UNIT 5-Special Welding processwelding.ppt

welding

1. UNIT-5 Special Welding Process

5. TUNGSTEN INERT GAS WELDING (TIG)
•Tungsten inert gas welding or gas tungsten arc welding (GTAW) is a group of
welding process in which the workpieces are joined by the heat obtained from an
electric arc struck between a non-consumable tungsten electrode and the
workpiece in the presence of an inert gas atmosphere.
•A filler metal may be added if required, during the welding process.
•Figure shows the TIG process.
05/19/24 5

6. Description
•TIGequipmentconsistsofaweldingtorchinwhicha
non-consumabletungstenalloyelectrodeisheld
rigidlyinthecollet.
•Thediameteroftheelectrodevariesfrom0.5-6.4
mm.
•TIGweldingmakesuseofashieldinggaslikeargonor
heliumtoprotecttheweldingareafromatmospheric
gasessuchasoxygenandnitrogen,otherwisewhich
maycausefusiondefectsandporosityintheweld
metal.
•Theshieldinggasflowfromthecylinder,throughthe
passageintheelectrodeholderandthenimpingeson
theworkpiece.
•Pressureregulatorandflowmetersareusedto
regulatethepressureandflowofgasfromthe
cylinder.
•EitherACorDCcanbeusedtosupplytherequired
current.05/19/24 6

7. Operation
•The workpiecesto be joined are cleaned to remove dirt, grease and other
oxides chemically or mechanically to obtain a sound weld.
•The welding current and inert gas supply are turned ON.
•An arc is struck by touching the tip of the tungsten electrode with the
workpiece and instantaneously the electrode is separated from the
workpiece by a small distance of 1.5 -3 mm such that the arc still remains
between the electrode and the workpiece.
•The high intensity of the arc melts the workpiece metal forming a small
molten metal pool.
•Filler metal in the form of a rod is added manually to the front end of the
weld pool.
•The deposited filler metal fills and bonds the joint to form a single piece
of metal
•The shielding gas is allowed to impinge on the solidifying weld pool for a
few seconds even after the arc is extinguished (shut off)
•This will avoid atmospheric contamination of the solidifying metal thereby
increasing the strength of the joint.
05/19/24 7

8. Advantages
•Suitable for thin metals.
•Clear visibility of the arc provides the operator to have a greater control
over the weld.
•Strong and high quality joints are obtained.
•No flux is used. Hence, no slag formation. This results in clean weld joints.
Disadvantages
•TIG is the most difficult process compared to all the other welding
processes. The welder must maintain short arc length, avoid contact
between electrode and the workpiece and manually feed the filler metal
with one hand while manipulating the torch with the other hand.
•Tungsten material when gets transferred into the molten metal
contaminates the same leading to a hard and brittle joint.
•Skilled operator is required.
•Process is slower.
•Not suitable for thick metals.
05/19/24 8

9. METAL INERT GAS (MIG) WELDING
•Metal inert gas welding or gas metal arc welding (GMAW) is a group of arc
welding process in which the workpieces are joined by the heat obtained from an
electric arc struck between a bare (uncoated) consumable electrode and the
workpiece in the presence of an inert gas atmosphere.
•The consumable electrode acts as a filler metalto fill the gap between the two
workpieces.
•Figure shows the MIG welding process.
05/19/24 9

11. Description
•The equipment consists of a welding torch in which a bare consumable electrode
in the form of a wire is held and guided by a guide tube.
•The electrode material used in MIG welding is of the same material or nearly the
same chemical composition as that of the base metal.
•Its diameter varies from 0.7 -2.4 mm.
•The electrode is fed continuously at a constant rate through feed rollers driven by
an electric motor.
•MIG makes use of shielding gas to prevent atmospheric contamination of the
molten weld pool.
•Mixture of argon and carbon dioxidein a order of 75% to 25% or 80% to 20% is
commonly used.
•The shielding gas flow from the cylinder, through the passage in the electrode
holder and then impinges on the workpiece.
•AC is rarely used with MIG welding; instead DC is employed and the electrode is
positively charged. This results in faster melting of the electrode which increases
weld penetration and welding speed.
05/19/24 11

