PAPER SOLUTION OF ADVANCED MANUFACTURING

TECHNIQUES

SUMMER-2018

1. a) Write with neat sketch of Hot & cold machining process and also write application of

it.

Sr.No.

Cold working

Hot working

1

It is done at a temperature below the

recrystallization temperature.

Hot working is done at a temperature above

recrystallization temperature.

2.

It is done below recrystallization temperature so it is accomplished by

strain hardening.

Hardening due to plastic deformation is completely eliminated.

3.

Cold working decreases mechanical

properties of metal like elongation, reduction of area and impact values.

It increases mechanical properties.

4.

Crystallization does not take place.

Crystallization takes place.

5.

Material is not uniform after this

working.

Material is uniform thought.

6.

There is more risk of cracks.

There is less risk of cracks.

7.

Cold working increases ultimate tensile strength, yield point hardness and

fatigue strength but decreases resistance

to corrosion.

In hot working, ultimate tensile strength, yield point, corrosion resistance are unaffected.

8.

Internal and residual stresses are

produced.

Internal and residual stresses are not produced.

9.

Cold working required more energy for

plastic deformation.

It requires less energy for plastic deformation

because at higher temperature metal become

more ductile and soft.

10.

More stress is required.

Less stress required.

11.

It does not require pickling because no oxidation of metal takes place.

Heavy oxidation occurs during hot working so pickling is required to remove oxide.

12.

Embrittlement does not occur in cold working due to no reaction with oxygen

at lower temperature.

There is chance of embrittlement by oxygen in hot working hence metal working is done at

inert atmosphere for reactive metals.

1.b.) What is non-traditional machining process. Explain its need and classification in brief.

A machining process is called non-traditional if its material removal mechanism is

basically different than those in the traditional processes, i.e. a different form of energy (other

than the excessive forces exercised by a tool, which is in physical contact with the work piece) is

applied to remove the excess material from the work surface, or to separate the workpiece into

smaller parts.

Need for development of Non Conventional Processes

The strength of steel alloys has increased five folds due to continuous R and D effort. In

aero-space requirement of High strength at elevated temperature with light weight led to

development and use of hard titanium alloys, nimonic alloys, and other HSTR alloys. The

ultimate tensile strength has been improved by as much as 20 times. Development of

cutting tools which has hardness of 80 to 85 HRC which cannot be machined economically in

conventional methods led to development of non –traditional machining methods.

1.Technologically advanced industries like aerospace, nuclear power, ,wafer fabrication,

automobiles has ever increasing use of High –strength temperature resistant (HSTR) alloys

(having high strength to weight ratio) and other difficult to machine materials like titanium,

SST,nimonics, ceramics and semiconductors. It is no longer possible to use conventional process

to machine these alloys.

2.Production and processing parts of complicated shapes (in HSTR and other hard to machine

alloys) is difficult , time consuming an uneconomical by conventional methods of machining

3.Innovative geometric design of products and components made of new exotic materials with

desired tolerance , surface finish cannot be produced economically by conventional machining.

4.The following examples are provided where NTM processes are preferred over the

conventional machining process:

♦ Intricate shaped blind hole – e.g. square hole of 15 mmx15 mm with a depth

of 30 mm with a tolerance of •} 100 microns

♦ Difficult to machine material – e.g. Inconel, Ti-alloys or carbides, Ceramics,

composites , HSTR alloys, satellites etc.,

♦ Low Stress Grinding – Electrochemical Grinding is preferred as compared to

conventional grinding

♦ Deep hole with small hole diameter – e.g. φ 1.5 mm hole with l/d = 20

♦ Machining of composites

Applications

Some of the applications of NTM are given below:

Classification of NTM processes

Classification of NTM processes is carried out depending on the nature of energy used for

material removal. NTM processes can be divided into four groups based upon the material

removal mechanism:

Chemical- Chemical reaction between a liquid reagent and the work piece results in

etching.

Electrochemical- An electrolytic reaction at the workpiece surface is responsible

material removal.

Mechanical- High velocity abrasives or liquids remove material.

Thermal- High temperatures in very localized regions evaporate materials.

1. Mechanical Processes

• Abrasive Jet Machining (AJM)

• Ultrasonic Machining (USM)

• Water Jet Machining (WJM)

• Abrasive Water Jet Machining (AWJM)

2. Electrochemical Processes

• Electrochemical Machining (ECM)

• Electro Chemical Grinding (ECG)

• Electro Jet Drilling (EJD)

3. Electro-Thermal Processes

• Electro-discharge machining (EDM)

• Laser Jet Machining (LJM)

• Electron Beam Machining (EBM)

4. Chemical Processes

• Chemical Milling (CHM)

• Photochemical Milling (PCM)

2.a) Write with neat sketch about High speed grinding. Also write application of high speed grinding.

High-speed grinding (HSG) is a rail care concept developed by the company Stahlberg

Roensch from Seevetal, Germany. It is based on the principle of rotational grinding and serves to

grind rails at up to 100 kilometres per hour (62 mph).

Principle of high-speed grinding

Since roughly the beginning of the 1990s, rail network operators have experienced increasing

problems with rail surface defects. Head checks, squats, corrugation and slip waves all contribute

to higher maintenance costs, intensified noise pollution, traffic obstructions, and ultimately a

shortened rail lifespan. These increasingly common flaws are problems , hence there is a

growing need for rail maintenance .The primary challenge for modern rail maintenance is that

less time is available to perform it due to higher traffic densities. Conventional rail maintenance

machines (e.g. rail milling, planing or grinding) working at speeds from 1 to 10 kilometres per

hour (0.62 to 6.21 mph) can work only during possession time (track closure) which is in most

cases available only at night.

HSG allows for working speeds of up to 100 kilometres per hour (62 mph) and is deployable

within regular traffic.

Principle

HSG is based on the principle of circumferential grinding. Cylindrical grinding stones are pulled

over the rail at an angle, inducing rotation as well as an axial grinding motion. The grinding

stones are mounted on grinding units hauled by a carrier vehicle.

Two things are achieved with this motion: First, the required material removal rate is obtained

through the relative motion between grinding stone and rail. Second, by rotating the stones,

overheating, glazing and uneven wear of the stones is prevented.

