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Unit.5

Additive

Manufacturing

Processes

SPPU Semester VII Mechanical Engineering

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ADVANCED MANUFACTURING PROCESS

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*Syllabus :

Introduction and principles, Development of additive manufacturing Technologies,

general additive manufacturing processes, powder based fusion process, extrusion

based system, sheet lamination process, direct write technologies.

Introduction :

Additive Manufacturing (AM) technology came about as a result of developments in a

variety of different technology sectors. Like with many manufacturing technologies,

improvements in computing power and reduction in mass storage costs paved the way for

processing the large amounts of data typical of modern 3D Computer-Aided Design (CAD) models

within reasonable time frames. Nowadays, we have become quite accustomed to having powerful

computers and other complex automated machines around us and sometimes it may be difficult for

us to imagine how the pioneers struggled to develop the first AM machines.

3D printing also known as additive manufacturing is any of various processes used to make

a three-dimensional object. In 3D printing, additive processes are used, in which successive layers

of material are laid down under computer control. These objects can be of almost any shape or

geometry, and are produced from a 3D model or other electronic data source. A 3D printer is a

type of industrial robot.

Additive Manufacturing refers to a process by which digital 3D design data is used to

build up a component in layers by depositing material. The term "3D printing" is increasingly used

as a synonym for Additive Manufacturing. However, the latter is more accurate in that it describes

a professional production technique which is clearly distinguished from conventional methods of

material removal. Instead of milling a work piece from solid block, for example, Additive

Manufacturing builds up components layer by layer using materials which are available in fine

powder form material. A range of different metals, plastics and composite materials may be used.

The technology has especially been applied in conjunction with Rapid Prototyping

(/industries markets /rapid prototyping) - the construction of illustrative and functional prototypes.

Additive Manufacturing is now being used increasingly in Series Production. It gives Original

Equipment Manufacturers (OEMs) in the most varied sectors of industry (/industries markets) the

opportunity to create a distinctive profile for themselves based on new customer benefits, cost-

saving potential and the ability to meet sustainability goals.

Additive Manufacturing Processes Unit-5.

Shri Swami Samarth

AMP


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Functional Principle

The system starts by applying a thin layer of the powder material to the building platform. A

powerful laser beam then fuses the powder at exactly the points defined by the computer-

generated component design data. The platform is then lowered and another layer of powder is

applied. Once again the material is fused so as to bond with the layer below at the predefined

points. Depending on the material used, components can be manufactured using stereo lithography,

laser sintering or 3D printing.

Development of Additive Manufacturing Technology

Like many other technologies, AM came about as a result of the invention of the computer.

AM takes full advantage of many of the important features of computer technology, both directly

(in the AM machines themselves) and indirectly (within the supporting technology), including:

*Processing power : Part data files can be very large and require a reasonable amount of

processing power to manipulate while setting up the machine and when slicing the data before

building. Earlier machines would have had difficulty handling large CAD data files.

*Graphics capability: AM machine operation does not require a big graphics engine except to

see the file while positioning within the virtual machine space. However, all machines benefit from

a good graphical user interface (GUI) that can make the machine easier to set up, operate, and

maintain.

*Machine control: AM technology requires precise positioning of equipment in a similar way to

a Computer Numerical Controlled (CNC) machining center, or even a high-end photocopy


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machine or laser printer. Such equipment requires controllers that take information from sensors

for determining status and actuators for positioning and other output functions. Computation is

generally required in order to determine the control requirements. Conducting these control tasks

even in real-time does not normally require significant amounts of processing power by todays

standards. Dedicated functions like positioning of motors, lenses, etc. would normally require

individual controller modules. A computer would be used to oversee the communication to and

from these controllers and pass data related to the part build function.

*Networking: Nearly every computer these days has a method for communicating with other

computers around the world. Files for building would normally be designed on another computer

to that running the AM machine. Earlier systems would have required the files to be loaded from

disk or tape. Nowadays almost all files will be sent using an Ethernet connection, often via the

Internet.

*Integration: As is indicated by the variety of functions, the computer forms a central component

that ties different processes together. The purpose of the computer would be to communicate with

other parts of the system, to process data, and to send that data from one part of the system to the

other. Figure.1 shows how the above mentioned technologies are integrated to form an AM

machine.

Figure.1 General integration of an AM machine


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Without computers there would be no capability to display 3D graphic images. Without 3D

graphics, there would be no Computer-Aided Design. Without this ability to represent objects

digitally in 3D, we would have a limited desire to use machines to fabricate anything but the

simplest shapes. It is safe to say, therefore, that without the computers we have today, we would

not have seen Additive Manufacturing develop. Additive Manufacturing technology primarily

makes use of the output from mechanical engineering, 3D Solid Modeling CAD software. It is

important to understand that this is only a branch of a much larger set of CAD systems and,

therefore, not all CAD systems will produce output suitable for layer-based AM technology.

Currently, AM technology focuses on reproducing geometric form; and so the better CAD systems

to use are those that produce such forms in the most precise and effective way.

NC machining, therefore, only requires surface modeling software. All early CAM systems were

based on surface modeling CAD. AM technology was the first automated computer-aided

manufacturing process that truly required 3D solid modeling CAD. It was necessary to have a fully

enclosed surface to generate the driving coordinates for AM. This can be achieved using surface

modeling systems, but because surfaces are described by boundary curves it is often difficult to

precisely and seamlessly connect these together. Even if the gaps are imperceptible, the resulting

models may be difficult to build using AM. At the very least, any inaccuracies in the 3D model

would be passed on to the AM part that was constructed. Early AM applications often displayed

difficulties because of associated problems with surface modeling software.

