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ESAB TRAINING & EDUCATION

MIG/MAG-welding

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IntroductionContent

MIG/MAG is the welding method that is experiencing the greatest growth, see the diagram on the next page. The reasons for this include the high productivity of the method and the fact that it is easy to automate. This increase is taking place at the expense of manual arc welding, which was previously the most com-mon welding method. MIG/MAG is cur-rently the most used welding method in Europe, Japan and the USA. The MIG/MAG method originated back in the 1940s in the USA, where it was introduced for aluminium welding. Argon or helium was used as the shield-ing gas. MIG/MAG was not used to weld

steel until it was understood that pure car-bon dioxide could be used as the shield-ing gas. The welding was performed in the horizontal position and produced a fair amount of spatter. Improved power sources and access to smaller-dimension welding electrodes and mixed gases made up of argon and carbon dioxide enabled the spatter to be reduced and made posi-tional welding possible. The industrial breakthrough took place in the 1960s. Since then, the method has continued to be developed and improved to keep pace with the development of new consumables, power sources and shielding gases.

Introduction............................................................. .3

Summary...................................................................4

Principle................................................................... .5Welding parameters ...............................................5-6What happens in the arc? ........................................7Short arc ...................................................................7 Mixed arc ..................................................................7Spray arc ...................................................................8Short pulsing ............................................................8

Advantages,.limitationsand.applications.......................................................9

Equipment.........................................................10-11Power source ..........................................................10Feed unit .................................................................10Welding guns and cable andhose packages ......................................................... 11Gas supply .............................................................. 11

Consumables...........................................................12Solid wire or flux-cored wire? ...............................12

Shielding.gases........................................................13

Welding.environment.............................................14Fumes and gases ....................................................14Ultraviolet radiation ..........................................14-15Miscellaneous .........................................................15

MIG/MAG.in.practice...........................................16Joint preparation ....................................................16Choice of consumable and shielding gas ..............16Importance of welding parameters ........................16Setting voltage and wire-feed speed ..................16-17Gun angle ...............................................................18Welding speed .........................................................18Contact tube distance .............................................18

4 5

The use of the MlG/MAG method is steadily in-creasing and it is now the most common welding method in Western Europe, the USA and Japan. The reasons include the high productivity of-fered by the method and the fact that it is easy to automate. In principle, a metal wire is fed continuously into the arc, where it is melted. This metal wire functions as both a consumable and an electrode. The electrical energy to the arc is supplied by a power source. The arc and the molten material are protected by a gas which is either inert or ac-tive. An inert gas is a gas that does not react with molten material. Argon and helium are examples of inert gases. Active gases, on the other hand, take part in the processes that occur in the arc and molten pool. Argon with the addition of carbon dioxide or oxygen is an example of an active gas. To obtain the best welding results, it is impor-tant that the welding parameters are correctly set. The welding parameters in connection with MlG/MAG welding include the current, wire feed speed and shielding gas. During MlG/MAG welding, as with all other welding, the welder is exposed to health risks, unless suitable protective action is taken. The health risks that should be primarily taken into consideration in conjunction with MlG/MAG

Summary

welding are fumes and gases, together with ul-traviolet radiation from the arc. Nowadays, there are excellent opportunities for welders to protect themselves. They include welding guns with in-tegral extraction, welding visors through which welders can look during preparation but which become darker the moment the arc is struck and shielding gases which sharply reduce the ozone content in the welder’s breathing zone.

Principle

The MIG/MAG method is regarded as an arc-welding method, which means that an electric arc is used to melt the parent material and the consum-able to produce a finished weld. Other arc-weld-ing methods include manual metal arc welding (MMA), TIG and plasma welding. Figure 2 shows the principle of MIG/MAG welding. The arc (1) burns between the workpiece and the metal wire (2), which is fed continuously and melts. This metal wire functions as both an electrode and a consumable. It is wound onto a spool (3) and is fed through the electrode conduit (5) in the cable and hose package (6) and welding gun (7) by feed rollers (4). The electrical energy to the arc is supplied by a power source (8). Current to the electrode is transferred in the contact nozzle (9) (also known as the contact tip), which is inside the welding gun. This contact nozzle is normally connected to the positive pole on the power source, while the workpiece is connected to the negative pole. When the arc is struck, a closed current cir-cuit is created. Through the gas nozzle (10) which surrounds the contact nozzle, a gas flows (11). Its principal

task is to protect the electrode, the arc and the mol-ten pool (12) from the harmful effects of the ambi-ent air. This shielding gas can be either inert, which means that it is inactive and does not take part in the processes that occur in the arc and molten pool, or active. Depending on the type of shielding gas that is used, the method is known as MIG (Metal Inert Gas) or MAG (Metal Active Gas). The full name of the method is gas metal arc welding, which is abbreviated as GMAW. Inthe USA, this abbreviation is the most common designation of the method. As the consumable is fed automatically while the welding gun is moved manually over the work-piece, MIG/MAG welding is usually described as a semi-automatic welding method. The method can be easily automated by mechanising the move-ments of the welding gun or allowing the work-piece to move.

Welding parameters

During MIG/MAG welding, the process is con-trolled by a number of different parameters.

They are:• Voltage (arc length)• Wire-feed speed (which

then determines current strength)

• Inductance (can be adjust-ed on most power sources)

• Shielding gas• Feed speed• Gun angle• Electrode stickout/contact

nozzle distance To obtain the best welding results, these parameters must be adapted to one another. The first three parameters are

set on the power source. Their settings depend on the parent material, metal thickness, type of weld joint, welding position, consumable and shielding gas. Reference values for these settings can be obtained from welding tables, see the

6

Summary

The use of the MlG/MAG method is steadily increasing and it is now the most common weld-ing method in Western Europe, the USA and Japan. The reasons include the high productivityoffered by the method and the fact that it is easy to automate.

In principle, a metal wire is fed continuously into the arc, where it is melted. This metal wirefunctions as both a consumable and an electrode. The electrical energy to the arc is supplied bya power source. The arc and the molten material are protected by a gas which is either inert oractive. An inert gas is a gas that does not react with molten material.

100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

0%1975 1980 1985 1990 1995 2000

SAWMMAMIG/MAG

Argon and helium are examples of inert gases. Active gases, on the other hand, take part inthe processes that occur in the arc and molten pool. Argon with the addition of carbon dioxideor oxygen is an example of an active gas.

To obtain the best welding results, it is important that the welding parameters are correctlyset. The welding parameters in connection with MlG/MAG welding include the current, wire-feed speed and shielding gas.

During MlG/MAG welding, as with all other welding, the welder is exposed to health risks,unless suitable protective action is taken. The health risks that should be primarily taken into con-sideration in conjunction with MlG/MAG welding are fumes and gases, together with ultravio-let radiation from the arc. Nowadays, there are excellent opportunities for welders to protectthemselves. They include welding guns with integral extraction, welding visors through whichwelders can look during preparation but which become darker the moment the arc is struck andshielding gases which sharply reduce the ozone content in the welder’s breathing zone.

Fig. 1. The distribution of different welding methods in Western Europe. They include solid wire andMMA = Manual Metal Arc welding and SAW = Submerged Arc Welding. Fig. 1. The distribution of different welding methods

in Western Europe. They include solid wire and MMA = Manual Metal Arc welding and SAW = Submerged Arc Welding.

PRINCIPLE

The MIG/MAG method is regarded as an arc-welding method, which means that an electricarc is used to melt the parent material and the consumable to produce a finished weld. Otherarc-welding methods include manual metal arc welding (MMA), TIG and plasma welding.

Figure 2 shows the principle of MIG/MAG welding. The arc (1) burns between the work-piece and the metal wire (2), which is fed continuously and melts. This metal wire functionsas both an electrode and a consumable. It is wound onto a drum (3) and is fed through theelectrode conduit (5) in the cable and hose package (6) and welding gun (7) by feed rollers(4). The electrical energy to the arc is supplied by a power source (8). Current to the electro-de is transferred in the contact nozzle (9) (also known as the contact tip), which is inside thewelding gun. This contact nozzle is normally connected to the positive pole on the power sour-ce, while the workpiece is connected to the negative pole. When the arc is struck, aclosed current circuit is created.

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25 25

20 20

15 15

10 10

5 5

1 10

50

100

150

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200

250

9

12

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2

17

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8

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Fig. 2. Principle of MIG/MAG welding. 1. Arc. 2. Electrode. 3. Drum. 4. Feed rollers. 5. Electrode conduit. 6. Cable and hose package.7. Welding gun. 8. Power source. 9. Contact nozzle. 10. Shielding gas. 11. Gas nozzle. 12. Molten pool.

Through the gas nozzle (10) which surrounds the contact nozzle, a gas flows (11). Its prin-cipal task is to protect the electrode, the arc and the molten pool (12) from the harmful effectsof the ambient air. This shielding gas can be either inert, which means that it is inactive anddoes not take part in the processes that occur in the arc and molten pool, or active. Dependingon the type of shielding gas that is used, the method is known as MIG (Metal Inert Gas) orMAG (Metal Active Gas).

The full name of the method is gas metal arc welding, which is abbreviated as GMAW. Inthe USA, this abbreviation is the most common designation of the method.

