WHAT IS ARC WELDING?
Arc welding is a type of welding process using an
electric arc to create heat to melt and join metals. A power supply creates an
electric arc between a consumable or non-consumable electrode and the base
material using either direct (DC) or alternating (AC) currents.
How Does it Work?
Arc welding is a fusion welding process used to join
metals. An electric arc from an AC or DC power supply creates an intense heat
of around 6500°F which melts the metal at the join between two work pieces.
The arc can be either manually or mechanically guided
along the line of the join, while the electrode either simply carries the
current or conducts the current and melts into the weld pool at the same time
to supply filler metal to the join.
Because the metals react chemically to oxygen and
nitrogen in the air when heated to high temperatures by the arc, a protective
shielding gas or slag is used to minimize the contact of the molten metal with
the air.
Once cooled, the molten metals solidify to form a
metallurgical bond.
Types
This process can be categorized into two different types;
consumable and non-consumable electrode methods.
Consumable Electrode Methods
Metal Inert Gas Welding (MIG) and Metal
Active Gas Welding (MAG), also known as Gas Metal Arc Welding
(GMAW), uses a shielding gas to protect the base metals from contamination.
Shielded Metal Arc Welding (SMAW),
also known as manual metal arc welding (MMA or MMAW), flux shielded arc welding
or stick welding is a process where the arc is struck between the metal rod
(electrode flux coated) and the work piece, both the rod and work piece surface
melt to form a weld pool. Simultaneous melting of the flux coating on the rod
will form gas, and slag, which protects the weld pool from the surrounding
atmosphere. This is a versatile process ideal for joining ferrous and
non-ferrous materials with a range of material thicknesses in all positions.
Created as an alternative to SMAW, Flux Cored Arc Welding
(FCAW) uses a continuously fed consumable flux cored electrode and a constant
voltage power supply, which provides a constant arc length. This process either
uses a shielding gas or just the gas created by the flux to provide protection
from contamination.
Submerged Arc Welding (SAW) is a frequently
used process with a continuously fed consumable electrode and a
blanket of fusible flux which becomes conductive when molten, providing a
current path between the part and the electrode. The flux also helps prevent
spatter and sparks while suppressing fumes and ultraviolet radiation.
Electro-Slag Welding (ESW) is
a vertical process used to weld thick plates (above 25mm) in a single pass. ESW
relies on an electric arc to start before a flux addition extinguishes the arc.
The flux melts as the wire consumable is fed into the molten pool, which
creates a molten slag on top of the pool. Heat for melting the wire and plate
edges is generated through the molten slag's resistance to the passage of the
electric current. Two water-cooled copper shoes follow the process progression
and prevent any molten slag from running off.
Like flash welding, Arc Stud Welding (SW) joins a
nut or fastener, usually with a flange with nubs that melt to create the join,
to another metal piece.
Non-consumable Electrode Methods
Tungsten Inert Gas Welding (TIG),
also known as Gas Tungsten Arc Welding (GTAW), uses a non-consumable tungsten
electrode to create the arc and an inert shielding gas to protect the weld and
molten pool against atmospheric contamination.
Like TIG, Plasma Arc Welding (PAW) uses an electric arc
between a non-consumable electrode and an anode, which are placed within the
body of the torch. The electric arc is used to ionize the gas in the torch and
create the plasma, which is then pushed through a fine bore hole in the anode
to reach the base plate. In this way, the plasma is separated from the
shielding gas.
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