Since it is important for AM systems to have accurate models that are fully enclosed, the preference

is for solid modeling CAD. Solid modeling CAD ensures that all models made have a volume and,

therefore, by definition are fully enclosed surfaces. While surface modeling can be used in part

construction, we can not always be sure that the final model is faithfully represented as a solid.

Such models are generally necessary for Computer-Aided Engineering (CAE) tools like Finite

Element Analysis (FEA), but are also very important for other CAM processes.

Additive Manufacturing Processes

The Powder Bed Fusion process includes the following commonly used printing

techniques: Direct metal laser sintering (DMLS), Electron beam melting (EBM), Selective heat

sintering (SHS), Selective laser melting (SLM) and Selective laser sintering (SLS).Powder bed

fusion (PBF) methods use either a laser or electron beam to melt and fuse material powder together.

Electron beam melting (EBM), methods require a vacuum but can be used with metals and alloys

in the creation of functional parts. All PBF processes involve the spreading of the powder material

over previous layers. There are different mechanisms to enable this, including a roller or a blade.

A hopper or a reservoir below of aside the bed provides fresh material supply. Direct metal laser

1. Powder Based Fusion Process


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sintering (DMLS) is the same as SLS, but with the use

of metals and not plastics. The process sinters the

powder, layer by layer. Selective Heat Sintering

differs from other processes by way of using a heated

thermal print head to fuse powder material together.

As before, layers are added with a roller in between

fusion of layers. A platform lowers the model

accordingly.

The technique fuses parts of the layer, and then

moves the working area downwards, adding another

layer of granules and repeating the process until the

piece has built up. This process uses the unfused

media to support overhangs and thin walls in the part

being produced, which reduces the need for temporary auxiliary supports for the piece. A laser is

typically used to sinter the media into a solid.

Fig. 2 Powder bed fusion process

* Powder Bed Fusion Step by Step

1. A layer, typically 0.1mm thick of material is spread over the build platform.

2. A laser fuses the first layer or first cross section of the model.

part

Energy source (laser)

roller

Build chamber Powder chamber

powder

Inert gas


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3. A new layer of powder is spread across the previous layer using a roller.

4. Further layers or cross sections are fused and added.

5. The process repeats until the entire model is created. Loose, unfused powder is remains in

position but is removed during post processing.

In powder bed fusion, particles of material (e.g., plastic, metal) are selectively fused

together using a thermal energy source such as a laser. Once a layer is fused, a new one is created

by spreading powder over the top of the object and repeating the process. Unfused material is used

to support the object being produced, thus reducing the need for support systems.

Selective laser sintering (SLS) is the first among many similar processes like Direct Metal

Laser Sintering (DMLS), Selective Laser Melting (SLM) and laser cusing. SLS can be defined as

powder bed fusion process used to produce objects from powdered materials using one or more

lasers to selectively fuse or melt the particles at the surface, layer by layer, in an enclosed chamber.

SLM is an advanced form of the SLS process where, full melting of the powder bed particles takes

place by using one or more lasers.

Fig. Laser based powder bed fusion technology

Laser cusing is similar to SLM process where laser is used to fuse each powder bed layer

as per required cross section to build the complete part in the enclosed chamber. The term laser

cusing comes from letter C (concept) and the word fusing. The special feature of laser cusing

machine is the stochastic exposure strategy based on the island principle. Each layer of the required

cross section is divided into number of segments called islands, which are selected stochastically

during scanning. This strategy ensures thermal equilibrium on the surface and reduces the

component stresses.

1.1 Laser based systems (DMLS/SLM/Laser cusing)

1. Build piston

2. Build platform

3. Powder dispenser

piston

4. Powder dispenser

platform

5. Metal powder supply

6. Recoater arm

7. Laser

8. Lenses

9. Laser beam

10. Sintered part

11. Powder bed

12. XY scanning mirror


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Most of these systems use one fiber laser of 200W to 1 KW capacity to selectively fuse the

powder bed layer. The build chamber is provided with inert atmosphere of argon gas for reactive

materials and nitrogen gas for non-reactive materials. Power of laser source, scan speed, hatch

distance between laser tracks and the thickness of powdered layer are the main processing

parameters of these processes. Layer thickness of 20-100 m can be used depending on the

material. All of these processes can manufacture fully dense metallic parts from wide range of

metal alloys like titanium alloys, inconel alloys, cobalt chrome, aluminium alloys, stainless steels

and tool steels.

Most of the laser based PBF systems have low build rates of 5-20 cm 3/hr and maximum

part size that can be produced (build volume) is limited to 250 x 250 x 325 mm 3 which increases

part cost and limits its use only for the small sized parts. So in recent years, the machine

manufactures and the research institutes are focusing on expanding the capabilities of their

machines by increasing the build rates and the build volumes. SLM solution from Germany has

launched SLM500 HL machine in 2012 which uses double beam technology to increase the build

rate up to 35 cm 3/hr and has a build volume of 500 x 350 x 300 mm 3.Two sets of lasers are used

in this machine, each set having two lasers (400W and 1000W). This means four lasers scan the

powder layer simultaneously.

