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EWM Welding Dictionary


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The Reason Behind the EWM Total System Concept.

Compromising on the quality of welding equipment doesnt pay

long-term. Many of our customers found this out for themselves

before choosing to place their trust in EWM. Rectifying welding

errors is costly. Outmoded processes may create extra work, while

hidden quality defects lead to unhappy customers and regress

claims. Downtime due to machine failure is also expensive.

For this reason, we offer our customers a fully coordinated

system where all components are systematically geared

towards delivering consistently high welding quality,

conserving resources and reducing the amount of

work involved.

Points to consider when calculatingthe costs for the perfect weld bead.

EWM quality will save you money. You will benefit

from extended service life, reduced down times,

reduced process costs and a reduced consumption

of gas and welding consumables.


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coldArc

forceArc

rootArc

pipeSolution

Highspeed

activArc

spotArc

forceTig

Welding processes designed and patented by EWM such as:

or

make it possible to handle welding tasks that were previously impossible.

Here highly dynamic voltage, current and wire values need to be transportedto the welding arc without electrical loss or distortion, in some cases across

large distances. It is easy to understand that only perfectly optimised transfer

elementssuch as:

Intermediate hose packages

Wire feed systems

Welding torch systems

can achieve the best possible results with regard to:

Minimal spatter

Gap bridging

Reduction in lack of fusion Reduction in post weld work

Reduced distortion of the welded material

Reduced consumption of materials, gas and energy

Reduced consumption of wearing parts/consumables

and therefore maximum cost savings.

Because Quality Saves You Money.

EWM develops and produces welding machines, wire feed units, torch systems

and intermediate hose packages of the highest quality, offering you the maximum

benefit when it comes to your welding tasks.

in conjunction with pulse welding

for MIG/MAG applications

in conjunction with cold/hot

wire for TIG applications


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MMA PRIMER


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The EWM MMA Primer

EWM HIGHTEC WELDING GmbHDr. Gnter-Henle-Str. 8, D-56271 Mndersbach/Ww., Germanywww.ewm.de

1 10.09

Contents1 Preface..............................................................................................................................................................2

2 The process.......................................................................................................................................................2

2.1 General remarks .....................................................................................................................................22.2 Current type ............................................................................................................................................2

2.3 Electrode types .......................................................................................................................................32.4 Properties of the coating types ...............................................................................................................4

3 Which electrode for what purpose.....................................................................................................................5

3.1 Welding-engineering considerations when choosing stick electrodes....................................................53.2 Material considerations when choosing stick electrodes ........................................................................6

4 Groove preparation ...........................................................................................................................................7

4.1 Groove shapes........................................................................................................................................74.2 Placement of the weld groove side walls................................................................................................9

5 Electrode holders and welding cables...............................................................................................................9

6 Power sources...................................................................................................................................................9

6.1 Power source designs...........................................................................................................................106.2 Special functions with inverters for MMA welding.................................................................................12

7 Performing welding work.................................................................................................................................12

7.1 Igniting the arc.......................................................................................................................................127.2 Moving the electrode.............................................................................................................................137.3 Magnetic arc blow .................................................................................................................................137.4 Set welding parameters ........................................................................................................................13

8 Work safety .....................................................................................................................................................14

9 Special notes for MMA welding on different materials ....................................................................................159.1 Unalloyed and low-alloy steels..............................................................................................................169.2 High-alloy steels and nickel-based alloys .............................................................................................169.3 GMA-surfacing ......................................................................................................................................17

10 Applications for MMA welding .........................................................................................................................17

10.1 Example applications ............................................................................................................................17

11 Literature .........................................................................................................................................................18

12 Imprint .............................................................................................................................................................18


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The EWM MMA Primer

EWM HIGHTEC WELDING GmbHDr. Gnter-Henle-Str. 8, D-56271 Mndersbach/Ww., Germanywww.ewm.de

2 10.09

1 PrefaceManual metal arc welding, known asMMA welding for short, is one of the old-est welding processes still in use today. Itgoes back to research carried out bySlawjanow who in 1891 was the first touse a metal rod that was simultaneouslythe arc carrier and the welding additive,rather than the standard carbon electrodethat had been used for arc welding up un-til that point. The first stick electrodeswere not coated and were therefore diffi-cult to weld with. Later on the electrodeswere coated with materials that madewelding easier, protected the weld metaland had a metallurgic affect on the proc-

ess. The first patent for a coated stickelectrode was created in 1908. Elec-trodes can be coated by dipping or bypressing on an extruder press. Todayonly electrodes with extruded coatingsare used.

MMA welding is characterised by a rela-tively low level of investment and an uni-versal application. The process can beused for a wide range of materials andensures high-quality weld seams. In re-

cent times, however, MMA welding hasbeen superseded, frequently for eco-nomic reasons, by other welding tech-niques that can be mechanised.

This primer clarifies the special featuresof this process and provides informationon the correct application of the tech-nique.

2 The process2.1 General remarks

MMA welding (process number 111) is afusion welding process, and more pre-cisely, a metal arc welding process. ISO857-1 (1998 edition) describes the weld-ing processes in this group as follows:

Metal arc welding: Arc welding processusing an electrode used up during theprocedure.

Metal arc welding without gas shielding:Metal arc welding process without theaddition of external shielding gas and

Manual metal arc welding: Metal arcwelding performed manually using acoated electrode.

In Germany the last process mentioned isknown as manual arc welding or MMAwelding for short, and is characterised by

the arc arcing between a melting elec-trode and the molten bath (Figure 1).

There is no external protection; any pro-tection against the atmosphere comesfrom the electrode. In this case the elec-trode is both the arc carrier and the weld-ing additive. The coating forms slagand/or shielding gas, which among otherthings protects the drop being transferredand protects the molten pool against theingress of the atmospheric gases oxygen

nitrogen and hydrogen.

2.2 Current typeFor manual arc welding (MMA welding),both d.c. and a.c. can in principle beused, but not all types of stick electrodecoatings can be welded on sinusoidala.c., e.g. not pure basic electrodes. Whenwelding with d.c., the minus pole is gen-erally connected to the electrode and theplus pole to the workpiece with most elec-

trode types. Basic electrodes are an ex-ception to this. They are better welded onthe plus pole. The same applies to certainmanufacturers of cellulose electrodes.More information on this can be found insection 2.3 Electrode types.

1 Workpiece 5 Coated electrode2 Weld seam 6 Electrode holder3 Slag 7 Power source4 Arc

Figure 1 Scheme of manual metal arc weld-ing irrespective to ISO 857-1


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The EWM MMA Primer

EWM HIGHTEC WELDING GmbHDr. Gnter-Henle-Str. 8 D-56271 Mndersbach/Ww., Germanywww.ewm.de

3 10.09

The electrode is the welder's tool. Thewelder moves the arc burning on theelectrode in the weld groove side walls,thus melting the edges of the groove(Figure 2).

Different current intensities are required

depending on the type of groove and thethickness of the parent material. The stickelectrodes are available in different di-ameters and lengths, since their diameterand length determine the current loadingpossible. Table 1 shows the standardiseddimensions as specified in DIN EN 759.

Higher welding currents can be used withlarger core wire diameters.

2.3 Electrode typesThere are stick electrodes with coatingsof very different compositions. The com-position of the coating determines themelt characteristics of the electrode, itswelding properties and the quality of theweld metal. Irrespective to DIN EN 499the coating types given in Table 2 existfor stick electrodes for welding unalloyedsteels.

A distinction is drawn here between sin-gle-material types and mixed types. Let-ters are used to designate the differenttypes of electrode. The letters stand forthe following: C=cellulose, A=acid,

R=rutile and B=basic. In Germany the ru-

tile type plays a leading role. Stick elec-trode may be thin-coated, medium-coatedor thick-coated. With rutile electrodes,which are available as standard in allthree coating thicknesses, the thick-coated electrodes are therefore known asRR for clearer identification.

With alloyed and high-alloy stick elec-trodes, there is no such variety in thetypes of coating. With stick electrodes forwelding stainless steels, which are stan-dardised in DIN EN 1600, a distinction isonly made between rutile electrodes andbasic types, for example, as with stickelectrodes for welding creep resistantsteels (DIN EN 1599), but in this casethere are only basic mixed types, as withthe rutile electrodes, although this is notspecifically marked. This is the case withelectrodes that have better welding char-acteristics in out-of-position welding, for

example. Stick electrodes for weldinghigh-tensile steels (DIN EN 757) are onlyavailable with basic coatings.

