Eucm Unit v Word

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P aava i I n s t i t u ti o n s D e pa r tme n t of M E C H

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THERMAL ENERGY BASED PROCESSES

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5.1 Introduction

5.2. Electron Beam Machining - Process

5.2.1. Electron Beam Machining - Equipment

5.2.2. Electron Beam Process - Parameters

5.2.3. Electron Beam Process Capability

5.2.4. Electron Beam Machining - Advantages and Limitations

5.3. Laser Beam Machining - Introduction

5.3.1. Laser Beam Machining - the lasing process

5.3.2. Lasing Medium

5.3.3. Laser Construction

5.3.4. Laser Beam Machining - Application

5.3.5. Laser Beam Machining - Advantages

5.3.6. Laser Beam Machining - Limitations

5.4. Plasma arc machining

5.4.1. Applications

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TECHNICAL TERMS 1. LASER BEAM MACHINING

Laser light is monochromatic, its wave length occupies a very narrow portion of the

spectrum hence a simple lens is able to focus and concentrate laser light to spot of much

smaller diameter and much higher density that than obtained by other of light.

2. PLASMA ARC CUTTING

An arc is a stable form of electric discharge between two electrodes in a gaseous medium. A

feature of a gaseous conduction is a continuous interchange of energy between

electrons, ions and neutral particles, the interchange occurring during the collision

resulting from their disorderly movement caused by beating.

3. LASER

It is acronym of light amplification by stimulated emission of radiation.

4. MASER

Laser can be melt diamond when focused by lens system. The energy density being of two

order 100,000 KW/cm2. This energy is due to atoms that have light energy level.When such

an atom impinge with electromagnetic waves having resonant frequency.

5. PHOTONS

In the Laser the photons are in ground state at 0oC they are brought to the excited state by

means of absorption of energy by temperature change, collision etc emission lines.The

atoms when this they are bringing down goes to the excited state by stimulated emission

and emit photons within 10 nano secs. They have the same wavelength as the excited

photons

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6. POPULATION INVERSION

If the atoms in the excited state are greater than that of the ground state then it is

known as population inversion.

7. EBM

It is the thermo-electrical material removal process on which the material is removed by the

high velocity electron beam emitted from the tungsten filament made to impinge on the

work surface, where kinetic energy of the beam is transferred to the work piece material,

producing intense heat, which makes the material to melt or vaporize it locally.

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5.1 Introduction

Electron Beam Machining (EBM) and Laser Beam Machining (LBM) are thermal processes

considering the mechanisms of material removal. However electrical energy is used to generate

high- energy electrons in case of Electron Beam Machining (EBM) and high-energy coherent

photons in case of Laser Beam Machining (LBM). Thus these two processes are often classified as

electro- optical-thermal processes.

There are different jet or beam processes, namely Abrasive Jet, Water Jet etc. These two are

mechanical jet processes. There are also thermal jets or beams. A few are oxyacetylene flame,

welding arc, plasma flame etc. EBM as well as LBM are such thermal beam processes. Fig. 5.1

shows the variation in power density vs. the characteristic dimensions of different thermal beam

processes. Characteristic length is the diameter over which the beam or flame is active. In case of

oxyacetylene flame or welding arc, the characteristic length is in mm to tens of mm and the power

density is typically low. Electron Beam may have a characteristic length of tens of microns to

mm depending on degree of focusing of the beam. In case of defocused electron

beam, power density would be as low as 1 Watt/mm2. But in case of focused beam the same can be

increased to tens of kW/mm2. Similarly as can be seen in Fig. 5.1 laser beams can be focused over a

spot size of 10 - 100 m with a power density as high as 1 MW/mm2. Electrical discharge typically

provides even higher power density with smaller spot size.

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Fig. 5.1 Variation in energy density with spot diameter of thermal beam processes

EBM and LBM are typically used with higher power density to machine materials. The

mechanism of material removal is primarily by melting and rapid vaporisation due to intense

heating by the electrons and laser beam respectively.

