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Dr. N.K. Singh
Associate Professor (Workshop)
Department of ME&MME
Indian School of Mines
Dhanbad
WELDING PROCESS
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Welding
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Welding is the process of joining two metal
pieces as a result of significant diffusion of
the atoms of the welded pieces into the joint
(weld) region.
Welding is carried out by heating the joined
pieces to melting point and fusing them
together (with or without filler material) or by
applying pressure to the pieces in cold or
heated state.
Advantages of welding:
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Strong and tight joining;
Cost effectiveness;
Simplicity of welded structures design;
Welding processes may be mechanized and
automated.
Disadvantages of welding:
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Internal stresses, distortions and changes of
micro-structure in the weld region;
Harmful effects: light, ultra violate radiation,
fumes, high temperature.
Applications of welding:
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Buildings and bridges structures;
Automotive, ship and aircraft constructions;
Pipe lines;
Tanks and vessels;
Machinery elements.
Classification of welding process
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Arc Welding
Gas Welding
Resistance welding
Solid State welding
Unique Processes
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Thermit welding
LBW
EBW
ESW
Welding processes
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Arc welding
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Carbon Arc Welding;
Shielded Metal Arc Welding (SMAW);
Submerged Arc Welding (SAW);
Metal Inert Gas Welding (MIG, GMAW);
Tungsten Inert Gas Arc Welding (TIG, GTAW);
Plasma Arc Welding (PAW);
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Resistance Welding (RW);
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Spot Welding (RSW);
Flash Welding (FW);
Resistance Butt Welding (UW) ;
Seam Welding (RSEW);
Gas Welding (GW);
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Oxyacetylene Welding (OAW);
Oxyhydrogen Welding (OHW);
Pressure Gas Welding (PGW);
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Solid State Welding (SSW);
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Forge Welding (FOW);
Cold Welding (CW);
Friction Welding (FRW);
Explosive Welding (EXW);
Diffusion Welding (DFW);
Ultrasonic Welding (USW);
Thermit Welding (TW);
Electron Beam Welding (EBW);
Laser Welding (LW).
Gas Welding

Gas Welding is a welding process, utilizing
heat of the flame from a welding torch. The
torch mixes a fuel gas with oxygen in the
proper ratio and flow rate, providing
combustion
process
at
a
required
temperature. The hot flame fuses the edges
of the welded parts, which are joined together
forming a weld after Solidification.
Gas Welding
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The flame temperature is determined by a
type of the fuel gas and proportion of oxygen
in the combustion mixture: 4500°F - 6300°F
(2500°C - 3500°C). Depending on the
proportion of the fuel gas and oxygen in the
combustion mixture, the flame may be
chemically neutral (equal ratio of the gases),
oxidizing (excess of oxygen),
carburizing (excess of fuel gas).
Gas Welding
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Filler rod is used when an additional supply of
metal to weld is required. Shielding flux may
be used if protection of weld pool is
necessary.
Gas Welding equipment:
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Fuel gas cylinder with pressure regulator;
Oxygen cylinder with pressure regulator;
Welding torch;
Trolley for transportation of the gas cylinders.
1. Oxyacetylene Welding (OAW)
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Oxyacetylene Welding is a Gas Welding
process using a combustion mixture of
acetylene (C2H2) and oxygen (O2) for
producing gas welding flame.
Temperature: 6000°F (3300°C).
Combustion of acetylene proceeds in two
stages:
1. Inner core of the flame. C2H2 + O2 = 2CO + H2
2. Outer envelope of the flame:
CO + H2 + O2 = CO2 + H2O
Arc welding

Arc welding uses a Electric power supply to create an
electric arc between an electrode and the base material
to melt the metals at the welding point.

Electric arc between the electrode and work piece closes
the electric circuit. The arc temperature may reach
10000°F (5500°C), which is sufficient for fusion of the
work piece edges and joining them.
WELDING PROCESS
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Arc welding
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They can use either direct (DC) or alternating (AC)
current, and consumable or non-consumable
electrodes.
The welding region is sometimes protected by some
type of inert or semi-inert gas, known as a shielding
gas, and/or an evaporating filler material.
The process of arc welding is widely used because
of its low capital and running costs.
Arc Welding process
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ARC Welding Power Supply
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Power Supplies

To supply the electrical energy necessary for arc
welding processes, a number of different power
supplies can be used.
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constant current power supplies
constant voltage power supplies.
In arc welding, the voltage is directly related to
the length of the arc, and the current is related to
the amount of heat input.
WELDING PROCESS
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Power Supplies

