5. gas– shielded metal arc welding - kau.ac.krmercury.kau.ac.kr/welding/welding technology i -...

16
5. Gas– Shielded Metal Arc Welding

Upload: phamnhan

Post on 15-Mar-2018

238 views

Category:

Documents


5 download

TRANSCRIPT

Page 1: 5. Gas– Shielded Metal Arc Welding - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...5. Gas-Shielded Metal Arc Welding 61 2005 The difference between gas-shielded

5.

Gas– Shielded Metal Arc Welding

Page 2: 5. Gas– Shielded Metal Arc Welding - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...5. Gas-Shielded Metal Arc Welding 61 2005 The difference between gas-shielded

5. Gas-Shielded Metal Arc Welding 61

2005

The difference between gas-shielded metal arc welding (GMA) and the gas tungsten 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 electrogas

and the narrow gap weld-

ing and also the gas-

shielded plasma metal arc

welding, a combination of

both plasma welding and

MIG welding, 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 ex-

ploited in MIG welding, as the positive pole is

strongly heated than the negative pole, thus

improving the melting characteristics of the

feed wire.

Figure 5.2 shows the principle of a GMA weld-

ing installation. The welding power source is

assembled using the following assembly

groups: The transformer converts the mains

voltage to low voltage which is subsequently

rectified.

Apart from the torch cooling and the shielding

gas control, the process control is the most

important installation component. The process

control ensures that once set welding data are

adhered to.

© 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

Page 3: 5. Gas– Shielded Metal Arc Welding - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...5. Gas-Shielded Metal Arc Welding 61 2005 The difference between gas-shielded

5. Gas-Shielded Metal Arc Welding 62

2005

A selection of common welding installation variants is depicted in Figure 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 elec-

trode over the contact tube. The shielding gas nozzle is shaped to ensure a steady gas flow

in the arc space, thus protecting arc and molten pool against the atmosphere.

A so-called “Two-Wire-Drive” wire feed system is of the most simple design, as shown in

Figure 5.5. The wire is pulled off a wire reel and fed into the hose package. The wire trans-

port roller, which shows different grooves depending on the used material, is driven by an

electric motor. The counterpressure roller generates the frictional force which is needed for

wire feeding.

© 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

© 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

Page 4: 5. Gas– Shielded Metal Arc Welding - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...5. Gas-Shielded Metal Arc Welding 61 2005 The difference between gas-shielded

5. Gas-Shielded Metal Arc Welding 63

2005

More complicated but following the same operation principle is the “Four-Wire-Drive”, Fig-

ure 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 rotation and the an-

gular 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

burning phase of the arc,

material is molten and ac-

© 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

© ISF 2002br-er5-05e.cdr

Wire Feed System

1

2

4 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 2002

Short-Circuiting Arc Metal Transfer

br-er5-07e.cdr

1 ms

1 mm

time

time

weld

ing c

urr

ent

weld

ing v

oltage

Figure 5.7

Page 5: 5. Gas– Shielded Metal Arc Welding - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...5. Gas-Shielded Metal Arc Welding 61 2005 The difference between gas-shielded

5. Gas-Shielded Metal Arc Welding 64

2005

cumulates at the electrode end. The voltage drops slowly while the arc shortens. Electrode

and workpiece make contact and a short-circuit occurs. In the short-circuit phase is the liquid

electrode material drawn as

result of surface tension into

the molten pool. The nar-

rowing liquid root and the

rising current lead to a very

high current density that

causes a sudden evapora-

tion of the remaining root.

The arc is reignited. The

short-arc technique is par-

ticularly suitable for out-of-

position and root passes

welding.

© ISF 2002

Choke Effect

br-er5-08e.cdr

timetime

weld

ing

cu

rre

nt

weld

ing

cu

rre

nt

choke effectlow medium

Figure 5.8

© ISF 2002br-er5-09e.cdr

Long Arc

we

ldin

g v

olta

ge

weld

ing

cu

rre

nt

time

time

Figure 5.9

© ISF 2002br-er5-10e.cdr

Spray Arc

weld

ing v

olta

ge

weld

ing c

urr

ent

time

time

Figure 5.10

Page 6: 5. Gas– Shielded Metal Arc Welding - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...5. Gas-Shielded Metal Arc Welding 61 2005 The difference between gas-shielded

5. Gas-Shielded Metal Arc Welding 65

2005

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 forma-

tion, 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

undefined and occurs as

illustrated in Figures 5.13

and 5.14. Short-circuits

with very strong spatter

formation are 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 deposi-

tion rate the spray arc is used for welding filler

and cover passes in the flat position.

