This document discusses metal inert gas (MIG) and tungsten inert gas (TIG) welding processes. It describes the key equipment, parameters and transfer methods used in MIG welding like globular, short circuiting, spray and pulsed spray. It also outlines the advantages of MIG welding as being a high deposition rate process with no slag and versatility. Limitations mentioned are irregular wire feed and burn back. For TIG welding, it explains that a tungsten electrode is used with an inert gas shield and filler metal can be added. TIG provides high quality welds needed for precision industries and can be mechanized easily.

1. 119 April 2020 Dr.Abhishek Sharma
By
Dr.Abhishek Sharma
Metal Joining (MIG,TIG)
KME-403
Unit - IV
GL BAJAJ INSTITUTE OF TECHONOLOGY & MANAGEMENT

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GMAW or MIG Welding
• Semi automatic or automatic arc welding process.
• Continuous and consumable wire electrode and a shielding Argon gas are fed through a
welding gun.
• Used in automatic industry, tank, ship and aircraft building.
• Semi inert gases like CO2 or Ar + He also used now a days to reduce process
cost.
• A fixed relationship b/w rate of wire burn off and welding current exist.
9 April 2020 Dr.Abhishek Sharma

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• Thus when wire feed rate is fixed, welding machine gives necessary current to
maintain arc.
• Current range 100 to 400 A, which depends on diameter of wire and speed of
melting of wire.
Equipments:
• Welding gun and wire feed unit.
• Power supply
• Electrode
• Shielding Gas
Metal transfer in MIG welding takes place majorly by following four methods:
1. Globular:
• Uses CO2, a less expensive shielding gas.
• Produces high heat, thus high deposition rate.
• Thus producing poor weld surface and spatters.
• Electrode wire used are larger diameter because of high heat produced.
Limitations of MIG welding:
• Irregular wire feed.
• Burn back
• Unstable arc
• Heavily oxidized weld deposit.
9 April 2020 Dr.Abhishek Sharma

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2. Short Circuiting:
• Uses CO2.
• Electrode wire is smaller and thus current is lower.
• Thus heat input is low, making possible to weld thinner materials.
• Here molten droplets formed on tip of electrode bridge the gap between
electrode and weld pool, causing short circuit and arc extinguish.
• Arc soon gets reignited as the surface tension of weld pool pulls the molten metal
off the electrode tip.
• This process is repeated about 100 times in second, making arc appear constant
to human eye.
• Better weld quality is received, since less spatter are formed.
• Slower process than globular welding.
3. Spray:
• Thick electrode used.
• Here dia of molten droplets is lesser than that of electrode unlike globular.
• droplets rapidly pass along stable arc from electrode to workpiece, eliminating
spatter and resulting high weld quality.
• High value of current and voltage is required, causing high heat input and large
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4. Pulsed Spray:
• It is based on principle of spray transfer.
• Pulsing current is used to melt the filler wire and allow one small molten droplet to fall with
each pulse.
• Can be employed for making thin work piece.
• Pulse provide stable arc and no spatter.
• Shield gas should be Ar (CO2 should be least used).
• Special power source, capable of providing pulsated current is required, having frequency 30 to
400 pulses per second.
Defects of GMAW:
• Undercutting, Incomplete fusion, Incomplete joint penetration, porosity
• Excessive melt through, weld metal crack, HAZ cracks.
Advantages of GMAW:
• Welding rate is very high with good quality weld.
• No slag formation, to be chipped off.
• Versatile process, permits welding in all directions.
Limitations:
• Irregular wire feed rate.
•Burn back and unstable arc
9 April 2020 Dr.Abhishek Sharma

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Tungsten Inert Gas Welding (TIG)
• Tungsten electrode is used as it can withstand high temperatures (4000oC).
• Electrode is surrounded by a nozzle which conducts shielding gas (Ar or He).
• Electrode is non consumable and separate filler material may be used.
• Tungsten alloyed with Zirconia is used to stabilize the arc and provide easy start.
• Since it can be mechanized easily and gives high quality weld, thus used in precision
work like atomic energy and instrument industries.
9 April 2020 Dr.Abhishek Sharma

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Tungsten Inert Gas
Welding (TIG)
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• Inert gas is supplied to welding zone through annular path surrounding tungsten electrode to
effectively displace atmosphere around weld puddle.
•Tubing for water cooling of electrodes is provided.
• Torches carrying current of 100A are usually water cooled.
• DC straight polarity or DCEN, as well as DCRP may be used.
• AC supply can also be used.
• DCEN provides deep penetration and faster welding.
• Dcep provides wide weld pool and shallow penetration thus used for thin w/p.
Defects in TIG:
• Under cutting, weld metal cracks.
• Tungsten inclusion
• Porosity.
• HAZ cracks
9 April 2020 Dr.Abhishek Sharma