12. Operation
•The workpieces to be joined are cleaned to remove dust, grease and other oxides
chemically or mechanically to obtain a sound weld. The tip of the electrode is also
cleaned with a wire brush.
•The control switch provided in the welding torch is switched ON to initiate the
electric power, shielding gas and the wire (electrode) feed.
•An arc is struck by touching the tip of the electrode with the workpiece and
instantaneously the electrode is separated from the workpiece by a small distance
of 1.5-3 mm such that the arc still remains between the electrode and the
workpiece.
•The high intensity of the arc melts the workpiece metal forming a small molten
pool.
•At the same time, the tip of the electrode also melts and combines with the
molten metal of the workpieces thereby filling the gap between the two
workpieces.
•The deposited metal upon solidification bonds the joint to form a single piece of
metal.
05/19/24 12

13. Advantages
•MIG welding is fast and economical.
•The electrode and inert gas are automatically fed, and this makes the operator
easy and to concentrate on the arc.
•Weld deposition rate is high due to the continuous wire feed
•No flux is used. Hence, no slag formation. This results in clean welds.
•Thin and thick metals can be welded.
•Process can be automated.
Disadvantages
•Equipment is costlier
•Porosity (gas entrapment in weld pool) is the most common quality problem in
this process. However, extensive edge preparation can eliminate this defect.
05/19/24 13

14. SUBMERGED ARC WELDING (SAW)
•Submerged arc welding is a group of arc welding process in which the workpieces
are joined by the heat obtained from an electric arc struck between a bare
consumable electrode and workpiece.
•The arc is struck beneath a covering layer of granulated flux.
•Thus, the arc zone and the molten weld pool are protected from atmospheric
contamination by being 'submerged under a blanket of granular flux.
•This gives the name 'submerged arc welding' to the process.
•Figure shows the submerged arc welding process.
05/19/24 14

15. Submerged Arc Welding(SAW)
05/19/24 15

16. Description
•Theequipmentconsistsofaweldingheadcarryinga
bareconsumableelectrodeandafluxtube.
•Thefluxtuberemainsaheadoftheelectrode,stores
thegranulatedorpowderedflux,anddropsthesame
onthejointtobewelded.
•Thefluxshieldsandprotectsthemoltenweldmetal
fromatmosphericcontamination.
•Theelectrodewhichisbare(uncoated)andintheform
ofwireisfedcontinuouslythroughfeedrollers.
•Itisusuallycopperplatedtopreventrustingandto
increaseitselectricalconductivity(sinceitis
submergedunderflux).
•Thediameteroftheelectroderangesfrom1.6-8mm
andtheelectrodematerialdependsonthetypeofthe
workpiecemetalbeingwelded.
•TheprocessmakesuseofeitherACorDCforsupplying
therequiredcurrent.
05/19/24 16

17. Operation
•Edge preparation is carried out to obtain a sound weld.
•Flux is deposited at the joint to be welded
•Welding current is witched ON.
•An arc is struck between the electrode and the workpiece under the layer of
flux.
•The flux covers the arc thereby increasing the heat near the weld zone.
•This heat melts the filler metal and the workpiece metal forming a molten weld
pool.
•At the same time, a portion of the flux melts and reacts with the molten weld
pool to form a slag.
•The slag floats on the surface providing thermal insulation to the molten metal
thereby allowing it to cool slowly.
•The welding head is moved along the surface to be welded and the continuously
fed electrode completes the weld.
•The un-melted flux is collected by a suction pipe and reused.
•The layer of slag on the surface of the weld portion is chipped out and the weld
is finished.
•Since the weld pool is covered by flux, solidification of molten metal is slow.
Hence, a backing plate made from copper or steel is used at the bottom of the
joint to support the molten metal until solidification is complete.
05/19/24 17

18. Advantages
•High productivity process, due to high heat concentration.
•Weld deposition rate is high due to continuous wire feed. Hence, single pass
welds can be made in thick plates.
•Deep weld penetration.
•Less smoke, as the flux hides the arc. Hence, improved working conditions.
•Can be automated
•Process is best suitable for outdoor works and in areas with relatively high winds.
•There is no chance of spatter of molten metal, as the arc is beneath the flux.
Disadvantages
•The invisible arc and the weld zone make the operator difficult to judge the
progress of welding.
•Use of powdered flux restricts the process to be carried only in flat positions.
•Slow cooling rates may lead to hot cracking defects.
•Need for extensive flux handling.
05/19/24 18

19. 1
9
•Friction welding is a
solid state joining
process that produces
coalescence by the heat
developed between two
surfaces by
mechanically induced
surface motion.
Definition of Friction Welding
Friction Welding

