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Welding ProcessesWelding Processes

K.R.Mondal

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A Brief History of WeldingA Brief History of Welding

• Late 19th Century

• Scientists/engineers apply advances in electricity to heat

and/or join metals (Le Chatelier, Joule, etc.

• !arly "#th Century• $rior to %%& 'elding 'as not trusted as a method to join

t'o metals due to crac issues

• 19)#*s and +#*s

• &ndustrial 'elding gains acceptance and is used etensively

in the 'ar e--ort to uild tans, aircra-t, ships, etc.

• odern %elding

• the nuclear/space age helps ring 'elding -rom an art to a

science

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Types of WeldingTypes of Welding

Fusion Welding Pressure Welding

Homogeneous Heterogeneous

Brazing SolderingGas Welding 

Electroslag

High Energy Beam

Electric Arc

MIG 

TIG 

Shielded Metal Arc – “Stick” 

Friction Welding

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Weldability of a MetalWeldability of a Metal

• etallurgical Capacity• $arent metal 'ill join 'ith the 'eld metal 'ithout

-ormation o- deleterious constituents or alloys

• echanical Soundness• Joint 'ill e -ree -rom discontinuities, gas porosity,

shrinage, slag, or cracs

• Serviceaility• %eld is ale to per-orm under varying conditionsor service (e.g., etreme temperatures, corrosiveenvironments, -atigue, high pressures, etc.

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Fusion Welding PrinciplesFusion Welding Principles

• 0ase metal is melted

• iller metal may e added

• 2eat is supplied y various means

• 3yacetylene gas

• !lectric 4rc

• $lasma 4rc

• Laser 

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Fusion WeldingFusion Welding

BASE METAL

WELD

SOLDFED SLA!

A"# POOL

WELD$! ATMOSPHE"E

#O"E W"E

ELE#T"ODE #OAT$!

A"# ST"EAM

PE$ET"ATO$

DEPTH

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Weld Metal ProtectionWeld Metal Protection

• 5uring -usion 'elding, the molten metal in the

'eld 6puddle7 is susceptile to oidation

• ust protect 'eld puddle (arc pool -rom theatmosphere

• ethods

• %eld lues

• &nert 8ases

• acuum

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Weld FluxesWeld Fluxes

• :ypical -lues

• Si3", :i3", e3, g3, 4l"3)

• $roduces a gaseous shield to prevent

contamination

•  4ct as scavengers to reduce oides

•  4dd alloying elements to the 'eld• &n-luence shape o- 'eld ead during

solidi-ication

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Inert asesInert ases

•  4rgon, helium, nitrogen, and carondioide

• orm a protective envelope around the'eld area

• ;sed in

• &8• :&8

• Shield etal 4rc

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!acuu"!acuu"

• $roduce highuclear/special metal applications

• ?r, 2-, :i

• @educes impurities y a -actor o- "#

versus other methods

• !pensive and time

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Types of Fusion WeldingTypes of Fusion Welding

• 3yacetylene Cutting/%elding

• Shielded etal 4rc (6Stic7

• etal &nert 8as (&8

• :ungsten &nert 8as (:&8

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#xyacetylene Welding#xyacetylene Welding

• lame -ormed y urning a mi o- acetylene(C"2" and oygen

• usion o- metal is achieved y passing theinner cone o- the -lame over the metal

• 3yacetylene can also e used -or cutting

metals

nner #one% &'''()*'' deg F #om+ustion En,elo-e *.'' deg F

/*'' deg FTO"#H TP

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$%ielded Metal Arc &$tic'($%ielded Metal Arc &$tic'(

•  4n electric arc is generated et'een a coatedelectrode and the parent metal

• :he coated electrode carries the electriccurrent to -orm the arc, produces a gas tocontrol the atmosphere and provides -illermetal -or the 'eld ead

• !lectric current may e 4C or 5C. &- thecurrent is 5C, the polarity 'ill a--ect the 'eldsiAe and application

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$%ielded Metal Arc &con)t($%ielded Metal Arc &con)t(

• $rocessB• &ntense heat at the arc melts the tip o- the

electrode• :iny drops o- metal enter the arc stream and are

deposited on the parent metal•  4s molten metal is deposited, a slag -orms over

the ead 'hich serves as an insulation against aircontaminants during cooling

•  4-ter a 'eld pass* is allo'ed the cool, the oidelayer is removed y a chipping hammer and thencleaned 'ith a 'irerush e-ore the net pass.

