Part A

1. How are cores classified based on their material?

Ans.:
Sand cores
Green sand cores.
Dry sand cores.
Core sand cores.
Chill cores.
2. List the factors to be considered in selecting a material for the pattern.
Ans.:
(1) Number of castings to be produced
(2) Shape, complexity and size of the casting
(3) Degree of accuracy and surface finish required.
(4) Design of casting, (5) Casting method to be used.
3. What is meant by grain texture?
Ans.:
Grain texture implies grain shape, average grain size and grain size distribution.
4. What is core and its requirement?
Ans.:
Core:
It a device used in casting and molding processes to produce internal cavities
Core Prints:
It is an added projection on the pattern and it forms a seat in the mold on which
the sand core rests during pouring of the mold.
Core Chaplets:
Additional support provided at the mold cavity.
5. How we are classifying the moulding machines?
Ans.:
Hand operated moulding machine
i. Pattern draw type
ii. Pin lift type
iii.
Roll over type

 Power operated moulding machine

(i)
Squeeze machine
(ii)
Jolt machine
(iii)
Jolt squeeze machine
(iv)
Sand slinger
6. Define the term electrode and mention its major classification?
An electrode is a piece of wire or a rod (or a metal or alloy), with or without flux
covering, which carries current for welding. At one end it is gripped in a holder and an
arc is set up at the other.
It is classified as follows:
Non-consumable (refractory)
Consumable (Metallic)
7. Differentiate between soldering and brazing?
S.No

Soldering

Brazing

.
It is a metal joining process in which the It employs filler metals having melting
1.

joint is made with the application of temperature above 450C but below the
filler metal having melting point less melting temperature of the base metal.
than 450C.
The solders are alloys of lead and tin in The filler metals commonly used in

2.

varying proportions having melting point brazing include copper and copper
between 180C to 320C

alloys, silver alloys and aluminium

alloys.
8. What are the advantages of AC equipment over DC equipment in arc welding
DC supply:
DC supply is more stable because of its unidirectional flow of current.
Straight and reverse polarities can be employed to advantage.
All ferrous and non-ferrous metals can be welded.
Diesel driven generator forms a self-contained unit.
Welding can be carried out in all positions.
AC supply
Theoretically current passes through zero value twice in each cycle. Unless power
source is specially designed for this, arc is extinguished twice in each cycle leading to
discontinuous welding.

The phenomenon of arc blow is not there with AC supply.

AC transformer system leads to lower power cost, low equipment cost and easy
maintenance due to absence of moving parts.

9. Mention the applications of friction welding?

Friction welding is used extensively in aviation and automobile industries.
10. What is application of carburizing flame?
Carburizing flame is used for welding of monel metal, nickel, certain alloy steels and

many of the non-ferrous hard surfacing materials like stellite.

The carburizing nature of the flame is taken advantage in welding of low carbon steels.

Part B
11. A.

(i). Discuss the properties of moulding sand.

(8)

(ii). What are the various moulding methods, explain them.

(8)

(OR)
11. B.
12. A.

(i). Explain the working principle of investment casting.

(8)

(ii). Discuss the casting defects and their inspection methods.

(8)

(i).What are the pattern making allowances and briefly explain them.

(8)

(ii). Describe centrifugal casting process.

(8)

(OR)
12. B.

(i).Describe the shell moulding process.

(8)

(ii). Explain the ceramic moulding process and state its merits and demerits.(8)
13. A.

(i). What are the factors which govern the selection of a proper material for

pattern making.

(8)

(ii). What are the specific advantages of match plate patterns? Explain how they
are used for making mould.

(8)
(OR)

13. B.

14. A.

(i). Distinguish between gas and arc welding.

(8)

(ii). What are the advantages of welding.

(4)

(iii). Explain percussion welding.

(4)

(i). Describe Electro slag welding.

(8)

(ii). Distinguish between soldering and brazing.

(8)

14. B.
15. A.
15. B.

(i). Explain spot welding.

(8)

(ii). Explain submerged are welding.

(8)

(i). Explain the electron beam welding process with a neat sketch.

(8)

(ii). Write a brief note on Welding defects .

(8)

(i). Sketch the three types of Oxy-acetylene flames and state their characteristics

and applications.
(ii). Describe the electro-slag welding process with a neat sketch.