EBM is another PBF based AM process in which electron beam is used to selectively fuse

powder bed layer in vacuum chamber. Electron beam melting (EBM) process is similar to the

SLM with the only difference being its energy source used to fuse powder bed layers: here an

electron beam is used instead of the laser . In EBM, a heated tungsten filament emits electrons at

high speed which are then controlled by two magnetic fields, focus coil and deflection coil as

shown in Fig.4a. Focus coil acts as a magnetic lens and focuses the beam into desired diameter up

to 0.1 mm whereas deflection coil deflects the focused beam at required point to scan the layer of

powder bed. When high speed electrons hit the powder bed, their kinetic energy gets converted

into thermal energy which melts the powder. Each powder bed layer is scanned in two stages, the

preheating stage and the melting stage. In preheating stage, a high current beam with a high

scanning speed is used to preheat the powder layer (up to 0.4 - 0.6 T m) in multiple passes. In

melting stage, a low current beam with a low scanning speed is used to melt the powder . When

scanning of one layer is completed, table is lowered, another powder layer is spread and the process

repeats till required component is formed. The entire EBM process takes place under high vacuum

of 10 -4 to 10 -5 mbar. The helium gas supply during the melting further reduces the vacuum

pressure which allows part cooling and provides beam stability . It also has multi-beam feature

which converts electron beam into several individual beams which can heat, sinter or melt powder

bed layer .

1.2 Electron beam melting (EBM)


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ARCAM EBM system uses high power electron beam of 3000 W capacity to melt powder bed

layers. Electron beam power, current, diameter of focus, powder pre-heat temperature and layer

thickness are main processing parameters of the EBM. Layer thickness of 50-200 m is typically

used in this process . EBM systems can work with wide range of materials like titanium alloys

(Ti6Al4V, Ti6Al4V EI), cobalt chrome, Titanium aluminide, inconel (625 and 718), stainless

steels, tool steels, copper, aluminium alloys, beryllium etc.

Fig. Schematic of EBM process

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Fig. Steps in EBM process

* Materials Used

The Powder bed fusion process uses any powder based materials, but common metals and

polymers used are:

SHS: Nylon DMLS, SLS,

SLM: Stainless Steel, Titainium, Aluminium, Cobalt Chrome, Steel

EBM: titanum, Cobalt Chrome, ss, al and copper

* Advantages:

1. Relatively inexpensive

2. Suitable for visual models and prototypes

3. (SHS) Ability to integrate technology into small scale, office sized machine.

4. Powder acts as an integrated support structure.

5. Large range of material options.

Build plate heating

Powder spreading

Powder preheating scan

Powder melting scan

Build Table lowering

Repeat process till part completion


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* Disadvantages:

1. Relatively slow speed (SHS).

2. Lack of structural properties in materials.

3. Size limitations.

4. High power usage.

5. Finish is dependent on powder grain size.

COMPARISON BETWEEN SLM AND EBM

As compared to the SLM system, the EBM has higher build rates (upto 80cm 3/hr because

of the high energy density and high scanning speeds) but inferior dimensional and surface finish

qualities.

In both the SLM/EBM process, because of rapid heating and cooling of the powder layer,

residual stresses are developed. In EBM, high build chamber temperature (typically 700- 900 0C)

is maintained by preheating the powder bed layer. This preheating reduces the thermal gradient in

the powder bed and the scanned layer which reduces residual stresses in the part and eliminates

post heat treatment required. Preheating also holds powder particles together which can acts as

supports for overhanging structural members. So, supports required in the EBM are only for heat

conduction and not for structural support. This reduces the number of supports required and allows

manufacturing of more complex geometries. Powder preheating feature is available in very few

laser based systems where it is achieved by platform heating. In addition, entire EBM process

takes place under vacuum since, it is necessary for the quality of the electron beam. Vacuum

environment reduces thermal convection, thermal gradients and contamination and oxidation of

parts like titanium alloys . In SLM, part manufacturing takes place under argon gas environment

for reactive materials to avoid contamination and oxidation whereas non-reactive materials can be

processed under nitrogen environment. So it can be expected that EBM manufactured parts have

lower oxygen content than SLM manufactured parts .

In spite of having these advantages, EBM is not as popular as SLM because of its higher

machine cost, low accuracy and non-availability of large build up volumes. Characteristic features

of SLM and EBM are summarized in Table 1.

TABLE I. CHARACTERISTIC FEATURES OF SLM AND EBM

SLM EBM

Power source One or more fiber lasers of 200 to 1000 W

High power Electron beam

of 3000 W

Build chambcr environment Argon or Nitrogen Vacuum / He bleed

Method of powder preheating Platform heating Preheat scanning


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Powder preheating temperature (

C) [3435] 100-200 700-900

Maximum available build volume

(mm) 500 x 350 x 300 350 x 38O(0xH)

Maximum build rate (cm /hr) 20-35 80

Layer thickness (pm) 20-100 50-200

Melt pool size (mm) 0.1-0.5 0.2-1.2

Surface finish [7] (Ra) 4-11 25-35

Geometric tolerance (mm) [12] 0.05-0.1 0.2

Minimum feature size(jim) [39] 40-200 100

Fuse deposition modelling (FDM) is a common material extrusion process and is

trademarked by the company Stratasys. Material is drawn through a nozzle, where it is heated and

is then deposited layer by layer. The nozzle can move horizontally and a platform moves up and

down vertically after each new layer is deposited. It is a commonly used technique used on many

inexpensive, domestic and hobby 3D printers.

The process has many factors that influence the final model quality but has great potential

and viability when these factors are controlled successfully. Whilst FDM is similar to all other 3D

printing processes, as it builds layer by layer, it varies in the fact that material is added through a

nozzle under constant pressure and in a continuous stream. This pressure must be kept steady and

at a constant speed to enable accurate results .Material layers can be bonded by temperature control

or through the use of chemical agents. Material is often added to the machine in spool form as

shown in the diagram.

2. Extrusion Based System


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* Material Extrusion Step by Step

1. First layer is built as nozzle deposits material where required onto the cross sectional area

of first object slice.

