ME 18302 – Manufacturing Processes

Unit-2 Welding
Course Instructor
Dr. S. Ramesh babu
Professor & head
Department of Mechanical Engineering
SVCE
rameshbabu@svce.ac.in

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 Introduction – Joining Process

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 Introduction
• Welding is a materials joining process which produces coalescence
of materials by heating them to suitable temperatures with or
without the application of pressure or by the application of
pressure alone, and with or without the use of filler material.

Welding is used for making permanent joints.

It is used in the manufacture of automobile bodies, aircraft

frames, railway wagons, machine frames, structural works, tanks,
furniture, boilers, general repair work and ship building.

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 Introduction

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 Classification of Welding

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 Classification of Welding
Plastic Welding or Pressure Welding
The piece of metal to be joined are heated
to a plastic state and forced together by external
pressure
(Ex) Resistance welding
Fusion Welding or Non-Pressure Welding
The material at the joint is heated to a molten state and
allowed to solidify

(Ex) Gas welding, Arc welding

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 Classification of Welding

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 Weldability
Capacity of being welded into inseparable joints having specified
properties such as definite weld strength, proper structure, etc

Factors –

Melting Point Proper shielding atmosphere

Thermal Conductivity Proper fluxing material

Thermal expansion Proper filler material

Surface condition Proper welding procedure

Change in microstructure Proper heat treatment

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 Oxyfuel Gas Welding (OFW)
• Group of fusion welding operations that burn
various fuels mixed with oxygen
• Oxyfuel gas is also used in flame cutting torches
to cut and separate metal plates and other parts
• Most important OFW process is oxyacetylene
welding

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 Welding techniques

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 Welding techniques

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 Weld Positions

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 Oxy Acetylene Welding
Oxy Acetylene Welding

Types of Flames in Gas Welding

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 Neutral Flame
A neutral flame results when
approximately equal volumes of
oxygen and acetylene are mixed in the
welding torch and burnt at the torch
tip.

The temperature of the neutral flame

is of the order of about 5900°F (3260°
C).

It has a clear, well defined inner cone,

indicating that the combustion is
complete.

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 Neutral Flame
The inner cone is light blue in color.

It is surrounded by an outer flame

envelope, produced by the combination of
oxygen in the air and superheated carbon
monoxide and hydrogen gases from the
inner cone.

This envelope is usually a much darker

blue than the inner cone.

The neutral flame is commonly used for

the welding of mild steel, stainless steel,
cast Iron, copper, and aluminium.

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 Oxidizing Flame
The oxidizing flame has an excess of
oxygen over the acetylene.

An oxidizing flame can be recognized by

the small cone, which is shorter, much
bluer in color and more pointed than that
of the neutral flame.

The outer flame envelope is much shorter

and tends to fan out at the end.

Such a flame makes a loud roaring sound.

It is the hottest flame (temperature as high
as 6300°F) produced by any oxy-fuel gas
source.

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 Oxidizing Flame
It is not used in the welding of steel.

A slightly oxidizing flame is helpful when welding (i)

Copper-base metals (ii) Zinc-base metals and (iii) A
few types of ferrous metals such as manganese steel
and cast iron.

The oxidizing atmosphere in these cases, create a

basemetal oxide that protects the base metal

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 Reducing Flame
The carburizing or reducing flame has
excess of acetylene and can be recognized
by acetylene feather, which exists
between the inner cone and the outer
envelope.

The outer flame envelope is longer than

that of the neutral flame and is usually
much brighter in color.

With iron and steel, carburizing flame

produces very hard, brittle substance
known as iron carbide.

A reducing flame may be distinguished

from carburizing flame by the fact that a
carburizing flame contains more acetylene
than a reducing flame.

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 ARC WELDING PROCESSES
The process, in which an electric arc between an electrode and a
workpiece or between two electrodes is utilized to weld base
metals, is called an arc welding process.

Most of these processes use some shielding gas while others

employ coatings or fluxes to prevent the weld pool from the
surrounding atmosphere.

ARC WELDING

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 Various arc welding process
1. Carbon Arc Welding
2. Shielded Metal Arc Welding
3. Submerged Arc Welding
4. Gas Tungsten Arc Welding
5. Gas Metal Arc Welding
6. Plasma Arc Welding
7. Atomic Hydrogen Welding
8. Electro-slag Welding
10. Electro-gas Welding

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 Electric Arc
Generated between two
conductors of electricity, upon
application of voltage and
separated by a small distance
Presence of ionisable gas
Sustained electric discharge
through ionized gas column
between the two electrodes

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 Electrode Polarities
• Direct Current Straight Polarity (DCSP) :
Electrode is negative. Deeper penetration.

• Direct Current Reverse Polarity (DCEP) :

Electrode is positive. Enhanced deposition rate
for consumable electrode.

• Alternating Current (AC) : Polarity is switched

at a frequency.

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 Electrode Polarities

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 Electrode Polarities

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 Carbon Arc Welding
Carbon Arc Welding (CAW) is
a welding process, in which
heat is generated by an electric
arc struck between
an carbon electrode and the
work piece. The arc heats and
melts the work pieces edges,
forming a joint.

Carbon arc welding is the

oldest welding process

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 Introduction
Electrode – Non Consumable - A pure graphite or baked
carbon rod
The electric arc produces heat and weld can be made with
or without the addition of filler material.
Classification
(1) Single electrode arc welding, and
(2) Twin carbon electrode arc welding
In single electrode arc welding, an electric arc is struck
between a carbon electrode and the workpiece.
Welding may be carried out in air or in an inert atmosphere.

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 Carbon Arc Welding
• Direct current straight polarity (DCSP) is
preferred to restrict electrode disintegration and
the amount of carbon going into the weld metal.
• This process is mainly used for providing heat
source for brazing, braze welding, soldering and
heat treating as well as for repairing iron and
steel castings.
• It is also used for welding of galvanized steel and
copper.

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 Twin Carbon Arc welding

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 Twin Carbon Arc Welding
• utilizes arc struck between two carbon electrodes.
• Work piece is not a part of welding electric circuit in Twin
Carbon Electrode Arc Welding,
• Therefore the welding torch may be moved from one
work piece to other without extinguishing the arc.
• The arc produced between these two electrodes heats the
metal to the melting temperature and welds the joint
after solidification.
• The power source used is AC (Alternating Current) to keep
the electrodes at the same temperature.

