UNIT 4 Welding process mechaniaclengineering.ppt

COURSE: MANUFACTURING PROCESSS
CODE: A40310
IV Semester
Regulation: R-23
G. Pullaiah College of Engineering and Technology
(Autonomous)
Pasupula, Kurnool- 518002
Dr G Praveen Kumar
Assistant Professor
Mechanical Engineering
Prepared by

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COURSE STRUCTURE
A40310 – MANUFACTURING PROCESSES
1.Course Description
Course Overview
• Know the working principle of different metal casting processes and gating system.
• Classify the welding processes, working of different types of welding processes and welding
defects.
• Know the nature of plastic deformation, cold and hot working process, working of a rolling mill
and types, extrusion processes.
• Understand the principles of forging, tools and dies, working of forging processes.
• Know about the Additive manufacturing.
Course Pre/corequisites
Engineering Workshop

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1. Course Outcomes (COs)
After the completion of the course, the student will be able to:
A40310.1 Design the patterns and core boxes for metal casting processes
A40310.2 Demonstrate the different types of bulk forming processes
A40310.3 Understand sheet metal forming processes
A40310.4 Understand the different welding processes
A40310.5 Learn about the different types of additive manufacturing processes

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Course Syllabus
Casting: Steps involved in making a casting – Advantage of casting and its applications. Patterns and Pattern making – Types of
patterns – Materials used for patterns, pattern allowances and their construction, Molding, different types of cores , Principles of Gating,
Risers, casting design considerations. Methods of melting and types of furnaces, Solidification of castings and casting defects- causes
and remedies. Basic principles and applications of special casting processes - Centrifugal casting, Die casting, Investment casting and
shell molding.
UNIT I I
UNIT II I
Bulk Forming: Plastic deformation in metals and alloys-recovery, recrystallization and grain growth.
Hot working and Cold working-Strain hardening and Annealing. Bulk forming processes: Forging-Types of Forging, forging defects and
remedies; Rolling – fundamentals, types of rolling mills and products, Forces in rolling and power requirements. Extrusion and its
characteristics. Types of extrusion, Impact extrusion, Hydrostatic extrusion; Wire drawing and Tube drawing.
UNIT III I
Sheet metal forming-Blanking and piercing, Forces and power requirement in these operations, Deep drawing, Stretch forming, Bending,
Spring back and its remedies, Coining, Spinning, Types of presses and press tools.
High energy rate forming processes: Principles of explosive forming, electromagnetic forming, Electro hydraulic forming, rubber pad forming,
advantages and limitations.
UNIT IV I
Welding: Classification of welding processes, types of welded joints and their characteristics, Gas welding, Different types of flames and
uses, Oxy – Acetylene Gas cutting. Basic principles of Arc welding, power characteristics, Manual metal arc welding, submerged arc
welding, TIG& MIG welding. Electro–slag welding.
Resistance welding, Friction welding, Friction stir welding, Forge welding, Explosive welding; Thermit welding, Plasma Arc welding, Laser
welding, electron beam welding, Soldering &Brazing.
Heat affected zones in welding; pre & post heating, welding defects –causes and remedies.
UNIT V I
Additive manufacturing - Steps in Additive Manufacturing (AM), Classification of AM processes, Advantages of AM, and types of
materials for AM, VAT photopolymerization AM Processes, Extrusion - Based AM Processes, Powder Bed Fusion AM Processes, Direct
Energy Deposition AM Processes, Post Processing of AM Parts, Applications

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UNIT IV I
Welding: Classification of welding processes, types of welded joints and their
characteristics, Gas welding, Different types of flames and uses, Oxy – Acetylene
Gas cutting. Basic principles of Arc welding, power characteristics, Manual metal
arc welding, submerged arc welding, TIG& MIG welding. Electro–slag welding.
Resistance welding, Friction welding, Friction stir welding, Forge welding,
Explosive welding; Thermit welding, Plasma Arc welding, Laser welding, electron
beam welding, Soldering &Brazing.
Heat affected zones in welding; pre & post heating, welding defects –causes and
remedies.

Welding processes
Welding is a process of joining similar or dissimilar metals by application
of heat with or without application of pressure and with or without addition of
filler material
OR
Welding is defined as an localized coalescence of metals, where in
coalescence is obtained by heating to suitable temperature, with or without the
application of pressure and with or without the use of filler metal.

• Until the end of the 19th century,
the only welding process was
forge welding, which blacksmiths
had used for centuries to join
iron and steel by heating and
hammering them.
• Arc welding and oxyfuel welding
were among the first processes
to develop late in the century,
and resistance welding followed
soon after.
History of welding

Welding, was transformed during the 19th century. In 1802,
Russian scientist Vasily Perov discovered the electric arc
and subsequently proposed its possible practical
applications, including welding.
From this many other forms, including current forms, have
been born including:
 Carbon arc welding
 Alternating current welding
 Resistance welding
 Oxyfuel welding
History of welding

Often done by melting the
work pieces and adding
a filler material to form
a pool of molten
material (the weld pool)
that cools to become a
strong joint.
Pressure sometimes
used in conjunction
with heat, or by itself, to
produce the weld.
How is it done?

TYPES OF 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
• 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) -Friction

Classification of Welding Process

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3 TYPES OF WELDING JOINTS
Welded joints

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Butt Joint
A connection between the ends or edges of two parts making
an angle to one another of 135-180° inclusive in the region of
the joint.
Common Joint Configurations

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T Joint
A connection between the end or edge of one part and the
face of the other part, the parts making an angle to one
another of more than 5 up to and including 90° in the region
of the joint.

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Corner Joint
A connection between the ends or edges of two parts making
an angle to one another of more than 30 but less than 135° in
the region of the joint.

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Edge Joint
A connection between the edges of two parts making an angle
to one another of 0 to 30° inclusive in the region of the joint.

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Cruciform Joint
A connection in which two flat plates or two bars are welded
to another flat plate at right angles and on the same axis.

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Lap Joint
A connection between two overlapping parts making an angle
to one another of 0-5° inclusive in the region of the weld or
welds.

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Welds Based on Configuration
Slot weld
Joint between two overlapping components made by
depositing a fillet weld around the periphery of a hole in one
component so as to join it to the surface of the other
component exposed through the hole.
Types of Welding Joints

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Welds Based on Configuration
Plug weld
Weld made by filling a hole in one component of a workpiece
with filler metal so as to join it to the surface of an
overlapping component exposed through the hole (the hole
can be circular or oval).

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Based on Penetration
Full Penetration weld
Welded joint where the weld metal fully penetrates
the joint with complete root fusion.

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Based on Penetration
Partial Penetration weld
Weld in which the fusion penetration is intentionally
less than full penetration.

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Based on Accessibility

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Features of Completed Welds

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Parent Metal
Metal to be joined or surfaced by welding, braze welding or
brazing.
Filler Metal
Metal added during welding, braze welding, brazing or surfacing.
Weld Metal
All metal melted during the making of a weld and retained in the
weld.
Heat Affected Zone(HAZ)
The part of the parent metal metallurgically affected by the weld
or thermal cutting heat, but not melted.
Fusion Line
Boundary between the weld metal and the HAZ in a fusion weld.
This is a non-standard term for weld junction.

