Arc Welding Processes w3

WELDING PROCESSES
1. Arc Welding
2. Oxyfuel Gas Welding
3. Other Fusion Welding Processes
Welding Processes
There are two groups of welding processes according to the

state of the base material during the welding process:
1. Liquid-state welding (fusion welding)
In fusion welding, the base material is heat to melt. The
most important processes are Oxyfuel gas welding and Arc
welding
2.Solid-state welding.
In solid-state welding, two parts are jointed together under
pressure or a combination of pressure and heat. If heat is
applied, the contact temperature is below the melting point
of the base metal.
Welding is a process of metallurgically joining two pieces of metals by
the application of heat with or without the application of pressure and
addition of filler metal.
Arc welding processes
Electric arc welding is one of the fusion welding
processes.
An arc welding joins two metals together by generating an electric arc between a
coated metal electrode and a base metal. The circuit operates at low voltage and high
current. This arc produces at temperature of the order of 5500oC or higher. The heat
of the electric arc melts the metal which mixes with the molten deposits of the coated
electrode. The solidified molten weld pool makes the strong welded joint.
AW Electrodes
Electrodes in AW process are classifid as

 consumable electrodes
 non-consumable electrodes
The same classification is applied to the arc welding
processes;
 Arc welding with consumable electrodes
 Arc welding with nonconsumable electrodes
Welding Electrodes
Consumable Electrodes are the source of filler metal in

case of arc welding. Consumable electrodes can further be
classified into two categories coated and bare electrodes.
Coated Consumable Electrodes, these are the most popular

arc welding electrodes. Covered electrodes consist of the flux
material coated on the core wire
 Forms of consumable electrodes
 Welding rods
 Weld wire
 In both rod and wire forms, electrode is consumed

by the arc and added to weld joint as filler metal
Rutil electrodes
In this type, about 35% in weight of the coating is

titanium dioxide (TiO2). This electrode type is used for
general purposes where good welding properties are
required. This is the universal electrode which may
perform welding in every position, using AC or DC
current.
 The main properties of rutile type electrodes are as
follows:
- Suitable mechanical properties of weld metal,
- Weld beam profile with good appearance due to slag
properties,
- Ability to perform welding in all position,
- Easy slag removal
Basic (Low Hydrogen) Electrodes
The coating of this type of electrode consist of calcium

fluoride plus calcium and other alkaline carbonates. The
coating is mostly thick. These substances make to slag
more viscose and fast freezing, thus unabling overhead
and overhead and vertical position applications.
 Basic electrodes are baked at 400-500 ºC during
production. As the coating is hygroscopic these
electrodes should be stored in dry place. Before
usage, basic electrodes should be redried for 30
minutes at a minimum of 250 ºC.
 This type of electrodes is preferred when welding
medium and thick steel plates that require high
strength, high welding quality and high crack
resistance.
 Main applications for basic electrodes:
- Welding of unalloyed or low alloyed steels with unknown
composition,
- Welding of steels with a high content of carbon, sulphur,
phosphorus and nitrogen,
- Welding of steels having different carbon contents,
- Welding of thick-sections,
- Welding of machinery, equipment and structures that work
under temperatures below 0 ºC,
- Welding of structures where high strength is required
against dynamic stresses,
- Welding of rigid constructions.
 When welding, basic electrodes are generally
connected to the positive pole with DC. Some types of
basic electrodes can also be used with AC.
 During the welding operation, rutile and acid coated
electrodes, should be held at a 45º angle with respect to
the surface of the work piece. For basic electrodes this
angle should be 85-90º.
 Basic electrode are mainly used in the heavy
machinery and equipments industries, such as ship
building, boiler and pressure vessels, and steel
constructions subjected to dynamic loads.
Cellulosic Electrodes
The coating of these electrodes contains organic

materials that turn into gases in the arc. About 30% of
the coating weight is cellulose. These organic
compounds in the coating decompose in the arc to
from carbon monoxide, carbon dioxide and hydrogen,
which increase the arc tension and thus, the welding
arc becomes stronger and harder.
 Compared with other types of electrodes, with the same
current values, a 70% deeper penetration is obtained
with cellulosic electrodes.
 The gap filling and vertical down welding capability as
well as penetration of the weld obtained by this
electrode is good.
 Since this electrode can be used in every position
(particularly in vertical down), it has a wide range
of applications in the ship building industry and in
the welding of pipelines with a wall thickness of
less than 12.5 mm.
 The main features of cellulosic electrodes are as
follows:
- Deep penetrating welding in every position,
- Vertical down welding capability,
- Weld metal with good mechanical properties.
 Non-consumable electrodes are used in case of gas
shielded welding processes (TIG). They are made
of tungsten or carbon. These do not melt in the
process of welding and so called non-consumable
electrodes.
 Made of tungsten which resists melting
 It is gradually depleted during welding
(evaporation is the basic mechanism)
 Any filler metal must be supplied by a separate
wire fed into weld pool
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Arc Shielding
 At high temperatures in AW, metals are chemically

