CHAPTER 1

INTRODUCTION

1.1 ADDITIVE MANUFACTURING

Additive manufacturing (AM) or additive layer manufacturing (ALM) is the industrial

production name for 3D printing, a computer-controlled process that creates three-dimensional
objects by depositing materials, usually in layers.

1.1.1 HOW DOES ADDITIVE MANUFACTURING WORK?

Using computer-aided or 3D object scanners, additive manufacturing allows for the

creation of objects with precise geometric shapes. These are built layer by layer, as with a 3D
printing process, which is in contrast to traditional manufacturing that often requires machining
or other techniques to remove surplus material.

1.1.2 ADDITIVE MANUFACTURING PROCESSES

There are several distinct AM processes with their standards, which include:

1. Binder Jetting
2. Directed Energy Deposition
3. Material Extrusion
4. Powder Bed Fusion
5. Sheet Lamination
6. Vat Polymerisation
7. Wire Arc Additive Manufacturing (Now known as Directed Energy Deposition-
Arc (DED-arc))

1.1.2.3 Material Extrusion

Material extrusion is an additive manufacturing (AM) technique that deposits a

continuous filament of composite or thermoplastic material to build 3D parts layer by layer.
The filament is fed from a spool through a heated extruding nozzle, which heats the material
and deposits it onto a build platform.

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 Although it is not as accurate or fast as other additive manufacturing processes, material
extrusion technology and materials are inexpensive, making it the most popular 3D
printing method for home hobby-grade use. In an industrial setting, material extrusion is used
for rapid prototyping.

The material extrusion process works as follows:

1. A heated nozzle deposits material into a build platform to create the first cross-sectional
slice of the final object
2. Further layers are added as required, with each layer fusing with the last either as a
result of temperature control or through the use of chemical agents

Advantages:

Material extrusion offers a range of advantages, as follows:

 Low set-up and running costs

 Wide selection of printing materials available
 Easy to learn and user-friendly
 Able to produce parts with a printing tolerance of +/- 0.1 (+/- 0.005″)
 Comparably fast print time for thin or small parts
 Low-temperature process
 Equipment is small-sized and able to be used in the home
 No supervision is required

Disadvantages:

Despite the many advantages, there are also several disadvantages associated with the material
extrusion process, as follows:

 Print materials are toxic

 Process can leave visible layer lines
 Creating finer resolution parts or depositing over a wide print area can dramatically
increase printing time
 The extrusion head must remain in motion to prevent the deposited material from
bumping up

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  May require support material for some structures
 Parts are susceptible to warping, delamination, and other temperature fluctuation-
related problems
 Tends towards poor part strength along the vertical Z-axis.

Applications:

Materials extrusion is used across commercial, research, and hobbyist sectors due to its
low complexity, ease of implementation, and compatibility with commercially-available
materials. Applications include the creation of functional engineering prototypes and systems,
including for clinical uses.

Examples:

Examples of material extrusion technology include composite filament fabrication (CFF),

fused filament fabrication (FFF), and fused deposition modeling (FDM).

Similar to other 3D Printing processes, material extrusion involves drawing the material
through a nozzle where it is heated and deposited layer by layer. The nozzle can move
horizontally along a platform, which moves up and down as each layer is deposited. To achieve
accurate results, the extruded material needs to be fed through the nozzle as a steady stream
under constant pressure.

With CFF, two print head nozzles are used at once, with one following the usual material
extrusion process to create the outer shell and internal matrix of the part, while the other
deposits a continuous strand of composite fiber inside the printed parts to add strength. This
can create parts with a strength comparable to metal.

Material extrusion is commonly used on inexpensive domestic and hobby 3D printers, although
it is also found in more industrial settings, such as for constructing buildings through concrete
extrusion or for making human tissues and organs for the medical profession.

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1.1.3 ADDITIVE MANUFACTURING TECHNOLOGIES

AM technologies can be broadly divided into three types.

 The first of which is sintering whereby the material is heated without being liquified
to create complex high-resolution objects. Direct metal laser sintering uses metal
powder whereas selective laser sintering uses a laser on thermoplastic powders so that
the particles stick together.
 The second AM technology fully melts the materials, this includes direct laser metal
sintering which uses a laser to melt layers of metal powder, and electron beam melting,
which uses electron beams to melt the powders.
 The third broad type of technology is stereolithography, which uses a process called
photopolymerization, whereby an ultraviolet laser is fired into a vat of photopolymer
resin to create torque-resistant ceramic parts able to endure extreme temperatures.

1.1.4 ADVANTAGES OF ADDITIVE MANUFACTURING

Similar to standard 3D printing, AM allows for the creation of bespoke parts with
complex geometries and little wastage. Ideal for rapid prototyping, the digital process means
that design alterations can be done quickly and efficiently during the manufacturing process.
Unlike with more traditional subtractive manufacturing techniques, the lack of material
wastage provides cost reduction for high-value parts, while AM has also been shown to reduce
lead times.

In addition, parts that previously required assembly from multiple pieces can be
fabricated as a single object which can provide improved strength and durability. AM can also
be used to fabricate unique objects or replacement pieces where the original parts are no longer
produced.

