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GMAW FundamentalsGMAW Fundamentals

Gas Metal Arc Welding

Metal Inert Gas

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SafetySafety

Electrocution hazard Skin burns from flying metal Skin burns from direct light from arc

Skin burns from indirect light from arc Cotton clothing and leather gloves elmet to !rotect eyes from light Safety glasses "hen chi!!ing slag

#entilation to remove dangerous fumes $o not "eld near "ater $o not "eld near combustible materials %ee! "elding cables and &obs free grease 'rotect bystanders from arc rays

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IntroductionIntroduction

GMAW is defined as arc "elding using a

continuously fed consumable electrode and

a shielding gas(GMAW is also kno"n as MIG )Metal Inert

Gas*(

'roduces high+,uality "elds

-ields high !roductivity

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AdvantagesAdvantages

.arge ga!s filled or bridged easily

Welding can be done in all !ositions

/o slag removal re,uired

igh "elding s!eeds

igh "eld ,uality.ess distortion of "ork !iece

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DisadvantagesDisadvantages

ard to reach locations are less easily "eldedbecause of bulky torch and cables

Wind or air drafts may com!romise gas shielding 0eactive metals )i(e( titanium* may need s!ecialshielding !rovisions

igh heat may be uncomfortable to "elders

Correct !arameter selection learning needsdedicated training E,ui!ment is more com!le1 and e1!ensive than

that of alternative !rocesses

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Several tips must be consider inSeveral tips must be consider in

selecting mode of transferselecting mode of transfer2y!e3 intensity and !olarity of "elding

current

Electrode size

Electrode com!osition

Electrode e1tension

Shielding gas mi1 com!osition

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Types of Metal TransferTypes of Metal Transfer

2he basic GMAW !rocess includes three

distinctive !rocess techni,ues4

5( Short Circuit )Short Arc*

6( Globular 2ransfer

7( S!ray Arc 2ransfer

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Modes of GMAW TransferModes of GMAW Transfer

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Short Circuit Short Arc!Short Circuit Short Arc!

8!erates at lo" voltages and "elding current

Small fast+freezing "eld !uddle obtained

9seful in &oining thin materials in any !osition3 as"ell as thick materials in vertical and overhead

!ositions

Metal transfer occurs "hen an electrical short

circuit is established this cycle can re!eat itself bet"een 6: and as

much as 6;: times !er second(

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Short CircuitShort CircuitA + Electrode is short circuited to base metal( /o

arc3 and current is flo"ing through electrode

"ire and base metal(

< + 0esistance increases in electrode "ire causing

it to heat3 melt and =neck do"n>(

C + Electrode "ire se!arates from "eld !uddle3creating an arc( Small !ortion of electrode "ire

is de!osited "hich forms a "eld !uddle(

$ + Arc length and load voltage are at ma1imum(

eat of arc is flattening the !uddle and increasing

the diameter ti! of electrode(

E + Wire feed s!eed overcomes heat of arc and"ire a!!roaches base metal again(

? + Arc is off and the short circuit cycle starts

again(

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All+!osition ca!ability3 including flat3 horizontal3

vertical+u!3 vertical+do"n and overhead(

andles !oor fit+u! e1tremely "ell3 and is ca!able

of root !ass "ork on !i!e a!!lications(

.o"er heat in!ut reduces "eldment distortion(

igher o!erator a!!eal and ease of use( igher electrode efficiencies3 @7 or more(

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"imitations"imitations

0estricted to sheet metal thickness range and o!en rootsof groove &oints on heavier sections of base material(

'oor "elding !rocedure control can result in incom!lete

fusion( Cold la! and cold shut are additional terms thatserve to describe incom!lete fusion defects(

'oor !rocedure control can result in e1cessive s!atter3and "ill increase "eldment cleanu! cost(

2o !revent the loss of shielding gas to the "ind3 "eldingoutdoors may re,uire the use of a "indscreen)s*(

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Globular TransferGlobular Transfer

