welding complete ppt

7/22/2019 Welding Complete PPT

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By SKMondal

WeldingDefinition

Welding is a process by which two materials, usuallymetals, are permanently joined together bycoalescence, which is induced by a combination oftemperature, pressure, and metallurgical conditions.

The particular combination of these variables canrange from high temperature with no pressure to highpressure with no increase in temperature.

Welding (positive process)

Machining (negative process)

Forming, casting (zero process)

Requirementforahighqualitywelding

1. A source of satisfactory heat and/or pressure,

2. A means of protecting or cleaning the metal, and

3. , ,

metallurgical effects.

ClassificationofweldingprocessesOxy fuel gas welding (OFW)

Arc welding (Aw)

Resistance welding

Solid state welding (friction welding, ultrasonic welding,forge welding etc.)

Unique processThermit welding

Laser beam welding

Electroslag welding

Flashwelding

Induction welding

Electron beam welding

Weldability /FabricationProcessesThe weldability of a material will depend on the

specific welding or joining process being considered.

For resistance welding of consistent quality, it is

usually necessary to remove the oxide immediatelybefore welding.

Fabrication weldability test is used to determinemechanical properties required for satisfactoryperformance of welded joint.

The correct sequence of the given materials inascending order of their weldability is

Aluminum < copper < cast iron < MSContd


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CaseofAluminiumThe oxide coating on aluminum alloys causes some

difficulty in relation to its weldability.

It also has high thermal conductivity and a very shorttemperature range between liquidus and solidus and when

.

Aluminium is poor absorberof laser light.

During fusion welding, the aluminum would oxidize soreadily that special fluxes or protective inertgasatmospheres must be employed.

Friction welding and TIG welding is good for aluminium.

Foraluminium AC current plus high frequency is must.

CaseofCastIronCast iron is more difficult to weld because of its high

carbon content and brittleness (poor ductility)

Massive carbon deposits have a tendency to form inthe areas adjacent to the weld, and highcarbon

.These microstructures are very brittle and may crackspontaneously while welding is in progress or later

when load is applied to the workpiece.

Cast iron can be joined by the oxyacetylene brazingprocess and shielded metalarc welding (stick)process.

Some cases preheating and/or post heating is required.

CaseofStainlessSteelStainless steel is a difficult metal to weld because it

contains both nickel and chromium.

The best method for welding stainless steel is TIGwelding.

steels. A heavily coated welding rod, which produce ashielded arc, is employed.

You mustdo a better jobof precleaning.

Using a low arc current setting with faster travelspeeds is important when welding stainless steel,

because some stainless steels are subject to carbideprecipitation.Contd..

CaseofStainlessSteelThe ferritic stainless steels are generally less weldable

than the austenitic stainless steel and require bothpreheating and postweld heat treatments.

Welds of ferritic stainless steel can be by. .

metal)

(ii) with an austenitic stainless steel

(iii) using a high nickel filler alloy.

(iv) Type 405 filler (low 11% Cr, low carbon and small0.2% Al)

Welding process: TIG, MIG, Shieldedmetal arcwelding and Plasma arc welding

IES2010Assertion (A): It is generally difficult to weld

Aluminum parts by normal arc welding process.

Reason (R): Hard and brittle Aluminumoxide filmis formed at thewelded joints.

correct explanation of A

(b) Both A and R are individually true but R is NOT thecorrect explanation of A

(c) A is true but R is false

(d) A is false but R is true

IES2006Assertion(A):Aluminium haspoorweldability.

Reason(R):Aluminium hashighthermalconductivityandhighaffinitytooxygen.

a BothA

and

R

are

individuall

true

and

R

is

the

correctexplanationofA

(b) BothAandRareindividuallytruebutRisnotthecorrectexplanationofA

(c) AistruebutRisfalse

(d) AisfalsebutRistrue


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IES2011During plasma arc welding of aluminium, improvedremoval of the surface oxide from the base metal is

obtained with typical polarity of :

(a) DC Straight

(b) DC reverse

(c) AC potential

(d) Reverse polarity of phase of AC potential

IES2011Considerthefollowingstatements.

Castironisdifficulttoweld,becauseof

1.Low

ductility

2.Poorfusion

3.TendencytocrackoncoolingWhichofthesestatementsarecorrect?

(a)1,2and3

(b)1and2only

(c)2and3only

(d)1and3only

IES2006

Fabricationweldability testisusedtodetermine

(a) Mechanicalpropertiesrequiredforsatisfactoryperformanceofweldedjoint

(c) Suitabilityforjointdesign

(d) Appropriatemachiningprocess

IES1999

Thecorrectsequenceofthegivenmaterialsinascendingorderoftheirweldability is

(a) MS,copper,castiron,aluminium

, ,

(c) Copper,castiron,MS,aluminium

(d) Aluminium,copper,castiron,MS

IES2010Weldability of ferritic stainless steel used inautomotive exhaust system is improved byselecting stainless steel electrode having low

content of(a) Carbon (b) Nitrogen

(c) Chromium (d) Carbon and Nitrogen

IES2010Consider the following statements regarding

welded joints:

1. It is a permanent type of joint.

2. It is reliable and economical for pressure vessel.

3. It is free from fabricational residual stresses.

4. Such joints are suitable for static loading only.

5. Welding is a versatile and f lexible metal joining process.

Which of the above statements are correct?

(a) 1, 2 and 3 only (b) 2, 3 and 4 only

(c) 1, 2, 3, 4 and 5 (d) 1, 2 and 5 only


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GasFlameProcesses:

Welding,CuttingandStraightening

Oxy

fuel gas Welding (OFW): Heat source is theflame produced by the combustion of a fuel gas andoxygen.

OFW has largely been replaced by other processes butit is still popular because of its portability and the lowcapital investment.

Acetylene is the principal fuel gas employed.

Combustionofoxygenandacetylene(C2H2)inaweldingtorchproducesatemp.inatwostagereaction.

Inthefirststage

+Heat

Thisreactionoccursnearthetipofthetorch.

C H O CO H + +2 2 2 22

InthesecondstagecombustionoftheCOandH2andoccursjustbeyondthefirstcombustionzone.

2CO+O22CO2+Heat

H2+ O2H2O+Heat

Oxygenforsecondaryreactionsisobtainedfromtheatmosphere.

1

2

Three types of flames can be obtained by varyingthe oxygen/acetylene (or oxygen/fuel gas) ratio.

If the ratio is about 1 : 1 to 1.15 : 1, all reactions arecarried to completion and a neutral flame is produced.

Most welding is done with a neutral flame, since it willave e eas c em ca e ec on e ea e me a .

Oxyacetylenegasweldingneutralflame

A higher ratio, such as 1.5 : 1, produces an oxidizingflame, hotter than the neutral flame (about 3300oC)but similar in appearance.

Used when welding copper and copper alloys butharmful when welding steel because the excess oxygenreac s w e car on, ecar ur z ng reg onaround the weld.

OxyacetylenegasweldingOxidisingflame


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Excess fuel, on the other hand, produces a carburizingflame.

The excess fuel decomposes to carbon and hydrogen,

and the f lame temperature is not as great (about3000oC).

Flames of this t e ar used in weldin Monel anickelcopper alloy), highcarbon steels, and somealloy steels, and for applying some types of hardfacingmaterial.

OxyacetylenegasweldingCarburizingflame

Metal Flame

M S NHigh carbon steel R

Grey cast iron N, slightly oxidizing

Alloy steel N

Aluminium Slightly carburizing

Brass Slightly oxidizing

Copper, Bronze N, slightly oxidizing

N ickel alloys Slightly carburizing

Lead N

IES2009Conventional

Explain the three types of oxyacetylene flames.

Indicate with the help of sketches the various

zones, respective temperature ranges and

applications of each type of f lame.

[20 Marks]

Uses,Advantages,andLimitationsOFW isfusion welding.

No pressure is involved.

Filler metal can be added in the form of a wire or rod.

Fluxes may be used to clean the surfaces and removecontaminating oxide. The gaseous shield produced byvaporizing f lux can prevent oxidation during welding,and the slag produced by solidifying flux can protectthe weld pool. Flux can be added as a powder, the

welding rod can be dipped in a f lux paste, or the rodscan be precoated.

Contd


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Exposer of the heated and molten metal to the various

gases in the flame and atmosphere makes it difficult to

preventcontamination.

Heat source is not concentrated lar e area of the,

metal is heated and distortion is likely to occur.

Flame welding is still quite common in field work, in

maintenance and repairs, and in fabricating small

quantities of specialized products.

Oxyacetyleneweldingequipment

Oxygen is stored in a cylinder at a pressure ranging

from 13.8 MPa to 18.2 MPa .Due to high explosiveness of free acetylene it is stored

in a cylinder with 8085% porous calcium silicate andthen filled with acetone which absorb upto 420 timesby its volume at a pressure 1.75 MPa .

