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B-7
OPERATION
B-7
CONSTANT CURRENT OPERATION WITH
A LINCOLN ELECTRIC WIRE FEEDER
Lincoln Electric does NOT recommend constant
current semiautomatic welding for applications
which need to meet specified weld metal chemical
or mechanical property requirements or weld
quality requirements.
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Most semiautomatic welding processes perform better
using constant voltage power sources. Welding codes
usually do not address the power source selection or
specifically, whether the welding process is to be
operated in the constant voltage or constant current
mode. Instead, codes typically specify limitations on
the current, voltage, heat input and preheat tempera-
ture based on the material to be welded. The intention
is to assure that proper weld material properties will
develop. Welding is sometimes performed using con-
stant current power sources. The operation can be
more convenient because it may allow the use of an
existing stick (SMAW) power source and the power
source can be placed at a distant location without any
provision for adjusting the output settings.
For constant current operation, the power source is
set to deliver the specified current. The power source
regulates this current regardless of changes in the
welding circuit, including cable length, electrode diam-
eter, wire feed speed, contact tip to work distance,
etc.
Changes in the wire feed speed (WFS) or contact tip
to work distance (CTWD) affect the arc voltage when
constant current power sources are used. Lowering
the wire feed speed raises the voltage, raising the
wire feed speed lowers the voltage. Lengthening the
contact tip to work distance raises the voltage, short-
ening the contact tip to work distance lowers the volt-
age. If the contact tip to work distance is properly
maintained, a satisfactory operating voltage range
may be achieved, and a sound weld may result.
However, when a welder uses a longer contact tip to
work distance, an arc-sensing wire feeder compen-
sates by increasing the wire feed speed to regulate
the voltage.
Even if the voltage and current remain unchanged, the
increased wire feed speed may result in a deposition
rate well beyond the specified range of the electrode.
Under these conditions, the specified weld metal prop-
erties may not be achieved. Constant voltage power
sources deliver large current surges to stabilize the
arc when the electrode is shorted or the arc length is
very short.
However, a constant current power source does not
provide such a response to stabilize the arc. It may be
difficult to achieve required weld metal properties, or
to achieve the required quality of welds needed to
pass nondestructive tests, when such welds are made
under constant current operation.
BIG RED™ 600