mag welding with solid wire - methods and equipment · 1 mag welding with solid wire - methods and...

1

MAG Welding with Solid Wire - Methods and Equipment

MIG/MAG WeldingGenerally

Gas Metal Arc Welding or welding with shieldinggas, as it is often called, is a welding arc processwhich utilizes the heat of an electric arcestablished between a continuoually feeded wireand the workpiece. During this process the wirewill melt and the weld metal is transferred to theworkpiece.

Shielding gas nozzle

The weld pool is always protected by a shield ofgas in order to protect both the melting wire andthe weld pool from the oxygen and nitrogen in theair. If these gases enter into the shielding gasatmosphere, it may cause porosities in the weld.Exterior disturbances such as draugths from opendoors and windows may cause the shielding gas toblow away. Also ventilating air currents mayinfluence on the welding place and the shieldinggas.

The shielding gas is usually divided into two sub-methods according to the applied type of shieldinggas.

MIG WeldingMIG welding is welding in an atmosphere ofinert gas, which means welding with a shieldinggas that does not react with other substances.Inert gases are for instance argon and helium ofwhich argon is more used within the Europeanregion. Usually, the process is called MIGwelding evenwhen the inert gas is mixed with small quantitiesof O2, CO2, H2 or similar substances.

Argon shielding gas

2

MAG WeldingMAG welding is welding in an atmosphere ofreacting gases, or as it is also called: shielded byan active gas. This means that the gas is separatedin the arc and to a smaller or larger extent reactswith the weld pool. CO2 is mainly used asshielding gas which is why the process is alsoknown as CO2 welding.

CO2 shielding gas

Advantages of MIG/MAG WeldingEvery welding process has its pros and cons. Theadvantages of MIG/MAG welding are for instanceas follows:• The method is financially attractive due to a

high welding speed and because a long arctime can be maintained as there is no frequentchanging of electrode rods.

• The method provides the opportunity forrational welding of materials which aredifficult to weld.

• Welding is possible in all positions.• The arc and the weld pool is clearly visible.• Usually only little aftertreatment of the weld

is necessary.

Disadvantages of MIG/MAGWeldingSome of the disadvantages of MIG/MAG weldingare as follows:• The method is very vulnerable to draughts

from ventilation systems, open doors andwindows and the fans of aircooled weldingmachines.

• There is a risk of serious welding errors suchas lack of fusion, etc. if the welder is notsufficiently skilled with a profoundknowledge of the process and its weldingparameters.

• The necessary, but costly, shielding of thewelding place at outdoor jobs.

• Greater investments in welding equipment• Greater expenses to maintenance to the

welding equipment.

ApplicationsMIG/MAG welding is usually used with:• Aluminium• Ordinary mild steels• Stainless steels• Copper and copper alloys

In addition to the above metals this method issuited for magnesium, nickel and a number ofother metals and their alloys.

3

Principle of Material TransferMIG/MAG welding is performed in two waysdepending on the transfer of the metal; eitherspray transfer welding or dip transfer welding.

At spray transfer welding the voltage and currentintensity are relatively high in relation to thediameter of the electrode. The material transfers asa lot of droplets which are flung from the arc liketurbulent jets into the weld groove.

Material Transfer

Dip TransferDip transfer takes place with a comparatively thinwire, low current and arc voltage in relation to thediamater of the wire.

The heat input to the workpiece is moderate, anddip transfer welding is therefore suitable forwelding in small plate thicknesses and for positionwelding as the weld pool is small and solidifiesquickly.

During dip transfer welding the material istransferred in rather big drops which momentarilyshort-circuit the arc.

The number of short-circuits is approximately 20to 200 times per second.

The below drawing shows a dip transfer cycle andthe variations which the process imposes on thewelding current and the voltage.

Dip Transfer Cycle

A droplet of melted material forms at the end ofthe wire. When it has grown big enough toestablish contact with the weld pool, the arc short-circuits. In this moment the welding currentincreases drastically and the droplet is pinchedoff.Afterwards the arc re-ignites.

The short-circuit causes the formation of spatterand in addition the sound can provide animpression of whether the relation betweenvoltage and current is adjusted correctly.

4

Spray Transfer WeldingSpray transfer welding is carried out with acomparatively high current and arc voltage inrelation to the wire diameter.

The transfer of material takes place as many smalldroplets which are slung from the electrode intothe weld pool.

There is no short-circuits of the arc. Spray transferwelding provides a stable arc.

The heat input to the workpiece is large whichmeans that the weld pool is big and very fluid andtherefore the method is only applicable for thevertical/down position.

Spray Transfer Welding

Welding EquipmentWelding equipment for MIG/MAG weldingconsists in principle of:• A shielding gas system with control• A power source• A wire feed unit• A complete welding torch• A reel of welding wire

Welding Methods

Older welding equipment can have quite a numberof buttons and two to three connections for theearth cable. On such equipment the welderhimself must adjust the welding parameters suchas current, arc voltage and inductance, whichdemands a very skilled welder.

On the latest inverters these parameters are set bya small incorporated computer. The welder onlyhas to adjust the welding current and the computertakes care of the rest. Furthermore, these newtypes of machines are programmable, andprograms can be chosen during the actual weldingprocess from a small remote control built-into thetorch handle

5

Shielding Gas SystemThe shielding gas is supplied in cylinders ofvarious dimensions and with a pressure of up to150 kp/cm2.The gas cylinder is fitted with a pressure reducingvalve in order to decrease the high pressure insidethe cylinder to a lower and less dangerousworking pressure, before the gas flows into thehoses. After the pressure reducing valve (inconnection with it) is a flowmeter indicating thegas consumption, usually in litres per minut.

The welding machine is equipped with a solenoidvalve which controls the gas supply.

Welding Methods

Power SourceIn order to obtain a stable arc the power sourceused for MIG/MAG welding must have a properlyset or adjustable characteristic and an outlet forthe appropriate inductance values. The staticcharacteristic is the curve for voltage (V) versuscurrent (A). A normal power source has a fallingstatic characteristic, while a power source with anapproximate flat characteristic is usually used forMIG/MAG welding.

If the welding result is to be good, the arc lengthshould very as little as possible.

When in MIG/MAG welding the wire is feededwith a constant speed, it is rather simple to obtainthe right welding conditions by means of a powersource of the constant voltage type. If the arclength is shorter than the set value, that is if thearc voltage lowered, is current intensity willautomatically increase dramatically and the wirewill melt quicker than it is feeded.

If on the other hand the arc length is increased, thecurrent intensity will automatically decrease andthe wire is feeded quicker than it can melt. Thismeans that the arc is kept constant even if thedistance between the torch and the workpiece ischanging for instance if the torch is not heldregularly. Another advantage of the constantvoltage power source is that there is a reduced riskof the wire burning up in the contact nozzle.

6

When welding is done by power sources of afalling characteristic, the current fluctuations

when the arc voltage changes are too small toadjust the arc length. It is therefore necessary thatthe wire feed unit is equipped with a motor whichreacts to impulses from the arc so that the wirespeed increases when the arc voltage increases

For dip transfer welding a welding rectifier withan approximately flat characteristic should beused in order for the wire to burn off quickly.Afterwards an inductor is often used in the weld-ing current circuit. When the inductor is connect-ed it has the effect that the speed of the currentincrease is slowed down at short-circuits andthereby less spatter is produced and a more stablearc is obtained because the pinch effect is reduced.

The speed of the pinch effect in relation to theamount of spatter

If the cable is connected to the first outlet, usuallymarked 1 or A, only few or none of the inductorwindings are used. Consequently, the effect issmall or non-existing and is called minimuminductance.