5.2. Electron Beam Machining - Process

Electron beam is generated in an electron beam gun. The construction and working principle of the

electron beam gun would be discussed in the next section. Electron beam gun provides high

velocity electrons over a very small spot size. Electron Beam Machining is required to be carried

out in vacuum. Otherwise the electrons would interact with the air molecules, thus they would loose

their energy and cutting ability. Thus the workpiece to be machined is located under the electron

beam and is kept under vacuum. The high-energy focused electron beam is made to impinge on the

workpiece with a spot size of 10 - 100 m. The kinetic energy of the high velocity electrons is

converted to heat energy as the electrons strike the work material. Due to high power density

instant melting and vaporisation starts an d melt - vaporisation front gradually progresses, as

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shown in Fig. 5.2. Finally the molten material, if any at the top of the front, is expelled from the

cutting zone by the high vapour pressure at the lower part.

Unlike in Electron Beam Welding, the gun in EBM is used in pulsed mode. Holes can be drilled in

thin sheets using a single pulse. For thicker plates, multiple pulses would be required. Electron

beam can also be manoeuvred using the electromagnetic deflection coils for drilling holes of any

shape.

`Fig. 5.2 Mechanism of Material Removal in Electron Beam Machining

5.2.1. Electron Beam Machining - Equipment

Fig. 5.3 shows the schematic representation of an electron beam gun, which is the heart of any

electron beam machining facility. The basic functions of any electron beam gun are to

generate free electrons at the cathode, accelerate them to a sufficiently high velocity and to

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focus them over a small spot size. Further, the beam needs to be maneuver if required by the

gun.

The cathode as can be seen in Fig. 5.3 is generally made of tungsten or tantalum. Such cathode

filaments are heated, often inductively, to a temperature of around 25000C. Such heating leads

to thermo-ionic emission of electrons, which is further enhanced by maintaining very low

vacuum within the chamber of the electron beam gun. Moreover, this cathode cartridge is

highly negatively biased so that the thermo-ionic electrons are strongly repelled away form the

cathode. This cathode is often in the form of a cartridge so that it can be changed very quickly

to reduce down time in case of failure.

Fig. 5.3 Electron Beam Gun

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Just after the cathode, there is an annular bias grid. A high negative bias is applied to this grid so

that the electrons generated by this cathode do not diverge and approach the next element, the

annular anode, in the form of a beam. The annular anode now attracts the electron beam and

gradually gets accelerated. As they leave the anode section, the electrons may achieve a velocity as

high as half the velocity of light.

The nature of biasing just after the cathode controls the flow of electrons and the biased grid is used

as a switch to operate the electron beam gun in pulsed mode.

After the anode, the electron beam passes through a series of magnetic lenses and apertures. The

magnetic lenses shape the beam and try to reduce the divergence. Apertures on the other hand allow

only the convergent electrons to pass and capture the divergent low energy electrons from the

fringes. This way, the aperture and the magnetic lenses improve the quality of the electron beam.

Then the electron beam passes through the final section of the electromagnetic lens and

deflection coil. The electromagnetic lens focuses the electron beam to a desired spot. The deflection coil

can maneuver the electron beam, though by small amount, to improve shape of the machined holes.

Generally in between the electron beam gun and the work piece, which is also under vacuum, there

would be a series of slotted rotating discs. Such discs allow the electron beam to pass and machine

materials but helpfully prevent metal fumes and vapour generated during machining to reach the

gun. Thus it is essential to synchronize the motion of the rotating disc and pulsing of the electron

beam gun. Electron beam guns are also provided with illumination facility and a telescope for

alignment of the beam with the work piece. Work piece is mounted on a CNC table so that holes of

any shape can be machined using the CNC control and beam deflection in-built in the gun.

One of the major requirements of EBM operation of electron beam gun is maintenance of desired

vacuum. Level of vacuum within the gun is in the order of 10-4 to 10-6 Torr. {1 Torr = 1mm of Hg}

Maintenance of suitable vacuum is essential so that electrons do not loose their energy and a

significant life of the cathode cartridge is obtained. Such vacuum is achieved and maintained using

a combination of rotary pump and diffusion pump. Diffusion pump, as shown in Fig. 5.4 is attached

to the diffusion pump port of the electron beam gun (vide Fig. 5.3).

