Arc Welding

Arc Welding
Presented by:
JAMSHED KHAN 2017-BT-MECH-761
HAFIZ ARSALAN HASSAN 2017-BT-MECH-762
WELDING
A process in which two or more metal parts are permanently joined together,
with or without the application of pressure and a filler material by the fusion
of the edges.
Filler material may be used to effect the union.
WELDING PROCESSES
There are two types of Welding processes,

 Fusion Welding
 Forge Welding
Fusion Welding
In case of fusion welding, the parts to be jointed are held in position
while the molten metal is supplied to the joint.
Examples: arc welding, oxyfuel gas welding
Forge Welding
Forge welding is a solid-state welding process that joins two pieces of

metal by heating them to a high temperature and then hammering
them.
Examples: diffusion welding
Arc Welding
A sustained arc generates the heat for melting the work piece and filler
material.
Electric energy from the arc thus formed produces temperatures of 5500C
(10,000F) or higher.
In AW process filler metal is added during the operation to increase the
volume and strength of the weld joint.
Power Source in Arc Welding
1. AC Machines
2. DC Machines
 AC machines less expensive to purchase and operate, but generally

restricted to ferrous metals.
 DC equipment can be used on all metals and is generally noted for better
arc control.
What is an Electric Arc?
An electric arc is a visible plasma discharge between two electrodes that is
caused by electrical current ionizing gasses in the air.
Electric arcs occur in nature in the form of lightning.

Arc Welding
Arc welding (AW) is a fusion-welding process in which coalescence of the
metals is achieved by the heat of an electric arc between an electrode and the
work.
Manual Arc Welding and Arc Time
Problems in manual welding:
 Low Weld joint quality
 Productivity issue
Arc Time = (time arc is on) divided by (hours worked)
 Also called “arc-on time”
 Manual welding arc time = 20%
 Machine welding arc time 50% (more or less, depending on the operation)
Types of Arc Welding
Based on their characteristics, arc welding electrodes can be broadly classified
into two types.
They are:
Consumable Electrode
Non-consumable electrode
Consumable Electrodes
 If the melting point of an arc welding electrode is less, it melts and

fills the gap in the workpiece. Such an electrode is called
consumable electrode.
Welding rods are typically 225 to 450 mm (9–18 in) long and 9.5 mm
(3/8 in) or less in diameter.
The electrode is consumed by the arc during the welding process
and added to the weld joint as filler metal.
Consumable Electrodes
Types of Consumable Arc Welding
Submerged Arc Welding (SAW)

Shielded Metal Arc Welding (SMAW)
Flux Core Arc Welding (FCAW)
Gas metal arc Welding (GMAW)
Electrogas Welding
Submerged Arc Welding (SAW)
Uses a continuous, consumable bare wire electrode, and arc shielding is

provided by a cover of granular flux. Low-carbon, low alloy, and stainless
steels can be readily welded by SAW.
Submerged Arc Welding Applications
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
Flux Core Arc Welding (FCAW)
FCAW) is a variation of the GMAW technique. FCAW wire is actually a fine
metal tube filled with powdered flux materials. The process is widely used in
construction because of its high welding speed and portability.
Flux Core Arc Welding Applications
Pipelines Welding
Shipbuilding
General Repairs
Underwater Welding
Quicker process than SMAW
Can be an automatic or semi-automatic process
Shielded Metal Arc Welding (SMAW)
Arc is struck between the rod (shielded metal covered by flux) and the
work pieces to be joined, the impurities rise to the top of the weld in the
form of slag.
Welding Stick in SMAW
Composition of filler metal usually close to base metal.
Coating: powdered cellulose mixed with oxides and carbonates, and held
together by a silicate binder.
Disadvantages of stick welding:
 Sticks must be periodically changed
 High current levels may melt coating prematurely
Shielded Metal Arc Welding 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)
(Metal + inert gas) electrode is continuously fed through the welding gun and
is shielded by an inert gas.
Shielding gases include argon and helium for aluminum welding, and CO2 for
steel welding.
No need for manual grinding and cleaning of slag.
Gas Metal Arc Welding (GMAW)
GMAW Advantages over SMAW
• Eliminates problem of slag removal

