Amp notes unit 4-6 by badebhau

UNIT 4.
ADVANCED MANUFACTURING PROCESS
Micro
Machining
Processes
Semester VII – Mechanical Engineering SPPU
badebhau4@gmail.com
Mo.9673714743

1.
SND COE & RC . Yeola. badebhau4@gmail.com
Mo.9673714743
Syllabus :
1. Diamond Micro Machining (DMM)
2. Ultrasonic Micro Machining (USMM)
3. Micro Electro Discharge Machining (MEDM)
Higher accuracy and performance requirements, coupled with demands to reduce costs,
has led to significant developments in advanced CNC diamond turning and grinding machines. A
long term manufacturing trend in which tolerances for many strategic products are decreasing by
a factor of 3 every 10 years, on critical dimensions, was highlighted in a USA report .
The use of diamond cutting tools has increased in importance as tighter tolerances and
greater surface integrities are required for high value components. Ultra precision cutting tools
need to be hard and sharp and to have enhanced thermal properties in order to maintain their size
and shape while cutting. Advantages offered by diamond include:
- Crystalline structure, which enables very sharp cutting edges to be produced,
- High thermal conductivity, the highest of any materials at room temperature,
- Ability to retain high strength at high temperatures,
- High elastic and shear moduli, which reduce deformation during machining.
The earliest documented evidence of diamond machining found to date describes the
diamond turning carried out by Jesse Ramsden, FRS in 1779. Ramsden machined a screw harned
and tempered steel , with a diamond pointed tool, for use in his linear dividing engine for precision
scale making. Diamond is, however, chemically attacked by ferrous materials at high temperatures,
and is generally unsuitable for the machining of steels and nickel alloys. This is because of the
very high wear rate of the diamond which results in nonviable tool costs.
More recently diamond machining has been used for the machining of nonferrous metals
such as aluminum and copper, which are difficult materials on which to obtain a mirror surface by
grinding, lapping, or polishing. This is because these metals are relatively soft and the abrasive
processes scratch the finished surface and, furthermore, are unable to produce high levels of
flatness at the edges of the machined surface. However, diamond grinding has become an
1. Diamond Micro Machining (DMM)
EaI svaamaI samaqa-
Micro Machining Processes
AMP
Unit.4

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important process for the machining of brittle materials, for example, glasses and ceramics. The
ability to control precisely the cutting tool position relative to the workpiece is a significant
advantage offered by advanced CNC diamond turning and grinding machines. This enables them
to produce components that are extremely precise and accurate. On the other hand, the relative
position of the tool and workpiece is “force” controlled with lapping and polishing. This makes it
very difficult to obtain precise control of the tool's path for shapes other than simple geometric
forms. Diamond machining is therefore proving to be a cost effective process for the production
of complex shaped components that have high accuracy requirements for form and / or surface
finish.
Diamond micromachining is of particular interest for the optical and electronic industries.
The processes are capable of simultaneously achieving high profile accuracy, good surface finish,
and low sub surface damage in brittle materials needed, for example, for semiconductors, magnetic
read-write heads, and optical components.
Single-point diamond turning and ultra-precision diamond grinding are both capable of
producing extremely fine cuts and small chips.
Fig.1 Scanning electron micrograph of electroplated copper, diamond turned at a depth of around 1 nm.
Figure 1. Shows a scanning electron micrograph of electroplated copper cut by a sharp
diamond on an ultra-precision machine tool. The undeformed chip thickness is approximately
1 nm. Because of the very fine chip thickness produced by the micro-cutting processes, the chip-
1.1 MACHINING PRINCIPLES

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forming model for turning is different from that for grinding , moving from concentrated shear to
micro extrusion as shown in Figure 2.
Fig.2 (a) Cutting concentrated shear model . (b) Fine grinding microextrusion model
Important characteristics of materials considered for diamond micromachining are
impurities (inclusions) in the material, grain boundaries of polycrystalline materials, and in
homogeneities. These can cause small vibrations of the cutting tool, resulting in a deterioration in
surface finish. Another factor affecting the quality of surface finish as well as consistency of form
is the high coefficient of expansion coupled with low thermal conductivity of some plastics which
are diamond turned. These thermal effects are, to some extent, minimized when cutting with a
diamond tool due to its sharp cutting edge, low coefficient of friction, and high thermal
conductivity which conducts the heat away. The theoretical peak-to-valley surface roughness
which can be achieved by diamond turning using a round-nosed cutting tool is limited to :
𝐑𝐭 =
𝐟 𝟐
𝟖∗𝐓𝐫
(1)
Where ,
Rt - Theoretical peak to surface roughness (mm),
F – Feed-rate per revolution of the work-spindle (mm. rev -1
),
Tr -Tool nose radius (mm).
Chip
Vch
Grit
Plastich
P
Vs

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However, this equation ignores any of the errors inherent in machine, and a more accurate
equation takes account of the asynchronous error motion of the machine in the direction normal to
the component surface. The actual peak-to-valley surface roughness now becomes:
𝐑𝐭 =
𝐟 𝟐
𝟖∗𝐓𝐫
+ 𝑓( 𝐸𝑠𝑦𝑛) (2)
where Esyn is the asynchronous error motion (mm) in the direction normal to the machined
surface.
The need for the micromachining of hard and brittle materials has led to significant
improvements in machine tool technology. It is now possible to produce plastically deformed
chips, when machining brittle materials, if the depth of cut is sufficiently small. This process is
known as ductile or shear mode machining. It has been shown that a “brittle-to-ductile” transition
exists when cutting brittle materials at low load and penetration levels. This “ductile” mode
machining is important for the cost-effective production of high-performance optical and advanced
ceramic components, with extremely low levels of subsurface damage (micro-cracking). This
enhances their performance and strength significantly and eliminates, or minimizes, the need for
post polishing.
Figure 3. Cutting model for the brittle/ductile regime diamond turning of brittle materials.
The transition from ductile to brittle fracture has been widely reported and is usually
described as the “critical depth of cut.” This is generally small (i.e. 0.1 to 0.3 μm), as is the
associated feed rate, and this results in relatively slow material removal rates. However it is a cost-
1.2 Brittle Materials

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effective technique for producing high quality spherical and non-spherical optical surfaces,
without the need for polishing.
Figure 3. shows the machining model for turning or fly cutting a brittle material , in which
the depth of cut and critical chip thickness (dc) are shown . The location of the critical chip
thickness is dependent on feed. For example, it is located towards the upper edge of the shoulder
when ne feed-rates (f) are used and the micro-fracture damage zone is removed during machining.
In this case subsurface damage does not extend into the cut surface. However, if the feed-rate
increases, the critical chip thickness moves down towards the cut surface and this results in the
micro-fracture damage penetrating into the final cut surface. In micromachining it is normally
important to ensure that these cracks do not occur by removing the material in a ductile mode.
The process requires careful selection of the machining parameters in order to maximize
the material removal rate while maintaining high surface and subsurface integrity. It also demands
high-precision, high stiffness machine tools with smooth motions.
Ductile mode machining is required when machining mirror like surfaces in hard and brittle
materials. However, in order to achieve this condition the actual depths of cut required, to avoid
crack generation, can be on the order of 0.1 to 0.01 of those used for cutting “mirror” surfaces in
metals.
Gerchman and McLain early work on the machining of germanium in which they diamond-
turned germanium to a surface roughness of 5 to 6 nm These were spherical surfaces, 50 mm in
diameter, for which the removal rate was given in terms of 2.5 μm per revolution of the workpiece
together with a 25-μm depths cut. More recently Shore has reported that removal rates the order
of 2 to 4 mm3
per minute have been obtained when diamond turning germanium optics of 100-mm
diameter. The tool life (expressed as the useful cutting distance of the too) when producing optical
surfaces (<1 nm Ra) at these removal rates was in excess of 12 kilometers. When machining silicon
at similar removal rates, as with germanium, tool life was found to be less than 8 kilometers. The
surface finish quality was also on the order of 1 nm Ra. Tool life was higher, when machining zinc
sulphide, being in excess of 20 kilometers, although the surface quality was lower, with a
roughness value of 3.6 nm Ra.
When diamond micro-turning a large area of brittle material (e.g., optical devices) the
continuous use of a single point tool can result in major problems if it is found necessary to change
the cutting tool when partway through a cut. A grinding wheel, however, has innumerable cutting
1.3 RATES OF MICROMACHINING FOR RELEVANT MATERIALS
1.3.1 Diamond Turning
1.3.2 Diamond Grinding

