Basic Welding ESAB

Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_1.ht

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Lesson 1 The Basics of A Welding

Current Chapter Table of Contents

Lesson 2 Common Electri

Arc Welding Processes

Lesson 3 Covered Electrodes

for Welding Mild Steels

BASIC WELDING FILLER METAL

TECHNOLOGY

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for Welding Low Alloy Steels A Correspondence Course

Glossary


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Lesson 5 Welding Filler Metals for Stainless Steels

Lesson 6 Carbon & Low Alloy Steel Filler Metals - GMAW,GTAW,SAW

LESSON II COMMON ELECTRIC ARC

WELDING PROCESSES

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Lesson 7 Flux Cored Arc

Electrodes Carbon Low Alloy Steels

Lesson 8 Hardsurfacing

Electrodes

Lesson 9 Estimating &

Comparing Weld Metal Costs

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Cutting Products

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Lesson 10 Reliability of Welding

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Lesson 1

The Basics of Arc Welding

TABLE OF CONTENTS

LESSON II COMMON ELECTRIC ARC WELDING

PROCESSES

Current

Chapter

Table of

Contents

Lesson 2

Common Electric

Arc Welding

Processes

Go To Test Lesson 3 Section Nr. Section Title Page

Covered Electrodes for Welding Print

Mild Steels 2.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2.2 SH IELDED METAL ARC WELDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 . 2. 1 E q u ip me n t & O p e r a t io n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 . 2. 2 W e ld in g P o w e r S o u r c e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 . 2. 3 E le c t r o d e Ho ld e r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 . 2. 4 G r o u nd C la mp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 . 2. 5 W e ld in g C a b le s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 . 2. 6 C o a t e d E le c t r o d e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.3 GAS -TUNGSTEN ARC WELDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2 . 3. 1 E q u ip me n t & O p e r a t io n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2 . 3. 2 P o w e r So u r c e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2 . 3. 3 T o r c he s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0

2 . 3. 4 S h ie ld ing G a s e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1

2 . 3. 5 E le c t r o d e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2

2 . 3. 6 S u mma r y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3

2.4 GAS METAL ARC WELDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2 . 4. 1 Cur r e nt De ns it y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2 . 4. 2 M e t a l T r a ns fe r Mo d e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 5

2 . 4. 3 E q u ip me n t a nd O p e r a t io n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2 . 4. 4 P o w e r S o u r c e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 8

2 . 4. 5 W ir e Fe e d e r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2 . 4. 6 We ld ing G u n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

2 . 4. 7 S h ie ld ing G a s e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1

2 . 4. 7 .1 S ho r t C ir c u i t i ng T r a ns fe r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

2 . 4. 7 .2 S p r a y Ar c T r a n s f e r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3

Lesson 10

Reliability of Welding

Filler Metals

© C O P Y R IG HT 2 0 0 0 T H E E S AB G R O UP , I N C

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Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5

Welding Filler Metals

for Stainless Steels

Lesson 6

Carbon & Low Alloy

Steel Filler Metals -

GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs


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© COPYRIGHT 2000 THE ESOS GROUP,

INC

Lesson 1 The Basics of Arc

Welding TABLE OF CONTENTS

LESSON II- Con't .

Lesson 2

Common Electric

Arc Welding

Processes Section Nr. Section Title Page

Lesson 3

2.4.7.3 Pulse Spray Transfer ........................................................ 23

Covered Electrodes for Welding

2.4.8 Electrodes ........................................................................................ 23

Mild Steels 2.5 FLUX CORED ARC WELDING ...................................................... 24

2.5.1 Sell-Shielded Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Lesson 4 2.5.2 Gas Shielded

Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Covered Electrodes for Welding Low 2.5.3 Current Density

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

26

Alloy Steels 2.5.4 Equipment ........................................................................................ 26

2.5.5 Power Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

2.5.6 Wire Feeder ..................................................................................... 26 Lesson 5

Welding Filler Metals 2.5.7 Welding Guns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

for Stainless Steels 2.5.8 Shielding Gases ............................................................................... 27

2.6 SUBMERGED ARC WELDING ...................................................... 27

Lesson 6 2.6.1 Submerged Arc Flux. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Carbon & Low Alloy 2.6.2 The Welding

Gun. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

28

Steel Filler Metals - GMAW,GTAW,SAW 2.6.3 Power Sources ................................................................................. 28

2.6.4 Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2.6.5 Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Lesson 7

Flux Cored Arc 2.6.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Electrodes Carbon

Low Alloy Steels 2.7 ELECTROSLAG AND ELECTROGAS WELDING ......................... 30

2.7.1 Electroslag Welding.......................................................................... 30

2.7.2 Flux .................................................................................................. 30 Lesson 8

Hardsurfacing 2.7.3 Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Electrodes 2.7.4 Equipment........................................................................................ 31

2.7.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

31

Lesson 9 Appendix A- GLOSSARY OF TERMS ................................................................ 32 Estimating &

Comparing Weld

Metal Costs

Lesson 10


Filler Metals

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COMMON ELECTRIC ARC WELDING PROCESSES

2 . 1 INTRODUCTION

After much ex perimentation by others in the ear(y 1800's, an Eng(ishman named Wi(de

obtained the first e(ectric we(ding patent in 1865. He successfu((y joined two sma(( pieces of

iron by passing an e(ectric current through both pieces producing a fusion we(d. Approximate(y

twenty years (ater, Bernado, a Russian, was granted a patent for an e(ectric arc we(ding

process in which he maintained an arc between a carbon e(ectrode and the pieces to be

joined, fusing the meta(s together as the arc was manua((y passed o'er the joint to be we(ded.

2.1.0.1 During the 1890's, arc we(ding was accom p(ished with bare meta( e(ectrodes that

were consumed in the mo(ten pudd(e and became part of the we(d meta(. The we(ds were of

poor qua(ity due to the nitrogen and oxygen in the atmosphere forming harmfu( oxides and

nitrides in the we(d meta(. Ear(y in the Twentieth Century, the im portance of shie(ding the arc

from the atmosphere was rea(ized. Co2ering the e(ectrode with a materia( that decomposed in

the heat of the arc to form a gaseous shie(d appeared to be the best method to accom p(ish

this end. As a resu(t, 2arious methods of co2ering e(ectrodes, such as wrapping and dipping,

were tried. These efforts cu(minated in the extruded coated e(ectrode in the mid - 1920's,

great(y im pro2ing the qua(ity of the we(d meta( and pro2iding what many consider the most

significant ad2ance in e(ectric arc we(ding.

2.1.0.2 Since we(ding with coated e(ectrodes is a rather s(ow procedure, more rapid

we(ding processes were de2e(oped. This (esson wi(( co'er the more common(y used e(ectric

arc we(ding processes in use today.

2.2 SHIELDED METAL ARC WELDING

Shielded Metal Arc Welding*, a(so known as manua( meta( arc we(ding, stick we(ding, or e(ectric arc

we(ding, is the most wide(y used of the 2arious arc we(ding processes. We(ding is performed with

the heat of an e(ectric arc that is maintained between the end of a coated meta( e(ectrode and the

work piece (See Figure 1). The heat produced by the arc me(ts the base meta(, the e(ectrode

core rod, and the coating. As the mo(ten meta( drop(ets are transferred across the arc and into

the mo(ten we(d pudd(e, they are shie(ded from the atmosphere by the gases produced from the

decom position of the f(ux coating. The mo(ten s(ag f(oats to the top of the we(d pudd(e where it

protects the we(d meta( from the atmosphere during so(idification.



Welding

LESSON II

Current

Chapter

T a b l e o f

Contents

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels

Lesson 8 Hardsurfacin Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

Lesson 10

Reliability of Weldin

Filler Metals

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Welding

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

Lesson 10


Filler Metals

Other functions of the coating are to provide

arc stabi(ity and contro( bead shape. More

information on coating functions wi(( be

covered in subsequent (essons.

* Shielded Metal Arc Welding (SMAW) is the

terminologyapproved by the American Welding

Society.

2.2.1 Equipment & Operation - One

reason for the wide acceptance of the SMAW

process is the simp(icity of the necessary

equipment. The equipment consists of the fo((owing

items. (See Figure 2)

1. We(ding power source

2. E(ectrode ho(der

3. Ground c(amp

4. We(ding cab(es and connectors

5. Accessory equipment (chipping

hammer, wire brush)

1. Protective equipment (he(met, g(oves, etc.)


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MOLTEN

POOL

LESSON II

COATING

CORE ROD

SHIELDING G A S E S S O L I D I F I E

D SLAG

WELD METAL

WORK PIECE

SHIELDED METAL ARC WELDING

FIGURE 1

AC OR DC POWER SOURCE

ELECTRODE

CABLE

ELECTRODE HOLDER

ELECTRODE

GROUND

CABLE WORK

SHIELDED METAL ARC WELDING CIRCUIT

FIGURE 2

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2.2.2 Welding Power Sources - Shie(ded meta( arc we(ding may uti(ize either

a(ternating current (AC) or direct current (DC), but in either case, the power source se(ected

must be of the constant current type. This type of power source wi(( de(iver a re(ative(y constant

amperage or we(ding current regard(ess of arc (ength variations by the operator (See Lesson I,

Section 1.9). The amperage determines the amount of heat at the arc and since it wi(( remain

re(ative(y constant, the we(d beads produced wi(( be uniform in size and shape.

2.2.2.1 Whether to use an AC, DC, or ACIDC power source depends on the type of we(ding

to be done and the e(ectrodes used. The fo((owing factors shou(d be considered:

1. Electrode Selection - Using a DC power source a((ows the use of a greater range of

e(ectrode types. Whi(e m ost of the e(ectrodes are designed to be used on AC or

DC, some wi(( work proper(y on(y on DC.

