ARC WELDINGPRESENTED BY

PRACTICAL APPLICATIONS OF WELDING • Aircraft construction

• Automobile construction• Bridges• Buildings• Pressure vessels• Storage tanks• Rail road equipments• Pipes and pipelines• Ships• Trucks and trailers• Machine tools

APPLICATIONS OF WELDING

• Earth moving machinery And Cranes

• Repair and maintenance work

• Hard-facing and rebuilding

• Fabrication of jigs and fixtures.

• House hold furniture

METAL JOINING METHODSTemporary joints

- Riveting, Seaming or Hooking, Brazing, Bolting & soldering

Permanent Joint -WELDING

METHOD OF WELDING

• Fusion welding - arc welding, gas welding

• Non-fusion welding - silver soldering, brazing.

• Pressure welding - Forge welding or resistance welding

CLASSIFICATION OF WELDING PROCESSES

Electric welding

• Electric arc welding• Electric resistance welding• Laser welding• Electron beam welding

Electric arc welding - Metallic arc welding - Carbon arc welding - Atomic hydrogen arc welding - Inert gas arc welding - Co2 welding - Submerged arc welding• - Electro-slag welding• - Plasma arc welding

Electric resistance welding

- Spot welding - Seam welding - Butt welding - Flash butt welding - Projection welding

Gas welding processes

- Oxy-acetylene gas welding - Oxy-hydrogen gas welding - Oxy-coal welding - Oxy-liquefied petroleum welding

The other welding processes

- Thermit welding - Forge welding - Friction welding - Ultrasonic welding - Explosive welding - Cold pressure welding - Plastic welding.

PRINCIPLE OF ARC WELDING

• When the high current passes through an air gap from one conductor to another, it produces very intense and concentrated heat in the form of a spark, which can melt and fuse the metal very quickly to produce a homogeneous weld.

ARC WELDING PROCESSES ORSHIEDED METAL ARC WELDING

• In Arc welding process the source of heat is electricity

• The flux coating melts produces a gaseous shield and slag to prevent atmospheric contamination of molten weld metal. (Hence this arc is called shielded arc).

Manual Metal Arc Welding-MMAW

• The welding current is provided by an AC or DC.

• The welding speed and feed of the electrode is controlled manually by the welder himself. (Called Manual Metal Arc Welding-MMAW)

• The arc welding temperature between 3600°C-4000°C

CURRENT • Electrons in motion is called

current.

• The rate of flow of electrons is `measured in amperes (unit). The measuring instrument is called ampere meter or ammeter.

ELECTRIC PRESSURE

• It is the pressure which makes the electric current to flow it is called voltage or electro motive force. Its measuring unit is VOLT. The measuring is called volt mete.

Open circuit voltage

• The voltage in between two terminals before strike the arc is called open circuit voltage.

Close circuit voltage

• The voltage in between two terminals during welding is called close circuit voltage.

AC• AC means alternating current. It

changes or reverses its direction of flow 50 times per second, if it is 50 cycles.Eg.50 cycles means it changes its direction 50 times per second.

• Its rate of change is called frequency i.e. hertz (HZ). In India the frequency of AC is 50 cycles per second.

DC

• Electric current which always flows in particular direction is known as direct current i.e. negative to positive (electric direction), positive to negative (conventional direction).

WELDING MACHINES

• Alternating current (AC) welding machine

• Direct current (DC) welding machine

• AC machines -- Transformers• DC Machines -- Motor generator set

Engine generator set Rectifier set.

AC WELDING TRANSFORMER• This is a type of welding machine which

converts AC main supply in to AC welding supply.

• AC main supply has high voltage – low ampere.

• AC welding supply has high ampere – low voltage.

AC TRANSFORMER• It is step down transformer, which

reduce the main supply voltage (220 or 440 volts) to welding supply open circuit voltage (OCV), between 40 to 100 volts.

A Transformer may be operated from the mains on single phase, two phases or three phases and may be air – cooled or oil cooled.

ADVANTAGES

• Less initial cost • Less maintenance cost• Freedom from arc blow• Noiseless operations• Higher work efficiency

DIS ADVANTAGES• Not suitable for non-ferrous metals• Fine current setting not possible• It is not suitable for bare and light

coated electrodes• It has more possibility for electrical

shock because of higher open circuit voltage

• It can only be used where electrical mains supply is available.

