welding, types arc welding, gas welding, fabrication, joinning process, forge welding, solid state welding, explosion welding, friction welding, tig welding, mig welding

1. Welding and Allied ProcessesWelding and Allied Processes
Dr.Dr. PulakPulak M.M. PandeyPandey
http://http://paniit.iitd.ac.in/~pmpandeypaniit.iitd.ac.in/~pmpandey
Manual Arc Welding

2. FundamentalsFundamentals
The termThe term joiningjoining refers to welding, brazing, soldering andrefers to welding, brazing, soldering and
adhesive bonding. In these process a permanent joint between theadhesive bonding. In these process a permanent joint between the
parts is formed and cannot be separated easily.parts is formed and cannot be separated easily.
The termThe term assemblyassembly usually refers to mechanical methods ofusually refers to mechanical methods of
fastening the parts together. Some of these methods allow easyfastening the parts together. Some of these methods allow easy
disassembly, while others do not.disassembly, while others do not.
Welding is a material joining process in which two or more partsWelding is a material joining process in which two or more parts
are coalesced (joined together) at their contacting surfaces byare coalesced (joined together) at their contacting surfaces by aa
suitable application of heat and/or pressure. Sometimes parts asuitable application of heat and/or pressure. Sometimes parts arere
united together by application of pressure only without externaunited together by application of pressure only without externall
heat.heat.
In some welding process aIn some welding process a fillerfiller material is added to facilitatematerial is added to facilitate
coalescence.coalescence.
Welding is most commonly associated with metallic parts but forWelding is most commonly associated with metallic parts but for
plastics also it is used.plastics also it is used.

3. Types of welding processesTypes of welding processes
Solid state welding processesSolid state welding processes
Liquid state welding processesLiquid state welding processes
Solid / Liquid state bonding processesSolid / Liquid state bonding processes

4. SolidSolid--state Welding Processesstate Welding Processes
In solid state welding the surfaces to be joined areIn solid state welding the surfaces to be joined are
brought into close proximity by:brought into close proximity by:
Heating the surfaces without causing melting andHeating the surfaces without causing melting and
applying normal pressureapplying normal pressure
Providing relative motion between the two surfaces andProviding relative motion between the two surfaces and
applying light normal pressureapplying light normal pressure
Applying high pressure without heatingApplying high pressure without heating
In these processes the materials remain in solidIn these processes the materials remain in solid
state and welding is achieved through thestate and welding is achieved through the
application of heat and pressure, or high pressureapplication of heat and pressure, or high pressure
onlyonly

5. Forge weldingForge welding
Forge welding is the oldest method of welding in the category ofForge welding is the oldest method of welding in the category of
solid state welding.solid state welding.
Surfaces to be joined are heated till they are red hot and thenSurfaces to be joined are heated till they are red hot and then
forced together by hammering.forced together by hammering.
It is a crude method of welding and quality depends upon theIt is a crude method of welding and quality depends upon the
skill of the welder.skill of the welder.
A modern version of this type of welding is manufacture of buttA modern version of this type of welding is manufacture of butt--
welded pipes. In this process, thewelded pipes. In this process, the skulpskulp heated up to the requiredheated up to the required
welding temperature is pulled through die which forces the twowelding temperature is pulled through die which forces the two
edges of the heatededges of the heated skulpskulp to contact under pressure and getto contact under pressure and get
welded.welded.

6. Friction WeldingFriction Welding
In this process the two surfaces to be welded are rotated relatiIn this process the two surfaces to be welded are rotated relativeve
to each other under light normal pressure. When the interfaceto each other under light normal pressure. When the interface
temperature reaches due to frictional rubbing and when it reachetemperature reaches due to frictional rubbing and when it reachess
the required welding temperature, sufficient normal pressure isthe required welding temperature, sufficient normal pressure is
applied and maintained until the two pieces get welded.applied and maintained until the two pieces get welded.