The usual grinding speed on Deutsche Bahn's rail network is 80 kilometres per hour (50 mph)

Applications

Preventive rail grinding

Low-friction coating removal

Acoustic grinding to reduce noise pollution emitted from the rail

Removal of the decarb layer

rail track

b) Discuss in details the historical development, economics and application of

non-traditional machining process.

History of Non Traditional processes:

Although, the non conventional machining processes have created a revolution in the field of

machining technology by the development of idea of various processes were initiated as early as

in nineteen- twenties in USSR.

1920 The initiation was first made by Gussev towards the end of 1920 in USSR. He

suggested a method of machining by combination of Chemical and mechanical means.

His work is basis for all Electro Chemical processes known today.

1941 Burgess, American Scientist had demonstrated the possibility of ECM process by

drawing a sharp contrast between the mechanical and electrolyte methods in metal

removal.

1942 The idea of Ultrasonic machining was invented by Balamuth .He invented at the time

of investigation of dispersion of solids in Liquids with the help of a vibrating magne-

tostrictive nickel tube.However, the origination of the process was made by

Rosenberg.

1943 DM was developed by B R Lazarenko and N I Lazarenko in USSR. They first

developed the idea of spark erosion machining. In the early nineteen-sixties, the idea

of Ultrasonic machining began to to develop widely in USSR and basis of this

development was laid on extensive investigation that took place in the mechanism of

ultrasonic machining and in the design of Magneto-strictive transducers, converters

and wave guides.

1950 The basis of laser machining was established by the process Which were developed

by Basov, Prokhorov and Fabrikanth in USSR in 1950.

1950 Electro chemical Grinding has practically been developed in about1950.

1960 The concept of whirling jet machining was innovated.

Many of these new techniques of machining have been developed in last few decades to meet the

challenges put forwarded by rapid development of hard to machine and high strength

temperature resistant (HSTR) alloys. It is anticipated that in near future , these new technologies

will find an ever increasing application in all branchesof mechanical

engineering industry.

Economics of the processes

The economics of the various processes are analysed on the basis of following factor and given

in Table

(i) Capital cost

(ii) Tooling cost

(iii) Consumed power cost

(iv) Metal removal rate efficiency

(v) Tool wear.

The capital cost of ECM is very high when compared with traditional mechanical contour

grinding and other non-conventional machining processes whereas capital costs for AJM and

PAM are comparatively low. EDM has got higher tooling cost than other machining processes.

Power consumption is very low for PAM and LBM processes whereas it is greater

in case of ECM. The metal removal efficiency is very high for EBM and LBM than for other

processes. In conclusion, the suitability of application of any of the processes is dependent upon

various factors and must be considered all or some of them before applying nonconventional

processes.

3.a) Explain the ultrasonic machining process, Also write mechanics of USM, Advantages

and application.

• Material removal primarily occurs due to the indentation of the hard abrasive grits

on the brittle work material.

• Other than this brittle failure of the work material due to indentation some

material removal may occur due to free flowing impact of the abrasives against

the work material and related solid-solid impact erosion,

• Tool’s vibration – indentation by the abrasive grits.

• During indentation, due to Hertzian contact stresses, cracks would develop just

below the contact site, then as indentation progresses the cracks would propagate

due to increase in stress and ultimately lead to brittle fracture of the work material

under each individual interaction site between the abrasive grits and the

workpiece.

• The tool material should be such that indentation by the abrasive grits does not

lead to brittle failure.

• Thus the tools are made of tough, strong and ductile materials like steel, stainless

steel and other ductile metallic alloys.

USM Machine

The basic mechanical structure of an USM is very similar to a drill press.

However, it has additional features to carry out USM of brittle work material. The work

piece is mounted on a vice, which can be located at the desired position under the tool

using a 2 axis table. The table can further be lowered or raised to accommodate work of

different thickness.

The typical elements of an USM are

Slurry delivery and return system

Feed mechanism to provide a downward feed force on the tool during machining

The transducer, which generates the ultrasonic vibration

The horn or concentrator, which mechanically amplifies the vibration to the

required amplitude of 15 – 50 μm and accommodates the tool at its tip.

Working of horn as mechanical amplifier of amplitude of vibration

The ultrasonic vibrations are produced by the transducer. The transducer is driven by

suitable signal generator followed by power amplifier. The transducer for USM works on

the following principle

• Piezoelectric effect

• Magnetostrictive effect

• Electrostrictive effect

PROCESS VARIABLES:

• Amplitude of vibration (ao) – 15 – 50 μm

• Frequency of vibration (f) – 19 – 25 kHz

• Feed force (F) – related to tool dimensions

• Feed pressure (p)

• Abrasive size – 15 μm – 150 μm

• Abrasive material – Al2O3

- SiC

- B4C

- Boronsilicarbide

- Diamond

Flow strength of work material

Flow strength of the tool material

Contact area of the tool – A

Volume concentration of abrasive in water slurry – C

Applications of USM

• Used for machining hard and brittle metallic alloys, semiconductors, glass,

ceramics, carbides etc.

• Used for machining round, square, irregular shaped holes and surface impressions.

• Machining, wire drawing, punching or small blanking dies.

Advantage of USM

USM process is a non-thermal, non-chemical, creates no changes in the microstructures,

chemical or physical properties of the workpiece and offers virtually stress free machined

surfaces.

· Any materials can be machined regardless of their electrical conductivity

· Especially suitable for machining of brittle materials

· Machined parts by USM possess better surface finish and higher structural integrity.

· USM does not produce thermal, electrical and chemical abnormal surface

Some disadvantages of USM

· USM has higher power consumption and lower material-removal rates than traditional

fabrication processes.

· Tool wears fast in USM.

Machining area and depth is restraint in USM

b) Explain the process of water jet machining process with its advantages &

applications.

Abrasive water jet cutting is an extended version of water jet cutting; in which the water

jet contains abrasive particles such as silicon carbide or aluminium oxide in order to

increase the material removal rate above that of water jet machining. Almost any type of

material ranging from hard brittle materials such as ceramics, metals and glass to

extremely soft materials such as foam and rubbers can be cut by abrasive water jet

cutting. The narrow cutting stream and computer controlled movement enables this

process to produce parts accurately and efficiently. This machining process is especially

ideal for cutting materials that cannot be cut by laser or thermal cut. Metallic, non-

metallic and advanced composite materials of various thicknesses can be cut by this

process. This process is particularly suitable for heat sensitive materials that cannot be

machined by processes that produce heat while machining.

