Too Fast Travel Speed
- A too fast travel speed produces too little heat per mm of travel resulting in
less penetration and reduced weld fusion, the weld bead solidifies very quickly trapping gases inside
the weld metal causing porosity. Undercutting of the base metal can also occur and an unfilled
groove in the base metal is created when the travel speed is too fast to allow molten metal to flow
into the weld crater created by the arc heat.
Too Slow Travel Speed
- A too slow travel speed produces a large weld with lack of penetration and
fusion. The energy from the arc dwells on top of the weld pool rather than penetrating the base
metal. This produces a wider weld bead with more deposited weld metal per mm than is required
resulting in a weld deposit of poor quality.
Correct Travel Speed
- The correct travel speed keeps the arc at the leading edge of the weld pool
allowing the base metal to melt sufficiently to create good penetration, fusion and wetting out of the
weld pool producing a weld deposit of good quality.
Gas selection
- The purpose of the gas in the MIG process is to protect / shield the wire, the arc and
the molten weld metal from the atmosphere. Most metals when heated to a molten state will react
with the air in the atmosphere, without the protection of the shielding gas the weld produced would
contain defects like porosity, lack of fusion and slag inclusions. Additionally some of the gas becomes
ionised (electrically charged) and helps the current flow smoothly. The correct gas flow is also very
important in protecting the welding zone from the atmosphere. Too low flow will give inadequate
coverage and result in weld defects and unstable arc conditions. Too high flow can cause air to be
drawn into the gas column and contaminate the weld zone. Use the correct shielding gas. Co2 is
good for steel and offers good penetration characteristics, the weld profile is narrower and slightly
more raised than the weld profile obtained from Argon Co2 mixed gas. Argon Co2 mix gas offers
better weld ability for thin metals and has a wider range of setting tolerance on the machine. Argon
80% Co2 20% is a good all round mix suitable for most applications.