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points (grits) yield a higher machining rate. Diamond micro-grinding therefore be expected to
improve the commercial viability the ductile mode machining of brittle materials.
While grinding is a multipoint process that relies on mechanical actions, it has been that
chemical effects also Play a significant role in material removal rates when using micron-size
abrasive grits to grind glasses in a ductile mode. A relatively soft hydrated layer is formed on the
glass surface the chemical reaction between the coolant and the glass.
For the ductile mode grinding of optical glasses ,the material removal rates of 0.75 to 1.55
mm3
per minute, when normalized for a 100-mm diameter optical component. This value was
obtained when producing surface rough-nesses of 1 to 3 nm Ra, which are close to what can be
achieved by the polishing process. A possible technique to obtain higher removal rates, when
ductile grinding, is to utilize very high grinding wheel speeds. These should, theoretically, reduce
the un-deformed chip thickness, and thus the cutting force per grit, resulting in more ductile flow
coupled with less strength degradation.
Diamond micromachining is used to produce either:
1. Small workpiece features, by means of tools with cutting features below 100 μm, or
2. Sub-μm or nanometric tolerances and/or surface finishes on macro-components.
Very sharp-edged diamond tools have been used in the production of ultrafine optical gratings
with an accuracy of 1 nm, and gratings with 1-nm resolution can now be obtained for use on ultra-
precision machine tools. The most accurate diamond turning and grinding machines currently
available are capable of achieving geometric accuracies of size and profile on the order of 100 nm
for dimensions of 250 mm. Surfaces of 0.8 nm Ra have also been diamond-machined on several
materials, including germanium. Diamond micromachining demands extremely smooth
movements, particularly between the spindle and the tool. In order to achieve this, hydrostatic oil
and air bearings are generally required for the spindles and guide ways. Other stringent
requirements required from the machine tool are:
1. Extremely high loop stiffness between the tool and workpiece,
2. The ability to apply and maintain very small depths of cut, as low as a few nm in some cases,
3. Low thermal drift, and
4. The ability to operate at uniform feed-rates over a wide range.
Other aspects to be considered during the design stage include:
1. The type of coolant and its application, filtration and temperature control,
2. Work-holding methods.
1.4 ACCURACY AND DIMENSIONAL CONTROL OF DMM

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Over the last 30 years the number of applications for diamond turning of a wide range of
materials, and the diamond grind-in£ of brittle materials (e.g. glasses and ceramics) has in-leased
significantly following the technological breakthrough in direct CNC machining in the so-called
“ductile regime,’ is free from retained brittle fracture damage. Diamonds are used in either single
crystal or compacted polycrystalline form to machine a wide range of essentially nonferrous
materials.
Single crystal diamond turning has been used to machine microgrooves 2.5-μm wide by
1.6-μm deep in copper . The slopes of the grooves were produced with a surface finish to 10 nm
Rmax, and the application was the fabrication of lens master discs for the molding of high efficiency
grating lenses. Diamond turning is being used increasingly as a high-precision, high-production
rate process for a wide range of products including:
1. Spherical and aspherical molds for plastic opthalmic lenses, and for medical
instrumentation and micro-laser optical disc/CD players.
2. A wide range of reflecting optics components. For example, aluminum scanner mirrors,
space communication and high-power machining laser optics, and aluminum substrates for
glancing incidence mirrors for X-ray telescopes.
3. Infrared hybrid lenses for thermal imaging systems. Typical materials include germanium,
zinc sulphide, zinc selenide, and silicon.
4. Aluminum alloy automotive pistons which are machined, in the cold state, to complex
profiles with tolerances on the order of 3 to 10 μm.
5. Aluminum alloy substrate drums for photocopying machines.
There are, however, numerous new applications where components are required to have
lower mass, higher hardness and wear resistance, improved chemical inertness, and higher strength
and fatigue life, often while working at higher temperatures than before.
The worldwide research and development, ceramic and intermetallic materials are ready to
be used in gas turbines, pumps, computer peripherals, piston engines, and many other engineering
products on a much wider scale. For many of these applications grinding, in the ductile mode, is
necessary in order to retain material integrity through the minimization of subsurface damage and
micro-cracking, which reduce the strength and fatigue life of ceramic components.
Diamond micromachining technology for the efficient manufacture of opto-electronics
devices is clearly of critical importance in ensuring its progress covering broadband light-wave
1.5 Application of DMM
1.5.1 Diamond Turning
1.5.2 Diamond Grinding

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communication, high-density optical memories, and optical parallel signal processing. Although
process development has concentrated on VSLI technologies such as lithography, there is clearly
scope for applying ductile mode grinding, slitting, and trenching techniques for the efficient
manufacture of monolithic integrated optics components. These techniques are analogous to the
ultra-precision grinding of magnetic memory disk file sliders (or flying heads), but now in the
ductile regime. The introduction of free abrasives into fixed abrasive processing can be shown to
improve surface finish and productivity. Several hundred components can be machined at one set-
up to submicron tolerances, producing low-energy-loss contacting optical surfaces (<2 nm Ra and
zero surface micro-cracks) lending themselves to kinematic design for submicron assembly, with
large consequent savings in assembly and test labor costs.
2.1 Principle of USMM
Micro ultrasonic machining (micro USM), is one of the efficient material removal
processes especially suitable for the micromachining of hard and brittle materials. The principle
of micro USM is shown in Figure.1. In micro USM workpiece which is placed on the workpiece
table vibrates at ultrasonic frequency (40 KHz). Abrasive slurry is injected on the top of the
workpiece. There is a rotating tool which hits the abrasive particles in the slurry which in turn hit
the workpiece and chip away the material from it. The vibrations given to the workpiece aid in
refreshing the slurry so that fresh abrasive particles are in contact with the workpiece and also in
removing the debris from the tool workpiece gap.
The abrasive slurry acts as lubricating agent as well as coolant in reducing the frictional
heat generated due to the movement of the abrasive particles on the workpiece and heat generated
by the vibrations due to the transducer. The slurry also collects the debris from the machined area.
In general micro USM is carried out with water as the medium due to its properties of excellent
coolant, easy removal of debris from machining zone due to low viscosity, low cost and easy
availability.
Particles affect both part and tool : material removal takes place at the workpiece; wear
occurs on both the tool and particles. The process is therefore characterized by removal rate on the
workpiece, tool wear, and abrasive wear.Ultrasonic machining can deal efficiently with brittle
materials. The tools should be made from materials that can resist wear: they should be either
ductile (aluminum alloys, steel, titanium alloys, nickel alloys) or extremely hard (diamond). The
abrasive particles have to be harder than the workpiece material: aluminum oxide, silicon carbide,
boron carbide, and diamond are used.
2. Ultrasonic Micro Machining (USMM)

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In many conventional machining processes like grinding, milling and broaching processes
oil has been successfully used as cutting fluid. These oils can be used either as straight oils, which
are pure petroleum based oils or emulsifiers which are water based oils. Use of straight oils have
excellent lubricating properties and are used especially for machining process involving low
speeds, low clearance requiring high quality surface finish. These oils have more viscosity and
good lubricating properties than water and causes less tool wear. Hence, it may be prudent to use
oil based slurry in micro USM.
An micro USM system based on the design concept of “vibration on work piece ” is
schematically shown in Figure 2 . A micro tool, attached to a mandrel rested on V- shaped block
is rotated by a DC motor and is free to move in X, Y and Z directions with six degrees of freedom.
Micro tools with different diameters are prepared by Wire Electrical Discharge Grinding (WEDG).
The micro tool is sensitive to elastic bending, vibration, and breakage. Therefore, the contact force
between tool and workpiece needs to be controlled and limited to a certain level during machining.
This is achieved by implementing a close-loop control strategy with force feedback. Key system
2.1.1 Working

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components such as electronic balance and three-axis stage have high resolution (0.1 mg and 25
nm, respectively) to meet the demand of accuracy in micro machining.
Fig.2 Schematic of Micro USM
The USM process is able to machine any material, but is more efficient on brittle materials.
Hard materials like stainless steel, glass, ceramics, carbide, quatz and semi-conductors are
machined by this process. It has been efficiently applied to machine glass, ceramics, precision
minerals stones, tungsten.
The actual cutting tools are the abrasive particles. Their characteristics and dimensions
have to be adapted to the material to be machined and to the specific application intended.
The hardness of the abrasive particles has to be higher than that of the workpiece material.
For example, silicon carbide can machine glass, graphite, silicon, aluminium oxide, or precious
stones; boron carbide has to be used for harder materials such as silicon carbide and silicon nitride.
Diamond is the only abrasive able to machine even harder materials like diamond. For ease of use,
and owing to cost, boron carbide is often chosen for machining every material except diamond,
1. X,Y,Z positions of
the tool
2. Tool holder
3. Tool
4. Workpiece
5. Ultrasonic transducer
6. Ultrasonic vibration
generator
7. Static load sensors
8. Static measurement
unit
9. Computer
2.2. Material of Micro USM
2.2.1 Workpiece Material
2.2.2 Abrasive Materials

