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LORCH
Fundamentals of the
MIG/MAG
welding
p rocess
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
electrod£---
-:
Gas
noz
-
--
---"
~Bntact
ti~:-=~~~~
Shielding
-,..---===--___,.~
gas
Welding
,._flem
Fig. 12:
MIG/MAG
welding
processes
(!>
Power
source
t:I
There
are two
types
of metal shielding-gas welding
that
are differentiated
by the
type of shielding gas that
is
used: metal
inert
gas welding
(MIG),
inert
shielding
gas)
and
metal active gas welding
(MAG,
active
shield-
ing
gas).
Welding
Shielding gas
process
inert
active
MIG
Helium (He)
Argon (Ar)
mixture of Ar/He
MAG-C
Carbon dioxide
100
%
C02
MAG-M
Mixtures
of Ar/
C02Ar/02
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
processes
by the
selection
of
the
suitable
current
intensity and the
associated arc
voltage,
although
the short
circuit fre-
quency and drop size are very
different,
according
to
the
shielding gas
being
used.
-
20
-
16.2
Arc
types
Short arc
This
type
of
arc
is particularly
suited
to the welding
of
thin
sheets,
in root
layers and
for
welding in
restricted
locations because
of its relatively
"cold" weld
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.
CD
The
transition
from short
to
spray arc is
de-
pendent upon
the
gas mixture and
the wire
diameter.
Transition arc
A
transition
arc is used for medium plate
thickness
and
for
vertical
down
welds.
The material transfer tales
place
both in
short
circuit
and
in
free
flow.
This produces
a
re-
duced
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
C02
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,
al the
point
or 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.
10.13
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