Connections between welding parameters,

shielding gas and arc type are shown in Fig-

ure 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 amperage has to be increased

in order to remain in the spray arc range. When

pure carbon dioxide is applied, the spray arc

© ISF 2002

Welding Parameters in Dependence on the Shielding Gas Mixture (SG 2, Ø1,2 mm)

br-er5-11e.cdr

weld

ing v

oltage

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: CO

M21: 82% Ar, 18% CO

M23: 92% Ar, 8% O

2

2

2

Figure 5.11

© ISF 2002br-er2-12e.cdr

argon helium

argon

helium

temperature

therm

al co

nd

uctivity

hydrogen

nitrogen

CO2

CO282%Ar+18%CO2

Figure 5.12

Page 7: 5. Gas– Shielded Metal Arc Welding - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...5. Gas-Shielded Metal Arc Welding 61 2005 The difference between gas-shielded

5. Gas-Shielded Metal Arc Welding 66

2005

cannot be produced. Figure 5.11 shows, moreover, that with the increasing CO2 content the

welding voltage must also be increased in order 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 con-

ductivity of the argon the arc core becomes

very hot – this results in a deep penetration in

the weld centre, the so-called “argon finger-

type penetration”. Weld reinforcement is

strongly pronounced. Application of CO2 and

helium leads, due to the better thermal conduc-

tivity of these shielding gases, to a wide and

deep penetration.

A recombination (endothermic break of the linkage in the arc space – exothermal 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 electrode end, Figure

5.13. This generates electromagnetic forces which bring about the detachment of the liquid

electrode material. This so-called “pinch effect” causes a metal transfer in small drops, Fig-

ure 5.14.

© ISF 2002br-er5-14e.cdr

wire elektrodes

current-carryingarc core

argon carbon dioxide

Figure 5.14

Figure 5.13

© ISF 2006

Influence of Shielding Gason Forces in the Arc Space

br-er5-13e.cdr

current-carryingarc core

argon carbon dioxider

argon carbon dioxide

r

tem

pe

ratu

re

Fr

FaF

Fa F

Fr

Page 8: 5. Gas– Shielded Metal Arc Welding - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...5. Gas-Shielded Metal Arc Welding 61 2005 The difference between gas-shielded

5. Gas-Shielded Metal Arc Welding 67

2005

The pointed shape of the arc attachment 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 Fig-

ure 5.15, are active inside the arc space;

however these forces are of less importance.

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 welding has

been applied since the beginning of the nine-

ties; the deposition rate, when this process is

used, is twice the size as, in comparison, to spray arc welding. Apart from a multicomponent

gas with a helium proportion, also a high-rating power source and a precisely controlled wire

feed system for high wire feed speeds are necessary.

Figure 5.17 depicts the

deposition rates over the

wire feed speed, as achiev-

able with modern high-

efficiency MAG welding

processes.

During the transition from

the short to the spray arc

the drop frequency rate in-

creases erratically while the

drop volume decreases at

© 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

Figure 5.16

Rotating Arc

© ISF 2002br-er5-16e.cdr

Page 9: 5. Gas– Shielded Metal Arc Welding - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...5. Gas-Shielded Metal Arc Welding 61 2005 The difference between gas-shielded

5. Gas-Shielded Metal Arc Welding 68

2005

the same degree. With an

increasing CO2-content,

this “critical current

range” moves up to higher

power ranges and is, with

inert gas constituents of

lower than 80%, hardly

achievable thereafter. This

effect facilitates the

pulsed-arc welding tech-

nique, Figure 5.18.

In pulsed-arc welding, a

change-over occurs be-

tween 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

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

dro

p v

olu

me

num

ber

of

dro

ple

ts 1/s 10 cm-4 3

critical currentrange

A

© ISF 2002br-er5-18e.cdr

Pulsed Arc

Figure 5.18

© 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

we

ldin

g c

urr

ent

ms

Um

Im

IEff

UEff

Figure 5.19

© ISF 2002

Deposition Rate

br-er5-17e.cdr

conventionalGMA

Ø 0,8 mm

Ø 1,0 mm

Ø 1,2 mm

wire feed speed

de

po

sitio

n r

ate

m/min

kg/hhigh performanceGMA welding

25

20

15

10

5

00 5 10 15 20 25 30 35 40 45

Figure 5.17

Page 10: 5. Gas– Shielded Metal Arc Welding - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...5. Gas-Shielded Metal Arc Welding 61 2005 The difference between gas-shielded

5. Gas-Shielded Metal Arc Welding 69

2005

and wire electrode and work

surface are preheated. Dur-

ing the pulsed phase the

material is molten and, as in

spray arc welding, super-

seded by the magnetic

forces. Figure 5.20.