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and diamond is used only when boron carbide is insufficiently hard.Wear of particles is a crucial
factor, since removal rate depends on particle diameter. Grains can be worn rapidly.
The abrasive slurry contains fine abrasive grains. The grains are usually boron carbide, aluminum
oxide, or silicon carbide ranging in grain size from 100 for roughing to 1000 for finishing. It is
used to microchip or erode the work piece surface and it is also used to carry debris away from
the cutting area .
Tool material should be tough and ductile. Low carbon steels and stainless steels give good
performance. Tools are usually 25 mm long ; its size is equal to the hole size minus twice the size
of abrasives. Mass of tool should be minimum possible so that it does not absorb the ultrasonic
energy. Two main considerations arise in the selection of the tool material; fabrication and cost.
Tool wear during ultrasonic machining also has to be taken into account.
Piezoelectric transducers utilize crystals like quartz whose dimensions alter when
being subjected to electrostatic fields. The charge is directionally proportional to the applied
voltage. To obtain high amplitude vibrations the length of the crystal must be matched to the
frequency of the generator which produces resonant conditions.
In machining with fine sized grains, the MRR increases with the increase in the abrasive
particles due to increase in the number of particles involved in the machining. MRR is more when
machining with the water as oil is more viscous than water hampers the process of debris removal
in the processing of machining thus accounting for less MRR.
Using medium sized particles, MRR increases with the increase in the concentration as
there are cutting edges for a given volume of abrasive slurry. The MRR is more when machined
with oil compared to water as shows the comparison of MRR between water based and oil based
slurry with respect to the varying abrasive slurry concentrations for the particle size of 1-3.
When machining with coarser grains the MRR is more when machined in aqueous medium
compared to oil. As the grains become coarser the grain boundaries try to interlock reducing the
number if cutting edges. Oil possessing more viscous property interlocks these grains strongly
compared to water thus contributing to less MRR.
In general, needed accuracy entails both roughing and finishing, since quality can seldom
be obtained in a single operation. Roughing is performed with large grains (20 to 120 μm) to give
2.2.3 Tool Materials
2.3.4 Piezoelectric Tranducer
2.4 Material removal rate (MRR)
2.5 ACCURACY AND TOLERANCE IN USMM

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sufficient removal rate; finishing is achieved through grains fine enough (0.2 to 10 μm) to obtain
the desired quality. Drilling of very small holes is performed in a single operation.Tool wear is of
major consideration for accuracy, since it affects both tool geometry and dimension.
Accuracy strongly depends on the machining mode (Fig 4.). In sinking, it is the result of tool initial
accuracy tool wear abrasive dimensions and working parameters. The lateral gap between tool and
part is found bet one and two times more than the abrasive main diameter, frontal gap is a little
larger, due to amplitude of vibrations. Fluctuations of gap are smaller for smaller grains. In general
when drilling, the use of roughing (40 μm) and finishing (5 μm) can provide +/-10-μm accuracy.
When finer grains, about 1 μm or less, are used, accuracy can be better than +/-5 μm. This includes
the tool accuracy. It is difficult to provide estimates of accuracy for very small holes (10 to 200
μm), because of difficulties with tool accuracy. In contouring, accuracy can even be better, since
tool imperfections can be compensated by 3-D movements.
In ultrasonic micromachining, since very fine grains are used, a +/—5 μm (or better) accuracy can
be obtained when tools are conventionally made. A higher accuracy can be achieved by using
specially manufactured tools (e.g„ the tool form is produced on the USM machine, by use of wire
EDM).
When machining with finer grains the surface , finer grains having constant cutting edges
hit the workpiece repeatedly. Further the debris is added in the process of material removal
increasing the frictional heat making the surface rougher with the increase in the concentration.
However oil acting as coolant reduces the surface roughness to some extent. Thus producing good
surface finish compared to machining in water medium.
Fluid +
AbrasiveFluid +
Abrasive
sonotrode
2.5.1 Surface Roughness

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Using medium sized abrasives the surface roughness, with the increase in the concentration
the particle size decreases in the process of machining, indicating more number of particles to
absorb the heat generated during the process which eventually reduces the surface roughness.
However surface roughness for oil is less compared to water since water acting as coolant absorbs
the generated heat.
When machining with coarser size grains, as the concentration increases there are more coarser
particles hitting the work surface thus making it rougher. Since oil acts as better coolant than water
thus giving better surface finish.
1. Machining any materials regardless of their conductivity
2. USM apply to machining semi-conductor such as silicon, germanium etc.
3. USM is suitable to precise machining brittle material.
4. Can drill circular or non-circular holes in very hard materials
5. Less stress because of its non-thermal characteristics .
6. It can be used machine hard, brittle, fragile and non conductive material.
7. It is burr less and distortion less processes.
1. USM has low material removal rate.
2. Tool wears fast in micro USM.
3. Machining area and depth is restraint in micro USM.
4. It is difficult to drill deep holes, as slurry movement is restricted.
It is mainly used for
(1) drilling (2) grinding, (3) Profiling (4) coining (5) piercing of dies
(6) welding operations on all materials which can be treated suitably by abrasives.
7. USM can be used to cut industrial diamonds
8. USM is used for grinding Quartz, Glass, ceramics.
Application of USMM can be found in electronics , aerospace , biomedicine , and surgery.
2.6 Advantages
2.7 Disadvantages
2.9 Applications

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Micro-electro-discharge machining (also known as micro-EDM, μ-EDM, and electro-
discharge micromachining) has been developed in the past 30 years from the nonconventional
manufacturing technique of electro-discharge machining (EDM) commonly known as spark
erosion.
While EDM has been used as a production tool for over 50 years, true μ-EDM only
commenced in 1967 when Kurafuji and Masuzawa succeeded in machining 6-μm diameter circular
holes through GTi 10 cemented carbide 50-μm thick, thus demonstrating the rapid production of
high aspect-ratio holes. Since that time, there has been a concerted effort to improve the micro-
machining rates of various materials, without loss of accuracy, and to improve the excellent surface
finish and dimensional control already associated with the EDM technique.
As might be expected, commercial μ-EDM equipment has been produced by companies
in Switzerland and Japan, acknowledged centers of excellence in micro-technology and precision
engineering , μ-EDM is now being to machine a wide variety of miniature and micro-parts from
electrically conductive materials such as metals, alloys, sintered metal, cemented carbides,
ceramics, and silicon , μ-EDM may also be used to produce molds and dies that can themselves be
utilized to manufacture other micro=parts from both conductive and nonconductive materials such
as plastics.
Micro electro discharge machining (Micro-EDM) is a derived form of EDM, which is
generally used to manufacture micro and miniature parts and components by using the
conventional electro discharge machining principles. Similar to conventional EDM, material is
removed by a series of rapidly recurring electric spark discharges between the tool electrode and
the workpiece in Micro-EDM. Actually main differences of Micro- EDM from conventional
EDM are being in the type of pulse generator, the resolution of the X-, Y- and Z- axes movement,
and the size of the tool used. In Micro-EDM; pulse generator produces very small pulses within
pulse duration of a few micro seconds or nano seconds. Because of this reason, Micro-EDM
utilizes low discharge energies to remove small volumes of material. The most important factor
which makes Micro-EDM very important in micromachining is its machining ability on any type
of conductive and semi-conductive materials with high surface accuracy irrespective of material
hardness. It is preferred especially for the machining of difficult-to-cut material due to its high
efficiency and precision.
Small volumetric material removal of Micro-EDM provides substantial opportunities for
manufacturing of micro-dies and micro-structure such as micro holes, micro slot, and micro gears
etc. The use of Micro-EDM has many advantages in micro-parts, the main advantage is that it
can machine complex shapes into any conductive material with very low forces. The forces are
3. Micro Electro Discharge Machining (MEDM)
3.1 Basic Principles of Micro Electro Discharge Machining

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very small because the tool and the workpiece do not come into contact during the machining
process. This property provides advantages to both the tool and the workpiece. For example, in
EDM, a very thin tool can be used because it will not be bent by the machining force. The other
advantages of Micro-EDM include low set-up cost, high aspect ratio, enhanced precision and
large design freedom. In addition, EDM does not make direct contact between the tool electrode
and workpiece material, hence eliminating mechanical stress, chatter and vibration problems
during machining. Therefore, relying on the above advantages, Micro-EDM is very effective to
machine any kind of holes such as small diameter holes down to 10 µm and blind holes with 20
aspect ratio.
Although Micro-EDM is a very efficient process in micro hole machining and having
many advantages, it has also some disadvantages. One of them is that it is a rather slow machining
process; the other is that while the workpiece electrode is being machined, the tool electrode also
wears at a rather significant rate. This tool-wear leads to shape inaccuracies. Another drawback
is the formation of a heat affected layer on the machined surface. Since it is impossible to remove
all the molten part of the workpiece, a thin layer of molten material remains on the workpiece
surface, which re-solidifies during cooling.
Another significant point of Micro-EDM is the inverted polarity of the tool electrode. Due
to polarity effect in conventional EDM with long pulse duration, the tool electrode is usually
charged as anode to increase material removal rate and to reduce electrode wear. At short pulse
durations as used in Micro-EDM, this effect is reversed. Therefore, in Micro-EDM, the tool
electrode is usually charged as cathode.
Micro-EDM can be used as variant machining processes; they are Micro-ED drilling,
Micro-ED milling, Micro-ED die sinking, Micro-ED contouring, Micro-ED dressing, and Micro
wire electrical discharge grinding (Micro-WEDG). All of these processes are integrated in a
today’s sophisticated micro-EDM machines.
Figure 1. shows the photograph of the Micro-EDM setup. The major components of the
Micro-EDM setup are the machine tool itself, the pulse generator, the CCD camera associated
with the monitor and the microscope for analysis. A more detailed image of the Micro-EDM
machine tool is shown in Figure 2. The Figure 2. shows different parts and components of the
Micro-EDM machine tool.