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Weld Zone
Zone containing the weld metal and the HAZ.
Weld Face
The surface of a fusion weld exposed on the side from which the
weld has been made.
Weld Root
Zone on the side of the first run furthest from the welder.
Weld Toe
Boundary between a weld face and the parent metal or between
runs. This is a very important feature of a weld since toes are
points of high stress concentration and often they are initiation
points for different types of cracks (eg fatigue cracks, cold
cracks).
In order to reduce the stress concentration, toes must blend
smoothly into the parent metal surface.

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Excess Weld Metal
Weld metal lying outside the plane joining the toes. Other non-
standard terms for this feature: reinforcement, overfill.
Note: The term reinforcement, although commonly used, is
inappropriate because any excess weld metal over and above the
surface of the parent metal does not make the joint stronger.
In fact, the thickness considered when designing a welded
component is the design throat thickness, which does not include
the excess weld metal.

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Run (pass)
The metal melted or deposited during one passage of an
electrode, torch or blowpipe.
Layer
Stratum of weld metal consisting of one or more runs.

CLASSIFICATION OF WELDING
PROCESSES:
 Gas welding(Oxy- Acetylene)
 Arc welding(Metal Arc)
 Resistance welding
 Solid state welding
 Thermo-chemical welding

Gas Welding:
Gas Welding is a fusion welding process, in which the
heat for welding is obtained by the combustion of
oxygen and fuel the gas may be acetylene ,hydrogen
or propene .
Types:
•Oxy- Acetylene
•Air-Acetylene
•Oxy-Hydrogen
•Oxy-Fuel

Oxy-Acetylene Welding:
When a combination of
Oxygen and acetylene is
used in correct
proportions to produce an
Intense gas flame, the
process is known as oxy-
acetylene welding.

Gas Welding Equipment :
1. Gas Cylinders
Pressure-
Oxygen – 125 kg/cm2
Acetylene – 16 kg/cm2
2. Regulators
• Working pressure of oxygen 1 kg/cm2
• Working pressure of acetylene 0.15 kg/cm2
• Working pressure varies depends upon the thickness of the work pieces
welded.
3. Pressure Gauges
4. Hoses
5. Welding torch
6. Check valve
7. Non return valve

This flame directly strikes the weld area and melts the weld surface and filler material.
The melted part of welding plates diffused in one another and create a weld joint after
cooling.
This welding method can be used to join most of common metals used in daily life.
Types of gases (Fuels):
Acetylene
hydrogen
propane
natural gas etc.
Types of gas welding :
Based on the combination of the gases used :
Oxy acetylene gas welding (most common type)
Air- acetylene gas welding
Oxy-hydrogen gas welding

Neutral Flame:
•Carburizing Flame: •Oxidizing Flame:
There are three basic flame types:
1.Neutral Flame (balanced)
2.Oxidizing (excess oxygen) and
3.Carburizing (excess acetylene)
Types of flames in gas welding

Types of flames in gas welding ….
Commonly used to weld:
Mild steel
Stainless steel
Cast Iron
Copper
Aluminum
There are two clearly defined zones in the neutral
flame.
The inner zone consists of a luminous cone that is
bluish-white.
Surrounding this is a light blue flame envelope or
sheath.
Neutral Flame:
-Equal volume of acetylene and oxygen.
-Obtains additional oxygen from the air and
provides complete combustion.
The oxygen to acetylene ratio is around 1.1 to 1.0.
Generally preferred flame.
The neutral flame has a clear, well-defined, or
luminous cone indicating that combustion is
complete

Oxidizing Flame:
 Excess oxygen.
 The oxygen to acetylene ratio in the case of Oxidizing flame is 1.5 to 1.
 When the flame is properly adjusted, the inner cone is pointed and slightly purple.
 An oxidizing flame can also be recognized by its distinct hissing sound.
 The temperature of this flame is approximately 3482ºC at the inner cone tip.
Oxidizing welding flames are commonly
used to weld these metals:
•Zinc
•Copper
•Manganese steel
•Cast iron

1. Clearly defined bluish-white inner cone,
2. White intermediate cone indicating the
amount of excess acetylene, and
3. A light blue outer flare envelope.
Carburizing Flame:
 Excess acetylene, the inner cone has a feathery edge extending beyond it.
 Oxygen to acetylene ratio in case of reducing flame varies from 0.85 to 1.
 The reducing or carburizing flame can always be recognized by the presence of three
distinct flame zones.
 It has a temperature of approximately 2900ºC at the inner cone tips.

FLAMES
ADJUSTMENT
FOR OAW
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Advantages:
Portable and most versatile process.
Better control over the temperature.
Suitable to weld dissimilar matter.
Low cost & maintenance.
Disadvantages:
Not suitable for heavy section.
Less working temperature of gas flame.
Slow rate of heating.

Arc Welding:
“Arc welding is a fusion welding process in which the heat required
to fuse the metal is obtain from the electric arc between the base
metal and an electrode.
Types:
1.Metal Arc Welding
2.Submerged Arc Welding
3.Tungsten Inert Gas Welding
4.Metal Inert Gas Welding

ARC WELDING
 The arc welding is a fusion welding process in which the heat required to fuse the
metal is obtained from an electric arc between the base metal and an electrode.
 The electric arc is produced when two conductors are touches together and then
separated by a small gap of 2 to 4 mm, such that the current continues to flow,
through the air. The temperature produced by the electric arc is about 4000°C to
6000°C.
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PRINCIPLE
• The source of heat for arc welding process is an 'electric arc' generated between
two electrically conducting materials.
• One of the workpiece material called 'electrode' is connected to one pole of the
electric circuit, while the other workpiece which forms the second conducting
material is connected to the other pole of the circuit.
• When the tip of the electrode material is brought in contact with the workpiece
material and momentarily separated by small distance of 2-4 mm, an arc can be
generated.
• The electrical energy is thus converted to heat energy.
• The high heat of the arc melts the edges of the workpieces.
• Coalescence takes place where the molten metal of the one workpiece combines
with the molten metal of the other workpiece.
• When the coalesced liquid solidifies, the two workpieces join together to form a
single component.
• The electrode material can be either a non-consumable material or a Consumable
material.
• The non-consumable electrode made of tungsten, graphite etc., serve only to
strike the arc and is not consumed during the welding process.
• Whereas, the consumable electrode which is made of the same material as that of
the workpiece metal helps to strike the arc and at the same time melt (gets
consumed) and combines with the molten metal of the workpiece to form a weld.
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ELECTRIC CURRENT FOR WELDING
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Both D.C. (direct current) and A.C. (alternating current) are used to produce an arc in
electric arc welding. Both have their own advantages and applications.
The D.C. welding machine obtains their power from an A.C. motor or diesel/petrol
generator or from a solid state rectifier.
The capacities of D.C. machine are:
Current:
Up to 600 amperes.
Open Circuit Voltage:
50 to 90 volts, (to produce arc).
Closed Circuit Voltage:
18 to 25 volts, (to maintain arc
The A.C. welding machine has a step down transformer which receives current from
main A.C. supply. This transformer step down the voltage from 220 V-440V to
normal open circuit voltage of 80 to 100 volts. The current range available up to 400
amperes in the steps of 50 ampere.

The capacities of A.C. welding machine are:
Current Range:
Up to 400 ampere in steps of 50 ampere.
Input Voltage:
220V- 440V
Actual Required Voltage:
80 – 100 volts. Frequency: 50/60 HZ.
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ELECTRIC CURRENT FOR WELDING

PROCEDURE OF ELECTRIC
ARC WELDING
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SIGNIFICANCE OF POLARITY
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When D.C. current is used for welding, the following two types of polarity are
available:
(i)Straight or positive polarity.
(ii)Reverse or negative polarity.
When the work is made positive and electrode as negative then polarity is called
straight or positive polarity.
In straight polarity, about 67% of heat is distributed at the work (positive terminal)
and 33% on the electrode (negative terminal). The straight polarity is used where
more heat is required at the work. The ferrous metal such as mild steel, with faster
speed and sound weld, uses this polarity.

