paper solution of advanced manufacturing techniques · 2019-04-05 · ultrasonic machining and in...
TRANSCRIPT
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.