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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. 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.
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