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 Carbon Arc Welding
This process is mainly used for joining copper alloys to each
other or to ferrous metal.

It can also be used for welding aluminium, nickel, zinc and

lead alloys.

Note :

Carbon Arc Welding has been replaced by Tungsten Inert

Gas Arc Welding (TIG, GTAW) in many applications.

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 Carbon Arc Welding
Advantages of Carbon Arc Welding:

• Low cost of equipment and welding operation;

• High level of operator skill is not required;
• The process is easily automated;
• Low distortion of work piece.
Disadvantages of Carbon Arc Welding:

• Carbon of electrode contaminates weld material

with carbides.
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 Shielded Metal Arc Welding (SMAW)
Manual Metal Arc Welding
This is an arc welding process
wherein coalescence is
produced by heating the
workpiece with an electric arc
setup between a flux-coated
electrode and the workpiece.

The electrode is in a rod form

coated with flux

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 Shielded Metal Arc Welding (SMAW)
Shielded metal arc welding (SMAW) is a commonly used arc
welding process manually carried by welder.

The process uses a consumable electrode which is primarily

a filler metal rod having a coating of chemicals that provide
flux and shielding.

The flux coating of electrode decomposes due to arc heat

and serves many functions, like weld metal protection, arc
stability etc.

Inner core of the electrode supply the filler material for

making a weld.

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 Shielded Metal Arc Welding (SMAW)
• Temperature greater than 5000°C.
• Clean the weld bead surface.
• The heat (or the temperature) generated in the arc
depends upon the amount of input electric power.
H= E I T
where H is heat (Joules or Watt-sec); E is voltage (Volts); I is
current (amperes); and T is time (seconds).
• If the parent metal is thick it may be necessary to make
two or three passes for completing the weld.

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 Shielded Metal Arc Welding (SMAW)
Advantages
1. Shielded Metal Arc Welding (SMAW) can be carried out in
any position with highest weld quality.
2. MMAW is the simplest of all the arc welding processes.
3. This welding process finds innumerable applications,
because of the availability of a wide variety of electrodes.
4. Big range of metals and their alloys can be welded easily.

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 Shielded Metal Arc Welding (SMAW)
Limitations

1. Due to flux coated electrodes, the chances of slag

entrapment and other related defects are more as
compared to MIG and TIG welding.

2. Duo to fumes and particles of slag, the arc and metal

transfer is not very clear and thus welding control in this
process is a bit difficult as compared to MIG welding.

3. Due to limited length of each electrode and brittle flux

coating on it, mechanization is difficult.

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 Shielded Metal Arc Welding (SMAW)
Limitations

4. In welding long joints (e.g., in pressure vessels), as

one electrode finishes, the weld is to be progressed with
the next electrode. Unless properly cared, a defect (like
slag inclusion or insufficient penetration) may occur at
the place where welding is restarted with the new
electrode.

5. The process uses stick electrodes and thus it is slower

as compared to MIG welding.

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 Submerged Arc Welding (SAW)
Arc welding process, in which
coalescence is produced by
heating the workpiece with
an electric arc setup between
the bare electrode and the
work piece.
Molten pool remains
completely hidden under a
blanket of granular material
called flux. (Lime, Silica,
magnesium oxide, calcium
SAW
fluoride)
SAW - Actual
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 Submerged Arc Welding (SAW)
• No pressure is applied for welding purposes. This
process is used for welding low carbon steel, bronze,
nickel and other non-ferrous materials.

• The molten weld metal pool is thus entirely covered

under a thick layer of flux and oxidation of weld metal
is prevented.

• In addition, spatter and sparks are prevented while

fumes and u-v radiations are suppressed. The flux also
acts as a thermal barrier, enabling faster weld pool
formation.

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 Submerged Arc Welding (SAW)
• The flux is fed into the weld zone by gravity flow through
a nozzle that delivers it ahead of the welding electrode.

• The portion of the flux closest to the arc is melted. It

mixes with the molten weld metal to remove impurities,
and then solidifies on the top of the weld joint to form a
glass-like slag.

• The slag and unfused flux granules on the top provide

good protection from the surrounding atmosphere and
good thermal insulation for the weld area.

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 Submerged Arc Welding (SAW)
• As a result of slow cooling, a high quality weld joint
is obtained. After welding, the unfused flux can be
recovered, treated and then reused.

• The power source used with SAW can be either ac or

dc.

• The electric currents range between 250 amp to

2500 amp.

• Higher the current, higher is the burn-off rate for a

given electrode wire diameter and material.

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 Submerged Arc Welding (SAW)
If the amount of flux is less, it would not cover, the
arc completely, thus, resulting in oxidation of the
weld metal as well as flashing and spattering.

Similarly, if the amount of flux is too much, the

weld gases generated during the process would not
be able to flow out, resulting in porosity in the
weld metal.

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 Submerged Arc Welding (SAW)
Advantages
• It is simple and versatile.
• It has high productivity. Weld metal deposition rates are
5 to 10 times as compared to SMAW process. Welding
speed as high as 5m/min can be achieved.
• It produces very high quality of the weld. The toughness
and uniformity of weld metal properties are
exceptionally good.
• It can be used to weld a large variety of sheet and plates
of carbon and alloy steels.
• It can be automated for greater economy.

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 Submerged Arc Welding (SAW)
Limitations
The process is not suitable for welding of some
materials such as high carbon steels, tool steels, and
most non-ferrous metals.
The parts to be welded by SAW must always be in
horizontal position. This is because granular flux is fed
to the joint by gravity.
A back-up plate is generally required beneath the joint
during welding operation.

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 Submerged Arc Welding (SAW)
Applications

Thick plate welding of ships and pressure vessels.

The process is also widely used for steel fabrication of

structural shapes (e.g., I-beams); longitudinal and
circumferential joints of large diameter pipes.

Circumferential welds can be made on pipes in this

manner. Low-carbon, low alloy, and stainless steels can
be easily welded by SAW.

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 Tungsten Inert Gas Welding
TIG welding is an electric
arc welding process in
which the fusion energy
is produced by an electric
arc burning between the
workpiece and the
tungsten electrode

TIG

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 Tungsten Inert Gas Welding
In this process a
non-consumable tungsten
electrode is used with an
envelope of inert shielding gas
around it.

The shielding gas protects the

tungsten electrode and the
molten metal weld pool from
the atmospheric contamination.

The shielding gases generally

used are argon, helium or their
mixtures.

