GMAW WELDING

7/27/2019 GMAW WELDING

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Copyright The McGraw-Hill Companies, Inc.

Permission required for reproduction or display.

PowerPoint to accompany

WeldingPrinciples and PracticesThird Edition

Sacks and Bohnart

1

Gas Metal ArcWelding Practice:

Jobs 22-J1J23

(Plate)

Chapter 22


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Objectives

1. Describe GMAW operating variables

2. Describe GMAW weld defects

3. Describe GMAW safe operation

4. 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


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Operating 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


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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


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Gas Metal Arc DCEP Welding:Wire Positive, Work Negative

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


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Direct Current ElectrodeNegative (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


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Gas Metal Arc DCEN Welding:Wire Negative, Work Positive



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Alternating Current

Seldom used in gas metal arc welding

Arc unstable because of current reversal

Combination of both DCEN and DCEPpolarity, rate of metal transfer and depth of

penetration falls between those polarities

Found some use for welding of aluminum


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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 ofweld


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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


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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, 25percent argon preferred

Low alloy steel: argon, plus 2 percent oxygen


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Specific Metal Recommendations

Mild steel: 15 percent argon, 25 percent carbon

dioxide (dip transfer); 100 percent CO2may

also be used with deoxidized wire

Nickel, Monel, and Inconel: argon

Titanium: argon

Silicon bronze: argon

Aluminum bronze: argon


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Joint Preparation

Joint design should provide for mosteconomical use of filler metal

Correct design for job depends on:

Type of material being weldedThickness of material

Position of welding

Welding process

Final results desiredType and size of filler wire

Welding technique


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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 " plate

in square butt joint welded from both sides


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Joint Preparation

No root face recommended for 60 single- ordouble-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 preparationRequire less weld metal; root face thickness shouldbe less than 3/32" and root spacing 1/32 and 3/32"


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V-Groove, Butt JointComparison



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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


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Comparison of Penetration in aFillet Weld

Carbon dioxide shieldedMAG weld versus coated

electrode weld.



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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


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Electrode Diameter

Filler wires should be same composition as materialsbeing 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


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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 ofextension 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 ofpenetration into work

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


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Electrode Extension

Short electrode extensions (1/81/2 inch) used forshort circuit mode of transfer, generally with smallerdiameter electrodes (0.0230.045 inches)

Stainless steel favors shorter electrode extension

because of its higher resistivity (1/81/4 inch) Longer and larger diameter electrode extensions used for

spray arcs (1/211/4 inches)

Excessive long arcs with active gases reduce the

mechanical properties in weld Various alloys being burned out as metal transferred across

longer arc


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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 voltagepower source, welding current decreased

As welding current decreased, depth of penetration alsodecreases

N l f A B


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Nomenclature of Area BetweenNozzle and Workpiece



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

increases

Increased travel speeds characteristic of push technique


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Travel and Work Gun Angles

Axis of Weld



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Travel and Work Gun Angles


Travel Angle

(T.A.)

Axis of Weld

(Drag) Travel Direction

(Push) Travel Direction

Work Angle(W.A.)


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Drag and Push Gun angles



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Work Angle

Position of wire to joint in plane perpendicularto line of travel

Filler weld joints: work angle normally half of

included angle between plates forming joint

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

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


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Work and Gun Angles



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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 ofburnoff rate of filler wire

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


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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


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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

R l ti hi f A L th t


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Relationship of Arc Length toWeld Bead Width


High VoltageLow Voltage

Arc Length

Arc Length

Electrode

Electrode


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Penetration Comparisons


Arc voltage too high

for travel speed.

Arc voltage too slow

for travel speed

Proper arc voltage

for speed


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Wire-Feed Speed

Fixed relationship between rate of filler wire burn offand 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 out

enough 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

Generallyhigh setting of filler wire speed rate resultsin short arc, slow speed in long arc


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Effect of Wire-Feed Speeds



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Welding Current

Determines amount of current delivered at arc

Often related to current density

Amperage per square inch of cross-sectional area

of 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


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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


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Welding Current

Table 22-3 gives comparative current ranges and otherparameters 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


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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


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Travel Speed

Excessively fast speeds causes undercut

Influenced by thickness of metal being welded,

joint design, cleanliness, joint fitup, and

welding 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


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Arc Position

Arc must be on

leading edge of

weld pool to

assure penetrationand fusion.



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Optimum Travel Speed



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Summary of Operating Variables

Height and width of bead depend on adjustment ofthese variables

Joint preparation

Gas flow rate

Voltage

Speed of travel

Arc length

Polarity

Variables adjusted on basis of type of material beingwelded, 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)


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Summary of Operating Variables

Welding current and travel speed have similar

effect on both bead height and width

Each variable increases or decreases both bead

height 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


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Weld Defects

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

Causes and corrective action entirely different

Incomplete penetrationResult of too little heat input in weld area

Correct by increasing wire-feed speed and reducing

electrode extension to obtain maximum current forparticular wire-feed setting

Also causes by improper welding techniques


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Excessive Penetration

Usually causes excessive melt-through

Result of too much heat in weld area

Reducing wire-feed speed to obtain lower amperage orincreasing 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 andopening