DC MACHINES

1. Welding generators (Motor generator set)

(Engine generator set) 2. Welding rectifiers

Welding generators • A motor connected to main supply.

(Generate DC welding supply with the help of welding supply.)

• A petrol or diesel engine. (Generate welding supply where electricity main supply is not available with help of engine driven sets.)

Welding rectifier • A welding rectifier set is used to

convert A/C welding supply in to DC welding supply. (It consists of a step down transformer and a welding current rectifier cell cooling fan.)

• It can be designed to provide either

AC/DC welding supply by changing a switch.

ADVANTAGES OF DC WELDING MACHINE

• 1. Polarity system

• 2. It can be used successfully to weld both ferrous and non- ferrous metals,

thin sheets, cast iron metals.

• 3. Bare wires and light coated electrode can be easily used.

ADVANTAGES

• 4. Positional welding is easy due to polarity advantage.

• 5. It can be run with the help of diesel or petrol engine where electrical mains supply is not available.

6. It has less possibility for electrical shock

because of less Open circuit voltage

DIS-ADVANTAGES

Higher initial cost A higher operating cost A higher maintance cost

Trouble of arc blow during welding Noisy operation Occupies more space.

ARC WELDING ACCESSORIES 1. Electrode holder 2. Earth clamp 3. Welding cables 4. Helmet and hand shield 5. Chipping hammer 6. Chipping goggles 7. Wire brush 8. Tongs 9. Lather gloves 10. Lather apron 11. Safety shoe.

Electrode holderElectrode holder

• It is a clamping device used to grip and manipulate the electrode during arc welding. It’s made of copper/copper alloy for better electrical conductivity. Holders are made in various sizes.

• i.e.200Ampsto 500 Amps.

Helmet and Hand shieldHelmet and Hand shield These are used to protect the eyes and face These are used to protect the eyes and face

of a welder from the arc radiation and sparks of a welder from the arc radiation and sparks during arc welding. during arc welding. Colored (filter) glasses are made Colored (filter) glasses are made in various shades: in various shades:

Shade no. Range of welding AmpsShade no. Range of welding Amps 8 - 9 up to 1008 - 9 up to 100 10-11 100 to 30010-11 100 to 300 12-14 above 30012-14 above 300

Earth clampEarth clamp

• It is used to connect the earth cable It is used to connect the earth cable firmly to the job or welding. It is also firmly to the job or welding. It is also made of copper/copper alloys made of copper/copper alloys

Welding cables

• These are used to carry the welding current from the welding machine. Cables are made of supper flexible rubber insulation, having fire copper wires and woven fabric reinforcing layers.

Chipping hammerChipping hammer

►It is a welding tool used to It is a welding tool used to remove the slag from the remove the slag from the weld bead. (Medium carbon weld bead. (Medium carbon steel)steel)

Wire brushWire brush

•It is used for to protect It is used for to protect the eyes while chipping the eyes while chipping the slag or grinding the the slag or grinding the job.job.

Tongs • Tongs are used for holding hot

work pieces and for holding the pieces in position.

Lather gloves These are used to protect the hands

of a welder from electric shock, arc flash, heat, sparks and spatters

Lather apron• It is used to protect the chest, the

front and rear body and the arms a welder during welding.

Safety shoes

It is used to protect the feet of the welder from metal spatter.

COMMONLY WELED BASE METAL

•Metals can be classified as

Ferrous metal Non-ferrous metal

Ferrous metal • Which metal contains iron

substance is called ferrous metal. Wrought iron Carbon steel Stainless steel Cast iron Cast steel Alloy steel.

Non-ferrous metal

• Non-ferrous materials are

those that are not iron-based. Aluminum and its alloys Magnesium and its alloys Nickel and its alloys,

etc.

Ferrous alloy One more ferrous metal added is

called ferrous alloy

Non ferrous alloy

One more non-ferrous metal added is called non ferrous alloy.

