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Non Conventional Welding

1. What is electron beam welding (EBW) process? Describe in brief,giving its scope of application. (UPTU 2003-4)

Electron beam welding utilizes the energy of a fast moving beam of electronsstriking a workpiece at a place where the welding to be done. The electrons

strike the workpiece with very high kinetic energy and this energy is converted

into heat energy as electrons lose their velocity after striking the workpiece. In

this method, a tungsten filament serves as a cathode which emits electrons.The electrons are focused into a narrow beam of high energy which is

accelerated and guided to a particular spot. The heat generated by the fast

moving electron beam is sufficient to melt the metals and make a metal weld

which takes place without any filler material. The electron beam welding isdone in vacuum chamber to avoid air interacting with the beam of electrons.

An electron beam machine works in same way as a cathode ray tube in a

television.

It consists of:

a. A cathode section which generates an electron beam. The concave shaped

cathode concentrates the stream of electrons toward the anode. The anode

applies a potential field that concentrates the beam which passes through

the anode coil.

b. An accelerating coil section having a high electrostatic field to accelerate the

electron beam.

c. A focusing electromagnetic coil section to focus the electron beam.

The electron beam welding has wide applications in welding

(i) titanium, (ii) molybdenum, (iii) tungsten, (iv) steel, (v) aluminium and (vi)

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refractory materials. As welding is done in vacuum, no contamination of weldtakes place due to the absence of air. This is the reason why this method gives

ultra high purity weld for reactive and refractory metals which are used in

atomic energy and rocketry fields.

2. Write short note on plasma arc welding. (UPTU 2004-5)Or

Explain what is plasma? Describe the plasma arc welding process and

few of its applications. (UTPU 2006-7)

Plasma arc welding is an arc welding process in which fusion is produced by

the heat obtained from a constricted arc set up between a tungsten electrodeand the job. The process employs two inert gases. One inert gas is used to

form arc plasma while other gas is used to shield this arc plasma. If any gas is

heated to a high temperature, then the gas dissociates into free electrons, ions

and neutral atoms. The gas in this state of dissociation is called plasma. Thegas in plasma state has higher electric conductivity and it helps in the

formation of strong arc.

The arc and plasma are generated within the confined space in the torch. The

high temperature developed by initial arc ionizes the plasma gas and the

plasma discharges through the orifice as shown in figure 8.20. The orifice

concentrates and collimates the plasma arc.

Two gases are used in plasma arc welding and they are called plasma gas andshielding gas. Plasma gas flows through the orifice having tungsten electrode.

DC power source is used to develop electric field between the tungsten

electrode and the job.

Tungsten electrode is connected to negative terminal and job is connected topositive terminal. Plasma gas gets ionized while flowing through the orifice in

the presence of arc. Shielding gas flows through the outer nozzle of the torchand it shields the molten weld from the contamination of oxygen and nitrogen

in air. Plasma arc has grater energy concentration and it has much larger arc

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length. This helps in ensuring a deep and narrow penetration of the plasma arcin the job.

The differences of plasma arc welding from arc welding "and oxy-acetylene gas welding are:

(a) The plasma arc has high density and velocity of electrons which can

penetrate deep in the metals. Hence plasma arc welding can make deepweld which is not possible by other methods. The ratio of depth of

penetration to the width of the weld is also very high. Hence plasma arc

welding can give narrow weld with least heat affected zone.

(b) The plasma arc welding can even cut stainless steel and other nonferrous

metals where as oxy-acetylene and arc welding can not do so.

(c) Plasma arc welding has high welding speed.

(d) Plasma arc welding can make both keyhole and non keyhole type of

welds.

(e) Plasma arc welding has inert gas shielding which does not exist in oxy-

acetylene and arc welding.

3. Distinguish between plasma arc welding and TIG.

Plasma Arc Welding TIG

1. It uses two inert gases as plasma

gas and shield gas.

2. A constricted and strong arc isformed.

3. Temperature as high as 11,OOOC

is obtained.

4. A narrow and deep penetration is

obtained.

5. Faster welding process.

6. Electrode does not getcontaminated.

7. Equipment cost is high.

8. Consumption of inert gases is large.

1. It uses one inert gas as shield gas

only.

2. A non constricted arc is formed.

3. Temperature of 4000C isobtained.

4. Deep penetration is not possible.

5. It is not much faster in

comparison.

6. There is possibility of

contamination of electrode.

7.Equipment is less costly in

comparison.

8.Consumption of inert gas is less.

4. What is explosive welding process? Describe briefly giving its field

of application. (UPTU 2002-3)

Or

Write short note on explosive welding. (UPTU 2004-5, 2008-9)

Or

Explain with the help of neat sketch how explosive welding takes

place. What are variables, limitations and uses of explosive welding.

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(UTPU 2005-6)

Explosive welding is solid state or pressure welding process in which weld is

effected by high velocity movement of metals towards each other which are tobe welded. The movement is made possible through a controlled detonation.

The metal weld is obtained by (i) heat generated due to impact of metals at

high velocity and (ii) pressure acting on the metals due to pressure wave

associated with the detonation.

A proper thickness of high explosive is placed on a plate which is to be claddedon the parent plate. The cladding plate with layer of explosive is placed at an

angle on the parent plate as shown in figure 8.25. The high explosive is now

detonated from a safe distance by ignition of detonator. This leads to a high

velocity impact of cladding plate with the parent plate. The molecular bondingof two plates is effected by this high velocity impact. In order to ensure more

safety, explosive welding can be done in buried state in sand or in water.

The variables of explosive welding are:(a) Type of explosive i.e. high or medium velocity explosive. TNT & RDX are

high explosive while ammonium nitrate is medium explosive.

(b) Thickness of explosive on the cladding plate.

(c) Angle at which cladding plate is kept on the parent plate.

(d) Thickness of cladding plate.

(e) Material of cladding plate.