reactive to oxygen, nitrogen, and hydrogen in air
 Mechanical properties of joint can be degraded
by these reactions
 To protect operation, arc must be shielded from
surrounding air in AW processes
 Arc shielding is accomplished by:
 Shielding gases, e.g., argon, helium, CO2
 ©2010
Flux John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Flux
A substance that prevents formation of oxides and other

contaminants in welding, or dissolves them and
facilitates removal
 Provides protective atmosphere for welding
 Stabilizes arc
 Reduces spattering.
 The coating produces slag that covers the weld
bead to make a smooth surface and protect it from
sudden cooling.
 To add alloying elements into weld metals
 To provide higher deposition efficiency
 To provide electrical and thermal insulation
Various Flux Application Methods
 Pouring granular flux onto welding operation

 Stick electrode coated with flux material that melts
during welding to cover operation
 Tubular electrodes in which flux is contained in
the core and released as electrode is consumed
Arc Welding Positions
 Welding positions defined here for groove welds:

(a) flat, (b) horizontal, (c) vertical, and (d)
overhead
Consumable Electrode
AW Processes
 Shielded Metal Arc Welding

 Gas Metal Arc Welding
 Flux-Cored Arc Welding
 Electrogas Welding
 Submerged Arc Welding
Shielded Metal Arc Welding
(SMAW)
 The shielded metal arc welding (SMAW) process uses

flux-coated electrodes (covered electrodes). Flux-coated
electrodes consist of a filler metal rod coated with
chemicals that provide flux and shielding.
 The coated welding stick (SMAW is sometimes called

stick welding) is typically 200 to 450 mm long and 1.5
to 9.5 mm in diameter. The heat of the welding process
melts the coating to provide a protective atmosphere
and slag for the welding operation.
(SMAW)
In this process the arc heat

generated between the covered
electrode and the base metal is
used for welding. Currents
typically used in SMAW range
between 30 and 300 A at voltages
from 15 to 45 V depending on the
metals being welded, electrode
type and length and depth of weld
penetration required.
 SMAW is best suited for workpiece thicknesses of 3 to19
mm, although this range can be extended easily by skilled
operators using multiple-pass techniques. The multiple-
pass approach requires that the slag be removed after each
weld bead.
 Shielded metal arc

welding (stick welding)
performed by a human
welder (photo courtesy
of Hobart Brothers Co.)
SMAW Applications
 Used for steels, stainless steels, cast irons,

and certain nonferrous alloys
 Not used or rarely used for aluminum and its
alloys, copper alloys, and titanium
Gas Metal Arc Welding (GMAW)
Uses a consumable bare metal wire as electrode with

shielding by flooding arc with a gas
 Wire is fed continuously and automatically from a
spool through the welding gun
 Shielding gases include argon and helium for
aluminum welding, and CO2 for steel welding
 Bare electrode wire plus shielding gases eliminate
slag on weld bead
 No need for manual grinding and cleaning of slag
Gas Metal Arc Welding
In gas metal arc welding (GMAW),

an arc is generated between the solid
wire electrode and the base metal,
while the arc is protected with a
shielding gas or gas mixture.
Depending on the type of the
shielding gas, this process is also
known as metal active gas (MAG)
welding or metal inert gas (MIG)
welding.
 Gases used for shielding include inert gases such as
argon and helium and active gases such as carbon
dioxide. Selection of gases depends mainly on the
metal being welded. Inert gases are used for welding
aluminum alloys and stainless steel and the process is
often referred to as MIG welding. In welding steel,
carbon dioxide (CO2), which is less expensive than
inert gases, is used.
 Wire diameters ranging from 1 to 6 mm are used in
GMAW, the size depending on the thickness of the parts
being joined. The bare wire is fed continuously and
automatically from a spool through the welding gun.
GMAW Advantages over SMAW
 Better arc time because of continuous wire electrode

 Sticks must be periodically changed in SMAW
 Better use of electrode filler metal than SMAW
 End of stick cannot be used in SMAW
 Higher deposition rates
 Eliminates problem of slag removal
 Can be readily automated
Flux-Cored Arc Welding (FCAW)
Flux cored arc welding (FCAW), also know as dual shield

welding, is a semi-automatic arc welding process that is
similar to metal active gas (MAG) welding.
In Pocket Welding Guide, Troy, OH, 1997, pp 108–138
FCAW uses a continuous wire fed electrode, a
constant-voltage welding power supply, and similar
equipment to MAG welding.
Flux-Cored Arc Welding
Presence or absence of externally supplied shielding gas

