Photo polymerization processes

Powder bed fusion processes

Extrusion-based systems
Module-2
Syllabus
• Photo polymerization processes: Stereo lithography (SL), Materials, SL
resin curing process, Micro-stereo lithography, Process Benefits and
Drawbacks, Applications of Photo polymerization Processes.
• Powder bed fusion processes: Introduction, Selective laser Sintering
(SLS), Materials, Powder fusion mechanism, SLS Metal and ceramic
part creation, Electron Beam melting (EBM), Process Benefits and
Drawbacks, Applications of Powder Bed Fusion Processes.
• Extrusion-based systems: Fused Deposition Modelling (FDM),
Principles, Materials, Plotting and path control, Bio-Extrusion, Process
Benefits and Drawbacks
• Photopolymerization processes make use of liquid, radiation curable
resins, or photopolymers as their primary materials.
• Most photopolymers react to radiation in the ultraviolet (UV) range of
wavelengths, but some visible light systems are used as welwell.
• Upon irradiation, these materials undergo a chemical reaction to
become solid. This reaction is called photopolymerization, and is
typically complex, involving many chemical participants.
Configurations
• Vector scan, or point-wise, approaches typical of commercial SL
machines
• Mask projection, or layer-wise, approaches, that irradiate entire
layers at one time,
• Two-photon approaches that are essentially high resolution point-by-
pointapproach
vector scan and two-photon approaches, scanning laser
beams are needed

mask projection approach utilizes a large radiation beam

that is patterned by another device, in this case a Digital
Micromirror DeviceTM (DMD).
In the two- photon case, photopolymerization occurs at
the intersection of two scanning laser beams, although
other configurations use a single laser and different
photoinitiator chemistries

Another distinction is the need to recoat, or apply a new layer

of resin in the vector scan and mask projection approaches,
while in the two-photon approach, the part is fabricated below
the resin surface, making recoating unnecessary. Approaches
that avoid recoating are faster and less complicated.
• Various types of radiation may be used to cure commercial
photopolymers, including gamma rays, X-rays, electron beams, UV,
and in some cases visible light. In SL systems, UV and visible light
radiation are used most commonly.
• In the microelectronics industry, photo mask materials are often
photopolymers and are typically irradiated using far UV and electron
beams. In contrast, the field of dentistry uses visible light
predominantly
Classification of RP Technologies
• There are various ways to classify the RP techniques that have
currently been developed
• The RP classification used here is based on the form of the starting
material:
1. Liquid-based
2. Solid-based
3. Powder-based
Liquid-Based Rapid Prototyping Systems
• Starting material is a liquid
• About a dozen RP technologies are in this category
• Includes the following processes:
• Stereolithography (STL)
• Solid ground curing (SLG)
• Droplet deposition manufacturing
 LIQUID BASED RAPID PROTOTYPING SYTEMS
Most liquid based rapid proto typing systems build parts in a vat
curable resin, which cures or solidifies under the effect of
exposure to laser radiation, usually in UV range.

The laser cures the resin near surface, forming a hardening

layer.

When a layer of a part is formed, it is lowered by an elevation

control system to allow the next layer of resin to be similarly
formed over it.

This continues until the entire part is completed.

The vat can then be drained out and the part is removed for
further processing.
Stereolithography (SLA)
SLA was pioneered by Chuck Hull in Current market leaders
the mid-1980s (see picture below). - 3D Systems
Hull founded 3D Systems to - Sony
commercialize its new manufacturing
process.

3D Systems iPro 9000 XL 11

 What is Stereolithography (SLA)?
• A "rapid-prototyping" process which produces a physical, three
dimensional object from a 3D CAD file.

• Fabricating a solid plastic part out of a photosensitive liquid

polymer using a directed laser beam to solidify the polymer

• Part fabrication is accomplished as a series of layers - each

layer is added onto the previous layer to gradually build the
3-D geometry
 Stereolithography (SLA)
1. A structure support base is
positioned on an elevator structure
and immersed in a tank of liquid
photosensitive monomer, with only a
thin liquid film above it
2. A UV laser locally cross-links the
monomer on the thin liquid film
above the structure support base
3. The elevator plate is lowered by a
small prescribed step, exposing a
fresh layer of liquid monomer, and
the process is repeated
A suitable photosensitive polymer
4. At the end of the job, the whole part must be very transparent to UV light in
is cured once again after excess uncured liquid form and very
resin and support structures are absorbent in cured solid form, to avoid
removed bleeding solid features into the layers
underneath the current one being
printed.
13
Stereolithography
• Stereo – three dimensions
• Lithography – printing
• Started with acrylic resins in the early 1980’s
• Epoxy resins are more common now
• Very good accuracy
• UV Laser cure
• Relatively slow speed
• Newer resins with improved properties

14
 Stereolithography

Stereolithography: (1) at the start of the process, in which the initial layer is
added to the platform; and (2) after several layers have been added so that
the part geometry gradually takes form.
 Principle:
The SLA process is based on the following principles.