(8)
(8)

Part A
1. What is meant by the gating system of mould?
Ans.:

The term gating system refers to all passage ways through which the molten metal

passes to enter the mould cavity.

A typical gating system consists of a pouring basin, a sprue, gates and the riser.
Sometimes a runner may also be provided for distributing the metal to several gates

around the cavity.

2. List the factors to be considered in selecting a material for the pattern.
Ans.:
(1) Number of castings to be produced
(2) Shape, complexity and size of the casting
(3) Degree of accuracy and surface finish required.
(4) Design of casting, (5) Casting method to be used.
3. Explain the term fettling?
Ans.:
Fettling is cleaning of metal casting. It involves
a) Removal of dry sand cores
b) Removal of gates and risers
c) Removal of unwanted metal projection and fins
d) Removal of adhered sand and oxide scale
1. Wire brushing
2. Tumbling
3. Sand blasting

4. Shot Blasting
5. Hydro blasting, 6. Pickling
4. Write a note on chilled casting?
Ans.:
The chills are used to provide directional solidification or to increase the rate of
solidification where the high hardness is required. Carbon becomes iron carbide to make
soft and highly malleable metal.
5. Merits and demerits of investment casting?
Ans.:
Advantage:
a) Good dimensional accuracy
b) Relatively inexpensive mold
c) Rapid production rates possible
d) Complex shapes
Disadvantage:
a. Long production cycle
b. Mold is not reusable
c. Many processing steps are required
6. Write down the types of flames?
The flames are classified into three categories namely;
(1)Balanced or neutral flame
(2) Reducing or carburizing flame
(3) Oxidizing flame
7. What do you mean by friction welding?
Friction welding is a solid state welding process in which the heat for welding is
obtained by friction between the ends of the parts to be joined. One of the parts to be
welded is rotated at about 3000rpm with the other part aligned with it.
8. Write short notes on diffusion welding?
Diffusion welding is the process of joining parts purely by diffusion. Diffusion is
achieved by holding the parts to be jointed in intimate contact under a pressure of 5 to
75 N/mm2 and temperature about 1000 C for steel.
9. Write short notes on transferred and non-transferred arc in plasma arc welding?

In the transferred mode, current is transferred from the tungsten electrode through the
orifice to the work piece and back to the power supply. This mode is most commonly
used for welding.
In the non-transferred mode, current flow is from the electrode to the nozzle containing
the orifice and back to power supply. This mode is used for plasma spraying or for very
low current applications as in non-metals.
10. What is the purpose of flux in welding?
Fluxes react with oxides present in the metal or formed during welding to produce

slags.
Oxides interfere with welding of many metals. If not removed, they may get entrapped

in the weld producing weak joints.

The slags formed with fluxes are more fluid and have lower melting point. They easily
float out to the surface of the weld metal from where they can be removed after
solidification.
The molten slag layer on top the weld metal also helps prevent contamination of the

molten weld metal from atmospheric oxygen, nitrogen and other gases.
Part - B

11. A.
11. B.

(i). Classify the types of patterns and sketch any three of them.

(8)

(ii). What is core and explain how to make a core.

(8)

(i). Explain the construction and operation of Cupola furnace with diagram.(8)
(ii). Write a short note on Chills .

(8)
(OR)

12. A .

(i). Describe various materials used for making patterns. What are its merits and

demerits
(ii). What are the basic requirements of core sand? How does it differ from the
moulding sand.
12. B.

(8)

(i). What are the different types of furnace used in foundry? Describe in detail

with neat sketches any one of them.

(8)

(ii). Describe the steps involved in the preparation of green sand mould with cope
and drag pattern.
13. A.
13. B.

(i). Briefly explain cold-chamber die casting process with a neat sketch.

(8)

(ii). What are the advantages of centrifugal casting.

(8)

(i). What is the principle of resistance welding and explain the seam welding. (8)
(ii). Describe plasma arc welding .

14. A.

15. A.

(8)

(i). What are the different types of electrode? What are the functions of flux

coating.
14. B.

(8)

(8)

(ii). What is the principle of friction welding.

(8)

( i). Describe metal inert Gas arc welding process with a neat sketch.

(8)

(ii). Briefly explain on butt welding process .

(8)

(i). Give a brief account of classification of welding processes.

