CO2 dissociates to CO and O2 at high temperature and the heat is absorbed during dissociation. Consequently, the arc heat is also absorbed and the arc concentrates at the bottom of the droplet. This phenomenon vibrates the bottom of the droplet and the weld pool strongly and makes the arc reaction force to push up the droplet.
There are two mechanisms that cause spatter for the different current ranges.
One is the “micro-short circuit (between the droplet and the work pieces)” that occurs in all current range. The arc power causes small spatter by vibrating the weld pool and the bottom of the droplet strongly. The other is the “arc reaction force” that occurs at the middle to high current range. The arc reaction force causes big spatter by pushing up the droplet. The “micro-short circuit” and “arc reaction force” are both caused by the property of the CO2 gas described above.
A high welding current immediately after short-circuit break makes a long arc and reduces the micro-short circuit. In contrast, a low welding current immediately after short-circuit break reduces the influence of the arc reaction force.
For these reasons, proper welding parameter must be optimized such that arc length is optimized which ultimately decreases the amount of spatter in CO2 welding.
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