The document discusses advanced welding technologies, including various welding processes such as arc welding, resistance welding, oxyfuel gas welding, and solid state welding. It provides details on common arc welding processes like shielded metal arc welding, gas metal arc welding, flux-cored arc welding, submerged arc welding, and gas tungsten arc welding. The summary discusses the key welding processes, their characteristics, and applications.

1. Advanced Welding Technology
By Lalit Yadav
Asst.Prof.(Mech.Engg.)

2. Introduction
• Welding is a process of joining two metal pieces by the
application of heat. Welding is the least expensive process and
widely used now a days in fabrication. Welding joints different
metals with the help of a number of processes in which heat is
supplied either electrically or by mean of a gas torch. Different
welding processes are used in the manufacturing of Auto
mobiles bodies, structural work, tanks, and general machine
repair work. In the industries , welding is used in refineries and
pipe line fabrication. It may be called a secondary
manufacturing process.
Modern welding technology started just before the end of 19th
century with the development of methods for generating high
temperature in localized zones to melt the material.
•

5. WELDINGPROCESSES
1. Arc Welding
2. Resistance Welding
3. Oxyfuel GasWelding
4. Other Fusion Welding Processes
5. Solid State Welding
6. Weld Quality
7. Weldability
8. Design Considerations in Welding

6. TwoCategoriesof Welding Processes
• Fusion welding - coalescence is accomplished
by melting the two parts to be joined, in some
casesadding filler metal to thejoint
– Examples: arc welding, resistance spot welding,
oxyfuel gaswelding.
• Solidstate welding- heat and/or pressureare
used to achieve coalescence, but no melting
of basemetals occurs and no filler metal is
added
– Examples: forge welding, diffusion welding,
friction welding.

7. ArcWelding (AW)
Afusion welding process in which coalescence
of the metals is achieved by the heat from an
electric arc between an electrode and the
work
• Electric energy from the arc produces
temperatures ~10,000 F(5500 C),hot enough
to melt anymetal
• Most AWprocessesadd filler metal to
increase volume and strength of weldjoint.

8. What is an Electric Arc?
An electric arc is adischarge of electriccurrent
acrossagapin acircuit
• It is sustained by an ionized column ofgas
(plasma) through which the currentflows
• Toinitiate the arc in AW,electrode isbrought
into contact with work and then quickly
separated from it by ashortdistance

9. Arc Welding
• Apool of molten metal is formed near
electrode tip, and aselectrode is moved
along joint, molten weld poolsolidifies in
its wake

10. Manual ArcWelding andArc Time
• Problems with manualwelding:
– Weld joint quality
– Productivity
• Arc Time =(time arc is on) dividedby
(hours worked)
– Also called “arc-on time”
– Manual welding arc time =20%
– Machine welding arc time ~50%

11. Two BasicTypesof AWElectrodes
• Consumable– consumed during welding
process
– Sourceof filler metal inarc welding
• Nonconsumable– not consumedduring
welding process
– Filler metal must be added separately if itis
added

12. ConsumableElectrodes
• Formsof consumableelectrodes
– Welding rods are 9 to 18 inches and 3/8 inch orlessin
diameter and must be changedfrequently
– Weld wire can be continuously fed from spools with long
lengths of wire, avoiding frequentinterruptions
In both rod and wire forms, electrode is consumed by the arc
and added to weld joint asfillermetal
•

13. NonconsumableElectrodes
•
•
Made of tungsten which resistsmelting
Gradually depleted during welding (vaporizationis
principal mechanism)
Any filler metal must be supplied by aseparate wirefed
into weldpool
•

14. ArcShielding
• At high temperatures in AW,metals arechemically
reactive to oxygen, nitrogen, and hydrogen inair
– Mechanical properties of joint can be degraded bythese
reactions
– Toprotect operation, arc must be shieldedfrom
surrounding air in AWprocesses
Arc shielding is accomplishedby:
–Shielding gases,e.g., argon, helium, CO2
– Flux
(In high-temperature metal joining processes (welding,
brazing and soldering), the primary purpose of fluxis to
prevent oxidation of the baseand filler materials. Tin-lead
solder (e.g.) attaches very well to copper, but poorly to the
various oxides of copper, which form quickly at soldering
temperatures.)
•