(8)

(ii). Explain TIG welding process variables and enumerate its advantages . (8)
15. B.

(i). Describe shielded metal arc welding process with suitable diagram. What are

its applications.

(8)

(ii). What is the difference between welding, brazing and soldering process.

(8)

13. B.(i). Briefly explain the working principle of plasma arc welding process and
mention their applications?
(10)
Plasma arc welding in arc welding process wherein coalescence is produced by the heat
obtained from a constricted arc set up between a tungsten/alloy tungsten electrode and the
water cooled nozzle or between a tungsten/alloy tungsten electrode and the job
(transferred arc).The process employs two inert gases,one forms the arc plasma and the
second shields the arc plasma.

a) Non- transferred arc process

The arc is formed between the electrode (-)and the water cooled constricting
nozzle(+).Arc plasma comes out of the nozzle as a flame.
The arc is independent of the work piece and the work piece does not form a part
of the electrical circuit. Just as an arc flame, it can be moved from one place to another
and can be better controlled.
The non transferred arc plasma possesses comparatively less energy density as
compared to transferred arc plasma and it is employed for welding and in applications
involving ceramics or metal plating
b) Transferred arc process
The arc is formed between the electrode (-) and the work piece (+). In other
words, arc is transferred from the electrode to the work piece. A transferred arc process
high energy density and plasma jet velocity. For this reason it is employed to cut and melt
metals. Transferred arc can also be used for welding at high arc travel speeds.
Equipment
1. Power supply
2. High frequency generator and current limiting resistors
3. Plasma torch
4. Shielding gases
5. Voltage control
6. Current and gas decay control
7. Fixture
Advantages
1.
2.
3.
4.
5.

Stability of arc
Uniform penetration
Simplified fixtures
Rewelding of the root of the joint saved
It is possible to produce fully penetrated keyhold welds on pieces upto and about
6mm thick with square but joint
6. Excellent weld quality
7. Plasma arc welding can produce radiographic quality welds at high speeds
Disadvantages
1.
2.
3.
4.

Infra-red and ultraviolet radiations necessitate special protection devices

Welders need ear plugs because of unpleasant, disturbing and damaging noise
More chances of electrical hazards are associated with this process
The process is limited to metal thickness of 25 mm and lower for butt welds

(ii). What are the advantages of friction welding process?

(6)
a) Simplicity of operation
b) Low power requirements
c) Once the welding parameters for a job have been determined, the welding takes
only a few seconds
d) Surface impurities and oxide films are broken up and thrown off during the
friction heating process.

14. A.(i).Briefly explain the working principle of electro gas welding process and
mention their applications?
(10)
Electrogas welding is very much similar to electroslag welding except that on inert gas
such as carbon-dioxide is used to shield the weld from oxidation and there is a continuous arc as

in the case of submerged arc welding to provide the heat for heating the weld pool.
Again the flux instead of being supplied to the weld zone through a hopper is
incorporated in electrode itself in the form of flux cored electrodes, or sometimes the process
may be carried out without using the flux in which case there is no flux covering on the top of
the molten metal pool.
Electrogas welding process can be used for welding low and medium carbon steels, alloy
steels and austhentic stainless steels.
Plates from 12.5 to 75mm thick can easily be welded by this process. For thicker plates it
is preferable to use electroslag welding instead of electrogas welding because it may be difficult
to obtain adequate shielding gas coverage with the later process.
In the thickness range in which electrogas welding is applicable this process has the
following advantages over electroslag welding:
1. Weld is better visible to the operator.
2. Restarting the weld is quicker.
3. Welded joints have better mechanical properties such as impact strength.
Electroslag welding however suffers from the disadvantages that the welds produced are not as
clean and crack free as those produced by electroslag welding and also have more porosity
particularly for the thicker jobs.
(ii). What are the functions of flux coating?

