UNIT4-Welding processcastingweldingdefect.ppt

welding

1. UNIT-4 Welding Process

5. Welding processes
Weldingisaprocessofjoiningsimilarordissimilarmetalsbyapplication
ofheatwithorwithoutapplicationofpressureandadditionoffillermaterial
OR
Welding isdefined as an localized coalescence of metals, where in
coalescence is obtained by heating to suitable temperature, with or without the
application of pressure and with or without the use of filler metal.

6. 6
Applications

7. •Until the end of the 19th century,
the only welding process was
forge welding, which blacksmiths
had used for centuries to join
iron and steel by heating and
hammering them.
•Arc welding and oxyfuel welding
were among the first processes
to develop late in the century,
and resistance welding followed
soon after.
History of welding

8. Welding,wastransformedduringthe19thcentury.In1802,
RussianscientistVasilyPerovdiscoveredtheelectricarc
andsubsequentlyproposeditspossiblepractical
applications,includingwelding.
From this many other forms, including current forms, have
been born including:
Carbon arc welding
Alternating current welding
Resistance welding
Oxyfuel welding
History of welding

9. Often done by melting the
work pieces and
adding a filler material
to form a pool of
molten material (the
weld pool) that cools to
become a strong joint.
Pressure sometimes
used in conjunction
with heat, or by itself, to
produce the weld.
How is it done?

10. TYPES OF WELDING :
Fusion Welding or Non-Pressure Welding:
The material at the joint is heated to a molten state and
allowed to solidify
(Ex)-Gas welding, Arc welding
•Plastic Welding or Pressure Welding:
The piece of metal to be joined are heated to a plastic
state and forced together by external pressure
(Ex) -Friction

11. Classification of Welding Process

12. 1
2 TYPES OF WELDING JOINTSWelded joints

13. 1
3
ButtJoint
Aconnectionbetweentheendsoredgesoftwopartsmaking
anangletooneanotherof135-180°inclusiveintheregionof
thejoint.
Common Joint Configurations

14. 1
4
TJoint
Aconnectionbetweentheendoredgeofonepartandthe
faceoftheotherpart,thepartsmakinganangletoone
anotherofmorethan5uptoandincluding90°intheregion
ofthejoint.
Common Joint Configurations

15. 1
5
CornerJoint
Aconnectionbetweentheendsoredgesoftwopartsmaking
anangletooneanotherofmorethan30butlessthan135°in
theregionofthejoint.
Common Joint Configurations

16. 1
6
EdgeJoint
Aconnectionbetweentheedgesoftwopartsmakinganangle
tooneanotherof0to30°inclusiveintheregionofthejoint.
Common Joint Configurations

17. 1
7
CruciformJoint
Aconnectioninwhichtwoflatplatesortwobarsarewelded
toanotherflatplateatrightanglesandonthesameaxis.
Common Joint Configurations

18. 1
8
LapJoint
Aconnectionbetweentwooverlappingpartsmakinganangle
tooneanotherof0-5°inclusiveintheregionoftheweldor
welds.
Common Joint Configurations

19. 1
9
Welds Based on Configuration
Slot weld
Jointbetweentwooverlappingcomponentsmadeby
depositingafilletweldaroundtheperipheryofaholeinone
componentsoastojoinittothesurfaceoftheother
componentexposedthroughthehole.
Types of Welding Joints

20. 2
0
Welds Based on Configuration
Plug weld
Weldmadebyfillingaholeinonecomponentofaworkpiece
withfillermetalsoastojoinittothesurfaceofan
overlappingcomponentexposedthroughthehole(thehole
canbecircularoroval).
Types of Welding Joints

21. 2
1
Based on Penetration
Full Penetration weld
Weldedjointwheretheweldmetalfullypenetrates
thejointwithcompleterootfusion.
Types of Welding Joints

22. 2
2
Based on Penetration
Partial Penetration weld
Weldinwhichthefusionpenetrationisintentionally
lessthanfullpenetration.
Types of Welding Joints

23. 2
3
Based on Accessibility
Types of Welding Joints

24. 2
4
Features of Completed Welds

25. 2
5
Features of Completed Welds

26. 2
6
Features of Completed Welds
ParentMetal
Metaltobejoinedorsurfacedbywelding,brazeweldingor
brazing.
FillerMetal
Metaladdedduringwelding,brazewelding,brazingorsurfacing.
WeldMetal
Allmetalmeltedduringthemakingofaweldandretainedinthe
weld.
HeatAffectedZone(HAZ)
Thepartoftheparentmetalmetallurgicallyaffectedbytheweld
orthermalcuttingheat,butnotmelted.
FusionLine
BoundarybetweentheweldmetalandtheHAZinafusionweld.
Thisisanon-standardtermforweldjunction.