7. Explosion WeldingExplosion Welding
Welding is achieved in this process by very high contact preWelding is achieved in this process by very high contact pressuressure
developed by detonating a thin layer of explosive placed over ondeveloped by detonating a thin layer of explosive placed over onee
of the pieces to be joined. The detonation imparts high kineticof the pieces to be joined. The detonation imparts high kinetic
energy to the piece which on striking the other piece causes plaenergy to the piece which on striking the other piece causes plasticstic
deformation and squeezes the contaminated surface layers out ofdeformation and squeezes the contaminated surface layers out of
the interface resulting in a high quality welded joint. No fillethe interface resulting in a high quality welded joint. No fillerr
material is used and no diffusion takes place. The nature of bonmaterial is used and no diffusion takes place. The nature of bond isd is
metallurgical, in many cases combined with a mechanicalmetallurgical, in many cases combined with a mechanical
interlocking that results from rippled or wavy interface betweeninterlocking that results from rippled or wavy interface between thethe
metals.metals.

8. Liquid State (Fusion) Welding ProcessesLiquid State (Fusion) Welding Processes
Arc WeldingArc Welding
Resistance weldingResistance welding
Oxyfuel gas weldingOxyfuel gas welding
Other processesOther processes
There are two inherent problems with fusionThere are two inherent problems with fusion
weldingwelding
Effect ofEffect of localized heating and rapid coolinglocalized heating and rapid cooling on theon the
microstructure and properties of the parent metals.microstructure and properties of the parent metals.
Effect of residual stresses developed in the parentEffect of residual stresses developed in the parent
metals due to restrained expansion or contraction. Thismetals due to restrained expansion or contraction. This
effect the impact and fatigue life ofeffect the impact and fatigue life of weldmentweldment..

9. Arc WeldingArc Welding
InIn Electric Arc WeldingElectric Arc Welding a sustained arc provides the heat requireda sustained arc provides the heat required
for melting the parent as well as filler material.for melting the parent as well as filler material.
TheThe workpieceworkpiece and the electrode are connected to the two materialsand the electrode are connected to the two materials
of the power source. The arc is started by momentarily touchingof the power source. The arc is started by momentarily touching
the electrode on to thethe electrode on to the workpieceworkpiece and then withdrawing it to a shortand then withdrawing it to a short
distance (a few mm) from thedistance (a few mm) from the workpieceworkpiece..
When the electrode andWhen the electrode and workpieceworkpiece are in contact, current flows andare in contact, current flows and
when they are separated an arc is generated and the currentwhen they are separated an arc is generated and the current
continues to flow.continues to flow.
The arc is generated by the electrons liberated form cathode andThe arc is generated by the electrons liberated form cathode and
moving towards anode.moving towards anode.
The arc changes electrical energy into heat and light.The arc changes electrical energy into heat and light.
Arc and power Source characteristics are given in theArc and power Source characteristics are given in the figurefigure..

10. About 70% of the heat liberated due to striking of electrons atAbout 70% of the heat liberated due to striking of electrons at
anode raises the anode temperature to a very values (5,000 toanode raises the anode temperature to a very values (5,000 to
30,00030,000ooC). This heat melts the base metal as well as tip of theC). This heat melts the base metal as well as tip of the
electrode in the area surrounding the arc.electrode in the area surrounding the arc.
A weld is formed when when when the mixture of molten baseA weld is formed when when when the mixture of molten base
and electrode metal solidifies in the weld area.and electrode metal solidifies in the weld area.
Since 70% heat is generated at anode aSince 70% heat is generated at anode a workpieceworkpiece connected toconnected to
anode will melt 50% faster as compared to if connected withanode will melt 50% faster as compared to if connected with
cathode. This is whycathode. This is why workpieceworkpiece is usually made positive andis usually made positive and
electrode as negative and is termed as straight polarity.electrode as negative and is termed as straight polarity.
When the work and electrode connections are reversed, reversedWhen the work and electrode connections are reversed, reversed
polarity is said to be employed.polarity is said to be employed.
Both direct current (DC) and alternating currents (AC) are usedBoth direct current (DC) and alternating currents (AC) are used
in arc welding. AC machines are less expensive to purchase andin arc welding. AC machines are less expensive to purchase and
operate, but generally restricted to welding of ferrous metals.operate, but generally restricted to welding of ferrous metals.
DC equipment can be used on all metals with good results and isDC equipment can be used on all metals with good results and is
generally noted for better arc control.generally noted for better arc control.