The schematic of abrasive water jet cutting is shown in Figure which is similar to water

jet cutting apart from some more features underneath the jewel; namely abrasive, guard

and mixing tube. In this process, high velocity water exiting the jewel creates a vacuum

which sucks abrasive from the abrasive line, which mixes with the water in the mixing

tube to form a high velocity beam of abrasives.

Figure: Abrasive water jet machining

Applications

Abrasive water jet cutting is highly used in aerospace, automotive and electronics

industries. In aerospace industries, parts such as titanium bodies for military aircrafts,

engine components (aluminium, titanium, heat resistant alloys), aluminium body parts

and interior cabin parts are made using abrasive water jet cutting.

In automotive industries, parts like interior trim (head liners, trunk liners, door panels)

and fibre glass body components and bumpers are made by this process. Similarly, in

electronics industries, circuit boards and cable stripping are made by abrasive water jet

cutting.

Advantages of abrasive water jet cutting

In most of the cases, no secondary finishing required

No cutter induced distortion

Low cutting forces on workpieces

Limited tooling requirements

Little to no cutting burr

Typical finish 125-250 microns

Smaller kerf size reduces material wastages

No heat affected zone

Localises structural changes

No cutter induced metal contamination

Eliminates thermal distortion

No slag or cutting dross

Precise, multi plane cutting of contours, shapes, and bevels of any angle.

4.a) Explain with neat sketch Abrasive jet machining process with mechanics, advantages

& application.

Abrasive water jet cutting is an extended version of water jet cutting; in which the water

jet contains abrasive particles such as silicon carbide or aluminium oxide in order to

increase the material removal rate above that of water jet machining. Almost any type of

material ranging from hard brittle materials such as ceramics, metals and glass to

extremely soft materials such as foam and rubbers can be cut by abrasive water jet

cutting. The narrow cutting stream and computer controlled movement enables this

process to produce parts accurately and efficiently. This machining process is especially

ideal for cutting materials that cannot be cut by laser or thermal cut. Metallic, non-

metallic and advanced composite materials of various thicknesses can be cut by this

process. This process is particularly suitable for heat sensitive materials that cannot be

machined by processes that produce heat while machining.

Working principle

In Abrasive Jet Machining (AJM), abrasive particles are made to impinge on the work

material at a high velocity. The jet of abrasive particles is carried by carrier gas or air.

The high velocity stream of abrasive is generated by converting the pressure energy of

the carrier gas or air to its kinetic energy and hence high velocity jet. The nozzle directs

the abrasive jet in a controlled manner onto the work material, so that the distance

between the nozzle and the work piece and the impingement angle can be set desirably.

The high velocity abrasive particles remove the material by micro-cutting action as well

as brittle fracture of the work material.

AJM Equipment

In AJM, air is compressed in an air compressor and compressed air at a pressure of

around 5 bar is used as the carrier gas. Figure also shows the other major parts of the

AJM system. Gases like CO2, N2 can also be used as carrier gas which may directly be

issued from a gas cylinder. Generally oxygen is not used as a carrier gas. The carrier gas

is first passed through a pressure regulator to obtain the desired working pressure. To

remove any oil vapour or particulate contaminant the same is passed through a series of

filters. Then the carrier gas enters a closed chamber known as the mixing chamber. The

abrasive particles enter the chamber from a hopper through a metallic sieve. The sieve is

constantly vibrated by an electromagnetic shaker. The mass flow rate of abrasive (15

gm/min) entering the chamber depends on the amplitude of vibration of the sieve and its

frequency. The abrasive particles are then carried by the carrier gas to the machining

chamber via an electro-magnetic on-off valve. The machining enclosure is essential to

contain the abrasive and machined particles in a safe and eco-friendly manner. The

machining is carried out as high velocity (200 m/s) abrasive particles are issued from the

nozzle onto a work piece traversing under the jet.

Process Parameters and Machining Characteristics.

The process parameters are listed below:

• Abrasive ⎯ Material – Al2O3 / SiC / glass beads

⎯ Shape – irregular / spherical

⎯ Size – 10 ~ 50 μm

⎯ Mass flow rate – 2 ~ 20 gm/min

• Carrier gas

o Composition – Air, CO2, N2

o Density – Air ~ 1.3 kg/m3

o Velocity – 500 ~ 700 m/s

o Pressure – 2 ~ 10 bar

o Flow rate – 5 ~ 30 lpm

Abrasive Jet

⎯ Velocity – 100 ~ 300 m/s

⎯ Mixing ratio – mass flow ratio of abrasive to gas

⎯ Stand-off distance – 0.5 ~ 5 mm

⎯ Impingement Angle – 600 ~ 900

• Nozzle

⎯ Material – WC / sapphire

⎯ Diameter – (Internal) 0.2 ~ 0.8 mm

⎯ Life – 10 ~ 300 hours

The important machining characteristics in AJM are

• The material removal rate (MRR) mm3/min or gm/min

• The machining accuracy

• The life of the nozzle

Parameters of Abrasive Jet Maching (AJM) are factors that influence its Metal Removal

Rate (MRR). In a machining process, Metal Removal Rate (MRR) is the volume of metal

removed from a given work piece in unit time. The following are some of the important

process parameters of abrasive jet machining:

1. Abrasive mass flow rate

2. Nozzle tip distance

3. Gas Pressure

4. Velocity of abrasive particles

5. Mixing ratio

6. Abrasive grain size

Abrasive mass flow rate:

Mass flow rate of the abrasive particles is a major process parameter that influences the

metal removal rate in abrasive jet machining.

In AJM, mass flow rate of the gas (or air) in abrasive jet is inversely proportional to the

mass flow rate of the abrasive particles.

Due to this fact, when continuously increasing the abrasive mass flow rate, Metal

Removal Rate (MRR) first increases to an optimum value (because of increase in number

of abrasive particles hitting the work piece) and then decreases.

However, if the mixing ratio is kept constant, Metal Removal Rate (MRR) uniformly

increases with increase in abrasive mass flow rate.

Nozzle tip distance:

Nozzle Tip Distance (NTD) is the gap provided between the nozzle tip and the work

piece.

Up to a certain limit, Metal Removal Rate (MRR) increases with increase in nozzle tip

distance. After that limit, MRR remains constant to some extent and then decreases.