As the consumable is fed automatically while the welding gun is moved manually over theworkpiece, MIG/MAG welding is usually described as a semi-automatic welding method. Themethod can be easily automated by mechanising the movements of the welding gun orallowing the workpiece to move.

Fig. 2. Principle of MIG/MAG welding.1. Arc. 2. Electrode. 3. Drum. 4. Feed rollers. 5. Electrode conduit. 6. Cable and hose package.

7. Welding gun. 8. Power source. 9. Contact nozzle. 10. Shielding gas. 11. Gas nozzle. 12. Molten pool.

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Welding parameters

During MIG/MAG welding, the process is controlled by a number of different parameters.They are: • Voltage (arc length) • Wire-feed speed (which then determines current strength) • Inductance (can be adjusted on most power sources) • Shielding gas • Feed speed• Gun angle • Electrode stickout/contact nozzle distance

To obtain the best welding results, these parameters must be adapted to one another. Thefirst three parameters are set on the power source. Their settings depend on the parent mate-rial, metal thickness, type of weld joint, welding position, consumable and shielding gas.Reference values for these settings can be obtained from welding tables, see the example inFigure 3. These tables help the welder to find a suitable working point, see the diagram inFigure 4. The working point should be within the working area for the relevant combinationof consumable and shielding gas and should also be at a level at which the thermal output ofthe arc is correct in relation to the workpiece.

In addition to wire-feed speed, voltage and shielding gas, the welding result can be affec-ted by the choice of inductance. The setting of these parameters is discussed in greater detailin the final section of this compendium. The parameters the welder controls during the wel-ding process – welding speed, gun angle and electrode stickout/contact nozzle distance – arealso discussed in the same section.

U (V)

1 (A)

3

2 1

Fig. 4. Definitions: 1. Working point. 2. Working area. 3. Thermal output of the arc. Fig. 4. Definitions: 1. Working point. 2. Working area. 3. Thermal output of the arc.

Fig. 3. Example of table for setting welding parameters.

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Plate thickness

mm

Gap

mm

Electrodecon-

sumption

kg/m

Welding speedWeldingcurrent

A

Wire feedrate

m/min

Deposi-tion rate

kg/m

Electrode

Ø mm m/h cm/min

1 0 0.02 0.6 1.0 7.0 60 50 831.5 0.5 0.02 0.8 1.0 6.0 90 48 802 1.0 0.03 0.8 1.0 6.8 110 50 833 2.0 0.06 1.8 1.0 8.0 125 50 553 2.0 0.06 2.1 1.0 6.0 150 50 63

4 1 0.09 1.0/-- 2.2/-- 6.4/-- 160/-- 24/-- 40/--5 1 0.09 1.0/-- 2.2/-- 6.4/-- 160/-- 17/-- 28/--

6 1.5 0.17 1.0/1.0 2.1/2.9 6.8/1.0 150/200 32/26 60/438 1.5 0.30 1.0/1.2 1.0/3.9 6.0/7.6 150/260 26/17 43/2810 2 0.50 1.0/1.2 1.0/5.1 6.0/10.0 150/320 21/31 35/21

Throat thickness

2 0.05 0.6 1.2 8.4 70 24 402 0.05 0.8 1.6 6.8 110 32 533 0.10 0.8 1.9 8.3 130 19 323 0.10 1.0 2.4 7.0 170 24 404 0.16 1.0 2.7 8.2 195 17 285 0.25 1.2 3.9 7.8 260 16 26

6 2 or 0.33 1.2 3.9 7.8 260 12 208 more 0.33 1.2 4.8 9.5 300 14 228 runs 0.58 1.2 4.8 9.5 300 8.5 14

1.5 0.02 0.6 1.0 7.0 60 50 832 0.03 0.8 1.6 6.8 110 53 883 0.05 0.8 1.9 8.2 130 38 634 0.07 1.8 2.0 9.0 140 29 484 0.07 1.0 2.6 7.5 180 37 625 0.10 1.0 2.6 7.5 180 26 436 0.15 1.2 3.5 7.0 240 23 38

8 2 or 0.26 1.2 3.7 7.5 250 18 3010 more 0.40 1.2 5.0 10.0 320 12 2012 runs 0.58 1.2 5.0 10.0 320 9 15

9


Plate thickness

mm

Gap

mm

Electrodecon-

sumption

kg/m


A

Wire feedrate

m/min

Deposi-tion rate

kg/m

Electrode

Ø mm m/h cm/min

1 0 0.02 0.6 1.0 7.0 60 50 831.5 0.5 0.02 0.8 1.0 6.0 90 48 802 1.0 0.03 0.8 1.0 6.8 110 50 833 2.0 0.06 1.8 1.0 8.0 125 50 553 2.0 0.06 2.1 1.0 6.0 150 50 63

4 1 0.09 1.0/-- 2.2/-- 6.4/-- 160/-- 24/-- 40/--5 1 0.09 1.0/-- 2.2/-- 6.4/-- 160/-- 17/-- 28/--

6 1.5 0.17 1.0/1.0 2.1/2.9 6.8/1.0 150/200 32/26 60/438 1.5 0.30 1.0/1.2 1.0/3.9 6.0/7.6 150/260 26/17 43/2810 2 0.50 1.0/1.2 1.0/5.1 6.0/10.0 150/320 21/31 35/21

Throat thickness

2 0.05 0.6 1.2 8.4 70 24 402 0.05 0.8 1.6 6.8 110 32 533 0.10 0.8 1.9 8.3 130 19 323 0.10 1.0 2.4 7.0 170 24 404 0.16 1.0 2.7 8.2 195 17 285 0.25 1.2 3.9 7.8 260 16 26

6 2 or 0.33 1.2 3.9 7.8 260 12 208 more 0.33 1.2 4.8 9.5 300 14 228 runs 0.58 1.2 4.8 9.5 300 8.5 14

1.5 0.02 0.6 1.0 7.0 60 50 832 0.03 0.8 1.6 6.8 110 53 883 0.05 0.8 1.9 8.2 130 38 634 0.07 1.8 2.0 9.0 140 29 484 0.07 1.0 2.6 7.5 180 37 625 0.10 1.0 2.6 7.5 180 26 436 0.15 1.2 3.5 7.0 240 23 38

8 2 or 0.26 1.2 3.7 7.5 250 18 3010 more 0.40 1.2 5.0 10.0 320 12 2012 runs 0.58 1.2 5.0 10.0 320 9 15

9


Plate thickness

mm

Gap

mm

Electrodecon-

sumption

kg/m


A

Wire feedrate

m/min

Deposi-tion rate

kg/m

Electrode

Ø mm m/h cm/min

1 0 0.02 0.6 1.0 7.0 60 50 831.5 0.5 0.02 0.8 1.0 6.0 90 48 802 1.0 0.03 0.8 1.0 6.8 110 50 833 2.0 0.06 1.8 1.0 8.0 125 50 553 2.0 0.06 2.1 1.0 6.0 150 50 63

4 1 0.09 1.0/-- 2.2/-- 6.4/-- 160/-- 24/-- 40/--5 1 0.09 1.0/-- 2.2/-- 6.4/-- 160/-- 17/-- 28/--

6 1.5 0.17 1.0/1.0 2.1/2.9 6.8/1.0 150/200 32/26 60/438 1.5 0.30 1.0/1.2 1.0/3.9 6.0/7.6 150/260 26/17 43/2810 2 0.50 1.0/1.2 1.0/5.1 6.0/10.0 150/320 21/31 35/21

Throat thickness

2 0.05 0.6 1.2 8.4 70 24 402 0.05 0.8 1.6 6.8 110 32 533 0.10 0.8 1.9 8.3 130 19 323 0.10 1.0 2.4 7.0 170 24 404 0.16 1.0 2.7 8.2 195 17 285 0.25 1.2 3.9 7.8 260 16 26

6 2 or 0.33 1.2 3.9 7.8 260 12 208 more 0.33 1.2 4.8 9.5 300 14 228 runs 0.58 1.2 4.8 9.5 300 8.5 14

1.5 0.02 0.6 1.0 7.0 60 50 832 0.03 0.8 1.6 6.8 110 53 883 0.05 0.8 1.9 8.2 130 38 634 0.07 1.8 2.0 9.0 140 29 484 0.07 1.0 2.6 7.5 180 37 625 0.10 1.0 2.6 7.5 180 26 436 0.15 1.2 3.5 7.0 240 23 38

8 2 or 0.26 1.2 3.7 7.5 250 18 3010 more 0.40 1.2 5.0 10.0 320 12 2012 runs 0.58 1.2 5.0 10.0 320 9 15

9


Plate thickness

mm

Gap

mm

Electrodecon-

sumption

kg/m


A

Wire feedrate

m/min

Deposi-tion rate

kg/m

Electrode

Ø mm m/h cm/min

1 0 0.02 0.6 1.0 7.0 60 50 831.5 0.5 0.02 0.8 1.0 6.0 90 48 802 1.0 0.03 0.8 1.0 6.8 110 50 833 2.0 0.06 1.8 1.0 8.0 125 50 553 2.0 0.06 2.1 1.0 6.0 150 50 63