If the cable is connected to the last outlet thewhole inductor is operating producing maximuminductance.

A power source with three outlets therefore hasthe possibility of minimum, medium or maximuminductance effect.

On modern power sources the inductance settingcan be infinitely variable.

Wire Feed UnitThe wire feed speed is connected with the controlof the wire feeding that is with the control system.For the actual mechanical feeding there are threedifferent systems in principle.

Separate Wire Feed UnitMethod 1The wire is pushed forward by the wire drive unitthrough the wire guide liner to the torch.

Wire Feed Unit in the Welding TorchMethod 2The wire is pulled forward to the torch by a wirefeed unit in the torch, figure A, Both the wire feedunit and the wire rolls are placed inside thewelding torch (sigmette), figure B.

Figure A

Figure B

7

Method 3The wire is pushed forward by a wire feed unit inthe welding machine and at the same time it ispulled through the wire liner by a wire feed unit inthe welding torch, the so-called push-pull system,figure C.

Figur C

Advantages and DisadvantagesMethod 1Method 1 is the most frequently used of the threesystems. It is a simple system and with regard toweight it offers the lightest torch. This system isnot suitable for welding with very thin wire of softmaterials.

Method 2This system makes the welding torch heavy, butin return the welding cable is very flexible evenwhen using very thin wires, and it is possible touse long welding cables to increase the workingrange.

The sigmette system with a small wire reel placedinside the welding torch is particularly suitable forwelding with a soft wire in thin materials, e.g. 0.8and 1.2 Al-wire. This system offers finepossiblities for welding in places otherwise hardlyaccessible.

Method 3If it is necessary to work in places at a longdistance from the wire feed unit, as for instancefitting jobs at shipyards, the push-pull system ispreferable, but also more expensive than the othertwo systems.

The Welding TorchThe welding torch can be either aircooled orwatercooled. In general aircooled torches are usedfor all materials at low current intensities and alsofor welding of ordinary mild steels at highercurrent intensities. An aircooled torch will berather heavy if it is to be used at higher currentintensities.

Aircooled torch

Torch with integral fume exhaust

Aircooled ergonomical torch

Watercooled torches are lighter. They are mostlyused for welding of metals and light metals at highcurrent intensities. Is is important to notice that awatercooled torch will quickly burn off if thesupply of water fails. Ususally this type of torch isfitted with some sort of protection which preventswelding if the torch is overheated (overheatingprotection) or if the water pressure fails (pressureprotection).

8

Special attention should be paid to leaks thatallow air to enter into the shielding gas. This cancause very serious welding errors.

Welding WireWelding wire is either delivered on wire reels orin coils for larger industrial installations. The wiremust always be strictly concordant with the basematerial and the welding process.

In MIG welding there is no reaction between thewelding wire and the shielding gas which meansthat concerning the chemical composition, thewelding result only depends on the quality of thewire and the penetration into the parent material.

In MAG welding there is a reaction between thefiller material, the shielding gas and the parentmaterial. Usually, this reaction means thatalloying elements are burned off in the arc. Wirefor welding of e.g. steels are therefore over-alloyed with Si and Mn which partly burn off, thatis they oxydize in the arc, and precipitate in a veryhard almost resin-like slag scattered alongside theweld seam.

Regardless of the materials to be welded the basisof a good welding result is a clean wire free fromgrease and other polluting elements.

When the welding changes from for instance A1alloys to welding in ordinary steel, the wire linermust also be exchanged in order to avoid thetransfer of steel shavings to A1 alloys and viceversa.

9

ErgonomicsWhen welding in difficult positions it is oftennecessary for the welder to work in an akward andunhealthy working position. Such a workingposition may in the long run cause damages to theback or innjuries that demand medical treatment,and in the worst cases will disable the welder.

Therefore it is important to avoid working instraining positions and always consider thepossibilities for making the working position ascomfortable as possible.

A complete watercooled torch is often very heavyto carry and imposes a strain on the welder's back.A relief arm for the torch can be very useful totake the strain off the welder's back.

Relief arms exist in a number of models for fiitingeither on the welding machine or on the ceiling,thus it should be possible to find a model suitablefor almost any working situation.

11

MAG Welding with Flux Cored Wire –Methods and equipment

MIG/MAG Welding –Flux Cored WireFor many years the industry has wanted a semi-automatic arc welding process with continuouslyfeeded wire without exterior coating and with ahigher deposition rate than that of solid wire,known from the MAG welding process. If inaddition a higher safety against welding errorscould be obtained, so such a semi-automaticprocess could be used for welding in thickerdimensions, where traditionally coated electrodeswere used, it would be even better.

In the early 1950s thin flux cored electrodes weredeveloped on the basis of the MAG weldingmethod. This type of wire can be used with thesame welding equipment which is used forwelding with solid wire.

By means of the wire flux it is possible toinfluence the physical conditions in the arc andthe transfer of material, and also influence themetallurgic conditions. In this way some of thedisadvantages and limitations of MAG weldingwith solid wire have been set up.

Flux cored wires for AC welding can be producedin the same way as coated electrodes.

The flux of the wire can contain elements whichdevelop substantial amounts of gas and providesadequate shielding of the weld pool, thuseliminating the need for outer shielding gas.

It is possible to add alloying elements to the weldmetal via the flux filling process which cannot bealloyed to a solid wire because it would destroythe drawing properties of the wire.

In the production of flux cored wires it has been apriority to seek to improve the transfer of materialat higher current intensities than it is possible toutilize in MAG welding with solid wires.

The outer gas shielding is maintained. However,there is another version of this process calledinnershield welding where welding is carried outwithout use of shielding gas.

Welding with flux cored wire is in fact a specialform of welding with shielding gas. It has thesame limitations because of the need for aneffecient gas shielding of the weld pool as theother welding methods with shielding gas, forinstance it is still vital to keep a short distancebetween the gas nozzle and the workpiece.

Exterior disturbances around the welding placee.g. draugths from open doors and windows maycause the shielding gas to blow away. Alsoventilating equipment in the shop og aircooledpower sources can influence the welding placeand the shielding gas.

The shielding gas is usually divided into two sub-methods according to the type of shielding gas.

12

MIG WeldingMIG welding is welding in an atmosphere of inertgas, which means welding under a shielding gaswhich does not react with other elements. It isamong others argon and helium of which argon isthe more used in our part of the world. Usuallythe process is called MIG welding also when theinert gas is mixed with small amounts of O2,CO2, H2 or limilar gases.

Argon Shielding Gas in MIG Welding

MAG WeldingMAG welding is welding in an atmosphere ofreacting gasses, or as it is also called, under coverof an active gas. This means that the gas splits inthe electric arc and reacts with the weld pool to alesser or greater extent. As active shielding gasCO2 is mainly applied for which reason theprocess is also called CO2 welding.

CO2 shielding gas when MAG welding

Advantages of MIG/MAG Welding with FluxCored WireThere is always advantages and disadvantageswith any welding process. The advantages ofwelding with flux cored wire are as follows:• The method is economical due to the high

welding speed and because it is possible tomaintain the arc in a long time as there is noneed to change the electrode.

• The method offers the possibility to weld so-called difficult weldable materials in arational way.

• Welding can be done in all positions• The arc and the weld pool are completely

visible.• Usually there is only little after-treatment.• The risk of serious welding errors is reduced

compared to welding with solid wire.

Disadvantages of MIG/MAG Welding withFlux Cored WireSome of the disadvantages of MIG/MAG weldingare as follows:• The method is very vulnerable to draught

from ventilation systems, open doors andwindows as well as fans of aircooled weldingmachines.