In addition to metal removal rate, nozzle tip distance influences the shape and diameter of

cut.

For optimal performance, a nozzle tip distance of 0.25 to 0.75 mm is provided.

Gas pressure:

Air or gas pressure has a direct impact on metal removal rate.

In abrasive jet machining, metal removal rate is directly proportional to air or gas

pressure.

Velocity of abrasive particles:

Whenever the velocity of abrasive particles is increased, the speed at which the abrasive

particles hit the work piece is increased. Because of this reason, in abrasive jet

machining, metal removal rate increases with increase in velocity of abrasive particles.

Mixing ratio:

Mixing ratio is a ratio that determines the quality of the air-abrasive mixture in Abrasive

Jet Machining (AJM).

It is the ratio between the mass flow rate of abrasive particles and the mass flow rate of

air (or gas).

When mixing ratio is increased continuously, metal removal rate first increases to some

extent and then decreases.

Abrasive grain size:

Size of the abrasive particle determines the speed at which metal is removed.

If smooth and fine surface finish is to be obtained, abrasive particle with small grain size

is used.

If metal has to be removed rapidly, abrasive particle with large grain size is used.

Applications

Abrasive water jet cutting is highly used in aerospace, automotive and electronics industries.

In aerospace industries, parts such as titanium bodies for military aircrafts, engine

components (aluminium, titanium, heat resistant alloys), aluminium body parts and interior cabin parts are made using abrasive water jet cutting.

In automotive industries, parts like interior trim (head liners, trunk liners, door

panels) and fibre glass body components and bumpers are made by this

process. Similarly, in electronics industries, circuit boards and cable stripping

are made by abrasive water jet cutting.

Figure: Steel gear and rack cut with an abrasive water jet

Advantages of abrasive water jet cutting

In most of the cases, no secondary finishing required

No cutter induced distortion

Low cutting forces on workpieces

Limited tooling requirements

Little to no cutting burr

Typical finish 125-250 microns

Smaller kerf size reduces material wastages

No heat affected zone

Localises structural changes

No cutter induced metal contamination

Eliminates thermal distortion

No slag or cutting dross

Precise, multi plane cutting of contours, shapes, and bevels of any angle

Limitations of abrasive water jet cutting

Cannot drill flat bottom

Cannot cut materials that degrades quickly with moisture

Surface finish degrades at higher cut speeds which are frequently used for

rough cutting.

The major disadvantages of abrasive water jet cutting are high capital cost and

high

noise levels during operation.

4. b) Explain the process parameters and control, effect of USM on materials.

Process parameters of Ultrasonic Machining processes 1. Amplitude of vibration ( 15 to 50 microns)

2. Frequency of vibration ( 19 to 25 kHz).

3. Feed force (F) related to tool dimensions

4. Feed pressure

5. Abrasive size

6. Abrasive material

Al203, SiC, B4C, Boron silicarbide, Diamond.

7. Flow strength of the work material

8. Flow strength of the tool material

9. Contact area of the tool

10. Volume concentration of abrasive in water slurry.

11. Tool

a. Material of tool

b. Shape

c. Amplitude of vibration

d. Frequency of vibration

e. Strength developed in tool

12. Work material

a. Material

b. Impact strength

c. Surface fatigue strength

13. Slurry

a. Abrasive – hardness, size, shape and quantity of abrasive flow

b. Liquid – Chemical property, viscosity, flow rate

c. Pressure

d. Density

Factors affecting MRR and surface finish in USM:

Tool amplitude and frequency.

Tool shape.

Abrasive grain size.

Abrasive concentration.

Work hardness-tool hardness ratio.

Feed force.

5. a) Explain with neat sketch Electron Beam machining. Also Write advantages,

disadvantages a application of it.

Electron Beam Welding (EBW) Fusion welding process in which heat for welding is provided by a highly-focused,

high-intensity stream of electrons striking work surface Electron beam gun operates at:

High voltage (e.g., 10 to 150 kV typical) to accelerate electrons

Beam currents are low (measured in milliamps)

Power in EBW not exceptional, but power density is

Advantages High-quality welds, deep and narrow profiles

Limited heat affected zone, low thermal distortion

High welding speeds

No flux or shielding gases needed

Disadvantages High equipment cost

Precise joint preparation & alignment required

Vacuum chamber required

Safety concern: EBW generates x-rays

5.b ) Write with neat sketch process of plasma Arc machining. Give its advantages

and application

It is also one of the thermal machining processes. Here the method of heat generation is different

than EDM and LBM. Working Principle of PAM In this process gases are heated and charged to

plasma state. Plasma state is the superheated and electrically ionized gases at approximately

5000oC. These gases are directed on the workpiece in the form of high velocity stream. Working

principle and process details are shown in Figure 5.7. Figure 5.7 : Working Principle and Process

Details of PAM Process Details of PAM Details of PAM are described below. Plasma Gun Gases are

used to create plasma like, nitrogen, argon, hydrogen or mixture of these gases. The plasma gun

consists of a tungsten electrode fitted in the chamber. The electrode is given negative polarity and

nozzle of the gun is given positive polarity. Supply of gases is maintained into the gun. A strong Dc

power Supply + ve - ve - ve Tungsten electrode (cathode) Flow of gases Machining zone Nozzle

(anode) Work piece 74 Manufacturing Processes-III arc is established between the two terminals

anode and cathode. There is a collision between molecules of gas and electrons of the established

arc. As a result of this collision gas molecules get ionized and heat is evolved. This hot and ionized

gas called plasma is directed to the workpiece with high velocity. The established arc is controlled by

the supply rate of gases. Power Supply and Terminals Power supply (DC) is used to develop two

terminals in the plasma gun. A tungsten electrode is inserted to the gun and made cathode and

nozzle of the gun is made anode. Heavy potential difference is applied across the electrodes to

develop plasma state of gases. Cooling Mechanism As we know that hot gases continuously comes

out of nozzle so there are chances of its over heating. A water jacket is used to surround the nozzle

to avoid its overheating. Tooling There is no direct visible tool used in PAM. Focused spray of ho0t,

plasma state gases works as a cutting tool. Workpiece Workpiece of different materials can be

processed by PAM process. These materials are aluminium, magnesium, stainless steels and carbon

and alloy steels. All those material which can be processed by LBM can also be processed by PAM

process.

