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WeldingPrinciples and PracticesThird Edition

Sacks and Bohnart

1

Gas Metal Arc

Welding Practice:

Jobs 22-J1±J23

(Plate)

Chapter 22



22 - 2

O bjectives

1. Describe GMAW operating variables

2. Describe GMAW weld defects

3. Describe GMAW safe operation4. Describe and demonstrate proper care, use, and

troubleshooting of equipment

5. Describe and demonstrate welding techniques

6. Make various groove and fillet welds with the

various modes of metal transfer with both solid and

metal cored electrodes



22 - 3

O perating Variables ThatAffect Weld Formation

Factors that affect operation of arc and weld

deposit

Sound welding of good appearance resultswhen variables in balance

Necessary to become familiar with all variables



22 - 4

Direct Current ElectrodePositive (DCEP)

Generally used for gas metal arc welding

± Provides maximum heat input into work allowing relatively

deep penetration to take place

± Assists in removal of oxides from plate

± Low current values produce globular transfer of metal from

electrode

On carbon steel shielding gas must contain minimum

of 80% argon

Ferrous metals need addition of 2 to 5% oxygen to gas

mixture



22 - 5

Gas Metal Arc DCEP Welding:Wire Positive, Work Negative

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.



22 - 6

Direct Current Electrode Negative (DCEN)

Limited use in welding of thin gauge materials

Greatest amount of heat occurs at electrode tip

Wire meltoff rate great deal faster than DCEP

Penetration also less than with DCEP

Arc not stable at end of filler wire

± Corrected by use of shielding gas mixture of 5%oxygen added to argon

± Meltoff rate reduced so benefit cancelled



22 - 7

Gas Metal Arc DCEN Welding:Wire Negative, Work Positive




22 - 8

Alternating Current

Seldom used in gas metal arc welding

Arc unstable because of current reversal

Combination of both DCEN and DCEP polarity, rate of metal transfer and depth of

penetration falls between those polarities

Found some use for welding of aluminum



22 - 9

Shielding Gas

Argon and helium first used for gas metal arc

± Continue to be basic gases

Argon used more than helium on ferrous metalsto keep spatter at minimum

± Also heavier than air so good weld coverage

Oxygen or carbon dioxide added to pure gases

to improve arc stability, minimize undercut,reduce porosity, and improve appearance of weld



22 - 10

Shielding Gas

Helium added to argon to increase penetration

Hydrogen and nitrogen used for only limited

number of special applications Carbon dioxide has following advantages:

± Low cost

± High density, resulting in low flow rates ± Less burn-back problems because of its shorter arc

characteristics



22 - 11

Specific Metal Recommendations

Aluminum alloys: argon

Magnesium and aluminum alloys: 75 percent

helium, 25 percent argon Stainless steels: argon plus oxygen

Magnesium: argon

Deoxidized copper: 75 percent helium, 25 percent argon preferred

Low alloy steel: argon, plus 2 percent oxygen



22 - 12

Specific Metal Recommendations

Mild steel: 15 percent argon, 25 percent carbon

dioxide (dip transfer); 100 percent CO2 may

also be used with deoxidized wire Nickel, Monel®, and Inconel®: argon

Titanium: argon

Silicon bronze: argon Aluminum bronze: argon



22 - 13

Joint Preparation

Joint design should provide for mosteconomical use of filler metal

Correct design for job depends on:

± Type of material being welded ± Thickness of material

± Position of welding

± Welding process

± Final results desired

± Type and size of filler wire

± Welding technique



22 - 14

Joint Preparation

Arc in gas metal arc welding more penetrating

and narrower than arc in shielded metal arc

welding therefore, smaller root openings may be used for groove welds

± Change in joint design increase speed of welding

100% penetration may be secured in ¼" plate

in square butt joint welded from both sides



22 - 15

Joint Preparation

No root face recommended for 60º single- or double-V butt joints

± Root opening should range from 0 to 3/32"

± Double-V joints may have wider root openingsthan single-V

Plates thicker than 1 inch should have

U-groove preparation ± Require less weld metal; root face thickness should

be less than 3/32" and root spacing 1/32 and 3/32"



22 - 16

V-Groove, Butt JointComparison




22 - 17

Joint Preparation

Multipass welding easier since absence of slag

ensures easier cleaning

For fillet welds deposit smaller weld beads onsurface of material

Certain types of joints backed up to prevent

weld from projecting through back side ± Blocks, strips and bars of copper, steel or ceramics



22 - 18

Comparison of Penetration in aFillet Weld

Carbon dioxide shieldedMAG weld versus coated

electrode weld.




22 - 19

Electrode Diameter

Influences size of weld bead, depth of penetration, andspeed of welding

General rule

± For same current, arc becomes more penetrating aselectrode diameter decreases and deposition rate increases

To get maximum deposition rate at given currentdensity, use smallest wire possible consistent with

acceptable weld profile Wire 0.045" and larger provide lower deposition rate

and deposit wider beads than small wires



22 - 20

Electrode Diameter

Filler wires should be same composition as materials being welded

Position of welding may affect size of electrode

Welding thin material ± Wires with diameters: 0.023/0.025, 0.030, 0.035"

Medium thick materials ± Wires with diameters: 0.045" or 1/16"

Heavy materials ± Wire with diameter: 1/8"

Small diameters recommended for vertical andoverhead positions



22 - 21

Electrode Extension

Length of filler wire that extends pas contact tube

Area where preheating of filler wire occurs

Also called the stickout

Controls dimensions of weld bead since length of extension affect burnoff rate

Exerts influence on penetration through its effect onwelding current ± As extension length increased, preheating of wire increases

and current reduced which in turn decreases amount of penetration into work

Stickout distance may vary from 1/8 to 1 1/4"



22 - 22

Electrode Extension

Short electrode extensions (1/8±1/2 inch) used for short circuit mode of transfer, generally with smaller diameter electrodes (0.023±0.045 inches)