2. Metal Thickness - DC power sources may be used for we(ding both heavy

sections and (ight gauge work. Sheet meta( is m ore easi(y we(ded with DC

because it is easier to strike and maintain the DC arc at (ow currents.


1 din 1 23.11.2009 10:24

Turn Pages

Lesson 1

The Basics of Arc

Welding

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels

Lesson 8

Hardsurfacing

Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

LESSON II

3. Distance from Work - If the distance from the work to the power source is great,

AC is the best choice since the voltage drop through the cables is lower than with

DC. Even though welding cables are m ade of copper or aluminum (both good

conductors), the resistance in the cables becomes greater as the cable length

increases. In other words, a voltage reading taken between the electrode and the

work will be somewhat lower than a reading taken at the output terminals of the

power source. This is known as voltage drop.

4. Welding Position (See Appendix A - Glossary of Terms) - Because DC may be

operated at lower welding currents, it is more suitable for overhead and vertical

welding than AC. AC can successfully be used for out-of-position work if proper

electrodes are selected.

5. Arc Blow- When welding with DC, m agnetic fields are set up throughout the

weldment. In weldments that havevarying thickness and protrusions, this m agnetic

field can affect the arc by m aking it stray or fluctuate in direction. This condition is

especially troublesome when welding in corners. AC seldom causes this problem

because of the rapidly reversing m agnetic field produced.

2.2.2.2 Combination power sources that produce both AC and DC are av ailable and

provide the versatility necessary to select the proper welding current for the application.

2.2.2.3 When using a DC power source, the question of whether to use electrode negative

or positive polarity arises. Some electrodes operate on both DC straight and reverse polarity,

and others on DC negative or DC positive polarity only. Direct current flows in one direction in

an electrical circuit and the direction of current flow and the composition of the elec trode

coating will have a definite effect on the welding arc and weld bead. Figure 3 shows the

connections and effects of straight and reverse polarity.

2.2.2.4 Electrode negative (-) produces welds with shallow penetration; however, the

electrode melt-off rate is high. The weld bead is rather wide and shallow as shown at 'A' in

Figure 3.

Electrode

p o s i t i v e ( + )

produces welds

with deep

penetration and a

narrower weld

bead as shown at

'B' in Figure 3.

STRAIGI-T POLARITY REVERSE POLARITY

Lesson 10 FIGURE 3


Filler Metals

© COPYRIGI-T 1998 TI-E ESAB GROUP, INC.

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WORK PIECE WORK PIECE

DC POWER SOURCE

I-IGI-ER BURN-OFF RATE, LESS PENETRATION

ELECTRODE

A

DEEP PENETRATION, LOW BURN-OFF RATE

ELECTRODE

B DC

POWER SOURCE


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Welding

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrode

for Welding

Mild Steels

Lesson 4

Covered Electrode

for Welding Low

Alloy Steels

Lesson 5

Welding Filler Metal


Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

Lesson 10


Filler Metals

LESSON II

2.2.2.5 While polarity affects the penetration and burn-off rate, the electrode coating also

has a strong influence on arc characteristics. Perform ance of indi.idual electrodes will be

discussed in succeeding lessons.

2.2.3 Electrode Holder-The electrode holder connects to the welding cable and con-

ducts the welding current to the electrode. The insulated handle is used to guide the electr ode

o'er the weld joint and feed the electrode o'er the weld joint and feed the electrode into the

weld puddle as it is consumed. Electrode holders are a. ailable in different sizes and are rated

on their current carrying capacity.

2.2.4 Ground Clamp - The ground clamp is used to connect the ground cable to the work

piece. It m ay be connected directly to the work or to the table or fixture upon which the work is

positioned. Being a part of the welding circuit, the ground clamp must be capable of carrying

the welding current without o.erheating due to electrical resistance.

2.2.5 Welding Cables - The electrode cable and the ground cable are important parts of

the welding circuit. They must be .ery flexible and ha.e a tough heat -resistant insulation.

Connections at the electrode holder, the ground clamp, and at the power source lugs must be

soldered or well crimped to assure low electrical resistance. The cross -sectional area of the

cable must be sufficient size to carry the welding current with a minimum of oltage drop.

Increasing the cable length necessitates increasing the cable diameter to lessen resistance

and voltage drop. The table in Figure 4 lists the suggested Mmerican Wire Gauge (MWG)

cable size to be used for .arious welding currents and cable lengths.

Welding Total Cable Length (Ground Lead Plus Electrode Lead) Voltage

Ser.ice Upto50 ft. Upto 100 ft. Upto250 ft. Upto500 ft. Drop

Range Cable Voltage Cable Voltage Cable Voltage Cable Voltage Figured

(Mmperes) Size Drop Size Drop Size Drop Size Drop Mt

20to 180 #3 1.8 #2 2.9 #1 5.7 #0 9.1 180 Mmps

30 to 250 #2 1.8 #1 2.5 #0 5.0 #0 9.9 200 Mmps

60 to 375 #0 1.7 #0 3.0 #00 5.9 #000 9.3 300 Mmps

80 to 500 #00 1.8 #000 2.5 #0000 5.0 #0000 9.9 400 Mmps

100to600 #00 2.0 #0000 2.5 ... ... ... 500Mmps

Voltage drops indicated do not include any drop caused by poor connection, electrode holder, or work metal

FIGURE 4

2.2.6 Coated Electrodes - Various types of coated electrodes are used in shielded

metal arc welding. Electrodes used for welding mild or carbon steels are quite different than

those used for welding the low alloys and stainless steels. Details on the specific types will be

covered in subsequent lessons.

© C OP YRIG HT 1 9 9 8 T HE E SM B GRO UP , I NC

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Gas Tungsten Arc Welding* is a welding process performed using the heat of an arc

established between a nonconsumable tungsten electrode and the work piece. See Figure 5.

The electrode, the arc, and the area surrounding the molten weld puddle are protected from

the atmosphere by an inert gas shield. The electrode is not consumed in the weld puddle as in

shielded metal arc welding. If a filler metal is

necessary, it is added to the leading

the molten puddle as shown in

2.3.0.1 Gas tungsten arc

welding

produces exceptionally clean welds no

slag is produced, the chance inclusions in

the weld metal is

and the finished weld requires virtually

no cleaning. Argon

and Helium, the primary

shielding gases em ployed,

are inert gases. Inert gases

do not chemically

combine with other

elements and therefore, are used to exclude

the reactive gases, such as oxygen and

nitrogen, from forming com pounds that could be

detrimental to the weld metal.

2.3.0.2 Gas tungsten arc welding may be used for welding almost all metals - mild

steel,

low alloys, stainless steel, copper and copper alloys, aluminum and aluminum alloys, nickel

and nickel alloys, magnesium and magnesium alloys, titanium, and others. This process is

most extensively used for welding aluminum and stainless steel alloys where weld integrity is of

the utmost im portance. Another use is for the root pass (initial pass) in pipe welding, which

requires a weld of the highest quality. Full penetration without an excessively high inside bead is

im portant in the root pass, and due to the ease of current control of this process, it lends itself

to control of back-bead size. For high quality welds, it is usually necessary to provide an inert

shielding gas inside the pipe to prevent oxidation of the inside weld bead.

* Gas Tungsten Arc Welding (GTAW) is the current terminology approved by the American Welding Society,

formerly known as "TIG" (Tungsten Inert Gas) welding.

© COPYRIGHT 1998 THE ESAB GROUP, INC


Welding 2 . 3 GAS TUNGSTEN ARC WELDING

LESSON II

Current

Chapter

Table of

Contents

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

Lesson 10


Filler Metals

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TRAVEL

DIRECTION TORCH

TUNGSTEN

ELECTRODE

ARC SHIELDING GAS

NOZZLE

INERT GAS

SHIELD

FILLER

@ETAL WORK PIECE

GAS TUNGSTEN ARC WELDING

IGURE 5


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Welding

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

LESSON II

2.3.0.3 Gas tungsten arc welding lends itself to both manual and automatic operation. In

manual operation, the welder holds the torch in one hand and directs the arc into the weld joint.

The filler metal is fed manually into the leading edge of the puddle. In automatic applications,

the torch may be automatically mo' ed o' er a stationary work piece or the torch may be

stationary with the work mo' ed or rotated in relation to the torch. Filler metal, if required, is

also fed automatically.

2 . 3 . 1 EQU IPMENT AND OPERAT ION - Gas tungsten arc welding may be accomplished

with relati' ely simple equipment, or it may require some highly sophisticated components.

Choice of equipment depends upon the type of metal being joined, the position of the weld

being made, and the quality of the weld metal necessary for the application. The basic equip -

ment consists of the following:

1. The power source

2. Electrode holder (torch)

3. Shielding gas

4. Tungsten electrode

5. Water supply when necessary

6. Ground cable

7. Protecti'e equipment

Figure 6 shows a basic gas tungsten arc welding schematic.

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Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels

L e s s o n 8 Hardsurfacing

Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

SHIELDING GAS SUPPLY GAS TUNGSTEN ARC WELDING CONNECTION SCHEMATIC

REGULATOR FLOW METER

GAS HOSE (WATER COOLED ONLY)

GAS COOLED ONLY TORCH

*COMPOSITE CABLE

WELDING CABLE WATER COOLER

WORK

*COMPOSITE CABLE GAS COOLED TORCH. CURRENT IN & GASIN.

WATER COOLED TORCH. CURRENT IN & WATER OUT

POWER SOURCE WATER

T O TORCH

WATER FROM TORCH

GROUND CABLE

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1 din 1 23.11.2009 10:24

FIGURE 6

Lesson 10


Filler Metals

© COPYRIGHT 1998 THE ESAB GROUP, INC.