27. 2
7
Features of Completed Welds
WeldZone
ZonecontainingtheweldmetalandtheHAZ.
WeldFace
Thesurfaceofafusionweldexposedonthesidefromwhichthe
weldhasbeenmade.
WeldRoot
Zoneonthesideofthefirstrunfurthestfromthewelder.
WeldToe
Boundarybetweenaweldfaceandtheparentmetalorbetween
runs.Thisisaveryimportantfeatureofaweldsincetoesare
pointsofhighstressconcentrationandoftentheyareinitiation
pointsfordifferenttypesofcracks(egfatiguecracks,cold
cracks).
Inordertoreducethestressconcentration,toesmustblend
smoothlyintotheparentmetalsurface.

28. 2
8
Features of Completed Welds
ExcessWeldMetal
Weldmetallyingoutsidetheplanejoiningthetoes.Othernon-
standardtermsforthisfeature:reinforcement,overfill.
Note:Thetermreinforcement,althoughcommonlyused,is
inappropriatebecauseanyexcessweldmetaloverandabovethe
surfaceoftheparentmetaldoesnotmakethejointstronger.
Infact,thethicknessconsideredwhendesigningawelded
componentisthedesignthroatthickness,whichdoesnotinclude
theexcessweldmetal.

29. 2
9
Features of Completed Welds
Run(pass)
Themetalmeltedordepositedduringonepassageofan
electrode,torchorblowpipe.
Layer
Stratumofweldmetalconsistingofoneormoreruns.

30. CLASSIFICATION OF WELDING
PROCESSES:
Gas welding(Oxy-Acetylene)
Arc welding(Metal Arc)
Resistance welding
Solid state welding
Thermo-chemical welding

31. Gas Welding:
Gas Welding is a fusion welding
process, in which the heat for welding is
obtained by the combustion of oxygen
and fuel the gas may be acetylene
,hydrogen or propene .
Types:
•Oxy-Acetylene
•Air-Acetylene
•Oxy-Hydrogen
•Oxy-Fuel

32. Oxy-Acetylene Welding:
Whenacombinationof
Oxygenandacetyleneis
usedincorrectproportions
toproduceanIntensegas
flame,theprocessisknown
asoxy-acetylenewelding.

33. Equipment:
(Red)

34. Gas Welding Equipment :
1. Gas Cylinders
Pressure-
Oxygen –125 kg/cm2
Acetylene –16 kg/cm2
2. Regulators
•Working pressure of oxygen 1 kg/cm2
•Working pressure of acetylene 0.15 kg/cm2
•Working pressure varies depends upon the thickness of the work pieces
welded.
3. Pressure Gauges
4. Hoses
5. Welding torch
6. Check valve
7. Non return valve

35. Thisflamedirectlystrikestheweldareaandmeltstheweldsurfaceandfillermaterial.
Themeltedpartofweldingplatesdiffusedinoneanotherandcreateaweldjointafter
cooling.
Thisweldingmethodcanbeusedtojoinmostofcommonmetalsusedindailylife.
Types of gases (Fuels):
Acetylene
hydrogen
propane
natural gas etc.
Types of gas welding :
Based on the combination of the gases used :
Oxy acetylene gas welding (most common type)
Air-acetylene gas welding
Oxy-hydrogen gas welding

36. Neutral Flame:
•Carburizing Flame:
•Oxidizing Flame:
There are three basic flame types:
1.Neutral Flame (balanced)
2.Oxidizing (excess oxygen) and
3.Carburizing (excess acetylene)
Types of flames in gas welding

37. Types of flames in gas welding ….
Commonly used to weld:
Mild steel
Stainless steel
Cast Iron
Copper
Aluminum
There are two clearly defined zones in the neutral
flame.
The inner zone consists of a luminous cone that is
bluish-white.
Surrounding this is a light blue flame envelope or
sheath.
Neutral Flame:
-Equal volume of acetylene and oxygen.
-Obtains additional oxygen from the air and
provides complete combustion.
The oxygen to acetylene ratio is around 1.1 to 1.0.
Generally preferred flame.
The neutral flame has a clear, well-defined, or
luminous cone indicating that combustion is
complete

39. Oxidizing Flame:
Excess oxygen.
 The oxygen to acetylene ratio in the case of Oxidizing flame is 1.15 to 1.5.
When the flame is properly adjusted, the inner cone is pointed and slightly purple.
An oxidizing flame can also be recognized by its distinct hissing sound.
The temperature of this flame is approximately 3482ºC at the inner cone tip.
Types of flames in gas welding ….
Oxidizing welding flames are commonly
used to weld these metals:
•Zinc
•Copper
•Manganese steel
•Cast iron

40. 1.Clearlydefinedbluish-whiteinnercone,
2.Whiteintermediateconeindicatingthe
amountofexcessacetylene,and
3.Alightblueouterflareenvelope.
Types of flames in gas welding ….
CarburizingFlame:
Excessacetylene,theinnerconehasafeatheryedgeextendingbeyondit.
Oxygentoacetyleneratioincaseofreducingflamevariesfrom0.85to0.95.
Thereducingorcarburizingflamecanalwaysberecognizedbythepresenceofthree
distinctflamezones.
Ithasatemperatureofapproximately3149ºCattheinnerconetips.