1. Parts are built from a photo-curable liquid resin that cures

when exposed to a laser beam which scans across the
surface of the resin.

2. The building is done layer by layer, each layer being

scanned by the optical scanning system and controlled by an
elevation mechanism which lowers at the completion of
each layer.
Photopolymerization Materials
• UV Curable Photopolymers
• In the mid-1980s, Charles (Chuck) Hull was experimenting with UV
curable materials by exposing them to a scanning laser, similar to the
system found in laser printers. He discovered that solid polymer
patterns could be produced. By curing one layer over a previous layer,
he could fabricate a solid 3D part. This was the beginning of
stereolithography (SL) technology.
Photopolymerization Materials
• Photopolymers, developed in the late 1960s, are used as photoresists in the
microelectronics industry, influencing the development of epoxy-based photopolymers
due to their critical accuracy and feature resolution requirements.
• Various radiation types can cure photopolymers, including gamma rays, X-rays, electron
beams, UV, and visible light. Commercially, UV and visible light are predominantly used in
additive manufacturing (AM) systems.
• The first US patents for stereolithography (SL) resins, published in 1989 and 1990,
described acrylate-based resins with high reactivity but significant shrinkage and curling,
resulting in weak parts.
• Epoxy-based resins, patented in 1988, produce more accurate and stronger parts with
significantly less shrinkage (1-2%) compared to acrylates (5-20%). They are less inhibited
by atmospheric oxygen but have slow photo speed and brittleness.
• To improve epoxy resins' performance, some acrylate is added, combining the benefits of
both materials. This hybrid formulation has greatly enhanced the accuracy and strength
of SL resins, boosting their commercial viability
Photopolymers

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.

The vast majority of photopolymers used in the commercial

RP systems are curable in the UV range.

UV curable photo polymers are resins which are formulated

from photo iniators and reactive liquid monomers.
Photo polymerization
The process through which photopolymers are cured is called
as photo polymerization process.

It is the process of linking small molecules (monomers) into

chain like larger molecules (polymers).

When the chain like polymers are linked further to one

another, a cross linked polymer is said to be formed.

Photo polymerization is polymerization initiated by a

photochemical process whereby the starting point is usually
the induction of energy from the radiation source.
 Layering Technology, Laser and Laser scanning:

Almost all RP systems use layering technology in the creation of

prototype parts. The basic principle is the availability of
computer software to slice a CAD model into layers and
reproduce it in an output device like a laser scanning system.
The layer thickness is controlled by a precision elevation
mechanism. It will correspond directly to the slice thickness of
the computer model and the cured thickness of the resin.
The important component of the building process is the laser
and its optical scanning system. The key to the strength of the
SLA is its ability to rapidly direct focused radiation of
appropriate power and wavelength onto the surface of the
liquid photopolymers resin, forming patterns of solidified
photopolymer according to the cross-sectional data generated
by the computer.
23
Microfabrication Processes:
• Several microfabrication processes using photopolymerization principles have been developed,
including Microstereolithography (MSL), Integrated Hardened Stereolithography (IH), LIGA, and Deep
X-ray Lithography (DXRL). These processes build complex parts typically less than 1 mm in size,
utilizing UV radiation to directly process photopolymer materials.
Laser Scanning Challenges:
• Traditional vector scan technologies move the vat in x, y, and z directions rather than scanning the
laser beam due to difficulties in focusing a typical laser to spot sizes less than 20 µm. For a high-
resolution micro-SL system, achieving a laser spot size of 10 µm requires specific optical
configurations, but scanning the laser beam without severe distortions remains challenging.
Integrated Hardening Method:
• Introduced in 1993 by Ikuta and Hirowatari, this method uses a laser spot focused to a 5 µm diameter
with the resin vat scanned underneath to cure layers. Applications of this method include constructing
tubes, manifolds, springs, microactuators, fluid channels, and connecting MEMS gears.
Specifications of Microstereolithography:
Typical specifications include a 5 µm spot size of the UV beam,
positional accuracy of 0.25 µm in the x-y directions and 1.0 µm in the z-
direction, and a minimum size of the hardened polymer unit of 5x5x3
µm. Maximum size of fabrication structure is 10x10x10 mm, allowing
for the building of intricate microstructures.
Applications and Future Potential:
• Proposed applications include fluid chips for protein synthesis and
bioanalysis systems with integrated valves and pumps.
Advantages

 Round the clock operation without much attention.