1 Weld groove side walls 4 Molten slag2 Stick electrode 5 Solidified slag3 Molten weld metal

Figure 2 Position of the electrode in theweld groove side walls

Table 1 Diameter and lengths of stick elec-trodes conforming to DIN EN 759Electrodes

Nominaldia-

meterinmm

Permissible

deviation

Nominal

lengthinmm

Permissible

deviation

1.6

2.02.5

0.06

200

to350 3

3.2

4.0

5.0

6.0

0.10350to

4503

Type Coating

A acid

C cellulose

R rutile

RR thick rutile

RC rutile cellulose

RA rutile acid

RB rutile basic

B basic

Table 2 Coating types to DIN EN 499


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2.4 Properties of the coating typesThe composition and the thickness of thecoating have a significant effect on thewelding characteristics. This relates bothto the stability of the arc and to the mate-rial transition during welding and the vis-

cosity of slag and molten bath.The size of the drop being transferred inthe arc is of particular significance. Figure3 shows a scheme diagram of the droptransferin the four basic types of coatings[1].

The cellulose type (Figure 3, c) has amedium- to large-drop material transfer.The coating consists primarily of organiccomponents that burn in the arc, thusforming shielding gas to protect thewelding position. As the coating containsonly small quantities of arc-stabilising ma-terials with the exception of cellulose andother organic materials, virtually no slagis produced. Cellulose types are espe-cially well suited to vertical-down welding(Figure 4, vertical-down position) be-cause there is no need to worry aboutslag formation.

The acid type (A), where the coating con-

sists primarily of iron ore and manganeseiron ore, provides the arc atmospherewith greater quantities of oxygen. Theweld metal also takes this up, thus reduc-ing the surface tension. The conse-

quences are a very fine, spray-type mate-

rial transfer and a fluid weld metal. Elec-trodes of this type are not therefore suit-able for out-of-position welding. The arcis also very "hot-running"; it permits highwelding speeds, but tends towards theformation of undercuts. The disadvan-tages described have meant that pureacid type stick electrodes are now barelyused in Germany. The rutile acid type(RA), a mixture of the acid and the rutileelectrode, has instead taken its place.

The electrode also has the correspondingwelding properties.

The coating of the rutile type (R/RR) con-sists primarily of titanium oxide in theform of the minerals rutile (TiO

2) or ilmen-

ite (TiO2

. FeO) or even artificial titanium

oxide. Electrodes of this type are charac-terised by a fine- to medium-sized dropmaterial transfer, quiet, low-spatter melt-ing off, very fine seam formation, goodslag removability and good re-ignitioncharacteristics. The latter is only ob-served in this form with rutile electrodeswith a high proportion of TiO

2in the coat-

ing. It means that with an electrode whichhas already meltdown, re-ignition is pos-sible without removing the coating crater(Figure 5) [2].

The slag film formed in the crater has vir-tually the conductivity of a semicon-ductor, if it has a sufficiently high TiO

2

content, which means that when the edgeof the crater is placed on the workpiece,enough current flows for the arc to be

a)

b)

c)

d)

a) Cellulose type c) Acid typeb) Rutile type d) Basic type

Figure 3 Material transition with dif-ferent coating types [1]

PA

PB

PG

PF

PE

PD

PC

Figure 4 Welding positions to ISO 6947


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able to ignite without the core wire touch-ing the workpiece. A spontaneous re-ignition of this type is always important ifthe welding process is being frequentlyinterrupted, e.g. with short seams.

In addition to the pure rutile type, there

are several mixed types in this group ofelectrodes. Of particular note is the rutile-cellulose type (RC) in which part of therutile has been replaced with cellulose.As cellulose combusts during welding,less slag is produced. This type cantherefore also be used for vertical-downwelding (vertical-down position). How-ever, it also has good welding character-istics in most other positions. Anothermixed type is the rutile/basic type (RB). It

also has a slightly thinner coating thanthe RR type. This and its special slagcharacteristics make it especially usefulfor welding in the vertical up position.

There only remains the basic type (B). Inthis case the coating consists primarily ofbasic oxides of calcium (CaO) and mag-nesium (MgO), to which fluorspar (CaF

2)

has been added as a slag thinner. Thefluorspar impairs a.c. weldability in higherproportions. Pure basic electrodes cannotbe welded on sinusoid a.c. current, butthere are also mixed types with lessfluorspar in the coating that can be usedwith this type of current. The materialtransfer of basic electrodes uses me-dium- to large-drops and the molten poolis viscous. The electrode has good weld-ing properties in all positions. However,

the beads produced are slightly rein-forced and more roughly rippled due tothe higher viscosity of the weld metal.The weld metal has very good toughnessproperties. Basic coatings are hygro-scopic. Care must therefore be taken thatthe electrode are stored especially care-fully in a dry location. Electrodes thathave become damp must be oven-dried.However, when the electrodes arewelded dry, the weld metal has a very lowhydrogen content.

In addition to stick electrodes with normalefficiency (160%. These electrodes are

known as iron powder types or high-efficiency electrodes. Thanks to their highdesposition efficiency, they can be usedmore efficiently for many applicationsthan normal electrodes, but their use isnormally restricted to vertical (flat posi-tion) and horizontal positions (horizontalvertical position).

3 Which electrode for whatpurpose

When choosing stick electrodes, materialand welding-engineering considerationsneed to be taken into account.

3.1 Welding-engineering considerationswhen choosing stick electrodes

Each type of electrode has highly specificwelding properties and is therefore alsoused for highly specific welding tasks.

Thanks to its suitability for vertical-down

welding (vertical down position), celluloseelectrodes (C) are used for welding cir-cumferentially seams on tubes with largerdiameters. The preferred application hereis for laying pipelines (Figure 6).

In comparison with welding in the verticalup position (vertical up position), rela-tively thick electrodes (4 mm) can beused here for the root pass. This makesfor increased efficiency.

The particular advantage of the mixed ru-tile/acid type (RA) is the slag residue innarrow grooves, where compact slag is

a)

b)

c)

d)

a) Core wire c) Slag film in coating craterb) Coating d) Workpiece

Figure 5 Re-ignition of the coating crater


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squeezed and is hard to remove. Theslag from the RA type itself is porous andbreaks into small pieces under the slaghammer, and then these pieces can beeasily removed.

The special properties of rutile electrodes

(R, RR), namely good re-ignition, easyslag removal and good seam appear-ance, determine their main applications.These are tacking work, as well as weld-ing fillet welds and final passes wherecomplete slag removal and good seamappearance are critical.

The rutile-cellulose type (RC) can bewelded in all positions including vertical-down. This means it has universal appli-cations, especially in the field of assem-

bly work. The thick-coated variant in par-ticular, which also meets high demands interms of the seam appearance, is there-fore often the all-round electrode insmaller companies.

The rutile/basic electrode (RB) is particu-larly well suited to welding root passesand welding in the vertical up positionthanks to its slightly thinner coating andits special characteristics.

The basic electrode (B) is suitable forwelding in all positions. Special types areeven suitable for vertical-down welding.However, the seam appearance is notquite as good as with other types. Havingsaid that, the weld metal does have "inner

qualities". Of all the types of electrode,basic electrodes have the best toughnessproperties and the best crack resistanceof the weld metal. They are thereforeused where difficult conditions in terms ofthe weldability of the parent materialsexist, e.g. with steels with restricted weld-ability or with very thick walls. Further ap-plications include those where consider-able toughness is required for the joint,e.g. in buildings which will be subjected tolow temperatures later on. The low hy-drogen content also makes this type par-ticularly well suited to welding high-tensilesteels.