41. FLAMES
ADJUSTMENT
FOROAW
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42. Advantages:
Portable and most versatile process.
Better control over the temperature.
Suitable to weld dissimilar matter.
Low cost & maintenance.
Disadvantages:
Not suitable for heavy section.
Less working temperature of gas
flame.
Slow rate of heating.

43. Arc Welding:
“Arc welding is a fusion welding process in which the
heat required to fuse the metal is obtain from the
electric arc between the base metal and an electrode.
Types:
1.Metal Arc Welding
2.Submerged Arc Welding
3.Tungsten Inert Gas Welding
4.Metal Inert Gas Welding

44. ARCWELDING
Thearcweldingisafusionweldingprocessinwhichtheheatrequiredtofusethe
metalisobtainedfromanelectricarcbetweenthebasemetalandanelectrode.
Theelectricarcisproducedwhentwoconductorsaretouchestogetherandthen
separatedbyasmallgapof2to4mm,suchthatthecurrentcontinuestoflow,
throughtheair.Thetemperatureproducedbytheelectricarcisabout4000°Cto
6000°C.
4
4

45. ARCWELDING
4
5
Ametalelectrodeisusedwhichsuppliesthefillermetal.Theelectrodemaybe
fluxcoatedorbare.Incaseofbareelectrode,extrafluxmaterialissupplied.Both
directcurrent(D.C.)andalternatingcurrent(A.C.)areusedforarcwelding.
Thealternatingcurrentforarcisobtainedfromastepdowntransformer.The
transformerreceivescurrentfromthemainsupplyat220to440voltsandstep
downtorequiredvoltagei.e.,80to100volts.Thedirectcurrentforarcisusually
obtainedfromageneratordrivenbyeitheranelectricmotor,orpatrolordiesel
engine.
Anopencircuitvoltage(forstrikingofarc)incaseofD.C.weldingis60to80volts
whileaclosedcircuitvoltage(formaintainingthearc)is15to25volts

46. PROCEDURE OF ELECTRIC ARC WELDING
4
6
Firstofall,metalpiecestobeweldarethoroughlycleanedtoremovethedust,
dirt,grease,oil,etc.Thentheworkpieceshouldbefirmlyheldinsuitable
fixtures.Insertasuitableelectrodeintheelectrodeholderatanangleof60to
80°withtheworkpiece.
Selectthepropercurrentandpolarity.Thespotaremarkedbythearcatthe
placeswhereweldingistobedone.Theweldingisdonebymakingcontactof
theelectrodewiththeworkandthenseparatingtheelectrodetoaproper
distancetoproduceanarc.

47. PROCEDURE OF ELECTRIC
ARCWELDING
Whenthearcisobtained,intenseheatsoproduced,meltstheworkbelowthe
arc,andformingamoltenmetalpool.Asmalldepressionisformedinthework
andthemoltenmetalisdepositedaroundtheedgeofthisdepression.Itis
calledarccrator.Theslagisbrushedoffeasilyafterthejointhascooled.After
weldingisover,theelectrodeholdershouldbetakenoutquicklytobreakthe
arcandthesupplyofcurrentisswitchedoff.
4
7

48. ELECTRIC CURRENT FORWELDING
4
8
Both D.C. (direct current) and A.C. (alternating current) are used to produce an arc in
electric arc welding. Both have their own advantages and applications.
The D.C. welding machine obtains their power from an A.C. motor or diesel/petrol
generator or from a solid state rectifier.
The capacities of D.C. machine are:
Current:
Up to 600 amperes.
Open Circuit Voltage:
50 to 90 volts, (to produce arc).
Closed Circuit Voltage:
18 to 25 volts, (to maintain arc
TheA.C.weldingmachinehasastepdowntransformerwhichreceivescurrentfrom
mainA.C.supply.Thistransformerstepdownthevoltagefrom220V-440Vtonormal
opencircuitvoltageof80to100volts.Thecurrentrangeavailableupto400
amperesinthestepsof50ampere.

49. The capacities of A.C. welding machine are:
Current Range:
Up to 400 ampere in steps of 50 ampere.
Input Voltage:
220V-440V
Actual Required Voltage:
80 –100 volts. Frequency: 50/60 HZ.
4
9
ELECTRIC CURRENT FORWELDING

50. SIGNIFICANCE OFPOLARITY
5
0
When D.C. current is used for welding, the following two types of polarity are
available:
(i)Straight or positive polarity.
(ii)Reverse or negative polarity.
When the work is made positive and electrode as negative then polarity is called
straight or positive polarity.
In straight polarity, about 67% of heat is distributed at the work (positive terminal)
and 33% on the electrode (negative terminal). The straight polarity is used where
more heat is required at the work. The ferrous metal such as mild steel, with faster
speed and sound weld, uses this polarity.