1 din 1 23.11.2009 10:24

LESSON II

2 .3 .2 Power Sources - Both AC and DC power sources are used in gas tungsten arc

we(ding. They are the constant current type with a drooping vo(t-ampere curve. This type of

power source produces very s(ight changes in the arc current when the arc (ength (vo(tage) is

varied. Refer to Lesson I, Section 1.9.

2.3.2.1 The choice between an AC or DC we(der depends on the type and thickness of the

meta( to be we(ded. Distinct differences exist between AC and DC arc characteristics, and if

DC is chosen, the po(arity a(so becomes an important factor. The effects of po(arity in GTAW

are direct(y opposite the effects of po(arity in SMAW as described in paragraphs 2.2.2.3

through 2.2.2.5. In SMAW, the distribution of heat between the e(ectrode and work, which

determines the penetration and we(d bead width, is contro((ed main(y by the ingredients in the

f(ux coating on the e(ectrode. In GTAW where no f(ux coating exists, heat distribution between

the e(ectrode and the work is contro((ed so(e(y by the po(arity. The choice of the proper we(ding

current wi(( be better understood by ana(yzing each type separate(y. The chart in Figure 7 (ists

current recommendations.

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Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

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Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

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WELDING CURRENT SHIELDING GAS

Material& AC Thickness DCEN DCEP High Freq. Argon Helium Ar/He

A(uminum Under 1/8 2 1 1 2 Over1/8' 2&3 1 1 3 2

Magnesium Under1/16" 2 1 1 2 Over 1/16 1 1

Carbon Stee(

Under 1/8 1

1

Over1/8' 1 1 2 3

Stain(ess Stee(

Under 1/8 1

1

2

Over 1/8' 1 1 2

Copper Under 1/8 1 1

Over 1/8 1 1

Nicke( A((oys Under 1/8 1 1 3 2

Over 1/8' 1 2 1

Titanium Under 1/8 1 1 2 Over 1/8' 2 1


1 din 1 23.11.2009 10:24

Lesson 9

Estimating &

Comparing Weld

Metal Costs

1. Preferred Choice - Manua( We(ding 2. Preferred Choice - Automatic We(ding 3. Second Choice - Automatic We(ding

CURRENT/SHIELDING GAS SELECTION, TUNGSTEN GAS ARC WELDING

FIGURE 7

Lesson 10


Filler Metals



1 din 1 23.11.2009 10:24

Lesson 1

The Basics of Arc

Welding

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels

Lesson 8

Hardsurfacing

Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

Lesson 10


Filler Metals

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Electrode

Polarity Penetration

O , i d e

Cleaning

I-eat

Concentration

Direct Current Deep

Penetration None At Straight Polarity Narrow Work

Electrode Negative Bead

Medium Penetration Good Cycle

Alternating Current Medium Width Cleans O,ide Alternates Between

Bead on Each I-alf Electrode and Work

Direct Current

Reverse Polarity

Shallow Penetration

Wide Bead

Ma,imum

At

Electrode

Electrode Positive

LESSON II

2.3.2.2 Direct current electrode negative (DCEN) is produced when the electrode is

connected to the negative terminal of the power source. Since the electrons flow from the

electrode to the plate, appro,imately 70% of the heat of the arc is concentrated at the work,

and appro,imately 30% at the electrode end. This allows the use of smaller tungsten elec -

trodes that produce a relatively narrow concentrated arc. The weld shape has deep penetra-

tion and is quite narrow. See Figure 8. Direct current electrode negative is suitable for weld -

ing most metals. Magnesium and aluminum have a refractory o,ide coating on the surface that

must be physically removed immediately prior to welding if DCSP is to be used.

2.3.2.3 Direct current electrode positive (DCEP) is produced when the electrode is

connected to the positive terminal of the welding power source. In this condition, the electrons

flow from the work to the electrode tip, concentrating appro,imately 70% of the heat of the arc

at the electrode and 30% at the work. This higher heat at the electrode necessitates using

larger diameter tungsten to prevent it from melting and contaminating the weld metal. Since

the electrode diameter is larger and the heat is less concentrated at the work, the resultant

weld bead is relatively wide and shallow. See Figure 8.

" GAS IONS

E L E C T R O N FLOW

!

! "

"

!

EFFECTS OF CURRENT TYPE - GAS TUNGSTEN ARC WELDING

FIGURE

2.3.2.4 Aluminum and magnesium are two metals that have a heavy o,ide coating that acts

as an insulator and must be removed before successful welding can take place. Welding with

electrode positive provides a good o,ide cleaning action in the arc. If we were to study the

physics of the welding arc, we find that the electric current causes the shielding gas atoms to

lose some of their electrons. Since electrons are negatively charged, these gas atoms now

are unbalanced and have an e,cessive positive charge. As we learned in Lesson I, unlike

charges attract. These positively charged atoms (or positive ions as they are known in

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Welding

Lesson 2 Common Electric


Lesson 3 Cove red Electrodes


Lesson 4 Cove red Electrodes for Welding Low

Alloy Steels






Electrodes


Comparing Wel Metal Costs


Filler Metals

LESSON II

chemical terminology) are attracted to the negative pole, in this case the work, at high velocity.

Upon striking the work surface, they dislodge the oxide coating permitting good electrical

conductivity for the maintenance of the arc, and elimi nate the impurities in the weld metal that

could be caused by these oxides.

2.3.2.5 Direct current electrode positive is rarely used in gas-tungsten arc welding. Despite

the excellent oxide cleaning action, the lower heat input in the weld area makes it a slow

process, and in metals having higher thermal conductivity, the heat is rapidly conducted away

from the weld zone. When used, DCEP is restricted to welding thin sections (under 118') of

magnesium and alumi num.

2.3.2.6 Alternating current is actually a combination of DCEN and DCEP and is widely

used for welding alumi num. In a sense, the adva ntages of both DC processes are combined,

and the weld bead produced is a compromise of the two. Remember that when welding with

60 Hz current, the electron flow from the electrode tip to the work reverses direction 120 times

every second. Thereby, the intense heat alternates from electrode to work piece, allowing the

use of an intermediate size electrode. The weld bead is a compromise having medium

penetration and bead width. The gas ions blast the oxides from the surface of alumi num and

magnesium during the positive half cycle. Figure 8 illustrates the effects of the different types

of current used in gas-tungsten arc welding.

2.3.2.7 DC constant current power sources - Constant current power sources, used for

shielded metal arc welding, may also be used for gas-tungsten arc welding. In applications

where weld integrity is not of utmost importance, these power sources will suffice. With

machines of this type, the arc must be initiated by touching the tungsten electrode to the work

and quickly withdrawi ng it to maintain the proper arc length. This starting method

contami nates the electrode and blunts the point which has been grounded on the electrode

end. These conditions can cause weld metal inclusions and poor arc direction. Using a

power source designed for gas tungsten arc welding with a high frequency stabilizer will

elimi nate this problem. The electrode need not be touched to the work for arc initiation.

Instead, the high frequency voltage, at very low current, is superimposed onto the welding

current. When the electrode is brought to within approximately 118 inch of the base metal, the

high frequency ionizes the gas path, making it conductive and a welding arc i s established.

The high frequency is automatically turned off immediately after arc initiation when using direct

current.

2.3.2.8 AC Constant Current Power Source - Designed for gas tungsten arc welding,

always incorporates high frequency, and it is turned on throughout the weld cycle to maintain a

stable arc. When welding with AC, the current passes through 0 twice in every cycle and the



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Welding

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

Lesson 10


Filler Metals

LESSON II

arc must be reestablished each time it does so. The oxide coating on metals, such as

aluminum and magnesium, can act much like a rectifier as discussed in Lesson I. The positi,e

half-cycle will be eliminated if the arc does not reignite, causing an unstable condition.

Continuous high frequency maintains an ionized path for the welding arc, and assures arc

re-ignition each time the current changes direction. AC is extensi,e ly used for welding

aluminum and magnesium.

2.3.2.9 AC/DC Constant Current Power Sources - Designed for gas tungsten arc

welding, are a,ailable, and can be used for welding practically all metals. The gas tungsten

arc welding process is usually chosen because of the high quality welds it can produce. The

metals that are commonly welded th this process, such as stainless steel, aluminum and

some of the more exotic metals, cost many times the price of mi ld steel; and therefore, the

power sources designed for this process ha,e many desirable features to insure high quality

welds. Among these are:

1. Remote current control, which allows the operator to control welding amperage ith a

hand control on the torch, or a foot control at the welding station.

2. Automatic soft-start, which presents a high current surge when the arc is

initiated.

. Shielding gas and cooling water solenoid valves, which automatically control

flow before, during and for an adjustable length of time after the weld is comp leted.

4. Spot-weld timers, which automatically control all elements during each

spot-weld cycle.

Other options and accessories are also a,ailable.

2.3.2.10 Power sources for automatic welding with complete programmable output are also

a,ailable. Such units are used extensi,e ly for the automatic welding of pipe in position. The

welding current is automatically ,aried as the torch tra,e ls around the pipe. Some units

pro,ide a pulsed welding current where the amperage is automatically ,aried between a low

and high se,eral times per second. This produces welds th good penetration a nd impro,ed

weld bead shape.

2 .3 .3 Torches - The torch is actually an electrode holder that supplies welding current to

the tungsten electrode, and an inert gas shield to the arc zone. The electrode is held in a

collet-like clamping de,ice that allows adjustment so that the proper length of electrode pro -

trudes beyond the shielding gas cup. Manual torches are designed to accept electrodes of 3


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Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

Lesson 10


Filler Metals

LESSON II

inch or 7 inch lengths. Torches may be either air or water-cooled. The air-cooled types actu-

ally are cooled to a degree by the shielding gas that is fed to the torch head through a compos -

ite cable. The gas actually surrounds the copper welding cable, affording some degree of

cooling. Water-cooled torches are usually used for applications where the welding current

exceeds 200 amperes. The water inlet hose is connected to the torch head. Circulat ing

around the torch head, the water leaves the torch via the current -in hose and cable assembly.