3.2 Material considerations when choos-ing stick electrodes

The strength and toughness properties ofthe parent material must normally also beachieved in the weld metal. To simplifythe process of choosing electrodes in thisregard, the full name for a stick electrodeconforming to DIN EN 499 also containsinformation on the minimum values forthe yield point, tensile strength andtoughness of the weld metal and on vari-ous welding properties. Table 3 clarifies

this using an example.The code E 46 3 B 42 H5 means:

The stick electrode for MMA welding (E)has a yield point of min. 460 N/mm

2, a

toughness between 530-680 N/mm2 and

a minimum expansion of 20% (46). Animpact energy of 47 joules is reached upto a temperature of -30C (3). The elec-trode has a basic coating (B). This is fol-lowed by various pieces of non-compulsory information on the efficiencyand the current suitable for the electrode.The stick electrode given in the examplehas an efficiency of 105 to 125% andshould only be used for welding on d.c.(4) in all positions except vertical-down(2). The hydrogen content of the weldmetal is below 5 ml / 100 g / weld metal(H5). If the weld metal contains alloyelements other than manganese, theseare given before the code for the coating

type with the code for the chemical ele-ments and sometimes with numbers forthe percentage (e.g. 1Ni).

Figure 6 Welding in pipeline constructionwith cellulose electrodes


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A low hydrogen content is importantwhen welding steel with a tendency to-wards hydrogen-induced crack formation,such as high-tensile steel. The code forthe hydrogen content provides the nec-essary information here.

Similar identification systems also existfor high-tensile electrodes (DIN EN 757),creep resistant electrodes (DIN EN 1599)and for stainless electrodes (DIN EN1600). For creep resistant and stainlesselectrodes, however, both the strengthproperties and the creep resistance andcorrosion properties of the weld metalsmust match those of the parent metals.The general rule here is therefore that theweld metal should ideally be the same

type or higher-alloy than the parent metal.

4 Groove preparation4.1 Groove shapes

Figure 7 shows the most importantgroove shapes used in MMA welding. Forsquare grooves, the root must begrooved out from the rear side for largersheet thicknesses. In order to avoidfaults, the same applies to welding with

backing runs and to welding on bothsides of double-V butt seam and double-V butt seams with root faces for largersheet thicknesses. With single-V buttseams and single-bevel butt seams, theroot phase can also be broken slightly;the root face thickness in single-V buttseams with broad root face is determinedby the current intensity that can be ap-plied. For economic reasons, single-Ubutt seams and double-U butt seams are

used primarily for larger wall thicknessesbecause the weld volume to be applied islower than with single-V butt, single-Vbutt with broad root face, double-V buttand double-V butt with root face weldsdue to the smaller opening angle.

With fillet welds, the gap between the twojoining members should be kept as smallas possible so that no slag can penetratethe gap. This applies in particular to T-

seams, lap seams and fillet welds.

Joint type Workpiecethickness (mm)

Diagram

Butt weldOne side 3-8both sides 10

Double-V buttweld

Both sides > 10

Single-U buttweld

One side > 12with backing runs>12

Single-V buttweld

One side 3-10with s.u. 3-30

Fillet weld T-joint

One side >2

Fillet weld -corner joint

One side >2Both sides > 3

Fillet weld -lap joint

One side >2

Fillet weld double filletweld

Both sides > 2

Figure 7 Groove shapes irrespective toDIN EN 29692-ISO 9692


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TheEWMMMAPrimer

EWMHIGHTECWELDINGGmbH

Dr.Gnter-Henle-Str.8,

D-56271Mndersbach/Ww.,Germany

www.ewm.de

8

10.09

Table3

ElectrodedesignationsirrespectivetoDINEN499

Codesforthestrengthandexpansionpropertiesoftheweldmetal

Code

Min.yield

strengthN/mm

2

Tensile

strength

N/mm

2

Min.fracturestrain

%

35

355

440to570

22

38

380

470to600

20

42

420

500to640

20

46

460

530to680

20

50

500

560to720

18

Codesfortheimpactenergyoftheweldmetal

Code

Temperatureformin.notch

impactenergy47JC

Z

Norequirements

A

+20

0

0

2

-20

3

-30

4

-40

5

-50

6

-60

Codesforthecoatingtypes

Type

Coating

A

acid

C

cellulose

R

rutile

RR

thic

krutile

RC

rutilecellulose

RA

rutileacid

RB

rutilebasic

B

bas

ic

Code

Hydrogencontentinml/100g

weldmetalmax.

H5

5

H10

1

0

H15

1

5

Codesforthehydrogencontent

oftheweldmetal

1.Allpositions

2.Allpositionsexceptvertical-down

3.Buttweld

inflatpos.,filletweldin

flatandhorizontalverticalpos.

4.Buttweld

inflatpos.filletweldinflat

pos.

5.Positiona

sfor3.plusverticaldown

pos.

Code

Efficiency%

Currenttype

1

A.c.andd.c.

2

105

D.c.

3

A.c.andd.c.

4

105

125

D.c.

5

A.c.andd.c.

6

125

160

D.c.

7

A.c.andd.c.

8

160

D.c.

E

463B42H5


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4.2 Placement of the weld groove sidewalls

The groove edges are normally bevelledby oxyacetylene cutting for unalloyed andlow-alloy steels. High-alloy steels andmetals that can be MMA welded, can be

fusion cut using a plasma arc. It is notabsolutely necessary to remove the oxideskin produced by thermal cutting, but maybe required in special cases.

If there are special requirements in termsof observing low tolerances, mechanicalundercutting of the edges of parts to bejoined may be recommended. This ap-plies to circumferential welds in particular.The modern options for cutting with anelectron or a laser beam are more com-monly available in automated productionand are the exception rather than the rulewith MMA welding.

5 Electrode holders and weldingcables

Figure 8 shows the current course in thewelding current circuit.

The electrode is connected to one pole ofthe current source via the electrodeholder (Figure 9) and the welding cable.The other pole is connected to the work-piece via the workpiece lead and theworkpiece clamp.

The electrode holder is available in differ-ent sizes depending on the electrode di-ameter being used and the current inten-sity being applied.

They were previously standardised into 5sizes in Germany in DIN 8569, Part 1. In

Europe DIN EN 60974, Part 11, coversthem.

The cross-section and the length of theleads must be such that the voltage drop

does not exceed certain values due to itsresistance. Irrespective to the VDE stan-dard, this is 2 volts up to 200 amperesand 5 volts up to 500 amperes. When

calculating the necessary lead cross-section, the lengths of the welding leadand the workpiece lead should be added.Standard lead cross-sections for MMAwelding are 25, 35, 50 and 70 mm

2 de-

pending on the current intensity beingapplied.

6 Power sourcesThe power source converts the highmains voltage to the main lower welding

voltage and supplies the high current in-tensities required for welding which themains cannot provide. It is also possibleto set and control the current. Both a.c.and d.c. can be used for welding.

Direct Power sources are general pur-pose because not all stick electrode typesare weldable on sinusoid a.c. see alsothe Current type section. Power sources

Electrode holder

Power source

Workpiece clamp

WorkpieceArc

Stick electrode(core rod + coating)

= or ~

- (+)

+(- )

Figure 8 The power circuit [2]

Figure 9 Example of an electrode holder

Figure 10 EWM power source PICO 162


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for MMA welding have a falling, staticcharacteristic, and with conventionalpower sources (such as for the PICO162, Figure 10) generally continuouslyfalling and with electronic power sourcesfalling vertically in the work area (Figure11).

This ensures that with the unavoidablechanges in length of the arc with MMAwelding, the most important parameter forthe quality of the welding connection

the current intensity is changed onlyslightly or not at all.

6.1 Power source designsThe simplest way to convert mains cur-rent into welding current is by means ofthe welding transformer. It converts thecurrent only in terms of the current inten-sity and voltage (transformer) and sup-plies sinusoid a.c. for welding. The trans-former principle is shown in Figure 12 [2].

With power line-fed networks, the trans-former is single-phase connected be-tween one phase and the outer conductoror between two phases of the three-phase network. Different current intensi-ties can be set via scattering kernel ad-justment, primary side turn tapping or viatransducer.

With the welding rectifier the current isrectified after transformation by diodes orthyristors, i.e. d.c. current is available forwelding. For basic welding rectifiers, thetransformer is single-phase or two-phaseconnected, but with more demandingmachines, connected three-phase to allphases of the three-phase network. Thelatter supplies a very even current without

significant current ripples. The evennessof the current is particularly useful whenwelding with basic electrodes and whenwelding with metal alloys, such as nickel-based alloys.

With simple machines the welding recti-fier is set in the transformer see Settingthe welding transformer. Modern weldingrectifiers are set using thyristors, whichare controllable rectifiers, using phaseshift control.