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Figure 1. Micro EDM Set-up
Figure 2. Detailed image of the Micro- EDM machine tool

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Figure 3. Schematic drawing of Micro-EDM system
A machine made four axis movements Micro-EDM machine as it is shown in Figure 2. is
used for micro hole machining. The machine has a pulse generator. This generator is able to
produce pulses from 50 ns to 2 µs with electrical current peak values up to 50 A. Power supply
can vary voltage levels from 50 V to 250 V, but this is limited up to 100 V for the used Micro-
EDM machine. In addition to the micro erosion generator, the micro-EDM machine is also
composed of the following parts; control unit panel. Micro-electro discharge machining (Micro-
EDM) is a process of removing electrically conductive materials by rapid, repetitive spark
discharges from pulse generator with dielectric flowing between tool and work piece.
Electro-discharge machining (EDM) is well suited for micro machining high-strength
conductive materials since neither mechanical contact nor cutting is necessary. Materials such as
stainless steel and tungsten carbide are machined easily with electro-discharge and negligible
cutting forces are applied to the tool or workpiece. The main disadvantage of electrical discharge
is that during each discharge some material is removed from the tool. The melting temperature,
conductivity, and change of yield stress due to temperature determine the wear rate of the tool and
workpiece.
Micro-electro discharge machining process is a widely used micro fabrication technique to
produce micro-parts and components needed in the micro-mechatronic systems and industrial
applications. Micro-hole fabrication is a primary task for this thesis because micro-hole is the most
simple and widely used micro products that can be manufactured by using Micro-EDM.
1. Sarix control unit
2. Wire dressing unit
3. Dielectric liquid
tank
4. GPIB connection
5. Oscilloscope
6. Low resistance3
resistor
7. PC
1.
2.
3.
4.
7.
6.
5.

Mo. 9673714743.
18
The WEDG process, illustrated in Figure 3, is similar to turning on a lathe. A simple RC
circuit generates pulses that produce electrical discharges between the workpiece (anode) and a
φ100 µm brass wire (cathode).
Fig 4.Wire Electro-Discharge Grinding
The discharges occur across a small gap (~ 2µm) filled with dielectric oil. The
workpiece is held vertically in a mandrel that rotates at 3000 RPM, and its position is slowly fed
in the z-direction. The wire is supported on a wire guide, and its position is controlled in the x-
and y-directions. Each electrical discharge erodes material from the workpiece and the brass wire.
To prevent discharges from worn regions of the brass wire, the wire travels at 340 µm/s, and is fed
around a reel and take-up system as illustrated in Figure .5
3.2 Wire Electro-Discharge Grinding (WEDG)

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19
Fig. 5 Traveling Wire in WEDG
Fig.6.Typical Steps and Conditions for WEDG
A micro shaft is usually produced in three consecutive steps as illustrated in Fig 4. In the
first step, the workpiece is positioned above the traveling wire, and the end of the shaft is machined
by feeding the wire/guide in the x-direction. The second step is to rough cut the shaft and reduce
the diameter of the stock material by feeding the workpiece in the z direction. A high material
removal rate (MRR) is achieved during the rough cut by increasing the energy of each discharge,
which depends upon the energy stored by the capacitor as given in Equation (1). The final step is
to finish cut the shaft. The voltage and capacitance are reduced to achieve improved form and
surface finish. Although the multi-step process is based on the premise that improved precision is
obtained by reducing the capacitance and voltage, a numerical relation for straightness or
roughness is not available.
E=
1
2
𝐶𝑉2
(1)
Substantial effort has concentrated on the precision of holes or cavities machined by micro
EDM using cylindrical electrodes made by WEDG. Masuzawa et al. [7,8] used a vibroscanning
method to measure holes drilled by micro EDM, and Yu et al. [9,10] developed the uniform wear
method to reduce inaccuracy arising from electrode wear when micromachining cavities. Yu et
al. [11] later studied the influence of current, voltage, layer depth, and feed on the material removal
rate, electrode wear ratio, and gap during contour milling with a cylindrical electrode.
3.3 RATES OF MICROMACHINING FOR RELEVANT MATERIALS
The rate of machining is dependent on the discharge energy, which for the
attainment of fine surface finish is kept low (<10-7
J per pulse) in μ-EDM.

Mo. 9673714743.
20
Various techniques have been utilized to try to increase the material removal rate
such as :
Switching a larger capacitance into the RC circuit, thus producing a large discharge energy,
pielectric flushing,
Jump action and vibrofeeding of the tool, premachining holes to allow debris to flow away
from the electrode , and
Use of controlled pulse generators in WEDM .
The accuracy and dimensional control of parts made by μ -EDM varies with the types of
machines used.
Maximun hole diameter =300 μm
Minimum hole dia. = 10 μm.
Wire material = Tungsten
Wire diameter = 30 μm
Part and part material =injection die and Inbox
Surface finish =0.15 μm
Max. dimensional variations ± 1
Machining time =47 min
The applications of μ-EDM are many and various. :
Micro-shafts and pins
Micropipes
Inkjet nozzles
High aspects ratio holes
High aspects ratio slots
Square cornered cavities
3.4 ACCURACY AND DIMENSIONAL CONTROL
3.5 Application of 𝛍-WEDM

Mo. 9673714743.
21
Dies
Micro-gear wheels
Special orifice
Micro-EDG appears to be the least common form of μ-EDM. However, it has been reported
that 60-mm long channels, 900-μm to deep and 60-μm wide with closed ends have been machined
Fig. Micro-EDG.
into both sides of a stainless steel plate to form part of a microreactor. Such microreactor
structures are also used in mixing chambers, heat exchangers, and pumping systems, and in such
materials as titanium diboride.
The electrode used to form the grooves comprises a round flat disc which is rotated as the
workpiece is moved along its circumference in the opposite direction to the peripheral movement
(see Fig.). A cylindrical electrode has been used to machine microgrippers for high-precision
assembly of RF circuits by pick-and-place units.
**********Thank you ***********
For full PDF Go to www.slideshare.com Search by My Gmail ID.
3.6 Applications of μ-EDM

Unit.5
Additive
Manufacturing
Processes
SPPUSemester VII – Mechanical Engineering
badebhau4@gmail.com
Mo.9673714743

badebhau4@gmail.com
Mo.9673714743SND COE & RC.Yeola.
1
Bb
*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 ProcessesUnit-5.
Shri Swami Samarth
AMP
For details Refer CAD-CAM Unit-5 Rapid
Prototyping
Prototyping

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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 point’s 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 today’s
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 chamberPowder chamber
powder
Inert gas
Prototyping

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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 µm 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 µm 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 0
C)
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
Prototyping

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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.
Prototyping

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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 model’s 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 *************
For details Refer CAD-CAM Unit-5 Rapid Prototyping