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Inert as WeldingInert as Welding

• or materials such as 4l or :i 'hich

=uicly -orm oide layers, a method to

place an inert atmosphere around the'eld puddle had to e developed

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• ;ses a consumale electrode (-iller 'ire made o- the

ase metal

• &nert gas is typically 4rgon

Metal Inert as &MI(Metal Inert as &MI(

BASE METAL P0DDLE

POWE"

SO0"#E

D"1E WHEELS#O$S0MABLE

ELE#T"ODE

A"# #OL0M$SHELD$! !AS

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• :ungsten electrode acts as a cathode

•  4 plasma is produced et'een the tungsten cathode and the

ase metal 'hich heats the ase metal to its melting point• iller metal can e added to the 'eld pool

Tungsten Inert as &MI(Tungsten Inert as &MI(

BASE METAL P0DDLE

POWE"

SO0"#E

A"# #OL0M$SHELD$! !AS

T0$!STE$

ELE#T"ODE

+ +

BASE METAL 2A$ODE3

T0$!STE$

ELE#T"ODE

2#ATHODE3

( ( (

+ +

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Welding PositionsWelding Positions

FLATFLAT

HO"4O$TALHO"4O$TAL

1E"T#AL1E"T#AL

O1E"HEADO1E"HEAD

$#"EAS$! DFF#0LT5

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Weld *efectsWeld *efects

• ;ndercuts/3verlaps

• 8rain 8ro'th•  4 'ide ∆: 'ill eist et'een ase metal and 24?. $reheating

and cooling methods 'ill a--ect the rittleness o- the metal inthis region

• 0lo'holes•  4re cavities caused y gas entrapment during the

solidi-ication o- the 'eld puddle. $revented y proper 'eldtechni=ue (even temperature and speed

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Weld *efectsWeld *efects

• &nclusions• &mpurities or -oreign sustances 'hich are -orced into the 'eld

puddle during the 'elding process. 2as the same e--ect as a crac.

$revented y proper techni=ue/cleanliness.• Segregation

• Condition 'here some regions o- the metal are enriched 'ith analloy ingredient and others aren*t. Can e prevented y proper heattreatment and cooling.

• $orosity• :he -ormation o- tiny pinholes generated y atmospheric

contamination. $revented y eeping a protective shield over themolten 'eld puddle.

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Residual $tressesResidual $tresses

• @apid heating and cooling results in thermal stressesdetrimental to joint strength.

• $revention

• !dge $reparation/4lignment D eveled edges and spaceet'een components to allo' movement

• Control o- heat input D sip or intermittent 'eld techni=ue• $reheating D reduces epansion/contraction -orces (alloys

and removes moisture -rom the sur-ace• $eening D help metal stretch as it cools y hitting 'ith a

hammer. ;se 'ith care since it may 'or harden the metal• 2eat :reatment D 6soa7 the metal at a high temperature to

relieve stresses• Jigs and itures D prevent distortion y holding metal -ied• >umer o- $asses D the -e'er the etter.

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+oint *esign+oint *esign

BUTT JOINTBUTT JOINT

ST"AP 6O$T

LAP 6O$T

FLLET 6O$T

#O"$E" 6O$T

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enerali,ed Welding $y"bolenerali,ed Welding $y"bol

FAR SIDE DETAILS

ARROW SIDE DETAILS

Field 7eld sym+ol

Weld all(around 8or

 -i-es9 etc:

L1-L2

L1-L2

D ; Weld De-th 2usually e ; Weld Length

L/ ; Distance +et7een centers 8or stitched 7elds

:he ield %eld Symol is a guide -or installation. Shipyards

normally do not use it, ecept in modular construction.

Electrode

Material

D

D

Weld !eometry

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-xa"ple Welding $y"bol-xa"ple Welding $y"bol

>?/@ >?/@

>?/

>?/

3ne

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Weld $y"bols &Butt +oints(Weld $y"bols &Butt +oints(

Backing

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Weld $y"bol &Fillet +oints(Weld $y"bol &Fillet +oints(

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Weld $y"bol &orner +oints(Weld $y"bol &orner +oints(