Figure 5.19 shows an ex-

ample of pulsed arc real

current path and voltage

time curve. The formula for

mean current is:

∫=

T

0

midt

T

1I

for energy per unit length of weld is:

∫=

T

0

2eff dti

T

1I

By a sensible selection of welding parameters, the GMA welding technique allows a selection

of different arc types which

are distinguished by their

metal transfer way. Figure

5.21 shows the setting

range for a good welding

process in the field of con-

ventional GMA welding.

Figure 5.22 shows the ex-

tended setting range for the

high-efficiency MAGM weld-

ing 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%CO2

wire diameter: 1,2 mmwire type: SG 2

vo

ltag

e [

v]

welding current

Figure 5.21

we

ldin

g c

urr

en

t

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

Page 11: 5. Gas– Shielded Metal Arc Welding - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...5. Gas-Shielded Metal Arc Welding 61 2005 The difference between gas-shielded

5. Gas-Shielded Metal Arc Welding 70

2005

Some typical applications of the different arc types are depicted in Figure 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 weld-

ing voltage, Figure 5.24.

The weld seam shape is

considerably influenced by

the arc length. A long arc

produces a wide flat weld

seam and, in the case of

fillet welds, generally under-

cuts. A short arc produces a

narrow, banked weld bead.

On the other hand, the arc length is inversely proportional to the wire feed speed, Figure

5.25. This has influence 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 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 obtained.

At equal arc lengths, the

current intensity is de-

pendent 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 resistance which

leads to a decreased current

© ISF 2002

Applications of Different Arc Types

br-er5-23e.cdr

arc types

ap

plic

atio

ns

spray arc long arc short arc pulsed arc

MIG

MA

GM

MA

GC

weld

ing m

eth

ods

seam

type, po

sitio

ns

work

pie

ce thic

kness

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

Setting Range or Welding Parameters in Dependence on Arc Type

br-er5-22e.cdr Quelle: Linde, ISF2002

10

20

30

50

Vvo

lta

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

Page 12: 5. Gas– Shielded Metal Arc Welding - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...5. Gas-Shielded Metal Arc Welding 61 2005 The difference between gas-shielded

5. Gas-Shielded Metal Arc Welding 71

2005

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

considered.

The torch position has considerable influ-

ence on weld formation and welding proc-

ess, Figure 5.27. When welding with the torch

pointed in forward 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 sur-

face 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 base metal fusion

© 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 5.24

© ISF 2002br-er5-24e.cdr

Wire Feed Speed

operating point:

wire feed speed:

arc length:

welding current:

deposition efficiency:

low

long

low

low

AL

medium

medium

medium

medium

high

short

high

high

AM AK

weld appearance:

arc length:

long

medium

short

v , ID

U

ALAM

AK

Figure 5.25

© 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

conta

ct

tub

e-t

o-w

ork

dis

tance l

k

mm

current

30

20

10

0200 250 A300 350

3

2

1

operating rule:

l = 10 to 12 dk D

Figure 5.26

Page 13: 5. Gas– Shielded Metal Arc Welding - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...5. Gas-Shielded Metal Arc Welding 61 2005 The difference between gas-shielded

5. Gas-Shielded Metal Arc Welding 72

2005

by the arc is better, although the weld bead

surface is irregular and banked.

Figure 5.28 shows a selection of different ap-

plication areas for the GMA technique and the

appropriate shielding gases.

The welding current may be produced by dif-

ferent welding power sources. In d.c. welding

the transformer must be equipped with down-

stream rectifier assemblies, Figure 5.29. An

additional ripple-filter choke suppresses the

residual ripple of the rectified current and has

also a process-stabilising effect.

