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2003
5.
Gas– Shielded Metal Arc Welding
5. Gas-Shielded Metal Arc Welding 56
The difference between gas-shielded metal arc welding (GMA) and the gas tung-
sten arc welding process is the consumable electrode. Essentially the process is
classified as metal inert gas welding (MIG) and metal active gas welding (MAG).
Besides, there are
two more process
variants, the elec-
trogas and the nar-
row gap welding
and also the gas-
shielded plasma
metal arc welding,
a combination of
both plasma weld-
ing and MIG weld-
ing, Figure 5.1.
In contrast to TIG welding, where the
electrode is normally negative in order
to avoid the melting of the tungsten
electrode, this effect is exploited in
MIG welding, as the positive pole is
strongly heated than the negative pole,
thus improving the melting characteris-
tics of the feed wire.
Figure 5.2 shows the principle of a
GMA welding installation. The weld-
ing power source is assembled using
the following assembly groups: The
transformer converts the mains volt-
age to low voltage which is subse-
quently rectified.
© ISF 2002
gas-shielded arc welding (SG)
Classification of Gas-ShieldedArc Welding Processes
br-er5-01e.cdr
gas-shielded metal-arc welding (GMAW)
tungsten gas-shielded welding
metal inert gas welding
(MIG)
plasma jetplasma
arcwelding(WPSL)
plasmaarc
welding
(WPL)
Narrow-gap gas-shielded arc
welding (MSGE)
electrogaswelding(MSGG)
plasma gasmetal arcwelding
(MSGP)
gas mixturemetal-arcwelding
(GMMA)
gas metal-arc COwelding
(MAGC)
2
hydrogentungsten arc
welding
(WHG)
plasmajet
welding
(WPS)
metalactive gaswelding
(MAG)
tungsteninert-gaswelding
(TIG)
tungstenplasmawelding
(WP)
consumable electrode non consumable electrode
Figure 5.1
wire feed unit
water cooling
shielding gascontrol device
control switch
cooling watercontrol
rectifier
transformer
welding power source
GMA Welding Installation
br-er5-02e.cdr © ISF 2002
Figure 5.2
5. Gas-Shielded Metal Arc Welding 57
Apart from the torch cooling and the
shielding gas control, the process
control is the most important installa-
tion component. The process control
ensures that once set welding data
are adhered to.
A selection of common welding in-
stallation variants is depicted in Fig-
ure 5.3, where the universal device
with a separate wire feed housing is
the most frequently used variant in
the industry.
Figure 5.4 shows in detail a manually
operated inert-gas shielded torch
with the common swan-neck shape. A
machine torch has no handle and its
shape is straight or swan-necked. The
hose package contains the wire core
and also supply lines for shielding gas,
current and cooling water, the latter for
contact tube cooling. The current is
transferred to the wire electrode over
the contact tube. The shielding gas
nozzle is shaped to ensure a steady
gas flow in the arc space, thus protect-
ing arc and molten pool against the
atmosphere.
© ISF 2002br-er5-03e.cdr
Types of Welding Installations
compact device universal device
mini-spool device push-pull device
10, 20 or 30m 5 to 10m
3 to 5m5, 10 or 20m
3 to 5m
Figure 5.3
© ISF 2002br-er5-04e.cdr
Manual Gas-Shielded Arc Welding Torch
1 torch handle 2 torch neck 3 torch trigger 4 hose package 5 shielding gas nozzle 6 contact tube 7 contact tube fixture 8 insulator 9 wire core10 wire guide tube11 wire electrode12 shielding gas supply13 welding current supply
Figure 5.4
5. Gas-Shielded Metal Arc Welding 58
A so-called “Two-Wire-Drive” wire
feed system is of the most simple de-
sign, as shown in Figure 5.5. The wire
is pulled off a wire reel and fed into
the hose package. The wire transport
roller, which shows different grooves
depending on the used material, is
driven by an electric motor. The coun-
terpressure roller generates the fric-
tional force which is needed for wire
feeding.