The applications of explosive welding are:(a) Cladding of thinner alloy on a parent metal.

(b) Reinforcing of aerospace surface with dissimilar strong metal ribs.

(c) Joining of two pipes in a socket.

(d) Spot or seam welding inside water can be done.

The advantages of explosive welding are:

(a) It can bond dissimilar metals.

(b) Inexpensive.(c) Simple and inexpensive equipment is required.

(d) Larger area can be cladded in one explosion.

(e) No surface preparation is required.

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(f) It does not disturb the metal treatment given to the plates.

Disadvantages of this method are:

(a) Metals must have high impact strength.

(b) Geometries of weld should be simple.

(c) Protection is required from noise and blast for the workers.

5. Write short note on friction welding. (UPTU 2004-5)

Or

Write advantages and limitations of friction process welding? Explainthe effect of various parameters on friction welding. UPTU 2005-6)

Friction welding is a solid state welding process in which welding of metals isachieved by (i) heating the metals to plastic state by the heat obtained from

sliding friction between the rubbing surfaces of the metals and (ii) exertingforging pressure on the metals.

The steps in friction welding are:

(a) One metal is rotated at constant speed by the spindle.

(b) Second metal is held in a clamp which is slided forward to press first

metal under pressure by a piston cylinder arrangement.

(c) Rubbing between two metals produces heat to bring the surfaces to a

plastic state.

(d) Additional pressure is exerted to weld the surfaces when they are in

plastic state due to rubbing. A flash is formed at the interface whichindicates the completion of weld.

The variables of friction welding are:

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(a) Rotational speed of the spindle.

(b) Axial pressure exerted.

(c) Heating time.

(d) Area of weld.

The applications of friction welding are:

(a) Assembly of axels.

(b) Fabrication of brake discs and wheel rims.

(c) Fabrication of suspension rods, steering columns and engine valves.

(d) Joining of forged parts to a simple bar.

Advantages of friction welding are:

(a) It has simplicity of operation.

(b) Low power consumption.(c) A quick method.

(d) No heat treatment of weld required.

(e) No filler or flux is required.

(f) No smoke, fume or spatter of metals.

Limitations of this method are:

(a) It is only suitable for flat butt weld.

(b) Suitable for small components.(c) It requires a very rigid machine for the operation.

(d) Flash has to be removed after completion of metal weld.

6. Write short note on ultrasonic welding. (UPTU 2006-7)

Ultrasonic welding is a solid state welding process in which a weld is produced

by local application of high frequency vibratory energy to the metals held

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together under pressure. The combined effect of pressure and vibrationscauses movement of the molecules of metals which brings out a sound union

between the faces of the metals in contact as shown in figure 8.27.

The ultrasonic welding machine consists of (i) an ultrasonic oscillator which

generates high frequency current of about 15,000 cycles/s, (ii) a transducer

which consists of a piezoelectric crystal to convert high frequency electrical

energy into mechanical vibration energy, (iii) a welding tip attached to thetransducer to force the mechanical vibration energy to metals and (iv) a

clamping arrangement for holding of the metals and (v) a clamping force

applying unit.

The ultrasonic welding has following advantages:

(a) It can join two materials quickly and securely without producing much

heat.

(b) It can join dissimilar metals.

(c) It can join non metals such as plastic to a metal.

(d) It can join brittle alloys.

(e) It can join thin metals to a thick metal.

7. What is the principle of laser welding? What are the advantages,disadvantages and applications of laser welding?

Laser welding is a fusion welding process in which heat for fusion is produced

by the application of concentrated coherent light beam on the metals to bejoined. 'Laser' word is an acronym which stands for' Light Amplified

Simultaneous Emission of Radiation. When a quantum of energy from a light

source is made to fall on the atoms of a ruby crystal at ground energy state(E0)' it causes absorption of radiation. The electrons of the atoms get excited

and they jump to upper energy levels before coming to metastable state (E 1).

From metastable state, each electron emits one photon before falling to

original ground state (E0). The simultaneous emission of photons from allexcited atoms give a monochromatic (same frequency) and collimated (same

phase) light which is called laser.

The narrow laser beam is focused by an optical lens system to produce a small

intense spot on the metals where optical energy is converted into heat energy.

The temperature raised by this heat energy is sufficient to melt the metals to

weld them.

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The set up for laser welding is as shown in figure 8.29. A weak light from flashlamp is amplified in laser crystal rod (Ruby). Photons generated in laser crystalbounce back and forth between two ends of the rod which are reflective. The

intensity of beam of photons or laser increases in this process before it leaves

the rod from the partial reflective end. A lense system is provided below the

ruby rod to focus the laser on the desired place on the job to carry outwelding. Ruby rod has to be maintained at - 196C. Hence it becomes

essential to keep the ruby rod in vacuum to avoid any increase of its

temperature from the atmosphere.

The advantages of laser welding are:

(a) It gives precise welding.

(b) It can weld all types of metals, composites, plastics and ceramics.

(c) It is a quick method.

(d) It has small heat affected zone.

(e) It is a neat and clean method.

The disadvantages of laser method are:

(a) Laser welding equipment is costly.

(b) Laser beam can be dangerous if not handled correctly.

(c) Produced holes have slight taper.

The applications of laser welding are:

(a) Used in electronic industry.

(b) Used in automobile industry.

(c) Used in food processing and packaging industry.

(d) Used in manufacturing of medical equipment.

(e) It is ideal method where automation or robotic control of welding is to bedone.