 Good user support

 Build volumes. From small to large size to suit the needs.

 Good Accuracy

 Good surface finish. Best among many RP technologies.

 Wide range of materials. For general purpose materials to

specific applications.
Process Benefits and Drawbacks, Applications
of Photopolymerization Processes
Benefits:
• High Precision and Detail: Ability to create complex, intricate designs with
high precision and fine details.
• Rapid Prototyping: Quick turnaround time from design to finished product,
suitable for rapid prototyping.
• Material Versatility: Wide range of photopolymer materials available,
including those with different mechanical, thermal, and optical properties.
• Scalability: Capable of fabricating micro to macro-scale structures, making
it versatile for various applications.
• Reduced Waste: Efficient use of materials with minimal waste compared to
traditional manufacturing methods.
Drawbacks:

• Material Limitations: Photopolymer materials may have limitations in

mechanical strength and thermal stability compared to traditional
materials.
• Cost: High initial setup costs and material costs can be expensive for small-
scale production.
• Post-processing: Requires additional post-processing steps such as
cleaning, curing, and finishing, which can add to the overall production
time and cost.
• Size Limitations: Limited build volume and difficulty in producing very large
parts.
• Resolution Constraints: Achieving high resolution can be challenging,
especially for larger structures.
Applications:

• Medical Devices: Fabrication of customized medical implants, dental devices, and

surgical instruments.
• Microelectronics: Creation of micro-scale electronic components, MEMS (Micro-Electro-
Mechanical Systems), and sensors.
• Biotechnology: Development of lab-on-a-chip devices, microfluidic systems, and tissue
engineering scaffolds.
• Aerospace: Production of lightweight, high-precision components for aircraft and
spacecraft.
• Automotive: Manufacturing of prototypes and small-scale production parts for
automotive applications.
• Consumer Goods: Customization and rapid production of consumer products such as
jewelry, eyewear, and home decor items.
• Research and Development: Enabling new research possibilities in material science,
nanotechnology, and other fields
Disadvantages
Requires support structures

Requires post processing

Requires post curing

 Applications:

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 molding

Tools for fixture and tooling design, and production tooling.

A part produced by stereolithography (photo courtesy of 3D
Systems, Inc.).
 Conclusions
• Stereolithography is a liquid based RP process. Fast and effective.

• Material: Photosensitive resin

• Tool: Low powered laser (UV light)

• Process: Curing the photo polymer through photo polymerization

process.

• Can be applied to almost every industry, including oil refining,

petrochemical, power, marine, and municipal

• Saves time, money, allows speed delivery, and improve designs.