Electronic power sources (inverters) arealso increasingly being used for MMAwelding in practise (Figure 13).

Figure 14 shows the block diagram of a3

rd generation inverter with a clock fre-

quency of up to 100 kHz.

These Power sources have a completelydifferent layout to conventional powersources. The current coming from themains is first rectified and then "hacked"

U [V]

I [A]

a)

100A 200A 300A

b)

a) Continually falling characteristic

b) Vertically falling characteristic(constant current characteristic)

Figure 11 Characteristics for MMA welding

Iron core

Primarycircetmain~

Magneticflux

Secondarycurcetweldingcurcet~

Figure 12 Transformer principle [2]

Figure 13 EWM power source STICK 350


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into small particles by switching on andoff by means of transistorss using a clockfrequency of up to 100 kHz. This chop-ping process is necessary so that the cur-rent can be transformed. The choppedcurrent is then discharged as alternatingcurrent into a transformer. This producesa square-wave alternate current on the

secondary side with the correspondingfrequency. This is then rectified andsmoothed using a choke. The high fre-quency of the current being transformedpermits the use of transformers with a lowmass. This permits high deposition powerwelding machines to be manufacturedthat nevertheless have a very low weight.They are therefore especially useful foruse on construction sites. Figure 15shows the EWM Inverter Triton 220

AC/DC that can be used for MMA weldingup to a current intensity of 180 amperesand which weighs only 17.9 kg.

With inverters, the gradient of the staticcharacteristic can be changed withinbroad limits. They can therefore also beused as multiprocess systems for multiplewelding processes. With MMA welding

the characteristic is generally verticallyfalling (constant current characteristic) inthe work area.

With electronic Power sources, much ofwhat is achieved using components suchas resistors, chokes and capacitors, is

triggered electronically by the control.The control for these Power sources istherefore just as important as the powerunit. The current is adjusted, for examplewith switched-mode sources, by changingthe ratio between the current in-put/current output times. The clock fre-quency can also be changed to adjust thecurrent level. The new technology alsomeans that controlled Power sources arepossible, which is precisely what welding

technology had been waiting for. A con-trol device measures the welding currentand welding voltage and compares it tothe set values. If the set set welding pa-rameters change, for example due to un-wanted resistances in the welding currentcircuit, the control will regulate it as ap-propriate. This is carried out very quickly,

in the s range. In a similar way, theshort-circuit current can also be limitedand the cos improved [3]. An improvedlevel of efficiency and lower open circuitlosses in the inverter Power sources areproduced simply from the lower mass ofthe transformer.

Modern inverters now also supply sinu-soid and square-wave A.C. in addition toD.C. Electrodes such as those with purelybasic coatings, which cannot be used forwelding on sinusoid, deposition can suc-cessfully meltoff with square-wave A.C.

D.C. - A.C.converter Rectivier (diode)

Rectivier (diode)

Mains

Transformer Choke

Figure 14 Block diagram of a 3rdgeneration in-

verter clock frequency up to100kHz

Figure 15 EWM inverter TRITON 220 AC/DC forTIG and MMA welding

Figure 16 Control (operating panel) for amodern STICK power source


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The EWM MMA Primer


12 10.09

This may be necessary if undesirablemagnetic arc blow conditions exist.

6.2 Special functions with inverters forMMA welding

Modern inverter Power sources also offera range of special functions, which sim-

plify welding and make the process safer[4]. This is how the arc force is set(Figure 16).

For example, if the arc voltage becomestoo short due to a large drop forming onthe electrode, and drops to below 8 volts,the current intensity is automatically in-creased (Figure 17).

This means that the arc can burn freelyonce more and does not go out. This

function is particularly important whenwelding using cellulose-coated elec-trodes, as well as those with basic coat-ings.

The width of the arc and thus the archardness can be infinity adjusted usingan adjustable choke. A hard arc is advan-tageous for difficult magnetic arc blowconditions exist, for example.

The Hotstart function used ensures safe

ignition of the arc and sufficient warm-upof the cold parent material at the start ofwelding. The ignition process is carriedout at an increased current intensity(Figure 18).

The Antistick function prevents the elec-trode annealing if the ignition processfails and the electrode "sticks" to theworkpiece. The warning up of the elec-trode caused by the resistance heatingmay damage the coating until it breaks

off. With Power sources equipped withthe relevant function, the current is im-mediately regulated down to few amperesif the voltage does not rise after the igni-tion short-circuit. The electrode can thenbe removed from the ignition point veryeasily.

7 Performing welding workThe welder requires good training, notjust in terms of skills, but also in terms ofthe relevant specialist knowledge in orderto avoid errors. The training guidelinesfrom the DVS Deutscher Verband frSchweien und verwandte Verfahren e.V.(German Association for Welding and Re-lated Procedures) are recognised world-

wide and have now been adopted by theInternational Institute of Welding (IIW).

Before starting welding, the workpiecesare generally tack-welded. The tackpoints must be long and thick enough toensure that the workpieces cannot con-tract to a non-permissible extent duringwelding and that the tack points do notbreak.

7.1 Igniting the arcThe welding process is initiated by con-tact ignition with MMA welding. To closethe power circuit, a short-circuit needs tobe created between the electrode and theworkpiece first and the electrode raisedslightly immediately afterwards; the arcwill ignite. The ignition process shouldnever take place outside the groove, butonly at points that will be fused again im-

U [V]

U krit.

R B C I [A]

Figure 17 Principle for setting the arc force R=rutile electrode; B= basic electrode;C= cellulose electrode

I [A]

t

a)

b) a) Hotstart current

b) Hotstart time

Figure 18 Principle of the Hotstart function


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The EWM MMA Primer


13 10.09

mediately once the arc is burning. This isbecause at ignition points where thisdoes not occur, cracks may occur insuitably sensitive materials due to thesudden heating.

When using basic electrodes with a ten-

dency to initial porosity, the ignition proc-ess must actually take place significantlybefore the start of the weld. The arc isthen moved back to the starting point forthe seam and during the course of thewelding process the first drops deposited,which are generally porous, will be fusedonce more.

7.2 Moving the electrodeThe electrode is positioned vertically or at

a slight slant to the panel surface. It is ti-tled slightly in the direction of welding.The visible arc length, i.e. the distancebetween the edge of the crater and theworkpiece surface should be roughlyequal to the core wire diameter. Basicelectrodes must be welded with a veryshort arc (distance=0.5 x core wire di-ameter). To ensure this, they need to beheld in a more steeply inclined positionthan rutile electrodes.

In most positions, stringer beads arewelded or a slight weaving movement isused with an increasingly large groovewidth. Only in the vertical up position areweave beads drawn across the entirewidth of the groove. Welding is normallycarried out with the torch directed at thefinished part of the joint; only in the verti-cal up position is forehand welding usedwith the electrode.

7.3 Magnetic arc blowArc blow is where the arc being divertedfrom its central axis lengthens and ahissing noise is emitted as a result. Thisdiversion could result in discontinuities,such as the fusion penetration becominginadequate and, in slag-forming weldingprocesses, slag inclusions being pro-duced in the seam due to the slag flowingahead of the molten pool.

Forces arising from the surroundingmagnetic field cause the diversion. Justlike any other current-carrying conductor,

the electrode and arc are also sur-rounded by a toroidal magnetic field, inthe area of the arc it is diverted, when itcomes into contact with the parent mate-rial. This compresses the magnetic linesof force on the inside and expands themon the outside (Figure 19, a) [2].

The arc slips into the area of reduced fluxline density, is thereby lengthened andemits a hissing noise due to the in-creased arc voltage created. The oppo-site pole therefore exerts a repulsive ef-fect on the arc.

The presence of another magnetic forcemeans that the magnetic field can spreadmore easily in a ferromagnetic materialthan in air. The arc is therefore attracted

by large ferric masses (Figure 19, b). Thisis reflected, for example, in the arc mov-ing inwards at the ends of the sheet whenwelding a magnetic material.

The movement of the arc can be coun-teracted by tilting the electrode as appro-priate (Figure 19, c). As arc blow is par-ticularly noticeable with d.c. welding, itcan be avoided, or at least reduced, bywelding with a.c.

