Continuous Wire Welding (Mig/Mag) - voestalpine Böhler Welding URANOS 2700 SMC Betriebsanweisung

7.3 Continuous wire welding (MIG/MAG)

Introduction
A MIG system consists of a direct current power source, wire
feeder, wire spool, torch and gas.
MIG manual welding system
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 pre-
sent and they can be classified according to the means by which
metal is transferred from the electrode to the workpiece. The
first one, defined "SHORT-ARC", produces a small, fast-solid-
ifying 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 therefore 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).
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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 current.
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.