15. Power Sourcein ArcWelding
• Direct current (DC)vs.Alternating current (AC)
– ACmachines lessexpensive to purchase and
operate, but generally restricted toferrous metals
– DCequipment can be used on all metals and is
generally noted for better arccontrol

16. Consumable Electrode
AWProcesses
• Shielded Metal Arc Welding(SMAW)
• GasMetal Arc Welding(GMAW)
• Flux-CoredArc Welding (FCAW)
• Electrogas Welding (EGW)
• SubmergedArc Welding (SAW)

17. Shielded Metal Arc Welding (SMAW)

18. Welding Stick in SMAW
• Composition of fillermetal ( aluminum ,tin
or lead)usually close to basemetal
• Coating: powdered cellulose mixed with
oxides and carbonates, and held togetherby
asilicate binder
• Welding stick is clamped in electrodeholder
connected to powersource
• Disadvantages of stickwelding:
– Sticksmust be periodically changed
– High current levels may melt coatingprematurely

19. SMAWApplications
• Usedfor steels, stainless steels,cast
irons, and certain nonferrousalloys
• Not used or rarely used for
aluminum and its alloys,copper
alloys, and titanium

20. GasMetal ArcWelding(GMAW)
Usesaconsumable bare metal wire aselectrode
with shielding by flooding arc withagas
• Wire is fed continuously andautomatically
from aspool through the weldinggun
• Shielding gasesinclude argon and helium for
aluminum welding, and CO2
for steelwelding
• Bare electrode wire plus shieldinggases
eliminate slagon weld bead
– No need for manual grinding and cleaning ofslag

21. Gas Metal Arc Welding

22. GMAWAdvantages over SMAW
• Better arc time becauseof continuouswire
electrode
– Sticksmust be periodically changed in SMAW
• Better useof electrode filler metalthan
SMAW
– Endof stick cannot be usedinSMAW
• Higher deposition rates
• Eliminates problem of slagremoval
• Canbe readily automated

23. Flux-CoredArcWelding (FCAW)
Adaptation of shielded metal arc welding, to
overcome limitations of stick electrodes -two
versions
– Self-shielded FCAW- core includes compounds that
produce shielding gases
– Gas-shielded FCAW- usesexternally applied shielding
gases
• Electrode is a continuous consumable tubing (in
coils) containing flux and other ingredients (e.g.,
alloying elements) in itscore

24. Flux-Cored Arc Welding
Presenceor absenceof externally supplied shielding gas
distinguishes: (1) self-shielded - core provides ingredientsfor
shielding, (2) gas-shielded - usesexternal shieldinggases

25. ElectrogasWelding (EGW)
Usesacontinuous consumable electrode,
flux-cored wire or bare wire with externally
supplied shielding gases,and molding shoesto
contain molten metal.
• When flux-cored electrode wire is used and no
external gasesare supplied, then special caseof
self-shielded FCAW
• When a bare electrode wire used with shielding
gases from external source, then special caseof
GMAW

26. • Electrogas welding using flux-cored electrode wire: (a) front view
with molding shoe removed for clarity, and (b) side view showing
molding shoeson both sides
Electrogas Welding

27. SubmergedArcWelding (SAW)
Uses a continuous, consumable bare wire
electrode, with arc shielding by a cover of
granular flux
• Electrode wire is fed automatically froma
coil
• Flux introduced into joint slightlyahead
of arc by gravity from ahopper
– Completely submerges operation, preventing
sparks, spatter, andradiation

28. Submerged Arc Welding

29. SAWApplications andProducts
• Steel fabrication of structural shapes(e.g.,
I-beams)
• Seamsfor large diameter pipes, tanks,and
pressure vessels
• Welded components for heavymachinery
• Most steels (except hi Csteel)
• Not good for nonferrousmetals

30. NonconsumableElectrode
Processes
• GasTungstenArc Welding
• PlasmaArc Welding
• CarbonArc Welding
• Stud Welding

31. GasTungsten Arc Welding (GTAW)
Usesanon-consumable tungsten electrode
and an inert gasfor arcshielding
• Melting point of tungsten =3410C(6170F)
• A.k.a.Tungsten Inert Gas(TIG)welding
– In Europe, called "WIGwelding"
• Usedwith or without afillermetal
– When filler metal used, it is added to weld pool from
separate rod or wire
• Applications: aluminum and stainlesssteel
mostly