51. SIGNIFICANCE OFPOLARITY
Ontheotherhand,whentheworkismadenegativeandelectrodeaspositivethen
polarityisknownasreverseornegativepolarity,asshowninFig.7.16(b).
Inreversepolarity,about67%ofheatisliberatedattheelectrode(positiveterminal)
and33%onthework(negativeterminal).
Thereversepolarityisusedwherelessheatisrequiredattheworkasincaseofthin
sheetmetalweld.Thenon-ferrousmetalssuchasaluminum,brass,andbronze
nickelareweldedwithreversepolarity.
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52. Equipments Required for Electric ArcWelding
5
2
Thevariousequipment'srequiredforelectricarcweldingare:
1.WeldingMachine:
TheweldingmachineusedcanbeA.C.orD.C.weldingmachine.TheA.C.welding
machinehasastep-downtransformertoreducetheinputvoltageof220-440Vto
80-100V.
TheD.C.weldingmachineconsistsofanA.C.motor-generatorsetordiesel/petrol
engine-generatorsetoratransformer-rectifierweldingset.
A.C.machineusuallyworkswith50hertzor60hertzpowersupply.
TheefficiencyofA.C.weldingtransformervariesfrom80%to85%.Theenergy
consumedperKg.ofdepositedmetalis3to4kWhforA.C.weldingwhile6to10
kWhforD.C.welding.
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53. 62
Equipments Required for Electric ArcWelding
2.ElectrodeHolders:
Thefunctionofelectrodeholderistoholdtheelectrodeatdesiredangle.Theseare
availableindifferentsizes,accordingtotheampereratingfrom50to500amperes.
3.CablesorLeads:
Thefunctionofcablesorleadsistocarrythecurrentfrommachinetothework.
Theseareflexibleandmadeofcopperoraluminum.Thecablesaremadeof900to
2000veryfinewirestwistedtogethersoastoprovideflexibilityandgreater
strength.
Thewiresareinsulatedbyarubbercovering,areinforcedfibrecoveringandfurther
withaheavyrubbercoating.
4.CableConnectorsandLugs:
Thefunctionsofcableconnectorsaretomakeaconnectionbetweenmachine
switchesandweldingelectrodeholder.Mechanicaltypeconnectorsareused;as
theycanheassembledandremovedveryeasily.Connectorsaredesigned
accordingtothecurrentcapacityofthecablesused.
5.ChippingHammer:
Thefunctionofchippinghammeristoremovetheslagaftertheweldmetalhas
solidified. It has chisel shape and is pointed at oneend.
5
3

54. Equipments Required for Electric ArcWelding
5
4
6.WireBrush,PowerWireWheel:
Thefunctionofwirebrushistoremovetheslagparticlesafterchippingbychipping
hammer.Sometimes,ifavailableapowerwirewheelisusedinplacemanualwire
brush.
7.ProtectiveClothing:
Thefunctionsofprotectiveclothing'susedaretoprotectthehandsandclothesof
thewelderfromtheheat,spark,ultravioletandinfraredrays.Protectiveclothing
usedareleatherapron,cap,leatherhandgloves,leathersleeves,etc.Thehigh
ankleleathershoesmustbewearbythewelder.
8.ScreenorFaceShield:
Thefunctionofscreenandfaceshieldistoprotecttheeyesandfaceofthewelder
fromtheharmfulultravioletandinfraredradiationsproducedduringwelding.The
shieldingmaybeachievedfromheadhelmetorhandhelmet

55. ARC WELDINGELECTRODES
5
5
Arc welding electrodes can be classified into two broad categories:
1.Non-Consumable electrodes.
2.Consumable electrodes.
1.Non-ConsumableElectrodes:
Theseelectrodesdonotconsumedduringtheweldingoperation,hencetheynamed,
non-consumableelectrodes.Theyaregenerallymadeofcarbon,graphiteor
tungsten.Carbonelectrodesaresofterwhiletungstenandgraphiteelectrodesare
hardandbrittle.
CarbonandgraphiteelectrodescanbeusedonlyforD.C.welding,whiletungston
electrodescanbeusedforbothD.C.andA.C.welding.Thefillermaterialisadded
separatelywhenthesetypesofelectrodesareused.Since,theelectrodesdonot
consumed,thearcobtainedisstable.
2.Consumable Electrodes:
These electrodes get melted during welding operation, and supply the filler material.
They are generally made with similar composition as the metal to be welded.

56. 5
6
Arc Welding
Consumable Electrodes
Mild Steel Electrodes Copper Electrodes

57. 5
7
Arc Welding
Non Consumable Electrodes
Carbon Electrodes Tungsten Electrodes

58. Advantages of Arc Welding
Someofthechiefadvantagesoftheelectricarcweldingaregivenas
follows−
Theelectricarcweldingisthesuitableweldingprocessforhighspeed
welds.
Apparatusrequiredforarcweldingisverysimpleandportable.
Theelectricarcweldinggivessuperiortemperatureatthepointofwelding.
ElectricarcweldingcanworkonbothACandDCsupply.
Itisinexpensivetoinstall.
Disadvantages of Electric Arc Welding
Thedisadvantagesofelectricarcweldingareasfollows−
Theweldingprocesswithelectricarcweldingrequiresskilledoperators.
Electricarcweldingcannotbeusedforweldingofreactivemetalssuchas
aluminium,titanium,etc.
Electricarcweldingisnotsuitableforweldingthinmetals.