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Diffusion pump is essentially an oil heater. As the oil is heated the oil vapour rushes upward where

gradually converging structure as shown in Fig. 5.4 is present. The nozzles change the direction of

motion of the oil vapour and the oil vapour starts moving downward at a high velocity as jet.

Such high velocity jets of oil vapour entrain any air molecules present within the gun. This oil is

evacuated by a rotary pump via the backing line. The oil vapour condenses due to presence of

cooling water jacket around the diffusion pump.

Fig. 5.4 Working of diffusion pump

5.2.2. Electron Beam Process - Parameters

The process parameters, which directly affect the machining characteristics in Electron Beam

Machining, are:

The accelerating voltage

The beam current

Pulse duration Energy per pulse

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Power per pulse

Lens current

Spot size

Power density

As has already been mentioned in EBM the gun is operated in pulse mode. This is achieved by

appropriately biasing the biased grid located just after the cathode. Switching pulses are given to

the bias grid so as to achieve pulse duration of as low as 50 s to as long as 15 ms.

Beam current is directly related to the number of electrons emitted by the cathode or available in

the beam. Beam current once again can be as low as 200 amp to 1 amp.

Increasing the beam current directly increases the energy per pulse. Similarly increase in pulse

duration also enhances energy per pulse. High-energy pulses (in excess of 100 J/pulse) can

machine larger holes on thicker plates.

The energy density and power density is governed by energy per pulse duration and spot size. Spot

size, on the other hand is controlled by the degree of focusing achieved by the

electromagnetic lenses. A higher energy density, i.e., for a lower spot size, the material removal

would be faster though the size of the hole would be smaller.

The plane of focusing would be on the surface of the workpiece or just below the surface of the

workpiece. This controls the kerf shape or the shape of the hole as schematically shown in Fig. 5.5

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Fig. 5.5 Typical kerf shape of electron beam drilled hole

As has been indicated earlier, the final deflection coil can manoeuvre the electron beam

providing holes of non-circular cross-section as required.

5.2.3. Electron Beam Process Capability

EBM can provide holes of diameter in the range of 100 m to 2 mm with a depth upto 15 mm, i.e.,

with a l/d ratio of around 10. Fig. 5.5 schematically represents a typical hole drilled by electron

beam. The hole can be tapered along the depth or barrel shaped. By focusing the beam below the

surface a reverse taper can also be obtained. Typically as shown in Fig. 5.5, there would be an edge

rounding at the entry point along with presence of recast layer. Generally burr formation does not

occur in EBM.

A wide range of materials such as steel, stainless steel, Ti and Ni super-alloys, aluminium as well as

plastics, ceramics, leathers can be machined successfully using electron beam. As the

mechanism of material removal is thermal in nature as for example in electro-discharge machining,

there would be thermal damages associated with EBM. However, the heat-affecte zone is rather

narrow due to shorter pulse duration in EBM. Typically the heat-affected zone is around 20 to 30

m.

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Some of the materials like Al and Ti alloys are more readily machined compared to steel.

Number of holes drilled per second depends on the hole diameter, power density and depth of the

hole as well as material type as mentioned earlier. Fig. 5.6 depicts the variation in drilling speed

against volume of material removed for steel and Aluminium alloy.

EBM does not apply any cutting force on the workpieces. Thus very simple work holding is

required. This enables machining of fragile and brittle material s by EBM. Holes can also be at a

very shallow angle of as less as 20 to 30 .

Fig. 5.6 Variation in drilling speed with volume of material removal for steels and

aluminium

5.2.4. Electron Beam Machining - Advantages and Limitations

EBM provides very high drilling rates when small holes with large aspect ratio are to be drilled.

Moreover it can machine almost any material irrespective of their mechanical properties. As it

applies no mechanical cutting force, work holding and fixturing cost is very less. Further for the

same reason fragile and brittle materials can also be processed. The heat affected zone in EBM is

rather less due to shorter pulses. EBM can provide holes of any shape by combining beam

deflection using electromagnetic coils and the CNC table with high accuracy.

