electric arc welding electricity is passed through an electrode which jumps between the electrode...

Electric Arc WeldingElectric Arc Welding

Electricity is passed through an Electricity is passed through an electrode which jumps between electrode which jumps between the electrode and the work the electrode and the work piece. This causes an arc which piece. This causes an arc which produces great heat melting produces great heat melting the electrode and the work the electrode and the work piece causing the edges to fuse piece causing the edges to fuse together. (consumable together. (consumable electrode.)electrode.)

Manual Metal Arc Manual Metal Arc Welding.Welding.

• The weld pool is protected from The weld pool is protected from oxidation by the gasses produced by oxidation by the gasses produced by melting the chemicals on the melting the chemicals on the electrode coating. electrode coating.

• This wire electrode also acts as a This wire electrode also acts as a filler material to fill the gap between filler material to fill the gap between the two parts being joined. the two parts being joined.

• Its third function is to form a slag Its third function is to form a slag which protects the weld area form which protects the weld area form cracking as it allows the joint cool cracking as it allows the joint cool slowly and protect it from oxidation.slowly and protect it from oxidation.

Operation of the Operation of the electrodeelectrode

UsesUses

This has many operational This has many operational uses such as repair work to uses such as repair work to constructional steel. It is constructional steel. It is ideal for outdoor uses as the ideal for outdoor uses as the gasses needed to form the gasses needed to form the shield are not blown away.shield are not blown away.

The Transformer.The Transformer.•This is a device used to This is a device used to

change the voltage of A.C. change the voltage of A.C. current. It can either step up current. It can either step up (increase) or step down (increase) or step down (decrease) the voltage. It is (decrease) the voltage. It is necessary to change the necessary to change the voltage when welding thicker voltage when welding thicker or different types of steel.or different types of steel.

Transformer-rectifier Transformer-rectifier circuitcircuit

Transformer-rectifier circuit - A.C. to Transformer-rectifier circuit - A.C. to D.C.D.C.

• The The transformertransformer circuit element of the circuit element of the circuit take AC current and pass it through circuit take AC current and pass it through a step down transformer reducing the a step down transformer reducing the voltage, the current is increased.voltage, the current is increased.

• The low voltage AC is then passed through The low voltage AC is then passed through a series of diodes which only allow current a series of diodes which only allow current flow in one direction causing it to be flow in one direction causing it to be changed into Direct Current, this is called changed into Direct Current, this is called a a bridge rectifierbridge rectifier..

• Finally the DC current is passed through a Finally the DC current is passed through a ‘smoothing’ ‘smoothing’ capacitorcapacitor which causes the which causes the current flow more evenly.current flow more evenly.

Electric Arc Welding Electric Arc Welding SafetySafety

• Pg 370Pg 370

Metal Arc Gas Shielded Metal Arc Gas Shielded Welding. (MAGS/MIG)Welding. (MAGS/MIG)

MIG (Metal Inert Gas) MIG (Metal Inert Gas) weldingwelding

• Also called MAGS (Metal Arc Gas Also called MAGS (Metal Arc Gas Shielded) weldingShielded) welding

• It uses an inert gas such as Argon or It uses an inert gas such as Argon or CO2 to shield the weldCO2 to shield the weld

• The bare wire electrode is fed The bare wire electrode is fed continuously to the weld - semi-continuously to the weld - semi-automatic processautomatic process

• Can be used on light and heavy plate.Can be used on light and heavy plate.• Does not produce a slag and can be Does not produce a slag and can be

used for multi run welds and by robots.used for multi run welds and by robots.


Electricity is passed through an Electricity is passed through an electrode which jumps between the electrode which jumps between the electrode and the work piece. The electrode and the work piece. The electrode is touched briefly against electrode is touched briefly against the work, this causes an arc which the work, this causes an arc which produces great heat melting the produces great heat melting the electrode and the work piece electrode and the work piece causing the edges to fuse together. causing the edges to fuse together.


Uses.Uses.

•This is one of the most common This is one of the most common ways of welding. It can be used ways of welding. It can be used to weld sheet metal as well as to weld sheet metal as well as heavy plates. As the electrode is heavy plates. As the electrode is fed automatically and no slag is fed automatically and no slag is formed it is ideal for robotic formed it is ideal for robotic welding for example car welding for example car production.production.

Tungsten Arc Gas Shielded Tungsten Arc Gas Shielded Welding. (TAGS/TIG)Welding. (TAGS/TIG)


Principle.Principle.• Two separate current flow in the circuit in this Two separate current flow in the circuit in this

welding process. One is for the arc and is similar to welding process. One is for the arc and is similar to MAGS, the other is a high frequency current used to MAGS, the other is a high frequency current used to start the arc. This means an arc is not stuck by start the arc. This means an arc is not stuck by touching the work piece as before. touching the work piece as before.