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Non Conventional Machining

1. How are non-conventional machining processes different from

conventional machining processes? Classify the different types of non-

conventional machining processes. (UPTU 2005-6)

The conventional machining processes utilize cutting tools to exert pressure onthe workpiece to stress the work piece material beyond its yield point. Thishelps in rupturing and removal of the material. This removal of material is only

possible when material of cutting tool is harder than that of work material. The

shearing process is the basic for the material removal in conventional

machining. In recent times, new materials and alloys of exceptional hardnessare to be shaped. They are difficult to be machined by conventional machining

process. They also have complex shapes and requirements. It is difficult to

shape to shape such materials using conventional machining process. These

materials have to be shaped using nonconventional machining processes whichdepend on a number of other ways to remove the material such as (i)

mechanical erosion (ii) chemical reaction (Hi) electrolytic displacement and (iv)

vapourisation of metal. The reasons for extensive applications of non-

conventional machining processes are:

(a) The hardness of new materials being used in dies and other applications

is very high. These materials can not be machined by conventionalmethods.

(b) The shapes of the parts are complex which cannot be processed by

conventional machining methods.(c) The slender, long and flexible parts can not be machined by conventional

machining methods as they cannot stand cutting forces.

(d) High temperature while cutting and residual stresses in the work are

unacceptable as they lead to surface defects.

(e) Conventional machining methods cannot give superfinished surfaces.

(f) Very small or miniature parts can not be produced by conventional

machining methods.

(g) Computer integration in possible with non-conventional machining

methods

Conventional Machining Non- conventional machining

1. Cutting tolls are employed for the

removed of materials. The shearingof the material is the basic for the

material removal.

2. Cutting tools remove materials

which are lesser harder

3. Complex shapes cannot be

machined

4. High dimensional accuracy cannot

1. This process uses other ways than

using cutting tool for the removalof material such as (i) mechanical

erosion (ii) chemical reaction (iii)

electrolytic displacement and (iv)

vaporization of metals2. High hardness materials can be

processed

3. Complex shapes can be processed

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be obtained due to vibrations in

cutting tool and machine tool.

5. Simpler, faster and cheaper

processes

6. High surface finish is obtained by

subsequent operation

7. Very small and miniature parts

cannot be produced.

8. Computer integration is possible

using CAD/CAM

4. High dimensional accuracy can be

obtained or processes involve nocutting force loading

5. Complex, slow and expensiveprocesses

6. High surface finish is obtained byprimary operation

7. Very small and miniature parts canbe produced

8. Computer integration is possible

The non-conventional machining processes can be classified as:

(a) Mechanical Methods: Mechanical methods remove the material using

the mechanical energy in the form of (i) mechanical vibrations and (ii)

kinetic energy of abrasive particles. Ultrasonic machining (USM) andabrasive jet machining are examples of mechanical methods.

(b) Electro chemical Methods: These methods are based on Faraday's

laws of electrolysis. The machining consists ofthe metal removal by the

controlled dissolution of any material at anode of an electrolytic cell. If

two suitable metals are placed at the terminals in a conductingelectrolyte and direct current is passed through them, then metal on

positive terminal starts depleting and its material is deposited on the,

negative terminal. Electro chemical machining (ECM) and electro

chemical grinding (ECG) are the examples of these methods.

(c) Electro Thermal Methods: These methods use controlled or localized

heating on a workpiece so that the material removal can take place by

localized melting and evaporation of the work material. Electro dischargemachining (EDM), wire EDM, plasma arc machining (PAM), electron beam

machining (EBM) and laser beam machining (LBM) are examples of these

methods

2. What is electro discharge machining (EDM) process? Obtain theexpression of material removal rate in EDM process in terms of the

process parameters. (UPTU 2002-3, 2006-7)

Or

Explain the role of any two of the following in electro discharge

machining process (1) A electric media (it) capacitance of the circuit

and (iii) resistance of the circuit (UPTU 2003-4)

Explain the application of the following electode material in EDM: (i)

copper and (ii) graphite (UPTU 2004-5)What is the principle of electro-discharge machining?

(UPTU 2006-7 carryover)

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The process of erosion of metals by the electric discharges between the tool atcathode and the workpiece at anode in the electrolytic solution is called electro

discharge machining. The Process is also called spark erosion, electro-erosion

or spark machining. It is primarily used for hard material which are impossible

to be machined with conventional machining methods. However EDM can beonly used for machining materials which are electrically conductive. EDM is

used to cut (i) small or odd shaped angles (ii) intricate contours or cavities inextremely hard steel and (iii) exotic metals such as carbide, titanium and

kovar. The work material is removed as each spark generates a localized hightemperature which vaporizes the metal in the form of small. Crater on the

work surface. The tool is kept close to the work surface without any physical

contact so that to produce a burst of sparks.

As the material is gradually eroded from the work surface by the sparks

between tool and the work surface, the tool shape is reproduced on the work

surface. The particles removed from the work surface are washed away by the

continuously flushing dielectric fluid pumped in between tool and work.Principle of EDM

The workpiece made of an electrically conductive material is connected to

anode and the tool is connected to cathode of a pulsating DC Power supply. Asmall gap is maintained between the workpiece and the tool. A dielectric fluid

is flooded between the tool and the workpiece. The dielectric fluid is to (i)

provide and control electric resistance in the gap and (ii) remove the eroded

material from the spark area. The sparks between tool and workpiece

gradually erode the material from the workpiece as it is at anode. The form or

shape of the tool is slowly reproduced on the workpiece. As the erosionprogresses, the too is advanced by a servo control mechanism toward the

workpiece to maintain a constant gap and sparking process through DC pulses

(1,00,000 pulses for second) in between tool and workpiece until required

depth of cavity is formed. As no cutting force is involved, hence material

removal by this method can be done on thin surfaces.

Electro Discharge Machine

The main parts of electro discharge machine is as shown in the figure 9.1.