More complicated but following the
same operation principle is the “Four-
Wire-Drive”, Figure 5.6. Here, the
second pair of rollers guarantees
higher feeding reliability by reducing
the risk of wheel slip. Another design
among the wire feed drive systems is
the planetary drive, where the wire is
fed in axial direction by the motor. A
rectilinear rotation-free wire feed mo-
tion is the outcome of the motor rota-
tion and the angular offset of the drive
rollers which are firmly connected to
the motor shaft.
Figure 5.7 depicts the metal transfer in
the short arc range. During the burn-
ing phase of the arc, material is molten
and accumulates at the electrode end.
The voltage drops slowly while the arc
shortens. Electrode and workpiece
© ISF 2002br-er5-05e.cdr
Wire Feed System
1
24 2
F
65
1 wire reel
2 wire guide tube
5 wire feed roll with a V-groove for steel electrodes
6 wire feed roll with a rounded groove for aluminium
3 wire transport roll
4 counter pressure roll
4 4 3
Figure 5.5
© ISF 2002br-er5-06e.cdr
Wire Drives
4-roller drive
1 wire guide tube2 drive rollers3 counter pressure rollers4 wire guide tube
3 4 3
3
3
1
1
1
2 2
2
1 wire guide tube2 roller holding device3 drive rollers
planetary drive
direction of rotation
Figure 5.6
5. Gas-Shielded Metal Arc Welding 59
make contact and a short-circuit occurs. In the short-circuit phase is the liquid elec-
trode material drawn as result of surface tension into the molten pool. The narrowing
liquid root and the
rising current lead
to a very high cur-
rent density that
causes a sudden
evaporation of the
remaining root.
The arc is reig-
nited. The short-
arc technique is
particularly suitable
for out-of-position
and root passes
welding.
The limitation of the rate of the current rise during the short-circuit phase with a
choke leads to a pointed burn-off process which is smoother and clearly shows less
spatter formation, Figures 5.8
In shielding gases
with a high CO2
proportion a long
arc is formed in the
upper power range,
Figure 5.9. Material
transfer is unde-
fined and occurs as
illustrated in Fig-
ures 5.13 and 5.14.
Short-circuits with
very strong spatter
formation are
Short-Circuiting Arc Metal Transfer
br-er5-07e.cdr
1 ms
1 mm
time
time
wel
ding
cur
rent
wel
ding
vol
tage
Figure 5.7
© ISF 2002
Choke Effect
br-er5-08e.cdr
timetime
wel
ding
cur
rent
wel
ding
cur
rent
choke effectlow medium
Figure 5.8
5. Gas-Shielded Metal Arc Welding 60
caused by the formation of very large droplets at the electrode end.
If the inert gas content of the shielding gas exceeds 80%, a spray arc forms in
the upper power range, Figure 5.10. The spray arc is characterised by a non-short-
circuiting and
spray-like material
transfer. For its
high deposition
rate the spray arc
is used for welding
filler and cover
passes in the flat
position.
Connections be-
tween welding
© ISF 2002br-er5-09e.cdr
Long Arc
wel
ding
vol
tage
wel
ding
cur
rent
time
time
© ISF 2002br-er5-10e.cdr
Spray Arc
wel
ding
vol
tage
wel
ding
cur
rent
time
time
Figure 5.9 Figure 5.10
© ISF 2002
Welding Parameters in Dependence on the Shielding Gas Mixture (SG 2, Ø1,2 mm)
br-er5-11e.cdr
wel
ding
vol
tage
150 200 250 300A
15
20
25
V
35
contact tube distance: approx. 15 mm
spray arc
long arc
short arc
contact tube distance: approx. 19 mm
mixedcircuiting arc
C1
M21
M23
welding current
wire feed 5,53,5 4,5 7,0 8,0 10,5m/min
shielding gas composition:C1: COM21: 82% Ar, 18% COM23: 92% Ar, 8% O
2
2
2
Figure 5.11
5. Gas-Shielded Metal Arc Welding 61
parameters, shielding gas and arc
type are shown in Figure 5.11. When
the shielding gas M23 is used, the
spray arc may already be produced
with an amperage of 260 A. With the
decreasing argon proportion the am-
perage has to be increased in order to
remain in the spray arc range. When
pure carbon dioxide is applied, the
spray arc cannot be produced. Figure
5.11 shows, moreover, that with the
increasing CO2 content the welding
voltage must also be increased in or-
der to achieve the same deposition
rate.