(6)

Fluxes are used in welding to remove the oxide film and to maintain a clean surface.
Unless removed by fluxing such oxides cause poor quality welds or in some cases, even
make welding impossible. The flux melts at the melting point of base metal. It reacts with
oxides of the base metal formed during welding to form slags with melting temperature
and density lower than that of the molten metal so that they float on the top of the heavier
molten metal pool.
After the weld has cooled, the solidified slag deposited on the top of the weld can be
removed by slightly hammering the weld.
Among the commonly used metals which require fluxing for good results are cast iron,
stainless steel, brass, bronze and aluminium.
Carbon steels do not require any fluxing because the silicon and manganese present in
these steels act as deoxidizing and fluxing agents.
The flux used may be either acidic or basic depending on the nature of the oxides
formed in welding. If the oxides present in the puddle are mainly basic on acidic flux
should be used and vice versa.
Nonferrous metals especially copper and copper base alloys arc welded with acidic
fluxes such a boron compounds. The common examples are borax (boric acid) and their
mixtures.

14. B. With a neat sketch briefly explain the thermit welding process.(6)(MAY/JUN-09)
Thermit welding comprises a group of welding processes wherein coalescence is
produced by heating with superheated liquid metal and slag resulting from chemical reaction
between and metal oxide and aluminium, with or without the application of pressure. The liquid
metal acts as filler metal too.
Procedure of thermit welding
The mold is non-repetitive in nature and is used for repair welds.
1. Clean the joint
An oxyacetylene torch may be used to clean the metal surfaces by heating. During
cleaning,all dirt ,grease, loose oxides, scale etc., must be removed.
2. Allow for contraction
After cleaning, the part to be welded arc to be lined up with a space of
About 1.5 to 6 mm between the ends, depending upon the size of the parts to be joined.
This space makes up for
i.
ii.

The contraction of the thermit steel in cooling.

The shrinkage of the base metal which has been heated during the welding
operation.
3. Construct the mold

After the parts have been cleaned and spaced properly, the next stage is the
making of the wax pattern from which the mould will be formed and which must in shape
constituted a replica of the eventual weld
The molding material should be about 100 mm thick between the wax patterns
and themolding box at all points.
The mold should be provided with the necessary number of pouring gates,heating
gates and risers depending on the size of the weld.
4. Preheating the mold
The mold prepared as above is then preheated in order to:
i. Melt away and remove the wax thereby leaving a mold cavity in the
Exact shape of the weld
ii. Dry the mold thoroughly otherwise the superheated molten metal will
Form steam within the mold and cause porous weld.

5. Crucible and its charging

Thermit mixture is charged in the container known as crucible or reaction vessel.

This vessel is a magnesia shape and is lined with magnesia tar-lining.
The outside shell of this vessel is made up of sheet steel. Located at the bottom of
the vessel is a magnesia stone and magnesia thimble through which the tapping pin is
suspended.
The thimble is plugged by suspending the tapping pin through the thimble and
placing a metal disc above the pin. This disc is then covered with refractory sand.
After drying the crucible, a small quantity of the thermit powder is first
introduced, the object being to avoid damage to the refractory sand layer and to cushion
off the plugging material in the bottom of the crucible from the impact of the full weight
of the thermit charge.
6. Igniting the thermit mixture
A low ignition point thermit in the form of a powder is placed on the top of the
thermit in the crucible.
To initiate the reaction, the low ignition-temperature thermit is contacted with a
hot rod. This ignition immediately starts the reaction in the main thermit charge.
7. Opening the mold
The actual period for which the mold is left unopened depends upon the
dimensions of the weld, being shorter (two or three hours) for small sections and longer
(about four hours) for heavy sections. The longer the mould can be left unopened, the
better it in.
8. Finishing the weld
After removing the mold, the risers and gates arc cut away with a cutting
torch. In case of shafts or parts requiring specific finished contour the same can be given
by either machining or grinding.
15. A. Briefly explain the electron beam welding process and write its applications and
de merits?
(16)
Electron beam welding is defined as a fusion welding process wherein
coalescence is produced by the heat obtained from a concentrated beam composed primarily
of high velocity electrons.
As the velocity electrons strike the surfaces to be joined, their kinetic energy
changes to thermal energy thereby causing the workpiece metal to melt and fuse.
Electron beam welding equipment
Electron beam welding equipment includes the following sub system:
a) An electron beam gun with a high voltage power supply and controls
(From 5 to 150 KV)
b) A vacuum pumping system
c) Mechanical tooling-fixtures, drives and motor controls, and
d) A beam-alignment system, including optics, scanner, tape control and tracker