Stainless steel favors shorter electrode extension because of its higher resistivity (1/8±1/4 inch) ± Longer and larger diameter electrode extensions used for

spray arcs (1/2±11/4 inches)

Excessive long arcs with active gases reduce the

mechanical properties in weld

± Various alloys being burned out as metal transferred across

longer arc



22 - 23

Electrode Extension

Tests indicated that when electrode extensionincreased from 3/16 to 5/8 inch, welding current thendrops approximately 60 amperes

Current reduced because of change in amount of preheating that takes place in wire

± As electrode extension increased, preheating of wire increases

± Thus less welding current required from power source at agiven feed rate

± Because of self-regulating characteristics of constant voltage power source, welding current decreased

± As welding current decreased, depth of penetration alsodecreases



22 - 24

Nomenclature of Area Between Nozzle and Workpiece




22 - 25

Position of the Gun

Expressed by two angles: travel and work

Bead shape changed by changing direction of wire asgoes into joint in line of travel

Gun Angle ± Can be compared to angle of electrode in shielded metal arc

welding

± Drag technique results in high narrow bead with deeper

penetration (10º drag angle) ± As drag angle reduced, bead height decreases, width

increases

± Increased travel speeds characteristic of push technique



22 - 26

Travel and Work Gun Angles

Axis of Weld




22 - 27

Travel and Work Gun Angles


Travel Angle

(T. A.)

Axis of Weld

(Drag) Travel Direction

(Push) Travel Direction

Work Angle

(W. A.)



22 - 28

Drag and Push Gun angles




22 - 29

Work Angle

Position of wire to joint in plane perpendicular to line of travel

Filler weld joints: work angle normally half of included angle between plates forming joint

Butt welds: work angle normally 90º to surfaceof plate being joined

Utilizes natural arc force to push weld metalagainst vertical surface to prevent undercut and provide good bead contour



22 - 30

Work and Gun Angles




22 - 31

Arc Length

Constant voltage welding machine used for gas metalarc welding provides for self-adjustment of arc length

± Arc length shortened, arc voltage reduced

± Arc length lengthened, arc voltage increased No change in wire-feed speed occurs

Corrected by automatic increase or decrease of burnoff rate of filler wire

Welder has complete control of welding current andarc length by setting wire-feed speed on wire feeder and voltage on welding machine



22 - 32

Arc Voltage

Decided effect upon penetration, bead height,and bead width

Chief function to stabilize welding arc and provide smooth, spatter-free weld bead

Higher or lower causes arc to become unstable

± Higher: produces wider, flatter bead and increases

possibility of porosity and increases spatter andincreases undercut in fillet welds

± Lower: causes bead to be high and narrow



22 - 33

Arc Voltage

High arc voltages result in globular transfer

± Spatter prone and reduces deposition efficiency

Has sharp crackling sound when proper arcvoltage for short circuit transfer

± Spray arc have hissing sound

Not set to control penetration Better control of weld profile and arc stability



22 - 34

Relationship of Arc Length toWeld Bead Width


High VoltageLow Voltage

Arc Length

Arc Length

Electrode

Electrode



22 - 35

Penetration Comparisons


Arc voltage too high

for travel speed.

Arc voltage too slow

for travel speed

Proper arc voltage

for speed



22 - 36

Wire-Feed Speed

Fixed relationship between rate of filler wire burn off and welding current

Electrode wire-feed speed determines welding current

± Current set by wire-feed speed control on wire feeder

Excessive speed, welding machine cannot put outenough current to melt wire fast enough

± Stubbing or roping of wire occurs

± Causes convex weld beads and poor appearance

Decrease in speed results in less electrode being melted

Generally ± high setting of filler wire speed rate resultsin short arc, slow speed in long arc



22 - 37

Effect of Wire-Feed Speeds




22 - 38

Welding Current

Determines amount of current delivered at arc

Often related to current density

± Amperage per square inch of cross-sectional areaof electrode

At given amperage, current density of electrode 0.035"in diameter higher than of electrode 0.045" in diameter

Area of current-carrying sheath of metal coredelectrode more complex to calculate

± Current densities much higher with metal coredelectrodes than solid wire



22 - 39

Welding Current

If going to maintain given amperage and switch from

solid wire to metal core, either jump one wire

diameter size and keep wire-feed speed same or keep

same wire size and increase wire-feed speed

Each type and size of electrode has minimum and

maximum current density

± Best working range lies between

Direct relationship between welding current and

penetration

± Welding current increases, penetration increases



22 - 40

Welding Current

Table 22-3 gives comparative current ranges and other parameters for welding carbon steel, stainless steel,and aluminum

Increases in current will increase bead height andwidth (voltage must also be increased)

Too high

± Possibility of electrode burn-back into tube, arc unstable

and gas shielding disturbed, spatter Too low

± Arc unstable, poor fusion, electrode becomes red hot, arcmay be extinguished, less penetration



22 - 41

Travel Speed

Has decided effect on penetration, bead size, andappearance

At given current density, slower travel speeds provide

proportionally larger weld beads and more heat inputin base metal per unit length of weld

± Too slow, unusual weld buildup occurs

Progressively increased travel speeds have opposite

effects ± Less weld metal deposited with lower heat input per unit

length of weld

± Produces narrower weld bead and lower contour



22 - 42

Travel Speed

Excessively fast speeds causes undercut

Influenced by thickness of metal being welded,

joint design, cleanliness, joint fitup, andwelding position

If increased, necessary to increase wire-feed

speed, which increases current and burnoff rate

Too low produces overlap of base metal and

even burn-through on this material



22 - 43

Arc Position

Arc must be on

leading edge of

weld pool to

assure penetrationand fusion.