Applications of PAM The chief application of this process is profile cutting as controlling movement

of spray focus point is easy in case of PAM process. This is also recommended for smaller machining

of difficult to machining materials.

Advantages of PAM Process Advantages of PAM are given below : (a) It gives faster production rate.

(b) Very hard and brittle metals can be machined. (c) Small cavities can be machined with good

dimensional accuracy. Disadvantages of PAM Process (a) Its initial cost is very high. (b) The process

requires over safety precautions which further enhance the initial cost of the setup. (c) Some of the

workpiece materials are very much prone to metallurgical changes on excessive heating so this fact

imposes limitations to this process. (d) It is uneconomical for bigger cavities to be machined.

6. a) Explain with neat sketch Electrical discharge machining. Write its

advantages and application.

Working principle of EDM

As shown in Figure at the beginning of EDM operation, a high voltage is applied

across the narrow gap between the electrode and the workpiece. This high voltage

induces an electric field in the insulating dielectric that is present in narrow gap

between electrode and workpiece. This cause conducting particles suspended in the

dielectric to concentrate at the points of strongest electrical field. When the potential

difference between the electrode and the workpiece is sufficiently high, the dielectric

breaks down and a transient spark discharges through the dielectric fluid, removing

small amount of material from the workpiece surface. The volume of the material

removed per spark discharge is typically in the range of 10-6

to 10-6

mm3.

The material removal rate, MRR, in EDM is calculated by the following foumula:

MRR = 40 I / Tm 1.23

(cm3/min)

Where, I is the current amp,

Tm is the melting temperature of workpiece in 0C

EDM removes material by discharging an electrical current, normally stored in a

capacitor bank, across a small gap between the tool (cathode) and the workpiece

(anode) typically in the order of 50 volts/10amps.

Dielectric fluids

Dielectric fluids used in EDM process are hydrocarbon oils, kerosene and deionised

water. The functions of the dielectric fluid are to:

Act as an insulator between the tool and the workpiece.

Act as coolant.

Act as a flushing medium for the removal of the chips.

The electrodes for EDM process usually are made of graphite, brass, copper and

copper-tungsten alloys.

Design considerations for EDM process are as follows:

Deep slots and narrow openings should be avoided.

The surface smoothness value should not be specified too fine.

Rough cut should be done by other machining process. Only finishing

operation should be done in this process as MRR for this process is low.

Application of EDM

The EDM process has the ability to machine hard, difficult-to-machine materials.

Parts with complex, precise and irregular shapes for forging, press tools, extrusion

dies, difficult internal shapes for aerospace and medical applications can be made by

EDM process. Some of the shapes made by EDM process are shown in Figure.

Advantages of EDM

The main advantages of DM are:

By this process, materials of any hardness can be machined;

No burrs are left in machined surface;

One of the main advantages of this process is that thin and fragile/brittle

components can be machined without distortion;

Complex internal shapes can be machined

Limitations of EDM

The main limitations of this process are:

This process can only be employed in electrically conductive materials;

Material removal rate is low and the process overall is slow compared to

conventional machining processes;

Unwanted erosion and over cutting of material can occur;

Rough surface finish when at high rates of material removal.

6. b) Explain the process of LASER Beam machining. Give its advantages and application.

Laser-beam machining is a thermal material-removal process that utilizes a high-

energy, coherent light beam to melt and vaporize particles on the surface of metallic

and non-metallic workpieces. Lasers can be used to cut, drill, weld and mark. LBM is

particularly suitable for making accurately placed holes. A schematic of laser beam

machining is shown in Figure.

Different types of lasers are available for manufacturing operations which are as

follows:

CO2 (pulsed or continuous wave): It is a gas laser that emits light in the

infrared region. It can provide up to 25 kW in continuous-wave mode.

Nd:YAG: Neodymium-doped Yttrium-Aluminum-Garnet (Y3Al5O12) laser is a

solid-state laser which can deliver light through a fibre-optic cable. It can

provide up to 50 kW power in pulsed mode and 1 kW in continuous-wave

mode.

Figure: Laser beam machining schematic

Laser beam cutting (drilling)

In drilling, energy transferred (e.g., via a Nd:YAG laser) into the workpiece

melts the material at the point of contact, which subsequently changes into a

plasma and leaves the region.

A gas jet (typically, oxygen) can further facilitate this phase transformation

and departure of material removed.

Laser drilling should be targeted for hard materials and hole geometries that

are difficult to achieve with other methods.

A typical SEM micrograph hole drilled by laser beam machining process employed in

making a hole is shown in Figure

Laser beam cutting (milling)

A laser spot reflected onto the surface of a workpiece travels along a

prescribed trajectory and cuts into the material.

Continuous-wave mode (CO2) gas lasers are very suitable for laser

cutting

providing high-average power, yielding high material-removal rates, and

smooth cutting surfaces.

Advantage of laser cutting

No limit to cutting path as the laser point can move any path.

The process is stress less allowing very fragile materials to be laser cut

without any support.

Very hard and abrasive material can be cut.

Sticky materials are also can be cut by this process.

It is a cost effective and flexible process.

High accuracy parts can be machined.

No cutting lubricants required

No tool wear

Narrow heat effected zone

Limitations of laser cutting

Uneconomic on high volumes compared to stamping

Limitations on thickness due to taper

High capital cost

High maintenance cost

Assist or cover gas required

7. a)Explain with neat sketch process of oxy acetylene pressure welding. Also

explain different types of flames. Give its advantages & application.

Types of Flames

• Oxygen is turned on, flame immediately changes into a long white inner area (Feather) surrounded by a transparent blue envelope is called Carburizing flame (30000c)

• Addition of little more oxygen give a bright whitish cone surrounded by the transparent blue envelope is called Neutral flame (It has a balance of fuel gas and oxygen) (32000c)

• Used for welding steels, aluminium, copper and cast iron

• If more oxygen is added, the cone becomes darker and more pointed, while the envelope becomes shorter and more fierce is called Oxidizing flame

• Has the highest temperature about 34000c

• Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations:

•

• (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame.

7.b) Explain the process of resistance welding with any two process of resistance welding.

Resistance Welding (RW)

A group of fusion welding processes that use a combination of heat and pressure to accomplish coalescence

Heat generated by electrical resistance to current flow at junction to be welded

Principal RW process is resistance spot welding (RSW)

Fig: Resistance welding, showing the components in spot welding, the main process in the RW group.

