fundamentals of welding - technology

7/25/2019 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+

fundamentals of welding - technology

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