32. Gas Tungsten Arc Welding

33. AdvantagesandDisadvantagesof
GTAW
Advantages:
•
•
•
High quality welds for suitable applications
No spatter becauseno filler metal througharc
Little or no post-weld cleaning because noflux
Disadvantages:
• Generally slower and more costly thanconsumable
electrode AWprocesses

34. PlasmaArcWelding (PAW)
Specialform of GTAWin which aconstricted
plasma arc is directed at weldarea
• Tungsten electrode is contained in anozzle
that focuses ahigh velocity stream of inert gas
(argon) into arc region toform ahigh velocity,
intensely hot plasma arcstream
• Temperatures in PAWreach 28,000C
(50,000F), due to constriction of arc,
producing aplasma jet of small diameterand
very high energydensity

35. Plasma Arc Welding

36. AdvantagesandDisadvantagesof
PAW
Advantages:
• Good arc stability and excellent weldquality
• Better penetration control than otherAW
processes
• High travel speeds
•Canbe used to weld almost anymetals
Disadvantages:
• High equipment cost
• Larger torch sizethan other AWprocesses
– Tendsto restrict accessin somejoints

37. ResistanceWelding (RW)
Agroup of fusion welding processesthat usea
combination of heat and pressure to
accomplish coalescence
• Heat generated by electrical resistanceto
current flow at junction to be welded
• Principal RWprocess is resistance spot
welding (RSW)

38. Resistance Welding
• Resistance welding,
showing
components in spot
welding, the main
process in the RW
group

39. Componentsin ResistanceSpot
Welding
• Parts to be welded (usually sheetmetal)
• Two opposing electrodes
• Means of applying pressure tosqueezeparts
between electrodes
• Power supply from which acontrolledcurrent
canbe applied for aspecified time duration

40. AdvantagesandDrawbacksof
ResistanceWelding
Advantages:
• No filler metalrequired
• High production rates possible
• Lendsitself to mechanization andautomation
• Lower operator skill level than forarc welding
•Goodrepeatability andreliability
Disadvantages:
• High initial equipment cost
• Limited to lap joints formost RWprocesses

41. ResistanceSpotWelding (RSW)
Resistance welding process in which fusionof
faying surfaces of alap joint is achieved at
one location by opposingelectrodes
• Usedto join sheet metalparts
• Widely used in massproduction of
automobiles, metal furniture, appliances,and
other sheet metalproducts
– Typical car body has~10,000 spot welds
– Annual production of automobiles in the world is
measured in tens of millions of units

42. (a) Spot welding cycle
(b)Plot of forceand
current
Cycle:
(1)parts inserted
between electrodes,
(2) electrodes close,
(3) current on,
(4) current off,
(5)electrodes
opened
Spot Welding Cycle

43. ResistanceSeamWelding (RSEW)
Usesrotating wheel electrodes to producea
series of overlapping spot welds along lap
joint
• Canproduce air-tight joints
• Applications:
– Gasoline tanks
– Automobile mufflers
– Various sheet metal containers

44. Resistance Seam Welding

45. ResistanceProjectionWelding (RPW)
Aresistance welding process in which coalescence occurs at one
or more small contact points on the parts
Contact points determined by design of parts tobe joined
– May consist of projections, embossments, or localized
intersections of parts
•

46. (1) Start of operation, contact between parts is at projections;
(2)When current is applied, weld nuggets similar tospot
welding are formed at theprojections
Resistance Projection Welding

47. Other ResistanceProjection Welding Operations
(a) Welding of fastener on sheetmetal
(b) cross-wire welding

48. Oxy-fuel GasWelding(OFW)
Group of fusion welding operations thatburn
various fuels mixed with oxygen
• OFWemploys several types of gases,which is the
primary distinction among the members of this
group
• Oxyfuel gasis also used in flame cutting torches
tocut and separate metal plates and other parts
• Most important OFWprocess is oxyacetylene
welding

49. OxyacetyleneWelding (OAW)
Fusion welding performed by ahigh temperature flame from
combustion of acetylene andoxygen
Flame is directed by awelding torch
Filler metal is sometimesadded
– Composition must be similar to basemetal
– Filler rod often coated with flux to clean surfaces and
prevent oxidation
•
•

