Download - Fundamentals of Welding - Technology
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Welding ProcessesWelding Processes
EN358 Ship Structures
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A Brief History of WeldingA Brief History of Welding
Late 19thCentury
Scientists/engineers apply advances in electricity to heat
and/or join metals (Le Chatelier, Joule, etc.
!arly "#thCentury $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 etalWeldability of a etal
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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!usion Welding "rinciples!usion Welding "rinciples
0ase metal is melted
iller metal may e added
2eat is supplied y various means
3yacetylene gas
!lectric 4rc
$lasma 4rc
Laser
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!usion Welding!usion Welding
BASE METAL
WELD
SOLDFED SLA!
A"# POOL
WELD$! ATMOSPHE"E
#O"E W"E
ELE#T"ODE #OAT$!
A"# ST"EAM
PE$ET"ATO$
DEPTH
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Weld etal "rotectionWeld etal "rotection
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 !lu#esWeld !lu#es
:ypical -lues
Si3", :i3", e3, g3, 4l"3)
$roduces a gaseous shield to prevent
contamination
4ct as scavengers to reduce oides
4dd alloying elements to the 'eld &n-luence shape o- 'eld ead during
solidi-ication
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$nert %ases$nert %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 !usion WeldingTypes of !usion Welding
3yacetylene Cutting/%elding
Shielded etal 4rc (6Stic7
etal &nert 8as (&8
:ungsten &nert 8as (:&8
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(#yacetylene Welding(#yacetylene 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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Shielded etal Arc )Stic*+Shielded etal Arc )Stic*+
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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Shielded etal Arc )con,t+Shielded etal Arc )con,t+
$rocessB &ntense heat at the arc melts the tip o- the
electrode :iny drops o- metal enter the arc stream and are
deposited on the parent metal 4s molten metal is deposited, a slag -orms over
the ead 'hich serves as an insulation against aircontaminants during cooling
4-ter a 'eld pass* is allo'ed the cool, the oidelayer is removed y a chipping hammer and thencleaned 'ith a 'irerush e-ore the net pass.
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$nert %as Welding$nert %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
etal $nert %as )$%+etal $nert %as )$%+
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 $nert %as )$%+Tungsten $nert %as )$%+
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 "ositionsWelding "ositions
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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.esidual Stresses.esidual Stresses
@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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%enerali0ed Welding Sy'bol%enerali0ed Welding Sy'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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E#a'ple Welding Sy'bolE#a'ple Welding Sy'bol
>?/@ >?/@
>?/
>?/
3ne
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Weld Sy'bols )Butt /oints+Weld Sy'bols )Butt /oints+
Backing
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Weld Sy'bol )!illet /oints+Weld Sy'bol )!illet /oints+
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Weld Sy'bol )1orner /oints+Weld Sy'bol )1orner /oints+