Powder bed fusion processes
• Powder Bed Fusion (PBF) processes, including Selective Laser Sintering (SLS), were among the first
commercialized additive manufacturing (AM) processes, developed at the University of Texas at
Austin.
Basic Characteristics:
• All PBF processes use thermal sources to fuse powder particles, control fusion in specific regions
of each layer, and add and smooth powder layers.
Material Versatility:
• Initially developed for plastic prototypes, PBF processes now handle a wide range of materials,
including polymers, metals, ceramics, and composites.
Technological Advancements:
• Over time, PBF methods have incorporated additional thermal sources and techniques for layer-
wise fusion, enhancing productivity and material compatibility.
Applications:
• PBF processes are used globally for direct digital manufacturing of end-use products, with
material properties comparable to many engineering-grade polymers, metals, and ceramics.
Selective laser Sintering (SLS)
Powder Layering and Heating:
• SLS fuses thin layers of powder (~0.1 mm thick) spread across the build area using a counter-rotating
powder leveling roller. The build chamber is filled with nitrogen gas to minimize oxidation and material
degradation.
Temperature Control:
• The powder in the build platform is maintained just below its melting or glass transition temperature
using infrared heaters and resistive heaters to reduce laser power requirements and prevent warping due
to thermal expansion and contraction.
Laser Fusion:
• A CO2 laser beam, controlled by galvanometers, thermally fuses the material to form the slice cross-
section. Loose surrounding powder serves as support, eliminating the need for secondary supports.
Layer-by-Layer Process:
• After fusing a layer, the build platform is lowered by one layer thickness, and a new layer of powder is
spread and leveled. The laser then scans the subsequent slice cross-section. This process repeats until the
complete part is built.
Post-Build Cooling and Finishing:
• A cool-down period is required to prevent warping and material degradation. Once cooled, parts are
removed from the powder bed, cleaned, and subjected to any necessary finishing operations
Materials
• Nylon Polyamide in Powder Bed Fusion: The most common material used
in powder bed fusion is nylon polyamide, a semi-crystalline material with a
distinct melting point. For optimal part strength, these materials need to
be fully melted during processing.
• Challenges in Full Melting: Fully melting nylon polyamide can lead to part
growth due to elevated temperatures. Therefore, many optimization
studies balance accuracy and strength by setting parameters at the
threshold between full melting and Liquid Phase Sintering (LPS).
• Metal Powder Bed Fusion: In metal powder bed fusion processes,
engineering alloys such as Ti, Stainless Steel, and CoCr are typically fully
melted. The rapid melting and solidification of these alloys produce unique
properties that can be more desirable than those of cast or wrought parts
made from the same alloys.
• Binding Mechanisms and Process Variability: Technologies like Selective
Laser Sintering, Selective Laser Melting, and Electron Beam Melting can
utilize multiple binding mechanisms depending on the powder particle
combinations and energy input
Powder fusion mechanism
There are 4 different fusion mechanisms which are present in PBF processes
• solid-state sintering,
• chemically-induced binding,
• liquid-phase sintering,
• full melting.
Most commercial processes utilize primarily liquid-phase sintering and
melting.
Solid-state Sintering
• The use of the word sintering to describe mechanisms for fusing powders
as a result of thermal processing predates the advent of AM.
• Sintering, in its classical sense, indicates the fusion of powder particles
without melting (i.e., in their “solid state”) at elevated temperatures.
• This occurs at temperatures between one half of the absolute melting
temperature and the melting temperature.
• The driving force for solid-state sintering is the minimization of total free
energy, Es, of the powder particles.
• The mechanism for sintering is primarily diffusion between powder
particles
• Surface energy Es is proportional to total particle surface area SA,
through the equation Es = gs x SA (where gs is the surface energy per
unit area for a particular material, atmosphere, and temperature).
When particles fuse at elevated temperatures (see Fig. 5.2), the total
surface area decreases, and thus surface energy decreases.
• As the total surface area of the powder bed decreases, the rate of
sintering slows. To achieve very low porosity levels, long sintering
times or high sintering temperatures are required.
• As total surface area in a powder bed is a function of particle size, the
driving force for sintering is directly related to the surface area to
volume ratio for a set of particles.
• The larger the surface area to volume ratio, the greater the free
energy driving force. Thus, smaller particles experience a greater
driving force for necking and consolidation, and thus, smaller particles
sinter more rapidly and initiate sintering at lower temperature than
larger particles.
• As diffusion rates exponentially increase with temperature, sintering
becomes increasingly rapid as temperatures approach the melting
temperature, which can be modeled using a form of the Arrhenius
equation.
• However, even at temperatures approaching the melting temperature
diffusion-induced solid-state sintering is the slowest mechanism for
selectively fusing regions of powder within a PBF process.
Chemically-induced Sintering
• Mechanism and Applications: Chemically-induced sintering uses
thermally-activated chemical reactions between powders or with
atmospheric gases to create a by-product that binds the powders, primarily
applied to ceramic materials.
• Examples and Process: Specific examples include laser processing of SiC
with oxygen to form SiO2, ZrB2 with oxygen to form ZrO2, and Al with
nitrogen to form AlN. Mixtures of ceramic or intermetallic precursors react
exothermically when heated by a laser, facilitating high-melting-
temperature structures at lower laser energies.
• Challenges and Limitations: A common issue is part porosity,