20. 2
0
•One of the workpiecesis
attached to a rotating
motor drive, the other is
fixed in an axial motion
system.
•One workpieceis rotated
at constant speed by the
motor.
•An axial or radial force is
applied.
Workpieces
Non-rotating viseMotor
Chuck
Spindle
Hydraulic cylinder
Brake
Continuous Drive Friction Welding

21. 2
1
•The work pieces are
brought together under
pressure for a predeter-
mined time, or until a
preset upset is reached.
•Then the drive is
disengaged and a break
is applied to the rotating
work piece.
Workpieces
Non-rotating viseMotor
Chuck
Spindle
Hydraulic cylinder
Brake
Continuous Drive Friction Welding

22. 2
2
Friction Welded Automotive Halfshaft
Friction Welded Joint
Courtesy AWS handbook
Friction Welded Joints

23. 2
3 Friction Stir Welding
•Parts to be joined are
clamped firmly.
•A rotating hardened steel
tool is driven into the joint
and traversed along the joint
line between the parts.
•The rotating tool produces
friction with the parts,
generating enough heat and
deformation to weld the
parts together.
Butt welds
Overlap welds

24. 2
4
•Frequently competes with flash or upset
welding when one of the work pieces to
be joined has axial symmetry.
•Used in automotive industry to
manufacture gears, engine valves, and
shock absorbers.
•Used to join jet engine compressor
parts.
Friction Welding Applications

25. 2
5
2
a
Laser beam welding

26. 2
6
LaserBeamWeldingisafusionweldingprocessinwhich
twometalpiecesarejoinedtogetherbytheuseoflaser.
Thelaserbeamsarefocusedtothecavitybetweenthe
twometalpiecestobejoined.Thelaserbeamshave
enoughenergyandwhenitstrikesthemetalpieces
produceheatthatmeltsthematerialfromthetwometal
piecesandfillsthecavity.Aftercoolingastrongweldis
formedbetweenthetwopieces.

27. 2
7
Thelaserbeamweldingworksonthe
principlethatwhentheelectronsofan
atomareexcitedbyreceivingsome
energy.Andthenaftersometimewhenit
returnstoitsgroundstate,itemitsa
photonoflight.
Theconcentrationofthisemittedphoton
isincreasedbytheexcitedemissionof
radiationandwegethighenergyfocused
laserbeam.Thelightamplificationby
stimulatedemissionofradiationisnamed
asalaser
Working Principle

28. 2
8
LaserBeamWelding(LBW)isaweldingprocess,inwhichheatis
generatedbyahighenergylaserbeamtargetedontheworkpiece.The
laserbeamheatsandmeltstheedgesoftheworkpiece,formingajoint.
Theenergyofanarrowlaserbeamishighlyconcentratedat108-
1010W/cm2,soaweakweldpoolisformedveryrapidly(forabout10-
6sec)
Thesolidificationoftheweldpoolsurroundedbycoldmetaloccursas
rapidlyasthemelt.Sincethetimethemoltenmetalisincontactwith
theatmosphereislow,thereisnocontaminationandthereforeno
gradient(neutralgas,flow)isrequired.

29. 2
9Advantages and Disadvantages of Laser Beam Welding
Following are the advantages:
1.Easily automated process.
2.Controllable process parameters.
3.The very narrow weld may be obtained.
4.High quality of the weld structure.
5.Very small heat-affected zone.
6.Dissimilar materials may be welded.
7.Very small delicate workpieces may be welded.
8.The vacuum is not required.
9.Low distortion of the workpiece.

30. 3
0Followingarethedisadvantages:
1.Theinitialcostishigh.TheequipmentappliedinLBWhasa
highcost.
2.ThemaintenancecostofLBMishigh.
3.Duetotherapidcooling,fracturescanoccurinsome
metals.
4.HighskilledlaboursarerequiredtoperformLBW.
5.Theweldingthicknessisrestrictedto19mm.
6.TheenergyconversionefficiencyinLBWisextremelylow.It
isusuallybelowthan10%.