59. Applications of Electric Arc Welding
Theimportantapplicationsofelectricarcweldingareas
follows−
Electricarcweldingisusedinrepairingofbrokenpartsof
machines.
Itisusedforweldingofcastironorsteelhousingsand
frames.
Electricarcweldingisusedinvariousindustriessuchas
automotiveindustries,constructionindustries,mechanical
industries,etc.
Electricweldingisalsousedforweldingprocessin
shipbuilding.

60. 6
0
Resistance Welding
Theweldingprocessstudiedsofararefusion-weldingprocesses
whereonlyheatisappliedinthejoint.Incontrast,resistance
weldingprocessisafusion-weldingprocesswherebothheat
andpressureappliedonthejointbutnofillermetalorfluxis
added.
Theheatnecessaryforthemeltingofthejointisobtainedbythe
heatingeffectoftheelectricalresistanceofthejointandhence,
thenameresistancewelding.

61. 6
1
Resistance Welding
Principle
Inresistancewelding(RW),alowvoltage(typically1V)andvery
highcurrent(typically15000A)ispassedthroughthejointfora
veryshorttime(typically0.25Sec).Thishighamperageheatsthe
joint,duetothecontactresistanceatthejointandmeltsit.
Thepressureonthejointiscontinuouslymaintainedandthe
metalfusestogetherunderthispressure.
Theheatgeneratedinresistanceweldingcanbeexpressedas:
H = k I² R t

62. 6
2
Resistance Welding
H = k I² R t
Where,
H = the total heat generated in the work, J
I = electric current, A
R = the resistance of the joint, ohms
t = time for which the electric current is passing through the joint, Sec
k = a constant to account for the heat losses from the weld joint.
The resistance of the joint, R, is a complex factor to know because it is
composed of the
a)Resistance of the electrode,
b)Contact resistance between the electrode and the workpiece,
c)Contact resistance between the two workpiece plates, and
d)Resistance of the workpiece plates.

63. 6
4
Resistance Welding
1.Theschematicrepresentationoftheresistanceweldingisshown
andthemainrequirementoftheprocessisthelowvoltageand
highcurrentpowersupply.
2.Thisisobtainedbymeansofastepdowntransformerwitha
provisiontohavedifferenttappingsontheprimarysideas
requiredfordifferentmaterials.
3.Thesecondarywindingsareconnectedtotheelectrodes,which
aremadeofcoppertoreducetheirelectricalresistance.
4.Thetimeoftheelectricsupplyneedstobecloselycontrolledso
thattheheatreleasedisjustenoughtomeltthejointandthe
subsequentfusiontakesplaceduetotheforceonthejoint.

64. 6
5
Resistance Welding
5.Theforcerequiredcanbeprovidedeithermechanically,
hydraulicallyorpneumatically.
6.Topreciselycontrolthetime,sophisticatedelectronictimersare
available.
7.Thecriticalvariableinaresistanceweldingprocessisthecontact
resistancebetweenthetwoworkpieceplatesandtheir
resistancesthemselves.
8.Thecontactresistanceisaffectedbythesurfacefinishonthe
plates,sincetheroughersurfaceshavehighercontactresistance.

65. 6
6
Resistance Welding
9.Thecontactresistancealsowillbeaffectedbythecleanlinessof
thesurface.
10.Oxidesorothercontaminantsifpresent,shouldberemoved
beforeattemptingresistancewelding.
11.Thelowerresistanceofthejointrequiresveryhighcurrentsto
provideenoughheattomeltit.
12.Theaverageresistancemaybeoftheorderof100microohms,
asaresult,thecurrentrequiredwouldbeoftheorderoftensof
thousandsofamperes.Witha10000Acurrentpassingfor0.1
sec,theheatliberatedis
H=(10000)²(0.0001)(0.1)=1000J

66. 6
7
Resistance Welding
13.Thisistypicalfortheweldingof1-mmthicksheets.
14.Theactualheatrequiredformeltingwouldbetheorderof339J.
15.Therestoftheheatisactuallyutilizedinheatingthesurrounding
areasandlostatotherpoints.
16.Theweldingforceusedhastheeffectofdecreasingthecontact
resistanceandconsequently,anincreaseintheweldingcurrent
fortheproperfusion.

67. 6
8Types of Resistance Welding
Following are the 4 different types of resistance
welding:
1.Spot resistance welding
2.Projection resistance welding
3.Seam resistance welding
4.Flash or Butt resistance welding

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77. 7
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Resistance Welding
The Process ofResistance Welding

78. THERMITWELDING
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9
Isaprocessthatusesheatfromanexothermicreactiontoproduce
coalescencebetweenmetals.Thenameisderivedfrom'thermite'the
genericnamegiventoreactionsbetweenmetaloxidesandreducing
agents.

