Wednesday, 5 April 2017

MIG Welding: Principle, Working, Equipment's, Applications, Advantages and Disadvantages

Today we will learn about What is MIG welding principle, working, equipment’s, applications, advantages and disadvantages. MIG stands for metal inert gas welding or sometimes it is known as Gas Metal Arc welding. This welding is same as TiG welding except a non-consumable electrode replaced by consumable electrode wire. This process is automated or semi-automated arc welding process in which inert gases are used as shielding gas and a consumable wire electrode is used. This welding was developed to welding aluminum or other non-ferrous metals in 1940. Now days, this is find in every industrial or manufacturing process due to its high speed, easy operation and easily automated qualities. It is mostly used in sheet metal industries or in automobile industries.

MIG Welding:


Principle:

Mig works on same principle of TIG or arc welding. It works on basic principle of heat generation due to electric arc. This heat is further used to melt consumable electrode and base plates metal which solidify together and makes a strong joint. The shielded gases are also supplied through nozzle which protect the weld zone from other reactive gases. This gives good surface finish and a stronger joint.

Equipment’s:

MIG Welding: Principle, Working, Equipment's, Applications, Advantages and Disadvantages

Power Source:

In this type of welding process, a DC power supply is used with reverse polarity. Reverse polarity means the electrode or in case of MIG welding electrode wire is connected positive terminal and work piece to negetive terminal. It is due to principle of electric circuit which state that 70% of heat is always on positive side. So reverse polarity ensures that the maximum amount of heat liberate at tool side which melt the filler metal in proper way. Straight polarity can cause unstable arc that result into large spatter. The power source consist a power supply, a transformer, a rectifier which change AC into DC and some electronic controls which control the current supply according to weld requirement.

Wire Feeder System:

We know that MIG welding needs continuous consumable electrode supply for welding two plates. This consumable electrode used in form of wire. These wire is continuously supplied by wire feed mechanism or system. It controls the speed of the wire and also pushes the wire form welding torch to welding area. These are available in different shapes and sizes. It consist a wire pool holder, a driving motor, a set of driving rollers and wire feed controls. The wire feed speed is directly control the current supply through power supply. If the wire feeding speed is high, it required more current in welding zone to produce proper heat for melting of it.

Welding Torch:

This torch is slightly different as used in TIG welding. In this torch there is a mechanism which hold the wire and supply it continuously with the help of wire feed. The front end of the torch is fitted with a nozzle. The nozzle is used to supply inert gases. These gases form a shielding area around the weld zone and protect it from oxidization. The welding torch is air cooled or water cooled according to the requirement. For high current supplied, the torch is water cooled and for low supply it is air cooled.

Shielding Gases:

The primary function of shielding gases is to protect weld area from other reactive gases like oxygen etc. which can affect the strength of welding joint. These shielding gases are also form plasma which helps in welding. The choice of gas is depend on the welding material. Mostly argon, helium and other inert gases are used as shielding gases.

Regulators:

As the name implies, they are used to regulate the flow of inert gases from the cylinder.  The inert gases are filled into cylinder at high pressure. These gases cannot be used at this pressure so a regulator is used between the gases supply which lower down the gases pressure according to welding requirements.


Working:

Its working can be summarized as follow.

MIG Welding: Principle, Working, Equipment's, Applications, Advantages and Disadvantages

  • First, a high voltage current is change into DC current supply with high current at low voltage. This current passes though welding electrode.
  • A consumable wire is used as electrode. The electrode is connected to the negative terminal and work piece from positive terminal.
  • A fine intense arc will generate between electrode and work piece due to power supply. This arc used to produce heat which melts the electrode and the base metal. Mostly electrode is made by the base metal for making uniform joint. 
  • This arc is well shielded by shielding gases. These gases protect the weld form other reactive gases which can damage the strength of welding joint.
  • This electrode travels continuously on welding area for making proper weld joint. The angle of the direction of travel should be kept between 10-15 degree. For fillet joints the angle should be 45 degree.


Applications:

  • MIG is best suited for fabrication of sheet metal.
  • Generally all available metals can be weld through this process.
  • It can be used for deep groove welding.


Advantages and Disadvantages: 

Advantages:

  • It provide higher deposition rate.
  • It is faster comparing to arc welding because it supply filler material continuously.
  • It produce clean weld with better quality.
  • There is no slag formation.
  • Minimize weld defects.
  • This welding produces very little slag.
  • It can be used to make deep groove weld.
  • It can be easily automated. 

Disadvantages:

  • It cannot be used for welding in difficult to reach portions.
  • Higher initial or setup cost.
  • It cannot be used for outdoor work because wind can cause damage of gas shield.
  • It required high skilled labor.


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