esab basic welding filler technology lesson ii common electric arc weldingprocesses

8/25/2015 Lesson 2 - Common Electric Arc Welding Processes

http://www.esabna.com/euweb/awtc/lesson2_1.htm 1/1

BASICWELDING FILLER METAL

TECHNOLOGY

A Correspondence Course

LESSON IICOMMON ELECTRIC ARC

WELDING PROCESSES

ESAB ESAB Welding &Cutting Products

©COPYRIGHT 2000 THE ESAB GROUP, INC.

Lesson 1The Basics of Arc

Welding

CurrentChapter Table ofContents

Lesson 2Common Electric

Arc WeldingProcesses

Lesson 3Covered Electrodes

for WeldingMild Steels

Lesson 4 Covered Electrodesfor Welding Low Alloy

Steels

Go To Test

Lesson 5Welding Filler Metalsfor Stainless Steels

Print

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

Glossary

Lesson 7Flux Cored Arc

Electrodes CarbonLow Alloy Steels

SearchChapter(Faster

Download)

Lesson 8HardsurfacingElectrodes

Turn Pages

Lesson 9 Estimating &

Comparing WeldMetal Costs

SearchDocument(Slower

Download)

Lesson 10Reliability of Welding

Filler Metals

http://www.esabna.com/euweb/awtc/Lesson5_1.htm


http://www.esabna.com/euweb/awtc/search2.html







http://www.esabna.com/euweb/awtc/search.html







© COPYRIGHT 1998 THE ESAB GROUP, INC.

LESSON II

2.3.2 Power Sources - Both AC and DC power sources are used in gas tungsten arc

welding. They are the constant current type with a drooping volt-ampere curve. This type of

power source produces very slight changes in the arc current when the arc length (voltage) is

varied. Refer to Lesson I, Section 1.9.

2.3.2.1 The choice between an AC or DC welder depends on the type and thickness of the

metal to be welded. Distinct differences exist between AC and DC arc characteristics, and if

DC is chosen, the polarity also becomes an important factor. The effects of polarity in GTAW

are directly opposite the effects of polarity in SMAW as described in paragraphs 2.2.2.3

through 2.2.2.5. In SMAW, the distribution of heat between the electrode and work, which

determines the penetration and weld bead width, is controlled mainly by the ingredients in the

flux coating on the electrode. In GTAW where no flux coating exists, heat distribution between

the electrode and the work is controlled solely by the polarity. The choice of the proper welding

current will be better understood by analyzing each type separately. The chart in Figure 7 lists

current recommendations.

FIGURE 7

Material &Thickness DCEN DCEP

ACHigh Freq. Argon Helium Ar/He

AluminumUnder 1/8"Over 1/8"

22 & 3

11

11

23 2

MagnesiumUnder 1/16"Over 1/16"

2 11

11

2

Carbon SteelUnder 1/8"Over 1/8"

11

11 2 3

Stainless SteelUnder 1/8"Over 1/8"

11

11

22

CopperUnder 1/8"Over 1/8"

11 1

1

Nickel AlloysUnder 1/8"Over 1/8"

11

1 32

21

TitaniumUnder 1/8"Over 1/8"

1 12

21

WELDING CURRENT SHIELDING GAS

1. Preferred Choice - Manual Welding2. Preferred Choice - Automatic Welding3. Second Choice - Automatic Welding

CURRENT/SHIELDING GAS SELECTION, TUNGSTEN GAS ARC WELDING


Welding







Steels

Go To Test


Print


Glossary




Download)


Turn Pages




Download)


Filler Metals


















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, approximately 70% of the heat of the arc is concentrated at the work,

and approximately 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 oxide 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 approximately 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.