Components in Resistance Spot Welding

Parts to be welded (usually sheet metal)

Two opposing electrodes

Means of applying pressure to squeeze parts between electrodes

Power supply from which a controlled current can be applied for a specified time duration

Advantages

No filler metal required

High production rates possible

Lends itself to mechanization and automation

Lower operator skill level than for arc welding

Good repeatability and reliability

Disadvantages

High initial equipment cost

Limited to lap joints for most RW processes

Resistance Seam Welding

8. a) Write with neat sketch Atomic Hydrogen welding with advantages, disadvantages

& applications.

Atomic hydrogen welding (AHW) is an arc welding process that makes use of an arc

between two tungsten metal electrodes within an atmosphere composed of hydrogen.

Shielding is obtained from the hydrogen.

The electric arc produced in the process efficiently breaks up the molecules of

hydrogen that later recombine through an extreme release of heat.

Equipments and Parameters required in AHW

2 tungsten electrode.

Hydrogen gas cylinder with regulator and hose.

Electrode holder or torch.

300 V AC power supply machine with controller.

Filler rod if needed.

The equipment consists of a welding torch with two tungsten electrodes inclined

and adjusted to maintain a stable arc.

Annular nozzles around the tungsten electrodes carry the hydrogen gas supplied from

the gas cylinders.

AC power source is suitable compared to DC, because equal amount of heat will be

available at both the electrodes.

A transformer with an open circuit voltage of 300 volts is required to strike and

maintain the arc.

The work pieces are cleaned to remove dirt, oxides and other impurities to obtain a

sound weld. Hydrogen gas supply and welding current are switched ON.

An arc is stuck by bringing the two tungsten electrodes in contact with each other

and instantaneously separated by a small distance, say 1.5 mm, such that the arc still

remains between the two electrodes.

As the jet of hydrogen gas passes through the electric arc, it disassociates into atomic

hydrogen by absorbing large amounts of heat supplied by the electric arc.

H2 = H + H – 422KJ (endothermic reaction)

Recombination takes place as the atomic hydrogen touches the cold work piece

liberating a large amount of heat.

H + H = H2 + 422 KJ (Exothermic reaction)

Heat liberated is used for producing the joint between two workpieces.

Advantages

Intense flame is obtained which can be concentrated at the joint. Hence less distortion.

welding is faster.

Workpiece do not form part of electric circuit. Hence , problems like striking the arc

and maintaining the arc column are eliminated.

Separate flux/ shielding gas is not required, hydrogen itself prevents oxidation of

metal and tungsten electrode.

Limitations

Cost of welding by this process is slightly higher than with the other process.

Welding is limited to flat positions only.

Because of the high levels of heat produced in this welding process, welders need to

be even more aware of the dangers they are exposed to.

Skilled welder is required.

Due to advances in inert gases AHW may be limited.

Hydrogen is highly inflammable gas so it should be taken care.

Applications of AHW

Atomic hydrogen welding is used in those applications where rapid welding is

necessary, as for stainless steels and other special alloys.

For most of the ferrous and non ferrous metals.

For thick as well as thin sheets or small diameter wires (2-10mm).

Can be applied almost to any metal, specially in light gauge metal, special ferrous

alloys, and most non ferrous metals and alloys.

8.b)Explain with neat sketch submerge Arc welding? Also give its advantages,

disadvantages & Applications

Submerged arc welding

• Weld arc is shielded by a granular flux , consisting of silica, lime, manganese oxide, calcium fluoride and other compounds.

• Flux is fed into the weld zone by gravity flow through nozzle

• Thick layer of flux covers molten metal

• Flux acts as a thermal insulator ,promoting deep penetration of heat into the work

piece

• Consumable electrode is a coil of bare round wire fed automatically through a tube

• Power is supplied by 3-phase or 2-phase power lines

Fig : Schematic illustration of the submerged-arc welding process and equipment. The unfused flux is recovered and reused.

9. a) What do you mean by solid phase welding? Explain the process of friction welding

with its limitations.

Solid Phase Welding (Solid State Welding

Solid State Welding is a welding process, in which two work pieces are joined under a

pressure providing an intimate contact between them and at a temperature essentially below

the melting point of the parent material.

A welding process in which coalescence takes place at temperatures below the

melting point of the metals being joined and without use of a brazing filler

metal.

Dissimilar metals may be joined .

Joining takes place without fusion at the interface

No liquid or molten phase is present at the joint

Two surfaces brought together under pressure

For strong bond, both surfaces must be clean:

– No oxide films

– No residues

– No metalworking fluids

– No adsorbed layers of gas

– No other contaminants……

Advantages

• Weld (bonding) is free from microstructure defects .

• Mechanical properties of the weld are similar to those of the parent metals

• No consumable materials (filler material, fluxes, shielding gases) are required.

• Dissimilar metals may be joined .

Disadvantages

• Expensive equipment

Types of Solid State welding

• Forge Welding (FOW)

• Cold Welding (CW)

• Explosive Welding (EXW)

• Diffusion Welding (DFW)

• Friction Welding (FRW)

• Ultrasonic Welding (USW)

Friction Welding Process (IMP) Principles:

Friction Welding (FRW) is a solid state welding process which produces welds due to the

compressive force contact of workpieces which are either rotating or moving relative to one

another. Heat is produced due to the friction which displaces material plastically from the

contact surfaces.In friction welding the heat required to produce the joint is generated by

friction heating at the interface. The components to be joined are first prepared to have

smooth, square cut surfaces. One piece is held stationary while the other is mounted in a

motor driven chuck or collet and rotated against it at high speed. A low contact pressure may

be applied initially to permit cleaning of the surfaces by a burnishing action. This pressure is

then increased and contacting friction quickly generates enough heat to raise the abutting

surfaces to the welding temperature. As soon as this temperature is reached, rotation is

stopped and the pressure is maintained or increased to complete the weld. The softened

material is squeezed out to form a flash. A forged structure is formed in the joint. If desired,

the flash can be removed by subsequent machining action. Friction welding has been used to

join steel bars upto 100 mms in diameter and tubes with outer diameter upto 100 mm.

Inertia Friction Welding

The energy for frictional heating is supplied by the kinetic energy of a flywheel

The flywheel is accelerated to the correct speed and disconnected from the drive

Spinning and stationary components are then brought together and an axial force is

applied

Friction slows the flywheel and heats the surface - the axial force is then increased

The process is complete when the flywheel comes to a stop.