necessitating post-process infiltration or high-temperature furnace
sintering to achieve desired properties, which increases cost and time, thus
limiting commercial adoption.
• Liquid-phase sintering (LPS) is arguably the most versatile mechanism for
PBF.
• Liquid-phase sintering is a term used extensively in the powder processing
industry to refer to the fusion of powder particles when a portion of
constituents within a collection of powder particles become molten, while
other portions remain solid.
• In LPS, the molten constituents act as the glue which binds the solid
particles together. As a result, high-temperature particles can be bound
together without needing to melt or sinter those particles directly.
• LPS is used in traditional powder metallurgy to form, for instance,
cemented carbide cutting tools where Co is used as the lower melting-
point constituent to glue together particles of WC
Liquid-phase Sintering and Partial Melting
Full Melting
• Full melting is the mechanism most commonly associated with
powder bed fusion processing of engineering metal alloys and semi-
crystalline polymers. In these materials, the entire region of material
subjected to impinging heat energy is melted to a depth exceeding
the layer thickness.
• Thermal energy of subsequent scans of a laser or electron beam
(next to or above the just-scanned area) is typically sufficient to re-
melt a portion of the previously solidified solid structure; and thus,
this type of full melting is very effective at creating well-bonded, high-
density structures from engineering metals and polymers
SLS Metal and ceramic part creation
Metal Parts
• There are four common approaches for using powder bed fusion processes
in the creation of complex metal components: full melting, liquid-phase
sintering, indirect processing, and pattern methods.
• As discussed previously, in the full melting approach a metallic powdered
material is fully melted using a high-power laser or electron beam; and in
the liquid-phase sintering approach a mixture of two metal powders or a
metal alloy is used where a higher-melting-temperature constituent
remains solid and a lower-melting-temperature constituent melts.
• In both of these approaches, a metal part is typically usable in the state in
which it comes out of the machine, after separation from a build plate.
• In indirect processing, a polymer coated metallic powder or a mixture of metallic and polymer powders are used
for part construction. Figure 5.7 shows the steps involved in indirect processing of metal powders.
• During indirect processing, the polymer binder is melted and binds the particles together, and the metal powder
remains solid. The metallic powder particles remain largely unaffected by the heat of the laser.
• The parts produced are generally porous (sometimes exceeding 50 vol.% porosity).
• The polymer-bound green parts are subsequently furnace processed. Furnace processing occurs in two stages: (1)
debinding and (2) infiltra- tion or consolidation. During debinding, the polymer binder is vaporized to remove it
from the green part. Typically, the temperature is also raised to the extent that a small degree of necking (sintering)
occurs between the metal particles.
• Subsequently, the remaining porosity is either filled by infiltration of a lower melting point metal to produce a fully
dense metallic part, or by further sintering and densification to reduce the part porosity. Infiltration is easier to
control, dimensionally, as the overall shrinkage is much less than during consolidation.
• However, infiltrated structures are always composite in nature whereas consolidated structures can be made up of
a single material type.
Pattern approach.
• For the previous 3 approaches, metal powder is utilized in the PBF process; but in
this final approach, the part created in the PBF process is a pattern used to create
the metal part.
• The two most common ways PBF-created parts are utilized as patterns for metal
part creation are as investment casting patterns or as sand-casting molds.
• In the case of investment casting, polystyrene or wax-based powders are used in
the machine; and subsequently invested in ceramic during post-processing, and
melted out during casting.
• In the case of sand-casting molds, mixtures of sand and a thermosetting binder
are directly processed in the machine to form a sand-casting core, cavity or insert.
These molds are then assembled and molten metal is cast into the mold, creating
a metal part.
Ceramics
• Methods for Creating Ceramic Parts in PBF: Similar to metals, ceramic parts in powder
bed fusion (PBF) processes can be made using direct sintering, chemically-induced
sintering, indirect processing, and pattern methods.
• Direct Sintering: This method involves maintaining a high temperature in the powder
bed and using a laser to accelerate sintering in specified locations. The resulting ceramic
parts are porous and typically require post-processing in a furnace to increase density.
• Indirect Processing: This method is similar to indirect processing of metal powders. After
debinding, the ceramic part is consolidated to reduce porosity or infiltrated with another
material, which can result in composite structures.
• Infiltration and Composite Formation: Infiltration can involve using metal powders to
create ceramic/metal composites. For example, infiltrating a SiC structure with molten
silicon will react with residual carbon from a polymer binder to form more SiC, increasing
the SiC content and enhancing the properties of the final part. These methods produce
ceramic-matrix composites and ceramic-metal structures for various applications
Variants of Powder Bed Fusion Processes
• Laser-based Systems for Low-temperature Processing
• Laser-based Systems for Metals and Ceramics
• Electron Beam Melting
Laser-based Systems for Low-temperature
Processing
Selective Laser Sintering (SLS)
• Materials: Polymers (e.g., nylon, polyamide), composites
• Laser Type: CO₂ laser
• Power: Typically 10-200 W
• Layer Thickness: 50-150 microns
• Scan Speed: 500-2000 mm/s
• Bed Temperature: 90-180°C (dependent on polymer type)
• Environment: Often inert gas (nitrogen) to prevent oxidation
• Applications: Functional prototypes, end-use parts, low-volume production
Laser-based Systems for Metals and Ceramics