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 Tungsten Inert Gas Welding
Electrode materials
• Electrode material - tungsten, or tungsten alloy (thoriated
tungsten or zirconated tungsten).
• The oxides of thorium and zirconium help the electrodes to
maintain its shape at the tip for a longer time and improve the
ease of electron emission.
• Alloy-tungsten electrodes possess higher current carrying capacity,
produce a steadier arc as compared to pure tungsten electrodes
and high resistance to contamination.
• Size may vary from 0.5 mm to 10 mm.
• There is hardly any wear loss of tungsten, since its melting point is
quite high (3410 °C)
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 Tungsten Inert Gas Welding
Electric power source
• Both AC and DC power source - used for TIG welding.
• DC (Straight polarity) is preferred for welding of cast iron, copper,
copper alloys, nickel and stainless steel, titanium.

• DC reverse polarity (DCRP) or AC is used for welding aluminium,

magnesium or their alloys. DCRP removes oxide film on magnesium
and aluminium and improves the weld quality.

• Welding voltage is 20 to 40 V and the weld current varies between

100 to 500 amperes.

Inert gases - Argon, Helium, Argon-helium mixtures ,

Argon-hydrogen mixtures

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 Tungsten Inert Gas Welding
TIG Nozzle
• The nozzle to be chosen depends on the shape of the groove to
be welded as well as the required gas flow rate.
• The gas flow rate depends on the position of the weld as well as its
size.

• Too high a gas consumption would give rise to turbulence of the

weld metal pool and consequently porous welds.

• Because of the use of shielding gases, no fluxes are required to be

used in inert gas shielded arc welding.

• However for thicker sections, it may be desirable to protect the

root side of the joint by providing a flux.

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 Tungsten Inert Gas Welding
Advantages –
• Operating costs are low.
• Very high quality of welds.

• There is no spatter (unwanted small droplets of weld metal) because the

filler metal is not transferred across the arc gap.

• No post-welding grinding or finishing operation – due to no spatter

• A variety of metals (both ferrous and non-ferrous) especially aluminum,

magnesium, titanium and refractory metals can be welded.

• The process is particularly suitable for welding high alloyed metals where
weld purity is essential.

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 Tungsten Inert Gas Welding
Limitations
• Tungsten electrode cannot be allowed to touch the work-metal
because some tungsten may get deposited.
• Cast iron, wrought iron, and lead are difficult to weld by this
process.
• For welding, of steel the process is slower and more costly than
consumable electrode arc welding.
Applications
• Suited for high quality welding of thinner workpieces rather than
for welding thicker workpieces.
• The process is generally used for welding aluminium, magnesium
and stainless steel.

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 Gas Metal Arc welding (GMAW)
Also Known as Metal Inert Gas
welding (MIG) / CO2 Welding

Gas Metal Arc Welding

(GMAW), by definition, is an
arc welding process which
produces the coalescence of
metals by heating them with
an arc between a continuously
fed filler metal electrode and
the work.

MIG

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 Gas Metal Arc welding (GMAW)
• The process uses shielding from an externally supplied gas to protect the molten
weld pool.

• Utilizes a consumable bare wire electrode

• The consumable electrode is in the form of a wire reel which is fed at a constant
rate, through the feed rollers.

• The welding torch is connected to the gas supply cylinder which provides the
necessary inert gas.

• The electrode and the work-piece are connected to the welding power supply.

• The current from the welding machine is changed by the rate of feeding of the
electrode wire.

• Normally DC arc welding machines are used for GMAW with electrode positive

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 Gas Metal Arc welding (GMAW)
• The DCRP increases the metal deposition rate and also provides for
a stable arc and smooth electrode metal transfer.

• With DCSP, the arc becomes highly unstable and also results in a
large spatter.

• But special electrodes having calcium and titanium oxide mixtures

as coatings are found to be good for welding steel with DCSP.

• The gas metal arc welding (GMAW) process uses Three basic
modes to transfer metal from the electrode to the workpiece.

• Each mode of transfer depends on the welding process, the

welding power supply, and the consumable, and each has its own
distinct characteristics and applications.

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 Gas Metal Arc welding (GMAW)

Modes of Metal transfer

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 Globular Transfer
• In Globular method, the wire is heated
longer and creates a large volume of weld
metal that drips into the weld joint.

• Limited to flat and horizontal fillet welds

with this method.

• Globular transfer is usually used with

relatively low current compared to
spray transfer mode but higher
current than the short circuit
transfer.
 Spray Transfer
• Small droplets of molten metal from
the consumable electrode are
sprayed into the weld joint.
• High welding current density results
in high melting rate and greater pinch
force
• Droplets are formed rapidly and
pinched off quickly by high pinch
force
• This method uses a high heat input
and you risk burn-through on thinner
materials and only allows for limited
to flat and horizontal weld positions.
 Short Circuit Transfer
• The consumable electrode wire arcs and
touches the base material and shorts.

• This creates a small, quickly solidifying,

weld metal puddle that drips into the
weld joint fusing the materials together
sometimes referred to as “fast freezing.”

• Short Circuit method is great for thinner

materials

• Low welding current - droplet grows

slowly
 Pulse Transfer
• Modified form of the Spray Arc method, taking the best
parts of all the transfer methods and minimizing their
disadvantages.
• Pulse MIG welding does require a special power source,
which pulses the voltage many times per second.
• This allows one droplet of molten metal to form at the
end of the consumable wire and the current, and then
pushes the droplet across the arc into the weld puddle.
• A droplet is formed every pulse.
• Since the voltage drops on every pulse, this creates a
longer cooling off period and may reduce the HAZ from
the weld.
• Pulse MIG transfer minimizes spatter or the risk of cold
lapping, and weld positioning is not as limited as the
Globular and Spray methods.
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 Electro Slag Welding
Electro-slag welding is mostly used for welding very thick
components or plates (up to 40 to 500 mm thickness) where the
joint to be welded is in a vertical position.

The components to be welded are set in the required vertical position

with the necessary gap between the butted edges and a backing plate
is tacked at the bottom.

Water-cooled copper shoes which can travel along the joint are
initially located at the lowermost position.

Electro Slag Welding

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 Electro Slag Welding

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 Electro Slag Welding
• These shoes close off the space between the parts to be welded so
that a V-shaped starting block is formed that prevents the slag and
molten metal from spilling out of the pool.

