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• Welding is a fabrication technique that involves joining materials together
by heating them to suitable temperatures, by applying heat with or
without the use of pressure.
• Heating is generated through various sources; electric arc, gas flame, laser,
electron beam, friction, current resistance & ultrasound.
• Apart from the materials to be welded, an additional “filler” material may
be used for welding. The filler material is added to the weld joint.
• Welding is used to produce permanent joints unlike bolting and riveting.
• Certain literature refer to soldering and brazing as sub-types of welding.
Types of Welding
Arc Welding Process
• In arc welding, a welding power supply is used to create an arc between
the base metals (metals to be welded) and electrode.
• Heat is generated in the base metals causing them to melt and fuse
together. The electrode can either be consumable or non-consumable.
• Filler material may or may not be added to enhance weld quality and
protect the welding area from external contamination.
• Following are typical arc welding processes:
– Shielded Metal Arc Welding (SMAW)
– Gas Metal Arc Welding (GMAW)
– Gas Tungsten Arc Welding (GTAW)
Shielded Metal Arc Welding (SMAW)
• This process uses a consumable electrode which serves as the filler
material as well.
• The electrode is covered with a “flux” that gives off vapors to shield
the welding area. The core of the electrode melts into the welding
area and provides the necessary filler material.
• SMAW is the most common and easiest to employ welding
technique and is suitable for welding ferrous materials.
• Welding electrodes are composed of material compatible with the
material(s) being welded.
Gas Metal Arc Welding (GMAW)
• GMAW employs a continuously fed wire that serves both as the
electrode and filler material. Shielding gas is flowed around the wire
to protect from weld site contamination.
• Unlike SMAW, this process is relatively faster since the electrode is
fed continuously to the welding area along with inert gas. NO TIME
IS WASTED IN REPLACING A CONSUMED ELECTRODE !
• Though GMAW is faster, the separate supply of shielding gas and
continuous feeding of wire requires bulky mechanisms. This
reduces the ease of use.
• GMAW is also referred to as Metal Inert Gas (MIG) Welding.
Gas Tungsten Arc Welding (GTAW)
• A non-consumable tungsten metal electrode is used in this process.
The shielding gas and filler material are fed separately into the weld
along side the electrode.
• GTAW is characterized by high and uniform weld quality however it
requires considerable welding operator skill.
• GTAW is used to weld thin section of stainless steel and light metals
such as aluminum.
• GTAW is also know as Tungsten Inert Gas (TIG) Welding.
• Lack of Fusion: Arises due to little heat input or too rapid motion of the
• Cracking: Occurs due to rapid thermal shrinkage as the welded joint cools
down. Can be avoided by controlled cooling/heating of the weld.
• Excess Penetration: It occurs either due to excessive heat input or too slow
motion of the welding electrode. Avoiding it requires a delicate balance
between operator speed and welding heat.
• Porosity: Arises due to air trapped in the solidified weld metal.
• Inclusions: Occurs due to inclusion of slag from various sources such as the
flux coating of welding electrode.