At the time of acetylene release if acetone comes withacetylene the flame would give a purple colour.

Another option is acetylene generator.

2 2 2 2 22 ( )CaC H O C H Ca OH + +

PressureGasWeldingPressure gas welding (PGW) or Oxyacetylene

Pressure Welding is a process used to make buttjoints between the ends of objects such as pipeandrailroad rail.

The ends are heated with a gas flame to atemperature below the melting point, and the softmetal is then forced together under considerablepressure.

This process, therefore, is actually a 'form of solidstate welding.

IES2010The ratio between Oxygen and Acetylenegases for neutral flame in gas welding is

(a) 2 : 1 (b) 1 : 2

(c) 1 : 1 (d) 4 : 1

GATE1994

The ratio of acetylene to oxygen isapproximately. for a neutral flames used ingas welding.

a 1 : 1

(b) 1 : 2

(c) 1 : 3

(d) 1.5 : 1

GATE2003InOxyacetylenegaswelding,temperatureattheinnerconeoftheflameisaround

(a) 3500C

b 200C

(c) 2900C

(d) 2550C


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IES2010Assertion (A): Oxidizing flame is used in gas

welding to join medium carbon steels having high

melting point.Reason (R): In gas welding, oxidizing flame

roduces the maximum tem erature com ared toneutral and reducing f lame.

(a) Both A and R are individually true and R is thecorrect explanation of A




GATE2002The temperature of a carburising flame in gas

welding is that of a neutral or an oxidising flame.(a) Lowerthan

b Hi herthan

(c) Equalto

(d) Unrelatedto

IES2009

By which one of the following methods gray castiron is usually welded?

(a) TIGwelding (b) MIGwelding

IES1998

In oxyacetylene gas welding, for completecombustion, the volume of oxygen required perunit of acetylene is

a 1

(b) 1.5

(c) 2

(d) 2.5

IAS1994

In gas welding of mild steel using an oxyacetylene flame. the total amount of acetyleneconsumed was 10 litre. The oxygen consumption

from the cylinder is(a) 5litre

(b) 10litre

(c) 15litre

(d) 20litre

IAS1995

Assertion (A): If neutral flame is used in oxyacetylene welding, both oxygen and acetylenecylinders of same capacity will be emptied at the sametime.

Reason (R): Neutral flame uses equal amounts ofoxygen an acety ene.(a) BothAandRareindividuallytrueandRisthecorrect

explanationofA(b) BothAandRareindividuallytruebutRisnotthe

correctexplanationofA(c) AistruebutRisfalse(d) AisfalsebutRistrue


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OxygenTorchCutting(GasCutting)

Iron and steel oxidize (burn) when heated to a

temperature between 8000

C to 10000

C.Highpressure oxygen jet (300 KPa) is directed against

a heated steel plate, the oxygen jet burns the metal andblows it away causing the cut (kerf).

For cutting metallic plates shears are used. These areuseful for straightline cuts and also for cuts up to 40mm thickness.

Contd

For thicker plates with specified contour, shearingcannot be used and oxyfuel gas cutting (OFC) isuseful.

Gascutting is similar to gas welding except torch tip.

Fig differencesintorchtipsforgasweldingandgascutting

Contd

Larger size orifice produces kerf width wider and largeroxygen consumed.

At kindling temperature (about 870oC), iron form ironoxide.

Reaction:

3 + 2 2 3 4+ . 7

The other reactions:

2Fe + O22FeO + 3.18 MJ/kg of iron

4Fe + 3O22Fe2O3+ 4.9 MJ/kg of iron

All exothermic reactions preheat the steel.

Contd

For complete oxidation 0.287 m3 oxygen/kg of iron isrequired

Due to unoxidized metal blown away the actualrequirement is much less.

Torch ti held verticall or sli htl inclined in thedirection of travel.

Torch position is about 1.5 to 3 mm vertical from plate.

Contd

The drag lines shows the characteristics of the movementof the oxygen stream.

Drag is the amount by which the lower edge of the dragline trails from the topedge.

Good cut means negligible drag.

Fig positioningofcuttingtorchinoxyfuelgascutting

Contd


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If torch moved too rapidly, the bottom does not getsufficient heat and produces large drag so very roughand irregularshapedcut edges.

If torch moved slowly a large amount of slag isgenerated and produces irregular cut.

Contd

Gas cutting is more useful with thick plates.

For thin sheets (less than 3 mm thick) tip size shouldbe small. If small tips are not available then the tip isinclined at an angle of 15 to 20 degrees.

Fig.Recommendedtorchpositionforcuttingthinsteel

Application

Useful only for materials which readily get oxidized

and the oxides have lower melting points than the

metals.

Widelyused for ferrous materials.

Cannot be used for aluminum, bronze, stainless steel

and like metals since they resist oxidation.

Difficulties

Metal temperature goes beyond lower criticaltemperature and structural transformations occur.

Final microstructure de ends on coolin rate.

Steels with less than 0.3 % carbon cause no problem.

Contd

For high carbon steel material around the cut should

be preheated (about 250 to 300oC) and may post heat

also necessary.

Cuttin CI is difficult since its meltin tem . is lower,

than iron oxide.

If chromium and nickel etc are present in ferrous

alloys oxidation and cutting is difficult.


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IES1992

The edge of a steel plate cut by oxygen cutting will

get hardened when the carbon content is(a) Less than 0.1 percent

.

(c) More than 0.3 percent

(d) Anywhere between 0.1 to 1.0 percent

IES2007

Considerthefollowingstatementsinrespectofoxyacetylenewelding:1. Thejointisnotheatedtoastateoffusion.2. Nopressureisused.

Ox enisstoredinsteelc linderata ressureof1 . MPa.

4. Whenthereisanexcessofacetyleneused,thereisadecidedchangeintheappearanceofflame.

Whichofthestatementsgivenabovearecorrect?(a) 1,2and3 (b) 2,3and4

(c) 1,3and

4 (d) 1,

2and

4

IES2001

Oxyacetylenereducingflameisusedwhilecarryingouttheweldingon

(a) Mildsteel (b) Highcarbonsteel

IES1992

Thick steel plate cut with oxygen normally showssigns of cracking. This tendency for cracking canbe minimised by

a Slows eed cuttin(b) Cutting in two or more stages

(c) Preheating the plate

(d) Using oxyacetylene f lame

IES2005

Considerthefollowingstatements:1. Ingaswelding,thetorchshouldbeheldatanangleof

30 to45 fromthehorizontalplane.

2. In

gas

welding,

the

Size

of

the

torch

depends

upon

the

c nesso me a o e orme .

3. Dragingascuttingisthetimedifferencebetweenheatingoftheplateandstartingtheoxygengasforcutting.

Whichofthestatementsgivenabovearecorrect?

(a) 1,2and3 (b) 1and2

(c) 2and3 (d) 1and3


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PlasmaCuttingUses ionized gas jet (plasma) to cut materials resistant to

oxyfuel cutting,

High velocity electrons generated by the arc impact gasmolecules, and ionize them.

The ionized as is forced throu h nozzle (u to 00 m/s), andthe jet heats the metal, and blasts the molten metal away.

More economical, more versatile and much faster (5 to 8times) than oxyfuel cutting, produces narrow kerfs andsmooth surfaces.

HAZ is 1/3 to th than oxyfuel cutting.

Maximum plate thickness = 200 mm

ElectricArcWelding

Fig.Basiccircuitforarcwelding

PrincipleofArc

An arc is generated between cathode and anode when

they are touched to establish the flow of current and

then se arated b a small distance.

65% to 75% heat is generated at the anode.

If DC is used and the work is positive (the anode of the

circuit), the condition is known as straight polarity

(SPDC).

Contd

Work is negative and electrode is positive is reverse

polarity (RPDC).

SPDC conditions are preferred.

arcwe ng ma n an a s a e arc an pre erre or

difficult tasks such as overhead welding.

For a stable arc, the gap should be maintained.

Contd


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Manual arc welding is done with shielded (covered)electrodes

Baremetal wire used in automatic or semiautomaticmachines.

Non consumable electrodes (e.g tungsten) is notconsume y t e arc an separate meta wire is useas filler.

There are three modes of metal transfer (globular,spray and shortcircuit).

Threemodesofmetaltransferduringarcwelding

MajorForcestakepartinMetalTransfer

(i)gravityforce

(ii)Surfacetension

(iii)electromagneticinteraction

(iv)hydrodynamicactionofplasma

JWM2010

Assertion (A) : Bead is the metal added duringsingle pass of welding.

Reason (R) : Bead material is same as base metal.