2. The following layers are added on top of previous layers.

3. Layers are fused together upon deposition as the material is in a melted state.

Material Extrusion operates in a similar fashion to a hot glue gun; plastic filament is heated

to a malleable state and extruded through a nozzle. In order to create a part, a CAD model is sliced

into layers.

If the part has large overhangs, support material is required to prevent sagging and protect

part integrity. This support material is created either through thin, breakable trusses of the build

material or a second soluble material.

Advantages of the material extrusion process include use of readily available ABS plastic,

which can produce models with good structural properties, close to a final production model. In

low volume cases, this can be a more economical method than using injection moulding. However,

the process requires many factors to control in order to achieve a high quality finish. The nozzle

which deposits material will always have a radius, as it is not possible to make a perfectly square

nozzle and this will affect the final quality of the printed object. Accuracy and speed are low when

compared to other processes and the quality of the final model is limited to material nozzle

Material spool

Object/ model

Support material

Nozzle

Heated Element

Build Platform


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thickness .When using the process for components where a high tolerance must be achieved,

gravity and surface tension must be accounted for. Typical layer thickness varies from 0.178 mm

0.356 mm.

* Materials Used

The Material Extrusion process uses polyers and plastics.

Polymers: ABS, Nylon, PC, PC, AB

* Advantages:

1. Widespread and inexpensive process.

2. ABS plastic can be used, which has good structural properties and is easily accessible.

* Disadvantages:

1. The nozzle radius limits and reduces the final quality .

2. Accuracy and speed are low when compared to other processes and accuracy of the final

model is limited to material nozzle thickness.

3. Constant pressure of material is required in order to increase quality of finish.

Sheet lamination processes include ultrasonic additive manufacturing (UAM) and

laminated object manufacturing (LOM). The Ultrasonic Additive Manufacturing process uses

sheets or ribbons of metal, which are bound

together using ultrasonic welding.

The process does require additional CNC

machining and removal of the unbound metal,

often during the welding process. Laminated object

manufacturing (LOM) uses a similar layer by layer

approach but uses paper as material and adhesive

instead of welding. The LOM process uses a cross

hatching method during the printing process to

allow for easy removal post build. Laminated

objects are often used for aesthetic and visual

models and are not suitable for structural use.

UAM uses metals and includes aluminium, copper,

stainless steel and titanium. The process is low

3. Sheet Lamination Process


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temperature and allows for internal geometries to be created. The process can bond different

materials and requires relatively little energy, as the metal is not melted.

* Sheet Lamination Step by Step 1. The material is positioned in place on the cutting bed.

2. The material is bonded in place, over the previous layer, using the adhesive.

3. The required shape is then cut from the layer, by laser or knife.

4. The next layer is added.

5. Steps two and three can be reversed and alternatively, the material can be cut before being

positioned and bonded.

6.Sheet is adhered to a substrate with a heated roller.

7. Laser traces desired dimensions of prototype.

8. Laser cross hatches non-part area to facilitate waste removal.

9. Platform with completed layer moves down out of the way.

10. Fresh sheet of material is rolled into position.

11. Platform downs into new position to receive next layer.

12. The process is repeated.


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Laminated object manufacturing (LOM) is one of the first additive manufacturing

techniques created and uses a variety of sheet material, namely paper. Benefits include the use of

A4 paper, which is readily available and inexpensive, as well as a relatively simple and inexpensive

setup, when compared to others.

The Ultrasonic Additive Manufacturing (UAM) process uses sheets of metal, which are

bound together using ultrasonic welding. The process does require additional CNC machining of

the unbound metal. Unlike LOM, the metal cannot be easily removed by hand and unwanted

material must be removed by machining. Material saving metallic tape of 0.150mm thick and

25mm wide does however, result in less material to cut off afterwards. Milling can happen after

each layer is added or after the entire process. Metals used include aluminium, copper, stainless

steel and titanium. The process is low temperature and allows for internal geometries to be created.

One key advantage is that the process can bond different materials and requires relatively little

energy as the metal is not melted, instead using a combination of ultrasonic frequency and pressure.

Overhangins can be built and main advantage of embedding electronics and wiring . Materials are

bonded and helped by plastic deformation of the metals. Plastic deformation allows more contact

between surface and backs up existing bonds .

Post processing requires the extraction of the part from the surrounding sheet material.

With LOM, cross hatching is used to make this process easier, but as paper is used, the process

does not require any specialist tools and is time efficient. Whilst the structural quality of parts is

limited, adding adhesive, paint and sanding can improve the appearance, as well as further

machining.

* Materials

Effectively any sheet material capable of being rolled. Paper, plastic and some sheet metals.

The most commonly used material is A4 paper.

* Advantages: 1. Benefits include speed, low cost, ease of material handling, but the strength and integrity

of models is reliant on the adhesive used .

2. Cutting can be very fast due to the cutting route only being that of the shape outline, not

the entire cross sectional area

3. Relatively large parts may be made.

4. Paper models have wood like characteristics, and may be worked and finished accordingly

* Disadvantages: 1. Finishes can vary depending on paper or plastic material but may require post processing

to achieve desired effect

2. Limited material use

3. Fusion processes require more research to further advance the process into a more

mainstream positioning.

4. Dimensional accuracy is slightly less


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Direct-write technologies are the most recent and novel approaches to the fabrication of

electronic and sensor devices, as well as integrated power sources, whose sizes range from the

meso- to the nanoscales. The term direct write refers to any technique or process capable of

depositing, dispensing, or processing different types of materials over various surfaces following

a preset pattern or layout. The ability to accomplish both pattern and material transfer processes

simultaneously represents a paradigm shift away from the traditional approach for device

manufacturing based on lithographic techniques. However, the fundamental concept of direct

writing is not new. Every piece of handwriting, for instance, is the result of a direct-write process

whereby ink or lead is transferred from a pen, or pencil onto paper in a pattern directed by our

hands. The immense power and potential of direct writing lies in its ability to transfer and/or

process any type of material over any surface with extreme precision resulting in a functional

structure or working device.