2.3.2.4 Aluminum and magnesium are two metals that have a heavy oxide coating that acts

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

electrode positive provides a good oxide 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 excessive positive charge. As we learned in Lesson I, unlike

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

FIGURE 8

Electrode Oxide HeatPolarity Penetration Cleaning Concentration

Direct Current

Alternating CurrentMedium Penetration

Medium WidthBead

GoodCleans Oxideon Each Half

CycleAlternates BetweenElectrode and Work

Straight PolarityElectrode Negative

DeepPenetrationNarrowBead

Direct Current

Reverse PolarityElectrode Positive

Shallow Penetration

Wide BeadMaximum

None AtWork

AtElectrode

GAS IONS

+

_

ELECTRONFLOW

_

_

+

+

EFFECTS OF CURRENT TYPE - GAS TUNGSTEN ARC WELDING


Welding







Steels

Go To Test


Print


Glossary




Download)


Turn Pages




Download)


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 eliminate 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 1/8") of

magnesium and aluminum.

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

used for welding aluminum. In a sense, the advantages 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 aluminum 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 withdrawing it to maintain the proper arc length. This starting method

contaminates 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

eliminate 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 1/8 inch of the base metal, the

high frequency ionizes the gas path, making it conductive and a welding arc is 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


Welding







Steels

Go To Test


Print


Glossary




Download)


Turn Pages




Download)


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 positive

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 extensively used for welding aluminum

and magnesium.

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

welding, are available, 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 with this process, such as stainless steel, aluminum and

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

power sources designed for this process have many desirable features to insure high quality

welds. Among these are:

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

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

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

initiated.

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

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

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

spot-weld cycle.

Other options and accessories are also available.

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

available. Such units are used extensively for the automatic welding of pipe in position. The

welding current is automatically varied as the torch travels around the pipe. Some units

provide a pulsed welding current where the amperage is automatically varied between a low

and high several times per second. This produces welds with good penetration and improved

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 device 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



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




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. Circulating

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 gastungsten 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. When 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



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















LESSON II

relatively narrow. Argon is more 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 more available heat at the arc. This makes it more 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 to

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 1/4" in diameter and standard lengths range from 3" to 24". The most commonly

used sizes, however, are the .040", 1/16", 3/32", and 1/8" diameters.

2.3.5.1 The shape of the tip of the electrode is an important 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. Narrow joints 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

composition, 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 wave or continuous high frequency.


Welding







Steels

Go To Test


Print


Glossary




Download)


Turn Pages




Download)


Filler Metals


















LESSON II

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

Good current carrying capacity, easy arc starting and provide 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 groove 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 very 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 extensively in the aircraft and aerospace industry, where

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

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

controlling the current.

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

consumable electrodes and is little used on thicknesses over 1/4" for this reason. Shielding

gas and tungsten electrode costs make the process relatively expensive.

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 "MIG" (Metal Inert Gas) Welding.


Welding







Steels

Go To Test


Print


Glossary




Download)


Turn Pages




Download)


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, reactive gases, and gas mixtures are used for shielding. The

metal transfer mode is dependent on shielding gas choice and welding current level. Figure 9

is a sketch of the process showing the basic features.

FIGURE 9

WELDING WIRE

WELDING CABLE

SHIELDING GAS

GAS NOZZLE

CONTACT TIP

WORK PIECE

MOLTEN POOL

WELD METAL

ARC

GAS SHIELD

SOLID WIREELECTRODE

TRAVELDIRECTION

GAS METAL ARC WELDING

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

variety 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

relatively heavy 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, voltage, 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 relatively

constant arc length. In automatic welding, the gun is mounted on a travel carriage that moves

along the joint, or the gun may be stationary with the work moving or revolving beneath it.

2.4.0.2 Practically all GMAW is done using DCEP (Electrode positive). This polarity

provides deep penetration, a stable arc and low spatter levels. A small amount 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 1/4" coated electrode and a 1/16" solid wire drawn to scale. Both are capable of

carrying 400 amperes. Notice that the area of the 1/16" wire is only 1/16 that of the core wire

of the coated electrode. We can say that the current density of the 1/16" wire is 16 times



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















LESSON II

greater than the current density

of the 1/4" wire at equal welding

currents. The resultant melt-off

rate of the solid wire is very high.

If we were to increase the current

through the 1/4" coated

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 1/16" wire carries the high

current a distance of less than 3/4", the

approximate 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% Oxygen is used for

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

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

FIGURE 10

AREA = .049 SQ. IN.

