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8/19/2019 Welding Processes 1
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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(