Direct-write technologies are a subset of the larger area of rapid prototyping and deal with

coatings or structures considered to be two-dimensional in nature. With the tremendous

breakthroughs in materials and the methods used to apply them, many of which are discussed in

this book, direct-write technologies are poised to be far-reaching and influential well into the

future. The industry's push toward these technologies and the pull from applications rapidly

changing circuits, designs, and commercial markets are documented for the first time here.

Although direct-write technologies are serial in nature, they are capable of generating patterns, of

high-quality electronic, sensor, and biological materials among others--at unparalleled speeds,

rendering these technologies capable of satisfying growing commercial demands.

4.1. Laser Direct-Write From the earliest work on laser interactions with materials, direct-write processes have

been important and relevant techniques to modify, add, and subtract materials for a wide variety

of systems and for applications such as metal cutting and welding. In general, direct-write

processing refers to any technique that is able to create a pattern on a surface or volume in a serial

or spot-by-spot fashion. This is in contrast to lithography, stamping, directed self-assembly, or

other patterning approaches that require masks or pre-existing patterns. At first glance, one may

think that direct-write processes are slower or less important than these parallelized approaches.

However, direct-write allows for precise control of material properties with high resolution and

enables structures that are either impossible or impractical to make with traditional parallel

techniques. Furthermore, with continuing developments in laser technology providing a decrease

in cost and an increase in repetition rates, there is a plethora of applications for which laser direct-

write (LDW) methods are a fast and competitive way to produce novel structures and devices.

This issue of MRS Bulletin seeks to assess the current status and future opportunities of LDW

processes in the context of emerging applications.

4. Direct Write Technologies


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In LDW, the beam is typically focused or collimated to a small spot (in industrial

processes, this small spot can be several millimeters in diameter). Patterning is achieved by

either rastering the beam above a fixed surface or by moving the substrate or part within a fixed

beam. An important feature of LDW is that the desired patterns can be constructed in both two

and three dimensions on arbitrarily shaped surfaces, limited only by the degrees of freedom and

resolution of the motion-control apparatus. In this manner, LDW can be considered a rapid

prototyping tool, because designs and patterns can be changed and immediately applied without

the need to fabricate new masks or molds.

The key elements of any LDW system can be divided into three subsystems: (1) laser

source, (2) beam delivery system, and (3) substrate/target mounting system (Shown in Figure

1). At the heart of any LDW process is the laser source. Typical experiments and applications use

anywhere from ultrafast femtosecond-pulsed systems to continuous-wave systems employing

solid-state, gas, fiber, semiconductor, or other lasing media. In choosing an appropriate source,

one must consider the fundamental interactions of lasers with the material of interest. This requires

knowledge of the pulse duration, wavelength, divergence, and other spatial and temporal

characteristics that determine the energy absorption and the material response. In beam delivery,

there are a variety of ways to generate a laser spot, including fixed focusing objectives and mirrors,

galvanometric scanners, optical fibers, or even fluidic methods such as liquid-core wave- guides

or water jets. The choice depends on the application demands, for instance, the required working

distances, the focus spot size, or the energy required. The ultimate beam properties will be

determined by the combination of laser and beam delivery optics. Finally, the substrate mounting

is done in accordance with experimental or industrial requirements and can be manipulated in

multiple directions to achieve a desired result. Robotics and active feedback control, on either

the substrate or beam delivery optics, can add further design flexibility to the technique.

There is a vast range of LDW processes. For the purposes of this issue, we categorize them

into three main classes: 1.laser direct- write subtraction (LDW-), where material is removed by

ablation; 2.laser direct-write modification (LDWM), where material is modified to produce a

desired effect; and 3.laser direct-write addition (LDW+), where material is added by the laser.



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Figure 1. Schematic illustration of a laser direct-write system.

The basic components of an LDW system are (left to right) a substrate mounting system, a

beam delivery system, and a laser source. Motion control of either the beam delivery system or the

substrate mounting system is typically accomplished using computer-assisted design and

manufacturing (CAD/CAM) integrated with the laser source.

4.1.1. Laser Direct-Write Subtraction (LDW)

LDW (-) is the most common type of laser direct-write. In general, this entails processes

that result in photochemical, photo thermal, or photo physical ablation on a substrate or target

surface, directly leading to the features of interest. Common processes include laser scribing, cut-

ting, drilling, or etching to produce relief structures or holes in materials in ambient or controlled

atmospheres. Industrial applications using this technique range from high-throughput steel

fabrication, to inkjet and fuel-injection nozzle fabrication, to high-resolution manufacturing and

texturing of stents or other implantable biomaterials. At a smaller scale, inexpensive bench top

laser cutting and en- graving systems can be purchased by the hobbyist or small company for

artistic and architectural renderings. More recent developments in LDW- include chemically

assisted techniques such as laser-drilling ceramics or biomaterials and laser-induced backside wet

etching (LIBWE) of glass. In fact, one may also consider laser cleaning to be a controlled LDW-

process. The fundamental interactions leading to material removal can be thermal or a thermal,

depending primarily on the material/environment characteristics and the pulse duration of the laser.