The arc blow effect may be particularlystrong due to the surrounding ferricmasses when welding root passes. In thiscase it is helpful to support the magneticflux by closely positioned and sufficientlylong tack welds.

7.4 Set welding parametersIn MMA welding only the current intensityis set; the arc length being used by thewelder gives the arc voltage. When set-

ting the current intensity, the current car-rying capacity of the electrode diameterbeing used needs to be taken into ac-

a) b) c)

Fe

+

Figure 19 Deviation of the arc caused by sur-rounding magnetic fields


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The EWM MMA Primer


14 10.09

count. Table 4 provides guideline valuesfor the current carrying capacity for thevarious electrode diameters.

The rule which can be used here is thatlower limit values are used for weldingroot passes and for the vertical up posi-

tion, and the upper values apply to allother positions and for intermediate andfinal passes. As the current intensities in-crease, the melt deposition power in-creases and therefore also the weldingspeed. The fusion penetration also in-creases with increasing current levels.The current intensities given only apply tounalloyed and low-alloy steels. With high-alloy steels and nickel-based materials,lower values should be set due to the

greater electrical resistance of the corewire.

Settings for various welding tasks aregiven in Table 5, Table 6 and Table 7, [2],[5].

8 Work safetyIn MMA welding, risks to the welder arisefrom the smoke and gases of the stickelectrode coatings and from metal va-

pour, as well as from visible and ultravio-let rays and infrared radiation emitted bythe arc; electrical risks are also present.

Irrespective to current accident preven-tion regulations, an extraction system isrequired directly at the point of emissionfor MMA welding at fixed workstations.Only for short-term and mobile welding isair ventilation or a welding-engineeringventilation device permissible in certaincircumstances.

The beam from the arc dazzles eyes and

may cause "arc eye", i.e. an eye inflam-mation. However, the beam can alsocause skin burns and symptoms similarto sunburn. Welders must therefore pro-tect themselves using suitable workclothing and a welding safety shield withthe relevant safety filters conforming toEN 166 and EN 169. The safety filters tobe used should be of protection level 9 for thin electrodes and low current inten-sities up to 14 for thick electrodes and

high current intensities. A plain coverglass in front of the safety filters or a pairof clear glasses protect against eye inju-ries from slag breaking.

Diameter(d in mm)

Length(l in mm)

Currentintensity(I in A)

Rule ofthumb forcurrent in-tensity in A

2.0 250/300 40... 80

2.5 350 50...10020...40 x d

3.2 350/400 90...150

4.0 350/400 120...200

5.0 450 180...270

30...50 x d

6.0 450 220...360 35...60 x d

Table 4 Current intensities irrespective to theelectrode diameter

Table 5 Settings for butt welds on unalloyedand low-alloy sheet materials, val-ues from [2] and [5]

Sheetthickness

mm

Weldingposition

Seamtype

Electrodetype

Electrodediameter

(mm)

Currentintensity

(ampere)

Note

4 2.5 75 -3.2 140 Root

6RA

4.0 180 Final pass

3.2 120 Root

Flat

B4.0 170 Final pass

3.2 95 Root10

V-up

RB4.0 160 Final pass

3.2 130 RootFlat B

4.0 170Fill and

final pass

3.2 90 Root

15

V-up

B4.0 140 Final pass

4.0 160 RootFlat B

5.0 220Fill and

final pass

3.2 90 Root20

V-up

V

B4.0 140

Fill andfinal pass


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The EWM MMA Primer


15 10.09

Electrical dangers occur in arc weldingmainly from the open-circuit voltage be-cause this is the maximum voltage pre-sent between the two poles when thepower source is on when no welding isbeing carried out. The arc voltage pro-duced during the actual welding process

is much lower, on the other hand, anddepending on the electrode diameter andarc length may be around 20-30 volts.The level of open-circuit voltage is there-fore limited by the accident preventionregulations. It must not exceed a peakvalue of 113 volts with d.c. and a peakvalue of 113 volts with a.c. and an r.m.s.value of 80 volts.

The electrical risk to the welder is espe-

cially great when welding in small anddamp areas and when welding on and inlarge ferric masses. In this situation, d.c.power sources with a peak value of 113volts are permissible. With a.c. the levelof open-circuit voltage is restricted evenfurther. It must not exceed a peak valueof 68 volts and an r.m.s. value of 48 volts.Power sources fulfilling these require-ments are identified as such. Newlymanufactured machines bear the "S" sign

(safety), and with older machines themark "K" for d.c. machines and "42 V" fora.c. machines can still be found.

However, welders must also protectthemselves from contact with current car-rying parts by wearing insulated clothing,shoes with undamaged rubber soles andleather gloves. When working on metalconstructions, use of an insulating mat isalso recommended.

9 Special notes for MMA weldingon different materials

MMA welding is today used mainly forwelding unalloyed and low-alloy steels, inother words, constructional steels, creepresistant, high tensile and low tempera-ture steels, as well as stainlesschrome/nickel steels and nickel-based al-loys. Another application for stick elec-

trodes is GMA surfacing.The welding of aluminium and aluminiumalloys and of copper and copper alloyswith coated stick electrodes has been allbut overtaken by shielded arc weldingand is now only used as an emergencysupport measure, if for some reason it isnot possible to use shielded arc welding,such as on construction sites.

Given below are some special features

and possible uses with different materi-als.

Wallthickness

mm

Weldingposition

Seamtype

Electrodetype

Electrodediameter

(mm)

Currentintensity

(ampere)

Note

125 Root170 Hotpass

150 Fill pass8 4.0

130 Final pass

130 Root4.0

180 Hotpass

190 Fill pass10

5.0175 Final pass

130 Root4.0

180 Hotpass

200 Fill pass12

Ver-ticaldow

n

V C

5.0175 Final pass

Table 6 Settings for butt welds on pipesmade from unalloyed and low-alloysteel, values from [2]

Eff.throatthick-

nessmm

Weldingposition

Seamtype

Electrodetype

Electrodediameter

(mm)

Currentintensity

(ampere)

Note

2V-

dow

n

RC 2.5 70 -

3 3.2 130 -RR

180 -4

RR160 190 -4.0

180 Root5 RR

240 Final

RR1605.0

290 -

4.0 180 Root

240 Final6

Hor.vert.

RR5.0

255 -

3.2 110 Root8 V-up

T

B4.0 140 Final

Table 7 Settings for fillet welds on unal-loyed and low-alloy steels, valuesfrom [2]


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The EWM MMA Primer


16 10.09

9.1 Unalloyed and low-alloy steelsDue to the low level of investment re-quired, MMA welding is still used with un-alloyed and low-alloy steels in smallercompanies with less intense welding re-quirements where purchasing larger,

automated welding systems would not beeconomically viable. Stick electrodes arealso still used on construction sites, e.g.out-of-doors welding, where shielded arcwelding would necessitate complex pre-cautions to shield against the wind,Figure 20.

In all other cases, the process has yet toprove its efficiency in contrast to other,automated arc-welding techniques. Highdeposition power electrodes with an effi-

ciency of 160-180% are therefore usedwherever possible. High efficiency rutileelectrodes are especially well suited towelding fillet welds with effective throatthickness of 3-5 mm, thanks to highwelding speed and good seam appear-ance.

In the construction of pressurised con-tainers and boilers, basic stick electrodescontinue to enjoy a certain degree of

popularity because of the excellent qual-

ity values of the welding join, with the im-proved quality of the welds sometimesproving more important than economicconsiderations.

High-tensile steels, including constructionsteel S355 if present in larger wall thick-

nesses (20 mm), have a tendency tocrack during welding if three contributoryfactors are combined, namely, a high hy-drogen content, high stresses and rapidcooling after welding. Such hydrogen-induced cracks can be most safelyavoided if the hydrogen content of theweld metal is kept low (


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The EWM MMA Primer


17 10.09

As austenitic steels do not become brittleeven under the influence of hydrogen,and do not have a tendency to crack,electrodes with rutile coatings are usedmainly for these steels, as they provide agood seam appearance. This applies tofillet welds and to final passes in particu-lar. High deposition power electrodes withan efficiency of 160% are also availablefor this purpose.