GATE1993Ind.c.welding,thestraightpolarity(electrodenegative)resultsin

(a) Lowerpenetration

b Lowerde osition

rate

(c) Lessheatingofworkpiece

(d) Smallerweldpod


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Arcweldingequipments

1. Droopers: Constant current welding machines

Good for manual welding2. Constant voltage machines

Contd

Fig.Machinewithdifferentsettings

Fig.Characteristiccurveofaconstantvoltagearcweldingmachine

Formula

V I

OCV SCC

Requires a large current (150 to 1000 A), voltage is

between 30 and 40 V, actual voltage across the arc

varying from 12 to 30 V.

To initiate a we , t e operator stri e t e e ectro e an

start arc.

IES2010In arcwelding, the arc length should be equal to

(a) 4.5 times the rod diameter

(b) 3 times the rod diameter

(c) 1.5 times the rod diameter(d) Rod diameter


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IES2005Considerthefollowingstatements:

1. Inarcwelding,65%to75%heatisgeneratedatthe

anode.2. Dutycycleincaseofarcweldingisthecycleof

com leteweldin ofwork iecefromthebeginning.

3. ArcblowismorecommonwithDCwelding.


(a) 1,2and3 (b) 1and2

(c) 2and3 (d) 1and3

IES2001

Inmanualarcwelding,theequipmentshould

havedroopingcharacteristicsinordertomaintain

(b) Currentconstantwhenarclengthchanges

(c) Temperatureintheareconstant

(d) Weldpoolredhot

IES2001

Inarcwelding,d.c.reversepolarityisusedtobeargreateradvantagein

(a) Overheadwelding

(c) Edgewelding

(d) Flatweldingofbuttjoints

IES1998

The voltagecurrent characteristics of a dcgenerator for arc welding is a straight linebetween an opencircuit voltage of 80 V and shortcircuit current of 300 A. The generator settings formaximum arc powerwill be

(a) 0 V and 150 A (b) 40 V and 300 A

(c) 40 V a nd 150 A (d) 80 V a nd 300 A

IAS1999

Opencircuit voltage of 60 V and current of 160Awere the welding conditions for arc welding of acertain class of steel strip of thickness 10 mm. For

arc welding of 5mm thick strip of the same steel,the welding voltage and current would be

(a) 60 V and 80 A

(b) 120 V and 160 A

(c) 60 V and 40 A

(d) 120 V and 40 A

IAS1998

AssumingastraightlineVIcharacteristicsforadcweldinggenerator,shortcircuitcurrentas400Aandopencircuitvoltageas400whichoneofthe

followingis

the

correct

voltage

and

current

setting

formaximumarcpower?

(a) 400Aand100V (b) 200Aand200V

(c) 400Aand50V (d) 200Aand50V


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DutyCycle

The percentage of time in a 5 min period that a

welding machine can be used at its rated outputwithout overloading.

Time is spent in setting up, metal chipping, cleaningand inspection.

For manual welding a 60% duty cycle is suggested andfor automatic welding 100% duty cycle.

Contd

Requireddutycycle,

=

2

a

IT T

I

Where,T=rateddutycycle

I=ratedcurrentattherateddutycycle

Io=Maximumcurrentattherateddutycycle

Electrode

1. NonconsumableElectrodes

2. ConsumableElectrodes

Madeofcarbon,GraphiteorTungsten.

CarbonandGraphiteareusedforD.C.

Electrodeisnotconsumed,thearclengthremainsconstant,arcisstableandeasytomaintain.

Contd

ConsumableElectrodes

Provides filler materials.

Same composition.

This requires that the electrode be moved toward oraway from the work to maintain the arc andsatisfactory welding conditions.

Contd

Consumableelectrodes are three kinds:

(a) Bare

(b) Fluxed or lightly coated

(c) Coated or extruded / shielded

,continuous wire (coil).

Electrodecoatingcharacteristic

1. Provide a protectiveatmosphere.

2. Stabilize the arc.

3. Provide a protective slag coating to accumulate

im urities revent oxidation and slow th coolin ofthe weld metal.

4. Reduce spatter.

5. Add alloying elements.

6. Affect arc penetration

7. Influence the shape of the weld bead.

8. Add additional filler metal.


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GATE1994Theelectrodesusedinarcweldingarecoated.

This

coating

is

not

expected

to(a) Provideprotectiveatmospheretoweld

b Stabilizetheare

(c) Addalloyingelements

(d) Preventselectrodefromcontamination

Electrodecoatings

l. Slag Forming Ingredients. asbestos, mica, silica,

fluorspar, titanium dioxide, Iron oxide, magnesiumcarbonate, Calcium carbonate and aluminium oxide.

2. Arc Stabilizing Ingredients. or ionizing agents:potassium silicate, TiO2 + ZrO2 (Rutile), Mica,Calcium oxide, sodium oxide, magnesium oxide,feldspar (KAI Si3 O8)

Contd

3.DeoxidizingIngredients.Cellulose,Calciumcarbonate,dolomite,starch,dextrin,woodflour,graphite,aluminium,ferromanganese.

4.BindingMaterialsSodiumsilicate,potassiumsilicate,asbestos.

5.AlloyingConstituentstoImproveStrengthofWeld

6.TiO2andpotassiumcompoundsincreasethemeltingrateofthebasemetalforbetterpenetration.

7.Ironpowderprovideshigherdepositionrate.

Contd Contd

The slag is then easily chipped.

Coatings are designed to melt more slowly than thefillerwire.

Binders

AC arc welding used potassium silicate binders.

DC arc welding used sodium silicate binders.

Potassium has lower ionization otential as com ared

with sodium.


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IES2007

The coating material of an arc welding electrode

contains which of the following?1. Deoxidising agent

.

3. Slag forming agent

Select the correct answer using the code given below:

(a) 1, 2 and 3 (b) 1 and 2 only

(c) 2 and 3 only (d) 1 and 3 only

IES1997

Assertion (A): The electrodes of ac arc welding arecoated with sodium silicate, whereas electrodes usedfor dc arc welding are coated with potassium silicatebinders.Reason (R): Potassium has a lower ionizationpotent a t anso um.(a) Both A and R are individually true and R is the correct

explanation of A(b) Both A and R are individually true but R is not the

correct explanation of A(c) A is true but R is false(d) A is false but R is true

IES2002

MatchListIwithListIIandselectthecorrectanswer:

ListI(Ingredients) ListII(Weldingfunctions)

A. Silica 1. Arc stabilizer

B. Potass um oxa ate 2. Deox zer

C. Ferrosilicon 3. Fluxingagent

D. Cellulose 4. Gasformingmaterial

Codes:A B C D A B C D

(a) 3 4 2 1 (b) 2 1 3 4

(c) 3 1 2 4 (d) 2 4 3 1

WeldingFlux

Availableinthreeforms

Granular

Electrodewirecoating

Electrodecore

WeldingPositions

Fig.Thepositionofelectrodeforhorizontalwelding

Fig.Positioningofelectrodeforweldinginverticallyupwardposition

WeldingCurrent

Weldingcurrentdependsupon:thethicknessoftheweldedmetal,typeofjoint,weldingspeed,positionoftheweld,thethicknessandtypeofthecoatingonthe

electrode

and

its

working

length.Weldingcurrent,I =k.d,amperes; disdia.(mm)


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WeldingVoltage

Thearcvoltagedependsonlyuponthearclength

V=k1+k2l Volts

Wherelisthearclengthinmmandk1andk2areconstants,

k1=10to12;andk2=2to3

TheminimumArcvoltageisgivenby

Vmin=(20+0.04l) Volt

ArcLength

For good welds, a short arc length is necessary,

because:1. Heat is concentrated.

2. Morestable

3. More protective atmosphere.

Contd

A long arc results in

Large heat loss into atmosphere.

Unstable arc.

Weld pool is not protected.

, ,excessive spatter.

Fig.ArcPowerVsArcLength

Arclengthshouldbeequaltothe diameteroftheelectrodesize

Beadwidthshouldbeequaltothreediameteroftheelectrodesize

GATE2002,Conventional

The arc lengthvoltage characteristic of a DC arc is given

by the equation: V = 24 + 4L, where V is voltage in volts

and L is arc length in mm. The static volt

amperecharacteristic of the power source is approximated by a

straight line with a no load voltage of 80 V and a short

circuit current of 600A. Determine the optimum arc

length for maximum power.


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ArcblowinDCarcwelding

Contd

Arc blow occurs during the welding of magneticmaterials with DC.

The effect of arc blow is maximum when weldingcorners where magnetic field concentration ismaximum.

The effect is particularly noticeable when welding withbare electrodes or when using currents below or above

Again the problem of arc blow gets magnified whenwelding highly magnetic materials such as Ni alloys,because of the strong magnetic fields set up by thesemetals.

Cause: Unbalanced magnetic forces.

Contd

Effectofarcblow

Low heat penetration.

Excessive weld spatter.