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These interactions have a direct effect on the quality of the resulting features. For instance, a heat-

affected zone (HAZ) tends to occur in the vicinity of thermally removed material. This region has

structures and properties that can differ from the bulk material and can exhibit additional surface

relief. Either of these effects may be beneficial or detrimental, depending on the application. In

contrast, a thermal and multiphoton absorption processes caused by ultrafast lasers can reduce the

formation of a HAZ and enable features smaller than the diffraction limit.

4.1.2. Laser Direct-Write Modification (LDWM)

In LDWM, the incident laser energy is usually not sufficient to cause ablative effects but

is sufficient to cause a permanent change in the material properties. Typically, these processes rely

on thermal modifications that cause a structural or chemical change in the material. A common

example of such processes is the rewritable compact disc, in which a diode laser induces a phase

transition between crystalline and amorphous material. In industrial applications, one may consider

laser cladding, where a surface layer different from the bulk material is produced through melting

and resolidification, or solid free-form fabrication (SFF) approaches such as selective laser

sintering (SLS), as important modifying processes that would fall under the umbrella of LDWM.

Many LDWM applications require a specific optical response in the material of interest beyond

simple thermal effects. Optically induced defects or changes in mechanical properties can lead to

many non-ablative material modifications. For instance, photoresists respond to light by breaking

or reforming bonds, leading to pattern formation in the material. Alternatively, LDW can cause

defects in photo- etchable glass ceramics or other optical materials through single- and multiphoton

mechanisms, enabling novel applications in optical storage, photonic devices, and microfluidics.

4.1.3. Laser Direct-Write Addition (LDW+)

LDW+ is perhaps the most recent of the laser direct-write processes. In this technique,

material is added to a substrate using various laser-induced processes. Many techniques are derived

from laser- induced forward transfer (LIFT), where a sacrificial substrate of solid metal is

positioned in close proximity to a second substrate to receive the removed material. The incident

laser is absorbed by the material of interest, causing local evaporation. This vapor is propelled

toward the waiting substrate, where it recondenses as an individual three-dimensional pixel, or

voxel, of solid material. Such an approach has found important use in circuit and mask repair and

other small-scale applications where one needs to deposit material locally to add value to an

existing structure. This general technique has significant advantages over other additive direct-

write processes, in that these laser approaches do not require contact between the depositing

material and a nozzle, and can enable a broad range of materials to be transferred. Variations on

the general LIFT principle allow liquids, inks, and multi- phase solutions to be patterned with


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computer-controlled accuracy for use in a variety of applications such as passive electronics or

sensors.

Alternatively, LDW+ techniques can rely on optical forces to push particles or clusters into

precise positions, or on chemical changes in liquids and gases to produce patterns. For instance,

laser-induced chemical vapor deposition, or multiphoton polymerization schemes of liquid

photoresists, can be used to fabricate three-dimensional stereographic patterns. Examples of this

have been demonstrated and show promise for many applications such as fabricating photonic

structures or biological scaffolding.

*Applications

In many cases, applications tend to drive the development of new technologies, and direct

writing is one such technology. The need for direct writing electronic and sensor materials is

founded in exciting and often revolutionary applications, numerous examples of which will be

given here. The specific applications presented individually in each chapter are representative of

some areas where direct-write technologies could have an impact. As successful applications are

commercialized demonstrating the inherent flexibility of direct-write techniques the potential for

using direct-write products in other areas grows. Part I is devoted to applications of direct-write

material deposition, in particular, applications to defense electronics, chemical and biological

sensors, industrial applications, and small-scale power-management applications. Other exciting

applications are on the horizon for use in medicine, tissue engineering, wireless and other

communications, optoelectronics, and semiconductors.

Directed Energy Deposition (DED) covers a range of terminology: Laser engineered net

shaping, directed light fabrication, direct metal deposition, 3D laser cladding It is a more complex

printing process commonly used to repair or add additional material to existing components.

A typical DED machine consists of a nozzle mounted on a multi axis arm, which deposits

melted material onto the specified surface, where it solidifies. The process is similar in principle

to material extrusion, but the nozzle can move in multiple directions and is not fixed to a specific

axis. The material, which can be deposited from any angle due to 4 and 5 axis machines, is melted

upon deposition with a laser or electron beam. The process can be used with polymers, ceramics

but is typically used with metals, in the form of either powder or wire.

Typical applications include repairing and maintaining structural parts.

5. Directed Energy Deposition


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* Direct Energy Deposition Step by Step

1. A4 or 5 axis arm with nozzle moves around a fixed object.

2. Material is deposited from the nozzle onto existing surfaces of the object.

3. Material is either provided in wire or powder form.

4. Material is melted using a laser, electron beam or plasma arc upon deposition.


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5. Further material is added layer by layer and solidifies, creating or repairing new material features

on the existing object.

The DED process uses material in wire or powder form. Wire is less accurate due to the

nature of a pre- formed shape but is more material efficient when compared to powder (Gibson et

al., 2010), as only required material is used. The method of material melting varies between a laser,

an electron beam or plasma arc, all within a controlled chamber where the atmosphere has reduced

oxygen levels. With 4 or 5 axis machines, the movement of the feed head will not change the flow

rate of material, compared to fixed, vertical deposition.

* Materials

The Electron Beam Melting process uses metals and not polymers or ceramics.

Metals: Cobalt Chrome, Titanium

* Advantages: 1. Ability to control the grain structure to a high degree, which lends the process to repair work of

high quality, functional parts.

2. A balance is needed between surface quality and speed, although with repair applications, speed

can often be sacrificed for a high accuracy and a pre- determined microstructure.

* Disadvantages: 1. Finishes can vary depending on paper or plastic material but may require post processing to

achieve desired effect.