The different thermal conductivity of
the shielding gases has a considerable
influence on the arc configuration and
weld geometry, Figure 5.12. Caused
by the low thermal conductivity of the
argon the arc core becomes very hot –
this results in a deep penetration in the
weld centre, the so-called “argon fin-
ger-type penetration”. Weld reinforce-
ment is strongly pronounced. Applica-
tion of CO2 and helium leads, due to
the better thermal conductivity of these
shielding gases, to a wide and deep
penetration.
A recombination (endothermic break
of the linkage in the arc space – exo-
© ISF 2002br-er2-12e.cdr
argon helium
argon
helium
temperature
ther
mal
con
duct
ivity hydrogen
nitrogen
CO2
CO282%Ar+18%CO2
Figure 5.12
© ISF 2002br-er5-13e.cdr
current-carryingarc core
argon carbon dioxider
argon carbon dioxide
r
tem
pera
ture
Fr
FaF
Fa F
Fr
Figure 5.13
5. Gas-Shielded Metal Arc Welding 62
thermal reaction 2CO + O2 ->2CO2 in
the workpiece proximity) intensifies
this effect when CO2 is used.
In argon, the current-carrying arc core
is wider and envelops the wire elec-
trode end, Figure 5.13. This gener-
ates electromagnetic forces which
bring about the detachment of the
liquid electrode material. This so-
called “pinch effect” causes a metal
transfer in small drops, Figure 5.14.
The pointed shape of the arc attach-
ment in carbon dioxide produces a
reverse-direction force component,
i.e., the molten metal is pushed up
until gravity has overcome that force
component and material transfer in the
form of very coarse drops appear.
Besides the pinch effect, the inertia
and the gravitational force, other
forces, shown in Figure 5.15, are ac-
tive inside the arc space; however
these forces are of less importance.
© ISF 2002br-er5-14e.cdr
wire elektrodes
current-carryingarc core
argon carbon dioxide
Figure 5.14
© ISF 2002br-er5-15e.cdr
Forces in Arc Space
work piece
electrostaticforces
surfacetension S
acceleration due to gravity
wire electrode
viscosity
droplets necking down
inertia
suction forces, plasma flowinduced
electromagnetic force F(pinch effect)
L
backlash forces fof the evaporating material
r
Figure 5.15
5. Gas-Shielded Metal Arc Welding 63
If the welding voltage and the wire feed speed are further increased, a rotating arc
occurs after an undefined transition zone, Figure 5.16. High-efficiency MAG weld-
ing has been applied since the beginning of the nineties; the deposition rate, when
this process is used, is twice the size as, in comparison, to spray arc welding. Apart
from a multicompo-
nent gas with a he-
lium proportion,
also a high-rating
power source and a
precisely controlled
wire feed system for
high wire feed
speeds are neces-
sary.
Figure 5.17 depicts the deposition rates over the wire feed speed, as achievable with
modern high-efficiency MAG welding processes.
During the transi-
tion from the short
to the spray arc the
drop frequency rate
increases erratically
while the drop vol-
ume decreases at
the same degree.
With an increasing
CO2-content, this
“critical current
range” moves up to
higher power ranges
© ISF 2002
Deposition Rate
br-er5-17e.cdr
conventionalGMA
Ø 0,8 mm
Ø 1,0 mm
Ø 1,2 mm
wire feed speed
depo
sitio
n ra
te
m/min
kg/hhigh performanceGMA welding
25
20
15
10
5
00 5 10 15 20 25 30 35 40 45
Figure 5.17
Figure 5.16
Rotating Arc
© ISF 2002br-er5-16e.cdr
5. Gas-Shielded Metal Arc Welding 64
and is, with inert gas constituents of lower than 80%, hardly achievable thereafter.
This effect facilitates the pulsed-arc welding technique, Figure 5.18.