• To start the welding operation, an arc is created between the tip of

the consumable electrodes and the bottom plate and upon the
introduction of granular flux into the joint, a 3-4 mm thick layer of
molten slag starts floating at the top of weld metal pool.

• As the molten slag reaches the tip of the electrode the arc is
extinguished and current is conducted directly from the electrode
wire to the base metal through the conductive slag.

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 Electro Slag Welding
• Thereafter, the high electrical resistance of the slag
causes most of the heating required for welding, i.e., for
melting the wire electrode and the workpiece metal.

• As the welding progresses, single or multiple electrode

wires along with flux are continuously fed into the
molten slag pool confined between the copper shoes.

• The slag being lighter than the molten metal remains on

top to protect the weld metal pool.

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 Electro Slag Welding
• The shoes are made to slide upwards along the joint at
a speed determined by the speed at which the
electrode and the work-material at the joint are
melted.

• The lower part of the weld-metal bath is solidified as

heat is conducted away by the copper shoes and the
work material.

• The welding operation takes place at 40-50 V, and the

current requirements are 500-600 amps, although
higher currents are used for very thick plates.

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 Electrogas welding
• Electrogas welding is very similar in principle
to electroslag welding.
• The main difference being that the heat for welding is
generated by an arc which is formed between a
flux-cored electrode and the molten weld pool.
• The flux from the electrode forms a protective layer over
the weld pool, but additional protection in the form of a
gaseous shield (usually CO2) is used. The electrogas
process is generally faster than electroslag welding when
used on relatively thin sections.
• The resulting weld metallurgy is similar to a high-current
submerged-arc weld.
 Plasma Arc Welding
• PAW is process where a coalescence is produced by the heat
which is developed from a special setup between a tungsten
alloy electrode and the water cooled nozzle (Non transferred
ARC ) or between a tungsten alloy electrode and the job
(transferred ARC) .

• This process employs two different gases for two different purposes
–

• One gas is used to form the Arc plasma.

• Second gas is used to shield the arc plasma.

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 Plasma Arc Welding

Plasma Arc Welding

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 Plasma Arc Welding - Equipment
Power supply: A DC power source
Typical welding parameters:
Current: 50-350A
Voltage: 27-31v
Gas flow rate: 2-40 l/minute
Plasma torch: The torch has an electrode and water cooling
system which saves the life of the nozzle and the electrode from
melting due to excessive heat produced while welding.
Fixture: It is required to avoid atmospheric contamination of the
molten metal under bead.
Shielding gas: An inert gas ,either Argon, helium,or a mixture, is
used for shielding the arc area from the atmosphere.
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 Working Concept of Plasma Arc Welding:
• The process works by ionizing gas.

• When gas gets ionized it can conduct electricity.

• The gas is used to transfer an electric arc to the piece of job

being welded.

• The gas can be argon plus a secondary gas helium which shield
arc weld puddle.

• The plasma torch contains an electrode made out of tungsten

fixed in a nozzle which is made of copper .

• The arc is started between the electrode and the tip of nozzle.
Then the arc or flame is transferred to the material to be welded.

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 Working Concept of Plasma Arc Welding:
• The small opening forces the gas to travel through a constricted
opening or orifice.

• This concentrates the heat to smaller area. This ability allows

welder to produce a very high quality weld .

• The result is a process that gives higher welds speed ,less

distortion, more consistent welds ,less spatter and more control on
the weld area.

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 Plasma Arc Welding - Advantages
• Constricted opening or orifice gives you more concentrated
heat in smaller area.
• It is more stable and does not gets deflected from the base
metal.
• Plasma arc welding has deeper penetration capabilities and
produces a weld.
• It gives high speed welds.
• Less distortion of base metals.
• More control on the small welding areas.

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 Plasma Arc Welding - Disadvantages

• Orifice replacement is necessary.

• It’s equipment's are very much expensive.

• An individual needs more skills to use PAW.

• Nozzle gets melt which has to be change frequently

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 Plasma Arc Welding - Comparison
Transferred Plasma Arc Non-Transferred Arc Welding
Welding Process Process
Arc is established between Arc is established between
electrode and workpiece electrode and nozzle
The workpiece is a part of the The workpiece is not part of
electrical circuit and heat is the electrical circuit and heat is
obtained from the anode spot obtained from plasma jet.
and the plasma jet. Therefore, Therefore, less energy is
higher amount of energy is transferred to work. This is
transferred to work. This is useful for cutting
used for welding
Higher penetration is obtained, Less penetration is obtained,
so thicker sheets can be so thin sheets can be welded
welded
Higher process efficiency Less process efficiency
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 Atomic Hydrogen Welding
Atomic Hydrogen Welding (AHW) is
a combination of electric are and
gas welding technique.
It is a thermo-chemical arc welding
process in which the workpieces are
joined by heat obtained on passing
a stream of hydrogen through an
electric are struck between two
tungsten electrodes.
The arc supplies the energy for a chemical reaction to take place,
During the process, more heat is released due to exothermic reaction.
The electric arc efficiently breaks up the hydrogen molecules which
recombine with tremendous release of heat with the temperature
from 3400 to 4000°C.
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 Applications of Atomic Hydrogen Welding:

1. These welding processes are used in welding of tool

steels which contains tungsten, nickel and
molybdenum.

2. They are used in joining parts, hard surfacing and

repairing of dies and tools.

3. Atomic hydrogen welding is used where rapid

welding is necessary in stainless steels, non-ferrous
metals and other special alloys.

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 Thermit Welding
Thermite welding is a liquid state chemical welding process, in
which joint formation takes place in molten state.

Practically, it is combination of welding and casting process in

which, the molten iron is poured at the welding plates and is
allowed to solidify to make a permanent strong joint.

The molten state of iron is obtained without application of

external heat or conventional furnace so this is taken as a welding
process.

In this type of welding, a mixture of aluminum and iron oxide is

used in ratio 1:3 by weight.

Thermit Welding

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 Thermit Welding

(1) Thermit ignited; (2) crucible tapped, superheated

metal flows into mold; (3) metal solidifies to produce
weld joint.

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 Thermit Welding

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 Thermit Welding

• Finely mixed powders of aluminum and iron oxide (in a 1:3

mixture), when ignited at a temperature of around 1300°C
(2300°F), produce the following chemical reaction.

• The temperature produced in the thermit reaction is of the order

of 3000°C.

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 Thermit Welding
• Filler metal is obtained from the liquid metal; and although the
process is used for joining, it has more in common with casting
than it does with welding.