Pinch effect in welding is the result of electromagneticforces

Weld spatter occurs due to

High welding current

Too small an electrode arc

Contd

The effects of arc blow can be minimized with D.C.welding by

Shortening the arc.

Reduce current

Reducing weld speed.

Balance magnetic field by placing one ground lead ateach end of the work piece.

Wrapping the electrode cable a few turns around thework piece.

IES2001

Arcblowismorecommonin

(a) A.C.welding

(b) D.C.weldingwithstraightpolarity

c . .we ngw aree ec ro es

(d) A.C.weldingwithbareelectrodes

IES2001

Pincheffectinweldingistheresultof

(a) Expansionofgasesinthearc

(b) Electromagneticforces

c ec r c orce

(d) Surfacetensionofthemoltenmetal


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GATE1992

A low carbon steel plate is to be welded by the manual

metal arc welding process using a linear V

Icharacteristic DC Power source. The following data areavailable :

OCV of Power source = 62 V

Short circuit current = 130 A

Arc length, L = 4 mm

Traverse speed of welding = 15cm/s

Efficiency of heat input = 85%

Voltage is given as V = 20 + 1.5 L

Calculate the heat in ut into the work rice

Gasshields

An inert gas is blown into the weld zone to drive away

other atmospheric gases.

, , ,

a mixture of the above gases.

Argon ionizes easily requiring smaller arc voltages.It is

good for welding thin sheets.

Contd

Helium, most expensive, has a better thermal

conductivity, is useful for thicker sheets, copper and

aluminium welding, higher deposition rate.

The arc in carbon dioxide shielding gas is unstable,

least expensive, deoxidizers needed.

It is a heavy gas and therefore covers the weld zone

very well.

CarbonArcwelding

Arc is produced between a carbon electrode and the

work.

.

No pressure

With or without filler metal

May be used in "twin arc method", that is, between

two carbon (graphite) electrodes.

IES2010Assertion (A): Straight polarity is alwaysrecommended for Carbonelectrode welding.

Reason (R): Carbon arc is stable in straight polarity.

(a) Both A and R are individually true and R is the




TungstenInertGaswelding(TIG)

Arc is established between a nonconsumabletungsten electrode and the workpiece.

Tungsten is alloyed with thorium or zirconium for

better currentcarryin and electron

emission

characteristics.

Arc length is constant, arc is stable and easy tomaintain.

With or without filler.

Contd


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Very clean welds.

All metals and alloys can be welded. (Al, Mg also)

Straight polarity is used.

Weld voltage 20 to 40 V and weld current 125 A for

RPDC to 1000 A for SPDC.

Shielded Gas: Argon

Torch is water or air cooled.

Fig.TIG

GATE2011Whichoneamongthefollowingweldingprocessesusednon consumableelectrode?

(a)Gasmetalarcwelding

(b)Submergedarcwelding

(c)Gastungstenarcwelding

(d)Fluxcoatedarcwelding

IES2010In an inert gas welding process, the commonly usedgas is

(a) Hydrogen

(b) Oxygen

c e um o r rgon

(d) Krypton

GATE2002Whichofthefollowingarcweldingprocessesdoesnotuseconsumableelectrodes?

(a) GMAW

b GTAW(c) SubmergedArcWelding

(d) Noneofthese


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IES1994

Whichoneofthefollowingweldingprocesses

usesnon

consumable

electrodes?

(a) TIGwelding

(c) Manualarcwelding

(d) Submergedarcwelding.

IES2000

Whichoneofthefollowingstatementsiscorrect?

(a) Noflux

is

used

in

gas

welding

of

mild

steel

(b) Boraxisthecommonlyusedfluxcoatingon

(c) Laserbeamweldingemploysavacuumchamberandthusavoidsuseofashieldingmethod

(d) ACcanbeusedforGTAWprocess

GasMetalArcWelding(GMAW)orMIG

Aconsumable electrode in a gas shield.

Arc is between workpiece and an automatically fedbarewire electrode.

Ar on helium and mixtures of the two can be used.

Any metal can be welded but are used primarily withthe nonferrous metals.

When welding steel, some O2 or CO2is usually addedto improve the arc stability and reduce weld spatter.

Contd

Fast and economical.

A reversepolarity dc arc is generally used.

Fig.MIG


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IES2007

InMIGwelding,themetalistransferredintothe

formof

which

one

of

the

following?

(a) Afinesprayofmetal

(c) Weldpool

(d) Molecules

IES1997

Considerthefollowingstatements:

MIGwelding

process

uses

1. Consumableelectrode 2.nonconsumableelectrode

. D.C. owersu l .A.C. owersu l. . . . . .

Ofthesestatements

(a) 2and4arecorrect

(b) 2and3arecorrect

(c) 1and4arecorrect

(d) 1and3arecorrect

IES2010Assertion(A):InertgasandbareelectrodeinsteadoffluxcoatedelectrodeisusedinthecaseofautomaticTIGandMIGweldingprocesses.

Reason(R):Betterprotectionisprovidedbyacloudofinert asthanthecovercreatedb theflux.





SubmergedArcwelding(SAW)

A thick layer of granular flux is deposited just ahead of

a bare wire consumable electrode, and an arc is

maintained beneath the blanket of f lux with onl a few

small flames being visible.

A portion of the flux melts. Molten flux and flux

provides thermal insulation, slows cooling rate and

produce soft, ductile welds.

Contd

Most suitable for flat butt or fillet welds in low

carbonsteel (< 0.3% carbon).

The process is not recommended for highcarbon

steels, tool steels, aluminum, magnesium,

titanium, lead, or zinc.


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Characteristicofsubmergedarcwelding

Highspeeds,

Highdepositionrates,

,

Highcleanliness(duetothefluxaction).

Advantages

Wireelectrodesareinexpensive.

Noweldspatter.

.

Lesserelectrodeconsumption.

Limitations

Extensive flux handling,

Contaminationof the flux by moisture.

argegra ns ze s ruc ures.

Welding is restricted to the horizontal position.

Chemical control is important

IES2011The welding process in which bare wire is used aselectrode, granular f lux is used and the process ischaracterized by its high speed welding, is known as:

(a) Shielded arc welding(b) Plasma arc welding

(c) Submerged arc welding

(d) Gas metal arc welding


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IES2006

Inwhichofthefollowingweldingprocesses,flux

isused

in

the

form

of

granules?

(a) ACarcwelding

(c) Argonarcwelding

(d) DCarcwelding

IES2005

Whichofthefollowingarethemajor

characteristics

of

submerged

arc

welding?1. Highweldingspeeds.

2. Highdepositionrates.

3. Lowpenetration.

4. Lowcleanliness.

Selectthecorrectanswerusingthecodegivenbelow:

(a) 2and3 (b) 1,2and3

(c) 3and4 (d) 1and2

IES2008

Assertion (A): Submerged arc welding is notrecommended for high carbon steels, tool steels,aluminium, magnesium etc.Reason (R): This is because of unavailability ofsuitable fluxes, reactivity at high temperatures andowsu mat on temperatures.

(a) Both A and R are true and R is the correct explanationof A

(b) Both A and R are true but R is NOT the correctexplanation of A

(c) A is true but R is false(d) A is false but R is true

GATE1999For buttwelding 40 mm thick steel plates, whenthe expected quantity of such jobs is 5000 permonth over a period of 10 year, choose the bestsuitable welding process out of the followingavai a e a ternatives.

(a) Submerged arc welding

(b) Oxyacetylene welding

(c) Electron beam welding

(d) MIG welding

AtomicHydrogenwelding(AHW)

An a.c. arc is formed between two tungsten electrodesalong which streams of hydrogen are fed to the

welding zone. The molecules of hydrogen aredissociated by the high heat of the arc in the gap

.hydrogen proceeds with the absorption of heat:

H2= 2H 421.2 k J/mol

This atomic hydrogen recombines to form molecularhydrogen outside the arc, particularly on the relativelycold surface of the work being welded, releasing theheat gained previously:

2H = + 421.2 k J/mol.H2Contd

Temperature of about 3700oC.

Hydrogen acts as shielding also.

Used for very thin sheets or small diameter wires.

Lower thermal efficiency than Arc welding.

Ceramics may be arc welded.

AC used.


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IES2005

Inatomichydrogenwelding,hydrogenactsas

(a) Aheating

agent

(b) Oneofthegasestogeneratetheflame

c ne ec ves e nggaspro ec ng ewe

(d) Alubricanttoincreasetheflowcharacteristicsofweldmetal


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ResistanceWelding

By SKMondal

ResistanceWeldingPrinciple

Both heat and pressure are used.

Heat is generated by the electrical resistance of thework pieces and the interface between them.

Pressure is supplied externally and is variedthroughout the weld cycle.

Due to pressure, a lower temperature needed thanoxyfuel or arc welding.

