The procedure for arc cutting is shown in figure
pressure to the work; (3) transmit current to the
work; and (4) control the intensity and the duration
10-74. When cutting thin plate (under one-half
of both current and pressure.
inch), you do not need to manipulate the electrode
except as required to maintain the arc and to
As may be seen in figure 10-79, the electrodes
advance the arc as the cut progresses (fig. 10-74,
are held in arms (often called horns). The work is
view A). When cutting heavier plate, manipulate
placed between the two electrodes, and the machine
the electrode with an up-and-down motion in the
is adjusted for the control of current, pressure, and
cut so as to displace the molten metal; keep the
time. The electrode in the lower horn supports the
electrode at an angle to the plate (fig. 10-74, view
work, provides backing as pressure is applied by the
B) so that the bottom of the plate is cut slightly
electrode in the upper horn, and completes the
before the top. In general, metal-arc cutting is
better than carbon-arc cutting through heavy
in the machine. A foot pedal control permits the
Metal-arc cutting is also generally
operator to start the welding sequence while using
preferred for rivet cutting and for hole piercing.
both hands to position the work between the
Gas tungsten-arc cutting is an arc-cutting process
electrodes. When the foot pedal is depressed, the
used for cutting aluminum alloys. A
upper electrode moves down into contact with and
high-temperature, high-velocity arc is established
applies pressure to the work. At the instant the foot
between the tungsten arc and the workpiece. A
pedal is depressed, a preset, automatic timing device
shielding gas mixture of hydrogen and argon
takes over. First, the timer provides for SQUEEZE
emerges from the nozzle at a sufficiently high
TIME, during which pressure is built up in the
velocity to blow the molten metal from the cut.
pressure system and is applied to the work. Next, at
Most of the safety precautions concerning arc
the end of squeeze time, the timer provides WELD
welding that are given in chapter 1 of this training
TIME, which controls the duration of current flow.
manual also apply to arc cutting. Be sure that you
Finally, the timer provides HOLD TIME, during
are entirely familiar with all appropriate safety
which pressure is maintained on the electrodes after
current flow stops. Hold time permits the weld
nugget to cool and solidify under pressure. The
weld that results depends on many factors, including
current, pressure, and timing settings; the condition
of the electrodes; and the surface condition of the
workpiece. Each kind and thickness of material
requires an individual setup. These adjustments are
based on tables of resistance welding data furnished
by the manufacturer.
Arc cutting is a melting process rather than a
burning process. The heat of the arc is used to melt
the metal along the line of cut. This method does
not produce cuts of the quality produced by
oxyacetylene cutting, but it has the advantage of
being applicable to almost all metals (including
Two arc-cutting procedures are commonly used.
CARBON-ARC CUTTING is done with a carbon
or graphite electrode. SHIELDED METAL-ARC
CUTTING is done with a covered metal electrode.
DC and straight polarity are preferred for both of
these types of arc cutting. Conventional arc welding
power sources are used for both of these types of
Figure 10-74.--Techniques for arc cutting. (A) Thin plate.
(B) Heavy plate.