• This mixture in superheat liquid state is poured around the parts

to be joined.

• The joint is equipped with the refractory mold structure all

around.

• After the reaction is complete (about 30 sec, irrespective of the

amount of Thermit involved), the crucible is tapped and the
liquid metal flows into a mold built specially to surround the
weld joint.

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 Thermit Welding
Because the entering metal is so hot, it melts the edges of the base
parts, causing coalescence upon solidification.

After cooling, the mold is broken away, and the gates and risers are
removed by oxyacetylene torch or other method.

Thermit welding is used for welding pipes, cables, conductors, shafts,

and broken machinery frames, rails and repair of large gear tooth.

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 Working – Thermit Welding
• First both the work pieces which are needed to be weld, are
cleaned.

• Now a wax pattern is created around the weld cavity.

• A moulding flask is fixed around the joint with the help of mold
handle clamp. This wax pattern is situated at the middle of the
flask.

• Now the molding sand rammed around the wax pattern to create
mold in which the molten metal will pour. This mold involves all
necessary parts like runner, riser, pouring basin, gating system,
opening for wax pattern etc. same as involves in casting.

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 Working – Thermit Welding
• Now this mold is heated to remove wax pattern. The wax is
melted and run off from the wax pattern outlet prepared at
bottom of the sand mold.
• Now the thermite mixture is taken into the refectory crucible.
The ignite powder is placed over the mixture. This mixture is
ignited by a magnesium ribbon.
• This will start the thermite reaction which liberates a huge
amount of heat. This reaction form molten state of iron which
flows from crucible to sand mould.
• This molten metal fills the weld cavity and fuses the parent metal
to make a permanent joint. This will allow to cool down. After
proper cooling, flask is removed from the joint.
• After removing the flask, machining is done to remove the
welding burr or other extra metal.
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 Solid State Welding
• Solid state welding is a group of welding processes
which produces coalescence at temperatures essentially
below the melting point of the base materials being
joined, without the addition of brazing filler metal.

• Pressure may or may not be used.

• These processes are sometimes erroneously called solid

state bonding processes

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 Solid State Welding Process - Types
• Friction Welding

• Friction Stir Welding

• Forge Welding

• Cold Pressure Welding

• Explosive Welding

• Diffusion Welding

• Thermo-compression Welding

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 Friction Welding
• 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 faying surfaces.
Friction Welding

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 Friction Welding
• 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.
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 Friction Welding
• 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.

• Most of the metals and their dissimilar combinations such as aluminium and
titanium, copper and steel, aluminium and steel etc. can be welded using
friction welding

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 Benefits of Friction Welding Process

• Enables joining of dissimilar materials normally not compatible for welding by other
joining methods.

• Creates narrow, heat-affected zone

• Consistent and repetitive process of complete metal fusion

• Joint preparation is minimal – saw cut surface used most commonly

• No fluxes, filler material, or gases required

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 Benefits of Friction Welding Process
• Environmentally friendly process – no fumes, gases, or smoke generated

• Solid state process – no possibility of porosity or slag inclusions

• Creates cast or forge-like blanks – without expensive tooling or minimum quantity

requirements

• Reduces machining labor, thereby reducing perishable tooling costs while increasing
capacity

• Full surface weld gives superior strength in critical areas

• Reduces raw material costs in bi-metal applications. Expensive materials are only used
where necessary in the blank

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 Friction Stir Welding (FSW)
• Friction stir welding (FSW) is a solid state welding process in which
a rotating tool is fed along the joint line between two work pieces,
generating friction heat and mechanically stirring the metal to
form the weld seam.
• The process derives its name from this stirring or mixing action.
• FSW is distinguished from conventional FRW by the fact that
friction heat is generated by a separate wear-resistant tool rather
than by the parts themselves.

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 Friction Stir Welding (FSW)
• FSW was developed in 1991 at The Welding Institute in Cambridge,
UK.

• The rotating tool is stepped, consisting of a cylindrical shoulder

and a smaller probe (pin) projecting beneath it.

• During welding, the shoulder rubs against the top surfaces of the
two parts, developing much of the friction heat, while the probe
generates additional heat by mechanically mixing the metal along
the butt surfaces.

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 Friction Stir Welding (FSW)
• The probe has a geometry designed to facilitate the mixing action.

• The heat produced by the combination of friction and mixing does not melt the metal but
softens it to a highly plastic condition.

• As the tool is fed forward along the joint, the leading surface of the rotating probe forces
the metal around it and into its wake, developing forces that forge the metal into a weld
seam.

• The shoulder serves to constrain the plasticized metal flowing around the probe.

• The welding of the material is facilitated by the severe plastic deformation in the solid
state, involving dynamic recrystallization of the work material.

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 STAGES OF FSW PROCESS
1. Plunge Stage
2. Dwell Stage
3. Welding Stage
4. Pull out Stage

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 Advantages - FSW
• Good mechanical properties of the weld joint,

• Avoidance of toxic fumes, warping, shielding issues, and other problems associated with
arc welding.

• Low environmental impact.

• Little distortion or shrinkage

• Process is easy to perform.

• Process can be easily automated on simple milling machines.

• Process can be carried out in all positions (horizontal, vertical, etc.), as there is no weld
pool formation.

• Welds produced are of high quality. Welds have good appearance so that there is no need
for expensive machining after welding.

• No microstructural change in the work material since the process is completed at low
temperature.

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 Disadvantages
• Exit hole left when tool is withdrawn.

• Large forces required for clamping of the plates for keeping them together.

• Less flexible than manual arc welding processes (difficulties with thickness variations
and non-linear welds).

• Often slower traverse rate than some fusion welding techniques.

Applications

• The FSW process is used in the aerospace, automotive, railway, and shipbuilding
industries.

• Typical applications are butt joints on large aluminum parts.

• Other metals, including steel, copper, and titanium, as well as polymers and composites
have also been joined using FSW.

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 RESISTANCE WELDING
• Resistance welding (RW) is a group of fusion-welding processes
that uses a combination of heat and pressure to accomplish
coalescence.

• The heat being generated by electrical resistance to current flow at

the junction to be welded

• Resistance Welding

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 Resistance Welding
• The principal components include workparts to be welded (usually
sheet metal parts), two opposing electrodes, a means of applying
pressure to squeeze the parts between the electrodes, and an AC
power supply from which a controlled current can be applied.