• Selective Laser Melting (SLM)

• Materials: Metals (e.g., stainless steel, aluminum, titanium)
• Laser Type: Fiber laser or Ytterbium laser
• Power: 100-1000 W
• Layer Thickness: 20-100 microns
• Scan Speed: 500-2000 mm/s
• Bed Temperature: Preheated to 80-200°C (varies with material)
• Environment: Inert gas (argon or nitrogen) to prevent oxidation
• Applications: Aerospace, medical implants, tooling, automotive
Laser-based Systems for Metals and Ceramics

• Direct Metal Laser Sintering (DMLS)

• Materials: Metals and alloys (similar to SLM)
• Laser Type: Typically fiber laser
• Power: 100-400 W
• Layer Thickness: 20-100 microns
• Scan Speed: 500-2000 mm/s
• Bed Temperature: Preheated, similar to SLM
• Environment: Inert gas (argon or nitrogen)
• Applications: Prototyping, production of complex metal p
Electron Beam Melting (EBM)
• EBM is a PBF process that uses an electron beam as the energy source to melt
metal powder. This process is performed in a vacuum and is particularly suited for
high-performance materials used in demanding applications.
• Process Parameters:
• Electron Beam Power: Typically ranges from 3 to 6 kW.
• Scanning Speed: Up to 8000 mm/s.
• Layer Thickness: Commonly between 0.05 to 0.2 mm.
• Build Temperature: High, often between 600 to 1100°C, depending on the
material to reduce residual stresses and improve mechanical properties.
• Atmosphere: Conducted in a vacuum to prevent oxidation and contamination.
• Materials: High-performance metals such as titanium alloys, cobalt-chrome, and
nickel-based superalloys
Electron Beam Melting
• Electron Beam Melting (EBM) has become a successful approach to
PBF.
• In contrast to laser-based systems, EBM uses a high-energy electron
beam to induce fusion between metal powder particles
Electron Beam melting (EBM),
Material suitability
• The Powder bed fusion process can use any powder-based materials,
but the following materials are the most common
• Selective heat sintering – Nylon (monochrome white thermoplastic
powder)
• DMLS, SLS, SLM: Stainless Steel, Titanium, Aluminium alloy, Cobalt
Chrome, Steel
• EBM: Stainless Steel, Titanium, Aluminium, Cobalt Chrome and
copper
Process Benefits
• High Precision and Detail: PBF processes allow for the creation of highly
detailed and complex geometries with excellent dimensional accuracy.
• Material Efficiency: Unused powder can often be recycled and reused,
reducing material waste.
• Versatility: Can process a wide range of materials, including metals,
polymers, and ceramics.
• Customizability: Ideal for producing customized and one-of-a-kind parts,
including intricate internal structures.
• Minimal Post-Processing: Often requires less post-processing compared to
other additive manufacturing methods.
Drawbacks:
• High Cost: Equipment and materials for PBF processes can be
expensive, making it less accessible for small-scale operations.
• Long Build Times: The layer-by-layer process can be slow, especially
for larger parts.
• Powder Handling: Handling and storing fine powders can pose
health and safety risks and requires specialized equipment.
• Surface Finish: Parts may require additional finishing processes to
achieve desired surface quality.
• Thermal Stresses: The high temperatures involved can introduce
thermal stresses and potential warping in the parts.
Applications of Powder Bed Fusion Processes

• Aerospace: Manufacturing lightweight, complex components like

turbine blades and structural parts.
• Medical: Producing customized implants, prosthetics, and surgical
tools with precise specifications.
• Automotive: Fabricating prototype parts, custom tools, and low-
volume production components.
• Tooling: Creating molds and dies with intricate cooling channels for
better thermal management.
• Consumer Goods: Developing bespoke and high-end products, such
as jewelry and eyewear, with detailed features.
Extrusion-based systems: Fused Deposition
Modelling (FDM),
• Extrusion-based systems, exemplified by Fused Deposition Modeling (FDM),
utilize a nozzle to extrude molten thermoplastic material layer by layer, gradually
building up a three-dimensional object
• The most commonly used approach in extrusion-based systems, like Fused
Deposition Modeling (FDM), relies on temperature control to liquefy material in a
reservoir. This molten material flows through a nozzle, bonding with adjacent
layers before solidifying. This process mirrors traditional polymer extrusion but is
vertically mounted on a plotting system for layer-by-layer construction.
• · Alternatively, some systems utilize chemical changes to induce solidification.
This can involve curing agents, residual solvents, reactions with air, or drying of
wet materials, allowing bonding without reliance solely on temperature. While
commonly used in biochemical applications requiring biocompatible materials,
industrial uses also exist where material choice may be
Basic Principles