MELTING POINTS OF METALSMELTING POINTS OF METALS

•Tin 232ºC•Lead 343ºC•Zinc419ºC•Silver 960ºC•Copper 1082ºC•Nickel 1449ºC•Cast iron1232ºC

•AluminiumAluminium 621 - 648ºC621 - 648ºC•BronzeBronze 882 - 915ºC882 - 915ºC•BrassBrass 926 - 982ºC926 - 982ºC•Monal metalMonal metal 1343ºC1343ºC•High carbon steelHigh carbon steel 1371ºC1371ºC•Medium carbon steelMedium carbon steel 1426ºC1426ºC

MELTING POINTS OF METALSMELTING POINTS OF METALS

• Mild steelMild steel 1500 - 1530ºC1500 - 1530ºC• Stain less steelStain less steel 1426ºC1426ºC• Low carbon steelLow carbon steel 1510ºC1510ºC• Wrought ironWrought iron 1593ºC1593ºC• TungstenTungsten 3410ºC3410ºC

MELTING POINTS OF METALSMELTING POINTS OF METALS

SAFETY RECOMMENDATIONS IN WELDING

• Welding and cutting of metals involve the application of intense heat to the objects being welded or cut.

• The intense welding heat and the sources employed to produce it can be potentially hazardous. There fore, to protect persons from injury and to protect building and equipment against fire, etc,.

welding and cutting safety

• Safety recommendations for installation and operation of arc welding & cutting equipment.

• Explosion, fire and other hazards and protection against them.

• Protection of welders.• Ventilation and health

protection.

GENERAL PRECATIONS• Fire extinguishers or sand should be

available at hand.• Do not pick up hot jobs or objects.• Use goggles with non-flammable

lenses and frames.

• Never do any chipping or grinding without suitable goggles.

• Do not use matches for lightning torches. This may result in hard burns.

GENERAL PRECATIONS….

• If welding or cuttings is to be stopped permanently, release all pressures from the regulators.

• Arc welding machines should be properly ground.

• Welder should wear dry and fire-proof protective clothes (apron, gloves, etc.) to prevent the arc rays from reaching his body.

• To prevent welders from radiation, spatter and hot slag, a helmet or hand shield must be worn.

ARC LENGTH

•The distance between the Tip of Electrode and the surface of the job it is called a ‘ARC Length’.

MEDIUM ARC

•The correct arc length or Medium or Normal arc length is approximately equal to the diameter of the core wire of the electrode.

SHORT ARC

•If the distance between the tip of electrode and the base metal is less than the dia. of the core wire, it is called a ‘short arc’.

LONG ARC

•If the distance between the tip of the electrode and the base metal is more than the diameter of the core wire it is called a ‘long arc’.

POLARITY SYSTEMPOLARITY SYSTEM Polarity indicates the direction of current Polarity indicates the direction of current flow in the welding circuit.flow in the welding circuit.In DC welding machine heat distribution In DC welding machine heat distribution between the electrode and the base metal between the electrode and the base metal and welding of non-ferrous metaland welding of non-ferrous metal 2/3 2/3 of of the heat is liberated from the positive end the heat is liberated from the positive end and and 1/31/3 from the negative end. from the negative end.To have this advantage of unequal heat To have this advantage of unequal heat distribution in the electrode and the base distribution in the electrode and the base metal, the polarity is an important factor for metal, the polarity is an important factor for successful welding.successful welding.

Kinds of polarityKinds of polarity

1. Straight polarity: -1. Straight polarity: - In straight In straight polarity the electrode is connected to the polarity the electrode is connected to the negative (-) and the work to the positive negative (-) and the work to the positive (+) terminal of the power source.(+) terminal of the power source.

2. Reverse polarity: -2. Reverse polarity: - In reverse In reverse polarity the electrode is connected to the polarity the electrode is connected to the positive (+) and the work to the negative positive (+) and the work to the negative

(-) terminal of the power source.(-) terminal of the power source.

Straight polarity is used Straight polarity is used forfor

Welding with bare, light coated and Welding with bare, light coated and medium coated electrodes.medium coated electrodes.

welding the thicker sections to obtain welding the thicker sections to obtain more fusion and penetration.more fusion and penetration.