11. The used can be either nonThe used can be either non--consumable or consumable.consumable or consumable.
Consumable electrodes usually have a coating on its outer surfacConsumable electrodes usually have a coating on its outer surfacee
which on melting release gases like hydrogen or carbon dioxide twhich on melting release gases like hydrogen or carbon dioxide too
form a protective covering around the molten pool.form a protective covering around the molten pool.
The electrode coating also reacts to from slag which is a liquidThe electrode coating also reacts to from slag which is a liquid, lighter, lighter
than the molten metal. The slag therefore rises to the surface athan the molten metal. The slag therefore rises to the surface and onnd on
solidification forms a protective covering over the hot metal. Tsolidification forms a protective covering over the hot metal. This alsohis also
slows down the rate of cooling of the weld. The slag layer can bslows down the rate of cooling of the weld. The slag layer can bee
removed by light chipping. Electric arc welding of this type isremoved by light chipping. Electric arc welding of this type is knownknown
asas Shielded Metal Arc WeldingShielded Metal Arc Welding. More than 50% industrial arc welding. More than 50% industrial arc welding
is done by this method. Limitation of this process is that onlyis done by this method. Limitation of this process is that only straightstraight
electrodes can be used as the coating is brittle.electrodes can be used as the coating is brittle.
For continuous arc welding operations, the consumables electrodeFor continuous arc welding operations, the consumables electrode isis
bare wire in the form of a coil and the flux us fed into the welbare wire in the form of a coil and the flux us fed into the weldingding
zone, or the weld area is covered by an inert gas. Inzone, or the weld area is covered by an inert gas. In Submerged ArcSubmerged Arc
WeldingWelding the base electrode is shielded by granular flux supplied fromthe base electrode is shielded by granular flux supplied from
a hopper, while isa hopper, while is Gas Metal Arc WeldingGas Metal Arc Welding shielding of the area isshielding of the area is
provided by an inert gas such as argon, helium, carbon dioxide ,provided by an inert gas such as argon, helium, carbon dioxide , etc.etc.

12. Non consumable arc welding processes use tungsten electrodesNon consumable arc welding processes use tungsten electrodes
and shielding is provided by an inert gas around the weld area.and shielding is provided by an inert gas around the weld area.
Once such process, the Gas Tungsten Arc Welding (GTAW) isOnce such process, the Gas Tungsten Arc Welding (GTAW) is
also called asalso called as Tungsten Inert Gas (TIG)Tungsten Inert Gas (TIG) welding.welding.
It uses tungsten alloy electrode and helium gas shield. BecauseIt uses tungsten alloy electrode and helium gas shield. Because
of inert gas atmosphere tungsten is not consumed. Fillerof inert gas atmosphere tungsten is not consumed. Filler
materials supplied by a separate rod or wire.materials supplied by a separate rod or wire.

13. Arc WeldingArc Welding
Back

14. Back

15. Arc and Power Source Characteristics inArc and Power Source Characteristics in
Arc WeldingArc Welding
Arc Characteristics Power Source Characteristics
Back