AREA = .0031 SQ. IN.CORE WIRE

FLUXCOATING

COATED ELECTRODE

RELATIVE SIZE OF ELECTRODES FOR WELDING AT 400 AMPS

SOLID WIRE

1/4"

1/16"

.049 ÷ .0031 = 16

AA × 16

FIGURE 11

SPRAYTRANSFER

GLOBULARTRANSFER

PULSETRANSFER

MODES OF METAL TRANSFER

1 2 3SHORT CIRCUITING ARC METAL TRANSFER

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

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

flat or horizontal fillet position. See Figure 11.



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




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 even 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, moves 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 level 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-voltage 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 achieved each time the wire actually short circuits (makes contact) with the weld

puddle. This happens very 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 visible

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 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.

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

work. Upon 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 move forward until

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

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

of thinner gauge metals, or of a thin gauge metal to a heavier 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



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















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, approximately 70% of the heat of the arc is concentrated at the work,

and approximately 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 oxide 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 approximately 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.

2.3.2.4 Aluminum and magnesium are two metals that have a heavy oxide coating that acts

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

electrode positive provides a good oxide 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 excessive positive charge. As we learned in Lesson I, unlike

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

FIGURE 8

Electrode Oxide HeatPolarity Penetration Cleaning Concentration

Direct Current

Alternating CurrentMedium Penetration

Medium WidthBead

GoodCleans Oxideon Each Half

CycleAlternates BetweenElectrode and Work

Straight PolarityElectrode Negative

DeepPenetrationNarrowBead

Direct Current

Reverse PolarityElectrode Positive

Shallow Penetration

Wide BeadMaximum

None AtWork

AtElectrode

GAS IONS

+

_

ELECTRONFLOW

_

_

+

+

EFFECTS OF CURRENT TYPE - GAS TUNGSTEN ARC WELDING


Welding







Steels

Go To Test


Print


Glossary




Download)


Turn Pages




Download)


Filler Metals


















LESSON II

gas flows for a short interval 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 interval 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 weldingis more complicated than that required for shielded metal arc welding. Initial cost is relatively

high, but the cost is rapidly amortized due to the savings in labor and overhead achieved by

the rapid weld metal deposition.

2.4.3.1 The equipment necessary for gas metal arc welding is listed below:

1) Power source

2) Wire feeder

3) Welding gun

4) Shielding gas supply

5) Solid electrode wire

6) Protective equipment

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

in Figure 12.

FIGURE 12

FLOWMETERREGULATOR

SHIELDINGGAS

POWERSOURCE

GROUND CABLEWORK

WELDING GUN

WELD CABLE115V CONTACTOR

MAGNETIC

VALVE

TRIGGERCONTROL LEADFEED ROLLS

GAS HOSE

WIRE FEEDER

WIRE SPOOL

+ _

SCHEMATIC DIAGRAM SEMI-AUTOMATIC GMAW EQUIPMENT


Welding







Steels

Go To Test


Print


Glossary




Download)


Turn Pages




Download)


Filler Metals


















LESSON II

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

most 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

welding, it must have

"slope" or slope control.Slope control is a

means of limiting the

high short-circuit current

that is characteristic of

this type welder. Figure

13 shows the effect of

slope on the short-

circuiting current.

2.4.4.1 If we were

short-arc welding at

approximately 150 amperes

and 18 volts, as shown in Figure 13,

and had no slope components 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

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

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

amperes, and the molten ball is sort of pinched off the end of the wire more 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.

FIGURE 13

25

20

15

10

5

200 400 600 800 1000 1200 1400

OPERATING POINT

CONSTANT VOLTAGE V/A CURVE

SHORT CIRCUITINGCURRENT NO SLOPE

SHORT CIRCUITING CURRENTWITH SLOPE

EFFECT OF SLOPE ON SHORT CIRCUITING CURRENT

VOLTS



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




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

current flow, but it acts

somewhat like a fly wheel or

damper by retarding the rate of

rise as shown by the solid

line. By preventing the

rapid current rise, the arc

becomes smoother,

spatter is reduced, and

bead shape and

appearance are

improved. 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

several 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. Inverters, as well as microprocessor controls, have created the greatest attention. In

addition, multipurpose machines have provided the user with greater flexibility 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 more

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 deliver

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

FIGURE 14

TIME - MILLISECONDSEFFECT OF INDUCTANCE ON CURRENT RISE

400 AMPSWITHOUT INDUCTANCE

WITH INDUCTANCE

150 AMPS



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















LESSON II

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

speed, even though the load on the motor varies or the input voltage to the motor may fluctuate.