Cooling the welding cable in this manner allows the use of a smaller diameter cable that is

more flexible and lighter in weight.

2.3.3.1 The gas nozzles are made of ceramic materials and are available in various sizes

and shapes. In some heavy duty, high current applications, metal water -cooled nozzles are

used.

2.3.3.2 A switch on the torch is used to energize the electrode with welding current and start

the shielding gas flow. High frequency current and water flow are also initiated by this switch if

the power source is so equipped. In many installations, these functions are initiated by a foot

control that also is capable of controlling the welding current. This method gives the operator

full control of the arc. The usual welding method is to start the arc at a low current, gradually

increase the current until a molten pool is achieved, and welding begins. At the end of the

weld, current is slowly decreases and the arc extinguished, preventing the crater that forms at

the end of the weld when the arc is broken abruptly.

2 .3 .4 Shielding Gases - Argon and helium are the major shielding gases used in gas

tungsten arc welding. In some applications, mixtures of the two gases prove advantageous.

To a lesser extent, hydrogen is mixed with argon or helium for special applications.

2.3.4.1 Argon and helium are colorless, odorless, tasteless and nontoxic gases. Both are

inert gases, which means that they do not readily combine with other elements. They will not

burn nor support combustion. Commercial grades used for welding are 99.99% pure. Argon

is .38% heavier than air and about 10 times heavier than helium. Both gases ionize when

present in an electric arc. This means that the gas atoms lose some of their electrons that

have a negative charge. These unbalanced gas atoms, properly called positive ions, now

have a positive charge and are attracted to the negative pole in the arc. Whe n the arc is

positive and the work is negative, these positive ions impinge upon the work and remove

surface oxides or scale in the weld area.

2.3.4.2 Argon is most commonly used of the shielding gases. Excellent arc starting and

ease of use make it most desirable for manual welding. Argon produces a better cleaning

action when welding aluminum and magnesium with alternating current. The arc produced is


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Welding

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

Lesson 10


Filler Metals

LESSON II

relatively narrow. Argon is m ore suitable for welding thinner material. At equal amperage,

helium produces a higher arc voltage than argon. Since welding heat is the product of volts

times amperes, helium produces m ore available heat at the arc. This makes it m ore suitable

for welding heavy sections of metal that have high heat conductivity, or for automatic welding

operations where higher welding speeds are required.

2.3.4.3 Argon-helium gas mixtures are used in applications where higher heat input and the

desirable characteristics of argon are required. Argon, being a relatively heavy gas, blankets

the weld area at lower flow rates. Argon is preferred for many applications because it costs

less than helium.

2.3.4.4 Helium, being approximately 10 times lighter than argon, requires flow rates of 2

3 times that of argon to satisfactorily shield the arc.

2.3.5 Electrodes - Electrodes for gas tungsten arc welding are available in diameters

from .010' to 114' in diameter and standard lengths range from 3' to 24'. The m ost comm only

used sizes, however, are the .040', 1116', 3132', and 118' diameters.

2.3.5.1 The shape of the tip of the electrode is an imp ortant factor in gas tungsten arc

welding. When welding with DCEN, the tip must be ground to a point. The included angle at

which the tip is ground varies with the application, the electrode diameter, and the welding

current. Narrowjoints require a relatively small included angle. When welding very thin

material at low currents, a needlelike point ground onto the smallest available electrode may

be necessary to stabilize the arc. Properly ground electrodes will assure easy arc starting,

good arc stability, and proper bead width.

2.3.5.2 When welding with AC, grinding the electrode tip is not necessary. When proper

welding current is used, the electrode will form a hemispherical end. If the proper welding

current is exceeded, the end will become bulbous in shape and possibly melt off to

contaminate the weld metal.

2.3.5.3 The American Welding Society has published Specification AWS A5.12-80 for

tungsten arc welding electrodes that classifies the electrodes on the basis of their chemical

comp osition, size and finish. Briefly, the types specified are listed below<

1) Pure Tungsten (AWS EWP) Color Code: Green

Used for less critical applications. The cost is low and they give good results at

relatively low currents on a variety of metals. Most stable arc when used on AC, either

balanced waveor continuous high frequency.


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Good current carrying capacity, easy arc starting and pro ide a stable arc. Less susceptible to

contamination. Designed for DC applications of nonferrous materials.

3) 2% Thoriated Tungsten (AWS EWTh-2) Color Code: Red

Longer life than 1% Thoriated electrodes. Maintain the pointed end longer, used for

light gauge critical welds in aircraft work. Like 1%, designed for DC applications for nonferrous

materials.

4) .5% Thoriated Tungsten (AWS EWTh-3) Color Code: Blue

Sometimes called "striped" electrode because it has 1.0-2.0% Thoria inserted in a

wedge-shaped groo e throughout its length. Combines the good properties of pure and

thoriated electrodes. Can be used on either AC or DC applications.

5) Zirconia Tungsten (AWS EWZr) Color Code: Brown

Longer life than pure tungsten. Better performance when welding with AC. Melts more

easily than thoriam-tungsten when forming rounded or tapered tungsten end. Ideal for

applications where tungsten contamination must be minimized.

2.3.6 Summary - Gas Tungsten Arc Welding is one of the major welding processes

today. The quality of the welds produced and the ability to weld ery thin metals are the major

features. The weld metal quality is high since no flux is used, eliminating the problem of slag

inclusions in the weld metal. It is used extensi ely in the aircraft and aerospace industry, where

high quality welds are necessary and also for welding the more expensi e metals where the

weld defects become ery costly. Metals as thin as .005" can be welded due to the ease of

controlling the current.

2.3.6.1 The major disad antages of the process are that it is slower than welding with

consumable electrodes and is little used on thicknesses o er 114"for this reason. Shielding

gas and tungsten electrode costs make the process relati ely expensi e.

2.4 GAS METAL ARC WELDING

Gas Metal Arc Welding* is an arc welding process that uses the heat of an electric arc

established between a consumable metal electrode and the work to be welded. The electrode

is a bare metal wire that is transferred across the arc and into the molten weld puddle. The

* Gas Metal Arc Welding (GMAW) is the current technology approved by the American Welding Society. Formerly known as "M IG" (Metal Inert Gas) Welding.


Welding 2) 1% Thoriated Tungsten (AWS EWTh-1) Color Code: Yellow

LESSON II Current

Chapter

T a b l e o f

Contents

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

Lesson 10


Filler Metals

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Welding

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

Lesson 10


Filler Metals

LESSON II

wire, the weld puddle, and the area in the arc zone are protected from the atmosphere by a

gaseous shield. Inert gases, reacti,e gases, and gas mixtures are used for shielding. The

metal transfer mode is dependent on shielding gas choice and welding current le,el. Figure 9

is a sketch of the process showing the basic features.

MOLTEN POOL

GAS METAL ARC WELDING

FIGURE 9

2.4.0.1 Gas metal arc welding is a ,ersatile process that may be used to weld a wide

,ariety of metals including carbon steels, low alloy steels, stainless steels, aluminum alloys,

magnesium, copper and copper alloys, and nickel alloys. It can be used to weld sheet metal or

relati,ely hea,y sections. Welds may be made in all positions, and the process may be used

for semiautomatic welding or automatic welding. In semiautomatic welding, the wire feed

speed, ,oltage, amperage, and gas flow are all preset on the control equipment. The operator

needs merely to guide the welding gun along the joint at a uniform speed and hold a relati,ely

constant arc length. In automatic welding, the gun is mo unted on a tra,el carriage that mo,es

along the joint, or the gun may be stationary with the work mo,ing or re,ol,ing beneath it.

2.4.0.2 Practically all GMAW is done using DCEP (Electrode positi,e). This polarity

pro,ides deep penetration, a stable arc and low spatter le,els. A small amo unt of GMAW

welding is done with DCEN and although the melting rate of the electrode is high, the arc is

erratic. Alternating current is not used for gas metal arc welding.

2.4.1 Current Density- To understand why gas metal arc welding can deposit weld

metal at a rapid rate, it is necessary that the term ' current density' be understood. Figure 10

shows a 114' coated electrode and a 1116' solid wire drawn to scale. Both are capable of

carrying 400 amperes. Notice that the area of the 1116' wire is only 1116 that of the core wire

of the coated electrode. We can say that the current density of the 1116' wire is 16 times

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GAS SHIELD CONTACT TIP

ARC

WELDING WIRE

WELDING CABLE

SHIELDING GAS

TRAVEL DIRECTION

SOLID WIRE ELECTRODE

GAS NOZZLE

WELD METAL

WORK PIECE

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Lesson I The Basics of Arc

Welding

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 9

Estimating &

Comparing Weld

Metal Costs

Lesson 10


Filler Metals

greater than the current density

of the 114' wire at equal welding

currents. The resultant melt-off

rate of the solid wire is very

high. If we were to increase the

current t h r o u g h t h e

1 1 4 ' c o a t e d electrode to

increase the current density, the

resistance heating

through the 14'electrode length would be excessive, and the rod would

become so hot that the coating would crack, rendering it useless. The 1116'wire carries the

high current a distance of less than 314', the

appro0imate distance from the end of the contact tip to the arc.

2 .4 .2 Metal Transfer Modes

2.4.2.1 Spray transfer is a high current density process that rapidly deposits weld metal in

droplets smaller than the electrode diameter. They are propelled in a straight line from the

center of the electrode. A shielding gas mixture of Argon with 1% to 2% O0ygen is used for

welding mild and low alloy steel, and pure Argon or Argon-Helium mixtures are used for welding

aluminum, magnesium, copper, and nickel alloys. Welding current at which spray transfer

F~GJRE ii

takes place is relatively high and will vary with the metal being welded, electrode diameter, an d

the shielding gas being used. Deposition rates are high and welding is usually limited to the

flat or horizontal fillet position. See Figure 11.