Welding current and "ire s!eed are

increased above ma1imum for short arc

$ro!lets of metal have a greater diameter

than the "ire being used

S!atter !resent

Welding is most effectively done in the flat

!osition "hen using globular transfer

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Globular transfer is often a

high voltage3 higham!erage3 high "ire feed

s!eed transfer3 and is the

result of using C86

shielding gas )or B; A0+

6; C86* "ith !arameters

higher than the short+

circuiting range

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9ses ine1!ensive C86 shielding gas3 but is

fre,uently used "ith argonC86 blends(

Is ca!able of making "elds at very high

travel s!eeds(

Ine1!ensive solid or metal+cored electrodes(

Welding e,ui!ment is ine1!ensive(

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igher s!atter levels result in costly cleanu!( 'rone to cold la! or cold shut incom!lete fusion defects3

"hich results in costly re!airs(

Weld bead sha!e is conve13 and "elds e1hibit !oor "ettingat the toes(

igh s!atter level reduces electrode efficiency to a rangeof DB @7(

.ess desirable "eld a!!earance than s!ray arc transfer Welding is limited to flat !ositions and horizontally fillet

"elds Welding is limited to metal 5D inch )7 mm* or thicker

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Spray Arc TransferSpray Arc Transfer

8ccurs "hen the current and voltage settings areincreased higher than that used for Globular2ransfer

9sed on thick sections of base material3 best suitedfor flat !osition due to large "eld !uddle

S!atter is minimal to none 9ses ; to 5: co6 mi1 "ith argon or o1ygen(

F?orms very small dro!lets of metalF#ery good stabilityF#ery little s!atter

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S!ray arc transfer =s!rays> a stream

of tiny molten dro!lets across thearc3 from the electrode "ire to the

base metal(

S!ray arc transfer uses relatively

high voltage3 "ire feed s!eed andam!erage values3 com!ared to short

circuit transfer(

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igh de!osition rates( igh electrode efficiency of @D or more( Em!loys a "ide range of filler metal ty!es in an e,ually

"ide range of electrode diameters( E1cellent "eld bead a!!earance( igh o!erator a!!eal and ease of use( 0e,uires little !ost "eld cleanu!(

Absence of "eld s!atter( E1cellent "eld fusion( .ends itself to semiautomatic3 robotic3 and hard

automation a!!lications(

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0estricted to the flat and horizontal "elding!ositions(Welding fume generation is higher( 2he higher+radiated heat and the generation of a

very bright arc re,uire e1tra "elder and bystander!rotection( 2he use of a1ial s!ray transfer outdoors re,uires

the use of a "indscreen)s*( 2he shielding used to su!!ort a1ial s!ray transfer

costs more than 5:: C86(

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#ulse Spray Transfer#ulse Spray Transfer

GMAW+' "as develo!ed for t"o demanding reasons4control of "eld s!atter and the elimination of incom!letefusion defects common to globular and short+circuiting

transfer( 2he "elding current alternates bet"een a !eak current and

a lo"er background current(

2his faster+freezing "eld !uddle is "hat allo"s the !ulsed+

s!ray transfer to be used fort thinner metals3 better control on out+of+!osition "ork(

allo"s for larger "ire sizes to be used on varied metalthicknesses(

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In !ulse s!ray transfer )GMAW+'* the

"elding !o"er sources !ulse control!ulses the "elding out!ut "ith

high !eak currents )am!erage* "hich are

set at levels "hich "ill cause the transfer

to go into a s!ray( 2he backgroundcurrent )am!erage* is set at a level that

"ill maintain the arc3

but is too lo" for any metal transfer to

occur(

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#ulsed arc transfer#ulsed arc transfer

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AdvantagesAdvantages Absent or very lo" levels of s!atter(

More resistant to lack of fusion defects than other modes ofGMAW metal transfer(

E1cellent "eld bead a!!earance and offers an engineeredsolution for the control of "eld fume generation(

0educed levels of heat induced distortion and tendency for arc

blo" Ability to "eld out+of+!osition and handles !oor fit+u!( When com!ared to ?CAW3 SMAW3 and GMAW+S3 !ulsed s!ray

transfer !rovides a lo" cost high+electrode efficiency of @D( .ends itself to robotic and hard automation a!!lications(

Is combined for use "ith 2andem GMAW or other multi!le arcscenarios( Ca!able of arc travel s!eeds greater than ;: inches !er minute

)5(6 Mmin(*(

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"imitations"imitationsE,ui!ment to su!!ort the !rocess is more

e1!ensive than traditional systems(

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Manual GMAW $%uipmentManual GMAW $%uipment

2hree ma&or elements are 4

5(* Welding torch and accessories

6(* Welding control H Wire feed motor

7(* 'o"er Source

GMAW e,ui!ment can be used either

manually or automatically

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GMAW Schematic DiagramGMAW Schematic Diagram

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WI0E C8/208.