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Constant current supply is more important
because in manual welding, it can be difficult
to hold the electrode perfectly steady, and as
a result, the arc length and thus voltage tend
to fluctuate.
Constant voltage power supplies hold the
voltage constant and vary the current, and as
a result, are most often used for automated
welding processes such as gas metal arc
welding, flux cored arc welding, and
submerged arc welding.
WELDING PROCESS
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Consumable electrode methods
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One of the most common types of arc welding is
shielded metal arc welding (SMAW), which is also
known as manual metal arc welding (MMA) or stick
welding.
An electric current is used to strike an arc between
the base material and a consumable electrode rod
or 'stick'.
The electrode rod is made of a material that is
compatible with the base material being welded and
is covered with a flux that protects the weld area
from oxidation and contamination by producing CO2
gas during the welding process.
The electrode core itself acts as filler material,
making a separate filler unnecessary.
WELDING PROCESS
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Schematic representation of MIG Welding
WELDING PROCESS
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MIG Welding
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Gas Metal Arc Welding (GMAW) is frequently
referred to as MIG welding.
MIG welding is a commonly used high
deposition rate welding process.
Wire is continuously fed from a spool.
MIG welding is therefore referred to as a
semiautomatic welding process.
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MIG Welding Shielding Gas
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The shielding gas, forms the arc plasma,
stabilizes the arc on the metal being welded,
shields the arc and molten weld pool, and
allows smooth transfer of metal from the weld
wire to the molten weld pool.
There are three primary metal transfer
modes:
- Spray transfer
- Globular transfer
- Short circuiting transfer
WELDING PROCESS
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The primary shielding gases
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Argon
Argon - 1 to 5% Oxygen
Argon - 3 to 25% CO2
Argon/Helium
CO2 is also used in its pure form in some
MIG welding processes.
However, in some applications the presence
of CO2 in the shielding gas may adversely
affect the mechanical properties of the weld.
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MIG Welding taking place
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Glow of MIG Welding Process
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Photographic view of MIG Weld
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Gas tungsten arc welding (GTAW, TIG)
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GTAW or tungsten inert gas (TIG) welding, is
a manual welding process that uses a nonconsumable electrode made of tungsten , an
inert or semi-inert gas mixture, and a
separate filler material.
Especially useful for welding thin materials,
this method is characterized by a stable arc
and high quality welds, but it requires
significant operator skill and can only be
accomplished at relatively low speeds.
WELDING PROCESS
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Gas tungsten arc welding(GTAW)
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It can be used on nearly all weldable metals,
though it is most often applied to stainless
steel and light metals.
It is often used when quality welds are
extremely important, such as in aircraft and
naval applications.
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GTAW Welding
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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.
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Schematic View of the TIG Welding Process
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TIG Welding taking place
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Welded surface of TIG welding
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TIG Welder
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TIG Welding Benefits
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Superior quality welds
Welds can be made with or without filler
metal
Precise control of welding variables (heat)
Free of spatter
Low distortion
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Shielding Gases of TIG Welding
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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.
WELDING PROCESS
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Plasma Arc Welding Process
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The plasma welding process was introduced
to the welding industry in 1964 as a method
of bringing better control to the arc welding
process in lower current ranges.
Today,
plasma
retains
the
original
advantages it brought to industry by providing
an advanced level of control and accuracy to
produce high quality welds in miniature or
precision applications and to provide long
electrode
life
for
high
production
requirements.
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The Plasma Arc Welding Process
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Plasma Arc Welding is a welding process
utilizing heat generated by a constricted arc
struck between a tungsten non-consumable
electrode and either the work piece
(transferred arc process) or water cooled
constricting nozzle (non-transferred arc
process).
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Plasma is a gaseous mixture of positive ions,
electrons and neutral gas molecules.
WELDING PROCESS
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Transferred arc process produces plasma jet of high
energy density and may be used for high speed
welding and cutting of Ceramics, steels, Aluminum
alloys, Copper alloys, Titanium alloys, Nickel alloys.
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Non-transferred arc process produces plasma of
relatively low energy density. It is used for welding of
various metals. Since the work piece in nontransferred plasma arc welding is not a part of
electric circuit, the plasma arc torch may move from
one work piece to other without extinguishing the
arc.
Plasma Arc Welding Process
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How Plasma Welding Works
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A plasma is a gas which is heated to an
extremely high temperature and ionized so
that it becomes electrically conductive.
Similar to GTAW (TIG), the plasma arc
welding process uses this plasma to transfer
an electric arc to a work piece.
The metal to be welded is melted by the
intense heat of the arc and fuses together.
WELDING PROCESS
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How Plasma Welding Works
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In the plasma welding torch a Tungsten
electrode is located within a copper nozzle
having a small opening at the tip.
A pilot arc is initiated between the torch
electrode and nozzle tip.
This arc is then transferred to the metal to be
welded.
WELDING PROCESS
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How Plasma Welding Works
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By forcing the plasma gas and arc through a
constricted orifice, the torch delivers a high
concentration of heat to a small area.
With high performance welding equipment,
the plasma process produces exceptionally
high quality welds.
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How Plasma Welding Works
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Plasma gases are normally argon.
The torch also uses a secondary gas, argon,
argon/hydrogen or helium which assists in
shielding the molten weld puddle thus
minimizing oxidation of the weld.
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Equipment List of Plasma Arc Welding
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Power Supply
Plasma Console (sometimes external,
sometimes built in)
Water re-circulator (sometimes external,
sometimes built in)
Plasma Welding Torch
Torch Accessory Kit (Tips, ceramics, collets,
electrodes set-up gages)
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Resistance Welding