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THERMITWELDING

80. 8
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81. THERMIT
WELDING
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82. 83
Forge Welding
1.Forgewelding(FOW)isasolid-stateweldingprocessthatjoins
twopiecesofmetalbyheatingthemtoahightemperatureand
thenhammeringthemtogether.
2.Itmayalsoconsistofheatingandforcingthemetalstogether
withpressesorothermeans,creatingenoughpressureto
causeplasticdeformationattheweldsurfaces.
3.Theprocessisoneofthesimplestmethodsofjoiningmetalsand
hasbeenusedsinceancienttimes.
4.Forgeweldingisversatile,beingabletojoinahostofsimilarand
dissimilarmetals.
5.Withtheinventionofelectricalandgasweldingmethodsduring
theindustrialrevolution,manualforge-weldinghasbeenlargely
replaced,althoughautomatedforge-weldingisacommon
manufacturingprocess.

83. 84
Forge Welding

84. 85
Applications Forge Welding
Thesignificantapplicationsofweldforginginblacksmithing
include;
1.Itisusedtocreateamoresubstantialmetalfromsmaller
piecesbyallowingblacksmithstojoinmetalandsteel.
2.Itisparticularlyusefulintheweldingprocessofweaponslike
swords.
3.Itiscrucialincreatingarchitecturalstructuressuchasgates
andprisoncells.
4.Itisusefulintheweldingbarrelsofshotguns.
5.Forgeweldingisusuallyemployedintheproductionof
variouscookware.

85. 86
Advantages Forge Welding
Theadvantagesofforgeweldinginclude;
1.Itisrelativelystraightforwardandlesscomplicated.
2.Itcaneasilybecarriedoutbymostblacksmithsbecauseit
doesn’tcostmuchandrequiresonlysmallpiecesofmetal.
3.Forgemeltingissufficienttojoinbothdissimilarandsimilar
metals.
4.Theweldjointusuallytakesmostofitspropertiesfromthe
basematerial.
5.Forgeweldingofmetalsdoesnotrequireanyfillermaterial
tobereliable.

86. 87
Disadvantages Forge Welding
Thedisadvantagesofblacksmithinginclude;
1.Itisnotusefulformassproductionofmaterials.
2.Itispreferableforsteelandiron.
3.Theforgeweldingprocessisrelativelyslow.

87. 88
Heat Affected Zone
Theheataffectedzone(HAZ)isanon-meltedareaofmetalthat
hasundergonechangesinmaterialpropertiesasaresultof
beingexposedtohightemperatures.Thesechangesinmaterial
propertyareusuallyasaresultofweldingorhigh-heatcutting.
TheHAZistheareabetweentheweldorcutandthebase
(unaffected),parentmetal.
TheHAZareacanvaryinseverityandsizedependingonthe
propertiesofthematerials,theconcentrationandintensityof
theheat,andtheweldingorcuttingprocessused.

88. 89
Heat Affected Zone

89. 90
Heat Affected Zone
WhataretheCausesofHeat-AffectedZones?
1.Theheatingassociatedwithweldingand/orcuttinggenerally
usestemperaturesuptoandoftenexceedingthe
temperatureofmeltingofthematerialinquestion,
dependingontheweldingprocessused.
2.However,theheatingandcoolingthermalcycleassociated
withtheseprocessesisdifferenttowhateverprocessinghas
occurredwiththeparentmaterialpreviously.Thisleadstoa
changeinmicrostructureassociatedwiththeheatingand
coolingprocess.

90. 91
Heat Affected Zone
3.Thesizeofaheataffectedzoneisinfluencedbythelevelof
thermaldiffusivity,whichisdependentonthethermal
conductivity,densityandspecificheatofasubstanceaswell
astheamountofheatgoingintothematerial.
4.Thosematerialswithahighlevelofthermaldiffusivityare
abletotransfervariationsofheatfaster,meaningtheycool
quickerand,asaresult,theHAZwidthisreduced.
5.Ontheotherhand,thosematerialswithalowercoefficient
retaintheheat,meaningthatthattheHAZiswider.
6.Generallyspeaking,theextensionoftheHAZisdependenton
theamountofheatapplied,thedurationofexposuretoheat
andthepropertiesofthematerialitself.Whenamaterialis
exposedtogreateramountsofenergyforlongerperiodsthe
HAZislarger.

91. 92
Heat Affected Zone
7.Withregardtoweldingprocedures,thoseprocesseswithlow
heatinputwillcoolfaster,leadingtoasmallerHAZ,whereas
highheatinputwillhaveaslowerrateofcooling,leadingtoa
largerHAZinthesamematerial.
8.Inaddition,thesizeoftheHAZalsogrowsasthespeedofthe
weldingprocessdecreases.Weldgeometryisanotherfactor
thatplaysaroleintheHAZsize,asitaffectstheheatsink,anda
largerheatsinkgenerallyleadstofastercooling.
9.HightemperaturecuttingoperationscanalsocauseaHAZand,
similarlytoweldingprocedures,thoseprocessesthatoperateat
highertemperaturesandslowspeedstendtocreatealarger
HAZ,whilelowertemperatureorhigherspeedcuttingprocesses
tendtoreducetheHAZsize.