• Can be readily automated
• Better use of electrode filler metal than SMAW
• Better arc time because of continuous wire electrode
Electrogas Welding
Electrogas welding using flux-cored electrode wire.
It is used for welding the edges of sections vertically and in one pass with the
pieces placed edge to edge (butt joint).
Electrogas Welding Applications
Building of storage tanks

Vertical vessels
Blast furnaces
Chemical furnaces
Non-Consumable Electrodes
If the melting point of the arc welding electrode is high, it does not melt to fill
the gap in the workpiece. Such an electrode is called non-consumable
electrode.
Types of Non- Consumable Arc Welding
Gas Tungsten ARC welding (GTAW)

Plasma-Arc welding (PAW)
Gas Tungsten Arc Welding (GTAW)
GTAW (Tungsten inert gas, a.k.a. TIG) – Tungsten electrode not consumed,
but surrounded by an inert gas and produces an arc.
Melting point of tungsten = 3410C (6170F)
Gas Tungsten ARC Welding Advantages
High quality welds for suitable applications

No spatter because no filler metal through arc
Little or no post-weld cleaning because no flux
Plasma-Arc welding (PAW)
When an arc is created in a plasma (ionized) gas and a filler material may or
may not be applied to the weld joint.
Temperatures in PAW reach 28,000C (50,000F), due to constriction of arc,
producing a plasma jet of small diameter and very high energy density.
Advantages & 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
Arc Blow
Arc blow is the, usually unwanted, deflection of the arc during arc welding.
There are two types of arc blow commonly known in the electric welding
industry,
Magnetic arc blow
Thermal arc blow
Magnetic arc blow:
It is the deflection of welding filler material within an electric arc deposit by a
buildup of magnetic force surrounding the weld pool.
Thermal Arc Blow:

It is widely attributed to variations in resistance within the base metal
created by the weld pool as it is moved across the workpiece.
Arc Shielding
At high temperatures in AW, metals are chemically reactive to oxygen,

nitrogen, and hydrogen in air.
To protect operation, arc must be shielded from surrounding air in AW
processes.
Shielding gases, e.g., argon, helium, CO2
Flux
Is a substance used to prevent the formation of oxides and other unwanted
contaminants, or to dissolve them and facilitate removal.
Provides protective atmosphere for welding

Stabilizes arc
Reduces spattering
Selection of Welding Rods
 Filler rod should have a tensile strength greater than the metal to be joined.
 Rod must also be compatible with the welded metal
 Welding positions required
 Welding current (ac or dc)
 Joint design (groove, butt, fillet, etc.)
 Thickness and shape of the base metal
 Service conditions and specifications
 Production efficiency and job conditions
Welding Rod Classification (ex. E-6010)
The E- stands for electrode.

The first two numbers indicate the tensile strength
The next-to-last number gives the welding positions
The last digit of the weld rod number indicates the type of current for which
the rod may be used (ac, dc straight, dc reverse), the penetration, and the
type of flux around the rod.
Example: E-6010 would have a tensile strength of 60,000 psi, could be used in
all positions, has a cellulose-sodium flux, could give deep penetration, and
must be used with dc reverse current.
Advantages of Arc Welding
Cost – equipment for arc welding is well-priced and affordable, and the
process often requires less equipment in the first place because of the lack of
gas
Portability – these materials are very easy to transport
Works on dirty metal
Shielding gas isn’t necessary – processes can be completed during wind or
rain, and spatter isn’t a major concern.
Disadvantages of Arc Welding
Lower efficiency – more waste is generally produced during arc welding than
many other types, which can increase project costs in some cases
High skill level – operators of arc welding projects need a high level of skill
and training, and not all professionals have this
Thin materials – it can be tough to use arc welding on certain thin metals
Eye damage, Heat, fire, and explosion hazard, Inhaled matter

Arc Welding

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Arc Welding

There are two types of Welding processes,

Forge welding is a solid-state welding process that joins two pieces of

 AC machines less expensive to purchase and operate, but generally

Electric arcs occur in nature in the form of lightning.

 If the melting point of an arc welding electrode is less, it melts and

Submerged Arc Welding (SAW)

Uses a continuous, consumable bare wire electrode, and arc shielding is

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

• Eliminates problem of slag removal

Building of storage tanks

Gas Tungsten ARC welding (GTAW)

High quality welds for suitable applications

Thermal Arc Blow:

At high temperatures in AW, metals are chemically reactive to oxygen,

Provides protective atmosphere for welding

The E- stands for electrode.

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