Types of Friction Welding

Spin Welding:

-A rotating chuck along with flywheel.

-After reaching to required speed motor is removed form flywheel.

Linear Friction Welding:

-Oscillating Chuck is used.

-Use for non-round shapes as compare to Spin welding.

-Material should be of high shear strength.

9.b) Explain the process of Ultra sonic welding. Give its advantages & application.

Ultrasonic Welding (USW): Ultrasonic welding is an industrial technique whereby high frequency ultrasonic acoustic

vibrations are locally applied to work pieces being held together under pressure to create a

solid-state weld. Although there is some increase in temperature at the contact surfaces, they

generally do not exceed one-half of the melting point of the material. Instead, it appears that

the rapid reversals of stress along the contact interface facilitates the coalescence by breaking

up and dispersing the oxide films and surface contaminants, allowing clean material to form a

high strength bond.

MAIN PARTS

TRANSDUCER

It Produces high frequency ultrasonic vibrations.

CONVERTOR

Converts the electrical signal into a mechanical vibration

BOOSTER

It Modifies the amplitude of vibrations

SONOTRODE

It Applies the mechanical vibrations to the parts to be welded

ANVIL

It Used for holding overlapping plates.

Ultrasonic Welding Mechanism

The parts are placed between a fixed shaped nest (anvil) and a sonotrode(horn) connected to a

transducer, and a ~20KHz low-amplitude acoustic vibration is emitted.

A static clamping force is applied perpendicular to the interface between the work

pieces.

Solid

State

Welding

Electrical

Chemical

Mechanical

Friction

PressureUltrosonic

Weld

The contacting sonotrode oscillates on the interface.

Combined effect of static and oscillating force produces deformation which promotes

welding.

Principle of Ultrasonic Welding

In US welding, frictional heat produced by the ultrasonic waves and force is used for

joining process.

US waves(15to60 kHz) are transferred to the material under pressure with a

sonotrode.

It can proceed with or without the application of external heat.

Types of US welding

Spot Welding

Line Welding

- Uses Linear Sonotrode

Continuous Seam Welding

- Uses Roller Sonotrode

Advantages

No heat is applied and no melting occurs

Permits welding of thin to thick sections

Welding can be made through some surface coatings

Dissimilar metals having vastly different melting points can be joined

Pressures used are lower, welding times are shorter, and the thickness of deformed

regions are thinner than for cold welding

Limitations

This process is limited to small welds of thin, malleable metals Eg: Aluminium,

Copper, Nickel

Competitively not economical

Process is limited to lap joints.

Butt welds can not be made because there is no means of supporting the work pieces

and applying clamping force.

Due to fatigue loading the life of equipment is short.

10.a) Explain the Economics and application of non-traditional welding process.

Welding and joining are essential for the manufacture of a range of engineering

components,which may vary from very large structures such as ships and bridges, to very

complex structuressuch as aircraft engines or miniature components for micro-electronic

applications.

Joining processes

The basic joining processes may be subdivided into:

mechanical joining;

adhesive bonding;

brazing and soldering;

welding.A large number of joining techniques are available and, in recent years, significant

development shave taken place, particularly in the adhesive bonding and welding areas.

Existing

welding processes have been improved and new methods of joining have been introduced. Th

e proliferationof techniques which have resulted makes process selection difficult

and may limit their effective exploitation. The aim of this book is to provide an objective

assessment of the most recent developments in welding process technology in an attempt to

ensure that the most appropriate welding process is selected for a given application.This

chapter will introduce some of the basic concepts which need to be considered and highlight

some of the features of traditional welding methods.

Classification of welding processes

Several alternative definitions are used to describe a weld, for example:A union between two

pieces of metal rendered plastic or liquid by heat or pressure or both. Afiller metal with a

melting temperature of the same order as that of the parent metal may or may not be used, or

alternatively:A localized coalescence of metals or non-metals produced either by heating the

materials to thewelding temperature, with or without the application of pressure, or by the

application of pressure alone, with or without the use of a filler metal.Many different

processes have been developed.

10.b ) Differentiate between solid phase welding with Arc welding. Write about recant development in friction welding.

Fusion welding Solid-state welding

Faying surfaces of base metal are fused to form coalescence. Filler metal, if used, is also fused.

No such melting takes place. However the base metal may be heated to an elevated temperature but below its melting point.

Heat must be applied for welding. Heat can be supplied by various means such as electric arc, fuel-gas flame, resistance heating, laser beam, etc.

No external heat source is required but pressure may be applied externally for welding.

Filler material can be applied easily. Usually no filler is applied.

Because of melting, palpable HAZ (heat affected zone) exists in the welded components.

HAZ is usually not noticeable.

Mechanical properties of parent materials are affected by intense heating.

Mechanical properties usually remain unaltered.

Dissimilar metal joining by fusion welding is challenging task, especially if the duo have substantially different melting point and coefficient of thermal expansion.

Joining dissimilar metal is comparatively easier as processes don’t involve melting and solidification.

Level of distortion is very high with fusion welding.

Solid-state welding causes minimal distortion.

Joint design and edge preparation are not crucial. These parameters mainly influence achievable penetration.

It requires special type of joint design and edge preparation. In few cases, very smooth surfaces are required.

Examples of fusion welding processes:

Arc welding (SMAW, GMAW, TIG, SAW, FCAW, ESW, etc.)

Gas welding (AAW, OAW, OHW, PGW)

Resistance welding (RSW, RSEW, PW, PEW, FW, etc.)

Intense energy beam welding (PAW, EBW, LBW)

Examples of solid-state welding processes:

Cold Welding (CW) Roll Welding (ROW) Pressure Welding (PW) Diffusion Welding (DFW) Friction Welding (FRW) Friction Stir Welding (FSW) Forge Welding (FOW), etc.

11.a) Explain with neat sketch ceramic shell casting, write its application. 6

Ceramic Shell Investment Casting Process (CSIC)

Ceramic Shell Investment Casting (CSIC) is one of the near net shape casting technologies.