2. Limited material use

3. Fusion processes require more research to further advance the process into a more mainstream

positioning

6. Material Jetting (Not in Syllabus)

Material jetting creates objects in a

similar method to a two dimensional ink

jet printer. Material is jetted onto a build

platform using either a continuous or Drop

on Demand (DOD) approach. Material is

jetted onto the build surface or platform,

where it solidifies and the model is built

layer by layer. Material is deposited from

a nozzle which moves horizontally across

the build platform. Machines vary in

complexity and in their methods of

controlling the deposition of material. The

material layers are then cured or hardened

using ultraviolet (UV) light. As material must be deposited in drops, the number of materials


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available to use is limited. Polymers and waxes are suitable and commonly used materials, due to

their viscous nature and ability to form drops.

* Material Jetting Step by Step

1. The print head is positioned above build platform.

2. Droplets of material are deposited from the print head onto surface where required, using either

thermal or piezoelectric method.

3. Droplets of material solidify and make up the first layer.

4. Further layers are built up as before on top of the previous.

5. Layers are allowed to cool and harden or are cured by UV light. Post processing includes

removal of support material.

Drop on Demand (DOD) is used to dispense material onto the required surface. Droplets

are formed and positioned into the build surface, in order to build the object being printed, with

further droplets added in new layers until the entire object has been made. The nature of using

droplets, limits the number of materials available to use. Polymers and waxes are often used and

are suitable due to their viscous nature and ability to form drops. Viscosity is the main determinant


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in the process; there is a need to re-fill the reservoir quickly and this in turn affects print speed.

Unlike a continuous stream of material, droplets are dispensed only when needed, released by a

pressure change in the nozzle from thermal or piezoelectric actuators. Thermal actuators deposit

droplets at a very fast rate and use a thin film resistor to form the droplet. The piezoelectric method

is often considered better as it allows a wider range of materials to be used. The designs of a typical

DOD print head changes from one machine to another but according to Ottnad, typically include

a reservoir, sealing ring, Piezo elements and silicon plate with nozzle, held together with high

temperature glue.

* Materials The material jetting process uses polymers and plastics.

Polymers: Polypropylene, HDPE, PS, PMMA, PC, ABS, HIPS, EDP

* Advantages: 1. The process benefits from a high accuracy of deposition of droplets and therefore low waste.

2. The process allows for multiple material parts and colours under one process.

* Disadvantages: 1.Support material is often required.

2. A high accuracy can be achieved but materials are limited and only polymers and waxes can be

used.

7. Binder Jetting (Not in syllabus)

The binder jetting process uses two

materials; a powder based material and a binder.

The binder acts as an adhesive between powder

layers. The binder is usually in liquid form and

the build material in powder form. A print head

moves horizontally along the x and y axes of the

machine and deposits alternating layers of the

build material and the binding material. After

each layer, the object being printed is lowered

on its build platform.

Due to the method of binding, the material

characteristics are not always suitable for

structural parts and despite the relative speed of

printing, additional post processing (see below)

can add significant time to the overall process.


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* Binder Jetting Step by Step

1. Powder material is spread over the build platform using a roller.

2. The print head deposits the binder adhesive on top of the powder where required.

3. The build platform is lowered by the models layer thickness.

4. Another layer of powder is spread over the previous layer. The object is formed where the

powder is bound to the liquid.

5. Unbound powder remains in position surrounding the object.

6. The process is repeated until the entire object has been made.

The binder jetting process allows for colour printing and uses metal, polymers and

ceramic materials. The process is generally faster than others and can be further quickened by

increasing the number of print head holes that deposit material. The two material approach allows

for a large number of different binder-powder combinations and various mechanical properties of

the final model to be achieved by changing the ratio and individual properties of the two materials.

The process is therefore well suited for when the internal material structure needs to be of a specific

quality.


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* Materials

1. Metals: Stainless steel

2. Polymers: ABS, PA, PC

3. Ceramics: Glass

All three types of materials can be used with the binder jetting process.

* Advantages: 1. Parts can be made with a range of different colours.

2. Uses a range of materials: metal, polymers and ceramics.

3. The process is generally faster than others.

4. The two material method allows for a large number of different binder-powder combinations

and various mechanical properties.

* Disadvantages: 1. Not always suitable for structural parts, due to the use of binder material.

2. Additional post processing can add significant time to the overall process.

# Use and Benefits of AMP Additive manufacturing offers consumers and professionals alike the ability to create,

customize and/or repair products, and in the process, redefine current production technology. It is

a means to create highly customized products, as well as produce large amounts of production

parts. Products are brought to market in days rather than months and designers save money by

using additive manufacturing instead of traditional manufacturing methods. In addition, the risk

factor is much lower and those involved can receive near-immediate feedback because prototypes

take less time to produce.

For those looking to do rapid prototyping, additive manufacturing is extremely beneficial.

The technology lends itself to efficiently create quick prototypes, allowing designers and

businesses to get their products more quickly. When done in a large printer, multiple parts can be

done at once in less time.

A variety of industries use additive manufacturing to fabricate end-use product, consumer

and otherwise, including aerospace, architecture, automotive, education, game and medical

industries. The technology is popular among design and architecture firms as well. Industries and

businesses that build products and prototypes, as well as short run and on demand manufacturing

of components benefit from the use of additive manufacturing.



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ADDITIVE MANUFACTURING : THE OPPORTUNITIES AND CHALLENGES

The main AM opportunities lie in the design flexibility and in mass customization,

industrial secrecy protection, process sustainability and rapid product development, while the

challenges are related to Intellectual Property protection, standards certification, mass production

applications, regulatory issues and - at the moment - limited scalability. Hybrid machine tools that

incorporate CNC and AM could represent the next step for the development of the industry.

