Arc welding processes like shielded metal arc welding, gas metal arc welding and gas tungsten arc welding are described. Shielded metal arc welding uses a consumable electrode covered with a flux to shield the weld. Gas metal arc welding employs a continuously fed wire and shielding gas. Gas tungsten arc welding uses a non-consumable tungsten electrode, shielding gas and a separate filler material. The document discusses welding techniques, processes, defects and includes illustrations of welding joints and processes.

1. Welding
Workshop Technology
Department of Mechanical Engineering
College of E&ME, NUST Pakistan

2. Contents
• Welding Definition
• Types of Welding Processes
• Types of Major Welding Joints
• Arc Welding
• Shielded Metal Arc Welding
• Gas Metal Arc Welding
• Gas Tungsten Arc Welding

3. WELDING & ITS TYPES

4. Welding
• 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.

5. Types of Welding
Arc Welding
Shielded
Metal Arc
Welding
Gas Metal
Arc Welding
Gas Tungsten
Arc Welding
Gas Welding
Oxyacetylene
Welding
Resistance
Welding
Resistance
Spot Welding
Resistance
Seam
Welding
Energy Beam
Welding
Electron
Beam
Welding
Laser Beam
Welding
Solid State
Welding
Ultrasonic
Welding
Friction
Welding

6. Weld Joints

7. ARC WELDING

8. 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)

9. 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.

10. SMAW - Illustrated

11. 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.

12. GMAW - Illustrated

13. 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.

14. GTAW - Illustrated

15. Welding Defects
• Lack of Fusion: Arises due to little heat input or too rapid motion of the
welding electrode.
• 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.