1) An electron beam gun consist

Tungsten

Anode
Focusing oil

of a
filament
Cathode (control) electrode

When
in
emits
The electrons
the heated filament

tungsten filament is electrically heated

vacuum to approximately 20000 C, it
electrons
emitted from
carry a
negative charge, are
repelled by the

cathode(control) electrode
and
are made to pass through
the central hole of the anode.
The cathode electrode (-) and the anode (+) electrode concentrate and propel the
electrons. The electrons are not free flowing but are instead greatly accelerated by the
tremendous difference of potential, voltage between the cathode and anode.
The electron beam is then focused by means of an electromagnetic focusing coiled
(lens). The focusing coil concentrates or spreads the electron beam of the users
needs.
Thus concentrated electron beam and focused on to the workpiece in a spot from
0.75 to 3 mm in diameter when strikes the workpiece, the kinetic energy of the
electrons changed into heat that is great enough to melt the workpiece material. The
greater the kinetic energy, the greater is the amount of heart released.
The power source furnished the main high voltage supply upto 150KV and a low
filament power upto 6 volts
2) Vacuum pumping system
The vacuum chamber is usually rectangular in shape, has heavy glass windows to
permit viewing the work while the welding is in progress.
Vacuum pumping system evacuates the interior of
a) Electron gun
b) Work chamber
When electron gun is evacuated.
a) Electrons are emitted at a low filament temperature
b) It eliminates air or metal vapour molecules from within the gun
c) Electron beam does not lose energy within the gun by being scattered or
absorbed by molecules of air or metal vapour.
Process variable

 Small thon parts can be welded to heavy sections.

Edge and butt welds can be made in metals as thin 0.025 mm
Disadvantages of electron beam welding
Initial cost of equipment is high and portable equipment is rare.
Work is to be manipulated through vacuum seals.
Time and equipment is required to create vacuum very time a new job is to be
welded
Precautions are needed to prevent damage from X-rays
Electron beam travels on a line of sight, therefore obstructed joints cannot be
welded.
15. B. Briefly explain the laser beam welding process and write their applications and
demerits
(16)
Laser beam welding is defined as a welding process wherein coalescence is produced
by the heat obtained from the application of a concentrated coherent light beam
impinging upon the surfaces to be joined.
Laser welding system consist of
a) A man-made cylindrical ruby crystal. Ruby is aluminium oxide with chromium
dispersed throughout it, forming about 1/2000 of the crystal which is less than a
natural ruby contains.
b) Around the outside of the crystal is placed flash tube containing inert gas xenon.
The flash tube is designed for operation of a rate of thousands of flashes per
second.
c) The capacitor bank (storage) stores electrical energy. It is charged by high
voltage power supply, it energies the flash tube by an appropriate triggering
systems.
When subjected to electrical discharge from the capacitors, Xenon transforms a
high proportion of the electrical energy into white light flashes.
As the ruby is exposed to the intense light flashes, the chromium atoms of the
crystal are excited and pumped to a high energy level.
These chromium atoms immediately drop to an intermediate energy level with the
evolution of heat, and eventually drop back to their original state with the evolution of
discrete quantity of radiation in the form of red fluorescent light.
As the red light emitted by one excited atom his another excited atom, the second
atom gives off red light which is in phase with the colliding red light wave.

The effect is enhanced because the parallel ends of ruby rod are mirrored so that the red
light that is produced reflects back and forth along the length of the crystal.
This narrow laser beam is focused by an optical focusing lens to produce a small intense
spot of laser (light) on the job.
Optical energy as it impacts the workpiece is converted into heat energy.
The temperatures generated can be made sufficient to melt (and vaporize) the materials to
be welded or cut.
Advantages of laser beam welding

Welds can be made inside transparent glass or plastic housings.

A wide variety of materials can be welded, including some formerly considered as

unweldablecombinations.
As no electrode is used, electrode contamination or high electric current effects

are eliminated.
Areas not readily accessible can also be welded
Laser beam welding being highly concentrated and narrowly defined produces
narrow size of the heat affected zone.

Disadvantages of laser beam welding

Laser welding is limited to depths of approximately 1.5 mm and additional energy

only tends to create gas voids and undercuts in the work.

Materials such as magnesium tend to vaporize and produce severe surface voids.
13. B.(i). Explain the Metal Inert Gas (MIG) welding process with neat sketch and its process
capabilities?

(8)

Although GAS-METAL-ARC (GMA) is the official description of this welding method.