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

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

wire feed speed as the arc length varies to maintain a constant voltage.

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 valve (magnetic valve) 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 prevent a

long length of wire protruding from the gun when the weld is terminated. Most feeders have 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 drive 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, isto deliver the welding wire, welding current, and shielding gas to the welding arc. Guns are

available for semi-automatic operation and for automatic operation, where they are fixed in the

automatic welding head.

2.4.6.1 Guns for GMAW have several characteristics in common. All have a copper alloy

shielding gas nozzle, that delivers the gas to the arc area in a nonturbulent, angular pattern to

prevent 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 welding wire as the wire travels 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.



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















LESSON II

2.4.6.2 The curved neck or "goose neck" type is probably the most commonly used. It

allows the best access to a variety 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 curved 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 variety of shieldinggases that can be used, either alone or in combinations of varying degrees. The choice is

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

CURVED NECK PISTOL TYPE

SELF CONTAINEDPULL TYPE

SEMI-AUTOMATIC GMAW GUN TYPES

FIGURE 15



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




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.

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

CO2 is minimized because of the low amperage and voltage settings used with this process.

Compared to other gas mixes, CO2 will 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).

FERROUS METALS NON-FERROUS METALS

CO2 ARGON + CO2 ARGON + O2 ARGON HELIUM

BEAD PROFILE

FIGURE 16

FIGURE 17

UNDERCUT WETTING

2.4.7.1.2 The 75% Argon/25 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



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




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 - 7-1/2% argon

- 2-1/2% CO2 is sometimes chosen. This combination, known as a trimix, 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 move away 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 nonferrous

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 Argon/CO2/O2/He (He less than 50%)

Alloy Steel Argon/CO2/O2/He (He less than 50%)

Stainless Argon/O2/CO2 (CO2 max. 2%)

Copper, Nickel, & Cu-Ni Alloys Argon/Helium

Aluminum Argon/Helium

2.4.8 Electrodes - The solid electrodes used in GMAW are of high purity when they comefrom the mill. Their chemistry must be closely controlled and some types purposely contain

high levels of deoxidizers for use with CO2 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 1/16" 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.



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















LESSON II

2.5 FLUX CORED ARC WELDING

Flux Cored Arc Welding (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 very

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 primary ways this is accomplished (See Figure 18). The gas is either

applied 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 cored electrode produces a slag covering for

further protection of the weld metal as it cools. The slag is manually removed with a wire brush

or chipping hammer.

2.5.1 Self Shielded Process - The main advantage of the self shielding method is that

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

FIGURE 18

GAS CUP

GAS SHIELD

FLUX CORE

GAS SHIELDED

CONTACT TIP

INSULATEDGUIDE TUBE

SELF SHIELDED

CONTACT TIP

FLUX CORE

FLUX-CORED ARC WELDING



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















LESSON II

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

steels, they are most widely used on mild 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

available 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 high level of deoxidizing and denitrifying

alloys, primarily aluminum, in its core. Although the aluminum 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 mild 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 1/2" to 3/4" are common on all diameters, and 3/4" to 1-1/2" 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.



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















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 electrical conductors and therefore, the current is carried primarily

through the outer metal sheathing. When an equal diam-

eter 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 solid

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 grooved 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.