Unit.6
Measurement
Techniques in
Micro Machining
Semester VII – Mechanical Engineering SPPU
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Syllabus :
Introduction, Classification of measuring System, Microscopes : Optical Microscope, Electron
Microscopes, Laser based System, Interference Microscopes and comparators, Surface
profiler, Scanning Tunneling Microscope, Atomic force micro scope, Applications.
The last two decades have shown an ever-increasing interest in higher precision and
miniaturization in a wide range of manufacturing activities. These growing trends have led to new
requirements in machining, positioning control, and metrology down to nanometer tolerances.
Recent developments in silicon micromachining have made possible the fabrication of
micromechanical elements of sizes typically ranging from 0.1 to 100 μm . Slots and apertures for
some applications such as color TV, electron gun masks, and. jet-engine turbines are made as small
as 5 um.-Microcircuit, elements of ,0.5.to 1 𝛍m are commonly manufactured using X-ray or
electron-beam lithography . In order to assess and control the quality of micromachined parts it
has been necessary to develop new measuring techniques, capable of effectively and accurately
measuring the dimensions, geometry, profile, and surface roughness of microholes, slots, very thin
films, microspheres, steps, and grooves of different configurations in micromachined parts. These
parts and features can be either checked for configuration and completeness, or measured to
determine actual sizes. Inspection and measurement of these features raise the demand for special
equipment some of which depends on entirely new principles.
In addition to high-resolution calipers and coordinate measuring machines, equipment used
for measurement of micro-machined parts includes high resolution microscopes, laser-based
surface followers, scanning electron microscopes (SEM), interferometers, profilometers and
scanning probes (e.g., scanning tunneling microscopes STM), and scanning force micro-scopes
(SFM). The practical use of almost all these methods depends on the development of high
precision scanning tables as well as high resolution linear transducers. Measurements are carried
out offline, in a metrology laboratory, as well as online, or in process while the parts are being
fabricated. In most measuring applications, noncontact methods are eventually used. Measuring
systems rely, in their function, upon different principals and apply several technological methods.
The systems used for dimensional measurement and topographic inspection can ,however be
classified into two categories :
Shri Swami Samarth
Measurement Techniques in Micro machining
AMP
Unit-6
Introduction
6.1 CLASSIFICATION OF MEASURING SYSTEMS

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In this category the size of an inspected features is determined by measuring the distance
between its edges Fig.a .Accordingly , the system consists of three main parts : a precision table
and a displacement transducer. By such an arrangement, the sensor determines the exact position
of the feature edges while the precision table moves the object or the sensor for edge location. The
displacement transducer can then measure the distance moved between edges and indicate the size
of the feature in the specific direction .
Figure 1. Different configurations of
measuring instruments.
Sensors can be mechanical, magnetic, capacitive, and in many instances optical. Tables of
stable and precise movement have recently been developed. For short travels of sub micrometer
and nanometer resolution levels, piezoelectric driven stages are recommended.
In optical sensors, the position of the measured edge is realized by the change in the
reflected pattern as a light beam crosses an edge. In optical microscopes, the edge position is
determined by a stationary index line placed inside the eye piece unit. For capacitive and magnetic
sensors the position of the edge is determined by the change in output signal noted as the sensor
crosses the edge. Mechanical sensors (e.g., in coordinate measuring machines (CMM)) touch the
inside (or outside) walls of the part with a preset pressure. The translation of the sensor is
determined with account being taken of the site of the sensor tip. When mechanical sensors are
6.1.1 Category 1
Sensor
Object
Table
Linear
Tanducer

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used, which are not stationary in the case of CMM, the minimum internal dimension to be
measured is limited by the size of the sensor (stylus) tip.
Displacement transducers of different resolutions can be used depending on the accuracy
required. Linear variable differential transducers (LVDT), optical grating encoders , and
displacement interferometers are widely used in many applications. These transducers have a
major advantage of being readily integrated in a computer controlled measurement system.
Consequently, electric output signals from these transducers are fed to the computer for direct
measurement and/or control. The above-mentioned category of measuring instruments is used to
measure sizes of object features other than the height except for the case of CMM.
In order to measure height, profile, or surface topography another category is used. This
can be classified into two main types, whole field contouring and single profile methods. Whole
field contouring includes interferometric and holographic techniques. Single profile (SP) methods
include mechanical stylus instruments, optical profile followers (OPF), scanning tunneling
microscopy, scanning electron microscopy, and atomic force microscopy (AFM).
 Single Profile And Height Measuring Methods
Here the sensor is forced to follow the profile of the inspected surface based on specific
criteria (Fig. 1.b). Height variations can be recorded provided they are small enough to maintain
the validity of the working principle. The sensor can be of the contact type as in most CMM
machines and stylus type roughness meters or it may be noncontact utilizing several principles.
CMM machines can accurately measure step height provided there is sufficient room for the
insertion of the sensor tip (Fig. 1 c). The resolution depends on the operating principle, and values
as small as 1A are characteristic of some of these instruments (e.g., SEM, STM, AFM), The
working principles of some of those systems that have potential use in the measurement of micro
machined parts are illustrated in the following sections. The range of their application, accuracy,
and resolution limits are also examined.
 Whole Field Contouring
In whole field contouring (WFC), a contour image (inter ferogram) of the inspected object
surface is recorded by use of several inter ferometric or holographic arrangements. The contour
images are analyzed by means of appropriate computer algorithms, and surface height ordinates
are accordingly determined. In this case, the resolution depends on both the arrangement used as
well as the algorithm adopted. Some interference microscopes have vertical resolution on the order
of 0.1 nm, with maximum vertical step height of 100 μm. Besides roughness such methods can
also measure and evaluate height of microsteps and grooves.
6.1.2 Category 2

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Microscopes are widely used for the inspection and measurement of tiny object features.
Basically, a microscope produces a magnified virtual image of the inspected object, Three types
of microscopes, namely, optical, electron, and interference are used. The principle and application
of the first two types are discussed in the following :
6.2.1 Optical Microscopes :
An optical microscope consists basically of two lenses (Fig. 3) high-power short focal
length objective, and a low-power, longer focal length, eyepiece. In practice the objective and the
eyepiece are not single lenses. To reduce the effects of aberrations, each is assembled from two or
more lenses. Generally a microscope is equipped with several objectives to provide different
magnifications, which can be as high as 1000x . Optical microscopes can be used as stand-alone
inspection instruments that are commonly employed for the visual inspection of printed circuit
boards. Modem microscopes are equipped with video or CCD cameras where the field of view is
observed on a cathode ray tube (CRT) monitor. Such advanced systems are presently fitted on
production lines to monitor the quality of microfeatures of manufactured parts.
Figure 3. The principle of the optical microscope
6.2 MICROSCOPES
Eyepiece
Image
object
objectives

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The resolving power of an optical microscope a is given by the Abbe equation,
𝒂 =
𝟏.𝟐𝟐𝝀
𝟐𝒏𝒔𝒊𝒏(𝒊)
(1)
Where
a : distance between two points on the surface of an object that can be seen separated in
the image plane
λ : effective wavelength of illumination used
n: refractive index of objective medium λ
i: suspended angle of lens which depends on its diameter and focal length
(n sin(i)) is the numerical aperture (NA) of the objective lens which is higher for a high-power
lens having short focal length. For white light illumination, λ = 5.6 X 10-4 mm and, assuming NA
= 1, then, a = 0.27 μm. An optical microscope with NA = 0.6 can effectively detect two points less
than 0.5 μm apart.
Many commercially available measuring machines integrate the high resolving power of
an optical microscope with a high resolution x-y stage to measure different dimensional features
of a product. Examples of these machines are the tool maker’s microscopes (TMM), and the
universal measuring machines (UMM) (Fig. 4). The microscope helps to form a magnified image
of the inspected workpiece. An appropriate reticle with cross-lines fixed inside the eyepiece is
used to mark the ends of the dimensions to be measured.
Fig. 4 The principle of the tool makers microscope (TMM).
microscope
Precision
table
Sample
Light
source
condenser

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The dimension size is determined by the distance moved with the x-y stage between the
two ends. An accuracy level of 1 μm is commonly available with Abbe’s metroscopes. Better
resolutions are achieved from interferometric displacement measurement. Indeed, dimensions of
holes, slots, and other features of an object less than 200 μm can easily be measured with accuracy
better than 1 μm. TMMs are used for dimensional measurement of both internal and external part
features.
6.2.2 Electron Microscopes :
In electron microscopes the inspected surface is interrogated by a focused beam of
electrons. The beam is collimated and then focused by means of coils that generate a radial
magnetic field to control the shape of the electron beam. Focusing is achieved by varying the focal
length of the objective lens coil through the control of the coil current. The effective resolution is
almost 105
that of an optical microscope . In this case the wave length λ is given by the De Broglie
formula ,
𝛌 =
𝒉
𝒎𝒗
(2)
where
h: Plank’s constant
m: mass of electron
v: electron velocity
As an electron of mass m and charge e pass through a potential difference V, its kinetic energy is,
𝟏
𝟐
𝒎𝒗 𝟐
= 𝒆𝑽 (3)
And
𝛌 = 𝒉
( 𝟐𝒎𝒆𝑽)
𝟏
𝟐
(4)
It is obvious that the wavelength λ depends on the potential difference V. For V = 60 kV, λ is about
0.05 A. From Abbe’s equation (1), the resolving power a for the electron microscope can be on
the order of 2.4 A for λ = 0.05 A.
Two main types of electron microscopes are available namely, transmission electron
(TEM) and scanning electron (SEM) types. In most engineering applications SEM is used Figure
5(a) shows a schematic diagram of the main components of an SEM microscope. The electron gun
generates a stream of electrons (electron beam) that is collimated by a coil (lens). The objective
(lens) focuses the electron beam onto the surface of the specimen. In order to scan the specimen