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1.2 POLYMER THERMOPLASTICS
1.2.1 THERMOPLASTIC POLYURETHANE

Thermoplastic polyurethane (TPU) is a popular material in additive manufacturing, also known

as 3D printing, due to its favourable properties and versatility.

Figure 1. Thermo Plastic Polyurethane

1. Elasticity and Flexibility

TPU's inherent elasticity and flexibility make it suitable for producing

prototypes, functional parts, and products requiring impact resistance or
cushioning. In additive manufacturing, TPU can be extruded or fused using
techniques like Fused Deposition Modelling (FDM) or Selective Laser Sintering
(SLS) to create complex shapes with these desired properties.

2. High Precision Printing

TPU's ability to maintain its properties during the printing process enables
high precision printing of intricate designs and fine details. This makes it suitable
for applications in industries such as fashion, footwear, and medical devices,
where intricate designs and custom-fit products are required.

3. Chemical Resistance

TPU exhibits resistance to various chemicals, oils, and greases, making it

suitable for applications where exposure to such substances is common. Additive
manufacturing allows for the creation of custom parts with specific chemical
resistance requirements, such as seals, gaskets, and protective covers.

4. Ease of Recycling

As a thermoplastic material, TPU can be melted and reformed multiple

times without significant degradation in properties, making it suitable for

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 recycling in additive manufacturing processes. This supports sustainability
initiatives by reducing waste and promoting the circular economy.

5. Multi-Material Printing

TPU can be used in multi-material printing setups, allowing for the

creation of hybrid parts with different properties in one print. This capability
expands the range of applications for TPU in additive manufacturing, enabling
the production of complex assemblies and functional prototypes.

1.2.2 PHYSICAL PROPERTIES

PROPERTY VALUE
Density 1.10 - 1.25 g/cm³
Tensile Strength 25 - 55 MPa
Flexural Modulus 5 - 50 MPa
Melting Point 180 - 220°C
Table 1. Physical properties of Thermo Plastic Polyurethane

1.4 3D PRINTING
Three-dimensional (3D) printing is an additive manufacturing process that creates a
physical object from a digital design. The process works by laying down thin layers of material
in the form of liquid or powdered plastic, metal, or cement, and then fusing the layers.

1.5.1 FDM 3D printing

1.5.1.1 What is FDM
Fused deposition modeling (FDM) 3D printing, also known as fused filament
fabrication (FFF), is an additive manufacturing (AM) process within the realm of
material extrusion. FDM builds parts layer by layer by selectively depositing melted
material in a predetermined path, and uses thermoplastic polymers that come in the
form of filaments.

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 Composing the largest installed base of desktop and industrial-grade 3D printers
worldwide, FDM is the most widely used technology and likely the first process you
think of when 3D printing comes up.

Figure 5. Properties of FDM & other 3D printing method.

1.5.1.2 How does FDM 3D printing work

Figure 6. Schematic of a typical FDM printer

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 An FDM 3D printer works by depositing melted filament material over a build platform
layer by layer until you have a completed part. FDM uses digital design files that are uploaded
to the machine itself and translates them into physical dimensions. Materials for FDM include
polymers such as ABS, PLA, PETG, and PEI, which the machine feeds as threads through a
heated nozzle.

To operate an FDM machine, you first load a spool of this thermoplastic filament into
the printer. Once the nozzle hits the desired temperature, the printer feeds the filament through
an extrusion head and nozzle.

This extrusion head is attached to a three-axis system that allows it to move across the
X, Y, and Z axes. The printer extrudes melted material in thin strands and deposits them layer
by layer along a path determined by the design. Once deposited, the material cools and
solidifies. You can attach fans to the extrusion head to accelerate cooling in some cases.

To fill an area, multiple passes are required, similar to coloring in a shape with a marker.
When the printer finishes a layer, the build platform descends and the machine begins work on
the next layer. In some machine setups, the extrusion head moves up. This process repeats until
the part is finished.

1.5.1.3 What are the print parameters for FDM 3D printers

Most FDM systems allow you to adjust several process parameters. These include the
nozzle and build platform temperatures, build speed, layer height, and cooling fan speed. If
you’re a designer, you normally don’t have to worry about these adjustments, as an AM
operator probably already has that covered.

Factors that are important to consider, though, are build size and layer height. The
common build size of a desktop 3D printer is 200 x 200 x 200 mm, while industrial machines
can reach sizes of 1,000 x 1,000 x 1,000 mm. If you prefer to use a desktop machine to print
your part, you can break down a big model into smaller parts and then reassemble it.

FDM’s typical layer height ranges between 50 and 400 microns. Printing shorter layers
produces smoother parts and more accurately captures curved geometries, though printing
taller layers mean you can create parts quickly and for a lower price tag.

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1.5.1.4 What are the characteristics of FDM 3D printing

While FDM 3D printers vary in terms of their extrusion systems and the part quality you get
from various machines, there are common characteristics that you can expect from every FDM
printing process.