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However, EBM has its own share of limitations. The primary limitations are the high capital cost of

the equipment and necessary regular maintenance applicable for any equipment using vacuum

system. Moreover in EBM there is significant amount of non-productive pump down period for

attaining desired vacuum. However this can be reduced to some extent using vacuum load locks.

Though heat affected zone is rather less in EBM but recast layer formation cannot be avoided.

5.3. Laser Beam Machining - Introduction

Laser Beam Machining or more broadly laser material processing deals with machining and

material processing like heat treatment, alloying, cladding, sheet metal bending etc. Such

processing is carried out utilizing the energy of coherent photons or laser beam, which is mostly

converted into thermal energy upon interaction with most of the materials. Nowadays, laser is also

finding application in regenerative machining or rapid prototyping as in processes like stereo-

lithography, selective laser sintering etc.

Laser stands for light amplification by stimulated emission of radiation. The underline working

principle of laser was first put forward by Albert Einstein in 1917 though the first industrial laser

for experimentation was developed around 1960s.

Laser beam can very easily be focused using optical lenses as their wavelength ranges from half

micron to around 70 microns. Focussed laser beam as indicated earlier can have power density in

excess of 1 MW/mm2. As laser interacts with the material, the energy of the photon is absorbed by

the work material leading to rapid substantial rise in local temperature. This in turn results in

melting and vaporisation of the work material and finally material removal.

5.3.1. Laser Beam Machining - the lasing process

Lasing process describes the basic operation of laser, i.e. generation of coherent (both temporal

and spatial) beam of light by light amplification using stimulated emission.

In the model of atom, negatively charged electrons rotate around the positively charged nucleus

in some specified orbital paths. The geometry and radii of such orbital paths depend on a

variety of parameters like number of electrons, presence of neighbouring atoms and their

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electron structure, presence of electromagnetic field etc. Each of the orbital electrons is

associated with unique energy levels. At absolute zero temperature an atom is considered to be

at ground level, when all the electrons occupy their respective lowest potential energy. The

electrons at ground state can be excited to higher state of energy by absorbing energy form

external sources like increase in electronic vibration at elevated temperature, through chemical

reaction as well as via absorbing energy of the photon. Fig. 5.7 depicts schematically the

absorption of a photon by an electron. The electron moves from a lower energy level to a higher energy

level.

On reaching the higher energy level, the electron reaches an unstable energy band. And it comes

back to its ground state within a very small time by releasing a photon. This is called

spontaneous emission. Schematically the same is shown in Fig. 5.7 and Fig. 5.8. The

spontaneously emitted photon would have the same frequency as that of the exciting photon.

Sometimes such change of energy state puts the electrons in a meta-stable energy band. Instead of

coming back to its ground state immediately (within tens of ns) it stays at the elevated energy state

for micro to milliseconds. In a material, if more number of electrons can be somehow pumped to

the higher meta-stable energy state as compared to number of atoms at ground state, then it is called

population inversion. Such electrons,

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Fig. 5.7 Energy bands in materials

Fig. 5.8 Spontaneous and stimulated emission

at higher energy meta-stable state, can return to the ground state in the form of an avalanche

provided stimulated by a photon of suitable frequency or energy. This is called stimulated

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emission. Fig. 5.8 shows one such higher state electron in meta-stable orbit. If it is stimulated by a

photon of suitable energy then the electron will come down to the lower energy state and in turn

one original photon, another emitted photon by stimulation having some temporal and spatial

phase would be available. In this way coherent laser beam can be produced.

Fig. 5.9 schematically shows working of a laser. There is a gas in a cylindrical glass vessel. This

gas is called the lasing medium. One end of the glass is blocked with a 100% reflective mirror and

the other end is having a partially reflective mirror. Population inversion can be carried out by

exciting the gas atoms or molecules by pumping it with flash lamps. Then stimulated emission

would initiate lasing action. Stimulated emission of photons could be in all directions. Most of the

stimulated photons, not along the longitudinal direction would be lost and generate waste heat. The

photons in the

longitudinal direction would form coherent, highly directional, intense laser beam.