H

WI0E ?EE$ M8280

'8WE0 S890CE

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Welding Torch & AccessoriesWelding Torch & Accessories

2he "elding torch guides the "ire and

shielding gas to the "eld zone(

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'thers types of torch'thers types of torch

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20IGGE0

I/S2A..E$

C8M'8/E/2S

/8.E

C8/2AC2 2I'

GAS $I??9SE0

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Welding Control & WireWelding Control & Wire

Feed MotorFeed MotorWelding control H Wire feed motor are

combined into one unit

Main function is to !ull the "ire from thes!ool and feed it to the arc

Controls "ire feed s!eed and regulates the

starting and sto!!ing of "ire feedWire feed s!eed controls Am!erage

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Types of Wire Feed MotorTypes of Wire Feed Motor

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Types of WFM (ollerTypes of WFM (oller

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Types of Wire FeederTypes of Wire Feeder

WI0E ?EE$E0

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WI0E ?EE$E0

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#o)er Source#o)er Source

Almost all GMAW is done "ith reverse !olarityalso kno"n as $CE'

'ositive )J* lead is connected to the torch/egative )+* lead is connected to the "ork !iece

'rovides a relatively consistent voltage to thearc

Arc #oltage is the voltage bet"een the end ofthe "ire and the "ork !iece

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Contact Tip To Wor* DistanceContact Tip To Wor* Distance

In constant current3the C2W$ )contact ti! to"ork distance* determines the arc length(

As the C2W$ increases the arc length increases3 andas the

C2W$ decreases the arc length decreases( 2his!resented a

!roblem for semiautomatic "elding because it isdifficult to

maintain the same C2W$( 2o com!ensate for this!roblem an arc voltage controlled "ire

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Constant voltage !o"er source designs !rovide a s!ecificarc voltage for a given !re+selected "ire feed s!eed 2hevolt+am! curve3 or slo!e3 is com!aratively flat( As theC2W$ increases "ith these ty!es of !o"er sources3 there

is a decrease in the "elding current( As the C2W$decreases there is an increase in the "elding current( 2hearc in this case becomes a series circuit3 and the C2W$

!rovides resistance to current( In either scenario3 thevoltage remains the same and the arc length remains thesame

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'8SI2I#E

2E0MI/A.

/EGA2I#E

2E0MI/A.

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Shielding GasesShielding Gases

'ur!ose of shielding gas is the !rotect the"eld area from the contaminants in the

atmos!hereGas can be Inert3 0eactive3 or Mi1tures of

both

Gas flo" rate is bet"een 6;+7; C?Argon3 elium3 and Carbon $io1ide are the

main three gases used in GMAW

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#roperties of Gases#roperties of Gases

Affect the !erformance of the "elding !rocess

include4

5* 2hermal !ro!erties at elevated tem!eratures( 6* Chemical reaction of the gas "ith the various

elements in the base !late and "elding "ire(

7* Effect of each gas on the mode of metal

transfer(

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Types of shielding gasesTypes of shielding gases

Inert Gas

5( Argon

6( elium

7( Ar J e

Active Gas

5( Carbon $io1ide

6( Inert gas J any ty!e of active gas

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Argonis an inert gas "hich is used both

singularly and in combination "ith other

gases to achieve desired arc characteristicsfor the "elding of both ferrous and non+

ferrous metals(

Carbon Dioxide'ure carbon dio1ide is not aninert gas3 because the heat of the arc breaks do"n

the C86 into carbon mono1ide and free o1ygen(

2his o1ygen "ill combine "ith elements

transferring across the arc to form o1ides "hich are

released from the "eld !uddle in the form of slag

and scale(

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Heliumis an inert gas "hich is used on

"eld a!!lications re,uiring higher heatin!ut for im!roved bead "etting3 dee!er

!enetration and higher travel s!eed( In

GMAW it does not !roduce as stable an arc

as argon( Com!ared to argon3 helium has a

higher thermal conductivity and voltage

gradient

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?.8W ME2E0

C-.CI/$E0

'0ESS90E

GA9GE

C? '0ESS90E

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