Warping

Warping is one of the most common defects in FDM. When extruded material cools during
solidification, its dimensions decrease. Since different sections of the printed part cool at
different rates, their dimensions also change at different speeds. Differential cooling causes the
buildup of internal stresses that pull the underlying layer upward, causing it to warp.

There are several ways to prevent warping. One method is to closely monitor the temperature
of your FDM system, especially the build platform and chamber. You can also increase the
adhesion between the part and the build platform to mitigate warping.

Making certain choices during the design process can also reduce the likelihood of your part
warping. Here are a few examples:

 Large, flat areas - like you’d see on a rectangular box - are more prone to warping. Try
to avoid these whenever possible.

 Thin protruding features - think of the prongs on a fork - are also prone to warping.
Adding extra guiding or stress-relieving material at the edges of thin features to increase
the area that makes contact with the build platform helps to avoid this.

 Sharp corners warp more often than rounded shapes, so we recommend adding fillets
to the design.

 Every material has its own susceptibility to warping. For instance, ABS is generally
more sensitive to warping than PLA or PETG.

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 Figure 7. As newly deposited layers cool they shrink, pulling the underlying layer upward
and resulting in warping.

Layer adhesion

Secure adhesion between deposited layers of a part is critical in FDM. When an FDM machine
extrudes molten thermoplastic through the nozzle, this material presses against the previously
printed layer. High temperature and pressure cause this layer to re-melt and enable it to bond
with the previous layer.

And since the molten material presses against the previously printed layer, its shape deforms
to an oval. This means that FDM parts always have a wavy surface, no matter what layer
height is used, and that small features, such as small holes or threads, may require post-
processing.

Figure 8. The FDM material extrusion profile.

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Support structure

FDM printers can’t feasibly deposit molten thermoplastic in thin air. Certain part
geometries require support structures, which are usually printed in the same material as the
parts themselves.

Oftentimes, removing support structure materials can be difficult, so it’s often far easier
to design parts in such a way that minimizes the need for support structures. Support materials
that dissolve in liquid are available, but you generally use them in tandem with higher-end
FDM 3D printers. Be aware that using dissolvable supports will increase the overall cost of a
print.

Infill and shell thickness

To reduce print time and save on materials, FDM printers usually don’t produce solid
parts. Instead, the machine traces the outer perimeter - called the shell - over several passes,
and fills the interior - called the infill - with an internal, low-density structure.

Infill and shell thickness significantly affect the strength of FDM-printed parts. Most
desktop FDM printers have a 20% infill density default setting and 1 mm shell thickness, which
provides a suitable compromise between strength and speed for quick prints.

Figure 9. The internal geometry of FDM prints with different infill density

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1.5.1.5 What are common materials for FDM 3D printing

Figure 10. Common materials for FDM 3D printing

One of the key advantages of FDM (both desktop and industrial) is the technology’s
wide range of materials. This includes commodity thermoplastics such as PLA and ABS,
engineering materials like PA, TPU, and PETG , and high-performance thermoplastics,
including PEEK and PEI.

PLA filament is the most common material used in desktop FDM printers. Printing with
PLA is relatively easy and can produce parts with finer details. When you need higher strength,
ductility, and thermal stability, you normally use ABS. However, ABS is more prone to
warping, especially if you are using a machine that doesn’t have a heated chamber.

Another alternative for desktop FDM printing is PETG, which is comparable to ABS
in its composition and how easy it is to print with. All three of these materials are suitable for
most 3D printing service applications, from prototyping to form, fit, and function, to low-
volume production of models or functional parts.

Industrial FDM machines, on the other hand, mainly use engineering thermoplastics,
including ABS, polycarbonate (PC), and Ultem. These materials usually come equipped with
additives that alter their properties and make them particularly useful for industrial needs like
high impact strength, thermal stability, chemical resistance, and biocompatibility.

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 Printing in different materials will affect your part’s mechanical properties and
accuracy, as well as its cost.

1.5.1.6 Post-processing for FDM 3D printing

FDM 3D printed parts can be finished to quite a high standard via several post-
processing methods, including sanding and polishing, priming and painting, cold welding,
vapor smoothing, epoxy coating, and metal plating.

1.5.1.7 What are the best practices for printing with FDM
 FDM can produce prototypes and functional parts quickly and cost-effectively.

 There is a wide range of materials available for FDM.

 Typical build size of a desktop FDM 3D printer is 200 x 200 x 200mm. Industrial
machines have a larger build size.

 To prevent warping, avoid large flat areas and add fillets to sharp corners.

 FDM is inherently anisotropic, so it is unsuitable for mechanically critical components.

 The minimum feature size of FDM machines is limited by the diameter of the nozzle
and the layer thickness.

 Material extrusion makes it impossible to produce vertical features (in the Z direction)
with geometry smaller than the layer height (typically 0.1 - 0.2 mm).

 FDM typically can’t produce planar features (on the XY plane) smaller than the nozzle
diameter (0.4 - 0.5 mm).

 Walls have to be at least 2 to 3 times larger than the nozzle diameter (i.e. 0.8 - 1.2 mm).

 If you’re looking to produce smooth surfaces and very fine features, you may need
additional post-processing, like sandblasting and machining. Another AM technology
like SLA may be more suitable in this case.

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