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Electro discharge machine consists of (i) DC power supply unit (ii) servocontrolled mechanism (iii) dielectric fluid system and (iv) tool electrode. DC

power supply unit has electric circuit which provides pulsating DC pulses

across the work and tool gap. In electric circuit, a capacitor is used for storing

the electric charge before discharge takes place across the gap. The seroo-mechanism controls the infeed of the tool into the work. The dielectric fluids

used are kerosene, transformer oil, try ethyl glycol and paraffin. The dielectricfluid must ensure (i) non-conducting any electricity until voltage reaches the

required breakdown value (ii) the ability to permit spark in shortest possibletime (iii) The rapid quenching of spark or deionizing the spark gap after the

discharge (iv) effective cooling (v) the rapid washing away the eroded particles

of the work (vi) inertness (vii) non emission of any toxic vapours and (viii) the

easy and inexpensive availability. The dielectric fluid is generally fed throughthe tool. After usage, it is taken to reservoir after filtering to remove the

eroded particles. It is again pumped to the tool from the reservoir to be

reused. The EDM tool determines the shape of the cavity to be developed in

the work. The tool material must have (i) high electric and heat conductivity

(ii) easy machinability, (iii) low wear rate (iv) high melting point and (v)capacity to give good surface finishes.

The materials such as (i) graphite (ii) copper graphite (iii) copper and (iv)brass are used as tool materials. The wear ratio is main criteria for the

selection of tool material. The wear ratio is the ratio of the volume lost by the

tool material to the volume of metal removed from the work. Graphite is

widely used as EDM tool material as it has (i) good machinability (ii) best wearradio and (iii) excellent stability. However graphite has more porosity and it

produces rough finishes. Copper graphite has (i) best characteristics of both

copper and graphite (ii) more conductivity, (iii) little lower wear ratio than

graphite (iv) good machinability and (v) two times more expensive thengraphite. Copper has (i) excellent wear ratio (ii) good conductivity (Hi) poor

machinability and (iv) ability to provide fme fmishes:

Process characteristics

The metal removal rate in EDM depends upon (i) current in each spark (ii)frequency of the discharge (iii) tool material (iv) work material (v) dielectric

flushing conditions.The amount of material removed and the surface finish produced depends

upon the current in the spark. The crater depth due to spark depends upon the

current. The material removal increases but surface finish diminishes as

current increases. The best way is to decrease the current in spark to increasethe surface finish and also increasing spark frequency to increase the material

removal rate. The rate of cut, wear ratio and surface finishes depend upon the

tool material. Softer and lower melting point work materials are easier to be

processed by EDM. The machining speed increases in EDM when the flushing

pressure of the dielectric increases.

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Relaxation circuit

Relaxation circuit is used to provide ~e pulsating DC (pulses of DC) across the

work and tool gap. The circuit consists of resistance and capacitance and itoperates on the principle of self oscillation. The relaxation circuit is as shown in

the figure 9.4.

The circuit can provide high energy sparks or pulses having the range offrequency from 3000 to 10,000 sparks or pulses per second. The circuit

consists of (i) DC source of voltage 'Vo'. When current flows in the RC circuit,

the capacitor starts charging itself and the voltage reaches the dielectric

breakdown voltage 'V' depending upon the spark gap. On reaching breakdownvoltage 'V, the capacitor discharges and a spark is produced in the tool-work

gap. The voltage across the capacitor falls almost to zero voltage after the

spark. The capacitor now restarts charging itself with the flow of current till thevoltage again reaches 'V' when a fresh spark takes place. The cycle of chargingof capacitor and sparking in the gap on fully charging of the capacitor repeats.

Hence this resistance and capacitance relaxation circuit operates on the

principle of self oscillation of charging and discharging of voltage access the

capacitor. The variation of voltage across the capacitor is as shown in thefigure 9.5.

The function of resistance and capacitance in RC circuit are:(a) Resistance: A resistance is used in the circuit to prevent premature

charging of the capacitance before the spark in gap is deionised. Higherresistance lowers the value of currant in the circuit and the charging of

the capacitor to the breakdown voltage is slowed down. This slowing

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down prevents the possibility of a continuous arc occurring across thegap. The frequency of spark depends upon (i) the capacity of the

capacitor and (ii) both the induction and resistance of the circuit. Higher

the resistance, more time is needed for charging and lower is the

frequency of spark. An optimum value of resistance is kept so as toprevent (i) continuous arcing in the gap when resistance is low and (ii)

low metal removal rate (mrr) when resistance is high.(b) Capacitor: If capacitance is high, then it takes more time for the

capacitor to be charged to the breakdown voltage, thereby reducing the

frequency of sparking. The trequency of sparking increases, whenever

the capacitance is reduced. The metal removal rate (mrr) decreaseswhen capacitance increases and mrr increases when capacitance

decreases.

3. What are the applications of EDM? What are the advantages andlimitations of EDM?

The EDM can be economically used for the jobs which are good conductor ofelectricity. The applications of EDM are:

1. Machining of dies for forging, blanking and extrusion work.

2. Drilling of fine holes such as micro hole in fuel injection nozzle

3. Processing of fragile components as no cutting force acts on the work

during EDM process.

4. Tool manufacturing

5. Tool reshorpening

The advantages of EDM are:

1. Machining time is less

2. Complicated shaped works can be processed.

3. All conducting materials can be processed irrespective of hardness,

brittleness, toughness and meting points

4. Fragile and slender works can be processed5. Fine holes can be drilled

6. High accuracy can be achieved

7. Subsequent operations such as polishing can be done on the works.

The limitations of EDM are:

1. Power required is high

2. Surface cracking may take place

3. Sharp corners can not be made

4. Material removal rate is low

5. Non conducting materials can not be processed

6. Tool wear rate is high

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4. What are the advantages of a wire cutting EDM machine?

(UPTU 2006-7)

Electric discharge wire cutting or wire EDM is a process of producing complex

2-D shapes using a copper wire as electrode to erode or remove the material

from aconducting workpiece. The wire undergoes fast wears with sparking.

Hence wire is made to move so that near wire for sparking is always available.Wire diameter is about 0.2 mm.