4 1 0.09 1.0/-- 2.2/-- 6.4/-- 160/-- 24/-- 40/--5 1 0.09 1.0/-- 2.2/-- 6.4/-- 160/-- 17/-- 28/--

6 1.5 0.17 1.0/1.0 2.1/2.9 6.8/1.0 150/200 32/26 60/438 1.5 0.30 1.0/1.2 1.0/3.9 6.0/7.6 150/260 26/17 43/2810 2 0.50 1.0/1.2 1.0/5.1 6.0/10.0 150/320 21/31 35/21

Throat thickness

2 0.05 0.6 1.2 8.4 70 24 402 0.05 0.8 1.6 6.8 110 32 533 0.10 0.8 1.9 8.3 130 19 323 0.10 1.0 2.4 7.0 170 24 404 0.16 1.0 2.7 8.2 195 17 285 0.25 1.2 3.9 7.8 260 16 26

6 2 or 0.33 1.2 3.9 7.8 260 12 208 more 0.33 1.2 4.8 9.5 300 14 228 runs 0.58 1.2 4.8 9.5 300 8.5 14

1.5 0.02 0.6 1.0 7.0 60 50 832 0.03 0.8 1.6 6.8 110 53 883 0.05 0.8 1.9 8.2 130 38 634 0.07 1.8 2.0 9.0 140 29 484 0.07 1.0 2.6 7.5 180 37 625 0.10 1.0 2.6 7.5 180 26 436 0.15 1.2 3.5 7.0 240 23 38

8 2 or 0.26 1.2 3.7 7.5 250 18 3010 more 0.40 1.2 5.0 10.0 320 12 2012 runs 0.58 1.2 5.0 10.0 320 9 15

Plate Thikness

GapElectrodeConsumption

ElectrodeDepositionrate

Wire feedrate

WeldingCurrent

Welding Speed

mm mm kg/m ø mm kg/m m/h A m/h cm/min

1 0 0,02 0,6 1,0 7,0 60 50 83

1,5 0,5 0,02 0,8 1,0 6,0 90 48 80

2 1,0 0,03 0,8 1,0 6,8 110 50 83

3 2,0 0,06 1,8 1,0 8,0 125 50 55

3 2,0 0,06 2,1 1,0 6,0 150 50 63

4 1 0,09 1,0/-- 2,2/-- 6,4 160/-- 24/-- 40/--

5 1 0,09 1,0/-- 2,2/-- 6,4 160/-- 17/-- 28/--

6 1,5 0,17 1,0/1,0 2,1/2,9 6,8/1,0 150/200 32/26 60/43

8 1,5 0,30 1,0/1,2 1,0/3,9 6,0/7,6 150/260 26/17 43/28

10 2 0,50 1,0/1,2 1,0/5,1 6,0/10,0 150/320 21/31 35/21

Throatthickness

2

2 or

more

runs

0,05 0,6 1,2 8,4 70 24 40

2 0,05 0,8 1,6 6,8 110 32 53

3 0,10 0,8 1,9 8,3 130 19 32

3 0,10 1,0 2,4 7,0 170 24 40

4 0,16 1,0 2,7 8,2 195 17 28

5 0,25 1,2 3,9 7,8 260 16 26

6 0,33 1,2 3,9 7,8 260 12 20

8 0,33 1,2 4,8 9,5 300 14 22

8 0,58 1,2 4,8 9,5 300 8,5 14

1,5

2 or

more

runs

0,02 0,6 1,0 7,0 60 50 83

2 0,03 0,8 1,6 6,8 110 53 88

3 0,05 0,8 1,9 8,2 130 38 63

4 0,07 1,8 2,0 9,0 140 29 48

4 0,07 1,0 2,6 7,5 180 37 62

5 0,10 1,0 2,6 7,5 180 26 43

6 0,15 1,2 3,5 7,0 240 23 38

8 0,26 1,2 3,7 7,5 250 18 30

10 0,40 1,2 5,0 10,0 320 12 20

12 0,58 1,2 5,0 10,0 320 9 15

example in Figure 3. These tables help the welder to find a suitable working point, see the diagram in Figure 4. The working point should be within the working area for the relevant combination of consumable and shielding gas and should also be at a level at which the thermal output of the arc is correct in relation to the workpiece. In addition to wire-feed speed, voltage and shielding gas, the welding result can be affected by the choice of inductance. The setting of these parameters is discussed in greater detail in the final section of this compendium. The parameters the welder controls during the welding process – welding speed, gun angle and electrode stickout/contact nozzle distance – are also discussed in the same section.

What happens in the arc?

The way the molten consumable is transferred to the molten pool is an important procedure in the welding process. This transfer is affected by different factors, such as the shielding gas, current, arc voltage, consumable and electrode diameter. Depending on how the transfer takes place, a distinction is drawn between short arc, mixed arc and spray arc. A fourth type of transfer is obtained using pulsed welding, a variant of the MIG/MAG method that has become increasingly common in recent years.

Short arc

Welding with a short arc has become the most common variant of MIG/MAG welding. Short-arc welding is performed at a relatively low voltage and current, see Figure 5. This means that the supply of heat to the workpiece is not so great, so the short arc is good for welding in thin metal and for positional welding, as the mol-ten pool is small and solidifies quickly. During short-arc welding, fairly large droplets are crea-

10

What happens in the arc?

The way the molten consumable is transferred to the molten pool is an important procedure inthe welding process. This transfer is affected by different factors, such as the shielding gas,current, arc voltage, consumable and electrode diameter. Depending on how the transfer takesplace, a distinction is drawn between short arc, mixed arc and spray arc. A fourth type of trans-fer is obtained using pulsed welding, a variant of the MIG/MAG method that has become in-creasingly common in recent years.

Short arc Welding with a short arc has become the most common variant of MIG/MAG welding. Short-arc welding is performed at a relatively low voltage and current, see Figure 5. This means thatthe supply of heat to the workpiece is not so great, so the short arc is good for welding in thinmetal and for positional welding, as the molten pool is small and solidifies quickly.

U (V)

40

30

20

10

0

100 200 300 1(A)

1

2

3

Fig. 5. Working areas for different arc types. The type and exact positions are dependent on the shieldinggas and electrode diameter that are used. 1. Short arc. 2. Mixed arc. 3. Spray arc.

During short-arc welding, fairly large droplets are created and they short-circuit the arcmomentarily, see Figure 6. There are between 30 and 200 short circuits a second.

These short circuits disrupt the arc, producing welding spatter. The spatter that is left on theworkpiece means that finishing work may be needed. The exchange of consumables is alsonegatively affected. A correctly adjusted arc produces a rattling sound.

Fig. 5. Working areas for different arc types. The type and exact positions are dependent on the shielding gas and electrode diameter that are used. 1. Short arc. 2. Mixed arc. 3. Spray arc.

ted and they short-circuit the arc momentarily, see Figure 6. There are between 30 and 200 short circuits a second. These short circuits disrupt the arc, producing welding spatter. The spatter that is left on the workpiece means that finishing work may be needed. The exchange of consumables is also negatively affected. A correctly adjusted arc produces a rattling sound.

Mixed arc

When the current and voltage are slightly higher, something known as the mixed-arc range occurs. The droplets, which vary in size, are made up of a mixture of short-circuiting and nonshort- circuiting droplets. This results in an unstable arc which produces a great deal of welding spatter and fumes. Welding in this range should there-fore be avoided.

11

Mixed arc When the current and voltage are slightly higher, something known as the mixed-arc rangeoccurs. The droplets, which vary in size, are made up of a mixture of short-circuiting and non-short-circuiting droplets. This results in an unstable arc which produces a great deal of wel-ding spatter and fumes. Welding in this range should therefore be avoided.

Spray arc When the current and voltage are sufficiently high in relation to electrode diameter and shiel-ding gas, the molten material is transferred in the form of fine droplets which do not short-cir-cuit the arc, see Figure 7. In spray-arc welding, the arc is stable and no sticky spatter is pro-duced. Very high productivity can be obtained and the method is therefore used to weld thefilling passes in thicker metals, for example. A large amount of heat is supplied to the work-piece and, as a result, a large, fluid molten pool is created. Spray-arc welding is therefore bestsuited to welding in the horizontal position.

1 (A)

100

50

U (V)

20

10

1

2 3

Fig. 6. A droplet of molten material develops at the end of the electrode. When it has become sufficientlylarge to make contact with the molten pool, the arc short-circuits. At this moment, the welding current risessharply and the droplet is burnt off. The arc is struck again. Some welding spatter is produced in conjunc-tion with the large increase in current at the moment the short-circuit occurs. 1. Short-circuit cycle.2. Arc time. 3. Short-circuit time.

Fig. 6. A droplet of molten material develops at the end of the electrode. When it has become sufficiently large to make contact with the molten pool, the arc short-circuits. At this moment, the welding current rises sharply and the droplet is burnt off. The arc is struck again. Some welding spatter is produced in conjunction with the large increase in current at the moment the short-circuit occurs. 1. Short-circuit cycle. 2. Arc time. 3. Short-circuit time.

