Secondary Adjustable Variables
These variables cause changes in primary adjustable variables
which in turn cause the desired change in the bead formation.
They are:
1.
Stick-Out -
(distance between the end of the contact tube (tip) and
the end of the electrode wire). Maintain at about 10mm stick-out
2.
Wire Feed Speed -
increase in wire feed speed increases weld
current. Decrease in wire feed speed decreases weld current.
3.
Nozzle Angle -
This refers to the position of the welding gun in
relation to the joint. The transverse angle is usually one half the
included angle between plates forming the joint. The longitudinal
angle is the angle between the centre line of the welding gun and
a line perpendicular to the axis of the weld.
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
(1.5mm or 2.0mm) mild steel plate (150 x 150mm). Use (0.8mm) flux
cored gasless wire or a solid wire with shielding gas.
Setting of the Power Source
Power source and Current (Wire Speed) setting requires some
practice by the operator, as the welding plant has two control
settings that have to balance. These are the Current (Wire Speed)
control and the welding Voltage Control.
The welding current is determined by the Current (Wire Speed)
control, the current will increase with increased Current (Wire
Speed), resulting in a shorter arc. Less Current (Wire Speed) will
reduce the current and lengthen the arc. Increasing the welding
voltage hardly alters the current level, but lengthens the arc.
By decreasing the voltage, a shorter arc is obtained with a little
change in current level.
When changing to a different electrode wire dia eter, different
control settings are required. A thinner electrode wire needs
more Current (Wire Speed) to achieve the same current level.
A satisfactory weld cannot be obtained if the Current (Wire
Speed) and Voltage settings are not adjusted to suit the electrode
wire diameter and the dimensions of the work piece.
If the Current (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
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MULTIMIG 200 PFC MV
OWNER’S MANUAL
voltage is too high, large drops will form on the end of the wire,
causing spatter. The correct setting of voltage and Current (Wire
Speed) can be seen in the shape of the weld deposit and heard
by a smooth regular arc sound.
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
• Type of joint
• 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