The earlier name of metal inert gas (MIG) is still widely used, especially in the shops.
Gas-metal-arc welding is a gas shielded metal arc welding process which uses the high
heat of an electric are between a continuously fed, consumable electrode wire and the material to
be welded. Metal is transferred through protected arc column to the work.
In this process, the wire is fed continuously from a reel through a gun to constant surface
which imparts a current upon the wire. A fixed relationship exists between the rate of wire burn-

off and the welding current so that the welding machine at a given wire feed rate will produce
necessary current to maintain the arc. The current ranges from 100 to 400 A depending upon the
diameter of the wire, and the speed of melting of the wire may be upto 5m/min. The welding
machine is DC constant voltage, with both straight and reversed polarities available.

The welding gun can be either air or water cooled depending upon the current being used.
With the higher amperages, a water cooled gun is used. The welding wire is very often bare. Very
lightly coated or flux-cored wire is also used. The wire is usually in diameters of 0.09 to 1.6mm,
however, sizes upto 3.2mm, are made.
In gas-metal-arc welding, the welding area is flooded with a gas (an inert gas) which will
not combine with the metal. The rate of flow of this gas is sufficient to keep oxygen of the air
away from the hot working with steel, as GMA is a clean, faster method welding steel. Carbon
dioxide is used principally because it is inexpensive. For welding aluminium or copper, argon or
argon-helium mixtures are used. For stainless-steel, MIG welding is done with either argonoxygen or helium-argon gas mixtures. Titanium requires pure argon gas shielding, and the
copper-nickel and high-nickel alloys use argon-helium mixture.
Advantages of this process:

1. No flux required.
2. High welding speed.
3. Increased corrosion resistance.
4. Easily automated welding.
5. Welds all metals including aluminium and stainless-steel.
6. High economic.
(ii). Explain with a neat sketch the equipment and process of submerged arc welding? (8)

The first patent on the submerged-arc welding (SAW) process was taken out in
1935 and covered an electric arc beneath a bed of granulated flux. Developed by the E O Paton
Electric Welding Institute, Russia, during the Second World War, SAW's most famous application
was on the T34 tank.
Process features
Similar to MIG welding, SAW involves formation of an arc between a continuously fed
bare wire electrode and the work piece. The process uses a flux to generate protective gases and
slag, and to add alloying elements to the weld pool. A shielding gas is not required. Prior to
welding, a thin layer of flux powder is placed on the work piece surface.

The arc moves along the joint line and as it does so, excess flux is recycled via a hopper.
Remaining fused slag layers can be easily removed after welding. As the arc is completely
covered by the flux layer, heat loss is extremely low. This produces a thermal efficiency as high
as 60% (compared with 25% for manual metal arc). There is no visible arc light, welding is
spatter-free and there is no need for fume extraction.
Operating characteristics
SAW is usually operated as a fully mechanized or automatic process, but it can be semiautomatic. Welding parameters: current, arc voltage and travel speed all affect bead shape, depth
of penetration and chemical composition of the deposited weld metal. Because the operator
cannot see the weld pool, greater reliance must be placed on parameter settings.
Process variants
According to material thickness, joint type and size of component, varying the following
can increase deposition rate and improve bead shape.
Wire
SAW is normally operated with a single wire on either AC or DC current. Common variants
are:

Twin wire

Multiple wire (tandem or triple)

Single wire with hot or cold wire addition

Metal powder addition

Tubular wire

All contribute to improved productivity through a marked increase in weld metal deposition
rates and/or travel speeds.
A narrow gap process variant is also established, which utilizes a two or three bead per layer
deposition technique.
Flux
Fluxes used in SAW are granular fusible minerals containing oxides of manganese, silicon,
titanium, Aluminium, calcium, zirconium, magnesium and other compounds such as calcium

fluoride. The flux is specially formulated to be compatible with a given electrode wire type so
that the combination of flux and wire yields desired mechanical properties. All fluxes react with
the weld pool to produce the weld metal chemical composition and mechanical properties. It is
common practice to refer to fluxes as 'active' if they add manganese and silicon to the weld; the
arc voltage and the welding current level influence the amount of manganese and silicon added.
The main types of flux for SAW are:

Bonded fluxes - produced by drying the ingredients, then bonding them with a low
melting point compound such as a sodium silicate. Most bonded fluxes contain metallic
deoxidizes which help to prevent weld porosity. These fluxes are effective over rust and
mill scale.