22 - 44

O ptimum Travel Speed




22 - 45

Summary of O perating Variables

Height and width of bead depend on adjustment of these variables

± Joint preparation

± Gas flow rate ± Voltage

± Speed of travel

± Arc length

± Polarity Variables adjusted on basis of type of material being

welded, thickness of material, position of welding,deposition rate required, and final weld specifications

± Gun angle

± Size and type of filler wire ± Electrode extension

± Characteristics of the shieldinggas

± Wire-feed speed (current)



22 - 46

Summary of O perating Variables

Welding current and travel speed have similar

effect on both bead height and width

± Each variable increases or decreases both beadheight and width at same time

Arc voltage

± As arc voltage increases, bead height decreases and

bead width increases, flattening bead

± Affects shape and size of bead



22 - 47

Weld Defects

Defects found in welds made by gas metal arc process similar to those in other welding

± Causes and corrective action entirely different

Incomplete penetration

± Result of too little heat input in weld area

± Correct by increasing wire-feed speed and reducing

electrode extension to obtain maximum current for particular wire-feed setting

± Also causes by improper welding techniques



22 - 48

Excessive Penetration

Usually causes excessive melt-through

Result of too much heat in weld area

± Reducing wire-feed speed to obtain lower amperage or

increasing speed of travel Another cause is improper joint design

± Root opening too wide or root face too small

± Correct by checking position of welding and root face and

opening Remedied during welding by increasing electrode

extension distance and weaving gun



22 - 49

Whiskers

Short lengths of electrode wire sticking through

weld on root side of joint

Caused by pushing electrode wire past leadingedge of weld pool

Can be prevented by

± Reducing wire-feed speed

± Increasing electrode extension distance

± Weaving gun



22 - 50

Voids

Referred to as wagon tracks because of resemblancein radiographs to ruts in dirt road

May be continuous along both sides of weld

Found in multipass welding ± Underneath pass has bead with large contour or bead with

too much convexity or undercut

± Next bead does not completely fill void between previous

pass and plate Prevent by making sure edges of all passes filled in so

undercut cannot take place and arc melts previous bead and fuses into sides of joint



22 - 51

Incomplete Fusion

Also referred to as overlap

Result of improper gun handling, low heat and

improper speed of travel

To prevent:

± Direct arc so it covers all areas of joint

± Keep electrode at leading edge of pool

± Reduce size of pool as necessary by adjusting travel speed ± Check current values carefully; keep short electrode

extension



22 - 52

Porosity

Most common defect in welds

Exists on face of weld readily detected

Below surface must be determined byradiograph ultrasonic or other testing methods

Causes of most porosity are contamination byatmosphere, change in physical qualities of

filler wire, and improper welding technique Also caused by entrapment of gas evolved

during weld metal solidification



22 - 53

Causes of Porosity

Travel so fast that part or all of shielding gaslost, and atmospheric contamination occurs

Shielding gas flow rate too low so gas does notfully displace all air in arc area

Shielding gas flow rate too high drawing air into arc area and causing turbulence

Shielding gases must be of right type for metal being welded

Shielding gases must be pure and dry



22 - 54

Causes of Porosity

Gas shield may be blown away by wind or

drafts

May be defects in gas system Excessive voltage for arc required can cause

loss of its deoxidizers and alloying elements

Foreign material such as oil, dirt, rust, grease,and paint on wire or material to be welded

Improper welding techniques are used



22 - 55

Other Defects

Warpage

± Occurs when forces of expansion and contraction

poorly controlled

Spatter

± Made up of very fine particles of metal on plate

surface adjoining weld area

± Usually caused by high current, long arc, irregular and unstable arc, improper shielding gas, improper

gun angle, electrode extension, or clogged nozzle



22 - 56

Other Defects

Weld cracking

± Comes from compositional problems, poor joint design, and poor welding technique

± Prevent by making sure filler metal has compositionsuitable for base metal and providing for expansion andcontraction forces during welding

Irregular weld shape

± Include too wide, too narrow, excessively convex or

concave surface and those with coarse, irregular ripples ± Caused by poor gun manipulation, too fast or too slow

speed of gun travel, too high or too low current, improper arc voltage, improper shielding gas, improper extension



22 - 57

Undercutting

Cutting away of base material along toes of weld

May be present in cover pass weld bead or inmultipass welding

Condition usually result of high current, high voltage,excessive travel speed, low wire-feed speed, poor guntechnique, improper gas shielding, or wrong filler wire

To correct, move welding gun from side to side in joint, and hesitate at each side before returning toopposite side



22 - 58

Safe Practices

Safety most important consideration to both

worker and employer

Welding no more dangerous than other industrial operations

Safety precautions and protective equipment

required for MIG/MAG process essentially

same as for any other electric welding process



22 - 59

Eye, Face, and Body Protection

Welding helmets and protective clothing

necessary

Radiant energy produced by gas-shielded process 5 to 30 times more intense than

produced by shielded metal arc welding

± Lowest intensities produced by gas tungsten arc

± Highest by gas metal arc

± Argon produces greater intensities than helium



22 - 60

Clothing Regulations

Standard arc welding helmets with lenses ranging inshade from no. 6 for work using up to 30 amperes tono. 14 for work using more than 400 amperes should

be worn ± Arc should never be viewed with the naked eye whenstanding closer than 20 feet

Skin should be covered completely to prevent burnsand other damage from ultraviolet light

± Back of the head and neck should be protected fromreflected radiation

± Gloves should always be worn



22 - 61

Clothing Regulations

Shirts should be dark in color to reduce

reflections

± Have tight collar and long sleeves

± Leather, wool and aluminum-coated cloth can

withstand action of radiant energy reasonably welld



22 - 62

Handling of Gas Cylinders

Stored cylinders should be in protected area

away from fire, cold, and grease and away

from general shop activity

Cylinders must be secured to equipment to

prevent their being knocked over

Proper regulators and flowmeters must be used

with each special type of cylinder



22 - 63

Handling of Gas Cylinders

Cylinders should not be dropped, used as

rollers, lifted with magnets, connected into

electric circuit, or handled in any other way

that might damage cylinder or regulator

When cylinders empty, should be stored in

upright position with valve closed



22 - 64

Ventilation

Ozone generated in small quantities, generally below allowable limits of concentration