Electrodes

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels

1 2 3 SHORT CIRCUITING ARC METAL TRANSFER

MODES OF METAL TRANSFER

SPRAY TRANSFER

GLOBULAR TRANSFER

PULSE TRANSFER

Current

LESSON I I Chapter Table of

Contents

AREA x .0031 SQ. IN.

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A

1/16'

SOLID WIRE

Print

.049* .0031 x 16

AREA x .049 SQ. IN.

CORE WIRE

FLU( COATING

Ax 16

1/4'

COATED ELECTRODE

RELATIVE SIZE OF ELECTRODES FOR WELDING AT 400 AMPS

F~GJRE10

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Welding





Lesson 4 Covered Electrodes for Welding Low

Alloy Steels






Electrodes




Filler Metals

LESSON II

2.4.2.2 Globular transfer takes place at lower welding currents than spray transfer. There

is a transition current where the transfer changes to globular e'en when shielding gases using

a high percentage of argon are used. When carbon dioxide (CO2) is used as a shielding gas,

the transfer is always globular. In globular transfer, a molten drop larger than the electrode

diameter forms on the end of the electrode, mo'es to the outer edge of the electrode and falls

into the molten puddle. Occasionally, a large drop will 'short circuit' across the arc, causing

the arc to extinguish momentarily, and then instantaneously reignite. As a result, the arc is

somewhat erratic, spatter le'el is high, and penetration shallow. Globular transfer is not

suitable for out-of-position welding. See Figure 11.

2.4.2.3 Short circuiting transfer is a much used method in gas metal arc welding. It is

produced by using the lowest current-'oltage settings and the smaller wires, usually .030',

.035', and .045' diameters. The low heat input makes this process ideal for sheet metal, out -

of-position work, and poor fit-up applications. Often called 'short arc welding'because metal

transfer is achie'ed each time the wire actually short circuits (makes contact) with the weld

puddle. This happens 'ery rapidly. It is feasible for the short circuit frequency to be 20-200

times a second, but in practice, it occurs from 90-100 times a second. Each time the

electrode touches the puddle, the arc is extinguished. It happens so rapidly that it is 'isible

only on high speed films.

2.4.2.4 Pulse transfer is a mode of metal transfer somewhat between spray and short

circuiting. The specific power source has built into it two output le'els: a steady background

le'el, and a high output (peak) le'el. The later permits the transfer of metal across the arc.

This peak output is controllable between high and low 'alues up to se'eral hundred cycles per

second. The result of such a peak output produces a spray arc below the typical transition

current.

2.4.2.4.1 Figure 11 shows the transfer method. The arc is initiated by touching the wire to the

work. 1pon initial contact, a bit of the wire melts off to form a molten puddle. The wire feeds

forward until it actually contacts the work again, as at 1 in Figure 11, and the arc is

extinguished. The short circuiting current causes the wire to neck down, as shown in 1, until it

melts off, as shown at 2. As soon as the wire is free of the puddle, the arc is reignited and a

molten ball forms at the end of the electrode, as at 3. The wire continues to mo'e forward until

it makes contact with the puddle, and the cycle is repeated.

2.4.2.5 Gas metal arc spot welding is a 'ariation of the process that allows spot welding

of thinner gauge metals, or of a thin gauge metal to a hea'ier section. The gun is placed

directly against the work and is equipped with a special nozzle to allow escape of the shielding

gas. When the trigger switch is actuated, the following sequence takes place. The shielding



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Welding

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

Lesson 10


Filler Metals

LESSON II

gas flows for a short inter$al before wire feeding starts; wire feeding starts; the arc is initiated

and continues for a preset time (usually a few seconds). The welding current and wire feeding

stops, and the shielding gas flows for a short inter$al before it automatically stops. The

process is also useful for tacking welding pieces in position prior to running the final weld

bead.

2 . 4 . 3 EQUIPMENT AND OPERATION - The equipment used for gas metal arc welding

is more complicated than that required for shielded metal arc welding. Initial cost is relati$ely

high, but the cost is rapidly amorti2ed due to the sa$ings in labor and o$erhead achie$ed by

the rapid weld metal deposition.

2.4.3.1 The equipment necessary for gas metal arc welding is listed below6

1) Power source

2) Wire feeder

3) Welding gun

4) Shielding gas supply

5) Solid electrode wire

6) Protecti$e equipment

2.4.3.2 The basic equipment necessary for semiautoma tic gas metal arc welding is shown

in Figure 12.

SCHEMATIC DIAGRAM SEMI-AUTOMATIC GMAW EQUIPMENT

FIGURE 12


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WELDING GUN

TRIGGER CONTROL LEAD FEED ROLLS

WELD CABLE

GAS HOSE

GROUND CABLE WORK

115V CONTACTOR ~ ~

MAGNETIC

VALVE

WIRE FEEDER

WIRE SPOOL

SHIELDING GAS

POWER SOURCE

FLOWMETER REGULATOR


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2.4.4 Power Source - A direct current, constant voltage power source is recommended

for gas metal arc welding. It may be a transformer-rectifier or a rotary type unit. The lower

open circuit voltage and self-correcting arc length feature, as described in Lesson I, makes it m

ost suitable. Constant voltage power sources used for spray transfer welding and for flux cored

electrode welding (to be covered later) are the same. However, if the unit is to be used for

short-circuiting arc

w e l d i n g , i t m u s t h a v e

'slope' or slope control.

25

Slope control is a

m e a n s o f l i m i t i n g t h e 2 0 V

O

high short-circuit current L

T

that is characteristic of S

this type welder. Figure

10

13 shows the effect of

slope on the short-

5

circuiting current.

2.4.4.1 I f w e w e r e

s ho r t - a r c w e l d i n g a t approximately 150 amperes

and 18 v olts, as shown in Figure 13,

and had no slope comp onents in the power source, the current at short-circuit or when the wire

touches the work, would be over 1400 amperes. At this high current, a good length of the wire w

ould literally explode off the end, cause much spatter, and the arc would be erratic. With the

slope comp onents in the circuit, the short-circuiting current is in the neighborhood of 400

amperes, and the m olten ball is sort of pinched off the end of the wire m ore gently. For those

with an electrical background, it might be added that in some machines, slope is achieved by

adding a reactor in the AC secondary of the power source. In others, a slope resistor is added in

the DC output portion of the circuit. Slope may be adjustable for varying wire diameters or it

may be fixed, giving a good average value for .035' and .045' diameter wires, the two most

popular sizes.

2.4.4.2 Another factor influencing the arc in short-circuiting welding is the rate that the

amperage reaches the short-circuiting current level. Using the example in Figure 13, we know

that the current goes from 150 amperes to 400 amperes during each shorting period. If we

were to plot the current rise on a graph, as in Figure 14, we would see that the current rise if

very rapid, as shown by the broken line.


Welding

LESSON II

Current

Chapter

T a b l e o f

Contents

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

Lesson 10


Filler Metals

Print

OPERATING POINT

CONSTANT VOLTAGE VIA CURVE

Glossary

SHORT CIRCUITING CURRENT NO SLOPE

SHORT CIRCUITING CURRENT WITH SLOPE

200 400 e00 800 1000 1200 1400

EFFECT OF SLOPE ON SHORT CIRCUITING CURRENT

FIGURE 13 Turn Pages

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TIIvE - MILLISECONDS

EFFECT OF IND~CTANCE ON CLRRENT RISE

FIGURE 14


Welding

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Cove red Electrodes

for Welding

Mild Steels

Lesson 4

Cove red Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

Lesson 10


Filler Metals

LESSON II

This rapid current rise can be

by using a device called an

(sometimes called a stabilizer)

output circuit of the welder. An

merely an iron core wound

turns of heavy wire. It does

c u r r e n t f l o w , b u t

i t a c t s somewhat like a fly

wheel or

damp er by retarding the rate

of rise as shown by the solid line.

By prev enting the rapid

current rise, the arc

becomes smoother,

spatter is reduced, and

b e a d s h a p e a n d

appearance are

improv ed. Because the inductor influences the time function, its design determines arc

on-off

time, and short-circuit frequency. Some power sources have a selector that can switch in

sev eral different inductance values to finely tune the arc.

2.4.4.4 Welding power sources designed for gas metal arc welding have a 115 volt outlet to

provide power to operate the wire feeder. They also have a receptacle to receive the electrical

power required to close the main contactor in the power source, which turns on the welding

power to the welding gun when the gun trigger is actuated.

2.4.4.5 Additional advancements in equipment technology have introduced many new

models. Inv erters, as well as microprocessor controls, have created the greatest attention. In

addition, multipurpose machines have provided the user with greater fle6ibility with a variety of

capabilities.

2.4.4.6 Global competition will continue to have a profound influence on future

advancements in arc welding equipment. As energy prices rise, greater demands for mor e

efficient equipment will follow.

2.4.5 Wire Feeder - When welding with a constant voltage power source, as is the case

in most gas metal arc welding applications, the prime function of the wire feeder is to deliv er

the welding wire to the arc at a very constant speed. Since the wire feed speed determines

the amperage, and the amperage determines the amount of heat at the arc, inconsistent wire

feed speed will produce welds of varying penetration and bead width. Advanced electronics

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WITHOUT IND~CTANCE

400 AIVPS

150 AMPS

WITH INDIJCTANCE

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Welding

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

LESSON II

technology makes it possible to design motor speed controls that will produce the same

speed, e'en though the load on the motor 'aries or the input 'oltage to the motor may fluctuate.