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Short pulsing Short pulsing is designed to combine the advantages of the short arc and the spray arc – inother words, a calm, stable arc with a moderate supply of heat to the workpiece. This can beachieved by pulsing the welding current, see Figure 8. Every time a welding pulse occurs, adroplet is burnt off. As the droplet does not short-circuit the arc, very little spatter is producedand the arc is stable. The background current is kept at a low level to ensure that the averagecurrent is low. The heat supply to the workpiece is therefore small, thereby enabling posi-tional welding and welding in thin plate.

Fig. 7. Spray arc

I (A)1

2

3

4

t (s)

Fig. 8. The principle of short pulsing. 1. Pulse current. 2. Critical current. 3. Average current. 4. Background current

Fig. 7. Spray arc.

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Short pulsing Short pulsing is designed to combine the advantages of the short arc and the spray arc – inother words, a calm, stable arc with a moderate supply of heat to the workpiece. This can beachieved by pulsing the welding current, see Figure 8. Every time a welding pulse occurs, adroplet is burnt off. As the droplet does not short-circuit the arc, very little spatter is producedand the arc is stable. The background current is kept at a low level to ensure that the averagecurrent is low. The heat supply to the workpiece is therefore small, thereby enabling posi-tional welding and welding in thin plate.

Fig. 7. Spray arc

I (A)1

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t (s)

Fig. 8. The principle of short pulsing. 1. Pulse current. 2. Critical current. 3. Average current. 4. Background currentFig. 8. The principle of short pulsing. 1. Pulse current. 2. Critical current. 3. Average current. 4. Background current

Spray arc

When the current and voltage are sufficiently high in relation to electrode diameter and shiel-ding gas, the molten material is transferred in the form of fine droplets which do not short-circuit the arc, see Figure 7. In spray-arc welding, the arc is stable and no sticky spatter is produced. Very high productivity can be obtained and the method is therefore used to weld the filling passes in thicker metals, for example. A large amount of heat is supplied to the workpiece and, as a result, a large, fluid molten pool is created. Spray-arc welding is therefore best suited to welding in the horizontal position.

Short pulsing

Short pulsing is designed to combine the advan-tages of the short arc and the spray arc – in other words, a calm, stable arc with a moderate supply of heat to the workpiece. This can be achieved by pulsing the welding current, see Figure 8. Every time a welding pulse occurs, a droplet is burnt off. As the droplet does not short-circuit the arc, very little spatter is produced and the arc is sta-ble. The background current is kept at a low le-vel to ensure that the average current is low. The heat supply to the workpiece is therefore small, thereby enabling positional welding and welding in thin plate.

Advantages, limitations and applications

The principal advantages of the MIG/MAG method include the high productivity, the rela-tively low supply of heat to the workpiece and the fact that the method is so easy to automate. The level of productivity is far higher than that produced by MMA welding, as no stops need to be made to change the electrodes and less or no slag removal is required. In addition, the melting speed is higher as a result of the higher current density in the electrode.

MIG/MAG welding is an extremely flexible welding method as it can be used to weld:

• a large plate thickness range (from 0.5 mm and upwards). When welding thin sheet metal, the low heat supply is utilised to avoid deforma-tion and warp. When welding thicker metal, the filler passes can be performed with high pro-ductivity

• all the standard structural materials, such as non-alloyed, low-alloyed and stainless steel, aluminium and its alloys and a large number of other non-ferrous metals

• in all the welding positions. The above-men-tioned advantages have enabled the MIG/MAG method to find many applications in large-scale industries and at small work shops. The sectors in which the method is common include the au-tomotive, construction, offshore and shipbuild-ing industries.

The MIG/MAG method can be described as be-ing both easy and difficult to learn and use. If the task is to weld together two pieces of metal without any requirements when it comes to the finished weld, the method is easy to use. If, on the other hand, requirements have been set in areas such as complete penetration, no lack of penetration, few pores and so on, the MIG/MAG method imposes rigorous demands on the weld-er’s experience and skills. The limitations of the MIG/MAG method are that the welding equipment is more complex and thereby more expensive and less portable than MMA equipment. Furthermore, the use of the method outdoors is limited, as the gas shield must not be exposed to draughts. The design of the welding gun can result in poorer accessibility in certain welding situations.

10 11

Fig. 8. Example of a power source – the AristoMig 500 with AristoFeed and the U8 panel.

Fig. 9. Example of a wire-feed unit – the AristoFeed 30.

Equipment

Feed unit

The feed unit has two main components, the attach-ment for the wire drum and the feed unit, see Fig-ure 10. The attachment for the drum should have a built-in brake which can be set in such a way that the drum stops the moment wire feed ceases. It is the task of the wire-feed unit to feed the electrode through the electrode conduit in the cable and hose package to the welding gun. The feed unit can be designed in different ways. They include:

• two feed rollers, one of which is the pull roller, while the other is the push roller

• two pull rollers with the same motor• four rollers with the same motor• four rollers that are powered by two series-con-

nected motors

The common denominator when it comes to all these variants is that they push the electrode into the conduit. There are also combined systems in which the electrode is pushed forward using a standard feed unit, while a drive unit in the welding gun pulls the electrode through. Using this system, which is known as a push-pull system, far longer cable and hose packages can be used. The push-pull system is also recommended for aluminium wire, as it may otherwise cause wire-feed problems because of its softness. The feed rollers have to be adapted to match the electrode diameter that is be-

ing used. Some types of roller have grooves for several electrode diameters. In this case, only the position of the rollers needs to be changed for the electrode to enter the correct groove.

In principle, MIG/MAG equipment is made up of the following parts: a power source, feed unit, welding gun with a cable and hose package and a gas supply system, see Figure 2 on page 5.

Power source

The power source supplies the system with direct current at a suitable voltage level. The differ-ent kinds of power source include step switched welding machines, thyristor rectifiers and transis-tor inverters. An example is shown in Figure 9. The current power sources for pulsed welding are often of the synergy type. This means that the welder only needs to set the wire-feed speed and enter information about the consumable, shield-ing gas and electrode diameter. The power source then sets the pulsing parameters and appropriate voltage itself. The parameters that are set on the power source are the voltage, wire-feed speed and, if appro-priate, inductance. The arc voltage is directly dependent on the length of the arc. To prevent the welding process being overly affected by tempo-rary variations in arc length, the power source should have constant or slightly falling charac-teristics.

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Welding guns and cable and hose packages

The way the welding gun and cable and hose package are organised is illustrated in Figure 11.The most important parts of the welding gun are the contact nozzle and the switch for startingand stopping the welding process.

Fig. 11. Welding gun with cable and hose package. 1. Contact nozzle. 2. Gas nozzle. 3. Switch.4. Cable and hose package. 5. Electrode. 6. Electrode conduit. 7. Shielding gas. 8. Cable.

In the contact nozzle, the current is transferred to the electrode. The part of the electrodewhich carries the current is called the stickout. The contact nozzle is exchangeable to enableit to be adapted to different electrode diameters and electrode types. The contact nozzle is sur-rounded by the gas nozzle, which has the task of providing the electrode, arc and molten poolwith an effective gas shield. This gas nozzle is also exchangeable and can be adapted to gasflow, parent material and current, among other things. To ensure that an effective gas shield ismaintained, this gas nozzle needs to be cleaned regularly to remove welding spatter.

There are many different types of welding gun. When it comes to semi-automatic welding,the “goose-neck” or “swan-neck” is the most common, see the above figure. This type of gunimproves accessibility in difficult locations and in conjunction with positional welding. In thecase of automatic welding, the gun is usually straight. Welding guns can be either water cooledor self cooled. In the second of these types, the gun is cooled by the ambient air and the shiel-ding gas. Water cooling is most effective. The choice between water cooling and self coolingdepends on factors such as the current, the type of shielding gas, arc times and joint type

The cable and hose package consists of a sheath containing conduits for the electrode,power and shielding gas. Water hoses are also included in the cable and hose packages forwater-cooled equipment. The usual lengths for hose packages are 3 or 4,5 m.

68 7

4

3

5

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1

The cable and hose package consists of a sheath con-taining conduits for the electrode, power and shield-ing gas. Water hoses are also included in the cable and hose packages for water-cooled equipment. The usual lengths for hose packages are 3 or 4,5 m.

Gas supply

Shielding gases for welding can be supplied in three forms:• gas cylinder • gas cylinder package • in liquid form in tanks

The last two require the user to have a central gas system. The gas can then be accessed at a number of extraction points in the workshop. Figure 12 shows what happens when gas is supplied from a gas cylinder. The gas hose is connected to the feed unit. The gas is then con-ducted through the cable and hose package to the welding gun. Asolenoid valve regulates the flow of gas when the gas process is started and stopped. The pressure in a full cylinder of shielding gas is normally 200 bar. To reduce the pressure to a suitable working pressure, a regulator must be connected to the gas cylinder, see Figure 12. This regulator also has the task of supplying a constant flow of shielding gas. Regulators and flow meters are often designed for a specific gas and should only be used for that gas; otherwise, the flow will be incorrect as the density of the different gases varies.

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Gas supply

Shielding gases for welding can be supplied in three forms: – gas cylinder– gas cylinder package – in liquid form in tanks

The last two require the user to have a central gas system. The gas can then be accessed at anumber of extraction points in the workshop.