Nitrogen dioxide also present around area of

arc in quantities below allowable limits

Carbon dioxide shielding may create hazardfrom carbon monoxide and carbon dioxide if

welder¶s head in path of the fumes or if welding done in confined space

± Special ventilation should be provided



22 - 65

Ventilation

Eye, nose, and throat irritation can be produced when

welding near such degreasers as carbon tetrachloride,

trichlorethylene, and perchloroethylene

± Break down into phosgene under action of powerful raysfrom arc

± Locate degreasing operations far away from welding

activities

Much of welding smoke and fumes can be engineeredout of GMAW arc by use of higher argon percent and

pulse-spray mode of transfer



22 - 66

Ventilation

During welding, certain metals emit toxicfumes that may cause respiratory irritation andstomach upset

± Most common toxic metal vapors given off bywelding of lead, cadmium, copper, zinc, and beryllium

± Fumes can be controlled by general ventilation,local exhaust ventilation, or respiratory protective

equipment Welding guns can be purchased with smoke

extractor capability



22 - 67

Electrical Safety

Hazard less than that with shielded meal arc

process

± O pen circuit voltage considerably less

Electrical maintenance should be done only by

qualified person

± NEVER worked on in electrical HOT condition



22 - 68

Wire-Feeder Safety

Turn power off when aligning and adjustingdrive rolls

Avoid pinch points when working near drive

rolls

Remember force being applied to wiresufficient to push it through your hand or other

body parts Never let exposed wire come in contact with or

be pointed at your body



22 - 69

Fire Safety

Welding should not be done near areas whereflammable materials or explosive fumes present

Paint spray or dipping operations should not be

located close to any welding operation Combustible material should not be used for floors,

walls, welding tables, or in immediate vicinity of welding operation

When welding on containers that have previouslycontained combustible materials, special precautionsshould be taken

Use ³hot work permit´ as required



22 - 70

Care and Use of Equipment

Do not push gun into arc like an electrode

± Wire feeder pushes wire into arc

Either push or drag travel angle can be used

If possible, welding should be done in flat welding position to take advantage of increased penetrationand deposition rate characteristic of the MIG/MAG process

Small fillets and butt welds should be positioned soarc can run slightly downhill

Equipment has to be kept clean, in proper adjustment,and in good mechanical condition



22 - 71

Drag and Push Methods

Produces large wide beads Produces flatter bead shape




22 - 72

Care of Nozzles

Keep the gun nozzle, contact tube, and wire-feeding system clean to eliminate wire-feedingstoppages

± Nozzle is natural spatter collector

If spatter builds up thick enough, it can actually bridge gap and electrically connectinsulated nozzle to contact tube

To remove spatter, use soft, blunttool for prying




22 - 73

Care of Nozzles

Spatter almost falls out by itself if nozzle kept

clean, shiny and smooth

Antispatter compound may be applied to gunnozzle and contact tube end

Do not clean by tapping or pounding on solid

object

± Bends gun nozzles, damages threads and high

temperature insulation in nozzle can break



22 - 74

Care of Contact Tubes

Transfers welding current to electrode wire

Hole has to be big enough to allow wire with slight

cast to pass through easily

Wire wears hole to oval shape

± Wire slides more easily, but transfer of current not as good

and arcing in tub results

± Spatter flies up into bore and wire slows down because of

friction

± Must be replace; secure tightly in gun and check

periodically for tightness



22 - 75

Care of Wire-Feed Cables

Wire-feed conduit flexible steel tube that does

not stretch

Main source of friction in wire-feed system Should be kept clean and straight as possible

± Clean with dry compressed air

Lubricate with dry powdered graphite reducesfriction

Clean every time spool or coil changes



22 - 76

Bird Nesting

Wire coils sideways between wire-feed cable

and drive rolls

Prevent by accurate alignment of wire-feedcable inlet guide

± Aligned exactly with rollers so wire does not have

to make reverse bend

± Notch in drive rolls must be in perfect alignment to provide smooth passage for wire



22 - 77

Cleanliness of Base Metal

Clean area thoroughly before welding

Remove all rust, scale, burned edges and

chemical coatings ± Gas producers

± Porosity is result

Intense heat of arc burns away some of the

contaminants



22 - 78

Arc Blow

Arc blown to one side or other by condition of pull

and counter-pull as magnetic field is distorted

± Ionized gases carrying arc from end of electrode wire to

work act as flexible conductor with magnetic field around it ± When placed in location such as corner of joint or end of

plate, magnetic field distorted and pulls in another direction

± Magnetic field tries to return to state of equilibrium

Does not occur with a.c. welding arcs ± Forces exerted by magnetic field reversed 120 times per

second thus keeping magnetic field in equilibrium

Connecting Work to Minimize



22 - 79

Connecting Work to MinimizeArc Blow

Suggestions to shorten trial-and-error process

to correct or minimize arc blow

Attach work lead or leads directly onworkpiece if possible

Connect both ends of long, narrow weldments

Use electrical conductors of proper length

Weld away from work connection




22 - 80


On parts that rotate, use rotating work connection or allow work cable to wind up nomore than one or two turns

In making longitudinal welds on cylinders, usetwo work connections²one on each side of theseam as close as possible to point of starting

If multiple work connections necessary, makesure cables are same size and length and haveidentical terminals




22 - 81


On multiple-head installations, all heads shouldweld in same direction and away from work connection

Use individual work circuits on multiple-headinstallations

Do not place two or more arcs close to one

another on weldments that are prone tomagnetic disturbance with one arc such astubes or tanks requiring longitudinal seams



22 - 82

Setting Up Equipment

Constant voltage d.c. power source

Wire-feeding mechanism with controls and spooled or reeled filler wire mounted on fixture