Mo.9673714743
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surface with the focused electron beam (electron probe), a beam deflecting unit is used. When an
electron beam impinges on the surface of the specimen different phenomena are observed.
Figure. 5. Schematic of the electron microscope (a), emissions resulting from electron
bombardment (b).
Some electrons are absorbed (losing their energy on collision). Others are back scattered
(reflected) either elastically or inelastically and these are called primary electrons. In elastic
reflection, electrons do not lose any of their energy but change their direction. For inelastic
reflection, electrons interact with specimen atoms and lose some of their energy before deflecting
back out of the specimen surface. Electrons that penetrate inside the specimen interact with the
material atoms resulting in the ejection of secondary electrons. Secondary electrons formed near
the surface may escape producing secondary electron emits. In addition to primary scattered
electrons and secondary emitted ones, X-ray and even light photons are also produced as a result
of electron bombardment (Fig. 5 b). The amount and ratio of back-scattered electrons, secondary
emission, and other radiation depend on the beam energy, specimen geometry, and substrate
atomic number. Since the atomic number and beam energy are practically constant, specimen
geometry is therefore the main controlling factor.
A detector is used to collect the emission from the specimen surface (Fig. 5 a). Several
types of detectors are available for the different phenomena resulting from electron bombardment.
The detector signal is amplified by the electronic unit and used to modulate the brightness of a
1.elctron gun
2.collimating coil
3. focusing coil
4.deflecting coil
5. Sample
6. Detector
7.signal processing
unit
8.display unit

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cathode ray tube. The CRT is adjusted to scan synchronously with the electron probe. Variations
in the recorded brightness produce the highly magnified image of the scanned object.
SEM are used in two modes. In the conventional raster scanning mode the deflection coils
(Fig. 5.a) move the electron beam across the stationary object to produce a two -dimensional image
of the surface. In the second mode the specimen is fixed to a precision table which scans the
specimen under a stationary focused electron beam to produce a trace of the surface relief. This
intensity profile mode provides quantitative linear measurement of an object feature. Swyte and
Jensen used SEM for the calibration of linear dimensions in the range 0.1 to 100 μm. The table
translation is measured by a laser interferometer with measurement precision of 0.01 μm. Electron
detector and interferometer signals are fed to a computer that analyzes the electron intensity with
respect to position profile to obtain the linear dimension for a specific feature. A typical example
of inspected objects is a microscopic chromium metal line deposited on a glass substrate by means
of a photolithography technique. In such an application, line is 0.5μm wide, and l-um thick, with
an edge slope of 700.
A newly developed SEM featuring two secondary electron detectors was used to measure
the cutting edge radius which is on the order of 45 nm. The image created by the difference signal
of the two detectors emphasizes the convexity and concavity of the sample surface.
As well as profile recording, SEM is used for roughness measurement. Based on the
principle that the back-scattered electron signal is proportional to the slope of the surface in the
direction of scanning, the surface profile can be obtained. By integrating the signal, Sato and
Ohmori detected a roughness profile of surfaces having slope in a specific direction. Three-
dimensional surface topography of the specimen can be obtained by integrating scans covering the
entire image, at resolutions on the order of 0.001 μm. To measure the roughness of surfaces having
slope in an arbitrary direction, Sato and Ohmori proposed a method to detect the normal of the
object surface by comparing the intensity of the back- scattered electron signal of the specimen
with that of a standard ball. The surface topography is processed from the measured data of the
normal.
In laser-based systems optical phenomena, observed as laser light scans across an
engineering surface, are applied for online and in-process inspection of surface features. These
phenomena include diffraction, reflection, refraction, scattering, and others. Some methods that
depend on such phenomena are explained below.
6.3 LASER - BASED SYSTEMS

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6.3.1 Diffraction Method
In micromachining, slots of dimensions on the order of few nanometers up to 200 μm are
produced. In the range of 50 μm or higher, these dimensions can readily be measured, in the
laboratory with high magnification microscopes; however, for online measurement other
techniques are adopted.
A focused laser beam for online measurement of fine surface grooves having different
cross-sections (Fig. 6). The principle of this technique depends on the condition that the reflected
pattern from a flat surface will be modulated by the presence of a micro surface groove. A flat
smooth surface reflects the beam into a single spot (Fig. 6 b); however, as the focused beam crosses
the edge of a groove, the reflected pattern is divided into two parts (Fig. 6 c). Scanning of this
field, therefore, produces a double-peaked signal (Fig. 6 d), the relative amplitudes of which
change as the surface moves against the focused spot. The slot width can be evaluated from the
recorded signal of a photosensitive device (PSD) as the sample scans beneath the stationary laser
spot. Moreover, the recorded signal also represents an approximation of the slot profile (cross-
section). Fig. 6(a) shows the arrangement used, while the PSD signals recorded as the focused
spot scanned three different grooves are shown in Fig. 6(e). In-spected surfaces should be smooth,
since a speckle pattern limits the measurement accuracy.
The double-peaked pattern can be explained by the Pekrinck and Kennedy model . Levy
observed a similar pattern when inspecting the height of a submicrometer step. The method
described above is noncontact and can be used online provided the specimen travel is precisely
controlled. The proposed system is sensitive to changes in groove width; however, variations in
depth are less detectable especially for high depth-to-width ratios, or steep sides. Although
different incidence angles can be used, normal incidence re- suits in more accurate slot description.
The resolution of measurement is directly proportional to the sampling rate of the data acquisition
unit R and inversely proportional to the table speed u. For v =300 mm/min, and R = 10 kHz, the
resolution can be on the order of 0.5 μm. A linear photodetector array can be used to indicate the
start and finish of the double-peaked pattern, while a linear transducer measures the distance
covered during this event.

Mo.9673714743
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Figure 6. The principle of online dimensional measurement using diffraction method: (a) setup;
(b) reflection from a flat surface; (c) diffraction by a microgroove; (d) intensity distribution of the
diffrac-tion pattern in (c); (e) PSD signal when scanning typical grooves.
1.PSD , 2.amplifier , 3.ADC , 4.PC-computer . 5.Sample
PSDoutputarbitrary
Angular Position
Table Travel mm table travel mm table travel mm
e
PSDoutputarbitrary
PSDoutputarbitrary

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6.3.2 Optical Triangulation Method :
In this method (Fig. 7), the geometric principle of triangulation is applied to perform
distance measurements. The sample surface is illuminated with a laser beam, through a projection
lens. The spot image formed by the imaging lens is received on the position sensor. Variations in
surface height ∆Z cause the image on the PSD to be displaced from its reference position by a
distance S which is directly proportional to ∆Z. A position sensor produces an electrical signal
proportional to the distance S that can be calibrated to give the height variation. For the
configuration shown in Figure (7), the displacement S, corresponding to a height variation ∆Z is:
𝑺 =
𝑴∆𝐙 𝐬𝐢𝐧(𝛂+𝛃)
𝐜𝐨𝐬(𝛂)
. (5)
where
M - magnification in the image receiver system
α - illumination angle
β- imaging angle
∆Z- height deviation from a reference level
Fig .7 The principal of the triangular method
Some applications use normal illumination (α = 0), for which Equation (5) reduces to
S = M .∆Z • sin(θ) (6)
1. Projection lens
2. Imaging lens
3. Position sensor
4. Samlpe surface

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Where ,
θ is the angle between the illumination and imaging directions.
The height resolution and range of this method depend on the wavelength of the
illumination γ, the numerical aperture (NA) of the imaging lens, and the geometrical configuration,
Using inclined illumination and normal imaging, Costa achieved height resolution of 0.49 μm (λ
= 0.6328 μm, NA = 0.6, inclination angle = 65°); however, it can be as high as a few microns. The
range of height variation detected can be as small as few micrometers or as large as several
millimeters. The application ranges from the measurement of surface topography, in-process
measurement and control , range-finding, and as noncontact probes on coordinate measuring
machines. A critical analysis of errors evolved in triangulation-based systems is given by Kilgus
and Svetkoff.
6.3.3 Optical Followers :
The optical follower is a measuring instrument that scans an object surface with a focused
laser beam. If the beam is initially focused on a specific surface point, height variations as the
object moves set the beam out of focus. The out-of-focus condition is detected by a sensory unit
that activates a servomechanism to bring the beam back in focus. The vertical displacement
required to bring the beam back in focus is recorded against the linear displacement of the object.
This record represents the profile of the surface along the scanned line. Figure 8. shows the main
components of an optical follower.
Figure 8. The main components of an optical follower.
1. Laser light
2. Spatial filter
3. Collimating lens
4. Focusing lens
5. Sample
6. Beam splitter
7. Imaging lens
8. PSD
9. PC-computer
10. Table
11. Linear transducer
12. Servo mechanism
13. Linear transducer

