Tweco 400i Transmig - Manual (Page 26)

TRANSMIG 400 i
4-4 July 18, 2008
ARC CONTROL
This parameter operates in STICK mode only and is used to adjust percentage increase in welding current
and is proportional to arc length (arc voltage). This control provides an adjustable amount of arc control
(or dig). This feature can be particularly beneficial in providing the operator with the ability to compensate
for variability in joint fit up in certain situations with particular electrodes, e.g. cellulose and hydrogen
controlled electrodes. In all welding processes, the amount of penetration obtained is dependent on the
welding current; i.e. the greater the penetration, the greater the current.
Arc Force Position Current Increase when Arc
Voltage is less than 18V
Effect on Welding Performance
Minimum (0) 0A Soft arc, Low spatter, Low
penetration
Medium (20%) 32A Normal arc, Improved fusion
characteristics,
Normal penetration
Maximum (100%) 160A Hard arc, Deep penetration
Table 4-4: Arc Control Parameters
In general, having the ARC CONTROL set at 100% (maximum) allows greater penetration control to be
achieved. With the ARC CONTROL set at 0% (minimum) the Power Source has a constant current
characteristic. In other words, varying the arc length does not significantly affect the welding current.
When the ARC CONTROL set to 100%, it is possible to control the welding current by varying the arc
length. This is very useful for controlling penetration on root runs and side wall wash on vertical up fillet
welds.
Root Runs
During root runs the weld pool forms a "keyhole" shape. If too much weld current is used, the hole
blows out and the weld collapses. If too little weld current is used, the hole closes up and penetration
is lost. The size of the hole also determines the arc length; i.e. as the hole gets bigger, the arc gets
longer.
If arc force is used, the increase in the arc length causes the weld current to decrease until the hole
starts to close up but if the hole closes up to much then the arc length decreases which causes the
weld current to increase. Too little or too much arc force makes this process unstable. The operator
must adjust the arc force until a happy medium is reached.
Vertical Up Welding
When welding vertical up with arc force on, the operator can control the amount of current by
changing arc length, i.e. voltage. Weld metal is deposited by "digging" the electrode into the side of
the base metal joint and then increasing the arc length with a flicking motion, to allow the weld pool
to freeze, before digging the electrode into the other side of the base metal joint.
Without arc force, increasing the arc length does not decrease the weld current sufficiently and the
operator has to manually decrease the current via a remote current control to freeze the weld pool.
This welding current reduction also reduces the penetration.
The arc force allows the weld pool to freeze during the "flick" phase without decreasing the amount
of weld current available during the "dig" phase thus maximizing penetration.