There are a number of key features that are common to any extrusion-based
system:
• – Loading of material
• – Liquification of the material
• – Application of pressure to move the material through the nozzle
• --Extrusion
• – Plotting according to a predefined path and in a controlled manner
• – Bonding of the material to itself or secondary build materials to form a
coherent solid structure
• – Inclusion of support structures to enable complex geometrical features
Material Loading
• Extrusion-based systems require a chamber from which material is
extruded, which can be preloaded or continuously supplied.
Continuous material supply enhances efficiency.
• Material is typically supplied in solid form, such as pellets, granules,
powders, or continuous filament. The chamber facilitates the
liquefaction process, either through gravity, screw feeding, or
continuous filament insertion.
• Screw feeding not only propels material to the base of the reservoir
but also generates the necessary pressure to extrude it through the
nozzle. Continuous filament insertion can also create pressure for
nozzle extrusion
Liquification
• The extrusion method works on the principle that what is held in the
chamber will become a liquid that can eventually be pushed through the
die or nozzle.
• As mentioned earlier, this material could be in the form of a solution that
will quickly solidify following the extrusion, but more likely this material
will be liquid because of heat applied to the chamber.
• Such heat would normally be applied by heater coils wrapped around the
chamber and ideally this heat should be applied to maintain a constant
temperature in the melt (see Fig. 6.1).
• The larger the chamber, the more difficult this can become for numerous
reasons related to heat transfer, thermal currents within the melt, change
in physical state of the molten material, location of temperature sensors,
etc
• The material inside the chamber should be kept in a molten state but
care should be taken to maintain it at as low a temperature as
possible since some polymers degrade quickly at higher temperatures
and could also burn, leaving residue on the inside of the chamber that
would be difficult to remove and that would contaminate further
melt.
• A higher temperature inside the chamber also requires additional
cooling following extrusion.
Extrusion
• The extrusion nozzle determines the shape and size of the extruded
filament. Alarger nozzle diameter will enable material to flow more rapidly
but would result in a part with lower precision compared with the original
CAD drawing.
• The diameter of the nozzle also determines the minimum feature size that
can be created. No feature can be smaller than this diameter and in
practice features should normally be large relative to the nozzle diameter
to faithfully reproduce them with satisfactory strength.
• Extrusion-based processes are therefore more suitable for larger parts that
have features and wall thicknesses that are at least twice the nominal
diameter of the extrusion nozzle used.
• Material will flow through the nozzle is controlled by the pressure drop
between the chamber and the surrounding atmosphere
Solidification
• Once the material is extruded, it should ideally remain the same shape and size.
Gravity and surface tension, however, may cause the material to change shape,
while size may vary according to cooling and drying effects.
• If the material is extruded in the form of a gel, the material may shrink upon
drying, as well as possibly becoming porous.
• If the material is extruded in a molten state, it may also shrink when cooling.
• The cooling is also very likely to be nonlinear. If this nonlinear effect is significant,
then it is possible the resulting part will distort upon cooling.
• This can be minimized by ensuring the temperature differential between the
chamber and the surrounding atmosphere is kept to a minimum (i.e., use of a
controlled environmental chamber when building the part) and also by ensuring
the cooling process is controlled with a gradual and slow profile
Positional Control
• Like many AM technologies, extrusion-based systems use a platform that
indexes
in the vertical direction to allow formation of individual layers. The extrusion
head is typically carried on a plotting system that allows movement in the
horizontal plane.
• This plotting must be coordinated with the extrusion rate to ensure smooth
and consistent deposition.
• Since the plotting head represents a mass and therefore contains an
inertial element when moving in a specific direction, any change in
direction must result in a deceleration followed by acceleration.
• The corresponding material flow rate must match this change in speed or
else too much or too little material will be deposited in a particular region.
Bonding
• For heat-based systems there must be sufficient residual heat energy to
activate the surfaces of the adjacent regions, causing bonding.
• Alternatively, gel-based systems must contain residual solvent or wetting
agent in the extruded filament to ensure the new material will bond to the
adjacent regions that have already been deposited.
• In both cases, we visualize the process in terms of energy supplied to the
material by the extrusion head.
• If there is insufficient energy, the regions may adhere, but there would be a
distinct boundary between new and previously deposited material. This
can represent a fracture surface where the materials can be easily
separated.
• Too much energy may cause the previously deposited material to flow,
which in turn may result in a poorly defined part.
Support Generation
• ll AM systems must have a means for supporting free-standing and
disconnected features and for keeping all features of a part in place
during the fabrication process.
• With extrusion-based systems such features must be kept in place by
the additional fabrication of supports. Supports in such systems take
two general forms:
• – Similar material supports
• – Secondary material supports
 Plotting and path control,
• There must be clear access for the extrusion head to deposit fill material
within the outline without compromising the material that has already
been laid down.
• Additionally, if the material is not laid down close enough to adjacent
material, it will not bond effectively.
• In contrast, laser-based systems can permit, and in fact generally require, a
significant amount of overlap from one scan to the next and thus there are
no head collision or overfilling-equivalent phenomena
Materials,
• ABS (acrylonitrile butadiene styrene)
PLA (Polylactic Acid):
• Properties: Biodegradable, derived from renewable resources, easy to print with,
low warping, and emits less fumes.
• Applications: Prototyping, hobbyist projects, educational models.
ABS (Acrylonitrile Butadiene Styrene):
• Properties: Durable, impact-resistant, heat-resistant, higher warping tendency
compared to PLA, emits moderate fumes.
• Applications: Functional prototypes, automotive parts, consumer products.
PETG (Polyethylene Terephthalate Glycol):
• Properties: Strong and durable, resistant to moisture and chemicals, less prone to
warping compared to ABS.
• Applications: Mechanical parts, containers, outdoor signage
Nylon:
• Properties: High strength, flexibility, and impact resistance, good chemical resistance, prone to
warping if not properly controlled.
• Applications: Functional prototypes, gears, bearings, and parts requiring flexibility.
TPU (Thermoplastic Polyurethane):
• Properties: Flexible, elastic, and abrasion-resistant, excellent layer adhesion, can be challenging to
print due to flexibility.
• Applications: Gaskets, seals, phone cases, footwear.
PC (Polycarbonate):
• Properties: High strength, toughness, and heat resistance, can be challenging to print due to high
printing temperature requirements.
• Applications: Engineering prototypes, aerospace components, automotive parts.
ASA (Acrylonitrile Styrene Acrylate):
• Properties: UV-resistant, weather-resistant, similar to ABS but with improved outdoor durability.
• Applications: Outdoor signage, automotive exterior parts, architectural models
Bio-Extrusion,
• Extrusion-based technology offers a wide range of materials suitable for
processing, particularly if the material can be liquified and solidified quickly. This
can be achieved through thermal processing or chemical processes, making it
applicable to bioextrusion for tissue engineering applications.
• Bioextrusion involves creating biocompatible and/or biodegradable
components, such as scaffolds, which host animal cells for tissue formation.
These scaffolds require specific porosity, with micro-pores for cell adhesion and
macro-pores for cell growth.
• Commercial bioextrusion systems, like the modified FDM process used by
Osteopore, are available for creating scaffolds, especially in areas like head
trauma recovery.
• However, most tissue engineering remains in the research phase, exploring
aspects like material selection, scaffold strength, coatings, and biocompatibility.
While many systems are developed in-house for specific research needs, a few
commercial options are available for research lab
• Advantages:
• Widespread and inexpensive process
• ABS plastic can be used, which has good structural properties and is
easily accessible
Disadvantages:
• The nozzle radius limits and reduces the final quality
• Accuracy and speed are low when compared to other processes and
accuracy of the final model is limited to material nozzle thickness
• Constant pressure of material is required in order to increase quality
of finish
Benefits:

• Material Versatility: FDM systems can process a wide variety of thermoplastic

materials, offering flexibility in material selection based on application
requirements.
• Cost-Effectiveness: Compared to other additive manufacturing technologies,
FDM printers are relatively affordable, making them accessible to a wide range of
users, including hobbyists and small businesses.
• Ease of Use: FDM printers are user-friendly and require minimal setup, making
them suitable for rapid prototyping and small-scale production without extensive
training.
• Customization: FDM allows for easy customization and iteration of designs,
enabling rapid iteration and development of prototypes and functional parts.
• Minimal Waste: FDM generates minimal material waste since unused filament
can be easily stored and reused for future prints, contributing to cost savings and
environmental sustainability.
Drawbacks:

• Limited Resolution: FDM typically produces parts with visible layer lines, resulting in
lower surface finish and dimensional accuracy compared to other additive manufacturing
methods.
• Mechanical Strength: Parts fabricated using FDM may have reduced mechanical strength
along the Z-axis due to layer-by-layer construction, limiting their suitability for load-
bearing applications.
• Warping and Delamination: Warping and delamination can occur in FDM prints due to
uneven cooling, layer adhesion issues, or material shrinkage, affecting part quality and
dimensional accuracy.
• Material Properties: While FDM can process a wide range of materials, some materials
may have limited mechanical properties or may be prone to degradation during printing,
affecting part performance and durability.
• Post-Processing Requirements: FDM parts may require additional post-processing, such
as sanding, smoothing, or painting, to improve surface finish and aesthetic appearance,
adding time and effort to the manufacturing process.
Applications
• Prototyping: FDM is widely used for rapid prototyping due to its affordability and
ease of use, enabling quick iteration and validation of design concepts in
industries ranging from automotive to consumer goods.
• Custom Manufacturing: FDM is employed for the production of customized
parts, tooling, and fixtures, offering flexibility in material selection and design
customization for applications in aerospace, medical, and manufacturing sectors.
• Education and Research: FDM is extensively used in educational institutions and
research laboratories for teaching, experimentation, and academic projects,
facilitating hands-on learning and innovation in engineering and design fields.
• Functional Parts: FDM produces functional parts for various applications,
including jigs, fixtures, end-use components, and architectural models, catering
to the needs of industries seeking cost-effective and rapid manufacturing
solutions.