Reverse polarity is used Reverse polarity is used for:for:

welding of non-ferrous metalwelding of non-ferrous metal welding of cast ironwelding of cast iron welding with heavy and super-heavy welding with heavy and super-heavy

coated electrodes.coated electrodes. Positional welding, sheet metal Positional welding, sheet metal

welding can possible.welding can possible. (Choice of the polarity depends on (Choice of the polarity depends on

the instruction of the electrode the instruction of the electrode manufacturers.)manufacturers.)

How will you deter mind How will you deter mind the wrong polarity?the wrong polarity?

Lack of fusion of base metalLack of fusion of base metal Rabbit burning of electrodesRabbit burning of electrodes More spatterMore spatter Poor penetration Poor penetration Bead appearance will not be goodBead appearance will not be good Elements will be lossElements will be loss Difficulty in manipulation of arcDifficulty in manipulation of arc Abnormal sound of the arc. Abnormal sound of the arc.

CHARACTERISTIC OF ARC

• Gravity force• Gas expansion• Surface tension• Electro magnetic force

GRAVITY FORCE

• Molten globules formed at the arcing end of the electrode travel towards the job in the molten pool.

• Gravitational force helps the transfer of metal in flat or down-hand position and thus the deposition rate of weld metal is increased.

• WELDING TECHNOLOGY

Presented by

WELDING TECHNOLOGY

ARC WELDING MIG WELDING GAS CUTTING

GAS EXPANSION

SURFACE TENSION

• It is the characteristic (force) of the base metal to attract and retain the molten metal in it. This effect is more useful in the case of positional welding. The short arc promotes more surface tension effect.

ELECTRO MAGNETIC FORCE

• The current passing through the electrode forms magnetic lines of force in the form of concentric circles. This force exerts a pinch effect on the molten metal globule formed at the arcing end of the electrode.

The globule is detached from the electrode and reaches the molten pool under the influence of the magnetic force. This effect is more useful in positional welding.

ARC BLOW

When the arc deviates from the regular path due to the Magnetic disturbances it is

called ‘Arc blow’.

ARC BLOW IN DC WELDING • Whenever a current flows in the

electrode a magnetic field is formed around the electrode. Likewise a similar magnetic field is also formed around the base metal.

Due to interaction of these two magnetic fields, the arc is blown to one side forward or backward of the joint.

EFFECTS OF ARC BLOW • More spatter with less deposition

of weld metal.• Poor fusion/penetration.• Weak weds.• Difficulty in depositing weld metal

at the required place in the joint.

METHODS USED TO CONTROL THE ARC BLOW

• Welding away from the earth connection• Changing the position of the earth connection

of the work.• Changing the position of the work on the

welding table• Wrapping the welding cable fewer times

around the work,• Holding the correct electrode angle with a

short arc.• Use ‘run on’ and ‘run off’ plates.

Effect of variations in welding procedure

ARC WELDING

Correct weld • With the correct arc length, rate of

travel, current setting, angle of electrode, and technique, the deposited metal will be uniform width and height, and will produce fine ripple face appearance, free from surface defects i.e. slag inclusion, porosity, lack of penetration, undercut, overlap, etc.

Current too low

•Uneven of bead•Poor penetration•Slag inclusions in weld• Irregular ripples

Current too high

• Wide and flat beads in uneven shape

• Excessive penetration• More spatter• Ripples very poor in appearance• Porosity in crater and bead• Undercut

Arc too short

• Unequal width height of bead• Irregular ripple• Burn through and more

chances of Electrode freezing

Arc too long

• Unequal height of bead• Wide, coarse ripples• Crater with Blowholes and more

spatter• Insufficient root and base metal

penetration

Travel too slow

• More width and height of bead• Control of deposited metal poor• Slag inclusion may appear• Overlap

Travel too past

• Narrow width bead• Porosity in crater• Inadequate fusion of bead with parent metal• Elongated ripples.

Welding PositionWelding Position

1. Down hand / Flat position1. Down hand / Flat position2. Horizontal position2. Horizontal position3. Vertical position3. Vertical position4. Overhead position4. Overhead position5. Inclined position5. Inclined position

Welding jointsWelding joints

Butt jointButt jointTee jointTee jointLap jointLap jointCorner jointCorner joint

ELECTRODESELECTRODES

DefinitionDefinition

An electrode is a metallic wire of An electrode is a metallic wire of standard size and length standard size and length generally coated with flux ( may generally coated with flux ( may be bare or without flux coating be bare or without flux coating also).also).