2.4.5.1 A li mited amount of gas metal arc welding is performed with constant current type

power sources. In this case, the motor speed automatically 'aries to increase or decrease the

wire feed speed as the arc length 'aries to maintain a constant 'oltage.

2.4.5.2 The wire feeder also controls the main contactor in the power source for safety

reasons. This assures that the welding wire will only be energized when the switch on the

welding gun is depressed.

2.4.5.3 The flow of shielding gas is controlled by a solenoid 'al'e (magnetic 'al'e) in the

wire feeder to turn the shielding gas on and off when the gun switch is actuated. Most feeders

utilize a dynamic breaking circuit to quickly stop the motor at the end of a weld to pre'ent a

long length of wire protruding from the gun when the weld is terminated. Most feeders ha'e a

burn-back circuit that allows the welding current to stay on for a short period of time after wire

feeding has stopped, to allow the wire to burn back exactly the right amount for the next arc

initiation.

2.4.5.4 The feed rolls, sometimes called dri'e rolls, pull the wire off the spool or reel, and

push it through a feed cable or conduit to the welding gun. These rolls must usually be

changed to accommodate each different wire diameter, although some rolls are designed to

feed a combination of sizes.

2 . 4 . 6 Welding Gun - The function of the welding gun, sometimes referred to as a torch, is

to deli'er the welding wire, welding current, and shielding gas to the welding arc. Guns are

a'ailable for semi-automatic operation and for automatic operation, where they are fixed in the

automatic welding head.

2.4.6.1 Guns for GMAW ha'e se'eral characteristics in common. All ha'e a copper alloy

shielding gas nozzle, that deli'ers the gas to the arc area in a nonturbulent, angular pattern to

pre'ent aspiration of air. The nozzle may be water cooled for semiautomatic welding at high

amperage and for automatic welding where the arc time is of long duration. Welding current is

transferred to the weldingwire as the wire tra'els through the contact tip or contact tube

located inside the gas nozzle (Refer to Figure 9). The hole in the contact tip through which the

wire passes is only a few thousandths of an inch larger than the wire diameter. A worn contact

tip will result in an erratic arc due to poor current transfer. Figure 15 shows a few different

semiautomatic gun configurations that are commonly used for GMAW.

Lesson 10


Filler Metals


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Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

Lesson 10


Filler Metals

FIGURE 15

2.4.6.2 The cur~e d neck or 'goose neck'type is probably the most commonly used. It

allows the best access to a ~ariety of weld joints. The wire is pushed to this type of gun by the

feed rolls in the wire feeder through a feed cable or conduit that usually is 10 or 12 feet in

length. The shielding gas hose, welding current cable, and trigger switch leads are supplied

with the welding gun.

2.4.6.3 The pistol type gun is similar to the cur~e d neck type, but is less adaptable for

difficult to reach joints. The pistol type is also a 'push' type gun and is more suitable for gas

metal arc spot welding applications.

2.4.6.4 The self contained type has an electric motor in the handle and feed rolls that pull the

wire from a 1 or 2 pound spool mounted on the gun. The need for a long wire feed cable is

eliminated, and wire feed speed may be controlled by the gun. Guns of this type are often

used for aluminum wire up to .045'diameter, although they may also be used for feeding steel

or other hard wires.

2.4.6.5 The pull type gun has either an electric motor or an air motor mounted in the handle

that is coupled to a feeding mechanism in the gun. The spool of wire is located in the control

cabinet that may be located as far as fifty feet from the gun. When feeding such long

distances, a set of 'push' rolls located in the control cabinet assist in feeding the wire. This

then becomes known as a push-pull feed system and is especially useful in feeding the softer

wires such as aluminum.

2 .4 . 7 SHIELDING GASES - In gas metal arc welding, there are a ~ariety of shielding

gases that can be used, either alone or in combinations of ~arying degrees. The choice is

dependent on the type of metal transfer employed, the type and thickness of metal, the bead



Welding

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

LESSON II

CURVED NECK PISTOL TYPE

SELF CONTAINED PU:i TYPE

SEMI-AUTOMATIC GMAW GUN TYPES

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Lesson 1 The Basics of A Welding

Lesson 2 Common Electri





Alloy Steels






Electrodes




Filler Metals

LESSON II

profile (See Figure 16), penetration, and speed of welding. In our discussion, we will deal with

the more common choices used for the various transfer processes.

FERROUS METALS NON-FERROUS METALS

CO2 ARGON + CO2 ARGON + O2 ARGON HELIUvI

BEAD PROFILE

FIGURE 16

2.4.7.1 Short Circuiting Transfer - Straight carbon dioxide (CO2) is often used for short

circuiting arc welding because of its low cost. The deep penetration usually associated with

CO 2 is minimized because of the low amperage and voltage settings used with this process.

Compared to other gas mixes, CO 2will produce a harsher arc and therefore, greater spatter

levels. Usually, this is minimized by maintaining a short arc length and by careful adjustment of

the power supply inductance. The temperatures reached in welding will cause carbon dioxide

to decompose into carbon monoxide and oxygen. To reduce the possibility of porosity caused

by entrapped oxygen in the weld metal, it is wise to use electrodes that contain deoxidizing

elements, such as silicon and manganese. If the current is increased above the short circuiting

range, the use of carbon dioxide tends to produce a globular transfer.

2.4.7.1.1 Mixing argon in proportions of 50-75% with carbon dioxide will produce a

smoother

arc and reduce spatter levels. It will also widen the bead profile, reduce penetration, and

encourage 'wetting'. Wetting, i.e., a uniform fusion, along with joining edges of the base metal

and the weld metal, minimizes the

weld imperfection known as

undercutting (See Figure 17).

UNDERCUT WETTING

FIGURE 17

2.4.7.1.2 The 75% ArgonI25 CO2 mixture is often chosen for short circuit welding of thin

sections, whereas the 50-50 combination works well on thicker sections.

2.4.7.1.3 It should be noted that shielding gases can affect the metallurgy of the weld metal.

As an example, a combination of argon and carbon dioxide may be used for welding stainless

steel, but as the carbon dioxide breaks down, excessive carbon may be transferred into the


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Welding

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

Lesson 10


Filler Metals

LESSON II

weld metal. Corrosion resistance in stainless steel is reduced as the carbon content

increases. To counteract this possibility, a less reactive mixture of 90% helium - 7-112% argon -

2-112% CO2 is sometimes chosen. This combination, known as a trimiç provides good arc

stability and wetting.

2.4.7.2 Spray Arc Transfer - Pure argon produces a deep constricted penetration at the

center of the bead with much shallower penetration at the edges (Figure 16). Argon performs

well on nonferrous metals, but when used on ferrous metals, the transfer is somewhat erratic

with the tendency for the weld metal to moveaway from the center line. To make argon suit -

able for spray transfer on ferrous metals, small additions of 1 to 5% oxygen have proven to

provide remarkable improvements. The arc stabilizes, becomes less spattery, and the weld

metal wets out nicely. If the percentage of argon falls below 80%, it is impossible to achieve

true spray transfer.

2.4.7.2.1 Pure helium or combinations of helium and argon are used for welding nonferrou

metals. The bead profile will broaden as the concentration of helium increases.

2.4.7.3 Pulse Spray Transfer - The selection of shielding gas must be adequate enough to

support a spray transfer. Material type, thickness, and welding position are essential variables

in selecting a particular shielding gas. The following is a list of recommended gases:

Carbon Steel ArgonICO20O20He (He less than 50%)

Alloy Steel ArgonICO20O20He (He less than 50%)

Stainless ArgonilO20CO2 (CO2max. 2%)

Copper, Nickel, & Cu-Ni Alloys ArgonlHelium

Aluminum ArgonlHelium

2 .4 .8 Electrodes - The solid electrodes used in GMAW are of high purity when they come

from the mill. Their chemistry must be closely controlled and some types purposely contain

high levels of deoxidizers for usewith CO 2 shielding.

2.4.8.1 The electrode manufacturer draws down the electrode to a finished diameter that,

with GMAW, is usually quite small. Diameters from .030' thru 1116' are common.

2.4.8.2 Most steel GMAW electrodes are copper plated as a means of protecting the

surface. The copper inhibits rusting, provides smooth feeding, and helps electrical

conductivity.

2.4.8.3 Information on types and classifications will be covered in a future lesson.


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Flux CoredArc Weld~ng (FCAW) is quite similar to GMAW as far as operation and

equipment are concerned. The major difference is that FCAW utilizes an electrode that is -e ry

different from the solid electrode used in GMAW. The flux cored electrode is a fabricated

electrode and as the name implies, flux material is deposited into its core. The flux cored

electrode begins as a flat metal strip that is formed first into a 'U shape. Flux and alloying

elements are deposited into the 'U' and then the shape is closed into a tubular configuration

by a series of forming rolls.

2.5.0.1 The flux cored electrode is a continuous electrode that is fed into the arc where it is

melted and transferred into the molten puddle. As in GMAW, the flux cored process depends on

a gas shield to protect the weld zone from detrimental atmospheric contamination. With FCAW,

there are two prima ry ways this is accomplished (See Figure 18). The gas is either a pplied

externally, in which case the electrode is referred to as a gas shielded flux cored electrode, or it

is generated from the decomposition of gas forming ingredients contained in the electrode's

core. In this instance, the electrode is known as a self-shielding flux cored

electrode. In addition to the gas shield, the flux co red electrode produces a slag co-e ring for

FIGURE 1

further protection of the weld metal as it cools. The slag is manually remo-ed with a wire brush or chipping

hammer.

2.5.1 Se l f Sh ie l de d Proces s - The main ad-antage of the se lf shie lding method is that

its operation is somewhat simplified because of the absence of external shielding equipment.