The main difference between investment casting and ceramic shell investment casting is that,

in the investment casting process, before de-waxing the wax pattern, it is immersed in a

refractory aggregate. Whereas in the ceramic shell investment casting, a ceramic shell gets

built around the tree assembly through repeated dipping of the pattern into slurry (refractory

material such as zircon with binder). After getting the required thickness of cross section, the

tree assembly is de-waxed. The shell obtained is further immersed in a refractory coating and

the metal is poured into it.

In this process, a wax pattern/assembly is first dipped into a ceramic slurry bath for its

primary coating. Thereafter, the pattern is withdrawn from the slurry and is manipulated to

drain of the excess slurry to produce a uniform coating layer. The wet layer further stuccoes

through sprinkling the relatively coarse ceramic particles on it or by immersing it into such

fluidized bed of particles. The ceramic coating is built by successive dipping and stuccoing

process. This procedure is further repeated till the shell thickness as desired is obtained. Upon

completion, the entire assembly is placed into an autoclave or flash fire furnace at a high

temperature. In-order to burnout out any residual wax, the shell is heated to about 982oC

which helps to develop a bonding of high-temperature in shell. Such molds are stored for

future use wherein they are preheated for removing the moisture content from it and then,

molten metal can be poured into it.

Steps:

1. Manufacturing of the master pattern of wax through the master dies.

2. Preparation of wax blend and injecting it into the die.

3. Manufacture of wax pattern and assembly of wax pattern

4. Investment of wax with slurry (coating the slurry)

5. Drying of shell thickness (stuccoing)

6. De-waxing of raw moulds followed by heating and baking of the shells

7. Pouring of moulds with molten metal

8. Once the metal is solidifed, the shells are removed.

9. Cuting off the gates / risers (fettling) followed by finishing operations

Advantages

Complex shapes that are difficult to produce by other casting methods are very easily

possible to be produced by this method.

Thin cross sections and intricacies can be made by this process.

Finish machining is considerably reduced or eliminated on the castings made by this

process, making it economical in cost.

The process has no metallurgical limitations.

This process produces castings with excellent surface finish.

Disadvantages

Expensive process due to the cost of ceramics and pattern (wax cost).

As the shells are delicate, the process is limited by the size and mass obtained.

Making intricate and high quality pattern increases the process costs.

Applications

Aircraft: Turbine blades; carburetor and fuel-pump parts; cams; jet nozzles;

special alloy valves.

Chemical Industries: Impellors; pipe fittings; evaporators; mixers

Tool and Die: Milling cutters; lathe bits; forming dies; stamping dies; permanent molds

General and Industrial applications: cloth cutters, sewing machine parts; welding torches;

cutter, spray nozzles; metal pumps; etc

Steps of producing ceramic shell investment casting

11.b)Write with neat sketch centrifugal casting with its advantages &

limitations.

Centrifugal casting

Centrifugal casting uses a permanent mold that is rotated about its axis at a speed between

300 to 3000 rpm as the molten metal is poured. Centrifugal forces cause the metal to be

pushed out towards the mold walls, where it solidifies after cooling. Parts cast in this method

have a fine grain microstructure, which is resistant to atmospheric corrosion; hence this

method has been used to manufacture pipes. Since metal is heavier than impurities, most of

the impurities and inclusions are closer to the inner diameter and can be machined away.

surface finish along the inner diameter is also much worse than along the outer surface.

As the name implies, the centrifugal-casting process utilizes the inertial forces caused by

rotation to distribute the molten metal into the mold cavities.

First suggested in the early 1800s.

There are three types of centrifugal casting: True centrifugal, semi-centrifugal, and

centrifuging casting.

12.a)What do you mean by evaporative pattern casting? Explain the process with the neat sketch. Also write its applications

Evaporative Pattern Casting Process

The Evaporative Pattern Casting Process is also known by several other names such

as Full Mold Process, Lost Foam Process etc.

Sometimes reffered to as expendable mold-expendable pattern processes

In this process, a pattern used refers to an expandable polystyrene or foamed

polystyrene part which gets vaporized by the molten metal. For every casting process,

a new pattern is required.

Typical applications arte cylinder heads, engine blocks, crankshafts, brake

components, and machine bases.

This process has become one of the more important casting process for ferrous and

nonferrous metals, particularly for the automotive industry.

This process uses a polystyrene pattern, which evaporates upon contact with molten

metal to form a cavity for the casting (lost-foam casting).

In this process:

a) Raw expendable polystyrene (EPS) beads, containing 5% to 8% pentane (a volatile

hydrocarbon), are placed in a preheated die which is usually made of aluminum.

b) The polystyrene expands and takes the shape of the die cavity. Additional heat is applied

to fuse and bond the beads together.

c) The die is then cooled and opened, and the polystyrene pattern is removed.

d) The pattern is coated with water-based refractory slurry, dried, and placed in a flask.

e) The flask then is filled with loose fine sand, which surrounds and supports the pattern

and may be dried or mixed with bonding agents to give it additional strength.

f) The sand is periodically compacted by various means.

g) Without removing the polystyrene pattern, the molten metal is poured into the mold. This

action immediately vaporizes the pattern and fills the mold cavity, completely

replacing the space previously occupied by the polystyrene pattern. The heat degrades

the polystyrene, and the degradation products are vented into the surrounding sand.

Schematic illustration of the expendable pattern casting process, also known as lost foam or

evaporative casting

12.b) Explain the process of continuous casting with its limitations.

Continuous casting Continuous casting process is widely used in the steel industry. In principle,

continuous casting is different from the other casting processes in the fact that there is no

enclosed mold cavity. Figure 3.2.10 schematically shows a set-up for continuous casting

process. Molten steel coming out from the furnace is accumulated in a ladle. After

undergoing requisite ladle treatments, such as alloying and degassing, and arriving at the

correct temperature, the ladle is transported to the top of the continuous casting set-up. From

the ladle, the hot metal is transferred via a refractory shroud (pipe) to a holding bath called a

tundish. The tundish allows a reservoir of metal to feed the casting machine. Metal is then

allowed to pass through a open base copper mold. The mold is water-cooled to solidify the

hot metal directly in contact with it and removed from the other side of the mold. The

continuous casting process is used for casting metal directly into billets or other similar

shapes that can be used for rolling. The process involves continuously pouring molten metal

into a externally chilled copper mold or die walls and hence, can be easily automated for

large size production. Since the molten metal solidifies from the die wall and in a soft state as

it comes out of the die wall such that the same can be directly guided into the rolling mill or

can be sheared into a selected size of billets.