16. Submerged Arc WeldingSubmerged Arc Welding
Back

17. Gas Metal Arc WeldingGas Metal Arc Welding
Back

18. Tungsten Inert Gas WeldingTungsten Inert Gas Welding
(TIG)(TIG)

19. Resistance Spot WeldingResistance Spot Welding

20. Two opposing solid cylindrical electrodes are pressed against thTwo opposing solid cylindrical electrodes are pressed against the lape lap
joint and two metallic sheets to be welded.joint and two metallic sheets to be welded.
Current ranges 3,000 to 40,000 Ampere depending on theCurrent ranges 3,000 to 40,000 Ampere depending on the
requirement causes a weld nugget of size varying from 6 to 10 mmrequirement causes a weld nugget of size varying from 6 to 10 mm
diameter to be formed at the metallic interface.diameter to be formed at the metallic interface.
The current is switched on for a duration lasting 0.1 to 0.5 secThe current is switched on for a duration lasting 0.1 to 0.5 sec..
At low pressures, the resistance and heat are high and melted meAt low pressures, the resistance and heat are high and melted metaltal
tend to squeeze out of the weld.tend to squeeze out of the weld.
At high pressure, the resistance decreases and heat is less andAt high pressure, the resistance decreases and heat is less and
smaller weld formed provides lower weld strength. Thus, for a gismaller weld formed provides lower weld strength. Thus, for a givenven
set of conditions, optimum electrode current and electrode pressset of conditions, optimum electrode current and electrode pressureure
are indicated.are indicated.
The time duration of current flow should not be beyond certainThe time duration of current flow should not be beyond certain
critical, because the heat then has a chance to spread out and hcritical, because the heat then has a chance to spread out and harmarm
workpieceworkpiece and electrode.and electrode.
Optimum values of current, pressure and their application timingOptimum values of current, pressure and their application timing areare
dependent on weld size and material.dependent on weld size and material.

21. Seam WeldingSeam Welding

22. Automatic Spot Welding OperationAutomatic Spot Welding Operation
Performed by a RobotPerformed by a Robot

23. Oxyfuel WeldingOxyfuel Welding
OFW is the term to describe the group of fusionOFW is the term to describe the group of fusion
operations that burn various fuels mixed with oxygen tooperations that burn various fuels mixed with oxygen to
perform welding.perform welding.
The OFW processes employ several type of gases, whichThe OFW processes employ several type of gases, which
is the primary distinction among the members of thisis the primary distinction among the members of this
group.group.
The most important OFW process is oxyacetyleneThe most important OFW process is oxyacetylene
welding. Filler materials are used to supply additionalwelding. Filler materials are used to supply additional
material to the weld zone. Flux is often used to clean thematerial to the weld zone. Flux is often used to clean the
surfaces and to retard oxidation by providing inert gassurfaces and to retard oxidation by providing inert gas
shield around the weld area. It also helps in removingshield around the weld area. It also helps in removing
oxide and other impurities. Borax, is the most commonoxide and other impurities. Borax, is the most common
flux, but sometimes other substances are added toflux, but sometimes other substances are added to
improve its effectiveness.improve its effectiveness.

26. Salient points about oxyacetylene weldingSalient points about oxyacetylene welding
The heat is obtained by combustion of acetyleneThe heat is obtained by combustion of acetylene
and oxygen. Here primary combustion occurringand oxygen. Here primary combustion occurring
in the inner zone gives:in the inner zone gives:
and the second reaction in the outer zone givesand the second reaction in the outer zone gives
The maximum temperature temperature at the tipThe maximum temperature temperature at the tip
of inner cone reaches up to 3000of inner cone reaches up to 3000--35003500°°C.C.
Therefore, most gas welding is performed byTherefore, most gas welding is performed by
keeping this inner zone tip just above the metal tokeeping this inner zone tip just above the metal to
be welded so that maximum temperature isbe welded so that maximum temperature is
available for welding.available for welding.
HeatHCOOHC ++→+ 2222 2
HeatOHCOOHCO ++→++ 2222 25.12

27. Temperature distribution along the flameTemperature distribution along the flame

28. AA neutral flameneutral flame is obtained when the ratio of isis obtained when the ratio of is
oxygen and acetylene is 1. Most gas weldingoxygen and acetylene is 1. Most gas welding
operations are carried out by this flame.operations are carried out by this flame.
AnAn oxidizing flameoxidizing flame is obtained when this ratio is moreis obtained when this ratio is more
than 1. This type of flame is not suitable for welding ofthan 1. This type of flame is not suitable for welding of
steels since excess oxygen present reacts with carbon insteels since excess oxygen present reacts with carbon in
steel and is generally used for welding of copper and itssteel and is generally used for welding of copper and its
alloys.alloys.
When the ratio in mixture is less than 1 aWhen the ratio in mixture is less than 1 a carburizingcarburizing
flameflame is obtained. In this type of flame acetyleneis obtained. In this type of flame acetylene
decomposes into carbon and hydrogen and the flamedecomposes into carbon and hydrogen and the flame
temperature gets reduced. Joining operations such astemperature gets reduced. Joining operations such as
brazing and soldering which require lower temperaturebrazing and soldering which require lower temperature
generally use this flame.generally use this flame.