• Risk of serious welding errors such as lack offusion if the welder is not trained to have aprofound knowledge of the welding processand its parameters.

• Increased costs for coverage of the weldingplace at outdoor jobs.

• Increased investments in welding equipment.

Application areaMIG/MAG welding with flux cored wire is nowused for every job for which previously coatedelectrodes were used, e.g. at shipyards and otherheavy industries working in material thicknessesmore than 6 mm.

Today flux cored wire is used with ordinary mildsteels and heat-resistant, acid-resistant andstainless steels.

13

Principle of Material TransferMIG/MAG welding is performed in two waysdepending on the transfer of the metal; eitherspray transger welding or dip transfer welding.

At spray transfer welding there is a relatively highvoltage and current intensity in relation to thediameter of the electrode. The material transfers asa lot of droplets to the arc like turbulent jets flunginto the weld groove.

Dip transfer takes place with a comparatively thinwire, low current and arc voltage in relation to thediamater of the wire.

The heat input to the workpiece is thereforemoderate. Dip transfer welding therefore suitablefor welding in small plate thicknesses and forposition welding as the weld pool is small andhardens quickly.

During dip transfer welding the material istransferred in rather big drops which momentarilyshort-circuit the arc.

The number of short-circuits is approximately 20to 200 times per second.

The below drawing shows a dip transfer cycle andthe variations the process imposes on the weldingcurrent and the voltage.

Dip Transfer Cycle

A droplet of melted material forms at the end ofthe wire. When it has grown big enough to estab-lish contact with the weld pool, the arc shortci-cuits. In this moment the welding current increas-es drastically and the droplet is pinched offAfterwards the arc re-ignites.

The short-circuit causes the formation of spatterand in addition the sound can provide animpression of whether the relation betweenvoltage and current is adjusted correctly.

14

Welding EquipmentWelding equipment for MIG/MAG weldingconsists in principle of:• A shielding gas system with control• A power source• A wire feed unit• A complete welding torch• A reel of welding wire

Welding Methods

Older welding equipment can have quite a numberof buttons and two to three connections for theearth cable. On such equipment the welderhimself must adjust the welding parameters suchas current, arc voltage and inductance, whichdemands a very skilled welder.

On the latest inverters these settings are made by asmall incorporated computer. The welder only hasto adjust the welding current and the computertakes care of the rest. Furthermore, these newtypes of machines are programmable, andprograms can be chosen during the actual weldingprocess from a small remote control built-into thetorch handle

Shielding Gas SystemThe shielding gas is supplied in cylinders ofvarious dimensions and with a pressure of up to150 kp/cm2.The gas cylinder is fitted with a pressure reducingvalve in order to decrease the high pressure insidethe cylinder to a lower and less dangerousworking pressure, before the gas flows into thehoses. After the pressure reducing valve (inconnection with it) is a flowmeter indicating thegas consumption, usually in litres per minut.

The welding machine is equipped with a solenoidvalve which controls the gas supply.

Gas cylinder with equipment

Power SourceIn order to obtain a stable arc the power sourceused for MIG/MAG welding must have a properlyset or adjustable characteristic and an outlet forthe appropriate inductance values. The staticcharacteristic is the curve for voltage (V) versuscurrent (A). A normal power source has a fallingstatic characteristic, while a power source with anapproximate flat characteristic is usually used forMIG/MAG welding.

15

If the welding result is to be good, the arc lengthshould as little as possible.

When in MIG/MAG welding the wire is feededwith a constant speed, it is rather simple to obtainthe right welding conditions by means of a powersource of the constant voltage type. If the arclength is shorter than the set value, that is if thearc voltage lowered, is current intensity willautomatically increase dramatically and the wirewill melt quicker than it is feeded.

If on the other hand the arc length is increased, thecurrent intensity will automatically decrease andthe wire is feeded quicker than it can melt. Thismeans that the arc is kept constant even if thedistance between the torch and the workpiece ischanging for instance if the torch is not heldregularly. Another advantage of the constantvoltage power source is that the reduced risk ofthe wire burning up in the contact nozzle.

When welding is done by power sources of afalling characteristic the current fluctuationswhen the arc voltage changes are too small toadjust the arc length. It is therefore necessary thatthe wire feed unit is equipped with a motor whichreacts to impulses from the arc so that the wirespeed increases when the arc voltage increases

For dip transfer welding a welding rectifier withan approximate flat characteristic should be usedin order for the wire to burn off quickly.

Afterward an inductor is often used in the weldingcurrent circuit. When the inductor is connected ithas the effect that the speed of the current increaseis slowed down at short-circuits and thereby lessspatter is produced and a more stable arc isobtained because the pinch effect is reduced.

The speed of the pinch effect in relation to thamount of spatter

If the cable is connected to the first outlet usuallymarked 1 or A only few or none of the inductorwindings are used. Consequently the effect issmall or non-existing and is called minimuminductance.

If the cable is connected to the last outlet thewhole inductor is operating producing maximuminductance.

A power source with three outlets therefore hasthe possibility of minimum, medium or maximuminductance effect.

On modern power sources the inductance settingcan be infinitely variable.

16

Wire Feed UnitThe wire feed speed is connected with the controlof the wire feeding that is with the control system.For the actual mechanical feeding there are twodifferent systems in principle.

Separate Wire Feed UnitMethod 1The wire is pushed forward by the wire drive unitthrough the wire guide liner to the torch.

Method 2The wire is pushed forward by a wire feed unit inthe welding machine and at the same time it ispulled through the wire liner by a wire feed unit inthe welding torch, the so-called push-pull system,figure C.

Figur C

Advantages and DisadvantagesMethod 1Method 1 is the most frequently used of the threesystems. It is a simple system and with regard toweight it gives the lightest torch. This system isnot suitable for welding with very thin wire of softmaterials.

Method 2If it is necessary to work in places at a longdistance from the wire feed unit, as for instancefitting jobs at shipyards, the push-pull system ispreferable, but also more expensive than the othersystem.

The Welding TorchThe welding torch can be either aircooled orwatercooled. In general aircooled torches are usedfor all materials at low current intensities and alsofor welding of ordinary mild steels at highercurrent intensities. An aircooled torch will berather heavy if it is to be used at higher currentintensities.

Aircooled torch

Torch with integral fume exhaust

Aircooled ergonimical torch

Watercooled torches are lighter. They are mostlyused for welding of metals and light metals at highcurrent intensities. Is is important to notice that awatercooled torch will quickly burn off if thesupply of water fails. Ususally this type of torch isfitted with some sort of protection which preventswelding if the torch is overheated (overheatingprotection) or if the water pressure fails (pressureprotection).

17

Particular attention should be paid to leaks thatallow air to enter into the shielding gas. This cancause very serious welding errors.

Welding WireWelding wire is either delivered on wire reels orin coils for larger industrial installations. The wiremust always be strictly concordant with the basematerial and the welding process.

In MIG welding there is no reaction between thewelding wire and the shielding gas which meansthat concerning the chemical composition, thewelding result only depends on the quality of thewire and the penetration into the base material.

In MAG welding there is a reaction between thefiller material, the shielding gas and the basematerial. Usually this reaction means that alloyingelements are burned off in the arc. Wire forwelding of for instance steels are therefore over-alloyed with Si and Mn which partly burn off,which means oxydize in the arc, and precipitate ina very hard almost resin-like slag scatteredalongside the weld seam.

Regardless of the materials to be welded the basisof a good welding result is a clean wire free fromlubricates and other contaminations.

When the welding changes from for instance A1alloys to welding in ordinary steel, the wire linermust also be exchanged in order to avoid thetransfer of steel shavings to A1 alloys and viceversa.

