4
POWER SOURCE Almost
all mig welding is done with reverse polarity. The positive (+) lead is connected
to the torch while the negative
(–) lead is connected to the workpiece. Since wire feed speed and, hence,
current, is regulated by the
welding control, the basic adjustment made through the power source is arc length.
Arc length is set by adjusting
the power source voltage. Power source may also have one or two additional adjustments
for use with other
welding applications. Most
power sources require either 230V or 460V AC input power. Except for the power
cable, the only other connection
to the power source is a multi-connector cable from the control, so as to have
the power in sequence
with other control functions. Power sources will be discussed further in the next
section. SEQUENCE
OF OPERATION As
an example, consider the operation of the welding installation pictured in Figure
2-1: 1) Main
line power to power source turned on. 2) Set
power source switch to ”READY” to turn on power source
cooling fan motor and control circuit.
3) Turn the
welding control switch to ”ON”
to energize the control. 4) Close
torch switch to cause shielding gas and cooling water to flow. Weld power goes
to torch and wire
feed begins at set speed. The feeding wire electrode touches the workpiece. Welding
begins. 5) Release
torch switch – No. 4 above reversed. Most
welding installations operate in a similar manner. However, the design and construction
of the equipment
will differ. It is for this reason that the equipment instruction booklet should
be consulted. Complete
troubleshooting data is generally supplied with all equipment.