Figure 12 shows what happens when gas is supplied from a gas cylinder. The gas hose isconnected to the feed unit. The gas is then conducted through the cable and hose package tothe welding gun. A solenoid valve regulates the flow of gas when the gas process is started andstopped.

The pressure in a full cylinder of shielding gas is normally 200 bar. To reduce the pressu-re to a suitable working pressure, a regulator must be connected to the gas cylinder, see Figure12. This regulator also has the task of supplying a constant flow of shielding gas. Regulatorsand flow meters are often designed for a specific gas and should only be used for that gas;otherwise, the flow will be incorrect as the density of the different gases varies.

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150

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20 20

15 15

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5 5

1 10

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Fig. 12. Gas supply with a gas cylinder.Fig. 12. Gas supply with a gas cylinder.

Welding guns and cable and hose packages

The way the welding gun and cable and hose pack-age are organised is illustrated in Figure 11. The most important parts of the welding gun are the contact nozzle and the switch for starting and stop-ping the welding process.

In the contact nozzle, the current is transferred to the electrode. The part of the electrode which car-ries the current is called the stickout. The contact nozzle is exchangeable to enable it to be adapted to different electrode diameters and electrode types. The contact nozzle is surrounded by the gas nozzle, which has the task of providing the electrode, arc and molten pool with an effective gas shield. This gas nozzle is also exchangeable and can be adapted to gas flow, parent material and current, among other things. To ensure that an effective gas shield is maintained, this gas nozzle needs to be cleaned regularly to remove welding spatter. There are many different types of welding gun. When it comes to semi-automatic welding, the “goose-neck” or “swan-neck” is the most com-mon, see the above figure. This type of gun im-proves accessibility in difficult locations and in conjunction with positional welding. In the case of automatic welding, the gun is usually straight. Welding guns can be either water cooled or self cooled. In the second of these types, the gun is cooled by the ambient air and the shielding gas. Water cooling is most effective. The choice be-tween water cooling and self cooling depends on factors such as the current, the type of shielding gas, arc times and joint type.

Fig. 11. Welding gun with cable and hose package. 1. Contact nozzle. 2. Gas nozzle. 3. Switch.4. Cable and hose package. 5. Electrode. 6. Electrode conduit. 7. Shielding gas. 8. Cable.

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Solid wire or flux-cored wire A distinction is made between solid wire and tubular or flux-cored wire. The second of theseis a metal sheath filled with flux or metallic powder, see Figure 15. Until now, solid wire hasbeen most common, but the use of flux-cored wire is steadily increasing. Measured by thekilogram, flux-cored wire is far more expensive than solid wire, as the production cost ishigher. However, in certain applications, flux-cored wire offers the kind of benefits that justi-fy the higher costs. Some flux-cored wires, for example, have top-class characteristics inconjunction with upward vertical welding, while others provide good impact strength at lowtemperature or high productivity. Some flux-cored wires are designed to be used with shiel-ding gas. They are known as “self-shielding or self-shielding. Self-shielding flux-cored wireis suitable for outdoor welding, as it is not sensitive to draughts in the same way as gas-shiel-ded wire/electrodes. The disadvantage is that self-shielding wire produces a great deal of spat-ter, slag and welding fumes. Welding fumes frequently contain barium, a substance with a verylow hygienic limit value.

Sold wire is available in dimensions ranging from 0.6 to 2.4 mm. Flux-cored wire comesin dimensions ranging from 0.9 to 2.4 mm.

1

2

Fig. 14. Checking the pre-bending diameter (1) and twist (2).

Fig. 15. Flux-cored wire

Consumables for MIG/MAG welding are avail-able in different materials and in a number of dimensions. They are supplied on drums or some other kind of reel. The consumable also functions as an electrode. It is important that the electrode is fed without interruption and that the electrical contact between the electrode and contact nozzle is good. This electrical contact is influenced by the surface finish of the electrode and contact nozzle. Electrodes for nonalloyed and low-alloyed steel are usually covered with a thin copper coating. This copper coating pro-tects the electrode during storage and transport and also has a lubricating effect. The electrode can either be normally wound, which is the most common type, or layer wound, see Figure 13.

Two factors that are important for wire weed are the pre-bending (cost) diameter and the twist(helix) of the electrode. The way these parameters are measured is illustrated in Figure 14 on the next page. If the pre-bending radius is too small, wire feed is obstructed. If it is too large, the contact be-tween the electrode and the nozzle is negatively af-fected. A suitable radius is 400 to 1,200 mm. The twist should not be more than 25 mm, if problems associated with a wandering arc are to be avoided. When selecting consumables, the main principle is that the weld should have the same composition and mechanical properties as the base material. The suppliers’ product catalogues provide assist-ance when it comes to choosing the correct con-sumables. It is important to keep the consumables in their packaging until they are used. Moisture, dirt, dust or grease on the wire can cause welding defects.

Fig. 13. Layer-wound electrode.

CONSUMABLES

Consumables for MIG/MAG welding are available in different materials and in a number ofdimensions. They are supplied on drums or some other kind of reel. The consumable alsofunctions as an electrode. It is important that the electrode is fed without interruption and thatthe electrical contact between the electrode and contact nozzle is good. This electrical contactis influenced by the surface finish of the electrode and contact nozzle. Electrodes for non-alloyed and low-alloyed steel are usually covered with a thin copper coating. This copper coa-ting protects the electrode during storage and transport and also has a lubricating effect. Theelectrode can either be normally wound, which is the most common type, or layer wound, seeFigure 13.

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Two factors that are important for wire weed are the pre-bending (cost) diameter and the twist(helix) of the electrode. The way these parameters are measured is illustrated in Figure 14 onthe next page. If the pre-bending radius is too small, wire feed is obstructed. If it is too large,the contact between the electrode and the nozzle is negatively affected. A suitable radius is400 to 1,200 mm. The twist should not be more than 25 mm, if problems associated with awandering arc are to be avoided.

When selecting consumables, the main principle is that the weld should have the samecomposition and mechanical properties as the base material. The suppliers’ product catalo-gues provide assistance when it comes to choosing the correct consumables.

It is important to keep the consumables in their packaging until they are used. Moisture,dirt, dust or grease on the wire can cause welding defects.

Consumables

Solid wire or flux-cored wire

A distinction is made between solid wire and tu-bular or flux-cored wire. The second of these is a metal sheath filled with flux or metallic powder, see Figure 15. Until now, solid wire has been most common, but the use of flux-cored wire is steadily increasing. Measured by the kilogram, flux-cored wire is far more expensive than solid wire, as the production cost is higher. However, in certain applications, flux-cored wire offers the kind of benefits that justify the higher costs. Some flux-cored wires, for example, have top-class characteristics in conjunction with upward vertical welding, while others provide good im-pact strength at low temperature or high produc-tivity. Some flux-cored wires are designed to be used with shielding gas. They are known as “self-shielding or self-shielding. Self-shielding flux-cored wire is suitable for outdoor welding, as it is not sensitive to draughts in the same way as gas-shielded wire/electrodes. The disadvantage is that self-shielding wire produces a great deal of spatter, slag and welding fumes. Welding fumes frequently contain barium, a substance with a very low hy-gienic limit value. Sold wire is availa-ble in dimensions ranging from 0.6 to 2.4 mm. Flux-cored wire comes in di-mensions ranging from 0.9 to 2.4 mm.

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Solid wire or flux-cored wire A distinction is made between solid wire and tubular or flux-cored wire. The second of theseis a metal sheath filled with flux or metallic powder, see Figure 15. Until now, solid wire hasbeen most common, but the use of flux-cored wire is steadily increasing. Measured by thekilogram, flux-cored wire is far more expensive than solid wire, as the production cost ishigher. However, in certain applications, flux-cored wire offers the kind of benefits that justi-fy the higher costs. Some flux-cored wires, for example, have top-class characteristics inconjunction with upward vertical welding, while others provide good impact strength at lowtemperature or high productivity. Some flux-cored wires are designed to be used with shiel-ding gas. They are known as “self-shielding or self-shielding. Self-shielding flux-cored wireis suitable for outdoor welding, as it is not sensitive to draughts in the same way as gas-shiel-ded wire/electrodes. The disadvantage is that self-shielding wire produces a great deal of spat-ter, slag and welding fumes. Welding fumes frequently contain barium, a substance with a verylow hygienic limit value.

Sold wire is available in dimensions ranging from 0.6 to 2.4 mm. Flux-cored wire comesin dimensions ranging from 0.9 to 2.4 mm.

1

2





Shielding gases

In MIG/MAG welding, the principal task of shield-ing gas is to protect the molten pool, the electrode and the arc from the harmful effect of the ambi-ent air, see Figure 16. If air is allowed to enter the molten pool, the mechanical properties of the final weld could deteriorate. The arc sequence is also affected if air is sucked into the shielding gas at-mosphere. The purity of the gas is guaranteed by the gas supplier up to the delivery point. After that, it is the user who is responsible for ensuring that the gas is not contaminated on its way from the delivery point to the gas hood in the welding gun. By taking the following action, the risks of con-taminating the gas shield can be reduced.

• Flush the regulator and hose with shielding gas after a long break.

• Check that the gas hoses and connections are airtight.