Classification of Classification of ElectrodesElectrodes

MMAW Electrodes are classified MMAW Electrodes are classified based on the following factors.based on the following factors.

1.1. Method of coating Method of coating 2.2. Coating factorCoating factor3.3. Type of flux coatingType of flux coating4.4. Purpose of flux coatingPurpose of flux coating5.5. Core wire material.Core wire material.

Method of coatingMethod of coating

Dipping MethodDipping Method

Extrusion MethodExtrusion Method

Dipping MethodDipping Method

The core wire is dipped in a The core wire is dipped in a container Carrying flux paste. container Carrying flux paste.

The coating thus obtained on the The coating thus obtained on the core wire is not uniform resulting core wire is not uniform resulting in non- uniform melting; hence in non- uniform melting; hence this method is not popular.this method is not popular.

Extrusion MethodExtrusion Method A straightened wire is fed into an A straightened wire is fed into an

extrusion press where the coating is extrusion press where the coating is applied under pressure. The coating applied under pressure. The coating thus obtained on the core wire is thus obtained on the core wire is uniform and concentric, resulting in uniform and concentric, resulting in uniform melting of the electrode. uniform melting of the electrode.

This Method is used by all the This Method is used by all the electrode manufacturers. electrode manufacturers.

Coating FactorCoating FactorThe ratio of the coating diameter The ratio of the coating diameter

to the core wire diameter is called the to the core wire diameter is called the coating factor.coating factor.

Coating factor =Coating factor =coating dia.of electrode/core wire dia.ofcoating dia.of electrode/core wire dia.of

electrodeelectrode 1.25 to 1.3 1.25 to 1.3

mmmmLight coated electrodeLight coated electrode

1.4 to 1.5 mm1.4 to 1.5 mm Medium coated Medium coated electrodeelectrode

1.6 to 2.2 mm1.6 to 2.2 mm Heavy coated Heavy coated electrodeelectrode

Types of Flux coatingTypes of Flux coating

Cellulosic Cellulosic Rutile Rutile Iron oxideIron oxideBasic coatedBasic coated

Cellulose coatingCellulose coatingThese electrodes have a thin These electrodes have a thin

coating with contains mostly coating with contains mostly cellulose.cellulose.

These give deep penetration These give deep penetration because the flux coating because the flux coating produces more gases.produces more gases.

Very little slag is formed on Very little slag is formed on the weld. These electrode can be the weld. These electrode can be used for all position welding.used for all position welding.

Rutile coated electrodeRutile coated electrodeThese electrode have medium thick These electrode have medium thick

coating. These coating contains coating. These coating contains mostly silicates and a little % of mostly silicates and a little % of cellulose.cellulose.

These electrode are used for welding in These electrode are used for welding in - wider gap filling- wider gap filling- improperly prepared joints- improperly prepared joints- structural works, ship building,- structural works, ship building,- storage tanks, gas containers,- storage tanks, gas containers,- medium and high pressure pipe lines- medium and high pressure pipe lines

Iron oxide coated electrodesIron oxide coated electrodes

These electrodes have heavy These electrodes have heavy coating. The coating contains mainly coating. The coating contains mainly iron oxide and silicates.iron oxide and silicates.

Welding in vertical and overhead Welding in vertical and overhead position is difficult with these position is difficult with these electrodes.electrodes.

Basic coated electrodesBasic coated electrodes Low hydrogen type electrodes Low hydrogen type electrodes called Basic coated electrodes.called Basic coated electrodes. These electrodes have super These electrodes have super heavy coating of flux.heavy coating of flux.

It is only used in DC machine It is only used in DC machine reverse polarity.reverse polarity.

It is mainly used for the welding It is mainly used for the welding of pressure vessels for the of pressure vessels for the following reasons.following reasons.

The arc gives less heatFusion of bigger to medium dropsMolten pool solidifies quicklyVery good quality weldThick and H.S.steels can be welded successfully.