FIGURE 19

CURRENT PATH

1/16" FLUX-COREDELECTRODE 1/16" SOLID

ELECTRODE



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















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

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

2.5 FLUX CORED ARC WELDING ....................................................... 24

2.5.1 Self-Shielded Process ....................................................................... 24

2.5.2 Gas Shielded Process....................................................................... 25

2.5.3 Current Density .................................................................................. 26

2.5.4 Equipment ......................................................................................... 26

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

2.5.6 Wire Feeder ...................................................................................... 26

2.5.7 Welding Guns .................................................................................... 26

2.5.8 Shielding Gases ................................................................................ 27

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

2.6.1 Submerged Arc Flux .......................................................................... 28

2.6.2 The Welding Gun ............................................................................... 28

2.6.3 Power Sources .................................................................................. 28

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

2.6.5 Electrodes ......................................................................................... 29

2.6.6 Summary ........................................................................................... 29

2.7 ELECTROSLAG AND ELECTROGAS WELDING .......................... 30

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

2.7.2 Flux ................................................................................................... 30

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

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

2.7.5 Summary .......................................................................................... 31

Appendix A - GLOSSARY OF TERMS ................................................................. 32

TABLE OF CONTENTSLESSON II - Con't.

Section Nr. Section Title Page


Welding







Steels

Go To Test


Print


Glossary




Download)


Turn Pages




Download)


Filler Metals











































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

and 25% CO2.

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

previously discussed, CO2 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 75/25 mixture, others are formulated specifically for the CO2 shield or the Argon/

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 CO2 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 75/25 mixture. These

electrodes are usually designed for high yield and tensile strength. If a high percentage of CO2

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



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















LESSON II

is picked up at the contact tube. The electrode moves into the loose flux and the arc is

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

electrode assuring complete coverage (See Figure 20).

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

rate, and acts as a protective shield. The flux, which is in close contact with the arc, is fused

into a slag cover 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 have the ability to slightly alter the weld chemistry.

FIGURE 20

FLUX HOPPER

LOOSE GRANULAR FLUX

MOLTEN PUDDLE

FUSED SLAG COVERSOLIDIFIED WELD METAL

BASEMETAL

ELECTRODE

SUBMERGED ARC WELDING

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 automatic equipment. The basic compo-

nents include a wire feeder, a power source, a flux delivery system, and in some instances, an

automatic flux recovery system.

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

may be a DC rectifier or generator of either the constant current or constant voltage variety.

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

the value 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 with DCEP because it provides

easy arc starting, deep penetration and excellent bead shape. DCEN provides the highest



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















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 advantage

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 1/16 inch to 1/4 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 minimal 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, make 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 flux, 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 materials, it usually is not satisfactory for thin gauge

material. The process requires care in the operation. The amperages commonly used may

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



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















LESSON II

2.7 ELECTROSLAG AND ELECTROGAS WELDING

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 very 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.

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 flux, base metal, and electrode in a

molten state. This axis of the weld joint is on a vertical 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 travels vertically as the joint is

filled. To contain the molten puddle, water cooled copper shoes or dams are placed on the

sides of the vertical cavity. As the weld joint solidifies, the dams move vertically so as to

always remain in contact with the molten puddle.

2.7.3 Process - A variation 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

WATER INLET/OUTLET

COPPER SHOE

BASE METAL

SOLIDIFIED METALWELD POOL

MOLTEN FLUX

GUIDE TUBE(CONSUMABLE GUIDE METHOD)

ELECTRODE

ELECTROSLAG WELDING

FIGURE 21



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















LESSON II

also consumed. The chief advantage with this method is the elimination of the electrode

holder which must move vertically 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 ESW 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 ESW as far as the mechanical as-

pects are concerned. The equipment is automatic, the welding head travels vertically, and the

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

Welding utilizes 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.



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















LESSON II

APPENDIX A

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

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

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

ReversePolarity

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

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

electrodes, flux cored electrodes, submerged arc welding and other slag

producing welding processes. Welds made with the gas metal arc and the

gas tungsten arc welding processes are slag free.

Manual ArcWelding

- Welding with a coated electrode where the operator's hand controls travel

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

Semi-Automatic

Welding- 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.

SlagInclusion

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

the surface.

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



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















LESSON II

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

more electrons and therefore, carry a positive electrical charge. The provide

a more electrically conductive path for the arc between the electrode and the

work piece.

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

An alternating current consisting of over 50,000 cycles per second at high

voltage, 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 inactive. 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 dissolving 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 covering. The flux also serves 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 SlopeControl - A necessary feature in welding power sources used for short 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.



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















LESSON II

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

transfers the welding current to the welding wire immediately before the wire

enters the arc.