Remedied during welding by increasing electrodeextension distance and weaving gun


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Whiskers

Short lengths of electrode wire sticking through

weld on root side of joint

Caused by pushing electrode wire past leading

edge of weld pool

Can be prevented by

Reducing wire-feed speed

Increasing electrode extension distance

Weaving gun


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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 previouspass and plate

Prevent by making sure edges of all passes filled in soundercut cannot take place and arc melts previous

bead and fuses into sides of joint


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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


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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


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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 not

fully displace all air in arc area

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

Shielding gases must be of right type for metalbeing welded

Shielding gases must be pure and dry


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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


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Other Defects

Weld cracking

Comes from compositional problems, poor joint design, andpoor welding technique

Prevent by making sure filler metal has composition

suitable 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, improperarc voltage, improper shielding gas, improper extension


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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 fillerwire

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


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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


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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


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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

l hi l i


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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

dli f G C li d


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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

H dli f G C li d


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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

V il i


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Ventilation

Ozone generated in small quantities, generallybelow allowable limits of concentration

Nitrogen dioxide also present around area of

arc in quantities below allowable limits Carbon dioxide shielding may create hazard

from carbon monoxide and carbon dioxide if

welders head in path of the fumes or ifwelding done in confined space

Special ventilation should be provided

V il i


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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

V il i


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Ventilation

During welding, certain metals emit toxicfumes that may cause respiratory irritation andstomach upsetMost common toxic metal vapors given off by

welding of lead, cadmium, copper, zinc, andberyllium

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

equipment Welding guns can be purchased with smoke

extractor capability

El i l S f


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Electrical Safety

Hazard less than that with shielded meal arc

process

Open circuit voltage considerably less

Electrical maintenance should be done only by

qualified person

NEVER worked on in electrical HOT condition

Wi F d S f t


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Wire-Feeder Safety

Turn power off when aligning and adjustingdrive rolls

Avoid pinch points when working near drive

rolls Remember force being applied to wire

sufficient to push it through your hand or other

body parts Never let exposed wire come in contact with or

be pointed at your body

Fi S f t


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Fire Safety

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

Paint spray or dipping operations should not belocated close to any welding operation

Combustible material should not be used for floors,walls, welding tables, or in immediate vicinity ofwelding operation

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

Use hot work permit as required

C d U f E i t


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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 weldingposition 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

D d P h M th d


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Drag and Push Methods

Produces large wide beads Produces flatter bead shape


C f N l


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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


C f N l


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Care of Nozzles

Spatter almost falls out by itself if nozzle kept

clean, shiny and smooth

Antispatter compound may be applied to gun

nozzle 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

C f C t t T b


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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

C f Wi F d C bl


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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 reduces

friction

Clean every time spool or coil changes

Bird Nesting


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Bird Nesting

Wire coils sideways between wire-feed cable

and drive rolls

Prevent by accurate alignment of wire-feed

cable inlet guide

Aligned exactly with rollers so wire does not have

to make reverse bend

Notch in drive rolls must be in perfect alignment toprovide smooth passage for wire

Cleanliness of Base Metal


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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

Arc Blow


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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


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gArc Blow

Suggestions to shorten trial-and-error process

to correct or minimize arc blow

Attach work lead or leads directly on

workpiece if possible

Connect both ends of long, narrow weldments

Use electrical conductors of proper length

Weld away from work connection



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gArc Blow

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

In making longitudinal welds on cylinders, usetwo work connectionsone 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



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Arc Blow

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

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

Setting Up Equipment


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Setting Up Equipment

Constant voltage d.c. power source

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

Gas-shielding system consisting of one or more

cylinders 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

Assumed Safety Precautions


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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

Starting Procedure


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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 onbutton

or, in case of engine drive, start engine

3. Turn on wire-feed unit

4. Check gas-shielding supply system

5. Check water flow if gun water cooled

Starting Procedure


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Starting Procedure

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

6. Voltage rheostat should be set to conform to typeand thickness of material being welded, diameter offiller 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 properplace on weld joint, usually just ahead of weld bead,with current shut off; lower helmet and press guntrigger on torch

Shutting Down the Equipment


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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

Starting the Weld


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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

Finishing the Weld


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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 ofwelding 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

Gun Angle


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Gun Angle

Push angle of 5to 15generally 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

Control of Arc


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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

Process and Equipment Problems


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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

Practice Jobs


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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 Observe WhenDoing Practice Jobs


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Doing 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 ofjoint; 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 rootpass on first side deeply penetrated by root pass onsecond side

MIG/MAG Welding ofC b St l


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Carbon 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:J b 22 J1 d J2


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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



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Jobs 22-J1 and J2

For code welding, plate thicknesses from 3/16to 1" should be beveled60 single- or double-V without root face

recommended

Root opening of 0 to 1/16" should be maintainedWider 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



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Jobs 22-J1 and J2

Open 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



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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% CO2sometimes 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

Fillet Welds: Jobs 22-J3-J10


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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


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Outside corner joint in steel plate welded with gas metalarc welding process in the flat position.