In pulsed-arc welding, a change-over occurs between a low, subcritical background
current and a high, supercritical pulsed current. During the background phase which
corresponds with the
short arc range, the
arc length is ionised
and wire electrode
and work surface are
preheated. During the
pulsed phase the
material is molten
and, as in spray arc
welding, superseded
by the magnetic
forces. Figure 5.20.
Setting parameters:
- background current I- pulse voltage U- impulse time t- background time t or frequency f with f = 1 / ( t + t ), resp.- wire feed speed v
G
P
P
G
G P
D
300 300
time
200
I G I m I krit
400 600
t Gt P
200 200
100 100
0 00
drop
vol
ume
num
ber
of d
ropl
ets 1/s 10 cm-4 3
critical currentrange
A
© ISF 2002br-er5-18e.cdr
Pulsed Arc
© ISF 2002br-er5-19e.cdr
500
time
arc
volta
ge
150 5 10 20 300
50
100
150
200
250
300
350
400
5
10
15
20
25
35
A
V
wel
ding
cur
rent
ms
Um
Im
IEff
UEff
Figure 5.18 Figure 5.19
wel
ding
cur
rent pulsed current intensity
Non-short-circuiting metal tranfer range
backround current intensity
time
Pulsed Metal Transfer
br-er5-20e.cdr © isf 2002
Figure 5.20
5. Gas-Shielded Metal Arc Welding 65
Figure 5.19 shows an example of pulsed arc real current path and voltage time
curve. The formula for mean current is:
∫=T
0m idt
T1
I
for energy per unit length of weld is:
∫=T
0
2eff dti
T1
I
By a sensible se-
lection of welding
parameters, the
GMA welding
technique allows a
selection of differ-
ent arc types which
are distinguished
by their metal
transfer way. Fig-
ure 5.21 shows the
setting range for a
good welding
process in the field
of conventional
GMA welding.
Figure 5.22 shows
the extended set-
ting range for the
high-efficiency
MAGM welding
process with a
rotating arc.
© ISF 2002
Parameter Setting Range in GMA Welding
br-er5-21e.cdr
optimal settinglower limitupper limit
working range welding current / arc voltage
400325
50
10
15
20
25
30
35
40
45
50 75 100 125 150 175 200 225 250 275 300 350 375
spray arc
transition arc
short arcshielding gas: 82%Ar, 18%CO2wire diameter: 1,2 mmwire type: SG 2
volta
ge [v
]
welding current
Figure 5.21
Setting Range or Welding Parameters in Dependence on Arc Type
br-er5-22e.cdr Quelle: Linde, ISF2002
10
20
30
50
V
volta
ge high-efficiency spray arc
rotating arc
transition zones
short arc
high-efficiency short arc
100 200 300 400 600A
filler metal: SG2 -1,2 mmshielding gas: Ar/He/CO /O -65/26,5/8/0,52 2
welding current
spray arc
Figure 5.22
5. Gas-Shielded Metal Arc Welding 66
Some typical ap-
plications of the
different arc types
are depicted in Fig-
ure 5.23. The
rotating arc, (not
mentioned in the
figure), is applied
in just the same
way as the spray
arc, however, it is
not used for the
welding of copper
and aluminium.
The arc length within the working
range is linearly dependent on the set
welding voltage, Figure 5.24. The
weld seam shape is considerably in-
fluenced by the arc length. A long arc
produces a wide flat weld seam and, in
the case of fillet welds, generally un-
dercuts. A short arc produces a nar-
row, banked weld bead.