Spray

Transfer

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

smaller than the electrode diameter and are axially directed to the weld puddle.

Requires high voltage and amperage settings and a shielding gas of at least

80% argon.

Globular

Transfer

- 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.

Pulse

Transfer

- 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.

Short-circuiting

Transfer

- 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.

Trimix or

Triple Mix

- A shielding gas consisting of approximately 90% helium, 7-1/2% argon, and

2-1/2% 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.



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















LESSON II

ElectricalStick-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.

Out-of-PositionWelds

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

Weld

Positions

-

FLAT HORIZONTAL FILLET

VERTICAL OVERHEAD

HORIZONTALBUTT

POSITIONED FILLET(FLAT)



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















LESSON II

COMMON ELECTRIC ARC WELDING PROCESSES

2.1 INTRODUCTION

After much experimentation by others in the early 1800's, an Englishman named Wilde

obtained the first electric welding patent in 1865. He successfully joined two small pieces of

iron by passing an electric current through both pieces producing a fusion weld. Approximately

twenty years later, Bernado, a Russian, was granted a patent for an electric arc welding

process in which he maintained an arc between a carbon electrode and the pieces to be

joined, fusing the metals together as the arc was manually passed over the joint to be welded.

2.1.0.1 During the 1890's, arc welding was accomplished with bare metal electrodes that

were consumed in the molten puddle and became part of the weld metal. The welds were of

poor quality due to the nitrogen and oxygen in the atmosphere forming harmful oxides and

nitrides in the weld metal. Early in the Twentieth Century, the importance of shielding the arc

from the atmosphere was realized. Covering the electrode with a material that decomposed in

the heat of the arc to form a gaseous shield appeared to be the best method to accomplish

this end. As a result, various methods of covering electrodes, such as wrapping and dipping,

were tried. These efforts culminated in the extruded coated electrode in the mid-1920's,

greatly improving the quality of the weld metal and providing what many consider the most

significant advance in electric arc welding.

2.1.0.2 Since welding with coated electrodes is a rather slow procedure, more rapid

welding processes were developed. This lesson will cover the more commonly used electric

arc welding processes in use today.

2.2 SHIELDED METAL ARC WELDING

Shielded Metal Arc Welding*, also known as manual metal arc welding, stick welding, orelectric arc welding, is the most widely used of the various arc welding processes. Welding is

performed with the heat of an electric arc that is maintained between the end of a coated metal

electrode and the work piece (See Figure 1). The heat produced by the arc melts the base

metal, the electrode core rod, and the coating. As the molten metal droplets are transferred

across the arc and into the molten weld puddle, they are shielded from the atmosphere by the

gases produced from the decomposition of the flux coating. The molten slag floats to the top

of the weld puddle where it protects the weld metal from the atmosphere during solidification.


Welding







Steels

Go To Test


Print


Glossary




Download)


Turn Pages




Download)


Filler Metals


















LESSON II

Other functions of the coating are to provide

arc stability and control bead shape. More

information on coating functions will be

covered in subsequent lessons.

* Shielded Metal Arc Welding (SMAW) is theterminology approved by the AmericanWelding Society.

2.2.1 Equipment & Operation - One

reason for the wide acceptance of the SMAW

process is the simplicity of the necessary equipment.

The equipment consists of the following items. (See

Figure 2)

1. Welding power source

2. Electrode holder

3. Ground clamp

4. Welding cables and connectors

5. Accessory equipment (chipping

hammer, wire brush)

6. Protective equipment (helmet, gloves, etc.)

2.2.2 Welding Power Sources - Shielded metal arc welding may utilize either

alternating current (AC) or direct current (DC), but in either case, the power source selected

must be of the constant current type. This type of power source will deliver a relatively constant

amperage or welding current regardless of arc length variations by the operator (See Lesson I,

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

relatively constant, the weld beads produced will be uniform in size and shape.

2.2.2.1 Whether to use an AC, DC, or AC/DC power source depends on the type of welding

to be done and the electrodes used. The following factors should be considered:

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

of electrode types. While most of the electrodes are designed to be used on AC or

DC, some will work properly only on DC.