Fig. 5.9 Lasing action 5.3.2. Lasing Medium

Many materials can be used as the heart of the laser. Depending on the lasing medium lasers are

classified as solid state and gas laser. Solid-state lasers are commonly of the following type

Ruby which is a chromium - alumina alloy having a wavelength of 0.7 m

Nd-glass lasers having a wavelength of 1.64 m

Nd-YAG laser having a wavelength of 1.06 m

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These solid-state lasers are generally used in material processing. The

generally used gas lasers are

Helium - Neon

Argon CO etc.

Lasers can be operated in continuous mode or pulsed mode. Typically CO gas laser is operated 2 in

continuous mode and Nd - YAG laser is operated in pulsed mode.

5.3.3. Laser Construction

Fig. 5.10 shows a typical Nd-YAG laser. Nd-YAG laser is pumped using flash tube. Flash tubes can

be helical, as shown in Fig. 5.10, or they can be flat. Typically the lasi ng material is at the focal

plane of the flash tube. Though helical flash tubes provide better pumping, they are difficult to

maintain.

Fig. 5.10 Solid-state laser with its optical pumping unit

Fig. 5.11 shows the electrical circuit for operation of a solid-state laser. The flash tube is

operated in pulsed mode by charging and discharging of the capacitor. Thus the pulse on time is

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decided by the resistance on the flash tube side and pulse off time is decided by the charging

resistance. There is also a high voltage switching supply for initiation of pulses.

Fig. 5.12 shows a CO laser. Gas lasers can be axial flow, as shown in Fig. 5.12, transverse flow

and folded axial flow as shown in Fig. 5.13. The power of a CO2 laser is typically around 100

Watt per metre of tube length. Thus to make a high power laser, a rather long tube is required

which is quite inconvenient. For optimal use of floor space, high-powered CO2 lasers are made of

folded design.

In a CO2 laser, a mixture of CO2 , N2 and He continuously circulate through the gas tube. Such

continuous recirculation of gas is done to minimize

Fig. 5.11 Working of a solid-state laser

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Fig5.12 Construction of a CO laser

2

consumption of gases. CO2 acts as the main lasing medium whereas Nitrogen helps in sustaining

the gas plasma. Helium on the other hand helps in cooling the gases.

As shown in Fig. 5.12 high voltage is applied at the two ends leading to discharge and formation of

gas plasma. Energy of this discharge leads to population inversion and lasing action. At the two

ends of the laser we have one 100% reflector and one partial reflector. The 100% reflector redirects

the photons inside the gas tube and partial reflector allows a part of the laser beam to be issued so

that the same can be used for material processing. Typically the laser tube is cooled externally as

well. As had been indicated earlier CO2 lasers are folded to achieve high power. Fig. 5.13 shows a

similar folded axial flow laser. In folded laser there would be a few 100% reflective turning mirrors

for manoeuvring the laser beam from gas supply as well as high voltage supply as shown

in_Fig.5.13.

Fig. 5.13 Construction of folded gas laser

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5.3.4. Laser Beam Machining - Application

Laser can be used in wide range of manufacturing applications

Material removal - drilling, cutting and tre-panning

Welding

Cladding

Alloying

Drilling micro-sized holes using laser in difficult - to - machine materials is the most dominant

application in industry. In laser drilling the laser beam is focused over the desired spot size. For thin

sheets pulse laser can be used. For thicker ones continuous laser may be used.

Ta bl e 5. 1 sho w s th e ca p a bil i ty a n d c h arac t er isti c s o f c om m o n l a s e r s .

Ta bl e 5 . 2 P r o ce s s c h arac t er is t i c s o f di ffere n t l a s er s

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5.3.5. Laser Beam Machining - Advantages

In laser machining there is no physical tool. Thus no machining force or wear of the tool

takes place.

Large aspect ratio in laser drilling can be achieved along with acceptable accuracy or

dimension, form or location

Micro-holes can be drilled in difficult - to - machine materials

Though laser processing is a thermal processing but heat affected zone specially in pulse

laser processing is not very significant due to shorter pulse duration.