50. Oxyacetylene Welding

51. Acetylene (C2H2)
• Most popular fuel among OFWgroupbecause
it is capable of higher temperatures than any
other
– Up to 3480C(6300F)
• Two stage reaction of acetylene andoxygen:
– First stage reaction (inner cone offlame)
C2
H2
+O2 2CO+H2+heat
– Secondstage reaction (outer envelope)
2CO+H2+1.5O2 2CO2+H2
O+heat

52. • Maximum temperature reached at tip of inner cone, while
outer envelope spreads out and shields work surface from
atmosphere
Shown below is neutral flame of oxyacetylene torch indicating
temperatures achieved
•
Oxyacetylene Torch

53. Safety Issuein OAW
• Together, acetylene and oxygen arehighly
flammable
• C2
H2
is colorless and odorless
– It is therefore processed to have characteristicgarlic
odor

54. OAWSafety Issue
• C2
H2
is physically unstable at pressuresmuch
above 15 lb/in2 (about 1atm)
– Storage cylinders are packed with porous fillermaterial
saturated with acetone(CH3
COCH3
)
– Acetone dissolves about 25 times its ownvolume of
acetylene
• Different screw threads are standard on C2
H2
and O2cylinders and hosesto avoidaccidental
connection of wronggases

55. Alternative Gasesfor OFW
• Methylacetylene-Propadiene (MAPP)
• Hydrogen
• Propylene
• Propane
• Natural Gas

56. Other Fusion Welding Processes
FWprocessesthat cannot be classified asarc,
resistance, or oxyfuelwelding
• Useunique technologies to develop heatfor
melting
• Applications are typically unique
• Processesinclude:
– Electron beam welding
– Laserbeam welding
– Electroslag welding
– Thermit welding

57. Electron BeamWelding (EBW)
Fusion welding process in which heat for
welding is provided by ahighly-focused,
high-intensity stream of electronsstriking
work surface
• Electron beam gun operatesat:
– High voltage (e.g., 10 to 150 kVtypical) toaccelerate
electrons
– Beamcurrents are low (measured inmilliamps)
• Power in EBWnotexceptional.

58. Electron BeamWelding (EBW)

59. EBWVacuumChamber
• When first developed, EBWhad to becarried
out in avacuum chamber to minimize
disruption of electron beam by airmolecules
– Serious inconvenience in production
• Pumpdown time can take aslong asan hour

60. Three Vacuum Levelsin EBW
1. High-vacuum welding – welding in same vacuum
chamber as beam generation to produce highest
quality weld
2. Medium-vacuum welding – welding in separate
chamber but partial vacuum reducespump-down
time
3. Non-vacuum welding – welding done at or near
atmospheric pressure, with work positionedclose to
electron beam generator - requires vacuum divider
to separate work from beamgenerator

61. AdvantagesandDisadvantagesof EBW
Advantages:
• High-quality welds, deep and narrowprofiles
• Limited heat affected zone, lowthermal
distortion
•No flux or shielding gasesneeded
Disadvantages:
• High equipment cost
• Precisejoint preparation & alignmentrequired
• Vacuum chamber required
• Safety concern: EBWgeneratesx-rays

62. LaserBeamWelding (LBW)
Fusion welding process in which coalescenceis
achieved by energy of ahighly concentrated,
coherent light beam focused onjoint.
• LBWnormally performed with shieldinggases
to preventoxidation
• Filler metal not usuallyadded
• High power density in smallarea
– SoLBWoften used for small parts

64. Comparison: LBWvs. EBW
• No vacuum chamber required for LBW
• No x-rays emitted in LBW
• Laserbeams canbe focused and directed by
optical lensesandmirrors
• LBWnot capable of the deep welds andhigh
depth-to-width ratios ofEBW
– Maximum LBWdepth =~19 mm (3/4 in), whereas
EBWdepths =50 mm (2in)

65. Thermit Welding (TW)
FWprocess in which heat for coalescenceis
produced by superheated molten metal fromthe
chemical reaction of thermite
• Thermite = mixture of Al and Fe3
O4finepowders
that produce an exothermic reaction when
ignited
• Also used for incendiarybombs
• Filler metal obtained from liquidmetal
• Processused for joining, but hasmorein
common with casting thanwelding

66. • (1) Thermit ignited; (2) crucible tapped, superheated metalflows
into mold; (3) metal solidifies to produce weld joint
Thermit Welding