Welding 2 . 5 F LUX CORED ARC WELD ING

LESSON II

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FLUX-CORED ARC WELDING

CONTACT TIP

GAS CUP

GAS SHIELD

FLUX CORE

GAS SHIELDED

CONTACT TIP

INSULATED GUIDE TUBE

FLUX CORE

SELF SHIELDED


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Welding

Lesson 2

Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for Welding

Mild Steels

Lesson 4

Covered Electrodes

for Welding Low

Alloy Steels

Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

Lesson 9

Estimating &

Comparing Weld

Metal Costs

Although self shielding electrodes have been developed for welding low alloy and stainless

steels, they are most widely used on m ild steels. The self shielding method generally uses

a long electrical stick-out (distance between the contact tube and the end of the unmelted elec-

trode) commonly from one to four inches. Electrical resistance is increased with the long

extension, preheating the electrode before it is fed into the arc. This enables the electrode

to burn off at a faster rate and increases deposition. The preheating also decreases the

heat ava ilable for melting the base metal, resulting in a more shallow penetration than the

gas shielded process.

2.5.1.1 A major drawback of the self shielded process is the metallurgical quality of the

deposited weld metal. In addition to gaining its shielding ability from gas forming ingredients

in the core, the self shielded electrode contains a h igh level of deoxidizing and denitrifying

alloys, primarily aluminum, in its core. Although the alum inum performs well in neutralizing the

affects of oxygen and nitrogen in the arc zone, its presence in the weld metal will reduce

ductility and impact strength at low temperatures. For this reason, the self shielding method is

usually restricted to less critical applications.

2.5.1.2 The self shielding electrodes are more suitable for welding in drafty locations than

the gas shielded types. Since the molten filler metal is on the outside of the flux, the gases

formed by the decomposing flux are not totally relied upon to shield the arc from the

atmosphere. The deoxidizing and denitrifying elements in the flux further help to neutralize the

affects of nitrogen and oxygen present in the weld zone.

2.5.2 The Gas Shielded Process - A major advantage with the shielded flux cored

electrode is the protective envelope formed by the auxiliary gas shield around the molten

puddle. This envelope effectively excludes the natural gases in the atmosphere without the

need for core ingredients such as aluminum. Because of this more thorough shielding, the

weld metallurgy is cleaner which makes this process suitable for welding not only m ild steels,

but also low alloy steels in a wide range of strength and impact levels.

2.5.2.1 The gas shielded method uses a shorter electrical stickout than the self shielded

process. Extensions from 112' to 314' are common on all diameters, and 314' to 1 -112' on

larger diameters. Higher welding currents are also used with this process, enabling high

deposition rates to be reached. The auxiliary shielding helps to reduce the arc energy into a

columnar pattern. The combination of high currents and the action of the shielding gas

contributes to the deep penetration inherent with this process. Both spray and globular

transfer are utilized with the gas shielded process.

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CURRENT PATH


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Lesson 2

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Mild Steels

Lesson 4

Covered Electrodes

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Flux Cored Arc

Electrodes Carbon

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LESSON II

2.5.3 Current Density - Flux cored arc welding utilizes the same principles of current

density, as explained in section 2.4.1, but there is one significant difference between the flux

cored electrode and the solid electrode. With the flux cored electrode, the granular core

ingredients are poor electr ica l conductors and therefore, the current is carr ied primarily

through the outer metal sheathing. When an equal diameter cross

section of the two are compared (See Figure 19), it is seen that the

flux cored electrode has

a smaller current carrying area than the soli

electrode. This greater concentration of

current in a smaller area increases the

burnoff rate.

2.5.3.1 When all other factors are

equal,

the deposition rate of the flux cored

electrode is somewhat higher than the

solid electrode.

2.5.4 EQUIPMENT - The equipment used for flux cored arc welding is the same as

shown previously in Section 2.3.2.2, Figure 12, with the exception that the self shielded

method does not need the external gas apparatus.

2.5.4.1 Flux cored arc welding is done with direct current. All of the gas shielded electrodes

are designed for DCEP operation. The self shielded electrodes are either designed

specifically for DCEN or DCEP.

2.5.5 Power Source - The recommended power source is the direct current constant

voltage type. The constant current type can be used but with less satisfactory results.

2.5.6 Wire Feeder - The function of the wire feeder in FCAW is the same as discussed in

the section on GMAW. Since the flux cored electrode is tubular in construction, precautions

must be taken not to flatten the electrode. To facilitate feeding by means other than pressure

alone, specially designed feed rolls with knurled or groove d surfaces are used. Some feeders

use four feed rolls rather than two to minimize unit pressure on the electrode.

2.5.7 The Welding Gun - As compared to GMAW, the main difference in FCAW welding guns

is in those used with the self shielding process. The gun is somewhat more compact due to the

absence of an external gas shielding nozzle. Since the self shielding process normally requires

a longer electrode extension, the self shielding gun may have an insulated guide tube (Refer

back to Figure 18) to give stability to the electrode. Water cooled guns are available for high

duty semi-automatic welding and for automatic welding.


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1/16 FLU?-CORED

ELECTRODE 1/16 SOLID ELECTRODE

FIGURE 19

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Flux Cored Arc

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LESSON II

2.5.7.1 Flux cored welding generates fumes, that for environmental reasons, must be

removed from the welding area. This is usually done with an external exhaust system, but

welding guns with internal fume extractors have been developed. They are heavier than the

regular gun and must be properly maintained so that the extracting mechanism does not

disturb the shielding gas.

2 .5 .8 SHIELDING GASES - Carbon dioxide is the most widely used gas for auxiliary

shielding of the flux cored electrode. The other commonly used gas is a mixture of 75% Argon

and 25% CO2.

2.5.8.1 A ca rbon dioxide shield produces deep penetration and the transfer is globular. As

previously discussed, CO 2 will dissociate in the heat of the arc. To counteract this

characteristic, deoxidizing elements are added to the core ingredients of the electrode. The

deoxidizers react to form solid oxide compounds that float to the surface as part of the slag

covering.

2.5.8.2 The addition of Argon to CO2 will increase the wetting action, produce a smooth arc

arc, and reduce spatter. The transfer is spray-like, and the penetration is somewhat less than

with the straight carbon dioxide.

2.5.8.3 While some flux cored electrodes are designed to operate well on both the 100%

CO2 or the 75125 mixture, others are formulated specifically for the CO 2 shield or the Argonl

CO2 mixture. If the recommended gas is not used with these electrodes, the weld chemistry

may be affected. The reason for this is that inert gas, such as Argon, does not react with the

other elements; therefore, allowing them to be transferred across the arc into the weld metal.

An electrode designed for CO 2 shielding contains deoxidizing elements, such as silicon and

manganese. If a high percentage of Argon is used in the shielding medium, a large portion of

these elements may pass into the weld metal causing the weld metallurgy to be less ductile

than intended.

2.5.8.3 The opposite happens with electrodes formulated for a 75125 mixture. These

electrodes are usually designed for high yield and tensile strength. If a high percentage of CO 2

is used with them, the CO2 may react with the elements needed to attain these strength levels,

thereby preventing them from passing into the weld metal.

2.6 SUBMERGED ARC WELDING

Submerged Arc Welding (SAW) is different from the previously explained arc welding processes in

that the arc is not visible. The arc is submerged beneath loose granular flux. A continuous

electrode is fed by automatic drive rolls through an electrode holder where current


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Welding

LESSON II

is picked up at the contact tube. The electrode mo'es into the loose flux and the arc is

initiated. The flux is deposited from a separate container that mo'es at the same pace as the

electrode assuring complete co'erage (See Figure 20).

2.6.1 Submerged Arc Flux - The flux helps form the molten puddle, slows the cooling

rate, and acts as a protecti'e shield. The fluç which is in close contact wi th the arc, is fused

into a slag co'er and that which is not fused is collected for reuse. The flux can contain alloying

elements that, when molten, will pass into the weld metal affecting the metallurgy. Some fluxes

are specifically prepared for their alloy altering capabilities while others, known as neutral

fluxes, are chosen when a minimal alloy change is desired. Although these latter fluxes are

called 'neutral', they still ha'e the ability to slightly alter the weld chemistry.

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Carbon & Low Alloy


GMAW,GTAW,SAW

FLUX HOPPER

LOOSE GRANULAR FLUX ELECTRODE

MOLTEN PUDDLE BASE METAL

Glossary

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Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


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SUBMERGED ARC WELDING

FIGURE 20

2.6.2 The Welding Gun - Although there are hand-held welding guns for the submerged

arc process, the majority of SAW is done with fully automa tic equipment. The basic compo-

nents include a wire feeder, a power source, a flux deli'ery system, and in some instances, an

automa tic flux reco'ery system.

2.6.3 Power Sources - The power source can be a constant current AC transformer, or i

may be a DC rectifier or generator of either the constant current or constant 'oltage 'ariety.

The power source must be rated for high current output. When current requirements exceed

the 'alue of a single machine, two or more of the same type may be connected in parallel.

2.6.4 Equipment - Most submerged arc welding is done wi th DCEP because it pro'ides

easy arc starting, deep penetration and excellent bead shape. DCEN pro'ides the highest

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Lesson 5



Lesson 6

Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

LESSON II

deposition rates but minimum penetration. Alternating current is often used as a trailing arc in

tandem arc applications. In this type of application, the leading DCEP arc provides deep

penetration, and the closely trailing AC arc provides high deposition with a minimum of arc

blow.

2.6.5 Electrodes - A variety of ferrous and nonferrous electrodes are used in submerged

arc welding. They are usually solid electrodes refined with the appropriate alloys at the steel

mill, and then shipped to electrode manufacturers where they are drawn down to a specific

diameter and packaged. There is another type of sub arc electrode known as a composite

electrode, that is fabricated in the same manner as a flux cored electrode. A chief adv antage

of this type is that the alloying elements can be added to the core of the electrode more

cheaply than a steel mill can produce those same alloys in a solid form. The electrodes for

SAW vary in diameter from 1116 inch to 114 inch with the larger diameters being the most

widely used.