5.3.6. Laser Beam Machining - Limitations High initial capital cost High maintenance cost

Not very efficient process

Presence of Heat Affected Zone - specially in gas assist CO2 laser cutting Thermal process - not suitable for heat sensitive materials like aluminium glass fibre laminate as

shown in Fig.5.14

Fig. 5.14 Aluminium Glass Fibre Laminate - heat sensitive glass fibre layer due to presence of

resin as binder

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5.4. Plasma arc machining

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or

sometimes other materials) using a plasma torch. In this process, an inert gas (in some units,

compressed air) is blown at high speed out of a nozzle; at the same time an electrical arc is formed

through that gas from the nozzle to the surface being cut, turning some of that gas to plasma. The

plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten

metal away from the cut.

Fig. 5.15. Plasma Arc Machining

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Fig. 5.16 Plasma arc cutting

1.A plasma arc machining method in which a work piece is pierced by a plasma arc and is cut

from a piercing position, the plasma arc being formed by jetting plasma gas from a nozzle of a

plasma torch such that the plasma arc is formed between an electrode of the plasma torch and the

work piece, said method comprising: positioning the plasma torch at an initial height with respect to

the work piece, said initial height being less than or substantially equal to a cutting height of the

plasma torch with respect to the workpiece at which a cutting operation is performed, and said initial

height being at a position at which a double arc does not occur; forming a main arc between the

electrode and the workpiece by initiating a pilot arc between the electrode and the nozzle to form

the main arc; relatively moving the plasma torch and the workpiece, while maintaining the main

arc, to position the plasma torch at a piercing height with respect to the workpiece to perform a

piercing operation, the piercing height being larger than the initial height; maintaining the main

arc while the plasma torch is positioned at the piercing height, until completion of the piercing

operation; and relatively moving the plasma torch and the workpiece to position the plasma torch at

the cutting height to perform the cutting operation, after the completion of the piercing operation.

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2. The plasma arc machining method according to claim 1, wherein a semiconductor switch is

provided in a pilot current circuit in a line that leads to the nozzle to supply a pilot current,

and wherein the pilot current is cut off by the semiconductor switch immediately after transfer

of the pilot arc into the main arc.

In cases where a steel plate is cut by the piercing start, during piercing operation in which a

through hole is made at a cutting start position by a plasma arc, the metal melted by the plasma arc

is blown up in the form of spatter (molten metal droplets) and this blown spatter is likely to adhere

to the nozzle. The spatter adhered to the nozzle could be a cause of melting-damage to the nozzle

or occurrence of a double arc, which gives damage to the nozzle, resulting in a considerable

decrease in cutting quality.

Where the level at which a plasma arc is first formed is defined as initial level, the level at which

piercing is carried out is defined as piercing level, and the level at which cutting is carried out is

defined as cutting level, the initial level h, is equal to the piercing level and higher than the

cutting level h2 in the typical piercing method shown in FIG. 5.16(a). In the raising piercing

method shown in FIG. 5.16 (b), the initial level H1 is lower than the piercing level H2 and higher

than the cutting level H3

Fig. 5.17 500 325 - Schematic of a plasma CVM device with a hemispherical tip electrode.

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5.4.1. Applications

Cutting: With appropriate equipment and techniques, the plasma arc can be successfully employed

to make cuts in electrically conductive metals.

In hole piercing, reproducible and high-quality holes are made rapidly in a variety of materials with

the plasma arc. Holes can be pierced much faster than they can be drilled. Plasma arc hole

piercing is performed with conventional plasma arc cutting equipment that has been modified to

produce a short, carefully controlled arc operating time, suitable arc current programming during

the short operating cycle, and effective slag ejection.

Almost instantly after ignition the arc rapidly penetrates through the plate forming a hole

approximately the same size as the diameter of the arc stream. Continued plasma exposure

increases the size of the hole to 4 or 5 times the arc stream diameter. Moving the torch or workpiece

in a circular motion can produce larger holes.

In stack cutting, Plasma is effectively stack-cut stainless steel and aluminum. Plasma stack-

cutting of thin carbon steel tends to weld the layers making them difficult to separate after cutting.