On the other hand, the arc length is
inversely proportional to the wire
feed speed, Figure 5.25. This has in-
fluence on the current over the internal
adjustment with a slightly dropping
power source characteristic. This
again is of considerable importance for
the deposition rate, i.e., a low wire
feed speed leads to a low deposition
© ISF 2002
Applications of Different Arc Types
br-er5-23e.cdr
arc typesap
plic
atio
ns
spray arc long arc short arc pulsed arcM
IGM
AG
MM
AG
Cw
eldi
ng m
etho
dsse
am ty
pe, p
ositi
ons
wor
kpie
ce th
ickn
ess
aluminiumcopper
aluminiumcopper
aluminium(s < 1,5 mm)
steel unalloyed, low-alloy, high-alloy
steel unalloyed, low-alloy
steel unalloyed, low-alloy
steel unalloyed,low-alloy
steel unalloyed, low-alloy,high-alloy
steel low-alloy, high-alloy
-
-
-fillet welds or butt welds at thin sheets, all positions
root layers of butt welds
all positions
inner passes and cover passes of fillet or butt welds in position PC, PD, PE, PF, PG (out-of-position)
at medium-thick or thickcomponents,
fillet welds or innerpasses and cover passes of thin and medium-thick components, all positions
root layer welds only conditionally possible
fillet welds or inner passes and cover passes of butt welds at medium-thick or thickcomponents in positionPA, PB
fillet welds or inner passes and cover passes of butt welds at medium-thick or thickcomponents in positionPA, PB
welding of root layers in position PA
Figure 5.23
© ISF 2002br-er5-24e.cdr
Wire Feed Speed
operating point:
wire feed speed:arc length:welding current:deposition efficiency:
lowlonglowlow
AL
mediummediummediummedium
highshorthighhigh
AM AK
weld appearance:
arc length:longmediumshort
v , ID
U
AL AM AK
Figure 5.24
5. Gas-Shielded Metal Arc Welding 67
rate, the result is flat penetration and
low base metal fusion. At a constant
weld speed and a high wire feed
speed a deep penetration can be ob-
tained.
At equal arc lengths, the current in-
tensity is dependent on the contact
tube distance, Figure 5.26. With a
large contact tube distance, the wire
stickout is longer and is therefore
characterised by a higher ohmic resis-
tance which leads to a decreased cur-
rent intensity. For the adjustment of
the contact tube distance, as a thumb
rule, ten to twelve times the size of
the wire diameter should be consid-
ered.
The torch position has considerable
influence on weld formation and
welding process, Figure 5.27. When
welding with the torch pointed in for-
ward direction of the weld, a part of the
weld pool is moved in front of the arc.
This results in process instability.
However, it ha s the advantage of a
flat smooth weld surface with good
gap bridging. When welding with the
torch pointed in reversing direction of
the weld, the weld process is more
stable and the penetration deeper, as
© ISF 2002br-er5-26e.cdr
Contact Tube-to-Work Distance
lk1 lk2 lk3
wire electrode:
shielding gas:
arc voltage:
wire feed speed:
welding speed:
1,2 mm diameter
82% Ar + 18% CO
29 V
8,8 m/min
58 cm/min
2
cont
act t
ube-
to-w
ork
dist
ance
l k
mm
current
30
20
10
0200 250 A300 350
3
2
1
operating rule:
l = 10 to 12 dk D
© ISF 2002br-er5-25e.cdr
Welding Voltage
weld appearancebutt weld
weld appearancefillet weld
operating point:welding voltage:arc length:
highlong
mediummedium
lowshort
arc length:longmediumshort
U
v , ID
AL
AM
AK
AL AM AK
Figure 5.25
Figure 5.26
5. Gas-Shielded Metal Arc Welding 68
base metal fusion by the arc is better,
although the weld bead surface is ir-
regular and banked.
Figure 5.28 shows a selection of dif-
ferent application areas for the GMA
technique and the appropriate shield-
ing gases.
The welding current may be produced
by different welding power sources. In
d.c. welding the transformer must be
equipped with downstream rectifier
assemblies, Figure 5.29. An additional
ripple-filter choke suppresses the re-
sidual ripple of the rectified current
and has also a process-stabilising
effect.
