17034 Welding

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TIG Welding

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TIG Welding

TIG welding is a commonly used high quality welding

process. TIG welding has become a popular choice ofwelding processes when high quality, precision welding isrequired.

In TIG welding an arc is formed between a non consumabletungsten electrode and the metal being welded.

Gas is fed through the torch to shield the electrode and

molten weld pool.

If filler wire is used, it is added to the weld pool separately.

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TIG MeldingTIG Welding Benefits

Superior quality welds

Welds can be made with or without filler metal

Precise control of welding variables (heat)

Free of spatter Low distortion

Shielding Gases

Argon

Argon + Hydrogen

Argon/Helium

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TIG Melding

The TIG welding process uses an arc struck between the

tungsten electrode and the metal to be welded.

The arc heats and melts the metal, a filler rod being added

as required.

The electrode does not melt as welding takes place, and an

inert shielding gas (argon) flows out around the tungsten

and the weld preventing oxidisation

welding because it produces accurate results of the highest

quality across a wide range of metals, including stainless

steel, aluminium, copper and a range of alloys.

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MIG Welding

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MIG Welding

MIG welding is a commonly used high deposition rate welding

process. Wire is continuously fed from a spool. MIG welding

is therefore referred to as a semiautomatic welding process.

MIG Welding Shielding Gas

Argon

Argon - 1 to 5% Oxygen

Argon - 3 to 25% CO2

Argon/Helium

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MIG weldingMIG Welding Benefits

All position capability Higher deposition rates.

Less operator skill required

Long welds can be made without starts and stops

Minimal post weld cleaning is required

Mig welding problem

Heavily oxidized weld deposit Irregular wire feed

Porosity

Unstable arc

Difficult arc starting

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Gas metal arc welding / stick welding

The flux covering the electrode melts during welding. This forms

the gas and slag to shield the arc and molten weld pool. The slagmust be chipped off the weld bead after welding. The flux also

provides a method of adding scavengers, deoxidizers, and alloying

elements to the weld metal

Benefits

Equipment used is simple, inexpensive, and portable

Electrode provides and regulates its own flux

Lower sensitivity to wind and drafts than gas shielded welding

processes

All position capability

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GMAW

Stick Welding Problems

Arc Blow

Arc Stability Excessive spatter

Incorrect weld profile

Rough surface

Porosity

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Principle of Electricity

Principles of Electricity - Arc welding is a method of joining metals

accomplished by applying sufficient electrical pressure to an electrode to maintain a

current path

(arc) between the electrode and the work piece. In this process,electrical energy is

changed into heat energy, bringing the metals to a molten state;whereby they are joined.

The electrode (conductor) is either melted and added to the basemetal or remains in its

solid state. One of these particles is the electron, which has the ability

to move from one place to another. The electron is classified as anegative electrical

charge. Another particle, about 1800 times as heavy as the electron, isthe proton and

under normal conditions the proton will remain stationary.

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Material is said to be in an electrically uncharged state when itsatoms contain an

equal number of positive charges (protons) and negative charges(electrons). This balance

is upset when pressure forces the electrons to move from atom toatom. This pressure,

sometimes referred to as electromotive force, is commonly known

as voltage. It should be noted that voltage that does not move through a conductor, but

without voltage, there would

be no current flow

The transfer of electrons from a negative to a

positive charge throughout the length of a conductor constitutes anelectrical current. The

rate that current flows through a conductor is measured in amperes

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Submerged Arc Welding

Submerged Arc Welding is process by which metals are joined

by an arc or arcs between a bare metal electrode or electrodes

and the work. Shielding is supplied by a granular, fusible

material usually brought to the work from a flux hopper. Filler

metal comes from the electrode and sometimes from a second

filler rod. Flux:

Fluxes used in SAW are granular fusible minerals containing

oxides of manganese, silicon, titanium, aluminum, calcium,

zirconium, magnesium and other compounds such as calciumfluoride. The flux is specially formulated to be compatible with a

given electrode wire type so that the combination of flux

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Submerged arc welding

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Thermit welding

Thermit welding is basically a process in which a mixture containing

Aluminium powder, Iron Oxide and suitable alloying elements.

Mixture is ignited in a crucible to form molten steel and slag.

This molten steel is then directed into the pre-fabricated moulds

where it fuses with the preheated rail ends to form a Thermit weldedjoint.

This process is based on the exothermic reaction.

Thermit mixture contains the following items

Aluminium powder, Steel chips and Various ferro alloys

Thermit Powder". The thermit powder ignites at a temperature of

about 300 deg C. On ignition, the reaction starts and the mixture

melts. The temperature of the molten metal rises to about 2700 degc

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Thermit welding

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Thermo chemical reaction

Fe2O3+ 2 Al 2 Fe + Al2O3 + (3090 DEG.C )

Iron oxide+ aliron +al oxide

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Complete process

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Thermit welding

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applications

Rail road joining

Long crank shaft

Propeller shaft

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Gas Welding

The Heat derives from the combustion of a fuel gas such as acetylene in

combination with oxygen.

It is a fusion welding process wherein the joint is completely melted toobtain the fusion.

The heat produced by the combustion of gas is sufficient to melt any metaland as such is universally applicable.

In all the oxy-fuel gas welding processes, the combustion takes place in twostages.

The first reaction takes place when the fuel gas such as acetylene andoxygen mixture burn releasing intense heat.

C2H2+ O22CO + H2+ 18.75 MJ/m3

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Gas welding

The carbon monoxide (CO) and hydrogen produced in thefirst stage further combine with the atmospheric oxygen andgive rise to the outer bluish flame, with the followingreaction.

4 CO + 2H2+ 3O24CO2+ 2H2O + 35.77 MJ/m3

Neutral flame (O2/C2H2=1)

Carburising flame (O2/C2H21=1.15)

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Oxy Actylene Gas welding

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It is versatile.

Also the source of heat is separate from the

filler rod and hence, the filler metal can be

properly controlled and heat properly

adjusted giving rise to a satisfactory weld.

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Welding