• The operation results in a fused zone between the two parts,

called a weld nugget in spot welding.
• The amount of heat generated in the
workpiece Mathematically, H = IVt
= I(IR)t = I2Rt;
Where H = heat generated in
joules; I = current in Amp; R =
resistance in ohms; t = time of current
flow in seconds.

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 Types of Resistance Welding
(1) Spot Welding

(2) Seam Welding

(3) Projection Welding

(4) Resistance Butt Welding

(5) Flash Butt Welding

(6) Percussion Welding

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 Resistance Spot Welding

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 Resistance Spot Welding
• It is widely used in mass production of automobiles, appliances, metal furniture,
and other products made of sheet metal.

• A typical car body has approximately 10,000 individual spot welds, and that the
annual production of automobiles throughout the world is measured in tens of
millions of units; the economic importance of resistance spot welding is very
high.

• The total resistance in the welding circuit is the sum of:

i. Resistance of the electrodes.

ii. Contact resistance between electrodes and the workpieces.

iii. Resistance of the workpieces.

iv. Resistance between the surfaces to be joined. These surfaces are called the
faying surfaces.

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 Resistance Spot Welding
• Resistance spot welding (RSW) is an RW process in which fusion of the faying
surfaces of a lap joint is achieved at one location by opposing electrodes.

• The process is used to join sheet-metal parts of thickness 3 mm or less, using a

series of spot welds, in situations where an airtight assembly is not required.

• The size and shape of the weld spot is determined by the electrode tip, the
most common electrode shape being round, but hexagonal, square, and other
shapes are also used.

• The resulting weld nugget is typically 5 to 10 mm in diameter, with a

heat-affected zone extending slightly beyond the nugget into the base metals.

• If the weld is made properly, its strength will be comparable to that of the
surrounding metal.

• The equipment includes rocker-arm and press-type spot-welding machines, and

portable spot-welding guns.

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 Resistance Spot Welding
It essentially consists of two electrodes, out of which one is fixed.

The other electrode is fixed to a rocker arm (to provide mechanical advantage) for
transmitting the mechanical force from a pneumatic cylinder. (This is the simplest type of
arrangement. )

A resistance welding schedule is the sequence of events that normally take place in each of
the welds. The events are:

1. The squeeze time is the time required for the electrodes to align and clamp the two
work-pieces together under them and provide the necessary electrical contact.

2. The weld time is the time of the current flow through the work-pieces till they are
heated to the melting temperature.

3. The hold time is the time when the pressure is to be maintained on the molten
metal without the electric current. During this time, the pieces are expected to be
forged welded.

4. The off time is time during which, the pressure on the electrode is taken off so that
the plates can be positioned for the next spot.

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 Resistance Spot Welding
Before spot welding one must make sure that

(i) The job is clean, i.e., free from grease, dirt, paint, scale, oxide etc.

(ii) Electrode tip surface is clean, since it has to conduct the current into the
work with as little loss as possible. Very fine emery cloth may be used for routine
cleaning.

(iii) Water is running through the electrodes in order to

(a) Avoid them from getting overheated and thus damaged,

(b) Cool the weld.

(iv) Proper welding current has been set on the current selector switch.

(v) Proper time has been set on the weld-timer

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 Resistance Spot Welding
• Copper base alloys such as copper beryllium and copper tungsten
are commonly used materials for spot welding electrodes.

• For achieving the desired current density, It is important to have

proper electrode shape for which three main types of spot
welding electrodes are used which are pointed, domed and flat
electrodes.

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 Applications of Resistance Spot Welding
(i) It has applications in automobile and aircraft industries

(ii) The attachment of braces, brackets, pads or clips to formed

sheet-metal parts such as cases, covers or trays is another application
of spot welding.

(iii) Spot welding of two 12.5 mm thick steel plates has been done
satisfactorily as a replacement for riveting.

(iv) Many assemblies of two or more sheet metal stampings that do

not require gas tight or liquid tight joints can be more economically
joined by spot welding than by mechanical methods.

(v) Containers and boxes frequently are spot welded.

Applications Spot Welding Robots

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 Resistance Seam Welding
• It is a continuous type of spot welding wherein spot welds overlap
each other to the desired extent.

• In this process coalescence at the faying surfaces is produced by

the heat obtained from the resistance to electric current (flow)
through the work pieces held together under pressure by circular
electrodes.

• The resulting weld is a series of overlapping resistance-spots welds

made progressively along a joint by rotating the circular electrodes.

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 Resistance Seam Welding

Resistance Seam
Welding
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Applications of Resistance Seam Welding
1. It is used for making leak proof joints in fuel tanks of
automobiles.

2. Except for copper and high copper alloys, most other metals can
be seam welded.

3. It is also used for making flange welds for use in watertight tanks.

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 Resistance Projection Welding
• This process is a resistance welding process in which two or more
than two spot welds are made simultaneously by making raised
portions or projections on predetermined locations on one of the
workpiece.

• These projections act to localize the heat of the welding circuit. The
pieces to be welded are held in position under pressure being
maintained by electrodes.

• The projected contact spot for welding should be approximately

equal to the weld metal thickness.

• The welding of a nut on the automotive chasis is an example of

projection welding.
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 Resistance Projection Welding

Resistance Projection Welding

Resistance Projection Welding

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Resistance Upset Butt and Flash Butt Welding

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 Resistance Upset Butt Welding
• In a basic butt weld, the two workpieces to be welded are first
brought together under pressure.
• Current is then applied, heating the contact area enough to allow
the applied pressure to forge the parts together.
• In other words, a butt weld is a single-stage operation of both
current and pressure.
• The pressure and current are applied throughout the weld cycle
until the joint becomes plastic.
• The constant pressure (normally from an air cylinder) overcomes
the softened area, producing the forging effect and subsequent
welded joint.
• This is done without a change in current or pressure throughout
the cycle.

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 Resistance Upset Butt Welding
• The true butt weld has no flash splatter.
• The final upset at the weld joint is usually smooth and
symmetrical. Very little ragged expulsion of metal is evident.
• Examples of modern-day applications of the AC butt welding
process are joining small-diameter wires and rods, such as coils for
continuous line operations, band saw blade manufacture, and
wire frame applications.