Resistance Welding is a welding process, in
which work pieces are welded due to a
combination of a pressure applied to them
and a localized heat generated by a high
electric current flowing through the contact
area of the weld.
Resistance Welding
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Heat produced by the current is sufficient for
local melting of the work piece at the contact
point and formation of small weld pool
(”nugget”). The molten metal is then solidifies
under a pressure and joins the pieces.
Process parameters:
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Time of the process
Applied pressure
flowing current
resistance
Resistance Welding
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AC electric current (up to 100 000 A) is
supplied
through
copper
electrodes
connected to the secondary coil of a welding
transformer.
The most popular methods of Resistance
welding are:
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Spot Welding (RSW);
Flash Welding (FW);
Resistance Butt Welding (UW) ;
Seam Welding (RSEW).
Spot Welding (RSW)
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Spot Welding is a Resistance Welding (RW) process, in which
two or more overlapped metal sheets are joined by spot welds.
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The method uses pointed copper electrodes providing passage
of electric current. The electrodes also transmit pressure required
for formation of strong weld.
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Diameter of the weld spot is in the range 1/8” - 1/2” (3 - 12 mm).
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Spot welding is widely used in automotive industry for joining
vehicle body parts.
Flash Welding (FW)
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Flash Welding is a Resistance Welding (RW)
process, in which ends of rods (tubes, sheets) are
heated and fused by an arc struck between them
and then forged (brought into a contact under a
pressure) producing a weld.
The welded parts are held in electrode clamps, one
of which is stationary and the second is movable.
Resistance Butt Welding (UW)
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Resistance Butt Welding is a Resistance
Welding (RW) process, in which ends of
wires or rods are held under a pressure and
heated by an electric current passing through
the contact area and producing a weld
Resistance Butt Welding (UW)
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The process is similar to Flash Welding, however in
Butt Welding pressure and electric current are
applied simultaneously in contrast to Flash Welding
where electric current is followed by forging
pressure application.
Butt welding is used for welding small parts. The
process is highly productive and clean. In contrast to
Flash Welding, Butt Welding provides joining with no
loss of the welded materials.
Seam Welding (RSEW)
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Seam Welding is a Resistance Welding
(RW) process of continuous joining of
overlapping sheets by passing them between
two rotating electrode wheels. Heat
generated by the electric current flowing
through the contact area and pressure
provided by the wheels are sufficient to
produce a leak-tight weld.
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Advantages of Resistance Welding:
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High welding rates;
Low fumes;
Cost effectiveness;
Easy automation;
No filler materials are required;
Low distortions.
Disadvantages of Resistance Welding:
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High equipment cost;
Low strength of discontinuous welds;
Thickness of welded sheets is limited - up to 1/4” (6 mm);
Safety issues
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Welding can be a dangerous and unhealthy practice
without the proper precautions; however, with the
use of new technology and proper protection the
risks of injury or death associated with welding can
be greatly reduced.
Because many common welding procedures involve
an open electric arc or flame, the risk of burns is
significant.
To prevent them, welders wear protective clothing in
the form of heavy leather gloves and protective long
sleeve jackets to avoid exposure to extreme heat,
flames, and sparks.
Additionally, the brightness of the weld area leads to
a condition called arc eye in which ultraviolet light
causes the inflammation of the cornea and can burn
the retinas of the eyes.
WELDING PROCESS
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Safety issues
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Goggles and helmets with dark face plates are worn to
prevent this exposure and, in recent years, new helmet
models have been produced featuring a face plate that
self-darkens upon exposure to high amounts of UV light.
To protect bystanders, transparent welding curtains often
surround the welding area.
These curtains, made of a polyvinyl chloride plastic film,
shield nearby workers from exposure to the UV light from
the electric arc, but should not be used to replace the
filter glass used in helmets.
WELDING PROCESS
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Safety issues
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Welders are also often exposed to dangerous
gases and particulate matter.
Processes like flux-cored arc welding and
shielded metal arc welding produce smoke
containing particles of various types of
oxides.
The size of the particles in question tends to
influence the toxicity of the fumes, with
smaller particles presenting a greater danger.
WELDING PROCESS
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Safety issues
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Additionally, many processes produce
various gases (most commonly carbon
dioxide and ozone, but others as well) that
can prove dangerous if ventilation is
inadequate.
Furthermore, the use of compressed gases
and flames in many welding processes pose
an explosion and fire risk; some common
precautions include limiting the amount of
oxygen in the air and keeping combustible
materials away from the workplace.
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