4
EQUIPMENT REQUIREMENTS
Most mig welding controls are now being
produced with the necessary timing devices to control arc duration,
shielding gas flow, and ”anti-stick.”
The arc duration timer controls the amount of time the arc will actually be
maintained. Accuracy of timing to within
+1 cycle (.017 sec.) and range adjustment up to two seconds time
is desirable. The post-flow timer is
needed to regulate the gas flow after the arc has been broken. It is
important that the spot weld be shielded
during the solidification time. Adjustment of an ”anti-stick” timer
keeps the power supply on briefly after
the wire feed motor is shut off and allows the wire electrode to burn
back to a predetermined length. This
prevents the end of the wire from freezing in the weld puddle when the
weld is completed.
The only other addition to the welding
system is a different shielding gas nozzle. As shown in Figure 11-4,
this nozzle is longer than that normally
used for continuous mig welding. This longer cup is necessary
because the weld is made inside the
cup. The slots are required to allow hot gases to escape. Spot welding
cups are also available in different
sizes. As the thickness of the sheets to be welded increases, the weld
size will increase, and the shielding
cup size should also be increased. Continued
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