Electrodes for steels with high corrosion-resistance and nickel-based alloys aregenerally supplied with basic coatings,however. This coating type can also berequired for compound steels that, be-cause of their two-phase structure, arerather more susceptible to becoming brit-

tle due to hydrogen.When welding high-alloy materials, over-heating must be avoided because this re-duces the strength and corrosion-resistance of the welded joint, and mayresult in heat cracks. Therefore, withthinner workpieces, including occasionalcooling breaks or accelerating the coolingprocess by underlaying pieces of copperis recommended.

9.3 GMA-surfacingStick electrodes enable hard alloys thatcannot be manufactured in the form ofsolid wire for reasons of ductility (such ascast iron alloys with a high chrome con-tent) to be applied by alloying via thecoating. One alternative here is coredwires, which can be alloyed via the core,but MMA welding is still used in this sec-tor with relative frequency.

10 Applications for MMA weldingMMA welding can in principle be used forwall thickness starting at 1.5 mm, butmany manufacturers produce stick elec-trodes starting at 2.0 mm , becausevery thin sheets are now generally TIG-welded. This increases the minimum wallthickness for MMA welding to 2 mm.

The proportion of MMA welding has con-tinued to fall continuously over the past

few years to be superseded by MIG/MAGwelding. Irrespective to more recent sta-tistics, the proportion today in relation to

all arc-welding processes is still around7.5% [6].

The main applications remain shipbuild-ing, where fillet welds are predominantlyused, and steel construction work, wherestick electrodes are used mainly on con-struction sites. Previous sections havecovered some of the advantages of MMAwelding in boiler, equipment and pipeline

construction. A further application is inrepair workshops, both for joint weldingand GMA-surfacing.

10.1 Example applicationsIn place of many different applications,typical possible uses of MMA welding aregiven below using two examples.

Figure 21 shows an application from con-tainer construction.

Add-on pieces have yet to be weldedonto a container manufactured by auto-mated welding. MMA welding is ideal forthis application. The use of a lightweightinverter as a power source is particularlyuseful for this purpose. Thick and lessflexible welding leads are no longerneeded, because the inverter can bemoved onto or close to the workpiece.

The second example shows one applica-tion of MMA welding in beam construc-

tion.Many metalworking firms or small steelconstruction companies manufacture rail-

Figure 21 Use of MMA welding in containerconstruction


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The EWM MMA Primer


18 10.09

ings, balconies or beams prefabricated in

the workshop and then installed on con-struction sites. Multiple short weld seamsare used for this purpose, to which MMAwelding is ideally suited.

11 Literature[1] Killing, R.: Kompendium Schwei-technik Band 1 Verfahren der Schwei-technik Fachbuchreihe SchweitechnikBand 128/1, DVS-Verlag Dsseldorf 1997

[2] Killing, R.: Handbuch der Lichtbogen-schweiverfahren Band 1 Lichtbogen-schweiverfahren, FachbuchreiheSchweitechnik Band 76/I, DVS-VerlagDsseldorf 1999.

[3] Killing, R. und H. Lorenz: Schweige-rte fr das Lichtnetz Schein und Wirk-lichkeit Metallbau H. 3/2000, p. 62-64.

[4] Susa, F. und R. Killing: Moderne Multi-funktionsanlagen Eigenschaften undAnwendung DVS-Jahrbuch Schwei-

technik 2002, p. 158-164, DVS-VerlagDsseldorf 2001

[5] G. Aichele: Leistungskennwerte frSchweien und Schneiden, Fachbuchrei-he Schweitechnik Band 72, DVS-VerlagDsseldorf 1994.

[6] Killing, R.: Metallschutzgasschweienhat weiter zugenommen Anwendungs-umfang der Schmelzschweiverfahren,Praktiker H. 11/2001, p. 435-436.

12 ImprintThe MMA Primer, 3

rdedition 2009

From the EWM Knowledge range of pub-lications All about welding

All rights reserved.

Reprinting, including extracts, is forbid-den. No part of this brochure may be re-produced or electronically processed, re-produced or distributed in any form (pho-tocopy, microfilm or any other procedure)without the written permission of EWM.

EWM HIGHTEC WELDING GmbH

Dr.-Gnter-Henle-Str. 8

D-56271 Mndersbach, Germany

Fon: +49(0)2680.181-0

Fax: +49(0)2680.181-244

mailto:[email protected]

http://www.ewm.de

Figure 22 Use of MMA welding in beam con-struction


25/144

TIG PRIMER


26/144

AS A LEADER IN TECHNOLOGY, EWM HAS BEEN

INVOLVED IN RESEARCH AND DEVELOPMENT FOR

DECADES, MAKING WELDING EVEN EASIER, MORE

COSTEFFECTIVE AND ABOVE ALL, SUSTAINABLY

SECURING THE WELDING RESULTS. AT THE SAME

TIME, WE HAVE BEEN EXAMINING AND ANALYSING

THE CO MPLEX INTERPL AY OF THE INDIVIDUA L

COMPONENTS AND PARAMETERS AND THUS

OPTIMISING THE ENTIRE WELDING PROCESS.

We claim to define not only characteristics and configurations alone,

but to develop totally new, innovative welding processes. We use

our core electrical engineering know-how to come up with

the latest inverter and microprocessor technology.

Welding is one of humanitys key technologies. It has

supported, in fact it has made our industrial progress

possible for hundreds of years. Today, we come across

welding in the most versatile of forms. We join metals

to gigantic structures and join the finest materials to

delicate constructions. In our daily routine, we place

our confidence often without being aware we are

doing so in the quality and durability of these joints.

The welding codehas been broken!


27/144

Improving quality and cost-effectiveness!

Focusing on TIG/plasma welding (subcategories 141 and 15 according to DIN ISO 4063) EWM has developed

functions and processes with which their customers are able to carry out welding tasks faster, more cost-

effective and with the highest level of quality.

The innovative TIG/plasma welding processes

A host of functions which save time and money

TIG welding process with especially

concentrated arc for greater fusion

penetration and faster welding

speeds.

Effective and productive TIG pro-

cesses thanks to the mechanised

addition of the welding consumable.

Use TIG spotArc spot welding and

metal sheets are joined perfectly.

Focused arc with high energy density.

Detailed information on the functions can be found on Pages 15, 16 and 17.

Dynamic TIG arc with compensated

arc performance.

AC special

AC frequency AC balance

AC pulsing

Pulsing kHz pulsingAutomated

pulsing

Spotmatic

spotArc

AC wave forms

activArc forceTig

Plasma

Cold wire

Hot wire


28/144

Tetrix

forceTig

Dynamic TIG arc for targeted and concentrated heat

input

Safe TIG welding in all positions and panel thicknesses

Full control over the arc energy

Influence over the viscosity of the molten pool

Stable arc at very high joining speeds of more than 3

m/min, e.g. when brazing vehicle body panels

Strongly focused TIG arc with high energy density Narrow seams comparable to plasma or laser welding

Single-pass welding of thin and thick metal sheets is

possible

Noticeable concentration of the energy and incre-

asing arc pressure as the arc becomes shorter

Prevents mistakes while tack welding Tungsten

electrode does not st ick in case of light touching

of the molten pool

For fully mechanised and automated manufactu-

ring processes

Brazing and welding of thin metal sheets at highspeed

Dynamic TIG arc

with compensated arc performance.

TIG welding process with especially concentrated arc

for greater fusion penetration and higher welding speeds.

PATENTED

activArc

activArc

forceTig

forceTig


29/144

Tetrix

Plasma

microplasma

Focused, directionally stable arc

Ignition reliability for repeated ignitions

Stable microplasma process, even with very low wel-

ding currents (as from 0.1 A)

Plasma keyhole welding with excellent root formation

Different materials can be joined together (e.g.

non-ferrous metals, plastic)

High welding speeds in fully mechanised and

automated applications

Minimal heat input, resulting in less distortion

Focused arc

with high energy density.

Effective handling of the TIG process

Also advantageous when manually welding long seams

and large cross-sections

Greater welding speed and deposition rate in compari-

son to conventional TIG welding

Also suitable for non-ferrous metals, e.g. aluminium and

aluminium alloys

High deposition rates comparable to MIG/MAG welding

High welding speed

Minimal risk of a lack of fusion

Highly suitable for narrow-gap welding and GMA-

surfacing High-quality, fine-flaked seam

Especially effective in mechanised and automated ap-

plications

Effective and productive TIG processes

thanks to the mechanised addition of the

welding consumable.