Fused fluxes - produced by mixing the ingredients, then melting them in an electric
furnace to form a chemically homogeneous product, cooled and ground to the required
particle size. Smooth stable arcs, with welding currents up to 2000A and consistent weld
metal properties, are the main attraction of these fluxes.

Applications
SAW is ideally suited for longitudinal and circumferential butt and fillet welds. However,
because of high fluidity of the weld pool, molten slag and loose flux layer, welding is generally
carried out on butt joints in the flat position and fillet joints in both the flat and horizontalvertical positions. For circumferential joints, the workpiece is rotated under a fixed welding head
with welding taking place in the flat position.

Depending on material thickness, either single-pass, two-pass or multipass weld

procedures can be carried out. There is virtually no restriction on the material thickness, provided
a suitable joint preparation is adopted. Most commonly welded materials are carbon-manganese
steels, low alloy steels and stainless steels, although the process is capable of welding some nonferrous materials with judicious choice of electrode filler wire and flux combinations.

14. A. Explain the following welding process with neat sketch.

a) Resistance seam welding
b) Friction stir welding

(16)

a) Resistance seam welding:

The seam welding is similar to spot welding, except that circular rolling electrodes are
used to produce a continuous air- tight seam of overlapping welds. Overlapping (spot) welds are
produced by the rotating electrodes and a regularly interrupted current.

The work pieces to be seam welded are cleaned, overlapped suitably and placed between
the two circular electrodes, which clamp the work pieces together by the electrode force.
A current impulse is applied through the rollers to the material in contact with them. The
heat generated thus rollers to the material in the pressure from the electrodes completes the weld.
If the current is put off and on quickly, a continuous fusion zone made of overlapping
nuggets is obtained and the process is known as stitch welding.
On the other hand, if individual spot welds (or nuggets) are obtained by constant and
regularly timed interruptions of the welding current, the process is known as roll (Spot) welding.
Roll welding simply joins two work pieces various stitch welding produces gas tight and
liquid tight joints.
b) Friction Stir Welding:
Friction welding is a solid state welding process where in coalescence (merging) is
produced by the heat obtained from mechanically induced sliding motion between rubbing
surfaces. The work parts are held together under pressure.

OPERATIONAL STEPS:
i.
ii.
iii.
iv.

The two components to be friction welded are held in axial alignment.

One component that is held in the chucking spindle of the machine is rotated and
accelerated to the desired speed.
The other component that is stationary and is held in the movable clamp is moved
forward to come into pressure contact with the rotating component.
Pressure and rotation are maintained until the resulting high temperature makes
the components metals plastic for welding with sufficient metal behind the
interface becoming softened to permit the component to be forged together.
During this period metal is slowly extruded from the weld region to form on
upset.
(OR)

14. B. With the help of suitable diagram explain the following type of welding.
a) TIG welding process
b) Electro slag welding process (16)
TIG Welding:
Gas Tungsten Arc Welding (GTAW) is frequently referred to as TIG welding. TIG
welding is a commonly used high quality welding process. TIG welding has become a popular
choice of welding processes when high quality, precision welding is required.
In TIG welding an arc is formed between a non-consumable tungsten electrode and the
metal being welded. Gas is fed through the torch to shield the electrode and molten weld pool. If
filler wire is used, it is added to the weld pool separately.

TIG Welding Benefits

Superior quality welds

Welds can be made with or without filler metal

Precise control of welding variables (heat)

Free of spatter

Low distortion

Shielding Gases

Argon

Argon + Hydrogen

Argon/Helium

Helium is generally added to increase heat input (increase welding speed or weld
penetration). Hydrogen will result in cleaner looking welds and also increase heat input,
however, Hydrogen may promote porosity or hydrogen cracking.
GTAW Welding Limitations

Requires greater welder dexterity than MIG or stick welding

Lower deposition rates

More costly for welding thick sections

Common GTAW Welding Concerns

We can help optimize your welding process variables. Evaluate your current welding
parameters and techniques. Help eliminate common welding problems and discontinuities such
as those listed below:
Weld Discontinuities

Undercutting

Tungsten inclusions

Porosity

Weld metal cracks

Heat affected zone cracks

TIG Welding Problems

Erratic arc

Excessive electrode consumption

Oxidized weld deposit

Arc wandering

Porosity

Difficult arc starting

c) Electro slag welding:

Electro slag welding is a welding process wherein coalescence is produced by molten
slag which melts the filler metal and the surfaces of the work to be welded.