SIGNIFICANCE OF POLARITY
On the other hand, when the work is made negative and electrode as positive then
polarity is known as reverse or negative polarity, as shown in Fig. 7.16 (b).
In reverse polarity, about 67% of heat is liberated at the electrode (positive
terminal)
and 33% on the work (negative terminal).
The reverse polarity is used where less heat is required at the work as in case of thin
sheet metal weld. The non-ferrous metals such as aluminum, brass, and bronze
nickel are welded with reverse polarity.
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Equipments Required for Electric Arc Welding
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The various equipment's required for electric arc welding are:
1. Welding Machine:
The welding machine used can be A.C. or D.C. welding machine. The A.C. welding
machine has a step-down transformer to reduce the input voltage of 220- 440V to
80-100V.
The D.C. welding machine consists of an A.C. motor-generator set or diesel/petrol
engine-generator set or a transformer-rectifier welding set.
A.C. machine usually works with 50 hertz or 60 hertz power supply.
 The efficiency of A.C. welding transformer varies from 80% to 85%. The energy
consumed per Kg. of deposited metal is 3 to 4 kWh for A.C. welding while 6 to 10
kWh for D.C. welding.
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2. Electrode Holders:
The function of electrode holder is to hold the electrode at desired angle. These are
available in different sizes, according to the ampere rating from 50 to 500 amperes.
3. Cables or Leads:
The function of cables or leads is to carry the current from machine to the work.
These are flexible and made of copper or aluminum. The cables are made of 900
to 2000 very fine wires twisted together so as to provide flexibility and greater
strength.
The wires are insulated by a rubber covering, a reinforced fibre covering and further
with a heavy rubber coating.
4. Cable Connectors and Lugs:
The functions of cable connectors are to make a connection between machine
switches and welding electrode holder. Mechanical type connectors are used; as
they can he assembled and removed very easily. Connectors are designed
according to the current capacity of the cables used.
5. Chipping Hammer:
The function of chipping hammer is to remove the slag after the weld metal has
solidified. It has chisel shape and is pointed at one
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6. Wire Brush, Power Wire Wheel:
The function of wire brush is to remove the slag particles after chipping by chipping
hammer. Sometimes, if available a power wire wheel is used in place manual wire
brush.
7. Protective Clothing:
The functions of protective clothing's used are to protect the hands and clothes of
the welder from the heat, spark, ultraviolet and infrared rays. Protective clothing
used are leather apron, cap, leather hand gloves, leather sleeves, etc. The high
ankle leather shoes must be wear by the welder.
8. Screen or Face Shield:
The function of screen and face shield is to protect the eyes and face of the welder
from the harmful ultraviolet and infrared radiations produced during welding. The
shielding may be achieved from head helmet or hand helmet

ARC WELDING ELECTRODES
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Arc welding electrodes can be classified into two broad categories:
1.Non-Consumable electrodes.
2.Consumable electrodes.
1.Non-Consumable Electrodes:
These electrodes do not consumed during the welding operation, hence they
named, non-consumable electrodes. They are generally made of carbon, graphite or
tungsten. Carbon electrodes are softer while tungsten and graphite electrodes are
hard and brittle.
Carbon and graphite electrodes can be used only for D.C. welding, while tungston
electrodes can be used for both D.C. and A.C. welding. The filler material is added
separately when these types of electrodes are used. Since, the electrodes do not
consumed, the arc obtained is stable.
2.Consumable Electrodes:
These electrodes get melted during welding operation, and supply the filler material.
They are generally made with similar composition as the metal to be welded.

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Arc Welding
Consumable Electrodes
Mild Steel Electrodes Copper Electrodes

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Arc Welding
Non Consumable Electrodes
Carbon Electrodes Tungsten Electrodes

Advantages and Disadvantages of Arc Welding
Advantages
 Most efficient way to join
metals
 Lowest-cost joining
method
 Affords lighter weight
through better utilization
of materials
 Joins all commercial
metals
 Provides design flexibility
Disadvantages
Manually applied, therefore
high labor cost.
Need high energy causing
danger
Not convenient for
disassembly.
Defects are hard to detect at
joints.

Applications:
 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 etc.

1. METALARC WELDING (MAW)
• In metal arc welding an arc is established between work and the filler metal
electrode.
• The intense heat of the arc forms a molten pool in the metal being welded,
and at the same time melts the tip of the electrode.
• As the arc is maintained, molten filler metal from the electrode tip is
transferred across the arc, where it fuses with the molten base metal.
• Arc may be formed with direct or alternating current.
.
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METALLIC ARC WELDING (MAW) ( continued…….)
• A simple transformer however widely employed for A.C. arc welding.
• The transformer sets are cheaper and simple having no maintenance cost as
there are no moving parts.
• With AC system, the covered or coated electrodes are used, whereas with
D.C. system for cast iron and non-ferrous metals, bare electrodes can be used.
• In order to strike the arc an open circuit voltage of between 60 to 70 volts is
required.
• For maintaining the short arc 17 to 25 volts are necessary.
• The current required for welding, however, varies from 10 amp. to 500 amp.
depending upon the class of work to be welded.
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METALLIC ARC WELDING
•Process: Uses a flux-coated electrode which melts and forms the weld.
• The coating produces a shielding gas when heated.
•Shielding: From the flux on the electrode.
•Electrode: Consumable.
•Common Uses: Construction, repair work, outdoor jobs.
•Pros: Simple, portable, low cost.
•Cons: Slag needs to be chipped off, lower weld quality for precision jobs.

TUNGSTEN INERT GAS WELDING (TIG)
• Tungsten inert gas welding or gas tungsten arc welding (GTAW) is a group of
welding process in which the workpieces are joined by the heat obtained from
an electric arc struck between a non-consumable tungsten electrode and the
workpiece in the presence of an inert gas atmosphere.
• A filler metal may be added if required, during the welding process.
• Figure shows the TIG process.
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Description
• TIG equipment consists of a welding torch in which a
non-consumable tungsten alloy electrode is held
rigidly in the collet.
• The diameter of the electrode varies from 0.5 - 6.4
mm.
• TIG welding makes use of a shielding gas like argon or
helium to protect the welding area from atmospheric
gases such as oxygen and nitrogen, otherwise which
may cause fusion defects and porosity in the weld
metal.
• The shielding gas flow from the cylinder, through the
passage in the electrode holder and then impinges on
the workpiece.
• Pressure regulator and flow meters are used to
regulate the pressure and flow of gas from the
cylinder.
• Either AC or DC can be used to supply the required
current.
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Operation
• The workpieces to be joined are cleaned to remove dirt, grease and other
oxides chemically or mechanically to obtain a sound weld.
• The welding current and inert gas supply are turned ON.
• An arc is struck by touching the tip of the tungsten electrode with the
workpiece and instantaneously the electrode is separated from the
workpiece by a small distance of 1.5 - 3 mm such that the arc still remains
between the electrode and the workpiece.
• The high intensity of the arc melts the workpiece metal forming a small
molten metal pool.
• Filler metal in the form of a rod is added manually to the front end of the
weld pool.
• The deposited filler metal fills and bonds the joint to form a single piece
of metal
• The shielding gas is allowed to impinge on the solidifying weld pool for a
few seconds even after the arc is extinguished (shut off)
• This will avoid atmospheric contamination of the solidifying metal
thereby increasing the strength of the joint.
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Advantages
• Suitable for thin metals.
• Clear visibility of the arc provides the operator to have a greater control
over the weld.
• Strong and high quality joints are obtained.
• No flux is used. Hence, no slag formation. This results in clean weld joints.
Disadvantages
• TIG is the most difficult process compared to all the other welding
processes. The welder must maintain short arc length, avoid contact
between electrode and the workpiece and manually feed the filler metal
with one hand while manipulating the torch with the other hand.
• Tungsten material when gets transferred into the molten metal
contaminates the same leading to a hard and brittle joint.
• Skilled operator is required.
• Process is slower.
• Not suitable for thick metals.
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2. Tungsten Inert Gas (TIG) Welding
(also called GTAW – Gas Tungsten Arc Welding)
•Process: Uses a non-consumable tungsten electrode with
a separate filler rod if needed.
•Shielding: Inert gas (usually Argon or Helium).
•Electrode: Non-consumable.
•Common Uses: Aerospace, automotive, precision welding.
•Pros: Clean, high-quality welds, precise control.
•Cons: Slower, requires skilled operators.