Principle of wire cutting EDM

The copper or brass wire having diameter of 0.05 mm to 0.25 mm is used as

electrode in wire cutting EDM. The wire wound between the two spools as

shown in the figure 9.8. The wire moves past the workpiece at the speed of

about 3m/min. The wire and workpiece are connected to power supply as it isdone in EDM. The spark is struck between the moving wire (electrode) and the

workpiece which removes the material from the workpiece. De-ionised water is

most commonly used as dielectric fluid which is localized applied using a

nozzle in the sparking area. The main parts of a wire cutting EDM machine are

(i) a source of power supply (ii) an electrode wire and wire movingarrangement (iii) a CNC control to move the wire relative to work and (iv) a

system to apply dielectric fluid which is deionized water in this case.

The wire cutting EDM has following applications:

1. Manufacturing of dies

2. Manufacturing of profile gauges and templates

3. Cutting of complicated shapes on the works with high accuracy.

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4. Manufacturing of electrodes for EDM work

5. Manufacturing of punches and parts having 3-D complex surfaces.

The advantages of wire cutting EDM:

1. Wire acts as tool which means tha1 there is no requirement of separate

operation for the fabrication of tool as it is necessary for normal EDM

process.

2. Fine finish is obtainable

3. Three dimensional cutting is possible

4. Complicated slots can be cut which are not possible by other methods.

5. Different works can be machined with the change of set up and CNC

programming

5. What are the principal features of an ECM process? What is the roleof electrolyte in ECM process? (UPTU 2008-9)

Electro chemical machining is based on faraday's law of electrolysis. Electric

current is used in this to remove the unwanted metal. However it does not use

current for sparking in the gap of tool and workpiece unlike EDM but it usescurrent as per the principle of electrolysis for material removal. Faraday has

discovered that if two electrodes are placed in a conducting solution

(electrolyte) and a direct current voltage is applied across them, then metal

can be removed from the anode electrode which gets deposited on the cathode

electrode. This principal was earlier only used for the electroplating of the workpiece by making the workpiece as cathode electrode. However it was realized

later that this principle could be usefully employed for the removal of the

metal or machining by reversing the process of electroplating. This process ofremoval of material by placing the workpiece at anode is called electro

chemical machining (ECM). The materials which are extremely hard can be

easily machined by ECM. ECM can also machine small or odd shaped angles,

intricate contours or cavities and that too in very hard materials such astitanium, kovar and carbide. It is now routinely used for machining (i)

aerospace components (ii) critical deburring (iii) fuel injection system

components (iv) armament components (v) dies and (vi) moulds. ECM is

limited to electrical conducting of materials only.

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Electrochemical machining (ECM) is a non conventional machining process inwhich controlled removal of metal from the workpiece is achieved by anodic

dissolution of the workpiece in electrolytic solution with cutting tool forming a

cathode. The electrolytic solution is pumped through the gap between the tool

and the work piece and thereby these three forming an electrolytic cell whendirect current is passed through them. This results into dissolution and

removal of the material from the workpiece.Elements of ECM: The elements of ECM are:

1. Workpiece which is placed at anode

2. Tool which is placed at cathode

3. Electrolytic solution which is a conductive liquid. The electrolytic solution

is forced under pressure in the gap between the tool and the workpiece,

thereby forming an electrolytic cell when DC voltage is applied across thetool and the workpiece. The electrolytic solution also flushes away the

removed material from the workpiece.4. DC power source having low voltage and high current.

Principle of ECM: ECM is based on electrolysis process consider a workpieceof iron and a typical arrangement of an electrolytic cell as shown in the figure.

9.1 O.

A DC voltage is applied on anode (iron workpiece) and cathode. The

dissolution of anode starts in the electrolyte solution which has chemical

reaction as:

Fe Fe++ + 2e-

At cathode, hydrogen gas is released from the electrolysis.

H2O + 2e- H2 +2OH

The iron ions and hydroxyl ions combine to form iron hydroxide

Fe++ + 2OH- Fe (OH)2

Iron hydroxide as residue in the electrolytic solution is removed by flushing of

'electrolytic solution. Hence electrochemical reactions lead to:

(a) The metal nom the anode is dissolved in electrolytic solution. The metalremoval rate depends upon Faraday's laws depending upon (i) atomic

weight and valency of the metal (ii) the time for which the current

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passes. The shape of anode changes due to metal removal depending theshape of tool at cathote.

(b) The formation of hydrogen gas at electrode. The shape of cathode or tooldoes not change.

ECM process uses these electro chemical reactions for metal removal by

electrolysis. It is carried out using tool (cathode) which has the complimentaryshape of the part to be produced and the workpiece placed at anode. In the

small gap between the tool and the workpiece, electrolytic solution is pumped

at high pressure when DC voltage is applied between the tool and workpiece,thereby dissolution of metal starts from the workpiece as per the shape of the

tool. There is no change of shape of the tool while dissolution of the metal

takes paces on the workpiece.

ECM Equipment or Machine: The ECM equipment or machine is as shown in the

figure 9.12. The workpiece (electric conductor) is placed in a tank and it is

connected to the positive terminal of a high current (1500 to 40,000 amp) andlow voltage DC power supply. The tool electrode designed to develop the

required cavity in the workpiece is connected to the negative terminal of DC

supply. The electrolyte is made to flow through the gap between the tool andthe workpiece.

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The tool can be fed into the workpiece using a servomotor so that a constantgap (about 0.25 mm) is maintained between the tool and the workpiece during

machining. The metal is dissolved by the action of electric current from the

workpiece wherever the workpiece is having small gap in relation to the tool.

As tool is fed to maintain the gap with the workpiece, the form or shape of thetool is reproduced as a cavity on the workpiece. The electrolyte is used to (i)

provide the medium for electrolysis (ii) remove the heat generated duringelectrolysis and (iii) remove the debris formed during metal removal. The

electrolyte is recycled using (i) pump and (ii) filter system. Stainless steel tankis used as electrolyte is corrosive. Explosion proof blower is used to remove

the hydrogen gas generated during the electrolysis. Salt solutions with water

are used as electrolytes. The desirable properties of an electrolyte are

i. high electric conductivity

ii. low viscosity

iii. high specific heativ. chemical stability

v. non corrosiveness

vi. non toxicity

vii. easy availability and

viii. inexpensive.

