19
Establishing the Arc and Making Weld Beads
Before attempting to weld on a finished piece of work, it is recommended that practice welds be made on a
sample
metal of the same material as that of the finished piece
The easiest welding procedure for the beginner to experiment with MIG welding is the flat position. The equipment is
capable of flat, vertical and overhead positions.
For practicing MIG welding, secure some pieces of 16 or 18 gauge (0.06” 1.5mm or 0.08” 2.0mm) mild steel plate 6” x 6”
(150 x 150mm). Use 0.030” (0.8mm) flux cored gasless wire or a solid wire with shielding gas
Setting of the Power Source
Power source and Wire feeder setting requires some practice by the operator, as the welding plant has two control
settings that have to balance. These are the Wire speed control and the welding Voltage Control. The
welding
current
is
determined
by the Wire speed control, the current will increase with increase Wire speed,
resulting
in
a
shorter
arc. Less wire
speed
will
reduce
the
current
and
lengthen
the Increasing
the
welding
voltage
hardly
alters
the
current
level,
but
lengthens
the
arc.
By
decreasing voltage, a shorter arc is
obtained with a little change in current level.
When
changing
to
a
different
electrode
wire
diameter,
different
control
settings
are
required.
A
thinner electrode wire needs more Wire speed to achieve the same current level
A satisfactory weld cannot be obtained if the Wire speed and Voltage settings are not adjusted to suit the electrode wire
diameter and the dimensions of the work piece.
If the Wire speed is too high for the welding voltage, “stubbing” will occur as the wire dips into the molten pool and does
not melt. Welding in these conditions normally produces a poor weld due to lack of fusion. If, however, the welding
voltage is too high, large drops will form on the end of the wire, causing spatter. The correct setting of voltage and Wire
speed can be seen in the shape of the weld deposit and heard by a smooth regular arc sound. Refer to the Weld Guide
located on the inside of the wire feed compartment door for setup information.
Electrode Wire Size Selection
The choice of Electrode wire size and shielding gas used depends on the following
Thickness of the metal to be welded
Capacity of the wire feed unit and Power Source
The amount of penetration required
The deposition rate required
The bead profile desired
The position of welding
Cost of the wire