METAL INERT GAS (MIG) WELDING
• Metal inert gas welding or gas metal arc welding (GMAW) is a group of arc
welding process in which the workpieces are joined by the heat obtained from
an electric arc struck between a bare (uncoated) consumable electrode and the
workpiece in the presence of an inert gas atmosphere.
• The consumable electrode acts as a filler metal to fill the gap between the two
workpieces.
• Figure shows the MIG welding process.
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Description
• The equipment consists of a welding torch in which a bare consumable electrode
in the form of a wire is held and guided by a guide tube.
• The electrode material used in MIG welding is of the same material or nearly the
same chemical composition as that of the base metal.
• Its diameter varies from 0.7 -2.4 mm.
• The electrode is fed continuously at a constant rate through feed rollers driven
by an electric motor.
• MIG makes use of shielding gas to prevent atmospheric contamination of the
molten weld pool.
• Mixture of argon and carbon dioxide in a order of 75% to 25% or 80% to 20% is
commonly used.
• The shielding gas flow from the cylinder, through the passage in the electrode
holder and then impinges on the workpiece.
• AC is rarely used with MIG welding; instead DC is employed and the electrode is
positively charged. This results in faster melting of the electrode which increases
weld penetration and welding speed.
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Operation
• The workpieces to be joined are cleaned to remove dust, grease and other oxides
chemically or mechanically to obtain a sound weld. The tip of the electrode is also
cleaned with a wire brush.
• The control switch provided in the welding torch is switched ON to initiate the
electric power, shielding gas and the wire (electrode) feed.
• An arc is struck by touching the tip of the electrode with the workpiece and
instantaneously the electrode is separated from the workpiece by a small distance
of 1.5-3 mm such that the arc still remains between the electrode and the
workpiece.
• The high intensity of the arc melts the workpiece metal forming a small molten
pool.
• At the same time, the tip of the electrode also melts and combines with the
molten metal of the workpieces thereby filling the gap between the two
workpieces.
• The deposited metal upon solidification bonds the joint to form a single piece of
metal.
05/19/24 71

Advantages
• MIG welding is fast and economical.
• The electrode and inert gas are automatically fed, and this makes the operator
easy and to concentrate on the arc.
• Weld deposition rate is high due to the continuous wire feed
• No flux is used. Hence, no slag formation. This results in clean welds.
• Thin and thick metals can be welded.
• Process can be automated.
Disadvantages
• Equipment is costlier
• Porosity (gas entrapment in weld pool) is the most common quality problem in
this process. However, extensive edge preparation can eliminate this defect.
05/19/24 72

Metal Inert Gas (MIG) Welding
(also called GMAW – Gas Metal Arc Welding)
•Process: Uses a continuously fed consumable wire as electrode and
filler.
•Shielding: Inert or semi-inert gas (Argon or CO mixtures).
₂
•Electrode: Consumable wire.
•Common Uses: Fabrication, automotive industry.
•Pros: Fast, easy to automate, minimal slag.
•Cons: Less effective outdoors due to wind disturbing the shielding gas.

SUBMERGED ARC WELDING (SAW)
• Submerged arc welding is a group of arc welding process in which the
workpieces are joined by the heat obtained from an electric arc struck between
a bare consumable electrode and workpiece.
• The arc is struck beneath a covering layer of granulated flux.
• Thus, the arc zone and the molten weld pool are protected from atmospheric
contamination by being 'submerged under a blanket of granular flux.
• This gives the name 'submerged arc welding' to the process.
• Figure shows the submerged arc welding process.
05/19/24 74

Submerged Arc Welding(SAW)
05/19/24 75

Description
• The equipment consists of a welding head carrying a
bare consumable electrode and a flux tube.
• The flux tube remains ahead of the electrode, stores
the granulated or powdered flux, and drops the same
on the joint to be welded.
• The flux shields and protects the molten weld metal
from atmospheric contamination.
• The electrode which is bare (uncoated) and in the
form of wire is fed continuously through feed rollers.
• It is usually copper plated to prevent rusting and to
increase its electrical conductivity (since it is
submerged under flux).
• The diameter of the electrode ranges from 1.6-8 mm
and the electrode material depends on the type of the
work piece metal being welded.
• The process makes use of either AC or DC for
supplying the required current.
05/19/24 76

Operation
• Edge preparation is carried out to obtain a sound weld.
• Flux is deposited at the joint to be welded
• Welding current is witched ON.
• An arc is struck between the electrode and the workpiece under the layer of
flux.
• The flux covers the arc thereby increasing the heat near the weld zone.
• This heat melts the filler metal and the workpiece metal forming a molten weld
pool.
• At the same time, a portion of the flux melts and reacts with the molten weld
pool to form a slag.
• The slag floats on the surface providing thermal insulation to the molten metal
thereby allowing it to cool slowly.
• The welding head is moved along the surface to be welded and the continuously
fed electrode completes the weld.
• The un-melted flux is collected by a suction pipe and reused.
• The layer of slag on the surface of the weld portion is chipped out and the weld
is finished.
• Since the weld pool is covered by flux, solidification of molten metal is slow.
Hence, a backing plate made from copper or steel is used at the bottom of the
joint to support the molten metal until solidification is complete.
05/19/24 77

Advantages
• High productivity process, due to high heat concentration.
• Weld deposition rate is high due to continuous wire feed. Hence, single pass
welds can be made in thick plates.
• Deep weld penetration.
• Less smoke, as the flux hides the arc. Hence, improved working conditions.
• Can be automated
• Process is best suitable for outdoor works and in areas with relatively high winds.
• There is no chance of spatter of molten metal, as the arc is beneath the flux.
Disadvantages
• The invisible arc and the weld zone make the operator difficult to judge the
progress of welding.
• Use of powdered flux restricts the process to be carried only in flat positions.
• Slow cooling rates may lead to hot cracking defects.
• Need for extensive flux handling.
05/19/24 78

2. Submerged Arc Welding (SAW)
•Process: Uses a continuously fed consumable wire and
a blanket of granular flux covering the weld zone.
•Shielding: From the granular flux (submerges the arc).
•Electrode: Consumable wire.
•Common Uses: Long, straight welds in heavy industries
(e.g., pressure vessels, shipbuilding).
•Pros: High deposition rate, deep welds, minimal spatter.
•Cons: Not suitable for thin materials or out-of-position
welding.