2.6.6 Summary - Submerged arc welding has some advantages over other welding

processes. Since the radiance of the arc is blanketed by the loose flux, there is no need for a

protective welding hood (although safety glasses are recommended), there is no spatter and

only a very minim al amount of fumes escape from under the blanket. High welding currents,

quite commonly in the 300 to 1600 ampere range, are used. These high currents, combined

with fast travel speeds, m ake SAW a high deposition process that is especially suitable for

applications that require a series of repetitious welds. Some setups allow two or more elec -

trodes to be fed simultaneously into the joint, further increasing the deposition rate and speed.

2.6.6.1 Although SAW has these advantages, it does have some limitations. The flux must

be deposited and collected for every welding pass. This requires additional equipment and

handling. Also because of the loose fluç the process is limited to the flat and horizontal

positions. The equipment for SAW is commonly quite bulky which limits its mobility, and

although the process works well on thick m aterials, it usually is not satisfactory for thin gauge

m aterial. The process requires care in the operation. The amperages commonly used m ay

cause excessive heat buildup in the base metal, that m ay result in distortion or brittleness.

Lesson 9

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Electroslag Welding (ESW) and Electrogas Welding (EGW) comprise only a minor portion of all welding

done in the country, but they are uniquely adapted to certain applications, primarily the joining

of -ery thick materials. The joining of a 12 inch material along a 40 foot line is not an

uncommon application for the Electroslag process.

2.7.1 Electroslag Welding (See Figure 21) is technically not an arc welding process,

although it utilizes a current carrying consumable electrode. The only time there is an arc

between the electrode and the work piece is when current is initially charged through the

electrode. This initial charge heats a layer of loose flux that becomes molten and extinguishes

the arc.

ELECTROSLAG WELDING

FIGURE 2

2.7.2 Flux - The flux used in ESW is high in electrical resistance. As current is applied,

enough heat is generated from this resistance to keep the fluç base metal, and electrode in a

molten state. This axis of the weld joint is on a -ertical plane. The two pieces of metal, usually of

the same thickness, are positioned so that there is an opening between them. One or more electrodes

are fed into the opening through a welding bead that tra-els -ertically as the joint is filled. To

contain the molten puddle, water cooled copper shoes or dam s are placed on the

sides of the -ertical ca-ity. As the weld joint solidifies, the dam s mo-e-ertically so as to

always remain in contact with the molten puddle.

2.7.3 Process - A -ariation of ESW is the consumable guide method. The process is the

same with this method except that the guide tube that feeds the electrode to the molten pool is


Welding 2 .7 ELECTROSLAG AND ELECTROGAS WELDING

LESSON II

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Carbon & Low Alloy


GMAW,GTAW,SAW

Lesson 7

Flux Cored Arc

Electrodes Carbon

Low Alloy Steels


Electrodes

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WATER INLET/OUTLET

ELECTRODE

COPPER SHOE

GUIDE TUBE (CONSUVIABLE GUIDE IvETHOD)

BASE IVETAL

MOLTEN FLUX

WELD POOL SOLIDIFIED METAL


1 din 1 23.11.2009 10:26


1 din 1 23.11.2009 10:26


Welding

LESSON II

also consumed. The chief ad antage with this method is the elimination of the electrode holder

which must mo e ertically with the weld pool. Also since the guide tube is consumed, the deposition

rate is slightly increased with this method.

2.7.4 Equipment - The equipment used in E S W is all automatic and of special design.

The power source may use either AC or DC current. The electrode may be either solid or flux

cored, although if the flux cored is used, it must be specially formulated so as not to contain its normal

amount of slag forming ingredients.

2.7.5 Summary - Electrogas Welding is similar to E S W as far as the mechanical as-

pects are concerned. The equipment is automatic, the welding head tra els ertically, and the

molten puddle is retained by shoes on the sides of the joint. The difference is that Electrogas Welding

utili2es an arc and it is externally gas shielded. The power source is also limited to

DC operation. The electrodes used in EGW can be either solid or flux cored.

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1 din 1 23.11.2009 10:26

LESSON II- GLOSSARY OF TERMS

Arc Blow - Deviation of the direction of the welding arc caused by magnetic fields in the

work piece when welding with direct current.

Straight - Welding condition when the electrode is connected to the negative terminal

Polarity and the work is connected to the positive terminal of the welding power source.

Reverse - Welding condition when the electrode is connected to the positive terminal

Polarity and the work is connected to the negative terminal of the welding power

source.

Slag - The brittle mass that forms over the weld bead on welds made with coated

e l e c t ro des , f lu x c o re d e l e c t r o des , s ub me r ge d a rc w e ld ing a nd

o t he r s l a g p r o d u c i n g w e l d i n g p r o c e s s e s . W e l d s m a d e w i t h

t h e g a s m e t a l a r c a n d t h e gas tungsten arc welding processes are slag

free.


Welding APPENDIX A

LESSON II




Lesson 3 Cove red Electrodes


Lesson 4 Cove red Electrodes for Welding Low

Alloy Steels






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- Welding with a coated electrode where the operator1s hand controls travel

speed and the rate the electrode is fed into the arc.

- Welding with a continuous solid wire or flux cored electrode where the wire

feed speed, shielding gas flow rate, and voltage are preset on the equipment,

and the operator guides the hand held welding gun along the joint to be

welded.

- A weld defect where slag is entrapped in the weld metal before it can float to

the surface.

Manual Arc

Welding

Semi-Automatic

Welding

Slag

Inclusion

Root Pass - The initial pass in a multi-pass weld, usually requiring 100% penetration.


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LESSON II

Gas Ions - Shielding gas atoms that, in the presence of an electrical current, lose one or

more electrons and therefore, carry a positi'e electrical charge. The pro'ide a

more electrically conducti'e path for the arc between the electrode and the

work piece.

High

Frequency - (as applied to gas-tungsten arc welding)

An alternating current consisting of o'er 50,000 cycles per second at high

'oltage, low amperage that is superimposed on the welding circuit in GTAW

power sources. It ionizes a path for non-touch arc starting and stabilizes the arc

when welding with alternating current.

Inert Gases - Gases that are chemically inacti'e. They do not readily combine with other

elements.

Flux - In arc welding, fluxes are formulations that, when subjected to the arc, act as

a cleaning agent by dissol'ing oxides, releasing trapped gases and slag and

generally cleaning the weld metal by floating the impurities to the surface

where they solidify in the slag co'ering. The flux also ser'e s to reduce spatter

and contributes to weld bead shape. The flux may be the coating on the

electrode, inside the electrode as in flux cored types, or in a granular form as

used in submerged arc welding.

Current

Density - The amperes per square inch of cross-sectional area of an electrode. High

current density results in high electrode melt-off rate and a concentrated, deep

penetrating arc.

Slope or Slope

Control - A necessary feature in welding power sources used forshort circuiting arc

welding. Slope Control reduces the short circuiting current each time the

electrode touches the weld puddle (See Section 2.5.3).

Inductance - (as applies to short circuiting arc welding)

A feature in welding power sources designed for short circuiting arc welding to

retard the rate of current rise each time the electrode touches the weld puddle.


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Contact Tip - That part of a gas metal arc welding gun or flux cored arc welding

gun that

t r ans fe r s the we ld ing cur rent to the we ld ing wire immed ia te ly be fo r e the w ire

enters the arc.

Spray - Mode of metal transfer across the arc where the molten metal droplets are

Transfer smaller than the electrode diameter and are axially directed to the

weld puddle.

R e q u i r e s h i g h v o l t a g e a n d a m p e r a g e s e t t i n g s a n d a s h i e l d i n g g a s o f a t l e a s t

80% argon.


Welding

LESSON II



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Alloy Steels






Electrodes



- Mode of metal transfer across the arc where a molten ball larger than the

electrode diameter forms at the tip of the electrode. On detachment, it takes

on an irregular shape and tumbles towards the weld puddle sometimes

shorting between the electrode and work at irregular intervals. Occurs when

using shielding gases other than those consisting of at least 80% argon and

at medium current settings.

- Mode of metal transfer somewhat between spray and short circuiting. The

specific power source has built into it two output levels: a steady background

level, and a high output (peak) level. The later permits the transfer of metal

across the arc. This peak output is controllable between high and low values

up to several hundred cycles per second. The result of such a peak output

produces a spray arc below the typical transition current.

- Mode of metal transfer in gas metal arc welding at low voltage and amperage.

Transfer takes place each time the electrode touches or short-circuits to the

weld puddle, extinguishing the arc. The short-circuiting current causes the

electrode to neck down, melt off, and then repeats the cycle.

- A shielding gas consisting of approximately 90% helium, 7-112% argon, and

2-112% carbon dioxide used primarily for short-circuiting arc welding of

stainless steels. Maintains corrosion resistance of the stainless steel and

produces good wetting and excellent weld bead shape.


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Transfer

Pulse

Transfer

Short-circuiting

Transfer

Trimixor

Triple Mix

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Electrical

Stick-Out

- In any welding process using a solid or flux cored wire, the electrical stick -out

is the distance from the contact tip to the unmelted electrode end. Sometimes

called the 'amount of wire in resistance'. This distance influences melt-off

rate, penetration, and weld bead shape.

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LESSON II



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for Welding

Mild Steels


Alloy Steels

Out-of-Position

Welds

Weld

Positions

- Welds made in positions other than flat or horizontal fillets.

-

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Glossary

FLAT HORIZONTAL FILLET


Lesson 6 Carbon & Low Alloy Steel Filler Metals -

GMAW,GTAW,SAW

VERTICAL OVERHEAD

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Basic Welding ESAB

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