• Adapt the flow of shielding gas to the welding situation.

• Do not angle the welding gun excessively. If the angle is too sharp, air will be sucked in by the injector effect.

The shielding gas influences several factors, such as material transfer, the shape and penetration of the weld and the welding speed. It is therefore es-sential to choose the right shielding gas for the ap-propriate application. AGA’s gas guide will help you to choose the right shielding gas. When MIG-welding aluminium, the inert gases, argon and helium or a mixture of the two, are used. Pure argon cannot be used for welding steel, as the arc will then be far too unstable. So argon mixtures with a carbon dioxide or oxygen content of just a few per cent are therefore used for stainless steel.

Fig. 17b. If the flow of shielding gas is too high, it causes turbu-lence.

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SHIELDING GASES

In MIG/MAG welding, the principal task of shielding gas is to protect the molten pool,the electrode and the arc from the harmful effect of the ambient air, see Figure 16. If air is allo-wed to enter the molten pool, the mechanical properties of the final weld could deteriorate. Thearc sequ-ence is also affected if air is sucked into the shielding gas atmosphere. The purity ofthe gas is guaranteed by the gas supplier up to the delivery point. After that, it is the user whois responsible for ensuring that the gas is not contaminated on its way from the delivery pointto the gas hood in the welding gun. By taking the following action, the risks of contaminatingthe gas shield can be reduced.

– Flush the regulator and hose with shielding gas after a long break. – Check that the gas hoses and connections are airtight. – Adapt the flow of shielding gas to the welding situation. – Do not angle the welding gun excessively. If the angle is too sharp, air will be sucked

in by the injector effect.

The shielding gas influences several factors, such as material transfer, the shape and pene-tration of the weld and the welding speed. It is therefore essential to choose the right shieldinggas for the appropriate application. AGA’s gas guide will help you to choose the right shiel-ding gas.

When MIG-welding aluminium, the inert gases, argon and helium or a mixture of the two,are used. Pure argon cannot be used for welding steel, as the arc will then be far too unstable.So argon mixtures with a carbon dioxide or oxygen content of just a few per cent are there-fore used for stainless steel. When welding non-alloyed or low-alloyed steel, argon mixtureswith a fairly high carbon dioxide content (8-23%) are used. These gas mixtures are regardedas active and the term MAG-welding is therefore used. Non-alloyed steel can also be weldedwith pure carbon dioxide. The advantage of carbon dioxide is that it is less expensive thanargon mixtures, but there are also many disadvantages. Compared with mixed gases, the wel-ding speed is lower and the welding parameters are more difficult to set. In addition, far more

Fig. 16. The gas shield in MIG/MAG welding.

fumes and spatter are produced. Using carbon dioxide, it is also impossible to establish a purespray arc, no matter how much the wire-feed speed and voltage are increased. To obtain thebest results in connection with pulsed welding, the carbon dioxide content should be less than16%.

The shielding gas also has an effect on the welder’s working environment. This is illustra-ted by the AGA series of shielding gases that are marketed under the MISON® brand nameand have been developed with the aim of reducing the ozone content during welding. Ozoneis a gas that is harmful to the health and is produced to a greater or lesser degree in all kindsof arc welding. The amount of welding fumes can also be influenced by the choice of shiel-ding gas. Changing from an argon mix with 20% carbon dioxide to an argon mix with 8%carbon dioxide can reduce the amount of welding fumes by as much as 50%.

In addition to the choice of shielding gas, the setting of the gas flow is important. If the gasflow is too low, it is unable to penetrate the air in a satisfactory manner, see Figure 17a. If, onthe other hand, the flow is too high, it will be turbulent and there is a risk that the air will besucked into the arc, see Figure 17b. The flow is set on the cylinder regulator. When recom-mending shielding gas flows, the following rule of thumb can be applied: The flow of shiel-ding gas in litres per minute is the same as the diameter of the gas hood in mm. One rule ofthumb is that the gas flow is measured in mm. If you want to be absolutely sure that the flowis sufficient at the gas nozzle, it can be checked using a small flow meter which should be pres-sed against the exhaust on the gas cover.

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Fig. 17a. If the flow of shielding gas is too low,it is unable to penetrate the air.

Fig. 17b. If the flow of shielding gas is too high,it causes turbulence.

fumes and spatter are produced. Using carbon dioxide, it is also impossible to establish a purespray arc, no matter how much the wire-feed speed and voltage are increased. To obtain thebest results in connection with pulsed welding, the carbon dioxide content should be less than16%.

The shielding gas also has an effect on the welder’s working environment. This is illustra-ted by the AGA series of shielding gases that are marketed under the MISON® brand nameand have been developed with the aim of reducing the ozone content during welding. Ozoneis a gas that is harmful to the health and is produced to a greater or lesser degree in all kindsof arc welding. The amount of welding fumes can also be influenced by the choice of shiel-ding gas. Changing from an argon mix with 20% carbon dioxide to an argon mix with 8%carbon dioxide can reduce the amount of welding fumes by as much as 50%.

In addition to the choice of shielding gas, the setting of the gas flow is important. If the gasflow is too low, it is unable to penetrate the air in a satisfactory manner, see Figure 17a. If, onthe other hand, the flow is too high, it will be turbulent and there is a risk that the air will besucked into the arc, see Figure 17b. The flow is set on the cylinder regulator. When recom-mending shielding gas flows, the following rule of thumb can be applied: The flow of shiel-ding gas in litres per minute is the same as the diameter of the gas hood in mm. One rule ofthumb is that the gas flow is measured in mm. If you want to be absolutely sure that the flowis sufficient at the gas nozzle, it can be checked using a small flow meter which should be pres-sed against the exhaust on the gas cover.

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Fig. 17a. If the flow of shielding gas is too low,it is unable to penetrate the air.

Fig. 17b. If the flow of shielding gas is too high,it causes turbulence.

Fig. 16. The gas shield in MIG/MAG welding.

Fig. 17a. If the flow of shielding gas is too low, it is unable to penetrate the air.

Fig. 13. Layer-wound electrode.

When welding non-alloyed or low-alloyed steel, argon mixtures with a fairly high carbon dioxide content (8-23%) are used. These gas mixtures are regarded as active and the term MAG-welding is therefore used. Non-alloyed steel can also be weld-ed with pure carbon dioxide. The advantage of car-bon dioxide is that it is less expensive than argon mixtures, but there are also many disadvantages. Compared with mixed gases, the welding speed is lower and the welding parameters are more diffi-cult to set. In addition, far more fumes and spat-ter are produced. Using carbon dioxide, it is also impossible to establish a pure spray arc, no mat-ter how much the wire-feed speed and voltage are increased. To obtain the best results in connection with pulsed welding, the carbon dioxide content should be less than 16%. The shielding gas also has an effect on the weld-er’s working environment. This is illustrated by the AGA series of shielding gases that are market-ed under the MISON® brand name and have been developed with the aim of reducing the ozone con-tent during welding. Ozone is a gas that is harmful to the health and is produced to a greater or lesser degree in all kinds of arc welding. The amount of welding fumes can also be influenced by the choice of shielding gas. Changing from an argon mix with 20% carbon dioxide to an argon mix with 8% carbon dioxide can reduce the amount of weld-ing fumes by as much as 50%. In addition to the choice of shielding gas, the set-ting of the gas flow is important. If the gas flow is too low, it is unable to penetrate the air in a sat-isfactory manner, see Figure 17a. If, on the other hand, the flow is too high, it will be turbulent and there is a risk that the air will be sucked into the arc, see Figure 17b. The flow is set on the cylin-der regulator. When recommending shielding gas flows, the following rule of thumb can be applied: The flow of shielding gas in litres per minute is the same as the diameter of the gas hood in mm. One rule of thumb is that the gas flow is measured in mm. If you want to be absolutely sure that the flow is sufficient at the gas nozzle, it can be checked using a small flow meter which should be pressed against the exhaust on the gas cover.

Ultraviolet radiation

The electric arc emits radiation made up of vis-ible light and infrared (IR radiation) and ultra-violet radiation (UV radiation). UV radiation can damage the cornea (welding flash), cause cataracts or produce burns on the skin. IR radia-tion and intensive light can damage the retina. It is therefore vital that the welder protects his/her eyes by using some form of protective glass (welding glass). This glass is normally classified in different levels of density. The higher the den-sity, the less radiation that is allowed to penetrate the glass. The intensity of the radiation depends, among other things, on the current. The density that is needed for different currents is shown in Table 1.

In recent years, a new type of protective glass, so-called LCD glass, has been developed. This glass is light and allows the light to penetrate during welding preparations. When the arc is struck, the glass automatically darkens within the space of 0.6 thousandths of a second. After welding, the glass once again becomes light and allows the light through. Welding with LCD glass is safer and more comfortable. At the same time, the weld quality is enhanced. It is also important to think about protecting other workers from the intensive radiation gener-ated by the arc. The best way of doing this is to screen off the workplace with curtains or mov-able screens. Not only the eyes but also the skin need to be protected from UV radiation. Burns in the form of redness of the skin can otherwise be caused.

Table 1. Suitable protective glass density in connection with MIG/MAG welding.

