Fundamentals of the MIG/MAG welding process
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16
Fundamentals of the MIG/MAG welding process
16.1 Principle of the MIG/MAG welding
process
The wire feed rollers feed the wire electrode from the
reel to the contact tip. An arc is created between the wire
electrode and the workpiece. The wire electrode thus
becomes the arc carrier. The arc melts the workpiece
point by point and forms the weld pool. The wire elec-
trode melts and drips into the weld pool, thus forming the
filler metal. The inert gas flows from the gas nozzle and
protects the arc and weld pool from atmospheric gases.
Wire feed rollers
Shielding gas
Arc
Power source
Workpiece
Welding seam
Contact tip
Gas nozzle
Wire electrode
Abb. 15: MIG/MAG welding processes
There are two types of metal inert gas welding, which are
differentiated by the type of inert gas used: metal inert
gas welding (MIG) and metal active gas welding (MAG).
Welding
process
Shielding gas
inert
active
MIG
Helium (He) Argon (Ar)
mixture of Ar/He
MAG-C
Carbon dioxide
100 % CO2
MAG-M
Mixtures of Ar/
CO2 Ar/O2
Tab. 7: MIG/MAG welding processes
The welding processes are further differentiated by arc
type. This means that there are differences in the form of
the arc, short circuit tendency and metal transfer mode.
Selection of the type of arc is only possible to a limited
extent e. g. when short arc welding. Short arc welding
is possible using all metal shielding gas welding proc-
esses by the selection of the suitable current intensity
and the associated arc voltage, although the short circuit
frequency and drop size are very different, according to
the shielding gas being used.
16.2 Arc types
Short arc
This type of arc is particularly suitable for welding thin
sheets, in root layers and for welding in restricted loca-
tions because of its relatively "cold" melt flow. In this
case, the welding takes place with a very short arc, at
low arc voltage and at low current intensity. Due to the
surface tension of the melt pool, the drop is drawn into
the molten metal and the arc is reignited. This recurring
cycle creates a continuous alternation between the short
circuit and the arcing period.
The transition from short to spray arc is de-
pendent upon the gas mixture and the wire
diameter.
Transition arc
The transition arc is used for medium plate thickness
and for vertical down welding. The material transfer tales
place both in short circuit and in free flow. This produc
-
es a reduced short circuit index and a slightly "hotter"
molten pool than in the short arc. Transition arc welding
has a higher melting rate than short arc, and is therefore
more economical.
Long arc
Long arcs are typically used for welding under carbon
dioxide and under high CO2 containing gas mixtures in
the upper performance range. Long arc welding is not
really suitable for welding in tight spaces. Larger drops
fall into the molten pool largely by gravity. This some-
times involves short circuits which, at the point of the
short circuit, can produce spatter when the arc ignites
again, because of the upslope.
Spray arc
Due to the thinness of the melt pool, spray arc welding
is not suitable for welding in tight spaces. It is used for
welding in the higher power range using inert gases or
gas mixtures with high argon content. The spray arc has
a very fine drop, short-circuit free material transfer.
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