29. Flame CuttingFlame Cutting
Metal is merely melted by theMetal is merely melted by the
flame of theflame of the oxyfueloxyfuel gas torchgas torch
and blown away to form a gap orand blown away to form a gap or
kerfkerf..
When ferrous metal is cut,When ferrous metal is cut,
actually burning of iron takesactually burning of iron takes
place according to one or more ofplace according to one or more of
the following reactions.the following reactions.
QOFeOFe
QOFeOFe
QFeoOFe
+→+
+→+
+→+
322
432
234
23

30. Because, these reactions cannot take place below 815Because, these reactions cannot take place below 815°°CC oxyfueloxyfuel flameflame
is first used to raise the metal temperature where burning can bis first used to raise the metal temperature where burning can bee
initiated. Then a stream of pure oxygen is added to the torch (oinitiated. Then a stream of pure oxygen is added to the torch (or ther the
oxygen content of theoxygen content of the oxyfueloxyfuel mixture is increased) to oxidize themixture is increased) to oxidize the
iron. The liquid iron and iron oxides are then expelled from theiron. The liquid iron and iron oxides are then expelled from the jointjoint
by the kinetic energy of the oxygen gas stream.by the kinetic energy of the oxygen gas stream.
Low rate of heat input, and need of preheating ahead of the cut,Low rate of heat input, and need of preheating ahead of the cut,
oxyfueloxyfuel produces a relatively large heat affected zone and thusproduces a relatively large heat affected zone and thus
associated distortion zone.associated distortion zone.
The process is suitable when edge finish or tolerance is not criThe process is suitable when edge finish or tolerance is not critical.tical.
Theoretically heat generated due to burning of Fe is sufficientTheoretically heat generated due to burning of Fe is sufficient toto
continue cutting however due to losses additional heat supply iscontinue cutting however due to losses additional heat supply is
needed. If the work is already hot due from the other processes,needed. If the work is already hot due from the other processes,
supply of oxygen through a small diameter pipe is needed to contsupply of oxygen through a small diameter pipe is needed to continueinue
cut. This is called Oxygen Lance Cutting. Acut. This is called Oxygen Lance Cutting. A workpieceworkpiece temperature oftemperature of
12001200°°C is needed to sustain the cutting.C is needed to sustain the cutting.
Low carbon steel from 5 to 75 mm can be cut.Low carbon steel from 5 to 75 mm can be cut.

31. Welding DefectsWelding Defects
Cracks (Cracks (figurefigure))
–– This causes significant reduction in the strength ofThis causes significant reduction in the strength of weldmentweldment..
Welding cracks are caused byWelding cracks are caused by embrittlementembrittlement or low ductilityor low ductility
of the weld and/or base metal combined with high restraintof the weld and/or base metal combined with high restraint
during contraction.during contraction.
CavitiesCavities
–– These includes porosity and shrinkage voids.These includes porosity and shrinkage voids.
Solid inclusionsSolid inclusions
–– These are metallic or nonThese are metallic or non--metallic solid material particlesmetallic solid material particles
entrapped in the weld metal. The most common form is slagentrapped in the weld metal. The most common form is slag
inclusion or metallic oxides.inclusion or metallic oxides.
Incomplete fusion (Incomplete fusion (figurefigure))
–– A similar defect is lack of penetration.A similar defect is lack of penetration.
Imperfect shape (Imperfect shape (figurefigure))
Miscellaneous defects like arc strike, excessive spatterMiscellaneous defects like arc strike, excessive spatter

32. Various forms of Welding Cracks
Several form incomplete fusion

34. Solid / Liquid State BondingSolid / Liquid State Bonding
Low temperature joining methods are used whenLow temperature joining methods are used when
the metal to be joined cannot withstand highthe metal to be joined cannot withstand high
temperature, or intricate sections are to be joined,temperature, or intricate sections are to be joined,
or dissimilar metals are to be joined, oror dissimilar metals are to be joined, or
weldabilityweldability of material is poor.of material is poor.
In these methods, the gap between the metalIn these methods, the gap between the metal
pieces to be joined is filled with molten fillerpieces to be joined is filled with molten filler
material after heating the base metal. Meltingmaterial after heating the base metal. Melting
point of filler material is much lower than basepoint of filler material is much lower than base
metals.metals.
The bonding is not due to melting of parent metalThe bonding is not due to melting of parent metal
and fusion.and fusion.