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 Resistance Flash Welding

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 Resistance Flash Welding
• The term "flash welding" is fairly self-descriptive—a "flashing"
action is produced during the process.
• The heat is produced in the flash welding process by the flashing
action resistance at the interface surfaces rather than contact
resistance, as in the butt weld process.
• Whereas butt welding is a single-stage operation, flash welding is a
two-stage process.
• The first stage is the flashing action.
• The current applied to the workpieces produces a flashing or
arcing across the interface of the two butting ends of the material.
• The flashing action increases to the point of bringing the material
to a plastic state.
• This flashing action forms a HAZ very similar to a butt weld.
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 Resistance Flash Welding
• Once the area has become plastic and reached the proper
temperature, the second stage of the operation begins – the upset
or forging action.

• The two ends of the workpieces are then brought together with a
very high force sufficient enough to cause the material to upset.

• This forces the plastic metal along with most of the impurities out
of the joint.

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 Electron Beam Welding
• Electron Beam Welding Process is a fusion
welding process in which a high velocity electron
beam is used to join two metals together.

• The high velocity electron beam when strikes the

weld area of two metal pieces and very intense
heat is generated which melts the metal and they
fuse together to form a strong weld.

• The whole process is carried out in vacuum

chamber to prevent it from contamination.
 Electron Beam Welding
It works on the principle
that when a high velocity
beam of electron that has
Kinetic energy strikes the
two metal pieces, the kinetic
energy of the electron
transformed into heat.

The intensity of heat

produced is so much that it
melts the two metal pieces
and fuse them together to
form a strong weld.
Electron Beam Welding
 Electron Beam Welding
• The electrons are accelerated by applying high
potential difference (30kV to 175 kV) between
cathode and anode

• The higher the potential difference, the higher

would be the acceleration of the electrons.

• The electrons get the speed in the range of

50,000 to 2,00,000 km/s.
 Electron Beam Welding
• The electron beam is focused by means of
electromagnetic lenses.

• When this high kinetic energy electron beam

strikes on the workpiece, high heat is generated
on the workpiece resulting in melting of the
work material.

• Molten metal fills into the gap between parts to

be joined and subsequently it gets solidified and
forms the weld joint
 Equipment
1. Electron Gun

(i) Cathode (Emitter or Filament):

(ii) Anode:
(iii) Grid
(iv) Focusing Unit:
Two types of electron gun – Self accelerated and workpiece accelerated
2. Power Supply

3. Vacuum Chamber

4. Work Handling Devices:

 Advantages
• High welding speed.
• Welding of dissimilar metal can be done.
• High weld quality and precision.
• Less operating cost.
• Materials with high welding temperature can be
welded easily.
• Less distortion due to less affected heat zone.
 Advantages
• Cost of cleaning is negligible.
• It welds thicker sheets, ranges from .025 mm to 100
mm.
• It is capable of welding inaccessible joints.
• Reactive materials like beryllium, titanium can be
welded
• Materials of high melting point like columbium,
tungsten can be welded
 Disadvantages
• Cost of equipment is very high.

• High skilled operator is required to operate it.

• High vacuum is required.

• Due to operation in vacuum, large jobs can not

welded.

• High safety measures are need to work with it.

 Applications
• It is used in aerospace industries for manufacturing jet components,
parts of structures, transmission parts and sensors.
• It is used in power generation industries.
• It is used in space industries to build titanium tanks and sensors.
• It is used in automobile industries to manufacture transmission
system, gears and turbochargers.
• It used in electrical and electronica industries to manufactures parts of
copper structures.
• The other areas where it is used are nuclear industries, medical,
research centres etc .
 Laser Beam Welding
• Laser Beam Welding is a fusion welding process in which
two metal pieces are joined together by the use of laser.

• The laser beams are focused to the cavity between the

two metal pieces to be joined.

• The laser beams have enough energy and when it strikes

the metal pieces produces heat that melts the material
from the two metal pieces and fills the cavity.

• After cooling a strong weld is formed between the two

pieces.
 Working Principle - LBW
• It works on the principle that when electrons of
an atom gets excited by absorbing some energy,
and then after some time when it returns back to
its ground state, it emits a photon of light. The
concentration of this emitted photon increased
by stimulated emission of radiation and we get a
high energy concentrated laser beam.

• Light amplification by stimulated emission of

radiation is called laser.
Working Principle - LBW
 LBW - Working
• First the setup of welding machine at the desired
location (in between the two metal pieces to be
joined) is done.
• After setup, a high voltage power supply is applied on
the laser machine.
• This starts the flash lamps of the machine and it
emits light photons.
• The energy of the light photon is absorbed by the
atoms of ruby crystal and electrons get excited to
their higher energy level.
 LBW - Working
• When they return back to their ground state (lower Energy
state) they emit a photon of light.

• This light photon again stimulates the excited electrons of the

atom and produces two photons.

• This process keeps continue and we get a concentrated laser

beam.

• This high concentrated laser beam is focused to the desired

location for the welding of the multiple pieces together.

• Lens are used to focus the laser to the area where welding is
needed.
 LBW - Working
• CAM is used to control the motion of the laser
and workpiece table during the welding process.