31. 3
1
ApplicationsofLaserBeamWeldingProcess
1.Itisprominentintheautomotiveindustry.So,Itisused
intheareawherelargevolumeproductionisrequired.
2.Itisemployedforhighprecisionwelds.Asitdoesnot
useanyelectrode,thefinalweldwillbelightbutstrong.
3.Thelaserweldingisalsofrequentlyusedinmakingof
jewellery.
4.However,laserbeamweldingisusedinmedical
industriestoholdmetalstogetheronasmallscale

32. EXPLOSIVE WELDING

33. Explosiveweldingisasolidstateweldingprocess,
whichusesacontrolledexplosivedetonationtoforce
twometalstogetherathighpressure.Theresultant
compositesystemisjoinedwithadurable,
metallurgicalbond.
WHATISIT?
Thefearsomedestructivepowerofexplosivescanbe
harnessedtoprovideauniquejoiningmethod,known
asExplosiveWelding.
EXPLOSIVE WELDING

34. PROCESS
Thisisasolidstatejoiningprocess.
Whenanexplosiveisdetonatedonthesurfaceofa
metal,ahighpressurepulseisgenerated.
Thispulsepropelsthemetalataveryhighrateof
speed.Ifthispieceofmetalcollidesatananglewith
anotherpieceofmetal,weldingmayoccur.

35. Forweldingtooccur,ajettingactionisrequiredatthe
collisioninterface.Thisjetistheproductofthesurfacesofthe
twopiecesofmetalscolliding.
Thiscleansthemetalsandallowstopuremetallicsurfacesto
joinunderextremelyhighpressure.Themetalsdonot
commingle,theyareatomicallybonded.
Duetothisfact,anymetalmaybeweldedtoanymetal(i.e.-
coppertosteel;titaniumtostainless).

37. COMMONLY USED
EXPLOSIVE
Explosive Detonation velocity , m/s
RDX (Cyclotrimethylene
trinitramine) C6H6N6O6
8100
TNT (Trinitroluene,
C7H5N3O6)
6600
Lead azide(N
6Pb) 5010
Deta sheet 7020
Ammonium Nitrate (NH4NO3)2655

38. ADVANTAGES
Joiningofdissimilarmetals-Aluminumtosteel,TitaniumalloystoCr–Nisteel,Cuto
stainlesssteel,TungstentoSteel.
Attachingcoolingfins.

39. LIMITATIONS
Themetalsmusthavehighenoughimpactresistance,
andductility.
Noiseandblastcanrequireoperatorprotection,
vacuumchambers,buriedinsand/water.
Thegeometriesweldedmustbesimple–flat,
cylindrical,conical.

40. Isaformofweldingthatuseselectromagneticinductionto
heattheworkpiece.Theweldingapparatuscontainsan
inductioncoilthatisenergizedwitharadio-frequency
electriccurrent.
Inductionwelding

41. 4
1
Soldering and Brazing
•Soldering and Brazing are joining
processes where parts are joined
without melting the base metals.
•Soldering filler metals melt (Lead
and tin) below 450 °C.
•Brazing filler metals melt (Copper
& Zinc) (Cu& silver)above 450 °C.
•Soldering is commonly used for electrical connection or
mechanical joints, but brazing is only used for mechanical
joints due to the high temperatures involved

42. 4
2Soldering
•A method of joining metal parts using an alloyof low
melting point(solder) below 450 °C (800 °F).
•Heat is applied to the metal parts, and the alloy metal
is pressed against the joint, melts, and is drawn into
the joint by capillary actionand around the materials
to be joined by 'wetting action'.
•After the metal cools, the resulting joints are not as
strong as the base metal, but have adequate strength,
electrical conductivity, and water-tightness for many
uses.

43. 4
3
•One application of
soldering is making
connections between
electronic parts and
printed circuit boards.
•Another is in plumbing.
Joints in sheet-metal
objects such as cans for
food, roof flashing, and
drain gutters were also
traditionally soldered.
•Jewelaryand small
mechanical parts are
often assembled by
soldering.
Soldering can
also be used as a
repair technique
to patch a leak in
a container or
cooking vessel.

44. 4
4Brazing
•Is similar to soldering but uses higher melting temperature
alloys, based on copper, as the filler metal.
•"Hard soldering", or "silver soldering" (performed with high-
temperature solder containing up to 40% silver) is also a form
of brazing, and involves solders with melting points above 450
C.
•Since leadused in traditional solder alloys is toxic, much effort
in industry has been directed to adapting soldering techniques
to use lead-free alloys for assembly of electronic devices and
for potable water supply piping.

45. 4
5

46. 4
6
Brazing, Soldering

47. 4
7
Flux Material
(Brazing/Soldering)
Flux is used for following reasons :
1.Dissolve oxides from the surfaces to be joined
2.Reduce surface tension of molten materialcapillary action
3.Protect from further oxidation to parental material
Borax and Boricacid are commonly used Flux material in Brazing
Ammonia Chloride, Zinc Chlorideare commonly used Flux material
in Soldering.