Contd

They are not officially classified as solidstate welding

by the American Welding Society.

Very rapid and economical.

Extreme y we suite to automate manu acturing.

No filler metal, no flux, no shielding gases.

Contd

Overall resistance very low.

Very highcurrent (up to 100,000 A)

Very lowvoltage (0.5 to 10 V) is used.

FIG.Thefundamentalresistanceweldingcircuit

Fig. The desired temperaturedistribution across theelectrodes and the workpieces in lap resistancewelding.

Fig. Typical current and

pressure cycle for resistance

welding. The cycle includes

forging and post heating

operations. Fig. The arrangement of the electrodes and the work in spotwelding, showing design for replaceableelectrode tips.


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Advantages

1. Very rapid.

2. Fully automation possible.

. , ,

flux is required.

4. Skilled operators are not required.

5.Dissimilar metals can be easily joined.

6. High reliability and High reproducibility.

Limitations

1. High initial cost.

2. Limitations to the type of joints (mostly lapjoints).

.

4. special surface treatment needed.

Application

The resistance welding processes are among themost common technique for high volume

joining.

Differenttypes

1. Resistance spot welding

2. Resistance seam welding

3.

4. Upset welding

5. Flash welding

6. Percussion welding

Resistancespotwelding

The process description given so far is called resistancespot welding (RSW) or simply spot welding.

This is essentially done to join two sheetmetal jobs in

a lap joint, forming a small nugget at the interface ofthe two plates.

HeatinputandEfficiencyCalculations

Contd


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Electric Resistance Welding

Joules law applicableQ = I2 Rt, Joules

Calculate the melting efficiency in the case of arc

welding of steel with a potential of 20 V and current of200 A. The travel speed is 5 mm/s and the crosssectional area of the joint is 20 mm2. Heat required to

Example1

melt steel may be taken as 10 / and the heat transferefficiency as 0.85.

[PTU2004]

Example2

Calculate the melting efficiency in the case ofarcwelding of steel with a potential of 20 V anda current of 200 A. The travel speed is 5 mm/s

.mm2. Heat required to melt steel may be takenas 10 J/mm3 and the heat transfer efficiency as0.85.

Example3

Two steel plates each 1 mm thick are spotwelded at a current of 5000 A. The current flowtime is 0.1 s. The electrodes used are 5 mm in

.its distribution in the weld zone. The effectiveresistance in the operation is 200.

Example4

Two steel sheets of 1.0mm thickness areresistance welded in a lap joint with a current of10 000 A for 0.1 second. The effective resistance

.joint can be considered as a cylinder of 5 mmdiameter and 1.5mm height. The density of steelis 0.00786 g/mm3 and heat required for meltingsteel is 10 J/mm3.

How much heat would be generated in the spotwelding of two sheets of 1 mm thick steel that

re uired a current of 10000 A for 0.1 seconds?

Example5

An effective resistance of 100 . is assumed.


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Example6

Two 1.2 mm thick, flat copper sheets are being spot

welded using a current of 6000 A and a current f lowtime of t = 0.18 s. The electrodes are 5 mm in diameter.Estimate the heat generated in the weld zone. Takeeffective resistance as 150 .

Example7

Two steel sheets of 1.0mm thickness are resistance

welded in a projection welding with a current of 30000 A for 0.005 second. The effective resistance of thejoint can be taken as 100 micro ohms. The joint can beconsi ere as a cy in er o 5 mm iameter an 1.5 mmheight. The density of steel is 0.00786 g/mm3 and heatrequired for melting steel is 10 J/mm3.

Resistanceseamwelding

Weld is made between overlapping sheets of metal.

The seam is a series of overlapping spot welds.

.

except that the electrodes are now in the form of

rotating disks.

Timed pulses of current pass to form the overlapping

welds.

Contd

Welding current is a bit higher than spot welding, tocompensate short circuit of the adjacent weld.

In other process a continuous seam is produced bypassing a continuous current through the rotatingelectrodes with a speed of 1.5 m/min for thin sheet.

Contd

Fig.Resistanceseamwelding

Projectionwelding

Limitations of spot welding.

1. Electrode condition must be maintainedcontinually, and only one spot weld at a time.

2. Foradditional stren th multi le welds needed.Projection welding (RPW) overcomes above

limitations.

Contd


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Dimples are embossed on work pieces at the weldlocations and then placed between largeareaelectrodes, and pressure and current applied like spot

welding.Current f lows through the dimples and heats them

and ressur causes th dim les to flatten and form aweld.

Fig.Principleofprojectionwelding,(a)priortoapplicationofcurrentandpressure(b)andafterformationofwelds

Contd

Projections are pressformed in any shape.

Multiple welds at a time.

No indentation mark on the surface.

Bolts and nuts can be attached to other metal parts.

Upsetwelding

Made butt joint compared to lap joint.

Pieces are held tightly and current is applied.

name.

Useful for joining rods or similar pieces.

Contd Contd

This is the process used for making electric resistancewelded (ERW) pipes starting from a metal plate of suitablethickness.

The plate is first formed into the shape of the pipe with thehelp of the three roll set as shown in Fig. above. The ends

of the latewould then be formin the butt oint.The two rotating copper disc electrodes are made to

contact the two ends of the plate through which thecurrent is passed. The ends get heated and then forge welded under the pressure of the rolls.

The ends of the pieces to be upset welded must be perfectlyparallel. Any high spots if present on the ends would getmelted first before the two ends are completely joined.

FlashWelding

It is similar to upset welding except the arc rather than

resistance heating.

platen and other with is fixed platen.

Contd


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Two pieces are brought together and the power supply isswitched on. Momentarily the two pieces are separatedto create the arc to melt the ends of the two pieces.

Then again the pieces are brought together and thepower switched off while the two ends are fused underforce. Most of the metal melted would flash outthrough the joint and forms like a fin around the joint.

Faster than upset welding.

PercussionWelding

Similar to flash welding except arc power by a rapid

discharge of stored electrical energy.

The arc duration is only 1 to 10 ms, heat is intense and

highlyconcentrated.

Small weld metal is produced, little or no upsetting, and

low HAZ.

Application: Butt welding of bar or tube where heat

damage is a major concern.Contd

OtherWeldingTec nique

Thermit Welding

Heating and coalescence is by superheated molten

metal obtained from a chemical reaction between a

metal oxide and a metallic reducin a ent.

Used mixture one part aluminum and three parts iron

oxide and ignited by a magnesium fuse. (1150C).

8Al+3Fe3O4 9Fe+4Al2O3+heat

Contd

Temp. 2750C produced in 30 seconds, superheating

the molten iron which provide both heat and filler

metal.

Runnersand risers are rovided lik castin .

Copper, brass, and bronze can be welded using a

different starting mixture.

Used to joint thick sections, in remote locations.


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ElectroSlagWelding

Very effective for weldingthick sections.

Heat is derived from the passage of electrical current

.

Contd

A 65mm deep layer of molten slag, protect and

cleanse the molten metal.

Watercooled copper molding plates confined the

li uid and moved u ward.

Multiple electrodes are used to provide an adequate

supply of filler.

Contd

Applications: Shipbuilding, machine manufacture,

heavy pressure vessels, and the joining of large

castings and forgings.

Slow cooling produces a coarse grain structure.

Large HAZ.

Contd

ElectronBeamWelding

A beam of electrons is magnetically focused on the

work piece in a vacuum chamber.

.

Allows precise beam control and deep weld

penetration.

No shield gas (vacuum chamber used)


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LaserBeamWelding

Used a focused laser beam provides power intensities

in excess of 10kW/cm2

of vaporized metal with a surrounding liquid pool.

Depthtowidth ratio greater than 4: 1.

Contd

Very thin HAZ and little thermal distortion.

Filler metal and inert gas shield may or may not used.

Deep penetration.

o vacuum nee e .

No direct contact needed.

Contd

Heat input is very low, often in the range 0.1 to 10 J.

Adopted by the electronics industry.

Possible to weld wires without removing the

.

Contd

ForgeWelding

Blacksmith do this.

Borax is used as a flux.

anvil and hammered to the degree necessary to

produce an acceptable weld.

Quality depends on the skill of the worker and not

used by industry.

FrictionWelding

Heat is obtained by the friction between the ends of

the two parts to be joined.

axially aligned and pressed tightly against it.

Friction raises the temperature of both the ends. Then

rotation is stopped abruptly and the pressure is

increased to join.

Contd

Machine is similar to a centre lathe.

Power requirements 25 kVA to 175 kVA.

The axial pressure depends on the strength andhardness of the metals being joined.

Pressure 0 MPa for lowcarbon steels to as hi h as 0

MPa foralloy steels.

Contd


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Very efficient.

Wide variety of metals or combinations of metals can

be joined such as aluminium to steel.Grain size is refined

.