With the development of efficient transistors

the design of transistor analogue power

sources became possible, Figure 5.29. The

operating principle of a transistor analogue

power source follows the principle of an audio frequency amplifier which amplifies a low-level

to a high level input signal, possibly distortion-free. The transistor power source is, as con-

ventional power sources, also equipped with a three-phase transformer, with generally only

one secondary tap. The secondary voltage is rectified by silicon diodes into full wave opera-

tion, smoothed by capacitors

and fed to the arc through a

transistor cascade. The

welding voltage is steplessly

adjustable until no-load volt-

age is reached. The differ-

ence between source volt-

age and welding voltage

reduces at the transistor

cascade and produces a

comparatively high stray

power which, in general,

© 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

.6

Arg

on 4

.8

Heliu

m 4

.6

Ar/

He-m

ixtu

re

Ar

+ 5

% H

or

7,5

% H

99%

Ar

+ 1

% O

or

97%

Ar

+ 3

% O

97,5

%A

r +

2,5

% C

O

83%

Ar

+ 1

5%

He +

2%

CO

90%

Ar

+ 5

% O

+ 5

% C

O

80%

Ar

+ 5

% O

+ 1

5%

CO

92%

Ar

+ 8

% O

88%

Ar

+ 1

2%

O

82%

Ar

+ 1

8%

CO

92%

Ar

+ 8

% C

O

form

ing g

as (

N-H

-mix

ture

)

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

chemical-apparatus engineeringshopwindow constructionpipe productionaluminium-working industrynuclear engineeringaerospace engineeringfittings productionelectrical engineering industryautomotive industrymotor car accessoriesmaterials-handling technologysheet metal workingcraftsmotor car repairsteel productionboiler and tank constructionmachine engineeringstructural steel engineeringagricultural machine industryrail car production

industrial sections shie

ldin

g g

ases

application examples

Figure 5.28

Page 14: 5. Gas– Shielded Metal Arc Welding - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...5. Gas-Shielded Metal Arc Welding 61 2005 The difference between gas-shielded

5. Gas-Shielded Metal Arc Welding 73

2005

makes water-cooling necessary. The efficiency factor is between 50 and 75%. This disad-

vantage is, however, accepted as those power sources are characterised by very short reac-

tion times (30 to 50 µs). Along with the development of transistor analogue power sources,

the consequent separation

of the power section (trans-

former and rectifier) and

electronic control took

place. The analogue or

digital control sets the ref-

erence 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 varying 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 transis-

tor unit has only a switching

function, the stray power is

lower than that of analogue

sources. The efficiency

factor is approx. 75 – 95%.

The reaction times of these

clocked units are within of

© 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

© 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

Page 15: 5. Gas– Shielded Metal Arc Welding - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...5. Gas-Shielded Metal Arc Welding 61 2005 The difference between gas-shielded

5. Gas-Shielded Metal Arc Welding 74

2005

300 – 500 µs clearly longer

than those of analogue

power sources.

Series regulator power

sources, the so-called “in-

verter power sources”, dif-

fer widely from the afore-

mentioned welding ma-

chines, Figure 5.31. The

alternating voltage coming

from the mains (50 Hz) is

initially rectified, smoothed

and converted into a me-

dium frequency alternating voltage (approx. 25-50 kHz) with the help of controllable transistor

and thyristor switches. The alternating voltage is then transformer reduced to welding voltage

levels and fed into the welding process through a secondary 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 frequency of 20 kHz,

has, compared with a 50 Hz transformer, considerably 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 effi-

ciency factor are compa-

rable to the corresponding

values of switching-type

power sources.

All welding power sources

are fitted with a rating

plate, Figure 5.32. Here

the performance capability

and the properties of the

power source are listed.

© 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

© 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) cos�

min. and max. no-load voltage

Figure 5.32

Page 16: 5. Gas– Shielded Metal Arc Welding - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...5. Gas-Shielded Metal Arc Welding 61 2005 The difference between gas-shielded

5. Gas-Shielded Metal Arc Welding 75

2005

The S in capital letter (for-

mer K) in the middle shows

that the power source is

suitable for welding opera-

tions under hazardous

situations, i.e., the secon-

dary no-load voltage is

lower than 48 Volt and

therefore not dangerous to

the welder.

Besides the familiar 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.

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 atmosphere 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

different types of filler wire.

© 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

© 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 M2

M filling: metal powder S and M C and M2

V rutile- or fluoride-basic S without

W fluoride basic, slowly slagsoldifying

S 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