92. 93
Heat Affected Zone
10.DifferentcuttingprocesseshavedifferingeffectsontheHAZ,
regardlessofthematerialbeingcut.
11.Forexample,shearingandwaterjetcuttingdonotcreateaHAZ,
astheydonotheatthematerial,whilelasercuttingcreatesa
smallHAZduetotheheatonlybeingappliedtoasmallarea.
12.Meanwhile,plasmacuttingleadstoanintermediateHAZ,with
thehighercurrentsallowingforanincreasedcuttingspeedand
therebyanarrowerHAZ,whileoxyacetylenecuttingcreatesthe
widestHAZduetothehighheat,slowspeedandflamewidth.
13.Arcweldingfallsbetweenthetwoextremes,withindividual
processesvaryinginheatinput.

93. 94
Welding Defects, Causes and Remedies
Defectsarecommoninanytypeofmanufacturing,welding
including.Intheprocess,therecanbedeviationsintheshapeand
sizeofthemetalstructure.Itcanbecausedbytheuseofthe
incorrectweldingprocessorwrongweldingtechnique.
WeldCrack
Themostserioustypeofweldingdefectisaweldcrackandit’snot
acceptedalmostbyallstandardsintheindustry.Itcanappearon
thesurface,intheweldmetalortheareaaffectedbytheintense
heat.
Therearedifferenttypesofcracks,dependingonthetemperatureat
whichtheyoccur:

94. 95
Welding Defects, Causes and Remedies
1.Hotcracks:Thesecanoccurduringtheweldingprocessor
duringthecrystallizationprocessoftheweldjoint.
2.Coldcracks:Thesecracksappearaftertheweldhasbeen
completedandthetemperatureofthemetalhasgonedown.
Theycanformhoursorevendaysafterwelding.Itmostly
happenswhenweldingsteel.Thecauseofthisdefectisusually
deformitiesinthestructureofsteel.
3.Cratercracks:Theseoccurattheendoftheweldingprocess
beforetheoperatorfinishesapassontheweldjoint.They
usuallyformneartheendoftheweld.Whentheweldpool
coolsandsolidifies,itneedstohaveenoughvolumeto
overcomeshrinkageoftheweldmetal.Otherwise,itwillform
acratercrack.

95. 96
Welding Defects, Causes and Remedies
Causesofcracks:
1.Useofhydrogenwhenweldingferrousmetals.
2.Residualstresscausedbythesolidificationshrinkage.
3.Basemetalcontamination.
4.Highweldingspeedbutlowcurrent.
5.Nopreheatbeforestartingwelding.
6.Poorjointdesign.
7.Ahighcontentofsulfurandcarboninthemetal.

96. 97
Welding Defects, Causes and Remedies
Remedies:
1.Preheatthemetalasrequired.
2.Providepropercoolingoftheweldarea.
3.Useproperjointdesign.
4.Removeimpurities.
5.Useappropriatemetal.
6.Makesuretoweldasufficientsectionalarea.
7.Useproperweldingspeedandamperagecurrent.
8.Topreventcratercracksmakesurethatthecraterisproperly
filled.

97. 98
Welding Defects, Causes and Remedies
Porosity
Porosityoccursasaresultofweldmetalcontamination.The
trappedgasescreateabubble-filledweldthatbecomesweakand
canwithtimecollapse.

98. 99
Welding Defects, Causes and Remedies
Causesofporosity:
1.Inadequateelectrodedeoxidant.
2.Usingalongerarc.
3.Thepresenceofmoisture.
4.Impropergasshield.
5.Incorrectsurfacetreatment.
6.Useoftoohighgasflow.
7.Contaminatedsurface.
8.Presenceofrust,paint,greaseoroil

99. 100
Welding Defects, Causes and Remedies
Remedies:
1.Cleanthematerialsbeforeyoubeginwelding.
2.Usedryelectrodesandmaterials.
3.Usecorrectarcdistance.
4.Checkthegasflowmeterandmakesurethatit’soptimizedas
requiredwithproperwithpressureandflowsettings.
5.Reducearctravelspeed,whichwillallowthegasestoescape.
6.Usetherightelectrodes.
7.Useaproperweldtechnique

100. 101
Welding Defects, Causes and Remedies
Undercut
Thisweldingimperfectionisthegrooveformationattheweldtoe,
reducingthecross-sectionalthicknessofthebasemetal.The
resultistheweakenedweldandworkpiece.

101. 102
Welding Defects, Causes and Remedies
Causes:
1.Toohighweldcurrent.
2.Toofastweldspeed.
3.Theuseofanincorrectangle,whichwilldirectmoreheatto
freeedges.
4.Theelectrodeistoolarge.
5.Incorrectusageofgasshielding.
6.Incorrectfillermetal.
7.Poorweldtechnique.