18

ErgonomicsWhen welding in difficult positions it is oftennecessary for the welder to work in an akward andunhealthy working position. Such workingposition may in the long run cause damages to theback or innjuries that demand medical treatment,and in the worst cases disable the welder.

Therefore it is important to avoid working instraining positions and always consider thepossibilities for making the working position ascomfortable as possible.

A complete watercooled torch is often very heavyto carry and imposes a strain on the welder's back.A relief arm for the torch can be very useful totake the strain off the welder's back.

Relief arms exist in a number of models for fiitingeither on the welding machine or on the ceiling,thus it should be possible to find a model suitablefor almost any working situation.

19

Welding Equipment - Welding Errors

Errors in MAG WeldingWelding equipment for welding with shieldinggas are built of a considerably larger number ofcomponents than welding machine for MMAwelding with coated electrodes. Today weldingmachines for MAG welding is filled withelectronics for instance for programming of thewelding parameters.

All these advanced electronic components help toease the everyday life of the welder, and themodern welding machines also reduce the risk forwelding errors, but at the same time the electro-nics make the modern welding machine morefragile and sensitive than the welding rectifiers weuse for welding with coated electrodes.

In the following section we will describe some ofthe many components of the MAG weldingmachine, the more common errors in thesecomponents and of course the welding errors theybring about.

The Welding MachineThe heart of the welding machine - the electronics- is not the field of the welder. If errors occur inthis field, it is often necessary to call assistancefrom the aftersales service of the manufacturer.

For safety reasons the welder should not interferewith the mains voltage supply of the welding ma-chine or other electric components inside the caseof the welding machine.

Instead the welder can help and not least preventerrors is by treating his welding equipment care-fully.

Wire FeedingWhen the wire is fed through the contact nozzle itlooks very simple, but in fact the wire passesthought a number of individual parts which mustbe in order to achieve a fine welding result.

The wire rolls should be adjusted so that thegrooves fit the actual wire size, and the pressureof the rolls on the wire should be correct. If thepressure is too small the rolls will slide on thewire and the wire speed will be irregular.

The welder will register this error during thewelding process as a lack of wire feeding andirregular wire speed. The weld will get a poorappearance and lack fusion and porosities willalso be likely consequences.

This error can be precluded if the welder controlsthe pressure of the wire rolls on the wire beforewelding begins. If the wire can be held back withtwo fingers so the rolls slide on the wire, thepressure is correctly set.

If the pressure on the wire is too large, the wirewill almost be rolled, thus deformed anddestroyed. By letting the wire pass through thecontact nozzle without short-circuiting the wire,

the welder is able to see if the wire has beendeformed. If the wire is deformed, it will appearfrom the contact nozzle in a spiral.

20

When the depth and the diameter of the groove fitthe welding wire and the pressure of the rolls iscorrect, the wire should be fed evenly with thespeed set by the welder on the operation panel.However, if this is not the case it could be that thewire rolls are worn and need to be exchanged.

Furthermore, the quality of the wire feed unit is ofcrucial importance for a welding process withoutproblems. the wire rolls should be strong and thetransmission between wire motor and rolls shouldbe properly made gear transmission A wire feedunit with 4-roll drive works better than a singlewire unit with two rolls. Furthermore, the 4-rolldrive has more possibilities of application.

Wire GuidingAnother risk of errors in the wire feed unit is thecapillary tube. In the first place it must be firmlyfixed and adequately near the wire rolls. If thedistance between the wire rolls and the capillarytube is too large, the wire may tie knots in the gapbetween the two components.

Furthermore, it is important that the capillary tubeis aligned with the groove in the wire roll, and thatthe diameter of the capillary tube fits the chosenwire diameter.

The Complete TorchThe torch is a unit consisting of the wire liner,protection hose, wires for control current andmaybe hoses for cooling water to the weldingtorch. This is a point where many errors ordisturbances may appear.

Always avoid sharp bends on the hoses as theymay cause the wire feeding to be irregular and thewire liner to break.

Avoid too long hoses and cables, The thinner thewire the shorter the torch hoses. If longer hosesare necessary, you should use an extra wire feedunit (an intermediary station) to make sure thatthe wire is kept tight all the way from the wirefeed unit to the contact nozzle.

The wire liner should be blown regularly withcompressed air to clean out dirt which can preventthe wire from being fed evenly.

21

If the welder spent only 15 minutes every week tocheck and clean the welding equipment, a lot oftime and money could be saved on operationstops.

Most operation disturbances of a MAG machinecould be prevented by the welder by treating theequipment with care.

If the welding machine is watercooled, hoses,connections and packings should be checked forleaks at regular intervals.

If a watercooled welding machines has not been inoperation for some time and the packings havedried up, they should be exchanged beforewelding starts.

The Welding TorchOften welding errors due to errors in the weldingequipment are caused by errors in the weldingtorch and particularly the contact nozzle.

When welding in position a lot of spatter can stickto the contact nozzle causing irregular wirefeeding, porosities and in the worst case lack offusion.

The contact nozzle also wears and the hole willbecome so large that the current transferdeteriorate.

This also causes irregular wire feeding, porositiesand lack of fusion.

Depending on the type of the torch an insulator isfitted in the gas cup or a gas diffuser is fitted onthe torch right under the swan neck. The insulatoror the diffuser take care that the shielding gas isevenly distributed all around the contact nozzle toensure an effective shielding of the weld pool. Ifthe insulator or the diffuser is defective itimmediately causes welding errors such asporosities, long porosities and in the worst caselack of fusion. Therefore the welder should checkthe diffuser and insulator every day.

Another important thing to check is the wire liner.

Apart from the liner which runs from the wirefeed unit through the cable to the torch handlethere is a small piece of liner inside the swan neck

of the welding torch. This piece of liner needscleaning as regularly as the long wire liner andshould also be exchanged regularly.

Aircooled ergonomical torch

22

The Pressure Reducing ValveThe pressure reducing valve should be suitable forthe applied shielding gas and functionable, so thecontent of the cylinder and the outflow quantitycan be read with reasonable certainty.

An often occurring deficiency of the pressurereducing valve is that it tends to freeze. When itfreezes the gas flow to the welding torch isreduced or stopped which causes a weld withmany porosities and long porosities.

Therefore the pressure reducing valve and the gasflow should be controlled regularly. The gas flowcan be controlled by a small flowmeter which isheld on the torch while the gas flows and then theactual gas flow is indicated on the meter.

Remember to interrupt the wire feeding when youmake this check.

Pressure reducing valve with flowmeter.

Other Error Possibilities byEquipment or WelderErrors such as porosities or lack of fusion arealways caused by defective welding equipment orwrong welding technique and lack of reflection onthe welder’s part.

If there is not adequate supply of shielding gas tothe weld porosities will appear in the weld. Oftenthe porosities are caused by an empty cylinderwhich the welder ought to have noticed before theerrors occurred.

If the cylinder is adequately full and theflowmeter on the pressure reducing valve showsadequate gas flow, but there are porosities in theweld surface like those similar to lack of shieldinggas, it may be that the solenoid valve of thewelding machine is stuck.

Check the solenoid valve and its possible cableconnections.

It is important always to take the weather intoconsideration when MAG welding is carried out.Draught removes all shielding gas from the weldpool and the weld becomes filled with porosities.Make sure the welding place is carefully protectedfrom draught and wind. Even through the gap of aweld groove there may be draught under certainconditions.

Take care not to lie down the welding torch toomuch when welding. If the torch is lying too muchthere will be an injector effect in the gas nozzlecausing atmospheric air to be sucked into thetorch.