Only round bars or tubes of the same size, orconnecting bars or tubes to flat surfaces can join.

One of the components must be ductile.

Friction welding is a solid state welding.

Contd Figfrictionweldingprocess

UltrasonicWelding(USW)

USW is a solidstate welding.

Highfrequency (10 to 200, KHz) is applied.

Surfaces are held together under light normalressure.

Temp. do not exceed onehalf of the melting point.

The ultrasonic transducer is same as ultrasonicmachining.

Contd

Restricted to the lap joint

Weld thin materialssheet, foil, and wireor theattaching thin sheets to heavier structural members.

Maximum thickness 2.5 mm for aluminum and 1.0mm for harder metals.

um er o me a s an ss m ar me a com na onsand non metals can be joined such as aluminum toceramics or glass.

Equipment is simple and reliable.

Less surface preparation and less energy is needed.

Contd

Applications Joiningthedissimilarmetalsinbimetallics

Makingmicrocircuitelectricalcontacts.

Weldingrefractoryorreactivemetals

Bondingultrathinmetal.

ExplosionWelding

Done at room temperature in air, wateror vacuum.

Surface contaminants tend to be blown off the surface.

yp ca mpac pressures ar m ons o ps .

Well suited to metals that is prone to brittle joints

when heat welded, such as,

Aluminum on steel

Titanium on steel

Contd


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Important factors are,

Critical velocityCritical angle

supports at the edges, or the metal inserts.

Contd

Typically the detonation velocity should not exceed120% of the sonic velocity in the metal.

Contd

High velocity explosives, 45727620 m/s.TNTRDXPETNComposition BComposition C4Datasheet Primacord

Medium velocity explosives, 15244572 m/s Ammonium nitrate Ammonium perchlorate Amatol Nitroguonidine

Dynamites diluted PETN

Contd

Advantages,

Can bond many dissimilar, normally unweldablemetals

The lack of heating preserves metal treatment

e process s compact, porta e, an easy to conta n

Inexpensive

No need for surface preparation

Contd

Disadvantages,

The metals must have high enough impact resistance,and ductility (at least 5%)

The cladding plate cannot be too large.

,chambers, buried in sand/water.

Contd

Typicalapplications:

Verylargeplatescanbecladded.

Joinsdissimilarmetals.

(titaniumtosteel,Altosteel,AltoCuetc.)

Jointubetotubesheetsoflargeheatexchangers.

Contd


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Autogeneous Welding

Autogeneous welding or fusion of the parent

material in an inert gas shield without the useof filler metals.

MicroPlasmaArcWeld(PAW)

Similar to GTAW except the plasma caused by the arc

is constricted by a watercooled orifice

Argon is used as the shielding gas.

Brazin andSolderin

BrazingandSolderingBrazing is the joining of metals through the use of heat

and a filler metal whose melting temperature is above450C; but below the melting point of the metals beingjoined.

Comparison with welding and the brazing process1. e compos t on o t e raz ng a o y s s gn cant y different from that of the base metal.

2. Thestrength of the brazing alloy is substantially lowerthan that of the base metal.

3. Themelting pointof the brazing alloy is lower than thatof the base metal, so the base metal is not melted.

4. Capillary action or capillary attraction draws themolten filler metal into the joint, even against the flow ofgravity.


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Brazingprocesshasseveraldistinct

advantages:

1. All metals can be joined.

2. Suited for dissimilar metals.

3. Quick and economical.

4. Less defects.

Contd

Corrosion prone

Brazingmetalsaretypicallyalloyssuchas,

Brazingbrass(60%Cu,40%Zn)

Manganesebronze

Coppersilicon

Silveralloys(with/withoutphosphorous)

Copperphosphorous

Contd

Extremelyclean surface needed.

Fluxes used are combinations of borax, boric acid,

chlorides, fluorides, tetraborates and other wetting

agents.

Contd

A popular composition is 75% borax and 25% boric

acid.

Sodium cyanide is used in brazing tungsten to copper.

.


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BrazeWelding

Capillary action is not required.

Edge preparation needed.

.

Contd

Done with an oxyacetylene torch.

Fig.BrazeWelding

Soldering

By definition,solderingis a brazing type of operation

where the filler metal has a melting temperature

below 0C.

Strength of the filler metal is low.

Soldering is used for aneat leakproof jointor a low

resistanceelectrical joint.

Not suitable for hightemp. application.

Contd

Effective soldering generally involves six importantsteps:

(1) Design of an acceptable solder joint,

(2) Selection of the correct solder for the job,

(3) Selection of the proper type of flux,

(4) Cleaning the surfaces to be joined,

(5) Application of flux, solder, and sufficient heat toallow the molten solder to fill the joint by capillaryaction and solidify, and

(6) Removal of the flux residue, if necessary.

SolderMetals

Most solders are alloys of lead and tin.

Three commonly used alloys contain 60, 50, and 40%

.

Contd

SolderFlux

Ammonium chloride or rosin for soldering tin

Hydrochloric acid and zinc chloride for soldering

galvanized ironSome fluxes are corrosive and should be removed after

use


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Silver solders uses for highertemperature service,Electrical and Electronic purpose.

DifficultieswithGreyCastIronSoldering and brazing are difficult of grey cast Iron dueto surface contamination with graphite having a very low

surface energy.

Weldingdesignanddefect

Welding Problem Causes

Cracking of weld metal High joint rigidity

Cracking of base metal Excessive stresses

Spatter Arc blow

Distortion Poor oint selection

Slag inclusion Improper cleaning in multi-

pass welding

Porosity Excessive H2, O2, N2, in the

welding atmosphere or Damp

electrodes

LamellarTearing inclusionssuchasMn FeandS

inthe

base

metal

and/or

residualstress

Residualstress The residual stresses result from the restrained expansion

and contraction that occur during localized heating andcooling in the region of weld deposit.

The magnitude of residual stresses depends on the weldmentdesi n su ort and clam in of the com onents bein,welded, their materials, welding process used, partdimensions, welding sequence, post weld treatment, size ofthe deposited weld beads, etc.

Residual stresses should not have a harmful effect on thestrength performance of weldments, reduces fatigue

strength, May cause distortion. This residual stress mayresult in the cracking of a brittle material and is notimportant as far as a ductile material.


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Resistance

By SKMondalCompiledby:SKMondal MadeEasy

IES2003

Inresistancewelding,heatisgeneratedduetothe

resistancebetween(a) Electrodeandworkpiece

(c) Twodissimilarmetalsbeingincontact

(d) Interatomicforces

Ans.(b)

Compiledby:SKMondal MadeEasy

IES2001

Themaximumheatinresistanceweldingisatthe

(a) Tipofthepositiveelectrode

(b) Tipofthenegativeelectrode

c opsur aceo ep a ea e meo e ec r ccontactwiththeelectrode

(d) InterfacebetweenthetwoplatesbeingJoined

Ans.(d)


GATE2008In arc welding of a butt joint, the welding speed isto be selected such that highest cooling rate isachieved. Melting efficiency and heat transferefficiency are 0.5 and 0.7, respectively. The area oft e we cross section is 5 mm2 an t e unitenergy required to melt the metal is 10 J/mm3. Ifthe welding power is 2 kW, the welding speed inmm/s is closest to

(a) 4 (b) 14 (c) 24 (d) 34

Ans. (b)Compiledby:SKMondal MadeEasy

GATE2006In an arc welding process, the voltage and currentare 25 V and 300 A respectively. The arc heattransfer efficiency is 0.85 and welding speed is 8

mm/see. The net heat input (in J/mm) is(a) 64

(b) 797

(c) 1103

(d) 79700

Ans. (b)


GATE2007Two metallic sheets, each of 2.0 mm thickness, are welded in a lap jointconfiguration by resistance spot welding at a welding current of 10 kA andwelding time of 10 millisecond. A spherical fusion zone extending up to the fullthickness of each sheet is formed. The properties of the metallic sheets aregivenas:ambient temperature = 293 Kmelting temperature = 1793 K

latent heat of fusion = 300 kJ/kgdensity = 7000 kg/m3

specific heat = 800 J/kg KAssume:(i) Contact resistance along sheetsheet interface is 500 microohm and alongelectrodesheet interface is zero;(ii) No conductive heat loss through the bulk sheet materials; and(iii) The complete weld fusion zone is at the melting temperature.The melting efficiency (in %) of the process is(a) 50.37 (b) 60.37 (c) 70.37 (d) 80.37

Ans. (c)



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GATE2005Spot welding of two 1 mm thick sheets of steel

(density = 8000 kg/m3

) is carried out successfullyby passing a certain amount of current for 0.1second through the electrodes. The resultant weldnugget orme is 5 mm in iameter an 1.5 mmthick. If the latent heat of fusion of steel is 1400kJ/kg and the effective resistance in the weldingoperation in 200 , the current passing through theelectrodes is approximately