Plasma

Cold wire Hot wire

Plasma

Cold wireHot wire

Tetrix AW

Cold wire

Tetrix AW

Hot wire


30/144

Tetrix

Dynamic TIG arc with compensated arc performance

WITHOUT activArc

WITH activArc

CONTROLLED HEAT INPUT

Changing the arc length changes the voltage,

which results in output fluctuations in the arc.

The welding current is increased as the arc is

shortened.

The welding current is decreased as the arc is

lengthened.

Output fluctuations are compensated for when

the arc length is changed.

activArc

Large distance, approx. 12 V

Welding current: 60 A

Large distance, approx. 12 V


Smaller distance, approx. 10.5 V


Smaller distance, approx. 10.5 V

Welding current: 68.5 A

Voltage V

Voltage V

Current I

Current I


31/144

Requirement:

Sufficient energy density and high arc pressure for reliable sidewall fusion

Problem:

Constant welding current and dropping output due to dropping welding

voltage

Solution using activArc:

Dropping voltage with a shortening arc is compensated for by increasing the

welding current.

Requirement:

Low energy density and low arc pressure for better control of the molten pool

Problem:

Constant welding current and increasing output due to increasing voltage

Solution using activArc:

Dropping welding current as the arc becomes longer

Simpler and safer TIG welding

activArc

TIG Tungsten electrode sticks

when it makes brief contact

Tungsten electrode does

not stick when it makes

brief contact, tip is retained

Voltage

Voltage

Current

Current

Sufficient energy density

Increased arc pressure thanks to increasing welding current

Reliable sidewall fusion

Low energy density

Low arc pressure

Influence on molten pool viscosity


32/144

forceTig

TIG welding process with especially concentrated arc for greater fusion

penetration and faster welding speeds

Optimum for mechanised and automated applications,

with or without welding consumables

High torch power: 800 A at 100% DC

Very high current loadability, high current density

Stable torch design for increased crash safety

Closed, highly effective cooling circuit

Electrode easy to change without gauges thanks to

defined, calibrated geometry

100% reproducible TCP

Low procurement costs and energy requirement

PATENTED

forceTig

forceTig A COMBINATION OF ADVANTAGES

Low procurement costs

Low operating costs

Easy handling

High process stability

High joining speed

High energy density

Deep fusion penetration

ADVANTAGES OF TIG ADVANTAGES OF LASER


33/144

40

30

20

1010

50 100 150 200 250 300 350

0

Universal in use, from thin to thick

ARC PRESSURE COMPARISON

TIG/forceTig

Material: 1.4301

Panel thickness: 2 mm


Welding speed > 2 m/min

EDGE WELD IN VERTICALDOWN POSITION forceTigCORNER JOINT

Welding current [A]

Arcpressure[1

02P

a]

TIG

forceTig


34/144

TetrixPlasma

microplasma

Focused arc with high energy density.

PLASMA ARC: FEATURES

PLASMA ARC: ADVANTAGES FOR PROFESSIONALS

Constricted, nearly cylindrical arc

High energy density

Low divergence (temp. = 10,000 to 20,000K)

Stable, even with extremely low currents as from

0.1 A (microplasma welding)

Faster welding speed compared to TIG welding,

especially with metal sheets thicker than 2.5 mm

(plasma keyhole welding)

Reliable single pass penetration up to 8 mm

(high-alloy steels) and 10 mm (unalloyed steels)

Narrow heat-affected zones, less discolouration

Minimal distortion

Favourable ratio of seam width to seam depth

Controllable fusion penetration

PlasmaTIG

Very directionally stable

Insensitive to changes in distance between the

torch and workpiece

High ignition reliability thanks to pilot arc

Minimal excess weld material and root-side drop-

through, so normally no mechanical post weld

work of the weld seam is necessary

Advantageous in comparison to TIG welding in

preproduction

Insensitive to misaligned edges of the workpieces

Insensitive to component tolerances which

change the arc length

No risk of tungsten inclusions in the weld metal

Small molten pool

Plasma


35/144

0.202 mm

Fast, safe and for the moststringent of quality requirements

Container, equipment and pipeline construction

Vehicle, automobile, track and ship construction

Food and chemicals industry

Machine and plant construction

Production and repair work in the aviation and

aerospace industry

Mould making

Production of dished boiler heads

Cryogenics

Production and repair work in the aviation and

aerospace industry

Food and chemicals industry

Vehicle, automobile and ship construction

Mould making

Cryogenics

Measurement and control technology

Medical technology

Printing technology

Electronics

PLASMA/PLASMA KEYHOLE WELDING

Combination plasma keyhole/MAG

MICROPLASMA WELDING


36/144

Effective and productive TIG processes

thanks to the mechanised addition of the

welding consumable.

TIG WELDING

TIG COLD WIRE WELDING

TIG HOT WIRE WELDING

With regard to the materials to be used, wall

thicknesses and welding positions, TIG welding

is a universal welding process. It enables top-

quality welded joints to be created.

TIG cold wire welding was developed primar-

ily with the aim of making TIG welding easier

and more convenient to use and secondarily toincrease the welding speed. In this process, the

welding consumable is conveyed to the weld

pool by a wire feed unit. Deposition rates, how-

ever, remain limited.

TIG hot wire welding is a further development

of TIG cold wire welding. The welding consum-

able is heated by a separate power source using

resistance heating of the wire stick-out between

the contact tip of the hot wire torch and the

molten pool. There are many advantages over

cold wire welding thanks to the improved heat

balance provided by this process.

Cold wire

Hot wire

Tetrix AWCold wire

Tetrix AWHot wire


37/144

5

6

4

3

2

1

0

TIG hot wire100% faster welding speed

Up to 100% faster welding speed

Up to 60% increase in deposition rate

Dilution reduced by up to 60%

Greater deposition rate (3050%) with the same

welding performance

Simplified positional welding

ADVANTAGES OF TIG HOT WIRE WELDING

Comparison of deposition rate with TIG welding

Depositionrate[kg/h]

TIG manual

TIG cold wire

TIG hot wire


38/144

Use TIG spotArc spot welding

and Metal sheets are joined perfectly

USE TIG spotArcSPOT WELDING ANDMETAL SHEETS ARE JOINED PERFEC TLY

PERFECT SURFACE FORMATION

Universal in use thanks to the option of joining two metal sheets

of the same thickness and of different thicknesses

Optimal for tacking workpieces for manual and automated appli-

cations

Simple to use welding is only carried out on one side

Flatter spot formation in comparison to MAG spot welding

Exceptional spot connection characteristics thanks to minimal heat

input

Very low thermal tension and little distortion thanks to short welding

times

Optimal for visible joints thanks to the clean seam appearance

Excellent seam quality with low distortion thanks to the minimal amount of heat input

Ergonomic torch design for the best possible handling and optimum power utilisation

Economic solution consisting of standard components: EWM TIG DC welding machine, TIG spot welding

torch and optional spot remote control

Alternative to resistance welding with greatly simplified handling

Butt joint/lap joint

Butt weld Fillet weld Edge weld Circumferential seam

T-joint Corner joint Pipe butt joint

DN

(dia. in mm)

25

50

65

80

100

THE RIGHT NOZZLE SHAPE FOR EVERY APPLICATION

spotArc


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Spot for spot for a perfect TIG seam

with minimised spot and tacking times

Spotmatic UP TO 50% LOWERMANUFACTURING COSTS

RELIABLE FAST AND EASY TO USE

QUALITY AND REPRODUCIBILITY

Up to 50% less tacking time thanks to the elimi-

nation of the usual trigger pulling

Practical and innovative solution

Easily reproducible welding results

No special torches are required! Any "standard"

TIG welding torch is perfectly adequate!

Several hundred tack points can be made with-

out having to grind the tungsten electrode

Easier handling also easy to teach to non-

professionals

The arc is ignited by touching the tip of the

electrode to the workpiece instead of using the

torch trigger

The electrode does not stick to the metal

Even tack point appearance

Spot results comparable to mechanised or auto-

mated applications

No rocking motion when starting or stopping

the spot process

Prevents imprecise welding results

PATENTED

Spotmatic


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A host of functionswhich save time and money

Improved molten pool control in positional welding,

especially in the vertical-up position

Easy bridging of larger gaps and gaps of different sizes

Constriction of the arc with increasing frequency

Concentration of the arc energy to a smaller surface

Arc stability, even at very high welding speeds

Pulse frequency depends on welding current

Ideal for tacking and passing thanks to the vibrations in

the weld pool

Lower heat input

Targeted control of the heat input

Minimised material distortion

Reduction of the energy per unit length, optimum for

CrNi welding and heat-sensitive materials

Weld seam appearance with extraordinarily even bead

ripples optimal for visible seams

Safer TIG welding saves money.