2. Metal Thickness - DC power sources may be used for welding both heavysections and light gauge work. Sheet metal is more easily welded with DC

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

FIGURE 1

CORE ROD

SHIELDINGGASES SOLIDIFIED

SLAG

WELD METAL

WORK PIECE

MOLTENPOOL

SHIELDED METAL ARC WELDING

AC OR DCPOWERSOURCE

ELECTRODECABLE

ELECTRODEHOLDER

ELECTRODE

GROUNDCABLEWORK

SHIELDED METAL ARC WELDING CIRCUIT

FIGURE 2


Welding







Steels

Go To Test


Print


Glossary




Download)


Turn Pages




Download)


Filler Metals

COATING


















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 made 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, magnetic fields are set up throughout theweldment. In weldments that have varying thickness and protrusions, this magnetic

field can affect the arc by making 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 magnetic field produced.

2.2.2.2 Combination power sources that produce both AC and DC are available 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 electrode

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

positive (+)

produces welds with

deep penetration

and a narrower weld

bead as shown at

"B" in Figure 3.

FIGURE 3

DCPOWER SOURCE

ELECTRODE

DCPOWER SOURCE

ELECTRODE

A

HIGHER BURN-OFF RATE,LESS PENETRATION

DEEP PENETRATION,LOW BURN-OFF RATE

WORK PIECE

B

STRAIGHT POLARITY REVERSE POLARITYWORK PIECE



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




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. Performance of individual 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 electrode

over the weld joint and feed the electrode over the weld joint and feed the electrode into the

weld puddle as it is consumed. Electrode holders are available 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 workpiece. It may 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 overheating due to electrical resistance.

2.2.5 Welding Cables - The electrode cable and the ground cable are important parts ofthe welding circuit. They must be very flexible and have 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 voltage drop.

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

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

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

Total Cable Length (Ground Lead Plus Electrode Lead)Up to 50 ft. Up to 100 ft. Up to 250 ft. Up to 500 ft.

Cable Voltage Cable Voltage Cable Voltage Cable VoltageSize Drop Size Drop Size Drop Size Drop

20 to 180 #3 1.8 #2 2.9 #1 5.7 #0 9.1 180 Amps30 to 250 #2 1.8 #1 2.5 #0 5.0 #0 9.9 200 Amps60 to 375 #0 1.7 #0 3.0 #00 5.9 #000 9.3 300 Amps80 to 500 #00 1.8 #000 2.5 #0000 5.0 #0000 9.9 400 Amps100 to 600 #00 2.0 #0000 2.5 ... ... ... 500 Amps

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

WeldingServiceRange(Amperes)

VoltageDropFiguredAt

FIGURE 4

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



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















LESSON II

2.3 GAS TUNGSTEN ARC WELDING

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 employed,

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 compounds 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 importance. 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 important 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.

FIGURE 5

TRAVELDIRECTION

TORCH

SHIELDING GASNOZZLE

INERT GASSHIELD

WORK PIECE

TUNGSTENELECTRODE

ARC

FILLERMETAL

GAS TUNGSTEN ARC WELDING



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals


















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 moved over a stationary work piece or the torch may be

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

also fed automatically.

2.3.1 EQUIPMENT AND OPERATION - Gas tungsten arc welding may be accomplishedwith relatively 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. Protective equipment

Figure 6 shows a basic gas tungsten arc welding schematic.

FIGURE 6

REGULATORFLOW METER

GAS HOSE (WATER COOLED ONLY)

TORCH

* COMPOSITE CABLE

WATER COOLER

GAS COOLED ONLY

WELDING CABLE

SHIELDINGGAS SUPPLY

POWERSOURCE WATER

FROMTORCH

WATERTOTORCH

GROUND CABLE

WORK

* COMPOSITE CABLEGAS COOLED TORCH.CURRENT IN & GAS IN.

WATER COOLED TORCH.CURRENT IN & WATER OUT

GAS TUNGSTEN ARC WELDING CONNECTION SCHEMATIC



Welding





Go To Test


Steels

Print


Glossary



Download)



Turn Pages



Download)




Filler Metals















esab basic welding filler technology lesson ii common electric arc weldingprocesses

Documents