Gas-shielding system consisting of one or morecylinders of compressed gas, pressure-reducingcylinder regulator, flowmeter assembly

Combination gas, water, wire, and cable controlassembly and welding gun of correct type and size

Connecting hoses and cables, work lead, and clamp Face helmet, gloves, sleeves (if necessary), and

assortment of hand tools



22 - 83

Assumed Safety Precautions

Welding equipment installed properly

Welding machine in dry location, and no water

on floor of welding booth Welding booth lighted and ventilated properly

All connections tight, and all hoses and leads

arranged so they cannot be burned or damaged

Gas cylinders securely fastened so they cannot

fall over and not part of electrical circuit



22 - 84

Starting Procedure

1. Check power cable connections; connect guncable to proper welding terminal on weldingmachine and work cable end connected to

proper terminal on welding machine2. Start welding machine by pressing on button

or, in case of engine drive, start engine

3. Turn on wire-feed unit4. Check gas-shielding supply system

5. Check water flow if gun water cooled



22 - 85

Starting Procedure

5. Set wire-feed speed control for type and size of filler wire and for job

6. Voltage rheostat should be set to conform to type

and thickness of material being welded, diameter of filler wire, the type of shielding gas, and type of arc

7. Adjust for proper electrode extension beyondcontact tube

8. To start arc, touch end of electrode wire to proper place on weld joint, usually just ahead of weld bead,with current shut off; lower helmet and press guntrigger on torch

h i h i



22 - 86

Shutting Down the Equipment

1. Stop welding and release gun trigger

2. Return feed speed to zero position

3. Close gas outlet valve in top of gas cylinder

4. Squeeze welding gun trigger, hold it down,and bleed gas lines

5. Close gas flowmeter valve until finger-tight

6. Shut off welding machine and wire feeder

7. Hang up welding gun and cable assembly

S i h ld



22 - 87

Starting the Weld

Running start

± Arc started at beginning of weld

± Electrode end put in contact with base metal

± Trigger on torch pressed

± Tends to be too cold at beginning of weld

Scratch start

± Arc struck approximately 1 inch ahead of beginning of weld

± Arc quickly moved back to starting point of weld, direction

of travel reversed, and weld started

± Arc may also be struck outside of weld area on starting tab

Fi i hi h W ld



22 - 88

Finishing the Weld

Arc should be manipulated to reduce penetration

depth and weld pool size when completing weld bead

± Decreases final shrinkage area

± Reduction accomplished by rapidly increasing speed of welding for approximately 1 to 2 inches of weld length

± Trigger released, stopping wire feed and interrupting

welding current

Gun trigger can be turned on and off several times atend of weld to fill crater

G A l



22 - 89

Gun Angle

Push angle of 5° to 15° generally employed whenwelding in flat position

± Take care push angle not changed as end of weldapproached

Work angle equal on all sides when welding uniformthicknesses

Welding in horizontal position, point gun upwardslightly

Thick-to-thin joints, direct arc toward heavier section

Slight drag angle may help when welding thinsections

C l f A



22 - 90

Control of Arc

Arc voltage controls penetration, bead contour,

and such defects as undercutting, porosity and

weld discontinuities

Arc should be occasionally noisy for most

applications of spray arcs

P d E i P bl



22 - 91

Process and Equipment Problems

Study tables 22-6 which lists problems with

MIG/MAG short arc process and their

correction

Table 22-7 lists problems with MIG/MAG

process and equipment, their causes, and

possible remedies

P ti J b



22 - 92

Practice Jobs

Practice gas metal arc welding on mild steel,

aluminum, and stainless steel

Specifications given in Job Outline in order

assigned by instructor

Beyond these job, practice other forms of joints

in all positions

± Use various types and sizes of filler wire and

different shielding gases

Precautions to O bserve When



22 - 93

ecaut o s to Obse ve W eDoing Practice Jobs

Avoid excessive current values

Check your welding speed

Make sure that gas flow adequate

Keep wire centered in gas pattern and in center of joint; make sure correct electrode angle maintained atall times

Select proper filler wire for material being welded andfor such situations as rust, scale, and excessive oxygen

When welding from both sides of plate, be sure root pass on first side deeply penetrated by root pass onsecond side

MIG/MAG Welding of



22 - 94

gCarbon Steel

Bulk of all welding done on carbon steel

MIG/MAG welding on increase

± Welders find it relatively easy to master ± Consistently produces sound welds at high rate of

speed

Groove Welds:



22 - 95

Jobs 22-J1 and J2

Plate up to 1/8" thick may be butt welded with

square edges with root opening of 0 to 1/16"

Heavier plate, 3/16 and 1/4 inch may be

welded without beveling edges if 1/16 to 3/32"

opening provided

Bead should be wider than root spacing for

proper fusion

Two passes, one from each side usually needed

Groove Welds:



22 - 96

Jobs 22-J1 and J2

For code welding, plate thicknesses from 3/16to 1" should be beveled ± 60º single- or double-V without root face

recommended

± Root opening of 0 to 1/16" should be maintained

± Wider root openings may be provided for double-V joints

± Single-V grooves backing pass from reverse side

generally required Less distortion when welding from both sides

of joint

Groove Welds:



22 - 97

Jobs 22-J1 and J2

O pen root joint should be run using short

circuit or pulse spray for ferrous metals

Practice 3G using both uphill and downhill

techniques

U-grooves used on plate thicker than 1 inch

± Root spacing between 1/32 and 3/32" maintained

± Root face of 3/32" or less to assure penetration

± Requires less filler metal than V groove butt joint

Groove Welds:



22 - 98

Jobs 22-J1 and J2

Argon-oxygen mixture containing 1-5% oxygen

recommended for spray arc welding

± Oxygen improves flow of weld metal and reduces tendency

to undercut Argon with 10% CO2 sometimes used

Carbon dioxide at 100% used by arc not true spray arc

± Popular for MAG small wire welding

Short arc welding of carbon steel uses mixture of 75%

argon and 25% carbon dioxide

Fill t W ld J b 22 J3 J10



22 - 99

Fillet Welds: Jobs 22-J3-J10

Used in T-joints, lap joints, and corner joints

Deposit rate and rate of travel high with deep

penetration

Permits smaller fillet welds than with stick electrodewelding

Position of nozzle and speed of welding important

Welding may be single pass or multipass ± Multipass may be done with stringer or weave beads

Each pass must be cleaned carefully

Inspection and Testing



22 - 100



Outside corner joint in steel plate welded with gas metal

arc welding process in the flat position.