From 0.05 to 15 kHz

Pulsing

kHz pulsing

Automated pulsing

With "TIG pulsing", switching occurs back and forth between two different welding current levels, the pulse current and

the pause (fundamental) current. The times, and therefore the frequency and duty cycle, can be adjusted individually

at the machine or using the remote control. TIG pulsing is possible with direct current (DC) and alternating current (AC)

welding.

To increase the arc stability and the fusion penetration properties, especially with low currents, the current is pulsed

automatically.

The ideal area of use is the tacking and spot welding of workpieces

Difficult welding applications can be implemented easily Excellent weld seam quality

Smaller heat-affected zone

Improved seam surface

AC pulsing

CurrentCurrent FrequencyFrequency


41/144

AC functions optimal foraluminium welding

Highly suitable for welding in the vertical-up position,

even without weaving

Controlled root formation when welding thin metalsheets in the butt joint

Sinusoidal quiet arc noise, low-vibration molten

pool, ideal for welding with welding consumables, low

electrode load

Trapezoidal the all-rounder

High frequency narrow, constricted arc with deeperfusion penetration

Positive current proportion, good cleaning, high elect-

rode load

Faster welding speed with fully mechanised and

automated applications with and without wel-

ding consumables

Excellent seam appearance, deep fusion penetra-

tion thanks to the higher current loadability of the

tungsten electrode

Rectangular good cleaning effect, high electro-

de load, safe zero crossing

Low frequency wide arc

Negative current proportion deep fusion penet-

ration, low electrode load

AC special

AC wave forms

AC frequency

AC balance

50200 Hz

-30% to +30%

The "AC special" operating mode is a TIG pulse variant in which switching occurs between alternating current in the

pulse phase and direct current in the fundamental current phase. The welding current and the respective times can

also be set individually for each phase here.


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Machines and processes from EWM the optimum solution for every need.

Our welding systems enable our customers to carry out their individual welding tasks faster, for less

money and with top quality.

Overview of innovative TIG/plasma processes

Control Smart Classic Comfort Synergic

Tetrix

Tetrix plasma

Tetrix cold/hot wire

activArc

spotArc

Cold/hot wire

forceTig


43/144

Detailed information can be found in our product catalogue.

Overview of innovative TIG/plasma functions

Control Smart Classic Comfort Synergic

Spotmatic

Spot welding

Pulsing

Automated pulsing

kHz pulsing

Additional functions of AC/DC welding machines

AC pulsing

AC special

AC balance

AC frequency

AC wave forms


44/144


45/144

The EWM TIG Primer


1 10.09

Contents

1 Preface.................................................................................................................................................. 2

2 The process .......................................................................................................................................... 22.1 General ............................................................................................................................................ 22.2 Current type ..................................................................................................................................... 32.3 Electrodes ........................................................................................................................................ 3

2.4 Shielding gases................................................................................................................................ 4

3 Groove preparation ............................................................................................................................... 53.1 Groove shapes................................................................................................................................. 53.2 Placement of the weld groove side walls side walls ........................................................................ 53.3 Backing ............................................................................................................................................ 53.4 Forming............................................................................................................................................ 5

4 The welding torch.................................................................................................................................. 64.1 Cooling............................................................................................................................................. 64.2 Torch design .................................................................................................................................... 74.3 Shape of the electrode tip................................................................................................................ 7

5 Welding machines................................................................................................................................. 8

5.1 Control ............................................................................................................................................. 85.2 Power sources ................................................................................................................................. 9

6 Performing welding work..................................................................................................................... 116.1 Choice of welding filler................................................................................................................... 116.2 Setting the shielding gas quantity .................................................................................................. 116.3 Cleaning the workpiece surface..................................................................................................... 126.4 Igniting the arc ............................................................................................................................... 126.5 Moving the torch ............................................................................................................................ 136.6 Magnetic arc blow.......................................................................................................................... 136.7 Welding positions........................................................................................................................... 146.8 Set welding parameters ................................................................................................................. 146.9 Welding with current pulses........................................................................................................... 15

6.10 Automation options ........................................................................................................................ 166.11 Work safety .................................................................................................................................... 16

7 Special features of different materials ................................................................................................ 177.1 Unalloyed and non-alloy steels...................................................................................................... 187.2 Austenitic CrNi steels..................................................................................................................... 187.3 Aluminium and aluminium alloys ................................................................................................... 187.4 Copper and copper alloys.............................................................................................................. 207.5 Other materials .............................................................................................................................. 20

8 Applications for TIG welding ............................................................................................................... 218.1 Uses in manufacturing ................................................................................................................... 218.2 Example applications..................................................................................................................... 21

9 Literature ............................................................................................................................................. 22

10 Imprint ................................................................................................................................................. 23


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The EWM TIG Primer


2 10.09

1 PrefaceThe TIG welding process (Figure 1) thefull name of this process irrespective toDIN 1910 Part 4 is Tungsten Inert Gaswelding originated in the USA where in1936 it was known as argon arc welding.It was not introduced to Germany until af-ter the Second World War. The processdiffers from other fusion welding tech-niques in that it offers various interestingadvantages. For example, it is a generalpurpose technique. If a metallic materialis suitable for fusion welding, it can bejoined using this process. It is also a very"clean" process which generates virtuallyno spatter and a minimal amount of

harmful substances and when used cor-rectly, guarantees a high quality weldedjoint.

Another significant advantage of TIGwelding is that unlike other processeswhich use melting electrodes, there is nocorrelation between the addition of weld-ing filler material and the current intensity.This means that the welder can matchthe current optimally to the welding taskand only add the quantity of welding fillermaterial actually required. This makes theprocess especially well suited to weldingroot passes and for out-of-position weld-ing. These advantages have meant thatthe TIG process is used successfully inmany sectors of trade and industry today.However, for manual welding it does de-mand special skills on the part of thewelder, and a good level of training. This

brochure explains the particular featuresof this process and may even generateinterest in companies who are not yet us-ing the technique despite having welding

tasks which would be suitable for theprocess.

2 The process2.1 General

TIG welding is a gas-shielded weldingprocess with non-consumable electrode(Process No. 14). ISO 857-1 describesthe process as follows:

"Gas-shielded arc welding process usinga non-consumable electrode made frompure or doped tungsten in which the arcand the welding molten pool is protectedby a gas coating made from inert gas"

With tungsten inert gas welding (processno. 141) the arc burns freely, with plasmaarc welding (process no. 15), which isanother gas-shielded welding process us-ing a non-consumable electrode, it isconstricted. Figure 2 shows a diagram of

the process.

Figure 1 TRITON 260 DC, TIG welding ofcooling spirals

Torch

T-electrode

Seam

Molten bath

Arc

Welding rod

Parent material

Figure 2 Principle of TIG welding


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The EWM TIG Primer


3 10.09

The process is named after the type ofelectrode (tungsten) and the shieldinggas used (inert). The electrode does notmelt due to the high melting point oftungsten (3380C) when the process isused correctly. It acts solely as the arccarrier. The welding filler is added byhand in the form of a bar or with fullyautomated welding as a wire via a sepa-rate feed system. The shielding gas is

emitted from the shielding gas nozzle andsurrounds the electrode concentrically,protecting the electrode and the weldmetal underneath it from the atmosphere.

2.2 Current typeDirect current is normally used for TIGwelding. When welding steel and manyother metals and alloys, the colder minuspole is positioned against the electrodeand the hotter plus pole on the work-piece. The current-carrying capacity andthe service life of the electrode are con-siderably greater with this polarity thanwith plus pole welding. Alternating currentis used with aluminium and aluminium al-loys, and with some bronzes, in otherwords materials which form high-meltingor highly viscous oxides. This will be cov-ered in more detail later on. When weld-ing with alternating current, the current-

carrying capacity also is

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