3. Welding:
Welding is a material joining process which produces
coalescence of materials by heating them to suitable
temperatures with or without the application of pressure or
by the application of pressure alone, and with or without
the use of filler material.
Welding is used for making permanent joints.
4. Types of welding:
Welding processes are classified into two major categories-
1. Fusion Welding: This process uses heat to join or fuse two or more
materials by heating them to melting point. The process may or may not
require the use of filler material. Arc welding, resistance welding, oxy-fuel
welding etc. are commonly used fusion welding.
2. Solid state welding: Solid state welding is a welding process, in which
two work pieces are joined under a pressure providing an intimate contact
between them and at a temperature essentially below the melting point of the
parent material. No filler material is used. Friction welding, diffusion welding,
ultrasonic welding are commonly used solid state welding.
5. Classification of fusion welding processes:
A. Arc welding:
“Arc welding is a fusion welding process in which the heat required to
fuse the metal is obtain from the electric arc between the base metal and
an electrode.”
Types:
1) Shielded-Metal Arc Welding.
2) Submerged Arc Welding.
3) Flux-Cored Arc Welding
4) Gas-Metal Arc Welding
5) Gas-Tungsten Arc Welding
6. Shielded-Metal Arc
Welding:
Uses an electric arc to
coalescence metals.
Electricity travel from
electrode to bare metal to
ground.
The electrode is in a rod
form coated with flux.
Electric arc setup between a
flux-coated electrode and
workpiece.
7. Submerged Arc Welding:
Electric arc setup between the
bare electrode and the
workpiece.
Electrode is in a wire form and is
continuously fed from a reel.
Molten pool completely hidden
under a blanket of flux.
8. Flux-Cored Arc Welding:
This process is similar to the shielded-arc
stick welding process with the main
difference being the flux is inside the welding
rod.
Tubular, coiled and continuously fed electrode
containing flux inside the electrode is used.
This process saving the cost of changing the
welding.
In this process, sometimes, externally
supplied gas is used to assist in shielding the
arc.
9. Gas-Metal Arc Welding:
In this process an inert gas such as
argon, helium, CO₂ or a mixture of
them are used to prevent atmospheric
combination of the weld.
In this process, shielded gas is allowed
to flow through the weld gun.
The electrode used is in a wire form.
The wire is consumed during the
process and thereby provides filler
material.
10. Gas-Tungsten Arc Welding:
This process is also known as tungsten-
inert gas welding.
This process is similar to Gas-Metal Arc
Welding process.
Filler metal does not provide in this
process.
If the filler metal is required, an
auxiliary rod is used.
11. Plasma Arc Welding:
A non-consumable electrode is used
in this process.
In this process, the gas gets ionized
after the passage of electric current
and becomes a conductor of
electricity.
In this process, plasma consist of free
electrons, positive ions and neutral
particles.
12. B. Resistnace welding:
Resistance welding is a group of
welding process in which
coalescence is produced by the
heat obtained from the resistance
of the work to the flow of electric
current in a circuit of which the
work is a part and by the
application of pressure.
No filler metal is neeed in this
process.
13. C. Oxy-fuel Gas Welding:
Oxy-fuel welding are processes that
use fuel gases and oxygen to weld
metals.
This process is also known as oxy-
acetylene welding.
In this process, heat is supplied by the
combustion of acetylene in a stream
of oxygen.
Gases are supplied to the torch
through flexible hoses.
14. D. Electron-Beam Welding:
Electron beam welding is a fusion welding
process in which a beam of high-velocity
electrons is applied to two materals to be
joined.
In this process, coalescence is produced by
the heat obtained from a concentrated
beam of high velocity electron.
The electron beam generation takes place in
a vacuum, and the process works best when
the entire operation and workpiece are also
in a high vacuum of 10-4 torr or lower.