With the develop-
ment of efficient
transistors the de-
sign of transistor
analogue power
sources became
possible, Figure
5.29. The operating
principle of a tran-
sistor analogue
power source fol-
lows the principle of
an audio frequency
amplifier which am-
plifies a low-level to a high level input signal, possibly distortion-free. The transistor
power source is, as conventional power sources, also equipped with a three-phase
© ISF 2002br-er5-27e.cdr
Torch Position
penetration:
gap bridging:
arc stability:
spatter formation:
weld width:
weld appearance:
shallow average
average
average
average
average
average
bad
bad
good
good
low
smooth rippled
narrowwide
deep
strong
advance direction
Figure 5.27
© ISF 2002
Fields of Application ofDifferent Shielding Gases
br-er5-28e.cdr
Arg
on 4
.6A
rgon
4.8
Hel
ium
4.6
Ar/H
e-m
ixtu
reA
r + 5
% H
or 7
,5%
H99
% A
r + 1
% O
or
97%
Ar +
3%
O97
,5%
Ar +
2,5
% C
O83
% A
r + 1
5% H
e +
2% C
O90
% A
r + 5
% O
+ 5
% C
O80
% A
r + 5
% O
+ 1
5% C
O92
% A
r + 8
% O
88%
Ar +
12%
O82
% A
r + 1
8% C
O92
% A
r + 8
% C
Ofo
rmin
g ga
s (N
-H-m
ixtu
re)
22
2 2
2
2
22
22
2
2
2
2
22
autoclaves, vessels, mixers, cylinderspanelling, window frames, gates, gridsstainless steel pipes, flanges, bendsspherical holders, bridges, vehicles, dump bodiesreactors, fuel rods, control devicesrocket, launch platforms, satellitesvalves, sliders, control systemsstator packages, transformer boxespassenger cars, trucksradiators, shock absorbers, exhaustscranes, conveyor roads, excavators (crawlers)shelves (chains), switch boxesbraces, railings, stock boxesmud guards, side parts, tops, engine bonnetsattachments to flame nozzles, blast pipes, rollersvessels, tanks, containers, pipe linesstanchions, stands, frames, cagesbeams, bracings, cranewaysharvester-threshers, tractors, narrows, ploughswaggons, locomotives, lorries
industrial sections shie
ldin
g ga
ses
application examples
Figure 5.28
5. Gas-Shielded Metal Arc Welding 69
transformer, with generally only one secondary tap. The secondary voltage is recti-
fied by silicon diodes into full wave operation, smoothed by capacitors and fed to the
arc through a transistor cascade. The welding voltage is steplessly adjustable until
no-load voltage is reached. The difference between source voltage and welding volt-
age reduces at the transistor cascade and produces a comparatively high stray
power which, in general, makes water-cooling necessary. The efficiency factor is
between 50 and 75%. This disadvantage is, however, accepted as those power
sources are characterised by very short reaction times (30 to 50 µs). Along with the
development of transistor analogue power sources, the consequent separation of the
power section (transformer and rectifier) and electronic control took place. The ana-
logue or digital control sets the reference values and also controls the welding proc-
ess. The power section operates exclusively as an amplifier for the signals coming
from the control.
The output stage may also be carried out by clocked cycle. A secondary clocked
transistor power source features just as the analogue power sources, a transformer
and a rectifier, Figure 5.30. The transistor unit functions as an on-off switch. By vary-
ing the on-off period, i.e., of the pulse duty factor, the average voltage at the output of
the transistor stage may be varied. The arc voltage achieves small ripples, which are
of a limited amplitude, in the switching frequency of, in general, 20 kHz; whereas the
welding current shows to be strongly smoothed during the high pulse frequencies
caused by inductivities. As the transistor unit has only a switching function, the stray
power is lower than
that of analogue
sources. The effi-
ciency factor is
approx. 75 – 95%.
The reaction times
of these clocked
units are within of
300 – 500 µs
clearly longer than
those of analogue
power sources.
© isf 2002
GMA Welding Power Source,Electronically Controlled, Analogue
br-er5-29e.cdr
welding currentmainssupply
uist
u . . u1 n iist
three-phasetransformer
reference inputvalues
signal processor(analog-to-digital)
current pickup
transistorpower section
energystore
fully-controlledthree-phase
bridge rectifier
Figure 5.29
5. Gas-Shielded Metal Arc Welding 70
Series regulator power sources, the so-called “inverter power sources”, differ widely
from the afore-mentioned welding machines, Figure 5.31. The alternating voltage
coming from the mains (50 Hz) is initially rectified, smoothed and converted into a
medium frequency alternating voltage (approx. 25-50 kHz) with the help of controlla-
ble transistor and thyristor switches. The alternating voltage is then transformer re-
duced to welding voltage levels and fed into the welding process through a secon-
dary rectifier, where the alternating voltage also shows switching frequency related
ripples. The advantage of inverter power sources is their low weight. A transformer
that transforms
voltage with fre-
quency of 20 kHz,
has, compared with
a 50 Hz trans-
former, considera-
bly lower magnetic
losses, that is to
say, its size may
accordingly be
smaller and its
weight is just 10%
of that of a 50 Hz
transformer.
