Lincoln Electric K2613-5 Operator's Manual page 17

Constant current wire welding
(See Figure 11)
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
temperature based on the material to be welded. The
intention is to assure that proper weld material properties
will develop.
Welding is sometimes performed using constant 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
diameter, 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, shortening the contact
tip to work distance lowers the voltage.
Constant Current
Power Source
2. Wire feed speed knob
Use the Wire Feed Speed Knob to adjust the rate of wire
feed speed.
WFS range for standard torque:
High = 50 to 700 ipm
Low = 50 to 200 ipm
WFS range for extra torque:
High = 50 to 400 ipm
Low = 50 to 200 ipm
English
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 compensates 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 properties 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.
For these reasons, 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.
Current
Wire
Feeder
Current
Figure 11
Because the wire feeder is powered by the arc voltage,
the full range of wire feed speed may not be available at
low voltages.
3. Wire feed speed range switch
Use to select either the low range or high range for the
wire feed speed knob. Note – selecting the low range
does not increase the torque of the wire drive.
14
WFS
CTWD
English