67. TWApplications
• Joining of railroadrails
• Repair of cracksin large steel castingsand
forgings
• Weld surface is often smooth enough thatno
finishing is required

68. SolidState Welding (SSW)
• Coalescenceof part surfaces is achievedby:
– Pressure alone, or
– Heat and pressure
• If both heat and pressure are used, heat is not enough
to melt worksurfaces
– For some SSWprocesses, time is also afactor
• No filler metal isadded
• EachSSWprocess hasits own way of creating
abond at the fayingsurfaces

69. SuccessFactorsinSSW
• Essential factors for asuccessful solid state weld are thatthe
two faying surfaces mustbe:
– Very clean
– In very close physical contact with each other to permit
atomic bonding

70. SSWAdvantages over FWProcesses
• If no melting, then no heat affected zone, so
metal around joint retains originalproperties
• Many SSWprocessesproduce welded joints that
bond the entire contact interface between two
parts rather than at distinct spots or seams
• SomeSSWprocessescanbe used to bond
dissimilar metals, without concerns about
relative melting points, thermal expansions,and
other problems that arise inFW

71. Solid State Welding Processes
• Forge welding
• Cold welding
• Roll welding
• Hot pressurewelding
• Diffusion welding
• Explosion welding
• Friction welding
• Ultrasonic welding

72. Forge Welding
Welding processin which components tobe joined are
heated to hot working temperature range and then
forged together by hammering or similarmeans
•
• Historic significance in development ofmanufacturing
technology
– Processdates from about 1000 B.C.,when blacksmiths learned to
weld two pieces ofmetal
Of minor commercial importance today except forits
variants

73. Cold Welding (CW)
SSWprocess done by applying high pressure
between clean contacting surfaces at room
temperature
• Cleaning usually done by degreasing andwire
brushing immediately beforejoining
• No heat is applied, but deformation raiseswork
temperature
• At least one of the metals, preferably both, must
be very ductile
– Soft aluminum and copper suited to CW
• Applications: making electrical connections

74. Roll Welding (ROW)
SSWprocess in which pressure sufficient to
causecoalescenceis applied by meansof rolls,
either with or without external heat
• Variation of either forge welding or cold
welding, depending on whether heatingof
workparts is done prior toprocess
– If no external heat, called coldroll welding
– If heat is supplied, hot rollwelding

75. Roll Welding

76. Roll Welding Applications
• Cladding stainless steel tomild or low alloy
steel for corrosionresistance
• Bimetallic strips for measuringtemperature
• "Sandwich" coins for U.Smint

77. Diffusion Welding(DFW)
SSWprocess usesheat and pressure, usually in acontrolled
atmosphere, with sufficient time for diffusion and
coalescence to occur
•
•
•
•
Temperatures  0.5 Tm
Plastic deformation at surfaces isminimal
Primary coalescence mechanism is solid state diffusion
Limitation: time required fordiffusion can range from
secondsto hours

78. DFWApplications
• Joining of high-strength and refractorymetals
in aerospaceand nuclearindustries
• Canbe used to join either similarand
dissimilar metals
– For joining dissimilar metals, afiller layer of
different metal is often sandwiched betweenbase
metals to promotediffusion

79. Explosion Welding (EXW)
SSWprocess in which rapid coalescence of two metallic surfacesis
caused by the energy of adetonatedexplosive
• No fillermetal used,No external heat applied,No diffusion occurs -
time is too short
• Bonding is metallurgical, combined with mechanical interlocking
that results from arippled or wavy interface between the metals

80. Explosive Welding
• Commonly used to bond two dissimilar metals, e.g., to clad one
metal on top ofabasemetal over large areas
(1) Setup in parallel configuration, and (2) during detonation of the
explosive charge
•

81. Friction Welding (FRW)
SSWprocess in which coalescenceis achieved by
frictional heat combined with pressure
• When properly carried out, no meltingoccurs at
faying surfaces
• No filler metal, flux, or shieldinggasesnormally
used
• Processyields anarrow HAZ
• Canbe used to join dissimilarmetals
• Widely used commercial process, amenableto
automation and massproduction

82. • (1) Rotating part, no contact; (2) parts brought into contact to
generate friction heat; (3) rotation stopped and axial pressure
applied; and (4) weldcreated
Friction Welding