35. Filler material is drawn into the gap between theFiller material is drawn into the gap between the
metal pieces to be joined by capillary action and themetal pieces to be joined by capillary action and the
bond formation is initiated when the molten filerbond formation is initiated when the molten filer
metal comes under intimate contact with the solidmetal comes under intimate contact with the solid
surface as in solid state welding.surface as in solid state welding.
The nature of bond formed is much complex here,The nature of bond formed is much complex here,
and invariably there is some degree ofand invariably there is some degree of intersolubilityintersolubility
between filler and base metals.between filler and base metals.
This interThis inter--diffusion at the base metal surface anddiffusion at the base metal surface and
resulting alloy has a strength which is very close toresulting alloy has a strength which is very close to
that the base metal.that the base metal.

36. For a good joint strength theFor a good joint strength the
liquid filler metal; must flow intoliquid filler metal; must flow into
the gap between the metal piecesthe gap between the metal pieces
to be joined and cover the entireto be joined and cover the entire
surface area, without gaps or blowsurface area, without gaps or blow
holes. The following usuallyholes. The following usually
insures good bonding:insures good bonding:
–– Clean base metal surfacesClean base metal surfaces
–– Maintain optimum gapMaintain optimum gap
–– Heat the joining area above meltingHeat the joining area above melting
temperature of the filler materialtemperature of the filler material
–– Use fluxes for welding of base metalUse fluxes for welding of base metal
surfaces.surfaces.
Joint strength is sensitive to theJoint strength is sensitive to the
gap and there exists an optimumgap and there exists an optimum
gap for a filler material.gap for a filler material.

37. BrazingBrazing
Brazing methods
(a) Torch and
filler rods
(b) Ring of filler
metal at
entrance of
gap
(c) Foil of filler
metal between
flat part
surfaces

38. In brazing the joint is made by heating theIn brazing the joint is made by heating the
base metal red hot and filling the gap withbase metal red hot and filling the gap with
molten metal whose melting temperature ismolten metal whose melting temperature is
typically above 450typically above 450°°C but below meltingC but below melting
temperature o base metal. The filler metalstemperature o base metal. The filler metals
are generally copper alloys. Cuare generally copper alloys. Cu--Zn and CuZn and Cu--
Ag alloys are used for brazing because theyAg alloys are used for brazing because they
form alloy with iron and have goodform alloy with iron and have good
strength.strength.
Various brazing joints are shown inVarious brazing joints are shown in figurefigure..

39. (a) Conventional butt
(b) Scarf joint
(c) Stepped joint
(d) Increased crossest ion
(a) Conventional Lap
(b) Cylindrical part
(c) Sandwiched part
(d) Use of sleeve

40. Common braze metal familiesCommon braze metal families

41. SolderingSoldering
Soldering is very similar to brazing except thatSoldering is very similar to brazing except that
filler material is usually a leadfiller material is usually a lead--tin based alloytin based alloy
which has much lower strength and meltingwhich has much lower strength and melting
temperature around 250temperature around 250°°C.C.
In this process less alloying action between baseIn this process less alloying action between base
metal and filler material as compared to brazingmetal and filler material as compared to brazing
takes place hence the strength of joint is lesser.takes place hence the strength of joint is lesser.
It is carried out using electrical resistance heating.It is carried out using electrical resistance heating.

42. Joints in SolderingJoints in Soldering
(a) Flat lock seam (b) Bolted or riveted joint (c) Copper
pipe fitting (d) Crimping of cylindrical lap joint.

43. (a) Crimped lead
wire PC board
(b) Plated through
hole on PC
board to
maximize
solder contact
area
(c) Hooked wire
on flat
terminals
(d) Twisted wires

44. Some common solder alloySome common solder alloy
compositionscompositions

45. Comparison of welding processesComparison of welding processes