(a) 1480A (b) 3300 A

(c) 4060 A (d) 9400 A Ans. (c)Compiledby:SKMondal MadeEasy

GATE2001Resistance spot welding is performed on two

plates of 1.5 mm thickness with 6 mm diameterelectrode, using 15000 A current for a timeduration of 0.25 seconds. Assuming the interfaceresistance to e 0.0001 , t e eat generate toform the weld is

(a) 5625 Wsec (b) 8437 W sec

(c) 22500 Wsec (d) 33750 W sec

Ans. (a)


GATE2004Two 1 mm thick steel sheets are to be spot weldedat a current of 5000 A. Assuming effectiveresistance to be 200 microohms and current flowtime of 0.2 second, heat generated during theprocess wi e

(a) 0.2 Joule (b) 1 Joule

(c) 5 Joule (d) 1000 Joules

Ans. (d)


GATE1992For resistance spot welding of 1.5 mm thick steelsheets, the current required is of the order of

(a) 10 A

b 100 A

(c) 1000 A

(d) 10,000 A

Ans. (d)


GATE2010Two pipes of inner diameter 100 mm and outerdiameter 110 mm each joined by flash butt

welding using 30 V power supply. At the interface,1 mm of material melts from each pipe which has

. .64.4 MJm3, then time required for welding inseconds is

(a) 1 (b) 5 (c) 10 (d) 20

Ans. (c)


IAS2003

Assertion (A): Spot welding is adopted to weld twooverlapped metal pieces between two electrode points.

Reason (R): In this process when current is switched on,the lapped piecesof metal are heated in a restricted area.

a Both A and R are individuall true and R is the correctexplanation of A

(b) Both A and R are individually true but R is not thecorrect explanation of A



Ans. (a)



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Calculate the melting efficiency in the case of arc

welding of steel with a potential of 20 V and current of200 A. The travel speed is 5 mm/s and the crosssectional area of the joint is 20 mm2. Heat required to

Example1

melt steel may be taken as 10 / and the heat transferefficiency as 0.85.

[PTU2004]


Example2

Calculate the melting efficiency in the case of

arcwelding of steel with a potential of 20 V and

a current of 200 A. The travel speed is 5 mm/s.

mm2. Heat required to melt steel may be takenas 10 J/mm3 and the heat transfer efficiency as0.85.


Example3

Two steel plates each 1 mm thick are spotwelded at a current of 5000 A. The current flowtime is 0.1 s. The electrodes used are 5 mm in

.its distribution in the weld zone. The effectiveresistance in the operation is 200.


Example4

Two steel sheets of 1.0mm thickness areresistance welded in a lap joint with a current of10 000 A for 0.1 second. The effective resistance

.joint can be considered as a cylinder of 5 mmdiameter and 1.5mm height. The density of steelis 0.00786 g/mm3 and heat required for meltingsteel is 10 J/mm3.


How much heat would be generated in the spotwelding of two sheets of 1 mm thick steel that

re uired a current of 10000 A for 0.1 seconds?

Example5

An effective resistance of 100. is assumed.


Example6

Two 1.2 mm thick, flat copper sheets are being spotwelded using a current of 6000 A and a current f lowtime of t = 0.18 s. The electrodes are 5 mm in diameter.

Estimate the heat generated in the weld zone. Takeeffective resistance as 150.



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Example7

Two steel sheets of 1.0mm thickness are resistance

welded in a projection welding with a current of 30000 A for 0.005 second. The effective resistance of thejoint can be taken as 100 micro ohms. The joint can beconsi ere as cyin er o 5 mm iameter an 1.5 mmheight. The density of steel is 0.00786 g/mm3 and heatrequired for melting steel is 10 J/mm3.


OtherWeldingTec n que


IES2000

Considerthefollowingprocesses:

1. Gaswelding

2. Thermit welding

. Arcweldin

4. Resistancewelding

Thecorrectsequenceoftheseprocessesinincreasingorderoftheirweldingtemperaturesis

(a) 1,3,4,2 (b) 1,2,3,4

(c) 4,3,1,2 (d)4,1,3,2

Ans.(d)Compiledby:SKMondal MadeEasy

IAS2003

Whichoneofthefollowingisnotanelectricresistancemethodofwelding?

(a) Electroslagwelding

(c) Seamwelding

(d) Flashwelding

Ans.(a)


IAS2000

Considerthefollowingweldingprocesses:

1. TIGwelding 2. Submergedarcwelding

3. Electroslagwelding4. Thermit welding

c o esewe ngprocessesareuse orwe ngthickpiecesofmetals?

(a) 1,2and3 (b) 1,2and4

(c) 1,3and4 (d) 2,3and4

Ans.(d)


IES2004

Assertion (A): In electron beam welding process,vacuum is an essential process parameter

Reason (R): Vacuum provides a highly efficient

shield on weld zone(a) Both A and R are individually true and R is thecorrect explanation of A

(b) Both A and R are individually true but R isnotthecorrect explanation of A



Ans. (d)Compiledby:SKMondal MadeEasy


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IES2002

Inwhichoneofthefollowingweldingtechniques

isvacuumenvironmentrequired?(a) Ultrasonicwelding

(c) Plasmaarcwelding

(d) Electronbeamwelding

Ans.(d)


IES1993

Electronbeamweldingcanbecarriedoutin

(a) Openair

(b) Ashieldinggasenvironment

c pressur ze ner gasc am er

(d) Vacuum

Ans.(d)


IAS2004

WhichoneofthefollowingweldingprocessesconsistsofsmallerHeatAffectedZone(HAZ)?

(a) Arcwelding (b) Electronbeamwelding

Ans.(b)


IES2007

Considerthefollowingstatementsinrespectofthelaserbeamwelding:

1. Itcanbeusedforweldinganymetalortheircombinationsbecauseofveryhightemperatureofthe

.

2. Heataffectedzoneisverylargebecauseofquickheating.

3. Highvacuumisrequiredtocarrytheprocess.

Whichofthestatementsgivenaboveis/arecorrect?

(a) 1and2only (b) 2and3only

(c) 1only (d) 1,

2and

3

Ans.(c)Compiledby:SKMondal MadeEasy

IES2006

Whichoneofthefollowingweldingprocessesconsistsofminimumheataffectedzone(HAZ)?

(a) ShieldedMetalArcWelding(SMAW)

(c) UltrasonicWelding(USW)

(d) MetalInertGasWelding(MIG)

Ans.(b)


IAS2007

Consider the following welding processes:

1. Arc welding 2. MIG welding

3. Laser beam welding 4. Submerged arc

Select the correct sequence in increasing order of Heataffected zone (HAZ) using the code

given below:

(a) 123 4 (b) 142 3

(c) 324 1 (d) 432 1

Ans. (c)Compiledby:SKMondal MadeEasy


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IAS1999

Match List I (Shielding method) with List II (Weldingprocess) and select the correct answer using the codes

given below the lists:List I List IIA. Flux coating 1. Gas metal arc welding

. ux granu es 2. u merge arc we ngC. CO2 3. Shielded metal arc weldingD. Vacuum 4. Laser beam welding

5. Electron beam weldingCodes:A B C D A B C D(a) 1 2 5 3 (b) 1 4 2 5(c) 3 5 1 4 (d) 3 2 1 5

Ans. (d)


GATE2007Whichoneofthefollowingisasolidstatejoining

process?(a) Gastungstenarcwelding

b Resistances otweldin

(c) Frictionwelding

(d) submergedarcwelding

Ans.(c)


GATE1992Inanexplosiveweldingprocess,the..(maximum/minimum)velocityofimpactisfixedbythevelocityofsoundinthe(flyer/target)platematerial

(a) Maximum;target

(b) Minimum;target

(c) Maximum;flyer

(d) Minimum;flyer

Ans.(c)Compiledby:SKMondal MadeEasy

IES2011 S1ContdMatchListIwithListIIandselectthecorrectanswerusingthecodegivenbelowthelists:

ListI ListII

A.Laserbeamwelding

1.Canbeappliedforweldingorrefractorymetalslikeniobium,tantalum,molybdenumandtungsten.

B.Electron 2.Asoundandcleanweldedjointiscreatedduetobeamwelding rubbingoftwopartsagainsteachotherwith

adequatespeedandpressureproducingintenseheatraisingtemperatureabovemeltingpoint.

C.Ultrasonicwelding

3.Cleanheatsourcecreatedmuchawayfromjob,anarrowspotisheated,workchamber operatesinahighvacuum.

D.Friction

welding4.