83. Applications and Limitations of Friction
Welding
Applications:
• Shafts and tubular parts
• Industries: automotive, aircraft, farmequipment,
petroleum and naturalgas
Limitations:
• At least one of theparts must be rotational
• Flashmust usually be removed (extraoperation)
• Upsetting reduces the part lengths (whichmust
be taken into consideration in productdesign)

84. Friction Stir Welding(FSW)
SSWprocess in which arotating tool is fed along a
joint line between two workpieces, generating
friction heat and mechanically stirring themetal
to form the weldseam
• Distinguished from FRWbecauseheat is
generated by aseparate wear-resistant tool
rather than theparts
• Applications: butt joints inlarge aluminum parts
in aerospace, automotive, andshipbuilding

85. Friction StirWelding
• (1) Rotating tool just before entering work, and (2) partially
completed weld seam

86. Advantages and Disadvantages of
Friction Stir Welding
• Advantages
– Good mechanical properties of weldjoint
– Avoids toxic fumes, warping, and shieldingissues
– Little distortion orshrinkage
– Good weld appearance
• Disadvantages
– An exit hole is produce when tool iswithdrawn
– Heavyduty clamping of parts isrequired

87. Ultrasonic Welding (USW)
Two components are held together, and oscillatory
shear stresses of ultrasonic frequency are applied
to interface to causecoalescence
• Oscillatory motion breaks down any surfacefilms
to allow intimate contact and strong
metallurgical bonding betweensurfaces
• Temperatures are well belowTm
• No filler metals, fluxes, or shieldinggases
• Generally limited to lap joints on soft materials

88. • (a) General setup for alap joint; and(b)
close-up of weldarea
Ultrasonic Welding

89. USWApplications
• Wire terminations and splicing in
electrical and electronicsindustry
– Eliminates need for soldering
• Assemblyof aluminum sheetmetal
panels
• Welding of tubes tosheets in solar
panels
• Assemblyof small parts inautomotive
industry

90. Weld Quality
Concerned with obtaining an acceptableweld
joint that is strong and absent ofdefects
• Also concerned with the methods of
inspecting and testing the joint toassureits
quality
• Topics:
•
•
•
Residualstresses and distortion
Welding defects
Inspection and testing methods

91. Residual Stressesand Distortion
• Rapidheating and cooling in localizedregions
during FWresult in thermal expansion and
contraction that causeresidualstresses
• Thesestresses,in turn, causedistortion and
warpage
• Situation in welding is complicatedbecause:
– Heating is very localized
– Melting of basemetals in theseregions
– Location of heating and melting is in motion (at least in
AW)

92. Residual Stressesand Distortion
(a)Butt welding
two plates
(b) Shrinkage
(c)Residual
stresspatterns
(d)Likely
warping of
weldment

93. Techniques to MinimizeWarpage
Welding fixtures to physically restrain parts
Heat sinks to rapidly removeheat
•
•
• Tackwelding at multiple points along joint tocreate arigid
structure prior to seamwelding
Selection of welding conditions (speed, amount offiller
metal used, etc.) to reducewarpage
Preheating baseparts, Stressrelief heat treatment of
welded assembly
•
•

94. Welding Defects
• Cracks
• Cavities
• Solid inclusions
• Imperfect shape or unacceptablecontour
• Incomplete fusion
• Miscellaneous defects

95. Welding Cracks
Fracture-type interruptions either in weld orin basemetal
adjacent to weld
•
•
• Serious defect becauseit is adiscontinuity in themetal
that significantly reducesstrength
Causedby embrittlement or low ductility of weld and/or
basemetal combined with high restraint during
contraction
In general, this defect must berepaired

96. Cavities
Two defect types, similar todefects found in
castings:
1. Porosity - small voids in weld metal formed by gases
entrapped during solidification
– Causedby inclusion of atmospheric gases,sulfurin
weld metal, or surfacecontaminants
1. Shrinkage voids - cavities formed by shrinkageduring
solidification

97. Solid Inclusions
Nonmetallic material entrapped in weldmetal
•
• Most common form is slaginclusions generated duringAW
processes that useflux
– Instead of floating to top of weld pool, globules of slag
become encased during solidification
Other forms: metallic oxides that form during welding of
certain metals such asaluminum, which normally hasa
surface coating of Al2O3

98. Incomplete Fusion
Aweld bead in which fusion hasnot occurred
throughout entire crosssection ofjoint
• Several forms of incomplete fusionare
shown below