Mo.9673714743
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The laser beam is filtered using the lens-pinhole spatial filter, then collimated and focused
on the sample surface. The focused spot is imaged on the surface of the position sensor by use of
the beam splitter and the imaging lens. The detector signal is fed to the personal computer, where
the focusing condition is deter-mined. As the table moves, height variations in the sample surface
set the beam out of focus. Accordingly, the servomechanism is activated to bring the spot back in
focus by moving the focusing lens vertically. Two linear transducers are used: the first measures
the horizontal displacement of the tabtei while the other measures the vertical displacement of the
lens. A record of the vertical lens displacement against the horizontal table displacement produces
a profile trace of the sample surface along the scanned line. By use of an x-y table multiple traces,
and consequently, three-dimensional maps of surfece profiles can be constructed. The accuracy of
height measure ment depends on two main factors, the resolution of the displacement transducer,
and the precision of the sensory On the other hand, spatial resolution depends on the precision of
the stage moving the object. Several techniques are used to detect the focusing condition in optical
followers . They include defect-of-focus and astigmatic methods.
Interference microscopes provide higher resolution than their optical counterparts. They
form magnified images of the inspected part surface modulated by interference contour ; fringes.
These represent the micro topography of the inspected part surface and provide invaluable
information about micro surface features such as form, profile, and roughness as well as
dimensions of grooves, slots, and scratches. In many applications, calibrated reticles can be placed
inside the eyepiece unit to measure dimensions of surface features. Several arrangements are
adopted to produce the interferograms of examined parts. In all cases light is split into two wave
fronts, one going to a reference plane and the other to the inspected surface. After reflection,
wavefronts recombine undergoing constructive and destructive interference, producing the inter-
ferograms with dark and bright fringe pattern.
Figure9.(a) shows Tolansky’s arrangement for interference microscopy. By this
arrangement, it is possible to I measure microsteps of 500-μm height with an accuracy on the order
of ±3 μm. In the Tolansky interferometer the wavefront is divided into two types, the reference
and the object waves. In other types of interferometers, the two waves are formed by separating
the electric and the magnetic components of the electromagnetic wave of light. In the interference
microscope (Fig. 9.b) a Wollastone birefringence prism 5 is placed in the space between the
objective 2 and eyepiece 7. A polarizer plate 4 is placed in front of the Wollastone prism while an
analyzer 6 is in the back. The semireflecting plate 1 directs the light onto the surface of the
inspected object 3. With this arrangement the reflected wavefront imaged by the objective 2 is
divided into two wavefronts representing the electric and the magnetic fields. These wavefronts
interfere with each other after passing through the analyzer 6.
6.4 Interference Microscopes

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Figure 9. The principle of interference microscopy
The resulting interferogram shows minute variations in the inspected surface. This
procedure is useful for examining fine surface structures (e.g., grooves, slots, and scratches) as
well as surface roughness. Commercially available interference microscopes can measure height
variations as small as 0.1 nm. Moreover, roughness values in the sub-Angstrom range can also be
evaluated. Like optical microscopes, interference microscopes are now equipped with CCD
cameras that are interfaced to PCs (Fig. 9.c).
A major limitation of interferometry is the need for fairly reflective surfaces. Apart from
this limitation, it provides a powerful tool that produces a whole field image revealing
1. Beam spliter 2. Focusing lens 3.
Sample surface 4. Polarizer 5. Wollastone
prism 6. analyzer 7. Imaging lens
8.interferogram

Mo.9673714743
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microfeatures of inspected surfaces. The resulting interferogram can be used for direct visual
inspection, or numerical evaluation of dimensions and surface roughness.
Interference comparators are used for two major applications: to produce contour
interferograms of inspected surfaces or as displacement transducers. Evaluation of contour
interference patterns renders valuable information regarding surface topography, surface
roughness, as well as dimensions of micro surface features. Interferometric transducers are also
used to measure the translation of highly precise tables down to the nanometer resolution .
Figure 10. The principle of the Michelson interferometer
Many widely used interferometers are based on the Mi-chelson principle (Fig. 10.).
Coherent light from the monochromatic source 1, is collimated by lens 2, then divided into two
waves by the beam splitter 3. The reference wave is reflected back by the reference plane 4, while
the object type is reflected after being modulated by the object surface 5. The two waves recombine
to form a fringe pattern by using imaging unit 6. The fringe pattern is determined according to the
6.5 Interference Comparators

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phase relationship between the object and the reference waves, which in turn depends on the shape
and orientation of the object surface with respect to that of the reference.
If the object and reference surfaces are normal to each other, the pattern produced
represents contour fringes; however, for inclined surfaces, the fringes are rows of profiles. Parallel
equidistant straight fringes indicate a plane surface indined to the reference plane, Any out-of-
flatnen in the sample surface alters the obtained fringe pattern, In effect, the fringe pattern
represents contour lines of equidistant points from the reference plane. The contour step in this
case equal λ/2, where λ is the wavelength of the light used,
Personal computers (PCs) have recently been used for the analysis of interferograms, CCD
and video cameras are used to capture the fringe pattern, which is then analyzed, by means of
dedicated software. Different surface topography parameters are evaluated from the interference
pattern. The image of the fringe pattern is transferred electronically to digital values representing
the grey levels or intensity that are treated mathematically to produce contour maps and surface
profiles as well as surface parameters. Dimensions of microsurface grooves or steps can also be
evaluated from the interferograms.
Surface profilers are instruments that use a fine stylus or tip to trace the fine details of an
engineering surface. Height variations along the traced line modulate the force interacting between
tip and surface or the tunnel current passing between them when they are very close to each other.
By monitoring the deflection of the tip caused by the tip-surface force or the tunnel current, it is
possible to produce a profile record of the traced line. Multiple line traces generate three-
dimensional records of the inspect surfaces.
Mechanical stylus instruments are most widely used for surface topography
assessment. They have a wide range of height resolutions; however, their spatial resolution is
limited by the size of the stylus tip used. As shown in Figure 11, an arm (lever) carrying a microtip
(stylus) represents the sensor that scans across the inspected surface. Height variations along the
scanned line change the force between the stylus tip and the surface points, and consequently lever
deflection. An appropriate transducer transforms the lever deflection into an electrical signal
proportional to height variations. The signal is then amplified, digitized, and analyzed to evaluate
surface parameters.
6.6 Surface Profiler
6.6.1 Stylus Instruments

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Fig.11. The principal of the stylus instrument
The stylus movement is measured relative to a datum that should conform with the
nominal shape of the measured surface . While a straight-line datum has been used, a simple skid
arrangement (Fig. 11) is most common. Generally the stylus is a conical or pyramid diamond with
a flat or rounded tip. The pyramid is normally 90° with a 2 to 2.5-μm flat, while the cone is 60°
with 12.5-μm radius. Tips of 2.5 μm are also in use.
The tip radius should be smaller than the radius of curvature of the bottom of surface
valleys, otherwise the profile is commonly modulated by the stylus tip. A measuring force must
be applied to ensure contact between stylus tip and surface points. Typical force levels are about
70 mg giving a pressure of 2500 Nmm-2. Such pressure is less than the yield strength of most
materials. However, for soft materials or coatings this pressure may exceed the yield strength and
cause surface damage.
Stylus instruments provide profile records of traced lines.Three-dimensional surface
profile maps can also be plotted by Use of scanning tables. Since profile signals can be digitized,
8urface geometry is analyzed and different surface parameters valuated using PCs interfaced with
the measuring instrument. In addition to the assessment of surface roughness, sty. lus instruments
can be used to measure microsurface grooves with depth values on the order of several microns.
A major disadvantage of stylus instruments is that they rely on contact- type methods. They are
relatively slow and the measuring pressure may, in some cases, damage the inspected surface.
For Full PDF Go to www.slideshare.com Search by My Gmail ID
1.stylus 2.sensors 3.skid
4.data acquisition unit 5.
Analysis and display unit

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Scanning tunnelling microscopes (STM) are another family of stylus-type
instruments where the stylus does not contact the inspected surface. STM instruments are capable
of lateral resolution sufficient to resolve protruding atoms on reconstructed surfaces. The vertical
resolution is as small as 0.02 μm.
These instruments operate in vacuum, air, oil, liquid nitrogen, and water, giving
images which are direct topo graphs of inspected surfaces . In addition to the promising advantages
of STMs in micro topographic mapping of highly finished surfaces, other applications such as
microlithography, micromachining, polymer science, and biotechnology are also being studied.
The usefulness of STMs for the analysis of diamond-turned surfaces, ruled grating replicas, X-ray
reflecting optics, and optical discs has recently been demonstrated .
Although the concept of tunnelling in solid-state physics first appeared in the late
1920s , the first successful tunnelling experiment with an externally and reproducibly adjustable
vacuum gap was reported by G. Binnig et al. of the IBM Zurich Research Laboratory in 1982. The
principle of scanning tunnelling microscopy is demonstrated in Figure 12 (a), in which a stylus of
very sharp tip (ultimately one atom) is brought very close to the inspected surface (<1 nm apart)-
At such closely adjacent distances, free electrons from the conductive sample surface atoms tunnel
to the conductive stylus tip, producing a very weak current. In the one-dimension^ case, the tunnel
resistance and, consequently, the tunnelling current at low voltage and temperatures is
exponetially dependent on the tip-sample seperation ‘d’ :
𝑰 ∝ 𝐞𝐱𝐩(−𝟐𝒌𝒅) (7)
Where ,
I- tunnelling current
d: distance between tip and surface
k: constant.
6.6.2 Scanning Tunneling Microscope

