12
Operators Manual
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7 Basic Welding Information
MIG Welding (GMAW)
Choice of Shielding Gas
The choice of shielding gas is largely
determined by the consumable wire to
be used. Many proprietary shielding gas
mixtures are available.
Some recommended shielding gases are:
• Mild Steel
Argon + 18% Oxygen ;
Argon + 2%
5% Carbon dioxide;
• Aluminium
Argon;
• Stainless Steel Argon + 1 to 2%
Oxygen.
Argon + Helium
Consult your gas supplier if more specific
information is required.
Shielding Gas Flow Rate
In GMAW, one function of the shielding gas
is to protect the moulten weld pool from the
effects of oxygen in the atmosphere. Without
this protection the weld deposit becomes
‘honeycombed’ in appearance, an effect
which is described as weld porosity.
In draft-free conditions the gas flow rate
required to give adequate protection is
typically 10-12 litres/min. In situations where
drafts cannot be avoided, it may be necessary
to increase this rate up to 20 litres/min,
and/or to provide screening of the work area.
Weld porosity can also be caused by air
entering the gas stream through a damaged
hose, loose gas connection, or from
restriction in the nozzle, such as from excess
build-up of spatter.
When welding aluminium, particular care
must be taken with all aspects of shielding
gas delivery and workpiece preparation in
order to avoid weld porosity.
6 Normal Welding Sequence
Weld Start
Closing the welding gun switch initiates
this sequence of events:
• The gas valve is energised and gas flow
commences;
• Welding voltage is applied between the
work piece and the consumable wire.
• The wire drive motor is energised.
• The wire touches the work piece, and
the arc is established.
Weld End
Releasing the gun switch initiates this
sequence of events:
• The wire drive motor is de-energised,
and is dynamically braked to a stop;
• The welding current stops.
• The gas valve is de-energised and the
flow of shielding gas ceases.
The quality of the consumable wire
greatly affects how reliably a gas
metal arc welder will operate. For best
results when welding mild steel, we
recommend quality WIA AUSTMIG ES6.
Dirty, rusty or kinked wire will not feed
smoothly through the gun cable and
will cause erratic welding. Deposits from
the wire will clog the gun cable liner
requiring it to be replaced prematurely.