Penetration through back side of corner joint welded

in the flat position.




22 - 101


Fillet weld on lap joint in steel plate

welded with gas metal arc welding

process in 2F position.


Fillet weld on lap joint in steel plate weldedwith gas metal arc welding process in 3F

position, downhill. Note porosity caused

by poor gas shielding.




22 - 102



Fillet weld on T- joint welded

in the 2F position with thegas metal arc welding

process in steel plate.

Penetration through back side of a

V-groove butt joint weldedin the 1G position.

The f irst (root) pass of a V-groove

butt joint welded in the 1G positionwith the gas metal arc welding

process in steel plate.

Fillet and Groove Welding Combination Project:



22 - 103

g j

Job Qualification Test 1

Purpose

± Ability to read print

± Develop bill of materials

± Thermally cut

± Fit components together

± Tack and weld carbon steel project

Follow instructions found in Fig. 22-26

Fillet and Groove Welding Combination Project:



22 - 104

g j


Inspection and testing (visual inspection only)

± Shall be no cracks or incomplete fusion

± Shall be no incomplete joint penetration in groove weldsexcept as permitted for partial joint penetration groove

welds

± Undercut shall not exceed lesser of 10% of base metalthickness or 1/32 inch

± Frequency of porosity shall not exceed one in each 4 inches

of weld length, and maximum diameter shall not exceed3/32 inch

± Welds shall be free from overlap

± Only minimal weld spatter shall be accepted

Fillet and Groove Welding Combination



22 - 105

Project: Job Qualification Test2

Purpose


± Develop bill of materials

± Thermally cut


± Tack and weld carbon steel project

± Use spray arc mode of metal transfer

± Note on Fig. 22-27

Fillet and Groove Welding Combination



22 - 106

Project: Job Qualification Test2

Inspection and testing (visual inspection only)

± Shall be no cracks or incomplete fusion

± Shall be no incomplete joint penetration in groove weldsexcept as permitted for partial joint penetration groove

welds

± Undercut shall not exceed lesser of 10% of base metalthickness or 1/32 inch

± Frequency of porosity shall not exceed one in each 4 inches

of weld length, and the maximum diameter shall not exceed3/32 inch

± Welds shall be free from overlap

± Only minimal weld spatter shall be accepted

Groove Weld Project: Joblifi i



22 - 107

Qualification Test 3

Project



± Tack and weld carbon steel unlimited thickness test

plate

± Using spray arc mode of metal transfer

± Instructions in notes in Fig. 22-28




22 - 108


After tacking, have it inspected

After complete welding, use visual inspectionand cut specimens for bend testing

Use side bend test procedures and check:

Testing criteria:

± No cracks or incomplete fusion

± No incomplete joint penetration in groove weldsexcept as permitted for partial joint penetrationgroove welds




22 - 109


Testing criteria (cont.):

± Undercut shall not exceed lesser of 10 percent of

base metal thickness or 1/32 inch

± Frequency of porosity shall not exceed one in each

4 inches of weld length and maximum diameter

shall not exceed 3/32 inch

± Welds shall be free from overlap ± Only minimal weld spatter shall be accepted

Side Bend Acceptance Criteria as Measured



22 - 110

on Convex Surface of Bend Specimen

No single indication shall exceed 1/8 inch measured in

any direction on surface

Sum of greatest dimensions of all indications on

surface, which exceed 1/32 inch, but are less than or equal to 1/8 inch, shall not exceed 3/8 inch

Cracks occurring at corner of specimens shall not be

considered unless there definite evidence that they

result from slag inclusions or other internaldiscontinuities

MIG Welding of Aluminum



22 - 111


Readily joined by welding, brazing, soldering,adhesive bonding, and mechanical fastening

Lightweight

Alloyed readily with many other metals Highly ductile and retains ductility at subzero

temperatures

High resistance to corrosion, no colored salts, not toxic

Good electrical and thermal conductivity High reflectivity to both heat and light

Nonsparking and nonmagnetic




22 - 112


Easy to fabricate

May be given wide variety of mechanical,electrochemical, chemical and paint finishes

Needs high heat input for fusion welding

Aluminum and its alloys rapidly develop oxidefilm when exposed to air (melting point 3600ºF)

± Must be removed during welding Removed by fluxes, action of arc in inert gas

atmosphere or mechanical and chemical means




22 - 113


MIG and TIG replaced stick electrode

welding for aluminum and its alloys

± Small percentage still using stick electrodes

Type of joint and position of welding

determines process to used on thicknesses

1/8 inch and under

Factors that Make Gas Metal Arc Welding



22 - 114

Desirable Joining Process for Aluminum

Cleaning time reduced because there no flux on

weld

Absence of slag in weld pool eliminates

possibility of entrapment

Weld pool highly visible due to absence of

smoke and fumes

Welding can be done in all positions

Joint Preparation



22 - 115

Joint Preparation

Designed like those for steel

Narrower joint spacing and lower welding currentsused

Foreign substances must be removed ± Wiped off or removed by vapor degreasing

± Oxide film removed by chemical and mechanical cleaningmethods

Weld as soon as possible before oxide film has chanceto form again

Sheared edges can also cause poor quality welds

Shielding Gas



22 - 116

Shielding Gas

Argon preferred for welding aluminum platethicknesses up to 1 inch

Plate thicknesses 1-2 inches may use: ± Pure argon, mixture of 50% argon and 50% helium, or

mixture of 75% argon and 25% helium ± Helium provides high heat and argon excellent cleaning

action

Plate thicknesses from 2-3 inches ± Mixture of 50% argon and 50% helium or 25% argon and