Clean

heat

source

very

quick

heating,

very

small

focalspot,novacuumchamberisrequired.Compiledby:SKMondal MadeEasy

IES2011 FromS1Codes:

A B C D A B C D

(a) 4 3 1 2 (b) 2 3 1 4

(c) 4 1 3 4 (d) 2 1 3 4Ans.(a)


IES2009MatchListIwithListIIandselectthecorrectanswerusingthecodegivenbelowtheLists:ListI ListII(WeldingProcess) (Application )

A. Laserwelding 1. UnitinglargeareasheetsB. Frictionwelding 2. Repairinglargeparts

. . D. Explosivewelding 4 . Fab ri cati onofnuclearreactor

components5. Weldingverythinmaterials

Code:(a) A B C D (b) A B C D

5 4 3 2 1 4 2 5

(c) A B C D (d) A B C D1 3 4 2 5 3 4 1

Ans.(d)



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IAS2002

MatchListI,(Welding)withListII(Application)andselectthecorrectanswerusingthecodesgivenbelowtheLists:

ListI ListII(Welding) (Application)A. Explosive 1. JoiningthicksheetsB. Ultrasonic 2. ManufactureofheatexchangesC. Thermit 3. Joiningthinsheetsorwiresof

similar/dissimilar metalsD. Projection 4. Joininghydraulicpistonrodsfor

agricultural machinery5. Joiningrails,pipesandthicksteel

sectionsCodes:A B C D A B C D(a) 2 5 1 3 (b) 4 5 1 3(c) 2 3 5 1 (d) 4 3 5 1

Ans.(c)


IAS2001

MatchListI(Weldingprocesses)withListII(Features)andselectthecorrectanswerusingthecodesgivenbelowtheLists:

ListI ListIIA. Ultrasonicwelding 1. Gasheatedtoionizedcondition

forconductionofelectriccurrentB. Electronbeamwelding 2. Highfrequencyandhigh

intensityvibrationsC. Plasmaarcwelding 3. Concentratedstreamofhigh

energyelectrons4. Exothermalchemicalreaction

Codes: A B C A B C(a) 1 2 4 (b) 4 3 1(c) 2 1 4 (d) 2 3 1

Ans.(d)


JWM2010MatchListIwithListIIandselectthecorrectanswerusingthecodegivenbelowthelists:

ListI ListII

A.Atomichydrogenwelding

1.Twopiecesarebroughttogetherandpowersupplyisswitchedon

Code:A B C D A B C D

(a) 4 3 2 1 (b)

1

3 2 4(c) 4 2 3 1 (d) 1 2 3 4

. welding

.twoplates

C.Spotwelding 3.Gasisionized

D.Flashwelding 4.Inertgasshieldedarcwelding


Brazin andSolderin


GATE2005Thestrengthofabrazedjoint

(a) Decreaseswithincreaseingapbetweenthetwojoiningsurfaces

(b) Increases

with

increase

in

gap

between

the

two

o n ngsur aces

(c) Decreasesuptocertaingapbetweenthetwojoiningsurfacesbeyondwhichitincreases

(d) Increasesuptocertaingapbetweenthetwojoiningsurfacesbeyondwhichitdecreases

Ans.(d)


IES2006

Whichoneofthefollowingisnotafusionweldingprocess?

(a) Gaswelding

(c) Brazing

(d) Resistancewelding

Ans.(c)



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IES1994

MatchList IwithList IIandselectthecorrectanswerusingthecodesgivenbelowtheLists:

ListI(Filler) ListII(Joiningprocess)A. Cu,Zn,Agalloy 1. Brazewelding.B. Cu,Sn,alloy 2. BrazingC. Pb,Sb,alloy 3. SolderingD.Iron oxideandaluminium powder4. TIGweldingof

aluminiumCodes:A B C D A B C D(a) 2 1 3 (b) 1 2 4 (c) 2 1 3 4 (d) 2 3 4

Ans.(a)


IAS1996

MatchListIwithListIIandselectthecorrectanswerusingthecodesgivenbelowthelists

ListI ListII(Fillerrodmaterial) (Joiningprocess)A. Mildsteel 1. MIGweldingB. Bronze 2. SolderingC. Brass 3. BrazingD. Leadandtinalloy 4. Thermit welding

5. BrazeweldingCodes:A B C D A B C D(a) 1 5 3 2 (b) 4 3 2 5(c) 4 3 5 2 (d) 1 3 5 4

Ans.(a)


IES2004

MatchListI(Welding problems)withListII(Causes)andselectthecorrectanswerusingthecodesgivenbelowtheLists:ListI ListIIA. Crackingofweldmetal 1. ExcessivestressesB. Crackingofbasemetal 2. Highjointrigidity

. . frompreviousdeposit

D. Inclusions 4. Oxidation5. Exces siveH2,O2,N2,in

theweldingatmosphereCodes:A B C D A B C D(a) 2 1 5 3 (b) 3 4 2 1(c) 2 4 5 3 (d) 3 1 4 2

Ans.(a)


IES2003

MatchListI(WeldingDefects)withList II(Causes)andselectthecorrectanswerusingthecodesgivenbelowtheLists:ListI ListII(WeldingDefects) (Causes)

. patter 1. ampe ectro esB. Distortion 2. ArcblowC. Slaginclusion 3. Impropercleaningin

multipassweldingD. Porosity 4. PoorjointselectionCodes:A B C D A B C D(a) 4 2 3 1 (b) 4 2 1 3

(c)

2 4 1 3 (d)

2 4 3 1Ans.(d)


IES2004

Consider the following statements:

The magnitude of residual stresses in weldingdepends upon

1. Design

of

weldment2. Supportan c amp ngo components

3. weldingprocessused

4. Amountofmetalmelted/deposited


(a) 1,2and4 (b)1,2and3

(c) 1and3 (d)2and3

Ans.(b)Compiledby:SKMondal MadeEasy

GATE2003Matchthefollowing

Workmaterial Typeofjoining

P.Aluminium 1. SubmergedArcWelding

Q.DieSteel 2. Soldering

R.Copper

Wire 3. Thermit Welding

S.Titaniumsheet 4. AtomicHydrogenWelding

5. GasTungstenArcWelding

6. LaserBeamWelding

7. Brazing

(a)P2 Q5 R1 S3

(b)P6 Q3 R4 S4

(c)P4 Q1 R6 S2

(d)P5 Q4 R2 S 6

Ans.(d) Compiledby:SKMondal MadeEasy


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IES2004

Considerthefollowingstatements:

Thesize

of

the

heat

affected

zone

(HAZ)

will

increase

with

1. Increasedstartingtemperature

2. Increasedweldin s eed.

3. Increasedthermalconductivityofthebasemetal

4. Increaseinbasemetalthickness


(a) 1,2and3 (b) 1and3

(c) 1and4 (d) 2and3

Ans.(b)Compiledby:SKMondal MadeEasy

IES1992

Weldspatteroccursduetoanyofthefollowing

except(a) Highweldingcurrent

(c) Arc

(d) Wrongpolarity

Ans.(d)


JWM2010Assertion (A) : Spatter is one of the welding defects.

Reason (R) : In submerged arc welding process,there is no spatter of molten metal.

(a) Both A and R are individually true and R is the

(b) Both A and R are individually true but R isnot thecorrect explanation of A



Ans. (b)Compiledby:SKMondal MadeEasy

IES1998

Anarcweldedjointisshownintheabovefigure.Thepartlabelled 'B'inthefigureisknownas

(a) Weldpreparation

(b) Penetration

(c) Reinforcement

(d) Slag

Ans.(c)


IES2004

Assertion (A): A sound welded joint should not onlybe strong enough but should also exhibits a goodamount of ductility

Reason (R): Welding process is used for fabricating

(a) Both A and R are individually true and R is the correctexplanation of A

(b) Both A and R are individually true but R is not thecorrect explanation of A



Ans. (c)Compiledby:SKMondal MadeEasy

IAS2003

Toolmaterialnotsuitedtoresistanceweldingis

(a) Aluminium oxide (b) Stellite

(c) Highspeedsteel (d) Masonite

Ans.(a)



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GATE1996Preheatingbeforeweldingisdoneto

(a) Makethe

steel

softer

(b) Bumawayoil,grease,etc,fromtheplatesurface

(d) Preventplatedistortion

Ans.(c)


IES2011Coldcrackinginsteelweldments dependson

1.Carbonequivalent

2.Heat

input

3.Effectivethickness

3. y rogencontent nwe poo

(a)1,2and3only

(b)1,2and4only

(c)2,3and4only

(d)1,2,3and4

Ans.(d)


GATE2001Two plates of the same metal having equalthickness are to be butt welded with electric arc.

When the plate thickness changes, welding isachieved by

(a) Adjusting the current

(b) Adjusting the duration of current

(c) Changing the electrode size

(d) Changing the electrode coating

Ans. (a)

Compiledby:SKMondal MadeEasy Compiledby:SKMondal MadeEasy

welding complete ppt

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