48. 4
8
Brazing, Soldering or Braze Welding
In both these processes , the parental material does not melt, but
only filler material melts thus filling the joint through capillary
action.
Soldering ( or soft Soldering): The filler material has melting
point lower than 450 deg Cand also less than that of parental
material
Brazing ( or hard Soldering): The filler material has melting
point higher than 450 deg Cand also less than that of parental
material

49. 4
9 Brazing vs. Welding
Advantages
1.Dissimilar metals which can’t be welded can be joined by brazing
2.Very thin metals can be joined
3.Metals with different thickness can be joined easily
4.In brazing thermal stresses are not produced in the work piece, hence
there is no distortion.
5.Problems of Heat Affected Zone (HAZ) is avoided.
6.Less power is required and process is faster
Disadvantages
1.Brazed joints have lower strength compared to welding
2.Joint preparation cost is more
3.Colourof the metal in the brazed joint is different and aesthetic problem
4.high service temperature can cause failure to a brazed joint.

50. 5
0 Applications
-Automotive ( joining tubes and pipes)
-Electrical equipments (joining wires and cables)
-cutting tool ( brazing cemented carbide tips to steel shanks)
-repairs and maintenance in many fields
Brazing
Soldering
-electronics parts like PCB

51. 5
1
Destructive and Non-destructive Testing of Welds
Thetestsweredescribedtochecktheweldingoperator'sskill,the
weldmetal'squality,andthestrengthoftheweldedjointforeach
typeofmetalusedinjoiningmaterial.

52. Destructiveweldtesting,asthenamesuggests,involvesthe
physicaldestructionofacompletedweldtoevaluateits
strengthandcharacteristics.Thetestingprocedureis
conductedtounderstandaspecimen'smaterialbehavior,
strength,qualityoftheweldedjoint,andtheskillofthe
welder.
DESTRUCTIVE TEST IN WELDS

53. DESTRUCTIVE TEST IN WELDS
It is defined as during testing the metal component is get
damage due to which it cannot be reuse again.
1.tensile test
2.compression test
3.hardness test
4.Impact test
5.bend test
5
3

54. NON-DESTRUCTIVE TEST IN WELDS
It is defined as during testing the metal component is not
damaged or destroyed and can be use for its specific
application again.
1.Radiographic test
2.Ultrasonic test
3.Magnetic particle test
4.Dye penetrate test
5.Visual inspection

55. What can radiographic testing detect?
It uses x-rays or gamma rays to identifyflaws in weld
quality, castings, structures, and composites. It is
used predominantly in the fabricating and casting
industries for quality control, where it reveals faults such
as porosity, inclusions, and cracks.

57. What is ultrasonic testing?
Image result for 2.Ultrasonic test
Ultrasonic testing (UT) is a non-destructive test method that
utilizes sound waves to detect cracks and defects in parts
and materials. It can also be used to determine a material's
thickness, such as measuring the wall thickness of a pipe

59. What is magnetic particle testing in welding?
Magnetic Particle Inspection (MPI) or Magnetic Testing
(MT) is an NDT method for checking the surface integrity
of ferromagnetic materials. The material is magnetized
using a handheld yoke or a horizontal MPI bench setup.
Defects in the surface and shallow subsurface cause
magnetic field fluxes to "leak".

60. Dye penetrant inspection(DP), also calledliquid penetrate inspection(LPI) orpenetrant
testing(PT), is a widely applied and low-cost inspection method used to check surface-breaking
defects in allnon-porousmaterials (metals, plastics, or ceramics). The penetrant may be applied
to all non-ferrous materials and ferrous materials, although for ferrous componentsmagnetic-
particle inspectionis often used instead for its subsurface detection capability. LPI is used to
detect casting, forging and welding surface defects such as hairline cracks, surfaceporosity, leaks
in new products, andfatigue crackson in-service components.
Dye penetrant inspection(DP),

61. DPIisbaseduponcapillaryaction,wherelowsurface
tensionfluidpenetratesintocleananddrysurface-breaking
discontinuities.Thepenetrantmaybeappliedtothetest
componentbydipping,spraying,orbrushing.Afteradequate
penetrationtimehasbeenallowed,theexcesspenetrantis
removedandadeveloperisapplied.Thedeveloperhelpsto
drawpenetrantoutoftheflawsothataninvisibleindication
becomesvisibletotheinspector.Inspectionisperformed
underultravioletorwhitelight,dependingonthetypeofdye
used-fluorescentornonfluorescent(visible).

62. VISUAL
INSPECTI
ON
9
/
1
4
/
2
0
2
0
6
2