If the welding equipment has been checked and isOK, and there continues to be porosities in theweld, it may be caused by impurities in theshielding gas. However, this error is rather rare,but it may happen and can be controlled at the gassupplier’s.

Finally, it is important that the workpieces are freeof lubricants, grease, primer and similarsubstances as they may cause porosities and lackof fusion.

23

Other Interior Welding ErrorsIn the previous sections only errors such asporosities and lack of fusion has been mentioned.These are also the most common errors of MAGwelding, but other errors such as slag inclusionsmay occur.

CracksCracks may appear in the base metal for instanceif the cooling time is too long or too thick layersare welded. If a Welding Procedure Specification(WPS) has been made for the welding job, it isimportant that it is observed in order to avoidcracks. It is also a good idea to weld several thinpasses than a few thick passes as it reduces thetoughness of the fusion zone and thereby the riskof cracks and breaks.

When welding in low-alloyed materials ormaterials which usually require preheating, thereis a certain risk of hydrogen cracks, and thereforea WPS in which the risk of hydrogen cracks iscalculated according to DS 316/EN 1011 shouldbe used.

Geometric ErrorsAll welding errors, both interior and exterior,influence the geometry of the weld and istherefore called geometric errors. However, bygeometric errors are often meant exterior errorssuch as undercuts, excess weld metal, lack offilling, penetration errors, etc.

All these errors and their tolerances are describedin DS/EN 25817 and will not be mentionedfurther in this book.

Welders’ ErrorsThere are many other possibilities for errors thatthose mentioned here, but the most importanttypes of errors and their causes have beendescribed on the last few pages. However, theweaker link of the chain is often the welder, andthe more experienced the welder, the fewer errorsin the weld.

The biggest risk at MAG welding is the fact thatthe welding parameters can be set so low, thatthere will be no penetration into the base materialalthough the weld pool flows nicely and themachine sounds all right. Many welding errorscan be avoided by increasing current and voltage

to increase the heat of the material and therebyobtain a better penetration into the base material,and also by choosing the correct inductance levelon the welding machine. Remember, that whenthe welding machine “hums like an angry bee”you are welding is the dip transfer area and in thisarea it is only possible to weld bottom runs in buttwelds with full penetration or weld in very thinmaterial thicknesses.

It is also very important for the welder to befamiliar with his welding machine in order tomake the correct adjustments.

On some welding machines it is difficult to trimthe machine correctly as there is a wealth ofregulation buttons, but on the newer weldingmachines the regulation of welding parameters ismore simple, and the most frequently usedwelding data can be programmed in the memoryof the machine.

The geometric welding errors which can becontrolled visually are described in details in theDS/EN 25817. All geometric welding errors bothexterior and hidden interior errors are defined inthe DS/EN 26520.

25

MAG Welding - Setting of Welding ParametersSetting of the WeldingParameters

When being an inexperienced MIG/MAG welderit can be a problem to adjust the welding machineto weld with optimum welding data. The problemis that there are several variable parameters thatmust suit each other correctly if a satisfactorywelding result is to be achieved.

The following section is a description of thesignificance of the individual welding parametersand a method to get started on the welding job.

Types of transferThere are several forms of material transfer by thearc in MIG/MAG welding. The transfer isseparated in dip transfer welding, spray transferwelding, droplet transfer (mix-arc) and pulsewelding.

The choice of type of transfer depends on:• The thickness of the material• The type of weld• The welding position• The size and type of the welding machine

Dip Transfer Welding

DefinitionIn dip transfer welding the transfer of materialtakes place as an interplay between the formationof a droplet of welding wire and its short-circuiting. When the arc is established a dropletforms on the end of the wire. This droplet willgrow and eventually get into contact with the weldpool and then short-circuit. This means that thedroplet is pinched off at a speed of 80 to 200short-circuits per second. This issue is furtherdescribed in the section “Welding Methods andEquipment”.

Wire Dimension at Dip Transfer WeldingWhen welding within the dip transfer arearelatively thin wires between 0.8 and 1.0 mm areused. When welding in very thin base materialssuch as motorcar body sheets also very thin wiresof 0.6 mm are used, but also 1.2 mm wires can beused in the dip transfer area. As dip transferwelding is only applied on materials of smallerdimensions, welding with other dimensions ofwire is not possible.

Areas of ApplicationDip transfer welding is only suited for welding inordinary steel. If the method is used on aluminiumor stainless steels there will be produced asubstantial amount of spatter from the weld pool,and the risk of lack of fusion will be very high.Dip transfer welding is particularly used on platethicknesses < 5 mm and for welding of bottomruns in thicker materials, even very large platedimensions.Dip transfer welding is also suitable for positionwelding for instance when the bottom run iswelded vertically-downwards while the remainingruns are welded vertically-upwards.

Welding parametersAt dip transfer welding with 0.8 mm electrode thewelding current will be between 50 and 90 A,while the voltage is between 16 and 18 V. Thestick-out should be some 15 mm. Both CO2 andmixed gas are applicable with a gas flow of 8 to12 l/min. When welding with a 1 mm wire thecurrent should be around 80 and 150 A while thetypical arc voltage should be around 17 to 20 V.

26

PenetrationThe penetration in the dip transfer area issomewhat larger with CO2 than with mixed gas (atthe same wire feeding). The reason is that theweld pool of the mixed gas is shorter due to thehigher short-circuit frequency and the lower arcvoltage (2 to 3 V) than that of CO2.

As the mixed gas due to its stable arc has a muchlarger tolerance than CO2 for the variations ofwelding parameters, for instance the currentintensity, it is easy to increase the wire speed andcompensate for the smaller penetration and at thesame time increase the weld speed.

Welding with mixed gases usually offers higherwelding speed than welding with CO2, due to thefact that the mixed gas arc is more stable andtherefore allows higher wire speed.


DefinitionSpray transfer welding or spray arc welding iswelding where the wire is transferred as spray,hence the name Spray Arc. The transfer takesplace as a large amount of very fine drops withoutshort-circuits. The best result is obtained when thearc “snarls” a bit.

Welding parametersThe welding current at spray transfer welding isvery high, between 140 A with a 0.8 mm wire andsome 390 A with a 1.6 mm wire. The voltage willbe between 23 and 24 V with the same wirediameters.

Wire DimensionsUsually 1.0 and 1.2 mm wires are used for spraytransfer welding, but wire of 0.8 and 1.6 mm arealso applicable.

Shielding gasMixed shielding gases with a large content ofargon are always used for spray transfer welding,e.g. 82/18. Due to the large droplets welding withCO2 would make it impossible to control the weldpool.

Application AreaSpray transfer welding can be used with allmetals. However, with ordinary steel the onlywelding position is underhand welding. Themethod is used with material thicknesses morethan 3 mm and up to even very large thicknesses.Spray transfer welding is a very heat weldingprocess, but due to the speed it only causes smalldeformations.

Mixed Transfer WeldingWhen welding in the mixed transfer area thetransfer of material takes place as rather largedroplets. The mixed transfer welding lies betweendip transfer and spray transfer welding and thetransfer of material takes place in the form of verylarge droplets mostly without short-circuits.

27

Welding ParametersThe welding current lies between 110 and 130 Awith 0.8 and 1.6 mm wire respectively.

With the same wire dimensions the voltage liesbetween 18 and 28 V.

Concerning the choice of shielding gas bothmixed gas and CO2 are applicable, but if a smoothsurface is required, the best choice would bemixed gas, e.g. a 82/12. The gas flow should bebetween 8 and 12 l/min.