Introduction
Electro slag welding is a type of arc welding wherein
the coalescence is produced by molten slag which
melts the filler metal metal and the surface of the
work to be welded, electro slag welding is quite
similar to vertical submerged arc welding.

Woking principle
1. In electro slag welding process a granular flux
is placed in the gap between the plate being
welded and as the current is turned on, welding
takes place in a water-cooled copper shoes that
bridge the gap of the joint as the flux melts, a
slag blanket from 25.4 to 38.1 mm thickness is
formed , high resistance of the slag causes most
of the heating for the remainder of the weld thus
electro slag welding is a progressive process of
melting and solidification from the bottom to
upward.
2. The maximum thickness that can be weld by
this process is up to 100 mm
3. Molten metal and slag are retained in the joint
by means of copper shoes that automatically
move upward as the weld progresses by means
of a temperature sensitive mechanism.

Advantages
1.Joint preparation is quite simple as compared
to other welding processes.
2.Very high thickness plate can be very easily
welded in a single pass more economically .
3.It gives extremely high deposition rate.
4.Distortion and thermal stresses are in very low
percentage.
5.Flux consumption is very low.

disadvantages
1.Process is only limited to vertical position.
2.Electro slag welding tend to produce rather
large grain size.
3.Complex shape joint cannot be welded by this
process.
4.More chances of hot cracking and notch
sensitivity in the heat affected zone.

• 5. Electro-Slag Welding (ESW)
• Process: Vertical welding method where an electric arc starts
the weld and is then extinguished; the weld continues using
molten slag that conducts electricity and melts the filler wire.
• Shielding: Molten slag.
• Electrode: Consumable wire.
• Common Uses: Thick vertical joints in structural steel (like
columns in buildings).
• Pros: Welds very thick materials in one pass.
• Cons: Only for vertical position, complex setup.

8
7
Resistance Welding
The welding process studied so far are fusion-welding processes
where only heat is applied in the joint. In contrast, resistance
welding process is a fusion-welding process where both heat
and pressure applied on the joint but no filler metal or flux is
added.
The heat necessary for the melting of the joint is obtained by the
heating effect of the electrical resistance of the joint and hence,
the name resistance welding.

8
8
Resistance Welding
Principle
In resistance welding (RW), a low voltage (typically 1 V) and very
high current (typically 15000 A) is passed through the joint for a
very short time (typically 0.25 Sec). This high amperage heats
the joint, due to the contact resistance at the joint and melts it.
The pressure on the joint is continuously maintained and the
metal fuses together under this pressure.
The heat generated in resistance welding can be expressed as:
H = k I² R t

8
9
Resistance Welding
H = k I² R t
Where,
H = the total heat generated in the work, J
I = electric current, A
R = the resistance of the joint, ohms
t = time for which the electric current is passing through the joint, Sec
k = a constant to account for the heat losses from the weld joint.
The resistance of the joint, R, is a complex factor to know because it is
composed of the
a)Resistance of the electrode,
b)Contact resistance between the electrode and the workpiece,
c)Contact resistance between the two workpiece plates, and
d)Resistance of the workpiece plates.

9
1
Resistance Welding
1. The schematic representation of the resistance welding is shown
and the main requirement of the process is the low voltage and
high current power supply.
2. This is obtained by means of a step down transformer with a
provision to have different tappings on the primary side as
required for different materials.
3. The secondary windings are connected to the electrodes, which
are made of copper to reduce their electrical resistance.
4. The time of the electric supply needs to be closely controlled so
that the heat released is just enough to melt the joint and the
subsequent fusion takes place due to the force on the joint.

9
2
Resistance Welding
5. The force required can be provided either mechanically,
hydraulically or pneumatically.
6. To precisely control the time, sophisticated electronic timers are
available.
7. The critical variable in a resistance welding process is the contact
resistance between the two workpiece plates and their
resistances themselves.
8. The contact resistance is affected by the surface finish on the
plates, since the rougher surfaces have higher contact
resistance.

9
3
Resistance Welding
9. The contact resistance also will be affected by the cleanliness of
the surface.
10. Oxides or other contaminants if present, should be removed
before attempting resistance welding.
11. The lower resistance of the joint requires very high currents to
provide enough heat to melt it.
12. The average resistance may be of the order of 100 micro ohms,
as a result, the current required would be of the order of tens of
thousands of amperes. With a 10 000 A current passing for 0.1
sec, the heat liberated is
H= (10 000)²(0.0001) (0.1) = 1000 J

9
4
Resistance Welding
13. This is typical for the welding of 1-mm thick sheets.
14. The actual heat required for melting would be the order of 339 J.
15. The rest of the heat is actually utilized in heating the
surrounding areas and lost at other points.
16. The welding force used has the effect of decreasing the contact
resistance and consequently, an increase in the welding current
for the proper fusion.

9
5 Types of Resistance Welding
Following are the 4 different types of resistance
welding:
1.Spot resistance welding
2.Projection resistance welding
3.Seam resistance welding
4.Flash or Butt resistance welding

1
0
5
Resistance Welding
The Process of Resistance Welding

THERMIT WELDING
1
0
6
Is a process that uses heat from an exothermic reaction to produce
coalescence between metals. The name is derived from 'thermite' the
generic name given to reactions between metal oxides and reducing
agents.

110
Forge Welding
1. Forge welding (FOW) is a solid-state welding process that joins
two pieces of metal by heating them to a high temperature and
then hammering them together.
2. It may also consist of heating and forcing the metals together
with presses or other means, creating enough pressure to
cause plastic deformation at the weld surfaces.
3. The process is one of the simplest methods of joining metals and
has been used since ancient times.
4. Forge welding is versatile, being able to join a host of similar and
dissimilar metals.
5. With the invention of electrical and gas welding methods during
the industrial revolution, manual forge-welding has been largely
replaced, although automated forge-welding is a common
manufacturing process.

112
Applications Forge Welding
The significant applications of weld forging in blacksmithing
include;
1.It is used to create a more substantial metal from smaller
pieces by allowing blacksmiths to join metal and steel.
2.It is particularly useful in the welding process of weapons like
swords.
3.It is crucial in creating architectural structures such as gates
and prison cells.
4.It is useful in the welding barrels of shotguns.
5.Forge welding is usually employed in the production of various
cookware.

113
Advantages Forge Welding
The advantages of forge welding include;
1.It is relatively straightforward and less complicated.
2.It can easily be carried out by most blacksmiths because it
doesn’t cost much and requires only small pieces of metal.
3.Forge melting is sufficient to join both dissimilar and similar
metals.
4.The weld joint usually takes most of its properties from the
base material.
5.Forge welding of metals does not require any filler material to
be reliable.

114
Disadvantages Forge Welding
The disadvantages of blacksmithing include;
1.It is not useful for mass production of materials.
2.It is preferable for steel and iron.
3.The forge welding process is relatively slow.

