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11.0 Manual Metal Arc Welding Process
(MMAW)
TIG Welding techniques
Weld Metal
Slag
11.1 Process
Manual Metal Arc welding is the process of joining
metals where an electric arc is struck between
the metal to be welded (parent metal) and a flux-
coated filler wire (the electrode). The heat of the
arc melts the parent metal and the electrode which
mix together to form, on cooling, a continuous solid
mass.
Before arc welding can be carried out, a suitable
power source is required. Two types of power
sources may be used for arc welding, direct current
(DC) or alternating current (AC).
The essential difference between these two power
sources is that, in the case of DC, the current
remains constant in magnitude and flows in the
same direction. Similarly, the voltage in the circuit
remains constant in magnitude and polarity (i.e.
positive or negative).
In the case of AC however, the current flows first
in one direction and then the other. Similarly, the
Installation for MMA process
Flux Covering
Core Wire
Arc
Weld Pool
Workpiece
voltage in the circuit changes from positive to
negative with changes in direction of current flow.
This complete reversal is called a 'half cycle' and
repeats as long as the current flows. The rate of
change of direction of current flow is known as
the 'frequency' of the supply and is measured by
the number of cycles completed per second. The
standard frequency of the AC supply in Australia is
50 Hz (Hertz).
11.2 Welding Machine
The most important consideration when
contemplating the use of arc welding for the first
time is the purchase of a suitable welding machine.
BOC supplies a popular range of arc welding
machines. Machines range from small portable
welders that operate from standard 240 Volt
household power to heavy-duty welders used by
the largest steel fabricators.
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