Application AreaWelding in the mixed transfer area is often usedfor welding of bottom runs in heavy plates and forfilling of V-grooves. The method can also be usedfor welding of fillet welds for instance in inwardcorners and vertical/downward.

Welding DataWhen welding MIG/MAG it is very importantthat the welding data are correct as otherwise veryserious and even potentially dangerous weldingerrors may occur.

The correct welding data are set by the individualwelder as they depend on the welding speedamong many other things. The personal influenceis however, fairly limited why we in the followinghave made some tables of recommended weldingdata. The general idea is that the individual weldercan start with the indicated data and then adjustthe parameters to make them fit his particularwelding.

It is our hope that the tables will be of help in theworkshop.

28

Tables of Welding Data for Fillet and Butt Welds in SteelRecommended welding data - MIG/MAG welding - Fillet Welds

Plate thickness, mm 1 1,5 2 3 5 8 10 12Type of weld

Welding position 1 KP2 KP

1 KP2 KP

1 KP2 KP

1 KP2 KP

1 KP2 KP

1 KP2 KP

1 KP2 KP

1KP2 KP

Number of runs 1 1 1 1 1 1 2 3Wire diameter, mm 0,8 0,8 0,8 0,8 1,0 1,0 1,0 1,0Shielding gas 80/20 80/20 80/20 80/20 80/20 80/20 80/20 80/20Wire speed, m/min. 4,5 7,0 8,0 7,5 10,0 11,0 12,0

8,515,0

Current, A 90 125 140 200 225 235 240210

265

Voltage, V 18,5 21 21 22 28 32,5 3328

34

Gas consumption, l/min. 12 12 12 12 12 12 12 12

Recommended welding data - MIG/MAG welding - Fillet Welds

Plate thickness, mm 1 1,5 2 3 5 8 10 12Designation acc. DS/ISO2553Type of weldDesignation acc. DS 889Welding position

3 KP1/f

3 KP1/f

3 KP1/f

3 KP1/f

3 KP1/f

3 KP 1/f

3 KP1/f/l/s

3KP 1/f/l/s

Number of runs 1 1 1 1 1 1 2 2Wire diameter, mm 0,8 0,8 0,8 1,0 1,0 1,0 1,0 1,0Shielding gas 80/20 80/20 80/20 80/20 80/20 80/20 80/20 80/20Wire speed, m/min. 4,5 6,3 7,8 6,0 7,0 4,5 7,0

4,58,04,5

Current, A 90 120 145 175 185 140 185140

210140

Voltage, V 16,5 19,5 20,5 21,5 22,5 19,5 2220

2320

Gas consumption, l/min. 12 12 12 12 12 12 12 12

29

Recommended Welding Data - MIG/MAG Welding - Butt Welds

Plate thickness, mm 1 1,5 2 3 5 5 8 10 12Designation acc.DS/ISO 2553 – Type of weldWelding position 1 P 1 P 1 P 1 P 1 P 1 P 1 P 1 P 1 PGroove gap, mm 0 0.5 1.5 2 2 2 2 2 2Open angle, degrees - - - - 50 50 50 50 50Number of runs 1 1 1 1 2 2 2 3 3Wire diameter, mm 0.8 0.8 0.8 1.0 0.8 1.0 1.0 1.0 1.0Current, A 80 100 110 125 118

100125112

175175

175210

185220

Voltage, V 21 20 19.5 19.5 2122

1824

22.524

22.524

2427.5

Gas consumption, l/min 12 12 12 12 12 12 12 12 12

Recommended Welding Data - MIG/MAG Welding - Butt Welds

Plate thickness, mm 1 1,5 2 3 5 5 8 10 12 NotesDesignation acc.DS/ISO 2553 – Type of weldWelding position 3 P

1/f3 P1/f

3 P1/f

3 P1/f

3 P1/f1/s

3 P1/f1/s

3 P1/f1/s

3 P1/f1/s

3 P1/f1/s

Groove gap, mm 0 0,5 1,5 2 2 2 2 2 2Open angle, degrees - - - - 50 50 50 50 50Number of runs 1 1 1 1 2 2 3 3 4Wire diameter, mm 0,8 0,8 0,8 1,0 0,8 1,0 1,0 1,0 1,0Shielding gas 80/20 80/20 80/20 80/20 80/20 80/20 80/20 80/20 80/20

Wire speed, m/min. 4.0 5.0 5.5 4.0 7.03.7

4.02.5

6.53.0

7.03.8

7.54.5

Intermediary and toprunswelded inthe sameposition

Current, A 80 100 110 125 12580

13080

170100

180115

200135

Voltage, V 20 19.5 19 19 20.519.5

1818.5

20.520

21.520.5

2220.5

Gas consumption, l/min. 12 12 12 12 12 12 12 12 12

30

Recommended Welding Data - MIG/MAG Welding - Wire Speed

Amperage Wire Diameter ø (mm)Mild Steel Stainless Steel Aluminium

0.8 1.0 1.2 0.8 1.0 1.2 1.2 1.675

1003.55.0

6.08.0 4.0

125150175200

709.0

11.514.0

4.05.06.07.5

2.53.54.55.5

10.513.517.0

5.06.07.59.0

3.04.05.06.0

6.07.08.5

4.45.0

225250275300

19.0 10.013.016.019.0

6.57.59.0

11.0

10.513.015.519.0

7.59.0

11.014.0

10.011.513.014.5

5.66.36.97.5

325350375400

13.015.019.0

19.0 16.0 8.18.79.3

10.0

31

Parameters for MAG Welding of Fillet Welds with FluxCored WireSetting of the Welding MachineBeing an inexperienced MIG/MAG welder it canbe a problem to adjust the welding machine toweld with optimum welding data. The problem isthat there are several variable parameters thatmust suit each other correctly if a satisfactorywelding result is to be achieved.

The following section is a description of thesignificance of the individual welding parametersand a method to get started on the welding job.

Types of transferThere are several forms of material transfer by thearc in MIG/MAG welding. The transfer isseparated in dip transfer welding, spray transferwelding, large droplet transfer (mix-arc) and pulsewelding.

The choice of type of transfer depends on thethickness of the material, the type of weld, thewelding position and the size and type of thewelding machine

Dip Transfer WeldingIn dip transfer welding the transfer of materialtakes place as an interplay between the formationof a droplet of welding wire and its short-circuiting. When the arc is established a dropletforms on the end of the wire. This droplet willgrow and eventually get into contact with the weldpool and then short-circuit. This means that thedroplet is pinched off at a speed of 80 to 200short-circuits per second.

Flux Cored Wire and Dip Transfer WeldingFor welding fillet welds with flux cored wire a 1.2mm wire is used, and as the welding takes placeon rather heavy metal thicknesses (8 mm) it is notpossible to weld with an adequate quality in thedip transfer area. In order to weld fillet welds ofan adequate quality in 8 mm plates with 1.2 mmflux cored wire the welding parameters must beset to welding in the spray transfer area whichmeans more than 200 A.

Areas of ApplicationDip transfer welding is only suited for welding inordinary steel with solid wire. If the method isused on aluminium or stainless steels there will beproduced a substantial amount of spatter from theweld pool, and the risk of lack of fusion will bevery high. Dip transfer welding is particularlyused on plate thicknesses < 5 mm and for weldingof bottom runs in thicker materials, even verylarge plate dimensions.Dip transfer welding is also suitable for positionwelding for instance when the bottom run iswelded in the dip transfer area while theremaining runs are welded in the mixed transferarea.