1
5
• Friction welding is a
solid state joining
process that
produces coalescence
by the heat developed
between two surfaces
by mechanically
induced surface
motion.
Definition of Friction Welding
Friction Welding

1
6
• One of the workpieces is
attached to a rotating
motor drive, the other is
fixed in an axial motion
system.
• One workpiece is rotated
at constant speed by the
motor.
• An axial or radial force is
applied.
Workpieces
Non-rotating vise
Motor
Chuck
Spindle Hydraulic cylinder
Brake
Continuous Drive Friction Welding

1
7
• The work pieces are
brought together under
pressure for a predeter-
mined time, or until a
preset upset is reached.
• Then the drive is
disengaged and a
break is applied to the
rotating work piece.
Workpieces
Non-rotating vise
Motor
Chuck
Spindle Hydraulic cylinder
Brake
Continuous Drive Friction Welding

1
8
Friction Welded Automotive Halfshaft
Friction Welded Joint
Courtesy AWS handbook
Friction Welded Joints

1
9
Friction Stir Welding
• Parts to be joined are clamped
firmly.
• A rotating hardened steel tool is
driven into the joint and
traversed along the joint line
between the parts.
• The rotating tool produces
friction with the parts,
generating enough heat and
deformation to weld the parts
together.
Butt welds
Overlap welds

2
0
• Frequently competes with flash or upset
welding when one of the work pieces to
be joined has axial symmetry.
• Used in automotive industry to
manufacture gears, engine valves, and
shock absorbers.
• Used to join jet engine compressor parts.
Friction Welding Applications

2
2
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 produce 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.

2
3
 The laser beam welding works on the
principle that when the electrons of an
atom are excited by receiving some
energy. And then after some time
when it returns to its ground state, it
emits a photon of light.
 The concentration of this emitted
photon is increased by the excited
emission of radiation and we get high
energy focused laser beam. The light
amplification by stimulated emission of
radiation is named as a laser
Working Principle

2
4
 Laser Beam Welding (LBW) is a welding process, in which heat is
generated by a high energy laser beam targeted on the workpiece.
The laser beam heats and melts the edges of the workpiece,
forming a joint.
 The energy of a narrow laser beam is highly concentrated at 108-
1010 W/cm2, so a weak weld pool is formed very rapidly (for about
10-6 sec)
 The solidification of the weld pool surrounded by cold metal occurs
as rapidly as the melt. Since the time the molten metal is in contact
with the atmosphere is low, there is no contamination and
therefore no gradient (neutral gas, flow) is required.

2
5
Advantages and Disadvantages of Laser Beam Welding
Following are the advantages:
1.Easily automated process.
2.Controllable process parameters.
3.The very narrow weld may be obtained.
4.High quality of the weld structure.
5.Very small heat-affected zone.
6.Dissimilar materials may be welded.
7.Very small delicate workpieces may be welded.
8.The vacuum is not required.
9.Low distortion of the workpiece.

2
6
Following are the disadvantages:
1.The initial cost is high. The equipment applied in LBW
has a high cost.
2.The maintenance cost of LBM is high.
3.Due to the rapid cooling, fractures can occur in some
metals.
4.High skilled labours are required to perform LBW.
5.The welding thickness is restricted to 19 mm.
6.The energy conversion efficiency in LBW is extremely
low. It is usually below than 10%.

2
7
Applications of Laser Beam Welding Process
1.It is prominent in the automotive industry. So, It is
used in the area where large volume production is
required.
2.It is employed for high precision welds. As it does
not use any electrode, the final weld will be light but
strong.
3.The laser welding is also frequently used in making
of jewellery.
4.However, laser beam welding is used in medical

Electron Beam Welding
Working principle:
Electron beam welding is a radiant energy
welding process in which the work pieces
are joined by the heat obtained from a
concentrated beam composed primarily
of high-velocity electrons impinging on
the surface to be joined.

Working Procedure:
The system consists of an electronic gun and a
vacuum chamber inside which the work pieces to
be joined are placed. The electronic gun emits
and accelerates the beam of electrons and
focuses it on the work pieces.
When a tungsten filament is electrically
heated in vacuum to approximately 20000°C it
emits electrons. The electrons are then
accelerated towards the hollow anode by
establishing a high difference of voltage
potential between the tungsten filament and a
metal anode.

The electrons pass through the anode at
high speeds (approximately half the speed of
light), then collected into a concentrated beam
and further directed towards the work piece
with the help of magnetic forces resulting
from focusing and deflection coils.
The highly accelerated electrons hit the base
metal and penetrate slightly below the base
surface. The kinetic energy of the electrons is
converted into heat energy.

The succession of electrons striking at the
same place causes the work piece metal to
melt and fuse together.
It should be noted that, the greater the
kinetic energy of the electrons, the greater
is the amount of heat released.
Since electrons cannot travel well through
air, they are made to travel in vacuum which
is the reason for enclosing the electron gun
and the work piece in a vacuum chamber.

Advantages of Electron Beam Welding:
 Any metals, including zirconium, beryllium
or tungsten can be easily welded.
 High quality welds, as the operation is
carried in a vacuum.
 Concentrated beam minimizes distortion.
 Cooling rate is much higher.
 Heat affected zone is less.
 Shielding gas, flux or filler metal is not
required.

Disadvantages of Electron Beam Welding:
 High capital cost.
 Extensive joint preparation is required.
 Vacuum requirements tend to limit the
production rate.
 Size of the vacuum chamber restricts the size
of the work piece being welded.
 Not suitable for high carbon steels. Cracks
occur due to high cooling rates.

Applications of Electron Beam Welding:
Electron beam welding is mainly used in
electronic industries, automotive and
aircraft industries where the quality of weld
required forms the decisive factor.

Plasma ARC Welding
Plasma ARC Welding
(PAW)
(PAW)

Arc welding process that
Arc welding process that
produces coalescence of
produces coalescence of
metals by heating them
metals by heating them
with a constricted arc
with a constricted arc
between an electrode and
between an electrode and
the work piece
the work piece
Plasma: A gaseous mixture
Plasma: A gaseous mixture
of positive ions, electrons
of positive ions, electrons
and neutral gas molecules.
and neutral gas molecules.
Plasma ARC Welding
Plasma ARC Welding

How Plasma Welding Works
How Plasma Welding Works
Plasma
Plasma
Gas which is heated to an extremely high temperature and ionized so
Gas which is heated to an extremely high temperature and ionized so
that it becomes electrically conductive
that it becomes electrically conductive
PAW process uses this plasma to transfer an electric arc to the work
PAW process uses this plasma to transfer an electric arc to the work
piece
piece
The metal to be welded is melted by the intense heat of the arc and
The metal to be welded is melted by the intense heat of the arc and
fuses together
fuses together
Objective of PAW
Objective of PAW
To increase the energy level of the arc plasma in a controlled manner
To increase the energy level of the arc plasma in a controlled manner
This is achieved by providing a gas nozzle around a tungsten electrode
This is achieved by providing a gas nozzle around a tungsten electrode
operating on direct current electrode negativity
operating on direct current electrode negativity

Equipment
Equipment
Power Supply
Power Supply
 A DC power source (generator or rectifier) having
A DC power source (generator or rectifier) having
drooping characteristics and open circuit voltage of 70
drooping characteristics and open circuit voltage of 70
volts or above is suitable for PAW
volts or above is suitable for PAW
 Rectifiers are generally preferred over DC generators
Rectifiers are generally preferred over DC generators
 High frequency generator and current limiting resistors
High frequency generator and current limiting resistors
used for arc ignition
used for arc ignition

Shielding gases
Shielding gases
 Shields the molten weld from the atmosphere.
 Two inert gases or gas mixtures are employed.
 Argon(commonly used), Helium, Argon+Hydrogen and
Argon+Helium, as inert gases or gas mixtures.
 Helium is preferred where a broad heat input pattern and flatter
cover pass is desired.
 A mixture of argon and hydrogen supplies heat energy higher than
when only argon is used and thus permits higher arc alloys and
stainless steels.
 Hydrogen, because of its dissociation into atomic form and
thereafter recombination generates temperatures above those
attained by using argon or helium alone.