During cutting, the layers should be clamped firmly enough to minimize gaps, but loose enough to

permit slippage between layers due to differential expansion. The upper layer may buckle if

clamping does not allow slippage.

Machining: The plasma arc can be used for machining or removing the metal from the surface of

a rotating cylinder to simulate a conventional lathe or turning operation. As the workpiece is turned,

the torch is moved parallel to the axis of the work. The torch is positioned so the arc will impinge

tangentially on the workpiece and remove the outer layer of metal. Cutting can be accomplished

with the workpiece rotating in either direction relative to the torch, but best results are

obtained when the direction of rotation permits use of the shortest arc length for cutting. The flow

of molten metal being removed must be in such a direction that it does not tend to adhere to the

hot surface that has just been machined.

Generally, the plasma-arc metal removal process has little if any advantage on easy-to-machine

metals, but it has considerable economic advantage for rough metal removal of hard-to-machine

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metals. The process is generally considered to be a roughing operation, which should be followed by

a conventional machine finishing cut. Metal removal rates with the plasma arc process on hard-to-

machine metals are up to ten times faster than those achieved on a lathe using a tungsten carbide

cutting tool. The principal disadvantages are the metallurgical alteration of the characteristic of the

surface profile produced.

QUESTION BANK

PART-A (2 MARKS)

1. What is Laser?

2. What are the characteristics of Laser beam?

3. What are the gases commonly used in LASER?

4. What are the characteristics of Laser used in Laser machining?

5. Define plasma.

6. What are the advantages of plasma arc welding?

7. What are the metals that can't be machined by plasma arc machining?

8. How does the basic plasma is generated?

9. Write the principle of P.A.M

10. Define EBM?

11. What is the characteristic of the electron beam?

12. What are the main elements of the EBM equipment?

13. Write the advantage of EBM?

14. Write the disadvantages of EBM?

15. Write any four application of EBM?

16. Define electron beam. ( AU May 2006)

17. Contrast LBM and EBM. ( AU May 2006)

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18. Write the application of ASM. ( AU May 2006)

19. Describe the commonly used gas mixture in PAM and their corresponding work materilas (

AU May 2006) (AU Nov 2012)

20. What are the parameters that govern the performance of plasma arc machining? ( AU May

2010) (AU Nov 2011)

21.Write down the advantages of Laser Beam Machining Process. ( AU May 2010)

22.What does the word LASER stand for? ( AU Nov 2011)

PART-B (16 MARKS)

1. Explain the process of LBM and PAM with a neat sketchs. (16)

2. (i) Discuss the process parameters of EBM and their influence on machining quality. (8)

(ii)Explain the process capabilities of EBM and PAM. (8)

3. (i) Explain the principle of LBM with neat sketch (10)

(ii) List out the advantage and limitation of LBM process (6)

4. (i) Explain the principle of PAM with sketch (10)

(ii) List out the advantage and limitation of PAM process. (6) 5. (i) Mention the application of EBM (4)

(ii) What is EBM? Sketch its set up an indicate its main parts and explain the principle of

operation. (12)

6. (i) Explain the principles and elements of EBM, also how the work table is protected from

getting damaged by electron beam. (8)

(ii) Discuss how the process variables influence MRR, HAZ and pattern generation. (8)

7. (i) Explain the principle of LBM with neat sketch

(ii) List out the advantage and limitation of LBM process. (8+8) (AU May 2006)

8.(i) Explain the principle of PAM with sketch (AU Nov 2011)

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(ii) List out the advantage and limitation of PAM process. . (8+8) (AU May 2006) (AU Nov 2011)

9.(i) Mention the application of EBM. (AU Nov 2008)

(ii) What is EBM? Sketch its set up an indicate its main parts and explain the principle of

operation . (8+8) (AU May 2010)

10.(i) Briefly explain the various parameters that govern the performance of PAM(10) (AU Nov 2011)

(ii) Discuss the general guidelines for designing the plasma torches in PAM (6) ( AU Nov 2012)

11. Explain the construction and working principle of EBM with neat sketch. List its advantages and limitations (10+6) ( AU Nov 2012)

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