Reaction time and
efficiency factor
are comparable to
the corresponding
values of switching-
type power sources.
© ISF 2002
GMA Welding Power Source,Electronically Controlled, Secondary Chopped
br-er5-30e.cdr
weldingcurrent
mains supply
Uist
Iist
3-phasetransformer
reference inputvalues
signal processor(analog-to-digital)
currentpickup
transistorswitch
protectivereactor
energy store
3-phasebridgerectifier
U . . U1 n
Figure 5.30
© ISF 2002
GMA Welding Power Source, ElectronicallyControlled, Primary Chopped, Inverter
br-er5-31e.cdr
weldingcurrent
mainssupply
Uist
Iist
filter
reference input values
signal processor(analog-to-digital)
current pickup
transistorinverter
energystorage
3-phasebridgerectifier rectifier
U . . U1 n
mediumfrequency
transformer
Figure 5.31
5. Gas-Shielded Metal Arc Welding 71
All welding power sources are fitted with a rating plate, Figure 5.32. Here the per-
formance capability and the properties of the power source are listed. The S in capital
letter (former K) in
the middle shows
that the power
source is suitable
for welding opera-
tions under haz-
ardous situations,
i.e., the secondary
no-load voltage is
lower than 48 Volt
and therefore not
dangerous to the
welder.
Besides the famil-
iar solid wires also
filler wires are used
for gas-shielded
metal arc welding.
They consist of a
metallic tube and a
flux core filling.
Figure 5.33 depicts
common cross-
sectional shapes.
© ISF 2002
Rating Plate
br-er5-32e.cdr
Spower range
power capacity in dependence of current flow
power supply
manufacturer
rotary current welding rectifier
VDE 0542
typeproduction
numberswitchgearnumber
protective system
DIN 40 050
F F
IP21
35A/13V - 220A/25V
220
25
60%
15380
26
6,6 0,72
220 17
10
100%
15 - 38 23
170
insulations class
cooling type
~ _
X
I2
U2
I1U1
U1
U1
U1
I1
I1
I1
U0 V
EDED
A
A A
AV
V
V
V
A
A A
A A
A
V V
welding
MIG/MAG
input
3~50Hz
kVA (DB) cosj
min. and max. no-load voltage
Figure 5.32
© ISF 2002
Cross-Sections of Flux-Cored Wire Electrodes
br-er5-33e.cdr
a b c
form-enclosed flux-cored wire electrode
seamless flux-coredwire electrode
Figure 5.33
5. Gas-Shielded Metal Arc Welding 72
Filler wires contain arc stabilisators, slag-forming and also alloying elements which
support a stable welding process, help to protect the solidifying weld from the atmos-
phere and, more often than not, guarantee very good mechanical properties.
An important distinctive criteria is the type of the filling. The influence of the filling is
very similar to that
of the electrode
covering in manual
electrode welding
(see chapter 2).
Figure 5.34 shows
a list of the differ-
ent types of filler
wire.
© ISF 2002
Type Symbols of Flux-Cored Wire Electrodes According to DIN EN 12535
br-er5-34e.cdr
symbol slag characteristicscustomary application* shielding gas **
R rutile base, slowly soldifying slag
S and M C and M2
P S and M C and M2
B basic S and M C and M2M filling: metal powder S and M C and M2V rutile- or fluoride-basic S withoutW fluoride basic,
slowly slagsoldifyingS and M without
S and M withoutY
S other types
*) S: single pass welding - M: multi pass welding**) C: CO - M2: mixed gas M2 according to DIN EN 4392
rutile base, rapidly soldifying slag
fluoride basic, slowly slagsoldifying
Figure 5.34
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