75% helium

Plate thicknesses greater than 3 inches ± Mixture of 25% argon and 75% helium

Spray Arc Welding



22 - 117

Spray Arc Welding

Weld metal deposited continuously

More arc energy and greater heat provided for melting

filler wire and base material

Helium, helium-argon mixtures and argon used asshielding gases

± Choice dependent upon type of material, thickness and

welding position

Welding can be done in all positions

GMAW-P very effective when welding aluminum

Out-of-Position Welding



22 - 118

Out of Position Welding

Horizontal position

± Care must be taken to penetrate to root of joint

when welding butt joints and T-joints

± Overheating in any one area causes sagging,

undercutting or melt-through to back of joint

± Weld metal should be directed against upper plate

± In multipass welding, be sure fusion between passes

Horizontal Position



22 - 119

Horizontal Position

Welding T- joint in aluminum

plate in 2F position

Welding V-groove butt joint

in aluminum plate in 2G position.


Out-Of-Position Welding



22 - 120

Out Of Position Welding

Vertical position

± Travel-up technique on fillet and groove welds

± Do not use too high welding current nor deposit too large

weld bead ± Slight side-to-side motion helpful

Overhead position

± No problem with fillet and groove welds

± Welding current and travel speed lower than flat position

± Gas flow rate higher because gas has tendency to leave area

± Somewhat awkward ± assume relaxed position as possible

Out-Of-Position Welding



22 - 121

Out Of Position Welding


Welding V-groove butt joint in

aluminum plate in 3G position, uphill.

Welding T- joint in aluminum

plate in 3F position, uphill.

Butt Joints: Jobs 22-J11 and J12



22 - 122

Butt Joints: Jobs 22 J11 and J12

Easy to design

Require minimum of base material

Perform better under fatigue loading

Require accurate alignment and edge preparation Usually necessary to bevel edge on thicknesses of ¼"

or more to permit root pass penetration

± On heavier plate, chipping back side and welding back side

with one pass ± Sections with different thicknesses should be beveled before

welding

Lap Joints: Job 22-J13



22 - 123

Lap Joints: Job 22 J13

More widely used on aluminum alloys than on

other materials

Use double-welded, single-lap joints in

thicknesses of aluminum up to ½"

Require no edge preparation

Easy to fit

Require less jigging than butt joints

T-Joints: Jobs 22-J14-J16



22 - 124

T Joints: Jobs 22 J14 J16

Seldom require edge preparation on material ¼" or

less in thickness

Fully penetrated if weld fused into root of joint

Easily fitted and normally require no back chipping

Jigging usually quite simple

Better to put small continuous fillet weld on each side

of joint rather than one large weld on one side Continuous fillet welding recommended over

intermittent welding for longer fatigue life

Edge and Corner Joints



22 - 125

Edge and Corner Joints

Economical from standpoint of preparation,

base metal used, and welding requirements

Harder to fit up

Prone to fatigue failure

Edges do not require preparation





Main Causes of Cracking inAluminum Welds



22 - 128

Aluminum Welds

Generally in crater or longitudinal form

Crater cracks

± Cause: arc broken sharply and leaves crater

± Cure: manipulate gun properly

Longitudinal cracks caused by

± Incorrect weld metal composition

± Improper welding procedure ± High stresses imposed during welding by poor joint

design or poor jigging

Main Causes of Porosity inAluminum Welds



22 - 129

Aluminum Welds

Hydrogen in the weld area

Moisture, oil, grease, or heavy oxides in the weld area

Improper voltage or arc length

Improper or erratic wire feed

Contaminated filler wire (Use as large a diameter as

possible and GMAW-P if lower heat is needed.)

Leaky gun Contaminated or insufficient shielding gas

Major Causes of Incomplete Fusion of

Weld Metal ith Base Metal



22 - 130

Weld Metal with Base Metal

Incomplete removal of oxide film before

welding

Unsatisfactory cleaning between passes

Insufficient bevel or back chipping

Improper amperage (WFS) or voltage

Causes of Inadequate Penetration at Root

of Weld and Into Side Walls of Joint



22 - 131

of Weld and Into Side Walls of Joint

Low welding current (WFS)

Improper filler metal size

Improper joint preparation Too fast travel speeds for the selected wire-

feed speed

Causes of Metallic and Nonmetallic

Inclusions in Aluminum Welds



22 - 132

Inclusions in Aluminum Welds

Copper inclusions caused by burn-back of

electrode to contact tube

Metallic inclusions from cleaning weld with

wire brush which leaves bristles in weld

Nonmetallic inclusions from poor cleaning of

base metal

Always use push gun travel angle when

welding aluminum

Groove Weld Project:Job Qualification Test 4



22 - 133


Purpose



± Tack ± Weld aluminum test plates

± Using spray arc mode of metal transfer

Inspection and testing

± Visual inspection

± Perform side bend tests



22 - 134Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Performance Qualif ication

Test GM AW Spray Transfer, Aluminum

3G and 4G Positions

AWS SENSE

Shown only to illustrate what a qualif ication test would

look like. Follow it and inspect and test as listed in text.

