production applications in aerospace is the ability to generate complex
engineered geometries with a limited number of processing steps. Aerospace companies have access
to budgets significantly larger than most industries. This is, however, often necessary because of
the high-performance nature Of the products being produced.

Production application.

All of the major aerospace companies in the USA and. Europe have pursued production
applications of additive manufacturing for many years. Boeing, for example, has installed tens of
thousands of additive 'manufacturing parts on their military and commercial aircraft. Reportedly,
over 200 different parts are flying on at least 16 models of aircraft. Until recently, all of these were
nonstructural polymer parts for military or space applications.

Some of the first large scale, metal part production manufacturing applications is
emerging in the aerospace industry. GE purchased Morris technologies in 2012 as part of a
major investment in metal additive manufacturing for the production of gas turbine engin e
components. The part that has received the most attention is a new fuel nozzle design for
the eft leap (leading edge aviation propulsion) turbofan engine, as shown in fig.

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 Fig.1. 23 F ad nozzle and hinge used in aircraft done by additive
manufacturing

The new fuel nozzle took the part consolidation concept to new levels by reportedly
combining I 8-20 parts into one integrated design and avoiding many brazed joints - and
assembly operations. This new design is projected to have a useful life five times that of lilt;
original design, a 25 % weight reduction, and additional cost savings realized through
optimizing the design and production process. Additionally, the fuel nozzle was engineered
reduce carbon build up, making the nozzle more efficient.

Production manufacturing of the nozzles is scheduled to begin in 2015. Each engine

contains 19 fuel nozzles and more than 4,500engines have been sold to date, so production
volume could exceed 100,000 total parts by 2020. This is claimed to save 1000 lb. of weight
out of each engine. The nozzles are fabricated using the cobalt-chrome material fabricated in
EOS metal powder based fusion machines. Parts are likely to be stress relieved while still in
the powder bed, followed by hot isostatic pressing (hip) to ensure that the parts are fully
dense..

Airbus investigated topology optimization applications in order to develop part designs

that were significantly lighter than those suitable for conventional manufacturing processes.
Shown in fig, B is an a320 nacelle hinge bracket that was originally designed as a Cast steel
part but was redesigned to be fabricated in a titanium alloy using PBF reportedly, they trimmed
10 kg off the mass of the bracket, saving approximately 40% in weight: This study was
perform6d as part of a larger effort to compare life-cycle environmental impacts of part design.

Many more production applications of additive manufacturing can be expected in the sear
future as materials improve and production methods become standardized, repeatable,

and certified. New design concepts can be expected, such as the a320 hinge bracket, for not only
piece parts, but entire modules.

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1.9.9Automotive Application:
In automotive industry additive manufacturing companies pioneered many types of
manufacturing applications in product development. Companies in this automobile industry are
heavy users of additive manufacturing. Company accounts for approximately 17 % of all
expenditures on additive manufacturing. This positions the automotive industry behind compared
to industrial/business machines (18.5 %) and consumer products/electronics (18 0,) which are
very large and broad industries in terms of the largest users of additive manufacturing.

Since production volumes in the automotive industry are often high, additive manufacturing
has typically been evaluated as too expensive for production manufacturing. Till date, most
manufacturers have not committed to additive manufacturing parts of their mass-produced car
models

In addition, suppliers to this automotive industry uses additive manufacturing - parts to test
assembly operations and tools to • identify potential problems before production assembly
commenced. Since model line change-over involves huge investments, being. able to avoid
problems in production yielded very large savings.

In the metal powder based fusion area, concept laser, a German company, introduced their x
line 1000r machine recently, which has a build chamber large enough to accommodate a v6
automotive engine block. This machine was developed in collaboration with Daimler Ag for
production manufacture in mind. According to concept laser, the 1000r is capable of building at a
rate of 65 cm3 per hour, which is fast compared to some other metal PBF machines. Additionally,
the machine was designed with two build boxes (powder chambers) on a single turntable so that
one build box could be used for part fabrication, while the other could be undergoing cool-down,
part removal, pre-heating or other non-part building activities. For specialty cars or low-volume
production, additive manufacturing can he economical for some parts. Applications include
custom parts on luxury cars or replacement parts on antique cars.

Polymer powder based fusion was used to fabricate some custom interior components, such
as bezels, that were subsequently covered in leather and other materials. Typically, Bentley has
production volumes of less than 10,000 cars for a given model, so this qualifies as low
production volume.

Local motors is a small company that is experimenting with crowd sourcing and other novel
methods of new vehicle development. They participated in the Darpa fang, military vehicle
development exercise, for example. They utilize additive manufacturing when it makes sense
for their applications. In a separate initiative, they conducted a crowd-sourced car design
project, with„the requirement that the majority of the car would be fabricated by am. They plan
to fabricate the body and structural components using 'a new, large-frame material extrusion
machine from oak ridge national laboratories at the international machine technology. Among
the racing organizations, formula 1 has been a leader in adopting additive manufacturing.

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Originally using additive manufacturing for rapid prototyping; some of the teams started putting
additive manufacturing parts on their race cars in the early to inid-2000s. These were typically
nonstructural polymer PBF parts. Similarly to the aerospace industry, formula 1 teams utilized
additive manufacturing models for wind tunnel testing of scale models, as well as parts for full-
size car models. Teams from other racing organizations, including Indy and NASCAR, have
also made additive manufacturing an integral aspect of their car development process.

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