Welding parametersWhen welding fillet welds in 8 mm platethickness it will typically be within the spraytransfer area, when welded in positions 1 KP and2 KP2 as well as 2 KR and others. In the spraytransfer area the current is set to more than 200 A.At position welding, which means welding in forinstance positions PD and PF it will not bepossible to control the weld pool within the spraytransfer area, and therefore welding will usuallytake place in the mixed transfer area around 150 to200 A. If a really skilled welder holds the torch,the welding current could sneak into the loweredge of the spray transfer area.

The stick-out should for all the above jobs bebetween 20 and 25 mm and the welding voltagebetween 21 and 30 V.

Apart from the above, the welding parametersshould be set as specified in the WPS of the actualjob, and the welder then trims his parameterswithin the allowed tolerances. If there is not aWPS available, the welder can use the data sheetsdelivered from the wire supplier for adjustment ofhis welding parameters.

In order to avoid welding errors such as porositiesand long porosities it is important to see to it thatthere is adequate gas shielding of the weld pool.the gasflow should be about 20 l/min. or more ifthere is draught in the workshop. Atmospheric airis the worst enemy of the weld metal, as the air

32

causes a massive formation of porosities.Therefore it is important to avoid welding withshielding gas in places where there is a risk ofdraught.

PenetrationThe penetration in the dip transfer area issomewhat larger with CO2 than with mixed gas(at the same wire feeding). The reason is that theweld pool of the mixed gas is shorter due to thehigher short-circuit frequency and the lower arcvoltage (2 to 3 V) than that of CO2.

As the mixed gas due to its stable arc has a muchlarger tolerance than CO2 for the variations ofwelding parameters, for instance the currentintensity, it is easy to increase the wire speed andcompensate for the smaller penetration and at thesame time increase the weld speed.

Welding with mixed gases usually offers higherwelding speed than welding with CO2, due to thefact that the mixed gas arc is more stable andtherefore allows higher wire speed.


DefinitionSpray transfer welding or spray arc welding iswelding where the wire is transferred as spray,hence the name Spray Arc. The transfer takesplace as a large amount of very fine drops withoutshort-circuits. The best result is obtained when thearc “snarls” a bit.

Welding ParametersAt spray transfer welding the welding current isvery high; between 200 and 300 A with a 1.2 mmflux cored wire. With a wire of the same diameterthe voltage will lie between 22 and 26 Vdepending on the type of wire.

Current and voltage are very dependent on thetype of wire and its make, and in each case the

relevant welding parameters must be looked up inthe manufacturer’s data sheets or in the WPS.

The data given in this theoretical instruction aretherefore only intended as a guide and cannot bedirectly applied on actual workshop welding jobs.

Wire DimensionIn most cases 1.2 mm to 2.4 mm wire are used forspray transfer welding. When welding downhandhorizontal and vertical fillet welds 1.6 and 2.4 mmwire will be used depending on the thickness ofthe base material, while preferring 1.2 mm wirefor position welding.

Shielding gasMixed shielding gases with a large content ofargon are always used for spray transfer welding,e.g. 82/18. Due to the large droplets welding withCO2 would make it impossible to control the weldpool.

Application AreaSpray transfer welding can be used with allmetals. However, with ordinary steel the onlywelding position is underhand welding. Themethod is used with material thicknesses morethan 3 mm and up to even very large thicknesses.Spray transfer welding is a very heat weldingprocess, but due to the speed it only causes smalldeformations.

Mixed Transfer WeldingWhen welding in the mixed transfer area thetransfer of material takes place as rather largedroplets. The mixed transfer welding lies betweendip transfer and spray transfer welding and thetransfer of material takes place in the form of verylarge droplets mostly without short-circuits.

Welding ParametersThe welding current lies between 100 and 200 Awith 1.2 mm wire. With the same wire dimensionthe voltage lies between 18 and 26 V.

Concerning the choice of shielding gas bothmixed gas and CO2 are applicable, but if a smoothsurface is required, the best choice would be amixed gas, e.g. a 82/12. The gas flow should bebetween 15 and 25 l/min.

33

The shielding gas should always be chosen withdue regard to the chosen wire, as the quality of thewelding is very dependant on the type of shieldinggas.

The recommended shielding gas for a particulartype of wire is always indicated in the wirecatalogue together with the data sheet of the wirein question.

Area of ApplicationUsually welding in the mixed transfer area will beused for welding of bottom runs in heavy platesand for filling of V-grooves. The method is alsoapplicable for downhand and vertical/downwelding of fillet welds for instance in inwardcorners.

Welding DataWhen welding MIG/MAG with flux cored wire itis very important always to use the correctwelding data, as otherwise very serious and evenpotentially dangerous welding errors may occur.

The correct welding data is set by the individualwelder within the allowed tolerances indicated inthe WPS or on the data sheet of the wire inquestion. It is very important for the metallurgy ofthe construction that the welder does not adjustthe welding data beyond the allowed tolerancesindicated on the WPS or similar instructions.Excessive adjustments may cause unintentionaltension and hardness which will reduce thestrength and lifetime of the construction.

35

Parameters for MAG Welding of Butt Welds with FluxCored WireWelding ParametersA welding parameter is a detail of the weldingprocess which has influence on the weldingperformance and quality. A welding parametermay be the regulation of the welding voltage (V),setting of the welding current (A), the weldingspeed, the stick-out and if it leftward or rightwardwelding.

In addition to these parameters the shielding gashas a great influence of the welding performanceand quality, and last but not least the wireinfluences on the welding quality.

The Function of the Wire FluxJust as the manufacturers of coated electrodes,those producing flux cored wires each have theirown recipes for the flux mixture which makes thewelder prefer one brand to another, although thespecification and properties of the wires should beidentical.

The flux is mixed according to the area ofapplication for which the flux cored wire isdeveloped.

The function of the fluxThe main function of the flux is to clean the weldmetal for gases like oxygen and nitrogen whichhave a bad influence on the mechanical propertiesof the welding. In order to reduce the content ofoxygen and nitrogen in the weld metal, silicon andmanganese is added to the flux due to theirdeoxidizing and strength enhancing properties.

SlagElements such as calcium, potassium, silicon andsodium are added for the purpose of creating theslag which protects the weld pool against theatmospheric air during the solidification period.

Furthermore, the slag contributes to:• form the surface to the correct profile• hold the weld pool during position welding• slow down the solidifying of the weld pool

Elements like potassium and sodium furthermorecontribute to a soft arc and only little spatter.

Alloying ElementsThe possibilities for alloying a flux cored wire aremuch better than for alloying a solid wire as thealloying elements can be added to the wire flux.

Common alloying elements are molybdenum,chromium, nickel, carbon, manganese, etc.

The elements increase the strength and theductility and at the same increase the yield of thewire and improve its welding properties.

The combination of the flux determines whetherthe wire becomes sour (rutile) or basic.

36

The Function of the ShieldingGasMost flux cored wires requires a shielding gas asdoes welding with solid wire. However, it ispossible to purchase wires which produce so muchgas from the flux that external shielding gas is notnecessary. This method is called innershieldwelding.

For the types of wire which require externalshielding gas either CO2, mixed gas or pure argoncan be used according to the type of material andthe chemistry of the wire.

Due to the comparatively high current intensitiesof welding with flux cored wires, themanufacturers in most cases recommend a mixedgas consisting of approximately 80% argon and20% CO2. CO2 is not suitable for welding withflux cored wires as this shielding gas will make itvery difficult for welder to control the weld poolat the high intensities, which will cause welds ofinferior quality. Furthermore, the arc characteristicimproves by use of argon mixtures and so do themechanical properties of the weld metal.

The Significance of the WeldingParameters

Arc VoltageThe arc voltage determines the length of the arc.The higher the arc voltage, the longer the arc.