An electric arc is struck between the electrode and the joint bottom with the help of a
piece of steel wool.
Welding flux is added. It melts by the heat of the arc. When a sufficiently thick layer of
hot flux or molten slag is formed, arc action stops and the electric current passes from
the electrode to the work piece through the conductive slag pool.
The conductive slag pool remains molten because of its resistance to the electric current
passing between the electrode and the work through it.
The temperature of this molten slag pool is approximately 16500 C at the surface and
19300 C inside, under the surface.
This much heat is sufficient to fuse the edges of the work piece and the welding
electrode.
A Liquid metal coming from the welding electrode and the heated base metal collects in
a pool beneath the slag bath and slowly solidifier thereby forming the weld bead joining
the two work pieces.
Thus, electro slag welding is a progressive process of melting and solidification process
from the bottom upward. At any instant, there is molten metal above the solidifying weld
metal and molten conductive slag above the molten weld metal pool.

Benefits
The principal benefits of the process are:

Speed of joint completion; typically 1 hour per meter of seam, irrespective of thickness

Lack of angular distortion

Lateral angular distortion limited to 3mm per meter of weld

High quality welds produced

Simple joint preparation, i.e. flame-cut square edge

Major repairs can be made simply by cutting out total weld and re-welding

15. A.(i). Discuss the gas welding process and the necessary equipment needed with suitable
sketches. (10)
Gas welding is a fusion-welding process. It joins metals, using the heat of combustion
of an oxygen/air and fuel gas mixture.
The intense heat thus produced melts and fuses together the edges of the parts to be
welded, generally with the addition of a filler metal.
Gas welding equipment
Equipments required in gas welding include cylinders for compressed gases, regulators, blow
pipes, nozzles, house and house fittings.
Cylinders for compressed gases
The oxygen cylinder is painted black and is made of steel. Acetylene cylinder is painted
of maroon and I made of steel.
Pressure regulators
A pressure regulators or pressure reducing valve, located on the top of both O2and C2H2
cylinders, serves to reduce the high cylinder pressure of the gas to a suitable working value at the
blow pipe and to maintain a constant pressure. The pressure is regulated with the help of spring
loaded diaphragm
Pressure gauges
Each gas cylinder is provided with two pressure gauges. One gauge indicates the
pressure of the gas inside the cylinder and the other indicates pressure of the gas supplied to the
blow pipe.
Blowpipe
Blow pipe or welding torch serve to mix the gases in proper proportion and to deliver the
mixture to the nozzle or tip when it is burned. The gases from the cylinders are taken to the blow
pipe through the reducing valves and with the help of rubber tubes. On the shank of the blow

pipes, two control valves are provided, one for controlling the flow of acetylene and other of
oxygen, entering a chamber called mixing chamber were the two gases are mixed in a correct
proportion
Nozzle or tip
The nozzle is a device screwed to the end of blow pipes. It is used to permit the flow of
oxy-acetylene gas mixture from the mixing chamber of blow pipes to the tip of nozzle to
facilitate burning. In order to vary the size of flame necessary to weld varying thickness of metal,
a selection of tips is available for the blow pipes
Hose and hose fittings
The hose connects the outlet of the pressure reducing valve and blow pipe. Rubber tubing
is necessary for flexibility but it should be of highest quality, specifically manufactured for this
purpose. In accordance with international standards, hose is manufactured to a colour code: blue
for oxygen and red for acetylene. Hose fittings are provided at the ends of the hoses for
attachment to the blow pipe and the outlet of the pressure reducing valves.
The other equipment used during gas welding are:
1. Goggles. Welding googles must be worn to protect the eyes from heat and light
radiated from the flames and molten metal in the weld pool
2. Welding gloves. They protect the hands from heat and metal splashes
3. Spark lighter. It is used to conveniently and instantaneously light the blow pipe
10. It is made of steel and is used to remove metal oxides from the welded bead.
Wire brush
It is used to clean the weld joint before and after welding.