Electrolytes which are commonly used are

(i) common salt (Nacl)(ii) sodium chlorate (NaCIO3)

(iii)sodium nitrate (Na NO2)

(iv) Sulphuric acid (H2So4)and

(v)sodium hydrate (Na OH).

6. What are the advantages and limitations of ECM? What are the

application of ECM?The advantages of ECM are:

(a) Hard and complicated shaped parts can be machined

(b) Very little tool wear takes place.

(c) No thermal and mechanical stresses are developed on the workpiece.

(d) Faster material removal rate

(e) Better surface finish is obtained

(f) Fragile parts can be machined(g) Deburring of unaccessable areas can be done.

The limitation of ECM are:

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(a) High specific energy consumption (about ISO times more energy ascompared to conventional machining

(b) Cannot be used for non-conducting materials

(c) Expensive method rigid holding fixture for tool and workpiece to

withstand high flow rate of the electrolyte.

The applications of ECM are:

(a) Producing turbine wheels with integral blades

(b) producing blades (airfoil shaped) for aircrafts

(c) Producing blind complex cavities

(d) Machining of tungsten carbide

(e) Cutting of cavities in dies for forging work

(f) Machining of hard and heat resistant alloy

(g) Machining of parts from fragile materials.

(h) Producing nozzles from hard alloy steels.

EDM ECM

1. Economical for tools of

smaller cross-sectional area

2. Designing of EDM tool is

easier3. Surface finish is best when

current density is low

4. Tool wear is significant

5. Heat affected zone exists

6. Mechanical damage to themachined surface occurs

1. Economical for tools having

larger cross - sectional area

2. Designing of ECM tool is

difficult3. Surface finish is best when

current density is maximum

4. Tool wear is negligible

5. Heat affected zone does exist.

6. No mechanical damage tomachined surface occurs.

7. Write note on Laser Beam Machining (LBM) with uses andlimitations. (UPTU 2008-9)

Or

Write brief note about applications of laser beam for machining

(UPTU 2006-7 carryover)

Or

What is laser beam machining (LBM) process. With the help of suitable

sketch, explain its working. Also give scope of LBM application

(UPTU 2005-6)

The term laser is an abbreviation of "Light Amplification by Stimulated

Emission of Radiation". Laser is a very strong monochromatic (one frequency)

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beam of light that is highly collimated (in phase), resulting a very small beamdivergence while travelling. Laser beam machining is infact a thermoelectric

process. The machining is accomplished largely by material evaporation. Laser

has many scientific and industrial applications. Laser beam is used for (i)

cutting (ii) drilling (iii) slotting and (iv) engraving. Laser does not require avacuum for the workpiece. Laser can be obtained using (i) man-made ruby (ii)

carbon-di-oxide (iii) Nd: YAG (neodymium: yttrium aluminium garnet) (iv) Nd:glass and (v) excimer.

Working Principle: When a quantum of energy from a light source is made to

fall on the atoms of a medium at energy state' Eo' it causes the absorption of

radiation. The electrons of the atoms on absorption jumps to upper energylevels (excited states) before settling down to a metastable or intermediate

state E I' From metastable state, the electrones emit one photon each

simultaneous before falling to original level ' Eo'as shown in the figure 9.13.

The laser crystal emits photons as light beam which bounce back and forth

between the reflective ends in the laser crystal. The laser beam accelerates in

the laser crystal before leaving the crystal from the partially reflective end of

the crystal. The strong laser beam emitted from the crystal is focused on the

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workpiece by the lens. The laser causes a small volume of the material of theworkpiece to melt and partially vaporize. The laser has possessed the energy

density of the range of 100 watt/mm2.

The ruby laser is most efficient when it is maintained at low temperature.

Liquid nitrogen is used for cooling of ruby crystal. The vacuum chamber is

used to house the ruby crystal so that ruby crystal should not be unnecessarily

heated up by the surroundings.

8. What are the advantages and limitations of laser beam machining?

What are the applications of LBM?

The advantages of LBM are:

(a) Very precise machining

(b) Can machine metals, composites, plastics and ceramics

(c) Smooth and clean cuts can be obtained

(d) Very rapid process

(e) Small heat affected zone.

(f) Remote machining possible no tool wear or contamination

Limitations of LBM are:

(a) Costly process

(b) Holes produced have tapering effect

(c) Laser is dangerous to eyes

(d) Larger holes above 1.25 mm diameter cannot be drilled

(e) Unsuitable to cut metals having high conductivity and reflectivity such as

aluminium and copper

(f) Metal removal rate is low.

Applications of LBM are:

(a) Profile cutting with high accuracy with numerical control is possible

(b) Drilling small holes & cutting complex profiles on hard and thin materials

such as ceramics is possible.(c) Suitable for engraving and partial cutting operations

(d) Mass micro machining production can be obtained.

(e) Suitable for a variety of cutting and drilling operations.

9. What is Electron Beam Machining (EBM) process? With the help of a

suitable sketch, explain its working. Also give its limitations and scope

of applications. (UPTU 2002-3)

Electron beam machining as the name suggests consists of a focused beam of

high velocity electrons. When the beam strikes the workpiece, the kinetic

energy of electrons is converted into heat energy. A rapid melting andvapourization of the work material takes place due to this heat energy. The

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electrons can be accelerated up to 75% of the velocity of the light. Electronbeam machining can be used to cut holes and slots in almost any material.

Working Principle

The working principle of EBM depends upon an electron beam which is

accelerated through a potential field before it is focused on the workpiece for

machining. The electron beam machine works in the same way as a cathoderay tube operates in a television. The machine consists of (i) a cathode section

which generates an election beam (ii) an anode section which accelerates the

beam and (iii) a lens system consisting of electro magnetic coils to convergeand deflect the electron beam to the desired position on the workpiece.