In MIG/MAG welding, as in all other types of welding, the welder is exposed to health risks, unless suitable safety measures are implemented. The health risks that should be primarily consid-ered during MIG/MAG welding are air pollution, in the form of fumes and gases, and intensive ra-diation from the arc.

Fumes and gases

The pollution that is created in conjunction with welding is made up of fumes and gases. The fumes are created when molten metal va-porises in the arc. This vapour then condenses and oxidises when it comes in contact with the ambient air. So most of the fume particles are made up of oxides of various substances. During welding, it is first and foremost the consumable (and the flux-cored wire) which determines the substances that are included in the welding fumes. Coatings also influence the composition of the welding fumes. Depending on the substances that are included, the health hazard of inhaling welding fumes varies. The gases that are a health hazard and should be taken into account during MIG/MAG welding are ozone, nitrous gases (nitrogen monoxide, nitrogen dioxide) and carbon monoxide. These gases are formed as a result of the extremely high temperature or the ultraviolet radiationfrom the arc. The risks of welding fumes and gases can be reduced by:• ensuring that the general ventilation is good• using spot extraction, as it traps the contami-

nants before they reach the inhalation zone or are spread in the workshop. There are sev-eral different types of spot extraction, such as permanent extractors, extractor arms, mo-bile extractor nozzles or extractors that are integrated in the welding gun, see Figure 18. The type that is chosen depends on the situ-ation.

The welder should:• avoid having his/her head in the plume of

welding fumes and gases that rises from the welding point

• in special cases, such as welding with use some form of breathing protection. Breath-ing protection includes masks, welding hel-mets with a supply of fresh air and breathing equipment

• select a suitable shielding gas. To reduce the content of ozone, a gas that is hazardous to the health and forms during welding, one of AGA’s MISON® gases can be used. The amount of welding fumes can be reduced by as much as 50% if you change from argon with 20% carbon dioxide to argon with 8% carbon dioxide.

• weld with the correct welding parameters. A calm, stable arc without spatter produces

Welding environment

WELDING ENVIRONMENT

In MIG/MAG welding, as in all other types of welding, the welder is exposed to health risks,unless suitable safety measures are implemented. The health risks that should be primarilyconsidered during MIG/MAG welding are air pollution, in the form of fumes and gases, andintensive radiation from the arc.

Fumes and gases The pollution that is created in conjunction with welding is made up of fumes and gases. Thefumes are created when molten metal vaporises in the arc. This vapour then condenses and oxi-dises when it comes in contact with the ambient air. So most of the fume particles are made upof oxides of various substances. During welding, it is first and foremost the consumable (andthe flux-cored wire) which determines the substances that are included in the welding fumes.Coatings also influence the composition of the welding fumes. Depending on the substancesthat are included, the health hazard of inhaling welding fumes varies.

The gases that are a health hazard and should be taken into account during MIG/MAG wel-ding are ozone, nitrous gases (nitrogen monoxide, nitrogen dioxide) and carbon monoxide.These gases are formed as a result of the extremely high temperature or the ultraviolet radia-tion from the arc. The risks of welding fumes and gases can be reduced by:

– ensuring that the general ventilation is good – using spot extraction, as it traps the contaminants before they reach the inhalation

zone or are spread in the workshop. There are several different types of spot extraction, such as permanent extractors, extractor arms, mobile extractor nozzles or extractors that are integrated in the welding gun, see Figure 18. The type that is chosen depends on the situation.

The welder should: – avoid having his/her head in the plume of welding fumes and gases that rises from the

welding point – in special cases, such as welding with use some form of breathing protection. Breathing

protection includes masks, welding helmets with a supply of fresh air and breathing equipment

– select a suitable shielding gas. To reduce the content of ozone, a gas that is hazardous to the health and forms during welding, one of AGA’s MISON® gases can be used. The amount of welding fumes can be reduced by as much as 50% if you change from argon with 20% carbon dioxide to argon with 8% carbon dioxide.

– weld with the correct welding parameters. A calm, stable arc without spatter produces

22

Fig. 18. Welding gun with an integrated extractor.Fig. 18. Welding gun with an integrated extractor.

Scale number MIG MAG

Current (A) Current (A)

10 -100 -80

11 100-175 80-125

12 175-250 125-175

13 250-350 175-300

14 350-500 300-450

15 500- 450-

Fig. 19. Welding helmet with LCD glass.

Clothing should cover the entire body and should be done up firmly at the neck. Gloves should have a long cuff which overlaps the sleeve of overalls. The head and also the neck should be protected by a welding helmet, see Figure 19.

Miscellaneous

There is a whole range of other health risks as-sociated with welding, in addition to the ones discussed above. Some examples of risks that are not specifically associated with MIG/MAG welding but with welding in general or with oth-er procedures that are performed in conjunction with welding now follow: physical loads, noise, heat radiation, the risk of accidents and so on. When it comes to welding, musculoskeletal inju-ries still constitute the largest problem.

14 15

16 17

able and the shielding gas that are being used. The reference values for the various settings can be obtained from welding data tables. These tables can be used to set a suitable working point, see Figure 20. This working point should be in-side the working area and at a level at which the correct heat input is supplied to the workpiece.

During welding, it is impossible for the welder to see his/her position in the working area. Howev-er, by studying the arc and the result of the weld-ing, it is possible to make an assessment. If the settings are correct, the arc is stable and has the right length. The supply of heat to the workpiece is correct and no spatter is produced. The weld is smooth and the connection to the parent mate-rial is good. We shall now see what happens if the working point is moved outside the working area. What follows applies to short-arc welding with carbon dioxide as the shielding gas. Firstly, we increase the voltage but retain the same wire-feed speed, see Figure 21.

MIG/MAG in practice

During welding, it is impossible for the welder to see his/her position in the working area.However, by studying the arc and the result of the welding, it is possible to make an assess-ment. If the settings are correct, the arc is stable and has the right length. The supply of heat tothe workpiece is correct and no spatter is produced. The weld is smooth and the connection tothe parent material is good.

MIG/MAG IN PRACTICE

Joint preparation In MIG/MAG welding, basically the same types of joint are used as in MMA welding.Examples of joint types include I-joints with or without a gap for welding in thin material andV-joints with or without an unbevelled edge for welding in heavier gauge material. Before wel-ding begins, the joint surfaces and the area around the joint should be cleaned. Moisture, dirt,oxides, oil and other kinds of contamination could otherwise cause weld defects.

Choice of consumable and shielding gas Prior to welding, it is important to check that the correct shielding gas and consumable havebeen chosen in relation to the welding application. The choice of shielding gas has previouslybeen discussed in the chapter entitled “Shielding gases”. Recommendations relating to consu-mables and electrode dimensions can be obtained from the supplier. When changing electrodedimensions, it is important that the wire conduit, feed rollers and contact nozzle are adapted tomatch the new diameter.

Importance of welding parameters Welding parameters and their settings have an important effect on the welding result. A distinc-tion is drawn between equipment-dependent and person-dependent welding parameters. Thefirst group includes the voltage, wire-feed speed and inductance. Examples of person-dependentparameters include gun angle, contact tube distance and welding speed.

Setting voltage and wire-feed speed The setting of wire-feed speed (which then determines the current, I) and voltage (U) dependson the thickness of the parent material, the type of welding joint, the welding position, the con-sumable and the shielding gas that are being used. The reference values for the various settingscan be obtained from welding data tables. These tables can be used to set a suitable workingpoint, see Figure 20. This working point should be inside the working area and at a level atwhich the correct heat input is supplied to the workpiece.

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U (V)

1 (A)

3

2 1

Fig. 20. 1. Suitable working point. 2. Working area. 3. Heat output of the arc.

Joint preparation

In MIG/MAG welding, basically the same types of joint are used as in MMA welding. Examples of joint types include I-joints with or without a gap for welding in thin material and V-joints with or without an unbevelled edge for welding in heavier gauge material. Before welding be-gins, the joint surfaces and the area around the joint should be cleaned. Moisture, dirt, oxides, oil and other kinds of contamination could other-wise cause weld defects. Choice of consumable and

shielding gas

Prior to welding, it is important to check that the correct shielding gas and consumable have been chosen in relation to the welding application. The choice of shielding gas has previously been dis-cussed in the chapter entitled “Shielding gases”. Recommendations relating to consumables and electrode dimensions can be obtained from the supplier. When changing electrode dimensions, it is important that the wire conduit, feed rollers and contact nozzle are adapted to match the new diameter.

Importance of welding parameters

Welding parameters and their settings have an important effect on the welding result. A distinc-tion is drawn between equipment-dependent and person-dependent welding parameters. The first group includes the voltage, wire-feed speed and inductance. Examples of person-dependent pa-rameters include gun angle, contact tube distance and welding speed.

Setting voltage and wire-feed speed

The setting of wire-feed speed (which then deter-mines the current, I) and voltage (U) depends on the thickness of the parent material, the type of welding joint, the welding position, the consum-

Fig. 20. 1. Suitable working point.2. Working area.3. Heat output of the arc.

