Arc Welding, TIG, SMAW, MIG and Resistance Butt Welding

1. An electric current flows across a gap between an electrode and
the plate to be welded and produces enormous heat.
Ionisation of atmosphere in the gap
Arc welding

2. Tungsten Inert Gas (TIG) Welding or Gas Tungsten
Arc Welding (GTAW)
An arc is formed between a pointed tungsten electrode and the
workpiece at the joint line.
Electrode not consumed during welding.
Molten pool and arc shielded by by an inert gas (usually Ar)

3. Tungsten Inert Gas (TIG) Welding
• Current 10 to 300 A
• Heat input 0.2 to 8 kJ / s
Typical applications: High-quality welds in metals such as
aluminium, stainless steels, nimonic alloys, and copper in chemical
plant; sheet work in aircraft engines and structures.

4. Manual Metal Arc (MMA) Welding or Shielded Metal
Arc Welding (SMAW) or Stick Electrode Welding
Arc between a consumable flux coated electrode and the workpiece.
Electrode is consumed during welding so has to be moved towards weld pool to
maintain arc gap.
Flux coating of the electrode disintegrates during welding, giving off vapors that
serve as a shielding gas and providing a layer of slag, both of which protect the
weld area from atmospheric contamination.

5. Manual Metal Arc (MMA) Welding
• Current 25 to 350 A
• Heat input 0.5 to 11 kJ / s
Typical applications: Fabrication of pressure vessels, ships, structural
steelwork; joints in pipework and pipelines; construction and repair of
machine plant.
Versatile process
Simple equipment and operation
Most widely used arc welding

6. Welding electrode for MMA
Typically 460 mm long
When melted to 50 mm arc is
extinguished, solid slag / flux
cleaned from the surface and
welding is resumed.
The choice of electrode for MMAW depends on a number of factors,
including the weld material, welding position and the desired weld
properties. The electrode is coated in a metal mixture called flux, which
gives off gases as it decomposes to prevent weld contamination,
introduces deoxidizers to purify the weld, causes weld-protecting slag to
form, improves the arc stability, and provides alloying elements to
improve the weld quality.

7. Metal Inert Gas (MIG) Welding or Gas Metal Arc
Welding (GMAW), CO2 welding
Arc between a consumable electrode and the parent metal
Electrode is fed by at a constant rate by a motor. Power-supply unit controls
the arc length; the welder keeps the nozzle at a fixed height (~ 20 mm).
Molten pool and arc shielded by by a non-reacting gas (Ar or Ar + 5% O2 /
20% CO2 or pure CO2 (MAG welding))
GMAW torch nozzle cutaway image.
(1) Torch handle, (2) Molded phenolic
dielectric (shown in white) and
threaded metal nut insert (yellow), (3)
Shielding gas nozzle, (4) Contact tip,
(5) Nozzle output face

8. Metal Inert Gas (MIG) Welding
• Current 60 to 500 A
• Heat input 1 to 25 kJ / s
Typical applications: Medium-gauge
fabrications such as earth-moving
equipment, plate, and box girders;
sheet-metal work for car bodies.
GMAW Circuit diagram. (1) Welding torch,
(2) Workpiece, (3) Power source, (4) Wire feed
unit, (5) Electrode source, (6) Shielding gas
supply.

9. Submerged Arc Welding (SAW)
Arc between a bare consumable electrode and the parent metal
Motorised feeding of electrode wire into the arc at a rate matched by its
melting so that arc length is constant.
Molten pool and arc submerged beneath a layer of granulated flux added
separately. Flux melts to provide a protective blanket.

10. • Current 350 to 2000 A
• Heat input 9 to 80 kJ / s
Submerged Arc Welding (SAW)
Typical applications: Joints in
thick plate in pressure vessels,
bridges, ships, structural work,
welded pipe.

11. Resistance Spot Welding
The work, which is usually in the form of
a lap joint, is gripped between two
copper electrodes. A high current at a
low voltage flows through the parent
metal between the electrodes. At the
interface, heat is generated by the
resistance offered to the current flow. A
spot or slug of metal is melted and
bridges the interface. The current flows
for only a short time (typically 0.06 to 3
seconds). When the current is switched
off (automatically), the weld solidifies
under pressure.

12. Typical applications: Light fabrications from pressed sheet,
such as car bodies and domestic washing machines. Also
used for high-quality work in aircraft engines.