The beam of elections is started by a voltage difference between cathode andanode. The concave shape of the cathode helps in concentrating the electrons

as beam through the anode. The anode is also applied a potential field that

accelerates the electron beam. The beam is focused on the surface of the

workpiece by a series of electromagnetic lens and deflector coils. Thebombardment of the election beam on the workpiece causes the material to

heat locally and vapourize. Electrons are accelerated by applying potential field

of the range of 50 to 200 kV. Electrons gain speed of about 75% of light

speed. The entire process is carried out in vacuum chamber as shown in figure9.15. Vacuum is necessary to avoid air molecules colliding with the electron

beam and deflecting the beam.

The advantages of electron beam machining are:

a. Suitable for drilling a large number of small holes

b. Drilling can be done on hard materials

c. Brittle and fragile materials can be processed

d. Method is suitable for metals, composites, plastics and ceramics

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e. Accurate method

f. Very rapid process

g. Single step process for drilling, cutting and annealing

The limitations of EBM are:

(a) Part size is limited due to vacuum chamber size

(b) Expensive equipment.

The applications of EBM are:

(a) Cutting of small holes

(b) Cutting small slots

(c) Annealing can also be conveniently performed

(d) Welding can be conveniently performed.

10. What is abrasive jet machining (AJM) process? Explain the effectof stand off distance and abrasive grit size on distance on materialremoval rate in the AJM. (UPTU 2003-4)

Or

What are the important parameters that control the material removal

rate in AJM? Briefly write about any two factors. (UPTU 2004-5)

Or

With the help of neat sketch, explain the principle and working of

abrasive jet machining (AJM). List the variables and limitations of AJMprocess. (UPTU 2005-6)

Abrasive jet machining (AJM) process is a non conventional machining process

in which a stream of abrasive particles or abrasive powder loaded gas isfocused on a workpiece to remove material. The abrasive particles in high

Laser Beam Machining Electron beam machining1. Light energy consisting of

photons are converted in to

heat energy

2. Laser is generated by using

laser crystal like Ruby rod with

the help of flash lamp

3. Vacuum chamber is not

required for the workpiece.

4. Size of the part is unlimited

5. Laser crystal is cooled by liquid

nitrogen and crystal is kept in

vacuum to maintain

temperature of the crystal

1. Kinetic energy of electrons isconverted in to heat energy.

2. Electron beam is acceleratedusing potential field between

heated cathode and anode

3. Vacuum chamber is required

for the workpiece

4. Size of the part is limited dueto the size of vacuum chamber

5. Beam is protected from air

molecules to avoid any

deflection by keeping even the

workpiece in vacuum.

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pressure gas or air are focused on the workpiece through a nozzle as shown inthe figure 9.16. The abrasive particles act as a multipoint cutting tool and the

cutting force is provided by the high kinetic energy of the abrasive particles

due to gas or air flow. The hardened nozzles for this process are generally

made of tungsten carbide or gem (sapphire) like hard materials to convert thepressure energy into kinetic energy. Abrasive powder generally used are (i)

aluminium oxide (ii) silicon carbide (iii) sodium bicarbonate (iv) glass beadsand (v) dolomite.

Abrasive jet machine consist of (i) compressor to compress air or gas (nitrogen

or carbon dioxide) to a high pressure (ii) abrasive powder (Hi) mixer to mix air

and abrasive powder and (iv) nozzle to convert pressure energy into kineticenergy and to focus the air with abrasive particles on the workpiece. The metal

removal rate depends upon the gas pressure. It increases with gas pressure.

The cutting rate depends upon (i) type of abrasive particles (ii) the size of

abrasive particles (iii) the shape of abrasive particles. Abrasive particles are

not reused as their cutting action is degraded after one usuage. The usedabrasive particles are also found to clog the narrow orifice of the nozzle. The

abrasive particles have to be completely dry when they are used for AJM. The

amount of abrasive particles present in the gas affects the metal removal rate.The metal removal rate reduces as the amount of abrasive particles reduces ingas. The nozzle is provided to convert pressure energy of the gas into kinetic

energy. The nozzle material has to be very hard and it is generally made of

either tungsten carbide or gem (sapphire) which are hard materials. The

commonly used gases are (i) air (ii) nitrogen and (iii) carbon dioxide.

Metal Removal Rate & Operating Parameters

The factors affecting metal removal rate are (i) abrasive flow rate (ii) abrasive

grain size (iii) stand - off distance (iv) gas pressure and (v) mixing ratio.

Abrasive Flow Rate: The metal removal rate increases initially with abrasiveflow rate and then it decreases after a certain value as shown in figure 9.17.

The flow rate when increases, there are more abrasive particles to do thecutting. However when abrasive particles are more in the gas, the velocity of

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gas decreases. The lesser kinetic energy of the abrasive particles thereforereduces the metal removal rote.

Abrasive Grain Size: The bigger grains can remove more materials ascompared to smaller grains. Hence for same velocity, bigger grains can

remove more material as compared to small grains as shown in the figure

9.17. The bigger grains tend to (i) lower the velocity of gas and (ii) clog the

narrow orifice of the nozzle.

Stand Off Distance: When stand off distance is less, the abrasive jetimpinges smaller area of the workpiece. The impinged area increases with the

increase of stand off distance. However kinetic energy of the abrasive particles

decreases as Stand off distance increase substantially as show in the figure

9.18. The metal removal rate depends upon (i) area impinged and (ii) kineticenergy of the abrasive particles.

Gas Pressure: The higher gas pressure at nozzle can give higher kinetic

energy to abrasive particles. Hence metal removal rate increases with highergas pressure as shown in figure 9.19.