distinguishes: (1) self-shielded - core provides ingredients for
shielding, (2) gas-shielded - uses external shielding gases
 Flux core arc welding usually uses a shielding gas
similar to that used by MAG welding, but it can also
be performed without a shielding gas. It is more
productive than MAG welding.
 This is similar to MAG welding, except that FCAW
welding uses a hollow, tubular electrode filled with
flux rather than a solid metal electrode.
 It is used primarily for welding steels and stainless
steels over a wide stock thickness range.
 It is noted for its capability to produce very-high-
quality weld joints that are smooth and uniform.
 FCAW is preferable to MAG welding for outdoor use
as well as for joining of thicker materials.
 It offers higher wire deposition rates and improved
arc stability, allowing for high speed applications
without adversely affecting good quality weld.
 Flux cored arc welding can be an ‘all position’
process and also requires less skill among operators
than MAG.
 There are few disadvantages of the process
compared to other welding techniques, including
production of noxious smoke that can make it difficult
to see the weld pool. FCAW generates more smoke
than other processes such as MAG.
 Because of tubular nature, filler material can be
sometimes more expensive than the solid counter
parts.
 The removal of slag is essential to achieve a smooth,
finished weld surface.
Submerged Arc Welding (SAW)
Uses a continuous, consumable bare wire electrode,

with arc shielding by a cover of granular flux
 Electrode wire is fed automatically from a coil
 Flux introduced into joint slightly ahead of arc by
gravity from a hopper
 Completely submerges operation, preventing
sparks, spatter, and radiation
Submerged Arc Welding
The arc is hidden from sight with fluxes. The blanket of granular flux
completely submerges the arc welding operation, preventing sparks,
spatter, and©2010
radiation.
John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
 The submerged arc welding (SAW)
process is very efficient because
welding can occur using high currents
from 300 to 2000. A with deeper weld
penetration into the base metal. This
process is suitable for welding thick-
section steel materials.
SAW Applications and Products
 Steel fabrication of structural shapes (e.g., I-beams)

 Seams for large diameter pipes, tanks, and pressure
vessels
 Welded components for heavy machinery
 Most steels (except hi C steel)
 Not good for nonferrous metals.
 In these kinds of applications, steel plates of 25-mm
thickness and heavier are routinely welded by this
process.
 Because of the gravity feed of the granular flux,
the parts must always be in a horizontal
orientation. This process is unsuitable for short
and curved welding lines and for vertical and
overhead positions
Nonconsumable Electrode
Processes
 Gas Tungsten Arc Welding
 Plasma Arc Welding
 Carbon Arc Welding
 Stud Welding
Gas Tungsten Arc Welding
(GTAW)
Uses a nonconsumable tungsten electrode and an inert
gas for arc shielding
 Melting point of tungsten = 3410C (6170F)
 A.k.a. Tungsten Inert Gas (TIG) welding
 In Europe, called "WIG welding"
 Used with or without a filler metal
 When filler metal used, it is added to weld pool
from separate rod or wire
 Applications: aluminum and stainless steel mostly
Gas Tungsten Arc Welding
Advantages and Disadvantages
of GTAW
Advantages:
 High quality welds for suitable applications
 No spatter because no filler metal through arc
 Little or no post-weld cleaning because no flux
Disadvantages:
 Generally slower and more costly than consumable
electrode AW processes
Applications;This process is used for welding almost all types
of metals, particularly aluminum, magnesium, titanium, and
the refractory metals.
Plasma Arc Welding (PAW)
Special form of GTAW in which a constricted plasma arc

is directed at weld area
 Tungsten electrode is contained in a nozzle that
focuses a high velocity stream of inert gas (argon)
into arc region to form a high velocity, intensely hot
plasma arc stream
 Temperatures in PAW reach 28,000C, due to
constriction of arc, producing a plasma jet of small
diameter and very high energy density
Plasma Arc Welding
 When welding stainless steels, argon or a mixture of argon and
hydrogen is used as the plasma gas. When welding non-ferrous
metals, mixtures of argon and helium are used.
 The shielding gases are only inert gases like argon, helium or a
mixture of these gases.
 A variety of metals can be welded with part thicknesses
generally less than 6 mm.
Advantages and Disadvantages
of PAW
Advantages:
 Good arc stability and excellent weld quality
 Better penetration control than other AW processes
 High travel speeds
 Can be used to weld almost any metals
Disadvantages:
 High equipment cost
 Larger torch size than other AW processes
 Tends to restrict access in some joints
Oxyfuel Gas Welding (OFW)
Group of fusion welding operations that burn various

fuels mixed with oxygen
 OFW employs several types of gases, which is the
primary distinction among the members of this group
 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
Oxyacetylene Welding (OAW)
Fusion welding performed by a high temperature flame