Operation.Operation.1.1. The arc melts the two edges to be joined as well as The arc melts the two edges to be joined as well as

the filler rod forming the weld pool. the filler rod forming the weld pool. 2.2. Gas is pumped through the nozzle protecting the Gas is pumped through the nozzle protecting the

weld pool from oxidation.weld pool from oxidation.3.3. The electrode is only to maintain the arc supplying The electrode is only to maintain the arc supplying

the heat. A consumable filler rod fed by the operator the heat. A consumable filler rod fed by the operator gives the extra metal necessary for the weld pool.gives the extra metal necessary for the weld pool.


Uses.Uses.• This is suitable for welding most metals and This is suitable for welding most metals and

generally uses DC current for the power source. generally uses DC current for the power source. However when welding aluminium AC is used. However when welding aluminium AC is used. This is necessary to breakdown the oxide layer This is necessary to breakdown the oxide layer on the outside of the aluminium which has a high on the outside of the aluminium which has a high melting point. It is also suitable for stainless melting point. It is also suitable for stainless steel.steel.

FluxesFluxes

• Active fluxes – Active fluxes – these fluxes are able to these fluxes are able to dissolve oxide films and will prevent oxides dissolve oxide films and will prevent oxides reforming. Zinc chloride is an active flux. Active reforming. Zinc chloride is an active flux. Active fluxes are corrosive. Active fluxes remaining on fluxes are corrosive. Active fluxes remaining on the surface of the steel will corrode the surface in the surface of the steel will corrode the surface in a very short time.a very short time.

• Passive fluxes – Passive fluxes – all the joint surfaces must be all the joint surfaces must be thoroughly cleaned before using a passive flux. It thoroughly cleaned before using a passive flux. It does not have the ability to remove oxides from does not have the ability to remove oxides from the surface. the surface.

Submerged Arc Welding Submerged Arc Welding (SAW)(SAW)

Submerged Arc Welding Submerged Arc Welding (SAW)(SAW)

Principle.Principle.• Electricity is passed through an electrode which Electricity is passed through an electrode which

jumps between the electrode and the work piece. jumps between the electrode and the work piece. The arc produces great heat melting the The arc produces great heat melting the electrode and the work piece causing the edges electrode and the work piece causing the edges to fuse together. The electrode is a wire fed to fuse together. The electrode is a wire fed consumable.consumable.

Operation.Operation.1.1. The arc melts the two edges to be joined as well The arc melts the two edges to be joined as well

as the electrode forming the weld pool. as the electrode forming the weld pool. 2.2. The arc is submerged by a granulated flux The arc is submerged by a granulated flux

released from a hopper ahead of it. This flux released from a hopper ahead of it. This flux melts with the heat of the arc protecting the weld melts with the heat of the arc protecting the weld pool and forming a slag that controls cooling.pool and forming a slag that controls cooling.

Uses.Uses.• This is an ideal automated welding process. It is This is an ideal automated welding process. It is

ideal for long runs. It is used for producing steel ideal for long runs. It is used for producing steel girders or beams used in construction.girders or beams used in construction.

Electro-Slag Welding.Electro-Slag Welding.

Electro-Slag Welding.Electro-Slag Welding.Principle.Principle.• Electricity is passed between two couples on either Electricity is passed between two couples on either

side of the plates. This causes the materials in the side of the plates. This causes the materials in the gap to melt as well as the edges of the plates. This gap to melt as well as the edges of the plates. This form the weld pool. form the weld pool.

Operation.Operation.1.1. Two pieces of metal are placed between the Two pieces of metal are placed between the

electrodes.electrodes.2.2. The electrodes are then closed on the piece causing The electrodes are then closed on the piece causing

the circuit to complete.the circuit to complete.3.3. The resistance in the metal between the electrodes The resistance in the metal between the electrodes

causing them to melt and fuse together.causing them to melt and fuse together.Uses.Uses.• This is generally used to join very thick plates This is generally used to join very thick plates

together giving a series of overlapping welds until together giving a series of overlapping welds until the two plates are fully joined. It is suitable for the two plates are fully joined. It is suitable for automatic welding as it is used on large plates automatic welding as it is used on large plates usually.usually.

Resistance Welding. Resistance Welding. (Spot Welding)(Spot Welding)

Resistance Welding. Resistance Welding. (Spot Welding)(Spot Welding)

Principle.Principle.• Electricity is passed between two electrodes with Electricity is passed between two electrodes with

the pieces to be joined in between. As the electricity the pieces to be joined in between. As the electricity passes through the material the resistance of the passes through the material the resistance of the metals cause the metals to melt fusing them metals cause the metals to melt fusing them together. together.