• As the laser beam strikes the cavity between the

two metal pieces to be joined, it melts the base
metal from both the pieces and fuses them
together. After solidification we get a strong
weld.
 Advantages
• It produces high weld quality.
• LBW can be easily automated with robotic machinery
for large volume production.
• No electrode is required.
• No tool wears because it is a non-contact process.
• The time taken for welding thick section is reduced.
• It is capable of welding in those areas which is not
easily accessible
 Advantages
• It has the ability to weld metals with dissimilar physical
properties.
• It can be weld through air and no vacuum is required.
• X – Ray shielding is not required as it does not produce any
X-Rays.
• It can be focused on small areas for welding. This is because of
its narrower beam of high energy.
• Wide variety of materials can be welded by using laser beam
welding.
• It produces weld of aspect ratio (i.e. depth to width ratio) of
10:1.
 Disadvantages
• Initial cost is high. The equipment used in LBW has
high cost.
• High maintenance cost.
• Due to rapid rate of cooling, cracks may be produced
in some metals.
• High skilled labour is required to operate LBW.
• The welding thickness is limited to 19 mm.
• The energy conversion efficiency in LBW is very low. It
is usually below 10 %.
 WELDING DEFECTS
1. Lack of Penetration 7. Poor Weld Bead
2. Incomplete Appearance
penetration and 8. Distortion
Fusion
9. Overlays
3. Porosity
10. Blowholes
4. Slag Inclusion
11. Burn Through
5. Undercuts
12. Excessive Penetration
6. Cracking
 Incomplete Penetration
Incomplete Penetration
• It occurs when the weld
metal does not form a
cohesive bond with the
weld metal.
 Porosity
It is a group of small holes throughout the weld
metal. It is caused by the trapping of gas during
the welding process, due to
(a) Chemicals in the metal
(b) Dampness
(c) Too rapid cooling of the weld.
 Undercutting
• It is essentially an
unfilled groove along
the edge of the weld.
The causes are usually
associated with
incorrect electrode
angles, incorrect
weaving technique,
excessive current and
travel speed.
 OVERLAP
• The protrusion of weld metal beyond the weld
toe or weld root.
• Poor welding techniques
• The overlap can be repaired by grinding off
excess weld metal and surface grinding
smoothly to the base metal.
 UNDERFILL
• Underfill is a condition in which the weld face or
root surface extends below the adjacent surface
of the base metal.
• It can be cause by excessive heating and melting
of root pass during deposition of second pass.
• Cause: Excessive travel speed
 SPATTER
• AWS A 3.0 describes spatter as “metal particles expelled
during fusion welding that do not form a part of weld.
• Small particles of weld metal expelled from the welding
operation which adhere to the base metal surface.
• The cause for this discontinuity are: High welding
current which can cause excessive turbulence in the
weld zone, long arc length, severe electrode angles,
high amperages.
 MISALIGNMENT
Offset or mismatch occurs where two pieces welded together are
not properly aligned. It occurs because of carelessness and also
due to joining different thicknesses (transition thickness).
 INCLUSIONS
• Inclusion is entrapped foreign solid material, such as
slag, flux ,tungsten or oxide.
• Associated with Lack of Fusion(LOF).
• Only occurs when any welding technique uses Flux
shielding.
• Due to improper manipulation of welding electrode and
improper cleaning between multi run
 LACK OF FUSION (LOF)
• Weld discontinuity in which fusion did not occur between weld metal and fusion
faces joining or adjoining weld beads.
Factors promoting LOF:
• Improper manipulation of welding electrode.
• Weld joint design.
• Improper heat input.
• Surface contamination which leads slag formation and prevents fusion
 CRACKS
• A crack is a fissure produced in a metal by tearing action
due to in-adequate pre-heat or fast cooling problem.

• Cracks may also caused by shrinkage stresses in high

constraint areas.
 Distortion
Distortion is due to
• (a) high cooling rate,
• (b) small diameter electrode,
• (c)poor clamping and
• (d) slow arc travel speed.
 Poor Weld bead appearance
• If the width of weld bead
deposited is not uniform
or straight, then the weld
bead is termed as poor.
• It is due to
– improper arc length,
– improper welding
technique,
– damaged electrode coating
and
– poor electrode and
earthing connections.
 Brazing and Soldering
• Brazing and soldering both are solid liquid
processes primarily involve three steps
a) heating of plates to be joined using suitable heat
source,
b) placing and melting of solder or brazing materials
followed by heating to the molten state and
c) filling of molten filler metal between the faying
surfaces of the components to be joined by
capillary action and then solidification results in a
joint.
Brazing and Soldering
 Soldering
Soldering is a process of uniting two or more metal pieces
under heat with the help of a solder and a flux.
There are two types:
• Soft soldering
• Hard soldering.
• Soft solder: for Light joints using various proportions of
lead and tin which has low melting point.
• Hard solder: for strong joints using a mixture of copper,
zinc etc. which has high melting point.
 Brazing

• Process to join two metal pieces heated to a

suitable temperatures by using a filler metal
having a liquidus above 4270 C and below the
solidus of the base metals

• The filler metal is distributed between the

closely fitted surfaces of the joint by capillary
action
 Comparison of Welding, Brazing and Soldering

Welding Brazing Soldering

These are the These are stronger These are weakest
strongest joints used than soldering but joint out of three. Not
to bear the load. weaker than welding. meant to bear the
Strength of a welded These can be used to load. Use to make
joint may be more bear the load upto electrical contacts
than the strength of some extent. generally.
base metal.
Temperature required It may go to 600oC in Temperature
is upto 3800oC of brazing. requirement is upto
welding zone. 450oC.
 Comparison of Welding, Brazing and Soldering

Welding Brazing Soldering

Workpiece to be Workpieces are No need to heat the
joined need to be heated but below their workpieces.
heated till their melting point.
melting point.
Mechanical properties May change in No change in
of base metal may mechanical properties mechanical properties
change at the joint due of joint but it is almost after joining.
to heating and negligible.
cooling.
Heat cost is involved Cost involved and sill Cost involved and
and high skill level is required are in skill requirements are
required. between others two. very low.
 Comparison of Welding, Brazing and Soldering

Welding Brazing Soldering

Heat treatment is No heat treatment is No heat treatment is
generally required to required after required.
eliminate undesirable brazing.
effects of welding.
No preheating of Preheating is Preheating of
workpiece is required desirable workpieces before
before welding as it is to make strong joint soldering is good for
carried out at high as making good quality
temperature. brazing is carried out joint.
at relatively low
temperature.
Comparison of brazing and soldering
Particulars Soldering Brazing
Melting point of Soldering uses the brazing uses
filler filler metal system comparatively
having low melting higher melting point
point (183-2750 C (450-12000C) filler
generally metals (alloys of Al, Cu
than 4500C) called and Ni).
solder (alloy of lead
and tin)
Comparison of brazing and soldering

Particulars Soldering Brazing

Strength of Joint Strength of solder joint Brazed joints offer
is limited by the greater strength than
strength of filler metal solder joints.
Accordingly, brazed
joints are used for
somewhat higher
loading conditions
than solder joint
 Comparison of brazing and soldering

Particulars Soldering Brazing

Ability to solder joints are Braze joints offer
withstand under preferred mainly for higher resistance to
high temperature low temperature thermal load than
conditions applications soldered joint
primarily due to
difference in melting
temperature of solder
and braze metal.
Comparison of brazing and soldering
Particulars Soldering Brazing
Application Soldering is mostly Brazing is
used for joining commonly used for
electronic components joining of tubes, pipes,
where they are wires cable, and tipped
normally tool.
not exposed to severe
temperature and
loading conditions
during service
 Comparison of brazing and soldering
Particulars Soldering Brazing
Source of Heat for Soldering can be Brazing can performed
Joining carried out using heat using gas flame torch,
from soldering iron furnace heating,
(20-150W), dip induction heating, and
soldering infrared heating
and wave soldering. methods