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Mixing Ratio: Mixing ratio is the ratio of mass flow rate of abrasive particles

to the mass flow rate of the gas. High mixing ratio has more abrasive particlesto remove material. However the kinetic energy decreases as the mass of

abrasive particles increases substantially as shown in the figure 9.20.

11. What are the application of AJM? What are the advantages and

limitations of AJM?

The applications of Abrasive Jet Machining (AJM) are:

(a) Cleaning and polishing of plastics components made of nylon and teflons.

(b) Frosting of inner surface of glass tubes

(c) Etching or marking on glass cylinders

(d) Slotting, contouring and drilling in (i) metal foils and (ii) thin sections ofceramics and glasses .

(e) Deburring and cutting intricate shapes on hard materials

The advantages of AJMare:

(a) Intricate shapes and holes can be cut in hard and tough materials

(b) Ability to process fragile and heat sensitive materials

(c) Inexpensive process.

The limitations of AJM are:(a) Low material removal rate

(b) Poor accuracy

(c) High wear rate of nozzle

(d) Additional operation to remove abrasive particles from the workpiece is

required.

12. Explain water jet machining (WJM)

Water jet machining is a non conventional machining process in which a jet ofhigh pressure water is made to impinge a workpiece to remove or erode the

material. This process basically uses a mass of high pressure water to pass

through a nozzle in which pressure energy is converted into kinetic energy.

The water mass with high kinetic energy impinges on the surface of the

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workpiece and this kinetic energy is sufficient to rupture the material from thesurface.

The water jet machining is as shown in the figure 9.21. The water from the

reservoir is pumped at high pressure to the nozzle. The quantity of water is

controlled by the control valve. The jet has sufficient energy to remove thematerial fi'om the workpiece. The system consists of (i) water reservoir (ii)

pumping unit (iii) control valve (iv) nozzle (v) work with water collecting vessel(vi) filter and (vii) recirculating pump.

Process Parameters

Jet Velocity: The material removal rate incrases with jet velocity as shown in

the figure 9.22.

Nozzle Diameter: The material removal rate increases as diameter increasesas more mass of water can now impinge on the surface as shown in the figure

9.23

Nozzle Tip Distance: The area impinged on the workpiece increases asnozzle tip stand off distance increases. However jet energy per unit surface

area decreases. Hence initially metal removal rate increases which starts

reducing when diameter in creases substantially as shown in the figure 9.24.

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Abrasive Mixing Ratio: Abrasive powder can be used in WJM as additional

additive. The presence of abrasive improves the metal removal rate as shownin the figure 9.25.

The advantages of WJM are:

(a) Highly fragile and crushable materials can be machined

(b) Narrow jet facilitate a fine removal of material

(c) Workpiece can be positioned at any location

(d) Fine finish can be obtained

(e) High accuracy

(f) Drilling without any hole preparation is possible

(g) Inexpensive equipment

13. Briefly explain the working of ultrasonic machine (USM) showingimportant elements. Explain the advantages and disadvantages of

USM. (UPTU 2004-5)

Ultrasonic machining is a mechanical machining process in which material is

removed from the workpiece by micro chipping and erosion on the surface with

abrasive grains in slurry. The abrasive grains are moved in between the tool

and the workpiece at ultrasonic speed (high speed) by a tool oscillating normalto the work surface at high frequency (20 KHz). The tool forms a reverse

image in the workpiece as the abrasive loaded slurry abrades the work

materials.

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A schematic diagram of the ultrasonic machining set up is as shown in the figure9.26. The transducer when supplied with high frequency power, it generates the highfrequency vibrations (20 to 30 KHz) having amplitude of about 0.02 rom. The

vibrations are transmitted to the properly shaped tool through a coupler known astool holder. The tool is made of soft material so that the abrasive particles can beembedded in the tool and the tool can act as a multipoint tool with the embeddedabrasive particles. The tool shape is a close complimentary shape of the final surfaceto be generated.

The oscillating tool is pressed against the workpiece and it is fed continuously as themetal removal from the workpiece progressesas shown in figure 9.27. The feed iscontrolled by a servomechanism so that a constant gap is maintained between thetool and the workpiece. Though metal removal rate is relatively slow, but this is theonly way to produce economically complex cavities in brittle and fragile materials

without the risk of breakage or fracture. The components of USM are:

(a) Transducers: It converts the electrical energy into vibratory motion, usingpiezoelectric or magnetostrictive principles. Prezoelectric material such asquartz increases in size when current is applied and it comes to normal sizewhen current is removed, thereby it converts electrical energy into vibratorymotion.

(b) Tool Cone (Horn): A tool cone helps in amplifying the mechanical energy(vibratory energy) which is produced by the transducer. The tool cone must betuned to the required frequency. The tool tip is attached to the tool cone.

(c) Abrasive Slurry: The abrasive particles used should be harder that the workmaterial. Aluminum oxide, silicon carbide and boron carbide are used asabrasive particles. The abrasive particles are suspended in liquid (generallywater) to form slurry with liquid content varying from 30 to 60%. The liquid

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helps in (i) cooling the tool face (ii) carrying abrasive particles to cutting zoneand (iii) carrying and removal of used particles from the cutting zone.

The advantages of USM are:

(a) Machining hard and brittle materials

(b) Good accuracy and surface finish, can be obtainable

(c) Unaffected by electrical and chemical characteristics of the work material(d) Drilling holes of any shape are possible

(e) Unhazardous process

(f) Specific power consumption is not high.

The limitations of USM are:

(a) Metal removal rate is low

(b) Depth of drilled hole is limited(c) Tool wear is high

(d) Sharp comers cannot be made on work

(e) Flat surfaces at bottom of cavity can not be produced.

The applications of USM are:

(a) Drilling and finishing of dies made of hard materials such as tungsten carbide

(b) Grinding operation can be performed

(c) Welding operations

(d) Processing fragile and brittle materials such as ceramic and glass

(e) Coining, lapping, deburing and broaching operations can be performed.