7 - Applications
7 - Applications
 Aerospace Industries
Aerospace Industries
 Foodstuff and Chemical Industries
Foodstuff and Chemical Industries
 Machine and Plant Construction
Machine and Plant Construction
 Automobiles and Railways
Automobiles and Railways
 Ship Construction
Ship Construction
 Tank Equipment and Pipeline Construction etc
Tank Equipment and Pipeline Construction etc.
.

4
4
Soldering and Brazing
•Soldering and Brazing are joining
processes where parts are
joined without melting the base
metals.
•Soldering filler metals melt
(Lead and tin) below 450 °C.
•Brazing filler metals melt
(Copper & Zinc) (Cu&
silver)above 450 °C.
•Soldering is commonly used for electrical connection or
mechanical joints, but brazing is only used for mechanical
joints due to the high temperatures involved

4
5 Soldering
• A method of joining metal parts using an alloy of
low melting point (solder) below 450 °C (800 °F).
• Heat is applied to the metal parts, and the alloy
metal is pressed against the joint, melts, and is
drawn into the joint by capillary action and around
the materials to be joined by 'wetting action'.
• After the metal cools, the resulting joints are not
as strong as the base metal, but have adequate
strength, electrical conductivity, and water-
tightness for many uses.

4
6
• One application of
soldering is making
connections between
electronic parts and
printed circuit boards.
• Another is in plumbing.
Joints in sheet-metal
objects such as cans
for food, roof flashing,
and drain gutters were
also traditionally
soldered.
• Jewelary and small
mechanical parts are
often assembled by
soldering.
Soldering can
also be used as a
repair technique
to patch a leak in
a container or
cooking vessel.

4
7
Brazing
• Is similar to soldering but uses higher melting
temperature alloys, based on copper, as the filler metal.
• "Hard soldering", or "silver soldering" (performed with
high-temperature solder containing up to 40% silver) is
also a form of brazing, and involves solders with melting
points above 450 C.
• Since lead used in traditional solder alloys is toxic, much
effort in industry has been directed to adapting soldering
techniques to use lead-free alloys for assembly of
electronic devices and for potable water supply piping.

5
0 Flux Material (Brazing/Soldering)
Flux is used for following reasons :
1. Dissolve oxides from the surfaces to be joined
2. Reduce surface tension of molten material capillary action
3. Protect from further oxidation to parental material
Borax and Boric acid are commonly used Flux material in Brazing
Ammonia Chloride, Zinc Chloride are commonly used Flux material
in Soldering.

5
1
Brazing, Soldering or Braze Welding
In both these processes , the parental material does not melt, but
only filler material melts thus filling the joint through capillary
action.
Soldering ( or soft Soldering): The filler material has melting
point lower than 450 deg C and also less than that of parental
material
Brazing ( or hard Soldering): The filler material has melting
point higher than 450 deg C and also less than that of parental
material

5
2 Brazing vs. Welding

Advantages
1. Dissimilar metals which can’t be welded can be joined by brazing
2. Very thin metals can be joined
3. Metals with different thickness can be joined easily
4. In brazing thermal stresses are not produced in the work piece, hence
there is no distortion.
5. Problems of Heat Affected Zone (HAZ) is avoided.
6. Less power is required and process is faster

Disadvantages
1. Brazed joints have lower strength compared to welding
2. Joint preparation cost is more
3. Colour of the metal in the brazed joint is different and aesthetic problem
4. high service temperature can cause failure to a brazed joint.

5
3 Applications
-Automotive ( joining tubes and pipes)
-Electrical equipments (joining wires and cables)
- cutting tool ( brazing cemented carbide tips to steel shanks)
- repairs and maintenance in many fields
Brazing
Soldering
- electronics parts like PCB

Explosive welding is a solid state welding
process, which uses a controlled explosive
detonation to force two metals together at high
pressure. The resultant composite system is
joined with a durable, metallurgical bond.
WHAT IS IT?
The fearsome destructive power of explosives
can be harnessed to provide a unique joining
method, known as Explosive Welding.
EXPLOSIVE WELDING

PROCESS
 This is a solid state joining process.
 When an explosive is detonated on the surface of
a metal, a high pressure pulse is generated.
 This pulse propels the metal at a very high rate of
speed. If this piece of metal collides at an angle
with another piece of metal, welding may occur.

 For welding to occur, a jetting action is required at the
collision interface. This jet is the product of the surfaces
of the two pieces of metals colliding.
 This cleans the metals and allows to pure metallic
surfaces to join under extremely high pressure. The
metals do not commingle, they are atomically bonded.
 Due to this fact, any metal may be welded to any metal
(i.e. - copper to steel; titanium to stainless).

COMMONLY USED EXPLOSIVE
Explosive Detonation velocity , m/s
RDX (Cyclotrimethylene
trinitramine) C6H6N6O6
8100
TNT (Trinitroluene,
C7H5N3O6)
6600
Lead azide (N6Pb) 5010
Deta sheet 7020
Ammonium Nitrate (NH4NO3) 2655

ADVANTAGES
 Joining of dissimilar metals - Aluminum to steel, Titanium alloys to Cr – Ni steel, Cu
to stainless steel, Tungsten to Steel.
 Attaching cooling fins.

LIMITATIONS
 The metals must have high enough impact
resistance, and ductility.
 Noise and blast can require operator protection,
vacuum chambers, buried in sand/water.
 The geometries welded must be simple – flat,
cylindrical, conical.

162
Heat Affected Zone
The heat affected zone (HAZ) is a non-melted area of metal that has undergone
changes in material properties as a result of being exposed to high
temperatures. These changes in material property are usually as a result of
welding or high-heat cutting. The HAZ is the area between the weld or cut and
the base (unaffected), parent metal.
The HAZ area can vary in severity and size depending on the properties of the
materials, the concentration and intensity of the heat, and the welding or cutting
process used.

164
Heat Affected Zone
What are the Causes of Heat-Affected Zones?
1.The heating associated with welding and/or cutting generally
uses temperatures up to and often exceeding the temperature of
melting of the material.
2.The heating and cooling thermal cycle associated with these
processes is different to whatever processing has occurred with
the parent material previously. This leads to a change in
microstructure associated with the heating and cooling process.

165
Heat Affected Zone
3. The size of a heat affected zone is influenced by the level of
thermal diffusivity, which is dependent on the thermal
conductivity, density and specific heat of a substance as well
as the amount of heat going in to the material.
4. Those materials with a high level of thermal diffusivity are
able to transfer variations of heat faster, meaning they cool
quicker and, as a result, the HAZ width is reduced.
5. On the other hand, those materials with a lower coefficient
retain the heat, meaning that that the HAZ is wider.
6. Generally speaking, the extension of the HAZ is dependent on
the amount of heat applied, the duration of exposure to heat
and the properties of the material itself. When a material is
exposed to greater amounts of energy for longer periods the
HAZ is larger.