99. • (a) Desired profile for single V-groove weldjoint,
(b) undercut - portion of basemetal meltedaway,
(c)underfill - depression in weld below adjacent
basemetal surface, and (d) overlap - weld metal
spills beyond joint onto part surface but no fusion
occurs
Weld Profile in AW

100. Inspection and TestingMethods
• Visual inspection
• Nondestructive evaluation
• Destructive testing

101. Visual Inspection
•
•
Most widely used welding inspectionmethod
Human inspector visually examinesfor:
– Conformance to dimensions,wWarpage
– Cracks,cavities, incomplete fusion, and other surface
defects
Limitations:
– Only surface defects are detectable
– Welding inspector must also decide if additional testsare
warranted
•

103. Nondestructive Evaluation
(NDE)Tests
• Ultrasonic testing - high frequency sound waves
through specimen to detect cracks andinclusions
• Radiographic testing - x-rays or gammaradiation
provide photograph of internalflaws
• Dye-penetrant and fluorescent-penetrant tests -
to detect small cracksand cavities at partsurface
• Magnetic particle testing – iron filings sprinkled
on surface reveal subsurface defects bydistorting
magnetic field in part

104. Destructive Testing
Tests in which weld is destroyed eitherduring
testing or to prepare testspecimen
• Mechanical tests - purpose is similar to
conventional testing methods suchastensile
tests, shear tests, etc
• Metallurgical tests - preparation of metallurgical
specimens (e.g., photomicrographs) of weldment
to examine metallic structure, defects, extent
and condition of heat affected zone, and similar
phenomena

105. Mechanical Testsin Welding
• (a) Tension-shear test, (b) fillet break test, (c) tension-shearof
spot weld, and (d) peel test for spot weld

106. Weldability
Capacity of ametal or combination ofmetals to
be welded into asuitable structure, and for
the resulting weld joint(s) to possessthe
required metallurgical properties to perform
satisfactorily in intendedservice
• Goodweldability characterizedby:
– Easewith which welding isaccomplished
– Absenceof weld defects
– Strength, ductility, and toughness in weldedjoint

107. Weldability Factors – WeldingProcess
• Somemetals or metal combinations canbe
readily welded by one process but aredifficult
to weld byothers
– Example: stainless steel readily welded by most AWand
RWprocesses, but difficult to weld byOFW

108. Weldability Factors – BaseMetal
• Somemetals melt too easily; e.g.,aluminum
• Metals with high thermal conductivity
transfer heat away from weld, whichcauses
problems; e.g., copper
• High thermal expansion and contraction in
metal causesdistortion problems
• Dissimilar metals pose problems in welding
when their physical and/or mechanical
properties are substantiallydifferent

109. Other Factors Affecting Weldability
• Filler metal
– Must be compatible with basemetal(s)
– In general, elements mixed in liquid state that form
asolid solution upon solidification do not causea
problem
• Surfaceconditions
– Moisture can result in porosity in fusion zone
– Oxides and other films on metal surfacescan
prevent adequate contact andfusion

110. Design Considerations in Welding
• Design for welding - product should be
designed from the start asaweldedassembly
– Not asacasting or forging or other formedshape
• Minimum parts - welded assembliesshould
consist of fewest number ofparts possible
– Example: usually more cost efficient to perform simple
bending operations on a part than to weld an assembly
from flat plates andsheets

111. Arc Welding DesignGuidelines
• Good fit-up of parts - to maintain
dimensional control and minimize
distortion
– Machining is sometimes required to achieve
satisfactory fit-up
• Assembly must allow accessfor welding
gun to reach weldingarea
• Designof assembly should allow flat
welding to be performed asmuch as
possible, since this is the fastest andmost
convenient welding position

112. Arc Welding Positions
• Welding positions defined here for
groove welds: (a) flat, (b) horizontal,(c)
vertical, and (d) overhead

113. Design Guidelines - RSW
• Low-carbon sheet steel up to0.125 (3.2 mm) is
ideal metal for RSW
• How additional strength and stiffness can be
obtained in large flatsheet metal components
– Spot welding reinforcing parts intothem
– Forming flanges and embossments
• Spot welded assembly must provide accessfor
electrodes to reach weldingarea
• Sufficient overlap of sheet metal partsrequired
for electrode tip to make proper contact