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Figure 12. Scanning tunneling microscopy basic principle (a), constant current mode (b), and
constant height mode (c).
For vacuum tunnelling, k = h-1 (2m𝛟)1/2 where h is Planck's Constant, m is electron
mass, and φ is effective local work function, for a work, function of 4 eV, k = 1.0 A-1
. The current
decreases by an order of distance d is increased by 1.0 μm. If the current is kept constant within
±2% the gap remains unchanged to within 0.01μm. This condition represents the basis for
interpreting the image as simply a contour of constant height above the measured surface.
To record a topographic map of a surface, the tip scans in a raster pattern. It is stepped
in the positive X-direction; at each step the tunnel current is read, and tip height adjusted to get the
desired value. When the first scan is finished, the tip is returned to the starting position of this scan,
then moved one step in the y-direction until it covers the required area. Surface roughness
complicates the scanning process. In this regard, the rougher the surface, the more difficult it is to
obtain a proper image. Therefore, STMs are limited to conductive materials having fine surface
structures.
Two modes of operation can be used with STM, constant current and constant height
modes. In the first case, Figure 12(b), the tunnel current is kept constant by adjusting the tip height
to keep a constant separation between the tip and the surface. The displacement of the
servomechanism required to bring the tip to the constant current (separation) position is then
recorded as the z-ordinate. In this case, the scanning speed is determined by the response of the
(C)
1. stylus
2. sample
3. power
supply
4. meter

Mo.9673714743
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feedback circuit, which maintains the average current constant. The constant current mode can be
used for surfaces that are not atomically flat (i.e.≥ 10-nm peak-to-valley height).
In the constant height mode (Fig. 12.c) the tip scans the surface while its vertical
position, relative to a mean reference plane, and the current are kept constant, the voltage variation
being monitored. Under such circumstances, the scanning speed depends on how fast the feedback
circuit responds to achieve constant current by adjusting the voltage. Scanning is faster; however,
the tip may be damaged unless the surface is tolerably smooth.
Special attention should be paid to vibration conditions, since the performance of an
STM microscope can be enhanced by use of proper isolation. Fine resolutions, required for
scanning the tip and measuring height variations, are realized by using piezoelectric elements for
x, y, and z translations Controlled voltage is applied to the piezoelectric crystal in specified
directions. Consequently, the crystal contracts or elongates according to the sign of the electric
field. This effect is linear and precisely controlled . Separate piezoelectric elements for each axis
translation have been used . On the other hand, a single piezoelectric tube that provides translation
in the three axes has been described by Binnig and Smith .
STM microscopes have many potential applications in measurement and fabrication
of micromachined parts. They are successfully used for the measurement of surface topography as
low as the atomic scale. Yang and Talke used STM to investigate surface roughness of magnetic
recording disks, using line graphs and aerial images at sampling intervals of 125 and 5 nm. Fine
diffraction gratings, 2000 lines/mm, were also examined using STM to reveal detailed surface
topography. Besides measurement of surface topography STMs were used to modify surface
structure and manufacture parts bits on highly oriented pyrolytic graphite.
Atomic force microscopes (AFM) are noncontact profilometers which use a very fine
stylus fixed to the end of a thin cantilever. They trace actual profiles of highly smooth and flat
surfaces (Fig. 13.a). The profile is recorded by making the stylus follow the profile of a constant
force between stylus tip and surface points. As the fine stylus tip is brought close to the surface
(30 to 150 nm) attraction forces between atoms are generated. As the tip comes closer to the surface
the atomic force increases. Such a force is balanced by the plastic force generated by bending the
cantilever. Therefore the stationary cantilever bend is a direct measure of the atomic force . Most
probes use capacitive sensors to determine cantilever deletion, and hence the atomic force . A
feedback loop 18 usually used to keep the force at a specified value by mainlining a constant tip-
sample spacing. The signal, from the capacitive sensor, is fed to a servomechanism that controls
the tip-sample spacing.
6.6.3 Atomic Force Microscope

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Figure 13. The principle of atomic force microscopy with capacitive sensor (a), and with
vibrating tip (b).
Another arrangement (Fig. 13.b) uses a fine tip fixed to the end of a vibrating
lever. Changing the tip-sample spacing leads to proportional change in the attraction force, which
modifies the compliance of the lever. The vibration amplitude is also affected by the shift in the
lever resonance. The tip vibration amplitude as a function of the frequency ω is given by ,
𝐴 = 𝐴𝑜 (
𝜔
𝜔𝑜
) /[1 + 𝑄2
{(
𝜔
𝜔𝑜
) − (
𝜔𝑜
𝜔
)}2
]
1
2
(8)
Where,
A: amplitude of vibration
A0: amplitude at resonance
ω: tip frequency
ωo: tip resonance frequency, ωo = C1√k ,C1 is a function of lever mass, and
k is the spring constant
Q: quality factor (Q >>1), Q is a measure of system damping, and
Q = (l/c)√km
Where , c : damping factor
m: Lever mass
Sensor lever
Stylus
tip
sample
Laser light
(b)
Vibrator
Vibrating
lever
Sample
Table
Beam splitter
Interferometer

Mo.9673714743
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The larger the value of Q, the smaller is the damping. As the tip approaches
the sample surface, interatomic attraction forces reduce the spring constant of the lever by the
atomic force derivative f '. The resonance frequency then becomes 𝜔𝑜 = √𝑘 − √𝑓′
.Thus by
measurement of the shift in the lever resonance ∆ω= (ωo - ω), the force derivative can be found.
The change in the resonance frequency changes the amplitude of vibration. This means that, as the
tip approaches the surface, the attraction force rises leading to a proportional change in both lever
resonance frequency and vibration amplitude. By monitoring these values as the tip scans across
the surface, it is possible to trace the surface profile.
The amplitude of vibration can be measured optically, or by use of an
interferometer . A signal representing the amplitude of vibration is usually used in a feedback loop
to maintain the tip at a specific distance from the surface as the tip scans across a determined path.
This technique has been applied to measure surface roughness of ultrafine surfaces. Micro- and
sub-micrometer surface features can also be measured. Line profiles and 3-D maps of surfaces can
be recorded and presented. V-shaped grooves on silicon wafer and steps of height 50 μm have
been mapped and measured . Profiles of a photoresist grating (0.1 μm line width and 0.09 μm
thickness) have been recorded by the same technique.
New trends in manufacturing industries including miniaturization and large-scale
integration have enhanced the development of measurement science and technology.
Miniaturization calls for new measuring techniques to evaluate micro features of tiny parts at high
resolution. In addition, computer-integrated, high-speed, noncontact techniques are required for
applications including in-process and online inspection. In the future, accurate and intelligent
measurement systems will therefore be an integral part of industrial manufacturing lines.
Advances in the field of measurement are expected to be integrated in manufacturing
systems along four main lines: probe and sensor performance, precision and resolution of
translation mechanisms, accuracy and response of linear and angular transducers, together with
computer interfaces and software.
Probes and sensors are being greatly improved to achieve higher resolutions and better
accuracy. Fine details of micro machined parts, including features that are difficult to reach, need
to be inspected at an appropriate resolution. AFM, STM, and electron microscopes provide high
resolutions; however, the measuring time is relatively long, which limits the application of such
systems for online inspection especially for large-scale production.
Precision tables that can provide very accurate fine motion for both workpiece and sensor
at reasonable speed are another challenge facing the development of measuring instruments.
Piezoelectric actuators are highly precise; however, their speed and range of travel are limited.
6.7 Applications

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Linear transducers are used in measuring systems to determine the displacement of axes.
High-response long-range transducers are necessary for the realization of precise measurement.
Research is being undertaken to improve transducer response, resolution, and range of
measurement and to reduce environmental impacts on accuracy.
Integration of accurate sensors, precision tables, and high-resolution transducers in a
measuring system is only possible through computer control. Table movement, displacement
measurement, analysis of sensor signals, and activation of feedback systems will all be controlled
by computers. Great improvements are therefore expected in computer hardware and software, as
well as interfacing technology.
***********Thank You ************

Amp notes unit 4-6 by badebhau

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Amp notes unit 4-6 by badebhau