102. 103
Welding Defects, Causes and Remedies
Remedies:
1.Useproperelectrodeangle.
2.Reducethearclength.
3.Reducetheelectrode’stravelspeed,butitalsoshouldn’tbe
tooslow.
4.Chooseshieldinggaswiththecorrectcompositionforthe
materialtypeyou’llbewelding.
5.Useofproperelectrodeangle,withmoreheatdirected
towardsthickercomponents.
6.Useofpropercurrent,reducingitwhenapproachingthinner
areasandfreeedges.
7.Chooseacorrectweldingtechniquethatdoesn’tinvolve
excessiveweaving.
8.Usethemultipasstechnique

103. 104
Welding Defects, Causes and Remedies
IncompleteFusion
Thistypeofweldingdefectoccurswhenthere’salackofproper
fusionbetweenthebasemetalandtheweldmetal.Itcanalso
appearbetweenadjoiningweldbeads.Thiscreatesagapinthe
jointthatisnotfilledwithmoltenmetal.

104. 105
Welding Defects, Causes and Remedies
Causes:
1.Lowheatinput.
2.Surfacecontamination.
3.Electrodeangleisincorrect.
4.Theelectrodediameterisincorrectforthematerialthickness
you’rewelding.
5.Travelspeedistoofast.
6.Theweldpoolistoolargeanditrunsaheadofthearc.

105. 106
Welding Defects, Causes and Remedies
Remedies:
1.Useasufficientlyhighweldingcurrentwiththeappropriatearc
voltage.
2.Beforeyoubeginwelding,cleanthemetal.
3.Avoidmoltenpoolfromfloodingthearc.
4.Usecorrectelectrodediameterandangle.
5.Reducedepositionrate.

106. 107
Welding Defects, Causes and Remedies
IncompletePenetration
Incompletepenetrationoccurswhenthegrooveofthemetalis
notfilledcompletely,meaningtheweldmetaldoesn’tfullyextend
throughthejointthickness.

107. 108
Welding Defects, Causes and Remedies
Causes:
1.Therewastoomuchspacebetweenthemetalyou’rewelding
together.
2.You’removingthebeadtooquickly,whichdoesn’tallow
enoughmetaltobedepositedinthejoint.
3.You’reusingatoolowamperagesetting,whichresultsinthe
currentnotbeingstrongenoughtoproperlymeltthemetal.
4.Largeelectrodediameter.
5.Misalignment.
6.Improperjoint.

108. 109
Welding Defects, Causes and Remedies
Remedies:
1.Useproperjointgeometry.
2.Useaproperlysizedelectrode.
3.Reducearctravelspeed.
4.Chooseproperweldingcurrent.
5.Checkforproperalignment.

109. 110
Welding Defects, Causes and Remedies
SlagInclusion
Slaginclusionisoneoftheweldingdefectsthatareusuallyeasily
visibleintheweld.Slagisavitreousmaterialthatoccursasa
byproductofstickwelding,flux-coredarcweldingandsubmerged
arcwelding.Itcanoccurwhentheflux,whichisthesolidshielding
materialusedwhenwelding,meltsintheweldoronthesurfaceof
theweldzone.

110. 111
Welding Defects, Causes and Remedies
Causes:
1.Impropercleaning.
2.Theweldspeedistoofast.
3.Notcleaningtheweldpassbeforestartinganewone.
4.Incorrectweldingangle.
5.Theweldpoolcoolsdowntoofast.
6.Weldingcurrentistoolow.

111. 112
Welding Defects, Causes and Remedies
Remedies:
1.Increasecurrentdensity.
2.Reducerapidcooling.
3.Adjusttheelectrodeangle.
4.Removeanyslagfromthepreviousbead.
5.Adjusttheweldingspeed.

112. 113
Welding Defects, Causes and Remedies
Spatter
Spatteroccurswhensmallparticlesfromtheweldattach
themselvestothesurroundingsurface.It’sanespeciallycommon
occurrenceingasmetalarcwelding.Nomatterhowhardyoutry,
itcan’tbecompletelyeliminated.However,thereareafewways
youcankeepittoaminimum.

113. 114
Welding Defects, Causes and Remedies
Causes:
1.Therunningamperageistoohigh.
2.Voltagesettingistoolow.
3.Theworkangleoftheelectrodeistoosteep.
4.Thesurfaceiscontaminated.
5.Thearcistoolong.
6.Incorrectpolarity.
7.Erraticwirefeeding.

114. 115
Welding Defects, Causes and Remedies
Remedies:
1.Cleansurfacespriortowelding.
2.Reducethearclength.
3.Adjusttheweldcurrent.
4.Increasetheelectrodeangle.
5.Useproperpolarity.
6.Makesureyoudon’thaveanyfeedingissues.

115. 116
Destructive and Non-destructive Testing of Welds
Thetestsdescribedbelowhavebeendevelopedtochecktheskill
oftheweldingoperatoraswellasthequalityoftheweldmetal
andthestrengthoftheweldedjointforeachtypeofmetalusedin
ordnancematerial.
Manytestsdetectdefectsnotvisibletothenakedeye.

116. 117
Resistance Welding
Schematic of a resistance welding set-up