# Materials Used in AM Three types of materials can be used in additive manufacturing: polymers, ceramics and

metals. All seven individual AM processes, cover the use of these materials, although polymers

are most commonly used and some additive techniques lend themselves towards the use of certain

materials over others. Materials are often produced in powder form or in wire feedstock.

Other materials used include adhesive papers, paper, chocolate, and polymer/adhesive

sheets for LOM. It is essentially feasible to print any material in this layer by layer method, but

the final quality will be largely determined by the material. The processes above can also change

the microstructure of a material due to high temperatures and pressures, therefore material

characteristics may not always be completely similar post manufacture, when compared to other

manufacturing processes.

1. Polymers Common plastics can be used in 3D printing, including ABS and PC. The common

structural polymers can also be used, as well as a number of waxes and epoxy based resins. Mixing

different polymer powders can create a wide range of structural and aesthetic materials. The

following polymers can be used:

1. ABS (Acrylonitrile butadiene styrene)

2. PLA (polylactide), including soft PLA

3. PC (polycarbonate) Polyamide (Nylon)

4. Nylon 12 (Tensile strength 45 Mpa)

5. Glass filled nylon (12.48 Mpa)

6. Epoxy resin

7. Wax

8. Photopolymer resins

2. Ceramics Ceramic powders can be printed, including:

1. Silica/Glass

2. Porcelain

3. Silicon-Carbide


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3. Metals Metals: A range of metals can be used, including a number of options suitable for structural and

integral component parts. Common metals used:

1.Steel,

2.TItanium,

3. Aluminium,

4. Cobalt Chrome Alloy.

# Advantages of AM

Greater design ability. The technology allows assemblies to be printed in one process and

organic shapes to be easily produced. Traditional constraints of manufacture are reduced or

eliminated.

Unlike many widely used manufacturing techniques such as injection moulding, no tooling is

required, which can be a barrier to production due to the high cost.

Anywhere manufacture. Parts can be sent digitally and printed in homes or locations near to

consumers, reducing the requirement and dependence on transport.

Compared to conventional techniques with more geometric limitations, additive

manufacturing can produce models quickly, in hours, not weeks.

Fewer resources for machines and little skilled labour when compared to conventional model

making craftsmanship.

Customisation - Particularly within the medical sector, where parts can be fully customised to

the patient and their individual requirements.

Efficient material use due to the exact production of parts and no overproduction based on

estimated demand.

Commercial advantage and increased competitiveness, in the form of reduced costs and risk,

as the development time from concept to manufacture is minimised.

Material efficiency. Material required matches material used. Support material and powder can

often be recycled at source, back into the system.

Environmental benefits. The emissions from transport are reduced because of the ability to

manufacture anywhere.

With increasing numbers of machines, 3D printing is becoming more affordable, whereas

injection moulding machines remain relatively expensive and inaccessible.


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# Applications for Additive Manufacturing

technology Initially seen as a process for concept modelling and rapid prototyping, AM has expanded

over the last five years or so to include applications in many areas of our lives. From prototyping

and tooling to direct part manufacturing in industrial sectors such as architectural, medical, dental,

aerospace, automotive, furniture and jewellery, new and innovative applications are constantly

being developed.

It can be said that AM belongs to the class of disruptive technologies, revolutionising the

way we think about design and manufacturing. From consumer goods produced in small batches

to large scale manufacture, the applications of AM are vast.The number of users of these

technologies has been growing constantly, from artists, designers and individuals to large

companies and enterprises using AM to manufacture a wide range of final products.

INDUSTRIES CURRENT APPLICATIONS POTENTIAL FUTURE APPLICATIONS

COMMERCIAL AEROSPACE

AND DEFENSE

Concept modeling and prototyping Structural and non-structurat production

parts Low-volume replacement parts

Embedding additwely manufactured electronics directly on parts

Complex engine parts

Aircraft vring components

Other structural aircraft components

SPACE

Specialized parts for space exploration

Structures using Ight-weight, Ngh-strength materials

On-demand parts/spares in space large structures directly created in

space, thus circumventing launch

vehicle size Imitations

Automotive Rapid prototyping and manufacturing of

end-use auto parts

Parts and assemblies for antique cars andracecars

Quick production of parts or entire

Sophisticated auto components Auto components designed through

crowdsourcing

Health Care

Prostheses and implants

Medical instruments and models

Hearing aids and dental implants

Developing organs for transplants Large-scale pharmaceutical

production

Developing human tissues for regenerative therapies

CONSUMER PRODUCTS/

RETAIL

Rapid prototyping

Oeatmg and testing design iterations

Customized jewelry and watches

Umited product customization

Co-designing and creating with customers

Customized living spaces Growing mass customization of

consumer products

Currently, metal AM is not a process suitable for the mass production of millions of

identical simple parts. However, as systems and technologies advance, and processing time is

reduced, the use of AM for producing large quantities of parts will become a viable option.


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The advantages of AM derive from its high flexibility due to the product being produced

directly from a CAD model without the need for tooling. This also allows the AM process to

produce almost any geometry that can be designed.

There are some applications, for example dental restorations, that really tap the full

potential of AM. In this highly individualized production process it is economically viable to use

AM technologies, speeding up the production time without inflating the costs per part.

Applications in aerospace, for example the fuel nozzles for the GE LEAP engine, highlight

the possibilities of AM in this demanding sector. Additive Manufacturing allowed engineers to

design a fuel nozzle which is 25% lighter and five times more durable than the previous part.

********** Thank You *************



UNIT 5.Cover page.pdfAMP U 5.pdf

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