from combustion of acetylene and oxygen
 Flame is directed by a welding torch
 Filler metal is sometimes added
 Composition must be similar to base metal
 Filler rod often coated with flux to clean surfaces
and prevent oxidation
Oxyacetylene Welding
Acetylene (C2H2)
 Most popular fuel among OFW group because it is

capable of higher temperatures than any other
 Up to 3480C (6300F)
 Two stage reaction of acetylene and oxygen:
 First stage reaction (inner cone of flame)
C2H2 + O2  2CO + H2 + heat
 Second stage reaction (outer envelope)
2CO + H2 + 1.5O2  2CO2 + H2O + heat
Oxyacetylene Torch
 Maximum temperature reached at tip of inner cone, while

outer envelope spreads out and shields work surface from
atmosphere
 Shown below is neutral flame of oxyacetylene torch
indicating temperatures achieved
• The proportion of acetylene and oxygen in the gas mixture is an
important factor in oxyfuel-gas welding. At a ratio of 1:1 (i.e., when there is no
excess oxygen), the flame is considered to be neutral.
• With a greater oxygen supply, the flame can be harmful (especially for steels),
because it oxidizes the metal. For this reason, a flame with excess oxygen is
known as an oxidizing flame.
• If the oxygen is insufficient for full combustion, the flame is known as a reducing,
or carburizing, flame (a flame having excess acetylene).
Oxyacetylene welding uses equipment that is relatively inexpensive and portable. Gas
welding is widely used for maintenance and repair work because of the ease in
transporting oxygen and fuel cylinders. It is rarely used on the welding of sheet and
plate stock thicker than 6 mm because of the advantages of arc welding in such
applications.
Safety Issue in OAW
 Together, acetylene and oxygen are highly flammable

 C2H2 is colorless and odorless
 It is therefore processed to have characteristic
garlic odor
OAW Safety Issue
 C2H2 is physically unstable at pressures much above 15

lb/in2 (about 1 atm)
 Storage cylinders are packed with porous filler
material saturated with acetone (CH3COCH3)
 Acetone dissolves about 25 times its own volume
of acetylene
 Different screw threads are standard on C2H2 and O2
cylinders and hoses to avoid accidental connection of
wrong gases
Alternative Gases for OFW
 Methylacetylene-Propadiene (MAPP)
 Hydrogen
 Propylene
 Propane
 Natural Gas
Other Fusion Welding Processes
FW processes that cannot be classified as arc,

resistance, or oxyfuel welding
 Use unique technologies to develop heat for melting
 Applications are typically unique
 Processes include:
 Electron beam welding
 Laser beam welding
 Electroslag welding
 Thermit welding
1.The ABC's of Arc Welding and Inspection, 2011 by KOBE STEEL, LTD
2.Fusion Welding ,Valery Marinov, Manufacturing Technology
3.MANUFACTURING ENGINEERING AND TECHNOLOGY, Serope Kalpakjian, Steven
R. Schmid, 2009, Prentice Hall
4.FUNDAMENTALS OF MODERN MANUFACTURING Materials, Processes, and
Systems, Mikell P. Groover, 2010 John Wiley & Sons
5. Arc Welding Processes: TIG, Plasma Arc, MIG, Ulrich Krüger, 1994, EAA - European
Aluminium Association
6. The ABC's of Arc Welding and Inspection
7. https://www.twi-global.com/technical-knowledge/faqs/flux-cored-arc-welding-fcaw

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WELDING PROCESSES

There are two groups of welding processes according to the

Electrodes in AW process are classifid as

Consumable Electrodes are the source of filler metal in

Coated Consumable Electrodes, these are the most popular

 In both rod and wire forms, electrode is consumed

In this type, about 35% in weight of the coating is

The coating of this type of electrode consist of calcium

The coating of these electrodes contains organic

 At high temperatures in AW, metals are chemically

A substance that prevents formation of oxides and other

 Pouring granular flux onto welding operation

 Welding positions defined here for groove welds:

 Shielded Metal Arc Welding

 The shielded metal arc welding (SMAW) process uses

 The coated welding stick (SMAW is sometimes called

In this process the arc heat

 Shielded metal arc

 Used for steels, stainless steels, cast irons,

Uses a consumable bare metal wire as electrode with

In gas metal arc welding (GMAW),

 Better arc time because of continuous wire electrode

Flux cored arc welding (FCAW), also know as dual shield

Presence or absence of externally supplied shielding gas

Uses a continuous, consumable bare wire electrode,

 Steel fabrication of structural shapes (e.g., I-beams)

Special form of GTAW in which a constricted plasma arc

Group of fusion welding operations that burn various

Fusion welding performed by a high temperature flame

 Most popular fuel among OFW group because it is

 Maximum temperature reached at tip of inner cone, while

 Together, acetylene and oxygen are highly flammable

 C2H2 is physically unstable at pressures much above 15

FW processes that cannot be classified as arc,

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