The diffusion of heat is increased proportionallywith the length of the arc, as the arc will spreadover a larger area making the weld wider andflatter. If the arc voltage is too high, it will causean unstable arc, a lot of spatter and a poor weldsurface. If the voltage is too low, it will cause theweld to have too high a surface.

The below figure shows the weld profiles of threedifferent arc voltages while all other parametersremained the same.

Arc voltage (V) 28 32 36

Current Intensity (A) 450 450 450

Welding speed (cm/min) 56 56 56

Wire speed (cm/min) 445 445 445

Stick-out (mm) 28 28 28

Electrode angle 5/0 5/0 5/0

Wire diameter (mm) 2,4 2,4 2,4

Current IntensityAs before mentioned welding with flux coredwires requires power sources with a flatcharacteristic for instance a power source of theinverter type which would be very suitable.

The power source yields the amount of currentnecessary to maintain the melting speed of thewire providing the set arc voltage. When allparameters is kept constant and the wire speed isincreased it will automatically cause an increaseof the current intensity and thus the depositionrate. In this way more weld metal and more heatare transferred per welded meter. The result ismore welding fumes and deeper penetration.

By decreasing the wire speed the opposite result isachieved; less welding fumes and less deeppenetration.

37

The below figure shows a drawing of thepenetration profiles of three welds made withdifferent current intensity and otherwise the sameparameters.

Current Intensity (A) 400 450 500





Electode angle 5/0 5/0 5/0


The influence of the current intensity on thepenetration profile

Welding SpeedThe speed between the workpiece and the wire iscalled the wire speed, and it has great influence onthe penetration profile.

If all other parameters remain constant and thewire speed is increased, the deposition and theheat supply are reduced per meter weld. Thisresults in a more narrow weld profile and aninferior penetration. Too high speed and thereby ahigher current results in a more coarse surfacewhere the slag sticks more. Furthermore, a toohigh wire speed may cause a penetration notchand thus an increased risk of breaks.

By maintaining a slow wire speed it works theopposite way. More weld material is beingtransferred and the heat input per meter weld isincreased. The deposition rate is higher and thepenetration profile wider. By continuing to slowdown the wire speed you will reach to a pointwhere the volume of the weld pool and the slagbecomes so large that they will flow into the craterunder the arc. This creates an insulating effectbetween the arc and the base material. Only asmall amount of heat is transferred to the basematerial and the penetration profile will be widebut only with little deposition, which will create aserious risk of long systematic lacks of fusion.

The below drawing shows the penetration profilesof three welds, welded with different weldingspeed and otherwise identical parameters.


Current intensity (A) 450 450 450






The influence of the welding speed on thepenetration profile in butt welding

Stick-outA large stick-out causes a higher electricalresistance in the wire. The power yields the samecurrent in order to maintain a constant arc voltageand arc length for as long as the wire speedremains the same. The current intensity decreasesresulting in a colder welding and thereby lesspenetration. A too short stick-out produces morespatter and the weld may arch and become toohigh.

A too long stick-out also produces more spatterand an unstable arc.

When the stick-out and the wire speed increase,the electrical resistance heating of the wire willresult in an increase of the deposition rate.

38

The below drawing shows the importance of thestick-out on the penetration profile when all otherparameters remain the same.


Current intensity (A) 470 450 430







The influence of the stick-out on the penetrationprofile in butt welding

At leftward welding the penetration profile issmaller than at rightward welding.

Basic Flux Cored WiresBasic flux cored wires deposit a very crack-resistant weld metal with a low content ofhydrogen, about 5 ml/100 g weld metal.

The basic flux cored wires are particularly suitablefor welding of butt and fillet welds in heavymaterials and tightly fixed constructions. Thebasic weld metal makes the electrode very suitablefor welding of dynamically charged constructionsand construction which are to operate at lowtemperatures.

Typical applications areas are cranes, contractormachinery, offshore constructions, bridges, etc.

made of steel corresponding to Fe 510 Daccording to DS/EN 10025 or similar micro-alloyed steels and ship plates.

Basic flux cored wires are also suitable forwelding of cast steel and free-cutting steel, andfurthermore, it is very suitable for welding ofbottoms runs with ceramic backing.

The basic flux cored wires can be welded in allpositions. Choose a 1.2 mm wire for positionwelding, and for downhand welding choose 1.6 or2.4 mm wires.

The shielding gas should always be the gasrecommended by the wire manufacturer, as thewire may be approved for this type of gasexclusively, e.g. mixed gas 82/18.

Basic flux cored wires are available in dimensionsfrom 1.0 mm to 2.0 mm.

The basic flux cored wires have fine mechanicalproperties, typically:

Tensile strength: 470 N/mm2Breaking strength: 540 N/mm2Elongation: 25%Impact resistance, charpy V: +20°C 140 J

0°C110 J -20°C95 J-30°C 50 J

Rutile Flux Cored WiresRutile flux cored wires have very fine weldingproperties and they are very suitable for positionwelding. The weld will be smooth often with aself-releasing slag.

The rutile flux cored wires are used for welding offillet and butt welds in construction steel andcontainer plates corresponding to a quality up toFe 510 D, DS/EN 10025 or similar micro-alloyedsteels. Some of the rutile flux cored wires havevery fine impact resistance values down to -60oC.

Rutile flux cored wires can be used in all weldingpositions. Electrode dimension 1.2 mm isparticularly suited for position welding as it ispossible to weld in different positions with thesame current intensity and voltage settings. Fordownward welding in heavier plates, electrodeswith a diameter of ø1,6 and ø2.4 mm are used.

39

Rutile flux cored wires are available indimensions from ø1.0 to ø2.4 mm.

The shielding gas should be the mixturerecommended by the manufacturer of the wire,e.g. Ar/CO2 82/18.

As previously mentioned the mechanicalproperties for flux cored wires are generally fine,typically as indicated in the below table:

Tensile strength: 540 N/mm2Breaking strength: 570 N/mm2Elongation: 24%Impact resistance, charpy V: 0° 80 J

-20° 55 J

For rutile wires with improved impact resistancethe picture is a bit different:

Tensile strength: 420-496 N/mm2Breaking strength: 500-620 N/mm2Elongation: 22%Impact resistance, charpy V: -20° 80 J

-60° 35 J

Metal Flux Cored WiresThe flux of the metal flux cored wires largelyconsists of iron powder and some filteringelements known from the solid wires such assilicon and manganese. A few wires has 2% nickelcontent which improves the impact resistance atlow temperatures.

Metal flux cored wires are used for welding ofbutt and fillet welds in all positions. The metalfluxed wire welds very fast, and produces niceslag-free surfaces which means that welding canbe done in several layers without deslagging aftereach welded layer.

The metal flux cored wires are used for welding ofconstruction steels and container plates to aquality corresponding to Fe 510 d, DS/EN 10025.

The shielding gas should be the typerecommended by the manufacturer of the wire,e.g. Ar/CO2 80/20.

Metal flux cored wires are available in diametersfrom 1.2 to 2.4 mm. However, there can bedifferences from supplier to supplier, some

manufacturers can only deliver up to ø1.6 mmwhile others can deliver down to ø1.0 mm.

The metal flux cored wires have fine mechanicalproperties largely on level with the basic wires.Typically, the mechanical properties are asfollows:

Tensile strength: 520 N/mm2Breaking strength: 580 N/mm2Elongation: 24%Impact resistance, charpy V: +20° 100 J

0° 95 J-20° 60 J

With nickel content: -30° 90 J-60° 70 J

mag welding with solid wire - methods and equipment · 1 mag welding with solid wire - methods and...

Documents