Penetration through back side of corner joint welded

in the flat position.



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Fillet weld on lap joint in steel platewelded 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.



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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 first (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:

Job Qualification Test 1


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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:



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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

P j t J b Q lifi ti T t2


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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



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



Groove Weld Project: JobQualification Test 3


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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



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p g

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



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p g

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 each4 inches of weld length and maximum diameter

shall not exceed 3/32 inch



Side Bend Acceptance Criteria as Measured

on Convex Surface of Bend Specimen


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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 orequal 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


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g

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

Lightweight

Alloyed readily with many other metals

Highly ductile and retains ductility at subzerotemperatures

High resistance to corrosion, no colored salts, not toxic

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

Nonsparking and nonmagnetic



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g

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 oxide

film when exposed to air (melting point 3600F)

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

atmosphere or mechanical and chemical means



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g

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

Desirable Joining Process for Aluminum


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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


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p

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


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g

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 cleaningaction

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


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p y g

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


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g

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 betweenpasses

Horizontal Position


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Welding T-joint in aluminum

plate in 2F position

Welding V-groove butt joint

in aluminum plate in 2G position.


Out-Of-Position Welding


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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 awkwardassume relaxed position as possible

Out-Of-Position Welding


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22 - 121Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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


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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 "

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


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More widely used on aluminum alloys than on

other materials

Use double-welded, single-lap joints in

thicknesses of aluminum up to "

Require no edge preparation

Easy to fit

Require less jigging than butt joints

T-Joints: Jobs 22-J14-J16


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Seldom require edge preparation on material " orless 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


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Economical from standpoint of preparation,

base metal used, and welding requirements

Harder to fit up

Prone to fatigue failure

Edges do not require preparation



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Inspect carefully for defects

Use same inspection and testing procedures

used previously

Look for surface defects

High quality welds in aluminum can be

produced only if proper welding conditions and

good cleaning procedures been established and

maintained

Effect of Current onAluminum Welds


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Aluminum Welds


Aluminum weld bead

made with current

too high

Aluminum weld bead

made with current

too low

Aluminum weld bead

made with

correct current

Kaiser Aluminum & Chemical Corporation Kaiser Aluminum & Chemical Corporation Kaiser Aluminum & Chemical Corporation

Main Causes of Cracking inAluminum Welds


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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 procedureHigh stresses imposed during welding by poor joint

design or poor jigging

Main Causes of Porosity inAluminum Welds


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u u We ds

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 with Base Metal


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Weld Metal with Base Metal

Incomplete removal of oxide film beforewelding

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


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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


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Inclusions in Aluminum Welds

Copper inclusions caused by burn-back ofelectrode 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 whenwelding aluminum

Groove Weld Project:Job Qualification Test 4


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22 - 133

Q

PurposeAbility to read print


TackWeld aluminum test plates

Using spray arc mode of metal transfer

Inspection and testing

Visual inspection

Perform side bend tests


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

Performance Qualification

Test GMAW Spray Transfer, Aluminum

3G and 4G Positions

AWS SENSE

Shown only to illustrate what a qualification test would

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

MAG Welding of StainlessSteel


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Heat and corrosion resistant alloyAlways contains high percentage of chromium in

addition 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


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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


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

Continuous wire feed permits uninterruptedwelding

MAG lends itself to automation

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

Spray Arc Welding


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Electrode diameters as large as 3/32" can be used forstainless 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 "thick or more

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

Short Arc Welding (GMAW-S)


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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)


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For stainless steel in light gauges, triplemixture of gas gives good arc stability and

excellent coalescence

90% helium, 7 % argon and 2 % carbon dioxideProduces small heat-affected zone that eliminates

undercutting and reduces distortion

Does not lower corrosion resistanceFlow rates must be increased because of lower

density of helium

Pulse Spray Arc (GMAW-P)


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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 onall the time

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

Hot Cracking


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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 500F

Also reduce by GMAW-S or P welding

Stainless-Steel Sensitization


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Carbide precipitation Sensitizing chromium out of individual grains of austenitic

types of stainless steel

Occurs most readily in 1,200F 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


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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


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


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May be welded successfully by gas metal arc process Electrolytic copper can be joined by using special

techniques, 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



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Joint design like any other metalSteel backup necessary for sheets 1/8" or thinner

Welding currents on high side required

Preheat not required when welding " or less Always provide good ventilation when welding

copper and its alloys

Beryllium-copper alloy dangerous



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GMAW-BVariation 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-CopperAlloys


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Can be welded using gas metal arc process Remove all foreign material in vicinity since

susceptible to severe embrittlement andcracking when come in contact with foreign

materials Argon generally preferable for welding up to

about 3/8 inch in thicknessAbove that thickness, argon-helium mixtures

usually more desirable

Joint preparation like other metals

Magnesium


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

Melting point of 1,204F

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


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Bright white metal that burns in air

Only element that burns in nitrogen

Melting point of about 3,500F

Most important compound titanium dioxide

Used extensively in welding electrode coatings

Used as stabilizer in stainless steel

Zirconium


152/152

Bright gray metal

Melting point above 4,500F

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

Documents

GMAW WELDING