Selco Genesis 4000 GSM Manuel D'instructions page 59

The current is transferred to the arc through the fusible elec-
trode (wire connected to positive pole); in this procedure the
melted metal is transferred onto the workpiece through the arc
stream. The automatic feeding of the continuous filler material
electrode (wire) is necessary to refill the wire that has melted
during welding.
Methods
In MIG welding, two main metal transfer mechanisms are
present and they can be classified according to the means by
which metal is transferred from the electrode to the work-
piece. The first one, defined "SHORT-ARC", produces a small,
fast-solidifying weld pool where metal is transferred from the
electrode to the workpiece only for a short period when the
electrode is in contact with the weld pool. In this timeframe,
the electrode comes into direct contact with the weld pool
generating a short circuit that melts the wire which is there-
fore interrupted. The arc then turn on again and the cycle is
repeated (Fig. 1a).
Fig. 1a
Fig. 1b
SHORT cycle (a) and SPRAY ARC welding (b)
Another mechanism for metal transfer is called the "SPRAY-ARC"
method, where the metal transfer occurs in the form of very small
drops that are formed and detached from the tip of the wire and
transferred to the weld pool through the arc stream (Fig. 1b).
SELECTION GUIDE OF WELDING PARAMETERS WITH REFERENCE TO THE MOST TYPICAL APPLICATIONS AND MOST
COMMONLY USED WIRES
Wire diameter - weight per metre
Voltage
arc (v)
Low penetration for thin
16 - 22
SHORT - ARC
24 - 28
GLOBULAR-ARC
(transition area)
30 - 45
SPRAY - ARC
0,8 mm
Good penetration and
materials
60 - 160 A
Automatic fillet welding Automatic welding
150 - 250 A
Low penetration with Automatic welding
adjustment to 200 A
150 - 250 A
Welding parameters
The visibility of the arc reduces the need for the user to strictly
observe the adjustment tables as he can directly monitor the
weld pool.
- The voltage directly affects the appearance of the bead, but
the dimensions of the weld bead can be varied according to
requirements by manually moving the torch to obtain variable
deposits with constant voltage.
- The wire feeding speed is proportional to the welding cur-
rent.
Fig. 2 and 3 show the relationships between the various welding
parameters.
Fig. 2 Diagram for selection the of best working characteristic.
Fig. 3 Relationship between wire feeding speed and current
amperage (melting characteristic) according to wire diameter.
1,0-1,2 mm 1,6 mm
Good flat and vertical
melting control
100 - 175 A
120 - 180 A
Automatic welding down-
with high voltage
200 - 300 A 250 - 350 A
Good penetration
with multiple runs
200 - 350 A 300 - 500 A
2,4 mm
Not used
melting
150 - 200 A
Not used
wards
300 - 400 A
Good penetration, high
downwards deposit on thick materials
500 - 750 A
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