The voltage is now too high in relation to the wire-feed speed. The feed unit is unable to feed the wire at a speed to match the rate of melting. Irregular short circuits occur and some welding spatter is produced. The weld is too low and has undercuts at the edges. Increasing the wire-feed speed makes it possible to return to the working

area, see Figure 22. The arc becomes stable once again, but the working point is now at too high a level. The heat output is therefore too high and the arc is too hot in relation to the workpiece. There is now a risk of perforation, especially when welding in thin material. If the working point is moved outside the working area, by reducing the voltage in relation to the starting level, without changing the wire-feed speed, see Figure 23, the following occurs. The voltage is too low in rela-tion to the wire-feed speed. The heat output is not sufficiently high to melt the electrode. This results in a short arc so that the electrode bumps

against the parent material. It feels as though the welding gun is trying to lift itself. The low heat output also prevents the weld from spread-ing sufficiently smoothly and the result is a high, rounded weld with poor penetration. To return to the working area, the wire-feed speed is reduced. The working point then ends

25

U (V)

I (A)

Fig. 21. The voltage is too high in relation to thewire-feed speed.

Fig. 22. The voltage and wire-feed speed are toohigh, which means that the heat output istoo high.

U (V)

1 (A)

Increasing the wire-feed speed makes it possible to return to the working area, see Figure22. The arc becomes stable once again, but the working point is now at too high a level. Theheat output is therefore too high and the arc is too hot in relation to the workpiece. There is nowa risk of perforation, especially when welding in thin material.

If the working point is moved outside the working area, by reducing the voltage in relationto the starting level, without changing the wire-feed speed, see Figure 23, the following occurs.The voltage is too low in relation to the wire-feed speed. The heat output is not sufficiently highto melt the electrode. This results in a short arc so that the electrode bumps against the parentmaterial. It feels as though the welding gun is trying to lift itself. The low heat output also pre-vents the weld from spreading sufficiently smoothly and the result is a high, rounded weld withpoor penetration.

We shall now see what happens if the working point is moved outside the working area. Whatfollows applies to short-arc welding with carbon dioxide as the shielding gas. Firstly, we in-crease the voltage but retain the same wire-feed speed, see Figure 21.

The voltage is now too high in relation to the wire-feed speed. The feed unit is unable tofeed the wire at a speed to match the rate of melting. Irregular short circuits occur and somewelding spatter is produced. The weld is too low and has undercuts at the edges.

To return to the working area, the wire-feed speed is reduced. The working point then endsup at a lower level than before, see Figure 24. The arc once again becomes stable, but the heatoutput is far too low. The result is a cold weld that does not spread smoothly. In addition, pene-tration is incomplete.

To find the correct working point again, the voltage and wire-feed speed must be increasedin parallel. To summarise, it would be true to say that the working point – in other words, therelationship between voltage and wire feed – must fulfil two conditions.

25

U (V)

I (A)



U (V)

1 (A)







Fig. 21. The voltage is too high in relation to the wire-feed speed.

Fig. 22. The voltage and wire-feed speed are too high, which means that the heat output is too high.

Fig. 23. The voltage is too low in relation to thewire-feed speed.

26

U (V)

I (A)

U (V)

I (A)

Fig. 23. The voltage is too low in relation to the wire-feed speed.

Fig. 24. If the voltage and wire-feed speed are too low, the heat output of the arc will also be too low.

Gun angle The degree to which the welding gun should be angled in relation to the longitudinal directionof the weld depends on the weld position. One rule of thumb is that the angle in relation to the

Fig. 25. Suitable welding gun angles in relation to the welding direction for different joint types.

45°

45°

45°90°

1. The working point should be inside the working area for the combination of shielding gas and consumable in question.

2. The working point should be at a level at which the heat output of the arc is correct in rela-tion to the workpiece.

In addition to voltage and wire-feed speed, a third parameter can sometimes be set on the powersource, namely inductance. It is regulated via two or three fixed outlets on the power source orthrough stepless control. Low inductance results in less heat reaching the workpiece, a highshort-circuit frequency and a more viscous molten pool, which is suitable when welding thinplate. When welding heavier material, more heat needs to be supplied and higher inductance istherefore selected. During spray-arc welding, the inductance setting has no effect on the wel-ding process.

up at a lower level than before, see Figure 24. The arc once again becomes stable, but the heat output is far too low. The result is a cold weld that does not spread smoothly. In addition, pen-etration is incomplete. To find the correct working point again, the voltage and wire-feed speed must be increased in parallel. To summarise, it would be true to say that the working point – in other words, the re-lationship between voltage and wire feed – must fulfil two conditions.

1. The working point should be inside the work-ing area for the combination of shielding gas and consumable in question.

2. The working point should be at a level at which the heat output of the arc is correct in relation to the workpiece.

In addition to voltage and wire-feed speed, a third parameter can sometimes be set on the power source, namely inductance. It is regulated via two or three fixed outlets on the power source or through stepless control. Low inductance results in less heat reaching the workpiece, a high short-circuit frequency and a more viscous molten pool, which is suitable when welding thin plate. When welding heavier material, more heat needs to be supplied and higher inductance is therefore selected. During spray-arc welding, the induct-ance setting has no effect on the welding

Fig. 24. If the voltage and wire-feed speed are too low,the heat output of the arc will also be too low.

26

U (V)

I (A)

U (V)

I (A)





45°

45°

45°90°




25

U (V)

I (A)



U (V)

1 (A)







25

U (V)

I (A)



U (V)

1 (A)







Gun angle

The degree to which the welding gun should be angled in relation to the longitudinal direction of the weld depends on the weld position. One rule of thumb is that the angle in relation to the normal line of the weld should not exceed 15°, see Figure 26. This figure also illustrates the dif-ference between welding leftward and rightward welding. In rightward welding, the welding gun is angled towards the finished weld while weld-ing is in progress. A great deal of heat is therefore supplied to the molten pool and the penetration is deep. Rightward welding is the most common alternative and it is used, among other things, for welding in thin plates metal and aluminium.

Welding speed

The welding speed also has a large impact on the shape and penetration of the weld. If the welding speed is too high in relation to the voltage and wire-feed speed, the heat input per length unit will be too low. The weld will be narrow and its pen-etration will be insufficient. If the welding speed is low, the heat input and the amount of molten material per length unit will be too large. The mol-ten pool will therefore be too large, producing a large heat affected zone around the weld.

Contact tube distance

The welder can change the contact nozzle dis-tance, see Figure 27, by changing the position of the welding gun in relation to the workpiece. This distance should be kept constant through-out the welding process; otherwise, it will lead to current variations and a varying supply of heat to the workpiece. The correct contact tube distance is 10 to 20 mm when welding with solid wire and up to 25 mm when welding with flux-cored wire.

26

U (V)

I (A)

U (V)

I (A)





45°

45°

45°90°




Fig. 25. Suitable welding gun angles in relation to the wel-ding direction for different joint types.

Fig. 26. Welding gun angle in the longitudinal direction of the weld. 1. Rightward welding. 2. Leftward welding.

27

Contact tube distance The welder can change the contact nozzle distance, see Figure 27, by changing the position ofthe welding gun in relation to the workpiece. This distance should be kept constant throughoutthe welding process; otherwise, it will lead to current variations and a varying supply of heat tothe workpiece. The correct contact tube distance is 10 to 20 mm when welding with solid wireand up to 25 mm when welding with flux-cored wire.

1

5 - 15°

2

5 - 15°

21

normal line of the weld should not exceed 15°, see Figure 26. This figure also illustrates thedifference between welding leftward and rightward welding.

In rightward welding, the welding gun is angled towards the finished weld while weldingis in progress. A great deal of heat is therefore supplied to the molten pool and the penetrationis deep. Rightward welding is the most common alternative and it is used, among other things,for welding in thin plates metal and aluminium.

Welding speed The welding speed also has a large impact on the shape and penetration of the weld. If the wel-ding speed is too high in relation to the voltage and wire-feed speed, the heat input per lengthunit will be too low. The weld will be narrow and its penetration will be insufficient. If the wel-ding speed is low, the heat input and the amount of molten material per length unit will be toolarge. The molten pool will therefore be too large, producing a large heat affected zone aroundthe weld.


Fig. 27. Definitions:1. Contact nozzle distance 2. Electrode stickout

Fig. 27. Definitions:1. Contact nozzle distance2. Electrode stickout

27


1

5 - 15°

2

5 - 15°

21






27


1

5 - 15°

2

5 - 15°

21






1

2

18 19

Notes

ESAB AB

Box 8004, SE-402 77 Göteborg, Sweden

Phone: +46 31 50 90 00. Fax: +46 31 31 50 93 90

[email protected] www.esab.com

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Content

• Introduction

• Summary

• Principle

• Welding parameters

• What happens in the arc?

• Short arc

• Mixed arc

• Spray arc

• Short pulsing

• Advantages, limitations and applications

• Equipment

• Power source

• Feed unit

• Welding guns and cable and hose packages

• Gas supply

• Consumables

• Solid wire or flux-cored wire?

• Shielding gases

• Welding environment

• Fumes and gases

• Ultraviolet radiation

• Miscellaneous

• MIG/MAG in practice

• Joint preparation

• Choice of consumable and shielding gas

• Importance of welding parameters

• Setting voltage and wire-feed speed

• Gun angle

• Welding speed

• Contact tube distance

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