Operation.Operation.1.1. Two pieces of metal are placed between the Two pieces of metal are placed between the

electrodes.electrodes.2.2. The electrodes are then closed on the piece causing The electrodes are then closed on the piece causing

the circuit to complete.the circuit to complete.3.3. The resistance in the metal between the electrodes The resistance in the metal between the electrodes

causing them to melt and fuse together.causing them to melt and fuse together.Uses.Uses.• This is generally used to join light gauge steel sheet This is generally used to join light gauge steel sheet

metal. Sheets that are too thick will prevent the metal. Sheets that are too thick will prevent the current from flowing and will not workcurrent from flowing and will not work

Resistance Seam Resistance Seam Welding.Welding.

PrinciplePrinciple• This is exactly the same as spot welding except that This is exactly the same as spot welding except that

a continuous is produced.a continuous is produced.Operation.Operation.1.1. The first method is similar to spot welding. Here The first method is similar to spot welding. Here

however the spots are overlapped to form a however the spots are overlapped to form a continuous seam. This is called Stitch welding.continuous seam. This is called Stitch welding.

2.2. The second method is to replace the electrodes with The second method is to replace the electrodes with rollers that cause a continuous seam to be produces.rollers that cause a continuous seam to be produces.

Uses.Uses.• This is also used to weld sheet metal except that a This is also used to weld sheet metal except that a

continuous seam is required perhaps the production continuous seam is required perhaps the production of a water proof tank.of a water proof tank.

Welding TermsWelding TermsMulti-runs.Multi-runs.• This is a method of welding two pieces of This is a method of welding two pieces of

thick metal together. A number of thick metal together. A number of welding runs are necessary to build up welding runs are necessary to build up the gap between the two pieces.the gap between the two pieces.

Flash back arrestorFlash back arrestor..• This is a safety device used in gas This is a safety device used in gas

welding. It prevents the flame from the welding. It prevents the flame from the burning gas traveling through the hose burning gas traveling through the hose and into the tanks.and into the tanks.

Dissolved acetylene.Dissolved acetylene.• This is the form that acetylene is stored in This is the form that acetylene is stored in

the tank. The tank is similar to a sponge the tank. The tank is similar to a sponge which absorbs the acetylene. Liquid which absorbs the acetylene. Liquid acetylene would explode in the tank.acetylene would explode in the tank.

Shielded arc.Shielded arc.• This is the protection of the weld pool by This is the protection of the weld pool by

an inert gas preventing oxidation of the an inert gas preventing oxidation of the weld.weld.

Edge preparation.Edge preparation.• This is the preparation of the edges to be This is the preparation of the edges to be

welded. They should be free of rust and oil welded. They should be free of rust and oil to allow for a quality weld and should be to allow for a quality weld and should be tapered slightly to allow for a good joint.tapered slightly to allow for a good joint.

Slag inclusion.Slag inclusion.• This is a fault where the slag drops into This is a fault where the slag drops into

the weld pool and becomes part of it the weld pool and becomes part of it weakening the weld. This is caused by weakening the weld. This is caused by moving the welding apparatus to slowly. moving the welding apparatus to slowly. Welding at the correct pace will prevent Welding at the correct pace will prevent this.this.

Porosity.Porosity.• Porosity is the presence of air bubbles Porosity is the presence of air bubbles

in the weld. This is caused by moving in the weld. This is caused by moving the welding apparatus to quickly not the welding apparatus to quickly not giving the weld pool a chance to form giving the weld pool a chance to form properly. This is controlled by properly. This is controlled by welding at the correct pace.welding at the correct pace.

Lack of penetration.Lack of penetration.• This is again a problem with the weld This is again a problem with the weld

pool. Due to a lack of temperature the pool. Due to a lack of temperature the edges to be joined do not melt to form edges to be joined do not melt to form the weld pool and fuse together. This the weld pool and fuse together. This can be prevented by setting the can be prevented by setting the welder to the correct power setting.welder to the correct power setting.

Gas weldingGas welding

• Metals are fused together and the gap is Metals are fused together and the gap is filled with a filler rodfilled with a filler rod

• Oxygen and acetylene are mixed together Oxygen and acetylene are mixed together to generate a flame to melt the weld joint.to generate a flame to melt the weld joint.

• Oxygen is pressurised into the cylinder.Oxygen is pressurised into the cylinder.• Acetylene is dissolved in a porous Acetylene is dissolved in a porous

material called acetone, which will material called acetone, which will absorb 25 times it’s own volume of absorb 25 times it’s own volume of Acetylene. Acetylene would explode if it Acetylene. Acetylene would explode if it were stored under pressure. were stored under pressure.

Gas WeldingGas Welding

Oxy-acetylene flamesOxy-acetylene flames

electric arc welding electricity is passed through an electrode which jumps between the electrode...

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