166
Heat Affected Zone
7. With regard to welding procedures, those processes with low
heat input will cool faster, leading to a smaller HAZ, whereas
high heat input will have a slower rate of cooling, leading to a
larger HAZ in the same material.
8. In addition, the size of the HAZ also grows as the speed of the
welding process decreases. Weld geometry is another factor
that plays a role in the HAZ size, as it affects the heat sink, and a
larger heat sink generally leads to faster cooling.
9. High temperature cutting operations can also cause a HAZ and,
similarly to welding procedures, those processes that operate at
higher temperatures and slow speeds tend to create a larger
HAZ, while lower temperature or higher speed cutting processes
tend to reduce the HAZ size.

167
Heat Affected Zone
10. Different cutting processes have differing effects on the HAZ,
regardless of the material being cut.
11. For example, shearing and water jet cutting do not create a
HAZ, as they do not heat the material, while laser
cutting creates a small HAZ due to the heat only being applied
to a small area.
12. Meanwhile, plasma cutting leads to an intermediate HAZ, with
the higher currents allowing for an increased cutting speed and
thereby a narrower HAZ, while oxyacetylene cutting creates the
widest HAZ due to the high heat, slow speed and flame width.
13. Arc welding falls between the two extremes, with individual
processes varying in heat input.

168
Defects are common in any type of manufacturing, welding
including. In the process, there can be deviations in the
shape and size of the metal structure. It can be caused by the
use of the incorrect welding process or wrong welding
technique.
Welding Defects, Causes and Remedies

169
Types of defects
Slag Inclusion
Undercut
Porosity
Incomplete fusion
Spatter
Underfill
Hot cracks
Cold Cracks

170
Slag Inclusion
Slag inclusion is one of the welding defects that are usually easily
visible in the weld. Slag is a vitreous material that occurs as a
byproduct of stick welding, flux-cored arc welding and submerged
arc welding. It can occur when the flux, which is the solid shielding
material used when welding, melts in the weld or on the surface
of the weld zone.

171
Causes:
1.Improper cleaning.
2.The weld speed is too fast.
3.Not cleaning the weld pass before starting a new one.
4.Incorrect welding angle.
5.The weld pool cools down too fast.
6.Welding current is too low.

172
Remedies:
1.Increase current density.
2.Reduce rapid cooling.
3.Adjust the electrode angle.
4.Remove any slag from the previous bead.
5.Adjust the welding speed.

173
Undercut
This welding imperfection is the groove formation at the weld toe,
reducing the cross-sectional thickness of the base metal. The
result is the weakened weld and workpiece.

174
Causes:
1.Too high weld current.
2.Too fast weld speed.
3.The use of an incorrect angle, which will direct more heat to free
edges.
4.The electrode is too large.
5.Incorrect usage of gas shielding.
6.Incorrect filler metal.
7.Poor weld technique.

175
Remedies:
1.Use proper electrode angle.
2.Reduce the arc length.
3.Reduce the electrode’s travel speed, but it also shouldn’t be too
slow.
4.Choose shielding gas with the correct composition for the
material type while welding.
5.Use of proper electrode angle, with more heat directed towards
thicker components.
6.Use of proper current, reducing it when approaching thinner
areas and free edges.
7.Choose a correct welding technique that doesn’t involve
excessive weaving.
8.Use the multipass technique

176
Porosity
Porosity occurs as a result of weld metal contamination. The
trapped gases create a bubble-filled weld that becomes weak and
can with time collapse.

177
Causes of porosity:
1.Inadequate electrode deoxidant.
2.Using a longer arc.
3.The presence of moisture.
4.Improper gas shield.
5.Incorrect surface treatment.
6.Use of too high gas flow.
7.Contaminated surface.
8.Presence of rust, paint, grease or oil

178
Remedies:
1.Clean the materials before you begin welding.
2.Use dry electrodes and materials.
3.Use correct arc distance.
4.Check the gas flow meter and make sure that it’s optimized as
required with proper with pressure and flow settings.
5.Reduce arc travel speed, which will allow the gases to escape.
6.Use the right electrodes.
7.Use a proper weld technique

179
Incomplete Fusion
This type of welding defect occurs when there’s a lack of proper
fusion between the base metal and the weld metal. It can also
appear between adjoining weld beads. This creates a gap in the
joint that is not filled with molten metal.

180
Causes:
1.Low heat input.
2.Surface contamination.
3.Electrode angle is incorrect.
4.The electrode diameter is incorrect for the material thickness
welding.
5.Travel speed is too fast.
6.The weld pool is too large and it runs ahead of the arc.

181
Remedies:
1.Use a sufficiently high welding current with the appropriate arc
voltage.
2.Before begin welding, clean the metal.
3.Avoid molten pool from flooding the arc.
4.Use correct electrode diameter and angle.
5.Reduce deposition rate.

182
Spatter
Spatter occurs when small particles from the weld attach
themselves to the surrounding surface. It’s an especially common
occurrence in gas metal arc welding. No matter how hard you try,
it can’t be completely eliminated. However, there are a few ways
you can keep it to a minimum.

183
Causes:
1.The running amperage is too high.
2.Voltage setting is too low.
3.The work angle of the electrode is too steep.
4.The surface is contaminated.
5.The arc is too long.
6.Incorrect polarity.
7.Erratic wire feeding.

184
Remedies:
1.Clean surfaces prior to welding.
2.Reduce the arc length.
3.Adjust the weld current.
4.Increase the electrode angle.
5.Use proper polarity.
6.Make sure you don’t have any feeding issues.

185
Incomplete Penetration
Incomplete penetration occurs when the groove of the metal is
not filled completely, meaning the weld metal doesn’t fully extend
through the joint thickness.

186
Causes:
1.There was too much space between the metal welding together.
2.Moving the bead too quickly, which doesn’t allow enough metal
to be deposited in the joint.
3.Using a too low amperage setting, which results in the current
not being strong enough to properly melt the metal.
4.Large electrode diameter.
5.Misalignment.
6.Improper joint.

187
Remedies:
1.Use proper joint geometry.
2.Use a properly sized electrode.
3.Reduce arc travel speed.
4.Choose proper welding current.
5.Check for proper alignment.

188
1. Hot cracks: These can occur during the welding process or
during the crystallization process of the weld joint.
2. Cold cracks: These cracks appear after the weld has been
completed and the temperature of the metal has gone down.
They can form hours or even days after welding. It mostly
happens when welding steel. The cause of this defect is usually
deformities in the structure of steel.
3. Crater cracks: These occur at the end of the welding process
before the operator finishes a pass on the weld joint. They
usually form near the end of the weld. When the weld pool
cools and solidifies, it needs to have enough volume to
overcome shrinkage of the weld metal. Otherwise, it will form
a crater crack.

189
Causes of cracks:
1.Use of hydrogen when welding ferrous metals.
2.Residual stress caused by the solidification shrinkage.
3.Base metal contamination.
4.High welding speed but low current.
5.No preheat before starting welding.
6.Poor joint design.
7.A high content of sulfur and carbon in the metal.

190
Remedies:
1.Preheat the metal as required.
2.Provide proper cooling of the weld area.
3.Use proper joint design.
4.Remove impurities.
5.Use appropriate metal.
6.Make sure to weld a sufficient sectional area.
7.Use proper welding speed and amperage current.
8.To prevent crater cracks make sure that the crater is properly
filled.

UNIT 4 Welding process mechaniaclengineering.ppt

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UNIT 4 Welding process mechaniaclengineering.ppt