MAG Welding of StainlessSteel



22 - 135

Steel

Heat and corrosion resistant alloy

± Always contains high percentage of chromium inaddition to nickel and manganese

Excellent strength-to-weight ratios Many alloys possess high degree of ductility

Widely used in products such as tubing, piping,kitchen equipment, ball bearings

Supplied in sheets, strip, plate, shapes, tubing, pipe and wire extrusions

MAG Welding of StainlessSteel



22 - 136

Steel

Lower rate of thermal conductivity than carbon steel ± Heat retained in weld zone longer

Thermal expansion greater than carbon steel ± Causes greater shrinkage stresses and warpage

Has tendency to undercut All standard forms of joints used in fabrications

Copper backing bars necessary for welding sectionsup to 1/16" thick

No air must be permitted to reach underside of weldwhile weld pool solidifying (air weakens it) ± If no backing bar, argon should be used as purge gas shield

Advantages of MAG WeldingStainless Steel



22 - 137

Stainless Steel

Absence of slag-forming flux reduces cleaningtime and makes it possible to observe weld pool

Continuous wire feed permits uninterruptedwelding

MAG lends itself to automation

Welding may be performed with short-circuiting, spray, or pulsed spray modes of transfer

Spray Arc Welding



22 - 138

p y g

Electrode diameters as large as 3/32" can be used for stainless steel ± 1/16" wire used with high current to create spray arc

transfer of metal

DCEP used for most stainless-steel welding Most common gas: mixture of Ar and 1 to 2%O

± Recommended for single-pass welding

Push travel angle should be employed on plate ¼"thick or more

Gun should be moved back and forth in direction of travel and slightly from side to side

Short Arc Welding (GMAW-S)



22 - 139

g ( )

Requires low current ranging form 20 to 175 amperes;

low voltage of 12 to 20 volts, small diameter wires

Metal transfer occurs when filler wire short circuits

with base metal Ideally suited for most stainless-steel welding on

thicknesses from 16 gauge to 1/16"

± Also for first pass in which fitup is poor or copper

backing unsuitable

± Very desirable in vertical and overhead positions for

first pass

Short Arc Welding (GMAW-S)



22 - 140

g ( )

For stainless steel in light gauges, triple

mixture of gas gives good arc stability and

excellent coalescence

± 90% helium, 7 ½% argon and 2 ½% carbon dioxide

± Produces small heat-affected zone that eliminates

undercutting and reduces distortion

± Does not lower corrosion resistance ± Flow rates must be increased because of lower

density of helium

Pulse Spray Arc (GMAW-P)



22 - 141

Can be done with lower current levels andhigher wire-feed speeds

Can be used on all thickness ranges

Spray-type gas: 1 and 2% oxygen withremainder being argon most common

Weld more fluid and flows well because arc on

all the time Spatter reduced on thin base metals ascompared to short-circuiting mode of transfer

Hot Cracking



22 - 142

Tendency of some stainless steels

± More welding passes needed

± Stringer beads recommended instead of weave

Reduce contraction stresses and cooling more rapid

Can reduce when welding sections 1 inch or

thicker by preheating to 500ºF

± Also reduce by GMAW-S or P welding

Stainless-Steel Sensitization



22 - 143

Carbide precipitation

± Sensitizing chromium out of individual grains of austenitic

types of stainless steel

± Occurs most readily in 1,200ºF heat range

To reduce situation

± Use GMAW process with its rapid speed and high

deposition rate

± Use stabilized and low carbon grades of stainless steel ± Using proper filler metals such as ER308L which is low in

carbon

Inspection and Testing:Jobs 22-J17-J23



22 - 144

Jobs 22 J17 J23

Inspect each weld carefully for defects

Fillet weld on lap joint in 3/8" stainless-steel plate weldedin the 1F position with the gas metal arc welding process.


Inspection and Testing:Jobs 22-J17-J23



22 - 145

Jobs 22 J17 J23

Fillet weld on T- joint in 3/8" stainless-steel plate

welded in 1F position with gas metal arc welding process.

Fillet weld on T- joint in 3/8" stainless-steel plate

welded in 2F position with gas metal arc welding process.


Copper and Its Alloys



22 - 146

May be welded successfully by gas metal arc process

Electrolytic copper can be joined by using specialtechniques, but weldability not good

Various grades of deoxidized copper readily weldable

with MIG process ± Deoxidized filler wires necessary

Filler wires of approximately matching chemistryused

Argon preferred shielding gas for material 1" andthinner ± Flow of 50 cubic feet per hour sufficient

± Heavier material uses 65% and 35% argon




22 - 147

Joint design like any other metal

± Steel backup necessary for sheets 1/8" or thinner

Welding currents on high side required

± Preheat not required when welding ¼" or less

Always provide good ventilation when weldingcopper and its alloys

± Beryllium-copper alloy dangerous




22 - 148

GMAW-B

± Variation of GMAW process where B indicates

brazing or just MIG brazing

± Uses silicon-bronze type electrode with inertshielding with Argon 100% most common

± Main application for coated carbon steel sheet

metal (light gauge)

± Zinc coating applied for corrosion resistance

± Base metal not melted (hence brazing operation)

Nickel and Nickel-Copper Alloys



22 - 149

oys

Can be welded using gas metal arc process

Remove all foreign material in vicinity sincesusceptible to severe embrittlement andcracking when come in contact with foreignmaterials

Argon generally preferable for welding up toabout 3/8 inch in thickness ± Above that thickness, argon-helium mixtures

usually more desirable

Joint preparation like other metals

Magnesium



22 - 150

Silvery white metal, two-thirds weight of aluminumand one-quarter weight of steel

Melting point of 1,204ºF

Strength-to-weight ratio high when compared to steel Welding techniques like aluminum

± Rate of expansion greater

± Care taken that surface clean before welding

Arc characteristics of helium and argon withmagnesium different than with other metals

± Argon recommended in most cases

Titanium



22 - 151

Bright white metal that burns in air

Only element that burns in nitrogen

Melting point of about 3,500ºF

Most important compound titanium dioxide

± Used extensively in welding electrode coatings

Used as stabilizer in stainless steel

Zirconium



Bright gray metal

Melting point above 4,500ºF

Very hard and brittle and readily scratches

glass

Used in hard-facing materials

Often alloyed with iron and aluminum

Argon or helium-argon mixtures used for gas

GMAW chapter22[1]

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